Subjects -> MEDICAL SCIENCES (Total: 8642 journals)
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MEDICAL SCIENCES (2392 journals)            First | 3 4 5 6 7 8 9 10 | Last

Showing 1201 - 1400 of 3562 Journals sorted alphabetically
Journal of Foot and Ankle Research     Open Access   (Followers: 5)
Journal of Forensic Science and Research     Open Access   (Followers: 2)
Journal of Gandaki Medical College-Nepal     Open Access  
Journal of Generic Medicines     Hybrid Journal   (Followers: 2)
Journal of Geographical Sciences     Hybrid Journal   (Followers: 1)
Journal of Global Antimicrobial Resistance     Hybrid Journal   (Followers: 3)
Journal of Hand Therapy     Hybrid Journal   (Followers: 18)
Journal of Head & Neck Physicians and Surgeons     Open Access   (Followers: 2)
Journal of Health & Medical Informatics     Open Access   (Followers: 61)
Journal of Health and Biological Sciences     Open Access   (Followers: 1)
Journal of Health Design     Open Access   (Followers: 1)
Journal of Health Economics and Outcomes Research     Open Access   (Followers: 1)
Journal of Health Promotion and Behavior     Open Access  
Journal of Health Research and Reviews     Open Access  
Journal of Health Science and Medical Research     Open Access  
Journal of Health Science Research     Open Access  
Journal of Health Sciences     Open Access   (Followers: 1)
Journal of health sciences     Open Access  
Journal of Health Sciences / Sağlık Bilimleri Dergisi     Open Access  
Journal of Health Sciences and Medicine     Open Access  
Journal of Health Sciences and Medicine     Open Access   (Followers: 2)
Journal of Health Sciences and Surveillance System     Open Access  
Journal of Health Sciences Scholarship     Open Access  
Journal of Health Specialties     Open Access  
Journal of Health Studies     Open Access  
Journal of Healthcare Informatics Research     Hybrid Journal   (Followers: 1)
Journal of Heavy Metal Toxicity and Diseases     Open Access  
Journal of Helminthology     Hybrid Journal   (Followers: 2)
Journal of Herbs Spices & Medicinal Plants     Hybrid Journal  
Journal of HIV for Clinical and Scientific Research     Open Access   (Followers: 2)
Journal of Hospital Medicine     Hybrid Journal   (Followers: 10)
Journal of Huazhong University of Science and Technology [Medical Sciences]     Hybrid Journal  
Journal of Human Hypertension     Hybrid Journal   (Followers: 3)
Journal of Human Rhythm     Open Access  
Journal of Human Transcriptome     Open Access  
Journal of Ideas in Health     Open Access  
Journal of Inflammation     Open Access   (Followers: 2)
Journal of Inflammation Research     Open Access  
Journal of Injury and Violence Research     Open Access   (Followers: 7)
Journal of Innovation in Health Informatics     Open Access   (Followers: 17)
Journal of Institute of Medicine     Open Access  
Journal of Insulin Resistance     Open Access   (Followers: 1)
Journal of Interactional Research in Communication Disorders     Hybrid Journal   (Followers: 5)
Journal of Interferon & Cytokine Research     Hybrid Journal   (Followers: 3)
Journal of International Medical Research     Open Access   (Followers: 4)
Journal of Interventional Medicine     Open Access   (Followers: 1)
Journal of Investigative Medicine     Hybrid Journal   (Followers: 3)
Journal of Islamabad Medical & Dental College     Open Access   (Followers: 1)
Journal of Istanbul Faculty of Medicine     Open Access  
Journal of Karnali Academy of Health Sciences     Open Access   (Followers: 1)
Journal of Kathmandu Medical College     Open Access   (Followers: 1)
Journal of King Abdulaziz University : Medical Sciences     Open Access   (Followers: 2)
Journal of Laboratory Medicine     Hybrid Journal   (Followers: 27)
Journal of Laryngology and Voice     Open Access   (Followers: 11)
Journal of Lasers in Medical Sciences     Open Access  
Journal of Law, Medicine & Ethics     Hybrid Journal   (Followers: 24)
Journal of Legal Medicine     Hybrid Journal   (Followers: 7)
Journal of Limb Lengthening & Reconstruction     Open Access  
Journal of Lumbini Medical College     Open Access   (Followers: 1)
Journal of Mahatma Gandhi Institute of Medical Sciences     Open Access  
Journal of Manipulative and Physiological Therapeutics     Hybrid Journal   (Followers: 6)
Journal of Manmohan Memorial Institute of Health Sciences     Open Access   (Followers: 1)
Journal of Marine Medical Society     Open Access  
Journal of Materials Science : Materials in Medicine     Hybrid Journal   (Followers: 4)
Journal of Maternal and Child Health     Open Access  
Journal of Mechanics in Medicine and Biology     Hybrid Journal  
Journal of Medical and Biological Engineering     Hybrid Journal   (Followers: 4)
Journal of Medical and Biomedical Sciences     Open Access   (Followers: 2)
Journal of Medical Case Reports     Open Access   (Followers: 1)
Journal of Medical Cases     Open Access   (Followers: 6)
Journal of Medical Colleges of PLA     Full-text available via subscription  
Journal of Medical Disorders     Open Access  
Journal of Medical Economics     Hybrid Journal   (Followers: 8)
Journal of Medical Education and Curricular Development     Open Access   (Followers: 6)
Journal of Medical Ethics     Partially Free   (Followers: 25)
Journal of Medical Ethics and History of Medicine     Open Access   (Followers: 15)
Journal of Medical Humanities     Hybrid Journal   (Followers: 21)
Journal of Medical Hypotheses and Ideas     Open Access  
Journal of Medical Imaging and Health Informatics     Full-text available via subscription   (Followers: 1)
Journal of Medical Investigation and Practice     Open Access  
Journal of Medical Laboratory and Diagnosis     Open Access  
Journal of Medical Law and Ethics     Full-text available via subscription   (Followers: 15)
Journal of Medical Microbiology     Full-text available via subscription   (Followers: 6)
Journal of Medical Sciences     Open Access  
Journal of Medical Sciences     Open Access  
Journal of Medical Screening     Hybrid Journal   (Followers: 6)
Journal of Medical Signals and Sensors     Open Access   (Followers: 3)
Journal of Medical Society     Open Access  
Journal of Medical Systems     Hybrid Journal  
Journal of Medical Toxicology     Hybrid Journal   (Followers: 6)
Journal of Medical Ultrasound     Open Access   (Followers: 2)
Journal of Medicinal Botany     Open Access  
Journal of Medicinal Chemistry     Hybrid Journal   (Followers: 201)
Journal of Medicine     Open Access   (Followers: 1)
Journal of Medicine and Biomedical Research     Open Access   (Followers: 1)
Journal of Medicine and Philosophy     Hybrid Journal   (Followers: 8)
Journal of Medicine and the Person     Hybrid Journal  
Journal of Medicine in Scientific Research     Open Access  
Journal of Medicine in the Tropics     Open Access  
Journal of Medicine Research and Development     Open Access   (Followers: 3)
Journal of Medicine, Physiology and Biophysics     Open Access   (Followers: 5)
Journal of Medicines Development Sciences     Open Access   (Followers: 1)
Journal of Metabolomics & Systems Biology     Open Access   (Followers: 1)
Journal of Mind and Medical Sciences     Open Access   (Followers: 1)
Journal of Molecular Medicine     Hybrid Journal   (Followers: 11)
Journal of Movement Disorders     Open Access   (Followers: 2)
Journal of Muscle Research and Cell Motility     Hybrid Journal   (Followers: 1)
Journal of Nanotechnology in Engineering and Medicine     Full-text available via subscription   (Followers: 6)
Journal of Nanotheranostics     Open Access   (Followers: 1)
Journal of Natural Medicines     Hybrid Journal  
Journal of Natural Science, Biology and Medicine     Open Access   (Followers: 3)
Journal of Nature and Science of Medicine     Open Access   (Followers: 4)
Journal of Negative and No Positive Results     Open Access  
Journal of Nepalgunj Medical College     Open Access  
Journal of Neurocritical Care     Open Access  
Journal of Neurodegenerative Diseases     Open Access   (Followers: 2)
Journal of Neurorestoratology     Open Access  
Journal of Neuroscience and Neurological Disorders     Open Access  
Journal of Nobel Medical College     Open Access  
Journal of Obesity and Bariatrics     Open Access   (Followers: 1)
Journal of Occupational Health     Open Access  
Journal of Occupational Therapy Education     Open Access   (Followers: 10)
Journal of Ocular Biology, Diseases, and Informatics     Hybrid Journal  
Journal of Oral Biology and Craniofacial Research     Full-text available via subscription  
Journal of Oral Health and Craniofacial Science     Open Access  
Journal of Orofacial Sciences     Open Access  
Journal of Otorhinolaryngology, Hearing and Balance Medicine     Open Access   (Followers: 1)
Journal of Ovarian Research     Open Access  
Journal of Ozone Therapy     Open Access  
Journal of Palliative Medicine     Hybrid Journal   (Followers: 47)
Journal of Paramedical Sciences & Rehabilitation     Open Access  
Journal of Parkinsonism and Restless Legs Syndrome     Open Access   (Followers: 2)
Journal of Parkinson’s Disease and Alzheimer’s Disease     Open Access   (Followers: 1)
Journal of Participatory Medicine     Open Access  
Journal of Patan Academy of Health Sciences     Open Access  
Journal of Pathogens     Open Access   (Followers: 1)
Journal of Patient Experience     Open Access  
Journal of Patient Safety and Risk Management     Hybrid Journal   (Followers: 2)
Journal of Patient-Centered Research and Reviews     Open Access  
Journal of Patient-Reported Outcomes     Open Access  
Journal of Periodontal Research     Hybrid Journal  
Journal of Personalized Medicine     Open Access   (Followers: 3)
Journal of Pest Science     Hybrid Journal   (Followers: 1)
Journal of Pharmaceutical Policy and Practice     Open Access   (Followers: 4)
Journal of Physiobiochemical Metabolism     Hybrid Journal   (Followers: 2)
Journal of Physiology-Paris     Hybrid Journal   (Followers: 2)
Journal of Pioneering Medical Sciences     Open Access  
Journal of Postgraduate Medicine     Open Access  
Journal of Pregnancy     Open Access   (Followers: 4)
Journal of Prevention & Intervention Community     Hybrid Journal   (Followers: 6)
Journal of Preventive Medicine and Public Health     Open Access  
Journal of Primary Prevention     Hybrid Journal   (Followers: 7)
Journal of Prosthodontic Research     Full-text available via subscription   (Followers: 1)
Journal of Prosthodontics     Hybrid Journal   (Followers: 2)
Journal of Receptor, Ligand and Channel Research     Open Access  
Journal of Regenerative Medicine     Partially Free   (Followers: 4)
Journal of Research in Medical Sciences     Open Access   (Followers: 2)
Journal of Science and Applications : Biomedicine     Open Access   (Followers: 1)
Journal of Science and Technology (Ghana)     Open Access   (Followers: 3)
Journal of Scientific Innovation in Medicine     Open Access  
Journal of Scientific Perspectives     Open Access   (Followers: 1)
Journal of Sensory Studies     Hybrid Journal   (Followers: 4)
Journal of Shaheed Suhrawardy Medical College     Open Access  
Journal of Shoulder and Elbow Arthroplasty     Open Access  
Journal of Sleep Disorders : Treatment & Care     Hybrid Journal   (Followers: 10)
Journal of South American Earth Sciences     Hybrid Journal   (Followers: 5)
Journal of Spinal Cord Medicine     Hybrid Journal   (Followers: 4)
Journal of Spinal Disorders & Techniques     Hybrid Journal   (Followers: 2)
Journal of Sports Medicine and Allied Health Sciences : Official Journal of the Ohio Athletic Trainers Association     Open Access   (Followers: 1)
Journal of Stem Cell Therapy and Transplantation     Open Access   (Followers: 1)
Journal of Stomal Therapy Australia     Full-text available via subscription  
Journal of Strength and Conditioning Research     Hybrid Journal   (Followers: 75)
Journal of Substance Use     Hybrid Journal   (Followers: 14)
Journal of Surgical Academia     Open Access   (Followers: 1)
Journal of Surgical and Clinical Research     Open Access  
Journal of Surgical Case Reports     Open Access  
Journal of Surgical Education     Full-text available via subscription   (Followers: 3)
Journal of Surgical Technique and Case Report     Open Access  
Journal of Systemic Therapies     Full-text available via subscription   (Followers: 3)
Journal of Taibah University Medical Sciences     Open Access  
Journal of Telemedicine and Telecare     Hybrid Journal   (Followers: 12)
Journal of The Academy of Clinical Microbiologists     Open Access  
Journal of the American Association for Laboratory Animal Science     Full-text available via subscription   (Followers: 7)
Journal of the American College of Certified Wound Specialists     Hybrid Journal   (Followers: 2)
Journal of the American College of Clinical Wound Specialists     Hybrid Journal   (Followers: 2)
Journal of the American Medical Directors Association     Hybrid Journal   (Followers: 5)
Journal of the American Medical Informatics Association : JAMIA     Hybrid Journal   (Followers: 35)
Journal of the American Podiatric Medical Association     Full-text available via subscription   (Followers: 7)
Journal of the Anatomical Society of India     Full-text available via subscription  
Journal of the Anus, Rectum and Colon     Open Access  
Journal of The Arab Society for Medical Research     Open Access  
Journal of the Australasian College of Nutritional and Environmental Medicine     Full-text available via subscription  
Journal of the Australasian Society of Aerospace Medicine     Open Access   (Followers: 1)
Journal of the Ceylon College of Physicians     Open Access  
Journal of the Chinese Medical Association     Open Access   (Followers: 2)
Journal of the College of Community Physicians of Sri Lanka     Open Access  
Journal of The Egyptian Public Health Association     Open Access   (Followers: 1)
Journal of the Formosan Medical Association     Open Access   (Followers: 2)
Journal of the Georgia Public Health Association     Open Access   (Followers: 3)
Journal of the Ghana Science Association     Full-text available via subscription   (Followers: 3)

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Similar Journals
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Journal of South American Earth Sciences
Journal Prestige (SJR): 0.829
Citation Impact (citeScore): 2
Number of Followers: 5  
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 0895-9811 - ISSN (Online) 0895-9811
Published by Elsevier Homepage  [3207 journals]
  • First record of fossil procyonid (Mammalia, Carnivora) from Uruguay
    • Abstract: Publication date: June 2019Source: Journal of South American Earth Sciences, Volume 92Author(s): Leopoldo H. Soibelzon, Andrés Rinderknecht, Juliana Tarquini, Raúl UgaldeAbstractProcyonids were the first carnivorans that arrived from North America to South America during the late Miocene, before the full emergence of the Panama Isthmus. In South America, this family comprises five living genera (Bassaricyon, Nasua, Nasuella, Potos and Procyon) and two extinct genera (Cyonasua and Chapalmalania) that are recorded from the late Miocene to early Pleistocene. In this contribution, we report and describe specimen MNHN 2965 assigned to Cyonasua sp., which represents the first record of Procyonidae from Uruguay. This specimen was collected at the coastal cliffs of Río de La Plata on the San José Department, in stratigraphic levels that belong to the Camacho Formation (late Miocene). In addition, the presence of Cyonasua sp. in Camacho Fm. is in agreement with the substrate use and locomotor mode inferred for the genus (terrestrial and generalized, with some degree of climbing habits), and with what is known about the paleoenvironment of other formations were Cyonasua was found.
  • The Tithonian chrono-biostratigraphy of the Neuquén Basin and related
           Andean areas: A review and update
    • Abstract: Publication date: June 2019Source: Journal of South American Earth Sciences, Volume 92Author(s): Beatriz Aguirre-Urreta, Maximiliano Naipauer, Marina Lescano, Rafael López-Martínez, Ignacio Pujana, Verónica Vennari, Luis F. De Lena, Andrea Concheyro, Victor A. RamosAbstractThe main objective of this study is to provide a review of the Tithonian succession of the Neuquén Basin and related Andean areas with an update from recent results on biostratigraphy and radio-isotopic geochronology. The studied successions include continental clastics and volcaniclastics of the Tordillo Formation and economically-important hydrocarbon source rocks such as the widespread black shales of the Vaca Muerta Formation, which has been ranked in recent studies as one of the most important recoverable shale oil and gas resources at global level. Significant recent data include the discovery of hyaline calpionellids associated with global nannofossil markers which are relevant to investigations of the definition of the Tithonian/Berriasian boundary. In addition, new high precision radio-isotopic data provide robust evidence to modify the absolute ages presently assigned to the base and top of the Tithonian Stage by the International Commission on Stratigraphy.
  • Cretaceous extensional systems of the Golfo San Jorge basin: Insights from
           the analysis of fault length and displacement data
    • Abstract: Publication date: June 2019Source: Journal of South American Earth Sciences, Volume 92Author(s): Pablo GiampaoliDisplacement profiles and maps were used in the subsurface of the Golfo San Jorge basin in the Manantiales Behr region to analyze factors affecting the geometric and kinematic evolution of an extensional system and its relationship with the migration and trapping of hydrocarbons. Two fault types were recognized: faults affecting both the basement and the sedimentary cover, and faults restricted to the sedimentary cover. The vertical growth of the faults within the sedimentary cover was constrained by vertical lithologic variations and by intersection with the free surface. Faults involving the basement are synsedimentary and show Dmax/L relationships and aspect ratios that allow their distinction from the shallower fault planes. The geometric coherence shown in the aggregated displacement profile and map suggests a synchronous kinematic evolution for the faults developed inside the sedimentary cover. Observed fault trace lengths and throw values distributions may indicate that those faults grew by the early linkage of isolated fault segments followed by the progressive building of displacement. Reactivation of pre-existent basement fabric had little influence on faulting across overlying sedimentary cover probably because the fine-grained beds of Pozo D-129 Formation acted as a structural decoupling level. The low degree of connection between the shallow and deep portions of the faults disregards the hypothesis of vertical migration from a local source pod. The mapping of fault segments with higher values of displacement and the recognition of transfer zones may help to locate and delineate footwall hydrocarbon traps. Comparison and integration with other studies show that Cretaceous fault systems in the eastern Golfo San Jorge basin have grown mainly by rapid length establishment and subsequent displacement accumulation. Also, most of the basement-involved structures do not connect significantly with overlying fault arrays.Graphical abstractImage 1
  • Saline lake development in the Aptian post-rift phase of the Tucano Basin:
           Tectonic and paleogeographic implications
    • Abstract: Publication date: June 2019Source: Journal of South American Earth Sciences, Volume 92Author(s): Filipe Giovanini Varejão, Lucas Veríssimo Warren, Bernardo Tavares Freitas, Virginio Henrique Neumann, Mario Luis AssineAbstractThe Aptian is the age of the evaporitic transitional megasequence in the Brazilian marginal basins as well as in the interior rift basins of the northeast region. The Marizal Formation is interpreted as a fluvial system developed in the inherited rift axis of the Tucano Basin. In its middle portion, after a quick transgressive event, a mud-dominated interval took place, which is enclosed in the Amargosa Bed. This transgressive marker bed is rich in fish fossils with Tethyan affinity attesting to an estuarine environment in the southern portions of the basin. The same transgressive event occurs in the Barbalha Formation of the Araripe Basin, where a mud-dominated lacustrine system is interpreted in the Batateira Bed. While lakes developed in the Araripe Basin and a transitional marine environment is attested to the southern portions of the Tucano Basin, there is no information of how these systems were interconnected. Here we discuss sedimentologic, stratigraphic and geochemical data of the Amargosa Bed in the North Tucano Basin, correlating it with time equivalent marker beds of other locations in the Northeast Brazil. Our data show that deposition of the mixed carbonate-mud interval of the North Tucano Basin was developed in a saline lake with local evidences of seismic-induced soft-sediment deformation structures. Although climate seasonality controlled high-frequency base-level changes, our findings reveal that local fault reactivation was responsible for the space generation, triggering the lake formation in the basin depocenter. This situation is uncommon for thermal subsiding basins that lack mechanical influence and have several implications for the evolution of intracontinental rift basins of the Brazilian Cretaceous. Also, lakes from Araripe, Jatobá and North Tucano basins were probably connected by the continental paleodrainage existent in the Aptian, carrying sediments to the estuaries developed in the Central and South Tucano basins and, thus, to the developing South Atlantic Ocean.
  • Biomarkers in Cretaceous sedimentary rocks from the Codó Formation -
           Parnaíba Basin: Paleoenvironmental assessment
    • Abstract: Publication date: June 2019Source: Journal of South American Earth Sciences, Volume 92Author(s): Edymilaís da S. Sousa, Gustavo R.Sousa Júnior, Andrenilton F. Silva, Francisco de A. M. Reis, Alek A.C. de Sousa, Giovani M. Cioccari, Ramsés Capilla, Igor V.A.F. de Souza, Paulo M. Imamura, Rene Rodrigues, José A.D. Lopes, Sidney G. de LimaAbstractEarlier geological works showed that Codó Formation - CF (Parnaíba Basin, Brazil) has been deposited in the Aptian, and suffered the influence of various transgressive-regressive marine cycles, thus suggesting various depositional environment possibilities from saline lacustrine deltaic to shallow marine during sedimentation. Cretaceous potential source rock samples from the CF were investigated to identify diagnostic biomarkers in order to ascertain paleoenvironmental conditions of deposition and thermal evolution of organic matter. The TOC results showed low organic matter (OM) contents and Rock-Eval analysis implying low thermal evolution of organic matter. GC-MS analysis showed a great diversity of biomarkers within the five studied samples. The main features of organic matter composition were: low content of n-alkanes, Ph » Pr, presence of i-25, i-30 (squalane) and gammacerane thus suggesting saline to hypersaline depositional environment. The biomarkers fingerprint showed a full series of ββ hopanes and Δ13(18) hopenes, αααR and βααR steranes, and Δ5 and Δ8(14) sterenes, pointing out immature OM. Several C30 steranes have been detected, among them 4α(methyl)- and 4β(methyl)-24-ethylcholestane, 24-n-propylcholestane and 24-isopropylcholestane (all identified by co-injection) and dinosteranes, which some of them are indicative of a marine depositional system.
  • Cordierite-bearing granitic rocks in South America: Contrasting sources
           and conditions of formation
    • Abstract: Publication date: June 2019Source: Journal of South American Earth Sciences, Volume 92Author(s): V.P. Ferreira, A.N. Sial, A.J. Toselli, J.R. de Toselli, P.G. Molina, M.A. Parada, J.J. Celino, J. SaavedraAbstractMineralogy, geochemistry and isotopic data for Ediacaran, Ordovician to Devonian, and Upper Triassic cordierite-bearing granitoids respectively from Brazil, Argentina and Chile are discussed here. Syn-collisional Lower to Middle Ordovician, and post-collisional Upper Devonian garnet-free granitoids from Argentina intruded greenschist-to amphibolite-facies metasedimentary rocks. Garnet-bearing and garnet-free monzogranites of the Nanuque Suite, Brazil, intruded high-grade gneisses and migmatites, and in the High Andes Belt, the Los Tilos garnet-free granite was emplaced into an early Permian batholith during an extensional event. Mineralogical, geochemical and isotopic characteristics of the granites from Argentina and Brazil, such as presence of peritectic and (±) restictic cordierite, low-magnetic susceptibility (MS) values (0.03–0.2 × 10−3 SI), negative εNd (−7.3 to −5.0) and high δ18Ozircon values (>9‰), suggest a major aluminous metasedimentary source. Data for the Chilean pluton (small volume, associated with coeval metaluminous granites, low δ18Ozircon values (6.6–7.4‰), slightly negative εNd (−4), and high MS values (1.4–2.5 × 10−3 SI) are compatible with a less-evolved source, possibly a metaluminous granitic rock. P-T magma crystallization conditions of the cordierite-bearing granites from Argentina are 2–4 kbar and 630–720 °C; and 3.6–4.0 kbar and at 670−700 °C for their cordierite. The Nanuque magma formed P > 6 kbar; T = 750–800 °C, and magma emplaced at ∼3 kbar. Their cordierite formed at P = 5.0–5.2 kbar and T = 720−740 °C. P-T conditions of the Los Tilos magma emplacement are P ∼ 3 kbar and T ∼670 °C. Cordierite-paramorph β-quartz nodules in this pluton, surrounded by leucocratic rims, have been formed by biotite dehydration reactions. This study confirms that cordierite in granites can be produced from different source rocks by a number of processes, at different P-T conditions.
  • Relationship between diagenesis and the emplacement of bitumen in the
           Lower Triassic Piramboia Formation sandstones, Paraná Basin, SW Brazil
    • Abstract: Publication date: June 2019Source: Journal of South American Earth Sciences, Volume 92Author(s): Anderson J. Maraschin, Georgiana F. da Cruz, Laercio L. Martins, Hélio J.P. Severiano Ribeiro, Adolpho Herbert AugustinAbstractOutcrops of eolian sandstones of the Lower Triassic Piramboia Formation in the eastern margin of the intracratonic Paraná Basin are known as the main occurrence of tar sandstones in Brazil because contain heavy oil (“tar”). In order to investigate the migration of oil into the sandstones petrographic analyses of dune facies were performed. Optical (transmitted, reflected and epifluorescence lights) and Field Emission Scanning Electron (FE-SEM) microscope studies together with X-Ray Diffraction (XRD) analyses showed that the Piramboia Formation sandstones have not been affected by intense diagenesis. Eogenetic features includes mainly thin, continuous inherited ferruginous clay coatings and minor mechanically infiltrated clay coatings around detrital mineral grains. The authigenesis of smectite and K-feldspar overgrowths precipitation begin to develop and during shallow mesodiagenesis, authigenic smectite was gradually transformed into mixed-layer illite-smectite; K-feldspar overgrowths, quartz overgrowths continuous to develop, and pore-filling calcite cement were formed locally. In the late mesodiagenesis the emplacement of oil occurred, filling pores and covering grains, clay coatings and calcite. During later surface exposure, water washing by meteoric fluids and biodegradation transformed the oil into a heavy oil rich in asphaltenes. The influx of acid meteoric waters caused dissolution of detrital K-feldspars as well as meteoric waters generate organic acids which also caused the dissolution of K-feldspars and the consequent generation of secondary porosity with the precipitation of inter- and intragranular vermicular kaolinite. However, kaolinite can be also a product of eodiagenetic process similar to the occur in the telodiagenesis. To evaluate the porosity of the sandstones microtomography analysis were preformed revealing high porosity volume (ca. 26%) and high volume of porous with connectivity (ca. 26%). Although not currently commercially exploited nowadays the knowledge of the Piramboia tar sandstones diagenetic evolution contributes for a better understanding of the Paraná Basin sedimentary fill during the Lower Triassic.
  • Tentative integration of paleoseismic data from lake sediments and from
           nearby trenches: The central section of the Boconó Fault (northern
    • Abstract: Publication date: Available online 6 April 2019Source: Journal of South American Earth SciencesAuthor(s): Christian Beck, Eduardo Carrillo, Franck Audemard, Aurélien van Welden, Jean-Robert DisnarAbstractThe right-lateral strike slip Boconó Fault (Mérida Andes, northern Venezuela) accommodates an important part of the South-American Plate northern transform boundary. Along its central portion, preserved post-LMG lake fills are intersected by two surface-reaching active traces which could be trenched just beside. Outcropping and cored lacustrine sedimentary archives are combined with trench data in order to achieve a Holocene paleoseismicity record for a 7 km-long segment. For lakes sediments, several types of sedimentary “events” were taken into account as co-seismic: mass wasting on deltaic foreset, liquefaction and slumping, reflected tsunami effects, re-suspension, abrupt change in sedimentary dynamics and sources, abrupt emptying and lake surface changes. Time coincidences between two lacustrine archives and two trenches can be proposed for the last 10 kyr BP. Among a total of 24 events, 13 events are detected in two sites, 3 events in 3 sites. 9 possible correlations concern separate traces while 4 concern the same trace; a relay between the activity of the two traces is also deduced. This combination of surveys both reinforces and completes the trenches results, leading to a better knowledge of local to regional seismic hazard. Nevertheless, the total information results probably incomplete and/or biased. The co-seismic origin of lacustrine fills disturbances evidenced but the associated archive is incomplete and/or biased due to: changing recording potential through time, possible impacts by strong distant earthquakes. Trenches data appear to fill lacustrine “gaps” but with a number of events possibly overestimated if all ruptures and associated 14C data are considered as representing separated earthquakes.
  • Sedimentology and stratigraphy of the Puesto El Moro Formation, Patagonia,
           Argentina: Implications for upper cretaceous paleogeographic
           reconstruction and compartmentalization of the Austral-Magallanes Basin
    • Abstract: Publication date: Available online 6 April 2019Source: Journal of South American Earth SciencesAuthor(s): Augusto N. Varela, Sebastián Richiano, Leandro D´Elia, Damián Moyano Paz, Camila Tettamanti, Daniel G. PoiréAbstractDuring the Late Cretaceous, the Austral-Magallanes Basin (AMB) records the change from a thermal subsidence post-rift stage to a retroarc foreland basin scenario. The lower-Upper Cretaceous Puesto El Moro Formation (PMF) was deposited during the configuration of the foreland AMB. The aims of this contribution are: (i) to define the sedimentary paleoenvironments that are recorded by the PMF deposits and their spatio-temporal distribution, and (ii) to reconstruct the paleogeographic configuration and distributions of the sedimentary environments in the AMB during the early-Late Cretaceous onset of the foreland system. Based on detailed sedimentological observations and analysis of architectural elements, we divide the PMF into three informal sections. The lower section of the PMF represents a shallowing-upward estuary bay succession. The middle section of the PMF is characterized by braided and high-sinuosity meandering fluvial systems, flowing toward the southwest. Finally, the upper section of the PMF corresponds to a distributive fluvial system flowing toward the southwest. The PMF accumulated synchronously with the estuarine-fluvial Mata Amarilla Formation (MAF) located to the east of the study area. The results obtained in this contribution suggest that the type and vertical stacking of sedimentary paleoenvironments of the PMF could be correlated with the contemporary MAF. A subsurface dataset supported by the oil industry indicates the occurrence of the SE-trending Piedra Clavada High inside the northern AMB. We interpret that this topographic high controlled, during the Late Cretaceous, the types and distribution of sedimentary paleoenvironments of the AMB, indicating that an important compartmentalization of the basin occurred during the beginning of the foreland stage. The northern part of the AMB is divided into the Cardiel-Tres Lagos sub-basin and the Foredeep main depocentre.
  • The Lower Cretaceous Centenario Formation: A subsurface unit in the
           northeastern border of the Neuquén Basin revisited
    • Abstract: Publication date: Available online 5 April 2019Source: Journal of South American Earth SciencesAuthor(s): J.F.P. Iñigo, P.J. Pazos, M.E. Novara, M. ComerioAbstractThe Centenario Formation in the NE region of the Neuquén Basin is a lithostratigraphic unit that has been historically ascribed to continental deposits, being time-equivalent of the Agrio Formation in the basin border. The study of both the Lower and the Upper Members of the unit through detailed core analysis, electrofacies well correlation and seismic interpretation, was used to define depositional trends, main stratigraphic surfaces and develop paleoenvironmental models in the basin margin. The Centenario Formation presents at least two transgressive-regressive intervals. This mixed sandstone-shale succession is marine to marginal marine in the lower member and marine, marginal marine and fluvial in the upper member. The overall environmental configuration and evolution allow defining sedimentary supply from the NE and E. Facies characterization, paleoenvironmental interpretation, in addition to its vertical evolution and geographic distribution constitute key elements to evaluate and define remaining hydrocarbon potential for this interval, as well as allowing integration between outcrop and subsurface data.
  • The Cumbres Calchaquíes Range (NW-Argentina). Geochemical sedimentary
           provenance, tectonic setting and metamorphic evolution of a Neoproterozoic
           sedimentary basin
    • Abstract: Publication date: Available online 30 March 2019Source: Journal of South American Earth SciencesAuthor(s): José P. López, Uwe Altenberger, Laura I. Bellos, Christina GünterAbstractThe Cumbres Calchaquíes Range forms part of the Famatinian metamorphic basement of the Eastern Sierras Pampeanas. The sedimentary protoliths of the metamorphic sequence were deposited in a marine basin alongside the western margin of Gondwana during the Neoproterozoic. New petrologic, geochemical and thermobarometric data give insight into the evolution of the sedimentary basin, its sediment source area, its later metamorphic overprint and its regional relationship to other parts of the Famatinian basement.The metamorphic series studied here consists of banded schists and gneisses and rare calcsilcate-rocks and migmatites that have been reworked by mid-to deep-crustal metamorphic and tectonic processes. The bulk rock compositions indicate shale, wacke, marl and litharenitic protoliths. The metamorphosed clastic sediments have major and trace element compositions indicating a continental granitoid-dominated source area with low sediment recycling. Low SiO2/Al2O3 ratios suggest a relatively low maturity of the sedimentary protoliths. Therefore, the Cumbres Calchaquíes section represents a sequence of turbidity currents with progressive shallowing of the depositional environment, as indicated by quartz- and carbonate-rich sediments. The overall data are consistent with the geodynamic environment of a basin adjacent to a continental magmatic arc as the most probable scenario. Whereas the sedimentary protoliths of the metamorphic basement in the Sierra de Ancasti and Sierra de Aconquija, located ca 100–300 km south of the study area are interpreted as originating in an evolving back-arc basin, our results from the Cumbres Calchaquíes region indicate a sedimentary source in a felsic continental arc with no significant influx of basic rocks.The Famatinian metamorphic evolution of the Cumbres Calchaquíes rocks is of typical Barrow-type, culminating in partial melting of the metasediments. Conventional thermobarometry combined with thermodynamic models (pseudosections) reveal a prograde evolution reaching peak conditions of ca 665 °C/6.1 Kbar. This implies a geothermal gradient of ca 35 °C/km, which is slightly higher than the average for continental crust and suggests a period of crustal thinning, as known from back-arc basins, or additional heat supply by voluminous intrusions.
  • The relationship between Cenozoic shallow igneous bodies and thrust
           systems of the mountain front of the Cordillera Principal, Mendoza
           province, Argentina
    • Abstract: Publication date: Available online 30 March 2019Source: Journal of South American Earth SciencesAuthor(s): Vanesa Soledad Araujo, María Cristina Frisicale, Natalia Sánchez, Martín Turienzo, Fernando Lebinson, Luis Vicente DimieriAbstractWithin the Malargüe fold and thrust belt, located in the southern Central Andes, south of Mendoza province, Argentina, several shallow intrusive bodies which are part of an extensive Neogene magmatism are exposed and linked to the subduction of the Nazca plate beneath the western edge of South America. This study attempts to establish the relationship between these igneous bodies and thrusts that are part of fault systems that built the Andean orogen. It is interpreted that these thrusts have acted as feeding channels for the ascent of magma and therefore there is a direct link between the distribution of magmatism and fault systems. The igneous bodies are emplaced through low-angle faults and it results in longitudinal strips of intrusive bodies of younger ages towards the Andean foreland. The petrographic and geochemical analysis shows that the sills, dikes and laccoliths, outcropping in the Malargüe fold and thrust belt, have a calc-alkaline affinity indicating an origin related to the Andean magmatic arc. The evolutionary model of the emplacement of the intrusive bodies and their relationship with the Andean thrust systems has significant implications for geotectonic models that consider the shifting of the magmatic sources of the Andean Arc currently proposed for these regions of the Andes.
  • Petrogenesis of the Triassic Cuyo basin magmatism: Controls on the
           magmatic evolution of passive rifts basins in Western Gondwana
    • Abstract: Publication date: Available online 27 March 2019Source: Journal of South American Earth SciencesAuthor(s): Ana Paula Orellano R, Nora A. Rubinstein, Silvia I. CarrasqueroAbstractThe rifting magmatism of the Cuyo basin (Western Argentina) is characterized by the presence of pyroclastic rocks and basaltic lavas, Triassic in age, emplaced during active faulting that occurred along an ancient terrane boundary. The pyroclastic rocks display calc-alkaline signature and were generated in shallow magma chambers with plagioclase fractionation associated with underplating processes. The basaltic lavas have alkaline to transitional composition with an OIB signature along with a negative Nb-Ta anomaly and trace elements ratios that reflect crustal assimilation processes which are confirmed by their isotopic composition. Moreover, the Nd-Sm isotopes suggest the involvement of a Precambrian upper crust in their genesis. The geochemistry of the basalts also reveals that the magmas generated in deep magma chambers that evolved through amphibole or garnet fractionation. Considering the geodynamic scenario, crustal assimilation processes could have been favored by the presence of highly fracturated ancient suture zones which could have promoted magma-host rock interaction during the magma ascent.
  • The Blake Geomagnetic Field Event recorded in a sequence of marine and
           continental facies outcropping in the coast of Buenos Aires province,
    • Abstract: Publication date: Available online 25 March 2019Source: Journal of South American Earth SciencesAuthor(s): Haroldo Vizán, Carlos L. Azcuy, Ofelia Rita Tófalo, Silvana E. Geuna, Cecilia R. Amenabar, María Julia Orgeira, Emiliano M. Renda, Clara Braña Carreño, Héctor Panarello, Liliana CastroAbstractDifferent authors have suggested that there is a relationship between Quaternary geomagnetic field events and climate variability. Considering that in a recent paper a detailed stratigraphic study in a section of the coast of Claromecó (Buenos Aires province) indicates Late Pleistocene paleoclimatic changes, a paleomagnetic study was performed in the same stratigraphic succession. The analyzed sedimentary section belongs to “Belgranense” unit that is composed of continental and marine deposits. According to previously published dates and stable isotope results presented in this paper, it is proposed that 6 facies (sedimentary units) of the Claromecó section developed during the interglacial Marine Isotope Stage 5 (MIS 5). These units are presumably coeval with one of the best known geomagnetic field events, the Blake Event, occurred during the MIS 5, between ca. 120 and ca. 115 ka. The studied units from the base to the top are: 1) diagenetic wackestones with clasts of sand, 2) pedogenized loessian deposits, 3) lower marine wackestones, 4) lower tidal channel deposits, 5) upper marine wackestones and 6) upper tidal channel deposits. The section is capped by a continental gravity flow much younger than MIS 5. Different facies record distinct characteristic remanent magnetizations (ChRM) suggesting that these have a not modern origin. Low-field thermomagnetic curves and hysteresis loops were performed for all the sedimentary facies that provide magnetic remanences. Special sediment magnetism experiments were made for the units with reverse and/or oblique reverse components including isothermal remanent magnetization and anhysteretic remanent magnetization to perform the Lowrie-Fuller test. In these units opaque minerals were identified using polished and thin sections together with scanning electron microscopy analysis. According to all the results it is interpreted that the Blake Geomagnetic Field Event was recorded in the pedogenized loessian deposits with magnetite crystals generated during pedogenetic processes, and in extracellular biogenic magnetite crystals in the lower marine wackestones. The reverse and/or oblique reverse ChRM components were recorded before the lower tidal channel deposits, which have normal polarity directions. The Blake Geomagnetic Field Event was recorded in Claromecó during last interglacial MIS 5, however a direct correlation cannot be made between the recorded transitional polarity and a marine transgression corresponding to an important melting of ice sheets during this marine isotope stage. The magnetic components recorded in the studied sequence could be used as a stratigraphic tool to help identify “Belgranense” unit in Argentina or correlative sedimentary facies outcropping in South America.
  • Arthrophycus alleghaniensis Harlan, 1831 in the Tianguá Formation, Brazil
           (Silurian of the Parnaíba Basin)
    • Abstract: Publication date: Available online 23 March 2019Source: Journal of South American Earth SciencesAuthor(s): Maria De Jesus Gomes De Sousa, Maria Somália Sales Viana, João Victor Paula Moreira, Francisco Danilo Sales PaulaAbstractThis study deals with the Arthrophycus ichnogenus and its associates, recorded in Silurian deposits of the Tianguá Formation, Serra Grande Group of the Parnaíba Basin. The methodology used in the field followed traditional procedures of geology observation and the presence of fossils in outcrops, also including specific paleoichnological details. Samples collected in the field are deposited in the scientific collection of the Dom José Museum, in Sobral-CE. The Arthrophycus alleghaniensis ichnospecies is preserved in its typical form of bundle or isolated excavations, always endowed with transverse rings. The presence of Arthrophycus in rocks of the Tianguá Formation associated with an ichnofossiliferous assembly composed of Arenicolites, Didymaulichnus and Cruziana infers a shallow marine paleoenvironment. The hummocky cross stratification indicates deposition in an area dominated by storm wave action and links the ichnofauna of the Tianguá Formation to the Cruziana ichnofacies. This record, so far unpublished for the Silurian deposits of the Parnaíba basin, reinforces the preferential stratigraphic distribution of Arthrophycus to the lower Paleozoic and expands the paleobiogeographic distribution of the ichnogenus in South America.
  • The Quebrada del Diablo Lower West Au deposit (Gualcamayo mining district,
           Argentina): A Carlin-type mineralization'
    • Abstract: Publication date: June 2019Source: Journal of South American Earth Sciences, Volume 92Author(s): María Celeste D'Annunzio, Nora RubinsteinThe Gualcamayo Mining District (GMD), located in the eastern margin of the Argentini an Precordillera includes three Au deposits: Amelia-Ines, Magdalena, Quebrada del Diablo Main, and QDD Lower West. The district has reserves of 491,000 oz. and resources of 2.3 million oz of Au.The metallogenetic analysis of these Au deposits based on previous work and new micro-geochemistry (LA- ICP- MS), isotopic (C-O-S-Pb) and fluid inclusions studies revealed that they are genetically linked and share many characteristics with Carlin-type deposits, including the lithology of host rocks, structural control, geochemical signatures, ore paragenesis, and dissolution and decarbonization processes. However, they also display some noticeable differences. The sulfur isotopic composition supports a genetic link between these gold deposits and the precursor magmatism of the porphyry-type mineralization of the area. Besides, the fluids responsible for the Au mineralization proved to be neutral to slightly alkaline and Au-saturated. The link with the magmatism along with the character of the mineralizing fluids and the presence of significant base metal sulfides allowed classifying the GMD deposits as “distal disseminated gold deposits” that occur on the distal edges of magmatic-hydrothermal systems.Graphical abstractImage 1
  • Evolution of fluorite-mica-feldspar veins: Evidences of a fossil
           geothermal system in the são Gabriel terrane and consequences for
           Pb-Zn-Cu metallogeny
    • Abstract: Publication date: June 2019Source: Journal of South American Earth Sciences, Volume 92Author(s): Guilherme Sonntag Hoerlle, Marcus Vinicius Dorneles Remus, Norberto Dani, Marcia Elisa Boscato Gomes, Luiz Henrique RonchiAbstractFluorite-mica-feldspar hydrothermal veins and stockworks host Pb-Zn-Cu sulphides in the São Gabriel Terrane, Southern Brazil. The veins fill second- and third-order structures in Neoproterozoic calcitic marbles on the Cambaizinho Complex. Veins are mostly symmetrically zoned showing, from borders to the centre, fluorite and sericite, muscovite, adularia and albite (minor quartz, calcite and iron oxides). Galena, sphalerite, chalcopyrite, pyrite and minor cassiterite are disseminated in the veins and concentrated in ore pockets. Vein petrography, mineral chemistry and microthermometric measurements in fluorite fluid inclusions indicate that the hydrothermal veins were formed in a shallow crust environment from epithermal fluids near 140 °C. Their origin is attributed to a fossil geothermal system related to the post-collisional alkaline volcanism and caldera system of the Acampamento Velho Formation (574-549 Ma). This hydrothermal system is interpreted as genetically associated to fluorite and Pb-Zn-Cu occurrences on rhyolites and miarolitic cavities of related alkaline granitoids, Pb-Zn-Cu anomalies on stream sediment and soil analyses and Au quartz veins hosted by alkaline granitoids accompanied by pyrite, sericite and fluorite alteration halos in the same region. Although there is no mineral deposit discovered so far, the studied veins linked to the other base metal occurrences would indicate that the northwestern São Gabriel Terrane may host a poorly preserved mineralized epithermal system.
  • Formation and evolution of glauconite in the Demerara Contourite
           depositional system related to NADW circulation changes during late
           Quaternary (French Guiana)
    • Abstract: Publication date: June 2019Source: Journal of South American Earth Sciences, Volume 92Author(s): Cédric Tallobre, Pierre Giresse, Maria-Angela Bassetti, Lies Loncke, Germain Bayon, Roselyne Buscail, Alina Tudryn, Sébastien ZaragosiAbstractThe Demerara Plateau is a marginal plateau which forms a bathymetric relief on the sea floor. Here, contourite deposits have been studied in detail, following the recent discovery of contourite sequences likely related to the bottom currents and linked both to contour current and peculiar sea-floor morphology. A chronostratigraphic framework, based on δ18O relative variations and palaeomagnetic events in sediment cores allows correlating sediment processes to current intensity changes and major climate phases (glacial or interglacial). The studied sediments are enriched in glauconitic grains. In addition, the glauconite mineralogical maturity can easily correlate to low sedimentation rate and slightly energetic bottom currents on the seafloor. Based on these data and using the glauconitic authigenic mineral as proxy for inferring the degree of winnowing at the sediment-water interface, we might put forward the hypothesis that the intensity of NADW is higher during the glacial stages and lower during interglacial periods.
  • Geochemical mapping and background concentrations of iron and potentially
           toxic elements in active stream sediments from Carajás, Brazil –
           implication for risk assessment
    • Abstract: Publication date: June 2019Source: Journal of South American Earth Sciences, Volume 92Author(s): Gabriel Negreiros Salomão, Marco Aurélio Figueiredo, Roberto Dall'Agnol, Prafulla K. Sahoo, Carlos A. de Medeiros Filho, Marlene F. da Costa, Rômulo Simões AngélicaThe Companhia de Pesquisa de Recursos Minerais (CPRM - Geological Survey of Brazil) has conducted geochemical surveys in the south-central region of the Itacaiúnas River watershed (IRW) in the Carajás region. The surveyed area covers 9,650 km2 and the data obtained by CPRM is the basis for the present study. A total of 833 active stream sediment samples, including 144 duplicates were collected. The
  • Seismic interferometry applied to local fracture seismicity recorded at
           Planchón-Peteroa Volcanic Complex, Argentina-Chile
    • Abstract: Publication date: June 2019Source: Journal of South American Earth Sciences, Volume 92Author(s): J.A. Casas, D. Draganov, G.A. Badi, M.C. Manassero, V.H. Olivera Craig, L. Franco Marín, M. Gómez, E. RuigrokAbstractAlthough the Planchón-Peteroa Volcanic Complex (PPVC) has undergone many hazardous eruptions, only a small number of geological, geochemical, and geophysical studies have been performed to describe this active volcanic system. In order to characterize the subsurface structures present at the PPVC, we applied seismic interferometry to fracture seismicity originating in this volcanic complex and along active geologic faults located nearby. We utilized seismic data recorded by two arrays of stations deployed in Argentina and Chile. Nine of these stations (three in Chile and six in Argentina) recorded data simultaneously and were used for this application. Only seismic events with energy arriving (sub) vertically to the stations were chosen for processing. According to the magnitude and the location of the selected seismic events, relocated seismic sources were used for the Chilean stations while, for the Argentine stations, only seismic sources located near that array were used. We obtained seismic evidence of the location of the subsurface reflectors underneath each station using zero-offset reflection responses retrieved from seismic interferometry by autocorrelation of (time windows extracted from) the selected seismic events. Then, applying a comparative analysis between the seismic results and the available geological information, we imaged the shallow subsurface of the area enclosed by the Chilean stations, and also by the Argentine stations. The results are consistent with the available geological information, provide accurate depth values for several subsurface discontinuities, indicate areas of higher heterogeneity, and support the emplacement of a magma body at ∼4 km depth from the surface. This work shows the first application of a novel variation of seismic interferometry based on autocorrelations to local-earthquake data recorded in a volcanic area.
  • Pb+data&rft.title=Journal+of+South+American+Earth+Sciences&rft.issn=0895-9811&">The Cambrian peraluminous Santa Luzia granite suite in the Araguaia Belt,
           central Brazil: Evidence for closure of the Clymene Ocean based on zircon
           and monazite UPb data
    • Abstract: Publication date: June 2019Source: Journal of South American Earth Sciences, Volume 92Author(s): Pedro Victor F. de S. Alves, Nilson F. Botelho, Elton L. Dantas, Federico A. CuadrosAbstractThe Araguaia Belt (AB) in northcentral Brazil formed as the result of the amalgamation of the Amazonian and São Francisco-Congo cratons along with the Parnaíba Block during late Neoproterozoic times. Ediacaran/Cambrian late- to post-orogenic magmatism took place at ∼540 Ma following this continental collision at 550-540 Ma. Such magmatism is represented in the southern portion of the Araguaia Belt by the peraluminous Santa Luzia and Barrolândia granites, as well as by the Presidente Kennedy Granodiorite in the central portion of the AB. Inherited zircon cores with distinct rims are abundant in the Santa Luzia Granite. This pluton yields UPb MC-LA-ICP-MS zircon and monazite ages of 538 ± 1 Ma and 534 ± 5 Ma, respectively. In addition, UPb zircon and monazite ages of 536 ± 6 Ma and 524 ± 6 Ma, respectively, are obtained for the Barrolândia Granite. The data presented in this work and in the literature allow to group the studied Santa Luzia and Barrolândia granites, together with Presidente Kennedy Granodiorite, in a single suite, named Santa Luzia Suite, maintaining the Santa Luzia pluton as the type-area. Rocks related to this Cambrian magmatism are essentially peraluminous, magnesian to slightly ferroan, and calc-alkaline in character. Such rocks probably originated from magmas formed by partial melting of meta-igneous sources that were subsequently contaminated via assimilation of metasedimentary rocks. In the AB, both the collision related to the 550-540 Ma Brasiliano/Pan-African orogeny, and the intimately associated ∼540 Ma late- to post-orogenic Santa Luzia Suite magmatism record the closure of the Clymene Ocean as well as the late stages of compressional tectonics related to west Gondwana amalgamation. The latter was followed by exhumation related to collapse of the Araguaia orogen.
  • Revaluation of geomagnetic excursions recorded in lava flows from the
           Ceboruco and Tequila volcanic fields, trans-mexican volcanic belt
    • Abstract: Publication date: June 2019Source: Journal of South American Earth Sciences, Volume 92Author(s): M. Cervantes-Solano, A. Goguitchaichvili, J.H. García-Gómez, Rafael García Ruiz, J. Rosas-Elguera, R. Cejudo-Ruiz, J. Morales-ContrerasAbstractDetailed records of the Earth's magnetic field have shown that it has occasionally reversed its polarity. Several cases have also been found when the Earth Magnetic Field has significantly deviated for a relatively short time from its usual position defining a geomagnetic excursion, a kind of aborted reversal. Although many transitional paleodirections were revealed during the last decade in Central Mexico, their reliability was questioned. Recent paleomagnetic studies along the Trans-Mexican Volcanic Belt report contradictory results on the evidence of intermediary geomagnetic regimes. This work provides new paleomagnetic data which, combined with the information already reported, evaluate the fidelity of such events registered in the lava flows associated to the Tequila and Ceboruco Volcanic Fields. This critical reassessment allowed to discard the evidence of the Levantine geomagnetic excursion (362 ± 13 kA) but strongly confirms the occurrence of the Big Lost event (592 ± 20 ka). These findings represent an important contribution to the geomagnetic instability time scale for the last 1 Ma.
  • Pb+zircon+ages+and+metamorphic+conditions+of+mafic+granulites+from+the+basement+of+the+southern+Brasilia+Orogen,+Campinas-SP+region&rft.title=Journal+of+South+American+Earth+Sciences&rft.issn=0895-9811&">UPb zircon ages and metamorphic conditions of mafic granulites from the
           basement of the southern Brasilia Orogen, Campinas-SP region
    • Abstract: Publication date: June 2019Source: Journal of South American Earth Sciences, Volume 92Author(s): Wagner S. Amaral, Felipe H. Santos, Jozias C.S. Bravo, Henrique S. Fedel, George L. Luvizotto, Daniel F. GodoyAbstractIn the southern Brasília Orogen, slices of an intensively reworked Paleoproterozoic basement occur. These are partially covered by a Neoproterozoic sequence of high-metamorphic grade, corresponding to the Socorro–Guaxupé Nappe and intruded by several Neoproterozoic plutonic rocks. In this contribution, we present thermobarometric and geochronological data of the basement rocks in the Campinas city, southern part of the Brasilia Orogen. The occurrence of mafic granulites included as lenses in mylonitic gneisses is described for the first time in a quarry located in the southern part of Campinas. Petrographic studies revealed high temperature paragenesis composed of orthopyroxene, clinopyroxene, garnet, biotite, and plagioclase. We present thermobarometric results with conditions close to the metamorphic peak, at ca. 8.7–10 kbar and 820–890 °C, which characterize these rocks as medium-pressure mafic granulites. UPb zircon ages of 2134 ± 6 Ma and 2156 ± 6 Ma were obtained for the host gneisses and the mafic granulite, respectively and interpreted as the timing of their igneous crystallization. Metamorphic zircon overgrowths in the mafic granulites show a concordia age of 608 ± 3 Ma. This age is coeval with one of the several episodes of melt crystallization reported in the southern Brasilia Orogen. The Paleoproterozoic ages of ca. 2.15 Ga suggest that the protoliths of the gneisses and granulites in the Campinas region are similar to the rocks of the Pouso Alegre Complex, which represents part of the lower São Francisco plate overthrusted by the Brasilia Orogen during the Neoproterozoic orogenic collage in southeastern Brazil.
  • Multi-chronometer thermochronological modelling of the Late Neoproterozoic
           to recent t-T-evolution of the SE coastal region of Brazil
    • Abstract: Publication date: June 2019Source: Journal of South American Earth Sciences, Volume 92Author(s): Florian C. Krob, Ulrich A. Glasmacher, Markus Karl, Melissa Perner, Peter C. Hackspacher, Daniel F. StockliSouth-eastern Brazil is as an important geological archive for understanding and reconstructing various plate tectonic stages of the Wilson Cycle. In the Neoproterozoic, the area of the today's South Atlantic passive continental margin (SAPCM: e.g. between São Paulo and Laguna) of south-eastern Brazil underwent subduction, followed by the collision of the contemporary plates of South America and Africa creating a Neoproterozoic orogeny within the supercontinent Gondwana. During the Palaeozoic and Lower Mesozoic (stage 1), the future SAPCM, as an intracratonic area, experienced erosion, denudation of the Neoproterozoic mobile belts (Pan African/Brasiliano orogeny), and large basin formation (Paraná Basin) (stage 2). Possibly plume-driven pre-to syn-rift (embryonic), ocean spreading (juvenile), and post-break up (mature) processes led to the recent evolution of the SAPCM since the Upper Mesozoic (stage 3).For the first time, this research aims to reconstruct the syn-to post-orogenic t-T-evolution of Neoproterozoic basement rocks of the SE coastal region of Brazil covering the entire geological evolution since the Late Neoproterozoic. Therefore, this study uses geochronological and thermochronological data combined with numerical modelling. This includes published geochronological data of Neoproterozoic basement samples such as U-Pb, Sm-Nd and Rb-Sr analyses, and low temperature thermochronology (LTT) data revealed by K/Ar, 40Ar/39Ar analyses. To this existing LTT data set, we report new apatite (AFT) and zircon (ZFT) fission-track, and (U-Th-Sm)/He (AHe, ZHe) data. Numerical modelling of that LTT data attached to the existing geochronological data indicates the following evolution:- Stage 1: In the central part of the future SAPCM, the Pan African/Brasiliano post-orogenic cooling and exhumation (uplift and erosion of Neoproterozoic rocks to the surface) history occurs in three phases: (i) rapid Late Neoproterozoic exhumation, (ii) a period of relative thermal stability (temperatures of about 200–300 °C) in which rocks reside at upper crust levels during the Early Cambrian to Devonian, and (iii) a second rapid exhumation phase moving the Neoproterozoic basement rocks to the surface during the Devonian. The northern and southern parts indicate a distinct post-orogenic exhumation suggesting faster cooling and exhumation from the Late Neoproterozoic to Devonian/Carboniferous than in the central section.- Stage 2: A phase of subsidence leading to the formation of the Paraná Basin followed by pre-to syn-rift processes and the emplacement of the Paraná-Etendeka flood basalts.- Stage 3: Post-South Atlantic break up processes, such as erosion and exhumation.Graphical abstractImage 1
  • Metamorphic evolution of the Loma Marcelo skarn within the geotectonic
           context of the crystalline basement of the Ventania System (Argentina)
    • Abstract: Publication date: June 2019Source: Journal of South American Earth Sciences, Volume 92Author(s): Carlos A. Ballivián Justiniano, María F. Lajoinie, Clemente Recio, Ana M. Sato, Miguel A.S. Basei, Joaquín A. Proenza, Thomas H. Aiglsperger, Raúl E. de Barrio, Marcela V. Curci, Mabel E. LanfranchiniAbstractThis study describes the mineralogical and isotopic changes that carbonate xenoliths experienced under multiple metamorphic events and hydrothermal fluid circulation during the evolution of the Ventania System basement. The high reactivity of carbonate xenoliths allowed the preservation of mineral assemblages corresponding to at least three metamorphic events in the resulting Loma Marcelo skarn. The Ventania System basement is composed of Neoproterozoic granites and ignimbrites, Early Cambrian granites, and Middle Cambrian rhyolites. Carbonate xenoliths were incorporated during the intrusion of a calc-alkaline granite with an LA-ICP-MS U-Pb crystallization age of 621.6 ± 2.2 Ma. The intrusion induced pyroxene–hornfels facies metamorphism in the carbonate xenoliths and the associated metasomatism generated calcic and magnesian skarns depending on the protolith composition. Garnet, clinopyroxene, wollastonite, bytownite, and meionite were formed in the calcic skarn (CaS), whereas forsterite and spinel were formed in the magnesian skarn (MgS). Crystallization of Early Cambrian alkaline granites was accompanied by intense hydrothermal activity that was responsible for low temperature (≤300 °C) F-metasomatism in the skarn, as evidenced by the presence of F-rich vesuvianite (CaS) and chondrodite (MgS), among other minerals. Vesuvianite was formed from calc-silicate mineral assemblages of the previous metamorphic event, whereas chondrodite was formed by replacement of forsterite. The low temperature formation of these typical high-grade minerals could be an evidence of mineral formation under disequilibrium conditions favoured by the high reactivity of hydrothermal fluids. Neopalaeozoic basement mylonitization under greenschist facies metamorphism was accompanied by hydrothermal fluid circulation. This event promoted extreme mobility of chemical elements in the basement rocks and epidotization (CaS) and serpentinization (MgS) in the Loma Marcelo skarn. The elongated and boudinaged shape of the skarn bodies, parallel to the mylonitic foliation, is a consequence of dextral shearing that affected the basement rocks. Additionally, almost pure grossular crystallized post-tectonically in the CaS. Carbonates of the Loma Marcelo skarn are depleted in 13C and 18O (δ13CV-PDB = −2.5/−10.1‰; δ18OV-SMOW = +7.3/+14.0‰) relative to carbonate sedimentary rocks. The δ13C and δ18O variations can be attributed to the interaction between large amounts of hydrothermal fluids (W/R = 30–50) and Neoproterozoic carbonate sedimentary rocks.
  • A Permian (late Guadalupian) brachiopod fauna from northeast Mexico and
           their paleobiogeographic affinities
    • Abstract: Publication date: June 2019Source: Journal of South American Earth Sciences, Volume 92Author(s): Miguel A. Torres-Martínez, Daniela P. Heredia-Jiménez, Sara A. Quiroz-Barroso, Pilar Navas-Parejo, Francisco Sour-Tovar, Jesús Quiroz-BarragánAbstractIn this work, we report a brachiopod fauna composed of 30 species within 25 genera, belonging to the orders Productida, Orthotetida, Orthida, Rhynchonellida, Athyridida, Spiriferida, Spiriferinida and Terebratulida from the Capitanian (late Guadalupian) of Las Delicias, Coahuila, Mexico. The genera Probolionia, Anemonaria, Waagenoconcha, Grandaurispina, Edriosteges, Ramavectus, Enteletes and Thedusia, in addition to the species Linoproductus nasutus, Rhynchopora guadalupensis, Wellerella girtyi, Composita parasulcata, Composita prospera, Hustedia bipartita, Hustedia opsia, Hustedia stataria, Martinia rhomboidalis and Spiriferella sulcifer are reported for the first time in Mexico. Marginifera minor and Liosotella subquadrata are taxonomically reviewed and renamed. The finding of 15 species commonly recorded in the late Guadalupian, together with the presence of the ammonoid Timorites, corroborates the Capitanian age for the Las Manuelas I section. Thus, the stratigraphic location of the studied section allowed delimiting the age of the upper levels of La Difunta unit to the late Guadalupian. The occurrence of 13 species that had only been described in localities of Texas confirms that during Capitanian the brachiopod fauna studied was related to the biotic Grandian Province. Then again, taxa that had a wide distribution in the Guadalupian were recorded, such as Bathymyonia nevadensis, Enteletes wordensis, Linoproductus nasutus, Hustedia stataria and Martinia rhomboidalis from the United States and China, Japan, Turkey or Russia. This exchange of marine biota among Permian provinces has been associated with a marine connection located about the middle of the Panthalassa Ocean. Due to the proximity of Las Delicias and Texas, both regions could had been influenced by the same paleoequatorial current, suggesting that North American brachiopods found in Paleotethys provinces could also had come from Mexico.
  • The dorsal and pectoral fin spines of catfishes (Ostariophysi:
           Siluriformes) from the Bauru Group (Late Cretaceous), Brazil: A
           comparative and critical analysis
    • Abstract: Publication date: June 2019Source: Journal of South American Earth Sciences, Volume 92Author(s): Y.M. Alves, L.P. Bergqvist, P.M. BritoAbstractCatfish fossils are mainly represented by disarticulated material, most of which is dorsal and pectoral spines. Morphological data on dorsal and fin spines are described. These materials, collected from two sites of the Adamantina and Marilia formations, Late Cretaceous, of the Bauru Group, reveal the morphologic diversity of the freshwater siluriform taxa. This fauna represents one of the oldest samples of catfish diversity in South America, shortly posterior to its separation from Africa during the Cretaceous. A comparative analysis of these materials with the pectoral and dorsal spines of fossil and extant taxa demonstrated a mosaic of similarities shared with several catfishes, such as the families Bagridae - dorsal spine of morphotype one, Pimelodidae, Ictaluridae and †Bachmannidae - dorsal spine of morphotypes two and three, and Ictaluridae and †Hypsidoridae - pectoral spines of morphotypes one and two.
  • Provenance of upper Paleozoic siliciclastics rocks from two high-latitude
           glacially influenced intervals in Bolivia
    • Abstract: Publication date: June 2019Source: Journal of South American Earth Sciences, Volume 92Author(s): Katarzyna Kołtonik, Peter Isaacson, Agnieszka Pisarzowska, Mariusz Paszkowski, Carita Augustsson, Marek Szczerba, Jiří Slama, Bartosz Budzyń, Michał Stachacz, Wojciech KrawczyńskiAbstractThe Toregua Formation in northern Bolivia comprises a continuous succession of sedimentary rocks containing two glacial intervals related to the onset of the Late Paleozoic Ice Age (LPIA). The provenance and depositional tectonic setting of the Upper Devonian–Mississippian (lower) and Pennsylvanian (upper) glacial intervals are separated by non-glacial deposits observed in the Manuripi X-1 and Pando X-1 drill cores, from which petrography, geochemistry, detrital zircon UPb and monazite ThU-total Pb dating are described. Zircon age spectra of sandstone clasts and diamictite indicate an upward change in provenance. Zircon age data from the lower glacial interval yielded age groups at 700–500 Ma, 1300–900 Ma and 2200–1820 Ma, while the monazite gave ages in the range of 600-500 Ma. These age populations correspond to the Guaporé Shield and/or the Arequipa Massif. Detrital zircon from the upper glacial interval has a significant age population at 330–300 Ma that reflects prominent input from the Eastern Cordillera. The maximum depositional age of the upper glacial interval was constrained to ca. 308 Ma. Provenance discrimination diagrams, based on major element geochemistry and trace element ratios, suggest that the glacial and non-glacial sediments were mainly sourced from felsic source rocks. The moderate to high chemical index of alteration (CIA
  • Lithosphere structures of the Parnaíba Basin and adjacent provinces
           revealed by deep magnetotelluric imaging
    • Abstract: Publication date: June 2019Source: Journal of South American Earth Sciences, Volume 92Author(s): Nina S. Rocha, Sergio L. Fontes, Emanuele F. La Terra, Reinhardt A. FuckAbstractMagnetotelluric (MT) data from 49 broadband and 23 long period stations, covering periods between 10−3 and 104 s, were measured along a NNW-SSE profile of approximately 470 km, crossing the Parnaíba Basin, Borborema Province and São Francisco Craton in northeastern Brazil. The geotectonic scenario of the study region comprehends a complex structural framework formed during the Brasiliano orogenic collage. The MT data were processed to obtain the impedance tensor estimates for each MT site using a robust technique and then followed by a dimensional analysis via both the rotational invariants (WAL invariants) of the magnetotelluric tensor and the phase tensor. The two approaches indicated a three-dimensional nature of the region, allowing to proceed to 3D inversion, despite the data distribution along a profile. Several inversion trials of the full impedance tensor, tipper and tipper combined with impedance tensor resulted in a final 3D resistivity model, which suggests a division of the profile into three major zones. A sub horizontal resistive crustal block, interpreted as being part of the Parnaíba block, characterizes the western zone. A mosaic of resistive and conductive zones, which integrates the extended fold belt of the Borborema Province, composes the central zone. In the interface between the central and the eastern zones, there is a sub vertical conductive region limiting two resistive blocks, interpreted as a suture zone. This suture divides tectonic provinces and is supposed to be related with a Neoproterozoic collisional system. The 3D MT imaging recovered the structural framework under the Parnaiba Basin and marked the main lineaments. The paper suggests a distinct tectonic evolution for the complex assemblage of blocks in Northeast Brazil.
  • Nd+isotopy,+trace+element+geochemistry+and+inferences+on+their+origin+and+geological+settings&rft.title=Journal+of+South+American+Earth+Sciences&rft.issn=0895-9811&">Mafic dyke swarms at 1882, 535 and 200 Ma in the Carajás region,
           Amazonian Craton: SrNd isotopy, trace element geochemistry and inferences
           on their origin and geological settings
    • Abstract: Publication date: June 2019Source: Journal of South American Earth Sciences, Volume 92Author(s): Tommaso Giovanardi, Vicente A.V. Girardi, Wilson Teixeira, Maurizio MazzucchelliThe Carajás-Rio Maria region, together with the Rio Maria domain of the Central Amazonian province, comprises the eastern margin of the Amazonian Craton with the Neoproterozoic Araguaia belt. This region hosts several basaltic dyke swarms whose UPb baddeleyite ages highlighted three intrusive events at 1882, 535 and 200 Ma. New geochemical and SrNd isotopic data were obtained for the different groups of the Carajás dykes allowing new insights on i) the mantle source composition beneath the Carajás region through time and ii) the geodynamic setting of the intrusive events. The 1882 Ma swarm is coeval to the Uatumã SLIP event which is one of the oldest intraplate events of the proto-Amazonian craton. Trace elements and isotopic values suggest that the dyke parent melt for those dykes have a crustal component derived from a sedimentary source similar to GLOSS (GLObal Subducting Sediment compositions). This is consistent with the emplacement of the dykes in a supra-subduction setting or in a post-collisional setting. Trace and isotopic values of the 535 Ma dyke swarm are consistent with an enriched mantle source from EMII component. These geochemical features suggest an enrichment of the mantle from an oceanic lithosphere poor in sediments, different to that of the 1882 Ma source. The age of this swarm matches magmatic activity during a post-collisional extensive-transtensive event recorded in the marginal Araguaia belt after the amalgamation of the Amazonian Craton to the Western Gondwana during Neoproterozoic. The 200 Ma dyke swarm which is related to the CAMP (Central Atlantic Magmatic Province) and opening of the Atlantic Ocean shows trace element composition similar to Atlantic E-MORB. The coupled isotopic values are consistent with an enriched mantle source with EMII component. These particular geochemical features suggest that the plume activity responsible for the CAMP near the rifting zone has not affected the mantle beneath the Carajás region.Graphical abstractImage 1
  • The oldest known co-occurrence of dinosaurs and their closest relatives: A
           new lagerpetid from a Carnian (Upper Triassic) bed of Brazil with
           implications for dinosauromorph biostratigraphy, early diversification and
    • Abstract: Publication date: April 2019Source: Journal of South American Earth Sciences, Volume 91Author(s): Maurício S. Garcia, Rodrigo T. Müller, Átila A.S. Da-Rosa, Sérgio Dias-da-SilvaAbstractLate Triassic deposits from south Pangea (Argentina and Brazil) bear the oldest (so far) and most informative unequivocal records of dinosaurs worldwide. Herein we describe a new lagerpetid dinosauromorph from a classic dinosaur-bearing locality (Cerro da Alemoa site) from the Candelária Sequence (Santa Maria Formation), southern Brazil, and report the oldest co-occurrence of dinosaurs, lagerpetids and silesaurids, in the same layer of a Triassic outcrop. Although tentatively regarded as a skeletally immature specimen, the new lagerpetid represents a new morphotype due to the occurrence of the following features: (1) distal condyles transversely wider than deep; (2) absence of flange in the craniomedial margin of the femur; (3) round shaped and medially deflected medial condyle; (4) round shaped crista tibiofibularis. This suit of traits differentiates the new specimen from Ixalerpeton polesinensis, (which was so far the only lagerpetid found in Brazilian strata) and from other known lagerpetids. As non-dinosaurian dinosauromorphs are still relatively scarce in Brazilian Triassic rocks, recent records from this region are gradually providing new data regarding faunal turnovers and biostratigraphy of south Pangean terrestrial deposits. Additionally, new insights on the oldest dinosauromorph-bearing sites throughout the Triassic, as well as regarding taxonomic diversity and geographic distribution of early dinosauromorphs reinforces previous hypotheses where dinosaurs and dinosaur-relatives consistently coexisted (for at least 21 Ma) before their extinction.
  • Geochemistry and geochronology of orthogneisses across a major
           transcurrent shear zone (East Pernambuco shear zone, Borborema Province,
           Northeast Brazil): Tectonic implications
    • Abstract: Publication date: April 2019Source: Journal of South American Earth Sciences, Volume 91Author(s): Rafaela H.M. França, Sérgio P. Neves, João P.S. Bezerra, Olivier BruguierAbstractThe East Pernambuco shear zone (EPSZ) is a dextral shear zone bounding the Rio Capibaribe and Pernambuco-Alagoas domains of the Neoproterozoic Borborema Province (NE Brazil). This study reports new geological data from orthogneisses across the central segment of the EPSZ. Two samples from the Bezerros orthogneiss to the north of the EPSZ yielded 207Pb/206Pb weighted mean ages of 2111 ± 7 Ma and 2104 ± 8 Ma. The c. 2.1 Ga age is taken as the age of crystallization of the protolith. It is undistinguishable from the age of the 2.13–2.09 Ga-old Vertentes Complex, which is the main Paleoproterozoic unit of the Rio Capibaribe Domain, and of orthogneisses that occur immediately south of the EPSZ. Like the Vertentes Complex, the Bezerros orthogneiss has a subduction-zone geochemical signature (e.g., pronounced negative Nb-Ta anomalies), suggesting intrusion in a magmatic arc setting. South of the EPSZ, a migmatized granitic orthogneiss and the Encruzilhada de São João orthogneiss yielded 206Pb/238U weighted mean ages of 645 ± 3 Ma and 639 ± 5 Ma, respectively. Ages of 615 ± 17 Ma and 618 ± 12 Ma obtained at the rims of zircon grains from Encruzilhada de São João and migmatized granitic orthogneisses, respectively, are interpreted as dating the acquisition of the low-angle gneissic fabric. The age of the EPSZ is bracketed by the 591 ± 4 Ma age of a monazite grain from the Bezerros orthogneiss and by the of 575 ± 17 Ma age of a young zircon grain in the Encruzilhada de São João orthogneiss. Rather than being a terrane boundary, the EPSZ more likely represents an intracontinental shear zone that nucleated at preexisting crustal heterogeneities.
  • Dagon avendanoi gen. and sp. nov., an Early Cenomanian Enchodontidae
           (Aulopiformes) fish from the El Chango quarry, Chiapas, southeastern
    • Abstract: Publication date: April 2019Source: Journal of South American Earth Sciences, Volume 91Author(s): Jesús Alberto Díaz-Cruz, Jesús Alvarado-Ortega, Gerardo Carbot-ChanonaAbstractDagon avendanoi gen. and sp. nov. is described based on a single specimen from the Early Cenomanian marine deposits of the Cintalapa Formation at El Chango quarry, near Ocozocoautla de Espinosa, Chiapas, southeastern Mexico. This species is identified as a new member of Enchodontidae because it shows the predorsal scute series, a distinctive unique character of the family. Among enchodontids, Dagon is unique because its palatine bone has two large fang-like teeth longitudinally ordered; contrary, the palatine in other enchodontids has only one large terminal tooth (i.e. Enchodus) or many small teeth (i.e. Unicachichthys). The inclusion of the new genus within a phylogenetic analysis reveals that the family Enchodontidae is a natural group (Unicachichthys (Dagon (Palaeolycus (Eurypholis + Saurorhamphus) + (Parenchodus + Enchodus)))). This new fish represents the third enchodontid species described from Mexico; this, together with Enchodus zimapanensis and Unicachichthys multidentata, allows to recognize the early diversification of enchodontids during the lower limit of Late Cretaceous throughout the North American domain of the Tethys Sea.
  • A rock magnetic fingerprint of hydrothermal alteration in volcanic rocks -
           An example from the Los Azufres Geothermal Field, Mexico
    • Abstract: Publication date: April 2019Source: Journal of South American Earth Sciences, Volume 91Author(s): Kailasa Pandarinath, Rajasekhariah Shankar, E. Santoyo, Shwetha B. Shetty, America Yosiris García-Soto, Eduardo Gonzalez-PartidaAbstractDrill rock cuttings from different depths of two geothermal wells (Az-26 and Az-49) from the Los Azufres Geothermal Field (LAGF), Mexico, were analyzed for rock magnetic properties (magnetic susceptibility, χlf; frequency-dependent susceptibility, χfd; susceptibility of anhysteretic remanent magnetization, χARM; isothermal remanent magnetization, IRM; saturation isothermal remanent magnetization, SIRM; “hard” isothermal remanent magnetization, HIRM) and their inter-parametric ratios (SIRM/χlf, χARM/SIRM and S-ratio) to explore the relationship, if any, between these properties and hydrothermal alteration. In both the geothermal wells, the intensity of hydrothermal alteration increases with depth and temperature of the well. The samples exhibit hydrothermal alteration-induced changes in several rock magnetic properties: (1) a decreasing trend in the values of concentration-dependent rock magnetic parameters (χlf; χfd, χARM, IRM300mT, and SIRM); (2) a decrease in S-ratio (relative proportions of ferrimagnetic and anti-ferromagnetic minerals) values and an increase in HIRM (“hard” IRM; concentration of magnetically “hard” minerals, e.g., hematite) values; and (3) increasing SIRM/χlf and χARM/SIRM ratio values. Most of the rock cuttings in both the wells are characterized by coarse SSD grains and they exhibit χlf values between 1 × 10−6 m3kg−1 (acid igneous rocks) and 10 × 10−6 m3kg−1 (SSD/MD grain size).Our study also indicates that the initial (primary) mineralogy of reservoir rocks may have an influence on the type of hydrothermal minerals that would form at low reservoir temperatures and/or with low intensity of hydrothermal alteration; however, this may not have any significant influence at high reservoir temperatures and/or high intensity of hydrothermal alteration.Our study suggests that in a homogenous litho-unit (rocks of the same type and age) of a large area, a zone characterized by anomalously low values of concentration-dependent rock magnetic properties (χlf, χfd, χARM, IRM300mT and SIRM), high SIRM/χlf, χARM/SIRM and HIRM values and low S-ratio values may indicate intense hydrothermal alteration. Consequently, rock magnetic properties may be a simple, yet an important tool, to identify hydrothermally altered rocks and zones of hydrothermal alteration, particularly in the initial stages of geothermal exploration.
  • Tephra fallout hazard assessment at Tacaná volcano (Mexico)
    • Abstract: Publication date: April 2019Source: Journal of South American Earth Sciences, Volume 91Author(s): Rosario Vázquez, Rosanna Bonasia, Arnau Folch, José L. Arce, J. Luis MacíasAbstractTacaná volcano is one of the dormant volcanoes in Mexico. Its activity is demonstrated by recent phreatic explosions occurred in 1949 and 1986. At least four Plinian to sub Plinian eruptions have been recorded in the eruptive history of this volcano, which produced pumice and ash deposits that blanketed a vast area straddling the Mexican and Guatemalan territory. Currently, there is no quantitative tephra hazard study of the volcano fallout deposits nor of the dispersion of ash in the atmosphere.In this work, we present the first probabilistic tephra hazard assessment for the Tacaná volcano. Probabilistic hazard maps were computed both, for the tephra deposit, and for critical thresholds of airborne ash concentration at different flight levels. The FALL3D numerical model was used to perform hazard maps for a Plinian scenario defined on the basis of the Sibinal Pumice eruption occurred ∼23.5 kyrs ago, which is the most studied deposit of this type in the volcano's surroundings, even when just few of their most distal outcrops are preserved. Results of this work show that at ground level, the disturbance for this type of hazard would affect mainly Guatemalan territory and the state of Chiapas in Mexico. It could cause serious repercussions on the economy of the region, which is characterized mainly by cocoa, coffee and banana plantations. The ash dispersion into the atmosphere could disturb the airspace and major airports in Mexican territory and neighboring countries. In fact, probability ash dispersal maps show that the level of affectation to the air traffic would involve the possible closure of at least 23 airports in Mexico, Guatemala, Belize, Honduras, El Salvador and Nicaragua. Another collateral damage would be the remobilization of ash by lahars considering the near 4000 mm of rain in average poured yearly in the Soconusco region that would increase the sediment load of the Coatán and Suchiate rivers, and then could produce a severe damage to the lowlands, which in the case of the Mexican territory, is the most populated one.
  • Rare earth element distribution in main lithologies of the Atibaia and
           Jaguari rivers’ subbasins (Southeast Brazil)
    • Abstract: Publication date: April 2019Source: Journal of South American Earth Sciences, Volume 91Author(s): Bruno Cesar Mortatti, Luiza de Carvalho Mendes, Jacinta EnzweilerAbstractIn this study, we investigated the mineral and geochemical compositions of the main lithotypes constituting the Atibaia and Jaguari rivers’ subbasins (Southeast Brazil), with the aims of characterizing the distribution of rare earth elements (REE) in that diversified geological framework and identifying their source bearing minerals to the environment at the catchment scale. Samples from six geological units comprising granitoids of monzogabbroic to granitic compositions, orthogneisses (dioritic to granitic compositions), paragneisses and local occurrences of quartzites were studied. In estimates of mineral proportions in each analyzed lithotype, we identified plagioclase, K-feldspar, and Ca-amphibole followed by minor amounts of apatite, titanite, allanite and rarely monazite as the potential light REE hosting phases, while the dominant heavy REE carriers were Na-amphibole, garnet, and zircon. The ∑REE contents in the rocks ranged between 59 and 791 mg kg−1, with a significant surplus of light over heavy REE [(La/Yb)CN = 11–197]. The whole-rock negative Eu anomalies of most samples result from the combined Eu budget of the individual minerals. Metamorphic lithotypes dominate at the Atibaia subbasin, whereas the main lithology of the Jaguari subbasin are granitoids. Comparatively, the first rocks contain slightly more ∑REE and are more enriched in light REE. These features and the relative weathering susceptibility of the REE hosting minerals constitute the initial step to explain the behavior of these elements in the environment.
  • Acanthochaetetes huauclillensis nov. sp. (Porifera: Demospongiae) from the
           Lower Cretaceous of Oaxaca, Mexico, and its palaeoecological,
           palaeobiogeographic and stratigraphic implications
    • Abstract: Publication date: April 2019Source: Journal of South American Earth Sciences, Volume 91Author(s): Francisco Sánchez-Beristain, Pedro García-Barrera, Josep Antón Moreno-BedmarAbstractA new species of chaetetid demosponge, Acanthochaetetes huauclillensis nov. sp., is described from the Upper Hauterivian to Lower Barremian of Santiago Huauclilla, Oaxaca State, Southern Mexico. The presence of tylostyle spicule pseudomorphs allowed its assignment to the Demospongiae. Criteria which allowed the proposal of this new taxon were: the presence of a scalariform arrangement of tabulae in adjacente calicles, which is observable in longitudinal section and the dimensions of calicles and tabulae in cross and longitudinal sections. These two characters make Acanthochaetetes huauclillensis nov. sp. unique among Acanthochaetetidae.The finding of microbialites growing on top of specimens of Acanthochaetetes huauclillensis nov. sp, in addition to their association to rudist faunas and the lack of associated algae allow the determination of its palaeoecological settings as coming from a cryptic reef-like environment.Further assessements include the palaeogeographic implications of this finding, which extends the distribution of ancient Acanthochaetetidae to the Western Tethyan Realm. The westward broadening of the distribution area of this family would have thus allowed its diversification and thus the development of a new species, in addition to filling the hiatuses in occurrence between the Oxfordian (oldest record for Acanthochaetetidae) and the Lower Albian, when they started their major diversification.
  • Tracking of geological structures and detection of hydrothermal intrusion
           by geo-electrical methods in the highlands of Bolivia
    • Abstract: Publication date: April 2019Source: Journal of South American Earth Sciences, Volume 91Author(s): Etzar Gómez, Emil Svensson, Torleif Dahlin, Gerhard Barmen, Jan-Erik RosbergAbstractOruro city in the Bolivian highlands depends solely on groundwater to supply domestic consumption and irrigation. The top porous aquifer currently exploited is not fully understood in aspects like geometry, hydrogeological properties and interaction with other aquifers in the region. Recent studies detected traces of fractures in the bedrock beneath the porous aquifer; these geological structures seem to be part of a fractured aquifer in contact with thermal sources. The present study aims to fill the gap between those recently detected fractures and the well-mapped fault system to the east of the study area and identify hydrothermal flows by using geo-electrical methods like Electrical Resistivity Tomography and Transient Electromagnetic soundings. Thirteen tomographic lines, placed transversely to the direction of three main faults, were meant to identify prolongations of those structures by tracking distinctive low resistivity in sectors where saline water saturates the subsoil. This type of water is also present in some hot springs near Capachos, where hydrothermal flows discharge under artesian conditions. Two of the investigated faults seem extending to the northwest, in agreement with the expected linkage towards the recently detected fractures. These two faults appear to reach a volcanic formation since the hydrothermal flows, going mainly upwards, align with their strikes. The remaining fault seems not to be connected to any hydrothermal source. The study presents new information, data and interpretations intending to improve the knowledge about the geological structures in a sensitive part of the local aquifer system.
  • Late-latest Maastrichtian foraminiferal assemblage from the Angostura
           Platform, Chiapas, SE Mexico: Biostratigraphic, paleoenvironmental and
           paleobiogeographic significance
    • Abstract: Publication date: April 2019Source: Journal of South American Earth Sciences, Volume 91Author(s): Lourdes Omaña, Gloria AlencásterAbstractThe carbonate platform deposits of the Angostura Formation are widely distributed in the central and eastern part of the Sierra de Chiapas, SE Mexico. The Angostura Formation contains a rich assemblage of foraminifera associated with mollusks (rudists, gastropods), corals, and dasycladacean green algae.A detailed foraminiferal study was carried out on samples from the El Coyol section of the Angostura succession. The studied section crops out in the El Coyol Hacienda located north of the Angostura dam, SE of the city of Tuxtla Gutiérrez in Central Chiapas. The foraminiferal assemblage consists mostly of benthic larger foraminifera but minor pelagic influence is represented by the presence of a number of planktic foraminifera.The benthic foraminiferal association is taxonomically diverse, being composed of Chubbina jamaicensis Robinson, Chubbina macgillavry Robinson, Caribealveolina michaudi Pêcheux, C. fourcadei Vicedo, Caus and Frijia, C. obesa (Fourcade and Fleury), Praechubbina breviclaustra Fourcade and Fleury, Omphalocyclus macroporus (Lamarck), Asterorbis rooki Vaughan and Cole, Vaughanina cubensis (Palmer), V. barkeri, Brönnimann, Sulcoperculina dickersoni (Palmer), S. globosa de Cizancourt, S. vermunti (Thiadens), Lepidorbitoides minima Douvillé, Orbitoides cf. O. apiculata Schlumberger, Planorbulina cretae (Marsson), Smoutina cruysi Drooger, and Nezzazatinella sp. In addition, the occurrence of Fleuryana adriatica De Castro, Drobne and Gušić, Rhapydionina cf. R. liburnica Stache, Cuneolina ketini Inan, Valvulina cf. V. triangularis d'Orbigny and Minouxia sp. is documented for the first time from the Angostura Formation.The planktic foraminifera are Rugoglobigerina macrocephala Brönnimann, R. cf. R. hexacamerata Brönnimann, R. rugosa (Plummer), Kuglerina rotundata (Brönnimmann), Muricohedbergella monmouthensis (Olson), Planoglobulina cf. P. carseyae (Plummer), Globotruncanita stuarti (de Lapparent), Globotruncanita pettersi (Gandolfi), Planoheterohelix globulosa (Ehrenberg), Pseudoguembelina sp., Macroglobigerinelloides prairielillensis (Pessagno) and the pithonellids Pithonella ovalis (Kaufmann) and P. sphaerica (Kaufmann). The age of the Angostura Formation in the studied section is late to latest Maastrichtian. A Chubbina jamaicensis Taxon Range Zone is proposed on the basis of the occurrence of the nominal taxon and foraminiferal association.The lithological and faunal evidence enable the paleoenvironment to be reconstructed. The microfacies (wackestone–packstone, wackestone–floatstone, wackestone, grainstone and packstone) as well as the foraminiferal assemblage suggest that the deposit was developed in a shallow water marine setting with low to moderate energy, with sporadic intercropping of an open platform deposit characterized by planktic foraminifera and pithonellids.The paleobiogeographical distribution of the foraminiferal association from the Angostura Formation contains cosmopolitan genera as well as endemic forms of the Caribbean Province from the Tethys Realm.
  • Carbonate-clastic sedimentation in the Parnaiba Basin, northern Brazil:
           Record of carboniferous epeiric sea in the Western Gondwana
    • Abstract: Publication date: April 2019Source: Journal of South American Earth Sciences, Volume 91Author(s): Renato Sol Paiva de Medeiros, Afonso César Rodrigues Nogueira, José Bandeira Cavalgante da Silva Junior, Alcides Nobrega SialAbstractThe transgressive-regressive events due to changes in the eustatic sea level represent the occurrence of an epeiric sea in Western Gondwana. This event is recorded in the carbonate-siliciclastic succession exposed in the central portion of the Parnaiba Basin, Northern Brazil, mainly represented by densely fossiliferous deposits, with mollusks, brachiopods, corals and microfossils, related to the upper member of the Piauí Formation. Outcrop-based facies/microfacies and stratigraphic analysis of this succession allowed the individualization of two facies associations (FA), representative of a shallow carbonate platform system adjacent to a coastal dune field. The FA1– dune field/interdune, comprises well sorted, intensely biortubated, fine to medium-grained sandstone with even parallel and tabular cross stratification, as well as translatent climbing ripple cross-lamination. FA2-shallow sea deposits consist of fossiliferous pelletal carbonate and microspar carbonate layers, laterally continuous for hundreds of meters, interbedded with centimetric beds and lenses of organic shale with small pyrite crystals. Covariant values of positive δ18Ocarb and negative δ13Ccarb for the carbonate profiles, together with intense substitution of primary constituents by dolomite and an abundance of associated organic matter contributed towards determining an organogenic dolomitization model. Although the Pennsylvanian records a long icehouse event, glacioeustatic fluctuations were common during the Moscovian and Kasimovian. The icehouse periods contributed to the semi-arid to desert conditions that shaped the aeolic environments of the Piauí Formation. Later greenhouse events favored a rise in the sea level and development of an extensive epicontinental Pennsylvanian sea that extended throughout Western Gondwana called the Itaituba-Piauí sea in this paper, which connected the Andean, Solimões, Amazonas and Parnaíba basins.
  • The Nova Monte Verde metamorphic core complex: Tectonic implications for
           the southern Amazonian craton
    • Abstract: Publication date: April 2019Source: Journal of South American Earth Sciences, Volume 91Author(s): Gilmar José Rizzotto, Cléber Ladeira Alves, Francisco Sene Rios, Márcia Aparecida de Sant’Ana BarrosAbstractThe Nova Monte Verde metamorphic core complex is an arched structure located in the southern portion of the Rio Negro-Juruena geochronological Province and is part of a belt of metamorphic rocks containing gneiss and migmatite domes exhumed during Statherian extension of rifted Ventuari-Tapajós crust. This metamorphic core is bordered, both to the north and south, by felsic volcanic and plutonic rocks intensely foliated near the metamorphic core and becoming progressively undeformed as one moves away from the metamorphic core. U-Pb analyses of zircon and monazite from migmatites exposed in the core of the complex, coupled with a detailed structural analysis, enlighten the timing and duration of migmatite crystallization, indicating that crystallization, extensional deformation and exhumation of the core-complex were coeval.Analysis of a high melt fraction from migmatites outcroping near Bacaeri Farm suggest that the Nova Monte Verde metamorphic core complex records a history of neosome formation spanning at least 37 Ma, as indicated by 206Pb/238U ages (1800-1763Ma) for new zircon growth attributed to migmatization.Monazite from two samples yielded U-Pb ages of 1798 ± 29 Ma for the aluminous metatexite and 1754 ± 11 Ma for sillimanite-biotite metatexite. The former is interpreted as the metamorphic peak and main generation of leucosomes, and the latter as the second phase of partial melting or as an alternative, the timing of cooling and exhumation of metamorphic core complex.Crystallization of the Nova Monte Verde migmatites was therefore coeval in part with upper crustal extension and ductile flow of the mid-crust, suggesting that crustal anatexis was widespread over much of the mid-crust during Statherian time (∼1800-1760Ma). Therefore, the tectonic history of the Nova Monte Verde core complex involved regional extension and exhumation of high-grade metamorphic rocks by transtensional tectonics. The following results are at least more compatible with, if not suggestive of, a continental rift setting than the traditionally accepted continental arc setting.
  • Neotectonic, morphotectonic and paleoseismologic analysis of the Las
    • Abstract: Publication date: April 2019Source: Journal of South American Earth Sciences, Volume 91Author(s): Luis Martin Rothis, Laura Patricia Perucca, Paula Santi Malnis, Juan Manuel Alcacer, Federico Miguel Haro, Horacio Nicolas VargasAbstractLas Chacras Fault System is a Quaternary structure located in the western piedmont of Sierra de la Huerta in the Sierras Pampeanas Occidentales, in west-central Argentina. This fault system is subsidiary of the Valle Fértil Megafault System, the NW-striking master structure that affects the western flank of the Valle Fértil - La Huerta ranges. The Las Chacras Fault System comprise several sections including the Pan de Azúcar fault, which presents the most conspicuous evidence of tectonic Quaternary activity. The Pan de Azúcar fault affects three Quaternary alluvial surfaces (Q1, Q2 and Q3) along 26 km in the western piedmont of Sierra de La Huerta, where three natural exposures allowed us to observe Triassic rocks thrust over Quaternary deposits. The observation of different kinematic markers and the relative position of the units affected by the fault, allow us to define this fault as a reverse fault. This structure trends 325° and dips 25° NE. With a DGPS we carried out detailed topographic profiles perpendicular to the average strike of the fault, along interfluves and rivers that cross the structure, for the purpose of establishing the relationship between the topography and the slope of the terrain. This analysis indicates that Quaternary activity of the fault has played an essential role in controlling the piedmont geomorphology, generating west-facing scarps and drainage anomalies such as rivers with convex Hack profiles. Paleoseismic analyses indicate that the fault has moved after 18.360 ± 2990 yr BP. Furthermore, we calculated a net displacement for the Pan de Azúcar fault of ∼50 ± 0.2 m since the Late Pleistocene to Holocene, yielding a shortening rate and a slip rate of ∼0.16 ± 0.1 mm/yr. Thus, the Pan de Azúcar fault is a potential seismogenic source, which could produce a moderate earthquake between Mw = 6.4 and 7.0, with a recurrence interval between 2600 and 6900 years.
  • Late Cretaceous paleogeography of the Antarctic Peninsula: New
           paleomagnetic pole from the James Ross Basin
    • Abstract: Publication date: April 2019Source: Journal of South American Earth Sciences, Volume 91Author(s): Florencia Milanese, Augusto Rapalini, Sarah P. Slotznick, Thomas S. Tobin, Joseph Kirschvink, Eduardo OliveroAbstractTwo paleomagnetic poles of 80 and 75 Ma have been computed from 191 to 123 paleomagnetic samples, respectively, of the marine sedimentary units of the Upper Cretaceous Marambio Group exposed in the James Ross Island, Antarctic Peninsula. Paleomagnetic behaviors during stepwise thermal demagnetization and rock magnetic analyses indicate that magnetization is likely primary and carried by SD-PSD detrital titanomagnetite. Application of an inclination shallowing correction by the elongation-inclination method yielded a significant inclination shallowing affecting the older (ca. 80 Ma) succession exposed in the northwest area of the island. However, the paleomagnetic directions computed from the younger (ca. 75 Ma) succession outcropping in the southeast corner of the island yielded an indeterminate result using the same analysis. The inclination shallowing-corrected 80 Ma paleopole position plus previous ones of ca.110, 90 and 55 Ma were used to construct the Apparent Polar Wander Path (APWP) for the Antarctic Peninsula during the Late Cretaceous-Paleocene. This path confirms that oroclinal bending of the Antarctic Peninsula as well as relative displacement with respect to East Antarctica are negligible since 110 Ma. Comparison with the apparent polar wander path for South America for the 130-45 Ma period suggests that this continent and the Antarctic Peninsula kept a very similar relative paleogeographic position since 110 Ma until 55 Ma, which likely meant a physical link between both continental masses. During that period, both continents underwent a relatively fast southward displacement of around 7° and a clockwise rotation relative to the Earth spin axis that can be bracketed between around 100 and 90 Ma. Oroclinal bending of the Fuegian Andes was likely due to tectonic interactions between the Patagonian-Fuegian Andes and the Antarctic Peninsula promoted, at least partially, by such displacements. By 55 Ma the Antarctic Peninsula probably was starting or about to start its final separation from South America.
  • Statherian-Calymmian (ca. 1.6 Ga) magmatism in the Alto Moxotó Terrane,
           Borborema Province, northeast Brazil: Implications for within-plate and
           coeval collisional tectonics in West Gondwana
    • Abstract: Publication date: April 2019Source: Journal of South American Earth Sciences, Volume 91Author(s): Geysson Almeida Lages, Lauro Cézar Montefalco de Lira Santos, Roberta Galba Brasilino, Joseneusa Brilhante Rodrigues, Elton Luiz DantasAbstractWe present geochronological, geochemical, and isotopic data on Statherian–Calymmian metaplutonites located within the Alto Moxotó Terrane (Borborema Province, Brazil). The Carnoió Suite occurs within a large area of this terrane. It is characterized by slightly deformed syenogranites and quartz-syenites, which present a geochemical signature typical of within-plate magmas. In contrast, the Coloete Suite occurs in the northern border area of the terrane. Its petrographic and geochemical characteristics vary between those of granodiorite and syenogranite, while its geochemistry suggests an arc-related/syn-collisional origin. There are few Statherian A-type granites in the Borborema Province and in its African counterpart. Zircon crystals recovered from the Carnoió Suite (dated 1638 Ma) and from the Coloete Suite (dated 1652 Ma; LA-ICP-MS) provide some clues about magma volume and concentration during the Statherian-Calymmian transition. Coeval collisional magmas are scarce in this region: they are interpreted worldwide as a product of peripheral convergences and coeval with the fragmentation of cratonic blocks. Our results suggest that the Alto Moxotó Terrane was part of an ancient block affected by an intraplate event during at the Statherian-Calymmian transition; moreover, its northern limits might have experienced accretion during a crust-reworking episode.
  • Late Famennian conodonts from the Cerro la Cueva, Sonora, NW Mexico
    • Abstract: Publication date: April 2019Source: Journal of South American Earth Sciences, Volume 91Author(s): Pilar Navas-Parejo, Omar Ramos Martínez, Juan José Palafox, Martín Valencia-MorenoAbstractThis paper reports for the first time the presence of Famennian conodonts from a shallow marine succession exposed in the Cerro La Cueva, central Sonora, northwestern Mexico. The conodont fauna includes Bispathodus aculeatus aculeatus (Branson and Mehl), Bispathodus stabilis (Branson and Mehl), ‘Icriodus’ darbyensis Klapper, Polygnathus extralobatus Schäfer, Polygnathus semicostatus Branson and Mehl, Polygnathus cf. inornatus E.R. Branson, and Polygnathus aff. purus Voges, which are typical species from the late Famennian. The most biostratigraphically important species of this assemblage are “Icriodus” darbyensis and Polygnathus extralobatus, which indicate an expansa Zones age interval. This finding allows identification of Devonian rocks in the area of San Pedro de la Cueva located north of the El Novillo dam, where only Ordovician and Mississippian fossils have been previously documented. The identified conodont genera preliminarily indicate an outer marine shelf paleoenvironment. Studied strata are correlated with Devonian lithostratigraphic units previously defined in other areas of Sonora, especially in the Sierra Agua Verde, located approximately 15 km west of the Cerro La Cueva section.
  • A model for thermal gradient and heat flow in central Chile: The role of
           thermal properties
    • Abstract: Publication date: April 2019Source: Journal of South American Earth Sciences, Volume 91Author(s): Pablo Valdenegro, Mauricio Muñoz, Gonzalo Yáñez, Miguel A. Parada, Diego MorataAbstractThe aim of this work is to quantify variations in heat flow and thermal gradient patterns at the latitude of central Chile and to evaluate the role of thermal properties of macro-geological units within the lithosphere. We developed a numerical thermal model for a continental-scale cross section at 33∘S latitude, integrating available and new data on geometry and dynamics of subduction, as well as thermal and mechanical properties for the continental and oceanic lithosphere, and asthenosphere. The model compares heat flow and thermal gradient curves against homogeneous inputs for radiogenic heat production (RHP) and thermal conductivity. The results of this model were calibrated with results of thermal gradient measurements at different morpho-tectonic domains. The results show that both, cold slab subduction and mantle wedge advection, play major roles in the regional thermal structure. Variations with respect to regional tendency are due to changes in thermal properties. The fore-arc has an average thermal gradient from 12 to 16∘C/km, whereas in the High Andes Cordillera it reaches up to values in the range between 20 and 28∘C/km. Model results indicate that thermal gradient increases eastward up to ∼25∘C/km in the easternmost foreland, which is a stable domain. The consistency of the model with respect to seismic record is discussed. Variation in composition and thermal properties is common at subduction zones due to dynamic petrologic processes. The RHP of the exposed upper crust units was obtained from more than 1000 in-situ measurements, whereas thermal conductivity, specific heat capacity and density of samples were obtained in the laboratory. The calculated RHP of upper crust is ∼2.0 μW/m3, which is responsible for ∼15–40% of the heat flow that reaches the surface.
  • A new fossil genus of angiosperm leaf from the Olmos Formation (upper
           Campanian), of northern Mexico
    • Abstract: Publication date: April 2019Source: Journal of South American Earth Sciences, Volume 91Author(s): Naylet K. Centeno-González, Héctor Porras-Múzquiz, Emilio Estrada-RuizAbstractThe Olmos Formation (upper Campanian) is located in the Sabinas Basin in northern Mexico. It represents a deltaic-fluvial system, and it is known by its abundance of fossil plants mainly represented by leaves and woods. In this contribution, we describe angiosperm fossil leaves, related to 'Violaceae. The new fossil genus has pinnate venation, with a major secondaries festooned semicraspedodromous, tertiary venation opposite percurrent, quaternary veins irregular reticulate, margin crenulated with tooth terminating in a glandular tissue, and fimbrial vein present. This mosaic of characteristics supports the creation of a new genus and species, Mascogophyllum elizondoa Centeno-González, Porras-Múzquiz et Estrada-Ruiz ('Violaceae). This record could be the oldest of the family; also, a new family is added to the very diverse fossil flora record that established during the Cretaceous in the northern of Mexico.
  • Determination of the temperature of precipitation of aragonite in shells
           of Anadara brasiliana (Lamarck, 1819) from Playa Norte, Cazones de Herrera
           (Holocene, Veracruz, Mexico) by means of trace element analysis
    • Abstract: Publication date: April 2019Source: Journal of South American Earth Sciences, Volume 91Author(s): E. Aldrin Juárez-Aguilar, Francisco Sánchez-Beristain, J.P. BernalAbstractIn this work, data on the precipitation temperatures of aragonite were evaluated from the analysis of three shells of the bivalve species Anadara brasiliana (Lamarck, 1819). The material was collected in the locality known as Playa Norte, belonging to the municipality of Cazones de Herrera, Veracruz, Mexico.The LA-ICP-MS method was applied to determine the concentrations of the elements Mg, Sr and Li in the calcareous matrix of the shells, in order to assess their distribution along them, and to obtain values of the temperature of precipitation of aragonite, taking into account the arrangement of the clear and dark bands of the shell. Concurrently, 25 oxygen stable isotope values were determined for the shells via mass spectrometry to obtain quantitative data regarding the same variable. Finally, the values obtained by both methods were compared. Temperature data from Sr/Li ratios vary between 22.48 °C and 25.39 °C, while δ18O temperatures range from 26.2 °C and 33.1 °C. Sr/Li temperatures are in strong agreement with data from the Coastal Ocean Observation Lab (COOL), while δ18O are not. Possible causes for this include the influence of salinity and evaporation rates on δ18O values for the Gulf of Mexico. We conclude that the analysis of the Sr/Li ratio via LA-ICP-MS can be applied reliably to obtain data of precipitation temperatures in this bivalve species, and subsequently in other bivalve species from the Gulf of Mexico. δ18O is not a reliable proxy for interpreting temperature values in bivalves from this basin. In addition, we come to the conclusion that Sr/Li ratios can be effectively used as δ18O-independent temperature proxies for biogenic aragonite.
  • Integrated biozonation based on palynology and ostracods from the Neogene
           of Solimões Basin, Brazil
    • Abstract: Publication date: April 2019Source: Journal of South American Earth Sciences, Volume 91Author(s): Ana P. Linhares, Maria I.F. Ramos, Valber C.S. Gaia, Yuri S. FriaesAbstractBiostratigraphic analysis integrating spores-pollen and ostracods from boreholes 1AS-8-AM and 1AS-7D-AM, at Atalaia do Norte, Amazonas state, Brazil, allowed to infer Early to Late Miocene for studied sequences. Five palynological zones previously proposed for the Solimões Formation were identified: Verrutricolporites (Early Miocene), Psiladiporites–Crototricolpites (late Early to early Middle Miocene), Crassoretitriletes (Middle Miocene), Grimsdalea (late Middle to Late Miocene), and Asteraceae (Late Miocene). At the same time, four ostracods (Cyprideis) zones were identified but with limits modified: C. sulcosigmoidalis (late Early to early Middle Miocene); C. caraionae (late Middle to early Late Miocene); C. minipunctata (late Middle to Late Miocene); and C. cyrtoma (early Late Miocene). Furthermore, a new ostracod zone, Cyprideis paralela interval zone (Late Miocene), is formally proposed. Two main bioevents of Cyprideis radiation, related to marine incursions, have been identified: one at late Middle Miocene/early Late Miocene (Grimsdalea zone) and another at Late Miocene (Asteraceae zone). This study attests the viability and importance of using multiple microfossil for more accurate dating and correlation between basins.
  • Geochronology and geothermometry of the Laramide metamorphism in the
           Cambrian metabasalts from the Cerro Rajón Formation, Caborca region,
           northwest Mexico
    • Abstract: Publication date: April 2019Source: Journal of South American Earth Sciences, Volume 91Author(s): Barrón-Díaz Arturo J, Paz-Moreno Francisco A, Miggins Daniel P, Iriondo AlexanderAbstractEarly Cambrian volcanic rocks characterized by pyroclastic and lava flows of basaltic composition form the Cerro Rajón Formation are exposed in the Caborca region, northwest Sonora, Mexico. These rocks underwent greenschist facies metamorphism characterized by a metamorphic paragenesis of actinolite, sphene, chlorite, epidote and calcite with minor interstitial albite. This mineralogical association was characterized by electron microprobe analysis. Metamorphic temperatures were calculated by amphibole-plagioclase geothermometry, which indicates temperatures as high as 548 ± 40 °C. UPb geochronology of the pluton that may cause the metamorphism yielded an age of 71.1 ± 0.4 Ma, and an average estimated temperature of 664 ± 40 °C. Preliminary pressures in this intrusive show an average of 3.08 ± 1.5 kbar. Two metamorphic events where identified by 40Ar/39Ar geochronology. Metabasalt samples from the western part of the study area yielded ages from 55.89 ± 0.6 Ma to 60.26 ± 0.33 Ma, while an age of 81.37 ± 0.81 Ma was obtained from a sample collected in the eastern part. Combined results suggest that Laramide intrusives metamorphosed the Neoproterozoic and Cambrian rocks in the Caborca region.
  • New fossil remains of Quaternary capybaras (Rodentia: Caviomorpha:
           Caviidae) from the intertropical region of Brazil: morphology and taxonomy
    • Abstract: Publication date: April 2019Source: Journal of South American Earth Sciences, Volume 91Author(s): Anny Caroliny Gomes, Gisele Lessa, Cástor Cartelle, Leonardo KerberAbstractIn this work, new fossils of Hydrochoerinae rodents (Caviomorpha: Caviidae: Hydrochoerinae) from the Quaternary of the intertropical region of Brazil are described, almost 180 years after the first fossils of these animals were found in Lagoa Santa, Minas Gerais. The fossils studied herein were collected in caves of States of Bahia (Toca dos Ossos and Lapa dos Brejões) and Minas Gerais (Lapa Vermelha cave, Lagoa Santa karst). The analyzed material is assigned to the extinct large rodent Neochoerus sulcidens and is composed of skull portion, upper and lower cheek teeth, mandible, humerus, innominate, femur, tibia, and calcaneus. The specimens were assigned to this taxon based on the presence of an M3 with 14 prisms; incisor alveolus reaching the pr. II do m2; anteriormost level of the palatine at the level of the Pr. II of the M2; and larger size than the living species. The p4 is mesiodistally longer than the m1 and m2, distinct from previous interpretations in which the mesiodistal length of the p4 of N. sulcidens would be smaller than the m2, indicating the presence of a variable character. Except for the differences in size, the postcranial bones of N. sulcidens are quite similar to H. hydrochaeris.
  • Palynology of Bonito and Barro Branco coal seams from Rio Bonito Formation
           (Lower Permian of Paraná Basin) in the Criciúma coal region,
           southernmost Brazil
    • Abstract: Publication date: April 2019Source: Journal of South American Earth Sciences, Volume 91Author(s): Z. Pereira, M. Mendes, P.A. Souza, C. Rodrigues, P. Fernandes, M. Ade, C. Araújo, J.R.L. Almeida, E.M. Santos, H.V. Rocha, V.E.S. Santos, B.P. Araújo, L. Garavaglia, M.J. Lemos de SousaAbstractSeven coal seams were sampled from several mines and outcrops of the Rio Bonito Formation, Bonito and Barro Branco coal seams, in the coal mining region of Criciúma, Paraná Basin, Santa Catarina State (Brazil), for a detailed palynostratigraphic study. The coal seams sampled yield abundant, diverse and moderately to well preserved palynological assemblages. A total of twenty-seven spore species, fourteen pollen species and four microplanktonic or clorophyceae algae and fungi species were identified. The palyno-assemblages recovered in the Bonito and Barro Branco coal seams are assigned to the Vittatina costabilis Interval Zone, Protohaploxypinus goraiensis Subzone of the Paraná Basin, of Asselian' to Artinskian age (Lower Permian). The microflora assemblages identified in these coal seams are very similar in composition, presenting a dominance of arborescent and herbaceous lycophytes. The Barro Branco coal seam shows a relatively higher frequency of algae like composition than in the Bonito coal seam, suggesting a possible fluvial or lagoonal facies influence.
  • High-pressure medium-temperature metamorphism of semi-pelitic rocks in the
           Scotia Metamorphic Complex, Powell Island, South Orkney Islands,
    • Abstract: Publication date: April 2019Source: Journal of South American Earth Sciences, Volume 91Author(s): Rodrigo Vinagre da Costa, Renato de Moraes, Rudolph Allard Johannes Trouw, Luiz Sérgio Amarante Simões, Julio Cezar MendesAbstractThe Antarctic continent constituted the southwestern margin of Gondwana until its break-up in the early Cretaceous, when new margins were created along the separating fragments of South America and Antarctica, forming the Scotia Arc. In the Jurassic, part of this passive continental margin became active with subduction of oceanic lithosphere, leading to the introduction of ocean floor material into the accretionary wedge accompanied by deformation and metamorphism. One of these margins is preserved in the South Orkney Microcontinent, and crops out at the South Orkney Islands. At Powell Island, situated in the center of the South Orkney Islands, a gradual transition from very low-grade metarenite, interlayered with metasiltite and slate of the Greywacke Shale Formation, in the south, to biotite-garnet schist, in the north, belonging to the Scotia Metamorphic Complex, is present. The metamorphic map presents from south to north a pumpellyite muscovite chlorite zone, a garnet zone, a biotite-garnet zone and an abundant biotite-garnet zone. Thermobarometric calculations yielded for the garnet and garnet-biotite zones temperatures between 498 and 517 °C with pressures of 9–11 kbar and for the abundant biotite-garnet zone temperatures between 522 and 550 °C and pressures between 11.8 and 13 kbar. These results align well with earlier obtained data for the lower grade rocks and confirm the idea of metamorphism in an accretionary wedge. The relatively high-pressure is interpreted to be responsible for the inversion of the biotite and garnet isograds, for the albitic composition of plagioclase and for the relatively Ca-rich garnet. P-T conditions fall in the transitional field between greenschist, amphibolite, blueschist and eclogite facies.
  • Repeated turnovers in Late Jurassic faunal assemblages of the Gulf of
           Mexico: Correlation with cold ocean water
    • Abstract: Publication date: April 2019Source: Journal of South American Earth Sciences, Volume 91Author(s): Patrick Zell, Wolfgang Stinnesbeck, Dominik Hennhoefer, Aisha Al Suwaidi, Sven Brysch, Gabriele Gruber, Nils SchorndorfAbstractOur research on Late Jurassic–earliest Cretaceous (Kimmeridgian–earliest Berriasian) marine shelf to bathyal sediments in northeastern Mexico reveals significant repeated oceanic and biotic turnovers in the northwestern Proto-Gulf of Mexico. We here document these environmental changes based on alternating cold and warm water mollusk assemblages, element concentrations and organofacies, as well as associated changes in sea level. We hypothesize that oscillations in the oceanic current system of the Gulf of Mexico were responsible for appearance of cold-water assemblages of Boreal and possibly Austral origins, situated in specific horizons which were previously described as poor in fossil content or even as fossil-free. In addition, these specific horizons show significant changes in element concentrations and organofacies and correlate to relative sea-level changes.
  • Almandine garnet-bearing rhyolites associated to bimodal volcanism in the
           Mesa Central of Mexico: Geochemical, petrological and geochronological
    • Abstract: Publication date: Available online 22 March 2019Source: Journal of South American Earth SciencesAuthor(s): Pascal Sieck, Rubén López-Doncel, Pablo Dávila-Harris, Alfredo Aguillón-Robles, Klaus Wemmer, Rene C. MauryGarnet-bearing rhyolitic flows and ignimbrites occur together with an andesitic lava flow in the central part of the Mesa Central in the western part of the Mexican state of San Luis Potosí, forming a typical K-rich sub-alkaline intra-plate tectonic setting bimodal series. Electron microprobe analysis indicates that the garnet is homogeneous and primarily almandine with subordinately pyrope, grossular, spessartine, and andradite. The chemistry of the garnets as well as the chemistry of the host rhyolite implies the crystallization of garnet as a primary phase from a lower crustal peraluminous magma. Rhyolite-MELTS simulations on the crystallization confirms this information. Trace element analyses on the rhyolitic ignimbrite and the garnet-bearing rhyolite suggest that the petrogenesis of these acidic rocks involved partial melting of the lower crust and fractional crystallization. The andesitic lava flow is metaluminous and its trace element patterns suggest that the parental magma was derived from upper mantle partial melting and that it was stored at the mantle-crust boundary. We propose that the southern Basin and Range extension event favored the direct ascent of these magmas from the source through the brittle and thin crust (30–33 km), where slight interaction with the country rock took place, to the surface. UPb dating on zircons from the rhyolites yielded ages ranging from 32.26 ± 0.92 Ma to 31.52 ± 0.48 Ma, consistent with the 31.25 ± 0.70 Ma whole rock KAr age of the garnet-bearing rhyolite. This information supports the interpretation that the garnets are not xenocrysts but they are crystallized from a rhyolitic magma at lower crustal depths and ascended fast through the brittle crust, so the garnets could be preserved.Graphical abstractImage 1
  • Sediment provenance of Triassic and Jurassic sandstones in central Mexico
           during activity of the Nazas volcanic arc
    • Abstract: Publication date: Available online 20 March 2019Source: Journal of South American Earth SciencesAuthor(s): Marc Wengler, José Rafael Barboza-Gudiño, Tonny B. Thomsen, Guido MeinholdAbstractWe have investigated the provenance of Late Triassic and Jurassic siliciclastic sediments (Zacatecas, Nazas and La Joya formations) in the Mesa Central region (areas of La Ballena, Charcas and Real de Catorce) in central Mexico. The sediments were deposited during activity of the Nazas volcanic arc at the western margin of Pangaea. Provenance characteristics are essential for reconstructing the palaeotectonic setting of the region. Overall, 26 sediment samples and 3 volcanic rock samples from the Nazas volcanic arc were analyzed. The latter are potential source lithologies. Petrographic analysis reveals that the analyzed sediments are mainly composed of monocrystalline quartz, polycrystalline quartz (chert and composite quartz), feldspar, and rock fragments of mainly volcanic origin. Th/Sc vs. Zr/Sc values illustrate low sediment recycling in the source area(s). For the majority of the analyzed samples low Cr and Ni values exclude input from a mafic/ultramafic (ophiolitic) source. The majority of the translucent heavy minerals (Pxn, Amp, Ep, Spn, Grt, Chl, Tur, Ant, Rt) are scarce in almost all samples. The most abundant translucent heavy minerals occurring in the samples are apatite and zircon. Apatite grains decrease from the southeast (La Ballena) towards the northeast (Real de Catorce) either indicating stronger weathering conditions in the area of Real de Catorce or a source area that delivered detritus exclusively for the zone of Real de Catorce. Sediments of the Zacatecas Formation illustrate maximum depositional ages ranging from Norian (Late Triassic) to the Hettangian/Sinemurian boundary (Early Jurassic). Detrital zircon U–Pb ages suggest that they received detritus from the Amazonian craton (∼1780–1300 Ma), the Oaxaquia microcontinent (∼1290–900 Ma), the Maya (Yucatan–Chiapas), Oaxaquia, Coahuila and possible Chortis, and Florida blocks (∼720–450 Ma) and the Permian–Triassic magmatic arc (∼300–240 Ma). The Acatlán Complex and the Maya (Yucatan–Chiapas) block are likely source areas for ∼445–310 Ma-old zircon grains. The source of the ∼240–200 Ma-old detrital zircons are likely magmatic rocks related to the early disassambly of western Pangaea. Detrital zircons from sediments of La Joya Formation provide maximum depositional ages from the Pliensbachian (Early Jurassic) to Oxfordian (Late Jurassic). The most probably source areas are the Oaxaquia microcontinent (∼1290–900 Ma), and the Maya (Yucatan–Chiapas), and Coahuila blocks (∼720–450 Ma). Zircon ages ranging from ∼200 to 150 Ma are indicative of detritus from the Nazas volcanic arc, which explains the presence of the volcanic fragments in La Joya Formation deposits.
  • Late Holocene coastal dynamics, climate pulses and low terraces in the
           coast of the state of São Paulo, southeast, Brazil
    • Abstract: Publication date: Available online 20 March 2019Source: Journal of South American Earth SciencesAuthor(s): André de Oliveira Souza, Archimedes Perez FilhoAbstractThe lower Ribeira de Iguape stream – located in São Paulo, Brazilian southern coast, exhibits complex geomorphologic characteristics that resulted from multiple processes developed during the late Holocene. The present study proposes discussions about the possible relations between short-term climate events from the late Holocene (Climate Pulses) promoting the coastal dynamics and genesis of different levels of low fluvial-marine and marine terraces located in the study area, a subject rarely considered in other studies in humid tropical regions. The procedure of work included grain-size analyses and optically stimulated luminescence (OSL) dating of sediment samples collected from different depositional packages. Four depositional events resulted from transgressive and regressive events geochronologically related with climate pulses from the late Holocene were identified. The events can be summarized as follows: I) Marine Transgression (∼3.5–2.7 ka); II) Marine Regression (2.7–1.8 ka); III) Marine Transgression (1.8–0.65 ka); IV) Marine Regression (0.65–0.10 ka).
  • Contributions of morphospace and multivariate analyses to interpretations
           of phenotype patterns and trends in Mexican Idoceras
    • Abstract: Publication date: Available online 16 March 2019Source: Journal of South American Earth SciencesAuthor(s): Gabriela Contreras-Figueroa, Federico Olóriz, Ana Bertha VillaseñorAbstractMorphospace analysis and multivariate statistics are conducted for the first time on Mexican Idoceras, a Kimmeridgian ammonite genus known for more than one hundred years. The database investigated contains 108 specimens belonging to old collections and material collected under precise biostratigraphic control from 1985 onwards. The main objectives are to evaluate phenotype dynamics, in terms of morphologic patterns through the numerical evaluation and then interpretation of the proposed Standardized Morphotypes. The phenotype variation was analyzed through Raup's theoretical morphospace and compared with the observations obtained from representatives of the genus. The subsequent comparative analysis using Multivariate statistics through Discriminant Analysis, Principal Component Analysis, and Cluster Analysis highlights precise relationships between the selected Standardized Morphotypes and two assemblages of Idoceras previously established with recognized stratigraphic value. These analyses reveal persistent relationships among classic and Raupian variates, which points to covariation of shell features within an evolutionary line, here the case of Mexican Idoceras, while differences related to shell-size are interpreted as resulting from ontogenetic changes in shell morphology derived from the influence of differential age and/or growth rate in phenotype expression. An attempt is made to interpreting the morphological trends represented by the Standardized Morphotypes in terms of shell hydrodynamics and behavior of ammonites under changing paleoenvironmental conditions.
  • Marine reptiles from the Jurassic/Cretaceous transition at the High Andes,
           Mendoza, Argentina
    • Abstract: Publication date: Available online 15 March 2019Source: Journal of South American Earth SciencesAuthor(s): Marta S. Fernández, Yanina Herrera, Verónica V. Vennari, Lisandro Campos, Marcelo de la Fuente, Marianella Talevi, Beatriz Aguirre-UrretaAbstractUpper Jurassic and Lower Cretaceous deposits of the Vaca Muerta Formation (Neuquén Basin, central-west Argentina) have yielded abundant marine reptile remains. Most of them correspond to faunal assemblages recovered from outcrops in the Neuquén Province (Argentina). Herein we report two new marine reptile-bearing localities documenting the Tithonian–Berriasian transition at the High Andes (Mendoza Province, Argentina). Marine reptiles have been mapped and/or collected in connection with an accurate ammonoid-based biostratigraphic control. All the skeletons have been found preserved in, or associated with, calcareous nodules. At both localities they are frequent in beds assigned to the upper Tithonian Corongoceras alternans Ammonite Zone (Microcanthum to “Durangites” Standard Zones), and are rare to common in beds assigned to the upper Tithonian–lower Berriasian Substeueroceras koeneni Zone (“Durangites” to Jacobi Standard Zones). Newly discovered assemblages depict a similar pattern characterized by the lack of plesiosaurs (plesiosauroids and pliosaurids), and by the abundance of mesoconsumers represented by ophthalmosaurids and metriorhynchine metriorhynchids. Macropredator geosaurines, apex metriorhynchids predators, and thalassochelydian turtles are rare components of these assemblages.
  • A new genus of pipimorph frog (anura) from the early Cretaceous Crato
           formation (aptian) and the evolution of South American tongueless frogs
    • Abstract: Publication date: Available online 15 March 2019Source: Journal of South American Earth SciencesAuthor(s): Ismar de Souza Carvalho, Federico Agnolin, Mauro A. Aranciaga Rolando, Fernando E. Novas, José Xavier-Neto, Francisco Idalécio de Freitas, José Artur Ferreira Gomes de AndradePipimorpha is a clade of tongueless anurans with a wide fossil record. Furthermore, the oldest South American fossils come from the Late Cretaceous (Cenomanian) of Patagonia, Argentina. The aim of the present contribution is to describe a new genus and species of Pipimorpha from the Crato Formation (Aptian, Early Cretaceous), Araripe Basin, Brazil. The new specimen consists of a nearly complete skeleton that shows several anatomical similarities with other fossils from South America. Phylogenetic analysis resulted in the nesting of the new taxon within a previously unrecognized endemic South American clade. Further, some traditional groupings within Pipimorpha were not recognized. The new phylogenetic analysis reinforces previous biogeographical hypotheses sustaining dispersal of pipimorph between Africa and South America through an island chain or continental bridge across the Atlantic Ocean.Graphical abstractImage 1
  • Geochemistry of aggradational - Progradational sequence sets of the Upper
           Jurassic – Lower Cretaceous Vaca Muerta shales (Añelo area, Neuquén
    • Abstract: Publication date: Available online 9 March 2019Source: Journal of South American Earth SciencesAuthor(s): Luis A. Spalletti, Mariano N. Remírez, Guillermina SagastiAbstractUnconventional shale plays have received marked attention over the last years because of their economic potential for hydrocarbon generation. The size and geology of the Neuquén Basin of western Argentina lends to large volumes of unconventional shale gas, particularly within the marine shales of the Upper Tithonian -- Valanginian Vaca Muerta Formation. This unit is characterized by a well-developed lithological transition from Tithonian monotonous organic-rich marly shales of several hundred metres thickness, to Lower Cretaceous increasingly carbonate-rich marls and marly limestones. Samples from four wells located in the central sector of the Neuquén Basin (Añelo area) were selected for petrographic, X-ray fluorescence and TOC analysis. Based on seismic interpretation of the strata geometry, these data were grouped according to their location in aggradational (AAS) and progradational accommodation sets (PAS). The AAS is composed of basinal black shale facies showing a planar stacking pattern, whereas the PAS is characterized by low-angle sigmoidal strata in which bottomset, foreset and topset deposits (and coeval basinal deposits) are recognized. Petrographic studies allowed to distinguish lithological variations between basinal (organic-rich, laminated unbioturbated shales and marly shales), bottomset (dark gray, diffuse laminated, slightly bioturbated shaly marls and marls), and foreset and topset deposits (gray, massive, bioturbated marls and calcareous marls with a wacky texture). Basinal deposits show a clear tendency towards compositions rich in silica. These distal deposits, together with the distalmost bottomset facies of the clinoforms, are relatively enriched in Al2O3. In turn, the content of CaO, MgO and P2O5 supplied by carbonate biogenic activity are higher in the shallower topset and foreset deposits. Distal (basinal and bottomset) deposits are significantly enriched in redox-sensitive elements (Mo, V, Co, S, Cr) and in organic productivity indicators (Zn, Ba, Cu and TOC).Basinal deposits accumulated under conditions of maximum sediment starvation, restricted circulation and low dissolved oxygen levels. These conditions partially persisted for the more distal progradational (bottomset) deposits, together with a progressive increase in carbonate intrabasinal productivity. Conversely, the foreset and topset deposits of the PAS formed under normal seawater oxygenation. These conditions favoured the increase of carbonate productivity associated with an ostensible decline of organic matter productivity and preservation. This approach to geochemical analysis in the sequence stratigraphic framework of the Vaca Muerta Formation suggests that redox conditions, biogenic carbonate productivity, detrital siliciclastic fluxes and carbon accumulation rates, were closely related to basin isolation, space available for sediment accumulation, and changes in water depth and marine water circulation.
  • Magmatic evolution of the Cerro Maricunga gold porphyry-epithermal system,
           Maricunga belt, N-Chile
    • Abstract: Publication date: Available online 9 March 2019Source: Journal of South American Earth SciencesAuthor(s): Stephanie Lohmeier, Albrecht Schneider, Boris Belyatsky, Bernd LehmannAbstractThe Cerro Maricunga gold project is located in the Maricunga gold belt in northern Chile, within the remnant edifice of the Tertiary Ojo de Maricunga volcano. The gold mineralization is hosted within a 23‒15 Ma old complex system of interwoven porphyry intrusions, flows, dikes and diverse breccia types, all forming part of a large diatreme system. In particular, phreatomagmatic and phreatic processes contributed to the formation of the synmineral diatreme complex. The rocks are calc-alkaline (daci)andesites and very rare dacites of the medium-K series with a high-K tendency and a conspicuous “adakitic” signature. Rare-earth element patterns reflect formation during a period of distinctly thickened continental crust with retention of heavy rare-earth elements by a garnet-bearing residue at a depth of ≥45 km. U-Pb zircon ages show a wide spectrum from Proterozoic, over Permian and Triassic ages to Paleocene, Oligocene, early and mid-Miocene ages. The Phanerozoic zircon ages indicate the assimilation of country rocks, whereas the Proterozoic age reflects the presence of a lower crustal Neoproterozoic basement that is also suggested by εNd values of −3.9 to −3.1 for bulk rock, i.e. mantle depletion model ages around 1 Ga. The last magmatic activity at the Ojo de Maricunga volcano was at ∼14.9 Ma. Stable isotope data on hydrothermal barite and supergene acanthite and gypsum (δ34Sacanthite: −0.6 to −0.4; δ34Ssulfate: 0.2 to 4.6; δ18Osulfate: 9.2 to 13.8) indicate an igneous origin of sulfur and arid conditions during mineral formation. The emplacement of the diatreme complex took place during the adjustment of the Chilean flat slab setting in a time of increased crustal thickness. Although the rocks at Ojo de Maricunga show a pronounced adakite-like signature, they formed in a common MASH zone or a deep hot zone within the lower crust. Gold mineralization took place at ∼17.9 Ma (Re-Os on molybdenite), syngenetic with diatreme formation and emplacement of hydrous magma. The thickening of continental crust was more advanced in the northern part of the Maricunga belt in the early to mid-Miocene than previously assumed, and then shifted south where several younger gold porphyries formed.
  • Integrated sedimentological and palynological analysis from Early
           Cretaceous estuarine deposits in the Southern Neuquén basin, Argentina
    • Abstract: Publication date: Available online 6 March 2019Source: Journal of South American Earth SciencesAuthor(s): Mariana S. Olivo, Cosme RombolA, Valeria S. Perez Loinaze, Diego A. KietzmannAbstractThe Mulichinco Formation represents one of the main gas producer unit in the Neuquén Basin and particularly, an improvement in its reservoir qualities are mostly indicated in subsurface for its upper section. Because the economic importance of this interval, sedimentological and palynological analysis were made on deposits from outcrops of the upper section of the unit, located at the southern-central Neuquén Basin. The studied section includes four main facies association which represent accumulations in a wave-dominated estuary, non-previously described for the Mulichinco Formation in the study area. In addition, sixty-six new palynomorphs species were identified which were new for the unit, including fifty-six spore species, twenty-five pollen grain taxa, and two algae. Ferns and conifers species were identified as dominant taxa. Moreover, mega and palynofloristic assemblages provide information about drainage conditions of the inhabited environment, suggesting spatial variations when comparing upland subaerial well-drained plains with lowland subaqueous poorly-drained areas and, at the same time, climatic variations are considered, inferring temperate to warm and wet palaeoclimatic conditions. The integration of sedimentological and palynological interpretations provides a more complete picture of the Valanginian estuarine system and ecosystem that developed towards the southern-central area of the Neuquén Basin. Furthermore, the studied palynological assemblages are consistent with a Late Valanginian age, and can be referred to the Zone 2 and to the Cyclusphaera psilata-Classopollis Association suggested for the Neuquén Basin.
  • AAPG Memoir 117 “Petroleum Basins and Hydrocarbon Potential of the Andes
           of Peru and Bolivia.” Gonzalo Zamora Valcarce, Ken McClay, and Victor
           Ramos (eds.). 656 pages.
    • Abstract: Publication date: Available online 4 March 2019Source: Journal of South American Earth SciencesAuthor(s): Andrés Folguera
  • Significant late Neogene development of the Caroni basin, Trinidad and
    • Abstract: Publication date: Available online 1 March 2019Source: Journal of South American Earth SciencesAuthor(s): G. HugginsAbstractThe Manzanilla and Springvale Formations outcrop along a 1.9 km stretch on the eastern coast of Trinidad, and provide vital information about the development of the Caroni Basin and north-central Trinidad. The Manzanilla Formation contains deposits that range from deepwater to delta plain facies. Sandstone turbidites are the oldest deposits and these transition upward into muddy slope deposits then shelf mudstones, siltstones and sandstones. The occurrence of sporadic conglomerate beds suggests debris flows or other coarse-grained sediment gravity flows additionally entering the basin at this time. The upper parts of the Manzanilla succession reflect marginal marine environments with delta front (including mouth-bar), crevasse splay, bay fill and marsh deposits. Most of these deposits originated as the northernmost part of the east to northeast flowing paleo-Orinoco Delta. The anomalous interfingering of coarse-grained lithic-rich debris flow deposits with the delta-derived deposits, strongly suggests a derivation directly from the steep-sloped alluvial-fan and fan-delta deposits eroding off of the Northern Range orogenic belt, some 10 km to the north. The facies associations of the Springvale Formation reflect channelized estuarine environments strongly influenced by tidal processes. Subtidal channels associate with and are succeeded by wave and tidal influenced intertidal facies and their overlying supratidal mudstones, paleo-sols and lignite beds.Examination of these two formations reveals that the Neogene Caroni Basin developed quite differently from the coeval Southern and Columbus basins to the south. The Southern and Columbus Basins are true foreland basins with growing accommodation space and expanded shelf section due to the movement of huge listric faults. When compared to similar aged formations in the Southern Basin, the Caroni Basin succession is relatively thin, starved of sediment, contains internal discontinuities and tectonically derived coarse-grained conglomerates. This contrast is due to the fact that the Caroni Basin is sited immediately adjacent to the northern Trinidad zone of Caribbean and South American plate-margin convergence. The compressional forces acting on the basin produced alternating periods of uplift/erosion and subsidence which inhibited continuous deposition. The outcrops examined herein present new detail of the tectonic impact on the evolving Caroni foreland basin within northern Trinidad, where compression-driven base level changes left their signals in the foreland succession.
  • Pb+zircon+age+for+the+Pennsylvanian+in+Argentina:+Implications+in+palynostratigraphy+and+regional+stratigraphy&rft.title=Journal+of+South+American+Earth+Sciences&rft.issn=0895-9811&">New UPb zircon age for the Pennsylvanian in Argentina: Implications in
           palynostratigraphy and regional stratigraphy
    • Abstract: Publication date: Available online 28 February 2019Source: Journal of South American Earth SciencesAuthor(s): Silvia N. Césari, Carlos O. Limarino, Luis A. Spalletti, Ferrán Colombo Piñol, Valeria S. Perez Loinaze, Patricia L. Ciccioli, Richard FriedmanAbstractA continuous Pennsylvanian succession belonging to the Agua Colorada and De La Cuesta formations is exposed in the Las Angosturas area (Catamarca Province) of the Paganzo Basin. Glacial, postglacial, fluvial and shallow marine deposits are identified and referred to seven stratigraphic stages. The Agua Colorada Formation provides a persistent record of palynological assemblages in the first five stages, which are assigned to the Subzones A and B of the Raistrickia densa/Convolutispora muriornata Biozone. These palynofloras span the late Serpukhovian-Bashkirian interval. The first isotopic age for the basal section of the De La Cuesta Formation was obtained from shallow marine deposits. Zircons from a tuff intercalated with mudstones and sandstones in the marine interval were analyzed by the CA-TIMS technique providing an age of 311.89 ± 0.21 Ma, based on the weighted average of 206Pb/238U dates. This new age is compared with previous isotopic ages obtained from different successions of the Paganzo Basin, resulting the youngest, up to now, for the Moscovian transgression. Indeed, a late Moscovian age is already known by isotopic dating of the reddish fluvial deposits of the lower section of the Patquía Formation, which overlies the transgression in the Huaco area (San Juan Province). The record of this marine flooding surface in reddish strata at Las Angosturas area provides a cautionary note on considering the appearance of red beds as indicators of the onset of continental conditions in the Paganzo Basin.
  • Mineral chemistry and geothermometry of alteration zones in the IOCG
           Cristalino deposit, Carajás Mineral Province, Brazil
    • Abstract: Publication date: Available online 26 February 2019Source: Journal of South American Earth SciencesAuthor(s): Gustavo Souza Craveiro, Raimundo Netuno Nobre Villas, Roberto Perez XavierAbstractThe Cristalino deposit, located in the Serra do Rabo region (Pará State, Brazil), is related to a hydrothermal system in which two major alteration stages could be distinguished most likely with the involvement of a hyper-saline fluid. The first stage (410-650 °C) is characterized by a distal sodic metasomatism that produced almost pure chessboard albite, minor schorlitic tourmaline and REE-rich minerals (allanite-Ce, monazite). It was followed by a pervasive calcic-ferric alteration that generated abundant actinolite (XMg = 0.87–0.69, Cl up to 0.59 wt %) in addition to Ce-allanite and magnetite associated with sulfide disseminations and breccia-like bodies composed of chalcopyrite-pyrite-magnetite-Au (early ore association). Locally, Fe-edenite (XMg = 0.67–0.42, Cl up to 2.94 wt %) replaced calcic-ferric assemblages within restrict sodic-calcic alteration halos. From 410° down to 220 °C, the previous alteration assemblages were overprinted by the hydrothermal products of the second stage. Potassic (K-feldspar, minor biotite) and propylitic (epidote, chlorite, calcite) alterations came into play successively. K-feldspar is practically stoichiometric, but it contains some impurities, notably BaO (up to 1.21 wt %). Chlorite shows the greatest compositional variation among all minerals and its composition seems to have been particularly controlled by the type of host rock, chemistry of the hydrothermal fluid and temperature. Both chamosite and clinoclore (XFe = 0.37–0.80) are present, the former being more common. Chlorine contents are in general
  • Editorial from Editors in Chief
    • Abstract: Publication date: Available online 19 February 2019Source: Journal of South American Earth SciencesAuthor(s): Andres Folguera, Francisco J. Vega
  • Editorial
    • Abstract: Publication date: Available online 23 January 2019Source: Journal of South American Earth SciencesAuthor(s): James N. Kellogg
  • Comment on Zepeda et al. (2018) A major provenance change in sandstones
           from the Tezoatlán basin, southern Mexico, controlled by Jurassic,
           sinistral normal motion along the Salado River fault: Implications for the
           reconstruction of Pangea
    • Abstract: Publication date: Available online 4 December 2018Source: Journal of South American Earth SciencesAuthor(s): Roberto S. Molina Garza, Diego Osorio AfanadorAbstractZepeda et al. (2018) present the sandstone petrography of Lower-Middle Jurassic sedimentary rocks of the Tezoatlán basin, in Oaxaca, southern Mexico. These data are for a well-known locality, historically know for its plant and ammonite fossil content. They also present detrital zircon geochronology for two samples in a measured section about 200 m thick. Additional data include heavy mineral and paleocurrent data. Their data show a transition from volcanic rich conglomerates and sandstones, to metamorphic clast rich sandstone. Using this information, and a recently published age for micas in the Salado River Fault, they conclude that this WNW trending fault was active in the Jurassic and somehow influenced sedimentation in the Tezoatlán basin. They also conclude that fault activity is related to rupture of Pangea. We believe these data are over-interpreted and supported by an incomplete interpretation of depositional environments. The change in sediment provenance can be explained by gradual erosion of the volcanic cover of the local basement. Moreover, this section is part of a well recognized extensional system with continental rift characteristics. The Salado River fault appears to be a fault of complex geometry, perhaps a scissor fault, connecting two basins of a continental rift. There is no indication of a continental scale, crustal scale, left lateral strike slip fault linked to rupture of Pangea.
  • Reply to comment by Molina-Garza and Osorio-Afanador (2018)
    • Abstract: Publication date: Available online 29 November 2018Source: Journal of South American Earth SciencesAuthor(s): Michelangelo Martini, Mildred Zepeda-Martínez, Luigi Solari
  • Comment on Gold et al. “The biostratigraphic record of Cretaceous to
           Paleogene tectono-eustatic relative sea-level change in Jamaica, Journal
           of south American Earth Sciences (2018), doi:
    • Abstract: Publication date: Available online 5 October 2018Source: Journal of South American Earth SciencesAuthor(s): Simon F. MitchellAbstractGold et al. (2018) present a mid Cretaceous-early Cenozoic relative sea-level curve for Jamaica based on sedimentological and biostratigraphic data from spot samples made from Jamaican outcrop localities and well/corehole samples. They base their work on 200 samples from field outcrops and 600 samples from hydrocarbon exploration wells (many of the latter with cuttings contaminated with extensive cavings)/coreholes, of which 266 were assigned a depositional setting, palaeobathymetry and biostratigraphic age. Gold et al. (2018) use this dataset to revise the sequence stratigraphy of Jamaica, develop a relative sea-level curve and compare this with global sea-level curves. The paper by Gold et al. (2018) includes numerous errors of fact and doubtful interpretations. In this comment I highlight some of these problems based on my own, and my research students’ research over the last 22 years, my own collection of 20,000 + samples from Jamaica, and a thorough understanding of the literature.
  • Pb+geochronology+of+Jurassic+plutons+in+the+Upper+Magdalena+Valley-Colombia:+Implications+on+the+evolution+of+magmatic+arcs+in+the+NW+Andes’+by+Rodríguez+et+al.+(2018)&rft.title=Journal+of+South+American+Earth+Sciences&rft.issn=0895-9811&">Comment on ‘Petrotectonic characteristics, geochemistry, and UPb
           geochronology of Jurassic plutons in the Upper Magdalena Valley-Colombia:
           Implications on the evolution of magmatic arcs in the NW Andes’ by
           Rodríguez et al. (2018)
    • Abstract: Publication date: Available online 23 August 2018Source: Journal of South American Earth SciencesAuthor(s): Camilo Bustamante, Agustín Cardona, Andres Bustamante, Jakeline Vanegas
  • Pre-eruptive conditions and pyroclastic emplacement of the last known
           vulcanian eruption of Azufral Volcano, SW Colombia
    • Abstract: Publication date: Available online 11 August 2018Source: Journal of South American Earth SciencesAuthor(s): Silvia C. Castilla, Natalia Pardo, Patricia Larrea, Carlos A. Zuluaga, Sergio Sarmiento, David Noguera, Gustavo A. SarmientoAbstractAzufral is one of the most touristic, but also one of the most explosive active volcanoes of SW-Colombia. Although no historical eruptions have occurred, the potential thread is inferred from the predominance of dacitic pyroclastic units and lava domes since the Holocene. This paper presents new stratigraphical and compositional data of the uppermost and thickest proximal pyroclastic deposits exposed on the current inner and outer SE crater rim. The studied eruption units correspond to parallel and low-angle cross-bedded vitric-crystalline to lithic-crystalline tuffs. The absence of interbedded paleosols or epiclastic deposits indicates continuous eruptive activity throughout the studied succession. Criteria for stratigraphic package division at proximal sites includes erosive contacts, marked changes in grain sizes, and ballistic-bearing horizons. Each package comprises several bedsets consisting of two to three beds of distinctive lithofacies associations suggesting deposition from diluted pyroclastic density currents. Temporary partial or total conduit obstruction conditions could also be inferred from the presence of ballistic horizons.Petrographical and geochemical analyses from a type-bedset with fresh, poorly to moderately vesicular rhyolitic glassy particles and the mineral association Pl + Amp + Bt + Fe-Ti oxides ± Qz microcrysts suggest the presence of juvenile material. Textures and mineralogy of glassy ash particles are the same as those in large ballistic blocks, which are dacitic in whole-rock composition. Geochemical analyses suggest that magma evolution was mainly controlled by Pl + Amp + Bt + Py + Fe-Ti oxides fractionation and magma recharge events. All Pl and Amp microcrysts in the studied juvenile ash and ballistics can be grouped into two populations: (i) unzoned microcrysts and (ii) zoned microcrysts. Zoned microcrysts have evolved and partially corroded cores, coated by a more Mg-rich (Amp) or An-rich (Pl) mantle, and followed by an outermost Fe-rich (Amp) or Ab-rich (Pl) rim that broadly overlaps with the composition of the unzoned microcrysts.Textures, mineral composition, and pre-eruptive conditions obtained from similar-sized Amp, Pl and Fe-Ti oxide microcrysts within the juvenile ash and a juvenile ballistic provide evidence of complex crystallization paths before final decompression and eruption.
  • The early Miocene elasmobranch assemblage from Zamaca (Chilcatay
           Formation, Peru)
    • Abstract: Publication date: Available online 7 August 2018Source: Journal of South American Earth SciencesAuthor(s): Walter Landini, Alberto Collareta, Claudio Di Celma, Elisa Malinverno, Mario Urbina, Giovanni BianucciAbstractA newly discovered elasmobranch assemblage from the fossil-bearing area of Zamaca (Chilcatay Formation, southern Peru) is described herein, providing a first comprehensive view on the early Miocene shark and ray paleocommunities of the East Pisco Basin, whose sedimentary infill represents one of the most important Cenozoic Fossil-Lagerstätten worldwide. The studied assemblage includes at least twenty-two species attributed to twelve families and five orders. Thirteen taxa are recorded for the first time from the Chilcatay Formation, and four of them are recorded for the first time from the Pacific coast of South America. The reconstructed paleoenvironmental scenario is consistent with a shallow-marine coastal area, representative of a sheltered shelfal setting, influenced by both brackish and open-ocean waters. This paleoenvironment was inhabited by a community of small mesopredator elasmobranchs that exploited the Zamaca area as a nursery ground and recruitment area. The structure of the Zamaca assemblage is mainly explained by three key-features: 1) a taxonomic composition dominated by two shark lineages, Lamniformes and Carcharhiniformes, the former being predominant; 2) the leading role played by two species, Carcharhinus brachyurus and †Cosmopolitodus hastalis, accounting for about 60% of the analyzed specimens; 3) the distinctly juvenile imprint of the entire assemblage. Striking similarities emerge between the elasmobranch assemblage from Zamaca and the late Miocene one from Cerro Colorado (Pisco Formation, East Pisco Basin), thus suggesting the persistence of a peculiar “biological enclave” driven by the concurrence of the ecological, environmental, and oceanographic factors that characterized the coast of present-day Peru during the Neogene.
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Heriot-Watt University
Edinburgh, EH14 4AS, UK
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