Subjects -> PALEONTOLOGY (Total: 43 journals)
Showing 1 - 21 of 21 Journals sorted alphabetically
Alcheringa: An Australasian Journal of Palaeontology     Hybrid Journal   (Followers: 6)
Ameghiniana     Open Access  
Annales de Paléontologie     Full-text available via subscription   (Followers: 4)
Annals of Carnegie Museum     Full-text available via subscription   (Followers: 1)
Boreas: An International Journal of Quaternary Research     Hybrid Journal   (Followers: 12)
Comptes Rendus Palevol     Open Access  
European Journal of Protistology     Hybrid Journal   (Followers: 5)
EvoDevo     Open Access   (Followers: 4)
Facies     Hybrid Journal   (Followers: 9)
Fossil Record     Open Access   (Followers: 5)
Geobios     Full-text available via subscription   (Followers: 4)
Historical Biology: An International Journal of Paleobiology     Hybrid Journal   (Followers: 8)
Ichnos: An International Journal for Plant and Animal Traces     Hybrid Journal  
International Journal of Speleology     Open Access   (Followers: 3)
Journal of Paleolimnology     Hybrid Journal   (Followers: 5)
Journal of Paleontology     Hybrid Journal   (Followers: 8)
Journal of Quaternary Science     Hybrid Journal   (Followers: 29)
Journal of Vertebrate Paleontology     Full-text available via subscription   (Followers: 8)
Marine Micropaleontology     Hybrid Journal   (Followers: 2)
Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen     Full-text available via subscription   (Followers: 3)
Novitates Paleoentomologicae     Open Access   (Followers: 1)
Open Quaternary     Open Access  
Palaeogeography, Palaeoclimatology, Palaeoecology     Hybrid Journal   (Followers: 11)
Palaeontographica A     Full-text available via subscription   (Followers: 7)
Palaeontology     Hybrid Journal   (Followers: 17)
Palaeoworld     Hybrid Journal   (Followers: 3)
Paläontologische Zeitschrift     Hybrid Journal   (Followers: 4)
Paleobiology     Full-text available via subscription   (Followers: 5)
PaleoBios     Open Access   (Followers: 1)
Paleoceanography and Paleoclimatology     Full-text available via subscription   (Followers: 4)
Paleontological Journal     Full-text available via subscription   (Followers: 4)
Palynology     Hybrid Journal   (Followers: 1)
Papers in Palaeontology     Hybrid Journal  
Quaternaire     Open Access   (Followers: 3)
Quaternary Research     Full-text available via subscription   (Followers: 19)
Quaternary Science Reviews     Hybrid Journal   (Followers: 24)
Review of Palaeobotany and Palynology     Hybrid Journal   (Followers: 1)
Revue de Micropaleontologie     Full-text available via subscription  
Rivista Italiana di Paleontologia e Stratigrafia (Research In Paleontology and Stratigraphy)     Open Access   (Followers: 1)
Spanish Journal of Palaeontology     Open Access  
Swiss Journal of Palaeontology     Hybrid Journal   (Followers: 4)
Vertebrate Anatomy Morphology Palaeontology     Open Access   (Followers: 1)
Zitteliana     Open Access  
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Facies
Journal Prestige (SJR): 0.669
Citation Impact (citeScore): 2
Number of Followers: 9  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 1612-4820 - ISSN (Online) 0172-9179
Published by Springer-Verlag Homepage  [2469 journals]
  • Ichnology of Lower Cretaceous prodelta and delta front deposits of the
           Sidi Khalif Formation, Central Tunisia

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      Abstract: This paper describes the ichnology and sedimentology of the middle Berriasian sedimentary succession of the Sidi Khalif Formation outcropping in Jebel Meloussi, Central Tunisia. The succession records deltaic progradation above outer shelf deposits and shows the vertical stacking of thickening and coarsening-upward parasequences dominated by hummocky cross-stratification, parallel lamination and abundant gutter casts. The mudstones and the thinly bedded fine-grained sandstones of the prodelta are characterized by scarce and low diverse horizontal trace fossils of the impoverished distal Cruziana ichnofacies, including cf. Thalassinoides, Phycosiphon, Planolites, Helminthoidichnites and cf. Helminthoidichnites. In contrast, trace fossils of the wave-dominated delta-front are dominated by deposit-feeding ichnotaxa, such as Rhizocorallium commune, Arenicolites isp., R. 'jenense, Thalassinoides and Planolites, which represent the proximal Cruziana ichnofacies. The lack of bioturbation structures in the amalgamated hummocky cross-stratification beds of the delta front is mostly related to the high frequency and/or high intensity episodic erosional amalgamation and deposition associated with storms. The difference between Rhizocorallium ichnospecies help to depict the erosional discontinuities bounding parasequences. The transgressive surfaces (TS) are characterized by R. 'jenense and by R. commune.
      PubDate: 2022-01-04
       
  • Microbial mats and evaporite facies variation in a supralittoral,
           ephemeral lake, Red Sea coast, Saudi Arabia

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      Abstract: This study documents the deposits of an ephemeral, shallow lake that is recharged mainly from floods and torrential rainfalls from the Red Sea Mountains, in addition to seawater seepage at its western margin. The lake is desiccated in the summer months into several smaller, ephemeral pans and sabkhas due to excessive evaporation of its waters and decreased inflow of seawater seepage accompanied by the lowered hydraulic gradient between the Red Sea and the lake floor. The formation and distribution of microbial mats, gypsum and halite are discussed with respect to water supply and salinity. Microbial mats dominate the floor of the wintertime lake, and in the summertime, coastal pans where salinity is less than 126%. Gypsum crystals encrust microbial mats at salinities in excess of 182%. The central and eastern pans are floored with halite crusts at a salinity > 250% that develop into tepee polygons through desiccation. The slightly higher topographic sabkha areas around these pans contain subsurface, displacive, lenticular and tabular gypsum crystals, and clear, mosaic halite cement. Most of the water supplied to the supralittoral lake is during the wintertime, from episodic floods from the hinterland with a general increase in salinity towards the sea. However, the pattern of distribution and abundance of microbial mats-gypsum-halite facies are in a reverse order to the direction of water supply and increases in salinity. This ambiguity can be explained by the intermittent supply of seawater seepage from the Red Sea through an artificial barrier that is controlled by tidal range and fluctuations of sea level.
      PubDate: 2021-12-18
       
  • Changing depositional environments in the semi-restricted Late Jurassic
           Lemeš Basin (Outer Dinarides; Croatia)

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      Abstract: The up to 450 m-thick Upper Jurassic Lemeš Formation includes organic-rich deep-water (max. ~ 300 m) sedimentary rocks deposited in the Lemeš Basin within the Adriatic Carbonate Platform (AdCP). The Lemeš Formation was investigated regarding (1) bio- and chemostratigraphy, (2) depositional environment, and (3) source rock potential. A multi-proxy approach—microfacies, Rock–Eval pyrolysis, maceral analysis, biomarkers, and stable isotope ratios—was used. Based on the results, the Lemeš Formation is subdivided from base to top into Lemeš Units 1–3. Deposition of deep-water sediments was related to a late Oxfordian deepening event causing open-marine conditions and accumulation of radiolarian-rich wackestones (Unit 1). Unit 2, which is about 50 m thick and Lower early Kimmeridgian (E. bimammatum to S. platynota, ammonite zones) in age, was deposited in a restricted, strongly oxygen-depleted basin. It consists of radiolarian pack- and grainstones with high amounts of kerogen type II-S organic matter (avg. TOC 3.57 wt.%). Although the biomass is predominantly marine algal and bacterial in origin, minor terrestrial organic matter that was transported from nearby land areas is also present. The overlying Unit 3 records a shallowing of the basin and a return to oxygenated conditions. The evolution of the Lemeš Basin is explained by buckling of the AdCP due to ophiolite obduction and compressional tectonics in the Inner Dinarides. Lemeš Unit 2 contains prolific oil-prone source rocks. Though thermally immature at the study location, these rocks could generate about 1.3 t of hydrocarbon per m2 surface area when mature.
      PubDate: 2021-12-18
       
  • Cyclic nature of the biotic attributes of macroinvertebrate communities in
           the Cenomanian–Turonian strata of Sinai: water depth-driven biological
           responses

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      Abstract: The analysis of high-resolution stratigraphic data from the Cenomanian–Turonian successions in three sections from Sinai (northeast Egypt) revealed the mechanisms behind water depth-driven biological responses (visible in changes of biodiversity and community structure) of macroinvertebrates. Quantitative biostratigraphical analysis of 127 samples containing 6203 specimens representing 41 genera of molluscs, corals, and echinoids were used to construct changes in the community structure of Cenomanian–Turonian macroinvertebrates. We identified six assemblages that we assigned to two main categories and linked to regional sea-level changes. The first group of assemblages is associated with the initiation of transgression and/or late normal regression, is dominated mainly by opportunistic, epifaunal suspension feeders (oyster bivalves) and is characterized by lower diversity values (low Shannon Index and high dominance). The second category is associated with the maximum flooding zone and dominated by infaunal deposit feeders such as irregular echinoids and by nektonic ammonites and is characterized by higher diversity. The increase in nektonic and decrease in benthic taxa during the latest Cenomanian suggest deepening of the environment. Moreover, the change in the water depth was accompanied by a change in the structure of the macrobenthos.
      PubDate: 2021-11-17
       
  • Preferential dolomitization in Mio–Pliocene bioclastic clinoforms,
           Bonaire Island, South Caribbean: insights from petrographic and
           geochemical analyses

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      Abstract: Selective dolomitization, where certain carbonate components are preferentially dolomitized over others, can be significant in the overall dynamic context of the global magnesium cycle. Thus, the abundance of these components can modify the Mg balance between the ocean and sediments, thereby disrupting the Mg cycle in certain geological times. Selective dolomitization may be connected to the apparent correlation between global dolomitization events in the Neogene and the synchronous rise in species abundance of coralline red algae (CRA), but the underlying issue remains unclear. In the Caribbean islands, excellent examples of Neogene partially dolomitized carbonates containing coralline red algal facies are described to understand selective dolomitization of different components (grains and matrix) by examining the well-preserved outcrop of partially dolomitized Mio–Pliocene carbonates at the Seru Grandi locality on Bonaire Island, in the Caribbean. The degree and timing of selective dolomitization of various carbonate components are assessed using petrographical and geochemical methods. The micrite matrix is dolomitized first, followed by coralline red algal bioclasts, and subsequently all other grains. Dolomite crystals appear to originate from within and immediately around coralline algal fragments, suggesting that dolomite could have initiated from internally sourced Mg of the CRA’s high-magnesium calcite skeleton. Collectively, these observations suggest that selective dolomitization is controlled primarily by reactive surface area of the carbonate components, but it is less clear as to whether there is a dependency on original mineralogy.
      PubDate: 2021-10-08
      DOI: 10.1007/s10347-021-00638-9
       
  • 40Ar/39Ar dating and palaeoenvironments at the boundary of the
           early-late Badenian (Langhian-Serravallian) in the northwest margin of the
           Pannonian basin system

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      Abstract: The sedimentary fill of the Danube Basin represents the northwestern part of the Central Paratethys Sea. The middle Miocene opening of the basin was associated with volcanic activity. The altered tuff to tuffite layers from the northwest part of the Danube Basin occurs within the NN5 Zone and are accompanied by volcanic sediments with andesite clasts. The biotite 40Ar/39Ar age of 13.23 ± 1.95 Ma from the Trakovice-4 (1401–1406 m) tuff to tuffite layer covers a large time span, and this is caused by the fine grain size and alterations to biotite crystals. Nevertheless, the age range thus obtained agrees with biostratigraphic ranking. Fresh amphiboles from the Madunice-3 (1200–1195 m) volcanic sandstone give a more accurate age of 13.83 ± 0.11 Ma, and date the maximum fall in sea level to the beginning of late Badenian (Serravallian). The comparison of age data obtained from sedimentological, biostratigraphic and ecological analyses documents the following: (1) major deposition and subsidence took place in the Blatné depression during the late Badenian (early Serravallian, 13.82–12.6 Ma); (2) although the beginning of late Badenian stage is marked by the Badenian Salinity Crisis, only siliciclastic deposition is recorded within the Danube Basin; (3) during the entire late Badenian stage, upwelling conditions (estuarine circulation) are linked with diversified microfossil associations and dysoxic periods; (4) Moreover, the 40Ar/39Ar age of 13.83 ± 0.11 Ma supports the employment of Globoturborotalita druryi as an index fossil for the onset of the late Badenian. Thus, the Danube Basin represents a location with a well recognised 13.8 Ma early/late Badenian (Langhian /Serravallian) boundary.
      PubDate: 2021-10-03
      DOI: 10.1007/s10347-021-00637-w
       
  • Calcilobes wangshenghaii n. gen., n. sp., microbial constructor of
           Permian–Triassic boundary microbialites of South China, and its place in
           microbialite classification

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      Abstract: Permian–Triassic boundary microbialites (PTBMs) that formed directly after the end-Permian extinction in the South China Block are dominated by one structure, a lobate-form calcium carbonate construction that created extensive very thin (ca. 2–20 m thick) framework biostromes in shallow marine environments, effectively occupying the ecological position of the prior pre-extinction Permian reefs and/or associated carbonates. In the field, vertical sections show the microbialite is dendrolite (branched) and thrombolite (clotted), but because thrombolite may include branched portions, its structure is overall best classed as thrombolite. In the field and in polished blocks, the microbial material appears as dark carbonate embedded in lighter-coloured micritic sediment, where details cannot be seen at that scale. In thin section, in contrast to the largely unaltered micritic matrix, the microbial constructor is preferentially partly to completely recrystallised, but commonly passes gradationally over distances of a few mm to better-preserved areas comprising 0.1–0.2 mm diameter uneven blobs of fine-grained calcium carbonate (micrite to microsparite). The lobate architecture comprises branches, layers and clusters of blobs ca. 1–20 mm in size, and includes constructed cavities with geopetal sediments, cements and some deposited small shelly fossils. Individual blobs in the matrix may be fortuitous tangential cross sections through margins of accumulated masses, but if separate, may represent building blocks of the masses. The lobate structure is recognised here as a unique microbial taxon and named Calcilobes wangshenghaii n. gen., n. sp. Calcilobes reflects its calcium carbonate composition and lobate form, wangshenghaii for the Chinese geologist (Shenghai Wang) who first detailed this facies in 1994. The structure is interpreted as organically built, and may have begun as separate blobs on the sea floor sediment (that was also composed of micrite but is interpreted as mostly inorganic), by microbial agglutination of micrite. Because of its interpreted original micritic–microsparitic nature, classification as either a calcimicrobe (calcified microbial fossil) or a sedimentary microbial structure is problematic, so C. wangshenghaii has uncertain affinity and nature. Calcilobes superficially resembles Renalcis and Tarthinia, which both form small clusters in shallow marine limestones and have similar problems of classification. Nevertheless, Calcilobes framework architecture contrasts both the open branched geometry of Renalcis, and the small tighter masses of Tarthinia, yet it is more similar to Tarthinia than to Renalcis, and may be a modification of Tarthinia, noting that Tarthinia is known from only the Cambrian. Calcilobes thus joins Renalcis, Tarthinia and also Epiphyton (dendritic form) and others, as problematic microbial structures. Calcilobes has not been recognised elsewhere in the geological record and may be unique to the post-end-Permian extinction facies. C. wangshenghaii occurs almost exclusively in the South China Block, which lay on the eastern margin of Tethys Ocean during Permian–Triassic boundary times; reasons for its absence in western Tethys, except for comparable fabrics in one site in Iran and another in Turkey, are unknown.
      PubDate: 2021-09-27
      DOI: 10.1007/s10347-021-00636-x
       
  • Age, microfacies and depositional environment of the Middle to Late
           Paleocene shallow-marine carbonates in the Sirt Basin of Libya (Upper
           Sabil Formation): “Are Intisar domal structures pinnacle reefs'”

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      Abstract: In the central-eastern Sirt Basin, enigmatic Intisar domal structures host significant hydrocarbon accumulations. These structures have been commonly interpreted as pinnacle reefs/bioherms occurring in the open-marine basinal environment. Generally, pinnacle reefs/bioherms are mainly characterized by in situ carbonates. The current study challenges the Intisar pinnacle reef/bioherm model by examining one of the domal structures in terms of biostratigraphy, microfacies and depositional environment. These structures were dated using larger benthic foraminifera, which yielded a Middle to Late Paleocene age (Selandian–Early Thanetian). Thirteen microfacies types representing different carbonate ramp environments ranging from outer ramp to inner ramp, were defined. Outer ramp deposits have been observed adjacent to the domal structure, represented mainly by wackestone with small benthic and planktonic foraminifera. The outer ramp deposits are most likely isochronous to the domal structures. The lower part of the domal structures is composed mainly of foraminiferal–algal–echinodermal packstones. The upper part is characterized by foraminiferal–algal–echinodermal packstones with intercalated microbialite–coral boundstones. The euphotic inner ramp deposits are preserved on the crest of the domal structure, consisting of grainstone and packstone rich in Glomalveolina. As a result of this study, the Intisar domal structures are seen as erosional relics of a carbonate ramp and no evidence for pinnacle reef/bioherm model was found.
      PubDate: 2021-08-28
      DOI: 10.1007/s10347-021-00635-y
       
  • Late Aptian carbonate platform evolution and controls (south Tethys,
           Tunisia): response to sea-level oscillations, palaeo-environmental changes
           and climate

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      Abstract: The late Aptian Lower Serdj Formation (LSF) in the Northern Atlas of Tunisia records a mixed carbonate–siliciclastic system from the southern margin of Tethys. Sedimentological investigations of key sections in the Serdj-Bargou area along a NE–SW-platform-to-basin profile reveal five shallow-marine carbonate units (Cu1, Cu2, Cu3, Cu4a and Cu4b), dominated by subtidal deposits, separated by four terrigenous units (T1, T2, T3, T3a). Twelve basic facies are grouped into six facies associations or zones (FZA to FZF), representing particular palaeo-environments from proximal to distal settings. Carbonate units Cu1, Cu2 and Cu4a are dominated by coral algal-Orbitolina facies representative of a homoclinal ramp. However, units Cu3 and Cu4b are dominated by high-energy oolitic facies of a shoaled ramp. The terrigenous deposits (T1 to T4) are dominated by siliciclastics with shale, sandstone/siltstone and marl and have mostly been assigned to off-platform to basinal environments (FZF). The vertical facies changes are closely related to amplitudes of sea-level fluctuations and late Aptian Tethyan climatic perturbations. The terrigenous units were the result of short cooling periods and a humid climate. Moreover, this climate favoured the development of tide-influenced oolitic shoals, with the nuclei of ooids formed by fine quartz grains. Both the oolitic and siliciclastic deposits reflect episodes of maximum platform progradation basin-ward at a time of low accommodation space through the late Aptian period. Overall the new stratigraphic dataset from the southern Tethys margin is interpreted as reflecting the global Late Aptian cooling episode and sea-level lowstand.
      PubDate: 2021-08-16
      DOI: 10.1007/s10347-021-00634-z
       
  • Stable carbon and oxygen isotope data of Late Ediacaran stromatolites from
           a hypersaline environment in the Tarim Basin (NW China) and their
           reservoir potential

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      Abstract: The occurrence of Precambrian stromatolites is closely related to the ancient seawater composition and the evolution of life. It is also a potential oil and gas reservoir. In what kind of environment the stromatolites of the upper Ediacaran Qigebulak Formation in the Tarim Basin developed, and whether they constitute potential hydrocarbon reservoirs, remained unclear. Stromatolites occur in 1–5 m thick layers, interbedded with thrombolites and dolostones. Distinct stromatolite morphologies were observed, including columnar, sinuous, short columnar, domal, and conical shapes. The δ13C values of the stromatolites (6.1‰ on average) are slightly lighter than those of the dolostones, and the δ18O values (− 1.4‰ on average) are significantly heavier than that of the dolostones. The stromatolites have a relatively high content of rare-earth elements and a minor Ce anomaly. The geochemical results imply that the stromatolites formed in an evaporative hypersaline lagoon environment. The presence of barrier dams near the coast led to the formation of lagoons, where hypersalinity was achieved when evaporation was greater than marine or freshwater input. High salinity conditions inhibited the growth of Ediacaran metazoans, allowing the buildup of stromatolites in the restricted lagoons. The stromatolites are rich in primary fenestral pores and sheet-like cavities along the laminae, and the secondary dissolution pores and vugs are related to meteoric karstification. The stromatolites, together with dolostones and thrombolites, constitute the majority of the hydrocarbon reservoirs in the Upper Ediacaran in the Tarim Basin. The results clarify the environment where the stromatolites could still flourish and be well preserved whereas they significantly declined globally throughout the Neoproterozoic elsewhere. The results imply that extensive stromatolites in the Proterozoic strata are potentially important reservoir rocks of Precambrian petroleum systems.
      PubDate: 2021-06-26
      DOI: 10.1007/s10347-021-00633-0
       
  • Depositional setting and limiting factors of early Late Cretaceous
           glaucony formation: implications from Cenomanian glauconitic strata
           (Elbtal Group, Germany)

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      Abstract: Cenomanian strata of the Elbtal Group (Saxony, eastern Germany) reflect a major global sea-level rise and contain, in certain intervals, a green authigenic clay mineral in abundance. Based on the integrated study of five new core sections, the environmental background and spatio-temporal patterns of these glauconitic strata are reconstructed and some general preconditions allegedly needed for glaucony formation are critically questioned. XRD analyses of green grains extracted from selected samples confirm their glauconitic mineralogy. Based on field observations as well as on the careful evaluation of litho- and microfacies, 12 glauconitc facies types (GFTs), broadly reflecting a proximal–distal gradient, have been identified, containing granular and matrix glaucony of exclusively intrasequential origin. When observed in stratigraphic succession, GFT-1 to GFT-12 commonly occur superimposed in transgressive cycles starting with the glauconitic basal conglomerates, followed up-section by glauconitic sandstones, sandy glauconitites, fine-grained, bioturbated, argillaceous and/or marly glauconitic sandstones; glauconitic argillaceous marls, glauconitic marlstones, and glauconitic calcareous nodules continue the retrogradational fining-upward trend. The vertical facies succession with upwards decreasing glaucony content demonstrates that the center of production and deposition of glaucony in the Cenomanian of Saxony was the nearshore zone. This time-transgressive glaucony depocenter tracks the regional onlap patterns of the Elbtal Group, shifting southeastwards during the Cenomanian 2nd-order sea-level rise. The substantial development of glaucony in the thick (60 m) uppermost Cenomanian Pennrich Formation, reflecting a tidal, shallow-marine, nearshore siliciclastic depositional system and temporally corresponding to only ~ 400 kyr, shows that glaucony formation occurred under wet, warm-temperate conditions, high accumulation rates and on rather short-term time scales. Our new integrated data thus indicate that environmental factors such as great water depth, cool temperatures, long time scales, and sediment starvation had no impact on early Late Cretaceous glaucony formation in Saxony, suggesting that the determining factors of ancient glaucony may be fundamentally different from recent conditions and revealing certain limitations of the uniformitarian approach.
      PubDate: 2021-06-14
      DOI: 10.1007/s10347-021-00627-y
       
  • Applications of fossil taxonomy in palaeoenvironmental reconstruction: a
           case study of ostracod identification and diversity in Permian–Triassic
           boundary microbialites

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      Abstract: The value of taxonomy as a tool in palaeoenvironmental analysis depends on accuracy of determination of relevant taxa; in cases where taxa present unresolved problems of distinction (identification uncertainty and overlap), difficulties may exist in their application in facies studies. A prime example is found in ostracods of the Permian–Triassic boundary interval, considered here in sequences from south China. Low-latitude shallow-marine carbonate facies in the immediate aftermath of the end-Permian extinction (EPE) have common widespread microbialite biostromes containing abundant shelly fossils including ostracod assemblages not found elsewhere, stimulating the earlier idea that the microbialite was a refuge from stressors of extinction. These assemblages are dominated by the Family Bairdiidae that are mostly smooth-shelled ostracods notoriously difficult to resolve into sub-familial taxonomic units. Studies of ostracod taxonomy require a careful approach of integrating cornerstone aspects of their biology such as ontogenetic development and sexual dimorphism to disentangle taxonomically discrete groups. These significant difficulties of taxonomic resolution have a knock-on impact on application of the faunas in facies analysis; several studies remain open to interpretation because of these issues. Resolution of ostracod taxonomy is critical to the refuge hypothesis, because ostracods (mostly as complete closed carapaces, including juveniles and adults) accumulated in the microbialite; thus shell morphology is critical to analysis of ostracods in the microbialites so understanding the taxonomy is vital. The microbialites comprise two main facies where ostracods are abundant: (1) layers consisting of microbial components and intervening micrite; (2) uncommon shell-rich lenses of packstone-grainstone fabric between microbial layers. The refuge hypothesis is considered unlikely by some authors, who instead interpret the microbialites as a taphonomic window for imported ostracod shell preservation. However, post-extinction microbialite sheets are extensive on shallow marine carbonate platforms in Tethys and show little evidence of physical damage. We deduce that, instead of a taphonomic window, the well-preserved ostracod assemblages lived on the microbialite, and that the ‘refuge hypothesis’ remains viable. The concepts discussed in this study may be applicable to other fossil groups where taxonomic problems are acute.
      PubDate: 2021-06-10
      DOI: 10.1007/s10347-021-00632-1
       
  • Reconstruction of tectonically disrupted carbonates through quantitative
           microfacies analyses: an example from the Middle Triassic of Southern
           Italy

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      Abstract: The main goal of the paper is the reconstruction of a Middle Triassic buildup cropping out in the central part of the Southern Apennines. Middle Triassic reefs of the western Tethys realm are well known in the Northern and Southern Alps. In contrast, few studies of the Anisian–Ladinian carbonate platforms of the southern Apennines are available, due to the diagenetic alteration and tectonic disruption that hinder their paleoenvironmental and stratigraphic reconstruction. In an attempt to fill this gap, and to improve the knowledge on the Anisian–Ladinian carbonates of central Mediterranean area, this research is focused on a carbonate buildup cropping out in the “La Cerchiara” area, Sasso di Castalda (Basilicata, Southern Italy). The buildup, affected by intense tectonic deformation associated with the development of the Apennine thrust and fold belt, was studied using a statistical evaluation of the quantitative microfacies data. The research enabled a reconstruction of the original stratigraphic relationships of the various buildup fragments. A positive linear regression between the sample positions vs the percentage of autochthonous carbonates indicates an increase of the autochthons carbonate toward the top of the succession. The allochthonous fabrics (packstone/wackestone) at the base of the section (Unit IIIa) pass gradually upward into autochthonous (boundstones) facies (Units IIIb, I), consisting of microbialites (clotted peloidal micrite, microbial-derived laminae, and aphanitic micrite), microproblematica and cyanobacterial crusts, with few encrusting skeletal organisms. Statistical data suggest that units IIIa, IIIb, and I are in stratigraphic order while unit II appears to have been moved by tectonic dislocation from its original position at the base of the succession. The absence of metazoan reef framework, and the richness of micro-encrusters, autochthonous micrite and synsedimentary cements, suggest a mud-mound style of growth for the carbonate bodies of the Southern Apennine during the Anisian.
      PubDate: 2021-06-03
      DOI: 10.1007/s10347-021-00631-2
       
  • Development of a Mississippian–Lower Pennsylvanian isolated carbonate
           platform within the basinal griotte facies of the Cantabrian Mountains, NW
           Spain

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      Abstract: The Valdediezma platform consists of upper Tournaisian to lower Bashkirian (Carboniferous) shallow-water carbonates deposited in the core of the Picos de Europa Province (Cantabrian Mountains, northwest Spain). Although faulted in several thrust sheets, it is the only preserved platform developed in the Mississippian starved basins of the southern branch of the Variscan Orogen that is characterised also by pelagic sedimentation. This unusual platform provides an exceptional opportunity to study the lateral variation from the platform to the typical condensed griotte limestones developed in a starved basin, the origin of such a platform in a particularly unfavourable setting for carbonate accumulation, as well as the nucleation of the subsequent widespread Pennsylvanian carbonate platforms of the Cantabrian Mountains. Sixteen carbonate microfacies are differentiated in the Valdediezma Limestone, from shallow-water to slope to basinal environments. The carbonate production is related to the submarine topography and the rapid rates of microbial mound growth and accumulation, particularly from the upper Viséan to the lower Serpukhovian. A high-elevation platform and steep southern margin occurred during the deposition of condensed cephalopod-bearing limestones in the basin. A higher rate of carbonate accumulation is recognised from the upper Serpukhovian and younger, with similar thicknesses in shallow- and deeper water settings. The thickest part of the succession was coeval with the larger subsidence resulting from the migration of the Variscan deformation at the margin of the foreland basin of the Cantabrian Zone. The migration of deformation along the foreland uplifted the Valdediezma platform from the lower Bashkirian and caused its partial erosion. The Pennsylvanian carbonate platform developed on an exhumed Mississippian platform. Tectonic overloading due to the emplacement of nearby thrust sheets caused the subsidence and burial of the Valdediezma platform in the upper Moscovian.
      PubDate: 2021-06-01
      DOI: 10.1007/s10347-021-00629-w
       
  • Palaeozoic stromatoporoid diagenesis: a synthesis

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      Abstract: Palaeozoic stromatoporoids, throughout their 100-million + year history (Middle Ordovician to Late Devonian and rare Carboniferous), are better preserved than originally aragonite molluscs, but less well-preserved than low magnesium-calcite brachiopods, bryozoans, trilobites and corals. However, the original mineralogy of stromatoporoids remains unresolved, and details of their diagenesis are patchy. This study of approximately 2000 stromatoporoids and the literature recognises three diagenetic stages, applicable throughout their geological history. Timing of processes may vary in and between stages; some components are not always present. Stage 1, on or just below sediment surface, comprises the following: micrite filling of upper gallery space after death, then filling of any remaining space by non-ferroan then ferroan calcite in decreasing oxygen of pore-waters; partial lithification of associated sediment from which stromatoporoids may be exhumed and redeposited, evidence of general early lithification of middle Palaeozoic shallow-marine carbonates; microdolomite formation, with the Mg interpreted to have been derived from original high-Mg calcite (HMC) mineralogy (likely overlaps Stage 2). Stage 2, short distance below sediment surface, comprising the following: fabric-retentive recrystallisation (FRR) of stromatoporoid skeletons forming fabric-retentive irregular calcite (FRIC), mostly orientated normal to growth layers, best seen in cross-polarised light. FRIC stops at stromatoporoid margins in contact with sediment and bioclasts. FRIC geometry varies, indicating some taxonomic control. Evidence that FRIC formed early in diagenetic history includes syntaxial continuation of FRIC into some sub-stromatoporoid cavities (Type 1 cement), although others were pre-occupied by early cement fills (Type 2 cement) formed before FRR, preventing syntaxial continuation of FRIC into cavities. Likely contemporaneous with FRIC formation, stromatoporoids in argillaceous micrites drew carbonate from adjacent sediment during reorganisation of argillaceous micrite into limestone–marl rhythms that are also early diagenetic. Stage 3, largely shallow burial, comprises the following: dissolution and silicification, but these may have occurred earlier in stromatoporoid diagenetic histories (more data required); burial pressure dissolution forming stylolites.
      PubDate: 2021-05-20
      DOI: 10.1007/s10347-021-00628-x
       
  • Ribbon rocks revisited: the upper Cambrian (Furongian) Hwajeol Formation,
           Taebaek Group, Korea

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      Abstract: Alternations of thin-bedded limestone and shale, or ribbon rock, commonly occur throughout lower Palaeozoic carbonate successions; however, their formative processes are still unclear. In this study, we discuss the origin of the ribbon rocks of the upper Cambrian Hwajeol Formation, Korea, based on detailed microfacies analysis of a ~ 2-m-thick interval. Five sedimentary microfacies were identified: normally graded calcarenite to shale; parallel-laminated shale; lime mudstone; wackestone-to-packstone; and bioclastic–intraclastic packstone-to-conglomerate. Shale facies were most likely formed by frequent storm-induced bottom currents, whereas, lime mudstone facies were deposited in situ by suspension settling of micrite, mudflows, or growth of keratose sponges on the seafloor, and/or formed by early diagenetic growth. Conglomerate/packstone/wackestone indicate infrequent, larger-scale events, e.g., mega-storms, tsunamis, or earthquakes. We propose a new formative model for tempestite-type ribbon rock based on the Hwajeol example, and suggest that this model can be differentiated from the other types of ribbon rocks—tidalite, turbidite, and diagenetic types. Formation of the tempestite-type ribbon rocks would have been promoted by the characteristic environmental conditions of the early Palaeozoic, in particular sea-water chemistry that promoted calcite precipitation and the paucity of burrowers. Detailed microscopic observations can thus provide clues to elucidate previously unknown sedimentary processes in the deeper parts of carbonate platforms.
      PubDate: 2021-05-15
      DOI: 10.1007/s10347-021-00630-3
       
  • Facies analysis of the Upper Ordovician Xiazhen Formation, southeast
           China: Implications for carbonate platform development in South China
           prior to the onset of the Hirnantian glaciation

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      Abstract: The Upper Ordovician Zhe-Gan Platform was a short-lived carbonate platform that formed near the northern margin of the Cathaysian Land of the South China Block. The Zhe-Gan Platform is less well understood than the adjacent Yangtze Platform due to the absence of detailed sedimentological study as well as the structural complexity of the area. The aim of this study was to reconstruct the Zhe-Gan Platform based on detailed facies analysis of the middle to upper Xiazhen Formation. A total of 24 shallowing-upward depositional cycles (C1–24) are identified and subdivided into three types based on the vertical association of facies: (1) mixed carbonate–clastic subtidal cycles; (2) carbonate subtidal cycles; and (3) peritidal-capped subtidal cycles. The reconstructed depositional model indicates a ramp-type, mixed siliciclastic–carbonate platform, generally similar to other Late Ordovician carbonate platforms characterised by dominant skeletal grains, less common ooids, and an absence of skeletal barrier reefs. The newly developed Late Ordovician ramp-type carbonate platforms could have been induced by the evolution of skeletal organisms and the accompanying palaeoceanographic changes prior to the Hirnantian glaciation. The complex palaeogeography of the South China Block would have influenced the co-occurrence of the Xiazhen carbonate platform and black shales of the adjacent Yangtze Platform on the same block during the Late Ordovician.
      PubDate: 2021-03-10
      DOI: 10.1007/s10347-021-00626-z
       
  • Sedimentology and distribution of late quaternary calciturbidites and
           calcidebrites in the Mozambique Channel (Southwest Indian Ocean)

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      Abstract: Submarine gravity flow processes on carbonate platform slopes can lead to the deposition of calciturbidite and calcidebrite beds on the adjacent deep-water seafloor. Such deposits have been previously found to occur more frequently during sea-level highstands, leading to increased export of carbonates to the deep sea during interglacial periods. Here, we document a new occurrence of these types of event beds in cores near a series of volcano-cored carbonate platforms in the Mozambique Channel (SW Indian Ocean), describing them from a sedimentological perspective and analyzing the controls on their distribution. 32 event beds, located near four isolated platforms, are composed primarily of uncoated skeletal grains from primarily shallow-water and planktic taxa. Compositional analysis shows that planktic foraminifera are hydrodynamically sorted such that they form a greater proportion of the upper parts of event beds. Age models based on foraminifer δ18O isotope data allow for precise (ky-scale) dating of each gravity flow event; results show that events occurred with frequencies ranging from 2 to 4 events per 100,000 years over the past ~ 800 kyr regardless of the phase within the sea-level cycle (i.e., transgressive, regressive, highstand or lowstand). However, events were most frequent during periods, both relative and absolute, of highest sea level, and are therefore interpreted to be controlled in part by sea-level status or change, though additional causes are also possible.
      PubDate: 2021-03-09
      DOI: 10.1007/s10347-021-00624-1
       
  • Facies analysis and environmental interpretation of a late Pleistocene
           coastal lagoon sedimentary sequence containing a Coprinisphaera-bearing
           terrestrial episode (Kisimayo, southern Somalia)

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      Abstract: For the first time, we here report trace fossils of dung beetle brood balls (Coprinisphaera ichnogenus) in late Pleistocene sediments from Somalia. The sediments containing these traces represent a lagoonal sedimentary sequence, cropping out along some quarry walls in the outskirts of the Kisimayo town. The terrestrial ichnofossils are accompanied by some shells of the giant land snail Achatina, which confirms the subaerial exposure. Indeed, the rock, generally strongly weathered, shows a texture of a foraminiferal packstone-grainstone, rich in bivalve and gastropod molds, of marine origin. The related facies stack is indicative of a period of environmental changes, which took place in a sheltered shallow water coastal area of a tropical carbonate shelf. For a short time, due to a slight lowering in sea-level, this lagoonal area experienced subaerial conditions with accumulation of wave- and wind-driven marine sand in a backshore zone, so allowing the development of environmental conditions suitable for the appearance of terrestrial trace fossils and Achatina. The discovery of Coprinisphaera represents one of the rare African records of the ichnogenus; it is also a unique example for the Indian Ocean’s African coast of a terrestrial episode being found within a lagoonal sequence.
      PubDate: 2021-03-06
      DOI: 10.1007/s10347-021-00625-0
       
  • Upper Triassic–Lower Jurassic continental carbonates from the Apuseni
           Mountains, Romania: facies, lithology and paleoenvironments

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      Abstract: We studied deposits belonging to the Bihor Unit from the Northern Apuseni Mountains (Romania). The described outcrops are located in the SW of Șes Mountain and the northeastern Pădurea Craiului Massif. We determined the depositional environment and the mechanisms controlling the accumulation of Upper Triassic–Lower Jurassic continental deposits. The sedimentary formations contain carbonate breccia and calcretes embedded in continental clay deposits. Late Triassic–Early Jurassic depositional processes were influenced by the inherited paleobasement of the subaerially exposed Middle Triassic deposits. Numerous fragments of Anisian and Ladinian carbonate deposits are encased in weathered clay deposits accumulated on karstification surfaces developed at the top of Middle Triassic limestones. We integrated facies analysis and clay mineralogy to obtain an accurate interpretation of the continental processes acting at the Triassic–Jurassic boundary in the northern part of the Apuseni Mountains. The composition of the carbonate pebbles is described in terms of the carbonate facies, whereas the clay mineralogy was determined by applying X-ray powder diffraction. Thirteen facies associations are described consisting of carbonate, siliciclastic and ferilitic rock types. Such facies indicate sediment accumulation in a continental, mixed carbonate-siliciclastic depositional environment. A Late Triassic exposure event was followed by an Early Jurassic (Hettangian) transgression. Two major facies types are identified on the basis of their depositional environment. The first category includes subaerially exposed Triassic carbonates and ferilitic facies, while the second category consists of transgressive siliciclastic facies from the basal Lower Jurassic (Hettangian) sediments. The existing data suggest continental deposition in alternating, arid–humid warm climate conditions at the Triassic–Jurassic transition.
      PubDate: 2021-02-27
      DOI: 10.1007/s10347-021-00622-3
       
 
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