Search results for "TRIASSIC"
showing 10 items of 117 documents
Ocean Acidification and the End-Permian Mass Extinction: To What Extent does Evidence Support Hypothesis?
2012
International audience; Ocean acidification in modern oceans is linked to rapid increase in atmospheric CO 2 , raising concern about marine diversity, food security and ecosystem services. Proxy evidence for acidification during past crises may help predict future change, but three issues limit confidence of comparisons between modern and ancient ocean acidification, illustrated from the end-Permian extinction, 252 million years ago: (1) problems with evidence for ocean acidification preserved in sedimentary rocks, where proposed marine dissolution surfaces may be subaerial. Sedimentary evidence that the extinction was partly due to ocean acidification is therefore inconclusive; (2) Fossils…
Some sedimentological and geochemical characters of the late Triassic Noto formation, source rock in the Ragusa basin (Sicily)
1990
URA 724 du CNRS a intégré UMR 6113 - ISTO CNRS Université d'Orléans; In the Ragusa basin (southeastern Sicily), the late Triassic Noto formation is considered as the main oil source rock. We provide a detailed description of the sedimentary facies determined from core samples, and discuss geochemical results, obtained for both kerogens and chloroform extractable hydrocarbons from samples where sedimentary organic matter is immature. Two main sedimentary sequences were encountered: (i) layers of limestones and of marls (or shales) alternating at a metric scale, and (ii) laminites having various types and carbonate contents. The high petroleum potentials (S2 up to 100 kg HC/t rock) are relate…
The relationships between soft-sediment deformation structures and synsedimentary extensional tectonics in Upper Triassic deep-water carbonate succes…
2016
Abstract We describe soft-sediment deformation structures into the Upper Triassic cherty limestone outcropping in the Pizzo Lupo section (Central Sicily, Italy), pertaining to the deep-water palaeodomain of the Southern Tethyan margin. In the study section, mainly consisting of thin-bedded mudstone/marl alternations with bedded chert intercalations, some lithofacies have been separated on the basis of the abundance of the calcium carbonate/clay content and the overall textural features. The deformational structures, displaying different deformational styles as folded and faulted beds, disturbed layers, clastic dikes, and slumps occur mainly in the deformed horizons that involve marl-dominat…
Marine Early Triassic Actinopterygii from Elko County (Nevada, USA): implications for the Smithian equatorial vertebrate eclipse
2017
AbstractThe Early Triassic vertebrate record from low paleolatitudes is spotty, which led to the notion of an ‘equatorial vertebrate eclipse’ during the Smithian. Here we present articulated ray-finned fishes (Actinopterygii), collected from the marine Lower Triassic Thaynes Group at three new localities in Elko County (Nevada, USA), which were deposited within the equatorial zone. From the Smithian of the Winecup Ranch, we describe two partial skulls of the predatory actinopterygianBirgeria(Birgeriidae), attributed toB.americananew species andBirgeriasp.Birgeria americanan. sp. is distinguished from other species by a less reduced operculogular series. With an estimated total length of 1.7…
Transient metazoan reefs in the aftermath of the end-Permian mass extinction
2011
5 pages; International audience; Recovery from the devastating Permian-Triassic mass extinction about 252 million years ago is usually assumed to have spanned the entire 5 million years of the Early Triassic epoch1,2. The post-crisis interval was characterized by large-scale fluctuations of the global carbon cycle and harsh marine conditions, including a combination of ocean acidification, euxinia, and fluctuating productivity3. During this interval, metazoan-dominated reefs are thought to have been replaced by microbial deposits that are considered the hallmark of the Early Triassic4-7. Here we use field and microscopic investigations to document Early Triassic bioaccumulations and reefs f…
Diagenesis of clay minerals and K-bentonites in Late Permian/Early Triassic sediments of the Sichuan Basin (Chaotian section, Central China).
2014
10 pages; International audience; Detailed clay mineralogical analyses were carried out on Late Permian/Early Triassic carbonate sediments exposed on the Chaotian section (Sichuan Basin, Central China). The clay assemblages are dominantly composed of illite in platform carbonates and clay seams, and illite-smectite mixed-layers (I/S) in tuff layers (K-bentonites) intercalated in the carbonate succession. Detrital and authigenic volcanogenic clay minerals have been partially replaced through illitisation processes during burial, raising questions about diagenetic effects. The precise determination of I/S occurring in K-bentonites shows that the sediments reached a temperature of about 180 °C…
In the aftermath of the end-Permian extinction: the microbialite refuge?
2013
7 pages; International audience; We present the first study of micro-crustaceans (ostracods) associated with microbial crusts in the aftermath of the most devastating extinction, the end-Permian extinction (EPE). These post-extinction microbialites dominated shallow shelf marine environments and were traditionally considered as devoid of any associated fauna. We present a micro-palaeontological analysis of a large record from microbial and non-microbial settings following the EPE. This dataset documents the proliferation of ostracods strictly associated with microbialites. Based on the diet of extant ostracods and uniformitarianism, we propose that the abundant microbes in the mats served a…
Permian-Triassic extinctions and rediversifications.
2015
Ammonoids were a major component of Permian marine faunas, but were on the verge of extinction during the Permian-Triassic crisis ~ 252 myr ago. Despite the severity of this extinction, their recovery was explosive in less than 1.5 myr. By Smithian time, they had already reached levels of taxonomic richness much higher than those of the Permian. The causes for the rapid Early Triassic diversification and proliferation of these organisms still remain elusive, but the evolution of their spatio-temporal diversity and disparity patterns closely correlates with the numerous environmental changes recorded during this time interval.
Revision of the genus Anasibirites Mojsisovics (Ammonoidea): An iconic and cosmopolitan taxon of the late Smithian (Early Triassic) extinction
2016
34 pages; International audience; The family Prionitidae Hyatt represents a major component of ammonoid faunas during the Smithian (Early Triassic), and the genus Anasibirites Mojsisovics is the most emblematic taxon of this family. Its stratigraphical range is restricted to the beginning of the late Smithian (Wasatchites distractus Zone). The genus is also characterized by an unusual cosmopolitan distribution, thus contrasting with most earlier Smithian ammonoid distributions that were typically restricted by latitude. Because the late Smithian witnessed an extinction of the nekton (e.g. ammonoids, conodonts) whose amplitude is equal to or larger than that of the end-Permian crisis, the nu…
REWORKING OF FUSULINIDS AND CALCIPHAERIDS IN THE LERCARA FORMATION (SICILY, ITALY); GEOLOGICAL IMPLICATIONS
2004
Different fusulinids have been identified in the Lercara Formation (Sicily). They are: Reichelina sp., Schubertella paramelonica, Toriyamaia (?) sp., Neofusulinella lantenoisi, Yangchienia compressa, Rauserella staffi, Darvasites contractus, Chalaroschwagerina (Taiyuanella?) aff. davalensis, Levenella aff. evoluta, Pamirina darvasica, and Neoschwagerina ex gr. craticulifera. Small Permian foraminifers, as well as the calcispherid Asterosphaera pulchra also exist. The microfossils indicate reworking of different Permian stages, at different periods of time, and possibly also of the Mississippian (Early Carboniferous). All these resediments have been deposited within the Lercara Formation, a …