Stratigraphie et variations isotopiques du carbone dans le Permien supérieur et le Trias inférieur de quelques localités de la Néotéthys (Turquie, Oman et Iran)

The end of Paleozoic era and the beginning of the Mesozoic is a time of crisis and profound changes in ecosystems on Earth. It is the greatest of all extinctions in the Phanerozoic with a mass mortality in the marine environment (up to 96% of species, 83% of genera and 55% of families) and a nearly equally large loss of life on land. The process of progressive elimination of marine species is punctuated by a final extinction pulse. This pulse is generally correlated with a conspicuous depletion in 13C in particular in marine carbonates (D13 Ccarb), reflecting a dramatic disturbance in the global carbon cycle. There is still abundant discussion on the ultimate cause of the end-Permian crisis. Concepts differ with respect to source (terrestrial or extraterrestrial), rate (rapid or catastrophic) and chronology of event (between mass extinction in ocean, land and disturbance of the global carbon cycle). Among different causes, the most emphasized are oceanic anoxia, Siberian trap volcanism, methane release, meteorite impact and marine regression. Another important feature of the end-Permian crisis is the particularly long delay of faunal recovery to reach the pre-extinction level. For this time, microbial organisms dominate the marine environment. Together with sedimentological and paleontological studies, 16 sections were analysed to determine the bulk isotopic ratio of carbonates. Two sections were analysed to obtain isotopic values of the organic carbon. These sections are located in four different geographical area: Turkish Taurus, Oman Moutains, Transcaucasia (North-western Iran ) and Central Iran and correspond to the southern and northern margin of the Neotethys. They represent sediments from a continental platform (Arabic-African and Cimmerid), slope, isolated platform and more or less deep basins. The depletion 13C , which is distinctive for the end-Permian crisis, is divided into two parts. The first on is progressive and precedes the crisis but follows the first anomalies recorded in the benthic fauna. The classical rubber band model (accumulation of constrains before rupture) is favoured. Cause(s) of extinction have to have an influence on the carbon cycle for a certain time before the crisis. The second part of the negative shift occurs after the event and shows strong variations. Is the dominance of the marine environment by microbial organisms a key factor? This study tries to understand the influence of microbial community on the carbon cycle. An isotopic curve for the carbon has been established for the Early Triassic. It shows the largest shift amplitude of all the Phanerozoic. A first positive shift in D13C values occurs in the Griesbachian, reflecting the beginning of the faunal recovery. A first negative shift happens in the end-Griesbachian, basal Dienerian. A second one occurs in the Upper Dienerian and presents features of methane release induced shift. It is followed by a very positive double peak in the Early Smithian (up to 6%) and by very negatives values in the Middle and Upper Smithian (down to -2%). Another very positive double shift (up to 8%) occurs around the Smithian-Spathian boundary before going back to negative values (down to-2%). A positive shift marks the Olenekian-Anisian boundary. The constitution of such a curve allows us to correlate sections poorly biostratigraphically constrained, therefore a stratigraphic history of the Oman margin has been reconstructed for the Early Triassic

Basal Triassic carbonate of the Tethys: a microbialite world

Following the end of Permian mass extinction, primitive groups of microbial communities emerged from stressed palaeoenvironments to recolonize the normal marine area of the Tethys. The prolific upper Paleozoic skeletal carbonate factory was abruptly replaced by a nonskeletal carbonate factor

Micropaleontology of some Permian localities in the Tethyan realm: Inventory of foraminifers and calcareous algae, biostratigraphy and paleogeography

This inventory of Permian foraminifers and calcareous algae has been made for more than 5000 samples collected in six geographical areas (Fig.1). Almost all of them were taken from stratigraphical sections. This important and unique collection is kept at the Geological Museum of Lausanne (Switzerland) and are available on request to any further scientific investigations*. Several people carried out the field work. However, only one person is reponsible for the determinations in generea and species of these samples. Therefore, this work method offers a good homogeny of namings and has saved a lot of discussions over nomenclature. Some colleagues may not agree with one or more of the namings and we accept their dissensions. Nevertheless we adopted this method because we are sure that the homogeny of namings vouches for best correlations in both biostratigraphical and paleogeographical investigations. We already used with success this data set in geodynamical paleo-reconstruction maps (Jenny & Stampfli, 2000) (Chapter 3) and managed the same data through the Biograph Program (Savary & Guex, 1999) (Chapter 2). This program is able to compile a lot of data to extract maximal sets of intersecting taxa ranges. The objective was to establish discrete sequences of coexistence interval of taxa and ten to ensure good correlations for the different studied area

Proterozoic-like/type basal Triassic microbial build-ups of unusual height in Armenia.

The Griesbachian part of the Marmarasar Formation (Kara Baglyar) [1] in the Zangakatun (Sovetachen) section (Armenia) is characterized by microbial build-ups, spaced from 5 to 20m and surrounded by thin-bedded platy lime mudstone in a deep ramp environment. Above a basal carbonate fan crust follows a succession of thrombolitic domal forms, some of them up to 1.5m thick. The synoptic relief of the thrombolite head is estimated at 40-60cm above the muddy sea bottom. The overturned cone-shaped build-up geometry has a top head diameter up to 8m width consisting of numerous thrombolite domes, and an usual height of up to 15m. The water depth is interpreted below storm wave base and the asymmetrical build-up growth hints to a steady bottom current. Changes in the paleo-environment at the top of the kummeli conodont zone end the thrombolite growth. The overall duration of these post-extinction microbial build-ups is estimated at 700'000 years. Comparable Late Proterozoic Conophyton-Jacutophyton biostromes of the Atar area (Mauritania) [2], grown in apparently similar 80-100m water depth with quiet conditions, also show a high synoptic relief here of more than 2m above sea-bottom and decametric columnar branching build-ups. Due to a similarly large accommodation space the Zangakatun microbial reefs seem to follow the same build-up strategy

Multiple episodes of extensive marine anoxia linked to global warming and continental weathering following the latest Permian mass extinction

Copyright © 2018 The Authors. Explaining the ∼5-million-year delay in marine biotic recovery following the latest Permian mass extinction, the largest biotic crisis of the Phanerozoic, is a fundamental challenge for both geological and biological sciences. Ocean redox perturbations may have played a critical role in this delayed recovery. However, the lack of quantitative constraints on the details of Early Triassic oceanic anoxia (for example, time, duration, and extent) leaves the links between oceanic conditions and the delayed biotic recovery ambiguous. We report high-resolution U-isotope (δ238U) data from carbonates of the uppermost Permian to lowermost Middle Triassic Zal section (Iran) to characterize the timing and global extent of ocean redox variation during the Early Triassic. Our δ238U record reveals multiple negative shifts during the Early Triassic. Isotope mass-balance modeling suggests that the global area of anoxic seafloor expanded substantially in the Early Triassic, peaking during the latest Permian to mid-Griesbachian, the late Griesbachian to mid-Dienerian, the Smithian-Spathian transition, and the Early/Middle Triassic transition. Comparisons of the U-, C-, and Sr-isotope records with a modeled seawater PO43- concentration curve for the Early Triassic suggest that elevated marine productivity and enhanced oceanic stratification were likely the immediate causes of expanded oceanic anoxia. The patterns of redox variation documented by the U-isotope record show a good first-order correspondence to peaks in ammonoid extinctions during the Early Triassic. Our results indicate that multiple oscillations in oceanic anoxia modulated the recovery of marine ecosystems following the latest Permian mass extinction

THE CASE FOR THE GLOBAL STRATOTYPE SECTION AND POINT(GSSP) FOR THE BASE OF THE NORIAN STAGE

The Norian Stage is the longest stage in the Phanerozoic, and some members of the boundary working group have been evaluating suitable Carnian-Norian boundary sections for roughly two decades. This has identified two possible candidate boundary sections, at Black Bear Ridge (British Columbia, Canada) and Pizzo Mondello (Sicily, Italy). After a formal voting procedure within the working group, ending on the 26th July, 2021, the Pizzo Mondello section was selected as the global stratotype section and point for the base of the Norian. We evaluated the global correlation potential of the two proposed primary markers, the conodont Metapolygnathus parvus and the ‘flat-clam’ Halobia austriaca. Secondary markers were also evaluated around these boundary datums for correlation potential, and the veracity of the proposed sections for GSSP status. Data and arguments for the proposed sections and datums are presented here. Through a two-stage process of option elimination in voting, conforming with ICS guidelines, the working group decided by 60% majority to propose that the first occurrence datum of Halobia austriaca in the Pizzo Mondello section at the base of bed FNP135A should become the ‘golden spike’ for the base of the Norian. A secondary biotic marker for this boundary is the first occurrence of Primatella (Carnepigondolella) gulloae, in sample NA43, ca. 0 m below FNP135A, and the FA of Dimorphites noricus (sample NA42.1) ca. 3.5 m above bed FNP135 (indicating the first subzone of the Jandianus Zone). The best physical secondary marker is the magnetozone PM5n with the proposed boundary ca.40% through the thickness of PM5n. Strengths of the chosen datum are: 1) it also maintains historical priority for ammonoid zonations, which had placed the base Norian near to this level in Europe, North America and probably NE Asia; 2) Halobia austriaca is widely distributed in all paleolatitudes and is a long-established taxon

Synthèse des valeurs isotopiques du carbone au Trias inférieur

Un intérêt soutenu a été porté à l\u27anomalie isotopique du carbone, qui coïncide apparemment avec la limite Permien–Trias. De nouveaux travaux montrent que la chute des valeurs isotopiques est en escalier et débute avant l\u27extinction en masse fini-permienne ; ils prouvent aussi l\u27existence de variations extrêmes de celles-ci durant le Trias inférieur, et ceci jusqu\u27à l\u27Anisien précoce. Par la suite, en même temps que la diversité augmente, ces valeurs apparaissent beaucoup plus stables. Au vu de la magnitude des variations isotopiques et des excursions de grande ampleur au Trias inférieur, les explications « catastrophistes » de relâchement massif de méthane ou d\u27impact sont devenues moins attractives, sans cependant pouvoir être ignorées.Much attention has been given to the negative δ13C anomaly nearly coincident with the Permian–Triassic boundary. New data indicate a stepwise decline in δ13C initiating before the Latest Permian extinction event followed by highly variable δ13C values during the remaining Early Triassic. δ13C values appear much less erratic as global metazoan diversity increased in the Middle Triassic. Given the previously unappreciated magnitude of isotopic change and the number of large δ13C excursions that occurred during the Early Triassic, catastrophic mechanisms like methane release/bolide impact become less attractive to explain the Early Triassic carbon isotopic record as a whole.</p