0000000001180658
AUTHOR
Nicolas Olivier
A mechanism for brief glacial episodes in the Mesozoic greenhouse
[1] The Mesozoic, perhaps the longest period of warmth during the Phanerozoic Earth history, has been repeatedly affected by short-lived cold interludes lasting about one million years. While the origin of these cold snaps has been classically attributed to a temporary atmospheric CO2 drawdown, quantified mechanisms explaining these instabilities of the carbon cycle are still lacking. Based on a climate carbon cycle model, we show that the general demise of carbonate platforms accompanying these short-lived cold interludes is a powerful mechanism capable of generating a fast atmospheric CO2 decrease and a moderate sea level drop associated with ice sheet buildup. The temporary nature of the…
A diagenetic control on the Early Triassic Smithian-Spathian carbon isotopic excursions recorded in the marine settings of the Thaynes Group (Utah, USA)
17 pages; International audience; n the aftermath of the end-Permian mass extinction, Early Triassic sediments record some of the largest Phanerozoic carbon isotopic excursions. Among them, a global Smithian-negative carbonate carbon isotope excursion has been identified, followed by an abrupt increase across the Smithian–Spathian boundary (SSB; ~250.8 Myr ago). This chemostratigraphic evolution is associated with palaeontological evidence that indicate a major collapse of terrestrial and marine ecosystems during the Late Smithian. It is commonly assumed that Smithian and Spathian isotopic variations are intimately linked to major perturbations in the exogenic carbon reservoir. We present p…
Smithian shoreline migrations and depositional settings in Timpoweap Canyon (Early Triassic, Utah, USA).
AbstractIn Timpoweap Canyon near Hurricane (Utah, USA), spectacular outcrop conditions of Early Triassic rocks document the geometric relationships between a massive Smithian fenestral-microbial unit and underlying, lateral and overlying sedimentary units. This allows us to reconstruct the evolution of depositional environments and high-frequency relative sea-level fluctuations in the studied area. Depositional environments evolved from a coastal plain with continental deposits to peritidal settings with fenestral-microbial limestones, which are overlain by intertidal to shallow subtidal marine bioclastic limestones. This transgressive trend of a large-scale depositional sequence marks a lo…
Microbial deposits in the aftermath of the end-Permian mass extinction: A diverging case from the Mineral Mountains (Utah, USA)
40 pages; International audience; The Lower Triassic Mineral Mountains area (Utah, USA) preserves diversified Smithian and Spathian reefs and bioaccumulations that contain fenestral-microbialites and various benthic and pelagic organisms. Ecological and environmental changes during the Early Triassic are commonly assumed to be associated with numerous perturbations (productivity changes, acidifica-tion, redox changes, hypercapnia, eustatism and temperature changes) post-dating the Permian–Triassic mass extinction. New data acquired in the Mineral Mountains sediments provide evidence to decipher the relationships between depositional environments and the growth and distribution of microbial …
Tracking microbial signatures in stromatolites at micrometer scale with in situ iron isotopes. M-fed (Microbialites: formation, evolution, diagenesis)
International audience
Contrôles locaux vs globaux sur les alternances carbonates-silicoclastiques dans le bassin de Lorca (Tortonien-Messinien, Espagne)
International audience
Iron isotopes in micropyrites from the 2.7Ga Tumbiana Formation (Western Australia)
International audience; Stromatolites are considered to be the major drivers for the oceanic oxygenation during Archean time. However, respective rolesof photosynthetic and chemolithotroph organisms in these Archean rocks is not precisely demonstrated. Primarysub-micrometer pyrites associated with pristine organic matter are widespreadin Archean and modern sediments. Iron isotopes are fractionated by redox processesand biological activitiesand are widely used for tracing paleoredox conditions, diagenetic processes ormetabolic signaturesas iron respiration (DIR). Sub micrometer δ56Fevalues ofmicropyritesassociated with organic matter-laminae and CaCO3-SiO2matrixin stromatolites from the 2.7G…
Lithospheric strenght control over depositional environments and foreland accommodation in the Western USA Basin during the Early Triassic
International audience
Early Triassic proliferation of microbial deposit
International audience; In modern examples of well-developed microbial-dominated deposits associated with metazoan organisms can be currently found in various environments including but not restricted to lagoons in Polynesia (Sprachta et al., 2001), the warm water of the Cuba (e.g., Bouton et al., 2016; Pace et al., 2018), the hypersaline lakes of the Great Salt Lake (USA; e.g., Bouton et al., 2016; Vennin et al., 2019; Vanden Berg, 2019), or the alkaline Satonda Crater Lake in Indonesia (Arp et al., 2003; Satuyana et al., 2010). In Early Triassic, several authors indicated that microbial deposits are frequently associated with sponges, bivalves, brachiopods, ostracods and echinoderms and d…
Transient metazoan reefs in the aftermath of the end-Permian mass extinction
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…
Oligo-Miocene lacustrine microbial and metazoan buildups from the Limagne Basin (French Massif Central)
The Limagne Basin (French Massif Central) is an extensive continental lacustrine system accommodating microbial and metazoan buildups from Chattian to Aquitanian age. A description of these buildups and their associated biotic components in Grand Gandaillat and Crechy quarries provides insights into their spatio-temporal distribution patterns. Flats, cauliflowers, domes, cones and coalescent columnar morphologies have been identified with a main laminated mesofabric and laminated, columnar, filamentous and caddisfly-coated microfabrics. Two low-gradient margin models emerged based on the changes in the distribution, morphology and size of the microbial and metazoan-rich deposits through tim…
Molecular preservation of organic microfossils in Paleoarchean cherts
International audience; Fossilization processesandthe increase of temperature and pressure conditions associated withburialinevitably alter the original biochemical signatures of organic molecules.At a certain stage, biogenic and abiotic organic structures may become undistinguishable [1].Cherts (i.e.silica-rich rocks)are well known forthe morphologicalpreservationof fossilized microorganisms.Recently,spatially resolvedinvestigations usingsynchrotron-based XANESmicrospectroscopyrevealedthatmolecular information about the organic precursor of3.4 Gamicrofossils, was preservedintheStrelley Pool chert(Pilbara, Western Australia),despite a metamorphichistory so far believed to be incompatible wi…
Evolution of depositional settings in the Torrey area during the Smithian (Early Triassic, Utah, USA) and their significance for the biotic recovery
This work focuses on well-exposed Lower Triassic sedimentary rocks in the area of Torrey (south-central Utah, USA). The studied Smithian deposits record a large-scale third-order sea-level cycle, which permits a detailed reconstruction of the evolution of depositional settings. During the middle Smithian, peritidal microbial limestones associated with a rather low-diversity benthic fauna were deposited seaward of the tidal flat siliciclastic red beds. Associated with siliceous sponges, microbial limestones formed small m-scale patch reefs. During the late middle to late Smithian interval, the sedimentary system is characterized by tidal flat dolostones of an interior platform, ooid-bioclast…
Ages and stratigraphical architecture of late Miocene deposits in the Lorca Basin (Betics, SE Spain): New insights for the salinity crisis in marginal basins
International audience; Unlike most Neogene basins of the Betic Cordillera where the Salinity Crisis is dated to the Messinian, a contradictory Tortonian dating was proposed for evaporites of the Lorca Basin. As a consequence, complex structural models have been proposed in the literature to explain this discrepancy in the timing of evaporites. In order to integrate the Lorca Basin into the geological context of the western Mediterranean domain during the Late Miocene, new sedimentological and stratigraphical studies coupled with new dating were performed, which allow us to propose a Messinian age for both diatomite-bearing deposits and evaporites of the Lorca Basin. These new ages challeng…
Facies and depositional settings during the Smithin in the Torrey area (Early Triassic, Utah, USA)
International audience; The Permian-Triassic transition records the most devastating biotic crisis of the Phanerozoic with 90% of the marine genera being eradicated. The aftermath of this extinction is usually portrayed by large environmental perturbations such as ocean acidification, anoxia, euxinia and fluctuating productivity. However, these fluctuating conditions and their impact on the nature and tempo of the biotic recovery are still under debate. Thus, it is important to decipher the nature of the depositional settings and their putative spatio-temporal variations in order to improve our knowledge of post-crisis environments. The present work focuses on well-exposed Lower Triassic se…