JCJC SIMI 6 - JCJC - SIMI 6 - Système Terre, environnement, risques

AFTER the end: reassembly of marine communities during the Early Triassic recovery – AFTER

After the end: reassembly of marine communities during the Early Triassic recovery

The core idea of this project comes from recent discoveries on the PT crisis and its recovery by our team. These significant advances markedly<br />contrast with the classic, world-wide “delayed recovery” scenario and its associated paradigms.Our main goal is thus to test the “delayed recovery” model at a local to regional (i.e. ecologically functional) scale, looking for the potential drivers that influenced patterns and processes of the biotic recovery.

Main objectives

The Permian-Triassic boundary (~252 Myr) is marked by the largest mass extinction of the Phanerozoic. Recovery from this devastating event is usually assumed to be a long delayed process, spanning at least the entire Early Triassic (~5 myr). Indeed, the crisis aftermath is generally portrayed as a time of high ecological stress characterized by large-scale fluctuations of the global carbon cycle and harsh marine conditions, including a combination of ocean acidification, euxinia, and fluctuating productivity. This suggests tight links between these environmental variations and the restructuring of ecosystems, but the actual driver(s) remain elusive. Associated to the delayed recovery observed mainly among benthic organisms, other Early Triassic global-scale paradigms were consensually admitted by the scientific community. The best known among them are a global anoxia/euxinia event, the “reef gap”, a “chert gap”, a “coal gap” and the “Lilliput effect”.<br />Contrasting with these paradigms, recent analyses on nekto-pelagic taxa such as ammonoids and conodonts document an explosive rediversification. Moreover, metazoan reefs, supposed to re-establish during the Middle Triassic, were newly reported from the Early Triassic of western USA, suggesting a fast reef rebuilding wherever permitted by environmental conditions. These observations show that the western USA basin is a regional counterexample of commonly accepted Early Triassic global-scale paradigms of a slow and delayed recovery. The geological record of that region shows that the timing and the processes underlying the recovery are still poorly understood. This requires new studies integrating paleontology, geo- and bio-chronology, geochemistry and sedimentology at different geographical and temporal scales.

Our multidisciplinary project focuses on the geological and fossil records of the western USA basin, an area where our team has already evidenced some of the most intriguing PT recovery patterns. Paradoxically, these patterns contrast with several paradigms that were themselves first described in this basin.
Our priority is to first test the extent of validity of several Early Triassic paradigms. We will thus investigate the regional environmental perturbations during this crucial time interval (occurrence, magnitude, continuity) and then to test for (1) the spatial and temporal impacts of these fluctuations on the regional diversity, and (2) the influence of potential taphonomic biases on observed recovery patterns.
We will first conduct intensive fieldwork in the western USA basin. These original field data, obtained with controlled and replicated sampling protocols, will then be combined with innovative sedimentological and geochemical studies to establish a robust and high-resolution biochronological scheme, to test for potential environmental changes concomitant of biodiversity fluctuations, and to check to what extent the global-scale Early Triassic paradigms apply to the vast region investigated here. We will contrast the spatiotemporal differences in recovery between nekto-pelagic and benthic faunas and we shall infer the bias-corrected diversity dynamics.

Some of our observations in the western USA basin are in marked contradiction with the commonly assumed delayed recovery scenario. The most significant results are:
• Discovery of new Early Triassic exposures and significant extension of the known fossil diversity in the basin.
• Discovery of a highly unexpected biota exhibiting an exceptional preservation and being the most complex known for the Early Triassic marine realm. This biota also contains organisms previously unknown for this time interval.
• Discovery of the first Early Triassic starfish.
• Sampling of numerous large-size gastropods in several outcrops of the basin thus questioning the existence of a Lilliput effect on gastropods at the clade-level during the Early Triassic.
• Development of a new regional biostratigraphic scale at a high temporal resolution based on ammonoids, and first correlations of this time frame with other basins.
• New environmental reconstructions at the local and regional scales.
• No peculiar deleterious environmental conditions were evidenced in the studied localities.

This project will lead to a new basin-scale scenario for the Early Triassic recovery, illustrating the reassembly of local to regional marine communities after a mass extinction event. This could have direct implications on scenarios for the modern biosphere that is currently entering its sixth major extinction crisis.

Last publications:
Caravaca G., et al., 2017: Early Triassic fluctuations of the global carbon cycle: new evidence from paired carbon isotopes in the western USA basin. Global and Planetary Change 154: 10-22.
Brayard A., et al., 2017: Unexpected Early Triassic marine ecosystem and the rise of the Modern evolutionary fauna. Science Advances 3: e1602159.
Jattiot R., et al., 2017: Smithian ammonoid faunas from eastern Nevada: implications for Early Triassic biostratigraphy and correlations within the western USA basin. Palaeontographica A 309: 1-89.
Olivier N., et al., 2016: Evolution of depositional settings in the Torrey area during the Smithian (Early Triassic, Utah, USA) and their significance for the biotic recovery. Geological Journal 51: 600-626.
Thomazo C., et al., 2016: A diagenetic control on the Early Triassic Smithian-Spathian carbon isotopic excursions recorded in the shallow settings of the Thaynes Group (Utah, USA). Geobiology 16: 220-236.
Jattiot R., et al., 2016: Revision of the genus Anasibirites Mojsisovics (Ammonoidea): an iconic and cosmopolitan taxon of the late Smithian (Early Triassic) extinction. Papers in Palaeontology 2: 155-188.
Romano C., et al., 2016: Permian-Triassic Osteichthyes: Diversity dynamics and body size evolution. Biological Reviews 91: 106-147.
Ware D., et al., 2015: High-resolution biochronology and diversity dynamics of the Early Triassic ammonoid recovery: the Dienerian faunas of the Northern Indian Margin. Palaeogeography, Palaeoclimatology, Palaeoecology, 440: 363-373.
Brayard A., et al., 2015: Early Triassic Gulliver gastropods: spatio-temporal distribution and significance for the biotic recovery after the end-Permian mass extinction. Earth-Science Reviews, 146: 31-64.
Vennin E., et al., 2015: Microbial deposits in the aftermath of the end-Permian mass extinction: a diverging case from Mineral Mountains (Utah, USA). Sedimentology, 62: 753-792.

The Permian-Triassic boundary (~252 Myr) is marked by the largest mass extinction of the Phanerozoic. Recovery from this devastating event is usually assumed to be a long delayed process, spanning at least the entire Early Triassic (~5 myr). Indeed, the crisis aftermath is generally portrayed as a time of high ecological stress characterized by large-scale fluctuations of the global carbon cycle and harsh marine conditions, including a combination of ocean acidification, euxinia, and fluctuating productivity. This suggests tight links between these environmental variations and the restructuring of ecosystems, but the actual driver(s) remain elusive. Associated to the delayed recovery observed mainly among benthic organisms, other Early Triassic global-scale paradigms were consensually admitted by the scientific community. The best known among them are a global anoxia/euxinia event, the “reef gap”, a “chert gap”, a “coal gap” and the “Lilliput effect”.
Contrasting with these paradigms, recent analyses on nekto-pelagic taxa such as ammonoids and conodonts document an explosive rediversification. Moreover, metazoan reefs, supposed to re-establish during the Middle Triassic, were newly reported from the Early Triassic of western USA, suggesting a fast reef rebuilding wherever permitted by environmental conditions. These observations show that the western USA basin is a regional counterexample of commonly accepted Early Triassic global-scale paradigms of a slow and delayed recovery. The geological record of that region shows that the timing and the processes underlying the recovery are still poorly understood. This requires new studies integrating paleontology, geo- and bio-chronology, geochemistry and sedimentology at different geographical and temporal scales.
Our multidisciplinary project focuses on the geological and fossil records of the western USA basin, an area where our team has already evidenced some of the most intriguing PT recovery patterns. Paradoxically, these patterns contrast with several paradigms that were themselves first described in this basin.
Our priority is to first test the extent of validity of several Early Triassic paradigms, with a special emphasis on the Smithian and Spathian substages (corresponding to the major onset of the rediversification). This time interval is marked by several global extinction and origination pulses coeval with dramatic shifts in the sedimentological, geochemical and palynological records. Clearly, the relationships between biodiversity fluctuations and shifts in abiotic parameters need to be deciphered further. We will thus investigate the regional environmental perturbations during this crucial time interval (occurrence, magnitude, continuity) and then to test for (1) the spatial and temporal impacts of these fluctuations on the regional diversity, and (2) the influence of potential taphonomic biases on observed recovery patterns.
We will first conduct intensive fieldwork on the numerous outcrops of the western USA basin that record proximal to distal marine environments. These original field data, obtained with controlled and replicated sampling protocols, will then be combined with innovative sedimentological and geochemical studies to establish a robust and high-resolution biochronological scheme, to test for potential environmental changes concomitant of biodiversity fluctuations, and to check to what extent the global-scale Early Triassic paradigms apply to the vast region investigated here. We will contrast the spatio-temporal differences in recovery between nekto-pelagic and benthic faunas and we shall infer the bias-corrected diversity dynamics. This will lead to a new basin-scale scenario for the Early Triassic recovery, illustrating the reassembly of local to regional marine communities after a mass extinction event. This could have direct implications on scenarios for the modern biosphere that is currently entering its sixth major extinction crisis.

Project coordinator

Monsieur Arnaud Brayard (Biogéosciences )

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

Biogéosciences Biogéosciences

Help of the ANR 280,000 euros
Beginning and duration of the scientific project: October 2013 - 48 Months

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