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A diagenetic control on the Early Triassic Smithian–Spathian carbon isotopic excursions recorded in the marine settings of the Thaynes Group (Utah, USA)
Author(s) -
Thomazo C.,
Vennin E.,
Brayard A.,
Bour I.,
Mathieu O.,
Elmeknassi S.,
Olivier N.,
Escarguel G.,
Bylund K. G.,
Jenks J.,
Stephen D. A.,
Fara E.
Publication year - 2016
Publication title -
geobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.859
H-Index - 72
eISSN - 1472-4669
pISSN - 1472-4677
DOI - 10.1111/gbi.12174
Subject(s) - early triassic , authigenic , diagenesis , geology , extinction event , paleontology , carbonate , isotopes of carbon , phanerozoic , sedimentary rock , carbon cycle , permian , total organic carbon , ecosystem , cenozoic , chemistry , ecology , demography , organic chemistry , sociology , environmental chemistry , biology , biological dispersal , population , structural basin
In the aftermath of the end‐ P ermian mass extinction, E arly T riassic sediments record some of the largest P hanerozoic carbon isotopic excursions. Among them, a global S mithian‐negative carbonate carbon isotope excursion has been identified, followed by an abrupt increase across the S mithian– S pathian 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 L ate S mithian. It is commonly assumed that S mithian and S pathian isotopic variations are intimately linked to major perturbations in the exogenic carbon reservoir. We present paired carbon isotopes measurements from the T haynes G roup ( U tah, USA ) to evaluate the extent to which the E arly T riassic isotopic perturbations reflect changes in the exogenic carbon cycle. The δ 13 C carb variations obtained here reproduce the known S mithian δ 13 C carb ‐negative excursion. However, the δ 13 C signal of the bulk organic matter is invariant across the SSB and variations in the δ 34 S signal of sedimentary sulphides are interpreted here to reflect the intensity of sediment remobilization. We argue that M iddle to L ate S mithian δ 13 C carb signal in the shallow marine environments of the T haynes G roup does not reflect secular evolution of the exogenic carbon cycle but rather physicochemical conditions at the sediment–water interface leading to authigenic carbonate formation during early diagenetic processes.