T153 Permian-Triassic Changes and Extinction Event: New Insights from Sedimentary, Geochemical, and Paleobiological Records and Modeling Approaches I

Tuesday, 11 October 2011
8:00 AM - 12:00 PM
Room 200FG

CONSTRAINTS ON EARLY TRIASSIC CARBON CYCLE DYNAMICS FROM PAIRED ORGANIC AND INORGANIC CARBON ISOTOPE RECORDS

Paper number: T153-10
Program: Technical Sessions
Time: 10:20 AM – 10:40 AM

Authors

Abstract

Large δ13C excursions (CIEs), anomalous carbonate precipitates, and evidence for marine euxinia in the Late Permian and Early Triassic are reminiscent of Neoproterozoic geochemistry. Middle Triassic diversification coincided with the waning of anoxia and stabilization of the global carbon cycle, suggesting that environment-ecosystem linkages were important to biological recovery. However, the Earth system behavior responsible for these phenomena remains poorly constrained. Here we examine the extent to which the Early Triassic CIEs record changes in δ13C of marine dissolved inorganic carbon (DIC). Biostratigraphically correlated strata across the Paleo-Tethys and Panthalassic oceans display multiple coeval δ13C shifts, suggesting the record is reflective of large perturbations in the exogenic carbon cycle. However, diagenetic processes and oxidation of a large dissolved organic carbon (DOC) pool are other proposed drivers of large δ13C excursions, including the negative excursion in δ13C at the end-Permian extinction horizon. If paired δ13Ccarb and δ13Corg measurements are coupled and other evidence for diagenetic control of the δ13C record is absent, the record is likely driven by changes in marine DIC composition. If not, the perturbations may be related to non-steady state carbon cycle behavior and the buildup of a large DOC reservoir, as suggested for the Neoproterozoic.

Here we present one of the first Early Triassic δ13Corg records from south China and apply it as a test of carbon cycle coupling through this interval. Regression modeling demonstrates a clear correlation between δ13Corg and δ13Ccarb across multiple sections and spanning a paleoenvironmental gradient. A simple explanation is that a substantial fraction of the preserved Corg formed from the contemporaneous DIC pool, implying that the observed excursions reflect variation in the δ13C of the exogenic carbon reservoir. Our results do not rule out a large DOC pool during Late Permian time, but require that it was nearly entirely oxizided by the earliest Triassic.