T216 Mass Extinctions as Natural Experiments in Earth System Perturbations I

Wednesday, 18 October 2023
8:00 AM - 12:00 PM
301 / 302

PANIC! IN THE PANTHALASSIC: REDOX TRENDS LEADING UP TO THE END-TRIASSIC MASS EXTINCTION FROM EASTERN PANTHALASSA

Paper number: T216-7
Program: Technical Sessions
Time: 9:25 AM – 9:40 AM

Authors

Abstract

The latest Triassic represents a time of major disturbance to marine ecosystems that culminated in a mass extinction: the end-Triassic mass extinction or ETME. This interval was characterized by enhanced diversity loss and perturbations to the environment and global biogeochemical cycles. Marine deoxygenation has been proposed as an extinction mechanism for the ETME, however the record of marine redox during the ETME remains poorly documented. Further, studies that have investigated changes in marine redox have focused on the interval of greatest loss to biological diversity while new evidence suggests marine ecosystems became progressively stressed well before the ETME. Therefore, the temporal links between changes in marine ecosystems and deoxygenation need further investigation. Here we present sedimentary nitrogen isotopes (δ15N) to characterize local nitrogen cycling and marine redox conditions preceding, during, and after the ETME at two locations in the eastern equatorial Panthalassa: Grotto Creek (GC), Alaska, and Ferguson Hill (FH), Nevada. GC represents deeper water deposition on a siliceous-carbonate ramp on the Wrangellia terrane, and FH represents a shallow-water carbonate ramp deposited on the western Pangean margin. At GC, a δ15N excursion of ~+3‰ initiates near the Norian–Rhaetian boundary (~209 Ma) and declines just after the ETME. At FH, which does not expose Norian and lower Rhaetian strata, we observe a δ15N fall from 5‰ in the uppermost Rhaetian to ~3‰ in the lowermost Hettangian. We propose that the δ15N perturbations found in both sections indicate deoxygenation and incomplete denitrification within the water column, subsequently leaving behind residual nitrate enriched in δ15N. Therefore, these isotopic signals reflect a transient shift from a widely oxygenated local water column to a deoxygenated one that persisted through the ETME in eastern equatorial Panthalassa. The GC data also indicate that deoxygenation initiated up to ~8 Ma prior to, and persisted through, the ETME and may be linked to the stressed ecosystem observed during this time. In summary, our data adds to a growing body of evidence of marine environmental deterioration before the ETME and serves to sharpen our understanding of this critical interval of Earth History.

Geological Society of America Abstracts with Programs. Vol. 55, No. 6

doi: 10.1130/abs/2023AM-395214

© Copyright 2023 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.