Geological Society of America

T56 New Advances in Geobiology

Sunday, 22 September 2024
1:30 PM - 5:30 PM
208A

GLOBAL RECORDS REVEAL A STEEP OCEANIC DIC δ13C DEPTH GRADIENT DURING THE HIRNANTIAN GLACIATION

Paper number: T56-11
Program: Technical Sessions
Time: 3:50 PM – 4:05 PM

Authors

Shengchao Yang Presenting Author
Nanjing University, Nanjing, Jiangsu
Junxuan Fan
Nanjing University, Nanjing, Jiangsu
Junxuan Fan
Chinese Academy of Sciences, Beijing, Beijing
Thomas Algeo
University of Cincinnati, Cincinnati, OH
Thomas Algeo
China University of Geosciences, Wuhan, Hubei
Chao Li
Chengdu University of Technology, Chengdu, Sichuan

Abstract

The Hirnantian carbon isotopic excursion (HICE) was characterized by a global positive δ¹³C excursion (up to ~ + 7‰ in excursion magnitude) during the Ordovician-Silurian (O/S) transition, while its mechanism remains controversial, hampering our understanding of this global event and its environmental significance. In this study, we compiled a dataset of global carbon isotope records, including 65 paleogeographically widely distributed sections (4,612 carbon isotope data in total), which documents a steep oceanic δ¹³C water-depth gradient (e.g., a 4.6‰ offset in the HICE excursion magnitude within Laurentia and 3.3‰ within South China) during the Hirnantian Stage. We propose a hybrid hypothesis that the HICE records a shift towards more positive values due to a large glacio-eustatic fall (up to ~150 m) under the herein-identified steep oceanic δ¹³C water-depth gradient, with potential contributions from global-ocean δ¹³C_DIC changes and authigenic carbonates. This study provides the first large-data evidence for a steep oceanic DIC δ¹³C water-depth gradient and widely density-stratified ocean during the Hirnantian Glaciation, which has implications for reconstructions of the carbon cycle and ocean circulation during the Early Paleozoic.

Keywords: Ordovician; HICE; carbon cycle; dissolved inorganic carbon

Geological Society of America Abstracts with Programs. Vol. 56, No. 5

doi: 10.1130/abs/2024AM-404059

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