251-9 Local and diagenetic restructuring of carbon isotope records shape observed Early Triassic carbon cycle instability: insights from the Great Bank of Guizhou (China)

Session: Phanerozoic Earth System Shifts in the Marine Sedimentary Record

Presenting Author:

Jordan Todes

Authors:

Todes, Jordan P. ¹, Payne, Jonathan L.², Lau, Kimberly V.³, Herz, Susannah C.⁴, Bryant, Roger N.⁵, Kelley, Brian M.⁶, Lehrmann, Daniel J.⁷, Li, Xiaowei⁸, Meyer, Katja M.⁹, Schaal, Ellen K.¹⁰, Yu, Meiyi¹¹, Blättler, Clara L.¹²

(1) Department of the Geophysical Sciences, University of Chicago, Chicago, IL, USA, (2) Department of Earth and Planetary Sciences, Stanford University, Palo Alto, CA, USA, (3) Department of Geosciences and Earth and Environmental Systems Institute, Pennsylvania State University, University Park, PA, USA, (4) Department of Earth and Planetary Sciences, Stanford University, Palo Alto, CA, USA, (5) Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN, USA, (6) Department of Geosciences, Pennsylvania State University, University Park, PA, USA, (7) Department of Earth and Environmental Geosciences, Trinity University, San Antonio, TX, USA, (8) College of Resources and Environmental Engineering, Guizhou University, Guiyang, China, (9) Department of Environmental and Earth Sciences, Willamette University, Salem, OR, USA, (10) Department of Environmental Science and Studies, DePaul University, Chicago, IL, USA, (11) College of Resources and Environmental Engineering, Guizhou University, Guiyang, China, (12) Department of the Geophysical Sciences, University of Chicago, Chicago, IL, USA,

Abstract:

Our understanding of Earth history heavily relies upon carbonate geochemical records, but it is often challenging to decipher the extent to which these records reflect global paleoenvironmental patterns. This is especially true within the Early Triassic, which records substantial carbon cycle instability during the protracted recovery from the end-Permian mass extinction. As conventionally interpreted, these unusually large and rapid δ¹³C_carb excursions are commonly linked to changes in seawater δ¹³C_DIC values, driven in turn by patterns of thermo- and volcanogenic carbon release, organic carbon burial, methanogenesis, carbonate saturation, seafloor anoxia, and/or carbonate authigenesis. While these varied interpretations rely on the faithful preservation of globally-representative δ¹³C_carb values, both local variations in seawater chemistry and the ubiquity of early marine diagenesis in shallow-water carbonates may appreciably impact preserved carbonate geochemistry. Disentangling these local and diagenetic signatures is therefore crucial for understanding the causes of observed Early Triassic carbon cycle instability. Here, we leverage a multi-proxy carbonate geochemical framework to decipher potential local and diagenetic influences on δ¹³C_carb records from the Great Bank of Guizhou (south China), an iconic carbonate platform that forms the backbone of Early to Middle Triassic chemostratigraphic records.

 

In general, observed depositional gradients in δ¹³C_carb trends in the Great Bank of Guizhou are superimposed on broader secular (chemostratigraphic) patterns. During the Induan, δ¹³C_carb values vary by up to 5‰ from the platform top to the basin, with this gradient largely disappearing after the early Olenekian. Calcium isotope records reveal comparable patterns: δ^44/40Ca values vary by 1‰ across the platform in the Induan, consistent with the preservation of primary aragonite (platform top and basin) and primary and/or neomorphosed calcite (platform flank and slope) sediments. Subsequently, δ^44/40Ca values increase towards inferred Triassic seawater δ^44/40Ca values beginning in the early Olenekian, driven by early marine diagenetic resetting that would have likely influenced associated δ¹³C_carb records. These results suggest that the Guizhou δ¹³C_carb records may partially reflect a combination of local, facies-related controls (Induan), and early-marine diagenetic resetting (Olenekian), with this shift likely driven by the development of significant platform-to-basin architectural relief in the early Olenekian. These findings collectively underscore the potential implications of facies-specific and diagenetic signatures on carbonate geochemical records, and the importance of deconvolving them prior to inferring global palaeoceanographic trends.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9127

© Copyright 2025 The Geological Society of America (GSA), all rights reserved.