107-6 The Geochemical Expression and Implications of Early Triassic Authigenic Carbonates in the Thaynes Group (USA)

Session: Sedimentary Geology Division/SEPM Student Research Poster Competition: Dynamics of Stratigraphy and Sedimentation

Presenting Author:

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Abstract:

Modern marine carbonate production is predominantly driven by biogenic calcification, with only minor contributions from carbonate authigenesis (in this abstract, treated as any carbonate inorganically precipitated in situ at or below the sediment-water interface). However, authigenic carbonate precipitation is believed to have been more significant in the geologic record, when higher dissolved inorganic carbon concentrations and reduced oceanic oxygenation likely promoted carbonate authigenesis. As authigenic carbonates form under distinct environmental conditions and through different mechanisms than primary carbonates, they have been invoked as a potential driver of both local and global geochemical signatures, especially for explaining geochemical excursions that cannot be readily interpreted via primary models. Despite their significance, however, the geochemical influence of authigenic carbonates has been uniquely challenging to characterize – or even recognize – via conventional petrographic and geochemical signatures within dominantly carbonate successions.

Accordingly, there is a widespread need to study authigenic carbonate deposits within the geologic record to better characterize their potential impact on global geochemical records. In this context, the previously-characterized Mineral Mountains carbonate succession of the southern Thaynes Group (USA) poises a unique opportunity to explore the geochemical expression of authigenic carbonates during the Early Triassic – an interval when carbonate authigenesis may have been more widespread than the present, and thus may have significantly influenced geochemical cycling. 

Here, we leverage a novel multi-proxy carbonate geochemical framework (δ¹³C, δ¹⁸O, δ^44/40Ca, δ²⁶Mg, trace-metals) that can help distinguish authigenic signatures, together with existing bulk geochemical, paleoecological and stratigraphic records, to characterize the geochemical expression of authigenic carbonate precipitation within the Mineral Mountains. In turn, these constraints enable us to examine the local, regional, and global implications of authigenic carbonate precipitation. Our results suggest that the authigenic carbonate geochemistry of the Mineral Mountains succession is substantially driven by local controls, and is consequently decoupled from inferred global trends. The geochemical patterns expressed in the Mineral Mountains may therefore be broadly useful for disentangling the signals stored in carbonate geochemical records, both with regards to (i) understanding the nature of the unstable Early Triassic carbon cycle, and (ii) more broadly throughout the geologic record. 

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

doi: 10.1130/abs/2025AM-8755

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