266-7 Tiny Fossils, Big Anomaly: Single Fossil Organic Carbon Isotopes Through the Taishir Anomaly

Session: The Neoproterozoic Earth and Life Co-evolution (Posters)

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The Neoproterozoic Tsagaan-Olom Group of southwestern Mongolia records one of the most pronounced negative carbon isotope anomalies in Earth’s history, the Taishir anomaly. Baseline δ¹³C values in the Taishir Formation are approximately +8‰ in member T2, but decrease sharply at the beginning of member T3, reaching a low of about −7.5‰, though the exact values vary across the basin. Various potential mechanisms for this excursion have been proposed including global perturbations in seawater δ¹³C, large-scale oxidation of organic carbon reservoirs, and precipitation of isotopically enriched authigenic carbonates.

In this study we examined single red algal microfossils (OSM, organic spore-like microfossils) found in the Cryogenian Taishir and Ediacaran Ol Formations of the Tsagaan-Olom Group. To determine the δ13C values of individual microfossils, we apply a novel approach utilizing a nanoEA -- an elemental analyzer attached to a stable isotope mass spectrometer. We then compare the single fossil values to bulk organic and inorganic carbon isotope values. Previous studies of OSMs from the Tsagaan-Olom Group using this technique showed that fossils were particularly depleted in δ13C compared to normal organic matter, possibly due to their red algal affinity. However, these earlier analyses did not capture fossils from within the Taishir anomaly. Here we present new isotopic data through the Taishir anomaly from the Ho Daava and Northern Taishir localities. We measured δ13C values of 10 OSMs per horizon from 19 Northern Taishir horizons and 6 Ho Daava horizons. With these isotopic measures, we aim to better understand what may have caused the Taishir anomaly, the role OSMs played in the carbon cycle, and reveal more information on their ecology and taxonomic affinity.

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

doi: 10.1130/abs/2025AM-10380

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