T112 Oceans and Climates through Earth History: Modeling, Proxy, and Proxy Development Studies (Posters)

Monday, 23 September 2024
8:00 AM - 5:30 PM
Hall D

A COMPLEX MOSAIC OF SULFUR ISOTOPE RECORDS THROUGH THE LATE ORDOVICIAN MASS EXTINCTION IN THE GREAT BASIN AND ANTICOSTI ISLAND

Paper number: T112-4
Program: Technical Sessions
Time: 8:00 AM – 5:30 PM

Authors

Abstract

A suite of dramatic environmental, climatic, and geologic changes unfolded in association with the Late Ordovician mass extinction, including glaciation, marine anoxia, and volcanism. Stable isotope records of carbonate associated sulfate (δ34SCAS) and sedimentary pyrite (δ34Spyr) have provided a basis for interpretations of such changes. However, uncertainties in the degree to which these data reflect local vs. global conditions and the effects of depositional systems and early diagenesis complicate interpretations of the sulfur isotope record. Here we present δ34SCAS and δ34Spyr records from four sections of the Ely Springs Dolostone across the Great Basin and four limestone sections across Anticosti Island in order to document the variability inherent in these systems.

In the Great Basin, upper Katian dolostones are characterized by consistent baseline δ34SCAS values. These baseline values range from +20‰ at South Egan Range to +30‰ at Barn Hills. A large magnitude positive δ34SCAS excursion occurs in Hirnantian strata at both South Egan and Silver Island ranges, broadly synchronous with the positive HICE excursion (Hirnantian isotopic carbon excursion). δ34Spyr tracks the δ34SCAS excursion tightly at Silver Island (r2 = 0.52), but not at South Egan (r2 = 0.22). Cherry Creek Range lacks a δ34S excursion at the HICE. None of the studied sections contain the pre-Hirnantian negative δ34SCAS excursion previously reported in the deep-water limestones at Monitor Range.

On western Anticosti Island, limestones of the Katian Vaureal Formation record a negative excursion in δ34SCAS similar to that observed at Monitor Range, declining from +50‰ to +20‰ over 30 meters. However, viewed in the full context of δ34SCAS record of the exposed upper Ordovician strata, that excursion is the descending limb of a positive excursion that departed from a +30‰ baseline. In the east, upper Katian limestones are characterized by swings in δ34SCAS of >20‰ over several meters of stratigraphy, with no stable baseline. The Hirnantian Laframboise Member at the eastern sections hosts a prominent decline in Δ34S (= δ34SCAS - δ34Spyr) driven by a positive δ34Spyr excursion.

The lack of a consistent chemostratigraphic signal within and between sedimentary basins highlights the importance of local depositional and early diagenetic processes in shaping the archive of deep time δ34S.

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

doi: 10.1130/abs/2024AM-404517

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