DOUBLE TROUBLE: TRACKING (LATE WENLOCK) SILURIAN SULFUR AND CARBON CYCLE PERTURBATIONS ASSOCIATED WITH THE MULDE EVENT FROM TENNESSEE AND NEVADA

Despite its short duration, the Silurian period is defined by many marine biotic turnover events. The Late Wenlock Mulde (~429-428Ma) positive carbon isotope excursion (CIE) is one of seven major perturbations in the Silurian. The uniqueness of this particular excursion lies in its dual-peaked behavior and remains one of two of this type throughout the Paleozoic. High-resolution carbon isotope data has previously been produced for both field sites investigated here for this project: sections from the Simpson Park Range, Nevada and McCrory Lane, Tennessee. Oceanographic and climactic drivers for Silurian CIE’s and extinction events are poorly understood, however, this project aims to pair δ³⁴S_CAS (carbonate-associated sulfate), δ³⁴S_pyrite with δ¹³C_organic, δ¹³C_carbonate data to test hypotheses put forward for this CIE that are related to purported changes in oceanographic conditions that should have corresponding changes in the paleoredox state of marine environments.

For the first time, we present Late Wenlock paired δ³⁴S_CAS, δ³⁴S_pyrite, δ¹³C_org, and δ¹³C_carb data from two separate paleocean basins that have previous records of the Mulde CIE. Preliminary δ³⁴S_CAS data from Tennessee show a positive excursion of up to 9‰ magnitude coinciding with the onset and first positive δ¹³C_carb shift of the Mulde. The δ¹³C_org data covary with previously published δ¹³C_carb data; showing two positive shifts of 1–2‰ magnitude. Broader scale trends in δ¹³C_org data show a larger shift in δ¹³C_org values ~4‰ lighter after the return to baseline values during the Mulde CIE. Preliminary δ³⁴S_CAS data from Nevada show much more variation, that may be due to contamination from pyrite oxidation. Trends from the Nevada stable isotope data sets also demonstrate that we have likely only recorded data from the second positive shift and return to baseline values of the Mulde CIE. δ³⁴S_pyrite values are being generate from the Nevada sequence to assess any potential CAS contamination issues and local paleoredox conditions from this area of the Great Basin during the Late Wenlock. Regardless of any potential sulfate contamination, these new data do suggest that the extinction interval and onset of the CIE in the Late Wenlock are linked to expansion of reducing conditions in the global oceans that led to enhanced burial of organic matter and pyrite.