T84 A Matter of Time: The Stratigraphic Record of Time and the Future of Timescale Calibration

Tuesday, 27 October 2020
1:30 PM - 5:30 PM
Meeting Rooms

HIGH-RESOLUTION PAIRED ORGANIC AND CARBONATE CARBON ISOTOPE CHEMOSTRATIGRAPHY OF THE HANGENBERG EVENT FROM H28 AND H32 CORES IN SOUTHEAST IOWA

Paper number: T84-4
Program: Technical Sessions
Time: 2:05 PM – 2:20 PM

Authors

Abstract

This study uses new high-resolution organic (δ13Corg) and carbonate (δ13Ccarb) carbon isotope data from shelf deposits in Iowa to explore the Hangenberg Event, a mass extinction event and carbon isotope excursion spanning the Devonian-Carboniferous boundary. Biostratigraphic correlation of conodonts between the standard European section and strata in Iowa place the early and middle Hangenberg Crises in the siltstones and shales of the upper English River Formation (upper B. ultimus Zone) and the late Hangenberg Crisis in the limestone of the lower Louisiana Formation (lower-mid kockeli Zone). Our results show decoupling of the δ13Ccarb and δ13Corg curves followed by a positive excursion in both carbonate and organic carbon isotopes. The curves decouple in the upper English River Formation, where δ13Corg values decrease and values of δ13Ccarb increase simultaneously. Further investigation into the factors controlling the isotopic fractionation of carbon using Δ13C led us to conclude that the negative δ13Corg excursion is a global signal caused by the addition of chemoautotrophic organisms to the sediment. In the overlying Louisiana Formation δ13Ccarb and δ13Corg values reach sustained peaks of +6‰ and -26‰, respectively. Calculated ƒorg values increase in the Louisiana Formation, corresponding with the positive δ13Ccarb excursion and indicating the most likely cause of the positive carbon isotope excursion is increased organic carbon burial. This study emphasizes the importance of high-resolution sampling, as it was a critical component of our ability to decipher short-term changes in the carbon cycle.

Geological Society of America Abstracts with Programs. Vol. 52, No. 6

doi: 10.1130/abs/2020AM-359740

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