25 Integrated Studies of Paleozoic Black Shale

Friday, 8 April 2022
8:00 AM - 12:00 PM
North Meeting Room 205

MID-LATE GIVETIAN CARBON-CYCLE PERTURBATIONS IN BLACK SHALE AND ASSOCIATED DEPOSITS OF THE NORTHERN APPALACHIAN BASIN

Paper number: 25-6
Program: Theme Sessions
Time: 9:20 AM – 9:35 AM

Authors

Abstract

The Mid-Late Givetian (Middle Devonian) was a volatile time. Marine faunal migration and extinction, eustatic fluctuation, carbon-cycle perturbation, warming/cooling, and anoxia occurred over ~2 Myr through the complex Taghanic Crisis and into the onset of the Frasnes Crisis. In the Northern Appalachian Basin, an expanded stable isotope profile of inorganic carbon δ13Ccarb in the Lansing Core spans an incredible range of ~8‰ (~+3 to near -5) through a series of carbon-cycle perturbations in black shale and associated deposits. This overall positive-to-negative shift in values is seen globally as the lightest Devonian values, but this magnitude of negative shift is more extreme than previously reported.

­­In the Northern Appalachian Basin, carbon-cycle perturbations correspond to a series of paleoclimate, sea level, and faunal events that compose these crises. Recognized events include: 1) the Taghanic Lower Tully Event, during which a negative δ13Ccarb excursion is immediately followed by warming, transgression, and Appalachian Basin invasion by warm water taxa; 2) the Taghanic Upper Tully Event, seen as a positive δ13Ccarb excursion, cooling, sea level fluctuations including a major transgression (Taghanic Onlap) and the return of endemic cooler water taxa; 3) the latest Taghanic Geneseo Event, with the onset of a long-term negative δ13Ccarb shift, black shale deposition, warming, maximum flooding and the loss of a majority of Appalachian Basin endemic taxa; 4) the post Taghanic disparilis Event, a short-term ‘stabilization’ of the δ13Ccarb record, cooling and substantial sea level fall followed by transgression; 5) the Hubbard Quarry Event, the resumption of the long-term negative δ13Ccarb shift, black shale deposition, resumed warming and maximum flooding; and, 6) the Lodi Event at the onset of the Frasnes Crisis, with the lightest δ13Ccarb values observed (~-5‰) during warming, sea level fluctuations and warm water taxon incursion.

The light δ13Ccarb values and negative isotopic shifts in the Lansing Core coincident with transgression and warming suggest pulsed release of methane to the global ocean-atmosphere system. Future work will document carbon isotope patterns in Mid-Late Givetian age rocks along transects in the Appalachian Basin and globally to differentiate regional and global patterns.

Geological Society of America Abstracts with Programs. Vol. 54, No. 4

doi: 10.1130/abs/2022NC-375770

© Copyright 2022 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.