Geological Society of America

T11 New Developments in Geochemical Proxies for Paleoceanographic Research

Sunday, 4 November 2018
8:00 AM - 12:00 PM
Room 140

ARE OAES ACTUALLY CBES? EVIDENCE OF MARINE ANOXIA THROUGH THE EYES OF A NOVEL METAL ISOTOPE

Paper number: T11-13
Program: Technical Sessions
Time: 11:00 AM – 11:15 AM

Authors

Theodore R. Them Presenting Author
College of Charleston, Charleston, SC
Benjamin Gill
Virginia Polytechnic Institute and State University, Blacksburg, VA
Andrew H. Caruthers
Western Michigan University, Kalamazoo, MI
Darren R. Gröcke
University of Durham, Science Labs, Durham
Selva M. Marroquín
Virginia Polytechnic Institute and State University, Blacksburg, VA
João Trabucho Alexandre
Utrecht University, Utrecht
Jeremy D. Owens
Florida State University, National High Magnetic Field Laboratory, Tallahassee, FL

Abstract

The development of widespread anoxia in the oceans during past intervals of environmental deterioration is generally accepted as one of the main drivers of biotic crises. Many traditional proxies such as carbon isotopes, trace metal enrichments, and the deposition of organic matter-rich sediments have been utilized to demarcate the timing of increased anoxia. However, recent research has suggested that a novel geochemical proxy can fingerprint the timing and duration of deoxygenation associated with these events. The Early Jurassic Toarcian Oceanic Anoxic Event (OAE) is associated with perturbations to multiple elemental systems, deposition of organic matter-rich sediments, and a marine mass extinction. These changes have been linked to the emplacement of the Karoo-Ferrar large igneous province and associated biogeochemical feedbacks within the Earth system.

We will present a multi-proxy dataset of novel and traditional geochemical proxies across the T-OAE from eastern Panthalassa. Iron speciation data are used to constrain local water column redox that suggests anoxic and euxinic (anoxic and sulfidic water column) conditions. Thallium isotopes, a new and novel proxy, are utilized to determine the onset of widespread deoxygenation. Redox-sensitive trace metal contents are used to track the marine reservoir of the respective element. These combined data suggest that widespread deoxygenation initiated ~600 kyr before the traditional T-OAE interval at Pliensbachian/Toarcian boundary. A decrease in the trace metal inventory of the oceans is associated with the traditional T-OAE interval and related to the expansion of euxinia. These data are generally consistent with a Cretaceous OAE (Cenomanian/Turonian Boundary Event) but the timescales are vastly different. Thus, the use of novel and traditional geochemical proxies suggests that the traditional OAE interval is better defined as a carbon burial event (CBE) or oceanic euxinic event (OEE).

Geological Society of America Abstracts with Programs. Vol. 50, No. 6

doi: 10.1130/abs/2018AM-324309

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