Carboniferous chemostratigraphy: Do epicontinental seas reflect global ocean conditions?

Texas A&M Research Foundation, College Station TX

Investigators

Abstract

Carboniferous chemostratigraphy: Do epicontinental seas reflect global ocean conditions? Deborah J. Thomas, Ethan L. Grossman, Brent V. Miller, Thomas D. Olszewski, Thomas E. Yancey EAR-0643309 Texas A&M University ABSTRACT The Carboniferous Period (359 to 299 million years ago) was a time of dramatic tectonic, climatic, and biologic change in Earth's history. Several aspects of the Carboniferous are distinctive from the standpoint of Earth Systems Science: the onset of significant glaciation, signaled by global regression; a major change in carbon cycling manifested by coal accumulation in the paleotropics; and reconfiguration of the continents resulting in the Alleghanian-Variscan orogeny, assembly of Pangea, and closure of the Rheic Ocean, leading to severing of the marine connection between the North American paleotropics and the Tethyan paleotropics. A wealth of paleobiologic, paleobiogeographic, and paleochemical data has been generated, with recent emphasis on applying marine geochemical proxies to unraveling the potential links between tectonics, carbon cycling, and climate. The marine paleochemical data, in theory, provide oceanic proxy records of temperature (Delta 18 Oxygen ), carbon cycling (Delta 13 Carbon), and weathering (34S/32S, 87Sr/86Sr), but the application of these proxies to the Paleozoic is confounded by the fact that they are derived from marine sediments deposited in epicontinental seas. These shallow, shelf-like environments must have had connections to open ocean basins (e.g., Panthalassa and Rheic Oceans) in order to support marine communities, yet there is evidence to suggest geochemical decoupling between shallow epicontinental seas and the open ocean. In an effort to better understand the causes and consequences of climate change during the Carboniferous, PIs must first establish what can be inferred from marine geochemical records. Thus they propose to address the question, To what degree does the Carboniferous North American epicontinental sea record global open-ocean conditions? They will use radiogenic and stable isotope tracers of varying residence times along a transect spanning the Mixteco terrane in present-day southwestern Mexico (most oceanic), Arrow Canyon, US Midcontinent, Illinois Basin, and Appalachian Basin (most interior) to constrain the degree of geochemical coupling between the epicontinental sea and the open ocean (Panthalassa and Rheic Ocean).