GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 282-4
Presentation Time: 9:00 AM-6:30 PM


EMSBO, Poul, USGS, Central Mineral and Environmental Resources Science Center, P.O. Box 25046, MS 973, Denver Federal Center, Denver, CO 80225 and MCLAUGHLIN, Patrick I., Indiana Geological and Water Survey, Indiana University, 611 N. Walnut Grove, Bloomington, IN 47405

Modern restricted carbonate platforms can have sediment δ13Ccarb values that are decoupled from open ocean dissolved inorganic carbon (DIC) reservoirs. These studies indicate that caution is necessary when using δ13Ccarb values from marine carbonates to interpret global processes. In light of the proliferation of high-resolution carbon isotope chemostratigraphy from ancient epeiric seas over the last few decades, we test the reliability of δ13Ccarb records through some of the best-studied Paleozoic δ13Ccarb excursions as proxies of the global carbon cycle. Published data, bolstered with the data from this study, allow an unprecedented evaluation of these isotope excursions using established methodologies from studies of modern and ancient carbonate depositional environments to evaluate the fidelity of our results as a proxy for processes related to the global carbon cycle.

We present a series of δ13Ccarb transects spanning shallow ramp sections into their deep-water equivalents in four sedimentary basins, from two isolated paleocontinents. These transacts show a striking consistency in the range of values despite crossing a spectrum of paleogeographic and paleoenvironmental settings over hundreds of kilometers. Similarly, there is a remarkable correspondence between δ13C values from whole-rock, low-Mg brachiopod (extensively screened for evidence of diagenetic alteration) and organic carbon from these sections. Finally, the lockstep changes between δ13Ccarb values, other chemical/redox/climatic proxies and mass extinction events are in keeping those expected with variations in open ocean DIC values.

Combined our new and published high-resolution δ13Ccarb chemostratigraphy, sedimentology, and chrono-stratigraphic correlations, provide, arguably, some of the most thoroughly evaluated record of Paleozoic δ13Ccarb excursion events. Given previous approaches developed from studies of modern and ancient carbonates to test the fidelity between measured δ13Ccarb and open ocean DIC, our evaluation strongly suggests that the observed δ13Ccarb excursions and coincident paleo-biologic, -geochemical, and -environmental changes are, in fact, responding to changes in the global carbon cycle.