T49 New Advances in Geobiology

Sunday, 9 October 2022
1:30 PM - 5:30 PM
Mile High Ballroom 2C

TESTING THE INFLUENCE OF SEDIMENTARY FACIES AND DIAGENETIC ALTERATION ON GLOBAL CARBON ISOTOPE CORRELATION: A CASE STUDY FROM THE EARLY CAMBRIAN PERIOD

Paper number: T49-5
Program: Technical Sessions
Time: 2:25 PM – 2:40 PM

Authors

Abstract

The temporal frameworks arising from stratigraphic correlations serve as scaffolds upon which to interpret Earth history. Carbon isotope chemostratigraphy often is leveraged during intervals of Earth history with limited geochronologic and/or biostratigraphic constraints, such as the Proterozoic-Phanerozoic transition. Correlation commonly relies on the assumption that individual records reflect a globally synchronous signal. However, modern facies isotopic variability is of comparable magnitude to the amplitude of Phanerozoic isotopic excursions. Furthermore, the degree to which diagenesis has impacted carbon isotope records, and therefore all resulting correlations, rarely is considered. Here, we leverage four high-resolution early Cambrian litho- and chemostratigraphic records, each with bed-level generalized facies assignments, carbon isotopic records, and estimated sediment accumulation rates (and differing bank top positions), from the Anti-Atlas Margin, Morocco, to test the likelihood that a large fraction of carbon isotope signals used for global Cambrian correlation originates from local facies variability or diagenetic processes. We find that facies isotopic variability likely accounts for noise in carbon isotopic records but cannot explain the largest amplitude signals. While we do find statistically significant relationships between carbon isotope records, calcium isotope records, and sediment accumulation rates (here treated as a proxy (along with permeability) for time spent exposed to marine diagenetic fluids), it does not appear that diagenesis altered carbon isotope values in a way that degraded the isotopic signal profoundly enough to prevent accurate correlation. We conducted a series of numerical experiments with synthetic isotopic records to define guiding thresholds for stratigraphers when evaluating whether their isotopic correlations are significant. We conclude that, in some circumstances, global carbon isotope correlation is feasible (despite not necessarily reflecting changes in the global dissolved inorganic carbon reservoir) and present a new correlation protocol to guide the stratigraphic community.

Geological Society of America Abstracts with Programs. Vol. 54, No. 6

doi: 10.1130/abs/2022AM-382735

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