Are Co-Varying dC Records Really the Result of Changes in Global Carbon Cycling?

Abstract

Covariation between organic and inorganic carbon isotope (dC) records is traditionally interpreted to be the result of major changes in global carbon cycling. Although covariation between paired dC records is commonly observed in the ancient geological record in a variety of depositional environments, these types of comparisons are not widely applied in similar modern settings where data regarding sediment producers, eustatic sea level, and changes in global carbon cycling are readily available. This study is designed to test other mechanisms for generating positive covariation between inorganic and organic dC records that are unrelated to changes in the global carbon cycle. In order to assess the influence of margin architecture, depositional environment, and diagenetic history on the relationship between inorganic and organic dC records, thirteen pairs of inorganic and organic dC records were evaluated from a variety of depositional environments. Three transects of cores collected by the Ocean Drilling Program (ODP Legs 166, 182, and 133) have been analyzed to assess the influence of margin architecture on the covariance between inorganic and organic dC records. These results have been compared to paired records from two pelagic settings (ODP Sites 525 and 709) in order to determine the impact of depositional environment on the covariance between inorganic and organic dC records. Finally, a core drilled by the Bahamas Drilling Project through the meteoric, phreatic, mixing, and marine burial diagenetic zones of the Great Bahama Bank has evaluated the importance of diagenetic alteration and sub-aerial exposure on the relationship between inorganic and organic dC records. The novel comparisons generated by this study show that there are a variety of mechanisms that can produce isotopically distinct organic and inorganic materials, which when mixed, produce positive covariations with correlation coefficients similar to those observed in the ancient geological record. Consequently, paired dC records that exhibit a strong positive covariation may not be reliable records of changes in global carbon cycling through time.

AAPG Datapages/Search and Discovery Article #90189 © 2014 AAPG Annual Convention and Exhibition, Houston, Texas, USA, April 6–9, 2014