Finding a VOICE in the Southern Hemisphere: A new record of global organic carbon?

Abstract

Variations in the carbon isotopic composition of carbonate and organic carbon (δ13Ccarb and δ13Corg) are generally used to record perturbations in the global carbon cycle, which are in turn closely linked to changes in climate. However, because of climate gradients on Earth, assignment of the “global” signal in ancient records is not straightforward. Here, we report the δ13C values of organic material in the Upper Jurassic to Lower Cretaceous sedimentary record of the Vaca Muerta Formation, situated in the Neuquén Basin, Argentina, which show similar patterns to those observed in several northern latitude basins. This record of δ13C values in the organic material differs from those measured in the early Atlantic Ocean, a record previously considered to be representative of the global values of organic carbon. As a result of the global synchronicity observed in the δ13C values of organic material from both northern and southern latitudes, we suggest that these patterns may represent the global record of δ13C values in organic material rather than those measured in the proto−Atlantic Ocean. The δ13C values of the organic components show a slight initial decrease of ∼2‰ in the early Tithonian (149−145 Ma) and then another decrease of ∼2‰ before reaching a minimum of −30.29‰ in the late Tithonian (145−143 Ma), followed by a gradual increasing trend throughout the Berriasian (143.1−137.7 Ma). The early Valanginian (137.7−135.5 Ma) was marked by a more substantial increase in δ13C values up to −23.46‰. These changes mirror those seen in Northern Hemisphere locations during the Late Jurassic and Early Cretaceous, where this perturbation has been termed the Volgian isotopic carbon excursion (VOICE). This difference in the Late Jurassic and Early Cretaceous δ13C values between the early Atlantic Ocean and the Neuquén Basin is interpreted to be the result of the climate gradient at the time, which was characterized by more humid conditions in high latitudes compared to dry conditions in the Atlantic Ocean basin.