Structure and magnitude of the carbon isotope excursion during the Paleocene-Eocene thermal maximum

Abstract

The Paleocene-Eocene Thermal Maximum (PETM) was a geologically rapid and transient warming event that occurred ca. 56 million years ago (Ma). It was associated with a pronounced negative carbon isotope excursion (CIE) and with profound changes in the atmosphere, hydrosphere and biosphere. This event reflects injections of large amounts of carbon into the atmosphere-ocean system, but, whether single or multiple episodes of carbon release caused this event is uncertain. Here, we present carbon isotope data of bulk carbonate from two parallel limestone sections at Tingri (south Tibet), where the limestone was deposited on a tropical carbonate ramp during the PETM. Carbon isotope data of bulk carbonate from both sections are almost identical, displaying an expanded stepped CIE profile with large magnitude. The stepped CIE profile consists of three discrete intervals of decreasing carbon isotope values, which can be correlated on an inter-regional scale between sections from different depositional environments (lake, carbonate ramp, continental slope, and open ocean). The consistency of these correlations implies occurrence of at least three carbon releases within the CIE and indicates complex processes of carbon injection during the PETM. Moreover, the CIE magnitude of ~7‰ recorded at Tingri is tentatively interpreted to reflect carbon isotope changes in the atmosphere and the surface ocean, which is larger than the generally accepted value of ~4‰ but is still within the range of some previous records.