CARBON ISOTOPE VARIATIONS DURING THE PALEOCENE-EOCENE THERMAL MAXIMUM AND IMPLICATIONS FOR CARBON FLUXES (Invited Presentation)

The δ¹³C composition of biogenic sediments have proven to be a highly versatile tool in the effort to resolve the evolution of earth environments, with applications ranging from stratigraphic correlation to constraining carbon cycle fluxes (Scholle & Arthur, 1980). This is particularly evident in the study of the major climatic and biotic events of Earth’s past including mass extinctions, periods of ocean anoxia, and hyperthermals, specifically the Paleocene-Eocene Thermal Maximum (PETM), which was first recognized on the basis of a large negative δ¹³C excursion (CIE). Along with the constraints on ocean acidification, the CIE provided the basis for demonstrating that the PETM was caused by a massive release of carbon, on the order of several thousand Petagrams. However, interpretation of carbon isotope records has also been controversial, specifically regarding the rates of C fluxes. This stems primarily from uncertainties about the duration of the onset of the CIE with estimates ranging from 10 to 10⁴ years. The latter reflects limitations of chronostratigraphy as well as a variety of depositional artifacts, for example carbonate dissolution and diagenesis, and reworking. To circumvent these issues, strategies have been employed to constrain rates independent of time control. For example, identifying lags in the spatial propagation of the CIE within the ocean (as recorded in individual shells), patterns that could only occur with a rapid rate of C release (i.e., faster than the mixing time of the ocean). Similarly, where the relative thermal response of the ocean to forcing can be constrained independent of stratigraphic control, a fast carbon release should be characterized by a thermal lag. Such approaches assume continuous and relatively rapid sediment accumulation. Application of these strategies to suitable coastal and pelagic records suggest that the onset of the CIE spanned centuries to millennia, and was not geologically instantaneous, consistent with other independent constraints.

Scholle, P. A. and Arthur, M. A., 1980. Carbon isotope fluctuations in pelagic limestones: Potenial Stratigraphic and Petroleum Exploration Tool. American Association of Petroleum Geologists Bulletin, v. 64, p. 67-87, 1980.