Synchronizing early Eocene deep-sea and continental records – new cyclostratigraphic age models from the Bighorn Basin Coring Project

A consistent stratigraphic framework is required to understand the effect of major climate perturbations of the geological past on both marine and terrestrial ecosystems. Transient global warming events in the early Eocene, 56–54 Ma ago, show the impact of large scale input of carbon into the ocean-atmosphere system. Here we provide the first time-scale synchronization of continental and marine deposits spanning the Paleocene-Eocene Thermal Maximum (PETM) and the interval just prior to the Eocene Thermal Maximum 2 (ETM-2). Cyclic variations in geochemical data come from continental drill cores of the Bighorn Basin Drilling Project (BBCP, Wyoming, USA) and from marine deep-sea drilling deposits retrieved by the Ocean Drilling Program (ODP). Both are dominated by eccentricity modulated precession cycles that are used to construct a common cyclostratigraphic framework. Integration of age models results in a revised astrochronology for the PETM in deep-sea records that is now generally consistent with independent 3 He age models. The duration of the PETM is estimated at ~ 200 kyr for the CIE and ~ 120 kyr for the pelagic clay layer. A common terrestrial and marine age model shows a concurrent major change in marine and terrestrial biotas ~ 200 kyr before ETM-2. In the Bighorn Basin, the change is referred to as Biohorizon B, and it represents a period of significant mammalian turnover and immigration, separating the upper Haplomylus-Ectocion Range Zone from the Bunophorus Interval Zone and approximating the Wa-4–Wa-5 land mammal zone boundary. In sediments from ODP Site 1262 (Walvis Ridge), major changes in the biota at this time are documented by the radiation of a 2nd generation of apical spine-bearing sphenoliths species (e.g., S. radians and S. editus ), the emergence of T. orthostylus , and the marked decline of D. multiradiatus .