CHANGES IN HYDROLOGY AND SEDIMENTATION DURING THE PALEOCENE-EOCENE THERMAL MAXIMUM IN THE SALISBURY EMBAYMENT, USA

In response to greenhouse warming, the hydrological cycle is anticipated to intensify, as higher temperatures lead to higher rates of evaporation and the holding capacity of the atmosphere increases. Cores obtained from the Salisbury Embayment along the Mid-Atlantic Coast of the United States can serve as a case study into how the hydrologic cycle has responded to rapid warming in the past, specifically the Paleocene-Eocene Thermal Maximum (PETM). There is abundant evidence of hydrologic change in the region at the onset of the PETM, including increases in sedimentation rates and a marked increase in the kaolinite content. These observations have been argued to have been in response to hydrologic changes driving enhanced weathering and a reworking of previously deposited units, although the exact source and mechanism by which this has occurred has been debated.

Using data from Howard’s Tract and South Dover Bridge cores, this study seeks to expand upon previous work and identify the source of these sediments by coupling semi-quantitative XRD analysis of clay mineralogy to the strontium and lead isotopes of the siliciclastic fraction of sediment. Preliminary results show a shift in the lead and strontium isotopes that is coeval to an increase in the kaolinite fraction of sediments, suggesting a change in sediment source during the carbon isotope excursion (CIE) associated with the PETM. At Howard’s Tract, this shift occurs prior to the carbon isotope excursion, suggesting an alternate forcing for the beginning of the hydrologic change driving the changes in sedimentation.

This study seeks to further understand the mechanisms driving this shift in mineralogy and provenance by coupling the observed changes to high-resolution (25 km) CAM5 Earth-system model output of hydrologic and atmospheric systems changes. The model will be used to determine the regional hydrologic changes relevant to weathering processes, in response to seasonal, orbital, and CO₂ forcing. Preliminary results demonstrate shifts in seasonal precipitation occurring both in the PETM as well as during late Paleocene in response to orbital forcing. The modeled changes in the late Paleocene combined with the observed changes suggests the PETM onset coincided with an eccentricity maxima.