--> Understanding Sediment Supply to the Atlantic Margin (Maryland and Delaware, U.S.A.) During Paleocene-Eocene Thermal Maximum

AAPG ACE 2018

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Understanding Sediment Supply to the Atlantic Margin (Maryland and Delaware, U.S.A.) During Paleocene-Eocene Thermal Maximum

Abstract

The Paleocene-Eocene Thermal Maximum (PETM) global warming event caused significant changes to marine and terrestrial sediment-transport networks. On the Atlantic Margin of North America, continental shelf records show an abrupt increase in the supply of clay and silt to the marine system. Fine-sediment supply was high enough during the early Eocene to cause progradation during a eustatic sea-level rise. During the Paleocene, the Atlantic shelf was storm-dominated, but changed to a pro-delta environment during the peak of the PETM. The margin returned to a storm-dominated environment after the PETM recovery. Understanding the extent and source of sediments supplied to the clay-rich PETM interval is important for answering outstanding questions about the impacts of changes to terrestrial and marine environments during this time.

Here we evaluate changes in facies, provenance, and sediment distribution between the Paleocene Aquia Formation, the PETM Marlboro Clay, and the Eocene Nanjemoy Formation. Using core and well-log data, we map the thickness and extent of the units and we use core and thin-section observations to characterize the type and composition of sediments throughout each unit. Preliminary result suggests that the significant, abrupt increase in terrestrial clay flux coincided with a reduction in the amount of coarser (sand-sized) material delivered to the Atlantic shelf. There are several possible explanations for this trend. First, there could have been a reduction in the overall amount of sand-sized material produced and delivered to the shelf. Additionally, or alternatively, coarser sandy material may have been deposited and stored on land or at river mouths and therefore not transported out onto the shelf. Finally, the sedimentation rate could have increased significantly relative to storm frequency, thereby reducing the opportunity for wave reworking and winnowing of fine sediments. This cast study shows a counterintuitive example of a potential climate-driven increase in sediment supply that resulted in a progradation of clay-rich sediments rather than sandier facies.