49 Sedimentology (Posters)

Monday, 21 March 2011
1:30 PM - 5:30 PM
Grand Ballroom

MODIFIED PALEOSOL DEPOSITS FROM THE CHESAPEAKE BAY IMPACT STRUCTURE

Paper number: 49-3
Program: Technical Sessions
Time: 1:30 PM – 5:30 PM

Authors

Abstract

The Chesapeake Bay impact structure was created by an asteroid or comet impact during the Eocene (~35 Ma) which created a complex crater structure approximately 85 km wide. This site provides an excellent natural laboratory to study the effects of a large-scale impact event on buried coastal plain sediments. The Potomac Formation is composed of thick sedimentary beds of alternating channel sands and paleosol deposits. Representing the main depositional sequence of the Early Cretaceous (Aptian-Albian) to Late Cretaceous (early Cenomanian) coastal plain along the eastern margin of North America. At the time of impact in the Eocene the Potomac Formation was buried in the Chesapeake Bay region, however the crater structure and impact deformation extend into and below this formation.

This study examines the effects of an impact event on the buried paleosol deposits of the Potomac Formation to understand the dynamics of what, if any, impact-generated deformation occurs. Because of the ubiquitous nature of the Potomac Formation on the coastal plain of Eastern North America, impacted sediments can be compared with similar non-impacted sediments. Samples were obtained from several continuous core holes (Bayside and Eyreville) drilled by the USGS within both the center crater and annular trough of the structure. Preliminary results of geochemistry, clay mineralogy and micromorphology (clay fabrics, nodules, etc.) are presented. These samples are compared alongside similar results from a Virginia Department of Environmental Quality core hole, drilled at Surprise Hill, VA, which is located outside the impact structure approximately 25 km northwest of the outer rim of the annular trough of the crater.