Skip to Main Content
Book Chapter

Recent research on the Chesapeake Bay impact structure, Impact debris and reworked ejecta

By
J. Wright Horton, Jr.
J. Wright Horton, Jr.
U.S. Geological Survey, MS 926A, 12201 Sunrise Valley Drive, Reston, Virginia 20192, USAwhorton@usgs.gov
Search for other works by this author on:
John N. Aleinikoff
John N. Aleinikoff
U.S. Geological Survey, MS 963, Denver Federal Center, Denver, Colorado 80225, USA
Search for other works by this author on:
Michael J. Kunk
Michael J. Kunk
U.S. Geological Survey, MS 963, Denver Federal Center, Denver, Colorado 80225, USA
Search for other works by this author on:
Gregory S. Gohn
Gregory S. Gohn
U.S. Geological Survey, MS 926A, 12201 Sunrise Valley Drive, Reston, Virginia 20192, USA
Search for other works by this author on:
Lucy E. Edwards
Lucy E. Edwards
U.S. Geological Survey, MS 926A, 12201 Sunrise Valley Drive, Reston, Virginia 20192, USA
Search for other works by this author on:
Jean M. Self-Trail
Jean M. Self-Trail
U.S. Geological Survey, MS 926A, 12201 Sunrise Valley Drive, Reston, Virginia 20192, USA
Search for other works by this author on:
David S. Powars
David S. Powars
U.S. Geological Survey, MS 926A, 12201 Sunrise Valley Drive, Reston, Virginia 20192, USA
Search for other works by this author on:
Glen A. Izett
Glen A. Izett
Department of Geology, College of William and Mary, 3012 East Whittaker Close, Williamsburg, Virginia 23285, U.S. Geological Survey Emeritus
Search for other works by this author on:
Published:
January 01, 2005

Four new coreholes in the western annular trough of the buried, late Eocene Chesapeake Bay impact structure provide samples of shocked minerals, cataclastic rocks, possible impact melt, mixed sediments, and damaged microfossils. Parautochthonous Cretaceous sediments show an upward increase in collapse, sand fluidization, and mixed sediment injections. These impact-modified sediments are scoured and covered by the upper Eocene Exmore beds, which consist of highly mixed Cretaceous to Eocene sediment clasts and minor crystalline-rock clasts in a muddy quartz-glauconite sand matrix. The Exmore beds are interpreted as seawater-resurge debris flows. Shocked quartz is found as sparse grains and in rock fragments at all four sites in the Exmore, where these fallback remnants are mixed into the resurge deposit. Crystalline-rock clasts that exhibit shocked quartz or cataclastic fabrics include felsites, granitoids, and other plutonic rocks. Felsite from a monomict cataclasite boulder has a sensitive high-resolution ion microprobe U-Pb zircon age of 613 ± 4 Ma. Leucogranite from a polymict cataclasite boulder has a similar Neoproterozoic age based on muscovite 40Ar/39Ar data. Potassium-feldspar 40Ar/39Ar ages from this leucogranite show cooling through closure (∼150 °C) at ca. 261 Ma without discernible impact heating. Spherulitic felsite is under investigation as a possible impact melt. Types of crystalline clasts, and exotic sediment clasts and grains, in the Exmore vary according to location, which suggests different provenances across the structure. Fractured calcareous nannofossils and fused, bubbled, and curled dinoflagellate cysts coexist with shocked quartz in the Exmore, and this damage may record conditions of heat, pressure, and abrasion due to impact in a shallow-marine environment.

You do not currently have access to this article.
Don't already have an account? Register

Figures & Tables

Contents

GSA Special Papers

Large Meteorite Impacts III

Thomas Kenkmann
Thomas Kenkmann
Search for other works by this author on:
Friedrich Hörz
Friedrich Hörz
Search for other works by this author on:
Alex Deutsch
Alex Deutsch
Search for other works by this author on:
Geological Society of America
Volume
384
ISBN print:
9780813723846
Publication date:
January 01, 2005

GeoRef

References

Related

A comprehensive resource of eBooks for researchers in the Earth Sciences

Close Modal
This Feature Is Available To Subscribers Only

Sign In or Create an Account

Close Modal
Close Modal