Sunday, December 14, 2008

The Chesapeake Bay Crater Ejecta Blanket

It's an undisputed fact that a 90-km-diameter crater was discovered buried beneath the lower Chesapeake Bay on the U.S. Middle-Atlantic Coastal Plain in the early 1990s by members of the U.S. Geologic Survey (USGS) . The bold dashed ovoid in the map above demarcates the crater rim, and the pattern that it encloses comprises a gravity map of the crater interior published by USGS scientists.  The short-dashed curve at a radius of 115 km is provided to assess the radial relationship of the "upland deposits" to the crater center. This crater resulted from the impact of an asteroid or comet about 35.4 million years ago. On this, everyone agrees.

However, according to geologists concerned with this part of the U.S. Middle-Atlantic Coastal Plain, virtually every last shred of the approximately 2,000 cubic kilometers of material calculated to have been ejected landward of the crater was meticulously removed by erosion before the first homo sapiens walked the earth.  It is this claim that I dispute.

In fact, based on research I've been doing for the past 14 years including, but not limited to, collecting and analyzing by petrographic and solid-state-physics methods the rocks from our former neighborhood 14 kilometers south of Washington, DC -- and making full use of my acquired knowledge of the physics of large impacts on the Earth, Moon, and terrestrial planets (cf., H.J. Melosh, Impact Cratering - A Geological Process, Cambridge University Press, New York, 1989) -- I have built a multi-faceted case that approximately 10,000 square kilometers of land surface to the west and northwest of the crater is still blanketed by remnants of the original ejecta, specifically the light and dark shaded areas in the figure (the Bacons Castle Formation and "upland deposits," respectively).

In February of 2012 I published a paper in the new European journal Solid Earth Discussions (SED) that took into account virtually every geomorphological, geophysical, geological, petrological, paleontological, and paleoclimatological issue that in any way impinges on the question of which of the present-day surface features of the U.S. Middle-Atlantic Coastal Plain, if any, are likely to be surviving vestiges of the original Chesapeake Bay crater ejecta blanket ...finally concluding on the basis of what I believe to be more than adequate evidence and argument that approximately 10,000 km2 of the U.S. Middle-Atlantic Coastal Plain and Piedmont Province still display vestiges (commonly ~10 m deep) of the Chesapeake Bay crater ejecta blanket ...“in plain sight.”  This paper is available for viewing and/or downloading at:  However, I recommend that you download my "reader friendly" version with the figures inserted where they are first mentioned in the text.  

In 2003 I published a 20-page paper with 8 other authors in an issue of the Journal of Non-Crystalline Solids dedicated to the Proceedings of the 4th International Conference on Natural Glasses, held Lyon, France, 2002. This paper delves deeply into the petrology and materials science of a particular type of rock endemic to the upland deposits and is replete with a large amount of color photography (for example the second photograph on the right). I'd be happy to send you a free paper reprint, post paid, on request.  Just contact me at: .

I am actively seeking the opinions of others, and I plan to reply to anyone posting thoughtful comments either pro or con.  So please do post your comments below. Apropos, a nice review of my article can be found here.


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  2. Hi Dave, Very nicely illustrated. The internally brecciated marine chalk ball--you are calling it toasted on the outside. In the picture it looks like it might have an iron coating. Is it melted? What are some definitive ways to determine if a rock has been heat treated?

  3. I schistophrenic, Sorry to be so slow in answering. I don't monitor this site very often, since comments are few and far between. I suspect that the chalk contains a small amount of clay of a composition including ferric and/or ferrous iron. In the jetting phase with temperatures of tens of thousands of degrees, the surface would have been melted and the chalk evaporated leaving mostly melted clays and molten iron which later on oxidized to give the orange color to the surviving crust.