Evidence is given that the ejecta blanket of the 35.5-Myr-old Chesapeake Bay crater is still extant and covers ~5,000 km2 of the U.S. mid Atlantic Coastal Plain (Part 1 of 3)

1. The Case for Interpreting the ~5,000 km2 "Upland Deposits" of the U.S. Mid-Atlantic Coastal Plane as Chesapeake Bay Crater Ejecta Part I David L. Griscom impact Glass research international San Carlos, Sonora, M éxico Slightly modified and lengthened from talk presented at the: Penrose Conference “Late Eocene Earth,” Monte C ò n e ro, Italy, October 6, 2007

2. Geology of the State of Virginia Silurian and Devonian Sandstones The Chesapeake Bay Structure Southern Maryland Piedmont Coastal Plain Fall Line 50 km 50 mi This and other similar maps taken from K. Frye, Roadside Geology of Virginia (Missoula Press, 1986) Blue Ridge

3. Geology of U.S. Mid-Atlantic Coastal Plain Sandstones: Silurian Washington, DC Upper Chesapeake Bay Silurian and Devonian Sandstones Hypothetical Anticlines ~200 Million Years Ago, Now Eroded Atlantic Ocean Blue Ridge Fall Line Sand, Gravel and Clay (Soft) 350 km Ancient Metamorphic Rocks (Hard) , Devonian “ Upland Deposits”

8. The “Upland Deposits” Gravel-Size Data and Analyses of John Schlee (1957) -6.0 -5.5 -4.5 -4.0 -5.0 -3.5 -3.0 -2.5 -2.0 Washington, DC N.B. Schlee’s gravel-size contours are labeled by the negative log to the base 2 of the observed modal sizes (phi units). Noting that the contours were more or less equally spaced in phi units, Schlee (1957) perceived a possible exponential progression. To test this notion, he took four additional sets of gravel-size data along four approximately-linear paths running generally southeasterly of the U.S. Capitol.

9. 128 mm The “Upland Deposits” Gravel-Size Data and Analyses of John Schlee (1957) Direction of the Center of the Chesapeake Bay Crater Mean Direction of Apparent Dip of the Gravel Exposures Washington, DC 32 mm 16 mm 8 mm 4 mm My Interpretation: Atmospheric size sorting of ejecta in flight. * -6.0 -5.5 -4.5 -4.0 -5.0 -3.5 -3.0 -2.5 -2.0 - - - - - Extrapolates to 128-mm cobbles at ~15 km northwest of Washington, DC – where most rocks this size are petrologically different from the upland gravels ! *Schultz, Gault (1979) 64 mm + Factor of 15!