Evidence is presented 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 3 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 III 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. Response of Eustatic Sea Level Due to Polar-Ice-Cap Formation: A Major Constraint on Coastal-Plane Deposition Rates Chesapeake Bay Impact (35.5 Ma) Triassic Jurassic Cretaceous Eocene Miocene Holocene 155 m 65 m 0 m -140 m Oligocene 250 65 24 5 Time (Millions of Years) Arctic Ice Sheets Antarctic Ice Sheets Global deep-sea drill-core  18 O studies by Zachos et al., Science 292 , 686 (2001) Sea Level (meters above present) The highest point of the Calvert Formation (that I am aware of) is 78 m above sea level. Therefore, a high stand >78 m would have been needed to deposit Calvert I . 33.7 CALVERT I It follows that, Calvert I was more likely deposited earlier than ~34 Ma. - - - - - - - (Hallam, 1984) ~2 My 600 400 200 0 -200

3. Why? It’s harder than quartz! 500 μ m  3 cm  -> 6 mm External flange Red-brown material penetrates sandstone to uniform depth Thin section viewed under crossed polars reveals multiply fractured quartz grains instantly indurated by the matrix. There are no relative rotations of the fragments!

5. Missing Spall Internal Fractures with No External Expression Dark Stains Contiguous with the Flanges Penetrate Solid Rock!! External Flanges Join Rocks Together A New Type of Impactite Endemic to the Chesapeake Bay Crater All of these features can have been made by shock waves – and probably in no other way .

6. Model for Shock-Induced Iron-Oxide Melt Sheets Penetrating Sandstone Cobbles  Transmitted Pulse  First Reflection Vacuum  Distance I II III IV Second Reflection Unstained Rock Spall Probable fossil record of multiple reverberations Water (not shown elsewhere) Shock Front (Pressure Pulse)  Iron oxide melt sheet overtakes rock Reflected Pulse (Rarefaction) Pressure Pulse Pushes Fe-Oxide Melt into Inter-Granular Spaces Opened by the Rarefaction Pulse

9. Epilogue Otherwise, the following are figures from the manuscript submitted for the Penrose Conference proceedings and were not part of the original lecture. The viewer should understand that the original lecture was extensively animated and that these helpful animations cannot play on SlideShare.

11. A B Chickahominy River Pamunkey River Mattaponi River N 20 km 38° 37° N 77° 76°W Chesapeake Bay Crater: Possible Secondary Impact Chain and Relict Circumferential Course of the York River Lunar Crater Copernicus: Chain of Secondary Craters York River Possible Secondary Crater Chain Possible Paleo Channel of the York River