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Chesapeake Bay Crater

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  1. Chesapeake Bay Crater Montgomery College Planetarium at Takoma Park/Silver Spring By Dr. Harold Williams http://montgomerycollege.edu/Departments/planet/

  2. Synopsis • 35.5 ± 0.6 million years ago, when Washington, DC and Richmond VA were on the coast, (sea level was higher then) • an object hit the earth on the continental shelf in the Atlantic ocean, N 37° 17'  W 76° 1', • causing a crater 85 km in diameter.  • After sea level fell, this crater would help form the Chesapeake Bay.  • The impact site is now called the lower Chesapeake Bay in Virginia.

  3. Where did this information come from mostly. Who did most of the real work and research. http://woodshole.er.usgs.gov/epubs/bolide/index.html Principal Investigator C. Wylie Poag wpoag@usgs.gov

  4. Bolide? • Extraterrestrial body in the 1-10 km size range • Impacts the earth at velocities of 20-70 km/sec = Mach 75

  5. Simple Craters

  6. Earliest identified crater on Earth • Some Links • Meteor Crater http://www.meteorcrater.com/ • Barringer Crater http://www.barringercrater.com/

  7. Complex Craters Manicouagan, Quebec Canada, 70 km (43.4 miles) across, Formed around 212 million years ago, Lake surrounds the more erosion-resistant melt sheet created by the impact onto metamorphic and igneous rocks on the stable Canadian craton.

  8. Complex Crater on the far side of the Moon, King Crater

  9. Shoemaker-Levy 9 striking Jupiter

  10. Chesapeake Bay Crater

  11. First Evidence for Impact

  12. Shocked Quartz intersecting lamellae

  13. Some Shocked Quartz • PDF, Planar Deformation Features, Link http://www.unb.ca/fredericton/science/emunit/Trepmann/Shocked%20quartz.html

  14. S-1 Large shocked quartz grains with planar deformation features (PDFs) identified in the Fraser Park, Sydney Basin Permian-Triassic boundary layer. Inset in upper photo shows close-up of intersecting PDFs. Quartz grains are mounted in oil and photographed in plane polarized light.

  15. Cores from drilling

  16. Index microfossils give a date

  17. Radiometric ages in tektite glass • This age was confirmed by determining the ratio of two isotopes of argon gas contained in the tektite glass. • 35.5 ± 0.6 million years ago

  18. Virginia Core Sites

  19. Geological Column

  20. Seismic Profiles

  21. Ground Instability Due to Faulting

  22. Summary • During the late Eocene, the formerly quiescent geological regime of the Virginia Coastal Plain was transformed when a bolide struck in the vicinity of the Delmarva Peninsular

  23. Produced the following principal consequences: • The bolide carved a roughly circular crater twice the size of the state of Rhode Island (~6400 km2), and nearly as deep as the Grand Canyon (1.3 km deep). • The excavation truncated all existing ground water aquifers in the impact area by gouging ~4300 km3 of rock. • Structural and topographic low formed over the crater. • The impact crater may have predetermined the present-day location of Chesapeake Bay. • A porous breccia lens, 600-1200 m thick, replaced local aquifers, resulting in ground water ~1.5 times saltier than normal sea water.

  24. 2004MN4 now 99942 Apophis • Link http://en.wikipedia.org/wiki/2004_MN4 • Friday, April 13, 2029 near miss of 320 m 4.6×1010 kg asteroid • Magnitude 3.3 moving at 42 degrees/hour maximum angular speed with a diameter of 2 arc seconds from Europe and Africa • Change from Aten to Apollo