Chesapeake Bay Crater

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Chesapeake Bay Crater

• Montgomery College Planetarium
• at Takoma Park/Silver Spring
• By Dr. Harold Williams
• http//montgomerycollege.edu/Departments/planet/

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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.

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Where did this information come from mostly.

• http//woodshole.er.usgs.gov/epubs/bolide/index.ht
  ml

Who did most of the real work and research.
Principal Investigator C. Wylie Poag
wpoag_at_usgs.gov
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Bolide?

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

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Simple Craters
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Earliest identified crater on Earth

• Some Links
• Meteor Crater http//www.meteorcrater.com/
• Barringer Crater http//www.barringercrater.com/

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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.
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Complex Crater on the far side of the Moon, King
Crater
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Shoemaker-Levy 9 striking Jupiter
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Chesapeake Bay Crater
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First Evidence for Impact
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Shocked Quartz intersecting lamellae
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Some Shocked Quartz

• PDF, Planar Deformation Features, Link
  http//www.unb.ca/fredericton/science/emunit/Trepm
  ann/Shocked20quartz.html

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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.
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Cores from drilling
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Index microfossils give a date
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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

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Virginia Core Sites
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Geological Column
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Seismic Profiles
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Ground Instability Due to Faulting
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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

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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.

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2004MN4 now 99942 Apophis

• Link http//en.wikipedia.org/wiki/2004_MN4
• Friday, April 13, 2029 near miss of 320 m
  4.61010 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

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