HR: 14:00h
AN: U33A-01 INVITED     [Abstracts]
TI: The 35.4 Ma Chesapeake Bay Impact: Effects on Post-Impact Sedimentation
AU: * Miller, K G
EM: kgm@rci.rutgers.edu
AF: Rutgers Univ., Dept. Geol. Sci., Piscataway, NJ 08854, United States
AU: Gohn, G
EM: ggohn@usgs.gov
AF: U.S. Geol. Surv., 926A Natl. Ctr., Reston, VA 20192, United States
AU: Koeberl, C
EM: christian.koeberl@univie.ac.at
AF: Univ. Vienna, Dept. Geol. Sci., Vienna, Australia
AU: Reimold, W U
EM: reimoldw@geosciences.wits.ac.za
AF: Univ. Witwatersrand, Johannesburg, S.A., & Humboldt Univ., Institut fur Mineralogie, D- 10115, Berlin, Germany
AU: Browning, J V
EM: jvb@rci.rutgers.edu
AF: Rutgers Univ., Dept. Geol. Sci., Piscataway, NJ 08854, United States
AU: Hayden, T G
EM: travis.g.hayden@wmich.edu
AF: W. Mich. Univ., Dept. Geosci., Kalamazoo, MI 49008, United States
AU: Kulpecz, A A
EM: akulpecz@rci.rutgers.edu
AF: Rutgers Univ., Dept. Geol. Sci., Piscataway, NJ 08854, United States
AU: Kominz, M A
EM: michelle.kominz@wmich.edu
AF: W. Mich. Univ., Dept. Geosci., Kalamazoo, MI 49008, United States
AU: Edwards, L E
EM: leedward@usgs.gov
AF: U.S. Geol. Surv., 926A Natl. Ctr., Reston, VA 20192, United States
AU: McLaughlin, P P
EM: ppmclau@UDel.Edu
AF: Delaware Geol. Surv., Univ. Del., Newark, DE 19716, United States
AU: Pusz, A E
EM: aimeep@eden.rutgers.edu
AF: Rutgers Univ., Dept. Geol. Sci., Piscataway, NJ 08854, United States
AB: The late Eocene (35.4 Ma) Chesapeake Bay impact structure (CBIS) is a well-preserved, large (85 km, 7th largest known) crater with an `inverted sombrero' shape. The International Continental Scientific Drilling Program (ICDP) and the USGS completed three coreholes at Eyreville, VA to a composite depth of almost 1.8 km into the CBIS in the fall of 2005 and the spring of 2006. A total of 444 m of post-impact sediments were cored along with a 1,322 m impactite section which consists (in descending order) of sediment-clast breccia, sediment megablocks, a large granite megablock, smaller rock blocks in sediment, suevite and lithic breccia, and a section of brecciated mica schist and pegmatites with veins of different breccia types. Ongoing studies of the impactite section will test hypotheses including the source and formation of the North American tektite strewn field, the type of impactor, relationships with the late Eocene Popigai impact, implications of shock-pressure variations for constraining kinetic energy and cratering mechanics, and marine crater excavation and modification processes. Other than the immediate effects of resurge and a megatsunami indicated by the sediment clast breccia, regional and global environmental and stratigraphic effects of this large impact were surprisingly minimal as exemplified by results from Eyreville and backstripping of previously drilled crater coreholes. A thick, deep-water upper Eocene section is partly explained by excess accommodation produced by the impact due to compaction of the rapidly deposited impactites, with little evidence of thermal resetting of subsidence by impact. Possible tectonic effects continue into the early Oligocene. Oligocene and lower Miocene sections are thin regionally, both in the crater and outside in Virginia and Maryland, indicating relative uplift compared to NJ and Delaware apparently unrelated to impact. Middle to lower upper Miocene sequences correlate with sections outside the crater in Delaware and NJ, indicating a dominant control by eustatic change overprinted by regional subsidence in the Delmarva region. An uppermost Miocene-Pliocene marine section is well represented in Virginia, especially in the Eyreville C corehole, versus NJ and Delaware, where it is thin and largely nonmarine or absent. Though the Virginia sediments often are cited as evidence for a Pliocene high sea level (>25 meters) during a period of global warmth, preservation can be attributed to excess regional subsidence, again unrelated to impact. Thus, the dominant effects of this large impact were: 1) excavation; 2) collapse, block slumping, immediate catastrophic sedimentation due to the resurge; 3) rapid creation of accommodation due to compaction and subsequent uplift; 4) an apparent return to `normal' passive margin sedimentation dominated by sea-level and regional tectonic changes, though comparison of backstripping of the Eyreville corehole with coreholes from inside and outside of the crater are still needed.
DE: 1641 Sea level change (1222, 1225, 4556)
DE: 3036 Ocean drilling
DE: 4219 Continental shelf and slope processes (3002)
DE: 4901 Abrupt/rapid climate change (1605)
DE: 5420 Impact phenomena, cratering (6022, 8136)
SC: Union [U]
MN: 2007 Joint Assembly