HR: 09:45h
AN: U21E-08    [Abstracts]
TI: Post-Impact Sedimentation of the Chesapeake Bay Impact Structure: Local and Regional Effects
AU: * Kulpecz, A A
EM: akulpecz@rci.rutgers.edu
AF: Rutgers Univeristy, Dept. Geological Sciences, Wright Labs, 610 Taylor Road, Piscataway, NJ 08854,
AU: Hayden, T
EM: t4hayden@wmich.edu
AF: Western Michigan University, Dept. of Geosciences, 1187 Rood Hall, 1903 W. Michigan, Kalamazoo, MI 49008,
AU: Miller, K G
EM: kgm@rci.rutgers.edu
AF: Rutgers Univeristy, Dept. Geological Sciences, Wright Labs, 610 Taylor Road, Piscataway, NJ 08854,
AU: Browning, J V
EM: jvb@rci.rutgers.edu
AF: Rutgers Univeristy, Dept. Geological Sciences, Wright Labs, 610 Taylor Road, Piscataway, NJ 08854,
AU: Kominz, M A
EM: michelle.kominz@wmich.ed
AF: Western Michigan University, Dept. of Geosciences, 1187 Rood Hall, 1903 W. Michigan, Kalamazoo, MI 49008,
AU: Edwards, L E
EM: leedward@usgs.gov
AF: United States Geological Survey, National Center, Reston, VA 20192,
AU: Powars, D S
EM: dpowars@visuallink.com
AF: United States Geological Survey, National Center, Reston, VA 20192,
AB: The late Eocene (~34.5 Ma) Chesapeake Bay Impact Structure (CBIS) is one of the largest and best preserved impact sites in the world. The impact location on a shallow marine shelf preserved a record of the impact effects; 1) the initial crater excavation from the impactor; 2) collapse, mega block slumping, and immediate catastrophic sedimentation due to resurge; 3) rapid creation of accommodation due to compaction of impact generated sediments; and 4) a return to "normal" passive margin sedimentation dominated by sea-level and regional tectonic changes. We evaluate the post-impact effects of CBIS on local and regional sedimentation using USGS coreholes drilled on the annular trough (Exmore and Langley) and the recently drilled ICDP-USGS corehole at Eyreville, VA that recorded a 444 m section of post-impact sediments in the central crater. Lithostratigraphic, biostratigraphic, and Sr-isotopic studies of the Eyreville corehole identified 11 Pliocene to mid-Miocene and at least 6 lower Miocene to Oligocene depositional sequences. High rates of accommodation immediately following the impact event resulted in one upper Eocene sequence. Results from CBIS coreholes were compared to the greater mid-Atlantic Margin to examine local and regional tectonic effects. We use backstripping to show that CBIS annular trough sedimentation was strongly affected by the impact for 7 myr by crustal scale tectonics and the introduction and subsequent removal of a negative thermal anomaly. The area was subsequently dominated by passive margin thermal subsidence overprinted by intervals of regional scale uplift (10's m) and excess subsidence. The Oligocene-lower Miocene is thin regionally, both within and outside of the CBIS, indicating relative uplift compared to NJ and DE unrelated to impact. Miocene crater sequences from ca. 18-8 Ma correlate with DE and NJ, indicating a dominant control by eustatic change overprinted by excess regional subsidence. The ca. 8-2 Ma marine section is well represented in VA, especially in the Eyreville C corehole, versus NJ and DE, where it is largely nonmarine or absent. Though cited as evidence for high sea level (>25 meters), preservation of Pliocene sediments in VA was likely due to excess regional subsidence; even assuming no excess subsidence, maximum eustatic estimates for the early Pliocene are less than 20 m above present. The mechanisms behind intra-marginal changes in subsidence are unclear, but could be related to: 1) differential sediment loading on the shelf from thick, prograding clastic wedges; or 2) the response of fault-bounded Precambrian terranes to variations in the intensity and direction of far-field intraplate stress. Future backstripping of Eyreville and additional mid-Atlantic coreholes will further constrain the rates and timing of changes in subsidence, allowing for greater resolution of the processes at play.
DE: 1125 Chemical and biological geochronology
DE: 1165 Sedimentary geochronology
DE: 1225 Global change from geodesy (1222, 1622, 1630, 1641, 1645, 4556)
DE: 1630 Impacts of global change (1225)
SC: Union [U]
MN: 2007 Fall Meeting