THE 35.4 MA CHESAPEAKE BAY IMPACT: GLOBAL AND REGIONAL EFFECTS ON POST-IMPACT ENVIRONMENTS AND SEDIMENTATION

Two of the largest Cenozoic impact craters (Chesapeake Bay Impact Structure [CBIS] and Popigai) are late Eocene (~35.4 Ma). The CBIS is well preserved and associated with a major strewn field, yet the environmental and post-impact sedimentation response to this impact is poorly understood. We evaluated the effects of the CBIS impact in three settings: 1) far-field locations evaluating the global response; 2) locations drilled in the annular trough of the CBIS in comparison to “normal” sedimentation in the mid-Atlantic passive margin; and 3) the recently drilled ICDP-USGS corehole at Eyreville, VA that recovered 444 m of post-impact sediments from the deepest part (moat) of the central crater. First-order correlation of microtektites and cpx-spherules to magnetochron C16n.1n at southern ocean Site 1090 yields a magnetochronologic age of ~35.4 Ma, consistent with published radiometric ages. We generated high-resolution stable isotope records at Sites 1090 and 612 (NJ slope) that show: 1) a 0.4-0.5‰ carbon isotope decrease coincident with the impact horizons; and 2) no oxygen isotopic and temperature changes. We suggest this carbon cycle perturbation was global and was directly related to the impactors. We use backstripping to show that CBIS annular trough sedimentation was strongly affected by 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' 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 Delaware unrelated to impact. Miocene crater sequences from ca. 18-8 Ma correlate with Delaware 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 Virginia, especially in the Eyreville C corehole, versus NJ and Delaware, where it is largely nonmarine or absent. Though cited as evidence for high sea level (>25 meters), preservation of Pliocene sediments in Virginia was due to excess regional subsidence. Future backstripping of the Eyreville corehole will evaluate the post-impact sedimentation history of the deepest part of the CBIS.