Paper No. 12
Presentation Time: 4:45 PM
Post-Impact Integrated Litho-, Sequence, Sr-Isotopic, and Bio- Stratigraphy of the Eyreville Corehole, Chesapeake Bay Impact Structure Inner Basin
The Eyreville coreholes provide the first continuously cored record of post-impact sequences from within the deepest part of the central Chesapeake Bay crater and the best record to date of how a central crater basin fills through time. We analyzed the post-impact sediments at the Eyreville A and C coreholes for lithology, sequence stratigraphy, and chronostratigraphy. Age is based primarily on Sr-isotope stratigraphy supplemented by biostratigraphy (dinocysts, nannofossils, and planktonic foraminifera); age resolution is ±0.5 for early Miocene sequences and ~±1.0 m/myr for younger and older sequences. Eocene-lower Miocene sequences are subtle, upper middle to lower upper Miocene sequences are more clearly distinguished, and upper Miocene-Pliocene sequences that generally coarsen upward. The upper Eocene through Pleistocene strata at Eyreville record: 1) rapidly deposited, extremely fine grained Eocene strata that probably represent 2 sequences deposited in a deep (>200 m), partially isolated basin; 2) highly dissected Oligocene (3 very thin sequences) to lower Miocene (2 thin sequences) strata with a long hiatus from 26.0-18.4 Ma, 3) thick, rapidly deposited (43-73 m/myr), very fine grained, biosiliceous middle Miocene (16.5-12.8 Ma) sediments divided into 3 sequences deposited in middle neritic paleoenvironments; 4) a long hiatus (12.8 to ~8.3 Ma); 5) sandy, shelly upper Miocene to Pliocene strata (7.5-2.0 Ma) divided into 6 sequences deposited in shelf and shoreface environments; and 6) a sandy middle Pleistocene paralic sequence (~400 ka). The Eyreville cores record the development of a deep basin following impact, its modification in the Oligocene to early Miocene, the evolution of more typical shelf environments in the early to middle Miocene, erosion or nondeposition in the late middle to early late Miocene, and the progradation of coarse sediments and the shallowing of sequences to shoreface environments in the late middle Miocene to Pliocene.