STRUCTURAL OUTER RIM OF CHESAPEAKE-BAY IMPACT CRATER - SEISMIC AND BORE HOLE EVIDENCE

Nine seismic-reflection profiles and four continuous core holes define the gross structural and stratigraphic framework of the outer rim of the Chesapeake Bay impact crater. The rim is manifested as a 90 km dia meter ring of terraced normal-fault blocks, which forms a similar to 3 20 m-1200 m high rim escarpment. The top of the rim escarpment is cove red by a 20 m-30 m thick ejecta blanket. The escarpment encircles a fl at-floored annular trough, which is partly filled with an similar to 2 50 m thick breccia lens (Exmore breccia). The Exmore breccia overlies a 200 m-800 m thick interval of slumped sedimentary megablocks, which, in turn, rests on crystalline basement rocks. All postimpact strata ( upper Eocene to Quaternary) sag structurally into the annular trough, and most units also thicken as they cross the rim into the crater. Pos timpact compaction and subsidence of the Exmore breccia have created e xtensive normal faulting in overlying strata.