Post-Impact Evolution of the Chesapeake Bay Impact Structure: Eustasy, Passive-Aggressive Tectonism, and Impactite Compaction

The Eyreville and Exmore, VA cores provide the first continuous, high-resolution (> 1 myr) chronostratigraphic records linking the inner crater and annular trough of the late Eocene Chesapeake Bay Impact Structure (CBIS). We identify 13-15 post-impact depositional sequences within the annular trough, integrate the results with sequences identified from cores in the inner crater, and place them within a regional framework from New Jersey to Virginia. CBIS and regional sequence boundaries correlate with δ18O increases, indicating a primary glacioeustatic control. However, regional comparisons show that sequences are cut out in different time intervals in different regions: 1) the upper Eocene is thickest in the central crater but is thin outside; 2) the Oligocene is poorly represented throughout the mid-Atlantic region; 3) the lower Miocene is thick in New Jersey and Delaware, but very thin to absent in the CBIS and surrounding regions (hiatus 27-18 Ma); 4) the middle Miocene is thick across the mid-Atlantic, except for the late-mid Miocene (12-9.8 Ma) that pinches out within the CBIS; and the 5) upper Miocene-Pliocene is thick in the CBIS and adjacent regions, but absent in New Jersey. We explain these observations by tectonic movements of crustal blocks, compaction of impact materials, and changes in sediment supply: 1) thick upper Eocene crater sequences are attributed to crater infilling and subsequent impactite compaction; 2) regional sediment starvation and tectonism resulted in obscure Oligocene sequences; 3) regional uplift occurred in the early Miocene in the CBIS region; 4) progradation of thick sequences occurred during the middle Miocene, with tectonic uplift from 12-9.8 Ma; and 5) thick upper Miocene-Pliocene sequences in the CBIS reflect relative subsidence versus relative uplift in New Jersey and Delaware. We suggest that uplift and excess subsidence was caused by differential movement of basement structures in response to variations in intraplate stress.