Chronostratigraphic Sequences Beneath Northeastern United States Continental Margin: ABSTRACT

Chronostratigraphic sequences of wide areal extent beneath the United States Atlantic margin north of Cape Hatteras have been delineated by: (1) examination of four COST (Continental Offshore Stratigraphic Test) wells, 1 exploratory well (Shell, Blk. 272, No. 1, OCS A 0096), 14 shallow AMCOR (Atlanctic Margin Coring) core holes, and eight ASP (Atlantic Slope Project) core holes; (2) analysis of multichannel seismic reflection profiles collected along several thousand kilometers of track lines; and (3) comparison of these interpretations to the Canadian offshore chronostratigraphy. In the Baltimore Canyon Trough and Georges Bank basin, seismically identified regional unconformities are associated with Lower Jurassic, Middle Jurassic, Upper Jurassic-Lower Cretaceous, upper auterivian, Cenomanian, Turonian-Coniacian, Upper Cretaceous-lower Paleocene, Oligocene, and upper Miocene-Pliocene rocks. The Tertiary unconformities are identified best in the Baltimore Canyon Trough where the thickness of Tertiary rocks exceeds 1,400 m. There, seismic profiles near the COST B-3 well reveal several probable unconformities of Miocene to Pliocene age that are not documented in the wells. Across the Georges Bank basin, subtle Jurassic unconformities appear to be present on seismic records within a thick, poorly dated section of interbedded limestone, dolomite, and anhydrite. Microfossil records from the deep wells and shallow core holes reveal seven unconformities of regional extent, forming chronostratigraphic gaps in the early to middle Cenomanian, late Turonian-early Coniacian, late Maestrichtian-early Paleocene, late Eocene-early Oligocene, early Miocene, late Miocene-early Pliocene, and late Pliocene-early Pleistocene. These gaps in the fossil record are comparable with the gaps found in wells in the Scotian basin, and correspond to unconformities inferred from the seismic profiles. The chronostratigraphic sequences bounded by these unconformities help to better define the curve of coastal onlap during the Cretaceous and to support the major trends in sea level change during the late Mesozoic and Cenozoic noted by Vail, Pitman, and others. End_of_Article - Last_Page 973------------