Geologic Setting
The Baltimore Canyon Trough is an elongate Mesozoic and Cenozoic extensional basin approximately 300 km long, which is filled with up to 18 km of predominantly siliciclastic and carbonate sediments. Formation of the basin began with rifting of continental crustal material in the Early Jurassic (Manspeizer, 1988), followed by spreading between the North American and African plates, which generated the North Atlantic Ocean. The deepest depositional unit drilled in the Baltimore Canyon Trough is of Oxfordian age; the ages of older rock units are estimated from seismic correlation with stratigraphically deeper wells in the Georges Bank Basin (Poag and Sevon, 1989; Poag, 1991).
The Baltimore Canyon Trough during the Early Jurassic, immediately preceding sea-floor spreading, was a narrow, restricted basin, cut off from oceanic circulation at the southwest end, but open to the Tethys Ocean to the northeast (Jansa, 1986; Poag, 1991). Limited circulation and the inferred arid to semi-arid paleoclimate (Parrish and others, 1982; Manspeizer, 1985) are believed to have created hypersaline conditions necessary for salt deposition. Evaporite precipitation of varying amounts occurred near the southern ends of a series of gulfs that progressed down the margin from the Grand Banks in the Late Triassic to the Carolina Trough in the Early to Middle Jurassic (Evans, 1978; Grow, 1980; Jansa, 1986). The thickest evaporites in the North Atlantic rift system were formed in the rift and peripheral eastern basins as salt rock, mostly diapiric; the thinner, flat deposits were located in the generally shallow depressions along borders of the rift (Holser and others, 1988).
As the Baltimore Canyon Trough widened and subsided, progressively deeper marine conditions followed with the associated changes in sedimentation to marine deposits. There was rapid subsidence in the Early and Middle Jurassic followed by slower rates in the Cretaceous to present (Sawyer and others, 1982). The postrift siliciclastic and carbonate depositional history, integrating the effects of source-terrain uplift, basin subsidence, paleoclimate, and sea-level changes is discussed in more detail by Poag and Sevon (1989) and Poag (1991).
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