Upper Jurassic gray and red-brown shale, sandstone, and coal are the oldest strata penetrated by the Shell 272-1 and 273-1 wells, located approximately 66 mi (106 km) southeast of Atlantic City, New Jersey, in the northwest part of the Baltimore Canyon Trough. The Lower Cretaceous section consists of gray shale that is overlain by a sequence of thick-bedded sandstones interbedded with thin-bedded shales. The Upper Cretaceous section is dominated by slightly calcareous mudstone, but also contains a Coniacian to Campanian sandstone. The Cenozoic section is mainly mudstone and overlying unconsolidated sand.

Seven major lithologic units were established and correlated to the COST B-2 and B-3 wells. The depositional environments of the Upper Jurassic rocks range from an upper delta plain facies penetrated in the two Shell wells and the B-2 well to a back-reef facies penetrated in the B-3 well. The Lower Cretaceous strata, in a vertical sequence, consist of upper delta plain, lower delta plain, interdistributary bay and/or marginal marine, and distributary-mouth-bar deposits. A Cenomanian sandstone penetrated in the B-3 well is the youngest indicator of deltaic deposition; marine strata dominate the remainder of the Upper Cretaceous and Cenozoic.