Ocean Drilling Program (ODP) Leg 164 obtained core samples at three different regions off the southeast coast of the United States: Sites 991, 992, and 993 on or near the Cape Fear Diapir, Site 996 on the Blake Ridge Diapir, and Sites 994, 995, and 997 on the eastern edge of the Blake Ridge (Fig. 1; Paull, Matsumoto, Wallace, et al., 1996). Holes drilled at Sites 991-993 and Site 996 were relatively shallow, with penetrations of 50-60 m. Sites 994, 995 and 997 had much deeper penetrations of more than 700 m.
The geologic setting of the region is fairly complex. The Carolina Trough and the Blake Plateau Basin, both located west of the Blake Ridge, were formed and filled to a thickness of 12-13 km, as part of a five-stage continental margin-building process that also created the Blake Plateau (Dillon and Popenoe, 1988). The Cape Fear and Blake Ridge Diapirs (Paull, Matsumoto, Wallace, et al., 1996) are part of a linear set of diapirs that occurs along the seaward side of the Carolina Trough, apparently the result of the flow of evaporites that accumulated in the trough during its early development (Dillon et al., 1983). The Blake Ridge is characterized as a sediment drift deposit formed by contour currents, and consists of hemipelagic mud deposited at relatively rapid rates (Heezen et al., 1966; Shipboard Scientific Party, 1983; Dillon and Popenoe, 1988).
Normalized shipboard vane shear and pocket-penetrometer shear strength ratios are presented for all sites; however, Atterberg limit, vane shear strength, pocket-penetrometer strength, and constant-rate-of-strain consolidation results are presented only from Hole 995A, located on the Blake Ridge in the middle of a sequence of three sites. Site 994 is 3.0 km to the southwest of Site 995, and Site 997 is slightly further to the northeast (Fig. 1). Results of shipboard physical property measurements, typically performed at 3-m intervals, were very consistent among the different sites on the Blake Ridge (Paull, Matsumoto, Wallace, et al., 1996). The implication is that the results from Hole 995A, presented here, may also be applicable to the two adjacent sites. The similarity in physical properties is important because it enables analyses to be inferred over a larger region.
This study analyses the stress history of the Blake Ridge to determine if the high sedimentation rates, in conjunction with the presence of gas hydrates, which could cement the grains together, have influenced the normal compaction process. Hyndman and Davis (1992) have suggested that underconsolidation could be present in the Blake-Bahama outer ridge region.