A number of continental margin slumps have been linked to the dissociation of gas hydrates (Carpenter, 1981; Paull et al., 1991; Kayen and Lee, 1993, Rothwell et al., 1998). The stability of gas hydrates in the sediment column may be strongly influenced by changes in sea level (Carpenter, 1981; Schmuck and Paull, 1993; Paull et al., 1996). A lowering of sea level will cause a downward shift in the base of gas hydrate stability, thus stimulating the decomposition of gas hydrates. This process adds water and gas into sediment pore spaces, weakening sediment strength and inducing slope failure. Thus, correlation between the frequency of slumping activity relative to sea-level positions could be expected. Comparison of 14C ages to sea-level history at a number of slide sites may provide insight into the potential connection of submarine landslides to hydrate instability.
The Cape Fear Slide is a massive submarine landslide (~100 m thick, 25 km wide, and involving about 5000 km2 of area) located on the continental margin off of North Carolina (Embley, 1980; Cashman and Popenoe, 1985; Popenoe et al., 1993). This slide occurred in a region of prevalent gas hydrates (as indicated by the regional presence of bottom-simulating reflectors [BSR's]) and active diapirism. Both the emplacement of the diapirs (Dillon et al., 1982; Cashman and Popenoe, 1985; Popenoe et al., 1993) and potential sediment instability due to gas hydrate decomposition (Carpenter, 1981; Schmuck and Paull, 1993) have been suggested as mechanisms for this slumping event. Although the Cape Fear Slide is one of the more thoroughly studied mass-wasting events, both the cause and the timing of the slide are still uncertain (Paull et al. 1996).
One of the objectives for drilling over the Cape Fear Diapir (Sites 991, 992, and 993) was to investigate the timing of deformation. Sediments from Sites 991 and 992 recorded complicated deformation and several internal hiatuses between 2.06 and 47 mbsf at Site 991 (Paull, Matsumoto, Wallace, et al., 1996). At Site 991, however, a distinct contact, which was taken to be the sole of the most recent slide event, was identified at 2.06 mbsf.