Examination of the world-wide data suggests that submarine gas hydrates are of migration origin and generally occur under the control of comparatively coarse-grained sediments and fractured zones (Ginsburg and Soloviev, 1988, 1997; Soloviev and Ginsburg, 1994, 1997). Their confinement to the relatively coarse-grained sediments has been inferred, in particular, from the Deep Sea Drilling Project (DSDP) results obtained from the Blake Ridge area (Fig. 1, Fig. 2), although this suggestion was not sufficiently reliable because of inadequate sampling frequency. To support this suggestion, we undertook the present study.
We have studied the granulometric composition of sediments along the columns of three Ocean Drilling Program (ODP) sites drilled during Leg 164 (Sites 994, 995, and 997 [99, 125, and 121 samples, respectively]) and compared them with the distribution of the pore-water chlorinity, which is commonly accepted as a guide to a gas hydrate content of sediments (in particular, by participants of this leg). The chlorinity data are borrowed from Paull, Matsumoto, Wallace, et al. (1996). It is important to note that the grain-size analysis was carried out on the "cakes"—the same samples that were squeezed to get pore-water samples for chemical analysis.