Abstract: Statistical Characteristics of Gassy Sediment Sections in the Northwest Gulf Of Mexico

William R. Bryant, Aubrey L. Anderson, Thomas H. Orsi

Examination of seismic data from over 1000 MMS geohazard reports and core logs of 1670 foundation boreholes (drilled to an average subbottom depth of 125 m), has revealed that gassy sediment sections are most abundant near the Mississippi River delta, in buried stream channels eroded during the early and late Wisconsinan, and in Miocene and Pliocene-Pleistocene depocenters on the shelf and upper slope. Of all the boreholes that we examined, 1158 (68%) contained indications of gassy sediments.

The "average" Mississippi River delta related gassy sediment section occurs at a water depth of 53 m; the top of the section lies at a subbottom depth of 10 m; its thickness is 12 m; and the sediment water content is 45%, with liquid and plastic limits of 73% and 24%, respectively. For the nondeltaic areas of the continental shelf (areas west of 90°W), the average gassy sediment section lies at a water depth of 37 m, its depth below the sea floor is 37 m, its thickness is 8 m, the water content is 40%, and the liquid and plastic limits are 68 and 27%. For the upper continental slope in the northwestern Gulf of Mexico, the average gassy sediment section is found at a water depth of 265 m, is 25 m below the sea floor, and has a thickness of 60 m, a water content of 40%, and a liqui and plastic limit of 62 and 32%.

The median areal extent of gassy sediment sections within the entire shelf and upper slope of the northwestern Gulf area ranges from 238 to 546 m. Although large patches of gassy sediments exist, with some exceeding 10 km in size, most are less than 500 m.

AAPG Search and Discovery Article #90983©1994 GCAGS and Gulf Coast SEPM 44th Annual Meeting, Austin, Texas, October 6-7, 1994