Deformation of Continental Slope Sediments Resulting from Large-Scale Downslope Creep: ABSTRACT

Abstract

Recently acquired high-resolution seismic data suggest that a previously undescribed style of deformation may be common in sediments on the continental slope. This deformation is characterized by folds whose axes are oriented roughly parallel with the slope of the seafloor (perpendicular to isobaths). In cross section, the amplitude and wavelength of folds range from 5 to 50 ft (1.5 to 15 m) and from 300 to 2,000 ft (100 to 600 m) respectively. The amplitude generally decreases with depth, and undeformed sediments form the base of the folded sequence. Folded sequences up to 400 ft (120 m) thick have been observed on the continental slope offshore Louisiana. Where not buried beneath younger, undeformed sediments, these folds are expressed at the seafloor as a series of rid es and furrows which are mappable using side-scan sonar. Detailed mapping has shown that individual folds are several hundred to several thousand feet long and the areal extent of folding is tens of square miles. Where the continental slope is irregular, fold axes converge downslope into bathymetric lows forming a fanlike pattern. Folds are rare or absent where the continental slope is planar and on the crest of bathymetric highs. This style of deformation has been detected in sediments consisting primarily of cohesive clays on the upper continental slope off Louisiana, Texas, and California where seafloor slopes range from 2 to 15%. It is End_Page 549------------------------------ proposed that these cohesive sediments have moved downslope, and that folds developed in response to increasing lateral confinement as sediments converged within bathymetric lows. The general style of deformation, preservation of bedding, and absence of faults suggest that movement occurred at a slow rate, probably as creep. End_of_Article - Last_Page 550------------