Fish-produced Markings on the Outer Continental Margin East of the Middle Atlantic States

Abstract

Much of the fine-grained surficial sedimentary cover of the continental slope in the vicinity of Wilmington Canyon southeast of Delaware Bay has been disturbed by the activity of benthic fish. Underwater photographs and video recordings in the canyon area supplemented by observations of fish swimming over a soft surface in an aquarium provide information on the origin of different fish structures. The resemblance between many fish-produced markings and physically produced sedimentary structures noted in ancient slope and basin deposits is actually quite striking. Preserved fin marks, especially those produced by flatfish, would probably be confused with groove, slide and diverse tool marks preserved as casts on the base of siltstone and sandstone strata. Where fish resting or nesting depressions occur in large numbers, the seafloor surface superficially appears molded by low amplitude, round-crested interference ripple marks. Structures produced by fish burying themselves into the mud bottom disturb lamination; such structures would resemble some forms of load structures in cross-section. The generally random distribution of fish-markings, however, is in contrast with the normally down-slope and downcurrent orientation characteristic of physically produced structures.