The erosion—deposition boundary in the head of Hudson Submarine Canyon defined on the basis of submarine observations

Abstract

Submersible observations in the head of Hudson Canyon, to depths of 305 m, indicate that coarse relict sediment at and below the shelf edge (at about 105 m) has been reworked by currents and benthic organisms during the Holocene and at present. The sharp boundary between an upper gravel—shell—sand facies and a deeper mud facies is herein termed “mud line”. This “mud line”, present at depths ranging from 130 m to 175 m, appears to record a long-term separation of energy levels, i.e., below these depths, current speeds necessary to erode fine sediments decrease significantly in frequency and intensity. We observed that the shelf break and uppermost slope in the canyon is a zone of continuing resuspension where there is no permanent accumulation of fines above the “mud line”. Defining the “mud line” position relative to regional lithofacies patterns may provide an additional, albeit indirect, measure of depth of impingement of current speed sufficient to exceed the threshold of sediment transport on the outer continental margin.