Turbidites of the Hatteras and Sohm abyssal plains, western North Atlantic

Sohm Abyssal Plain: Evaluating Proximal Sediment Provenance

“…There is, in fact, ample documentation for the Northwest Atlantic Basin that the processes of turbidity currents and related gravity flows of sediment account for a significant proportion of abyssal plain deposits, especially the sands (Horn et al, 1971;Pilkey et al, 1980). In addition to this particular landderived component, most workers also call attention to the contribution from clastic particulate matter, of both terrigenous (fine silt and clay) and biogenic (largely planktonic tests) origin, which settle from suspension.…”

“…It is pertinent with respect to the problem of proximal versus distal provenance that our study area is situated in the southermost section of the Sohm Abyssal Plain because (a) it has received a dominant proportion of its sediment fill by turbidity-current processes, with materials derived largely from the Canadian Maritime Provinces (Horn et al, 1971); (b) it underlies the region of densest suspended particulate matter, or nepheloid layer, concentration (>3000 jug/cm 2 ) in the North Atlantic Ocean (Biscaye and Eittreim, 1977, fig. 5); (c) it is influenced by bottom-current activity (bottom photographs and seismic data, this study) resulting from large scale bottom-water circulation (Worthington, 1976;Laine, 1978); and (d) Northwest Atlantic Basin, remote from land sources and almost completely surrounded by major volcanic features (including the lower flanking hills of the Mid-Atlantic Ridge, Bermuda Rise, and Kelvin and Corner Rise seamounts, see Figure 1 and also Ewing et al, 1973).…”

“…The southern sector of the Sohm Abyssal Plain is bordered on three sides by abyssal hills of low to moderate relief (Heezen et al, 1959;Horn et al, 1971). Samples and seismic data were collected near the center of this region, specifically around Congress and Lynch seamounts, isolated bathymetric highs in this region (Figures 1 and 2).…”

“…This process has been proposed largely as a result of piston core investigations which show that surficial Atlantic sequences commonly contain a sand fraction comprising clastic, shallow-marine or land-derived components (Ericson et al, 1961;Heezen, 1963;Horn et al, 1971). The acoustic patterns on seismic reflection profiles of the Northwest Atlantic Basin show multiple returns (termed acoustically layered) that are generally interpreted as stacked sequences of turbidites (Ewing et al, 1973).…”

“…In order to focus more precisely on this potentially important aspect, we selected for study the southernmost part of the Sohm Abyssal Plain. This area represents a geographically distal sector with respect to the major source of the Quaternary terrigenous material transported onto the plain, i.e., the Canadian Maritime Margin (Horn et al, 1971). Thus, our study will attempt to assess the proportion of more locally introduced sediment relative to that derived from distal sources.…”