Clay-size minerals as indicators of modern sedimentary processes in submarine canyons: Application to the Wilmington Canyon System

Abstract

Recent sedimentary processes in the Wilmington Canyon area, U.S. east coast, are interpreted using high-resolution profiles of clay-size minerals from sediment cores collected using D.S.R.V. Alvin and the R.V. Atlantis II. Modern surficial sediments (< 100 years old) of the Wilmington Canyon system contain uniformly high relative abundances of illite (55–65%) and chlorite (25–35%). Where these assemblages occur downcore, relatively continuous hemipelagic sedimentation is inferred. Anomalously high concentrations of expandable minerals (to 58%) and kaolinite (to 15%) occur at discrete intervals within several cores from the Wilmington Canyon area. These anomalous intervals are bounded by sediments deposited within the past 100 years. Previous studies of DSDP sites along the U.S. Atlantic margin revealed relatively high abundances of montmorillonite and kaolinite in late Cretaceous-Tertiary strata. Similar signatures in the Wilmington Canyon system probably indicate that these sediments are derived from late Cretaceous-Tertiary outcrops on the canyon walls during episodic sediment transport events. Intervals rich in detrital clay-size minerals (quartz, feldspar, pyroxene and amphibole) also occur in cores from the Wilmington Canyon area and are probably derived from Pleistocene sediments which were delivered to the continental slope in great quantities during periods of lower sea level. The presence of distinct mineral zonations on the floor of the Wilmington Canyon suggests that local erosional forces rather than large-scale turbidity currents probably dominate the canyon area at present. Surficial sediments from the intercanyon area northeast of Wilmington Canyon reveal a downslope decrease in illite and corresponding increase in expandable minerals, suggesting an increased contribution of pre-Holocene sediments derived from erosion of the slope.