Abstract

The mineralogic composition of surface and core sand samples from the outer shelf, slope, and rise between Hudson and Norfolk Canyons off the mid-Atlantic states has been determined to evaluate the relative contributions of major drainage areas lying to the north and west. The observed mineralogic uniformity in space and time is largely attributable to the fact that the principal fluvial supply to this sector during the Pleistocene and Holocene Epochs was through river systems, all of which drain some part of a large and geologically variable glaciated region. Further complications in distinguishing specific sources probably result from the extensive migration of the Hudson River across the subaerially exposed continental shelf during various Pleistocene low sea-level stands, which produced considerable homogenizing of shelf sediment prior to their downslope transfer onto the continental rise.

Trends of the major light and heavy mineral groups on this outer continental margin show that the ancestral Hudson probably extended at least to the head of Baltimore Canyon. The distribution of a distinctive variety of the mineral axinite suggests that the Hudson may have even exerted its influence as far south as the head of Washington Canyon, or some 140 km farther to the south than previously postulated.

Vertical time-related changes in the mineral assemblages in slope and rise cores show a broadly similar pattern throughout the region. Vertical variability is particularly notable in cores on the slope off the Norfolk-Washington Canyon pair, where there appears to be a progressive increase in the influence of a western (Delaware-Susquehanna) supply in recent time. The marked compositional variation of sand with depth in cores from the lower rise is best explained by fluctuations in materials transported from adjacent shelf sources downslope to the southeast (lateral input and transport model) rather than by significant long-term dispersal parallel to isobaths (contour-current transport model).

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