Clay mineral distributions and source discrimination of upper Quaternary sediments,lower Chesapeake Bay,Virginia

Discriminant function analysis of clay mineral data from five cores of upper Quaternary sediment indicates that marine inputs are a significant source of fine-grained sediment near Thimble Shoal Channel, a major natural channel in lower Chesapeake Bay. Illite, of predominantly marine origin, is found to be enriched in clay fractions of three cores adjacent to the channel, relative to two cores near the mouth of the James River estuary. Thimble Shoal Channel is a significant repository and conduit for fine-grained sediment from the shelf. This result is analogous to previous results showing that the shelf is the dominant source of fine sand in the lower bay. Sediment in Thimble Shoal Channel reflects a shelf source even at the landward end, an area which was previously thought to be dominated by deposition from the James River.