The Hudson Shelf Valley: Its role in shelf sediment transport

Abstract

The Hudson Shelf Valley was deeply incised by Pleistocene lowstands of the sea. During the Holocene transgression, fluvial, estuarine, and estuary-mouth depositional environments were displaced landward, and sedimentation in these environments partially filled the valley. Holocene sediment thickness in the seaward half of the valley is about the same as on the shelf to either side, but in the landward half of the valley, 22 m of sediment is present versus 5–10 m on the adjacent shelf. Sediment volume calculations in the upper shelf valley show that there is about three times the infill volume east of the thalweg as compared to the infill to the west. This configuration indicates that the valley has served as a sediment trap and records the westward migration of the thalweg during the Holocene. Most of the infill was the result of littoral drift which transported sand westward along the south shore of Long Island during the Holocene transgression. Modern sediment transport, as calculated from currentmeter observations and inferred from bedform observations, is mainly south westward, along the regional trend of the isobaths and across the shelf valley. Therefore, infill on the eastern side of the shelf valley is continuing at present. Observations of the regional distribution of sediment types indicate that the asymmetrical valley fill is part of a pattern of bottom response to flow. The former drainage divides on both sides of the shelf valley are surfaced by coarse lag deposits on slopes facing northeast, into the direction from which the major storm flows come, while the down-current sides are mantled with fine sand.