Middle-Late Holocene Evolution of the Morphology of a Drowned Estuary System: The Delaware Bay.

摘要

The Delaware estuary lies along the axis of the pre-Holocene channel of the ancestral Delaware River, which was incised over 220 feet below present sea level near the mouth of the present estuary. This ancestral Delaware River drainage system was drowned by tidal waters as the estuarine environments migrated landwards and upwards in space and time through the Holocene Epoch. The pre-Holocene drainage system formed the initial control over the shape of the early Delaware estuary. In addition, Cape May ridge, a linear northeast-southwest trending ridge of Sangamon age coastal-marine sediments formed a barrier to the development of a wide mouth estuary. As a result, the main body of the present Delaware Bay is sub-circular in outline and its geographic form may be tectonic or geomorphic in origin. The shoreline of the estuary is one of erosional transgression across low-lying tidal marshes. Seismic and drill evidence has shown that the earlier Holocene estuarine system in the lower part of the present Delaware Bay was much like that of the present middle and upper Delaware estuary. Accordingly, cross-sectional profiles and sediment patterns of the present middle and upper estuary may be used as a model for the interpretation of the shape of the estuary, in the area of study, throughout Holocene time. This has made possible the construction of a series of palegeographic maps of the Delaware estuarine system as it evolved through Holocene time.