Abstract

Modern facies-distribution patterns, extensive core data, and chronostratigraphic cross sections provide a detailed history of Holocene inundation within the Delaware Bay estuary and sedimentation in adjacent coastal environments. Flooding of the estuary occurred with rising sea level as the shoreline retreated northwest along a path determined by the pre-transgression topography. Simultaneous migration of an estuarine turbidity maximum depocenter provided the bulk of fine sediments which form the coastal Holocene section of the estuary. Prior to 10 Ka, the ancestral bay was predominantly a tidal river, and the turbidity maximum depocenter was located southeast of the modern bay mouth. By 10 Ka, lowlands adjacent to the ancestral channel of the Delaware River were flooded, forming localized tidal wetlands, and the depocenter had initiated high rates of fine-grained sedimentation near the present bay mouth. At that time, coastal Holocene strata began to onlap the interfluve highlands. By 8 Ka, the fine-grained depocenter had migrated northwest along the main channel of the Delaware River, although the widened mouths of tributary valleys continued to be active sites of sediment accumulation. Following the passage of the fine-grained depocenter, coarse-grained sediments accumulated along the coast in response to increased wind-wave activity. During the middle Holocene, portions of the estuarine coast began to resemble modern geomorphology, and washover barrier sands and headland beach sandy gravels accumulated along the southwest shore. The late Holocene was characterized by erosional truncation and submergence of aggraded coastal lithofacies and by planation of remnant highland areas. Knowledge of the eroded Holocene section is fragmentary. At present, continued sea-level rise is accompanied by deposition of tidally transported muds in coastal environments and deposition of sandy sediments in some offshore regions. An unconformity marks the base of the developing open estuarine sequence of coarse clastic lithofacies and denotes the end of coastal accumulations. Modeling of coastal-lithofacies transitions identifies specific lithofacies complexes in the Holocene stratigraphic section which were influential in the evolution of the coast. Development of the Holocene section of the estuary coast involved both constructive, or aggradational, and destructive, or erosional, phases.

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