THE SHALLOW STRATIGRAPHIC FRAMEWORK OF THE INNER CONTINENTAL SHELF OF DELAWARE MAPPED FROM HIGH-RESOLUTION SEISMIC AND CORE DATA

The subsurface architecture of the Delaware Inner Continental Shelf is mapped from single-channel 'chirper' seismic data and archived core information to improve conceptual models of the region’s late Quaternary evolution. Stratigraphic boundaries are recognized in reflection imagery as surfaces of erosional truncation and/or depositional onlap while seismic facies are distinguished based on reflection amplitude and internal pattern. Core information provides litho-chronostratigraphic constraint, enabling correlation to well-established onshore models. Architectural blueprints are reconciled with results of prior offshore paleogeographic studies.

The inner shelf framework is characterized by a tripartite unit division, based on regional mapping of two unconformities. These surfaces delineate Quaternary paleovalley networks that contain fill successions of mid-Pleistocene to Holocene in age, as constrained by AAR and C-14 chronologies. Late Pliocene fluvio-deltaic deposits of the Beaverdam Formation, a prolific coastal-plain unit, comprise the substrate into which Quaternary shelf valleys incised. Holocene sediments form only thin veneers beyond valley confinement and Tertiary deposits are often exposed across valley interfluves, where Quaternary and Holocene unconformities amalgamate. While Pleistocene and Holocene valley-fill deposits occasionally crop out, there is no seafloor morphologic manifestation of subsurface paleotopographies.

Valley locations and depths are in general agreement with prior mapping studies. Most connect to modern estuaries and exhibit compound fill architectures of Pleistocene and Holocene muds and sands, documenting reoccupation over multiple glacio-eustatic cycles. A notable exception is found in a comparatively large paleovalley beneath the town of Bethany Beach. This system trends offshore at a coast-perpendicular and represents a late Pleistocene drainage divide, separating NE-trending valleys bound for the ancestral Delaware River from S-trending. Additional work is currently underway to reconcile stratigraphic models with those of adjacent shelf areas.