The interrelation and distinction between flood-tidal delta and washover deposits in a transgressive barrier island

Abstract

The distinction and interrelation between flood-tidal delta and washover deposits is described by comparing back-barrier sands associated with an active and a relict tidal inlet system on the south shore of Long Island. Guidelines for comparison include three-dimensional morphology, sedimentary structures, sediment texture, and facies sequences. The active, modern flood-tidal delta is covered by reversing small-scale ripples represented by bidirectional small-scale cross-bedding in the subsurface. Large-scale flood-oriented cross-beds are associated with non-reversing sand waves on the flood ramp. The relict flood-tidal delta is represented by medium- to fine-grained sands characterized by small-scale cross-bedding or massive bedding. Relict flood-tidal delta deposits are overlain by distinct washover deposits separated by thin units of salt-marsh peat. Dominant washover structures are parallel laminations. Well-preserved roots are commonly found in washover sands, but are largely absent in flood-tidal delta sands. Facies sequences of the relict inlet system indicate that flood-tidal delta deposits extend the width of the barrier island. Overwashing serves to infill abandoned channels of the delta and contributes to vertical buildup.