GEOLOGIC EVIDENCE FOR PALEO INLETS, ANCIENT FORESTS, AND COASTAL CHANGE ALONG A CAPE COD BARRIER BEACH, SOUTH CAPE BEACH, MASSACHUSETTS

South Cape Beach is a retrograding barrier system located along the south shore of Cape Cod Massachusetts. A 1 km segment of the barrier’s foreshore contains over 200 ancient Eastern Red Cedar (Juniperus virginiana) stumps. This portion of the barrier fronts a shallow salt pond and marsh system. Historical maps dating from 1846 indicate the presence of two former tidal inlets in proximity to the ancient forest, though no inlets exist today. Taken together, these preserved barrier facies provide evidence of coastal change at differing temporal and spatial scales.

Ground penetrating radar, sediment cores, and geospatial analysis were used to identify and map former tidal inlets and barrier stratigraphy. Relict tidal inlets provide a geologic signature of environmental change including past barrier breaches, overwash and shoreface hydrodynamics. The identification of former inlets is an important, as it enhances the understanding of coastal processes and response. AMS radiocarbon dating will provide constraint on the upper boundary of relative sea level and chronologic control for environmental reconstruction.

The existence of 2 mapped historical inlets and unknown inlets were identified with over 3 km of GPR data. Inlet facies were identified by the presence of broad U-shaped cut-and-fill structures incised into adjacent barrier facies. Inlets exhibit a variety of simple and complex geophysical morphology suggesting extremely ephemeral and longer-lived structures. In addition, 2 4 m sediment cores were taken along the foredune at the site of the two historic inlets. Core analysis is ongoing and initial results have identified an organic rich layer with small rootlets at 80 cm in each of the cores.

Geospatial and geotemporal analysis of the geological and geophysical data, coupled with the stump AMS dates (370, 970, 1010, 1240 ybp) suggest a detailed story of an evolving complex coastal system in response to changes in basin morphology, energy and recent anthropogenic influence. For example, the smaller inlet features are interpreted as short-lived breaches while geospatial analysis suggests that the two historical inlets are represented in the subsurface by complex geophysical structures, suggesting a longer-lived feature and the organic layer within sediment cores may correlate with the submerged forest.