Subsurface Evidence of Storm-Driven Breaching along a Transgressing Barrier System, Cape Cod, U.S.A.

Abstract

Maio, C.V.; Gontz, A.M.; Sullivan, R.M.; Madsen, S.M.; Weidman, C.R., and Donnelly, J.P., 2016. Subsurface evidence of storm-driven breaching along a transgressing barrier system, Cape Cod, U.S.A. Relict and historic tidal channels buried within coastal barriers provide a geologic signature of environmental change, thus enhancing our understanding of how barrier systems respond to extreme storm events. Earliest maps from 1846 depict three inlets along the Waquoit Bay barrier system located on Cape Cod, Massachusetts. These channels were not depicted on maps after 1846, and we lack any information pertaining to them before 1846. The principle objective of this study was to identify the location and map the internal geometry and channel-fill configuration of the buried inlet structures using geophysical and sedimentological data acquisition methods. This was done by collecting 6.2 km of shore-parallel ground-penetrating radar data and five sediment cores ranging in depth from 4 to 5 m. The sediment cores allowed for the ground truthing of the ground-penetrating radar data and provided six samples for radiocarbon dating. The 13 paleochannels identified ranged in depths from 1.3 to 3.7 m below the present beach surface. These appeared in the radar imagery as broad U-shaped cut-and-fill features incised into adjacent barrier facies. The 13 paleochannels composed 24% of the barrier lithosome totaling 704 m in length. Individual channels were primarily less than 65 m in length and between 2.5 and 1.3 m in depth, although an additional 275-m-wide, 3.7-m-deep channel sequence was imaged and likely represents a major and long-lived paleochannel. The results will contribute toward deciphering the evolution of the Waquoit system and identify areas vulnerable to storm-driven coastal change.