Coastal lithosome preservation: Evidence from the shoreface and inner continental shelf off Bogue Banks, North Carolina

Abstract

Seismic and vibracore data from the continental shelf as well as borehole data from an adjacent barrier island indicate that the migrating shoreface, responding to rising sea level, has nearly completely removed the entire coastal sedimentary record in northern Onslow Bay, North Carolina. This process was active throughout the Quaternary and even the late Tertiary as middle Tertiary sediments and rocks directly crop out on the sea floor in vast areas of this shelf sector. Seaward of Bogue Banks (a Holocene barrier island located along northern Onslow Bay) seismic sequences have been truncated by the modern shoreface which extends to about 12 m depth. Correlations with borehole data on the island indicate that these sequences are Pleistocene and Holocene in age. The Holocene sequences contain numerous channels which are interpreted to be relict tidal inlets. However, none extends vertically lower than the shoreface indicating that landward translation of the shoreface would remove most of even the deepest Holocene coastal lithosomes, parts of the Pleistocene and even a portion of the Tertiary. The middle and inner portions of the continental shelf have been incised by numerous channels. Channel facies are an important component of shelf sedimentary and stratigraphic sequences and comprise about one-third of northern Onslow Bay. Similar seismic infilling facies and vibracore data as well as the poor preservation potential of the tidal inlet throats indicate that the channels were lower coastal plain streams. The infilling sediments are mostly muds with some sands and shells. Dates from shells via the amino acid racemization technique are Pleistocene in age. These channels, with some having multiple infilling events, assume greater importance when one recognizes that essentially they alone hold the vast majority of the Quaternary record of numerous sea-level fluctuations.