Abstract

A continuous seismic reflection survey indicates that the post-Miocene section of the inner Virginia Shelf is 27 m in average thickness and unconformably overlies a discordant Tertiary substrate. Vibracore data and a faunal analysis reveal three distinct sedimentary sequences separated by prominent unconformities.

The oldest post-Miocene sequence has a radiocarbon age of more than 37,000 yrs B.P. It consists largely of a muddy, fine-grained sand and is characterized by lenticular stratification and prominent local channeling. It appears to represent a pre-Wisconsinan and early Wisconsinan assemblage, containing both a transgressive fluvial complex and a regressive coastal barrier complex.

The overlying sequence has a radiocarbon age ranging from 25,700 ± 800 yrs, to possibly as young as 20,400 ± 850 yrs B.P. It is comprised primarily of mud, and is characterized by relatively uniform horizontal stratification. The assemblage appears to represent a regressive paralicneritic sequence developed at the end of the mid-Wisconsinan interstadial.

The youngest sequence of the section has yielded a radiocarbon age of 4,200 ± 140 yrs B.P. It is comprised of a discontinuous sand sheet that mantles the modern sea floor, and which appears to have been generated through the shore face erosion of a retrograding coastal barrier complex during the Holocene transgression. Evidence suggests that it accumulated as a lag deposit on the sea floor, where it was subsequently molded into a ridge and swale topography by the Holocene hydraulic regime.

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