GEOCHRONOLOGY OF THE VIRGINIA COASTAL PLAIN: A REVIEW OF AGES, TECHNIQUES, AND CORE SAMPLING FOR LUMINESCENCE DATING

Geochronology is an important tool for correlating paleoshoreline deposits to mean sea level reconstructions. The elevation of these deposits within the Virginia Coastal Plain are incongruent with expected past sea level due to the displacement and deformation caused by glacial isostatic rebound, and blind Cenozoic faulting. Additionally, the lack of absolute age control makes regional (interstate) correlation challenging and uncertain. Therefore, there is a need for robust geochronologic datasets on mapped alloformations, which represent major intervals of sea level progradation and regression. Currently, there is insufficient age data for the Virginia Coastal Plain to support regional correlations or the development of a local sea-level curve.

We provide a review of geochronological techniques that are best suited for inland Coastal Plain, barrier island, and shallow-water shelf materials (i.e., clastic sediments, carbonates, and fossils). The dating techniques covered will include: trapped charge (luminescence and electron spin resonance), radiocarbon, cosmogenic radionuclide, amino acid racemization, Uranium-series, and paleomagnetism.

Much of the Coastal Plain is low-relief and subsurface investigations rely on drilling and coring for sample collection. When targeting core samples for luminescence dating, two important factors relate to the integrity of the natural luminescence signal and the representation of the dose rate environment. The equivalent dose sample should remain light-safe such that the burial dose is not reset (zeroed) by light exposure, and the sediment sampled for dose rate must accurately represent all units within at least 15 cm above and below the equivalent dose sample. Examples and discussion of guidelines for sampling sediment core for luminescence dating are discussed, and preferred protocols are dependent on the extraction method, sedimentology, core integrity, and storage conditions.