A FIELD METHOD OF DEFINING AND MAPPING EARLY PLEISTOCENE SEQUENCES USING GEOPROBE CORES – SURRY PALEOSHORELINE COMPLEX, COASTAL PLAIN, NORTH CAROLINA

Three-dimensional (3D) subsurface mapping techniques were used to characterize sedimentary facies, establish a sequence stratigraphic framework, and define surficial landforms for an Early Pleistocene relict landscape that includes the Surry Paleoshoreline Complex. The method combines comprehensive landscape analysis with targeted subsurface coring along key transects that crosscut landforms. To interpret landform elements, position cross sections, and define depositional systems, high-resolution LiDAR (2006 bare earth – vertically accurate to 25 cm per 1m X 1m tile) data was acquired (www.ncfloodmap.com), converted to rasters, and processed to produce hillshade, slope and contours (0.25 and 0.5 m). This was used with 2011 orthoimagery.

Geoprobe cores were collected along key transects using the continuous, discrete sampling method. Cores were acquired incrementally in 4 ft tubes. Maximum penetration depth was 72 ft; recovery was >80%. Tubes were split lengthwise and core was processed on site. Core tops were sliced off with piano wire. Core surfaces were washed to enhance stratigraphy and air dried. A graphic log was sketched in the field book (0.5 in = 4 ft) using a standardized method of textural classification (Farrell and others, 2013) that is independent from composition. Recent cores (Fall 2015) were photographed in the field using a cell phone camera; the results were remarkable. After transport to home base, cores are reprocessed, photographed with a digital camera, and logged in detail. For archiving purposes, high-resolution photomosaics provide a composite image of the whole core.

This method of coring provides an excellent record of Quaternary strata: recovery is high and cores are relatively undisturbed. Graphic logs constructed in the field permit on site identification of facies and stratigraphic boundaries, and tentative correlations between adjacent cores.