PRELIMINARY EVALUATION OF ALONG-STRIKE CORRELATIONS OF PLIOCENE AND EARLY PLEISTOCENE STRATIGRAPHIC UNITS, FALL ZONE PLACER REGION FOR NORTH CAROLINA AND VIRGINIA

State and federal scientists are collaborating to evaluate existing stratigraphic nomenclature for surficial Pliocene and Pleistocene deposits that include heavy mineral placers in the Fall Zone of Virginia (VA) and North Carolina (NC), through USGS STATEMAP and EARTH MRI programs. The NC Geological Survey (NCGS) drilled new core at 127 sites in Drake and Red Oak 7.5-minute quadrangles in NC. In VA, mappers use traditional methods and an auger rig to map and define units. NCGS and Virginia Dept. of Energy collaborated (STATEMAP) to drill new core in VA to support interstate correlation. As a result, 367 ft of core was obtained in VA in Dinwiddie and Cherry Hill 7.5-minute quadrangles at 13 sites along-strike.

To compare stratigraphy, core descriptions were standardized in graphic log format. Landscape positions were defined, and the logs with thick Coastal Plain units were chosen. In NC, the Daughtridge cores penetrated the Coharie terrace (150-246 ft; 45-75 m) between the Kenly and Wilson Mills paleoshorelines. In VA, the Clarke core cluster was situated on the Richmond Plain (205-240 ft; 62-73 m) between the Thornburg and Broadrock scarps in the Old Hickory heavy mineral deposit. The units targeted may be the Cold Harbor (informal) and Bacons Castle Formations.

All cores consist of 40 ft (12 m) of Coastal Plain section that overlies bedrock saprolite and occur at elevations of 200-217 ft (61-66 m). In VA, Clarke-03 was evaluated with a multi-sensor core logger system and sampled for cosmogenic nuclides. The Daughtridge cores are evaluated along a cross section constructed from nearby cores.

The Clarke cores include three sedimentary facies. The basal unit (7 ft: 2 m) is a med-coarse gravelly sand that coarsens upward into sandy gravel. Unit 2 (14 ft: 4 m) has a basal reworked gravel (2 ft: 0.6 m) that is sharply overlain by heavy mineral sands punctuated by quartz pebble layers; the unit may coarsen upward. Unit 3 (20 ft: 6 m) includes sands and gravels that become muddier upsection. In the Daughtridge cores, the three units are finer grained and less gravelly; the lower units (1 and 2) represent offshore facies (very fine silty sands).

This exercise shows a systematic approach to resolving interstate correlation problems by examining units in the context of landscape position and ultimately a chronostratigraphic framework.