GEOLOGIC MAPPING OF THE MIDDENDORF AND PATRICK QUADRANGLES, CHESTERFIELD COUNTY, SOUTH CAROLINA

The Middendorf and Patrick quadrangles in Chesterfield County, South Carolina are located in the updip portion of the Southeastern U.S. Atlantic Coastal Plain province within the Carolina Sandhills region. Outcrops in these quadrangles reveal Upper Cretaceous sand and clay capped by an unconformity and overlain by Quaternary sand. The Cretaceous strata are mapped as the Middendorf Formation, and include the following five lithofacies: (1) cross-bedded iron-cemented sandstone to pebbly sandstone; (2) poorly lithified cross-bedded sand to pebbly sand; (3) sand and interbedded sand and clay; (4) cross-bedded sand with clay drapes on the cross beds; and (5) beds of clay >4 m thick. The sandy and pebbly lithofacies contain angular-to-rounded quartz gravel up to 3.5 cm in length, kaolin clasts that are pseudomorphs of feldspar, rip-up clasts, cross-bedding up to 2 m tall, fining-upward sequences in excess of 8 m, evidence of scouring, and fossils of conifer wood. The combination of these features suggests a fluvial to estuarine origin. The Quaternary sand is mapped as the Pinehurst Formation, and consists predominantly of moderately sorted to well sorted, subangular-to-subrounded, medium-to-coarse quartz sand without obvious primary sedimentary structures. Where the Quaternary sand is relatively thick (1 to 4 m), imagery derived from LiDAR point cloud data reveals low-relief linear bedforms with lee sides on the southeast. Samples of this sand have yielded optically stimulated luminescence ages ranging from ca. 21 to 8 thousand years ago. This Quaternary sand is interpreted as eolian dunes and sandsheets derived from the immediately underlying Cretaceous sand during conditions of stronger wind and reduced vegetation cover, and then subsequently degraded and stabilized by pedogenesis and vegetation. Additional map units within the quadrangles include sand, mud, and peat with different degrees of soil profile development on terraces and flood plains adjacent to streams.