Clastic Dikes Associated with Soil Horizons in the North and South Carolina Coastal Plain

Abstract

A large number of clastic dikes occur in many areas of the North and South Carolina Coastal Plain. The dikes begin within the B soil horizon, and none have been observed cutting the A horizon. Most dikes are less than 6 in. in width and taper downward, usually about 5 ft, but dikes 22 ft in downward extension have been observed. Horizontally, they have been traced for a maximum distance of 75 ft. The dikes are not confined to any one formation or rock of a particular age, and they are composed of sandy mud, which is often thoroughly iron stained. The rock they cut is well drained clayey or muddy sand. The clay minerals found in the dike and adjacent country rock are kaolinite, dioctahedral vermiculite, and traces of clay mica. Within the dike is a consistent dioctahedral vermiculite/kaolinite ratio with depth; outside the dike the ratio decreases with depth. The clastic dikes may be oriented parallel to hillslopes and some are associated with collapse structures. We conclude that the clastic dikes in the Carolina Coastal Plain were formed through filling of fractures by soil material developed in the upper B horizon. Most fractures probably developed in weathered rock as a result of slump or hillside creep.