PALEOSEISMITES AND TECTONICS OF THE DEEP RIVER TRIASSIC BASIN, NORTH CAROLINA

Seismites are syndepositional features preserved in the sedimentary record that are indicative of paleoseismicity either collectively or individually. The Deep River Triassic basin contains many such features. Previous workers had noted zones of vertically oriented cobbles in conglomerates near the Jonesboro fault and repetitive joint-sequences in the stratigraphic section that formed during movement on different segments of the basin-bounding Jonesboro fault. The earliest two sets of Triassic joints were conduits for reducing fluids. Some of these joints were subsequently injected by either clastic or clay dikes indicating shallow depths of burial at the time of both joint and dike formation. Clastic dikes, found in the Colon cross structure, can be traced downward to sand-source beds of similar composition, indicating upward injection into pre-existing joints. Clay dikes also can be traced downward to clay-source beds. They are associated with low-angle extensional faults suggesting their upward injection into pre-existing joints during shallow-seated landsliding. The direction of slip on these low-angle faults is consistent with slip on nearby segments of the Jonesboro fault. The association of repetitive injection of clastic dikes with strata containing liquefied beds (disrupted laminations), or beds of soft-sediment deformation (convolute laminations), or beds with clay dikes, or beds with ball and pillow structures is suggestive of paleoseismicity.