REACTIVATION AND OVERPRINTING OF SOUTH GEORGIA RIFT EXTENSION

As part of U.S. Department of Energy-sponsored carbon sequestration project, seismic line SCCO2-1was shot southeast from Bamberg County into Colleton County, South Carolina. The line covered 61 km and was shot to investigate the South Georgia rift (SGR) as a potential storage reservoir. SGR is a Triassic-rift basin buried beneath the Coastal Plain of South Carolina and Georgia. SCCO2-1 data image the northwest margin and part of the main rift basin. Although a reversal in throw was imaged in the southeast end of the line, the southeast margin was not crossed. Three distinct periods of faulting are identified: early extension, reverse reactivation, and strike-slip overprinting. To the southeast, the northwest margin is marked by a disruption and steepening of sub-horizontal reflectors. A back-thrust, however, splays from a short-cut footwall thrust and partially masks the margin above 1 second twt. Southeast of the margin, harpoon-style reverse faults mark older, down-to-the-southeast extension faults. Antiformal warping also is present. Footwall buttressing may have produced this warping; but older, down-to-the-southeast extension faults have a planar geometry, instead of a listric shape. Antiformal warping may be related to ramping of younger, low-angle thrusts. Thrusting is concentrated in subhorizontal mafic layers and is interpreted as outward splaying of overprinting, transpressional strike-slip faulting. Thrusting also indicates that a component of partitioned deformation characterized transpression. Pronounced splaying to the northwest implies a half-flower structure with down throw to the northwest. Strike-slip faulting may be related to reactivation of a rift-related transfer fault or to an east-west-striking system of faults mapped along the margin. Regional patterns and splay directions support both possibilities. Presently, timing of reactivation and overprinting is poorly understood.