NEW CONSTRAINTS ON GEOMETRY AND STRUCTURE OF THE SOUTH GEORGIA RIFT FROM WELL DATA AND SEISMIC REFLECTION INTERPRETATION

Triassic sedimentary rocks and Jurassic diabase and basalt beneath the Coastal Plain of South Carolina were first described by Darton from a deep water well near Florence, South Carolina in 1896. Subsequent petroleum exploration activities in the Coastal Plain of South Carolina and Georgia since the 1920s led researchers to eventually consider that a vast Triassic rift basin, referred to as the South Georgia Rift (SGR), lay buried beneath the Coastal Plain. The SGR has been delineated by relatively sparse well penetrations (Chowns & Williams, 1983), potential field data (Daniels et al, 1983), and seismic reflection data (McBride et al, 1991).

This study integrates well data and seismic reflection data to better characterize the South Georgia Rift. A hypothesis is presented based on new interpretations of the data that the SGR is a rift zone made up of several smaller sub-basins and includes the Riddleville – Dunbarton basin and the Florence basin. The SGR is interpreted to be a series of half grabens which have a general NE-SW strike, and reverse polarity at two inferred transfer faults, which possibly correspond with onshore extensions of the Jacksonville Fracture Zone and the Blake Spur Fracture Zone.

Interpretation of the seismic lines throughout parts of the SGR are complicated by the presence of numerous diabase sills and dikes, which produce strong amplitude reflections previously thought to show basin structure. A revised interpretation of the western Georgia COCORP transect shows that the SGR pinches out to the northwest, and has a border fault along the southeastern boundary in Northern Florida with several interbasinal faults in-between. An inferred transfer fault is suggested to separate this portion of the SGR from the Riddleville – Dunbarton portion which has a well constrained northwestern boundary fault, and is interpreted to pinchout to the southeast. A second inferred transfer fault is hypothesized to exist in SC, between the Riddleville - Dunbarton basin and the Florence and Jedburg basins, to the northeast of which the general rift structure has again reversed polarity with a down to the northwest sense.