OFFSHORE SOUTHEASTERN UNITED STATES RE-EVALUATED: NEW INSIGHTS FROM WELL PENETRATIONS AND 2D SEISMIC REFLECTION DATA

Re-analysis of legacy 2D seismic reflection and well data from the offshore of the southeastern United States reveals a previously unmapped lower Paleozoic sedimentary section identified in two deep offshore wells. Paleozoic strata have been known onshore in Florida since the 1930’s, and were subsequently identified to be part of the exotic Suwannee terrane. The COST GE-1 and Transco 1005-1 wells drilled in the late 1970’s on the Georgia continental shelf both encountered Paleozoic strata in the lower sections of the wells, but have not previously been rigorously integrated with the Paleozoic strata onshore. The Paleozoic platform sequence in offshore seismic sections is identified as a package of low-frequency, subhorizontal reflectors which are clearly discordant with the overlying stratigraphy above the post rift unconformity (PRU). The inferred base of the Paleozoic sequence is marked by the downward diminution of parallel seismic reflectors, as well as a change in seismic velocities observed in offshore seicmic refraction surveys. These observations suggest a stratigraphic thickness for the Paleozoic sequence of 3-5 km. The Transco 1005-1 well encountered strata of Ordovician to Silurian age beneath the PRU, based on palynological data, whereas the COST GE-1 well reportedly penetrated strata as young as Devonian in age at a similar structural level. Provisionally, these relations imply the presence of either differential erosion or structural relief imparted to the Paleozoic section prior to deposition of the overlying passive margin sequence. Recognition of these strata offshore, and correlation with similar strata onshore, implies that the Suwannee terrane continues across the continental shelf of Florida and Georgia, at least to the western edge of the Blake Plateau Basin. Preliminary analysis of seismic reflection and refraction data across the Blake Plateau Basin proper suggests that these strata and their underlying basement may continue to the base of the continental slope.