ABSTRACT

The Suwannee Basin is located in the eastern Gulf Coast area and includes portions of Florida, Alabama, and Georgia. Its axis extends northeasterly from Apalachicola, Florida, into southwestern Georgia. It developed in Mesozoic time as a broad syncline on a smoothly eroded Paleozoic terrian.

Deep drilling in the eastern Gulf Coast region has penetrated the Tertiary and Mesozoic section, but wells have seldom extended very deeply into pre-Mesozoic rocks. Data relating to the deeper section were collected when Geophysical Service Inc. conducted a seismic reflection survey in the Suwannee Basin with associated gravity and vertical magnetic field measurements. The seismic sections provided the structural framework for an initial geologic interpretation. Drilling information established stratigraphic control for the upper part of the sections and verified interval velocity determinations. The velocity analyses were spaced one mile apart, with about 14 interval determinations at each point, and were used to convert time sections to depth sections. Synthetic gravity and magnetic fields were generated by a computer program for each hypothetical geologic interpretation and compared with the observed fields. The geologic interpretation was altered to test various hypotheses, and refinements continued until data were reconciled.

The final interpretation shows Tertiary and Cretaceous sediments lying above a remarkably smooth unconformity developed upon Paleozoic and Triassic rocks. The unconformity dips southward from a depth of 8400 ft. (2560 m.) near the Alabama-Florida boundary to about 12,000 ft. (3660 m.) near Panama City, Florida. Below the unconformity is a folded and faulted sequence of Lower Paleozoic rocks and Triassic continental red beds accompanied by volcanic flows or intrusives. Paleozoic rock types appear to include volcanics, quartzite, and a sandstone-shale sequence. Individual structures suggest broad anticlines developed above thrust faults. The Paleozoic rocks are tentatively correlated with African counterparts, and it is suggested that their hydrocarbon potential warrants further investigation.