The University of Texas Institute for Geophysics has collected 550 nmi of multichannel reflection seismic data from the western half of the southern Florida Bank. These data indicate that the structural framework underlying the area consists of several elements. Along the north, the Pinellas County arch is a basement feature oriented northeast-southwest and overlain by a relatively thin carbonate sedimentary section that thickens into the Tampa Embayment to the northwest and the South Florida basin to the southeast. The western margin of the bank is underlain by the Sheffield arch, a basement feature trending northwest-southwest and flanked by the Florida Escarpment on the west and the South Florida basin sedimentary section to the east. It is most likely a southeastward ontinuation of the Pinellas County arch. The southern terminus of the Sheffield arch is overlain by a structure interpreted as a buried Tertiary shelf margin, possibly a reef, within the present bank. Within the South Florida basin sedimentary section, there are two secondary basins trending approximately northeast-southwest. They probably originated in Jurassic to Early Cretaceous(?) time and were continuously reactivated into the Tertiary. In addition, an off-bank seismic facies is present between the southern end of the Sheffield arch and the Tortugas Bank. This feature is interpreted as a Jurassic(?) to Tertiary reentrant into the southern Florida Bank. Finally, the present southern shelf break is underlain by a series of prograding clinoforms estimated to be late Tertiary to Quatern ry in age.

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