ABSTRACT

A new stratigraphic unit, the Torreya Formation, is proposed, based on a revised cross-section along the Apalachicola River, including core holes near the river. A post-Tampa, pre-Chipola age for the unit is indicated by a study of its fauna.

The new unit is erected for strata containing a macrofauna including Pododesmus scopelus Dall and a microfauna with Miogypsina globulina Michelotti. It includes beds now mapped as equivalents of either lower Hawthorn, upper Chattahoochee (=upper Tampa), or Fort Preston formations in Liberty and adjoining counties.

The Torreya assemblage has little in common with the Tampa fauna, but is very closely affiliated with that of the Chipola formation. The pre-Chipola, post-Tampa stratigraphic position was determined by the presence in the fauna of miogypsinids, which to date have been reported only from sediments older than those containing the Chipola fauna, and by the superposition of the Chipola fauna on a weathered remnant of the Torreya formation.

The data suggest that this new unit was deposited in a marine to brackish water bay that appears to have been centered in Georgia and open only to the Atlantic Ocean. The Gulf Trough into the Apalachicola Embayment was apparently closed by a land bridge presumed to be an exposed carbonate bank. Since deposition of the new unit, the presumed carbonate bank has wasted away, whereas the Torreya formation with similar elevation persisted as a highland area.