ABSTRACT

Lithologic and micropaleontologic analyses of cuttings from 27 wells in Lee and Hendry Counties, southwest Florida, show that the Tamiami Formation as currently defined does transcend the Miocene/Pliocene boundary with a major stratigraphic discontinuity close to that boundary. Stratigraphic and temporal relationships of eight units traced within the formation have been discerned by the use of limited but useful coccolith and planktonic foraminiferal data, the establishment of an informal benthic foraminifera zonation, and the presence of a widespread diatom-rich key bed. Paleoecologic interpretations have been aided by the discrimination of three benthic foraminiferal assemblages which represent three environments: 1) hyposaline; 2) normal marine to hyposaline; and 3) normal marine to hypersaline.

The formation consists of a complex sequence of lithologies deposited in a bay-like, nearshore shallow shelf environment affected by differential subsidence, fluctuating sea levels, and the proximity of one or more rivers to the northeast, north or northwest which served at various times as sources of sediments, fresh water and nutrients. Facies changes are sharp in the clays, limestones and sandstones of the lower units which characteristically thin or wedge out updip. The units exhibit an overall transgressive-regressive-transgressive-regressive pattern with a marked regression just below the Miocene/Pliocene boundary believed due to a glacial-eustatic sea level drop. One unit is formally named and described.