CHRONOSTRATIGRAPHY OF THE UPPER CRETACEOUS DEPOSITS OF MISSISSIPPI AND ALABAMA AS A SPRINGBOARD FOR STUDY OF REGIONAL GEOLOGIC EVENTS

The lithostratigraphy, calcareous microfossil biostratigraphy and stratigraphic cyclicity of the Upper Cretaceous (Santonian-Maastrichtian) marine deposits of Mississippi and Alabama are well documented. The results of graphic correlation of composite reference sections in eastern Mississippi and central Alabama are presented herein, and include the stratigraphic ranges of 45 species of planktonic foraminifera and 112 species of ostracodes. The planktonic foraminiferal zonation is based on standard global biozones. These include the Dicarinella asymetrica Taxon Range Zone, the Globotruncanita elevata Interval Zone, the Globotruncana ventricosa Interval Zone, the Globotruncanita calcarata Taxon Range Zone, the Globotruncanella havanensis Interval Zone, the Globotruncana aegyptiaca Interval Zone, the Gansserina gansseri Interval Zone, and the Contusotruncana contusa-Racemiguembelina fructicosa Interval Zone. Three new ostracode zones are defined, and the upper boundary of two previously defined zones are amended. These zones are the Veenia quadrialira Interval Zone (amended), the Acuminobrachycythere acuminata Interval Zone (new), the Brachycythere pyriforma Interval Zone (new), the Ascetoleberis plummeri Taxon Range Zone (amended), the Curfsina communis Interval Zone (new), the Escharacytheridea pinochii Interval Zone, and the Platycosta lixula Interval Zone. The planktonic foraminiferal biostratigraphy indicates that the age of these deposits range from early Santonian to early Maastrichtian. These zones are tied to three transgressive-regressive cycles. The high-resolution biostratigraphy of the ostracodes, which are indigenous to the North American Coastal Plain, will enable subsequent studies of Late Cretaceous paleobiogeography and Gulf of Mexico-Caribbean tectonic development to be conducted. Preliminary results from a reconnaissance study in Cuba, in addition to published data from northeastern Brazil, indicate that the ostracode faunas differ fundamentally from those in North America, indicating the presence of faunal barriers during at least the mid- to Late Cretaceous. These observations indicate the value of high-resolution chronostratigraphy in solving regional geologic events, including evolving plate tectonic paleogeographies.