CORRELATION OF UPPER CRETACEOUS (SANTONIAN-MAASTRICHTIAN) DEPOSITIONAL SEQUENCES OF EASTERN ALABAMA

The Upper Cretaceous (Santonian-Maastrichtian) strata of eastern Alabama (Russell and Barbour Counties) include richly fossiliferous marine depositional sequences. The section includes the Eutaw and Blufftown Formations, Cusseta Sand, Ripley Formation and Providence Sand. For this research, sections of the Blufftown, Cusseta and Providence were measured and described at eight locations and samples were collected for their microfossil content, particularly ostracodes and planktonic foraminifera. Previous biostratigraphic and sequence stratigraphic studies in central Alabama and eastern Mississippi established composite reference sections that were used as standards to correlate the strata in eastern Alabama. Electric well log data and lithologic descriptions from water wells in the area were used to determine the elevations of the tops of the Blufftown and Eutaw Formations. Structure contour maps were then prepared to correlate the sections lithostratigraphically.

Ostracodes are often very abundant in the samples and more than 1320 specimens were picked for this study. Planktonic foraminifera are less abundant, although some of the key species useful for chronostratigraphic correlation were observed.

Samples collected from the lower Blufftown Formation are assigned to the Veenia quadrialira Taxon Range Zone of mid-Santonian age. Samples collected from the lower Blufftown about 100 feet above the previous samples are equivalent to the Brachycythere pyriforma Interval Zone of early, but not earliest, Campanian age. Samples collected from the upper Blufftown Formation are assigned to the Ascetoleberis plummeri Taxon Range Zone of mid-Campanian age. The chronostratigraphically-significant planktonic foraminiferan Rugotruncana calcarata of mid-Campanian age was found in the upper part of a measured section in the Cusseta Formation and these samples were assigned to the ostracode Escharacytheridea pinochii Interval Zone. A sample collected from the Providence Sand is equivalent to the Floricythereis lixula Interval Zone of Maastrichtian age.

According to the results of this research, the ranges of several species will be extended relative to the composite reference section in central Alabama and will result in improved, high-resolution chronostratigraphic ranges of the species.