Biostratigraphy of the Bluffport Marl Member of the Demopolis Chalk, Cretaceous of Alabama

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The Bluffport Marl Member of the Demopolis Chalk was sampled to find what lithologic and paleontologic variations occur along the strike of this unit. The Bluffport Marl Member has been traced in Alabama from Sumter County eastward into the western edge of Lowndes County, somewhat farther east than reported in earlier publications. Insolubles increase upward in the section and along strike towards the eastern extent of the Bluffport Member, implying an eastern source of clastics. The abundant invertebrate faunal assemblage of the Bluffport decreases upward in the section and to the east in direct relation to the increase in clastics. Although the Bluffport species vary in abundance at different localities, the total number of species found is nearly consistent from location to location in the lower part of the section. Morphologically, there is very little difference in the western and eastern Bluffport fauna, although there is a significant decrease in size of these assemblages toward the upper part of the section. Based on faunal changes, this increase in clastics reflects environmental conditions that were below those optimum conditions that existed in the lower and more western Bluffport section and in which these reef assemblages thrived.

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