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ABSTRACT

This report deals with the biostratigraphy, lithostratigraphy, and micropaleontology of the Corsicana Formation of North Central Texas. A comparison of strata at the type locality of the Corsicana Formation with the type area of the Kemp Formation clearly demonstrates that these units are lithostratigraphic equivalents and can be encompassed by one formational name. Since the Corsicana Formation has a well-defined type locality and contains by far the best exposures of these units in their respective type areas, it is suggested that the term Kemp be abandoned and the term Corsicana be retained. The definition of the Corsicana Formation is emended, therefore, to include the calcareous clays, mudstones, and marls that overlie the Nacatoch Formation and underlie the Paleocene Kincaid Formation (Midway Group).

The present investigation indicates that the Corsicana Formation is middle Maestrichtian in age and is assignable to the Globotruncana contusa-stuartiformis Assemblage Zone, G. gansseri Subzone. Through a detailed analysis of the planktonic foraminiferal assemblage, it has become possible to subdivide the Globotruncana gansseri Subzone into two new zonules: a lower Globotruncana aegyptiaca Zonule and an upper Racemiguembelina fructicosa Zonule.

The Corsicana Formation includes a rich, well preserved planktonic foraminiferal assemblage consisting of fortynine species (four of which are new) assigned to thirteen genera. The scanning electron microscope has been utilized extensively in this study to describe and illustrate these taxa. The genus Racemiguembelina Gallitelli (1957) is emended and a new term ponticulus is proposed for the unique umbilical cover plates that characterize this genus.

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