ABSTRACT

Strata of the Midway Group crop out in a belt from Georgia to Mexico, including well-exposed studied sections in northeast-central Texas. The benthic foraminiferal data assembled by Kellough (1959, 1965) has been subjected to cluster analysis. On the basis of these analyses five following biofacies are recognized in eastern Navarro County: 1) shallow water biofacies as represented in Littig, Kinkaid and lower parts of the Wills Point members (biofacies A); 2) upper parts of the Mexia clay represent a different community in which occasional increase in planktonic foraminiferal percentage may indicate deeper stages (biofacies B); 3) shallow-water environment as represented by uppermost part of the Mexia and the lowermost part of Kerens (biofacies C); 4) shallow-water environment as represented by the middle part of Kerens (biofacies D); and 5) marginal-marine biofacies as represented by upper Kerens and Solomon Creek (biofacies E). These shallow-water communities are similar to the Paleocene Atlantic Coastal Plain biofacies. Usually only a few characteristic species at any particular level dominate the populations. Fluctuations in diversity, high morphologic variability of species, and slow rates of evolution also have been observed. Many qualitative similarities occur between these biofacies and those occurring on and around modern deltas.