Upper Eocene Foraminifera from the type section of the Yazoo Formation of Mississippi



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The "Yazoo Clay", now elevated to Yazoo Formation, at its type section near Yazoo City, Mississippi, consists entirely of marine strata that are approximately 160 feet thick and represent only the lower one—third of the Yazoo Formation. It is conformably underlain by marine Moodys Branch Formation and unconformably overlain by non— marine Pliocene and Pleistocene sediments. The Foraminifora from 7 core samples of this section are described and compared with foraminiferal assemblages collected from the type localities of members of the Yazoo Formation in eastern Mississippi and with reported distributions in the literature. Herein are figured and described, or discussed, 69 benthortc species and subspecies belonging to 36 genera, 14 planktonic species and subspecies belonging to 8 genera; of these, 2 species find 1 subspecies are described as new: Globigerinoidcs eoccnica, Globorotalia johnportori, Tiuncorotaloides rohri eoccnica. The portion of the lower Yazoo Formation represented at the type section contains the same zonal assemblage (Textularia dibollcnsis) as the North Twistwood Creek Clay and Pachuta. Marl members of the Yazoo Formation in eastern Mississippi and is considered to be equivalent to these members. It belongs to the Cribrohantkenina danvillensis zone and is Middle Bartonian. (Late Middle Eocene) in age. Two zonules may be recognized at this type locality, the Truncorotaloides rohri eocenica zonule (lower 70 feet of the type section) and the Globorotalia opima nana zonule (upper 90 feet of the section). These zonules cannot be recognized in equivalent sections to the east. Paleoecologic interpretation indicates accumulation within the middle and outer shelf (depths of 200 to 600 feet) marine environment with open marine circulation.