AN ALTERNATIVE EXPLANATION FOR PLANT-BEARING "VARVED" SEQUENCES FROM THE WILBANKS CLAY PIT (MIDDLE EOCENE), WESTERN TENNESSEE

Western Tennessee clay deposits belonging to the Middle Eocene Claiborne Formation have yielded abundant plant fossils and have been well studied taxonomically; however, little agreement exists concerning their depositional environment or the events which formed the deposits. Clay lenses consisting of leaf-bearing dark-light "varved" laminae are typical. Berry (1916) suggested a tropical paleoenvironment laced with sluggish fresh water streams which allowed the suspended clay and organic materials to slowly settle out resulting in the formation of the clay deposits. Dilcher (1971) proposed a more seasonally dry subtropical to tropical paleoenvironment with clay deposited in abandoned oxbow channels or small lakes as a result clay particles settling out of seasonal flood waters over many years. As a result of study of the Wilbanks Pit, we suggest an alternative explanation for the varved nature. Well preserved, complete, undecayed leaves belonging to the families (in deceasing order of abundance) Moraceae, Legumacea, Lauraceae, Anonaceae, Taxodiaceae, and Theaceae, with additional members of the Apocynaceae, Sapindaceae, Myrtaceae, Anonaceae, Tiliaceae, Nyssaceae, Hamamelidaceae, and Fagaceae, suggest plants inhabiting annually wet soils to soils that are well drained and upland. The occurrence of well preserved leaves within single laminae belonging to upland/lowland assemblages, consistancy of clay sedimentology through the sequence, lack of change in flora vertically, absence of disrupting biogenetic structures, and "varve" like repetitions indicates that all of the "varves" may have formed in a short interval of time, rather than seasonally, as the result of repeated influxes during a single rainy season.