Paleoecological Aspects of a Late Wisconsinan Aquatic Mollusk Assemblage Associated With Mastodon Bone Recovered From the North Fork of Ward Creek, Baton Rouge, Louisiana

Abstract

A well-preserved freshwater molluscan assemblage is documented and illustrated. The malocofauna was collected from sediment samples closely associated with mastodon ulna fragments recovered from the base of a stream-cut bank in Baton Rouge, Louisiana in 1991. Mollusks and mastodon bone were deposited in a clay sediment varying to silty clay loam, dated 21,220 .±. 360 yr B.P. The mollusk assemblage is indicative of a perennial, well-vegetated, quiet, shallow water environment. Mollusks differ markedly from typical Peoria Loess mollusks. It is suggested that the clay/silty clay loam containing fossil mollusk shell and mastodon bone correlates with properties of basal zone loess reported by Miller and others (1985) as forming a transition zone between the Prairie Terrace and initial late Wisconsinan loess. Shell dates, soil traits, mollusk species, and paleoecology suggest that the excavation unit yielding a fossil mastodon ulna is part of a late Pleistocene swamp subsurface where Prairie Terrace clay combined with silts derived from reworked eolian loess as well as from probable glacial silt depositions. The fossil mollusk assemblage may be indicative of basal mixed zones in other localities.