ABSTRACT

A series of clays and silty clays with moderately developed paleosols were recovered from three 15 m cores drilled in the Castor Creek member or the Fleming Formation in western Louisiana. These cores were taken to provide stratigraphic control for the outcropping conglomeratic beds bearing small Miocene terrestrial mammal teeth. These fine-grained core sediments and outcropping conglomeratic units were deposited in a fluvial setting.

The conglomeratic units were not penetrated by coring indicating that they are very discontinuous, localized deposits. The sedimentology and distribution of these deposits and a thin interval of poorly sorted, cross-bedded sandstone found in one core, suggest that these coarse deposits formed at the bases of minor channels or gullies. The fine-grained core sediments are floodplain deposits. These thick sequences of massive gray clays with paleosol features such as mottles, roots, root casts, carbonate nodules and slickensides reflect deposition in moderate to well-drained, seasonally wet floodplain backswamps. Intervals of relatively unaltered parallel and wavy laminated silts and clays may represent crevasse-splay development or lacustrine delta-fill.

Moderately developed soil profiles, containing A, B, and C horizons, characterize these fine-grained sediments. Mottle coloring indicating oxidation and possible water table fluctuations is prevalent throughout the paleosols. Roots and large root burrows which characterize A horizons are abundant. Stage II carbonate development is common in most B and some C horizons. Slickensides, resulting from the alternating wetting and drying of soils, are common. In general, these paleosol features support the interpretation of a moderately-drained, seasonally wet fluvial setting.