ABSTRACT

The Pleistocene-aged Prairie Terrace is an east-west trending deposit of wide lateral extent that crops out in the southern portion of the Florida Parishes, southeastern Louisiana. It is characterized by low topographic relief and low surface gradient. Meandering streams dominate the drainage pattern; quartz sand is the primary component in channel deposits. Deposition of the terrace material occurred primarily during the Sangamon Interglacial period, when sea level stood higher than at present and sediment was being transported by the north-south trending streams and bayous in the area.

The clay mineral suite found throughout the study area is a mixture of smectite, kaolinite, and illite. An alteration zone of hydroxy-interlayered vermiculite (HIV) is present in St. Tammany Parish. The alteration zone represents an intermediate stage in the weathering process, where smectite is being chemically altered to kaolinite. The weathering process appears to occur preferentially in terraces of fluvial origin rather than in marine facies. This is the first recognized occurrence of HIV in late Pleistocene sediment in the eastern Florida Parishes.