Abstract

Five fluvial source-bordering eolian dune trends consisting of over 70 mounds and hills were recently recognized on the coastwise Prairie terrace surface in the Florida Parishes1 of southeastern Louisiana, north of Lake Maurepas and Lake Pontchartrain between the Co-mite and Tangipahoa Rivers. Oval plane outlines with dominantly near-parallel long axes characterize the dunes. Maximum dune length is 600 m, width 400 m, and height 10m. The dune sand is uniformly medium grained, mostly very well and well sorted and has predominantly near-symmetrical skewnesses; 2 to 13 percent of the 0.25 mm grains are rounded and well rounded. Surprisingly, no internal stratification is evident in the dunes, possibly due to reworking by biological activity during slow sand accumulation by westerly winds. The climate of dune formation was probably somewhat cooler and considerably drier than the present wet subtropical conditions. Until now the Prairie and other Pleistocene coastwise terrace deposits along the Gulf of Mexico were generally accepted as interglacial formations. New evidence suggests that the dunes, the Prairie terrace surface, and at least the upper section of the Prairie Formation in the study area, may be of Early Wisconsin (glacial) age. Later Wisconsin and Holocene ages are less likely, as the entrenched streams may not have provided adequate dune sand supply.

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