Loess and Quaternary Geology of the Lower Mississippi Valley

Abstract

A wealth of evidence demonstrates the Pleistocene age of the four depositional terraces which border the lower Mississippi alluvial valley and form the broad coastwise plains of Louisiana and Mississippi. This evidence also conclusively proves that the Mississippi Valley alluvium is of Recent age and fills a deeply entrenched valley system eroded during the late Wisconsin glacial stage. Both the Recent age and the mineralogy of the alluvium make it an impossible source for the several loess "formations" as described in the region by M. M. Leighton and H. B. Willman. Furthermore, the age of their loess "formations" does not conform with the age of the Pleistocene terrace deposits which the loess mantles. The distribution of lower-valley loess, its topographic expression, the absence of associated sand dunes and fossil trees, and the presence of colluvial features make it difficult to accept the hypothesis of eolian origin for loess in this region. The loessification theory held by R. J. Russell is the only hypothesis yet proposed that is in accord with known facts.