147 Structural Geology / Tectonics / Neotectonics/Paleoseismology (Posters)

Sand Blows on Late Quaternary Surfaces in Northeast Louisiana

Paper number: 147-7
Program: Technical Sessions
Time: 8:00 AM – 4:45 PM

Authors

Abstract

Three areas of light tonal anomalies on 1941 aerial photography in central Morehouse, southern Richland, and northern Franklin Parishes, northeast Louisiana are of the same size (~20 m diameter), shape (circular to elliptical), and arrangement (branching alignments) as seismogenic sand blows in southeast Arkansas (where sand blows often have the branching patterns of crevasse splay source sands). However, sand blows are easily confused with relict eolian pimple mounds on aerial photography. Indeed, sand blows were misidentified as pimple mounds on southeast Arkansas aerial photography until sand dikes were discovered by recent trenching. Typically, sand blows are found on liquefiable Holocene alluvial terraces and pimple mounds are found on Pleistocene terraces. The identity of these light spots is difficult to field check because decades of plowing and land-leveling of farmland have removed pimple mounds and sand blow deposits from the landscape and relief is very low making subsurface exposure rare.

Reconnaissance of central Morehouse Parish revealed sand bodies on middle-late Holocene terraces and small sand dikes exposed in a ditch, and we conclude this area to be a sand blow field. It is unlikely northern Franklin Parish contains sand blows because we found no sand bodies, we found an undisturbed acreage with prominent pimple mounds, and the light spots on photographs are on a late Pleistocene terrace. In southern Richland Parish, surficial sand bodies correspond to light spots on photographs and no pimple mounds could be found. However, these sand bodies are on a late Pleistocene terrace, so we cannot conclude this to be a sand blow field at this writing. Trenching in Morehouse and Richland Parishes scheduled for Fall 2008 will verify the identity of these features.