Origin of late quaternary dune fields on the Southern High Plains of Texasand New Mexico

Mostly stabilized late Holocene eolian sands on the Southern High Plains of the United States were studied to determine their origins and to assess wh ether present dune stability depends more strongly on sediment supply, sedi ment availability, or transport limitations. Geomorphic, sedimentological, and geochemical trends indicate that late Holocene dunes formed under weste rly paleowinds, broadly similar to those of today. Mineralogical and geoche mical data indicate that the most Likely source for the sands is not the Pe cos River valley, but the Pleistocene Blackwater Draw Formation, an older, extensive eolian deposit in the region. These observations suggest that new sand is supplied whenever vegetation cover is diminished to the extent tha t the Blackwater Draw Formation can be eroded, in agreement with modern obs ervations of wind erosion in the region. We conclude, therefore, that South ern High Plains dunes are stabilized primarily due to a vegetation cover. T he dunes are thus sediment-availability limited. This conclusion is consist ent with the observation that, in the warmest, driest part of the region (w here vegetation cover is minimal), dunes are currently active over a large area. Geochemical data indicate that Southern High Plains dunes are the mos t mineralogically mature (quartz rich) sands yet studied in the Great Plain s, which suggests a long history of eolian activity, either in the dune fie lds or during deposition of the Blackwater Draw Formation.