Sedimentology of Great Sand Dunes, Colorado

Abstract

Eolian and adjacent deposits of Great Sand Dunes Colorado form a small but sedimentologically complex deposit Eolian sediments can be subdivided into three provinces trending downwind northeast I low as much as 10 m high alkali cemented dunes forming discontinuous rings around broad flat bottomed ephemeral lakes II undulating vegetated dunes as high as 10 m of barchan parabolic shrub coppice and transverse type with varying interdune types III high as much as 200 m transverse dunes with little or no vegetation and no true interdune deposits Eolian deposits are in contact with or intercalated with fluvial lacustrine and alluvial fan deposits and lap onto crystalline basement rocks of the Sangre de Cristo Range. Analysis of a 40 year-span of aerial photographs and field observation of sand transport and cross bedding dip directions indicate that the main dune mass province III is accreting vertically and that dune types are growing in complexity in particular the star dunes This change from lateral migration to vertical growth most probably reflects Holocene changes in wind regime. The Great Sand Dunes are an example of a localized cool climate intermontane eolian deposit characterized by extensive fluvial reworking With its rapid variation in thicknesses sedimentary structures and associated sedimentary deposits such a deposit would be difficult to interpret accurately in the ancient rock record However such a deposit could be of economic importance in petroleum and uranium exploration and in aquifer evaluation