A complex origin for the Kelso Dunes, Mojave National Preserve, California, USA: A case study using a simple geochemical method with global applications

The Kelso Dune field in southern California is intriguing because although it is of limited areal extent (~100 km2), it has a wide variety of dune forms and contains many active dunes (~40 km2), which is unusual in the Mojave Desert. Studies over the past eight decades have concluded that the dunes are derived primarily from a single source, Mojave River alluvium, under a dominant, westerly-to-northwesterly wind regime. The majority of these studies did not, however, present data to support the Mojave River as the only source.We conducted mineralogical and geochemical studies ofmost of the 14 geomorphically defined dune groups of the Kelso Dune field aswell as potential sand sources, alluvial sediments fromthe surrounding mountain ranges. Results indicate that sands in the nine western dune groups have K/Rb and K/Ba (primarily fromK-feldspar) compositions that are indistinguishable from Mojave River alluvium (westerly/northwesterly winds) and Budweiser Wash alluvium (southwesterly winds), permitting an interpretation of two sources. In contrast, sands from the five eastern dune groups have K/Rb and K/Ba values that indicate significant inputs from alluvial fan deposits of the Providence Mountains. This requires either rare winds from the east or southeast or, more likely, aeolian reworking of distal ProvidenceMountain fan sediments bywinds fromthewest, at a rate greater than input fromtheMojave River or otherwestern sources. The results indicate that even a small dune field can have a complex origin, either from seasonally varying winds or complex alluvial-fan-dune interaction. Application of K/Rb and K/Ba in Kfeldspar as a provenance indicator could be used in many of the world\u27s ergs or sand seas, where dune origins are still not well understood or are controversial. Four examples are given from Africa and the Middle East where such an approach could yield useful new information about dune sand provenance