GPR AND GIS USE IN DOCUMENTING A DISTINCTIVE MODE OF STAR DUNE DEVELOPMENT

Research reports that most star dunes occur in clusters or chains and commonly develop from modification of linear or crescentic dunes within a multidirectional wind regime (e.g., Nielsen and Kocurek, 1987; Lancaster, 1989). Our research suggests another mode for star dune development involving the response of transverse dunes to a highly-localized modification of a unidirectional wind regime, resulting in a single, isolated star dune. The Coral Pink Sand Dunes, located in southern Utah, is the site of an ongoing investigation into factors influencing dunefield development.

This research presents the results of GPR transects around an isolated star dune, and the GIS-aided analysis of changes in dunefield organization between 1960 and 1997.Comparison of aerial photographs of the dunefield, acquired in 1960 and 1997, reveal the star dune developed over this period. The early photos show a semi-regular arrangement of transverse dune crests and dune spacing. The later photos show that, in the interim period, the most upwind transverse dune (aka First Dune) became impeded on a bedrock knob and was modified into a barchan-like crescentic dune. Immediately downwind, previously existing transverse dunes responded to the change in wind regime and merged to form a star dune. Interpretation of GIS-mapped dune crests in the two photos suggests the dunefield became less organized for about a kilometer downwind of the star dune, also thought to be a response to modified windflow.

GPR data (100 MHz, 1.0-meter offset, 0.5-meter step) were collected from transects bracketing the star dune and First Dune and provide radar imagery of the sedimentary structure and underlying bedrock of the star dune and First Dune. Processing of the GPR data consisted of a few basic steps, including dewowing and bandpass filtering, migration, and topographic correction. Image acquisition was excellent with up to 20 meter depths recorded.

The presence of high-angle cross-strata in the radar stratigraphy supports the transverse dune parentage of First Dune and the primary limbs of the star dune. This is in contrast to other models of star dune development which report the most common deposits from star dunes to be low- to moderate-angle cross-strata (Nielson and Kocurek, 1987).