AEOLIAN INTERNAL COMPLEXITY THRESHOLD AS A NEW APPROACH FOR DISTINGUISHING DUNE MORPHOTYPES IN SUBSURFACE RECORDS: WHITE SANDS, NEW MEXICO

Aeolian landforms are classified based on their plan morphology, making two-dimensional exposures insufficient for discriminating between 3D morphotypes (e.g., barchans vs. parabolic dunes). More than 25 km of high-resolution (500 MHz) ground-penetrating radar (GPR) data from the gypsum dunefield of White Sands National Monument, New Mexico were used to characterize the dip-section architecture of end-member morphologies. For dunes of comparable size (6-10 m high), a series of attributes were analyzed for unsaturated portions along the thickest (centerline) radargram sections. Given the limitations in vertical resolution (~8 cm in dry sand), the average slipface thickness in barchans ranges between 13.8-16.2 cm, whereas parabolic slipfaces are thinner at 11.5-13.1 cm. High-amplitude diffractions produced by buried vegetation, semilithified pedestals, and bioturbation structures are rare within barchans (0.01/m; targets per 1-m-wide cross-sectional area of the image), in contrast to 0.20/m in parabolics. We propose an aeolian internal complexity threshold – ϖ, which is a volumetric parameter that incorporates slipface thickness, area free of point-source diffractions (an inverse of diffraction density), and continuity of major bounding surfaces at mesoscale range resolved in available radargrams. For the study region, the first two variables are sufficient for discriminating barchan (high ϖ) and parabolic (low ϖ) dunes, with the analyzed attributes of 2D transitional dunes falling between these end members. The integration of GPR reflection continuity via semivariogram analysis will extend the utility of the proposed threshold to other dunefields and to the aeolian rock record.