Stratigraphic architecture resulting from dune interactions: White Sands Dune Field, New Mexico

Aeolian dune interactions provide the dynamics for field-scale pattern emergence and evolution within a set of boundary conditions. Although morphologies for a spectrum of dune interactions are recognized, associated stratigraphic architectures are unknown and have probably been misidentified in the rock record. A unique data set for the White Sands Dune Field in New Mexico (USA) allowed for a detailed analysis in which the morphological evolution of defect and bedform repulsion interactions is chronicled over a decadal time-series of images and coupled with the resulting stratigraphic architecture, documented from cross-strata exposed in interdune areas and ground-penetrating radar imaging of dune interiors. Defect and bedform repulsions represent a class of interactions in which the faster-migrating dune termination or defect (defect repulsion), or pair of defects (bedform repulsion), collides with the target dune downwind. Results document that during the collision, the defect(s) of the impactor dune recombine(s) with a segment of the target dune, and the redundant target dune segment is ejected as a parabolic-shaped ejecta dune. The ejecta dune assumes a more barchanoid shape as it migrates downwind. The interaction architecture consists of lateral truncation of the target set by an interaction bounding surface. Defect cross-strata tangentially approach the surface in plan-view, and downlap onto the surface in cross-section. The orientation of the defect cross-strata is at an acute angle to the trend of the interaction surface. Orientations of the defect cross-strata, which represent the defect approach angle, and the target dune cross-strata, which represent the general dune migration direction, diverge at a high angle. Defect cross-strata typically consist of wind-ripple laminae, in contrast to the target set that may house grainflow cross-strata. In the transport direction, the erosional interaction surface curves to become subparallel to subjacent and superjacent cross-strata where the defect and target unify into a single lee face.