SCOUR IN AEOLIAN SANDSTONE

Aeolian sandstones, known to be quality petroleum reservoir rocks, are partitioned by internal bounding surfaces. First-order bounding surfaces, formed from the passage of dunes across an accumulating section, divide aeolian sandstones into sets of cross-strata. Prior models of aeolian stratigraphy assume first-order bounding surfaces to be planar, however, that is not usually the case in nature. We investigated the relationship between scour along a bounding surface and the thickness of a set of cross-strata, with the hypothesis that thicker sets will have larger scour depths. Thicker sets are produced by larger dunes, and larger dunes migrate slowly, therefore, exposed interdune surfaces that become first-order bounding surfaces are subjected to more environmental conditions that can lead to scouring. We used a differential GPS to measure approximately every meter along bounding surfaces in various outcrops of Jurassic Navajo Sandstone. Thus far, there are two relationships defined by the data. One population of data appears to have a modest linear correlation where scour is dependent on set thickness. The other population of data indicates that scouring is randomly distributed around 0.2 meters, with no correlation to set thickness, which we attribute to the standard state of scour. Additional measurements are planned and will further refine this relationship. Future work will investigate the relationship between scour and incidence angle, hypothesizing that wind transport at oblique angles to the dune crest leads to more scour from along-crest transport in the interdune. The incidence angle is interpreted from stratification types and dip direction in the preserved sets. Future work will also focus on using a cellular automaton model called the Real-Space Cellular Automaton Laboratory (ReSCAL) to capture realistic bounding surface geometry, set accumulation, and stratification type based on our field measurements.