Abstract

Wavelengths of hummocky cross-stratified (HCS) beds (a common sedimentary feature of storm-dominated shorefaces) are documented for the first time using measurements in three-dimensional (3-D) ground-penetrating radar (GPR) data for a well-developed Upper Cretaceous lower-shoreface succession at Dry Wash in the Ferron Sandstone Member, Utah. The shallow-marine sequence consists of upward-thickening HCS sand beds alternating with interstorm deposits. The thickness variation of the storm beds indicates locally steadily growing storm intensity with at least four cycles. Weakly coarsening-upward (mud to very fine-grained sand) fair-weather background deposits suggest a slow progradation of deposition with no significant change in environment.

The GPR interpretation mapped three conformable, high-continuity, high-amplitude reflections throughout the 3-D GPR data volume. The interpreted radar surfaces (RSs) are well correlated with tops of HCS sand beds (and thus paleotopographic surfaces); the associated radar units (RUs) have a uniform thickness (on average ∼0.8 m [∼2.6 ft]). The RUs and the adjacent outcrop observations suggest that the shoreface sandstone at the Dry Wash site has a simple layered internal architecture. The hummocky-swaley surfaces generally dip westerly, as a product of postdepositional structural alterations that are mostly in the shoreline direction, and contain variable-size, structurally undulating rounded features.

A 2-D continuous wavelet transform analysis is applied to the detrended RSs, producing a multiresolution image decomposition of the GPR surfaces. Surface features with a wavelength range of 1–7 m (3–23 ft) are in good agreement with the observations on modern hummocky shallow-marine seabeds. Quantitative measurements indicate that the hummocky surfaces at the Dry Wash site are dominated by uniformly distributed circular to elongate bed forms with maximum correlation at 1.5–3.5-m (4.9–11.4 ft) wavelength and that the deltaic sedimentary layers were simultaneously deformed by the middle Campanian compressional stress of the Sevier orogeny transmitted from the northwest. Quantitative information on the subseismic-scale surface geometry of the HCS beds is expected to result in more refined reservoir models. In addition, the connectivity of units indicated by the scale of the morphology can be an indirect indicator of unit correlation and permeability paths.

You do not currently have access to this article.