Dune stratification types, which include grainfall, grainflow and ripple lamination, provide a record of the fine-scale processes that deposited sediment on palaeo-dune foresets. While these facies are relatively easy to distinguish in some cross-bedded sandstones, for otherslike the Permian Coconino Sandstone of northern and central Arizonadiscrete stratification styles are hard to recognize at the bedding scale. Furthermore, few attempts have been made to classify fine-scale processes in this sandstone, despite its renown as a classic aeolian dune deposit and Grand Canyon formation. To interpret depositional processes in the Coconino Sandstone, cross-bed facies were characterized using a suite of sedimentary textures and structures. Bedding parameters were described at multiple scales via a combination of field and laboratory methods, including annotated outcrop photomosaics, strike and dip measurements, sandstone disaggregation and laser-diffraction particle analysis, high-resolution scans of thin sections, and scanning electron microscopy. Cross-beds were observed to be laterally extensive along-strike, with most dip angles ranging from the mid-teens to mid-twenties. While some cross-bed sets are statistically coarser near their bases, others exhibit no significant vertical sorting trends. Both massive and laminated textures are visible in high-resolution scans of thin sections, but laminae contacts are commonly indistinct, making normal and reverse grading difficult to define. Diagenetic features, such as stylolite seams and large pores, are also present in some samples and might indicate alteration of original textures like detrital clay laminae and carbonate minerals. Observed textures and sedimentary structures suggest that the cross-beds may consist of grainflow and grainfall deposits, but these remain difficult to differentiate at outcrop and thin-section scales. This characterization of fine-scale processes will play a critical part in the development of depositional models for the Coconino Sandstone and elucidate interpretations for similar cross-bedded formations.

Sandstone textures provide critical information for reservoir modeling and interpreting depositional processes. While loose sand textures are easy to describe, various authors have developed thin-section and image-analysis techniques to characterize lithified deposits that were assumed impossible to disaggregate successfully. These methods are effective but tedious, and are generally not feasible for processing many samples. We present a new methodology for disaggregating quartz-dominated sandstones cemented by quartz overgrowths, with application to the Permian Coconino Sandstone of northern and central Arizona, USA. Textural parameters of the disaggregated sand were measured using a laser diffraction particle analyzer. Our average grain sizes from laser analysis are coarser than those from thin section (as expected), but trends from the analyzer correlate well with thin-section results. This strong correlation strengthens the validity of both methods and suggests that disaggregation and whole-particle analysis may effectively replace petrographic techniques in many textural studies. We hope that our methods, which increase the efficiency of grain-size analysis, will expand the potential for collecting textural data from quartz-cemented sandstones.

The Hopeman Sandstone is a cross-bedded sandstone of Permo-Triassic age that crops out in coastal exposures in northeastern Scotland. Although the unit has traditionally been interpreted as an aeolian deposit, partly on the assumption of well-sorted, well-rounded quartz sand and lack of micas, no detailed thin-section studies have been published to confirm these conclusions. The following report employs petrographical analysis to quantify the sorting, rounding and mineral composition of the Hopeman Sandstone. Our results indicate that the formation is not as well sorted or well rounded as previously suggested and that it contains significant orthoclase and trace amounts of muscovite, which may suggest that depositional models for at least some facies within the unit need to be revised. This report serves as a preliminary analysis of unusual textural trends across the Hopeman Sandstone and should prompt additional research to further characterize and interpret the sedimentology of the formation.

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