Characterization of hard‐to‐differentiate dune stratification types in the Permian Coconino Sandstone (Arizona, USA)

Abstract

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.

Small-Scale Soft-Sediment Deformation Structures in the Cross-Bedded Coconino Sandstone (Permian; Arizona, United States); Possible Evidence for Seismic Influence

“…Cross-bed dips range from 13 to 27 °. The grains in this strongly-cemented fine-grained sandstone are predominantly quartz (88-95%) with minor amounts of feldspar (Maithel et al, 2019(Maithel et al, , 2021. The internal structure of the cross-beds was described by Middleton et al (2003) as mostly thin laminae (<1 cm thick) that extend a considerable distance down dip within the set.…”

“…The internal structure of the cross-beds was described by Middleton et al (2003) as mostly thin laminae (<1 cm thick) that extend a considerable distance down dip within the set. As in other sandstones, the cross-beds are thought to represent preserved dune foresets, and Maithel et al (2021) suggested that grainflow and grainfall processes were responsible for most fine-scale sediment deposition.…”

“…McKee (1934) was the first to propose and develop an eolian depositional model for the Coconino SS. Subsequent studies followed this work (e.g., Reiche 1938;McKee 1945;Fisher 1961;Sorauf 1962;Lundy 1973;Elcock 1993;Sumner 1999;Maithel et al, 2021), focused on stratigraphic relationships (Blakey and Middleton 1983;Blakey 1990), tetrapod trackways (Brand 1979(Brand , 1992Brand and Tang 1991;Lockley and Hunt 1995;Brand and Kramer 1996;Millhouse 2009;Citton et al, 2012), or sedimentary properties (Maithel et al, 2019(Maithel et al, , 2021. Similarly to McKee (1934), most authors interpret the formation as an eolian dune deposit (Reiche 1938;Baars 1961;Mckee 1974;Blakey and Middleton 1983;Loope 1984;Blakey 1988;Middleton et al, 2003).…”

Analysis of the deposit conditions of sedimentary series of fluvio-lacustrine and aeolian origin in the Djourab desert, in Northern Chad

“…The detailed study of oblique bedding (Figure 5) shows an alternation of avalanche laminae (flow) made up of thick laminae of coarser sand and settling laminae (fall) made up of thin laminae of fine sand. These two types of laminae are described to be characteristic of eolian forests (Hunter, 1977;Maithel et al, 2021).…”

“…These sandy facies composed of fine to very fine sands, not at all cemented (all more recent sandy facies are) is mainly made up of many well-sorted, wellrounded, and non-micaceous quartz grains. For many authors, these are criteria that suggest a wind origin (Hunter, 1977(Hunter, , 1985Swezey, 1998;Maithel et al, 2021). However, the most important criterion is the presence of an alternation of avalanche lamina (flow) and settling lamina (fall) of different particle size, in the oblique bedding (Figure 6).…”