The Proceedings of the Eighth International Conference on Creationism (2018)

types and occur as sand avalanches down the lee slope scooping out and filling a long tongue-like feature on the dune (Fig. 22) which can often extend down the entire length of the lee slope (as seen in Fig. 22). Hunter (1977) illustrates cross-sections of the “tongue- like” features in his paper, which he calls “sand flow cross-strata.” Instead of finding these features in the Coconino, the foreset beds seem to be rather continuous beds of either laminated or massive sand (as it appears in the outcrop). The continuous nature of these beds along strike (Fig. 21) makes it appear that these beds may have formed from some type of continuous avalanche process across the entire lee face of the dunes. Maithel et al. (2013, 2014, 2015, 2016, 2017) have been working on an explanation for the sedimentology of the beds, but to date it does not appear that they are similar to any of the types of stratification in dunes outlined by Hunter (1977). Hunter (1981) reported a number of the features that he identified in modern sand dunes in supposed ancient dunes of the western United States. In his survey of sandstones, he mentions that he was on the Bright Angel Trail and looked at the Toroweap Formation (p. 321), which is just above the Coconino. However, he apparently did not make it down the trail a little further to look at the Coconino (which fails to get mentioned in the paper). However, Hunter recognized that the tongue-like sand flow cross-strata are quite common in modern dunes, but nearly absent in ancient sandstones. He comments (pp. 319-320): Whitmore and Garner ◀ The Coconino Sandstone ▶ 2018 ICC 595 Figure 18 . Chemical frosting of the Coconino sand grains (Whitmore et al. 2012). A. PCT 19 100x-02. A poor to moderately-sorted example of Coconino Sandstone. At this magnification, it is apparent that most of the grains have quartz overgrowths. B. PCT 19 200x-03. Clean crystal faces delineate growth of quartz into open pore spaces. Very few grains in this view do not have quartz overgrowths or clay coatings (authigenic kaolinite and illite). Dissolution of many feldspar grains provided a source for later quartz and clay precipitation. Large open pores, having roughly the same size as the grains, is a possible indication of almost complete dissolution of some grains with the only parts remaining being the clay rims. Undulose and conchoidal fracture surfaces give a “frosted” appearance. C. PCT 19 500x-04. A grain surface exhibiting deposits of individual flakes of kaolinite as well as small booklet structures (middle-upper). This grain surface also has quartz overgrowths present as at lower left. Quartz overgrowths (upper right and upper left) provide an interlocking structure providing cohesiveness to the rock. D. PCT 19 1000x-05. Image of a quartz overgrowth showing conchoidal fracturing (mid lower left), a face with an irregular surface (center) and a highly irregular surface (middle) that is most likely a parted contact between it and an adjacent grain surface. Illite has grown on this surface and is the white, wispy material. The grain surface on the left is highly irregular and is in contact with the quartz cement. This surface appears to be strongly chemically etched rather than abraded. This is not surprising given the degree of dissolution features and precipitation that has occurred in this rock.