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

“homogenized” zone at the base of the Coconino which is intimately associated with sand injectites. Here porosities are only a few percent compared to about 17 percent average porosity in most of the rest of the Coconino. Typical indicators of compaction in thin section are fractured grains, contorted ooids and mica flakes, extensive stylolites and relatively low porosities. These features are not widespread or common in the sandstone. 3. Sedimentology A. General appearance The most conspicuous feature of the Coconino is large-scale planar-tabular and planar-wedge cross-bedding in sets up to 20 m thick, separated by extensive bounding surfaces (Figs. 2 and 20). Some small-scale sets of trough cross-bedding (<1 m thick) are rarely present. Most of the cross-bedded units consist of thin, laterally continuous parallel laminae (2mm to 15cm in thickness) that can be traced for many meters along strike (Fig. 21). Along- strike cross-sections do not show any hint of concave avalanche beds that are typical on the slip faces of desert dunes (Fig. 22). The sandstone often breaks into slabs about 10-15 cm thick, which makes it ideal for flagstone quarrying operations, especially in the Ash Fork, Arizona area. Large-scale contorted bedding is observed in some localities, notably near Doney Crater in Arizona (McKee and Bigarella 1979a, p. 202) and in the Sedona area (Whitmore et al. 2015). Other occasional features include low-amplitude ripples with crests parallel to dip slopes (Fig. 23), small features within beds that have the appearance of slumps (Fig. 24) and small pits on bedding surfaces (Fig. 25) interpreted by some as raindrop impressions. Detailed work on the sedimentology of the Coconino is in the process of completion by Maithel who has published a number of abstracts (Maithel et al. 2013, 2014, 2015, 2016, 2017). Her work will not be commented on here as it was in the process of completion as this manuscript was being compiled. B. Cross-beds and cross-bed dips In our measurements of over 200 cross-bed dips from widespread locations in the Coconino, we found that the mean dip was about 20º (Fig. 26). This is at odds with some who say the dips are much steeper, closer to the angle of repose (Hill et al. 2016, p. 70), but almost identical with Reiche’s data (1938) who also measured large numbers of dips (Fig. 27). On large exposed foreset beds, cross-bed dip often remains fairly constant down- dip (Fig. 28). Dip only rapidly decreases at the bottom of foresets, less than a meter from the bounding surface. Our data confirmed Reiche’s data showing that the primary dip direction in the Coconino is to the south and southeast. C. Laminae The Coconino laminae are usually 1-2 mm thick and often graded both in outcrop and in thin section, but it is difficult to tell if they are normally or inversely graded because of the lack of clear erosional truncations from one lamina to the next (Fig. 29). In some cases, the rock appears to be laminated in outcrop, but under the microscope the grading is often difficult to find. Preliminary work by Rouse (2017) shows that thin sections that show macroscopic laminae are more poorly sorted than those that do not have visible laminae. She identified laminae as being present by 1) grain size differences, 2) changes in minerals and 3) the presence of stylolites (dissolution features). Some laminae in the Coconino are more massive in nature and occur as thicker, 2-5 cm beds. She also found that most laminae are difficult to trace under the microscope, even over the 5 cm or so length of a thin section. Whitmore and Garner ◀ The Coconino Sandstone ▶ 2018 ICC 585 Figure 5. Amap showing location information for the Coconino sites used in this study (from Whitmore et al. 2014).