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

DISCUSSION: DATA SUGGESTS A SUBAQUEOUS ORI- GIN FOR THE COCONINO 1. Areal extent and thickness The areal extent and thickness of many modern ergs are quite small compared to the Coconino and other ancient cross-bedded sandstones of similar nature (Table 3). Many of the larger ergs, for example those in northern Africa (“the Sahara”), are separated by large swaths of bare rock and sparse vegetation; so, the ergs are not directly continuous with each other. This is not true for the geological record. Sandstones like the Coconino can be traced through outcrops and cores (understanding some has been removed by erosion) for its entire extent. From examining Table 3 it quickly becomes clear that ancient cross-bedded sandstones are orders of magnitude different from modern ergs in areal extent and especially thickness. Pye and Tsoar (2009, p. 155) recognize this and offer three possible explanations for the differences: 1) there has been preferential preservation of ancient sequences because they were deposited in slowly subsiding basins or rift valleys, 2) some thick sequences represent multiple stacked ergs, 3) eolian processes may have been more effective in the past, especially before the development of land plants. Explanation (1) does not seem to apply to the Coconino because it crosses through many ancient basins. It does thicken and thin through these areas, like the Sedona Arch (Blakey and Knepp 1989). Explanation (2) may explain parts of the Coconino, especially in the Sedona area where there appear to be two members of the formation which Blakey (1990) calls the “Cave Springs Member” (upper part) and “Harding Point Member” (lower part). The contact is flat with no relief and forms a “green line” of vegetation about in the middle of the formation. Explanation (3) does not seem plausible because on a conventional time scale plants were around at least 100 million years before the Coconino was formed. These explanations do not seem reasonable for the Coconino or many of the other ancient cross- bedded sandstones. However, marine deposits do have the characteristics of being areally extensive and thick. 2. Petrology A. General petrology There is a great misconception that all desert sand grains become “well-rounded” over time. In a study of nearly 22,000 sand grains from many dunes, Goudie and Watson (1981) found very few “well-rounded” grains. Roundness is typically measured with a scale developed by Powers (1953) and modified by Folk (1955) which is shown in Fig. 46. Goudie and Watson found that sand grains in the 2.5 ϕ range had a mean roundness of 3.19 and in the 3.5 ϕ range had a slightly lower mean roundness of 3.04. Both of these values are on the lower end of the subrounded category. However, it is noteworthy that only negligible rounding takes place during non-eolian transport of sand grains. This has been observed in many experimental and real-world situations (Garzanti et al. 2012, 2015; Kuenen 1960; Russell and Taylor 1937; Twenhofel 1945). In the Garzanti et al. (2012, 2015) studies, sand was traced for hundreds of kilometers along the southwestern shoreline of Africa and no noticeable rounding occurred (despite active tidal and longshore currents) until the sand was picked up by eolian processes and transported to the Namib dunes. Then, “all minerals get rapidly rounded” (2015, p. 971). In considering ancient deposits that consist of nearly pure quartz grains and have abundant rounded and well-rounded grains (like the Ordovician St. Peter Sandstone, midwestern US) the consensus of most authors seems to be that the sand has endured multiple generations of eolian processing and that the “roundness” may not have come from the last depositional event (e.g., Dott 2003). Evidence for this is in the form of multiple Whitmore and Garner ◀ The Coconino Sandstone ▶ 2018 ICC 591 Figure 11. Map showing the extent and type of dolomite within the Coconino Sandstone (from Whitmore et al. 2014).