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

namely the presence or absence of mica. Mica is expected to be absent in eolian sandstones due to the difference in hardness between mica (Mohs = 2.5) and quartz (Mohs = 7). Observations and experiments show that ballistic impact of grains rapidly abrade and disintegrate mica during wind transport (Anderson et al. 2017, 2013; Marsland and Woodruff 1937). Water, however, provides a cushion between the grains, lessening grain collisions and allowing mica to survive, as suggested by Anderson et al. in their papers. Another example is found in coastal Namibia, where Garzanti et al. (2012) report mica in the Orange River, Kuiseb River, Gaub River, and the shoreline sediments but no mica in either the coastal or eastern dune fields; they credited this compositional discrepancy to the winnowing of micas by longshore currents and followed by deposition in offshore sediments. In Garzanti et al. (2015) the only dune sample in which they found mica was the Suzie dune, which they attributed to “sampling too close to outcrops of metamorphic rocks with the Namib Erg (p. 990)” that contained muscovite. It is important to note that the micas we have found in cross- bedded sandstones are detrital (transported) rather than diagenetic (altered from other minerals post-deposition) in character. For example, muscovite can be formed via the following chemical alteration of K-feldspar (orthoclase): 3KAlSi 3 O 8 (orthoclase) + 2H + → KAl 3 Si 3 O 10 (OH) 2 (muscovite) + 6SiO 2 + 2K + in the presence of an acid (H + ). The mica produced in this conversion is known as sericite, which most often occurs entirely within the host grain, and is visible in thin section as fibrous bundles. Consequently, sericite is generally much smaller than the host grain and randomly oriented. By contrast, many of the micas observed in this study were longer than the matrix grains (size inversion), and the characteristic fibrous textures were not observed. Furthermore, in our samples we observed 1) books of mica bent around other grains (often quartz), 2) contorted mica books with splayed ends, 3) mica grains don’t often occupy the fairly common empty spaces of dissolved K-feldspar grains and 4) significant amounts of orthoclase (often ~8- 15%) are often found in the thin sections along with the mica (i.e., orthoclase has not been diagenetically altered). Together, these clearly indicate that the micas we observed (and show in this paper) are detrital, and thus are part of the original depositional fabric. See Figures 2-9, but especially Figure 10 for numerous examples of these four points. There are some desert sands that contain detrital mica, but in all these cases the mica can be traced to a nearby source, such as an igneous pluton, beach, or wadi. For example, Venzo et al. (1985) report the presence of micas in the southern Algerian Sahara, where the source of this mica is likely the Hoggar Mountains in southern Algeria. We have found micas in various California dunes including in the Palm Canyon area, Johnson Valley, near the Salton Sea, and the Glamis Dunes. In all of these cases the micas (mainly biotite, but also sometimes phlogopite) were well-rounded and either adjacent to or within a few kilometers of igneous bedrock (mostly granite) or wadis. However, the contiguous area of the Coconino and its correlative deposits is many hundreds of kilometers across. If the Coconino was eolian, how could mica reach the center of this giant erg? Mica was not only found along the edges of the Coconino sand body, but everywhere we sampled, and our samples were collected from the entire exposed breadth and width of the Coconino. Field observations and laboratory experiments demonstrate that mica is unlikely to survive more than 10 km of transport by known eolian processes (and certainly not hundreds of km) without disappearing by abrasion. Moreover, there is no sedimentological evidence within the midst of the Coconino sand body of any nearby beach, nearshore or fluvial deposits, which would be the most reasonable sources for the mica. Based on the U-Pb signatures of zircons (Gehrels et al. 2011, p. 197), it is believed that the source of the Coconino sand is the mid- Proterozoic rocks of eastern North America (Appalachian orogen), or possibly, but less likely, from the Ouachita orogen. These authors suggested that large rivers and northeasterly trade winds carried the Coconino sand >3000km from these areas to where it was reworked into dunes during the final stages of the collision of North America with the African continent. We think the zircon evidence is compelling and does suggest a distant origin for some of the Coconino sand. However, the ubiquity of muscovite, as well as angular K-feldspar (Whitmore and Strom 2018), that we have documented in the formation, strongly suggests that the primary mode of transport was some type of aqueous process; eolian transport would have quickly rounded the K-feldspars and caused the micas to disappear. In a conventional model, mica does not have a reasonable way to be transported to the middle of an erg, except perhaps by fluvial processes, and no fluvial deposits are known in the immediate vicinity of the Coconino sand body. On a larger scale, many of the Coconino’s correlatives and stratigraphic units (that laterally or vertically bound the Coconino) are thought by most to be partly or completely marine. Below the Coconino, Blakey (1984) has reported marine sand waves within the Schnebly Hill Formation that in turn grade into typical Coconino lithologies. In the Grand Canyon region, a transitional contact between the water-laid Hermit and the Coconino occurs along Tanner Trail (McKee 1934) and in some places in Parashant Canyon (Fisher 1961). Laterally , the Coconino grades into water- deposited sediments. Peirce et al. (1977) describe what they think is a west to east transition of mostly eolian to mostly water-deposited Coconino along the Mogollon Rim. They report that nearly all of the 90 m of Coconino exposed near Show Low, in east central Arizona, was water-deposited. West of a line from about Sedona to Page, the Coconino “intertongues with and is overlain by the Toroweap” (Blakey and Knepp 1989, p. 336). Some authors also report that cross-bedding style, dip direction and grain size in the Toroweap is indistinguishable from the Coconino in the Oak Creek Canyon area, causing them to interpret part of the Toroweap as eolian (Rawson and Turner-Peterson 1980). Blakey (1990) names the upper part of the Coconino the “Cave Spring Member” and claims that it grades laterally into the Toroweap according to data from Rawson and Turner-Peterson (1980). The Coconino also grades into Toroweap at locations above the Coconino. In northern Arizona, Billingsley and Dyer (2003) report that the Coconino occurs as a thin and discontinuous cross-bedded unit incorporated within the base of the Toroweap. The Coconino probably correlates with the Scherrer Formation, which is a marine sandstone, in southeastern Arizona (Blakey 1990, p. 1216) and transitions eastwards into the Glorieta Sandstone of NewMexico which is also thought to be marine (Baars 1961, p. 199). Whitmore and Garner (2018, in these proceedings) provide some more of these details. Some of the Coconino’s correlatives are discussed in Appendix I, and the references there provide evidence for the marine origin of many of these units. Thus it was not surprising that we found mica in many of those units. In light of the fact that micas are not expected in eolian sandstones, it is odd that we have found micas in so many supposedly eolian sandstones from all over the world. Either every one of these Borsch et al. ◀ Micas in ancient sandstones ▶ 2018 ICC 317