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

lineation forms due to a “streamlining effect on loose sand grains parallel with the current direction.” Allen (1970b, p. 68) reports them “on the backs of active [subaqueous] sand ripples and dunes, where there is erosion.” Allen (1985, p. 111) believes that current lineation can form under a variety of subaqueous conditions probably due to parallel vortices traveling in the boundary layer next to the sediment/water interface. Current lineation is a well-known feature of upper flow regime plane beds (Allen 1984; Fielding 2006; Paola et al. 1989). At least one author has suggested that current lineation is also produced in eolian settings, but this was based on observations of the features in sandstones interpreted to be eolian, not observational evidence in actual eolian environments (Tanner 2001). He thought current lineation would only occur at the base of the dunes where grainfall and wind ripples are the dominant sedimentary processes and structures; we have found them on bedding planes far from the lower bounding surfaces where sand flow would likely be the dominant process. Except for this one instance, as far as we know, the literature has only associated current lineation with aqueous deposits. F. “Raindrop” prints It has often been claimed that raindrop prints are one of the most distinctive characteristics that indicate the Coconino is eolian (McKee 1934; McKee and Bigarella 1979a; Middleton et al. 2003; Ranney 2001). Often the crater-like features can even be found with slight disturbances down-dip, as one might expect from a raindrop impact on a steep sandy slope. However, the “raindrop” prints preserved in the Coconino have different characteristics than raindrop prints found in modern settings. First, when most think of raindrop prints, they usually think of well-defined crater-like depressions in mud. But, raindrop prints in sandy substrates do not typically form well-defined crater-like depressions. Instead, the surface becomes rather mottled and the prints do not form distinct craters (Fig. 35). Second, the “raindrop” prints in the Coconino typically occur in linear zones, not in randomly scattered patterns as one would expect (Fig. 36). Third, some things that look like raindrop prints are probably burrows or some other feature because the structures vertically penetrate the sand, some about 1 cm (Fig. 32). At this point we do not know for sure what the “raindrop” prints are. It appears that several different features have been referred to “raindrop” prints. At least some of them are closely related with current lineation features. Since they often form in “zones” perhaps they are related to some type of water or gas escape process occurring between the vortices that form current lineation (Allen 1985, p. 111). Others may be related to burrowing activity (Fig. 34). In any case, we do not think the small crater-like features can be raindrop prints, because raindrops make a mottled surface in sand, not well-defined craters (Fig. 35). G. Ripples In modern dunes, wind ripples can often be found parallel to dip on the lee slopes of dunes, often interfingering with sand flow avalanches. Lee slopes of modern dunes are almost always either covered with avalanches, wind ripples or both (Fig. 22B). Sometimes grainfall deposits are present resulting in a smooth dune surface, but these surfaces are often quickly modified either by avalanches or wind ripples. Down-dip wind ripples form as vortices travel perpendicular to the lee face of the dune, even when the wind is blowing over the top of the dune in a direction that parallels the ripples. Several authors have reported similar ripples in the Coconino (McKee 1945; McKee and Bigarella 1979a; Middleton et al. 2003) and we have found them as well, but they are not as common as one might expect if this was truly an eolian environment. They Whitmore and Garner ◀ The Coconino Sandstone ▶ 2018 ICC 604 Figure 31. Most surfaces of the Coconino foresets are covered with parting lineation features. WSC site. RS photo 0219-2008.