way as many of the sandstone measurements. Much other data were found but could not be used because it was reported in the form of histograms, like the Nebraska Sand Hills data (Ahlbrandt and Fryberger 1980). The data points in both sets probably could have been doubled if individual measurements had been reported. When individual measurements were reported, sometimes the plots were not sharp and there was some overlap of the points. It is not known from any of the sets whether the data were collected randomly, if every accessible point was collected, or if some data were ignored in favor of collecting easier measurements. This might have been especially true of the dune data because avalanching occurs so readily on steeper slopes. When collecting my data from sandstones, I always tried to spread out my measurements over a wide area, trying to collect reliable data from all exposed crossbed sets. In particular, I looked for flat, well-exposed foresets from which I could obtain reliable measurements. I tried not to ignore steep cross-beds or shallow ones, trying to make my measurements a representative sample of the exposures. Attempts were made not to repeat measurements on the same foresets. The assumption was made that other workers collected their data in much the same way that I did (authors almost never give precise details on how they make their strike and dip measurements). It is noteworthy that much of the data in this report (both sandstone and dune) were collected by Edwin McKee and his associates (like João Bigarella) who were firmly convinced of the eolian origin of sandstones like the Coconino and Navajo (see McKee and Bigarella 1979a). If someone was biased toward an eolian origin of a particular sandstone, they might tend to collect steeper dips over shallower ones. However, I am encouraged that my Coconino data set compared very favorably with that of Reiche (1938) and Maithel (2019), possibly indicating that the data in these three cases were consistently collected, despite philosophical differences. It is curious that McKee never reported any detailed data of his own Coconino cross-bed inclinations despite writing the first detailed paper on the Coconino (1934); using the Coconino as a “type” example of an eolian sandstone (McKee and Bigarella 1979a); and publishing extensive data on cross-bed inclinations of other formations, primarily in the Grand Canyon area (1940, and 1982). McKee seemed to ignore the data of Reiche (1938) when he reported the cross-bed inclinations in the Coconino were “mostly at 25-30°, but a few reach a maximum of 34°” (McKee and Bigarella 1979a, p. 199), although he was certainly aware of Reiche’s work (1940, p. 812). Fig. 10. A comparison of cross-bedded sandstone dip angles with “compacted” eolian dip angles (compare Fig. 7). The claim is often made that supposed eolian cross-bedded sandstones lack steep dip angles because the eolian sands have been compacted, lowering the dip angles by about 24% (according to Corey et al. (2005) and Walker and Harms (1972)). To test whether this is a reasonable hypothesis or not, each eolian dip from Fig. 7 was compacted 24% and then re-plotted with the sandstone dips to get an approximation of what the compacted dune angles would look like. Steeper cross-bed dips would be more affected than shallower ones. The result shows the two distributions do not match. A reasonable conclusion is that cross-bedded sandstones could not have been derived from compacted eolian dunes. In the past, most workers have focused on the average angle or the missing steep angles in sandstones. However, this distribution shows an even bigger problem: the missing shallow angles in sandstones. Note the bell-shaped curve of the sandstones. The eolian dune curve has become, more or less, a bell-shaped curve that is skewed to the right. It has largely lost the bimodality seen in Fig. 7. The curves were generated with Microsoft Excel using a 6th-order polynomial trendline fit. The R2 value for the sandstones was 0.98 and 0.66 for the compacted eolian dunes. The ends of the curves were truncated, as they contained some negative values and were beyond the set of data. WHITMORE Cross-bed inclinations 2023 ICC 607
RkJQdWJsaXNoZXIy MTM4ODY=