The Hopeman Sandstone is a cross-bedded sandstone of Permo-Triassic age that crops out in coastal exposures in northeastern Scotland. Although the unit has traditionally been interpreted as an aeolian deposit, partly on the assumption of well-sorted, well-rounded quartz sand and lack of micas, no detailed thin-section studies have been published to confirm these conclusions. The following report employs petrographical analysis to quantify the sorting, rounding and mineral composition of the Hopeman Sandstone. Our results indicate that the formation is not as well sorted or well rounded as previously suggested and that it contains significant orthoclase and trace amounts of muscovite, which may suggest that depositional models for at least some facies within the unit need to be revised. This report serves as a preliminary analysis of unusual textural trends across the Hopeman Sandstone and should prompt additional research to further characterize and interpret the sedimentology of the formation.
The Permian Coconino Sandstone is one of the most prominent layers of rock in the Grand Canyon and is important to creationists because it has often been used by conventional scientists to discredit the Bible since it is a supposed windblown (eolian) deposit. Their argument is that deposits like this would be impossible to form in the midst of a global flood as described in Genesis. Over the past forty years, new data has been collected by us and others that we believe indisputably identifies the Coconino as a subaqueous sandstone-data that will be difficult for our critics to counter. These data include evidence from petrology, fossil footprint studies, sedimentology, regional stratigraphy and soft sediment deformation features. In our studies we found that there are many misconceptions or "urban myths" about the Coconino Sandstone including its grain roundness, grain sorting, grain frosting and angle of cross-bed dips. There are no modern analogs that match the precise sedimentology of the Coconino, but we believe that subaqueous sand waves may be a start in the right direction to understand how the Coconino was deposited. Instead of the Coconino being a problem for creationists, it can be one of our most powerful arguments in support of the biblical account of the Flood. There are many other similar cross-bedded sandstones around the world; the Coconino may be the key to unlocking their origin as well.
According to evolutionary theory, the origin of tetrapods (or limbed vertebrates) from a fish-like ancestor during the Devonian Period was one of the major events in the history of life. Devonian sediments have yielded several families of tetrapod-like fishes, including the elpistostegids which range from the Givetian to Frasnian of the Middle to Upper Devonian and are regarded as close to the evolutionary ancestry of tetrapods. Two of the best-known 'early' tetrapods are Ichthyostega and Acanthostega, first described from fossil material discovered in the Famennian (uppermost Upper Devonian) sediments of East Greenland. These taxa (and others subsequently described) display mosaic combinations of fish-like and tetrapod-like characters, along with some unique traits (such as polydactyly) not found in more 'derived' tetrapods. Creationists have claimed that these organisms are not evolutionary intermediates, but were rather the inhabitants of aquatic environments associated with a pre-Flood floating forest biome, with morphologically intermediate traits that equipped them for life in an environment that was itself intermediate between the sea and the land. This paper evaluates the baraminic status of a range of Devonian and Carboniferous fishes and tetrapods using the techniques of statistical baraminology. Baraminic distance correlation (BDC) and three-dimensional multidimensional scaling (MDS) are applied to six previously published character-taxon matrices. The results reveal little evidence of continuity, and significant evidence of discontinuity, between the elpistostegids and tetrapods such as Ichthyostega and Acanthostega, consistent with the creationist claim of separate ancestry. However, further work will be required to elucidate the baraminic relationships within these presumably apobaraminic groups.
Edwin McKee published the first comprehensive study of the Coconino Sandstone in 1934, and since then, little original research has appeared on this prominent Grand Canyon formation. Over the past 20 years, we visited numerous outcrops covering the thickness and areal extent of the formation and studied 400 thin sections with the goal of better understanding the nature of this well-known but little-studied formation. The following is a summary of our published findings. Regarding petrology, the sand has an average grain size of about 3.0 ф, is moderately sorted, subrounded to subangular and increases slightly in grain size and sorting from north to south (in the same direction as cross-bed dip). Dolomite occurs widely as occasional beds, ooids, clasts, cement and rhombs. Detrital muscovite occurs in nearly every thin section; sometimes the flakes are bigger than the quartz grains that surround them. Detrital K-feldspar comprises about 10% of most samples and is often angular or subangular. Thin sections show little indication of significant compaction, most having 10-15% porosity. Regarding sedimentology, our large data set of cross-bed dips average about 20º and are similar to Reiche's data (1938). Narrow grainflow tongues, which commonly occur on eolian dunes, were not observed; instead, parallel laminae can be traced for many meters along strike on bounding surfaces. Patterns resembling primary current lineation occur on most foreset surfaces and trend down-dip. Especially in western outcrops of Coconino, linear bands of circular pits can be found, also trending down dip. Along Tanner Trail, the Coconino interfingers with the underlying Hermit Formation. Our published data suggest that tabular sand bodies extending downward into the Hermit in Grand Canyon are sand injectites and not desiccation cracks due to their orientation, internal structure, association with the Bright Angel Fault, and the sparsity of clay (< 3%) in the Hermit. In Sedona, multiple examples of large-scale soft sediment deformation features, confined between sets of planar-and cross-beds, extend continuously for 50-400 m in dip direction. The deformation matches the characteristics of subaqueous parabolic recumbent folds. Considering all these data, it is time for more work in order to refine depositional models for the Coconino Sandstone.
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