>I have found a major sedimentological difference between dunes deposited
>beneath the sea and those which are found above. I am currently looking for
>evidence either way from the Coconino and Navajo sands. I got a 400 article
>literature search today on these two deposists.
>
>The difference between these two types of dunes involves the smallest levels
>of crossbedding.
>
>"All the basic types of stratification found in dry windblown sand can also
>be found in water-laid sands. As far as is known, eolian and subaqueous
>planebed lamination cannot be distinguished by their structural
>characteristics, nor can eolian and subaqueous grainfall lamination. Eolian
>and subaqueous sandflow cross-strata of small slipfaces show some fairly
>consistent difference, but the differences between eolian and subaqueous
>climbing-ripple structures are even more distinct. The subcritically
>climbing translatent strata produced by subaqueous current ripples generally
>have distinct ripple-foreset crosslamination and are normally graded; both
>of these featrues re evidently produced by miniature sandflows down the lee
>slopes of the ripples. Other differences between eolian and subaqueous
>climbing-ripple structures are related to differences in the
>height-to-spacing ratios and plan forms of the ripples." ~Ralph E. Hunter,
>"Basic Types of Stratification in Small Eolian Dunes," Sedimentology,
>24(1977):361-387, p. 384-385
I don't see anything in these paragraphs that can be cited as a"major
sedimentological difference" unless by this you mean "smallest levels" or
"cannot be distinguished by their structural characteristics" or "generally
have" :-), but hyperbole aside (since I never am guilty of that myself),
these subtle bedforms are extremely difficult to see, even in the modern
environments, and I haven't seen them used to discriminate
paleoenvironments, probably because they are so subtle and difficult to
quantify.
>
>Other items which should be found if the dunes are subaqueous.
>
>1. Fish-droppings
There is no organic material found in the Coconino at all, except in the
marine interbeds. I think this rules out finding fish droppings.
>
>2. glauconite(which is generally accepted as being marine in spite of that
>GSA article)
I am glad to hear your accord on that point. We have been using the
tremendous quantities of glauconite to argue for deep water deposition of
the Tapeats, but have met considerable resistence to this from other
researchers who have worked on Cambrian clastics. Of course their
arguments are pretty much ad hoc, since they, like McKee have decided that
the deposition is shallow on the basis of sed structures representative of
shallow water deposition in the modern environment.
>
>3. no caliche. I know of no way for caliche to be deposited beneath the sea
>since its formation requries evaporation. (C. M. Rice Dictionary of
>Geological Terms, p. 463) The mongolian dunes have multiple caliche horizons
>
Good. caliche is certainly not present in the Coconino, anyway.
Now back to the Nubian. A stable depositional environment for 260 years,
across the Devonian, the Pennsylvanian, the Permian, the Great Permian
extinction, the Triassic, Jurassic and Cretaceous, there was only
continuous deposition of pretty much uniform sand, apparently uninterrupted
by major events that characterize sediments everywhere else? And a few
miles to the east, not a grain of sediment deposited during the same
interval, so that Lower Devonian sand is in sedimentological conformity
with Mid Cretaceous sand? Doesn't that beg for an explanation?
Art
http://chadwicka.swau.edu