>If this were a global flood, why the change in facies over such a short
>area? Why wouldn't some of those pebbles and cobbles make it far out into
>the sand dunes?
But it is you that keeps insisting this is a part of a global flood. I
have made no such assertion. In fact the cobbles and pebbles did make it
far out into the dune field, and even form a layer of conglomerate across
an extensive area of the deposit.
>
>Secondly, if the sands in Mongolia and other places were deposited in the
>ocean, why no glauconite, a mineral associated strongly with marine
>deposition? Why no fish fossils because surely the flood waters would
>contain a few fish to be captured with the dinos? Why are the dinosaurs
>found over circular nests which are carefully laid out with narrow ends of
>the eggs pointing in toward the center? When in a global flood would a dino
>have time to lay a clutch of eggs? Afterall there are several thousand feet
>of flood deposited sedimentary rock beneath the egg nests.
Again, you are painting my model for me. I have not tried to place this in
any scenario, I am just asserting certain findings of the most recent study
that support a reinterpretation as a shallow water deposit. There would be
no glauconite here unless the source area was glauconitic sand. I am not
arguing that the dinosaur nests are anything but what they appear to be.
Quit putting models in my mouth!
>And here I need a piece of information. I can't find a description for
>rhizolith in my geological dictionaries. Do you have a dictionary that would
>give me an official definition of a rhizolith? The Djadokhta Formation of
>Mongolia and Inner Mongolia has rhizoliths. My recollection from memory is
>that a rhizolith is a caliche or carbonate deposit which formed around
>roots. Such trace fossils are found in the Eolian (dune) deposits at Bayan
>Mandahu in the Djadokhta formation. (T. jerzykiewicz, et al, "Djadokhta
>Formation Correlative Strata in Chinese Inner Mongolia:..." Geological
>Survey of Canada Contribution 39793, Can. J. Earth Sci. 30:2180-2195(1993)
That is a correct definition of rhizolith. Lots of studies have been done
to ascertain the nature of these things, because they superficially
resemble roots in general aspect, and are often found where various
investigators might anticipate seeing roots. It remains problematic to
assign them wholesale to "roots", since there are rarely if ever actual
preserved tissues associated with the nodules. They probably do represent
the results of organic material case hardening of the surrounding matrix.
>I am not sure that this is true. There are a lot of cores taken in
>various marine environments.
True, and many of the same types of bedding structures found in modern
shallow, fluvial and subaerial environments are found associated with deep
water submarine fan sequences. We have been compiling a list of these, but
it is not complete yet.
>Is there any purely marine mineral found in either the Coconino, Navajo or
>in the Mongolian deposits?
What is a purely marine mineral? If you are talking about glauconite, it
is found in some non-marine deposits today, due to weathering out of
glauconite from marine deposits (although its half life in a sandstorm
would be about zip), and you may remember a paper at GSA a couple of years
ago entitled "The Present is not the Key to the Past" that had to do
specifically with the occurrence of glauconite (which today is formed only
in deep marine settings), in which the author was lamenting this
observation because so many of the glauconitic marine sands in the fossil
record (like the Tapeats) are currently described as shallow marine because
of the sed structures they exhibit that have traditionally been used as
shallow marine indicators.
>My understanding of the Nubian is that it has almost been a constant
>deposition of sand in parts of North Africa from the Devonian on.
Well, that's the data. Now all we need is a rational model to explain it.
>At least at present the winds are toward the west at that latitude. And no I
>don't know what they are in the past. But Saudi Arabia was busy depositing
>marine carbonates. The granitic shield dips to the east in Saudi Arabia
>separating the Saudi sediments from those of north Africa. Saudi Arabia was
>under water and was not recieving much clastic rock. (See AAPG 66:12 p. 2611)
Should then have been receiving marine carbonates during that 260 million
years, or something, don't you think?
Art
http://chadwicka.swau.edu