Re: Mongolian carbonate concretions

Arthur V. Chadwick (
Tue, 03 Feb 1998 07:30:43 -0800

At 08:51 PM 2/2/98 -0600, Glenn wrote:

>I agree that dendritic patterns can be indicative of nothing in particular.
>But do we find dendritic rhizoliths in association with rocks that are not
>considered to be terrestrial by most geologists? I don't know so here is
>your chance to whack me good. :-)

I thought I already had! :-), But, oh well....since rhizoliths are the
basis used to determine the depositional environment on the assumption that
they represent roots, that would make it impossible to find them in marine
sediments. Actually, I am not so much disputing their origin as I am
suggesting the need for caution in their uncritical assessment as roots or
their use as an environmental indicator. Such things are notoriously
misused and uncritically applied. An article in the latest issue of
Origins addressed this issue.

>I would not suggest this as possible in the generally accepted geological
>history. However if all these deposits, Tapeats, Muav Coconino etc are all
>deposited within a single year in a global flood, the sources for all of
>these rocks can not be that far away and there could be some intermixing.
>And considering the massive mixing of the flood waters why the lithological
>purity of the Coconino and Navajo and a different purity for the Redwall?
>Where is the sand mixed in with the Redwall?

I think the depositional history is vastly oversimplified, whether one
views the history as representing a global flood or eons of time. Very
rarely can a source area be pegged for any sedimentary deposit with any
degree of certainty. As you know, paleocurrent data indicates source areas
are not even available (for a variety of putative reasons) for most
sediments. Since you asked, there are crossbeds in the Redwall with huge
(75 foot) foreset slopes. So there is plenty of sand there. It obviously
had a different source than that of the Coconino though. I can define its
source as accurately as you can define the source from conventional models.