Re: Mongolian carbonate concretions

Glenn Morton (grmorton@waymark.net)
Tue, 27 Jan 1998 18:20:50 -0600

At 07:28 AM 1/27/98 -0800, Arthur V. Chadwick wrote:
>At 09:10 PM 1/26/98 -0600, Glenn wrote:
>
>>You had said earlier that the Mongolian sandstones contained boulders. Were
>>you referring to what the authors of the January Geology article said were
>>carbonate concretions? I didn't find any other reference to boulders or
>>cobbles in the article.
>
>The article mentioned (and I said) cobbles (and pebbles) too large to have
>been transported by wind. Specifically:
>
>"The pebbles and cobbles within some of the sand bodies of this facies were
>clearly derived from beyond the margins of the dune field. The
>conglomerate at tehe top of the section indicates that the dunes...were
>adjacent to a tectonic highland; large clasts in the structureless
>sandstone were transported into the dune field by sediment gravity flows
>originating in the highland." (Geology 26:29)
>
>This would indicate an origin by subaqueous debris flow is not only
>possible, but likely.

I am beginning to get some of the Mongolian geology articles in. One I just
finished iw (D. A. Eberth, "Depositional Environments and Facies Transitions
of Dinosaur-bearing Upper Cretaceous Redbeds at Bayan Mandahu (Inner
Mongolia, People's Republic of China)", Can. J. Earth Sci. 30(1993):2196-2213.

In it they talk about the pebbles. And in order to understand it requires a
facies map. At the Bayan Mandahu, correlative beds to the Djadokhta
sediments just across the border in the People's Republic of Mongolia were
examined by Eberth. He derived 3 different facies which parallel the uplift
of the Lang Shan (Wolf? Mountains). Deposition is from the south to the
north. It looks like this:

north
fine grained sediments
Zone 3--eolian dune deposits, crossbedding fluvial caliche conglomerates

Zone 2 structureless sandstones--caliche profiles occasional "pebbly sheet
sandstones of alluvial origin",fossil turtles dinosaurs, mammals and lizards.

Zone 1 Alluvial fan deposits; pebbly sandstone sheets, basal scours,
conglomeratic coarse sediments

^
|
LANG SHAN Direction of deposition

South

The cobbles or pebbles may have nothing to do with widespread flooding.

glenn

Adam, Apes, and Anthropology: Finding the Soul of Fossil Man

and

Foundation, Fall and Flood
http://www.isource.net/~grmorton/dmd.htm