Re: uniformitarianism

Arthur V. Chadwick (chadwicka@swac.edu)
Tue, 03 Feb 1998 09:31:39 -0800

At 01:25 AM 2/3/98 -0500, Steve wrote:
>Geologists do indeed think that carbonate sediments are produced in their
>environment of deposition (in situ). There are many good reasons for
>this, not just a uniformitarian worldview. Furthermore, some
>allochthonous (transported) carbonate deposits have been recognized in
>the statigraphic record--they form under specific circumstances, such as
>fore-reef talus deposits.

I would have to take exception to this generalization. I think a grest
deal of carbonate sediment is now recognized to represent transported
materials. For example the entire thickness of the Devonian Denay
Limestone in N. Central Nevada which is one Paleozoic carbonate I have
studied in detail, is a lime mud turbidite sequence. The entire several km
of the Jurassic/Cretaceous Great Valley Sequence in California, which I
have also studied in detail, is lime mud carbonates, deposited as
turbidites. These are not exceptions, as many limestone sequences
represent rather uniform beds of transported material that cannot have been
locally derived. While some limestones may be interpreted as forereef
talus, many others cannot be, and for these, transport is generally a valid
option, and is often the preferred interpretation.
Art
http://chadwicka.swau.edu