Re: definitions

[Tompaleo@aol.com]

In a message dated 97-08-09 18:30:40 EDT, you write:

<<  lacustrine, adjective, describes a sedimintary deposit laid down by a
 lake.  Lacustrine deposits are often comprised of limestone, such as the
 Solnhofen and Liaoning lacustrine deposits
  >>

Actually, lacustrine deposits are rarely comprised of limestone. Limestone is
_almost_ always of marine origin being composed of calcareous marine
organisms. And to my recollection, the Solnhoffen Ls was interpreted to be a
lagoonal deposit. 

I think the confusion here is that lacustrine sediments often are a fine to
very fine grain musdstone, clays and shales deposited in quiet, often
stagnant, conditions where fine materials settle to the bottom at a very slow
rate where theyare allowed to accumulate. As a consequence,  the sediments
can preserve allot of detail. My plant fossils from a deposit of Arundel Clay
(possibly an Oxbow lake deposit in some localities) show nice detail on some
specimens as an example. The Solnhoffen, I believe, was deposited in a quiet
lagoonal environment whereby fine sediments in this case CaCO3 could
accumulate (precipitate) in the absence of waves, currents, and other forms
of turbidity that usually prevent the accumulation of fines (micrite). The
result is a medium which also preserves much detail. So while the conditions
for the accumulation of fine grained sediment were similarly quiet , the
depositional, geological and biological settings of the above were quite
different.


Just a late night 2c worth! 

Regards,
Thomas R. Lipka
Paleontological/Geological Studies