Re: Widespread depositional systems (was re: inference)

David B. Fenske (
Mon, 17 Nov 1997 23:12:54 -0800

At 11:09 PM 11/17/97 -0800, you wrote:
>>Each age had a dominant to predominant type of deposition. There is the
>>widespread quartzites of the lowest Cambrian, the mottled, algal dolomites
>>of the lower Ordovician (Beekmantown, Red River etc), the red-beds and salt
>>of the Silurian, the black shales of the Devonian, the Crinoidal limestones
>>of the Mississipian, the coals and cyclicity of the Pennsylvanian, the
>>redbeds and salt of the Permian and Triassic, the oolites of the Jurassic,
>>the chalk and greensands of the Cretaceous, and the diatomites of the lower
>>Tertiary. Today we have widespread clastic deposition. This is merely a
>>continuation of what we have seen in previous geologic periods, only a
>>different lithology
>You raise an interesting question... Why is the geologic record a
>Why are different periods successively different lithologies (and different
>paleocurrent patterns?)
Art has raised a question here that I have wondered about for some time.
Being a Biochemist, my geological theory is a little sparse, so forgive me
if this is a painfully obvious question.

Why are there layers in the geological column that correspond to different
ages and that look the same? Let's say we have geological process #1
forming part of the layer 2.3 billion years ago in Canada (oh, upper left
BC, let's say). Over in Africa, or Asia, or even the Southern States,
geological processes are happening. Different landscapes, different
conditions, presumably different rocks(?). Why is there any similarity in
the part of the column that is deposited? Why is there a certain kind of
rock or layered pattern that forms in such different regions? Why are
there boundaries? If because of changing conditions, why would the
boundary be the same somewhere else where conditions haven't changed? Or
is that layer thicker because conditions continued longer?

Does this have to do with the changing conditions worldwide that resulted
from the development of life, that Keith Miller (I think) alluded to in one
of his posts?

Looking for geological enlightenment :-)

Dave F.