Re: Widespread depositional systems (was re: inference)

Glenn Morton (
Tue, 18 Nov 1997 18:10:33 -0600

At 11:09 PM 11/17/97 -0800, Arthur V. Chadwick wrote:

>You raise an interesting question... Why is the geologic record a singularity?
>Why are different periods successively different lithologies (and different
>paleocurrent patterns?)

Obviously no one can explain every single depositional system in the
geologic column. However, I can offer some explanations for some of the
features of the earth. I will explain this simply, not for Art's sake (he
is a better geologist than I) but for those who are unfamiliar with geology.
For instance, the early Paleozoic (Cambrian through Mississipian) have a
lot of carbonates. In order for the creatures to live in the sea which
deposit carbonate in their shells, there has to be a lack of clastics(sand
and shale). And these carbonates have very little clastic input. Here is how
I think the widespread lower paleozoic carbonates were deposited.

A look at the paleogeographic maps in Dott and Batton Evolution of the
Earth, 1972 show that much of the continent was under the sea at this time
with only a few regions emergent. Without much land surface there can not
be erosion and thus the deposition of sand and shale. This leaves the
continent covered by clear water, the perfect environment for crinoids,
brachs, etc. Their shells left piles of carbonate.

Now, how did the continents get covered with water if not in a global flood?
That is an obvious question from some on this board. Here is how. A
further look at the paleogeographic maps in both Dott and Batten and Charles
Atlas of Paleogeographic maps of North America, 1955, and Paleogerographic
Development of South America AAPG Oct 1962 all show that there is an trend
towards more and more exposure of hte continental surfaces over geologic
time. Why would this be? It can be explained on two facts: that the
continents float in the earth's mantle by their natural bouyancy and that in
the past the mantle was hotter meaning it was less dense. Of course there is
an oscillation superimposed upon this trend. A less dense mantle would cause
the continents to sink lower in relation to the oceans. Thus one can easily
explain the ocean on top of the continents without a global flood. The clear
ocean waters would allow a great deal of carbonate deposition like is now
occuring in the Bahamas which also lacks a clastic source nearby.

The deposits of other ages can be explained by equally unique circumstances.
The chalks required a proliferation of the coccoliths and they also covered
large areas of the continental land mass.


Foundation, Fall and Flood