Re: Meaning of the Geological Column


"Ken Rode" <karode@xxxxxxxxxxxx> wrote in message
news:1173066994.077534.116900@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx
| On Mar 4, 10:42 pm, Zoe <muz...@xxxxxxx> wrote:
| > On Sun, 04 Mar 2007 20:04:31 GMT, rmcbane <rmcb...@xxxxxxxxxxxx>
| > wrote:
| >
| >
| >
| > >Zoe wrote:
| > >> On 27 Feb 2007 19:48:16 -0800, "Steven J." <steve...@xxxxxxxxxxxxx>
| > >> wrote:
| >
| > >>> On Feb 27, 7:54 pm, Zoe <muz...@xxxxxxx> wrote:
| > >>>> After reading those posts that were informative about the
geological
| > >>>> column - thanks to those who know enough to respond informatively -
| > >>>> here is what I have learned so far.
| >
| > >>>> 1. The geological column does not exist in its entirety anywhere
in
| > >>>> the world. Do I have that correct now?
| >
| > >>> Yes, although, again, there are several places where one finds,
| > >>> superimposed and in their proper order, deposits from each of the
| > >>> major periods of geological time.
| >
| > >> I don't follow that. You agreed that the geological column does not
| > >> exist in its entirety anywhere in the world. And then you turn
around
| > >> and say that there are several places where one can find deposits,
| > >> superimposed and in proper order, from EACH of the major periods of
| > >> geological time.
| >
| > >> How did you manage to have it both ways?
| >
| > >You've asked this question a couple of times and it is hard to figure
| > >out why you are confused. Do you understand that when we say Devonian,
| > >we are not referring to a single layer of rock but rather a number of
| > >layers of different rock types that have been designated as Devonian?
| > >Your question seems to indicate that you don't understand that there
are
| > >multiple rock layers in each period and that a portion of the rocks
| > >could be missing in a period but not all the rocks from that period.
| >
| > layer/layers, that is not my problem. My problem is that certain
| > layers have been designated as Devonian, based on the fact that they
| > exist in Devonshire. Other layers have been designated as Silurian,
| > based on the fact that the dig site is located in the Welsh
| > borderland. Yet other layers have been designed as Permian because
| > they are located in the Ural Mountains. These layers are not
| > physically superimposed upon each other, yet they have been
| > superimposed on paper.
|
| "The Devonian is a geologic period of the Paleozoic era spanning from
| roughly 415 to 360 million years ago. It is named after Devon,
| England, where rocks from this period were first studied." --
| Wikipedia
|
| Layers designated as Devonian are so named because they were deposited
| during the Devonian period, not because they were laid down in the
| vicinity of Devon, England. Any layers laid down anywhere in the world
| are Devonian if they were deposited between 415 and 360 million years
| ago.
|
| In the same way, Silurian and Permian refer to time periods. In most
| (if not all) cases, the time periods are named after places because it
| is at these places where layers of the associated ages were studied.
| Devonian layers are exposed at Devon and were first studied there.

Moreover, when considering rocks laid down over the entire world (in
deposition zones), it would be absurd to think that the exact same type of
rocks would be present at exact same times at every site. Think of what is
happening today. Instead we might see a shale at one site and a limestone
at another and a sandstone at a third that ALL date to the same portion of a
given period. Moreover, dolomitization might later happen at one site but
not at another. The rocks will still date to the same period.

Furthermore, ALL these types of rocks might be found in a SINGLE deposit of
a SINGLE period. That is, periods are very long and can include many
formations of different rock types at a given location.

sharon

.

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