From: Bill Payne (bpayne15@juno.com)
Date: Tue Apr 01 2003 - 23:09:51 EST
On Mon, 31 Mar 2003 06:52:58 -0600 "Darryl Maddox" <dpmaddox@arn.net>
writes:
> I have seen the Texas Gulf
> Coast and I have seen pictures of the desert plains of Kuwait and Iraq
and
> am convinced that either will produce surfaces flat enough to be
considered
> peneplains when seen from the top or when their surface topography is
> mapped, and/or essentially straight line paraconformities or
> non-conformities - nonconformity in the case of PDC since there is a
> lithological difference across the boundary but in many places it isn't
much
> more, if any more different that other boundaries within the Permian
and
> within the Triassic which are not considered unconformities.
>
> Confirming or contrary thoughts or facts I should know about?
There is an interesting article at
http://www.grisda.org/origins/15075.htm – "Those Gaps in the Sedimentary
Record", by A.A. Roth, which discusses (from YEC POV) the PDC you refer
to.
Just off the top of my head, I would think that you don't consider the
effect of millions of years that either subaerial or submarine exposure
would have on topography.Yes we do see some fairly flat areas on the
earth today, but they are not as extensive nor as planar, and they have
not been eroding as long as many in the geologic record.
Glenn's post and another I received offline, and some other info cited
below, suggest that these contacts are not as simple as what I had said -
there is some evidence of both erosional and chemical weathering. It'll
take me a while to digest what I have, but my initial thoughts are that
the erosional features, while present in some areas, are not deep enough
to account for millions of missing years.
There are 3 posts in the ASA archives dealing with paraconformities:
http://www.asa3.org/archive/ASA/200101/0131.html
http://www.asa3.org/archive/ASA/200101/0099.html
http://www.asa3.org/archive/ASA/200101/0069.html
From what I understand at this point, the paraconformities do often
exhibit some erosion, but the generally planar features are difficult to
explain if there were truly millions of years in the intervening gaps.
The conclusion to Roth's article (cited above) summarizes this question:
"This flat and parallel, or near-parallel, arrangement at these gaps
seems to be different from the eroding surfaces of much of our present
earth.
The difficulty with the extended time proposed for these gaps is that
one cannot have deposition, nor can one have much erosion. With
deposition, there is no gap, because sedimentation continues. With
erosion, one would expect abundant channeling and the formation of deep
gullies, canyons and valleys; yet, the contacts are usually "nearly
planar." Over the long periods of time envisioned for these processes,
erosion would erode the underlying layers and much more. One has
difficulty envisioning little or nothing at all happening for millions of
years on the surface of our planet. The gaps seem to suggest less time.
Our current topography does not represent an extension from the
ancient past. Ashley's (1931) provocative study points out how recent our
present topography is and argues that 99% of it was formed in an assumed
15 Ma, which would be very recent on an earth assumed to be thousands of
millions of years old. Thornbury (1969, p. 25) states that little of
earth's topography is older than Tertiary (67 Ma ago), and most of it is
no older than Pleistocene (2 Ma ago).
This raises the question of what happened to the topography for the
assumed hundreds of millions of years before that. Our present topography
is so dramatic in places that it is difficult to think of ancient
topography being so poorly represented. Yet, our Everests and Grand
Canyons seem conspicuously absent in the record of the past, while that
past is still very well-represented in the older sedimentary layers of
the earth. Dramatic topography should be especially noticeable at the
assumed long time periods (gaps) between the layers, when there would be
ample time for uplift and erosion.
It is often difficult to discern what happened in the past; however,
the assumed gaps in the sedimentary layers witness to a past that was
very different from the present. In many ways, that difference is readily
reconciled with catastrophic models such as the Genesis flood that
proposes the relatively rapid deposition of these layers."
Bill
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