From: Michael Roberts (michael.andrea.r@ukonline.co.uk)
Date: Wed Apr 02 2003 - 12:24:41 EST
Re: Paraconformities (was test questions)Welcome Bill Payne to the true Christian understanding of geology as old earth and pioneered by such devout Christians as Sedgwick,Silliman and Hitchcock.
Thanks Joel for having a text book I havent
Michael
----- Original Message -----
From: Joel Moore
To: asa@lists.calvin.edu
Sent: Wednesday, April 02, 2003 4:12 PM
Subject: Re: Paraconformities (was test questions)
Date: Tue, 1 Apr 2003 12:23:32 -0500
To: Bill Payne <bpayne15@juno.com>
From: Joel Moore <jxm957@psu.edu>
Subject: Re: Paraconformities (was test questions)
Cc:
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Bill,
Your original statement about paraconformities (on Mar 17) was:
> Paraconformities, such as that between the Middle Cambrian Muav limestone
> and the overlying Lower Mississippian Redwall limestone of Grand Canyon,
> show lapses of time in deposition (in this case about 200 million years),
> yet show almost no physical evidence for the break in deposition. The
> lack of erosion and chemical weathering where there was supposedly a
> significant time break indicates continuous deposition, which would of
> course screw up the geologic time scale.
I flipped open my book from my undergrad Sedimentology and Stratigraphy class and found a number of problems with your statement.
1) The Muav and Redwall limestones are not in direct contact in many or most parts of the Grand Canyon. In the eastern part of the canyon, the sequence (from oldest to youngest) is the Cambrian Muav limestone, Devonian Temple Butte limestone, and the Mississippian Redwall limestone. For the western canyon, the sequence (from oldest to youngest) is the Cambrian Muav limestone, unclassified dolomites, Devonian Temple Butte Formation, and the Mississippian Redwall limestone. (the cited reference is Bachhuber, Rowland, and Huntoon (1987) "Geology of the Lower Grand Canyon and Upper Lake Mead by Boat--An Overview." _Ariz. Bur Geol. Min. Tech., Geol. Surv. Spec. Paper 5_ : 39-51)
2) In the places where the Redwall is in contact with the Muav, the Redwall fills in surfaces that have been eroded through the Temple Butte and into part of the Muav limestone.
3) It's important to remember that the Muav limestone was not deposited at the same time over the whole extent of the formation (i.e., a cake-layer model is not correct). The lower Muav limestone is the same age in the western part of the canyon as the Tapeats sandstone (an older Cambrian sandstone) is in the eastern part of the formation. Thus there are several millions years difference between the age of the bottom of the Muav limestone in the eastern and western parts of the canyon because the sediments are part of a trangressive sequence [transgressive means the shore was moving from west to east -- the sandstone was deposited closest to shore, next the shale, and then the limestone in progressively deeper water]. Thus, one sees the Muav thinning and eventually ending to the east as one moves closer to the paleoshoreline. [Note: For non-geologists, the relative ages in transgressive-regressive sequences are established by biostratigraphy where one finds an organism or set of organisms that only exists in a specific setting and/or small sequence of rocks.]
Another thing to keep in mind about paraconformities is that they're viewed with skepticism by some in the geologic community. Also from my textbook, "Some authors doubt the need for the paraconformity category, arguing that most reputed paraconformities, if traced laterally, eventually exhibit some physical evidence of erosion and thus prove actually to be disconformities (Davis, 1983)." My sense is that the number of people who are in favor of the paraconformity category has been declining over the last couple of decades.
Regarding sheet flow erosion, I can't claim any strength in physics, but my understanding of fluid flow is that flowing water cuts channels. Sheet flow is definitely the exception rather than the rule. If I remember correctly, I've seen channelized flow in some wave wash on beaches in Cape Cod (so low slopes and small water supply). The more water you have and the faster the water is flowing, the more likely the water is to channelize.
Joel
On Fri, 28 Mar 2003 20:19:59 -0500 "bivalve"
<bivalve@mail.davidson.alumlink.com> writes:
> Plains and plateaus are my modern analogs.
I have just completed 7 weeks of field work in the Great Plains of west
Oklahoma, and those Plains are too irregular to form the flat (plane)
strata we see in Grand Canyon and other locations of the West. We do see
mesas (tabletop mountains) which, I agree, are very flat, but not very
extensive, having been cut by erosional channels.
> Sure, they usually have
> river channels, but there is flat land between the channels that is
> eroding relatively evenly. The odds that a particular outcrop will
> have a channel running through it is less than 100 percent.
This is the weakness of your proposed mechanism. The Grand Canyon is
more than any "particular outcrop." The exposures there are tens of
miles long, some of the gaps in deposition are supposedly millions of
years, and yet the strata above and below the gaps are flat and
continuous. The only two ways I can see to accomplish these results are
by (A) sheet-flow erosion, or (B) nearly continuous deposition, i.e.,
breaks in deposition of minutes, days or possibly years, but not millions
of years.
> Ordinary rainfall will do the job nicely.
No, this will create channels and canyons - which we do see in the mesas,
but do not see in many paraconformities.
> However, this raises a
> more basic question that needs answering before this discussion can
> get anywhere. What is your flood model? You need to provide a
> coherent model and to show that it fits the evidence as well or
> better than conventional geologic explanations.
There you go, David. Michael said these arguments can't stand up to
scrunity. I have presented three arguments, two of which I yielded, but
this third one you first said you weren't motivated to research and
answer, now you have tried to respond and probably are beginning to see
that your answers are strained by the data. So you try to shift the
focus by jumping to the big picture. Michael tried to avoid this
altogether with his curt reply and his claim to be "bored" with this
argument. Both tactics, yours and Michael's, are common in these types
of discussions, and indicative of a certain insecurity.
> The fact that you
> can find problems with any scientific theory does not automatically
> mean that a particular alternative is better.
No, but if I can offer better solutions to the problems than you can,
then one begins to wonder. After all, isn't this how science is supposed
to work?
> Likewise, invoking
> the Flood to do anything they want is a popular way for Flood
> geologists to damage their scientific credibility.
First, I haven't invoked the Flood to do anything I want, and second, as
a PG, I am mildly offended (and also mildly amused) by your inference
that I have damaged my scientific credibility. In response to Michael's
challenge, I have attempted to offer empirically-based alternatives to
conventional interpretations of geology. I have yielded on two counts,
but in light of your and Michael's failure to provide reasonable support
for your view of paraconformities I am standing firm on this one until I
see a stronger defense.
> For example, why
> would the Flood produce sheet flow?
You are asking the wrong question. You should be asking if sheet flow is
the best explanation for the observations. You're letting your paradigm
drive your conclusions, rather than following the science where it leads.
> What layers were produced by
> the Flood?
Again, wrong question. You should be asking whether a Flood acting over
a short period of time or rainfall acting over millions of years would
best explain our observations of the paraconformities I have cited.
Bill
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--
Joel Moore
315 Hosler
Department of Geosciences
Pennsylvania State University
University Park, PA 16802
(814) 863-8055
--Joel Moore 315 Hosler Department of Geosciences Pennsylvania State University University Park, PA 16802
(814) 863-8055
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