From: Joel Moore (jxm957@psu.edu)
Date: Wed Apr 02 2003 - 10:12:22 EST
>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:
>Bcc:
>X-Attachments:
>
>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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