From: Bill Payne (bpayne15@juno.com)
Date: Tue Mar 25 2003 - 23:36:54 EST
With David's permission (he said he intended to reply on-line) I reply to
his post below:
On Mon, 24 Mar 2003 12:00:45 -0500 "bivalve"
<bivalve@mail.davidson.alumlink.com> writes:
> >In the strata containing burrowing bivalves, do you also see bedding
> structure, or is the bedding obliterated?<
>
> I am mainly looking at the bivalves rather than the bedding in the
> field. In general, the deposits that are rich in fossil shells show
> relatively large-scale sedimentary features but not fine bedding.
> Thus, large burrows, diastems, hardground surfaces, and
> outcrop-scale changes in sediment type are commonly associated with
> these bivalves, but not fine lamination. There are some shales that
> contain good bivalve fossils, but often these are relatively blocky
> rather than highly fissile. High levels of bioturbation are typical
> of normal marine environments and do disrupt finely bedded sediment.
>
>
> A few species of bivalves tolerate generally unpopular environments
> and may be associated with fine bedding. For example, various
> thin-shelled, flattened pteriomorphs apparently thrived in dysoxic
> settings, sitting on the surface of anoxic sediments.
>
> As Dave pointed out, there are several situations that can produce
> low levels of bioturbation in marine settings. These include
> marginal settings such as lagoons with abnormal salinity (too high,
> too low, or too variable) or tidal flats; anoxia (in the sediments
> or also in the water column); low bioturbator abundance (Precambrian
> to earliest Paleozoic, depending on the environment, and immediate
> post-Permian); or high sedimentation rates. However, fine bedding
> also requires some sort of shift in either sediment input or in
> water speed to produce the changes in sedimentation regime. For
> example, tidal flats are good for producing finely bedded
> alternations between sandier and muddier sediment because the water
> speed varies from fast (as the tides change) to slow (at high or low
> tide). Rapid flow will keep the mud suspended; slow flow will let it
> settle. Such changes in sedimentaiton regime require time, and the
> presence of fine-grained sediment imposes a maximum flow rate on the
> water. Both of these are problematic for trying to credit finely
> bedded layers to a catastrophic global flood.
>
>
> Dr. David Campbell
> Old Seashells
> University of Alabama
> Biodiversity & Systematics
> Dept. Biological Sciences
> Box 870345
> Tuscaloosa, AL 35487-0345 USA
> bivalve@mail.davidson.alumlink.com
OK, I will yield on the articulated bivalves. I don't see that they help
either view.
Fossiliferous limestone samples I have do commonly show evidence of
laminar bedding, although some certainly do appear to be massive, which I
suppose might result from bioturbation, from a massive deposition event,
or continuous deposition under uniform conditions. I don't see where
thin bedding helps either view, so I'll yield on that one also.
> Rapid flow will keep the mud suspended; slow flow will let it
> settle. Such changes in sedimentaiton regime require time, and the
> presence of fine-grained sediment imposes a maximum flow rate on the
> water. Both of these are problematic for trying to credit finely
> bedded layers to a catastrophic global flood.
I have seen a couple of references to deposition of fine-grained sediment
in high-energy regimes, so I'll take issue with your statement above.
"Tidal channels lined with coral rubble between the Florida Keys have
been oberved to accumulate a much as 10 cm of lime mud during such
events, in spite of the fact that these are areas of high energy where
normally only rubble and sand accumulate." "Deposits of lime mud as
thich as 20 cm and abundant lime mud intraclasts are interbedded with
ooid and in a tidal channel in the Exuma Islands (Dill and Steinen 1988),
where tidal currents as high as 100 cm/sec occur daily (Dill et al.
1986)." (from Whitings, A Sedimentologic Dilemma, by Shinn et al,
Journal of Sed Pet, v 59, no 1, Jan 1989, p159)
"Geologists often assume that the accumulation of thick layers of tiny
microscopic organisms such as the White Cliffs of Dover in England
required lengthy periods of time. But such accumulation can occur
rapidly. Along the coast of Oregon a three-day storm of high winds and
rain deposited 10-15 cm of microscopic diatoms for a distance of 32 km.
[Campbell, AS. 1954. Radiolaria. In: Moore RC, eidtor. Treatise of
invertebrate paleontology, Part D(Protista 3). NY: Geol. Soc of Amer.,
and Lawrence, Kans.: Univ of Dansas Press, p. D17.] I have seen a
well-preserved fossil bird and many fish in thick beds of microscopic
diatoms near Lompoc, California. A whale was also found in this deposit.
Such preservation would require rapid burial before disarticulation of
the organism would occur. Evidently microscopic organisms can be
deposited rapidly." (_Origins, Linking Science and Scripture_, Ariel
Roth, p 201)
Since no one has commented on the paraconformities of Grand Canyon, then
I assume it is reasonable that the lack of mechanical and chemical
erosion may demonstrate that there was little time elapsed during each
paraconformity. If such were the case, the elapsed time from the end of
the Precambrian to the Tertiary would collapse from the commonly
published ~500 my to ~250 million years by leaving out the gaps. The
geologic time scale is thus invalidated by paraconformities.
Bill
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