From: bivalve (bivalve@mail.davidson.alumlink.com)
Date: Tue Aug 13 2002 - 18:13:44 EDT
>Welcome to Alabama! <
Thanks! There are lots of fossil and modern mollusks here, so I am
enjoying my stay.
>On Mon, 22 Jul 2002 13:55:59 -0400 "bivalve"
><bivalve@mail.davidson.alumlink.com> writes:
>> The accumulation of organic material in the bottom of a swamp or
>>under a stationary floating mass (the existence of which is
>>incompatible with the global flood models that posit violent
>>activity such as rapid plate tectonics) can easily lead to anoxia
>>in the pore waters, inimical to most bioturbators. <<
>The "rapid plate tectonics" may have come later. I think you're
>creating a straw-man argument here. <
No, straw is principally grasses, which do not occur in the Paleozoic
and are not a good precursor for coal.
Seriously, the Carboniferous coals of Laurasia postdate the closure
of Iapetus, so the plate tectonics cannot be confined to afterwards.
Even under ordinary conditions, there are currents that would make a
mat difficult to hold still. Decreasing the time for rapid plate
tectonics makes the violations of the laws of thermodynamics and the
ignoring of geologic side effects (earthquakes, volcanoes, etc.) even
more problematic.
By commenting on rapid tectonics, I distracted from the point of my
statement, which is that anoxic conditions, such as in a swamp,
promote a low level of bioturbation from burrowing animals and from
roots and thus a more abrupt contact.
>"Sharper" is misleading. A better term in this context would be
>"less gradational." But you cannot take a gradational contact of
>less than 5% ash in the coal to greater than 25% ash in the
>substrate over a distance of 1 to 2 meters (see pp 30-31, 34-36 in
>GSA SP 286) and compress it into a razor-sharp contact with coal
>above the contact and shale or clay beneath. <
I am not sure what the difference is between sharper and less
gradational. Without comparative data on the patterns of
compositional change, I do not know enough to speculate on the
ability of compression to create these patterns.
>Since you're in Tuscaloosa now, you have many coal seams within an
>hour or two of your location. Contact me offline and I'll give you
>the names of a couple of geologists with the State Geological Survey
>who could give you locations of outcrops, and maybe you could go
>with them on a field trip. There is a coal seam within a mile of my
>office in Riverchase (B'ham) that we could look at together if you
>want let me know when you're going to be up here. <
They are probably a lot closer than an hour away, unless you count
digging time, as I live towards the east end of town. I would like
to get out in the field, but am tied to the DNA lab for the immediate
future.
>> Distinctive freshwater bivalves are associated with some Paleozoic
>>and later coal deposits, which is problematic for a floating mat in
>>a global flood. <<
>I can see why you say this would be problematic for a floating mat
>not in a flood, but not why it would be during a global flood. The
>bivalves may have been washed in, along with some sediment. Or, they
>may have been living in the coal swamp before the Flood and gotten
>caught /remained with the organic mat while it was floating and as
>it settled out of suspension. <
Your explanations seem to me to work equally well for a floating mat
not in a flood. In fact, a floating mat in a regional freshwater
flood would work better. Bivalves are benthic, aquatic filter
feeders. For these to be living in the mat would require a source of
fresh water with algae living in it. Washing in raises problems for
a global flood because of the need to sort freshwater bivalves from
marine bivalves and other hydrodynamically similar organisms, putting
the freshwater ones into the coal and the marine ones into the marine
deposits. Living in a swamp prior to the Flood seems to me to be
your most workable model, though requiring explanation for the first
appearance of the clams in the Devonian, as low-lying swamps should
be the first places inundated.
>Coal seams sometimes contain erratic boulders of rock which
>apparently were caught in the roots of trees and floated with the
>organic mat until it settled out of the water. If it could transport
>boulders, it could transport freshwater bivalves. At any rate, try
>explaining erratic boulders with the swamp model. <
The same mechanism seems feasible for a swamp-a tree washes in with a
rock caught in its roots. Steve Donovan has a paper, for which I
might be able to track down a reference, suggesting tree-root
transport for placing a boulder into the Bowden Formation (a Pliocene
Jamaican deepwater marine shell bed). Big local floods do occur in
modern swamp environments.
Dr. David Campbell
Old Seashells
University of Alabama
Biodiversity & Systematics
Dept. Biological Sciences
Box 870345
Tuscaloosa, AL 35487 USA
bivalve@mail.davidson.alumlink.com
That is Uncle Joe, taken in the masonic regalia of a Grand Exalted
Periwinkle of the Mystic Order of Whelks-P.G. Wodehouse, Romance at
Droitgate Spa
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