Paul,
Depends on what you mean by "common."
Rather than parallel orientation, I referred to
orientation relative to a "radiant" point, which
orientation is more consistent. I also was not
wed to the notion of a single cometary event
breaking up into 500,000 objects! It is quite
possible to have a cometary stream that intersects
the Earth's orbit at regular intervals. Or to have
an object or objects captured by the Earth in
low orbit decaying on successive passes, events
unlikely but not impossible. It's a big universe.
In any event, the radiants of multiple impact
events need not be any more regular than the
orientation of the Bays. It's not diagnostic.
Their "regularity of form" is quite remarkable
for a "natural" feature, however. The Alaska lakes
Eric Olsen provided a link to are very much more
irregular than the Bays and indeed most lakes
and ponds are.
The paleowind theory that is so popular as
the cause of the elipticity doesn't seem to account
for the fact that to get perfect elipses you have to
start with perfect circles just as regular. Wind stretching
would exaggerate prior irregularities. This leaves
the regularity problem untouched.
Geometric regularity is not characteristic of
local features, formed locally, and influenced by
local factors. Simple mathematical forms are rare:
the cone of a new ashy volcano, the circularity of
coral atolls, the geometry of dune fields. True,
lakes in low lying, flat, uniformly soft soils are
more regular, but the Bays are oddly too regular.
Those rim dates correspond to re-glaciation
(36,000 yr), cold peak (25,000 yr), melting (11,600
yr), so maybe the Bays are a glacial feature whose
mechanism we just haven't figured out yet. At the
time, this was a cold, windy place, with much less
plant cover, particularly trees, more like the northern
Great Plains than the semi-tropical Carolinas
of today.
Does anybody like giant Pleistocene beavers as
a candidate? If you assume certain behavioral
differences from the modern species, like building
regular embayments out of gravel, sand, and mud
instead of log dams (no trees!). I suppose you could
easily hypothesize any behavior, since Pleistocene
beavers are extinct and can hardly object to our
speculations!
Sterling K. Webb
-------------------------------------------------
----- Original Message -----
From: "Paul" <[EMAIL PROTECTED]>
To: <[email protected]>
Sent: Wednesday, March 29, 2006 1:53 PM
Subject: [meteorite-list] Part2: Professor Rejects Meteor Theory of
CarolinaBays' Origin
Susan Web wrote:
NOTE:
STERLING WEBB wrote:
"Their key mysterious features are their
number (half a million of them), their
regularity of form, their common
orientation, their extreme shallowness,
their low rim heights."
Their "common orientation" is not as consistent as the
proponents of an impact origin falsely claim them to be.
In the southern and northern ends of their distribution,
the long axis of Carolina Bays actually show a wide
range of orientations, which fails to support either an
air-burst or impact origin. Within the middle range of
their distribution, the orientation of the Carolina Bays
are consistent with Pleistocene paleowind directions as
determined from ancient dune fields, loess distribution
patterns, and paleoclimate models. I would find it quite
remarkable that either a meteorite or comet would take
the time and trouble to plan its impact as to perfectly
coincide with the prevailing winds at the time it hit like
an airplane landing at an airport. The wide spread of
orientations at the northern and southern ends of their
distributions is also consistent with what is known about
the variability of Pleistocene paleowind patterns over
time.
Another and major problem, which the proponents of either
an impact or air-burst origin is that the shape, orientation,
and depth of the Carolina Bays have been altered by over
a 100,000 years of modification by eolian and lacustrine
processes. For example, Ivester et al. (2003) found that
the multiple sand rims found within Big Bay in South
Carolina become progressively younger towards the center
of this Carolina Bay. In this case, Optically Stimulated
Luminescence (OSL) dates from sand rims starting from
the outer rim to the inner rim produced a perfectly
chronologically consistent set dates of 35,660±2600;
25,210±1900; 11,160±900; and 2,150±300 years BP. In
this case, the Big Bay has shrunk by 1.6 km over the last
36,000 years, with rims being produced about 36,000 BP,
25,000 BP, 11,000 BP, and 2,000 BP as it shrunk. If a
person wants to argue that these sand rims are of impact or
air-burst origin, they need to explain how either impacts or
air-bursts managed to precisely excavate tens of thousand
of years apart sucessive craters in precise center of Big Bay
and similar Carolina Bays and with ever decreasing energy
as to produce sand rims of smaller and smaller diameter,
which are nicely nested within each other.
Their nothing mysterious about these rims as (Ivester et al.
2004a) studied the sedimentology and stratigraphy of these
rims and found them to be "composed of both shoreface
and eolian deposits". Eolian and lacustrine processes are
perfectly capable of producing the low rims processes by
Carolina Bays. The low rims can be easily explained by a
combination of eolian and lacustrine processes.
As a result of the OSL dating of the rims of numerous Carolina
Bays, Ivester et al (2004b) concluded:
"The optical dating results indicate that
present-day bay morphology is not the
result of a single event, catastrophic
formation, but rather they have evolved
through multiple phases of activity and
inactivity over tens of thousands of years.
This is evidenced both by multiple rims
of differing ages along the same bay, and
by multiple ages within single rims."
Because the Carolina Bays have been modified for over a
100,000 years by both eolian and lacustine processes, their
form, orientation, shallowness, and sand rims are useless as
evidence of how they were originally created.
References Cited:
Ivester, A.H., Godfrey-Smith, D. I., Brooks, M. J., and
Taylor, B. E., 2003, Concentric sand rims document the
evolution of a Carolina bay in the Middle Coastal Plain
of South Carolina. Geological Society of America
Abstracts with Programs. vol. 35, no. 6, pp. 169.
Ivester, A. H., Godfrey-Smith, D. I., Brooks, M. J., and
Taylor B. E., 2004a, The timing of Carolina Bay and
inland activity on the Atlantic coastal plain of Georgia
and South Carolina. Geological Society of America
Abstracts with Programs. vol. 36, no. 5, p. 69
Ivester, A. H., Godfrey-Smith, D. I., Brooks, M. J., and
Taylor B. E., 2004b, Chronology of Carolina bay sand
rims and inland dunes on the Atlantic Coastal Plain, USA.
The 3rd New World Luminescence Dating Workshop. July
4 - 7, 2004, Department of Earth Science, Dalhousie
University, Halifax, Nova Scotia.
Mrs. Webb also wrote:
"It is also worth noting that all the
geological theories of their origins
are based on the erroneous notion
that the Carolina Bays are all to be
found in only one type of geological
terrain, the coastal plains. But they
have since been found in other terrain
types, which effectively rules out
most of the prior geological theories
(except for those fish fins, of course)."
Unfortunately, the only "erroneous notion" here is the
pervasive Internet folklore about Carolina Bays having
been found on a variety of geologic terrains. The fact
of the matter is that Carolina Bays are **not** found in
a diverse assortment geologic terrains. The Internet
fiction about Carolina Bays being found in a wide range
of geologic terrains was soundly refuted by the detailed
analysis, which May and Warme (1999) did of Carolina
Bays, including those found within the coastal plains of
Mississippi and Alabama. They found that these bays
are restricted to deeply weathered, very low relief, and
very poorly drained, geomorphic surfaces.
Reference Cited:
May, James H., and Warne, Andrews G., 1999, Hydrogeologic
and Chemical Factors Required for the Development of
Carolina Bays Along the Atlantic and Gulf of Mexico Coastal
Plain, USA. Environmental Engineering and Geoscience.
vol. 5, no. 3, pp. 261-270.
The abstract for May and Warme (1999) can be found at:
http://eeg.geoscienceworld.org/cgi/content/abstract/5/3/261
Best,
Paul
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