Re: U of South Carolina Releases Topper Radiocarbon Dates

From: Daryl Krupa (icycalmca_at_yahoo.com)
Date: 11/27/04 

Date: 26 Nov 2004 23:20:25 -0800

paleocity@hotmail.com (Lee Olsen) wrote in message news:<40a73547.0411241031.52c0085a@posting.google.com>...
<snip>
> The excavations have uncovered an enormous amount of ground and not
> just a tiny fireplace pit. Where's the beef (oops, I mean humus) and
> better yet, why should there be any in the first place 50 thousand
> years ago? Humus soil does not necessarily form in dunes, but it
> doesn't seem possible that some wouldn't have formed somewhere in that
> amount of time. I have never been to the Topper area, but I can assure
> you out here on the Pacific Coast vegetation takes hold in the dunes
> and on the over-bank flood-plains rather rapidly. For example, the
> Kennewick Man site has 14C dates on humus (this area gets only 7
> inches of rain a year and no oak, pine etc. grows there) and the
> Columbia River has a history of more violent flooding than anything
> seen on the Savannah River. The *no humus* seems like a legitimate
> puzzle.
<snip>

  I forgot to mention the most obvious (and most problematic) explanation
for the lack of humic paleosols at depth: consumption by fire.

  Open boreal woodland near Late Glacial Maximum:

"This vegetation map showing the eastern USA during the period
28,000-25,000 14C y.a. has been compiled by Paul & Hazel Delcourt.
An ice *** already covered most of Canada and extended south of
the Great Lakes. Boreal conifer woodlands and forests predominated
in what is now the cool temperate forest zone, and the cool and
warm temperate forest belts were compressed southwards."

http://www.esd.ornl.gov/projects/qen/NAm28-25kyr.gif

"28,000-25,000 14C y.a.; shortly before Last Glacial Maximum.
In the eastern USA, conditions may have been generally drier than today.
A xeric scrub cover existed in Florida at this time, instead of the
present forest (Watts & Stuiver 1980).
In Maryland (38N, 75W) pollen evidence indicates pine-birch barrens or
spruce parkland
dominating after 30,000 14C years ago (Wells 1992 p.612), and it is
possible that most of the eastern USA had an open wooded vegetation
cover at this time."

http://www.esd.ornl.gov/projects/qen/nercNORTHAMERICA.html

  Hmmm ... xeric scrubland ... fire-dominated ecosystem ... IIRC,
Georgia pines are well-adapted to both sandy soils and a regular
occurrence of fire.
  Dry piney duff burns ferociously, and fires in such environments
often totally consume what surface organics might have acculmulated.
  What ash remained could have been stripped by winds, to be
redeposited in lower ground (or carried away by the river when it
topped the bank [no pun intended]).
  The lack of humic horizons in the sediment face might indicate that
they tended to be catastrophically oxidised before being covered with
a preserving layer of sediment.
  Fragments of pine cones would be interesting to investigate.

  A shallow fire pit might be a localised site of aeolian redeposition
of burned remnants of forest or forest floor material, followed by
aeolian deposition of mineral material to flatten out the surface,
but then,
so would a hollow created by a wallowing bison.
  There's a site in northwestern Alberta (Saskatoon Mountain) that is
similar in many ways: a hillside above a source of aeolian sediment
(dried-out drained-glacial-lake bed), where the prevailing westerlies
tended to deposit layers of silty sand just below the crest of the hill,
where the wind velocity decreased after compression of the transporting
air mass by the hillside below.
  Some humic horizons there, along with some evidence of fire.
  The oldest artifacts, 9500 BP, predate the establishment of
coniferous boreal in the area, and thereafter vegetation cover
tended to anchor the lake surface and limit sediment removal to
the dig site, and so the record ends quite early.
  Conditions at the Topper site might possibly have been similarly
susceptible to climatic and vegetation-cover influences, creating
interruptions or hiatuses in the sedimentary record.

  The view upwind:

http://www.pinetreeline.org/photos/belodg/belod228.jpg

  The dig, with some evidence of paleosols:

http://www.pinetreeline.org/photos/belodg/belod226.jpg

  Reading:

Beaudoin, A. B., M. Wright and B. Ronaghan, 1996.
Late Quaternary Landscape History and Archaeology in the
"Ice-Free Corridor": Some Recent Results from Alberta.
Quaternary International, 32:113-126

  Zo, if the dominant vegetation at the Topper site during the
mid-Wisconsinan interstadial was subject to frequent intensive
fire distubance, then the lack of humic horizons might be
explained by conditions tending to act against the chance of
preservation of surface organic material.
 
 'Nuff said?

Daryl Krupa

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