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Re: Colville River, North Slope Alaska, Dinosaur Fossils Questions



>I have seen the bones recovered from  the Liscomb Bone Bed being described
as being "fresh" and "unaltered." However, other web pages, i. e. "DINOSAURS
on Alaska's North Slope" and "Diagenetic alteration of dinosaur bone" either
describe or conclude that these bones have been significantly diagenetically
altered.  Which one of these descriptions is correct?

It seems that the latter is correct. I don't know of any full studies that
have been published on them (anyone is free to correct me if I'm wrong), but
Mark Goodwin gave the following paper at NAPC in Berkeley. This is related
to one of the links (http://www.llnl.gov/ees/cams/microprobe/dinopixe.html)
that you posted. The abstract follows:

************************************************
>From PaleoBios 21, supplement to number 2, p. 57. (available on-line at
http://www.ucmp.berkeley.edu/napc/abs9.html)

EVIDENCE FOR POSTMORTEM ENRICHMENT IN LATE CRETACEOUS DINOSAUR BONE USING
MICROBEAM PIXE
GOODWIN, Mark B., Museum of Paleontology, University of California,
Berkeley, CA, USA; and Graham Bench and Patrick Grant, Center for
Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory,
Livermore, CA, USA

The effects of diagenesis on the geochemistry of fossils are poorly
understood. The alteration of stable isotopes by fossilization creates
uncertainty about the preservation of original biogenic isotope values. The
use of stable oxygen isotopes from dinosaur bones and teeth to reconstruct
dinosaur thermophysiology remains controversial due to potential
overprinting by diagenesis. Studies using stable isotopes for dietary or
physiological reconstructions are commonly based on the assumption that
postmortem alteration of the fossil did not occur or that its effects are
negligible. Successful isotope analysis of fossil bone for the purposes of
determining paleophysiology depends upon the retention of original isotope
atoms in the bone phosphate. If the chemical composition of dinosaur bone is
affected by dissolution, recrystallization, or mineral substitution from the
burial environment, the measured oxygen isotope ratio may reflect
groundwater temperature, not dinosaur body temperature. PIXE, coupled with
microsampling and mass spectrometry, is a potent analytical tool to assess
diagenesis in fossils.

Nuclear microscopy using Proton Induced X-ray Emission (or microbeam PIXE)
provides accurate quantitative values, multi-element detection, sub-micron
spatial resolution to ppm or mg/g sensitivity, and elemental maps of micron
regions of bone. A thin section from an exceptionally well preserved Late
Cretaceous hadrosaur femur (UCMP 179501) from Alaska's North Slope was
subject to PIXE analysis. This fossil does not show typical signs of
alteration at a macro and micron scale, but is highly altered nonetheless.
PIXE analysis reveals enrichment of Fe (180,000 ppm) and Mn (13,000 ppm) in
the lamellae surrounding Haversian canals and neighboring tissue of several
magnitudes higher than levels known in modern bone. A corresponding
depletion of Ca and P also occurs. This enrichment is most likely due to
diagenesis from the burial environment since Fe and Mn are present in modern
bone in only minute amounts. PIXE analysis of a modern Caiman and Rhea
confirm this.
*************************************************

I hope this answers your question. . .

Andy
_______________________________
Andrew A. Farke
South Dakota School of Mines and Technology
501 East St. Joseph Street
Rapid City, SD  57701

andyfarke@hotmail.com