Re: Dating "Old Swedes"
- From: Tom McDonald <tmcdonald2672@xxxxxxxxxxxxxxxxxxx>
- Date: Thu, 21 Jul 2005 07:12:54 -0500
Eric Stevens wrote:
On Thu, 21 Jul 2005 02:23:03 GMT, Philip Deitiker <Donevenask@xxxxxxxxxxxxxxx> wrote:
Journal of Archaeological Science, Article in Press
Radiocarbon dating and the “old shell” problem: direct dating of artifacts and cultural chronologies in coastal and other aquatic regions
Torben C. Ricka, , , René L. Vellanowethb and Jon M. Erlandsonc
Abstract: Archaeologists have long recognized the problem of the “old wood” effect in radiocarbon dating charcoal and wood samples, the age of which may be hundreds of years older than their use by humans. Such problems have resulted in significant changes in how most researchers select wood and charcoal samples for 14C dating, with many now using relatively short-lived carbonized materials for dating. Despite the significant strides made in our understanding of the potential biases of the “old wood” effect, little emphasis has been placed on the possible impacts of dating “old shell” in archaeological deposits. The use of marine shell for 14C dating is widespread in coastal areas around the world, including a growing emphasis on the dating of individual shell artifacts via Accelerator Mass Spectrometry (AMS). In dating shell artifacts, we have obtained several dates older than associated 14C dates for short-lived subsistence remains from the same deposits, including great disparities (>10,000 years) and more subtle differences (=100 years). These discrepancies appear to be due to the use of old shells by humans to make beads and other artifacts, including shells collected
from fossil deposits, older archaeological sites, and beaches. The
problems caused by the use of old shells to make beads and other artifacts are surmountable through careful sample selection, analysis of multiple 14C dates on a variety of materials, and proper calibration procedures
-----http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WH8-
4GJK8HT-1&_user=10&_handle=V-WA-A-W-AA-MsSAYZW-UUW-U-AAWVVYDYYE-
AAWWUZYZYE-WBYDECVYA-AA-
U&_fmt=summary&_coverDate=07%2F05%2F2005&_rdoc=5&_orig=browse&_srch=%
23toc%236844%239999%23999999999%2399999!&_cdi=6844&view=c&_acct=C0000
50221&_version=1&_urlVersion=0&_userid=10&md5=b6f10960aa62a1f1c7d1a5f
5736db657
----- http://tinyurl.com/b9cl7 ----(Like the title, for McD Only)
Putting spaces in makes it both easier and more obvious. :-)
Apart from that, I would have thought the well known reservoir effect
associated with marine shells would have posed a larger imponderable
than the 'old shell' effect.
See http://www.findarticles.com/p/articles/mi_qa3712/is_200203/ai_n9066397
A carbon reservoir effect exists even in lake water. See http://www.the-conference.com/2003/Gold2003/abstracts/A328.pdf
I think that the problem of 'old shell' is potentially greater than the 'well known reservoir effect,' for the very reason that the reservoir effect is well-known. IIRC, when shell is used for dating, it can only be useful if there is a calibration curve available for that specific area and environment.
From the bit Phil posted, it sounds like the authors were able to make reasonable corrections to, let's say, 'contemporaneous' shell. It seems to have been the anomalous nature of the 'old shell' results that caught their attention.
This is all off the top of my head. I have to go to work now, so don't have time right now to chase any of this down. Perhaps when I get back to the ng, some other soul(s) will have done my homework for me :-)!
-- Tom McDonald http://ahwhatdoiknow.blogspot.com/ .
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