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Dear Gerry,
In principle, stable isotope methodology can be diagnostic in such studies. Problems arise in that multiple sources often exist for a given element.  Also isotopic fractionation might occur during and post deposition. Competent interpretation of the data would probably require isotopic data from other relevant samples.
Interestingly, I have been involved with a colleague in a European city studying erosion of  sections of walls of older buildings at an elevation range from ground level up to about one meter.  It seems unlikely that industrial pollutants in the air would have such localized effects . Organic-N was present in the eroded areas. One possible  scenario is centuries of urination  against the walls by males particularly  after they had consumed beer in nearby taverns. (Although dogs might be a minor source close at ground level, they would not be effective contributors at the higher elevations!). 
My colleague and I have been pondering some isotope ( N,S) data for about a decade. They can best be described as consistent with the human urination scenario but to say that they definitely prove it would be a leap of faith. 
Isotope methodology is more definitive when many elements are studied particularly where different sources and biological conversions are involved. It often becomes a question of deciding the importance of the answer in relation to the costs in time and materials required to acquire it. To this end it is appropriate to  better "define" your sample  before proceeding with isotope measurements as suggested by Kurt Kyser.
One possibility  might be to examine the oxygen isotope composition of sulfate.  The sulfate concentration of urine exceeds that ingested by a few orders of magnitude. Most of the sulfate in urine arises from oxidation of dietary 
organic-S.  During oxidation, some of the oxygen in the sulfate is derived from body water. The latter in turn is close to but not identical isotopically to meteoric water. Consequently we have shown that the O-isotopic composition of sulfate in urine varies geographically dependent  upon the isotope composition of consumed water.  We have also verified the latter with O-isotope labeling studies in the laboratory. With our study of the old city walls and possibly with your deposit, there is possibly a post depositional complication. About half of the sulfur in urine is organic-S and some would probably be oxidized to sulfate after voiding.  The oxygen isotope composition of this sulfate might not differ radically from that produced in the animal but that assumption needs verification.

Along the lines of Kurt Kyser's comments, have you looked for evidence of bio-organic material such as hair which is remarkably resistant to weathering? 

Roy Krouse


At 06:26 PM 7/23/2004, you wrote:

Hi, 

We were referred to this list server by Prof. Robert Clayton (Univ. of Chicago), since this is not our field. 

We wonder if we can trouble you with a question on a rock specimen we have analyzed recently. 

that urine samples of mammals contain (C, N, O, Ca, Cl, Na, K, Si and S, among other cations). 

The reason that we are e-mailing you is to ask if isotopic abundance measurements which is your specialty might be of some value in approaching this problem. Previous studies on chlorine-36 in fossil rat urine(1) has shown that 36-Cl/Cl ratio could be used to track temporal patterns dating back ~ 38,000 years before the present (as measured by 14-C).  According to ref. 1, the 36-Cl/Cl ratio shows a discontinuity around 12,000 years before the present with a ratio between 125 %- 200% of modern pre-bomb values whereas during the past 10ky the ratio ranged from 50-100% of modern values.  

Since we appreciate this is a difficult matter and the cementum could have abiogenic origins, we wonder if isotopic abundance can be employed to ascertain if this rock specimen cementum is abiogenic or biogenic in origin in general.  We have ample specimens of the rock for analysis, if there is any interest.

All helpful comments and/or offers of assistance would be greatly appreciated by us.  Please reply off list. 

Sincerely 

Gerry Zajac 
BP research 
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