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Subject:
From:
Stephen Grimes <[log in to unmask]>
Reply To:
Stable Isotope Geochemistry <[log in to unmask]>
Date:
Thu, 25 Nov 2004 09:50:56 -0000
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Dear List Members

I am thinking of purchasing a New-Wave Micromill Sample Preparation
system to micro-drill carbonate samples from fish otoliths and
gastropods. If anyone has experience using this system could you please
help me answer the following questions
1. What is the smallest spot size you have been able to drill at? i.e.
100 micron?
2. What is the highest resolution you have been able to achieve? i.e.
samples every 500 microns?
3. Has anybody used this system to micro-drill coiled gastropod shells?
4. Has anybody used this system to micro-drill thin shelled freshwater
gastropods?
5. How long does it roughly take to drill say 20 micro-samples from a
single shell?

Cheers Steve

Dr Stephen Grimes
Lecturer in Stable Isotope Geochemistry and Climate Change
School of Earth Ocean and Environmental Sciences
Room 107 Kirkby Lodge
University of Plymouth
Drake Circus
Plymouth
Devon
PL4 8AA

Office: Room 101, 4 Portland Mews
Tel. +44 (0)1752 233109
Fax. +44 (0)1752 233117
e-mail. [log in to unmask]
Web page.
http://www.plymouth.ac.uk/pages/dynamic.asp?page=staffdetails&id=sgrimes

-----Original Message-----
From: Stable Isotope Geochemistry [mailto:[log in to unmask]] On
Behalf Of stephen crowley
Sent: 22 November 2004 13:54
To: [log in to unmask]
Subject: [ISOGEOCHEM] Dolomite-acid fractionation factors

Is anyone prepared to offer an opinion on the fractionation of oxygen
isotopes during the reaction between dolomite and phosphoric acid?

I have been happily using the fractionation factor published by
Rosenbaum &
Sheppard (1986, GCA 50, 1147), but I've recently had cause to reconsider
the validity of the value published by these authors.

The recent publication of a revised fractionation factor for magnesite
(Das
Sharma et al. 2002, GCA 66, 589) suggests to me that the R&S value may
be
incorrect. If one assumes that the acid fractionation factor varies
linearly as a function of chemical composition (mole fraction) in a
binary
solid-solution, then at a reaction temperature of 50oC the R&S value is
too
large by about 0.6 (on a 1000lnalpha scale). This assumes 1000ln alpha
values for calcite and magnesite of 9.25 and 10.79 respectively, and an
'average' dolomite value (using eqn 3 of R&S) of 10.60.

If a similar relationship is established for a reaction temperature of
25oC
then this allows the fractionation factor reported by Sharma & Clayton
(as
revised in Friedman & O'Neil, 1977, USGS Prof Pap 440-KK) to be
compared.
On this basis the S&C value plots extremely close to the 'predicted'
trend
and appears to provide some empirical evidence to support my uneasiness
regarding the R&S fractionation factor for reactions at 50oC.

I'd be very interested to receive views on this subject. I'd also like
to
gauge the general feeling regarding the preference for using
dolomite-acid
fractionation factors, as opposed to the Lynton Land approach of not
using
a dolomite specific fractionation factor.

Regards,

Steve Crowley

University of Liverpool

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