I’m keen to use CL as a quick method to identify appropriate samples for isotope analyses. From what I have read, CL is mostly used to analyse very small parts of a sample. However, I would like to see a large-scale effect on whole thin sections (75x50mm) so I can be confident about drilling sample that is as unaltered as possible. Advice?
Marissa,
First of all, I would like to warn you: CL analyses on carbonate is not the magical tool to identify diagenetic alteration, as often seen in publications. What a CL picture tells you (in carbonate) is how much Mn and Fe there is in the carbonate lattice. Nothing more! The rest is interpretation. Mn will activate CL and turn the color into a bright orange, whereas Fe will dim it, but it has to be at very high concentration.
In brachiopod, for instance, numerous people have assumed that as soon as orange color were to be seen, it was the signature of diagenesis within the bachiopod shell. But see for instance the publication of Barbin & Gaspard (1995, Geobios). Diagenetic alteration might also take place within Mn enrichment (so blue color in CL picture).
For large scale observation, the best is to make series of pictures and stitch them afterward using Photoshop for instance.
Stephane
Dear Marissa - Stéphane has answered you very well, and some of this is illustrated in the attached paper. Just by using CL you would reject a lot of samples that would be deemed diagenetic and yet in fact they are recording pristine isotopic ratios. I try to demonstrate in this paper that an array of techniques need to be used - including SEM. I hope the paper helps and the references I have in that paper on CL. Cheers, Darren
Thank you to both of you -I appreciate the advice and the references! Am feeling much better 'armed' before my CL attempts!
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