We are doing the petrographic study of some sandstones and found various kinds of cements such as the calcite, iron oxide and different clays ranging from 10-40 %. We are unable to decide whether these cements are primary or secondary in origin.
Dear Professor
What is the geological context of these rocks? What is their sedimentation environment? I would suggest the SEM-EDS analysis of grain contact zones.
Dear Michal,
Thanks for reply. These sandstones belong to fluvial environment, while a few units are of transitional environment. Yes, i have also performed SEM-EDS analysis and kindly find a few SEM images and EDS data of above two samples (whose micro photographs are given).
Hello,
is it possible for you to identify replacement structures under the optical microscope or SEM? I could imagine that you can try element mappings with SEM. Then you can at least make a qualitative temporal statement on the the cements.
Dear Christian,
Thanks for reply. Yes, I have already done element mapping and through which it is found that the major cement is calcite but the problem is that I could not decide that either it is primary in origin (depositional ) or diagenetic.
Dear Professor
Older generations of cement usually occupy more outer parts of the interstitial space, while younger generations crystallize in its central parts.During cementation, the former components may be replaced by younger ones. I think it would be worth doing a linear EDS or EPMA analysis between the grains to determine the mineral variability of the binder.
Dear Michael,
I can't understand that what do you mean by inner and outer parts. The cement is always interstitial between the grains and sometimes even the grains are covered or coated by it. I have already mentioned that the cement is calcite but I don't differentiate that either it is primary or secondary. It is the actual problem.
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