Geoscience Life - Micro-Sampling Shells to Determine Paleoclimate

This Spring 2022 semester, I had the opportunity to do an independent study under UTSA EPS's Dr. Godet. The subject of the study was to prepare a set of limestone samples from the Corbières region of France that included fossils of Aptian (Early Cretaceous) rudist bivalve shells for micro-sampling. When the rock samples were cut and polished, they were imaged on a cathodoluminescence microscope in order to determine if any chemical replacement in the fossil had taken place, which would render regions of the fossil area incapable of sampling as they would give the paleoclimate data of the replacement and not the original fossil. Photographs of viable areas for sample were taken and the samples were set aside for microsampling. The micro-sampling process uses a diamond tipped dremel drill bit to powderize the surface of the fossil. The powder is collected in a centrifuge tube and will be shipped to a laboratory for analysis of their clumped isotope composition which is used to derive the seawater temperatures of the paleoenvironment in which the shell originally existed.

I will have to wait for a few months to find out the result from the lab.

This was a very interesting experience to learn how paleoclimates are determined. The process of micro-sampling fossils to prepare them for lab testing was time consuming but very fun.

Cut piece of limestone revealing rudist shell fossil within. After being cut, pieces were polished in order to properly image through microscope.

Stage and tool for microsampling. top illumination and an 8x zoom microscope were used to ensure the proper areas were being microsampled.

Image of sample just prior to microsampling. The rudist shell is the dark grey on the surface. lighter grey is a matrix/replacement that is untestable. brown object in surface is unknown but also untestable.

Image of sample through 8x zoom microscope prior to testing. Bivalve sample is the darker grey.

additional photo showing bivalve.

Image of Bivalve fossil rock samples after micro-sampling. Note the scraped out areas within the darker grey that was visible earlier. That region of the sample is the only viable surface of the rock for testing to determine paleoclimate. centrifuge tubes in rear of box are ready to be shipped to the laboratory for testing.