Field of Science

Enhanced Technique for Separating Microvertebrates from Matrix

The Journal of Paleontological Techniques is an online, open access journal dedicate to publishing papers on fossil preparation.  The latest offering is this paper by Mitchell and Heckert describing the use of sodium polytungstate filtration to separate some Upper Triassic microfossils from collected matrix. Although there are some serious caveats to using these chemicals (such as how the chemicals react with metal and glass...ouch), the results are promising and the set-up looks fairly easy.  You can download this article free from here.

Mitchell, J. S. and A. B. Heckert. 2010. The setup, use and efficacy of sodium polytungstate separation methodology with respect to microvertebrate remains. Journal of Paleontological Techniques, 7: 1-12.

Abstract - Concentrated deposits of small remains from vertebrates, termed microvertebrate sites or vertebrate microsites, are a unique and detailed source of information about the history of life. Collecting fossils from these sites, however, presents unique challenges. The most time consuming, and thus most deterring, aspect by far is the separation of the fossils from the sediment. This study attempts to quantify to what extent the use of sodium polytungstate (=sodium metatungstate, Na6H2W12O40, abbr. SPT) filtration increases fossil concentration, how quickly fossils sink in SPT solutions, and what is a good working density for SPT. We do this by generally following the methodology set out by previous authors, although with some substantial modifications, on an Upper Triassic deposit dominated by clay minerals and lithic fragments, as well as on a second, smaller quartz sand dominated microsite. We also provide a revised and detailed guide with our modifications to former practices and our recommendations to other workers interested in creating a SPT laboratory, including the strong advisory to work over thin plastic sheets, as SPT can react with metal and adheres strongly to glass when it crystallizes.

Our experiments have shown a significant improvement in fossil concentration (from ~2% of the clasts being fossils to ~19%) at the main site, with a sample from the other site showing the treated concentrate as 25% fossil. We have also found very few fossils in the float (<0.5%), but noticeable rates of fossil loss in SPT solutions above ~2.80 g/mL (up to 16%). Further, we have found that 2.75 g/mL is a good working density for several lithologies, as it is high enough to float most rock, low enough to sink most fossils, and low enough to be manageably maintained. SPT has, in processing one particularly rich site, saved many person-hours that otherwise would have been spent picking through less concentrated sediment.

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