XMT micropalaeontological study of the silicites

The article deals with possibilities of the computed X-ray microtomography (XMT) in micropalaeontological (conodonts) study of the siliceous and clayey deposits. Using of the traditional methods in this type of deposits is difficult. The work is based on collection of silicites (lithological type xa1), clayey silicites (lithological type xa2), cherty argillites (lithological type xa3), and limy silicites (lithological type xa4) from the deep-water Devonian and Carboniferous sequences of the Subpolar Urals and NE Pay-Khoy. Thirty-eight samples (about 20.4 cm3) were studied with X-ray microtomographs SkyScan 1272 and SkyScan 1173 in the NMSU «Gornyi» (Saint-Petersburg, Russia) with spatial resolution of 4-7 um. About 190 conodont elements and their fragments were found in the tomograms. The possibility of recognition of the conodont elements depends on lithological type of the host rock. The best contrast between conodont elements and host rock is detected in lithological types xa1 and xa3. These lithological types demonstrate maximal concentration of the conodont elements in the rock as well. The concentration of conodonts is up to 90 spec./cm3. The present study shows that XMT method is useful for search and identification of the conodonts in siliceous and clayey deposits. Taxonomic identification is possible just in tomograms of high spatial resolution (5-7 um).