Currently, the techniques applied for extraction and study of conodonts from siliceous rocks are associated with a number of problems. This makes it difficult to solve many problems in the areas of development of the volcanic and volcanic-sedimentary rocks, where cherts, jaspers, and phtanites are the only sedimentary formations for dating these deposits. On X-ray computed microtomography it is possible to avoid some problems to obtain not only excellent 3-D images of conodonts, but sections in any direction too, as well as in video formats. It is shown that similar results are successful under the hollows after the dissolution of the conodonts. There is no problem in application of X-ray microcomputed tomography when conodonts have been already found on the surface or inside of the sample, or if the content of conodonts in the rock is obviously high. In such a case the scanning without preliminary search is ensured. In cases when conodonts are rare and not obvious, it is proposed the following technique of their discovery. The rock sample is cut into plates. The conodonts are search for on the surface of the plates, moistened with a mixture of glycerin and water under a binocular microscope. If it is necessary (when the rock is opaque), the result is checked by a chemical reaction: 5–10 % hydrochloric acid plus 1–2 crystals of ammonium molybdate are put on the surface of the sample. The appearance of a yellow sediment means the presence of phosphorus, to indicate the probability the detected object to be a conodont. Next, the sample should be washed from acid, its size should be decreased. Then the microtomographic study should be performed.

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Реферат: Рассматриваются особенности изменения конодонтов и брахиопод в ракушняке пограничного фран-фаменского интервала в классических карбонатных разрезах Западно-Уральской внешней зоны складчатости Южного Урала. В разрезах Ряузяк и Кук-Караук (Сиказа) по конодонтам обосновывается положение границы в подошве барминского горизонта. Она зафиксирована внутри литологически однородной толщи брахиоподового ракушняка одновременным появлением конодонтов Palmatolepis triangularis Sann. и брахиопод Parapugnax markovskii (Yud.). Ракушняк пограничного F/F интервала расчленен на конодонтовые зоны и подзоны Upper rhenana, linguiformis, Lower и Middle triangularis и детально охарактеризован конодонтами и брахиоподами. Биофациальный анализ по конодонтам показывает, что в верхней части зоны linguiformis во всех разрезах наблюдается смена пальматолепидной биофации с изобилием таксонов рода Palmatolepis крайне обедненной, практически монотаксонной, икриодидной (мелководной) биофацией. По-видимому, это связано с эвстатическими изменениями уровня Мирового океана и с событием массового вымирания (Upper Kellwasser Event) рубежа F/F.

Research subject. This article presents the results of a study undertaken to investigate the systematics of rare-earth elements (REE), Y, Th, U and Mn in the Upper Devonian conodonts of the Western Ural region of the foreland fold of the Southern Urals (Askyn and Makarovo horizons, Kukkarauk, Ryauzyak and Lemezinsky sections).Methods. The conodonts were isolated from carbonate rocks using the conventional method of their dissolution in organic acids, mainly formic acid. Sample preparation and mass spectrometric analysis were carried out in the class 1000 and 10 000 cleanroom facilities of the Zavaritsky Institute of Geology and Geochemistry. A PerkinElmer ELAN 9000 quadrupole ICP mass-spectrometer was used to determine the concentration of the trace elements under study. Sm and Nd isotope ratios were measured from a 3% nitric acid solution by a Thermo Fischer Neptune Plus multicollector inductively coupled plasma mass-spectrometer. The long-term reproducibility and accuracy of the measurement procedure were evaluated using a standard Merck Nd solution based on the NIST Nd2O3 and yielded 143Nd/144Nd = 0.511720 ± 15 (1 SD, n = 40).Results. The established features of PAAS-normalised lanthanide distributions in the conodont bulk samples (10.4–21.8 mg), Ce-anomalies, high REE values (173–1211 ppm) and a number of other parameters indicate the leading role of late diagenetic processes in the formation of conodont REE systematics. This is also evidenced by the Y/Ho values (≈26–32) specific for the studied conodont samples.Conclusions. In general, the distribution of lanthanides in the conodonts suggests that this process was mainly controlled by a lithogenic (from 90 to more than 99%) REE source. The εNd (t) (–4.0…–2.8) values characteristic of the cono donts of the Askyn and Makarovo horizons suggest that their Nd isotopic composition was either formed under the influence of the open ocean (island arc basin), characterised by a significant share of radiogenic Nd, or due to the entry of radiogenic waters of the ocean into the shelf zone at the peak of the marine transgression that took place in the region under consideration in the Famennian.