797 ISSN 1028-334X, Doklady Earth Sciences, 2017, Vol. 475, Part 1, pp. 797–802. © Pleiades Publishing, Ltd., 2017. Original Russian Text © A.V. Maslov, N.V. Kozina, V.P. Shevchenko, A.A. Klyuvitkin, Ph.V. Sapozhnikov, P.O. Zavialov, 2017, published in Doklady Akademii Nauk, 2017, Vol. 475, No. 2, pp. 195–201. REE Systematics in Modern Bottom Sediments of the Caspian Sea and River Deltas Worldwide: Experience of Comparison Corresponding Member of the RAS A. V. Maslov a *, N. V. Kozina b , V. P. Shevchenko b **, A. A. Klyuvitkin b , Ph. V. Sapozhnikov b , and Corresponding Member of the RAS P. O. Zavialov b Received September 30, 2016 Abstract—The results of comparison of a number of main parameters of the chondrite-normalized REE dis- tribution spectra in modern bottom, mainly pelitic, sediments of various sedimentary subsystems of the Cas- pian Sea and marginal filters of the Volga and Ural rivers with those characteristic of the pelitic fraction of modern bottom sediments of different river deltas worldwide are discussed. According to the features of the REE distribution spectra, as well as the ε Nd (0) values, it has been established that most samples of the Caspian bottom sediments are similar to those of large rivers and rivers, draining watersheds composed of sedimentary formations. DOI: 10.1134/S1028334X17070170 An analysis of the REE distribution and the sys- tematics of ε Nd (0) and the 87 Sr/ 86 Sr ratio in the mod- ern bottom sediments (MBS) of the Caspian Sea has made it possible to establish that there are no distinct differences in these parameters for bottom sediments of the Volga River delta and the northern, central, and southern regions of the Caspian Sea, i.e., all sedimen- tary subsystems of the Caspian Sea [3]. In general, the features of the REE distribution and 87 Sr/ 86 Sr systematics in modern bottom sediments of the Caspian Sea indicate that the suspended matter supplied by the Volga River dominates. Accordingly, the role of the clastics, including the ultrafine-grained fraction, which is supplied to the Caspian Sea from the surrounding mountainous structures (Caucasus, Elburz, etc.) is insignificant in the coastal area. This work aims to specify the contribution of lithologically different provenance areas to the creation of the geo- chemical image of the Caspian MBS, taking into account the modern data available on the REE distri- bution and ε Nd (0) variations in the pelitic fraction of modern bottom sediments of the river deltas world- wide, attributed to various types [11]. The catchment area of the Caspian Sea includes the Ural Fold System, the Russian Plate, Greater and Lesser Caucasus, Iranian mountain structures, and deserts of West Turkmenia and Kazakhstan, which are composed of various sedimentary, magmatic, and metamorphic rocks of a wide age range. The Urals are composed of Upper Precambrian and Paleozoic mag- matic, volcanogenic-terrigenous, and sedimentary complexes. Among rocks, mafic rocks and granitoids dominate [7, 10, etc.]. The cover of the Russian Plat- form is represented by Devonian, Carboniferous, Permian, Jurassic, and Cretaceous sedimentary rocks [8]. The Greater Caucasus is composed of Mesozoic– Cenozoic sedimentary and effusive formations, as well as Paleozoic metamorphic and igneous rocks [2], while the Lesser Caucasus consists of effusive, volca- nogenic–sedimentary, and sedimentary formations, intruded by ultramafic rocks and granitoids [3]. The northern flank of the Elburz Mountains, facing the Caspian Sea coast, is largely represented by Mesozoic sedimentary rocks and Cenozoic volcanics. In the Kopet Dagh Mountains, sedimentary formations dominate [12]. This makes it quite difficult to estimate the contribution of each of the above-mentioned provenance areas to accumulation of modern bottom sediments in the Caspian Sea and the creation of their geochemical image, inasmuch as there is a lack of pub- lished representative data on the distribution of a wide range of impurities in the suspended matter discharged by rivers into the Caspian Sea. For the Caspian Sea, such data, on the contrary, are available [1, 5, 6, etc.]. It is possible to a certain extent to fill this gap by using recently published data [11] on the REE distribution in pelitic and silty fractions of modern bottom sedi- GEOCHEMISTRY a Zavaritsky Institute of Geology and Geochemistry, Ural Branch, Russian Academy of Sciences, Yekaterinburg, 620016 Russia b Shirshov Institute of Oceanology, Russian Academy of Sciences, Moscow, 117997 Russia *e-mail: amas2004@mail.ru, **e-mail: vshevch@ocean.ru