Rare and trace elements in modern bottom sediments of the Barents sea. Nd, Pb and Sr isotopic composition

Abstract

The article presents a brief lithological description of the modern bottom sediments of the Barents Sea, selected in the 67th voyage of the R/V “Akademik Mstislav Keldysh” at the polygons: 1) “Pechora Sea”; 2) “Western slope of Kaninskoe shoal”; 3) “Central Barents Sea (Shtokman area)”; 4) “Russkaya Gavan’ fjord”; 5) “Medvezhinsky Trench”; 6) in the area to the south of Spitsbergen; 7) “Kola meridian”; 8) “Spitsbergen – Franz Josef Land archipelago”; 9) “Cambridge Strait”. The distribution of Cr, Ni, Cu, Zn, Cd, and Pb in samples of bottom sediments (pelitic, aleurite-pelitic and sandy-aleuritic-pelitic ooze) is compared with the background concentrations and contents of these elements in the Post-Archean Average Shale (PAAS). The data obtained are consistent with the notion that the distribution of heavy metals and other elements in the bottom sediments is controlled primarily by the global geochemical background. The relationship of the Sc, V, Cr, Ni, Y, Zr, Nb, Mo, Hf, Th, U and rare-earth elements concentrations with content of fine pelite (< 0.001 mm) fraction and organic carbon (Corg) is considered. It was found that most of these elements are characterized by a moderate positive correlation with the amount of fine pelite fraction in samples. By the magnitude of the correlation coefficient with the Corg content, all elements are attributed into three groups: (1) with moderate positive correlation, (2) weak positive correlation, (3) practically not pronounced correlation. The distribution in the bottom sediments of the Barents Sea of the element-indicators of the source rocks composition (Sc, Th, Co, Cr, La and Sm), as well as of rare earths, make it possible to consider that the majority of bottom sediments is mature in geochemical terms material, the sources of which were rocks of the Kola Peninsula and Spitsbergen (?). The bottom sediments of the Cambridge Strait are represented by geochemically less mature material, which, apparently, entered the sea as a result of erosion of the Franz Josef Land archipelago rocks. The established isotopic characteristics (εNd, 207Pb/206Pb and 87Sr/86Sr) of 17 samples of surface sediments suggest that the main contribution to the formation of bottom deposits of the central regions of the Barents Sea is made by rocks of the mainland part located in the influence zone of the North Cape Current. Archipelagos and islands (Franz Josef Land, Novaya Zemlya, etc.) that frame the Barents Sea supply a relatively small amount of clastic material that is carried by Arctic currents. The values of εNd and 87Sr/86Sr in the surface sediments of the central part of the Barents Sea and in the ice-rafted sediments carried by the Transpolar Drift showed a significant difference. This suggests that the contribution of such material to the formation of surface sediments of the Barents Sea is relatively small