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MUD VOLCANOES AS IMPORTANT PATHWAY FOR TRACE ELEMENTS INPUT TO THE ENVIRONMENT: CASE STUDY FROM THE KERCH-TAMAN PROVINCE, NORTHERN BLACK SEA

Ellina V. Sokol

Abstract

Twenty eight onshore mud volcanoes of the Kerch-Taman province were analysed to evaluate their current contribution to the trace-element budget of the landscape. The study area belongs to the Indol?Kuban Trough, where the anoxic marine mudrocks of the Maykop Formation were deposited in the Oligocene ? Early Miocene in the northern deep-water margin of the Parathetis ocean. The Maykopian Fm. mudrocks are main sources of solid matter for numerous mud volcanoes of the region. Mud masses (30 samples) and mud volcanic waters (65 samples) were analysed by the ICP-MS, ICP-AES and wet chemistry methods. Major and trace element compositions of the mud masses and the Maykopian sediments are comparable with mud enrichment in B (2-14 times), Sr (2-10), Hg (up to 7), P (1.2-1.9), and Na (1.5-2) but are depleted in K (0.7-0.8). Mud masses from the Taman Peninsula contain 5 times more sulphur than the Maykopian Fm. mudrocks due to gypsum and/or jarosite veinlets. The mud volcanic waters mainly have ???3-Cl/Na or Cl-???3/Na chemistry with variable salinity (5.2-53.2 g/l) and pH=7.7-8.7. The waters expulsed by salsas and gryphons are more diluted than those of large mud domes. Compared to seawater (SW), all mud volcanic (MV) waters have similar multi-element spectra with variable enrichment factors (MV/SW): 3.5 to 19 for Li, 6 to 1300 for Ba, 4 to 88 for Mn, 5.5 to 150 for B, 40 to 150 for P, and 4 to 25 for As. Generally, the mud volcanic waters of the province are depleted in alkaline and alkaline-earth cations, as well as in main seawater anions: MV/SW of 0.35-0.6 for Na, 0.05-0.4 for K, 0.01-1 for Rb, 0.01-0.3 for Mg, 0.03-0.25 for Ca, and 0.16-0.53 for Sr; 0.1-0.3 for sulphate, 0.2-0.7 for chloride, and 0.3-0.6 for bromide. The concentrations of Mg, Ca, Sr, and Ba in MV waters are highly variable due to surface and near-surface precipitation of borates (NaCa(B5O6(OH)6)В·5H2O; NaCa(B5O7(OH)4)В·5H2O), carbonates (CaCO3; Na2Ca(CO3)2В·5H2O; Na3Mg(CO3)2Cl), and sulphates (CaSO4В·2H2O; MgSO4В·6H2O; Na2SO4; Na2Mg(SO4)2В·4H2O). Thus the mud volcanoes of the Indol?Kuban Trough are active pathways for rising fluid and mud, which contribute significantly to the trace-element budget of the environment. Boron is mainly transported as polyanion and then immobilised as solid borates; Hg occurs as HgS; As is hosted by pyrite; Sr resides in CaCO3; but Li is progressively accumulated in evaporated water.

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DOI resolver: doi.org/10.5593/sgem2018/1.1/s01.040

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