Vol 53, No 6 (2018)

Based on materials obtained in Cruise 37 of the R/V Professor Logatchev (2014‒2015), the paper discusses formation conditions, morphology, isotope age, and mineral and chemical composition of sulfide ores in the Pobeda-1 (17°08.7′ N MAR) and Pobeda-2 (17°07.45′ N MAR) hydrothermal ore fields (Pobeda ore cluster) discovered in blocks 37 and 39 confined to the Russian exploration area. Morphogenetic types of ores are defined and their formation conditions are examined.

The structure of the southern marginal zone of the Upper Jurassic–Valanginian carbonate platform, Northeastern Caucasus, is considered with the Dagestan sector of the Shakhdag Massif as example. The massif consists of several large genetically diverse sedimentary complexes: (1) Upper Jurassic basal complex represented by the shallow-water terrigenous and carbonate sediments, which were formed under unstable sedimentation conditions; (2) reef complex ascribed to the barrier reef system; and (3) sedimentary sequence with the typical clinoform structure and the southwestward dip, toward the Dibrar trough. The formation of the marginal zone of the carbonate platform was mainly determined by (1) climatic conditions (transition from the humid climate in the Early and Middle Jurassic to the arid climate in the Late Jurassic) and (2) differences in the tectonic evolution of different structural-facies zones (weak subsidence of the Northeastern Caucasus, where carbonate platform was formed, and intense subsidence to the south in the flysch trough area). The formation of the internal structure of the Shakhdag Massif was mainly defined by the eustatic sea-level fluctuations.

The paper addresses zonation of the stratisphere: thermobaric conditions in its deep zones with anomalous high (AHP) and superhigh (SHP) fluid pressures, as well as main types of fluid-dynamic setting in the upper zone. Mechanisms of the clay dehydration and processes of oil-and-gas formation governing the development of superhigh fluid pressures in the lower zone of rock formation are also discussed.

New carbon and oxygen isotope data are reported on carbonate ores and host dolomites (upper Pod”emsk subformation) of the Porozhinsk manganese deposit. Manganese carbonates filling the karst depression of the Porozhinsk area are characterized by low δ¹³C (–14.6…–9.5‰, PDB) and δ¹⁸O (18.8…22.1‰, SMOW). These data indicate that the carbonate formation was contributed by the isotopically light carbon, which was released during the decomposition of organic matter, while waters of the ore-precipitating solutions were presumably of meteoric origin. Host dolomites (Porozhinsk and Mokhovoi areas) are characterized by the heavier carbon (–1.9…2.0‰) and oxygen (23.3…27.7‰) isotope compositions, which are presumably typical of carbonate sediments of the Late Neoproterozoic sea basin.