P.A. Fokin

Late Precambrian to Triassic history of the East European Craton: dynamics of sedimentary basin evolution

Abstract During its Riphean to Palaeozoic evolution, the East European Craton was affected by rift phases during Early, Middle and Late Riphean, early Vendian, early Palaeozoic, Early Devonian and Middle-Late Devonian times and again at the transition from the Carboniferous to the Permian and the Permian to the Triassic. These main rifting cycles were separated by phases of intraplate compressional tectonics at the transition from the Early to the Middle Riphean, the Middle to the Late Riphean, the Late Riphean to the Vendian, during the mid-Early Cambrian, at the transition from the Cambrian to the Ordovician, the Silurian to the Early Devonian, the Early to the Middle Devonian, the Carboniferous to Permian and the Triassic to the Jurassic. Main rift cycles are dynamically related to the separation of continental terranes from the margins of the East European Craton and the opening of Atlantic-type palaeo-oceans and/or back-arc basins. Phases of intraplate compression, causing inversion of extensional basins, coincide with the development of collisional belts along the margins of the East European Craton. The origin and evolution of sedimentary basins on the East European Craton was governed by repeatedly changing regional stress fields. Periods of stress field changes coincide with changes in the drift direction, velocity and rotation of the East European plate and its interaction with adjacent plates. Intraplate magmatism was controlled by changes in stress fields and by mantle hot-spot activity. Geodynamically speaking, different types of magmatism occurred simultaneously.

Extensional basins of the former Soviet Union: structure, basin formation mechanisms and subsidence history

Abstract We review the structure and evolution of a number of Riphean-Phanerozoic rifts and extensional basins within the territory of the former Soviet Union (FSU). Horst-and-graben formation in strong crustal and subcrustal lithosphere layers can explain the multi-trough character of rift systems observed in the Russian platform, the Vilyuy rift, the West Siberian rift system, the Pechora-Kolva rift system and the Laptev Sea rift. Many features in the evolution of these rifted basins are incompatible with predictions of classical stretching models. Basin subsidence often occurs in the absence of any noticeable stretching and over time scales much longer than predicted by models of thermal subsidence. Other observations include a time gap between rifting and the onset of post-rift basin subsidence of tens to hundreds Ma and a correlation in timing of subsidence phases of rifted basins and platforms with opening and closure events of adjacent ocean basins. These observations point to an important role for mechanisms such as ecologite formation within or beneath the lithosphere as well as intraplate compression and stress-induced lithospheric deflection.

Mesozoic to recent geological history of southern Crimea and the Eastern Black Sea region

Abstract We provide a synthesis of stratigraphic data to unravel the history of the geological evolution of South Crimea in the Mesozoic and Cenozoic. The South Crimea Orogen consists of three major mega-sequences: (1) the Triassic–Early Jurassic; (2) the Aalenian–Bathonian; and (3) the Callovian–Eocene. The Late Triassic–Early Jurassic deposits formed in the environment of a forearc basin and a remnant basin. The Aalenian–Bathonian deposits formed above subduction extension and a volcanic belt. Three main Callovian–Eocene tectonic units can be identified in South Crimea: (1) the South Crimean Shelf Basin; (2) the Sudak Deepwater Trough; and (3) the Alchak–Kaya Shelf Basin at the northern margin of the Shatsky Ridge. The Oligocene–Quaternary deposits are considered to be syn-orogenic. A description of the anticipated stratigraphic units on the Shatsky Ridge is suggested for the Middle Jurassic, Callovian–Late Jurassic, Neocomian, Aptian–Albian, Late Cretaceous–Paleocene, Eocene and Maykopian. We propose a model for the geological history of the Eastern Black Sea Basin. Graben formed during the Late Barremian–Albian at the location of the future Eastern Black Sea Basin and a phase of volcanism occurred in the Albian. The main phase of rifting and spreading of oceanic crust took place during Cenomanian–Santonian time. Supplementary material: A Google Earth kmz file of the location of the outcrops and sections is available at http://www.geolsoc.org.uk/SUP18850

Ar-40/Ar-39 dating, geochemistry and tectonic setting of Early Carboniferous dolerite sills in the Pechora basin, foreland of the Polar Urals.

Abstract Whole-rock laser-ablation 40 Ar/ 39 Ar dating of dolerite sills, penetrated at depths between 4479 and 5404 m during the drilling of the Kolva super-deep well in the Pechora basin, located in the northeastern part of the East European Platform (EEP) in the foreland of the Polar Urals, indicates an Early Carboniferous (Visean–Tournaisian boundary) emplacement age of 351±2 Ma. The sills are intruded into Early Devonian (Lochkovian) sediments, which constrains their maximum age to less than 400 Ma. They were previously considered to be of late Frasnian age (ca. 370 Ma) based on a comparison with the widespread Frasnian–Famennian magmatic activity of the EEP. Two samples from one of the sills are moderately altered and give younger ages (ca. 290–320 Ma) than the other samples. This apparent rejuvenation is most likely to be a consequence of thermal re-equilibration and alteration. Major- and trace-element geochemical data suggest that the sills represent the intrusion, into the deeper parts of the Pechora basin, of subalkaline (tholeiitic) basalt magmas generated by moderately high degrees of partial melting of a subduction-modified mantle source which may include an enriched mantle plume component. The inferred geodynamic setting is that of a back-arc basin associated with the Uralian subduction system, implying westward subduction beneath the EEP. The timing of sill emplacement corresponds to the age of a basal Carboniferous unconformity within the Kolva well at which Visean carbonates overlie a Frasnian–Famennian carbonate sequence and strata of Tournaisian age are missing.

The composition of the sandstone from the Oligocene turbidite of the Tuapse marginal trough

The lower part of the Maykop Group sediments of the Crimea-Caucasus region were studied. Available outcrops of every structure-facies zone were examined and the sandstone composition was determined in thin sections: as a result five main lithologies were distinguished. Sharply discrepant provenance sources for the Kerch Peninsula, Sochi area, and Abkhazia for the Early Oligocene are suggested and those feeding areas are assumed to be variably remote from a sedimentary basin. An updated Rupelian (early Oligocene) palaeogeographic scheme of the Crimea-Caucasus region is proposed.