Stratigraphy and Geological Correlation

The information on the Late Palaeozoic deposits of the New Siberian Islands is essential to clarify the palaeogeography of the surrounding Arctic Region and to quest the original location of the New Siberian continental block prior to the Amerasian ocean opening. The best Upper Palaeozoic section of the islands, located in the western part of the Kotel’ny Island (Tas-Ary Peninsula), was examined in detail. The studied rocks characterize a transitional facial zone between the northeastern shallow-water (central areas of the Kotel’ny Island) and the southwestern deep-water ones (Bel’kov Island). The stratigraphy of the Carboniferous and partly Permian strata was specified by the study of four fauna groups, detrital zircon dating, and structure interpretation. The section demonstrates a gradual change of depositional environments from shallow-marine in the Lower Carboniferous to deep-water in the middle Carboniferous and Permian. The Tournaisian and Visean rocks (Tas-Ary Formation, not less than 950 m) were formed on the open shelf or ramp with predominant carbonate sedimentation. They were deposited above the storm-wave base during the early Tournaisian and at greater depth later. The Serpukhovian–Middle (?) Permian rocks (Bel’kov Formation, not less than 300 m) were accumulated on the deep-water subaqueous slope and, possibly, at its base. Black shales and turbidite sandstones compose a significant part of the Bel’kov Formation. Sandstones have a siliciclastic–carbonate composition in the upper Lower Carboniferous and are carbonate-free up the section. The boundary between Tas-Ary and Bel’kov formations corresponds to a change in the shelf-to-basin profile and depositional style. At this time (the beginning of the Serpukhovian), the subsidence rate increased, a pronounced slope was formed, and a new source of clastics appeared on land. This reorganization was probably related to the Northern Taimyr orogen rise. The lithological similarity of the Lower Carboniferous deposits of the Tas-Ary Peninsula and Southern Taimyr, the synchronous shift in sedimentation from carbonate to terrigenous rocks, and the same source of clastic material for the Upper Carboniferous–Permian sandstones in both regions indicate their belonging to the same sedimentary basin in the Late Palaeozoic. We believe that the western part of the New Siberian Islands represented a continental margin in Late Devonian, Carboniferous and Permian times, and that it was a continuation of the Verkhoyansk margin. The latter is possible, taking into account rotation of the New Siberian Islands block according to the two-pole rotational model of the Amerasian basin opening.

The most stratigraphically representative section of Turonian–Coniacian in the right-bank part of the Volga region is found at the Kamennyi Brod-1 section (Olkhovka district of Volgograd oblast). The subdivision of carbonate rocks into zones is based on the complexes of benthic foraminifera and other accompanying groups of invertebrates. Regressive-transgressive tendencies in the evolution of the Turonian–Coniacian basin is also reflected in the quantitative ratio between benthic and planktonic foraminifera. The earlier unknown representatives of Turonian and Coniacian marine biota are revealed: silicon sponges, crinoids, starfish, brittle stars, and brachiopods. The magnetostratigraphic (magnetopolar and petromagnetic) characteristic of the section is obtained, and the magnetic zone of anomalous polarity is revealed against the background of normal polarity (N). It is supposed that anomalous directions of magnetization represent the stabilized vector sum of oppositely directed components, one of which (corresponding to reverse polarity) is the primary one.