N.V. Sennikov

Geological position, geochemistry, and geodynamic formation environments of late givetian-early frasnian basalts in the central gornyi altai region

1151 The active continental margins (ACMs) represent one of the most illustrative examples of convergent boundaries between lithospheric plates. It is tradition ally believed that diverse magmatism of these struc tures is determined by successive dehydration of the subsided oceanic plate in response to the increasing depth of primary magma generation away from the edge of the continent, on the one hand, and the pecu liar structure and composition of the continental lithosphere, which are responsible for the specific composition of silica melts and crust–mantle interac tion, on the other [1 and others].

The Cambrian-Ordovician boundary in Gornyi Altai

792 The modern development of a set of Global Series and Stages for the Ordovician system [9] and subse quent changes in the Stratigraphic Time Scale used in Russia [5] have demonstrated the necessity of refine ment of the position of the most significant strati graphic levels, namely lower boundaries of series and stages in key sections over the territory of Russia. One of these levels is the Cambrian–Ordovician boundary, the position of which at present is based on the first appearance of conodont species Iapetognathus fluctiv agus Nicoll, Miller, Nowlan, Repetski et Ethington in the Green Point stratotype section in Newfoundland [7]. It is placed now stratigraphically above the previ ously accepted level of the base of the Ordovician in the Russian stratigraphic scale suggested by the appearance of conodonts Cordylodus proavus [4]. As a result of these changes, some strata previously consid ered as Lower Ordovician must now be referred to as Upper Cambrian. The conodont studies through the Cambrian–Ordovician boundary interval on the Sibe rian platform showed that, on the scale of regional stages, the shift of the Cambrian–Ordovician bound ary can be quite significant [11]. As part of this problem, the conodonts in the Kam lak Formation, at the Kamlak River near the epony mous village in the Biya–Katun zone of Gorny Altai have been studied. This sequence is the most compre hensive and representative section through the Upper Cambrian–Ordovician boundary in the region. The Kamlak Formation [1, 3] is divided into three subformations [10]: the lower, which according to numerous trilobites correlated to the Dobrin Regional Stage; the middle, which, by trilobites and brachio pods, is ascribed to the lower part of the Tayanzin Regional Stage; and the upper, which, by trilobites, brachiopods, and graptolites is correlated with the upper Tayanzin. The Dobrin Regional Stage is recog nized by trilobite complexes from typical sections in the Kuznetsk Alatau, where it is subdivided into two biozones: Skljarella lidiae/Tropidopyge tevipis and Euloma limata/Harpides ulumandensis [2, 6]. The Tay anzin Regional Stage is distinguished in the Gornaya Shoria sections on the basis of trilobites, and is divided into three zones: Apatokephalus sibiricus/Nyaya oriens, Amzasskiella mirabilis/Shumardia pusillina and Tersella strobilata/Niobe zhulanica [2, 6]. In 1976, in the second unit of the middle Kamlak Subformation (Kamlak section), the first conodonts Oneotodus datsonensis Druce et Jones (as identified by T.A. Moskalenko) were found. These forms were later found by N. G. Izokh and P. Myannik at the top of the middle Kamlak Subformation [10]. In 2008– 2011 as a result of mass sampling of the Kamlak For mation, the authors obtained representative collec tions of conodonts from five samples (2–3 kg) from four stratigraphic levels of the section (Fig. 1, I). The Lower Kamlak Subformation is composed of interbedded siltstones and variegated silty sandstones with weakly layered beds of light gray and red lime stones. In red and reddish gray bioclastic limestones of the middle part of the subformation (Fig. 1), the fol lowing conodonts of the Proconodontus Zone (Late Cambrian) were found; Phakelodus tenuis (Müller), Proconodontus muelleri Miller, Prooneotodus gallatini (Müller), Prooneotodus sp., Furnishina furnishi Müller, and Westergaardodina sp. (Fig. 2). The Lower Kamlak subformation is comprised pre dominantly of carbonate rocks with subordinate varie gated conglomerates, sandstones, and siltstones. The lower part of the ninth unit of gray predominantly algal limestones was characterized by Cordylodus caseyi Druce et Jones emend. Landing, Hispidodontus cf. H. triangularis (Abaimova), Cordylodus proavus Müller, Hirsutudontus cf. H. simplex (Druce et Jones), Hispid odontus cf. H. kulumbense Tolmacheva et Abaimova, Semiacontiodus sp., and Eoconodontus notchpeakensis (Miller). Yellow and gray ballstone of the 10th unit of the uppermost middle Kamlak Subformation yielded conodonts of the lowermost Ordovician Iapetognathus fluctivagus Zone Iapetonudus sp., Iapetognathus sp., The Cambrian–Ordovician Boundary in Gornyi Altai

A new type of Cambrian section at the base of the pre-mesozoic complex of the West Siberian petroleum megabasin (based on Vostok-1 stratigraphic well data, Northern Tomsk Region)

A new type of Cambrian section penetrated by the Vostok 1 stratigraphic test well in the eastern part of the West Siberian Plate (WSP), Tomsk Region, is described in terms of paleontology. It can be considered a key section for this region. According to a complex of geological and geophysical characteristics, the section in the depth range of 2766‐5010 m was divided into the Churbiga, Paidugina, Pudzhelga, Podelga, Kondes, Shedelga, and Pyzhina Formations, and their first description was made. The Cambrian section in the Vostok 1 well is most similar to those of the Kotuy-Igarka area of the northwestern Siberian Platform, where Cambrian deposits formed in the prereef zone of an open sea basin. Down into the section penetrated by this well, there has been identified the highly carbonaceous siliceous-argillaceous-carbonate Paidugina Formation, which is an analog of the Lower-Middle Cambrian Shumnaya and Kuonamka Formations of the Siberian Platform. The Paidugina Formation, which accumulated on the shelf and slope of the open sea facing the Paleoasian ocean, is considered oil-producing and suggests a high petroleum potential of the cis-Yenisei basin. Furthermore, a highly promising generation‐ accumulation petroleum system has been revealed. Some paleontological evidence for Cambrian deposits in the basement rocks of the eastern West Siberian Plate were first obtained from core studies in the

Accumulations of Block Material in the Chuya and Katun River Valleys and Distribution of Late Pleistocene Glaciation in the Altai Mountains

The data presented introduce substantial changes into Quaternary stratigraphy, paleogeography, and the geological history of the Altai Mountains. The purpose of this investigation was thorough study of block accumulations in the Chuya and Katun river valleys. The new data shed light on the structure of these deposits, their composition, the geomorphological and stratigraphic position, and the morphology of blocks. The revealed morphological features of individual blocks imply their glacial origin.