The Yudomian of Siberia,Vendian and Ediacaran systems of the International stratigraphic scale

In Russia, the terminal Neoproterozoic formally includes the Vendian of western part of the East European platform and the concurrent Yudoma Group of Siberia. As is shown in this work, the designated subdivisions correspond in the stratotypes only to the upper, Yudomian Series of the Vendian. In the Siberian platform, the Ust-Yudoma and Aim horizons of the Yudomian are tightly interrelated. The lower of them, bearing remains of Ediacaran Fauna, represents the Ediacarian Stage, whereas the upper one containing small-shelled fossils (SSF) corresponds to the Nemakit-Daldynian Stage divided into the trisulcatus and antiqua superregional zones. In more complete sections of the platform periphery, sediments of these subdivisions conformably rest on siliciclastic succession that should be ranked as basal subdivision of the Yudomian. The succession is concurrent to the Laplandian Stage of the East European platform. According to geochronological dates obtained recently, the Yudomian Series spans interval of 600–540 Ma. In the East European platform, the Upper Vendian (Yudomian) begins with the Laplandian basal tillites of synonymous stage. In the west of the platform, tillites are dated at 600 Ma like the Upper Vendian base in Siberia. The next Ediacarian Stage of the East European platform is stratigraphic equivalent of the Redkino Horizon, while summary range of the Kotlin and Rovno horizons is concurrent to that of the Nemakit-Daldynian Stage. The Vendian of Russia is conformably overlain by the Tommotian Stage of the Lower Cambrian. Intense pre-Vendian events constrained distribution areas of the Lower Vendian sediments in Russia. The Lower Vendian deposits of the East European platform are most representative and well studied in the central Urals, where they are attributed to the Serebryanka Group. In Siberia, separate subdivisions representing the Lower Vendian are the Maastakh Formation of the Olenek Uplift, two lower members of the Ushakovka Formation in the Baikal region, and the Taseeva Group of the Yenisei Range. Chronological interval of the Lower Vendian corresponds to 650–600 Ma. The Marinoan Glaciation dated in Australia at 650–635 Ma is concurrent to basal part of the pre-Yudomian interval of the Vendian in Russia, whereas the Laplandian Tillite and Gaskiers Glaciation (600–580 Ma) correspond to onset of the Yudomian Epoch. The new Ediacaran System (Knoll et al., 2004) legalized in the International Neoproterozoic scale is close in range to the entire Vendian (635–544 Ma), although without basal beds (Marinoan Tillite) it deprives the terminal Neoproterozoic of its original sense. Inferiority of the system consists also in its indivisibility into stages. Hence, it is clear that the Vendian System subdivided in detail in Russia should be retained in the rank of terminal system of the Precambrian, one of the basic in general scale of the Neoproterozoic.     

To the problem of stage subdivision of the Lower Cambrian

It was a serious mistake when subdivision stratotypes had been disposed of in practice of constructing the General stratigraphic scale, because they cannot be substituted by the boundary stratotypes. A subdivision stratotype and respective GSSP are complementary parts characterizing any stratigraphic unit. The best candidates for stage stratotypes of the Lower Cambrian are certainly sections of the Lena-Aldan region in the Siberian platform, which have been studied in detail during many years, are well exposed, and contain abundant and diverse fossils, being insignificantly disturbed by tectonic dislocations. Nomenclature, stage and boundary stratotypes of the Siberian standard can be successfully used therefore for stratigraphic subdivision of the Lower Cambrian.     

Upper cretaceous radiolarians of the East European platform and their biostratigraphic significance

Radiolarian assemblages from the Upper Cretaceous carbonate-cherty deposits of the East European platform are analyzed. Biostratigraphic subdivisions ranked as radiolarian beds are distinguished in sediments of the Moscow syneclise, Voronezh anteclise, and the Ul’yanovsk-Saratov depression. The correlation between biostratigraphic beds established in three tectonic structures and variants of their coordination with radiolarian subdivisions in southern and northern areas of Russia are considered. The key importance of radiolarians for the subdivision and correlation of the Upper Cretaceous cherty deposits is demonstrated.     

Palynostratigraphy of the Erkovtsy field of brown coal (the Zeya-Bureya sedimentary basin)

The Erkovtsy brown coal field in the northwestern Zeya-Bureya sedimentary basin (129°–130° E, 46°–47° N) is structurally confined to southern flank of the Mesozoic-Cenozoic Belogor’e depression. The verified stratigraphic scheme of the coalfield sedimentary sequence is substantiated by palynological data on core samples from 18 boreholes sampled in the course of detailed prospecting and by paleobotanical analysis of sections in the Yuzhnyi sector of the coalfield (data of 1998 by M.A. Akhmetiev and S.P. Manchester). Sections of the Erkovtsy, Arkhara-Boguchan, and Raichikha brown-coal mines are correlated. Stratigraphic subdivisions distinguished in the studied sedimentary succession are the middle and upper Tsagayan subformations (the latter incorporating the Kivda Beds), Raichikha, Mukhino, Buzuli, and Sazanka formations.     

The regional stratigraphic scheme of the miocene sediments of the fore-urals and the major events in the southern Ural region

This work presents a clarified stratigraphic scheme of the Miocene sediments of the Fore-Urals and the territory of Bashkortostan. As a result of the work carried out, the regional stratigraphic divisions of the Miocene of the Fore-Urals were described and stratotypes and reference sections were established for the first time. The stratigraphic scheme of the Miocene sediments includes the sequences of the Lower (the upper part of the Tyulganskian Formation, Kuyurgazinskian and Voroshilovskian formations), the Middle-Upper (Ushkatlinskian Formation) and the Upper (the lower sub-formation of the Tchebenkovskian Formation) Miocene. In addition, the stratigraphic scheme developed was correlated with those of the Urals, the Russian Plain and the Lower Volga Region. The scheme is based on the data obtained from study of sediments, analysis of paleontological and lithological data, and summary of literary and library materials, which allowed us to elucidate in detail the Miocene events in the Fore-Urals.     

Stratigraphy of Middle-Upper Jurassic deposits in the East Russian plate

The work is aimed at litho-, bio- and magnetostratigraphic subdivision of the Middle-Upper Jurassic sedimentary succession in the northeast of the Ul’yanovsk-Saratov depression (the East Russian plate). Problems of regional and interregional correlation of distinguished subdivisions are considered. As is shown, the ammonite biostratigraphy is most effective method for solving problems of chronostratigraphy.     

New ammonite zonation of the lower Callovian in North Siberia

The lower Callovian succession observable in cliffs of Anabar Bay and Bolshoi Begichev Island is described with consideration of zonal subdivisions and beds with ammonites. The unified summary biozonation suggested for North Siberia includes the Cadoceras elatmae Zone with C. frearsi and C. elatmae (instead former C. anabarense) subzones, subsequent C. tschernyschewi and C. tolype zones, and successive C. cf. sublaeve, Rondiceras milaschevici, and Cadoceras ex gr. durum (formerly part of the middle Callovian) beds. As in Siberia and East Europe there are species in common C. elatmae (Nik.), C. frearsi (Orb.), C. tolype Buck., and C. emelianzevi Vor.; certain ammonite zones of Siberian succession are directly correlated with the East European, East Greenland and standard zonations. It is concluded that the lower Callovian is completely represented in Siberia. The lower part of the interval, formerly attributed to the middle Callovian, represents the upper part of the lower Callovian Substage. Zones established in the lower Callovian succession of Siberia are contiguous, whereas equivalents of the Elatmae Subzone and Tschernyschewi Zone have not been distinguished in sections of East Greenland. Evolutionary trends of species in subfamily Cadoceratinae are preliminary discussed.     

Holocene deposits in the Mangyshlak Peninsula,North Caspian Sea region

Comprehensive analysis of the data of high-precision seismoacoustic profiling, drilling and sampling of deposits using seabed corers, biostratigraphic studies, and radiocarbon age data was performed for the first time for Mangyshlak sediments in several bottom sites of the North Caspian. It was found that the Mangyshlak sediments comprise numerous linearly stretched depressions of 5–10 m in depth (morphologically similar to modern substeppe ilmen areas in the Volga River delta), which are covered by the Novocaspian sedimentary cover, and river incisions (among them the largest Volga River valley). In addition, the Mangyshlak sediments comprise the deltaic alluvial fans of different sizes along the shelf zone of the North Caspian. Analysis of mollusks and biogenic remains indicates that accumulation of the Mangyshlak sediments occurred in freshwater and slightly salty water environments under various hydrodynamic and hydrochemical conditions. According to radiocarbon dating of organic matter, the Mangyshlak sediments formed during sea regression in the range of 10-8 ka (isotopic age) or 11.5-8.5 ka (calendar age). Several types of sediments are distinguished: clayey-carbonate sediments, enriched with organic matter up to the formation of sapropel and peat, accumulated at the lowest sea level; weakly calcareous silty-clayey silts, formed during the subsequent intense filling of paleodepressions with terrigenous material. The features of the mineral composition of sediments are as follows: polymineral composition of clayey material with a high proportion of hydromica and disordered mixed-layered formations, a high content of minerals of the epidote group, amphiboles, and other accessory minerals. All of this indicates a genetic relationship between the Mangyshlak sediments and the Volga terrigenous material.     

Unit stratotypes for global stages: The Neogene perspective

Recent developments in integrated high-resolution stratigraphy and astronomical tuning of continuous deep marine successions invalidate arguments against the designation of unit stratotypes for global stages, the basic building blocks of the standard Global Chronostratigraphic Scale (GCS). For the late Neogene, Global Stratotype Section and Point (GSSP) sections may also serve as unit stratotypes, covering the interval from the base of a stage up to the level that–time-stratigraphically–correlates with the base of the next younger stage in a continuous and well-tuned deep marine succession. The added value of such sections as unit stratotype lies in the integrated high-resolution stratigraphy and astronomical tuning, which combined, provides an excellent age control with an unprecedented resolution, precision and accuracy within the entire stage. As such they form the backbone of the new integrated late Neogene time scale and provide the basis for reconstructing Earth's history. In this way a stage is also defined by its content and not only by its boundaries. Our unit stratotype concept strengthens the importance of time-rock units by allowing the introduction of astronomically defined chronozones as formal chronostratigraphic units, thereby arguing against the elimination of the dual classification of chronostratigraphy and geochronology.Extending this concept to older time intervals requires that well-tuned, continuous deep marine sections are employed, thus necessitating the employment of multiple hole (I)ODP sites for defining (remaining) stages and stage boundaries in at least the Cenozoic and Cretaceous and possibly the entire Mesozoic. Evidently the construction of the Geological Time Scale (including the GCS) should be based on the most appropriate sections available while, where possible, taking the historical concept of global stages into account.     

成矿带1∶20万水系沉积物地球化学分区的方法及地质意义:以西藏冈底斯铜多金属成矿带为例

以冈底斯铜多金属成矿带为例,阐述了利用1∶20万和1∶50万水系沉积物地球化学测量开展成矿区带地球化学分区的方法和思路,进一步对其地质意义进行了探讨。结果表明:小比例尺的水系沉积物地球化学数据具有地球化学分区示踪意义。总结出一套操作性强的地球化学分区方法,其方法具有指示找矿方向的实际意义,对区域构造单元划分具参考价值。地球化学分区为该区的找矿方向、成矿远景评价及基础地质调查奠定了基础。     

The eastern flank of the Caspian Basin: Sedimentary complexes and sedimentation conditions in the Early-Middle Carboniferous

Carboniferous and Lower Permian Carbonate and terrigenous rocks with the total thickness of >4000 m serve as the productive units in the Paleozoic subsalt complex at the eastern flank of the basin surrounding the northern area of the present-day Caspian Sea (hereafter, Caspian Basin in the broad sense). In recent years, several large oil and gas-condensate fields were discovered in these rocks. The complexity of geological evolution of this region, which is situated at the junction between the East European Platform and the Ural orogen, as well as multiple changes of sedimentation conditions during the Middle and Late Paleozoic, are reflected in the diversity of types of terrigenous and carbonate sediments and their facies alterations. Reconstruction of these environments makes it possible to elucidate specific features of the location of reservoir rocks in vertical and horizontal sections, as well as regularities of variations in their filtration-capacitive properties.     

First results of investigation into the relation between magnetic properties of bottom sediments in the Northern Caspian and variations in the Caspian Sea level in the Late Neo-Pleistocene

The first data of investigation into the relation between changes in magnetic properties of the Northern Caspian sediments and variations in the Caspian Sea level in the Late Neo-Pleistocene are presented. It is shown that there is a certain correlation between magnetic characteristics of sediments and variations in the Caspian Sea level that cause changes in the lithological and faunistic composition of sediments.     

Structure of the crust and upper mantle of the Black and Caspian Seas

Many geophysical characteristics of the Caspian and Black Seas' deep basins are similar, having: suboceanic type of the crust, low average seismic velocity, absence of earthquakes and relatively small variation of magnetic anomalies. However, the sediments in the Caspian Sea deep basin are folded whereas in the Black Sea they are approximately horizontal. The Caspian Sea also has a far greater thickness of sediment accumulation.

The deep basins of the Caspian, Black and Mediterranean seas represent a sequence having similar crustal structures but with a decreasing thickness of sediments and consolidated layer, in that order. It is possible that the intensive sinking and accumulation of sediments began earliest in the Caspian Sea and spreaded continuously to the Black Sea and then the Mediterranean Sea. The Caspian and Black Sea deep basins have existed for long time (perhaps from Paleozoic time or even earlier) as areas with a specific and related type of evolution.     

Lithology and Depositional Environments of Chaudian Sediments in the Taman Peninsula (Pekla and Tuzla Reference Sections)

The Chaudian sediments composing the Pekla and Tuzla sections are characterized by a variable lithology and transgressive structure. Their basal part is mainly composed of coarse terrigenous varieties with diverse structures indicating different depositional settings in the accumulation zone (shelf and upper part of the submarine slope). These sediments are characterized by strong lithification probably in subaerial environments under the influence of atmospheric precipitation. The Chaudian basin was a large brackish-water depression populated by malacofauna of the Caspian type.     

Plio-Quaternary continental deposits of the Castellamonte area, between Orco and Dora Baltea Basins (Torino Province, Italy)

New geologic mapping of the area near Castellamonte (Torino Province) describes a wide Plio-Quaternary continental succession, up to about 100-m thick. This sequence is distinguished according to allostratigraphic criteria. Altitude, degree of pedogenesis and sediment supply from different basins are also used. Within a single alloformation, several lithofacies are described.Fine-grained fan-delta sediments (Vespia Alloformation) are described in the lower part of the continental succession. The fossil plant remains indicate an Early–Middle Pliocene age. These sediments show an evident deformation and fill ancient lacustrine basins, likely associated with the Canavese Line trend. Their wide distribution and considerable thickness suggest subsidence.Coarse-grained glacial, outwash and fluvial sediments (Colleretto Castelnuovo, S. Defendente, Case Musso, Pagliero, Serra and Piverone Alloformations) are described in the upper part of the continental succession. They consist of undeformed sediments deposited during Middle to Late Pleistocene. These sediments indicate the presence of small local glaciers along the current valley trends. The terracing ratios among the different units and their small thicknesses indicate subsequent differential uplift.     

The lower Jyllandselv succession: evidence for three Weichselian glacier advances over coastal Jameson Land, East Greenland

Detailed investigations of sediments exposed along river sections in the coastal part of Jameson Land have revealed a Saalian to Holocene glacial history. Eleven sedimentary units have been distinguished. most of which are found in superposition at one single large section. Four subglacially formed till beds are recognized; three of which are of Weichselian age. All the tills are considered to have been deposited at the base of fjord glaciers restricted to the Scoresby Sund basin. The tills are separated by marine, fluvial or deltaic sediments, and demonstrate changes in the depositional environnient considered to represent changes in relative sea level during the ice-free periods. The fossil content. supported by a series of luminescence dates, suggest that most of the succession is of Eemian and Early Weichselian age. From the luminescence dates, a short duration of <10ka is suggested for the Early Weichselian glacial stades. Sedimentation during this period was partly controlled by glacio-isostatic subsidence caused by net growth of the Greenland Ice Sheet. The Middle Weichselian is represented by a large hiatus. whereas the Late Weichselian is represented by a subglacial till.     

The faunal-stratigraphy of the ludlovian rocks between Craven Arms and Bourton,near Much Wenlock,Shropshire

The Ludlovian Series has been mapped between the River Onny at Craven Arms and the village of Bourton which lies 2½ miles SW of Much Wenlock. Ten subdivisions are recognised on biostratigraphical and lithostratigraphical criteria. For these divisions the stratigraphical terminology established by Holland, Lawson and Walmsley (1959, 1963) in the Ludlow area has been utilised. Two breaks occur in the otherwise continuous succession of variable calcareous sediments: there is lithological and faunal discontinuity at the base of the Leintwardine Beds and within the Upper Leintwardine Beds. The latter can be recognised over a wide area of the Ludlovian shelf. Accordingly alternative correlations, to those presently accepted, are proposed for the Leintwardine Beds.     

Formation of the superdeep South Caspian basin: subsidence driven by phase change in continental crust

The large hydrocarbon basin of South Caspian is filled with sediments reaching a thickness of 20–25 km. The sediments overlie a 10–18 km thick high-velocity basement which is often interpreted as oceanic crust. This interpretation is, however, inconsistent with rapid major subsidence in Pliocene-Pleistocene time and deposition of 10 km of sediments because the subsidence of crust produced in spreading ridges normally occurs at decreasing rates. Furthermore, filling a basin upon a 10–18 km thick oceanic crust would require twice less sediments. Subsidence as in the South Caspian, of ≥20 km, can be provided by phase change of gabbro to dense eclogite in a 25–30 km thick lower crust. Eclogites which are denser than the mantle and have nearly mantle P velocities but a chemistry of continental crust may occur beneath the Moho in the South Caspian where consolidated crust totals a thickness of 40–50 km. The high subsidence rates in the Pliocene-Pleistocene may be attributed to the effect of active fluids infiltrated from the asthenosphere to catalyze the gabbro-eclogite transition. Subsidence of this kind is typical of large petroleum provinces. According to some interpretations, historic seismicity with 30–70 km focal depths in a 100 km wide zone (beneath the Apsheron-Balkhan sill and north of it) has been associated with the initiation of subduction under the Middle Caspian. The consolidated lithosphere of deep continental sedimentary basins being denser than the asthenosphere, can, in principle, subduct into the latter, while the overlying sediments can be delaminated and folded. Yet, subduction in the South Caspian basin is incompatible with the only 5–10 km shortening of sediments in the Apsheron-Balkhan sill and south of it and with the patterns of earthquake foci that show no alignment like in a Benioff zone and have mostly extension mechanisms.     

The refined Quaternary stratigraphic scale of the Fore-Urals and main events in Southern Urals Region

The refined Quaternary stratigraphic scale of the Cisuralian and Bashkortostan regions, approved by the Commission on the Quaternary System of the Interdepartmental Stratigraphic Committee in 2007, includes the Eopleistocene (with three superhorizons and seven horizons), Neopleistocene (with three superhorizons and 13 horizons), and Holocene (one horizon and three subhorizons). The first defined Holocene Agidel Horizon with three subhorizons, the Middle Neopleistocene Klimovka, and the Upper Neopleistocene Kushnarenkovo Horizon are correlated with the Shuvalov, Gorka, and Mikulino horizons, respectively. New names and reference sections are proposed for all the Eopleistocene units. Local formations are proposed for the horizons, whose stratotypes are located in the northern Fore-Urals. The Quaternary stratigraphic scale is correlated with similar scales of the Urals, the East European Platform, and the Lower Volga region. The scale takes into account all the available data derived from the analysis of original (sediments, faunal and floral remains), published, and archival materials, which make it possible to trace in detail the main Quaternary events that occurred in the Fore-Urals.     

REE systematics in modern bottom sediments of the Caspian Sea and river deltas worldwide: Experience of comparison

The results of comparison of a number of main parameters of the chondrite-normalized REE distribution spectra in modern bottom, mainly pelitic, sediments of various sedimentary subsystems of the Caspian Sea and marginal filters of the Volga and Ural rivers with those characteristic of the pelitic fraction of modern bottom sediments of different river deltas worldwide are discussed. According to the features of the REE distribution spectra, as well as the ε_Nd(0) values, it has been established that most samples of the Caspian bottom sediments are similar to those of large rivers and rivers, draining watersheds composed of sedimentary formations.