Peculiarities of Stratigraphic Distribution and Paleoecology of Jurassic Bivalve Mollusks of the Pre-Сarpathian Foredeep

Pre-Carpathian region is one of the oldest oil and gas producing regions of our country, which is attracting more and more attention of scientists. In the Outer zone of the Pre-Carpathian Foredeep, Jurassic deposits occur at considerable depths (up to 3,000 m), so we obtain almost all geological information about them exclusively during the study of core material selected during drilling. A comprehensive and detailed study of the Jurassic deposits of this zone during exploration drilling in the 1950s contributed to the discovery of the Kokhanivske and Sudovovyshnianske oil deposits and Rudkivske gas deposit, as well as a number of oil and gas manifestations. After that, the interest in the conditions of formation and stratification of Jurassic deposits increased. Researchers have begun to treat them as the promising objects for oil and gas exploration. Jurassic deposits in the Pre-Сarpathian Foredeep fill a single depression – the Stryi Jurassic deflection, covered by a thick layer of Cretaceous and Neogene rocks. The study of their geology and stratigraphy has acquired important applied and scientific significance, because stratigraphic research serves as a basis for clarifying the history of geological development of the region, performing tectonic constructions, reconstruction of paleogeographic and paleoecological conditions, comparison of productive horizons and specification of their stratigraphic position, search for new objects promising for hydrocarbons. Extremely rare finds of paleontological remains (which are not always well preserved) do not allow to unambiguously determining the age of the host rocks. It is still not always possible to clearly stratigraphically distinguish and correlate these rocks due to weak paleontological study and partial uncertainty in the interpretation of the geological structure of these strata. Despite the significant amount of research we have done, there are some debatable issues regarding the completeness of the section of these rocks and the presence of separate stratigraphic units in them. For many years, we have studied in detail and comprehensively bivalve mollusks found in the core of wells drilled in the Outer zone of the Pre-Carpathian Foredeep. As a result, the age of the host strata was specified and confirmed, as well as the thickness of individual stratigraphic units.

Petrography, geochemistry and depositional model of Ispikan Conglomerate, Makran Accretionary Prism, Southwest Pakistan

Sedimentology, petrography, and geochemistry of the Ispikan Conglomerate of southwest Makran have been studied to establish its stratigraphic position, age, provenance, and depositional environment. Very thin to massive beds, poor sorting, no fabric, and poor grading are the common features. It is composed of mostly reworked, medium- to coarse-grained pebbly sandstone, siltstone, and discontinuous lenses of matrix- and clast-supported conglomerate. The sandstone is composed of angular to sub-angular, poorly sorted, immature grains having Q72F13L15 as average composition. Pebbles are of mostly metamorphic and acidic igneous origin. Large angular boulders (~1.5m) of sandstone indicate quick debris flow conditions. Geochemical discriminants suggest the derivation of Ispikan sediments from an active continental margin. The Nb and Zr/Th and Ba/Y values indicate the continental island arc setting, whereas a high K/Rb ratio points to the derivation of detritus from an acid and intermediate source. Ispikan Conglomerate is interpreted as an Eocene olistostrome formed after a localized submarine debris flow triggered by slope failure.

THE UPPER ORDOVICIAN BIOSTRATIGRAPHY OF THE CHUNYA RIVER BASIN (RIGHT TRIBUTARY OF THE PODKAMENNAYA TUNGUSKA RIVER, SIBERIAN PLATFORM)

The article deals with presented results of studying Upper Ordovician sections of the Mangazeya Formation in the Chuya River basin (right tributary of the Podkamennaya Tunguska River) of the Siberian Platform. The given layer by layer section description and new data on leading groups of fauna (ostracods, trilobites, brachiopods, conodonts) allowed for significantly expanding paleontological characteristics of enclosing sediments. The description of the Baksan Horizon deposits is given for the first time, it updates the earlier description of underlying formations in the stratotypic section of the Dolbor Horizon 2 km above the mouth of the Upper Chunku R. (left bank). As a result of biostratigraphic analysis for different groups of fauna, both from published sources and newly obtained data, it has become possible to clarify the stratigraphic position of the section located 0.4 km below the mouth of the Amutkan River. The correlation of studied sections with the Gaindinskaya-3 test well was carried out.

The studies on the Sungir Upper Paleolithic site in 2014–2015

The article is devoted to the results of archaeological excavations carried out on the Sungir in 2014-2015. The main purpose of these works was to obtain new data on the spatial structure of the cultural layer of the Sungir site. The relevance of these studies is caused by still unsolved question of whether Sungir can be considered as a site with a complex archaeological stratigraphy or the features of its spatial structure are only the result of natural postdepositional processes. Descriptions and characteristics of the stratigraphy of sediments, the spatial organization of the cultural layer, the species’ attribution and taphonomy of the faunal collection, the typology and technology of the stone industry, as well as new radiocarbon dating are given. It is noted that the excavations of 2015 were conducted on the peripheral part of the accumulations which were opened in the excavation unit III by O.N. Bader. Most of the animal bones found during excavations can be considered as belonging to species that the settlers hunted. The analysis of the stone inventory allowed us to identify the following production chains of manufacture: the production of large flakes, the production of blades, and the production of thin bifaces. The data obtained during the typological and technological study of blades and bladelets make it possible to suggest the existence of the fundamental differences between the Sungir industry and the industries of the Aurignacian technocomplex. Predominance of large flakes in the Sungir stone industry, as well as the characteristic techniques in bifaces production, which were recorded in the collection, allow us to consider so-called Streletskian culture as a more reasonable analogy to it. The stratigraphic position both of artifacts and accumulations of archaeological material, as well as the spatial context of the dated bone samples from reconnaissance trench No. 4 (2014), support the conclusion that the cultural layer of the Sungir site was formed in several stages. The results of archaeological work carried out on Sungir in 2014–2015 indicate the real perspectives for its further study. One of the urgent tasks facing the researchers of this outstanding site is the reconstruction of the spatial structure, including its archaeological stratigraphy.

Neoproterozoic Deposits of the Bashkir Mega-Anticlinorium (Southern Urals): State of the Art in Regional Stratigraphy

—This paper presents an alternative variant of stratigraphic subdivision of the upper Riphean–Vendian deposits (approximately corresponding to the Neoproterozoic Erathem of the International Chronostratigraphic Chart (ICC)) of the Bashkir Mega-Anticlinorium (BMA), based on the modern concepts of changes in the biosphere, atmosphere, and hydrosphere (and, accordingly, in the climate and the course of sedimentary processes) in the period ~1000–540 Ma, with regard to the results of recent studies and the proposals for improving the Russian General Stratigraphic Scale (GSS) of the Precambrian. The strict necessity of subdividing chronostratigraphic and lithostratigraphic units is shown. The presented data give grounds to regard the Zil’merdak Formation as a Group and assign three of its lower formations to the Middle Riphean (Yurmatinian). It is shown that the period of accumulation of the Karatau Group (comprising the Katav, Inzer, Min’yar, and Uk formations) was significantly shorter than the duration of the Late Riphean (Karatavian). Special attention is focused on the age of the Uk Formation (analysis of the existing data made it possible to refine its stratigraphic position): It formed, most likely, in the period 780–740 Ma. A high uncertainty of the stratigraphic position of the overlying geologic bodies is demonstrated. The Bakeevo, Tolparovo, Suirovo, and Kurgashla formations must be regarded as part of the Terminal Riphean (Arshinian). The Arsha Group, comprising the Bainas, Makhmutovo, Igonino, and Shum formations in the Tirlyan trough and represented by the Krivaya Luka Formation in the Krivaya Luka syncline, should not be totally assigned to the Terminal Riphean. It is proposed to exclude the Bakeevo Formation and the Tolparovo–Suirovo sequence from the Asha Group, because these deposits are, most likely, a modification of the Arsha Group located on the western flank of the BMA. The Uryuk Formation is probably of pre-Vendian age. The current contradictory data on the stratigraphy of the supra-Uryuk unit of the Asha Group are interpreted. The ages of the geologic bodies composing the Group and its stratigraphic interval still call for a thorough study.

Facies Composition and Stratigraphic Position of the Quaternary Upper Yenisei Sequence in the Tuva and Minusa Depressions

—The paper concerns the sediment sequence, which is widespread in the Yenisei valley and in the Tuva and Minusa depressions and also present in the valleys of the southern Chulym plain. The sediments of this sequence were previously described as “Neogene mud-shedding”, as well as moraines, alluvial fan deposits, alluvium of Middle Pleistocene high terraces, and lacustrine sediments. The giant ripple marks on the Upper Yenisei terraces was commonly interpreted as ribbed moraines; however, in recent studies, these ridges have been repeatedly referred to as marks of giant current ripples. Besides, some recently published papers provide description of geology of this sequence fragments suggesting its deposition by cataclysmic floods. Geomorphological analysis of the area shows Pleistocene glaciers to have been localized within the medium–high mountainous areas. The glaciers did not reach the Tuva and Minusa depressions and occupied large areas only in the Todzha basin and on the periphery of the Darkhat basin, forming a glacial dam at its outlet, which resulted in glacial-dammed lakes filling the basin completely. These lakes outburst, and the resultant flooding led to the deposition of megaflood sediments, which we refer to here as the Upper Yenisei sediment sequence. A detailed analysis of its facies architecture revealed similarity of these sediments to those of the Sal’dzhar and Inya sequences in Gorny Altai. Most of the Upper Yenisei megaflood sediments are localized in topographic lows of the Tuva and Minusa depressions. Beyond the Altai–Sayan mountainous area, the megaflood sediments of the Upper Yenisei sequence compose high terraces of the Yenisei, Chulym, Chet’, and Kiya rivers in the southern Chulym plain. The formation of Upper Yenisei sequence dates to the first half of the Late Pleistocene, inasmuch as it contains inset alluvial sediments of the second terrace of the Yenisei River. The available data allow suggesting that the Upper Yenisei sequence formed in the first Late Pleistocene regional glaciation. The Sal’dzhar sequence in Gorny Altai and the fourth terrace of the Ob’ River on the Fore-Altai plain are stratigraphic analogs of the Upper Yenisei sequence. The Upper Yenisei and Sal’dzhar sequences can thus be considered future regional markers serving as a link for the local stratigraphic schemes of the Altai–Sayan mountainous area and adjacent West Siberian plains. The results obtained call for verification by geochronological dating, first of all, by modern luminescence dating methods covering a wider chronological interval than radiocarbon dating.

TIME CONSTRAINTS ON THE FORMATION OF THE KANDALAKSHA AND KERETSK GRABENS OF THE WHITE SEA PALEO-RIFT SYSTEM FROM NEW ISOTOPIC GEOCHRONOLOGICAL DATA

Initially, the age and stratigraphic position of the Tersk formation were determined with respect to the fact that this formation overlaps the Early Proterozoic granitoids. Its top was marked by the rocks penetrated by the Late Devonian alkaline intrusions, including explosion pipes.This article presents the U-Pb isotopic dating of detrital zircon grains (dZr) from sandstones of the Tersk formation. It describes the geochemical compositions of the rocks and the Sm-Nd study results. In our study, the weighted average age of four youngest dZr grains from the sandstones of the Tersk formation is 1145±20 Ma, which suggests that the rocks above the studied rock layer (see the Tersk formation cross-section) are is not older than the end of the Middle Riphean. The U-Pb isotopic ages of dZr grains (provenance signals) from the sandstones of the Tersk formation were compared to the ages of other Upper Precambrian clastic strata in the northeastern East European platform (EEP) and adjacent areas. Our comparative analysis shows that these rocks significantly differ in age. This conclusion is in good agreement with the idea that at the end of the Middle and during the Late Riphean, several small (mainly closed) basins separated by uplifts dominated in the paleogeographic setting of the area wherein the White Sea rift system (WSRS) formed and developed. Temporal connections of these basins with the ocean were possible. Such paleogeographic setting does not favour the development of large rivers; this is why the grabens are mainly filled with local rock materials. The Keretsk and Kandalaksha grabens (WSRS) are filled with marine sediments eroded from the grabens walls. The local sediment sources include eclogite complexes (~1.9 Ga), which basic magmatism is dated at ~2.4–2.5 and ~2.7–2.9 Ga. Any potential primary sources for dZr grains are lacking in the area near the Keretsk graben. We suggest that such grains occurred due to recycling of the secondary sources of zircon, i.e. originated from ancient local sedimentary formations.

Archaeological and Chemical Investigation on the High Imperial Mosaic Floor Mortars of the Domus Integrated in the Museum of Archaeology D. Diogo de Sousa, Braga, Portugal

This paper intends to characterize the floor mortar layers (nucleus, rudus and statumen) of the high imperial mosaics of the domus integrated in the Museum of Archeology D. Diogo de Sousa, the oldest roman housing testimonies known in Braga, Portugal. It offers an important archaeological and historical contextualization and first chemical characterization attempt on the mortars. The study of 13 mortar samples was carried out at a chemical level through X-ray fluorescence spectroscopy (XRF). All samples presented low lime content when compared to similar studies. A high chemical similarity between nucleus mortars (opus signinum) and chemical composition differences between rudus and statumen mortars was determined, confirmed by statistical analyses. Their composition was distinctly related to the stratigraphic position of each floor mortar layer, following Vitruvius’ model, and to the external conditions and treatments (e.g., capillary rise with soluble salts and application of chemical treatments), to which they were submitted.

Use of Seismic Spectral Decomposition, Phase, and Relative Geologic Age as Attributes to Improve Quantitative Porosity Prediction in the Daqing Field, China

The high production potential of the Daqing oilfield in China is recognized for seismically thin sand bodies that usually are not resolved with conventional seismic data. The present study assesses the usefulness of applying seismic multi-attribute analysis to bandwidth extended data in resolving and making inferences about these thin layers. In thin layers, tuning can obscure relationships between seismic amplitude and rock properties. In such cases, the seismic phase varies with the layer impedance and may hence aid in reservoir characterization. A seismically derived relative geologic age may also be a useful attribute in predicting rock properties because it helps define the stratigraphic position of a layer. When utilized in multi-attribute analysis in the Daqing field, spectral decomposition amplitude, phase, and a relative geological age attribute to improved prediction of well log effective porosity from seismic data and are preferentially selected by stepwise regression. The study follows standard methodology by implementing seismic multi-attribute analysis and discusses the improvement of applying it to bandwidth extended data. This will include a combination of attributes such as relative geologic age, phase, amplitude, and the magnitude components of spectrally decomposed data.

Chronological relationship between the fortified settlement of Kamennyi Ambar and the Kamennyi Ambar-5 cemetery in the Southern Trans-Urals: capabilities of the Bayesian statistics

By means of the Bayesian analysis of radiocarbon dates, a comparison of chronologies of the Kamennyi Ambar settlement and the cemetery of Kamennyi Ambar-5 of the Late Bronze Age Syntashta-Petrovka period has been carried out. Both sites are situated in the valley of the Karagaily-Ayat River in Kartalinsky district of Chelyab-insk Region (Russia). Comparison of the pottery assemblages of the settlement and the cemetery demonstrates their similarity, which suggests existence of a genetic link between the sites. The purpose of this work is devel-opment of a generalized chronological model of the two monuments. This is achieved by comparison of uncali-brated intervals of radiocarbon dates and calculation of chronological boundaries of the existence of the settle-ment and cemetery by means of Bayesian modeling of the calibrated dates. The method consists in that, in the beginning, the stratigraphic position of each date is determined, and then the dates suitable for the analysis are arranged in the chronological order and calibrated, while the algorithm of the OxCal 4.4 calibration program is queried for calculation of the boundaries of the given periods and their duration. Also, the paper reports complete sets of the radiocarbon dates: 61 dates have been obtained from the materials of the settlement of Kamennyi Ambar, while 19 measurements originate from the Kamennyi Ambar-5 cemetery. Correlation of the radiocarbon dates and development of the Bayesian chronological models have demonstrated contemporaneousness of the settlement and the cemetery with slightly later beginning of the activity at the latter. This observation is in agree-ment with the concept of the genetic link between the sites and, arguably, can be extended onto other pairs of fortified settlement — kurgan cemetery attributed to the Sintashta-Petrovka period. Our conclusion is also consis-tent with the concept of building the complex of monuments by a newly-arrived population, who founded a settle-ment, occupied the new territory for some time, while the first deaths occurred some time afterwards. That said, the settlement of Kamennyi Ambar existed for no longer than a century in the 1950s — 1860s BC, while the cemetery of Kamennyi Ambar-5 was used for 70–80 years within the same chronological interval.