Composition, structure and formation conditions of the Arydzhangsky Formation of the Maimecha-Kotuy District of the Siberian Trap Province

We studied 6 sections of the Arydzhangsky lava formation (P2-T1) in the Kotuy river valley. The results of petrographic and geochemical studies of the composition of rocks of the Arydzhangsky, Khardaksky and Pravoboyarsky formations are presented. The stratigraphic columns of the sections were built and the composition of the rocks was additionally determined using a scanning electron microscope. In this regard, the relative position of these formations was established, the mantle and crust sources of magmas were confirmed. A geochemical identity of the rocks of the Khardaksky formation with the rocks of the Arydzhangsky formation was established, which suggests a similar age of their formation.

On the classification diversity of oil and gas trappers and geochemical criteria for the productivity of shale formations

The article considers the classification attributes of non-anticlinal traps on the basis of analytical research and critical analysis of literary sources. A certain excess of classification definitions and characteristics of traps, used by researchers both to describe universal schemes and for specific oil and gas basins, and their frequent discrepancies reasonably lead ultimately to an enlargement of types and subtypes of traps, combining them into three main classes of accumulations: continuous and quasi-continuous (unconventional) and discontinuous (conventional). It is noted that in combination with geophysical, seismostratigraphic, paleogeographic, paleotectonic, hydrogeological and other methods of studying the genesis and morphology of traps, and their search, geochemical methods of forecasting and searching for hydrocarbon accumulations at all stages of prospecting and exploration are now widely introduced. The practical possibilities of geochemical methods for evaluating the effective productivity of thin traps of carbonaceous formations are shown on the example of the Bazhenov and Domanik deposits of Russia, as well as the shale plays of the Bakken, Eagle and others in the United States. Keywords: non-anticlinal traps; thin traps; reservoirs; oil and gas; classification of traps; carbonaceous formations; geochemical studies.

Lawsonite eclogites and metasomatites of the Utarbaev Association of the Maksyutov complex

Research subject. This article presents mineralogical, petrological and geochemical studies of lawsonite eclogites and metasomatites of the Utarbayev Аssociation of the Maksyutov complex. The Utarbayev Association forms an independent unit in the Maksyutovsky complex accretion structure. This Association features a variety of lawsonite-bearing metasomatites that form zonal halos in the frame of block-like diopside-grossular bodies included in the antigorite-serpentinite melange. The Utarbayev Association differs from typical lawsonite-blue shale complexes of collisional oro genes by the absence of mineral parageneses of lawsonite-bearing rocks of blue amphibolites.Methods. A microprobe analysis of the mineral composition was performed using a Cameca SX-100 microanalyzer. The content of petrogenic, rare and rare-earth elements was determined by X-ray spectroscopy (CPM-18) and mass spectroscopy (ICP-MS, ELAN-90). Results. An indicator mine ral paragenesis (Grt + Omp + Lws + Di) ± (Coe-Qz + Ttn) that characterizes lawsonite eclogite was found. Omphacite (Jd38–44) and unchanged lawsonite (Н2O-OH – 11.8%, Ca/Al = 0.48–0.51 и Fe/Al = 0.01 0.02%) are represented as inclusions in grossular-almandine garnet (Alm39–46Grs41–51), coesite – as microinclusions in omphacite. Thermobarometry (Grt-Omp, Grt-Omp-Ph) showed the following formation conditions of lawsonite paragenesis: T = 495–622°C under P = 2.2–2.4 GPa. The age of crystallization of lawsonite eclogite was found to be Lower Paleozoic (471–444 Ma).Conclusions. The lawsonite eclogite of the Utarbayev Association is similar to the complexes of «cold» eclogites, which are formed under the conditions of a very low geothermal gradient and are rarely preserved when removed into the upper crust. The latest review published in the «Journal of Metamorphic Geology» (2014) mentions 19 sites, where lawsonite eclogites were discovered on the earth’s surface. Тhe HP-UHP lawsonitebearing Utarbayev Rock Association complements this list.

Are there Pre-Variscan bedded cherts of endogenous origin in Bulgaria?

Geochemical studies of different Paleozoic intervals composed of bedded cherts, revealed in the western parts of the Srednogorie and Morava-Rhodope zones are presented: Saltar Fm; the lower and middle part of Katina Fm; the lowest part of Parchar Fm, and Tumba Fm. To determine whether the different bedded cherts intervals are hydrothermally affected, triangular diagrams of the A-F-Mn ratio were used. The low content of Fe compared to Al gives grounds to claim that the Pre-Varisian Paleozoic bedded cherts in Bulgaria are not associated with endogenous processes.

Study of the component composition of organic matter of the East Pre-Caucasian basin rocks based on the results of lithological, petrophysical and geochemical studies

This study introduces results of lithological, petrophysical and geochemical investigation of Lower Cretaceous (K1) and Middle Jurassic (J2a-b) rocks of East Pre-Caucasian basin. According to pyrolytic and bituminological studies method of separate determination of kerogen and bitumen concentration been developed. In accordance with this method differentiation of organic matter components in different lithotypes of rocks been described. Also relationship between bitumen and kerogen concentrations been revealed. The majority of samples have poor to fair organic richness and poor source potential. Kerogen type is commonly presented by type III and stages of maturity characterized by stages PC3 to MC3. Bitumen compounds have low concentrations of asphaltenes and aromatic hydrocarbons and mainly contains light and heavy resins. Based on petrophysical and geochemical studies a close relationship between the concentration of organic carbon and the weight concentration of potassium nuclides was obtained. This relationship indicates that kerogen in the sediments under consideration is associated with clay minerals, which is also confirmed by the mineral composition of the rocks.

Diagenesis and the Conditions of Deposition of the Middle Jurassic Siderite Rocks from the Northern Margin of the Holy Cross Mountains (Poland)

The aim of the present study is to reconstruct sedimentary conditions of Middle Jurassic rocks that contain siderites to identify the mineral composition of the inserbeds and to recognize the origin of the siderite. Thin inserbeds of siderite rocks occur most frequently within Bajocian siliciclastic deposits and, more rarely, Aalenian and Bathonian. The research material comes from 11 boreholes located in the north and northeastern margins of the Holy Cross Mountains. The research methods included sedimentological analyses, and studies in polarizing and scanning electron microscopes, staining of carbonates, cathodoluminescence, X-ray structural analysis, and stable carbon and oxygen isotopic determinations were used. Middle Jurassic sideritic rocks are most often represented by clayey siderites, which also include muddy and sandy varieties and siderite sandstones. There are also local occurrences of coquinas, claystones, mudstones, and siderite conglomerates. The main component of sideritic rocks is sideroplesite. Berthierine, pistomesite, calcite, and ankerite are important components, too. The action of diagenetic processes of cementation, compaction, replacement, and alteration within the Middle Jurassic deposits was most intense during the eo- and mesodiagenesis. The sedimentological analysis showed that most of the studied siderites were formed in a low-oxygenated marine environment, mainly in the transition zone between the normal and storm wave bases and in the lower and middle shoreface zones. The results of the petrographic, mineralogical, and geochemical studies indicated the origin of the sideritic rocks mainly in the marine environment, with the participation of meteoric water. There were slight differences in the chemical composition of sideroplesite depending on the environment it crystallized in. There was no correlation between the values of the carbon isotope determinations in the sideroplesite and the environmental conditions of its crystallization. Slight differences were visible in the case of the average values of δ18O in the sideroplesite.