The role of concentrations variability of organic matter in kerogenic shale defluidisation on the catagenic depths

The Baltic kerogenic shale – kukersites (О2kk) were considered high-carbon marls which consist of three rock-forming components: organic matter (kerogen), carbonates and terrigenous material. As example used are data of the other high-carbon rocks. It is shown that increased concentrations of organic matter predetermine a number of features of these rocks (reduced density, reduced strength, etc.). The concentrations variability of the organic matter makes conditions the heterogeneity of the intraformational space, the anisotropy of many parameters, as well as the manifestation unevenness of the fluid-generation and evacuation capabilities. It was found that in kukersite shales fluid-generating properties can appear at the earliest stages of catagenesis. The role of areas with the maximum qualities of organic matter in the defluidisation of the shale coals is emphasized: here the more intensive generation of gas-liquid products and increased strength contribute to the earlier formation of drainage microcracks and fluid fractures. The appearance of shrinkage cracks due to catagenic losses of organic matter and usually uneven volume contraction and due to fluidgenerating shale coals is substantiated. The possibility of fluid-generating shale coals losing it lithological individuality during of it defluidisation is found out. Keywords: organic matter; oil shale; kukersite; defluidization; catagenesis; hydrocarbons.

The study of Dominican amber-bearing sediments from Siete Cañadas and La Cumbre with a discussion on their origin

The paper presents comprehensive mineralogical and geochemical characteristics of Dominican amber-bearing sediments from Siete Cañadas, Hato Mayor Province of the Eastern Mining District (EMD) in the Cordillera Oriental. The characteristics of rocks collected from the borehole in Siete Cañadas area (EMD) were compared with petrography of coaly shales from La Cumbre in the Northern Mining District (NMD). The mineralogy of the rocks was determined using transmitted and reflected light microscopy, scanning electron microscopy, Powder X-ray diffraction and Fourier Transform Raman Spectroscopy. Biomarker analyses by the gas chromatography–mass spectrometry were used to trace the genetic source and transformation stage of organic matter hosted in the core sediments. In this study, the characteristics of rocks from La Cumbre were supplemented with the petrographic data from our studies reported earlier. Based on the findings, it has been concluded that the basins in the investigated parts of the EMD and NMD regions were likely characterized by different, isolated palaeosettings. Transformation and maturation of terrigenous material were affected by locally occurring physicochemical conditions. In both amber deposits, the sedimentation of clastic and organic material proceeded in the presence of marine conditions. In case of the La Cumbre deposit (NMD area), the sedimentation underwent probably in the conditions of the lagoon environment, a shallow maritime lake or periodically flooded plain that facilitated organic matter decomposition and carbonation from meta-lignite to sub-bituminous coal (random reflectance of coal—Rro = 0.39%). In the Siete Cañadas (EMD region), the sedimentation took place in a shallow saltwater basin, where terrigenous material was likely mixed with material found in situ (fauna fossils, carbonate-group minerals) to form the mudstones enriched in bituminous substance of low maturity. The organic matter found in the rocks from both deposits is of mixed terrestrial/marine origin and was deposited in the presence of low oxygen concentration and reducing and/or dysoxic conditions.

Sinuous stromatolites of the Chandi Formation, Chattisgarh Basin, India: their origin and implications for Mesoproterozoic seawater

Remnants of some of the planet’s most ancient life forms, stromatolites in the late Mesoproterozoic sea of the Chattisgarh Basin, India, preserve a conspicuous sinuous pattern. They occur as successive biostromes, 10–30 cm thick, separated by 2–5-cm-thick marly layers and discrete bioherms up to several metres thick and 20 m across. Stromatolite columns in the Chandi Formation are 5–10 cm high, sinuous, inclined and straight, with both branched and non-branched types. These stromatolites are composed of calcite micrite and show well defined light and dark laminae with evidence of erosion between lamina sets. The column sinuosity probably originated as a response to changes in direction and strength of currents. Successive flat beds of stromatolite (biostromes), separated by marl/clay horizons, impart a rhythmic pattern to the succession. The Chandi sinuous stromatolite columns resemble those occurring in China, North America and Siberia, of a comparable age, suggesting that similar marine conditions of stromatolite formation might have been operating in the late Mesoproterozoic seas worldwide. However, the petrographic and sedimentological analyses of these stromatolites indicate their development through in situ production of carbonate with some trapping and binding of detrital sediment. As a result of the presence of terrigenous material within the stromatolites, whole-rock geochemical analyses for trace elements and rare earth elements cannot be used for interpretation of seawater chemistry and the redox conditions at the time.

The Characteristics and Origin of Amber Deposits in the Dominican Republic

Mineralogical and geochemical characteristics of amber deposits located in the Dominican Republic, i.e., Hato Mayor Province of the Eastern Mining District (EMD) in the Cordillera Oriental, and Santiago Province of the Northern Mining District (NMD) in the Cordillera Septentrional were performed. The results of analyses of amber-bearing sediments collected from the borehole in Siete Cañadas area (EMD) were referenced to the petrological data obtained for the coaly shales from La Cumbre (NMD). The mineralogy of the rocks was described using transmitted and reflected light microscopy, scanning electron microscopy, Powder X-ray diffraction and Fourier Transform Raman Spectroscopy. Biomarker analyses by the gas chromatography-mass spectrometry were used to trace the genetic source and transformation stage of abundant organic matter hosted in the core sediments. Our findings indicated that basins in EMD and NMD regions were different isolated palaeosettings, in which under the influence of local physicochemical factors the terrigenous material was transformed and got maturated. In both amber deposits, the sedimentation of clastic and organic material proceeded in the presence of marine conditions. In case of the NMD area, the sedimentation underwent probably in the conditions of the lagoon environment, a shallow maritime lake or periodically flooded plain, that facilitated organic matter decomposition and carbonation from meta-lignite to sub-bituminous coal (random reflectance of coal - Rro = 0,39%). In the EMD region, the sedimentation took place in a deeper basin, where terrigenous material was likely mixed with material found in situ (fauna fossils, carbonate-group minerals) to form the mudstones enriched in bituminous substance of low maturity. The organic matter found in the rocks from both regions is of mixed terrestrial/marine origin and was deposited in the presence of low oxygen concentration and reducing and/or dysoxic conditions.

Peculiar features of the supracomplexes formation in the Keivy domain

The Keivy domain (the northeastern part of the Arctic zone of the Fennoscandian Shield) during the period of the maximum manifestation of the Late Archean collisional processes was overlapped by tectonic allochthons of adjacent microcontinents thrust over it, submerged relative to other blocks of the continental crust, and acquired the features of a classical middle massif. In the process of studies that allow a detailed description of the formation of the supracrustal complexes of the Keivy structure, it has been found that the formation processes of the Kola orogeny had a pronounced spatial and temporal zoning and impulsive character. The maximum degree of orogeny was experienced by the rock associations of the Murmansk domain, as a result of which terrigenous material transported from its mountain slopes prevailed in the metasedimentary complexes of the Keivy domain throughout the entire period of their formation. The substance removed from the Murmansk domain was more actively accumulated in the metasedimentary rocks of the Lebyazhinsky suite; then a regular attenuation was observed within all domains, but at the last stage of the formation of the section of the Keivy sedimentary strata, the structural-material complexes of the Murmansk domain again begin to degrade more actively. A detailed study of the compositional features of the supracrustal complexes of the Keivy structure refutes the currently emerging point of view on the coeval formation of alkaline granites and felsic metavolcanics of the Lebyazhinsky suite. It can be argued with a high degree of probability that the rocks used to draw this conclusion (for which the age of 2.678 ± 7 Ma) is not typical of the supracrustal section of the metavolcanics of the Lebyazhinsky suite and are metasomatites.

Early Miocene calc-alkaline felsic tuffs within deep-marine turbidites in the Kyrenia Range, north Cyprus, with a possible post-collisional eruptive centre in western Anatolia

Felsic tuff as a direct fallout deposit is known from one small area in the Kyrenia Range, north Cyprus, within deep-sea terrigenous turbidites. Nearby tuffaceous siltstones contain compositionally similar felsic volcanic rocks (c. 5–10%), mixed with terrigenous material. Sedimentary evidence indicates that the fallout tuff was variable reworked locally, whereas the tuffaceous siltstones are interpreted as turbidites mixed with terrigenous material derived from Anatolia. U–Pb dating of zircons that were extracted from a sample of relatively homogeneous tuff yielded a dominant age of 16.64 ± 0.12 Ma (Burdigalian). Zircon trace-element analysis indicates predominant derivation from within-plate-type felsic magma. Whole-rock chemical analysis of the tuffaceous sediments as a whole is compatible with a felsic arc source, similar to the post-collisional magmatism within Anatolia. Regional comparisons suggest that the nearest volcanism of similar age and composition is located c. 500 km away, within the Kırka area (Eskişehir region) of the Western Anatolia Volcanic Province. Evidence of tephra dispersal in the western Mediterranean region and climatic modelling suggests E-wards prevailing winds and therefore tephra transport over southern Anatolia and adjacent areas during early Miocene time. The north Cyprus tuffs could represent powerful Minoan (Plinian)-type eruptions in western Anatolia, coupled with SE-wards tephra transport during and soon after the onset of post-collisional magmatism.

Multiproxy sedimentological and geochemical analyses across the Lower–Middle Pleistocene boundary: chemostratigraphy and paleoenvironment of the Chiba composite section, central Japan

The Chiba composite section (CbCS) in the Kokumoto Formation, Kazusa Group, central Japan is a thick and continuous marine succession that straddles the Lower–Middle Pleistocene boundary and the well-recognized Matuyama–Brunhes paleomagnetic polarity boundary. Although recent studies extensively investigated the CbCS, its chemostratigraphy, particularly around the Lower–Middle Pleistocene boundary, is poorly understood. Therefore, in this study, we performed multiproxy sedimentological and geochemical analyses of the CbCS, including the Chiba section, which is the Global Boundary Stratotype Section and Point for defining the base of the Middle Pleistocene Subseries. The aim of these analyses is to establish the high-resolution chemostratigraphy and to reconstruct the paleoenvironments of its sedimentary basin in detail. We used the K/Ti ratio as a broad proxy for the clastic material grain size of the sediments. Although the K/Ti ratio generally varies throughout the studied interval, the K/Ti ratio especially during Marine Isotope Stage (MIS) 19a shows a variation pattern like those of the foraminiferal oxygen isotope (δ18O) records. The records of the C/N ratio of bulk samples and carbon isotope ratio of the organic carbon (δ13Corg) suggest that the organic matter in the CbCS sediments during MIS 19c mostly originated from marine plankton, whereas the organic matter during MIS 18 and 19a was characterized by a mixture of marine plankton and terrestrial plants. These records are clearly indicative of changes in mixing ratio of marine vs. terrestrial organic matter in association with glacial–interglacial cycles from the late MIS 20 to the early MIS 18. In addition, we calculated the mass accumulation rates (MARs) of organic carbon, biogenic carbonate, and terrigenous material for quantitative interpretations on the paleoenvironmental changes. MAR calculations revealed that the contribution of marine organic carbon relative to terrestrial organic carbon increased during MIS 19c, and that the contribution of the terrigenous material relative to biogenic carbonate decreased during MIS 19c. Furthermore, we observed relatively large variations in the total organic carbon and total nitrogen contents during MIS 19a. These variations were probably caused by the relative decrease in bottom-water oxygen level, which is also supported by our trace-fossil data, although it is not certain whether the increase in organic-carbon flux at ~ 760 ka was due to the synchronous increase in biogenic productivity in surface water. Such a relative decrease in bottom-water oxygen level was partly due to the increased ocean stratification because of the northward displacement of the Kuroshio Extension Front.

Lithogeochemical characteristics of metasandstones of the Chetlas series (Chetlassky Kamen, Middle Timan)

The lithological and geochemical features of the metasandstones of the Svetlinskaya and Vizingskaya formations of the Middle Late Riphean Chetlas series in the Middle Timan, which are a substrate of rare-metal-rare-earth mineralization in several ore occurrences of the Kosyus ore cluster, have been investigated. The interpretation of the results of traditional weight chemical and mass spectrometric inductively coupled plasma (ICP MS) analyses allowed us to identify differences in the material composition of metapesanics, mainly due to changes in the degree of sedimentation maturity of terrigenous material coming from the demolition areas. The composition of metasandstones in various ratios includes both weakly weathered products of destruction of volcanic rocks of intermediate/basic composition, and altered, including under conditions of the weathering crust, metaterrigenous formations. The accumulation of sediments took place in a shallow coastal-marine environment with changing hydrodynamics, which affected the rate of destruction of rocks in paleo-catchments.

GEOCHEMICAL FEATURES AND PALEOGEODYNAMIC SETTING OF PERMIAN AND TRIASSIC DEPOSITS ACCUMULATION IN THE SOUTH OF THE LAOELING-GRODEKOVO TERRANE (PRIMORYE)

New geochemical data on the Late Paleozoic and Early Mesozoic sandy rocks of the southern part of the Laoeling-Grodekovo terrane of the South-Western Primorye are presented. It is shown that terrane deposits differ significantly in geochemical parameters: sandstones of the Barabash and Mangugai formations most closely correspond to the graywackes, those of the Kazachka formation to the lithite arenites, and those of the Reshetnikovka formation to arkoses. The rocks are characterized by a rather high degree of maturity of the terrigenous material and contain mainly fragments of acidic igneous rocks in the clastic part. The geochemical data obtained were generalized and interpreted based on their comparison with the compositions of modern sediments and ancient deposits accumulated in the known geodynamic settings. The results of the studies, in general, suggest the formation of terrane deposits in a basin associated with the setting of transform slip of lithospheric plates. The main source of detrital material was eroded acid igneous rocks, to which a small fraction of products of disintegration of basic-middle volcanics and sedimentary rocks enriched in ancient components was added.

Paleocene deposits of the Ukrainian Carpathians: geological and petrographic characteristics, reservoir properties

The Paleocene Yamna Formation represents one of the main oil-bearing sequences in the Ukrainian part of the Carpathian petroleum province. Major oil accumulations occur in the Boryslav-Pokuttya and Skyba Units of the Ukrainian Carpathians. In the great part of the study area, the Yamna Formation is made up of thick turbiditic sandstone layers functioning as reservoir rocks for oil and gas. The reconstructions of depositional environments of the Paleocene flysch deposits performed based on well log data, lithological and petrographic investigations showed that the terrigenous material was supplied into the sedimentary basin from two sources. One of them was located in the northwest of the study area and was characterized by the predominance of coarse-grained sandy sediments. Debris coming from the source located in its central part showed the predominance of clay muds and fine-grained psammitic material. The peculiarities of the terrigenous material distribution in the Paleocene sequence allowed singling out four areas with the maximum development (> 50% of the total section) of sandstones, siltstones and mudstones. The performed petrographic investigations and the estimation of reservoir properties of the Yamna Formation rocks in these four areas allowed establishing priority directions of further exploration works for hydrocarbons in the study territory.