Lower Cretaceous Sediments Research Articles

Crustal structure of the Nogal basin, northern Somalia

Gravity, seismic and well data have been used to determine the crustal structure of the poorly-known Nogal basin, northern Somalia. Seismic data delineate a WNW-ESE trending graben infilled mainly by up to 6–7 km of Upper Cretaceous to Oligocene-Miocene sediments. Backstripping of well data show that the basin developed by thinning and rifting of continental crust during the Late Jurassic, Late Cretaceous and Oligocene. The Oligocene rift event is only observed at the centre of the basin, and correlates with the opening of the Gulf of Aden. The Late Jurassic rift event, which has been recognised in the northern Somalia, is largely absent in the basin.For the western part of the basin, Process Oriented Gravity and flexure Modelling (POGM) suggest a best-fit Te of 5 km, which explains both the amplitude and wavelength of the observed free-air gravity anomaly. However, the modelled anomaly in the eastern part of the basin is 30–40 mGal higher than the observed. Sediment-corrected Bouguer gravity anomalies show that the basin is associated with a relative high, which increases in amplitude to the east, towards the Kalis-1 well. We, therefore, propose that the eastern part of the basin to be locally intruded by dense magmatic material in the lower crust and/or upper mantle, which have elevated the gravity.The amount of crustal thinning inferred at Kalis-1 and Nogal-1 wells from backstripping is consistent with the results of POGM and flexure modelling. The models suggest the crust thins from about 35 km beneath the basin flanks to 32.6 km and 27.2 km at the Kalis-1 and Nogal-1 wells respectively. Moreover, the models suggest that Late Jurassic rifting was limited to the western part of the basin.The comparison of the long wavelength free-air gravity anomaly with the gravity effect of the topography based on different gravity/topography ratios suggest that while the crust is locally thinned beneath the basin it is also regionally domed, possibly by flexure due to magmatic intrusion. The doming predates the Late Cretaceous rifting and coincides with the same pre-Cenomanian uplift event during which substantial thicknesses of Upper Jurassic and Lower Cretaceous sediments were exhumed.

TECTONIC AND EROSION FEATURES, AND THEIR INFLUENCE ON ZONAL DISTRIBUTION OF THE UPPER TRIASSIC AND THE LOWER CRETACEOUS SEDIMENTS IN THE EUPHRATES GRABEN AREA, SYRIA

We have investigated the tectonic and erosion features of the Upper Triassic (Mulussa F Formation) and Lower Cretaceous (Rutbah Formation) sediments in the Euphrates graben area and analysed their influence on changes in the thickness and zonal distribution patterns of these sediments. In this study, the geological modeling software of Petrel Schlumberger is used to model the regional geological structure and stratigraphy from the available geological and geophysical data.The Upper Triassic and Lower Cretaceous sediments (in total, almost 800 m thick) are the major hydrocarbon reservoirs in the Euphrates graben, which contain approximately 80 to 90 % of the total hydrocarbon reserve in this area. These sedimentary zones experienced variable changes in thickness and zonal distribution due to erosion processes caused by the two major regional unconformities, the Base Upper Cretaceous (BKU) and Base Lower Cretaceous (BKL) unconformities. The maximum thickness of the Upper Triassic sediments amounts to 480 m in the central parts of the Euphrates graben and along the NW-SE trend, i.e. in the dip direction of the Upper Triassic Mulussa F Formation. Towards the NE flank of the graben near the Khleissia uplift and the SW flank near to the Rutbah uplift, the thickness of the Upper Triassic sediments is gradually decreased due to their partial or total erosion caused by the BKL unconformity, and also due to a less space for sediment accumulation near the uplifts. The thickness of the Lower Cretaceous sediments increases in the northern, NW and NE flanks of the graben. Their maximum thickness is about 320 m. The BKL unconformity is the major cause of erosion of the Lower Cretaceous sediments along the southern, SE and SW flanks of the graben. In the Jora and Palmyra areas towards the NW flank of the Euphrates graben, the Upper Triassic and Lower Cretaceous sediments show no changes in thickness. In these areas, there was more space for sediment accumulation, and the sediments were less influenced by the BKL and BKU unconformities and thus less eroded.

PECULIARITIES OF FORMATION OF THE LOWER CRETACEOUS TEСTONO-SEDIMENTATION SYSTEM OF THE BLACK SEA MEGADEPRESSION

Based on the analysis of the distribution of structural-material complexes, facial-genetic types and modeling of the history of immersion of the Lower Cretaceous sediments, the spatial-temporal differentiation of the tectonic regime of the Black Sea megadepression in the Early Cretaceous was established. It is shown that the structural and lithologicalfacial features of the Lower Cretaceous tectonic-sedimentation system were determined by the interaction of tectonic and geological-paleooceanographic factors. Thus, the low sea level and the initial phases of activation of sublatitudinal faults in the Hoterivian-Aptian determined the dominant influence of submeridional tectonic faults on the formation of the corresponding structural-facial block zonation. The increase in the area of the basin, the removal of denudation areas in the Late Albian reduced the intensity of terrigenous discharge, and the prolonged activity of sublatitudinal faults led to the formation of sublatitudinal structural-facial zonation. In the subsequent geological history, the tectonic regime was characterized by a complex mosaic-block character, which influenced the heterogeneity of oil and gas lithofluid systems of Cretaceous deposits.

Layer parallel stretching? Characterising magnetic and pore-fabric styles at a rifted continental margin: New insights from the Otway Ranges, Australia

This study presents the first analysis of the anisotropy of magnetic susceptibility (AMS) coupled with anisotropy of P-wave velocity (APV) in sedimentary rocks from a passive continental margin. In the Otway Ranges, Australia, the Lower Cretaceous sediments deposited during a period of subsidence and structural quiescence display triaxial-magnetic fabrics typical of extensional deformation. The extensional interpretation from AMS is also supported by the orientation of the pore fabric measured using APV.The inferred extensional azimuths from both AMS and APV analyses are in good agreement with axes for renewed Late Cretaceous rifting and the continental break up of Gondwana, a period of structural evolution characterised by abnormally-high levels of paleostress in the Otway Basin. Predicated on this we introduce the concept of layer parallel stretching (LPSt), a process that describes pore-scale structuring representative of the first phase of extensional deformation during periods of intense tectonic extension, in this case the LPSt was oriented NE-SW. These extensional structural fabrics in the Otway Basin were preserved during NE-SW oriented basin inversion, a process that involved reactivation of the local detachment, the partitioning of strain, and low levels of coupling between the basement and the cover. The results highlight the applicability of AMS and APV for characterising rock anisotropy in sedimentary basins at continental margins and have distinct outcomes with respect to the structural framework of the study area in the Otway Ranges.

ПРИМЕНЕНИЕ ОДНОМЕРНОГО ПАЛЕОТЕМПЕРАТУРНОГО МОДЕЛИРОВАНИЯ ДЛЯ ОЦЕНКИ УГЛЕВОДОРОДНОГО ПОТЕНЦИАЛА МЕЛОВЫХ ОТЛОЖЕНИЙ СРЕДНЕАМУРСКОГО ОСАДОЧНОГО БАССЕЙНА

The prospects of oil and gas content of the Cretaceous-Paleogene deposits of the Middle Amur sedimentary basin within the Pereyaslavsky graben are clarified on the basis of updated data on the tectonic-stratigraphic complexes of the basin using the method of one-dimensional paleotemperature modeling. It is established that throughout the history of formation of the studied part of Pereyaslavsky graben hydrocarbon generation could occur in lower Cretaceous sediments of the Assikaevsky and Alchansky/Strelnikovsky suites. The gas generation conditions for the Assykaevsky formation are still maintained.

Insights into the Thermal History of North-Eastern Switzerland—Apatite Fission Track Dating of Deep Drill Core Samples from the Swiss Jura Mountains and the Swiss Molasse Basin

This work presents new apatite fission track LA–ICP–MS (Laser Ablation Inductively Coupled Plasma Mass Spectrometry) data from Mid–Late Paleozoic rocks, which form the substratum of the Swiss Jura mountains (the Tabular Jura and the Jura fold-and-thrust belt) and the northern margin of the Swiss Molasse Basin. Samples were collected from cores of deep boreholes drilled in North Switzerland in the 1980s, which reached the crystalline basement. Our thermochronological data show that the region experienced a multi-cycle history of heating and cooling that we ascribe to burial and exhumation, respectively. Sedimentation in the Swiss Jura Mountains occurred continuously from Early Triassic to Early Cretaceous, leading to the deposition of maximum 2 km of sediments. Subsequently, less than 1 km of Lower Cretaceous and Upper Jurassic sediments were slowly eroded during the Late Cretaceous, plausibly as a consequence of the northward migration of the forebulge of the neo-forming North Alpine Foreland Basin. Following this event, the whole region remained relatively stable throughout the Paleogene. Our data show that the Tabular Jura region resumed exhumation at low rates in early–middle Miocene times (≈20–15 Ma), whereas exhumation in the Jura fold-and-thrust belt probably re-started later, in the late Miocene (≈10–5 Ma). Erosional exhumation likely continues to the present day. Despite sampling limitations, our thermochronological data record discrete periods of slow cooling (rates of about 1°C/My), which might preclude models of elevated cooling (due to intense erosion) in the Jura Mountains during the Miocene. The denudation (≈1 km) of the Tabular Jura region and the Jura fold-and-thrust belt (≈500 m) has provided sediments to the Swiss Molasse Basin since at least 20 Ma. The southward migration of deformation in the Jura mountains suggests that the molasse basin started to uplift and exhume only after 5 Ma, as suggested also by previous authors. The data presented here show that the deformation of the whole region is occurring in an out-of-sequence trend, which is more likely associated with the reactivation of thrust faults beneath the foreland basin. This deformation trend suggests that tectonics is the most determinant factor controlling denudation and exhumation of the region, whereas the recently proposed “climate-induced exhumation” mechanism might play a secondary role.

УСЛОВИЯ ФОРМИРОВАНИЯ ПЕСЧАНЫХ ПЛАСТОВ-КОЛЛЕКТОРОВ ЯКОВЛЕВСКОЙ СВИТЫ НА ТЕРРИТОРИИ ЛОДОЧНОГО НЕФТЕГАЗОКОНДЕНСАТНОГО МЕСТОРОЖДЕНИЯ

Актуальность исследования обусловлена необходимостью расширения ресурсного потенциала Российской Федерации за счет прироста месторождений углеводородов. На сегодняшний день нефть относится к полезным ископаемым, достигнутые уровни добычи которых недостаточно обеспечены запасами разрабатываемых месторождений. Подробное изучение строения продуктивных песчаных пластов-коллекторов в пределах Ванкорской группы месторождений на севере Красноярского края в перспективе даст возможность для прогноза и открытия новых залежей углеводородов в нижнемеловых отложениях Сибири. Цель: определить условия формирования продуктивных песчаных пластов по данным изучения кернового материала, изучить причины неоднородности сформированных отложений и выявить их характерные признаки для последующего прогноза нижнемеловых нефтеносных отложений на территории Красноярского края. Объект: продуктивные песчаные пласты яковлевской свиты нижнего мела Лодочного нефтегазоконденсатного месторождения. Методы: петрографический анализ шлифов, стадиальный анализ, гранулометрический анализ, фациальный анализ, исследование фильтрационно-емкостных и петрофизических свойств пород. Результаты. По данным петрографического анализа был изучен вещественный состав продуктивных песчаных отложений верхне- и нижнеяковлевской подсвит Лодочного месторождения, дана их сравнительная характеристика. Определена степень влияния постседиментационных процессов на формирование современного облика изучаемых отложений. Предложена фациальная модель, наиболее точно описывающая условия формирования продуктивных пластов. Установлено влияние условий осадконакопления в комплексе с последующими постседиментационными преобразованиями пород на фильтрационно-емкостные параметры песчаников. Объяснены причины наличия карбонатизированных прослоев во флювиальных отложениях. Сделаны выводы о возможности прогноза продуктивности отложений яковлевской свиты, накопленных в различных фациальных обстановках.

Lower Cretaceous Provenance and Sedimentary Deposition in the Eastern Carpathians: Inferences for the Evolution of the Subducted Oceanic Domain and its European Passive Continental Margin

AbstractReconstructing orogenic systems made up dominantly by sediments accreted in trenches is challenging because of the incomplete lithological record of the subducted oceanic domain and its attached passive continental margin thrusted by collisional processes. In this respect, the remarkable ~600 km long continuity of sediments exposed in the Eastern Carpathian thin‐skinned thrust and fold belt and the availability of quantitative reconstructions for adjacent continental units provide excellent conditions for a paleogeographical study by provenance and sedimentological techniques constraining sediment routing and depositional systems. These sediments were deposited in the Ceahlău‐Severin branch of the Alpine Tethys Ocean and over its European passive continental margin. We report sedimentological, paleomagnetic, petrographic, and detrital zircon U‐Pb data of Lower Cretaceous sediments from several thin‐skinned tectonic units presumably deposited in the Moldavides domain of the Eastern Carpathians. Sedimentological observations in the innermost studied unit demonstrate that deposition took place in a deepwater basin floor sheets to sandy turbidite system. Detrital zircon age data demonstrate sourcing from internal Carpathian basement units. The sediment routing changes in more external units, where black shales basin floor sheets to sandy mud turbidites were sourced from an external, European continental area. Although some degree of mixing between sources located on both margins of the ocean occurred, constraining a relatively narrow width of the deep oceanic basin, these results demonstrate that the internal‐most studied unit was deposited near an Early Cretaceous accretionary wedge, located on the opposite internal side relative to the passive continental margin domain of other Moldavides units.

Discovery of isolated leaves of Marskea (Taxaceae) in the Middle Jurassic sediments of Irkutsk Basin (East Siberia, Russia)

Study of isolated leaf compressions from Prisayan Formation outcrops on the right side of the Irkutsk reservoir resulted in identification of a new species: Marskea cuspidata sp. nov. The species has a strong morphological affinity with M. heeriana N. Nosova et Kiritchkova and T. ketovae Teslenko. The epidermis original texture differs well the Marskea cuspidata sp. nov. from other representatives of the genus Marskea which are known from the Jurassic and Lower Cretaceous sediments of Europe, Central Asia and Siberia.

Diverse provenance of the Lower Cretaceous sediments of the Eromanga Basin, South Australia: constraints on basin evolution

This study presents new geochemical and mineralogical data collected on 13 drill holes across the South Australian part of the Eromanga Basin, with a focus on the Lower Cretaceous Cadna-owie Formation, Bulldog Shale, Coorikiana Sandstone and Oodnadatta Formation. Mineralogical and geochemical data are used to determine the provenance of the sediments along with the paleoenvironments at the time of deposition. The dominant clay species across the formations are kaolinite and montmorillonite, although each drill hole shows individual mineralogical assemblages. The Cadna-owie Formation is mainly composed of quartz and kaolinite; montmorillonite is the dominant clay species in the other formations. Differences in major-element chemistry are best shown on the K–Na–Ca ternary diagram and display a strong relationship with mineralogy. Trace and rare earth elements are preserved at similar average concentrations between formations and are depleted relative to the upper continental crust. The signature of the sediments is interpreted to be derived from a mix of felsic and mafic igneous rocks with almost no sedimentary recycling. Sources of the sediments are likely to be from exposed basement packages surrounding the study area such as the Gawler Range Volcanics, the Musgrave Province, the Benagerie Volcanic Suite, the Mount Painter Inlier and the Arunta Block. The variations in dominant clay species between the formations could have been driven by an increase in temperature and a decrease in rainfall during the Early Cretaceous along with seasonal variations, and/or by the input in volcanogenic sediments from the active volcanoes located along the eastern margin of Australia. KEY POINTS Lower Cretaceous formations in the South Australian Eromanga Basin show limited regional lateral and vertical geochemical and mineralogical variations. Sediments are a mix of mafic through felsic igneous rocks derived from basement terranes exposed in the Early Cretaceous. The paleoclimate during deposition evolved from cold and humid to warm and arid.

Preliminary results of biostratigraphic studies of Lower Cretaceous sediments in the Ergel-Khaliv area, SE Mongolia

The research area is located in the territory of Khatanbulag soum, Dornogovi province, in the Great Govi Province (coordinates: 108°25'39.04"E and 43°10'11.43"N). Here, the authors studied the composition of sediments that had previously been classified as Lower Cretaceous Khukhteeg Formation, forming Mt. Ergel-Khaliv during earlier mapping work. The authors revealed fossils of faunas and floras, processing some data of biostratigraphic survey works taken on fossil-bearing sediments of the area. The fieldwork was conducted in April 2019 by researchers from the Institute of Paleontology, Mongolian Academy of Sciences. The area is very rich in fossils of mollusca, therefore, the local communities named it Dun-Ovoo (Conch hill). During the previous studies, the sediments outcropping around the Ergel-Khaliv were classified as Khukhteeg Formation (K1ht, Aptian-Albian) based on lithological characteristics and comparing them to the type section of the Khukhteeg Formation sediments. Our research revealed biostratigraphic basements and recorded previous data of collected fossils two types of mollusca; we have studied plant fossils, turtles, ostracods, fish and dinosaur bones had been revealed at first in that area. The results of the research work, the fossils that found in the mountain, were amended by more and new types and families of fauna and flora and their constituents. These new findings were helpful in the precise determination of the age of the sediments and provided some information on the paleoenvironmental conditions of the sedimentation period.

Anatomy and Jurassic evolution of a Hercynian basement high (Caloveto High - Calabria, Southern Italy)

The Caloveto area in North-East Calabria hosts a stratigraphic succession which documents the evolution from shallow water carbonates to deeper-water pelagic and hemipelagic deposits, bearing ample evidence for severe tectonic control on Jurassic and Lower Cretaceous sedimentation. Geological mapping indicates that the shallow-water carbonates, also with coral assemblages, formed a narrow fringe around a high of the Hercynian basement, made of lowgrade metamorphic rock, which remained emergent throughout the Pliensbachian and became an intrabasinal high which stood proud of the Longobucco basin, hosting thin pelagic sedimentation through most of the Jurassic. An extensional phase in the Toarcian disrupted and foundered the benthic carbonate factory, whose drowning isdocumented by a change to Rosso Ammonitico-type deposits. This resulted in a complex network of neptunian dykes (also intruding the basement) and in-situ breccias. Starting in the late Toarcian, the rugged submarine topography was gradually leveled by onlapping marls, radiolarites and pelagic limestone, which sealed the Toarcian fault zones producing a diverse array of unconformities. Colonization by microbial communities characterizes the initial stages ofmarine sedimentation around the cores of Paleozoic basement, as banded polychrome microbialites and “swollen” phyllites, a result of the microbially-influenced/induced displacive growth of calcium carbonate crystals along split cleavage planes, constitute an unexpected field tool for identifying basin margins. Silicified marginal zones in the shallow water limestone characterize, in analogy withother Tethyan regions, the onlap unconformities of chert-rich basinal units on the submerged carbonate fringes.

ПРОГНОЗНА ОЦІНКА НАФТОГАЗОНОСНОСТІ НИЖНЬОКРЕЙДОВИХ ВІДКЛАДІВ КАРКІНІТСЬКО-ПІВНІЧНОКРИМСЬКОГО ПРОГИНУ (за газогідрогеохімічними показниками)

Distribution features of formation waters in Karkinit-Northern Crimean deep were studied; the conditions of chemical composition origin of formation waters have been studied as well. The regional features for the distribution of formation waters and the conditions of their chemical composition forming of the Lower Cretaceous complex are established. The formation waters are salty or saline and commonly have low metamorphism intensity. The formation waters of the Lower Cretaceous complex are salt with often a low degree of metamorphosis. The values of the variation coefficients of five principal components (mineralization, (Na + K), chlorine (Cl), bromine (Br), and the water sampling depths) are estimated to range from 28.73 to 57.14 %, which indicates insignificant variability each of these indicators; this characteristic does not depend on the type of water and place of sampling. The seven objects of the correlation such as mineralization, chlorine, calcium, ammonium, bromine, sulfates and hydrocarbonates are closely associated with each other. The land waters are commonly of calcium chloride (Cl.Ca) or hydrocarbonate natrium (Hyd.Car.Na) type, whereas in the water area all variety of formation waters has been recognized. Formation waters of Late Cretaceous shelf complex as well as formation waters at Tarkhankut peninsula have close relation between chemical components, low variations in the composition of macro- and microcomponents. Therefore, the formation waters of these regions could be formed in quite similar conditions. The characteristic features of the shelf formation waters are high sulfate content, despite the fact that waters complex occurs at great depths. At the same time, a decrease in the metamorphism intensity is observed as well as an increase in the Cl/Br ratio up to 1000 or more, caused by low bromine content. It is apparent that such characteristic can be the result of extrusion of water at the late stages of clay rocks dehydration. Paleoinfiltration processes in Lower Cretaceous complex may be considered as an alternative explanation. High gas saturation in the waters of the folded basin bed has been recognized at Golytsyno area and at the Tarkhankut peninsula (Melova, Oktyabrska, Berezivska and Western Oktyabrska areas). This allows us to predict the prospects of the Lower Cretaceous sediments of the Karkinit-Northern Crimean deep.

The role of Late Cretaceous wrench tectonics in hydrocarbon endowment in El-Gindi Basin, northern Western Desert, Egypt

Abstract Detailed subsurface mapping and structural analysis of El-Gindi basin indicate the hydrocarbon potentiality of the Cretaceous reservoirs. El-Gindi basin is a Late Cretaceous-Eocene basin located at El-Fayium district, northeastern Western Desert of Egypt. The overwhelming impact of the Late Cretaceous wrench tectonics was evident during the inversion of the Jurassic-Early Cretaceous rift-related basins along the North Western Desert of Egypt and subsequent deposition of a thick succession of Eocene sediments (~6000 ft Apollonia Formation) within El-Gindi Basin. These tectonic events were developing the oil maturity and trapping through the Late Cretaceous reservoir sequences, Upper Bahariya Formation (Cenomanian) and the Abu Roash “G” Member (Turonian). The Gindi Fault, however, is a NW-trending basement feature breaching El-Gindi basin and bounding several deeper half grabens in the western half of El-Fayium district. It has been reactivated during the Cretaceous, Eocene and probably Oligocene-Early Miocene times, where extended northwestward to the Qarun Field at the footslopes of the Kattaniya inverted basin forming several oil traps along its strike. The Late Cretaceous dextral wrenching developed a regional system of ENE-oriented structural ridges such as Kattaniya and Silah (bounded El-Gindi basin to the north and south, respectively), associated with a series of NE-to ENE- oriented right-lateral strike-slip faults enclosing some structural closures in between. The development of such ridges causing regional subsidence and subsequent deposition of the Apollonia Formation creating several structural hydrocarbon traps. In addition, the structural closures formed between the ends of right-lateral strike-slip faults at Silah High became potential sites for hydrocarbon accumulation. The thermal maturity model of El-Gindi basin suggests a phase of hydrocarbon expulsion occurred during or immediately after deposition of the Apollonia Formation, where the Lower and Upper Cretaceous sediments passing the oil window. According to the analysis of well cores, E-logs and seismic data, shallow marine to deltaic environments have been assigned for the Cenomanian-Turonian reservoir sediments. Moreover, the deposition within channels, point-bars and estuarine environments for the hydrocarbon bearing sandstone reservoirs within El-Gindi Basin was identified.

Conditions of formation and forecast of natural reservoirs in clinoform complex of the Lower Cretaceous of the Barents-Kara shelf

Unique Leningradsky and Rusanovsky gascondensate fields in the Barrem-Cenomanian layer are discovered in the Kara Sea. Non-industrial accumulations of oil and gas have been discovered in the Lower Cretaceous sediments of the western part of the Barents Sea shelf. However, the structure and oil and gas potential of the Lower Cretaceous sediments of the Barents-Kara shelf remain unexplored. Based on the seismic-stratigraphic and cyclostratigraphic analysis, a regional geological model of the Lower Cretaceous deposits of the Barents-Kara shelf was created, the distribution area and the main stages of the accumulation of clinoforms were identified. As a result of a detailed analysis of the morphology of clinoform bodies, paleogeographic conditions were restored in the Early Cretaceous and a forecast of the distribution of sandy reservoirs was given

Manifestations of post-sedimentation processes in the Lower Cretaceous sediments of Bolshekhetskaya depression (Western Siberia)

Оbject.The article presents the results of studies of secondary mineral formation in the lower Cretaceous sediments of the Bolshekhetskaya depression, which contain highly promising oil and gas deposits, with established industrial performance at Pyakyakhinskoye, Khalmerpayutinskoye and South-Messoyakhskoye fields. The objects under consideration are located in the most submerged part of the Nadym-Taz syneclise in the zone, where the Taz and Urengoy facies regions meet.Materials and methods.Main types of postsedimentary changes of reservoir rocks selected on the basis of study of core material Pokurskaya, Angelovskaya, Sortymskaya and Megionskaya fms. Petrography and Mineralogy of the rocks under consideration were studied on the basis of stage analysis using optical and electron microscopy, and X-ray diffraction study at the Center of core and reservoir fluids research of “LUKOIL-Engineering’s KogalymNIPIneft branch In Tyumen” (Kogalym). Determination of the mineral type of zeolite was performed by X-ray phase analysis at the Institute of Geology and Geochemistry UrO RAS (Ekaterinburg).Resuts.It was found that for rocks Pokurskaya, Angelovskaya, Sortymskaya and Megionskaya fms characteristic a diverse range of secondary minerals and structures, evidence of the background stage catagenesis and the superimposed processes. The most important among them is the regeneration of quartz, the transformation of feldspar, violation of the crystal structure of biotite, the formation of various clay minerals, crystallization of zeolites and calcite.Conclusions.Studies show that the upper part of the section of the lower Cretaceous deposits of Bolshekhetskaya depression corresponds to the area of the middle catagenesis (gradation MK2), the bottom – changed to the stage of deep catagenesis (gradation MK3). In this case, the epigenetic process proceeded unevenly, pulsation, due to changing tectonic conditions. Particular attention is paid to the origin of zeolites, which is still debatable. It is assumed that their formation is associated with the transformation of “camouflage pyroclastic” in particular, feldspar clastics.

Геологическое строение и перспективы открытия нефтяных залежей в нижнемеловых и юрских отложениях акватории Обской и Тазовской губ Карского моря

Геологическое строение и перспективы открытия нефтяных залежей в нижнемеловых и юрских отложениях акватории Обской и Тазовской губ Карского моря

Boundary fault linkage and its effect on Upper Jurassic to Lower Cretaceous sedimentation in the Gudian half-graben, Songliao Basin, northeastern China

Abstract The Songliao Basin, northeastern China, is one of the few ultra-large petroleum basins in the world. Fault superposition, linkage, and stratigraphic architecture have produced a complicated basin evolutionary history. In this study, we report the boundary fault linkage and associated Upper Jurassic and Lower Cretaceous stratigraphic record using 3D seismic reflection data and well data. Our results show that the geometry of the boundary Gudian fault was originally controlled by six shorter fault segments, which grew and were linked during a syn-rift stage, then frictionally weakened and inverted in a post-rift stage. This boundary fault has variably controlled coeval syn-rift sedimentation. Fault segments in the middle section controlled the development of the limited, but thickest, Huoshiling and the first member of Shahezi Formations in the early syn-rift stage (ca. 150–133.9 Ma). Later, that control gradually weakened and vanished on succeeding the second member of Shahezi and Yingcheng Formations in the late syn-rift stage (ca. 133.9–105 Ma). The processes and the diverse syn-rift sedimentation response to Gudian fault growth and linkage have further implications for graben evolution and can guide hydrocarbon exploration in the Songliao Basin. This study will help elucidate the different controls of boundary fault linkage on associated sedimentation, as well as rift basins development in eastern China and similar areas throughout the world.

Cypridea species (Crustacea, Ostracoda) from the Lower Cretaceous Jinju Formation of the Gyeongsang Basin, South Korea

Based on a large quantity of fossil material and more detailed description of the morphological features, two Cypridea species are recognized from the Jinju Formation of the Gyeongsang Basin: Cypridea jinjuria Choi, 1990 and Cypridea samesi n. sp. These two species do not co-occur and are endemic to South Korea. However, they share the same morphological feature, a swelling/node-like swelling at the anterior cardinal angle area, with some other Cypridea species from the Lower Cretaceous sediments of China and Mongolia. This may suggest a close relationship between these species. Paleobiologically, we infer a parthenogenetic reproduction mode for Cypridea jinjuria Choi, 1990 and Cypridea samesi n. sp., and suggest that the Jinju Formation was deposited under conditions with long hydroperiods.

RETRACTED: Early Cretaceous origin of the Woyla Arc (Sumatra, Indonesia) on the Australian plate

Abstract Key to understanding the plate kinematic evolution of the Neotethys oceanic domain that existed between the Gondwana-derived Indian and Australian continents in the south, and Eurasia in the north, is the reconstruction of oceanic plates that are now entirely lost to subduction. Relics of these oceanic plates exist in the form of ophiolites and island arcs accreted to the orogen that stretches from Tibet and the Himalayas to SE Asia that formed the southern margin of Sundaland. The intra-oceanic Woyla Arc thrusted over western Sundaland – the Eurasian core of SE Asia – in the mid-Cretaceous. The Woyla Arc was previously interpreted to have formed above a west-dipping subduction zone in the Early Cretaceous, synchronous with east-dipping subduction below Sundaland. The oceanic ‘Ngalau Plate’ between the Woyla Arc and Sundaland was lost to subduction. We present paleomagnetic results from Lower Cretaceous limestones and volcaniclastic rocks of the Woyla Arc, Middle Jurassic radiolarian cherts of the intervening Ngalau Plate, and Upper Jurassic–Lower Cretaceous detrital sediments of the Sundaland margin. Our results suggest that the Woyla Arc was formed around equatorial latitudes and only underwent an eastward longitudinal motion relative to Sundaland. This is consistent with a scenario where the Woyla Arc was formed on the edge of the Australian plate. We propose a reconstruction where the Ngalau Plate formed a triangular oceanic basin between the N–S trending Woyla Arc and the NW-SE trending Sundaland margin to account for the absence of accreted arc rocks in the Himalayas. As consequence of this triangular geometry, accretion of the Woyla Arc to the western Sundaland margin was diachronous, accommodated by a southward migrating triple junction. Continuing convergence of the Australia relative to Eurasia was accommodated by subduction polarity reversal behind the Woyla Arc, possibly recorded by Cretaceous ophiolites in the Indo-Burman Ranges and the Andaman-Nicobar Islands.