Lower Cretaceous Deposits Research Articles

Ginkgoites villardeseoanii sp. nov., a ginkgophyte with insect damage from the Upper Cretaceous (Maastrichtian) Lefipán Formation (Chubut, Patagonia, Argentina)

Today, the ginkgophytes are represented by the single species Ginkgo biloba, naturally distributed in China and cultivated worldwide. However, the ginkgophyte lineage shows an extensive fossil record going back to the Paleozoic of both hemispheres. In South America, its record began in the upper Paleozoic and reached the middle Eocene, and it includes both vegetative and reproductive remains. The Cretaceous macrofossil record of this group in South America is restricted to Lower Cretaceous deposits, where it is relatively abundant, whereas there is a gap in its Upper Cretaceous to lower Paleogene record. We present the new species Ginkgoites villardeseoanii collected from Maastrichtian (uppermost Cretaceous) deposits of the Lefipán Formation (Patagonia, Argentina). The studied material consists of three specimens preserved as adpressions of isolated, flabellate, and petiolate (Ginkgo-like) leaves, with few epidermal characters preserved. One of the studied specimens shows evidence of insect damage consistent with hole feeding, constituting the first Cretaceous record of interaction between ginkgophytes and insects in the Southern Hemisphere. We infer that this damage was produced when the leaf was still attached to the plant, as the specimen shows evidence of a physiological reaction of the plant in the form of a border of necrotic tissue around the wound. Ginkgoites leaves are common among different lineages within the Ginkgoales, having been associated to three families (Ginkgoaceae, Karkeniaceae, and Yimaiaceae). Therefore, G. villardeseoanii was assigned to an incertae sedis family.

NATURAL RECREATIONAL RESOURCES OF CHORTKIV DISTRICT OF TERNOPIL REGION

The article presents a component-by-component analysis of natural recreational resources of the newly created territorial and administrative unit –Chortkiv district of Ternopil region. Geomorphological, water, biotic recreational resources are described. It is proposed to allocate the Chortkiv recreational area, which will include three recreational complexes: Monastyrysk and Buchach, Borshchiv and Zalishchyky, Chortkiv and Husyatyn. For the selected recreational complexes and nodes the types of recreational occupations according to the main groups of recreational resources are offered.The Monastyrysk and Buchach recreational complex has recreationally interesting landscapes that are part of the Dniester Canyon Landscape park, in particular the cascades of Rusylivsky and Sokiletsky waterfalls, the Zholoby cave (for cognitive recreation), and the mass recreation territory in the area of ​​the Lisova camp site, as well as the valley of the Strypa River from the village of Skomorohy (Buchach territorial community) to the village of Lytychi (Zalishchyky territorial community) for water tourism. Borshchiv and Zalishchyky recreational complex includes Borshchiv and Zalishchyky recreation centers and is characterized by very high recreational potential due to the aesthetic appeal of landscapes, a large number of living and inanimate objects, high climate comfort. The Dniester canyon, saturated with natural protection objects along its entire length, is favorable for the development of ecotourism, tourist and excursion cognitive recreation.Zalishchyky recreational center. Within the valley of the Dniester River in the vicinity of the village Khmelev, the valley of the river Dzhuryn near the village Nyrkiv and village Nahoryany (Chervonogorod waterfall) of Tovste territorial community, areas for mass recreation. The development of cognitive tourist and excursion recreation is promoted by Zhyzhavsk and Obizhevsk botanical reserves of national importance, in which forest and meadow and steppe groups with valuable relict shrubs are protected: Polish spiraea, Cyticus Podilskyy, dwarf cherry. Kasperivtsi Landscape Reserve of national importance with unique natural complexes in the valley of the Seret River with a picturesque reservoir, the presence of geological, paleontological and botanical objects of nature is a place of short-term recreation. In the valley of the Dniester and its tributaries there are ways to the surface of mineral waters – sulfate, chloride, like "Naftusya" or "Druskininkai" (Zalishchyky, Tovste), as well as medicinal peat bog (Tovste), which, in combination with a warm climate (climatotherapy), is the basis for the development of health and recreation.The unique flora of Western Podilsk Transdnistria is represented in Zhyzhavsk, Obizhevsk, Shutromyntsi, tract "Hlody" botanical nature reserves, can be the object of scientific and cognitive tourism for botanists, teachers, students, students of profile and secondary schools.Borshchiv recreation center also has a high recreational potential. Extremely interesting for the development of scientific and cognitive tourism are the outcrops of sediments belonging to the Paleozoic era (Trubchyn tract, Dzvenyhorodsk Silurian outcrops, Silurian and Devonian deposits in the Dniester, Khudykivsk outcrops of Lower Cretaceous deposits). In terms of completeness, number of fossil fauna and flora, accessibility for observation, most of them are of international importance and are stratotypes for the Eastern European platform.Chortkiv and Husyatyn recreation complex includes Husyatyn and Chortkiv recreation centers. Husyatyn recreation center specializes in the development of health and recreation. Husyatyn is a balneological resort with the use of low-mineralized water with a high content of organic substances such as "Naftusya" called "Novozbruchanska" and brines of high mineralization such as "Druskininkai" called "Husyatynska". Chortkiv recreational center specializes in short-term recreation, development of sports and recreation, which is facilitated by areas of river floodplains, slopes covered with forests, the river Seret for various types of water tourism.Key words: recreational resources, administrative district, recreational district, recreational complex.

Substantiation of paleohydrodynamic sedimentation modes and identification of missed oil-and-gas saturated areas that are promising for additional exploration of the Lower Cretaceous deposits of the Albian stage of the Achikulak oil field according to geophysical well logging data

In the development of the oil and gas complex, the improvement of methods for studying the patterns of distribution of hydrocarbon deposits is of particular importance. At the same time, scientific research can be carried out in different directions. These include increasing the resolution of various methods of borehole and areal geological and geophysical studies of lithological features and oil-and-gas content, developing new approaches to interpreting well logging results, analyzing the productivity of poorly studied regions and areas of the section, identifying low-amplitude folds and non-anticlinal deposits. The development of hydrocarbon deposits in the Stavropol Territory has been going on for many decades, which has led to reduction of deposits within medium and large anticlinal uplifts. Therefore, the main attention is now paid to the prospect for low-amplitude and small-size uplifts and traps of the non-anticlinal type, which include lithological and stratigraphic ones.

Types of river sources of the thin-grained aluminosilicaclastics for the Jurassic and lower cretaceous deposits of the West Siberian megabasin

Background. The lithogeochemical features of fine-grained detrital rocks (mudstones, shales, and fine-grained siltstones) allow, with a certain degree of success, the main parameters of the formation of sedimentary sequences to be reconstructed. These parameters include (primarily in terms of their REE and Th systematics) the types of river systems supplying thin terrigenous suspension in the sedimentation area: the rivers of the 1st category – large rivers with a catchment area of more than 100,000 km2; 2nd category – rivers feeding on the products of erosion of sedimentary deposits; 3rd category – rivers draining mainly igneous and metamorphic rocks; and 4th category – rivers carrying erosion products of volcanic associations.Aim.To reveal, based on the analysis of interrelationships between such parameters as (La/Yb)N, Eu/Eu* and the Th content, the types of river systems that fed the Jurassic and Lower Cretaceous deposits of the Shaim oil and gas region (OGR) (Sherkalinsky, Tyumen, Abalak and Mulymya formations) and the region of the North Pokachevsky field of the Shirotnoe Priobye region (Sherkalinsky, Tyumen and Bazhenov formations, Lower Cretaceous deposits).Materials and methods. The ICP MS data for almost 100 samples of mudstones and fine-grained clayey siltstones were used to analyse the features of distribution of lanthanides and Th in the Jurassic and Lower Cretaceous clayey rocks of the Shaim OGR and the area of the North Pokachevsky deposits. Individual and average composition points for formations, members and layers were plotted on the (La/Yb)N-Eu/Eu*, (La/Yb)N–Th diagrams developed by us with classification areas of the composition of fine suspended material of modern rivers of different categories.Results and conclusion. The results presented in the article showed that during the formation of the deposits of the Shaim OGR in the Early and Middle Jurassic, erosion affected either mainly sedimentary formations or paleo-catchment areas that were very variegated in their rock composition. In the Late Jurassic, the source area was, most likely, a volcanic province, composed mainly of igneous rocks of the basic composition, and located within the Urals. This conclusion suggested that the transfer of clastic material from the Urals to the Urals part of the West Siberian basin “revived” much earlier than the Hauterivian. The Jurassic-Lower Cretaceous section of the vicinity of the North Pokachevsky field was almost entirely composed of thin aluminosilicaclastics formed due to the erosion of volcanic formations. These volcanic formations were located, as followed from the materials of earlier performed paleogeographic reconstructions, probably within the Altai-Sayan region or Northern Kazakhstan. Thus, the supply of detrital material in the considered territories of the West Siberian basin had a number of significant differences in the Jurassic and early Cretaceous.

Microfacies and Depositional Conditions of Jurassic to Eocene Carbonates: Implication on Ionian Basin Evolution

In order to decipher the paleo-depositional environments, during the Late Jurassic to Early Eocene syn-rift stage, at the margins of the Ionian basin, two different areas with exposed long sequences have been selected, Kastos Island (external margin) and Araxos peninsula (internal margin), and were examined by means of microfacies analysis and biostratigraphy. On Kastos Island, based on lithological and sedimentological features, the following depositional environments have been recognized: an open marine/restricted environment prevailed during the Early Jurassic (“Pantokrator” limestones), changing upwards into deep-sea and slope environments during the Late Jurassic and Early Cretaceous (Vigla limestones). The Upper Cretaceous (Senonian limestones) is characterized by a slope environment, whereas during the Paleogene, deep-sea and toe of slope conditions prevailed. In Araxos peninsula, Lower Cretaceous deposits (“Vigla” limestones) were accumulated in a deep-sea environment; Upper Cretaceous ones (Senonian limestones) were deposited in slope or toe of slope conditions. Paleocene limestones correspond to a deep-sea environment. In Araxos peninsula, changes occurred during the Cretaceous, whereas on Kastos Island, they occurred during the Paleocene/Eocene, related to different stages of tectonic activity in the Ionian basin from east to west.

3-D seismic interpretation of stratigraphic and structural features in the Upper Jurassic to Lower Cretaceous sequence of the Gullfaks Field, Norwegian North Sea: A case study of reservoir development

The 3-D seismic dataset is a key tool to analyze and understand the mechanism of structural and stratigraphic hydrocarbon (HC) trapping in the subsurface. Conventionally used subsurface seismic characterization methods for fractures are based on the theory of effective anisotropy medium. The aim of this work is to improve the structural images with dense sampling of 3-D survey to evaluate structural and stratigraphic models for reservoir development to predict reservoir quality. The present study of the Gullfaks Field, located in the Norwegian North Sea Gullfaks sector, identifies the shallowest structural elements. The steepness of westward structural dip decreases eastward during the Upper Jurassic to Lower Cretaceous deposition. Reservoir sands consist of the Middle Jurassic deltaic deposits and Lower Jurassic fluvial channel and delta plain deposits. Sediment supply steadily prevails on sea-level rise and the succession displays a regressive trend indicated by a good continuous stacking pattern. The key factor for the development of reservoirs in the Gullfaks Field is fault transmissibility with spatially distributed pressure. The majority of mapped faults with sand-to-sand contacts are non-sealing, which provide restriction for the HC flow between the fault blocks. The traps for HC accumulation occur between the post-rift and syn-rift strata, i.e. antiform set by extensional system, unconformity trap at the top of syn-deposition, and structural trap due to normal faults. Overall reservoir quality in the studied area is generally excellent with average 35% porosity and permeability in the Darcy range. Our findings are useful to better understand the development of siliciclastic reservoirs in similar geological settings worldwide.

Sequence stratigraphy and distribution of organic-rich Lower Cretaceous mixed clastic-carbonate strata in Matruh Basin, northwestern Egypt: Constrains on the Tethyan sea level changes, palaeoclimate, and tectonics

Integrated palynological, lithological, and geophysical analyses of the Lower Cretaceous (upper Hauterivian-Aptian) in Matruh Basin enabled conducting a high-resolution sequence stratigraphic analysis. Fluctuations of the continental/marine palynomorphs ratio reflect changes in the Tethyan 3rd order sea levels and are mirrored by eminent vertical changes in the spontaneous potential and the lithofacies. These are used with abundance of the marine phytoplanktons and opaque/translucent phytoclasts ratio to identify three 3rd order (SQ1: 132.4–120.8 Ma, SQ2: 120.8–115.2 Ma, and SQ3: 115.2–113 Ma) and seven 4th order genetic sequences and to study the impact of the allogenic and autogenic processes on their deposition.Deposition of the deltaic clastic systems tracts of the lower-middle Alam El Bueib (late Hauterivian-early Barremian) and Dahab (late Aptian) formations reflect the interaction between the regional humid climate and the Tethyan 3rd order sea levels, which superimposed the Tethyan 2nd order sea level. Interferences of minor regional tectonics were also important. The argillaceous deposits possess large amounts of terrestrial organic matter of low hydrogen index (HI: 185.8–211.5 mg HC/g TOC) indicating gas organic facies. These deposits show relatively high organic richness (1.81–2.50 TOC wt %) due to relatively low sediment dilution and water circulation (i.e. suboxic-anoxic conditions) and high primary productivity due to high riverine nutrient inputs.Deposition of the inner-middle shelf clastic-carbonate systems tracts of the upper Alam El Bueib and Alamein formations (latest Barremian-middle Aptian) reflects the interaction between the climatically induced low terrigenous influx and carbonate sedimentation due to shift to relatively dry climate, changes in the Tethyan 3rd order sea levels, and the middle Aptian regional minor uplift. These systems tracts show relatively large amounts of terrestrial organic matter, a notable marine organic matter signature, and intermediate HI (283.1–239.0 mg HC/g TOC) indicating gas/oil organic facies. The shales and siltstones are relatively organic richer (1.88–2.28 TOC wt %) than the pure and the argillaceous dolostones (1.46–1.94 TOC wt %). This organic richness is related to combined low sedimentation rates, low water circulation (i.e. dysoxic-suboxic to suboxic-anoxic conditions), and relatively high primary productivity.Overall, the Tethyan sea level changes, regional climate, and regional tectonics played a major role in the deposition of the organic-rich syn-rift Lower Cretaceous deposits in Matruh Basin.

First record of Ginkgoxylon (Ginkgoales) fossil wood in the Lower Cretaceous of the Arctic region

A new species of the fossil wood genus Ginkgoxylon (Ginkgoales), Ginkgoxylon arcticum sp. nov., is described from the Lower Cretaceous deposits of Alexandra Land Island, Franz Josef Land Archipelago, Russia. The record of Ginkgoxylon represents the latest stratigraphic occurrence of this taxon in Russia and the first and only one from the Arctic region.

Provenance of the Phuquoc Basin fill, southern Indochina: Implication for Early Cretaceous drainage patterns and basin configuration in Southeast Asia

Cretaceous basins cover large parts of mainland SE Asia. Yet, the development during the Cretaceous is poorly understood including the establishment of the Cretaceous basin configuration. Based on detrital zircon and heavy mineral analysis, this study investigates the provenance of Lower Cretaceous deposits in the Phuquoc Basin, exposed in Cambodia and SW Vietnam and extending into the Gulf of Thailand. Our results document five major zircon populations with 130–145 Ma, 145–200 Ma, 200–270 Ma, 420–470 Ma, 1800–1900 Ma ages and two subordinate 2400–2700 Ma, 750–1000 Ma age clusters. These ages resemble those of the Qinling-Dabie and the Songpan-Ganzi orogenic belts and differ from other Asian terranes. These ages suggest that the Qinling-Dabie and Songpan-Ganzi orogenic belts were major sources of sediment for the Phuquoc Basin in the Early Cretaceous. Heavy mineral compositions including the presence of almandine, often co-occurring with silimanite and epidote, suggest metamorphic and granitic constituents in the hinterland, compatible with these orogenic belts being the source.The detrital zircon age pattern of the Phuquoc Basin closely resembles the zircon ages in Khorat and the Sichuan basins, suggesting a common sediment source, and bears great similarities with mid-Cretaceous strata in the Lanping-Simao Basin. These basins share a remarkable lithostratigraphic similarity and are confined by erosion. Taken altogether, this supports that the Phuquoc, Khorat, Sichuan, and probably the Lanping-Simao basins, formed part of a Cretaceous basin covering much of central SE Asia segregated by Late Cretaceous and Cenozoic denudation and translation. The absence of 130–145 Ma and 145–200 Ma aged zircons in the Lanping-Simao Basin suggests that another drainage system sprang from the Songpan-Ganzi Orogenic Belt and fed into this basin before merging with the Qinling-Dabie Orogenic Belt drainage system south of the Sichuan Basin. The combined drainage system likely passed through the Khorat Basin before entering the Phuquoc Basin.

Вулканогенный материал в верхнеюрско-нижнемеловых отложениях востока Русской плиты и его источники

. Widespread “camouflaged” pyroclastics including smectite, illite-smectite and heulandite are detected in the upper jurassic– lower cretaceous deposits of the Ulyanovsk-Saratov basin. Moreover, volcanic glasses are found in several stratigraphic units. The quantity of pyroclastic material in the study section (17–72%) is probably related to volcanic input in the basin. Concentrations of the trace and rare earth elements point to a predominantly acid source of ash material, except the Promzino and Ulyanovsk black shale formations linked to the mixed andesite-basaltic and felsic sources. Island arcs of the Northern Tethys basin and the High-Altitude Arctic Igneous Province are regarded as probable sources of the pyroclastic influx in the epeiric basin of the Russian Platform in the Jurassic-Early Cretaceous.

Connectivity between Petrophysical Parameters and Hydrodynamic Activity in Achikulak Oil Field

Researches on structure of detrital part of sedimentary rock, particularly granulometric composition of rocks give not only information about restoration of their condition of deposition, duration, direction and transfer ranges, but also for some reconstructions of demolition’s areas, in particular to fixe concern about structure of rocks in areas of sedimentation, and sometimes partially on the climate. Therefore, considering connectivity of petrophysical parameters specially porosity and permeability of rocks with hydrodynamic activity of layer of lower Cretaceous deposits in order to describe formation of reservoir rocks, condition of sedimentation, formation recoveries, sequences of changes and fluid traps bring us to lead subsequently these types of work in one of the Achikulak oil fields and determine future movements, settlements and sand body of the reservoir. The change of lithological structure of rocks by section, maybe define conditions of sedimentation on Achikulak deposits field, it is known that the initial signs that are stable over time are studied in the lithofacial analysis.

<p><strong>New early Barremian fossiliferous amber outcrop from North Lebanon</strong></p>

Lebanon is famous for its abundant Mesozoic amber deposits. Most of its amber outcrops are from the Lower Cretaceous [lower Barremian (Granier et al., 2016; Maksoud et al., 2017)] (ca. 430 outcrops found hitherto), while others are from Upper Jurassic (Kimmeridgian) [19 outcrops (Azar et al., 2010b; Nohra et al., 2013; Maksoud & Azar, 2020)]. Among the many Lebanese Lower Cretaceous amber deposits, only 24 of them gave biological inclusions to date (Azar et al., 2010a; Maksoud & Azar, 2020; Maksoud et al., 2020).

Quantifying Multiple Erosion Events in the Distal Sector of the Northern Alpine Foreland Basin (North-Eastern Switzerland), by Combining Basin Thermal Modelling with Vitrinite Reflectance and Apatite Fission Track Data

This work quantifies the amount of erosion associated with the Cretaceous and Miocene erosional unconformities recognised in the distal part of the Northern Alpine Foreland Basin (NAFB), north-eastern Switzerland. To achieve this goal, the basin thermal modelling approach is applied, calibrated by two different sets of data collected in previous studies: vitrinite reflectance (%Ro) and the temperature estimated from apatite fission tracks (AFT) data modelling. The novelty of this approach is the possibility to constrain the timing and magnitude of multiple erosion events by integrating thermal modelling with thermochronologic data. Combining these two methods allows the erosional events to be separated which would not be possible using only irreversible paleothermometers, such as vitrinite reflectance data. Two scenarios were tested, based on the data of two published thermochronology studies. For the Cretaceous unconformity, similar results are obtained for the two scenarios, both indicating that the deposition and the subsequent complete erosion of Lower Cretaceous deposits, in the order of 500–1300 m, depending on the area, are necessary, in order to attain the temperatures estimated by the thermal history modelling of AFT data. Thus, a depositional hiatus for this period is not likely. For the Miocene-Quaternary unconformity, the magnitude of erosion calculated for the two scenarios differs by 300–1400 m, depending on the AFT data considered. The two scenarios lead to a different evaluation of the subsidence and uplift rate of the study area, thus to a different interpretation of the tectono-stratigraphic evolution of this distal sector of the NAFB.

A new genus of fossil frog (Anura) from lower Cretaceous deposits in South America.

The frog clade Neobatrachia or "advanced frogs" represents more than 95% of the diversity within Anura. The neobatrachian fossil record is incomplete due to the small size and fragile nature of their bones but provides some clues on the time and rate of the current diversification of modern-day amphibians. The Crato Formation (Aptian) of northeastern Brazil is known for the presence of, at least, five species of neobatrachian fossils. Herein, we describe a well-preserved fossil that represents a new neobatrachian taxon from the Crato Formation (Cretaceous) in the Araripe Basin, northeastern Brazil, and perform phylogenetic analysis to assess its higher-level relationships. The new specimen is an almost complete and articulated skeleton with soft tissue preservation. Phylogenetic analysis recovered the specimen nested in the clade Hyloidea and our results highlight the remarkable value of the Crato Formation as a Laggerstätte.

Dinosaur Tracks from the Caucasian Mineral Waters Country in the Context of the Study of Lower Cretaceous Paleosols of This Region

This article examines the geological and stratigraphic context of several types dinosaur tracks discovered in Lower Cretaceous deposits exposed in the vicinity of city of Kislovodsk (Caucasian Spa Country; Stavropol Krai). The tracks occur on the bedding surfaces of Lower Cretaceous (Valanginian) limestones, dolostones and marls. Two track morphotypes are described. Some ideas are proposed on the paleoclimatic and environmental conditions in the region during Early Cretaceous times. We suggest that the tracks were produced in a coastal plain in the littoral zone of a marine basin (possibly, a brackish lagoon) during a warm, seasonally dry climate.

Regional subsurface mapping and 3D flexural modeling of the obliquely converging Putumayo foreland basin, southern Colombia

The Putumayo foreland basin (PFB) is an underexplored hydrocarbon-bearing basin located in southernmost Colombia. The PFB forms a 250 km long segment of the 7000 km long corridor of Late Cretaceous-Cenozoic foreland basins produced by eastward thrusting of the Andean mountain chain over Precambrian rocks of the South American craton. We have used approximately 4000 km of 2D seismic data tied to 28 exploratory wells to describe the basin-wide structure and stratigraphy. Based on seismic interpretation and comparison with published works from the southward continuation of the PFB into Peru and Ecuador, three main across strike, structural zones include (1) the 20 km wide, western structural zone closest to the Andean mountain front characterized by inversion of older, Jurassic half-grabens during the Late Miocene, (2) the 45 km wide, central structural zone characterized by moderately inverted Jurassic half-grabens, and (3) the 120 km wide, eastern structural zone (ESZ) characterized by the 40 km wide, north–south-trending Caquetá arch. The five mainly clastic tectonosequences of the PFB include (1) Lower Cretaceous pre-foreland basin deposits, (2) upper Cretaceous-Paleocene foreland basin deposits, (3) Eocene foreland basin deposits related to the early uplift of the eastern Cordillera, (4) Oligocene-Miocene underfilled, foreland basin deposits, and (5) Plio-Pleistocene overfilled, foreland basin deposits. We used 3D flexural modeling to identify the elastic thickness ([Formula: see text]) of the lithosphere below the PFB, and to model the location of the sedimentary-related and tectonically related forebulges of Cretaceous to Oligocene age. Flexural analysis finds two pulses of rapid, foreland-related subsidence first during the Late Cretaceous-early Paleocene and later during the Oligocene-Miocene. Despite the present-day oblique thrusting of the mountain front, flexure of the PFB basement has produced a tectonic forebulge now located in ESZ and controls a basement high that forms the eastern updip limit for most hydrocarbons found in the PFB.

Starogroznensky oil and gas field: historical background and current status

The paper is devoted to one of the largest deposits of the North Caucasus, i.e. Starogroznenskoye field. There are identified the main development stages of this field, i.e. well production, development of the Miocene and Mesozoic deposits, and the current stage. Well production continued almost until the end of the 19th century. At the Miocene stage, the production was carried out from thrust and subthrust sand formations of Karagan and Chokrak. The paper also mentions the experimental adit on Mamakayevskaya gill. Which was headed by mining engineers A.A. Klushin and A.E. Yeronin. The beginning of the Mesozoic stage dates to the end of the 1940s. The main production was associated with the Upper Cretaceous sediments. At the end, an assessment of the current state of the structure of proven reserves is given. In conclusion, an assessment of the opportunities aimed at further development of the field associated with the additional exploration and additional development of the Miocene and Lower Cretaceous deposits is given.

Geochemical Indicators of “Camouflaged” Pyroclastic Material in the Upper Jurassic–Lower Cretaceous Deposits of the Eastern Russian Platform

Based on the results of studying the lithological–geochemical features of the Upper Jurassic–Lower Cretaceous mudrocks and black shales in the Eastern Russian Platform, the continuous distribution of pyroclastic material in the whole section is established. Possible sources of acid pyroclastics were active volcanoes of the Transcaucasian ensialic island arc. The explosions of the Sanandaj–Senjan ensimatic island arc (in the Late Jurassic) and the Arctic Large Igneous Province (in the Aptian) could have been the source of basaltic pyroclastics in the black shale horizons. The highest activity of the Transcaucasian and Elburs island arcs in northwest Tethys was apparently recorded during the Albian, which determined the maximum content of felsitic material in the Middle Albian bentonite-like mud rocks.

Groundwater in the Mesozoic hydrogeological basin of the Middle Ob (a case study of the Ust-Balykskoye oil field)

Despite the fact that there is the large amount of accumulated factual material, formation of hydrogeochemical conditions of deep oil and gas horizons in the Middle Ob and the West Siberian megabasin still contains many questions. This is due to numerous hydrogeodynamic and hydrogeochemical anomalies that don't have an unambiguous explanation. The presence of inversion hydrogeochemical zoning in the Lower Cretaceous and Upper Jurassic deposits and the presence of low-mineralized reservoir water of a sodium-bicarbonate composition are the peculiarity of groundwater in the considered territory. A change in the genetic type of water, a decrease in mineralization, a decrease in the content of calcium ion, and an increase in the amount of bicarbonate ion in the Mesozoic hydrogeological basin are associated with the transformation of mineral and organic matter in sedimentary rocks, when they are immersed, at the water expelling stage. The determination of the origin of low-mineralized reservoir water of a sodium-bicarbonate lying at significant depths is of great practical importance, since the relationship between the inversion of groundwater and oil content has been revealed, so this fact can be considered a search criterion for petroleum potential.

Palaeoenvironmental reconstruction and sequence stratigraphy of the Lower Cretaceous deposits in the Zagros belt, SW Iran

Palaeoenvironmental reconstruction and sequence stratigraphy of the Lower Cretaceous deposits in the Zagros belt, SW Iran