Thermal conductivity of sediments in high-latitude West Siberia

The thermal conductivity of rocks (λ) used previously to estimate heat flow in high-latitude Siberia was assumed to be λ = 1.8–2.0 W/(m?K), according to published evidence, but was almost never measured specially. We measured the thermal conductivity of core samples from boreholes drilled in the northeastern West Siberian Plate and in the Yenisei–Khatanga basin in the 1990s, using two advanced instruments: a comparator and a scanner of thermal conductivity. Altogether there were 305 samples of air-dry sediments (λ_d) from the 1100–4200 m interval of 23 holes, out of which 77 samples were then moistened (λ_w). The average thermal conductivities of rocks in dry and wet conditions were found to be λ_d = 1.9 ± 0.2 and λ_w = 2.6 ± 0.1 W/(m?K), respectively. Thus, the true thermal conductivity of sediments, which are saturated with water in this northern area, must be about 20–30% higher than that assumed in the previous heat flow determinations, and the latter are thus underestimated correspondingly. The updates to the thermal conductivity values imply major revision to the existing ideas of the thermal regime in the Siberian high latitudes. Such a serious revision of geothermal data will obviously require a large amount of additional experimental work.     

Neocomian paleogeography,gas hydrate cementation of sediments,and abnormal sequences of the Bazhenov Formation (West Siberia)

Abnormal zones of the Bazhenov Formation originated in the Neocomian as a result of protobazhenite reworking by submarine slide and slump waste wedgings, which eroded and deformed slope toe protobazhenite. But gas hydrate (GH) cementation might restrict the rock ability for plastic deformation. The conditions for GH thermodynamic stability in protobazhenites are inferred from reconstructions of paleogeographic and paleo-oceanic evironments. Joint analysis of Neocomian marine paleodepths and deep water paleotemperatures provides an explanation of the Bazhenov abnormal-zone extension.     

A lithofacies description of Jurassic sediments in the south of the Predyenisei petroleum subprovince,West Siberia

We have studied Jurassic sections in the Predyenisei subprovince of the West Siberian petroleum basin, which were penetrated in the Vostok-1, Vostok-3, and Vostok-4 stratigraphic wells. The Urman, Togur, Ilan, Peshkovo, Tyumen’, Naunak, and Mar’yanovka Formations are described from a detailed comprehensive core analysis and log data. The depositional environment for these sediments was predominantly continental. There is evidence for short transgressions in the Ilan (Lower Toarcian) and Peshkovo (Upper Toarcian) Formations, as well as the Upper Urman (Upper Pliensbachian) and the Upper Tyumen’ (Bajocian) Subformations. In the Upper Naunak Subformation (Oxfordian), there was a change of facies from continental to littoral continental and littoral marine. The Mar’yanovka Formation developed in normal marine shallow- or moderately deep-water environments. Although good reservoirs are common throughout the Jurassic section in the southeast of West Siberia, only small, lithologically screened deposits are predicted here.     

Morphotectonics of the Baikal rift valley,Eastern Siberia,USSR

The Baikal rift valley, the central segment of the Baikal rift zone located in southern East Siberia, consists of two large depressions separated by an interdepressional uplift. The thickness of the Neogene-Quaternary sediments filling in the depression amounts to 5 km (Logatchev and Florensov 1978). The interdepressional uplift consists of subsiding residual steps and active tilted horsts.The NW slope of the Baikal rift is controlled by a system of faults diverging to the N. This system comprises tectonic scarps (faceted ridge spurs), an inclined piedmont surface and a summit slope. The facets indicate the position of the main dip slip faults behind which longitudinal strike slip faults are distributed. Between the branching faults, the so-called intermediate steps are situated. Their subsidence and destruction result in expansion of the rift valley. Transformation of normal faults into listric faults is manifested in the tectonic topography in the areas of the residual and intermediate steps. The large dimensions of the Baikal rift valley are evidently due to its being confined to the faults striking NE-SW.     

镇泾地区延安组底界侵蚀谷地震特征及其与煤层和砂体的关系

鄂尔多斯盆地延长组沉积后期的侵蚀谷发育十分广泛。在盆地西南缘镇泾地区三维地震所做的延10底等t₀图上可以识别出沿NE、NW延伸的主谷和沿NW、NE次谷体系。地震剖面上主谷为宽缓的不对称\     

Lithologic and facies characteristics of the Lower Cambrian Usolka Formation and its age analogs in the Cis-Yenisei sedimentary basin,West Siberia

Based on the correlation between Lower Cambrian sections of deep wells on the left bank of the Yenisei River and outcrops in the westernmost Yenisei Ridge, the sedimentologic characteristics of the Usolka Formation and coeval deposits are compared. Three paleogeographic regions (subbasins) are distinguished in the Cis-Yenisei basin in Usolka time. The leading role in the sediment genesis was played by the region of barrier reefs stretching northwestward and northward as a ~ 70 km wide band to their joint with the reefs of the Igarka-Noril’sk facies region in the north. The salt basin east of the barrier reef ridge was a bay of the East Siberian salt basin, separated from the latter by the Yenisei paleoislands (at the place of the Yenisei Ridge). Sedimentation in that basin was controlled by evaporite processes, the supply of terrigenous material from the islands and carbonate debris from the opposite side (barrier reef), and the predominance of storm processes. The subbasin west of the barrier reefs evolved under different scenario. Since the Early Cambrian, a trough has been forming here, which was initially characterized by a regime of starvation and the first appearance of carbonaceous rocks (Lower Churbiga Subformation), regarded as Domanic oil source rocks, in the general Cambrian section. On the estimation of the prospects for the distribution of reservoirs whose origin depends on the facies regularities, the leading role is played by the barrier reef region. Importantly, the Lower Cambrian section of the Cis-Yenisei basin contains two large adjacent paleogeomorphologic structures and the corresponding facies zones of a starved prereef depression with the Domanic oil source rocks of the Lower Churbiga Subformation at the early stage of evolution and a potentially productive barrier reef system with a steep slope toward the basin. The favorable combination of these factors suggests that the Cis-Yenisei basin has a high petroleum potential.     

The Cambrian sediments of the Cis-Yenisei basin (West Siberia): stratigraphy and correlation

A scheme is proposed for the stratigraphic division and correlation of the Cambrian sediments of the Upper Proterozoic-Paleozoic Cis-Yenisei basin. It is based on data from the drilling of parametric wells (Lemok-1, Averinskaya-150, Tyiskaya-1, Vostok-1, Vostok-3, Vostok-4, and others). Two structure-facies zones are recognized in the study area: Kas zone (Lemok-1, Averinskaya-150, Tyiskaya-1, Vostok-4, and Eloguiskaya-1 wells), in which the sedimentary complexes accumulated in a salt subbasin, and Ket’ zone (Vostok-1 and Vostok-3 wells) with open-sea-basin sedimentation. The boundary between the structure-facies zones passes along the reconstructed zone of a barrier reef stretching in the N-S direction. The Vostok-4 well is localized in the western Kas structure-facies zone, at the salt subbasin/barrier reef boundary. Local stratigraphic units (formations) are described and compared with the adjacent Turukhan-Irkut-Olekma facies region of the Siberian Platform.     

杭洲湾地区晚第四纪下切河谷内部相结构与生物气勘探

本文根据杭州湾沿海平原大量的钻井、静力触探井和分析化验等资料，研究了下切河谷（钱塘江和太湖下切河谷）充填物的沉积建造和沉积相，以及浅层生物气藏分布特征。研究表明，末次冰期以来，随着海平面变化，杭州湾地区下切河谷演化经历了深切、快速充填和埋藏三个阶段。末次冰盛期，海平面下降的幅度大，增加了河流梯度、加强了下切作用，本区形成了钱塘江和太湖下切河谷，随后在冰后期被充填和埋藏，下切河谷的两侧为暴露地表的古河间地。根据岩石学、沉积结构和沉积构造特征，本区下切河谷充填沉积物表现为向上变细的沉积层序，可以划分为4个沉积相类型，有河床滞留沉积物到部分曲流河沉积体系的边滩沉积、河漫滩-河口湾沉积、河口湾-浅海沉积和河口湾沙坝沉积。在河漫滩-河口湾相沉积期间，由于海平面上升、潮流体系、沉积物供给和可容空间条件适合一个潮流沙脊体系的发育，该相中砂质透镜体可能代表下切河谷内发育的潮流沙脊。对于河口湾-浅海沉积和河口湾沙坝沉积而言，由于沉积条件不再有利，没有形成沙脊沉积。所有的商业性生物气都存储在下切河谷内河漫滩-河口湾砂质透镜体中。     

北海盆地维京地堑新近纪下切谷发育主控因素及其内部充填特征*

下切谷是陆地上一种常见的侵蚀地貌,古今均十分发育,但是不同盆地、不同时代发育的下切谷,无论是在沉积充填特征还是平面展布形态等多个方面都大相径庭。为此,作者依据曼宁公式进行理论推导,再结合分析北海盆地维京地堑发育的典型下切谷实例以及前人进行的相关水槽实验结果总结认为: 地形坡度、基准面下降速率及幅度与下切谷所侵蚀地层的岩性是影响下切谷发育模式的最主要因素。这些因素共同控制了: (1)下切谷的弯度指数及宽深比,(2)下切谷平面上发育密度及其规模,(3)与下切谷伴生的陆棚三角洲、陆棚边缘三角洲沉积厚度及展布范围。海侵过程中下切谷的沉积充填类型及岩性,受平均基准面上升速率及沉积物供应量的共同控制,根据沉积充填类型及岩性的不同可将其划分为富砂型陆棚三角洲充填及富泥型河口湾充填两类。     

Seismic stratigraphy,formation history and gas potential of the Nadym-Pur interfluve area (West Siberia)

The study presents a seismic and geological characterization of the Meso-Cenozoic sedimentary cover of the Nadym-Pur interfluve area and discusses the morphology of the Jurassic and Aptian-Albian-Cenomanian sedimentary complexes, formation history of structures, and geologic processes responsible for the formation of Cenomanian gas accumulations.     

Diatoms,spatial distribution and physicochemical characteristics of the Wular lake sediments,Kashmir valley,Jammu and Kashmir

Lakes and wetlands are dynamic geomorphic units of a landscape that hold geochemical signatures of sediment provenance and paleo-environmental shifts and are major sinks for organic matter accumulation. The source of organic matter is diverse in lake sediments and varies widely with the type and size of the lake and hence it is important to understand the source of organic carbon (terrestrial or in situ) in lake systems in order to monitor the health of the lake. Wular lake, located in north Kashmir, is one of the largest fresh water lake in India, situated at an average elevation of 1580m ASL. The lake is fed by a number of watersheds that bring a diverse type of sediments and organic matter and thus deposit them into the Wular lake basin. In order to understand sediment distribution pattern, content and source of organic matter, sediment provenance and the persisting environment in the Wular lake, 32 lake floor sediment samples covering the entire lake were collected and analyzed for organic element analysis, CaCO3, organic matter, sediment texture and diatom analysis. The results indicated that sediments in the lake are dominated by silt and silty clay. The organic carbon in the lake ranged from 0.83%-4.52% and nitrogen varied from 0.06%-0.5%. The Carbon to Nitrogen (C/N) ratios (9.04 to 22.03) indicate a mixed source of organic carbon but dominated by in situ lake sources from the vascular and lake biota accumulation. The diatom analysis revealed the occurrence of a diverse type of species along the sampling sites present within the lake. The wide distribution of the diatom species such as Cymbella, Cyclotella and Tabularia etc. in the lake indicate high organic pollution and alkaline fresh water environment prevailing in the lake.     

The incised valley of Baffin Bay,Texas: a tale of two climates

Baffin Bay, Texas is the flooded Last Glacial Maximum incised valley of the Los Olmos, San Fernando and Petronila Creeks along the north‐western Gulf of Mexico. Cores up to 17 m in length and high‐resolution seismic profiles were used to study the history of Baffin Bay over the last 10 kyr and to document the unusual depositional environments within the valley fill. The deposits of the Baffin Bay incised valley record two major and two minor events. Around 8·0 ka, the estuarine environments backstepped more than 15 km in response to an increase in the rate of sea‐level rise. Around 5·5 ka, these estuarine environments changed from environments similar to other estuaries of the northern Gulf of Mexico to the unusual suite of environments found today. Another minor flooding event occurred around 4·8 ka in which several internal spits were flooded. Some time after 4·0 ka, the upper‐bay mud‐flats experienced a progradational event. Because of its semi‐arid climate and isolation from the Gulf of Mexico, five depositional environments not found in the other incised‐valley fills of the northern Gulf of Mexico are found today within Baffin Bay. These deposits include well‐laminated carbonate and siliciclastic open‐bay muds, ooid beaches, shelly internal spits and barrier islands, serpulid worm‐tube reefs and prograding upper‐bay mud‐flats. Based on these unusual deposits, and other characteristics of Baffin Bay, five criteria are suggested to help identify incised valleys that filled in arid and semi‐arid climates. These criteria include the presence of: (i) hypersaline‐tolerant fauna; (ii) aeolian deposits; and (iii) carbonate and/or evaporite deposits; and the absence of: (iv) peat or other organic‐rich deposits in the upper bay and bay‐margin areas; and (v) well‐developed fluvially dominated bayhead deltas.     

青海省贵南县过马营一带早中三叠世隆务河组沉积特征

青海贵南县过马营一带隆务河组为一套典型的浊流沉积,对此套浊积岩的沉积特征进行研究。通过对过马营一带隆务河组浊积岩的岩石组合特征、地层层序及鲍玛层序特征分析,探讨其沉积环境特征,并与典型浊积扇模式对比,建立沉积模型。综合分析认为,隆务河组由下向上的3个段分别位于浊积扇的外扇、中扇、内扇,其中中扇辫状河道发育。此研究对于西秦岭造山带的沉积环境分析及构造演化具有重要的意义。     

Comparative analysis of marine paleogene sections and biota from West Siberia and the Arctic Region

The analysis of the main biospheric events that took place in West Siberia and the Arctic region during the Early Paleogene revealed the paleogeographic and paleobiogeographic unity of marine sedimentation basins and close biogeographic relations between their separate parts. Most biotic and abiotic events of the first half of the Paleogene in the Arctic region and West Siberia were synchronous, unidirectional, and interrelated. Shelf settings, sedimentation breaks, and microfaunal assemblages characteristic of these basins during the Paleogene are compared. The comparative analysis primarily concerned events of the Paleocene-Eocene thermal maximum (PETM) and beds with Azolla (aquatic fern). The formation of the Eocene Azolla Beds in the Arctic region and West Siberia was asynchronous, although it proceeded in line with a common scenario related to the development of a system of estuarine-type currents in a sea basin partly isolated from the World Ocean.     

Geochemical technique of organic matter research in deposits enrich in kerogene (the Bazhenov Formation,West Siberia)

The international interest in shale oil has recently provoked special attention to the Russian unconventional oil-source formations, including the Bazhenov Formation of West Siberia, domanik deposits in the Volga–Ural region, and the lower Maikop Group of the Cis-Caucasus. High contents of para-autochthonous soluble organic matter (bitumen) in clayey–carbonate, clayey–siliceous, carbonate–clayey–siliceous rocks with low filtration–capacity properties results in significant uncertainties in the identification of the generation potential of organic matter (OM). Examination of a large database on the OM of the Bazhenov Formation allowed us to propose an optimum complex technique for study of the source rock potential and assessment of the amount of produced hydrocarbons in the kerogen-rich sediments. The investigations include a combination of Rock Eval pyrolysis prior to and after extraction with different solvents, the comparison of bituminological and pyrolytic characteristics, and the determination of the group composition of soluble organic matter, as well as chromatography and chromato-mass spectrometry.     

Study of petrological characteristics of coal deposits from Marki-Jhari-Jamni area, Wardha valley coalfield, Maharashtra

A detailed study of maceral composition and vitrinite reflectance of the coal deposits from Marki-Jhari-Jamni area, situated in the northwestern extremity of Wardha valley coalfield, Yeotmal district, Maharashtra has been carried out with special reference to their depositional set up. These coals have two distinct types of maceral organization, one having significantly high distribution of the vitrinite group of macerals (35–41%) and the other containing the dominance of inertinite (26–49%). Liptinite maceral group is recorded between 14 and 24%, barring a few coal bands having liptinite maceral group as high as 33–37%. The vitrinite reflectivity ranges from 0.38–0.43%. Thus, they have attained sub-bituminous C rank. Mineral matter in these coals varies between 15 and 22%. The present study suggests that the basin primarily experienced cold climate having intermittent brackish water influx with alternating dry oxidizing spells.     

滇东威信地区龙潭组致密砂岩矿物组成特征及其油气地质意义

致密气是发育于低孔、特低渗透砂岩中的一种非常规资源,具有丰富的潜在油气储量,但由于其致密低渗透性,压裂改造是致密气高效开发的必须手段,而砂岩储集特征及物质组成对初步评价致密砂岩储层的资源潜力和生产能力有重要意义.运用X射线衍射、显微镜及扫描电镜等技术手段,对滇东威信地区二叠系龙潭组10个致密砂岩露头样品进行定性和定量分...     

Study of petrological characteristics of coal deposits from Marki-Jhari-Jamni area,Wardha valley coalfield,Maharashtra

A detailed study of maceral composition and vitrinite reflectance of the coal deposits from Marki-Jhari-Jamni area, situated in the northwestern extremity of Wardha valley coalfield, Yeotmal district, Maharashtra has been carried out with special reference to their depositional set up. These coals have two distinct types of maceral organization, one having significantly high distribution of the vitrinite group of macerals (35–41%) and the other containing the dominance of inertinite (26–49%). Liptinite maceral group is recorded between 14 and 24%, barring a few coal bands having liptinite maceral group as high as 33–37%. The vitrinite reflectivity ranges from 0.38–0.43%. Thus, they have attained sub-bituminous C rank. Mineral matter in these coals varies between 15 and 22%. The present study suggests that the basin primarily experienced cold climate having intermittent brackish water influx with alternating dry oxidizing spells.     

Facies architecture in a tectonically influenced estuarine incised valley fill of Miocene age, northern Brazil

The Miocene Barreiras Formation in the Middle Rio Capim area records an incised valley system for which facies analysis and ichnology (Skolithos, Ophiomorpha, Planolites, Gyrolithes, Taenidium) suggest an estuarine character. Three stratigraphic units are recognized (from bottom to top): Unit 1 includes an inner estuarine tidal channel complex and tidal flat/salt marsh deposits; Unit 2 consists of estuarine bay/lagoon and flood tidal delta deposits related to the estuary mouth; and Unit 3 includes a tidal channel with a tidal point bar, as well as tidal flat/salt marsh deposits similar to those from Unit 1. These units and their bounding surfaces record the history of relative sea level changes in the estuary. After a sea level drop, the valley was inundated and formed an amalgamated sequence boundary and transgressive surface. Transgression (Unit 1) promoted the landward shift of flood tidal deltas and lagoon settings (Unit 2). The system then moved seaward, with the superposition of inner estuarine deposits (Unit 3) over Unit 2. Facies architecture seems to have been controlled by tectonics, as shown by: the paleovalley orientation according to the main tectonic structures of the basin; the presence of faults and fractures that displace the basal unconformity; and the abundance of soft sediment deformation.