Continental Lacustrine Research Articles

Machine learning-based grayscale analyses for lithofacies identification of the Shahejie Formation, Bohai Bay Basin, China

It is of great significance to accurately and rapidly identify shale lithofacies in relation to the evaluation and prediction of sweet spots for shale oil and gas reservoirs. To address the problem of low resolution in logging curves, this study establishes a grayscale-phase model based on high-resolution grayscale curves using clustering analysis algorithms for shale lithofacies identification, working with the Shahejie Formation, Bohai Bay Basin, China. The grayscale phase is defined as the sum of absolute grayscale and relative amplitude as well as their features. The absolute grayscale is the absolute magnitude of the gray values and is utilized for evaluating the material composition (mineral composition + total organic carbon) of shale, while the relative amplitude is the difference between adjacent gray values and is used to identify the shale structure type. The research results show that the grayscale phase model can identify shale lithofacies well, and the accuracy and applicability of this model were verified by the fitting relationship between absolute grayscale and shale mineral composition, as well as corresponding relationships between relative amplitudes and laminae development in shales. Four lithofacies are identified in the target layer of the study area: massive mixed shale, laminated mixed shale, massive calcareous shale and laminated calcareous shale. This method can not only effectively characterize the material composition of shale, but also numerically characterize the development degree of shale laminae, and solve the problem that difficult to identify millimeter-scale laminae based on logging curves, which can provide technical support for shale lithofacies identification, sweet spot evaluation and prediction of complex continental lacustrine basins.

Lithofacies Characteristics of Continental Lacustrine Fine-Grained Sedimentary Rocks and Their Coupling Relationship with Sedimentary Environments: Insights from the Shahejie Formation, Dongying Sag

Lacustrine fine-grained sedimentary rocks in the Dongying Sag of the Bohai Bay Basin in China exhibit significant potential for hydrocarbon exploration. This study investigates the lithofacies types and sedimentary evolution of the Paleogene Shahejie Formation’s lower third member (Es3l) and upper fourth member (Es4u), integrating petrological and geochemical analyses to explore the relationship between lithofacies characteristics and sedimentary environments. The results show that the fine-grained sedimentary rocks in the study area can be classified into 18 lithofacies, with seven principal ones, including organic-rich laminated carbonate fine-grained mixed sedimentary rock lithofacies and organic-rich laminated limestone lithofacies. In conjunction with analyses of vertical changes in geochemical proxies such as paleoclimate (e.g., CIA, Na/Al), paleoproductivity (e.g., Ba), paleosalinity (e.g., Sr/Ba), paleo-redox conditions (e.g., V/Sc, V/V + Ni), and terrigenous detrital influx (e.g., Al, Ti), five stages are delineated from bottom to top. These stages demonstrate a general transition from an arid to humid paleoclimate, a steady increase in paleoproductivity, a gradual decrease in paleosalinity, an overall reducing water body environment, and an increasing trend of terrestrial detrital input. This study demonstrates that the abundance of organic matter is primarily influenced by paleoproductivity and paleo-redox conditions. The variations in rock components are predominantly influenced by paleoclimate, and sedimentary structures are affected by the depth of the lake basin. Special depositional events, such as storm events in Stage II, have significantly impacted the abundance of organic matter, rock components, and sedimentary structures by disturbing the water column and disrupting the reducing conditions at the lake bottom. The present study offers crucial insights into the genesis mechanisms of continental lacustrine fine-grained sedimentary rocks, facilitates the prediction of lithofacies distribution, and advances the exploration of China’s shale oil resources in lacustrine environments.

Chemical Characteristics and Distribution Prediction of Hydrocarbon Source Rocks in the Continental Lacustrine Basin of the Chang 7 Member in the Heshui Area of the Ordos Basin, China

The Heshui area within the Ordos Basin holds significant strategic importance for the extraction and development of tight oil resources in the Changqing Oilfield. This study extensively explored the geochemical features and distribution tendencies of source rocks in the Chang 7 member, utilizing core samples and logging data for a comprehensive analysis. A more advanced model was utilized to predict the dispersion of Total Organic Carbon (TOC) in the Chang 7 member source rock. The properties and hydrocarbon generation potential of source rocks were thoroughly assessed through a comprehensive analysis that involved evaluating their total organic carbon content, pyrolysis parameters, and reflectance (Ro) values. The research concluded that the source rocks boast substantial organic matter, predominantly categorized as type II-I organic material. The thermal maturation levels span from low maturity to maturity, signifying significant potential for oil generation. Generally, the source rock quality falls within the range of good to excellent. Sedimentary patterns notably influence the distribution of hydrocarbon-source rocks. The northeastern sector of the study area is situated in an area characterized by deep to semi-deep lake sedimentation, making it the primary location for the presence of Chang 7 member hydrocarbon source rocks. With a thickness ranging from 40 to 70 m, this zone becomes a pivotal focus for the potential exploration of tight oil resources in the future. The results of this study offer crucial insights for understanding the geochemical characteristics of hydrocarbon source rocks, evaluating their potential for hydrocarbon generation, and forecasting favorable zones for oil and gas exploration in similar regions.

Exploration and Development of Shale Oil in China: State, Challenges, and Prospects

Abstract —This article presents the latest state of exploration and development of shale oil of continental lacustrine formations in the main basins of China, summarizes the main theoretical considerations and key technologies for exploration and development, and suggests prospects for exploration and development of shale oil in China. It is believed that the exploration and development of oil in shale formations rich in organic matter of types I and II of medium and high maturity are key to the breakthrough of production of 10 million tons in China. This will play an important role in China’s stable oil production at the level of 200 million tons per year in the future. The efficient development of medium- and low- maturity shale oil resources can be significantly improved and lead to serious changes in oil production only after new breakthroughs in the theory and technology of shale deposits.

The reservoir characteristics and their controlling factors of the sublacustrine fan in the Paleogene Dongying Formation, Bohai Sea, China

Sublacustrine fan is an important element in continental lacustrine basins and is significant for reservoir exploration. Oil and gas resources have been found in the sublacustrine fan sandstone reservoirs of the Paleogene Dongying Formation in the Bohai Sea. In this study, the characteristics of the sublacustrine fan reservoirs and the controlling factors are studied using information from logging, cores, physical properties, casting thin sections, X-ray diffraction of clay minerals, vitrinite reflectance, rock pyrolysis, manometry data, and 3D seismic data. The sublacustrine fans of the Dongying Formation in the LD10, QHD34, and BZ21 structures show high-quality reservoirs with porosity >15 % and permeability >5 mD. The main controlling factors of the high-quality reservoirs are attributed to the favorable sedimentary facies type and negligible compaction, and cementation, substantial dissolution of K-feldspar, overpressure, and the development of faults and fractures. A high-quality sublacustrine fan reservoir model has been established to explain how these factors affected the physical properties. The favorable targets for oil and gas exploration in the Dongying Formation of Bohai Sea include undercompacted sandy debris flow reservoirs showing the dissolution of K-feldspar, and the reservoirs which are connected to the source rocks by faults. This study provides insights to establish the relationship between sedimentology, diagenesis and reservoir quality. The results of this study are significant for the exploration and development of the sublacustrine fan sandstone reservoirs in the Bohai Sea and analogous sandstone reservoirs elsewhere.

Fine-grained gravity flow sedimentation and its influence on development of shale oil sweet sections in lacustrine basins in China

The geological conditions and processes of fine-grained gravity flow sedimentation in continental lacustrine basins in China are analyzed to construct the model of fine-grained gravity flow sedimentation in lacustrine basin, reveal the development laws of fine-grained deposits and source-reservoir, and identify the sweet sections of shale oil. The results show that fine-grained gravity flow is one of the important sedimentary processes in deep lake environment, and it can transport fine-grained clasts and organic matter in shallow water to deep lake, forming sweet sections and high-quality source rocks of shale oil. Fine-grained gravity flow deposits in deep waters of lacustrine basins in China are mainly fine-grained high-density flow, fine-grained turbidity flow (including surge-like turbidity flow and fine-grained hyperpycnal flow), fine-grained viscous flow (including fine-grained debris flow and mud flow), and fine-grained transitional flow deposits. The distribution of fine-grained gravity flow deposits in the warm and humid unbalanced lacustrine basins are controlled by lake-level fluctuation, flooding events, and lakebed paleogeomorphology. During the lake-level rise, fine-grained hyperpycnal flow caused by flooding formed fine-grained channel–levee–lobe system in the flat area of the deep lake. During the lake-level fall, the sublacustrine fan system represented by unconfined channel was developed in the flexural slope breaks and sedimentary slopes of depressed lacustrine basins, and in the steep slopes of faulted lacustrine basins; the sublacustrine fan system with confined or unconfined channel was developed on the gentle slopes and in axial direction of faulted lacustrine basins, with fine-grained gravity flow deposits possibly existing in the lower fan. Within the fourth-order sequences, transgression might lead to organic-rich shale and fine-grained hyperpycnal flow deposits, while regression might cause fine-grained high-density flow, surge-like turbidity flow, fine-grained debris flow, mud flow, and fine-grained transitional flow deposits. Since the Permian, in the shale strata of lacustrine basins in China, multiple transgression-regression cycles of fourth-order sequences have formed multiple source-reservoir assemblages. Diverse fine-grained gravity flow sedimentation processes have created sweet sections of thin siltstone consisting of fine-grained high-density flow, fine-grained hyperpycnal flow and surge-like turbidity flow deposits, sweet sections with interbeds of mudstone and siltstone formed by fine-grained transitional flows, and sweet sections of shale containing silty and muddy clasts and with horizontal bedding formed by fine-grained debris flow and mud flow. The model of fine-grained gravity flow sedimentation in lacustrine basin is significant for the scientific evaluation of sweet shale oil reservoir and organic-rich source rock.

Stratigraphy of the middle Triassic-lower Cretaceous succession in the Paraná and Uruguayan Chaco-Paraná Basins – An overview based on subsurface data

The Middle Triassic to Lower Cretaceous (MTLC) megasequence of the Paraná and Uruguayan Chaco-Paraná basins records a complex depositional history. It encompasses a dynamic interplay of continental lacustrine, fluvial, and aeolian sediments that have evolved under varying paleoenvironmental and climatic conditions, ranging from humid to arid and hyper-arid settings. The present subsurface study depicts a novel stratigraphic framework for the MTLC megasequence, drawing from an extensive dataset of over 400 well logs and drilling reports derived from exploratory petroleum and water wells distributed across these basins. The lithostratigraphic units within the MTLC megasequence, as delineated from the well logs, exhibit a consistent stacking pattern with well-defined hierarchic arrangement, which extends throughout the Paraná and Chaco-Paraná basins. Within the MTLC megasequence, three distinct sedimentary successions have been established, bounded by regional unconformities: the Middle to Upper Triassic sequence, the Upper Jurassic sequence, and the Lower Cretaceous sequence. The Middle to Upper Triassic sequence encompasses the Santa Maria/Caturrita, Piramboia, and Itacumbú formations. The Santa Maria/Caturrita sequence extends into the subsurface to Uruguay, where it is referred to as the Itacumbú Formation. The Piramboia Formation has been subdivided into two distinct units: the lower unit retains the name Piramboia Formation, while the upper unit has been designated as the Guará Formation, as it was originally defined in the Rio Grande do Sul State. The Upper Jurassic sequence encompasses the Guará and Tacuarembó formations, extending throughout the entire Paraná and Uruguayan Chaco-Paraná basins. The Lower Cretaceous sequence comprises the Botucatu and Rivera formations. These deposits are generally discontinuous and frequently intercalated with the volcanic rocks of the Serra Geral Formation.

Subaqueous volcanic eruptive facies, facies model and its reservoir significance in a continental lacustrine basin: A case from the Cretaceous in Chaganhua area of southern Songliao Basin, NE China

The conventional lithofacies and facies model of subaerial and marine pyroclastic rocks cannot reflect the characteristics of subaqueous volcanic edifice in lacustrine basins. In order to solve this problem, the lithofacies of subaqueous eruptive pyroclastic rocks is discussed and the facies model is established by taking the tuff cone of Cretaceous Huoshiling Formation in the Chaganhua area of the Changling fault depression, Songliao Basin as the research object. The results indicate that the subaqueous eruptive pyroclastic rocks in the Songliao Basin can be divided into two facies and four subfacies. The two facies are the subaqueous explosive facies and the volcanic sedimentary facies that is formed during the eruption interval. The subaqueous explosive facies can be further divided into three subfacies: gas-supported hot pyroclastic flow subfacies, water-laid density current subfacies and subaqueous fallout subfacies. The volcanic sedimentary facies consists of pyroclastic sedimentary rocks containing terrigenous clast subfacies. A typical facies model of the tuff cone that is formed by subaqueous eruptions in the Songliao Basin was established. The tuff cone is generally composed of multiple subaqueous eruption depositional units and can be divided into two facies associations: near-source facies association and far-source facies association. The complete vertical succession of one depositional unit of the near-source facies association is composed of pyroclastic sedimentary rocks containing terrigenous clast subfacies, gas-supported hot pyroclastic flow subfacies, water-laid density current subfacies and subaqueous fallout subfacies from bottom to top. The depositional unit of the far-source facies association is dominated by the subaqueous fallout subfacies and contains several thin interlayered deposits of the water-laid density current subfacies. The gas-supported hot pyroclastic flow subfacies and the pyroclastic sedimentary rocks containing terrigenous clast subfacies are favorable subaqueous eruptive facies for reservoirs in continental lacustrine basins.

Diversity of depositional architecture and sandbody distribution of sublacustrine fans during forced regression: A case study of Paleogene Middle Sha 3 Member in Dongying Sag, Bohai Bay Basin, East China

Currently, the differences in gravity flow deposits within different systems tracts in continental lacustrine basins are not clear. Taking the middle submember of the third member of Paleogene Shahejie Formation (Sha 3 Member) in the Shishen 100 area of the Dongying Sag in the Bohai Bay Basin as an example, the depositional architecture of sublacustrine fans during forced regression and the impact of the fourth-order base-level changes on their growth were investigated using cores, well logs and 3D seismic data. Sublacustrine fans were mainly caused by hyperpycnal flow during the fourth-order base-level rise, while the proportion of slump-induced sublacustrine fans gradually increased during the late fourth-order base-level fall. From rising to falling of the fourth-order base-level, the extension distance of channels inside hyperpycnal-fed sublacustrine fans reduced progressively, resulting in the transformation in their morphology from a significantly channelized fan to a skirt-like fan. Furthermore, the depositional architecture of distributary channel complexes in sublacustrine fans changed from vertical aggradation to lateral migration, and the lateral size of individual channel steadily decreased. The lobe complex’s architectural patterns evolved from compensational stacking of lateral migration to aggradational stacking, and the lateral size of individual lobe steadily grew. This study deepens the understanding of depositional features of gravity flow in high-frequency sequence stratigraphy and provides a geological foundation for the fine development of sublacustrine fan reservoirs.

Alternations of open and closed lakes in the Lower Aptian Codó Formation (Parnaíba Basin, Brazil)

Lakes can be classified as open, semi-closed, and closed based on the balance between accommodation space and sediment–water fill. Different lake types can coexist in adjacent basins and rapidly change throughout time from one type to another. Understanding the processes that result from shifts in a lake's hydrological properties can be challenging, as well as characterizing its sedimentary products. The Aptian Codó Formation, in the Parnaíba Basin, north–northeast Brazil, contains in its record a complex facies succession deposited in a continental lacustrine system. In order to better understand the depositional aspects of different lake types, we characterized the lower portion of the Codó Formation using a multi-proxy approach. We combined litho- and microfacies analysis, ichnology, bulk chemical data, mineralogy, isotopic geochemistry, and organic matter analysis in the recently drilled, fully recovered borehole, 2-CO-1-MA. We defined eight lithofacies: bioturbated siltstones, dark gray mudstones, laminites, stratiform and domal stromatolites, heterolites rich in ostracods and organic muddy, and anhydrite and gypsum rocks. The isotopic data and the palynofacies analysis pointed out the existence of restricted conditions (TOC up to 19.6 wt%) with intermittent connections with seawater. Integrating all techniques, we interpreted five depositional stages: expanded lake, brackish ephemeral lake, perennial shallow lake, evaporitic sabkha, and stratified lake. These stages were influenced by the relation between inflow and evaporation rate, which were the main controls on sedimentation in the lacustrine-sabkha system studied. Our findings provide a detailed description and interpretation of the paleoenvironmental conditions related to the alternation from open to closed lakes, combining sedimentological, geochemical, and palynological characteristics of an inland lake system.

Reservoir Characteristics and Development Model of Subaqueous Pyroclastic Rocks in a Continental Lacustrine Basin: A Case Study of the Chaganhua Subsag in the Changling Fault Depression, Songliao Basin

Industrial oil and gas eruptions underwater have been found in the pyroclastic rocks of the Huoshiling Formation in the continental lacustrine basin of the Changling fault depression, Songliao Basin. This paper investigates the reservoir space characteristics, physical characteristics, and pore structure differences of subaqueous pyroclastic reservoirs in the Huoshiling Formation, and the causes of physical property differences of different types of reservoirs and their formation and evolution processes are analyzed. (1) The content of volcanic glass in tuff is higher, the reservoir space is dominated by devitrification pores and dissolution pores, and the coarser the grain size, the more favorable the physical properties, with larger pore sizes and higher porosities. The content of clay minerals in sedimentary tuff is high, the pores between clay minerals are the main pores, and the physical properties of sedimentary tuff are poor. The content of soluble components such as feldspar, debris, and laumontite is high in tuffaceous sandstone, which is dominated by dissolution pores. (2) Primary pores are not developed in the pyroclastic reservoirs in the study area, and the reservoirs are relatively dense, with an average porosity of 2.43% and an average permeability of 0.076 mD. The coarse-grained tuff has the highest porosity, followed by tuffaceous sandstone and fine-grained tuff, and the sedimentary tuff has the least favorable physical properties. (3) Devitrification was an important cause of the high-porosity and ultralow permeability of tuff reservoirs. Two oil and gas charges in the middle diagenetic stage led to the organic acid dissolution of rocks. In addition, fractures can provide migration channels for organic acids and deep hydrothermal fluids, leading to late dissolution, and can connect various scattered dissolution pores to improve the effectiveness of the reservoir space. (4) Coarse-grained tuff reservoirs that developed in the proximal facies are favorable targets for hydrocarbon exploration.

Seismic interpretation and geological evaluation of hydrocarbon source rocks in volcanic-rich continental lacustrine rift basins: A case study of the Lower Cretaceous Yingcheng Formation from the Changling Fault Depression in the Songliao Basin, NE China

The Lower Cretaceous Yingcheng Formation in the Changling Fault Depression in the Songliao Basin is composed of volcanic-rich continental lacustrine rift basin sediments. Its complex stratigraphic structure and the difficulty in predicting the hydrocarbon source rock distribution restrict the exploration and evaluation of deep hydrocarbons in this region. This paper uses seismic stratigraphy to divide the strata and interpret dark mudstone layers based on logging and seismic. These data are combined with geochemical test data from hydrocarbon source rocks to assess its quality and predict its distribution. This study indicates that the three types of unconformities identified divide the Yingcheng Formation into four sedimentary sequences. In the Yingcheng Formation depositional period, the number of grabens or half-grabens associated with the Changling Fault Depression decreased, the size of the rift basins increased, and the depositional center migrated to the north and west. During the depositional period of the First and Second Members, volcanic rocks were widely developed, and mud sediments were deposited between several small grabens or half-grabens. During the depositional period of the Third and fourth Members, the study area became a unified lacustrine rift basin with clearly defined geological signatures developed in each sedimentary sequence, which can be divided into three systems tracts. Mudstones in the Lake Transgressive Systems Tract are laterally continuous and widely distributed. The organic matter in these mudstones, with fair to good abundance levels, is predominantly type II2 and type III kerogen and all have reached mature to highly mature stage of thermal evolution, which are favorable hydrocarbon source rock layers. In plan view, the favorable hydrocarbon source rock zones are mostly formed in the Changling Sag, Dongling Structural Zone and Longfengshan Sag. This study offers guidance and direction for deep hydrocarbon exploration in the Changling Fault Depression, and also provides a reference for methods and ideas to predict hydrocarbon source rock distribution in other lacustrine rift basins.

Authigenic silica in continental lacustrine shale and its hydrocarbon significance

Taking lake basin shales of the Triassic Yanchang Formation in the Ordos Basin, NW China and the Cretaceous Qingshankou Formation in the Songliao Basin, NE China as research objects, the characteristics and origins of different types of silica in the shales have been studied by means of core observation, thin section identification, cathodoluminescence, X-ray diffraction analysis, scanning electron microscope (SEM), electron probe and rock pyrolysis. The results shows that the origins of silica include felsic mineral dissolution, tuffite devitrification, clay mineral transformation and siliceous mineral metasomatism. The silica formed by feldspar dissolution commonly appears as spots and veins, with low degree of crystallization, and is largely aqueous opal mineral, with an average SiO2 content of 67.2%. Silica formed by devitrification of tuffite mainly occurs in two forms, amorphous silica and authigenic quartz with better crystal shape. The authigenic silica formed during the transformation of clay minerals is embedded in the clay minerals in the form of micron-scale plates and small flakes, or mixed with clay minerals in a dispersed state. The authigenic quartz formed by siliceous mineral metasomatism is in better angular crystal shape, and has an average SiO2 content of 87%. The authigenic siliceous mineral content is positively correlated with the content of terrigenous felsic minerals. The pressure solution of felsic minerals is the main source of authigenic siliceous minerals, followed by the transformation of clay minerals, and the organic matter has some boost on the formation of authigenic silica. The authigenic siliceous materials of different origins have different geological characteristics and occurrence states from terrigenous quartz, which would affect the storage performance, seepage capacity and fracturing effect of continental shale. Although the organic-rich shale has high silica content, different from terrigenous quartz, authigenic silica in this kind of shale mostly floats and disperse in clay minerals, which would have negative effect on the formation of complex fractures in fracturing, fracture support ability after fracturing, and formation of effective seepage channels. Calculating the brittleness index of shale intervals only based on the composition of brittle minerals cannot accurately characterize mechanical characteristics of continental shale oil reservoirs, and would affect comprehensive evaluation and selection of continental shale oil “sweet spots”.

Effect of saline sedimentary environment on pore throats of shale

Shale pore throat is one of the key factors affecting shale oil and gas exploitation. In order to study the effect of saline on shale pore throat in the continental lacustrine basin, the paleo-salinity of the lacustrine basin was analyzed using the Couth and Sr/Ba methods, and the pore throat characteristics of shale were observed by thin section and scanning electron microscope. The saline stage is divided into five stages: freshwater (0.5‰–1‰), brackish water (1‰–5‰), brackish water (5‰–15‰), brackish water (15‰–30‰), and high saltwater (>30‰). Shale is mainly reserved in micropores (organic, intercrystalline, and intergranular pores) and microcracks (along-layer, high pressure, structural, and mineral shrinkage cracks). Paleosalinity affects the pore throat characteristics of shale by controlling the mineral composition, rock combination type, and texture. Carbonate minerals tend to dissolve and form dissolution pores, resulting in pore throat enlargement and better physical properties. When salinity is low, the content of carbonate minerals increases with the increase in salinity. However, in the case of high salinity, the content of carbonate minerals gradually decreases, but that of sulfate and gypsum increases with the increase in salinity. The texture is conducive to the development of microcracks. With the increase in salinity, the number of textures first increases and then decreases. When the content is 15 ‰–30‰, there are most abundant textures, making it most likely to form microcracks. The results of this study play an important role in promoting the study of shale in the continental lacustrine basin.

Controlling effect of saline sedimentary environment on enrichment and exploitation of shale gas and oil in lacustrine basin

The salinity of continental lacustrine basin has a great influence on the properties of shale. The main objective of this paper is to present the characteristics of shale in different saline stages. In this study, we restored the saline process by the Kauchi method and evaluated the hydrocarbon generation capacity, reservoir property, oiliness and exploitability of shale in different saline stages. The sources of organic matter and paleoproductivity may vary among saline stages. Organic matter mainly originates from coccolithophyta and dinoflagellate in the saltwater stage, demonstrating the highest paleoproductivity. Meanwhile, paleosalinity has an important effect on the lithologic assemblage and mineral composition of shale, which controls its reservoir properties, oiliness and compressibility. The lithology in the saltwater stage is dominated by lamellar argillaceous limestone/calcareous mudstone and lamellar limestone, with good original physical properties. The carbonate content in such stage is the highest, making it easy to dissolve into dissolution pores and thus increasing the porosity and saturation of movable fluid. The high hardness of carbonate gives optimum compressibility to shale.

Continental lacustrine fine-grained lithofacies, assemblage and geological significance of unconventional petroleum: A case study of the Paleogene of the 4th member of the Shahejie formation in the Jiyang depression

Taking the upper sub-member of Sha 4 in Well Fanye 1 and Well Niuye 1 in Dongying Sag, Jiyang Depression, Bohai Bay Basin as a typical example, this paper adopts the method of combining macro and micro laminar characterization and complementing each other. The characteristics of laminar development are studied by means of fine description of rock thin sections by cores and electron microscopic observation Reconstruction of the Bohai Bay Basin in sand four period of ancient sedimentary environment, it is concluded that the sand on the four period of development of four complete filling sedimentary cycle. Using Milankovitch cycles method, reveals the ancient climate control mechanism of lithofacies, formed by organic laminae under hot and humid climate and a small amount of calcite laminated lithofacies, in hot and humid climate, the lithofacies is mainly composed of organic lamina and a small amount of calcite lamina, while in cold and dry climate, the lithofacies is mainly composed of calcite lamina, and the lithofacies is mainly composed of organic lamina, silty lamina and gypsum lamina. Micro-laminar research is an important scientific issue in unconventional oil and gas eology. It can provide basic data for unconventional oil and gas exploration, such as the types, distribution and extension of laminar, especially the determination of sampling targets. Different laboratory samples can be analyzed according to the laminar types.

Continental geological evidence for Solar System chaotic behavior in the Late Cretaceous

AbstractThe Earth’s geologic record of Milankovitch cycles closely tracks Solar System solutions for the past 50 million years. Prior to 50 million years ago (Ma), however, the solutions lose accuracy rapidly due to chaotic behavior of the Solar System. Here we reconstruct a 10.173 million year-long record from 82.358 Ma to 92.531 Ma of Earth’s orbital parameters from a continental lacustrine sequence in the Songliao Basin, China, constrained by four in situ high-resolution radioisotopic U-Pb ages and magnetic reversal stratigraphy. Analysis of thorium and ostracode shell abundance records from the Songliao Basin reveal evidence for two chaotic secular resonance transitions in the orbital motions of Earth and Mars from 85.2 Ma to 91.55 Ma. The evidence validates similar observations in western North American marine stratigraphy. A unique phasing between the observed orbital eccentricity and obliquity modulations may explain the anoxic events that occurred in both marine and continental environments during this time. Taken together, the continental and marine stratigraphic evidence demonstrates a strong global reach of Late Cretaceous Milankovitch cycles, and provides an important constraint on Solar System chaoticity and the calculation of accurate orbital solutions prior to 50 Ma.

Sedimentary Environment and Model for Organic Matter Enrichment: Chang 7 Shale of Late Triassic Yanchang Formation, Southern Margin of Ordos Basin, China

Shale oil is an unconventional oil resource that needs to be developed and utilized urgently. However, the Chang 7 shale in the Ordos Basin, as the most typical continental source rock in China, is limited by the study of organic matter (OM) enrichment factors in continental lacustrine facies, and there are still controversies about the controlling factors, which limit the progress of oil and gas exploration. This paper aims to reconstruct the paleoenvironment of Chang 7 shale in the southern margin of Ordos Basin and reveal the controlling factors of organic rich shale by organic and elemental analysis, X-ray diffraction (XRD) analysis, thin section observation, and scanning electron microscopy-energy dispersive spectrometer (SEM-EDS) analysis. The results show that during the deposition period of Chang 7 shale, the climate was warm and humid, the lake water has strong reducing, low salinity and rapid depth changes. Total organic carbon (TOC) is positively correlated with salinity and hydrothermal action and inversely proportional to terrigenous input. The high productivity, low consumption and low dilution result in high enrichment of shale OM in the southern margin of Ordos Basin.

Depositional evolution and models for a deep-lacustrine gravity flow system in a half-graben rifted sag, Beibuwan Basin, South China Sea

The Paleogene Liushagang Formation is part of the Fushan Sag, a continental lacustrine basin located at theSoutheastern margin of the Beibuwan Basin, South China Sea. Further understanding of the deep-water gravityflow deposits in this formation will be conducive to lithologic reservoir exploration in the sag. In this study,three members of the Liushagang Formation, SQEls3 SQEls2 and SQEls1, from old to young, are used withcore observation, well log data, and three-dimensional seismic data to identify four deep-lacustrine gravity flowlithofacies including their vertical and lateral relationships within the depositional system. The results are thenused to establish a deep-water gravity flow depositional model. Four types of gravity flow lithofacies developed inthe sag: sandy debrite, turbidite, sandy slump, and bottom-current deposits. Sand-rich sub-lacustrine fan depositswith typical turbidite channels were developed mainly in the western depression, whereas distal isolated lobesformed by sandy debrite flow deposits occurred mainly in the eastern depression. The results obtained in this studywill be helpful in the research of gravity flows in similar continental lacustrine environments.

Nitrogenous Altered Volcanic Glasses as Targets for Mars Sample Return: Examples From Antarctica and Iceland

AbstractMars exploration is focused on seeking evidence of habitable environments and microbial life. Terrestrial glassy basalts may be the closest Mars‐surface weathering analog and observations increasingly indicate their potential to preserve biogeochemical records. The textures, major and trace element geochemistry, and N concentrations and isotopic compositions of subaerial, subglacial and continental lacustrine hyaloclastites from Antarctica, Iceland, and Oregon, respectively, were studied using micro‐imaging and chemical methods, including gas‐source mass spectrometry. Alteration by meteoric‐sourced waters occurred in circum‐neutral, increasingly alkaline low‐temperature conditions of ∼60°C–100°C (Iceland) and ∼60°C–170°C (Antarctica). Incompatible large ion lithophile element (LILE) enrichments compared to mid‐ocean ridge basalt (MORB) are consistent with more advanced alteration in Antarctic breccias consisting of heulandite‐clinoptilolite, calcite, erionite, quartz, and fluorapophyllite. Granular and tubular alteration textures and radial apatite represent possible microbial traces. Most samples contain more N than fresh MORB or ocean island basalt reflecting enrichment beyond concentrations attributable to igneous processes. Antarctic samples contain 52–1,143 ppm N and have δ15Νair values of −20.8‰ to −7.1‰. Iceland‐Oregon basalts contain 1.6–172 ppm N with δ15Ν of −6.7‰ to +7.3‰. Correlations between alteration extents, N concentrations, and concentrations of K2O, other LILEs, and Li and B, reflect the siting of secondary N likely as NH4+ replacing K+ and potentially as N2 in phyllosilicates and zeolites. Although much of the N enrichment and isotope fractionation presented here is not definitively biogenic, given several unknown factors, we suggest that a combination of textures, major and trace element alteration and N and other isotope geochemical compositions could constitute a compelling biosignature in samples from Mars' surface/near‐surface.