Crystalline dolomite is a common carbonate mineral in lacustrine fine-grained rocks, but it has a confusing origin that has been a focus of much debate in recent years. In our research, the fine-grained rocks rich in crystalline dolomite were sampled from the upper fourth member (UMbr 4) and lower third member (LMbr 3) of the Shahejie Formation in the Jiyang Depression, and analyzed by a variety of analytical techniques, including field emission scanning electron microscopy (FESEM), cathodoluminescence (CL), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), micro-area carbon, oxygen, strontium isotopes and electron probe analyses. The results show: (1) The crystalline dolomites in the lacustrine fine-grained rocks are primarily composed of ferroan-poor dolomite (FeO < 1%), type I ferroan dolomite (FeO approximate to 5%) and type II ferroan dolomite (FeO approximate to 16%); (2) The delta O-18 of ferroan-poor dolomites in mudstone is between -0.89 and 0.32 parts per thousand, the precipitation temperature is less than 60 degrees C, and their formation is related to the microbial action during the early diagenetic stage A, while the ferroan-poor dolomites in dolostone are primarily formed by the recrystallization of micritic dolomite; (3) The delta O-18 of type I ferroan dolomites ranges from -3.74 to -3.89 parts per thousand, the precipitation temperature ranges from 68.4 to 69.4 degrees C, and they are primarily formed by the microbial action and clay mineral transformation during the early diagenetic stage B; (4) The delta O-18 of type II ferroan dolomites is between -7.78 and -8.33 parts per thousand, the precipitation temperature is more than 90 degrees C, and their formation is related to the dissolution of early carbonate and clay mineral transformation during the middle diagenetic stage; (5) The origin mechanism of crystalline dolomite indicates the diagenetic evolution of fine-grained rocks and the migration path and storage of shale oil.

The effect of various depositional parameters including paleoclimate, paleosalinity and provenance, on the depositional mechanism of lacustrine shale is very important in reconstructing the depositional environment. The classification of shale lithofacies and the interpretation of shale depositional environment are key features used in shale oil and gas exploration and development activity. The lower 3(rd) member of the Eocene Shahejie Formation (Es-3(x) shale) was selected for this study, as one of the main prospective intervals for shale oil exploration and development in the intracratonic Bohai Bay Basin. Mineralogically, it is composed of quartz (avg. 9.6%), calcite (avg. 58.5%), dolomite (avg. 7%), pyrite (avg. 3.3%) and clay minerals (avg. 20%). An advanced methodology (thin-section petrography, total organic carbon and total organic sulfur contents analysis, X-ray diffraction (XRD), X-ray fluorescence (XRF), field-emission scanning electron microscopy (FE-SEM)) was adopted to establish shale lithofacies and to interpret the depositional environment in the lacustrine basin. Six different types of lithofacies were recognized, based on mineral composition, total organic carbon (TOC) content and sedimentary structures. Various inorganic geochemical proxies (Rb/Sr, Ca/(Ca + Fe), Ti/Al, Al/Ca, Al/Ti, Zr/Rb) have been used to interpret and screen variations in depositional environmental parameters during the deposition of the Es-3(x) shale. The experimental results indicate that the environment during the deposition of the Es-3(x) shale was warm and humid with heightened salinities, moderate to limited detrital input, higher paleohydrodynamic settings and strong oxygen deficient (reducing) conditions. A comprehensive depositional model of the lacustrine shale was developed. The interpretations deduced from this research work are expected to not only expand the knowledge of shale lithofacies classification for lacustrine fine-grained rocks, but can also offer a theoretical foundation for lacustrine shale oil exploration and development.

在总结国内外相关文献的基础上,对砂质碎屑流的相关概念、沉积动力学过程及沉积特征进行系统梳理,并对争议问题进行了讨论。砂质碎屑流是一种富砂质具塑性流变性质的宾汉塑性流体,代表一个从黏性至非黏性碎屑流连续系列,具有中—高碎屑浓度（体积浓度25%～95%）、较低的泥质含量（体积浓度可低至0. 5%）、湍流不发育。其沉积物以块状砂岩、含碎屑逆粒序砂岩沉积为代表,局部可见滑动剪切构造和液化漩涡构造。砂质碎屑流的形成多经历滑动→滑塌→砂质碎屑流→浊流的有序演化过程;滑水作用和基底剪切润湿作用是克服砂质碎屑流与基底剪切摩擦拖拽的重要机制,流体强度则是克服上覆环境水体混入稀释的重要原因;砂质碎屑流头部和边部优先固结沉积,进而控制流体整体沉降。砂质碎屑流是形成深水块状砂岩的主要原因之一,砂质碎屑流在相对低流体效率的深水重力流沉积环境广泛发育。

Generally, researchers believe that authigenic quartz precipitates in acidic medium and authigenic albite precipitates in alkaline medium. However, the lacustrine carbonate-rich fine-grained sedimentary rocks in the upper fourth sub-member and the lower third sub-member (Es-4(s)-Es-3(x)) of the Shahejie Formation in the Jiyang Depression were observed and it was found that authigenic microcrystalline quartz and albite generally develop together. Moreover, authigenic quartz and albite also develop with microcrystalline Fe-rich dolomite and calcite in clay laminae, while in carbonate laminae, they primarily develop with recrystallized calcite. In this study, thin-section, cathodoluminescence, field-emission scanning electron microscopy (FESEM), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and inclusion analyses were conducted to study authigenic minerals. The results show that authigenic quartz and albite are characterized by rich Ge in mudstone, and the material components mainly originate from the transformation of clay minerals and the dissolution of terrigenous feldspar debris. In limestone, they are characterized by poor Ge, and the material components primarily originate from the transformation of clay minerals. The paragrowth and intergrowth of authigenic quartz and albite primarily depend on the degree of supersaturation of the corresponding ion concentration under high temperature, high or ultrahigh pressure. During the early diagenetic stage, authigenic quartz and albite initially formed in a weakly alkaline environment; however, on entering the middle diagenetic period, authigenic quartz, albite, and sparry calcite formed in a weakly acidic environment, and the formation rate reached its peak. Our results elucidate the migration direction and enrichment law of shale oil in calcareous fine-grained sedimentary rocks through the genetic mechanism of authigenic quartzs and albites. Shale oil is generated from organic matter in the clay lamina, following which it migrates, accumulates, and preserves to the adjacent sparry calcite lamina under the joint driving effect of organic matter hydrocarbon generation overpressure and clay mineral dehydration overpressure.

Eocene organic-rich shales in the Dongying Depression, Eastern China, are well preserved and ideal for examining stratigraphic controls on the variations of organic matter (OM). This study concerns the Eocene sedimentary succession in the Dongying Depression and recognizes a third-order sequence based on the stacking patterns of lithofacies, mineralogical changes, and geochemical proxies. The total organic carbon content, RockEval parameters S1 and S2 values, and the chloroform bitumen "A" content are low in the lowstand systems tracts, reaching their maxima within the transgressive systems tracts and gradually decreasing within the highstand systems tracts. The paleoclimate index and ratios of quartz/feldspar, Sr/Ca, TiO2/Al2O3, Cr/Al, Ni/V, Th/U, Zn/Al, and Ni/Al indicate that OM accumulation was influenced by primary productivity, sedimentation rate (SR), and redox conditions, which are intimately related to the sequence development under the influence of tectonics, climate, sediment supply, and relative lake-level fluctuations. The OM distribution is related to the sequence stratigraphy in three ways: (1) climate and relative lake-level fluctuations affected the primary productivity and OM production via algae blooms and terrestrial OM input; (2) relative lake-level fluctuations and sediment supply were influenced by tectonics and climate, causing a change in SR and OM deposition; and (3) relative lake-level fluctuations under different climatic conditions affected the development of anoxic bottomwater favoring OM preservation.

Complex mineral composition, multiple depositional processes, and strong reservoir heterogeneity cause the complexity and uniqueness of a lacustrine shale oil reservoir. Understanding the storage space development and hydrocarbon occurrence model should facilitate the analysis of the shale oil reservoir and hydrocarbon accu-mulation in lacustrine shales. In this study, the storage space development model for different lithofacies and the modes of hydrocarbon occurrence in different storage space were analyzed in the Es4s-Es3x shale in the Jiyang Sub-basin, East China, based on thin-section and field emission scanning electron microscopy (FE-SEM) obser-vations, X-ray diffraction (XRD) analysis, physical property testing, and geochemical analysis. Inorganic pores, particularly recrystallization intercrystalline pores in calcite, are the key matrix pores for lacustrine shale oil. However, the types and abundance of storage space are noticeably different in various lithofacies. The hydro-carbon occurrence is mainly manifested in three states: (A) free state in interlaminar fractures, structural frac-tures, and abnormal pressure fractures; (B) adsorbed state in organic pores, intercrystalline pores in pyrite, and floccule pores; and (C) free state in large pore spaces, including dissolution pores and recrystallization inter-crystalline pores, which can form a continuous hydrocarbon accumulation. The hydrocarbon generation po-tential and thermal maturity are closely associated with the lithofacies and mineral composition. The matching mechanisms of pore formation as well as hydrocarbon generation, migration, and accumulation are favorable. Among the various lithofacies, the organic-rich calcareous shale has abundant storage space, high porosity, total organic carbon content, and hydrocarbon potential, making it a "sweet spot" for shale oil exploration.

Y Pore types and pore structure parameters are the important factors affecting the storage capacity of a shale oil reservoir. Pore morphology and mineralogical composition of shales have diverse effects on the upgrading of various phases of shale oil. To interpret the formation and distribution of different pore types and their structure parameters in the lacustrine calcareous shale, a combination of polarizing microscopy, X-ray diffraction, total organic carbon (TOC), field-emission scanning electron microscopy, and low-pressure nitrogen adsorption experiments were conducted on the Es3x shale of the Eocene Shahejie Formation in the Zhanhua Depression. The interpretations regarding pore types, pore structure parameters, and pore size distribution indicate that the pore morphology and pore size distribution in the lacustrine shale are very complicated and demonstrate strong heterogenic behavior. Inorganic pores (interparticle pores, intraparticle pores, intercrystalline pores, dissolution pores, and microfractures) are the most commonly distributed pore types in the studied shale. However, organic matter pores are poorly developed due to the lower thermal maturity of the Es3x shale. The Brunauer-Emmett-Teller specific surface and pore volume range from 0.026 to 1.282 m(2)/g (average 0.697 m(2)/g) and 0.003 to 0.008 cm(3)/g (average 0.005 cm(3)/g), respectively. The shape of the pores varies from slit-like to narrow slit. Different minerals develop different types of pores with various sizes extending from micropores (<2 nm), mesopores (2-50 nm), to macropores (>50 nm). The relationship between mineral components and pore parameters indicates that the carbonate minerals act as the main contributors to the formation and distribution of different pore types in the studied shale. Pore volume and the pore specific surface area did not show a good relationship with mineral composition and TOC due to disordered pores, but pore size shows a good relationship with mineral composition and TOC of the Es3x shale. The whole pore system description showed that the mesopores and macropores are abundantly distributed and are the main contributors to the pore system in the Es3x shale. A comprehensive understanding of the formation mechanism and structural features of various sized pores in a variety of different minerals can provide a good tool for the exploration and development of shale oil reservoirs.

Algae-rich oil shales have great hydrocarbon potential, and the hydrocarbon generation processes of different quality oil shales are important for shale oil resource exploration. This study comparatively analyzed the hydrocarbon generation processes of the general- and fair-quality oil shales from the first member of the Qingshankou formation (K(2)qn(1)) and the first member of the Nenjiang formation (K(2)qn(1)), separately. Organic petrology and X-ray diffraction analyses revealed that the fair-quality oil shale contained more telalginite and lamalginite and had a lower clay mineral content than the general-quality oil shale. Thermal simulations revealed that the fair-quality oil shale underwent an earlier oil generation peak and exhibited higher oil yields than the general-quality oil shale, implying that the hydrocarbon generation processes were sequential. After a thermal maturity (Ro) of 1.05% was reached, the fair-quality oil shale generated plentiful hydrocarbons, whereby the contribution of illite content rapidly increased from the illite/smectite layer. Analysis suggested that fair-quality oil shales can generate large volumes of hydrocarbons and organic acids under the effect of temperature due to the presence of bulk telalginites, and these organic acids in turn promote the transformation of smectite into illite. This greatly increased the catalytic activity of smectite and thus the rate of hydrocarbon generation. Finally, it was determined that the synergistic effects of organic matter and clay minerals contributed to the rapid hydrocarbon generation of the fair-quality oil shale, implying that fair-quality oil shales that are rich in telalginites have value as sweet spot layers for early shale oil exploration. This is important for the development of shale oil resources.

Numerous volatile oil reservoirs and condensate gas reservoirs were discovered in the Member 4 of Shahejie Formation in the Paleogene system, northern Dongying Depression of Bohai Bay Basin, eastern China. Deep reservoirs were examined thoroughly, including biomarker, light hydrocarbon, and diamondoid in oil; composition and carbon isotope in natural gas; fluid inclusion; and thermal history. Based on diamondoid parameters, the equivalent vitrinite reflectance (EqVRo) of the crude oil ranges from 1.55% to 1.82%, indicating a state of high to over maturity, while the low absolute concentration of methyl diamantanes indicates that the oil is still in the early cracking stage. The deep gas is a mixture of kerogen degradation gas generated from hydrocarbon source rocks and oil cracking gas produced from the reservoirs. The EqVRo of gas is mostly between 0.8% and 1.3%, which is in a moderately mature state. The oil and gas are sourced from Member 4 of the Shahejie Formation, which was formed in a saline and reductive environment with a main input of I-II algal organic matter. The kerogen degradation gas was generated in the late sedimentary period of Member 2 of the Shahejie Formation, which was the first stage of petroleum charging. The early oil and gas reservoirs underwent noticeable evaporative fractionation due to the invasion of oil cracking gas after entering the late period of the Guantao Formation in the Neogene, resulting in the formation of the present volatile and condensate oil and gas reservoirs.

The sedimentary characteristics and preservation potential of lacustrine carbonates provide fundamental information on climate change. The lacustrine carbonate deposition in the Eocene Dongying Depression was investigated using a combination of mineralogical, petrological and geochemical analyses. Micritic calcite/dolomite, granular calcite, columnar calcite, calcareous shell fragments and reworked detrital calcite were identified. Varying patterns of carbonates (VPC) including lithofacies, geochemical indicators and carbonate distribution were revealed in the Dongying Depression: (i) carbonates hardly precipitate in the nearshore area (average 12 wt %); (ii) carbonate content is high (average 53 wt %) in the shallow lake and (iii) gradually decreases to reach a minimum (average 24 wt %) in the deeper part of the lake. Comparison of VPC in four Holocene lakes (the Qinghai Lake and Barkol Lake in China, Oro Lake in Canada and Montcortes Lake in Spain) with the Dongying Depression suggests that four distinct lake stages were developed, namely the terrigenous clastic/gypsum-rich, carbonate-rich, carbonate-decreasing and carbonate-poor stages. A depositional model of lacustrine carbonates influenced by detrital influx, climate, palaeoproductivity and salinity is developed. This study contributes to the understanding of the genetic mechanisms of lacustrine carbonate deposition to reconstruct environmental changes.