The classification of fine-grained sedimentary rocks is crucial for the deep and systematical study of the fine-grained sedimentary rocks. The classification scheme not only has to reflect the sources,sedimentation types of rock components,it also should be widely applicable. There are various sources of fine-grained sedimentary rocks, including terrigenous clastic sources, endogenic chemical precipitation sources, biological sources and volcanic clastic sources. Among different basins,there are significant differences in the sediment source of fine-grained sedimentary rocks;furthermore,in the same basin,the same mineral can also has multiple sources. Currently,there is no systematic classification scheme for fine-grained sedimentary rocks,a special type of rocks. Based on the components, sediment sources and sedimentation types,we propose a comprehensive four-component three-terminal classification scheme for fine-grained sedimentary rocks. Firstly,the sediment source is considered as the first principle,and three end-members, i.e.,terrestrial clastic substances,endogenic chemical precipitants,and volcanic clastic substances,are used to classify them into four types(terrigenous clastic fine-grained sedimentary rocks,chemical fine-grained sedimentary rocks,pyroclastic fine-grained sedimentary rocks,and mixed fine-grained sedimentary rocks), and according to the content of organic matter, the fine-grained sedimentary rocks can be further divided into three categories: high organic matter, medium organic matter and low organic matter. Secondly, fine-grained sedimentary rocks are divided into 11 subtypes following the three-level naming principle, combined naming principle and compound naming principle. Thus, fine-grained sedimentary rocks could be named according to the relative content of the components.

Cenozoic island dolostones found throughout the global oceans are considered as ideal natural laboratories for deciphering the classic “dolomite problem”due to their shallow burial,eogenetic formation,and weak diagenetic modifications. This paper systematically summarizes the research progress on these dolostones in term of their basic characteristics,time evolution,fluid properties,and genetic models,and discusses the paleoenvironmental and paleoclimatic factors that influence their formation. The Cenozoic island dolostones(tens to hundreds of meters thick)show similar petrological(texture-retentive and texture-destructive),stoichiometric(high-calcium dolomite and low-calcium dolomite),and geochemical(e.g.,carbon and oxygen isotopes,strontium content)properties,and are formed contemporarily during the 10-0.5 Ma interval. The strontium isotopes of the dolostones indicate that the age of dolomitization generally becomes progressively younger from the bottom to the top of the dolostone sections in a continuous or semi-continuous way on individual islands(atolls,carbonate platforms)under the influence of eustatic change and tectonic subsidence. Carbonate clumped and oxygen isotopes indicate that the primary fluid source for the island dolomitization is normal to slightly evaporated seawater. Furthermore,the high-calcium dolomite is formed primarily from normal seawater,while the low-calcium dolomite is formed from slightly evaporated seawater. A single fluid flowing mechanism(e.g.,seepage,reflux,geothermal convection)is insufficient to explain the genesis of the Cenozoic island dolostones;and available data demonstrate that the formation of the island dolostones is promoted by multiple flow mechanisms. During the island dolomitization period(10-0.5 Ma),there is no single paleoenvironmental or paleoclimatic factor(e.g.,seawater Mg/Ca ratio,temperature,$\text{SO}_{4}^{2-}$ concentration,redox state,pCO₂,pH)that corresponds to significant dolomitization,implying that the Cenozoic island dolomitization event was probably controlled by multiple paleoenvironmental and paleoclimatic factors. To better understand the genetic mechanisms of the Cenozoic island dolostones,future research should focus on the micro-processes of dolomitization,the application of new geochemical methods and numerical simulation.

Bioliths are the main research object of the new interdisciplinary biopetrology,are rocks formed by biological processes,including reef rocks,rocks composed of non-reef-building organisms and micrite,and rocks formed by microbial processes. Previously,reef rocks and microbialites were studied separately and not included in the same discipline. The classical classification system of reef rocks and microbialites only includes a part of reef rocks and microbialites,and some biolith types are not recognized and included. The incomplete classification of bioliths limited the research of bioliths. In this paper,a unified classification system of bioliths including reef rocks,non-reef-building skeletal carbonates,microbialites and other microbiogenic rocks is proposed. The new basic bioliths include biomicrite,microlithite,microbialite,microallolite,micromicrite,framelite,crustolite,wrapolite,and filalite. This classification of bioliths into 24 basic rock types in 4 levels may facilitate the study of bioliths. The author also modified and improved the definition of some rocks such as framestone and discussed some problems in the study of biolith.

In order to correctly and efficiently complete the research content of sedimentary petrology,its research methods need to be diversified and advanced,and can be improved and developed continuously in practice. This paper emphatically demonstrates the laboratory methods of sedimentary petrology,which mainly include mineral composition and structure analysis,inorganic and organic geochemistry analysis and other experimental methods. The mineral composition and structure analysis mainly comprise thin-section identification,grain-size analysis,heavy-mineral analysis,laser-Raman and fluorescence spectroscopy,micro-area elemental analysis and mineral recognition,cathodoluminescence,X-ray diffraction,infrared spectroscopy and thermal spectrum analysis. Inorganic geochemistry consist mainly of element analysis,quantification of weathering intensity,stable isotopic and dating analyses. Organic geochemistry primarily incorporates total organic carbon,pyrolysis,vitrinite, chromatography,biomarker chromatography-mass spectrometry,non-biomarkers,organic compound stable isotope composition,etc. In addition,magnetic mineralogy,physical and numerical simulation,petrogeophysical method,and big data analyses should also be included for sedimentary petrology study. This study will shed new light on the application and development of these technologies and methods,in favor of promoting the development of sedimentary petrology.

China is rich in saline lakes. Many previous studies were focused on analyzing the water chemistry of saline lakes,salt origins,the development of salt mine resources,but rarely paid attention on sedimentary characteristics and diagenetic processes of evaporites,making it difficult to understand the accumulation processes of hydrocarbon in ancient saline lacustrine basins. In this paper,the classification of saline lakes and the main genetic types of saline minerals in the evaporites are reviewed based on the extensive literature review on a large number of saline lakes. The sedimentary and diagenetic processes of common minerals including sulphates,chlorides,sodium carbonates and borates in lacustrine petroliferous basins and their significance for paleo-climate and paleo-environment were concluded. Meanwhile,the controversial and noteworthy issues in the studies of evaporites in petroliferous basins were discussed based on the latest research findings in saline lakes sedimentology: (1)The hydrothermal fluids can transport large amounts of elements into lakes,but the semi-arid and arid climate and the evaporation and concentration are the pre-conditions for accumulating the massive evaporates in the lakes. (2)The soluble evaporates(e.g.,halite)more easily concentrate in the sedimentary center characterized as a thick single layer,while they are missing in the slope and margins of the lakes,which is controlled by “halite aggregation effect at the center”caused by seasonal temperature and thermocline fluctuation. (3)Temperature affects the solubility,crystal structural morphology and formation depth of salt minerals in evaporites. Some anhydrous salt minerals cannot crystalize under normal temperature and pressure conditions,which are good indicators of paleo-temperature and burial history. (4)The sodium-bearing carbonates are closely related to pCO₂ and paleo-temperature of saline lakes of carbonate subtype.

Silicate rocks are factors that influence the global carbon cycle as well as climate change by chemically reacting with carbon dioxide,removing atmospheric carbon dioxide and sequestering it in weathering products or ocean carbonate rocks. Quantifying the total amount of carbon dioxide consumed by weathering of global silicate rocks is key to understanding the Earth’s current and past climate change. This paper systematically investigates the data sources,research methods,calculation formulas,and main influencing factors of five quantitative models of chemical weathering-CO₂ consumption of silicate rocks. The CO₂ consumption calculated by the latest Celine model serves as a reference standard for comparing the advantages,disadvantages and scope of application of each model. The existing models estimate the global carbon dioxide consumption of chemical weathering of rock silicate rocks to be 69-169 Tg/yr,in which the main parameters of each model include climate(temperature,runoff)and lithology,and the secondary parameters include tectonic uplift,volcanism and plant interaction. Future exploration of the quantitative calculation of carbon dioxide consumed by the chemical weathering of silicate rocks should consider more control effects and the interconnections between factors. In addition,the use of big data analysis methods to generalize these quantitative models to the reconstruction of the palaeoclimate of the deep earth may be a future research trend.

Molar tooth structure(MTS)refers to a series of peculiar, ptygmatically folded and spar-filled cracks in fine-grained carbonates of the Precambrian. Particular Precambrian carbonate with MTS is called the Molar tooth carbonate(MTC). Consensuses have been achieved that the MTS is globally distributed and composed of micro-sized sparry calcite,developed during a specific time limit,early diagenetic product,and has diversified morphologies. Based on a systematical summary of the palaeogeographical distribution,development time limit,macro morphology,and the micro fabric of MTS,this paper systematically analyzes the basic arguments and limitations of the three hypotheses of MTC origin, i.e.,the physical origin,biological origin,and the biogeochemical origin hypothesis. As a globally distributed special carbonate that only appeared during the Meso-and Neoproterozoic,the focuses and hot spots of the MTC researches are the formation and disappear mechanisms. Although there are still controversies about the formation mechanism,the early diagenetic characteristics of the MTC made a growing number of geologists regard the MTC as an important recorder to reestablish the geochemical properties of the Precambrian ocean. The flourishing and(or)dismissal of the MTC has a close relationship with the evolution of paleocean properties,the supercontinent cycles,and a series of global geological events. Further researches about the MTC can go in two aspects: one is to explore the reciprocal response,promotion or inhibition relationship between the MTC and global events such as stromatolites,glacial events, etc.,and how to couple the MTC events to the assembly and breakup processes of the Columbia and Rodinia supercontinents;the other is the microscopic fabric of the microspar in the MTS, select adopt effective geochemical methods,in order to combine the researches of the occurrence,evolution,and cessation of the MTC with the evolution and changes of atmosphere,biosphere,and the Precambrian ocean properties,and finally improve the theory of the MTC formation mechanism. All these researches will help and provide clues to solve several major Precambrian scientific problems.

Siliceous rocks are a chemical sedimentary rock formed from authigenic quartz,usually in layered or non-layered(condullary,banded)forms,either alone,interbedded,and in other lithologic Formations. Silica not only records a large amount of geological information of the basin's paleogeography,paleo-ocean and paleoclimate,but also plays an important role in the study of rock geotectonics. The previous research on siliceous rocks has achieved rich results. In recent years,new viewpoints on siliceous rocks have provided new ways of understanding and research clues for the study of siliceous rocks. By investigating the petrological characteristics,geochemical characteristics and sedimentary environment of siliceous rocks in recent years,this paper analyzes and summarizes the Formation modes,genetic types and discrimination methods of siliceous rocks in different geological historical periods,different depositional environments,and different occurrences. The sedimentation of siliceous rocks is not the result of single factor control,but the comprehensive result of geological tectonic activity intensity,biological type and activity,and sedimentary paleoenvironments. Conventional geochemical elements,combined with rock fabric and micro-area analysis,inclusion analysis,new isotope(Rb-Sr and Sm-Nd)analysis,and new geochemical criteria(Ge/Si)are an essential methodology for silica research and method.

Mudrock is a major category of fine-grained sedimentary rocks,and there have been different understandings of its definition and classification in China,resulting in much confusion for academic research. This paper reviews the evolution of mudrock-related concepts and definitions in the development of sedimentology at home and abroad and attempts to provide a practical classification system for mudrock. Scholars in European and American tend to use the term “mudrock”, which refers to fine-grained terrestrial clastic rocks with a grain size less than 0.063 mm,including siltstone(two-thirds or more silt content),mudstone(neither silt nor clay content greater than two-thirds)and claystone(more than two-thirds clay content),in which the laminated rock is called shale. However, scholars in the former Soviet Union tend to use the term “глинистые породы” (argillaceous rock) to refer to sedimentary rocks containing more than 50% of clay minerals,in which the fissile rock is called shale. There are essentially two classification schemes for mudrock and other fine-grained sedimentary rocks,classified by texture(grain size),composition and sedimentary structure. One is a multi-element comprehensive rock classification,and the other is an end-members diagrammatic classification. We recommend the term “mudrock”as a general name for the fine-grained terrestrial sedimentary rocks consisting mainly of silt-sized(0.004-0.063 mm)and clay-sized(less than 0.004 mm)clasts. A triangular prism diagram classification method is adopted to classify fine-grained sedimentary rocks into fine-grained terrestrial sedimentary rock(i.e. mudrock)and fine-grained endogenous sedimentary rock,based on three end-elements of detrital minerals(mainly felsic detrital minerals),clay minerals and other endogenous minerals. Mudrock is further classified into three subgroups of siltstone,mudstone and claystone,or “-shale” if laminations or fissility are developed. Taking the TOC contents of 0.5% and 2% as the dividing points,fine-grained sedimentary rocks are classified into organic-poor,organic-bearing,and organic-rich ones. It is expected that this classification scheme will contribut to the mudrock classification.

Burnt rocks are widely distributed in many sedimentary basins located in the northern China that are bounded by Kunlun mountain-Qinling-Dabie mountain. However,few studies have focused on the origin,age and geological significance of these kinds of metamorphic rocks. Based on our field investigation,four distribution modes of the burnt rocks are found: (1)large area distribution,(2)linear distribution along the mountain range alignment,(3)distribution along the river incised-valley and(4)covered by the Quaternary loess. These burnt rocks were mainly caused by the self-ignition of Jurassic and Carboniferous-Permian coals. Various burnt rocks developed in the burnt rock area on different levels. The vitrified structure,whitened structure,lava structure,residual structure,pore structure,columnar jointing structure,breccia structure,fissure structure and filling minerals are often found in these burnt rocks. The burnt rocks are mainly red,mixed with brown,black and steel-gray colors. The typical high temperature minerals as cristobalite,tridymite,cordierite,sekaninaite and mullite are common in these burnt rocks. The active tectonic movements and arid climate in northwestern China triggered the formation of burnt rocks since the Miocene. The relationship between the palaeotectonic,palaeoclimate,palaeo-wildfire and the coal self-ignition,however,has been seldomly studied. Such information implied from the formation of burnt rocks should be paid more attention in the future work.

Quartz is an important part of shale,making it crucial to clarify its genetic mechanism for the reconstruction of shale diagenetic process and the formation of shale oil and gas reservoir. The genesis of quartz in shale is complex,with the main types, including terrigenous detrital quartz,biogenic quartz and diagenetic authigenic quartz, identifiable through ordinary thin section observation,scanning electron microscopy,energy spectrum analysis and cathodoluminescence. The main sources of diagenetic authigenic quartz silica are clay mineral transformation,felsic dissolution and biosilicon dissolution,and volcano-hydrothermal activity. Terrigenous detrital quartz is mostly silt-grade and strongly emits light under cathodoluminescence,typically displaying a two-peak spectrum. Micron-sized biogenic quartz does not emit light,and clay mineral-derived quartz is predoninantly found around or embedded within clay minerals, such as illite. In addition to the morphology and occurrence characteristics of different types of quartz,there are also differences in geochemical elements. Quartz affected by hydrothermal activities is rich in Fe and Mn,while terrigenous detrital quartz is rich in Ti and Al elements. Detrital SiO₂ and Zr are positive correlation,as does biogenic quartz with TOC content. The biogenic quartz Fe/Ti ranges between 0.4 and 20. Diagenetic authigenic quartz is formed in multiple stages,which is closely related to the burial diagenesis process of shale and affects the properties of shale reservoirs. Diagenetic authigenic quartz is mainly formed in early and middle diagenetic stages. Terrigenous detrital quartz and biogenic quartz are conducive to inhibiting compaction and protecting primary pores. Processes involving diagenetic authigenic quartz, like clay mineral transformation and felsic dissolution create dissolution pores and organic pores,with quartz filling some pores,thereby reducing porosity. Identifying the origin of quartz in shale is of great significance to the analysis of shale sedimentary environment and the prediction of favorable reservoir distribution.

Organic-rich black shales,which represent shale oil and gas resources,have become a research hotspot in the field of oil and gas exploration and development in China and around the world in recent years. These lithologies consist mainly of complexly sourced fine-grained sedimentary rocks in continental lacustrine basins in China,among which a special type of laminated microcrystalline dolostone is developed. The petrological,mineralogical micro-features,and geochemical characteristics of this type of dolostone are distinct from the commonly dolostones formed by dolomitization and are also different from microbial mediated dolostones. Hence,the dolostones have been defined as a new type of volcanic-hydrothermal sedimentary dolostone. Based on extensive review of domestic and foreign literature,this paper summarizes the global distribution and environmental characteristics of modern lacustrine dolomites and presents the research progress on the models of origins of dolostone. The focus is on the comparative study of volcanic-hydrothermal sedimentary dolostones found in the Lucaogou Formation in Santanghu and Junggar Basins, the Xiagou Formation in Jiuxi Basin,and the Tengger Formation in Erlian Basin,all of which are formed in an extensional tectonic setting. Four characteristics are summarized as follows: (1)These dolostones are well-preserved with μm-scale laminated structure and microcrystallized,indicating latterly weak diagenesis. (2)They contain a variety of volcanic-hydrothermal minerals,and are interbedded with semi-deep to deep lacustrine black shale. Evaporite characteristics are lacking. (3)Strontium isotopes indicate that the diagenetic fluid has a deep source(crust-mantle mixed)characteristic. (4)They are rich in organic matters and show a strong coupling relationship with hydrocarbon distribution. Finally,it is recommended to enhance research on this type of dolostone,utilize its unique geological information for tracing tectonic backgrounds,and explore its relationship with hydrocarbon generation as future research directions.

Leopard skin (spot) limestone, a type of marine carbonate rock with unique morphology, is widely distributed in the Cambrian-Ordovician strata of North China. It has attracted significant attention due to its distinct characteristics and formation mechanism. Abundant leopard-skin (spot) carbonate rocks developed in Member 4 of the Middle Ordovician Majiagou Formation in the Ordos Basin. Eight species of 7 genera have been identified, including Thalssinoides network, Thalassinoides boxwork, Planolites isp., Palaeophycus tubularis, Phycodes isp., Chondrites isp., Skolithos isp.,?Zoophycos isp. Two morphologic types of Thalassinoides (horizontal enigmatic network and three-dimensional boxwork) are predominant, belonging to the Glossifungites ichnofacies under firm ground condition. Based on detailed macroscopic and microscopic characteristics of outcrops and drilling cores, this paper systematically summarizes the types of carbonate rocks caused by bioturbation. By examining the morphological characteristics of bioturbation and burrow, as well as the calcite/dolomite content, this paper proposes a classification for leopard-skin (spot) carbonate rocks formed by bioturbation. These rocks are categorized into leopard-skin limestone and leopard-spot dolomite, corresponding to the Thalassinoides network (two-dimensional horizontal mystery palace) and the Thalassinoides boxwork (three-dimensional box-like structure), respectively. The leopard-skin (spot) carbonate rocks in Member 4 of the Majiagou Formation in the Ordos Basin are primarily controlled by the interaction of bioturbation and early diagenesis during high-frequency sea level fluctuations. The bioturbated burrows in the firm substrates creat pathways for Mg²⁺ rich brines, promoting dolomitization within the burrows. Two distinct types of leopard-skin (spot) carbonate rocks, induced by bioturbation, were generated under varying bioturbation types, parasyngenesis, and buried dolomitization.