With increasing of the global energy consumption,exploration of medium- to large-sized oil and gas fields in conventional sandstone and carbonate rocks has encountered significant difficulties. The special coarse-grained reservoirs of conglomerates gradually entered the view of exploration geologists. Discovery of the large-scale,conglomeratic reservoirs in the Mahu area,Xinjiang, proved the enormous oil and gas potential,which indicates urgent,aimed research on it. Looking back on the development history of coarse-grained sedimentation,it has gone through three main stages: Initial stage of concept formation(1885-1947), rapid development stage of genetic analysis(1948-1987),and application stage of theoretical perfection(1988-present). Each stage was characterized by scientists from all over the world focused on analyzing and discussing hot spots and bottlenecks in coarse-grained deposits,which experienced scientific development processes including genetic discussions on practical phenomenon or issues induced by discovery of oil and gas fields,theory formation,and practice guiding. These academic events and cognitions provided a good example and foundation for the later researches. Based on literature reviewing of research topics,representative scientists,and events during each stage,as well as authors' thought from the long-term,comprehensive research,this paper proposed the key issues for coarse-grained sediments and suggestions for future research,including paleo-topography and slope gradients,sedimentary genetic mechanisms,facies and microfacies subdivision,flume experiments,conglomerate diagenesis,logging interpretation,seismic processing and interpretation,and quantitative data base.

Microbialites are carbonate bodies formed by microbial actions of benthic microbial communities or mainly composed of skeletons of planktonic microbes,and include the old types such as stromatolites,thrombolites,microbial laminated rocks,oncolites,leiolite,and the new types: Microbial framestones,microbial bindstone,and microbial caststone mainly composed of cast fossils of microbes,microbial grainstone,and microbial packstone. The Permian-Triassic boundary microbialites in South China include three types: Those with patchy coarse-mineral structures,those with dendroid coarse-mineral structures,and those with net-like coarse-mineral structures. The three types of structures are composed of spar-filled structures and the microsparry filling the space between the spar-filled structures. The spar-filled structure is defined as caves left by decay of some non-calcified organisms and filled by various minerals formed in diagenesis,and varies in inner fillings and fabric due to difference in diagenetic history. The rocks between the coarse-mineral structures are micrites with few fossils and scattered spar-filled structures. The shapes of the spar-filled structures in the PTB microbialites are very similar to those of the colonies of Microcystis,an extant cyanobacterial genus,in shape and size and are the cast fossils of the latter. The PTB microbialites are not thrombolites. As colonies of Microcystis sank to the floor and were buried by micrites,their sheaths did not decay until the micrites were slightly lithified. After their decay,the caves they left were firstly cemented by needle-like aragonite,and then altered by dolomitization forming dolomites,which mostly were altered to calcite and were dissolved by fresh water in surface environment. The caves finally were filled by blocky calcite. Diagenesis has destroyed the outlines of most spar-filled structures,making it difficult to recognize. Diagenetic fluids migrated along the sediments with abundant spar-filled structures,destroying them,forming coarse minerals,which resulted in the patchy,dendroid and netlike appearance of the PTB microbialites. Since the formation of the patchy,dendroid and netlike bodies is controlled by diagenesis rather than microbes,and are not composed of micrites but coarse minerals,they are not thrombolites. There is no calcified wall in the spar-filled structures,and they are not calcimicrobes. Small coccoid fossils occur in the upper part of the microbialite interval,but not the lower part,in small content,and is not responsible for formation of PTB microbialites.

In this study,Upper Jurassic-Lower Cretaceous aeolian deposits have been discovered from the stratigraphic succession overlying the Hongshuigou Formation in Wanggaxiu area,the Qaidam Basin. The typical lines of evidence for eolian deposits can be identified in both rock micro-structures and depositional features: The strata mainly consist of pure brown fine-medium grained sandstones dominated by well sorted and rounded quartz grains. Obvious eolian grain surface textures such as dish-shaped impact crater and crescent-shaped impact scars can be observed under SEM. Well-developed thick,large scale and high dip tabular cross-bedding is characteristic of eolian dune foresets. Synsedimentary deformation structures such as drag folds and overturned folds are common in the eolian strata. According to lithology and sedimentary structural characteristics,four subfacies are recognized in the Wanggaxiu eolian deposits. The dune subfacies is characterized by large-scale cross bedding. Waddy,inter dunes and desert lake are featured as aqueous deposits. The discovery of the Wanggaxiu eolian strata has enriched sedimentary types in the Mesozoic sediments in the Qaidam Basin and is of a certain significance for the study of regional stratigraphic correlation,and Late Mesozoic palaeoclimatic and palaeogeographic evolution of the northwest China.

The Upper Triassic Yanchang Formation was developed within a large depression basin deposits in the Ordos Basin. Chang 10 interval is the initial deposits of Yanchang Formation. However,its source characteristics,the division of sedimentary system and the type of sedimentary facies remain obscure,which,in turn,restricts the exploration and discovery of the Chang 10 interval in the Ordos Basin. Heavy and light minerals,together with zircon dating,suggest that three main provenances developed in the northeast,northwest and southwest of the Chang 10 interval in Ordos Basin. The sedimentary systems were divided into the northeast,northwest and southwest depositional systems,on the basis of the source characteristics. Comprehensive outcrop,core,drilling,logging and other data reveal that Chang 10 interval mainly contains fluvial and deltaic deposits. The northwestern depositional system is mainly composed of braided river deposits,while the northeastern depositional system is typified by meandering rivers and delta deposits. The southwestern depositional system is represented by braiding river deltas,with sedimentary center located in Taibai Yijun areas(mostly shallow lacustrine facies).

Using core observation,logging data and various analytical data,the provenance direction,sedimentary facies and models of the Permian Wutonggou Formation in Lükqün area of Turpan-Hami Basin were documented. Results from the current research suggest that the Wutonggou Formation of the Turpan-Hami Basin experienced the depositional change from the rift lake basin to depression-lacustrine basin. Subaqueous fans are developed on both sides of the study area during the first stage of the Wutonggou Formation. The multi-stage superimposed thick muddy conglomerate formed in the channel of the subaqueous fans. The regionally extensive glutenite has poor physical property. The water body of the lake basin became shallow at the end of the stage of the Wutonggou Formation,and the slope of the lake shore became gentler. Fan delta deposits were developed in the study area. The subaqueous distributary channels on fan delta fronts were filled by a few sets of glutenite of about 10~15 m. The sorting degree of glutenite in this period is better than that of the submarine fan,with good physical properties. The subaqueous distributary channel sand bodies in the fan delta fronts and the pebbly sandstone at the top of each submarine fan sand body represent good reservoirs.

The drilling of shale gas wells(CYY1,YD1 and YD2)was carried out in Yingjing depression. On the basis of core observations and sedimentary structures,a large number of soft-sediment deformation structures(SSDS)and brittle deformation structures were identified within the Middle-Lower Ordovician sandstone and shales,including load structures(e.g., ball-pillow structures,flame structures,load casts,etc.),liquefaction structures(e.g., sand dykes,liquefied breccia),boudinage,convolute lamination,shatter fissures,shatter breccia and syn-sedimentary faults,etc. These contemporaneous and penecontemporaneous deformation structures suggest that they were most likely triggered by earthquakes. Our results suggest that at least two strong seismic events happened,while the last one led to a tsunami,which was accompanied by several aftershocks. The tectonic movement occurred during Early-Middle Ordovician led to faulting,and can be related to an early episode of Douyun movement during Caledonian,which,in turn,was significant for Chuanzhong uplift. The earthquake greatly improved the quality of oil and gas reservoirs.

As an important target of the present-day hydrocarbon exploration and development,submarine channels have complex styles of sedimentary architecture and the associated controlling factors are still poorly understood,which significantly raises the risk of drilling of the hydrocarbon reservoirs and the difficulty of development. Taking the Niger Delta slope as an example,the present study,utilizing the high-resolution seismic data from the shallow subsurface,reveals the styles of channel-system external morphology and internal construction,probes the relationships among morphological parameters of the channel system and the channel complex,and analyzes the controlling factors of the submarine-channel sedimentary architecture. It is suggested that: (1)The channel system could be divided into three categories, i.e., confined channel system,semi-confined channel system and unconfined channel system. The boundaries of the confined and semi-confined channel system are obvious erosional surfaces and the latter commonly develops levee deposits;the unconfined channel system,however,does not have the erosional surface. In addition,each kind of the channel system could be further divided into two subgroups(the incised one and the enveloped one). (2)The channel complex within the channel system has the agrradational type as well as the accreted type;the former consists of the isolated,superposed as well as cut-and-fill group and the latter includes the cut-and-fill and detached group. (3)The slope gradient has closed relationship with the channel-system type and scale;in the reaches having steep gradients(>1°)and gentle gradients(0.5°~1°),confined channel system and semi-confined channel systems are respectively dominated,however,unconfined channel system mainly shows up in the flat section of the slope(<0.5°). With the increasing of slope gradients,the widths and heights of the channel system would respectively decrease and increase and thus,resulting the rapid decrease of the ratio of width to height. That is,the channel system tends to be‘narrow and deep’. The current study leads to some new interpretations of deep-water sedimentology and is of great significance for the high-efficient development of associated reservoirs.

Insufficient understanding in the characteristics of sedimentary sequences of the falling stage system tracts and unreasonable sequence division have hampered the breakthrough of oil and gas exploration in the Zhujiang Formation of Pearl River Mouth Basin. In this study,characteristics of the sedimentary sequence,evolution model and favorable sand body distribution in the falling stage system tracts of the Zhujiang Formation were investigated regarding the formation mechanism of forced regression. Guided by the concepts and methods of sequence stratigraphy,seismic sedimentology,and petroleum geology,comprehensive analyses of the high-resolution 3D seismic,core and logging data were conducted. Based on obvious toplap(erosion)geometries against the upper boundary,the falling stage system tracts should be attributed to the last system tract of the SQ1 sequence. The evolution model of the sedimentary sequence of the falling stage system tracts has also been summarized. The characteristics of the falling stage system tracts in seismic reflection show high angle oblique progradation and offlapping stratal stacking patterns,typical of shelf-edge deltas. The drilling and logging data show many reverse cycles consisting of delta front mud,distal bar,mouth bar and underwater distributary channel in the falling stage systems tract. The bioturbation,muddy strip deformation,slide and slump features,typical of slope areas,are commonly present in the cores of the falling stage system tracts. The turbidite fan with strong amplitude reflection structure is developed in the downdip direction of the falling stage system tracts. The favorable reservoirs include sand bodies of the shelf-edge delta front located close to the upper boundary of the falling stage system tracts and the sand bodies of the turbidite fan located close to the basal surface of forced regression,which are important exploration breakthroughs of lithologic reservoirs.

Based on analyses of cores,thin sections,scanning electron microscope,well-logging,X-ray diffraction and physical properties of the Upper Member of the Paleogene Lower Ganchaigou Formation(i.e. E_2-3xg²)in the Yingxi area of Qaidam Basin,this paper aims to investigate the influence and control of lake-level fluctuations on the formation and distribution of mixed saline lacustrine carbonate reservoir. Deposited in a saline lacustrine basin,the carbonate reservoir of the E_2-3xg² in the Yingxi area contains mixed lithologies and stacking sedimentary cycles resulting from multiple sets of lake-level fluctuations. The rock structure and mineral composition of the E_2-3xg² show similar periodical changes associated with the lake-level fluctuation cycles. Multiple reservoir types,dominated by mixed saline lacustrine carbonates,are present in this area. The vertical evolution and distribution of physical properties of various reservoirs have a good coupling relationship with a single lake-level fluctuation cycle. From bottom to top,the pore assemblage is characterized by primary intercrystalline micropores,slightly dissolved micropores,and dissolved pores. Accordingly,reservoir physical properties tend to get better upward. The formation mechanism and spatial distribution of various reservoirs are mainly controlled by the fluctuation of lake level. The reservoir dominated by dolomite intercrystalline micropores is developed during the early-to-mid regression when strong evaporation and concentration of water prompt penecontemporaneous dolomitization. This reservoir type is characterized by moderate reservoir property but wide distribution. Reservoirs dominated by slightly dissolved and expanded micropores and dissolved pores,however,are formed during the late regression. They are mainly developed in the ancient landform highlands,which are more likely to be exposed and altered by meteoric freshwater dissolution. Therefore,these reservoirs are characterized by good reservoir property but local distribution.

Multiple outcrops of the hydrothermal dolostone are distributed throughout the Cambrain Qingxudong and Loushanguan Formations in Tongren area,eastern Guizhou Province. The dolostones are generally massive,lenticular and brecciated. Based on investigations in the outcrops and rock slabs,measurement of temperature of fluid inclusions,and REE and Sr isotope analyses,we studied the genesis and fluid property of different types of hydrothermal dolostone and their relationship with the mineralization of Pb-Zn deposits. The results indicate: (1)Hydrothermal dolostone is composed of medium-coarse-crystalline to ultra-coarse-crystalline saddle dolomite crystals. The formation temperature varies from 96 to 223 ℃,with an average of 155.86 ℃. Salinities is between 8.28 and 16.15 wt% NaCl,with an average of 12.30wt% NaCl. Characterized by REE enrichment and a negative Ce anomaly with the LREE to HREE ratio of 16.51,δCe value of 0.79,and ⁸⁷Sr/⁸⁶Sr ratio of 0.708662. (2)Massive and lenticular hydrothermal dolostone formed by more complete metasomatism of dolomitized fluid,whereas brecciated hydrothermal dolostone formed by hydrofracturing. Dolomitized fluid may come from the underlying Sinian carbonate strata,with faults and fractures as fluid migration channels. (3)Dolomitized fluid and regional Pb-Zn ore-forming fluid have similar temperature,salinity and geochemical characteristics,and share similar origins. A few metallogenic materials of the hydrothermal dolostone were also formed around the main Pb-Zn metallogenic stage.

In this paper,the heavy-mineral assemblages and the trace-rare earth elements of Borehole SE2 sediments in the late Quaternary Qiantang River incised valley were analyzed systematically in order to investigate their provenance and evaluate the coupling relationship between the Qiantang River and Changjiang incised valleys. Results indicate that: (1)The sediments of the river bed(U5),flood plain(U4) and ancient estuary(U3) are characterized by a heavy-mineral assemblage of hematite-limonite,magnetite,zircon,leucoxene and anatase;show a similar composition of siderophile,large-ion-lithophile,and high field-strength elements with those of the UCC,and a similarity for large-ion-lithophile elements and most high field-strength elements with those of NASC;plot towards the felsic end members in the Th/Co vs. Cr/Th plot;and bear a different distribution pattern in comparison with the modern Changjiang sediments in the Chondrile-and NASC-normalized rare-earth elements diagram. (2)The sediments of the nearshore shallow sea(U2) and modern estuary(U1) are featured by a heavy-mineral assemblage of epidote,pyroxenite,hornblendite,garnet,sphere,rutile and tourmaline;show a similar composition of siderophile elements,and depleted large-ion-lithophile and high field-strength elements compared to the UCC,and a depleted composition of siderophile,high field-strength and large-ion-lithophile elements in comparison with the NASC;plot between the Changjiang River and Qiantang River end members in the Th/Co vs. Cr/Th plot;and resemble the distribution patterns of the modern Changjiang sediments in the Chondrile-and NASC-normalized rare-earth elements diagrams. (3)The deposits of the U5,U4 and U3 units bear a different provenance with those of the U2 and U1 units, with the former derived from the intermediate-felsic source rocks,i.e. from the Qiantang River drainage area,whereas,the latter mostly originated from intermediate-mafic source rocks,namely from the Changjiang catchment,and secondly from the Qiantang River drainage. The Changjiang-derived sediments began to significantly provide sediments for the evolution of the late Quaternary Qiantang River incised-valley fill since the formation of the nearshore shallow sea(U2).

The present paper reported the integrated study on the sedimentology,stratigraphy,chronology,micropaleontology of four boreholes with high core recovery located on the piedmont zone of Yanshan Mountain in northern Tianjin. The inclination curve consisting of 420 hot demagnetizm samples from Borehole Z3 (unconsolidated deposits with 147 m thickness) indicated that the lower strata belong to the Matuyama polarity chron—dated at 2.58 Ma. Following the crustal subsidence,just from Early Pleistocene the mud sediments of alluvial fan fringe started packing the sediment space above the basal conglomerate layer in studied area,and fluvial plain formed in the generalized piedmont basin. Bright yellowish brown-yellow orange-bright reddish brown clay was continuously developed during middle Early Pleistocene. The regional subsidence center situated at the site from the piedmont fault less than 4 km at that time. The Brunhes polarity zone—dated 0.78 Ma is 57.8 m thick. On the basis of the fact that the bottom of Late Pleistocene had determined prudently based on the Blake subchron—dated 120 ka at Borehole Z3,it can be found that a larger part of Middle Pleistocene series absented. This feature is very like to the stratal hiatus found on the Cangxian Uplift in Tianjin area and in the south part of the Yongdinghe River fluvial plain in Beijing at the same time. A total of 7 ¹⁴C dating collecting from three boreholes confirmed that the thickest stratum since 45 ka has 40.7 m occurred at the borehole from the piedmont fault less than 2 km. It represents that under the tectonic fault effect since the initial period of MIS(Marine Isotope Stage)3,the subsidence center northward migrated to toe of the piedmont fault,a new narrow sense piedmont basin formed. In the study area, the earliest 15 ka organic-clay and overlaying peat occurred, suggesting that the warming since Last Deglacial stage had affected the piedmont area in the North China Plain firstly. The present study provided a datum mark for study on subsidence of west coastal plain of Bohai Bay in the source-to-sink processes since Late Cenozoic.

The conventional data acquisition methods of outcrop knowledge database have many limitations. The unmanned aerial vehicle(UAV)oblique photography,however,has many advantages including agility,global perspective and high quantificational degree,and therefore was used in this study to collect,process,and interpret the outcrop data of Pingtouxiang section in Lüliang City Shanxi Province. By establishing an outcrop geological knowledge database,a 3D outcrop geological model was developed. Main findings of this study were summarized as follows. (1)The data model developed after UAV oblique photography acquisition and processing has 3D coordinates(latitude,longitude,altitude),and contains corresponding image information. This allows the coordinates of any position to be accurately determined,providing a solid foundation to develop a precise geological knowledge database. (2)The architecture and geostatistical parameters of the outcrop reservoir were statistically analyzed,and a typical geological knowledge database of the outcrop area was developed. Main parameters in the database include formation mechanisms of reservoirs,the continuity,dimension,number,proportion,geometry,and variations of sand bodies,etc.;(3)According to the setting of virtual well location,lithology calibration,and reservoir geological knowledge database,a typical 3D stratigraphic-structural model and two sets of lithological models in the outcrop areas were developed using the geostatistical variogram function.