The beach-bar deposits,which is a general term of the beach and bar,is an important kind of facies and petroleum reservoir developed in the nearshore zone. Most of the foreign researches on beach-bar deposits are focused on the interpretation of their formation mechanisms via geology investigation of modern deposits and field outcrops;while Chinese sedimentologists and petroleum geologists have focused on their sedimentary characteristics and petroleum significances,especially those formed in lake environments. In this paper,we reviewed and refined the advances in beach-bar researches. Firstly,we summarized the origin of beach-bars,and then followed by their classification,depositional model,controlling factors,and the palaeogeography and petroleum significances. We propose that the beach-bar is formed in the system combined of wind(wind wave),provenance and basin(basinal evolution), i.e.,waves are the original power of beach-bar formation,while the provenance provides the material base,and the evolution of tectonic and sequence of the basin determines the position and extent of beach-bars. Study on controlling factors of beach-bar formation could provide powerful supports in prospecting the distribution position of beach-bar sandbodies vertically and horizontally,which is of great significance in petroleum reservoir exploration. Ancient beach-bar deposits recorded the palaeogeographic conditions during their formation. Especially,palaeo-wave conditions could be quantitatively recovered based on sedimentology analyses on beach-bar deposits,and in turn,the palaeo-atmospheric flow field. This plays an important,promotive and supplemental role in the study area of palaeoclimatic recovery.

Based on the discovery of the karst differentiations of several carbonate layers with different lithofacies in Sichuan Basin,present research advance of eogenetic karstification abroad is collected and collated in this paper.(1)The karst host rocks can be divided into two types,namely eogenetic rock with high porosity-permeability and telogenetic rock with low porosity-permeability or with even totally compacted. The two type rocks mainly use the intergranular pores and the fracture for karst water transferring,respectively,and accordingly the so-called unconfined conduit and confined conduit develop. The whole process dominates the karst morphology of carbonate rocks during different diagenetic periods. It can be concluded that the porosity and permeability of carbonate rocks in different diagenetic periods control the development model of karst fissure and cave.(2)More attention should be given to the impact on the karstification by the geographical settings. The karstification type can be divided into island- and coastal-typed and continental typed. The former is mainly related to chemical dissolution associated with meteoroic lens,developing flank margin caves which can be regarded as identification marks for island- and coastal-typed karst,but with minor influence on the whole. The latter,on the contrast,mechanically interacts with underground and surface water,with mass underground river deposition and large influence on the range and depth.(3)We follow with interest of the related latest achievements for eogenetic karst investigation,such as the macro- and micro-characteristics,identification marks,and dissolution mechanism of eogenetic karstification,which poorly reported domestically. Finally,for multiple carbonate layers found in Paleozoic are pervasively featured by likely eogenetic karst in Sichuan Basin,it analyzes and concludes the development and distribution characteristics of eogenetic karst reservoir. The results may offer reference for the discovery,recognition for the similar karst,and also the exploration of related reservoir in future.

By use of drilling, logging,core,and thin section data,the karst characteristics of carbonate rocks of the Middle Permian Maokou Formation in southern Sichuan Basin are studied. Maokou Formation,a deposition of open-sea platform,is characterized by the interbedding of grainstone of bank facies and micrite limestone of non-bank facies with unequal thickness. The karst is mainly developed at the upper part of Maokou Formation,with a large amount of dissolved fissures and caves overwhelmingly filled by substances from various sources including dissociated carbonate fragments,calcite crystals and carbonous clays,and no sign of karst breccia. The karstification belongs to eogenetic karst in palaeo-continental settings,which is significantly featured by the dissolution-filling controlled by its lithology and lithofacies:Micrite limestone within non-bank facies is compact,and shows little sign of dissolution-filling,while grainstone within bank facies is characterized by good karst development,and three zones of dissolution-filling can be recognized including matrix,half-dissociated and mixed-filling zones. Based on the above characteristics,it is suggested that high porosity-permeability layers of grainstone and compact ones of micrite limestone were multi-cycle superimposed vertically,and primary porosity-permeability system accompanied by faults and fissures provided sufficient channels for karst water,which resulted in the whole karst system featured by contemporaneous mult￣layer and grain￣bank facies controlled. The karst reservoir, therefore,favored to develop in both karst platform and karst slope. The research result will not only provide supplement and reference for the existing studies of the subject,but also is of meaning to the oil and gas exploration of Maokou Formation.

Whether there exists exposed erosion near the top of non-reef facies strata of the Upper Permian Changxing Formation in eastern Sichuan Basin has not been reported. In this paper,we take the non-reef strata at the top of Changxing Formation at Fuling area in eastern Sichuan Basin as an example,comprehensively studying the macro- and micro-features,mineralogical and geochemical elements characteristics. The result shows that there exists a weathering crust at the top of Changxing Formation. The weathering crust is 3-7cm thick and shows very clear vertical zonation, i.e.,from bottom to top,it is divided into four zones:the bedrock(micritic bioclastic limestone),saprolite layer,partially￣weathered layer which is characterized by enrichment of Si and decalcification,completely weathering layer which are characterized by enrichment of Fe.Since almost all the clay minerals available are illites, secondary minerals such as kaolinites and gibbsites of strong weathering stages have not yet been found, and iron oxide minerals are concentrated, it reflects an overall moderate weathering stage,corresponding to the ferromanganese-rich phase of weathering crust evolution stages. Further analysis reveales the presence of abundant typical Permian macroscopic fossils buried in situ,such as corals,brachiopods(Oldhamina),bryozoans and trilobites, etc., in the 80cm thick interbed of shale and limestone at the bottom of Feixianguan Formation which directly overlies the weathering crust,indicating that the study area uplifted and exposed during the Late Permian. At the same time,outcrops and cores in the study area exhibit plenty of karst fabrics such as solution grooves and karst caves, which are filled by mixture of porous carbonate sands,breccias,bauxitic mudstones and carbonaceous mudstones,indicating that the non-reef facies strata are modified by supergene karstification. The regressive event in the Late Permian was not only of seawater shallowing,but may lead to the long-term exposure of platform area,which modified reefs and beach reservoirs, and even the non-reef facies strata of the Changxing Formation by supergene karstification. This result is not only a reference for the study of the Late Permian eustatic events,but also points out that non-reef facies modified by supergene karstification inside platforms may also be a favorable exploration zone,thus exhibits important practical significance for exploration.

Based on integrated application of drilling,logging and seismic data,the types of sedimentary facies and their distribution in Da'anzhai Member in Longgang area were studied. The lacustrine sediments of Da'anzhai Member were divided into 4 subfacies and several microfacies. Sedimentary distribution and evolution in the study area were mainly affected by lake-level fluctuation during the Da'anzhai period,experiencing a large-scale water transgression and regression. During the period of the third submember of Da'anzhai,water transgression occurred,the deposits were mainly shallow and semi-deep lacustrine. During the period of the first-third submember of Da'anzhai,the water was the deepest,the deposits were mainly of semi-deep lacustrine. Then,water regression occurred,lake-level dropped to a very low stand,the deposits were mainly shore-shallow lacustrine. Sedimentary facies distributed obviously in a ring shape on the plane,whereby the sedimentary facies model of Da'anzhai Member were established. There were mainly five shelly shoals in the first submember of Da'anzhai,which were the most conducive to the formation of reservoirs. The main types of reservoir rocks were shelly limestone and argillaceous shelly limestone. Combined with fracture analysis,three favorable reservoir zones were predicted.

The Upper Jurassic Penglaizhen Formation in Chuanxi Depression is a set of flood-overlake deposits at low angular ground,under arid climatic condition and with lake level frequently fluctuating. Based on high-resolution sequence stratigraphy,we analyzed the sedimentary characteristics of flood-overlake deposits by integrating outcrop,core,experiments and drilling data, summarized its vertical stacking as well as horizontal distribution patterns,and the sand-body superposed patterns of flood-ouerlake were constructed. (1)Distributary channels and beach bars constitute the main facies types in the study area;(2)Distributary channels stretched vertical to the lake shoreline,while beach bars developed along the lake shoreline,with the formers constantly cutting through phases of the latters from alternating destruction and sedimentation by wave erosion and debris progradation into the lake,during development of high-frequency sequences;(3)Four types of sandbody superimposed patterns of different origins were classified,namely same time same facies autogenic type,same time different facies autogenic type,different time same facies allogenic type and different time different facies allogenic type.

This paper systematically studied the characteristics of oolitic limestone of the Cambrian Xuzhuang Formation at Xiaweidian outcrop in Western Hills of Beijing. Core-beard and core-missed concentric-radial ooids,monocrystalline/polycrystalline ooids,micritic ooids and compound ooids have been found in this study. At the same time,we also found some special textures,such as dark-colored cortices,compounded granules and pyrite agglomerates. Dark-colored cortices are found for the first time,which are probably the remains of filamentous cyanobacteria bodies. Compounded granules,which may represent the oxygen-containing bubbles in microbial mats,are composed of crystals of calcite or dolomite. An attachment is found on the surface of a bioclast and ooid-like particles are found inside the attachment. Compounded ooids,which are loosely compacted and lack of outside cortices,may indicate that they are generated in a relatively quiet shallow water environment. Our research shows that ooids in the Xuzhuang Formation were probably generated in a quiet shallow water environment and microbes played a key role in this process.

Weihe Basin is a Cenozoic basin,located in the transitional area of the southern margin of the Ordos block and the Qinling orogenic belt. The Paleogene-Neogene successions are of several kilometers in thickness,and of various sedimentary types. Based on drilling data and fieldwork observation and measurement,the stratigraphy,sedimentology and lithofacies palaeogeography of the Weihe Basin were studied. The stratigraphic units of the Cenozoic in Weihe Basin were redefined. According to the sedimentary characteristics,five depositional types were distinguished in Weihe Basin, i.e.,alluvial fan,fluvial,lacustrine,deltaic and eolian deposits. The results suggest that:Due to fault,subsidence and filling during the depositional process,the basin is extremely dissymmetric in profile and has the depocenter locating southerly. The basin is narrower in the west and wider in the east. Alluvial fan is predominant in the marginal area,which gradually transforms into the delta and then the lake towards the center. The Weihe Basin began to deposit since the Eocene. It was uplifted and had a hiatus during the Late Oligocene. During the Miocene,it restarted to deposit in the Lengshuigou Age;as the distribution range of water body gradually expanded,it widely developed lakes in the Koujiacun Age,and reached the maximum sedimentation area up to the Bahe Age. During the Pliocene Youhe Age,it formed two major depositional depressions within the basin,i.e.,the Xi'an Depression and the Gushi Depression; meantime,the eolian deposits firstly appeared at the basin margin. During the Quaternary,the western region of the basin was uplifted,and the distribution range of lakes gradually shrinked. From the Middle Pleistocene to the Holocene,the lakes shrinked into small sags locally.

Combined with regional tectonic setting,this study identifies typical seismites of the Upper Triassic Yanchang Formation in Fuxian exploration area of Ordos Basin through observation of cores from 26 drillholes. In the study area,representative sedimentary structures include liquefied sand-veins,liquefied curled deformation structures,loop beddings,load structures,ball-and-pillows,pillows,micro-faults,micro-fissures,and shatter breccias. Among these,liquefied sand-veins and liquefied curled deformation structures are the major earthquake-induced soft sediment deformation structures. The vertical successions of seismites are classified into two types:One is dominated by brittle deformations underlying and overlying unshocked layers,and consists of disturbed bedding layer,layer of step micro-fault,micro-fissure and seismic breccias,liquefied curled deformation layer,layer of shatter breccias,and liquefied sand-veins layer,respectively,from bottom to top;the other is dominated by soft-sediment deformations,which also underlies and overlies unshocked layers,and is divided into loop bedding layer,disturbed bedding layer,layer of ball-and-pillow and load structure,liquefied sand-veins and liquefied curled deformation layer,and pillow layer,respectively,from bottom to top. The seismites in the Yanchang Formation of Fuxian exploration area prove that there existed a competent structure and active periods of palaeotectonic movement;the presence of micro-faults,micro-fissures,shatter breccias and liquefied sand-veins is conductive to the improvement of reservoir physical property;furthermore,the seismic breccias and reticulate sand-veins are both good reservoirs.

On the basis of core observation,logging data,heavy mineral analysis and seismic data,the provenance direction,sedimentary facies and models of the Xishanyao Formation in Malang Depression of the Santanghu Basin have been reseached. The research suggests that there are braided river delta facies and lacustrine facies. In the early sedimentary time of the Xishanyao Formation,the braided river delta widely distributed in the north of the lake. The underwater distributary channel sandbodies and the mouth bar sandbodies,distributing in the braided river delta front,are the main reservoir. In the late sedimentary time of Xishanyao Formation,the lacustrine facies was the main facies type in Malang Depression.The small-scale braided river delta and the beach bar also distributed in this period. There is a transgression process in the Xishanyao Formation period. According to the test analysis data,the lithic sandstone and the feldspathic lithic sandstone are the main sandstone types in the Xishanyao Formation. The cementation of sandstone is not strong. The compaction is the main factor of decreasing porosity. The intergranular dissolution pore and the residual intergranular pore are the main effective reservoir space. The reservior quality is greatly influenced by sedimentary microfacies. The sandstone of the Xishanyao Formation belongs to low porosity and low permeability reservoir,and it is the effective oil and gas reservoir.

Jianghan Basin is a typical saline lacustrine basin during the Mesozoic-Cenozoic in the eastern China. Recently,a tight oil reservoir has been found in the Xingouzui Formation of Xingou Oilfield in Jianghan Basin,and the lithology of the reservoir is dolostone and siltstone associated with salt rhythms. Based on core observation,the data of logging and all kinds of test,we have researched the characteristics of the salt rhythms and its geological significance. The scale of the salt rhythms can be divided into different levels according to the types of salts,the structure and thickness of profile. The profile characteristics of each level and their formation mechanism are analyzed. And the geological significance of salt rhythms from the perspective of palaeoclimate and oil and gas is investigated. Salt rhythms are a direct response to the lake-level variation. The wide development of eury-thermal saline minerals such as calcite and dolomite,indicates that the palaeoclimate was arid to semi-arid in Jianghan Basin during the deposition of Xingouzui Formation in Paleogene. A complete salt rhythm can form a source-reservoir-seal assemblage,which has an important meaning for hydrocarbon generation, accumulation and preservation.

In 1990s,Lehrmann et al. called the Early Triassic isolated “Luodian Carbonate Platform”in the Luodian area of southern Guizhou Province in South China as the “Great Bank of Guizhou”. This term “Great Bank of Guizhou”was cited in more than 300 articles in foreign countries. The authors of this paper have studied the lithofacies palaeogeography of the Early and Middle Triassic in South China. According to the geological data of us,in the Early Triassic and in the Luodian area of southern Guizhou Province,there was only an isolated “Luodian Carbonate Platform”,but there was no “Great Bank of Guizhou”. The isolated “Luodian Carbonate platform”should not be called as the “Great Bank of Guizhou”.This paper is a detailed abstract of the English article There was no “Great Bank of Guizhou”in the Early Triassic in Guizhou Province,South China(Journal of Palaeogeoraphy(English Edition),2015,4(1)). The aim of this paper is to let Chinese readers understand that the term “Great Bank of Guizhou”did not match the reality seriously and should not be used any more.