Geological characteristics of the southern segment of the Late Sinian–Early Cambrian Deyang-Anyue rift trough in Sichuan Basin, SW China

Based on the latest drilling, seismic and field outcrop data, the geological characteristics(e.g. strata, development and sedimentary evolution) of the southern segment of the Late Sinian–Early Cambrian Deyang–Anyue rift trough in the Sichuan Basin are analyzed. First, the strata in the southern segment are complete. The first to second members of Dengying Formation(Deng 1 + Deng 2) are found with relatively stable thickness(400–550 m), and the third to fourth members(Deng 3+ Deng 4) show great thickness difference between the marginal trough and the inner trough, which is up to 250 m. The Cambrian Maidiping Formation and Qiongzhusi Formation in southern Sichuan Basin are relatively thin, with the thickness changing greatly and frequently. Second, the Deyang–Anyue rift trough extended southward during the Deng 4 period, affecting southern Sichuan Basin. Compared to the middle and northern segments of the rift trough, the southern segment is generally wide, gentle and shallow, with multiple steps, and alternating uplifts and sags, which are distributed in finger shape. Third, the Deng 1 + Deng 2 in southern Sichuan Basin records the dominance of carbonate platform and unobvious sedimentary differentiation, and the Deng 4 exhibits obvious sedimentary differentiation, namely, basin–slope–secondary slope–slope–secondary slope–platform margin–restricted platform, from the inner trough to the marginal trough. Fourth, the rift trough in southern Sichuan Basin has evolved in four stages: stabilization of Deng 1–Deng 2, initialization of Deng 3–Deng 4, filling of Maidiping–Qiongzhusi, and extinction of Canglangpu Formation.

Types and Characteristics of Volcanostratigraphic Boundaries and Their Oil-Gas Reservoir Significance

Just like in sedimentary stratigraphy, the factor for constructing volcanostratigraphic volcanostratigraphic boundary is an important framework. The fundamental factor of volcanostratigraphic boundaries is to classify the types and define their characteristics. Based on field investigation and cross-wells section analysis of Mesozoic volcanostratigraphy in NE China, 5 types of volcanostratigraphic boundaries have been recognized, namely eruptive conformity boundary （ECB）, eruptive unconformity boundary （EUB）, eruptive interval unconformity boundary （EIUB）, tectonic unconformity boundary （TUB） and intrusive contacts boundary （ICB）. Except ICB, the unconformity boundaries can be divided into angular unconformity and paraconformity. The time spans and signs of these boundaries are analyzed by using age data of some volcanic fields that have been published. The time spans of ECB and EUB are from several minutes to years. In lava flows, cooling crust is distributed above and below ECB and EUB; in pyroclastic flows, airfalls and lahars, a fine layer below these boundaries has no discernable erosion at every part of the boundary. EUB may be curved or cross curved and jagged. The scale of ECB/EUB is dependent on the scale of lava flow or pyroclastic flows. The time span of EIUB is from decades to thousands of years. There is also weathered crust under EIUB and sedimentary rock beds overlie EIUB. In most instances, weathered crust and thin sedimentary beds are associated with each other laterally. The boundary is a smooth curved plane. The scale of EIUB is dependent on the scale of the volcano or volcano groups. The characteristics of TUB are similar to EIUB＇s. The time interval of TUB is from tens of thousands to millions of years. The scale of TUB depends on the scale of the basin or volcanic field. Both the lab data and logging data of wells in the Songliao Basin reveal that the porosity is greatly related to the boundaries in the lava flows. There is a high-porosity belt below ECB, EUB or EIUB, and the porosity decreases when it is apart from the boundary. The high-porosity belt below ECB and EUB is mainly contributed by primary porosity, such as vesicles. The high-porosity belt below EIUB is mainly contributed by primary and secondary porosity, such as association of vesicles and spongy pores, so the area near the boundary in lava flows is a very important target for reservoirs.

Geological and Geochemical Characteristics and Exploration Prospect of Coal-Derived Tight Sandstone Gas in China： Case Study of the Ordos, Sichuan, and Tarim Basins

This work extensively investigated global tight sandstone gas, and geologically and geochemically analyzed the tight sandstone gas in China＇s Ordos, Sichuan, and Tarim basins. We compared typical tight sandstone gas in China with that in North America. We proposed six conditions for the formation of China＇s tight sandstone gas, and illustrated the geological characteristics of tight sandstone gas. In China, gas-bearing tight sandstones were mainly deposited in continental lake deltas and marine-terrigenous facies basin environments, associated with coal-measure strata, and were mostly buried deeper than 2000 in under a formation pressure of 20-30 MPa, with pressure coefficients varying from overpressure to negative pressure. In other countries, tight gas bearing sandstones were dominantly deposited in marine to marine-terrigenous facies environments, occurred in coal-measure strata, and were mostly buried shallower than 2000 m in low-pressure systems. We systematically analyzed tight sandstone gas in the Ordos, Sichuan, and Tarim basins in terms of chemical compositions, geochemical characteristics of carbon isotopes, origins, and sources. Tight sandstone gas in China usually has a hydrocarbon content of 〉95%, with CH4 content 〉90%, and a generally higher dry coefficient. In the three above-mentioned large tight sandstone gas regions,δ13C1 and δJ3C2 mainly ranges from -42%o to -28%o and from -28%o to -21%o, respectively. Type III coal-measure source rocks that closely coexist with tight reservoirs are developed extensively in these gas regions. The organic petrology of source rocks and the carbon isotope compositions of gas indicate that tight sandstone gas in China is dominantly coal-derived gas generated by coal-measure strata. Our analysis of carbon isotope series shows that local isotope reversals are mainly caused by the mixing of gases of different maturities and that were generated at different stages. With increasing maturity, the reversal tendency becomes more apparent. Moreover, natural gas with medium-low maturity （e.g., Xujiahe Formation natural gas in the Sichuan Basin） presents an apparent reversal at a low-maturity stage, a normal series at a medium -maturity stage, and a reversal tendency again at a high-maturity stage. Finally, we proposed four conditions for preferred tight sandstone gas ＂sweep spots,＂ and illustrated the recoverable reserves, proven reserves, production, and exploration prospects of tight sandstone gas. The geological and geochemical characteristics, origins, sources, and exploration potential of tight sandstone gas in China from our research will be instructive for the future evaluation, prediction, and exploration of tight sandstone gas in China and abroad.

Geological characteristics and accumulation mechanisms of the "continuous" tight gas reservoirs of the Xu2 Member in the middle-south transition region,Sichuan Basin,China

＂Continuous＂ tight gas reservoirs are those reservoirs which develop in widespread tight sandstones with a continuous distribution of natural gas. In this paper, we summarize the geological features of the source rocks and ＂＇continuous＂ tight gas reservoirs in the Xujiahe Formation of the middle- south transition region, Sichuan Basin. The source rocks of the Xul Member and reservoir rocks of the Xu2 Member are thick （Xul Member： 40 m, Xu2 Member： 120 m） and are distributed continuously in this study area. The results of drilled wells show that the widespread sandstone reservoirs of the Xu2 Member are charged with natural gas. Therefore, the natural gas reservoirs of the Xu2 Member in the middle-south transition region are ＂continuous＂ tight gas reservoirs. The accumulation of ＂continuous＂ tight gas reservoirs is controlled by an adequate driving force of the pressure differences between source rocks and reservoirs, which is demonstrated by a ＂one-dimensional＂ physical simulation experiment. In this simulation, the natural gas of＂continuous＂ tight gas reservoirs moves tbrward with no preferential petroleum migration pathways （PPMP）, and the natural gas saturation of＂continuous＂ tight gas reservoirs is higher than that of conventional reservoirs.

Tectonic Evolution and Geological Characteristics of Hydrocarbon Reservoirs in Marine Mesozoic-Paleozoic Strata in the South Yellow Sea Basin

The South Yellow Sea Basin is the main body of the lower Yangtze area in which marine Mesozoic–Paleozoic strata are widely distributed.The latest geophysical data were used to overcome the limitation of previous poor-quality deep data.Meanwhile,the geological characteristics of hydrocarbon reservoirs in the marine Mesozoic–Paleozoic strata in the South Yellow Sea Basin were analyzed by comparing the source rocks and the reservoir and utilizing drilling and outcrop data.It is believed that the South Yellow Sea Basin roughly underwent six evolutionary stages:plate spreading,plate convergence,stable platform development,foreland basin development,faulted basin development,and depression basin development.The South Yellow Sea Basin has characteristics of a composite platform-fault depression geological structure,with a half-graben geological structure and with a ‘sandwich structure' in the vertical direction.Four sets of hydrocarbon source rocks developed – the upper Permian Longtan–Dalong formation,the lower Permian Qixia formation,the lower Silurian Gaojiabian formation,and the lower Cambrian Hetang formation/Mufushan formation,giving the South Yellow Sea Basin relatively good hydrocarbon potential.The carbonate is the main reservoir rock type in the South Yellow Sea area,and there are four carbonate reservoir types:porous dolomitic,reef-bank,weathered crust,and fractured.There are reservoir-forming horizons similar to the typical hydrocarbon reservoirs in the Yangtze land area developed in the South Yellow Sea,and there are three sets of complete source-reservoir-cap rock assemblages developed in the marine strata,with very good hydrocarbon potential.

Geologic Characteristics of Volcanic Hydrocarbon Reservoirs and Exploration Directions in China

Volcanic rocks are distributed widely in China, which are important exploration targets. By analyzing many discovered volcanic hydrocarbon reservoirs all over the world, the authors summarized the geologic characteristics of the formation of volcanic hydrocarbon reservoirs in China, and gave further exploration directions and advices. （1） There are mainly Carboniferous-Permian, Jurassic-Cretaceous, Paleogene-Neogene volcanic rocks in oil- and gas-bearing basins in China, which are mainly distributed in the Junggar Basin, Songliao Basin, Bohai Bay Basin, etc. There are mainly intermediate rocks and acidic rocks in east China, and intermediate rocks and basic rocks in west China. They primarily develop in intracontinentai rift settings and island arc environments. （2） Porefissure reservoirs are distributed widely in basins, which are volcanic rocks mainly in explosive and effusive facies. （3） Volcanic hydrocarbon reservoirs are chiefly near-source lithostratigraphic hydrocarbon reservoirs, and the oil and gas accumulation is predominantly controlled by lithotypes, faults and structural positions. （4） Deep-seated oil and gas reservoirs in the Songliao Basin and Carboniferous volcanic hydrocarbon reservoirs in the Junggar Basin are potential giant volcanic gas provinces, the volcanic hydrocarbon reservoirs in the Bohai Bay Basin and Santanghu Basin are favorable for oil and gas reserves increase, and volcanic rocks in the Turpan Basin, Sichuan Basin, Tarim Basin have exploration potentiality. （5） The technology series of oil and gas exploration in volcanic rocks have been preliminarily formed.

Prediction of geological characteristics from shield operational parameters by integrating grid search and K-fold cross validation into stacking classification algorithm

This study presents a framework for predicting geological characteristics based on integrating a stacking classification algorithm(SCA) with a grid search(GS) and K-fold cross validation(K-CV). The SCA includes two learner layers: a primary learner’s layer and meta-classifier layer. The accuracy of the SCA can be improved by using the GS and K-CV. The GS was developed to match the hyper-parameters and optimise complicated problems. The K-CV is commonly applied to changing the validation set in a training set. In general, a GS is usually combined with K-CV to produce a corresponding evaluation index and select the best hyper-parameters. The torque penetration index(TPI) and field penetration index(FPI) are proposed based on shield parameters to express the geological characteristics. The elbow method(EM) and silhouette coefficient(Si) are employed to determine the types of geological characteristics(K) in a Kmeans++ algorithm. A case study on mixed ground in Guangzhou is adopted to validate the applicability of the developed model. The results show that with the developed framework, the four selected parameters, i.e. thrust, advance rate, cutterhead rotation speed and cutterhead torque, can be used to effectively predict the corresponding geological characteristics.

Geology and mineralization of the Dayin’gezhuang supergiant gold deposit(180 t)in the Jiaodong Peninsula,China:A review

The Dayin’gezhuang gold deposit is located in the central part of the Zhaoping Fault metallogenic belt in the Jiaodong gold province-the world’s third-largest gold metallogenic area.It is a typical successful case of prospecting at a depth of 500-2000 m in recent years,with cumulative proven gold resources exceeding 180 t.The main orebodies(No.1 and No.2 orebody)generally have a pitch direction of NNE and a plunge direction of NEE.As the ore-controlling fault,the Zhaoping Fault is a shovel-shaped stepped fault,with its dip angle presenting stepped high-to-low transitions at the elevation of -2000-0 m.The gold mineralization enrichment area is mainly distributed in the step parts where the fault plane changes from steeply to gently,forming a stepped metallogenic pattern from shallow to deep.It can be concluded from previous studies that the gold mineralization of the Dayin’gezhuang gold deposit occurred at about 120 Ma.The ore-forming fluids were H_(2)O-CO_(2)-NaCl-type hydrothermal solutions with a medium-low temperature and medium-low salinity.The H-O isotopic characteristics indicate that the fluids in the early ore-forming stage were possibly magmatic water or mantle water and that meteoric water gradually entered the ore-forming fluids in the late ore-forming stage.The S and Pb isotopes indicate that the ore-forming materials mainly originate from the lower crust and contain a small quantity of mantle-derived components.The comprehensive analysis shows that the Dayin’gezhuang gold deposit was formed by thermal uplifting-extensional tectonism.The strong crust-mantle interactions,large-scale magmatism,and the material exchange arising from the transformation from adakitic granites to arc granites and from the ancient lower crust to the juvenile lower crust during the Early Cretaceous provided abundant fluids and material sources for mineralization.Moreover,the detachment faults formed by the rapid magmatic uplift and the extensional tectonism created favorable temperature and pressure conditions and space for fluid accumulation and gold precipitation and mineralization.

Geological and Geochemical Characteristics and Genesis of the Shaxi Porphyry Copper (Gold) Deposits, Anhui Province

The Shaxi porphyry copper (gold) deposits are a typical example of porphyry copper deposits associated with diorite in eastern China. Quartz diorite, which hosts the deposits, has a Rb-Sr isochron age of 127.9 ± 1.6 Ma. Geochemically, the rock is rich in alkalis (especially sodium), light rare earth elements (LREE) and large-ion lithophile elements (LILE), and has a relatively low initial strontium isotopic ratio (Isr=0.7058); thus it is the product of differentiation of crust-mantle mixing source magma. The model of alteration and mineralization zoning is similar to the Hollister (1974) diorite model. The ore fluids have a relatively high salinity and contain significant amounts of CO2, Ca2+, Na+ and ***CI?. The homogenization temperatures of fluid inclusions for the main mineralization stage range from 280 to 420°C, the δ18O values of the ore fluids vary from 3.51 to 5.52 %, the δD values are in the range between ?82.4 and ?59.8 %, the δ34S values of sulphides vary from ?0.3 to 2.49 %, and the δ13C values of CO2 in inclusions range between ?2.66 and ?6.53 %. Isotope data indicate that the hydrothermal ore fluids and ore substances of the Shaxi porphyry copper (gold) deposits were mainly derived from magmatic systems.

Geological and geochemical characteristics of Middle Jurassic granites in Bengbu uplift, Southeast of North China craton

1 Introduction The early formation and evolution of the North China craton has been widely concerned by scientists.The Bengbu uplift belt is located in the southeast of the craton,theresearch degree of the belt is relatively low and received increasing attention from many scholars in recent years.Through the author’s practical work and combined with

An overview of the geology and production of the Fuling shale gas field,Sichuan Basin,China

The Fuling shale gas field in China is the largest shale gas field as well as the largest of its type discovered in any Lower Paleozoic formation.In this study,the geology and production of the upper and lower gas layers in the Fuling shale gas field are evaluated in terms of structure,shale quality,fault,initial production,and estimated ultimate recovery(EUR).The shale in the lower gas layer of the Jiaoshiba anticline is a high-quality reservoir,where the space is dominated by organic pores in kerogen,and the gas content is high.The shale gas wells reveal relatively high initial production and EUR.However,the shale in the upper gas layer of the Jiaoshiba anticline has reservoir space mainly composed of clay mineral pores and organic pores within bitumen,and the gas content is low.In terms of structure,primary gas migration may occur in the upper gas layer,resulting in free gas accumulation in the structural high,where the development effects are generally better than those in the structural low.The lower gas layer in the Pingqiao anticline,is the main interval for shale gas accumulation and development due to the high-quality shale.Under the influence of faults,the efficiency of exploration wells emplaced on top of the anticline is much lower a compared with those in the flanks.The residual synclines close to the Sichuan Basin,including the Baima and Baitao anticlines,are characterized by more recent uplifts,larger area,greater distance from the deep and large faults,and early fracture closure.Therefore,we recommend that the shale gas exploration and development should be carried out preferentially in areas close to the center of the residual synclines,featuring relatively high-pressure coefficient and moderate burial depth.

Natural gas geology and exploration direction of the Cambrian Lower Canglangpu Member in central Sichuan paleo-uplift,Sichuan Basin,SW China

Based on drilling data of JT1 and CS1,outcrop profiles and seismic data,the sedimentary pattern,space configuration of source-reservoir-cap combinations and paleouplift evolution characteristics of the Cambrian Lower Canglangpu Member in the central Sichuan paleouplift have been investigated to determine the favorable exploration zones.Controlled by Deyang-Anyue rift,the Lower Canglangpu Member features differential characteristics from east to west in sedimentary framework.In the west side of the Deyang-Anyue rift,this member is composed of clastic sediments,while in the east side of the Deyang-Anyue rift,it is fresh water shelf sediments,with grain beaches occurring along edges of the depressions,shelf and lagoon.Among the beaches,the dolomitic ones are mainly distributed around the depression edge and in the north of the lagoon.The beach sediments could become high quality reservoirs under the effect of karstification.Underlying the Lower Canglangpu Member is the widespread source rock of the Qiongzhusi Formation,so oil and gas generated by the Qiongzhusi Formation source rock can directly charge into the beach reservoirs.The sandy mudstone of the Upper Canglangpu Member can serve as the caprock of the Lower Canglangpu Member reservoir.The dolomitic beaches are located at the higher part of the paleo-uplift during the main accumulation period,with good hydrocarbon accumulation elements.Blocks PT1-CS1,HT1-GT2 and east GT2 are favorable exploration zones.

Geological characteristics and genesis of subbottom pinnoite deposit of Da Qaidam salt lake in Qaidam Basin

Da Qaidam salt lake is known for its both liquid and solid boron resource.Data from previous investigation of the Da Qaidam salt lake provided a comparable framework for this study that focused on investigating the section beneath the bottom of the perennial salt lake,including the timing,

Geological characteristics and the origin of ore-forming materials of(Laozhaiwan gold deposit, Yunnan Province

"Golden triangle"area bordered on Yunnan-Guizhou-Guangxi was one of the most important Carlin-type gold deposits concentration areas.Deep understanding of Carlin-type gold deposits in Guizhou and Guangxi Province had reached through several decades studies,but geological environment was very complex in the southeastern Yunnan,and Carlin-type gold deposits produced in the southeastern Yunnan were different from that of America,few studies were taken there.Based on a large number of field work,studies on the geological characteristics combining with geochemistry characteristics were taken,and analysis the genesis of Laozhaiwan gold deposit.The types of alteration in Laozhaiwan gold deposit were mainly silicification and pyritization,and Gold grade was high when silicification and pyritization were both occurred.It could be caculated that fluid density(g/cm3)varied from 0.7 to 4.9,salinity varied from 0.76%to 0.95%and ore-forming pressure(Pa)varied from 1.81×105 to 49.96×105 according to fluid inclusion test results,showed that Laozhaiwan gold deposit was hypabyssal hydrothermal deposit in low temperature and low salinity.According to composition of fluid inclusion analysis,combining with H-O isotope,made theδD-δ18O figure,showed that the fluid of the deposit rooted in formation water and mixed with meteoric waters later.

Geological Characteristics and Its Metallogenesis of Daolundaba Copper Polymetallic Deposits,Inner Mongolia

1 Geology Daolundaba copper polymetallic deposit occurs in West Ujimqin Banner,the Xilin Gol League of Inner Mongolia,along the west side of South part of Daxinganling ore belt,whose tectonic position just lies at the junction of Siberian Block in the south part,North China Block in the north and Songliao block in the east.The Daolundaba copper polymetallic deposit is hosted by the Lower Proterozoic Baoyintu group of biotite-plagioclase gneiss(Pt1by),upper Permian Linxi formation of sandy slate(P2l),and the Hercynian Qianjinchang pluton of biotite granite.

Geological Characteristics of Potassium-Bearing Salt Layers in the Well Block Quele of the Kuqa Depression and their Significance

Potash is one of the long-term scare deposits in China,and potash prospecting has long been listed as a key brainstorm project for our nation and geological prospecting units.There have been considerable studies in search for potash deposits in the Kuqa depression of the Tarim basin(Jackson et al.,1991;Gemmer et al.,2004;Vendeville,2005;Vendeville and Jackson,1992a,1992b),

Geochemical characteristics and geological significance of picritic rocks in Permian Tiaohu Formation from Santanghu Basin, Xinjiang, NW China

1 Introduction Santanghu Basin is located between the Armantai and Karamaili suture zone,at the junction of the Siberia,Kazakhstan and Tarim plates(Chen and Jahn,2004;Xiao et al.,2008).As an important part of the Central Asian

Rock-forming mechanism of Qingshanjiao intrusion in Dongguashan copper(gold) deposit, Tongling area, Anhui province, China

Dongguashan deposit is a large porphyry-skarn copper（gold） deposit in Tongling ore district. The Qingshanjiao intermediate acid intrusion of Yanshanian had a direct genetic relationship with mineralization. The magma origin, rock-forming dynamic background and rock-forming process were studied, and the rock-forming mechanism of Qingshanjiao intrusion was discussed, based on geological characteristics, detailed observation of petrography and systematic investigation of petrochemistry, trace elements and REE geochemistry characteristics of Qingshanjiao intrusion. The results show that Qingshanjiao rock body belongs to high-K calc-alkaline series with higher LREE elements, Th, Rb and Sr abundance, but depleted in HREE elements, Ba, Nb and Ta. The primary magma originated from the mantle-crust mixtures which were caused by basaltic magma of mantle mixing with syenite magma of partial melting of the lower crust, and the formation environment of Qingshanjiao intrusion was emplaced in the transitional environment from compression to extension. The Harker diagram and hybrid structures of plagioclase and potassium feldspar indicate that the fractional crystallization occurred in the process of magmatic evolution. The petrochemistry, trace elements and REE geochemistry characteristics indicate that the magma was contaminated by crustal material during the rock-forming. These results suggested that the Qingshanjiao intrusion was formed by fractional crystallization and assimilation and hybridization of mantle-crust magma in the transitional environment from compression to extensional.