Depositional System of the Carboniferous Huanglong Formation,Eastern Sichuan Basin:Constraints from Sedimentology and Geochemistry

Using analyses of the lithology,sequences,paleoenvironment,and tectonic setting,the depositional system of the Carboniferous Huanglong Formation in the eastern Sichuan Basin was identified.The lithological characteristics of the Lower Member,Middle Member,and Upper Member were analyzed and classified.Before the use of carbon,oxygen,and strontium isotopes in the analysis,all of the geochemical data were tested for validity.On the basis of the Z values obtained from carbon and oxygen isotopes,the paleoenvironments of the three members were elucidated.Lower Member was dominantly an enclosed marine environment with intense evaporation and little freshwater input into the sea.Middle Member developed in a semi-enclosed to normal marine environment with many rivers.Upper Member was formed in a normal marine environment.The east Sichuan Basin was enclosed by paleouplifts before the deposition of the Huanglong Formation,forming a relatively enclosed depositional setting.Paleogullies developed in the Silurian strata that underlie the Carboniferous rocks;these paleogullies can be identified.On the basis of a comprehensive analysis,we propose that the Huanglong Formation developed in a platform system.Four microfacies were identified：supratidal flat,dolostone flat,grain shoal,and shelf microfacies.The high-permeability and high-porosity characteristics of the grain shoal microfacies are favorable for hydrocarbon accumulation,while the supratidal flat and shelf microfacies developed very few high-quality reservoirs.The paleogullies,in which increased amounts of grain shoal microfacies developed,controlled the distribution of high-quality reservoirs.

Geochemical characteristics and diagenetic fluids of dolomite reservoirs in the Huanglong Formation, Eastern Sichuan Basin, China

Based on a comprehensive study of texture,diagenetic behavior and evolution of dolomite in the Huanglong Formation,trace （e.g.,Fe,Mn and Sr） and rare earth element （REE） geochemistry,andisotopic characteristics （e.g.,C,O and Sr）,four types of diagenetic fluids are identified in the Huanglong Formation dolomite reservoirs of the Eastern Sichuan Basin,China：1）：marine-derived pore waters in the marine diagenetic environment,2） sabkha compaction brine conserved in the early shallowburied diagenetic environment,3） strongly-oxidizing low-temperature meteoric water in the seepagesubsurface flow diagenetic environment,and 4） strongly reducing deeply seated mixed hot brine in the middle and deep burial diagenetic environment.The fluids developed hereditarily from one environment to another,which resulted in its respective characteristics.Fluid characteristics play an important role in the development of dolomite reservoirs：1） dolomitization by marine-derived pore water in the quasisyngenetic stage did not form an effective reservoir; 2） early diagenetic burial dolomitization by the sabkha compaction brine formed the basis for reservoir development; 3） meteoric water karstification in the paleo-epidiagenetic stage expanded both the distribution and the size of the reservoirs,and improved the reservoir quality; 4） deep-burial dissolution and tectonic fracturing in the reburial diagenetic stage further improved reservoir porosity and permeability.

The Lowest Boundary Age of Travertine in Dawanzhangjia Ravine, Huanglong, China

Objective One of major challenges in paleoenvironmental reconstruction using travertine in the Huanglong area is whether one can accurately determinate the age of travertine through high-precision and high-resolution dating techniques. Previous works of 14C or ESR chronology, however, have shown that the variation of deposition ages of travertine was displayed inconsistent with each other even conflict. For instance, （1） The oldest travertine age （80 ka） located in the middle of this travertine succession is departure from sequential deposition; （2） Top or boundary ages in this sedimentary section, even with the same dating method （14C）, are three times errors, moreover, the age of the depositional sequence is not continuous. We report here the U230Th ages in lowest boundary of travertine in Dawanzhangjia Valley, Huanglong, China, to discuss the effectiveness of U-series dating for cold-water travertine and the significance of age for vicissitude of paleoenvironment.

Correlation between the tilt anomaly on the vertical pendulum at the Songpan station and the 2021 MS7.4 Maduo earthquake in Qinghai province,China

Understanding the relationship between precursory deformation anomalies and strong earthquakes is vital for physical earthquake prediction. Six months before the 2021 MS7.4 Maduo earthquake in Qinghai province, China, the vertical pendulum at the Songpan station was observed to tilt southward with a high rate and large amplitude. Studies conducted before the 2021 MS7.4 Maduo earthquake inferred the tilt anomaly to be an earthquake precursor. However, after the earthquake, the relation between the earthquake and the anomaly became controversial, partly because the Songpan station is located at a great distance from the epicenter. In this study, based on the deformation anomaly characteristics, relationship between the seismogenic fault and the fault near the anomaly, and associated quantitative analyses, we concluded that this anomaly may be associated with the 2021 MS7.4 Maduo earthquake. The duration and amplitude of this anomaly matched with the magnitude and epicenter distance of the Maduo earthquake. We have also interpreted the reason why the anomaly occurred near a fault that is obliquely intersected with the seismogenic fault and why the anomaly is located far from the earthquake epicenter.

The Origin of Paleokarst in the Huanglong Formation of the Eastern Sichuan Basin:Evidence from δ^(13)C, δ^(18)O and ^(87)Sr/^(86)Sr

Karst rocks from the Huanglong Formation exposed at the margin of the Eastern Sichuan Basin can be divided into four types：slightly corroded, moderately corroded porous, intensely corroded brecciated and intensely corroded and replaced secondary calcic karstic rocks. The carbon, oxygen and strontium isotope compositions of the various karst rocks are analyzed systematically and compared to rocks without karst corrosion. The results indicate that（1） the Huanglong Formation in the eastern Sichuan Basin was a restricted bay supplied and controlled by freshwater in which mudmicrite and mud-dolomicrite exhibit low δ13C and δ18O values and high 87Sr/86 Sr ratios;（2） all types of karstic rocks in the paleokarst reservoirs of the Huanglong Formation in the research area are affected by atmospheric freshwater with the δ13C and δ18O values and 87Sr/86 Sr ratios in the original formation approaching those of atmospheric freshwater, which reflects ancient hydrological conditions, fluid properties, isotopic source and the fractionation effect;（3） the intensely corroded and replaced secondary limestone is affected by a variety of diagenetic fluids, often reflected by δ13C and δ18O values, while the 87Sr/86 Sr ratios exhibit the strong degree of the corrosion;（4） after comparing the 87Sr/86 Sr ratios of each type of karst rock, the diagenetic fluids are determined to be mainly atmospheric freshwater, and depending on the strength of corrosion, and the low 87Sr/86 Sr ratio fluids in the layer will participate in the karst process. The carbon, oxygen, and strontium isotopes of different karstic reservoirs can provide meaningful geochemical information for forecasting and evaluating the development and distribution rules of the Huanglong Formation at the margin of the eastern Sichuan Basin in time and space.

Beautiful scenery of Huanglong

Huanglong is located between 103°44′ -104°3′ Lon. W. of Greenwich, and 32°41′-32°54′ Lat. N. of the Equator, in Sichuan Province, China. It is a neighbor of world-famous Jiuzhaigou, with an area of 40,000 hectares. The karst landscape of Huanglong is spectacular, with over 3,400 multicolored pools reflecting surrounding peaks, trees and waterfalls in an unending scroll. The 3.5-kilometer yellow-sand road is like a golden dragon flying up the snowy mountain, and from a distance the colored pools look like dragon scales. So, it is called

Huanglong Scenic and Historic Interest Area

SITUATED in the northwestern part of Sichuan Province, Huanglong Scenic and Historic Interest Area is renowned for its beautiful mountainous scenery, with relatively undisturbed and highly diverse forest ecosystems.

Land Remediation Projects in Poverty-stricken Counties in Tibetan Areas Promoting Poverty Alleviation——A Case Study of Songpan County,Sichuan Province

Songpan County is a poverty-stricken county in the four provinces of China,one of the concentrated areas in China. This paper analyzes the effectiveness of land consolidation in Songpan County to promote poverty alleviation and development through specific cases. The results show that land remediation has improved agricultural production conditions,promoted agricultural efficiency,increased farmers' income,improved rural living conditions,promoted the development of urban and rural integration,improved the ecological environment,solved the problem that restricts the survival and development of poverty-stricken areas,enhanced the ability of farmers to develop themselves,raised the level of civilization in rural areas,and promoted poverty alleviation and development. The poverty alleviation and development has provided certain financial support for land remediation. It has promoted land remediation,and pointed out key directions for land remediation. It has an indirect promotion effect on land remediation.

^(40)Ar/^(39)Ar Dating of Xuebaoding Granite in the Songpan-Garze Orogenic Belt,Southwest China,and its Geological Significance

Thus far, our understanding of the emplacement of Xuebaoding granite and the occurrence and evolution of the Songpan-Garze Orogenic Belt has been complicated by differing age spectra results. Therefore, in this study, the ^40Ar/^39Ar and sensitive high resolution ion micro-probe （SHRIMP） U-Pb dating methods were both used and the results compared, particularly with respect to dating data for Pankou and Pukouling granites from Xuebaoding, to establish ages that are close to the real emplacements. The results of SHRIMP U-Pb dating for zircon showed a high amount of U, but a very low value for Th/U. The high U amount, coupled with characteristics of inclusions in zircons, indicates that Xuebaoding granites are not suitable for U-Pb dating. Therefore, muscovite in the same granite samples was selected for ^40Ar/^39Ar dating. The ^40Ar/^39Ar age spectrum obtained on bulk muscovite from Pukouling granite in the Xuebaoding, gave a plateau age of 200.1±1.2 Ma and an inverse isochron age of 200.6±1.2 Ma. The 4^40Ar/^39Ar age spectrum obtained on bulk muscovite from Pankou granite in the Xuebaoding gave another plateau age of 193.4±1.1 Ma and an inverse isochron age of 193.7±1.1 Ma. The ^40Ar/^36Ar intercept of 277.0±23.4 （2σ） was very close to the air ratio, indicating that no apparent excess argon contamination was present. These age dating spectra indicate that both granites were emplaced at 200.6±1.3 Ma and 193.7±1.1 Ma, respectively. Through comparison of both dating methods and their results, we can conclude that it is feasible that the muscovite in the granite bearing high U could be used for ^40Ar/^39Ar dating without extra Ar. Based on this evidence, as well as the geological characteristics of the Xuebaoding W-Sn-Be deposit and petrology of granites, it can be concluded that the material origin of the Xuebaoding W-Sn-Be deposit might partially originate from the Xuebaoding granite group emplacement at about 200 Ma. Moreover, compared with other granites and deposits distributed in various positions in the Songpan-Garze Orogenic Belt, the Xuebaoding emplacement ages further show that the main rare metal deposits and granites in peripheral regions occurred earlier than those in the inner Songpan-Garze. Therefore, ^40Ar/^39Ar dating of Xuebaoding granite will lay a solid foundation for studying the occurrence and evolution of granite and rare earth element deposits in the Songpan-Garze Orogenic Belt.

Geochemistry of Late Triassic pelitic rocks in the NE part of Songpan-Ganzi Basin,western China:Implications for source weathering,provenance and tectonic setting

Major, trace and rare earth element （REE） concentrations of Late Triassic sediments （fine- grained sandstones and mudstones） from Hongcan Well 1 in the NE part of the Songpan-Ganzi Basin, western China, are used to reveal weathering, provenance and tectonic setting of inferred source areas. The Chemical Index of Alteration （CIA） reflects a low to moderate degree of chemical weathering in a cool and somewhat dry climate, and an A-CN-K plot suggests an older upper continental crust prove- nance dominated by felsic to intermediate igneous rocks of average tonalite composition. Based on the various geochemical tectonic setting discrimination diagrams, the Late Triassic sediments are inferred to have been deposited in a back-arc basin situated between an active continental margin （the Kunlun- Qinling Fold Belt） and a continental island arc （the Yidun Island Arc）. The Triassic sediments in the study area underwent a rapid erosion and burial in a proximal slope-basin environment by the petrographic data,while the published flow directions of Triassic turbidites in the Aba-Zoige region was not supported Yidun volcanic arc source. Therefore, we suggest that the Kunlun-Qinling terrane is most likely to have supplied source materials to the northeast part of the Songpan-Ganzi Basin during the Late Triassic.

Crustal structure beneath the Songpan——Garze orogenic belt

The Benzilan-Tangke deep seismic sounding profile in the western Sichuan region passes through the Song-pan-Garze orogenic belt with trend of NNE. Based on the travel times and the related amplitudes of phases in the record sections, the 2-D P-wave crustal structure was ascertained in this paper. The velocity structure has quite strong lateral variation along the profile. The crust is divided into 5 layers, where the first, second and third layer belong to the upper crust, the forth and fifth layer belong to the lower crust. The low velocity anomaly zone gener-ally exists in the central part of the upper crust on the profile, and it integrates into the overlying low velocity basement in the area to the north of Ma'erkang. The crustal structure in the section can be divided into 4 parts: in the south of Garze-Litang fault, between Garze-Litang fault and Xianshuihe fault, between Xianshuihe fault and Longriba fault and in the north of Longriba fault, which are basically coincided with the regional tectonics division. The crustal thickness decreases from southwest to northeast along the profile, that is, from 62 km in the region of the Jinshajiang River to 52 km in the region of the Yellow River. The Moho discontinuity does not obviously change across the Xianshuihe fault based on the PmP phase analysis. The crustal average velocity along the profile is lower, about 6.30 km/s. The Benzilan-Tangke profile reveals that the crust in the study area is orogenic. The Xianshuihe fault belt is located in the central part of the profile, and the velocity is positive anomaly on the upper crust, and negative anomaly on the lower crust and upper mantle. It is considered as a deep tectonic setting in favor of strong earthquake's accumulation and occurrence.

Crustal Structural and Tectonic Evolution and Oil Prospect Evaluation in the Songpan-Zoigê Block

Recent study of magnetotelluric （MT） inversion indicates that the basement of the Songpan- Zoige area could be a stable continental crust. There has developed quite thick and stable Paleozoic continental shelf margin-platform clastic and carbonate sediments during the Triassic. Preliminary field geologic investigation and hydrocarbon potential study show that good-quality source rocks, mainly argillaceous and carbonaceous shale, were deposited in the Cambrian and Silurian in this region, while diverse reservoirs of platform facies carbonate and clastic rocks were in the Carboniferous and Permian. The good vertical source-reservoir-seal configuration might indicate that there exists a certain potential for oil and gas exploration in this area.

Analysis of the Features of the Vernacular Plank Houses of the Qiang Ethnic Group in Southern Songpan County: A Case Study of Xiaoxinggou

The Qiang ethnic group in southern Songpan county lives in vernacular plank houses(VPHs) with an architectural tradition that dates to the period of the ancient Di people.VPHs are now mainly constructed in settlements of ethnic groups such as Baima Tibetans, Amdo Tibetans, and the Qiang people living in Wenxian county, Longnan city of Gansu province, and Maoxian, Lixian, Wenchuan, and Beichuan of Sichuan province respectively.Although VPHs of the Qiang people living in southern Songpan share many similarities with those of adjacent Tibetans in structure, construction, and spatial layout, they feature the Qiang people's unique architectural culture, and reflect a style transition from VPHs in the north to blockhouses in the south.The VPHs, as represented by those in Xiaoxinggou, play a significant role in the diversified architectural culture of this ethnic group.Their unique cultural value is worthy of further exploration and protection.

TECTONIC EVOLUTION OF THE YANGTZE PASSIVE MARGIN AND SONGPAN GARZ? FOLD BELT, CHINA

The Songpan Garzê Fold Belt records Triassic shortening of a relict Palaeo\|Tethyan basin during assembly and accretion of the Cimmerian continental chain to Laurasia’s southern margin. Enclosed by palaeo\|Laurasia and the Cimmerian fragments of Qiangtang (North Tibet) and Yangtze (South China), the Songpan Garzê Fold Belt was shortened by more than 50% during the Indosinian Orogeny c.200Ma. [BW(D(S,,)G2*7][BHDWG2*7,WK*2,WK5,WK15*2,WK17*2,WK*2W] 2000,7(增刊) 地 学 前 缘 [FK(K+6mm。17*2] 4\ Major Topic:Geology of the Inner Tibetan Plateau [BW(S(S,,)G2*7][BHDWG2*7,WK*2,WK17*2,WK15*2,WK5,WK*2W] [FK(K+6mm。17*2] 4\ Major Topic:Geology of the Inner Tibetan Plateau 地 学 前 缘 2000,7(增刊)South\|directed Indosinian compression decolléd onlapping basin sediments from the Yangtze Block’s passive margin—reactivating the margin’s tiered geometry and partitioning strain into margin\|normal and margin\|parallel structures on a large scale. Margin\|normal transport of the allochthonous sedimentary pile was accommodated by southeast\|directed nappe propagation in the Longmen Mountains Thrust—Nappe Belt, whilst conjugate, margin\|parallel (southwest\|directed) transport was accommodated by a flat\|lying detachment at the base of the sedimentary pile.The later is characteristic of deformation of the greater Songpan Garzê Fold Belt.

Multi-level Cooperation and Complementary Advantage Poverty Alleviation Model in Poverty-Stricken Counties of Tibetan Areas:A Case Study of Songpan County in Sichuan Province

Songpan County is a poverty-stricken county in Tibetan areas of Sichuan Province,it belongs to a concentrated poverty-stricken area in China.Through summarizing the specific conditions of multi-level cooperation and complementary advantage poverty alleviation model in Songpan County,this paper analyzed the effect of this model.Through the analysis on the cooperative poverty alleviation model(eastern-western cooperation,provincial targeted assistance,county-wide"four-leading and four-assistance"inner-party assistance,social force"10000 enterprises helping 10000 villages",and"visiting every household and keeping every person busy"),it summarized the implementation and actual results of each level.In addition,it summarized the problems encountered in the implementation process of multi-level cooperation and complementary advantage poverty alleviation model and came up with recommendations.With the aid of this successful multi-level cooperation and complementary advantage poverty alleviation model,Songpan County has achieved a decisive victory in the fight against poverty.At the end of April 2019,the poverty rate in the whole region fell to 0.45%,and it successfully took off the poverty hat.This paper analyzed and refined the specific practice,main achievements,successful experience,implications and reference significance of multi-level cooperation and complementary advantage poverty alleviation model,to provide necessary references for innovation of poverty alleviation model in poverty-stricken Tibetan areas,or even other similar provinces and regions.

The Songpan-Garze Massif: Its Relation to the QinlingFold Belt and Yangtze Platform and Developmental History

Whether there existed the Songpan-Garze massif is a controversial problem. This paper expounds and proves that the old basement of the massif is represented by the pre-Sinian granitic rock series. This massif and the South Qinling fold belt might both be a part of the old Yangtze platform. Rifting generated by the Caledonian orogeny in the terminal Early Palaeozoic caused the massif to be disintegrated from the northwestern part of the Yangtze platform. This disintegration, however, was not thorough, and the rift troughs were later gradually closed and filled up. The Emei taphrogeny that was initiated in the Early Permian Maokou' an Stage involved a second disintegration of this massif from the Yangtze platform. The rift line largely goes along the Muli-Pingwu line. This rifting belongs to synchronous extensional rifting at peripheries of the Yangtze platform and in its interior, showing that the posterior, lateral and interior extension resulting from rapid northward shift of the Yangtze platform led to isolation of this massif together with South Qinling from their adjacent areas. During the Ladinian Stage, the Songpan-Garze massif and southern Qinling sank strongly en masse. This subsidence continued till the end of the Late Triassic when the late Indosinian movement caused the sea trough to be closed and Songpan-Garze1 and southern Qinling to be folded and uplifted and become mountains.

Earthquake fault framework and seismotectonics of the Songpan-Garze region since 1900

Based on 4 781 observed faults （〉2 km length） from a 1：200 000 scale digital geologic map and 5 220 recorded seismic events since the year 1900, 993 earthquake faults are identified within the triangular Songpan-Garze study region. The study area is delineated by the nearly EW-trending East Kunlun fault zone to the north, the NW-trending Xianshuihe fault to the south and the NE-trending Longmenshan thrust belt to the east. Seismicity changes along these earthquake faults, spanning four 10-year intervals since 1970, show that following a strong earthquake swarm, which occurred in the Huya area in the mid-1970s, seismic activity increased from north to south, and migrated eastward along each major strike-slip fault zone. GPS observation data before 2008 indicate a displacement rate across the Xianshuihe fault zone to the south of -6.5- 8.6 mm/a, whereas across the East Kunlun fault zone to the north it was -1.8- 2.2 mm/a. The May 12, 2008 Ms8.0 Wenchuan earthquake, which occurred in the southeast corner of the study region, was the result of stable, high-speed left-lateral displacement along the Xianshuihe fault zone, and a sharp eastward bend of the fault trend in response to the presence of crystalline rocks in the Kangding area. Therefore, the 110-year established seismotectonic framework of the Songpan-Garze region can be defined by a network of various earthquake faults and the structural relations of the local earthquake activities.

Geological Characteristics of Oil and Gas Reservoirs in the Songpan-Aba Area,SW China

The Songpan-Aba area, similar to those basins on the Yangtze block, following the rifting and separation of the Yangtze block, gradually developed into a passive marginal basin on a passive continent margin in Early Paleozoic, and later, with the Qinling-Qilian oceanic crust subduction and ocean closure, the Caledonides were formed and the foreland basin was superimposed upon. Being influenced by the Paleo-Tethyan extension, intra-continental rifting-margin basins were formed in Late Paleozoic. Following the formation of peripheral orogenic belt, the Upper Triassic again superimposed the foreland basin. The Mesozoic and Cenozoic overprinted the faulted basin, forming the Qinghai-Tibet Plateau domes. Hydrocarbon source rock in the Early Paleozoic passive basin, the Upper Paleozoic platform carbonates and the Triassic mudstones comprise the main source-reservoircap combination. Each layer of this area is at the advanced stage of diagenetic evolution, being entered the middle and late diagenetic stages, and anadiagenetic stage. Besides the highly matured Triassic and Permian in Zoige and Hongyuan, almost all the area is at the early stage of over maturatation, generating much methane. This area has the potential for oil and gas.

鄂尔多斯盆地东南部黄龙背斜的构造几何学与运动学

研究克拉通内构造变形对于揭示克拉通的构造属性具有重要意义,对于油气勘探也具有重要的参考价值。本文应用钻井与高精度反射地震资料,剖析了鄂尔多斯盆地东南部黄龙背斜的构造几何学与运动学特征。研究表明,黄龙背斜发育在渭北隆起东端,是一长18 km、宽15 km的短轴状背斜,地层起伏幅度达200 ms;黄龙背斜自长城系往上至三叠系均具有相似的背斜形态;它是在燕山期基底断层复活而形成的断层传播褶皱背斜;黄龙背斜区内东西向与南北向剖面控制的缩短分别为70 m和90 m,缩短量较小,指示该部位处于燕山期冲断变形的前锋部位,变形即将终止。黄龙背斜响应于周缘构造边界挤压作用,是克拉通内部的基底正断层反转而在沉积盖层形成的褶皱背斜,因地层能干性差异发生了分层剪切。黄龙背斜是一个有利的天然气勘探目标。