Projecting the Dynamic Trends of Human Immunodeficiency Virus/Acquired Immunodeficiency Syndrome:Modeling the Epidemic in Sichuan Province, China

Objective Our study aimed to provide a comprehensive overview of the current status and dynamic trends of the human immunodeficiency virus(HIV)prevalence in Sichuan,the second most heavily affected province in China,and to explore future interventions.Methods The epidemiological,behavioral,and population census data from multiple sources were analyzed to extract inputs for an acquired immunodeficiency syndrome(AIDS)epidemic model(AEM).Baseline curves,derived from historical trends in HIV prevalence,were used,and the AEM was employed to examine future intervention scenarios.Results In 2015,the modeled data suggested an adult HIV prevalence of 0.191%in Sichuan,with an estimated 128,766 people living with HIV/AIDS and 16,983 individuals with newly diagnosed infections.Considering current high-risk behaviors,the model predicts an increase in the adult prevalence to 0.306%by 2025,projecting an estimated 212,168 people living with HIV/AIDS and 16,555 individuals with newly diagnosed infections.Conclusion Heterosexual transmission will likely emerge as the primary mode of AIDS transmission in Sichuan.Furthermore,we anticipate a stabilization in the incidence of AIDS with a concurrent increase in prevalence.Implementing comprehensive intervention measures aimed at high-risk groups could effectively alleviate the spread of AIDS in Sichuan.

Facies-controlled prediction of dolomite reservoirs in the Middle Permian Qixia Formation in Shuangyushi,northwestern Sichuan Basin

The Middle Permian Qixia Formation in the Shuangyushi area,northwestern Sichuan Basin,develops shoal-facies dolomite reservoirs.To pinpoint promising reservoirs in the Qixia Formation,deep thin shoal-facies dolomite reservoirs were predicted using the techniques of pre-stack Kirchhoff-Q compensation for absorption,inverse Q filtering,low-to high-frequency compensation,forward modeling,and facies-controlled seismic meme inversion.The results are obtained in six aspects.First,the dolomite reservoirs mainly exist in the middle and lower parts of the second member of Qixia Formation(Qi2 Member),which coincide with the zones shoal cores are developed.Second,the forward modeling shows that the trough energy at the top and bottom of shoal core increases with increasing shoal-core thickness,and weak peak reflections are associated in the middle of shoal core.Third,five types of seismic waveform are identified through waveform analysis of seismic facies.Type-Ⅰ and Type-Ⅱ waveforms correspond to promising facies(shoal core microfacies).Fourth,vertically,two packages of thin dolomite reservoirs turn up in the sedimentary cycle of intraplatform shoal in the Qi2 Member,and the lower package is superior to the upper package in dolomite thickness,scale and lateral connectivity.Fifth,in plane,significantly controlled by sedimentary facies,dolomite reservoirs laterally distribute with consistent thickness in shoal cores at topographical highs and extend toward the break.Sixth,the promising prospects are the zones with thick dolomite reservoirs and superimposition of horstegraben structural traps.

Depositional model of the Member Deng-2 marginal microbial mound-bank complex of the Dengying Formation in the southwestern Sichuan Basin, SW China: Implications for the Ediacaran microbial mound construction and hydrocarbon exploration

Recent advances in hydrocarbon exploration have been made in the Member Deng-2 marginal microbial mound-bank complex reservoirs of the Dengying Formation in the western Sichuan Basin, SW China,where the depositional process is regarded confusing. The microfacies, construction types, and depositional model of the Member Deng-2 marginal microbial mound-bank complex have been investigated using unmanned aerial vehicle photography, outcrop section investigation, thin section identification,and seismic reflections in the southwestern Sichuan Basin. The microbialite lithologic textures in this region include thrombolite, dendrolite, stromatolite, fenestral stromatolite, spongiostromata stone,oncolite, aggregated grainstone, and botryoidal grapestone. Based on the comprehensive analysis of“depositional fabrics-lithology-microfacies”, an association between a fore mound, mound framework,and back mound subfacies has been proposed based on water depth, current direction, energy level and lithologic assemblages. The microfacies of the mound base, mound core, mound flank, mound cap, and mound flat could be recognized among the mound framework subfacies. Two construction types of marginal microbial mound-bank complex have been determined based on deposition location, mound scale, migration direction, and sedimentary facies association. Type Jinkouhe microbial mound constructions(TJMMCs) develop along the windward margin owing to their proximity to the seaward subfacies fore mound, with a northeastwardly migrated microbial mound on top of the mud mound,exhibiting the characteristics of large-sized mounds and small-sized banks in the surrounding area. Type E'bian microbial mound constructions(TEMMCs) primarily occur on the leeward margin, resulting from the presence of onshore back mound subfacies, with the smaller southwestward migrated microbial mounds existing on a thicker microbial flat. The platform margin microbial mound depositional model can be correlated with certain lateral comparison profile and seismic reflection structures in the 2D seismic section, which can provide references for future worldwide exploration. Microbial mounds with larger buildups and thicker vertical reservoirs are typically targeted on the windward margin, while small-sized microbial mounds and flats with better lateral connections are typically focused on the leeward margin.

Atmospheric Sulfur and Nitrogen Deposition in Five Nature Reserves of Sichuan Basin to Qinghai-Tibetan Plateau Transect Region,Southwest-ern China

Enhanced sulfur and nitrogen deposition has been observed in many transect regions worldwide,from urban/agricultural areas to mountains.The Sichuan Basin(SCB),with 18 prefectural cities,is the most economically-developed region in western China,while the rural Qinghai-Tibetan Plateau(QTP)lies west of the SCB.Previous regional and national atmospheric modeling studies have sug-gested that large areas in the SCB-to-QTP transect region experience excessive deposition of sulfur and nitrogen.In this study,we ap-plied a passive monitoring method at 1l sites(one in urban Chengdu and 10 from fivenature reserves)in this transect region from September 2021 to October 2022 to confirm the high sulfur and nitrogen deposition fluxes and to understand the gaps between the mod-eling and observation results for this transect region.These observations suggest that the five reserves are under eutrophication risk,and only two reserves are partially under acidification risk.Owing to the complex topography and landscapes,both sulfur and nitrogen de-position and critical loads exhibit large spatial variations within a reserve,such as Mount Emei.Regional atmospheric modeling may not accurately capture the spatial variations in deposition fluxes within a reserve;however,it can capture general spatial patterns over the entire transect.This study demonstrates that a combination of state-of-the-art atmospheric chemical models and low-cost monitoring methods is helpful for ecological risk assessments at a regional scale.

Exploring Paths for the High-Quality Development of Forest-Based Wel ness Industry:A Case Study of Sichuan Province

The forest-based wellness industry,as a rapidly growing sector that integrates various business forms with extensive coverage and an extended industrial chain,is undergoing rapid development due to the increasing aging population and people's suboptimal health conditions.As a forerunner in developing the forest-based wellness industry,Sichuan province is known for its early development,proactive efforts,diverse models,and significant impact in this industry.It has achieved certain milestones in terms of top-level design,pilot demonstration,standardized guidance,and public awareness campaigns to promote the development of this industry.Therefore,this paper utilizes Sichuan as a case study to systematically summarize and analyze the key practices made by the province in promoting the rapid development of the industry by investigating the development trajectory of the forest-based wellness industry.Additionally,it examines the development trends of this industry from the perspectives of supply,demand,and consumption.Finally,this paper proposes several measures to facilitate the high-quality development of the forest-based wellness industry.These measures encompass nurturing specialized talent in forest-based wellness,enhancing market players'capabilities in this domain,conducting extensive research on technologies that promote this industry,actively seeking support from relevant policies,and promoting integrated development across diverse sectors.

Analysis of standardization development of TCM in Sichuan

Sichuan province is home to rich traditional Chinese medicine(TCM)resources.Recent years have seen unremitting efforts of TCM standardization in the province.By analyzing the measures and existing problems,this paper provides recommendations to boost TCM development through standardization.

The Impact of Contextual Teaching Method on Sichuan Folk Song Education and Students’Musical Expressiveness

This study explores the application of the contextual teaching method in Sichuan folk song education and its impact on students’musical expressiveness.By incorporating contextual teaching methods in music classes,this research investigates the effectiveness of this approach in enhancing students’understanding of Sichuan folk songs and improving their musical expressiveness and emotional expression.A mixed-method research approach is employed,utilizing classroom observations,questionnaires,interviews,and statistical analysis to assess the practical outcomes of contextual teaching in folk song education.

A Study of the Effect of Sichuan Opera Singing on the Vocal Skills of Music Students

The purpose of the article is to explore the effects of Sichuan opera singing on music majors’vocal skills,focusing on three key aspects:pitch test,assessment of rhythmic perception,and emotional expression.Through a quasi-experimental design,100 music majors were selected as research subjects and divided into an experimental group that received Sichuan opera singing instruction and a control group that received traditional vocal instruction.The results showed that compared with the control group,the experimental group receiving Sichuan opera singing teaching showed significant improvement in pitch mastery,rhythm perception,and emotional expression.

Electrical Characteristics of Tangjiawan Landslide in Lixian, Sichuan

A wide range of terrain features and landforms,which are exemplified by intricate geological formations and diverse rock compositions,are found in the western mountainous regions of China.These areas frequently encounter geological disasters.As one of the natural disasters,landslides lead to considerable loss of human life and property.Considering mitigation of the losses caused by landslide disasters,a necessary measure for disaster prevention and mitigation involves conducting detailed investigations and monitoring of landslides,which is also the cornerstone of landslide warning.This study compares and analyzes the feasibility of the magnetotelluric detection method for landslides using the results of engineering geological surveys and landslide monitoring.The study aims to address the scientific problem of the validity of using magnetotelluric methods to detect landslide development processes.The Tangjiawan landslide signal on the left side of the K94+000~K94+145 section of the Wenma Expressway is analyzed by employing engineering geological survey,magnetotelluric detection,landslide monitoring,landslide analysis,and other methods.Analysis results provide the static electrical characteristics of lithology,structure,and groundwater,as well as the dynamic electrical characteristics of landslide development.This study focuses on analyzing the relationship between the methods of magnetotelluric detection and engineering geological surveys and the results of landslide monitoring.The workflow and methods for data collection,processing,inversion,interpretation,and analysis using the magnetotelluric method to detect the dynamic development process of landslides are presented in the conclusion.Preliminary conclusions indicate a strong correlation between the dynamic changes in magnetotelluric wave impedance with the surface displacement of landslides and the dynamic changes in groundwater.The use of the magnetotelluric method for landslide detection and monitoring is a feasible example.The research results can offer certain technical references for the detection and monitoring of landslides using magnetotelluric methods and also provide references and guidance for the selection of diversified landslide monitoring methods in the future.

Comparative Analysis of Energy Characteristics of Two Southwest Vortices in Sichuan Under Similar Circulation Backgrounds

Based on ERA5 reanalysis data,the present study analyzed the thermal energy development mechanism and kinetic energy conversion characteristics of two extreme rainstorm processes in relation to the shallow southwest vortex in the warm-sector during a“rain-generated vortex”process and the deep southwest vortex in a“vortex-generated rain”process.The findings were as follows:(1)During the extreme rainstorm on August 11,2020(hereinafter referred to as the“8·11”process),intense surface heating and a high-energy unstable environment were observed.The mesoscale convergence system triggered convection to produce heavy rainfall,and the release of latent condensation heat generated by the rainfall promoted the formation of a southwest vortex.The significant increase(decrease)in atmospheric diabatic heating and kinetic energy preceded the increase(decrease)in vorticity.By contrast,the extreme rainstorm on August 16,2020(hereinafter referred to as the“8·16”process)involved the generation of southwest vortex in a low-energy and highhumidity environment.The dynamic uplift of the southwest vortex triggered rainfall,and the release of condensation latent heat from rainfall further strengthened the development of the southwest vortex.The significant increase(decrease)in atmospheric diabatic heating and kinetic energy exhibited a delayed progression compared to the increase(decrease)in vorticity.(2)The heating effect around the southwest vortex region was non-uniform,and the heating intensity varied in different stages.In the“8·11”process,the heating effect was the strongest in the initial stage,but weakened during the vortex's development.On the contrary,the heating effect was initially weak in the“8·16”process,and intensified during the development stage.(3)The available potential energy of the“8·11”process significantly increased in kinetic energy converted from rotational and divergent winds through baroclinic action,and the divergent wind energy continued to convert into rotational wind energy.By contrast,the“8·16”process involved the conversion of rotational wind energy into divergent wind energy,which in turn converted kinetic energy back into available potential energy,thereby impeding the further development and maintenance of the southwest vortex.

Insights into in-situ imbibition behavior of fracturing fluid in propped shale fractures based on nuclear magnetic resonance:A case study from Longmaxi Formation shale,Sichuan Basin,China

Shale gas is an important component of unconventional oil and gas resources.Studying the imbibition behavior is helpful to optimize flowback parameters and enhance gas recovery.Recent imbibition studies have focused on shale matrix,and the pressure conditions discussed were mostly atmospheric.The initial imbibition behavior begins from propped fractures to matrix,but there are few studies working on explaining the imbibition behavior in propped fractures or the phenomenon of many shale wells exhibit higher productivity after a“soaking”period.Therefore,propped fracture samples were designed for imbibition and migration experiments.In order to accurately study the mechanism and main influencing factors of fracturing fluid imbibition and migration in propped and unpropped shale fractures under high temperature and high pressure,a series of experiments based on nuclear magnetic resonance(NMR)were carried out.Results showed that NMR T_(2) spectra of all samples exhibited a bimodal distribution.The final imbibition volume of fracturing fluid was positively related to pressure and fracture width.The imbibition effect of fracturing fluid was more evident in matrix pores under high pressure.In the migration during soaking stage,the fracturing fluid gradually migrated from large pores to small pores and gradually displaced the shale gas from the matrix,thus allowing the water blocking in propped fractures to self-unlock to some extent.Gas permeability decreased in the imbibition stage,while it recovered in the migration stage to some extent.

Understanding livelihood vulnerability:a perspective from Western Sichuan’s ethnic rural settings

To explore the livelihood status and key influencing factors of rural households in the minority areas,we collected flat data from 284 rural households in 32 villages across 12 counties of Western Sichuan from 2021 to 2022.We conducted participatory household survey on the livelihood status of the rural households and try to identify the key factors to influence their livelihood vulnerability using multiple linear regression.The results showed that:the livelihood situation of the rural households is relatively vulnerable.The vulnerability varies significantly with the income levels,education levels,and income sources.The vulnerability of farm households,categorized from low to high livelihood types,follows the sequence:non-agricultural dominant households,non-agricultural households,agricultural dominant households,and pure agricultural households.The degree of damage to the natural environment,education costs,loan opportunities,the proportion of agricultural income to annual household income,and the presence of sick people in the household have significant positive effects on the livelihood vulnerability index(LVI)of rural households;while help from relatives and friends,net income per capita,household size,household education,agricultural land area,participation in industrial organizations,number of livestock,purchase of commercial houses,drinking water source,and self-supply of food have significant negative effects.Based on the findings,we believe that local rural households operate in a complex livelihood system and recommend continuous interventions targeting key influences to provide empirical research support for areas facing similar situations.

A New Species of the Genus Scincella Mittleman,1950(Squamata:Scincidae)from Sichuan Province,Southwest China

The genus Scincella Mittleman,1950,within the family Scincidae,is a diverse group comprising 39 described species.The taxonomy of the genus is complex due to morphological similarities among species,which often obscures the true extent of biodiversity,resulting in several undescribed species requiring further exploration.In China,particularly within the unique ecosystems of the Hengduan Mountains,the diversity of Scincella is notably underestimated,with only 12 species currently recognized.In the present study,we describe a new species of the genus Scincella,Scincella liangshanensis sp.nov.,from Sichuan Province,Southwest China.Morphological characteristics and phylogenetic analyses revealed that the putative new species is distinct from all other known congeners.This discovery not only expands the known diversity of Scincella but also emphasizes the inadequacies in our current understanding of herpetological diversity in China.The addition of this species to the scientific record highlights the necessity for ongoing biodiversity assessments to uncover hidden species and enhance our understanding of the intricate web of life in one of the world’s biodiversity hotspots.

Cassiterite U-Pb dating of the Yelonggou pegmatite-type lithium deposit in western Sichuan and its metallogenic age constraints

1.Objective Pegmatite hosts important resource of rare metals,e.g.,lithium(Li)and beryllium(Be).In recent years,increasingly more studies were dedicated to characterize and unravel the formation of pegmatite-type deposits,for which accurate dating of pegmatite formation and mineralization is essential.The Songpan-Ganzi orogenic belt is a major rare metal metallogenic belt in China,hosting many important pegmatite-type Li deposits,including the Lijiagou,Dangba,Jiajika,Yelonggou,Cuola,and Declalongba.Radiometric age data(mica Ar-Ar and zircon/cassiterite U-Pb)from these Li deposits are sparse,ranging from 210 to 152 Ma.However,obtaining reliable zircon U-Pb dates can be a challenge due to the strong decidualization in pegmatites.As a result,the formation and mineralization ages of these rare metal pegmatites remain controversial,which hampers the development of pegmatite-type metallogenic model for the Songpan-Ganzi orogenic belt.

Discovery of tuff in Wujiaping Formation of Upper Permian in the northern Sichuan Basin:Implications for the termination of Emeishan Large Igneous Province

1.Objective The Emeishan basalts is located in southwest China and northern Vietnam,covering an area of 2.5×10^(5) km^(2)(Zhong YT et al.,2014),which is the first widely recognized large igneous province(LIP)in China(Zhang ZS,2009).The Emeishan LIP has attracted a numbers of scholars for the reason that the LIP may play a significant role in the evolution of environment and climate.Yang JH et al.,(2018)pointed out that the weathering of the Emeishan basalts consumed carbon dioxide and caused a decrease in the climate of the early Wuchiapingian.However,the duration and termination of the Emeishan basalts eruption remain in doubt.This paper reports a new discovery of tuffaceous in the middle part of the Upper Permian Wujiaping Formation from the northern margin of the Sichuan Basin,applying of LA-ICP-MS to obtain zircon U-Pb ages of tuffaceous and to constrain the lasted eruption timing of Emeishan LIP.

Can whole steps of grain production be outsourced? Empirical analysis based on the three provinces of Jiangsu,Jilin,and Sichuan in China

Certain outsourcing services for agricultural management in China,such as pest control in grain production,have experienced prolonged sluggishness,contrasting with the relatively high level of outsourcing services observed in harvesting,land preparation,and sowing.This study examines the feasibility of implementing whole-step outsourcing in grain production by conducting a case study of rice and maize production in Jiangsu,Jilin,and Sichuan provinces in China.The provision of outsourcing services hinges on two essential conditions:technological advancements fostering specialized production and economies of scale,coupled with a market size sufficient to realize the aforementioned potential economies of scale.The results showed that outsourcing pest control or harvesting services had varying economies of scale.The outsourcing services in pest control were less common than in harvesting services,and their marginal growth space of the economies of scale with technological change was also smaller.Determined by the operational characteristics of pest control itself,the market scale of its professional services is small.Therefore,achieving the whole-step outsourcing of grain production necessitates not only technological innovation but also effective policy interventions to overcome the constraints of market scale.Such interventions include(1)optimizing crop layouts between planning regions and reducing land fragmentation and(2)supplying timely and effective inter-regional agricultural information for service providers aided by information technology.

Slaughter Performance, Muscle Quality and Nutritional Composition of Duoluo Goats in Sichuan Province

[Objectives] This study was conducted to understand the biological characteristics of Duoluo goats. [Methods] With male and female Duoluo goats as the research object, related performance indexes were determined and analyzed after slaughter. [Results] The weights of one-year-old male and female Duoluo goats before slaughter were (25.68±2.37) and (24.51±1.97) kg, respectively;the dressing percentages were (43.55±3.24) % and (43.84±3.42) %, respectively;and the net meat percentages were (33.02±2.32) % and (34.19±2.46) %, respectively. (2) The cooked meat rates of male and female Duoluo goats were (65.49±1.42) % and (65.36±1.55) %, respectively;the shearing force was (5.48±1.24) and (5.65±1.02) N, respectively;and the loin-eye muscle areas were (8.95±1.72) and (8.82±1.15) cm 2, respectively. (3) The protein contents of male and female Duoluo goats were (20.07±0.42) and (19.47±1.22) g/100 g, respectively;and the fat contents were (1.30±0.80) % and (2.92±0.55) %, respectively;and the cholesterol contents were (71.76±11.47) and (74.83±2.68) mg/100 g, respectively;(4) The Ca contents of male and female Duoluo goats were (69.53±10.89) and (63.00±4.56) mg/kg, respectively;the Fe contents were (16.73±1.83) and (14.77±0.58) mg/kg, respectively;and the Zn contents were (38.47±3.68) and (31.83±2.22) mg/kg, respectively. (5) In the muscles of male and female Duoluo goats, the contents of essential amino acids were (7.44±0.24) and (7.26±0.41) g/100 g , respectively;the contents of non-essential amino acids were (11.81±0.33) and (11.42±0.67) g/100 g, respectively;and the contents of flavor amino acids were (8.79±0.27) and (8.42±0.57) g/100 g, respectively. [Conclusions] This study lays a foundation for the excavation and utilization of the resource, Duoluo goats.

Rock physical characteristics of deep dolomite under complex geological conditions:A case study of 4th Member of Sinian Dengying Formation in the Sichuan Basin,China

The deep-ultra deep carbonate reservoir in China,commonly subjected to modification of multi-stage diagenesis,has extremely high heterogeneity.Conventional rock physics analysis cannot accurately identify the elastic responses of reservoir.Here,the rock physics properties of the dolomite from the 4th Member of the Sinian Dengying Formation are experimentally measured,and the change law of rock physics characteristics is investigated within the framework of the diagenetic processes by the analysis of the elastic and petrologic characteristics,pore structure,and sedimentary environments.The results show that the differentiated diagenesis results in different pore structure characteristics and microtexture characteristics of the rock.The microbial dolomite of the algal mound-grain beach facies is subjected to the contemporaneous microbial dolomitization and seepage-reflux dolomitization,penecontemporaneous selective dissolution,burial dolomitization,and hydrothermal dolomitization.The resultant crystalline dolomite is found with one main type of the dolomite crystal contact boundaries,and the dissolution pore is extensive development.The siliceous,muddy,and limy dolomite of the interbeach sea environment mainly experiences the weak capillary concentration dolomitization,intensive mechanical compaction-induced densification,and burial dolomitization.Such crystalline dolomite is observed with four types of contact boundaries,namely the dolomite contact,clay contact,quartz contact,and calcite contact boundaries,and porosity mostly attributed to residual primary inter-granular or crystalline pores.The samples with the same crystal boundary condition have consistent correlations between the compressional-and shear-wave velocities,and between the compressional-wave velocity and the velocity ratio.Additionally,the variation of the acoustic velocity with effective pressure and the intensity of pore-scale fluid-related dispersion are controlled by the differentiation of pore structure types of the samples.The varied effects of soft pores like micro-cracks on the compressional-and shearwave velocity causes considerable changes in the relationships between the compressional-and shearwave velocities,compressional-wave velocity and velocity ratio,and porosity and acoustic velocity.This research is an attempt to demonstrate a novel method for investigating the rock physics variation of rock during the geological process,and the obtained findings can provide the rock physics basis for seismic prediction of the characteristics of deep carbonate reservoirs.

Molecular Epidemiology and Clinical Characteristics of Hand, Foot and Mouth Disease in North Sichuan Region, China, 2018-2023: A Descriptive Study

Background: Hand, foot and mouth disease (HFMD) remains an important public health problem in China. Many studies on the epidemiological characteristics of HFMD have been reported, but studies in North Sichuan region have been neglected. Methods: HFMD-related enterovirus infected cases were clinically confirmed and underwent real-time RT-PCR (rRT-PCR) from May 2018 to October 2023 in Guangyuan Central Hospital. Results: During 2018-2023, other EV (437 cases, 81.08%) was the most predominant serotype followed by CV-A16 (94 cases, 17.44%), EV-A71 (8 cases, 1.48%) was the least predominant serotype. Peak infections occurred in July and October. There were no significant differences in gender, age and serotypes. HFMD was concentrated in children under 47 months of age, with the highest incidence in children aged 12 - 23 months and the highest proportion of other EV infections in the whole age group. COVID-19 did not cause significant changes in gender, age and serotype. Overall, there was a significant increase in the proportion of children aged 12 - 23 months infected with CV-A16, and an increase in the proportion of children aged over 36 months infected with other EVs. Conclusions: The incidence of HFMD caused by EV-A71 has decreased significantly, and other EVs have become the main pathogens of HFMD in North Sichuan region in recent years. In the prevention and control of CV-A16, more attention should be paid to children aged 12 - 23 months and the dominant serotype should be closely monitored. Our study highlights the importance of developing of new diagnostic reagents and vaccines for the prevention and control of enterovirus infection. This study for the first time provides insights into district interventions to local conditions.

Stratigraphic framework and sedimentary evolution during the Cryogenian-Ediacaran transition in northeastern Sichuan Basin,South China

The northeastern Sichuan area in the northern Yangtze margin has unique Ediacaran geological records,especially the Doushantuo Formation(DST),and become a hot research area in recent years.However,the Cryogenian-Ediacaran(C-E)boundary has not been precisely identified,which restricts the in-depth study of geological information during this crucial transitional period and is unfavorable for a systematic and complete understanding of the Yangtze Block and even the global paleogeographic pattern.This study conducted stratigraphy,sedimentology,and chronostratigraphy to establish the stratigraphic framework and sedimentary evolution of the C-E transition strata in northeastern Sichuan.The results showed that the Ediacaran sediments,without the cap dolomite,unconformably overlaid the Cryogenian sediments in the studied area.The Member II of the DST,characterized by 50-160 m of red-green sandstone(approximately equivalent to the original Chengkou“Guanyinya Formation”),directly overlaid the Cryogenian sediments and displayed a 623±2.3 Ma maximum depositional age from the detrital zircon U-Pb dating.Regional stratigraphic correlations indicate that the C-E transition strata in northeastern Sichuan had a consistent lithological association and sedimentary sequence characteristics but differed from the Three Gorges.Typically,the upper Nantuo massive glacial diamictites transition to the icebergs rafted lonestone-bearing mudstones at the top,then change upward to DST barrier coast sandstones.The proposed DST of the northeastern Sichuan Basin was divided into three lithostratigraphic members without the regional Member I cap dolomite:(i)Member II purple-red,gray-green sandstone strata,(ii)MemberⅢblack mudstone strata,and(iii)Member IV P-Mn bearing strata.During the C-E transition,the study area experienced(i)the global deglaciation stage in the terminal Marinoan glaciation and(ii)the filling-leveling up stage with clastic rocks in the early Ediacaran.Overall,the early Ediacaran of northeastern Sichuan succeeded the paleogeographic features of the late Cryogenian.