The tectonic regime of the Yangtze Block (craton of South China) related to the assembly of Rodinia remains debated due to the lack of systematic and integrative analyses of Late Mesoproterozoic to Early Neoproterozoic geological records. In this paper, we present an integrated dataset of zircon U-Pb ages, Hf isotopes, and wholerock geochemistry for two distinct granitoids from the Yuanmou area in the southwestern Yangtze Block. U-Pb zircon dating yielded crystallization ages of 1063.3 +/- 4.9 Ma and 820 +/- 13 Ma for the two granitoids, respectively. Both granitoids have high SiO2 (71.4-78.5 wt%) and alkali (Na2O + K2O = 6.7-9.4 wt%) contents, high 104*Ga/Al ratios (4.3-4.8), and elevated concentrations of Zr + Nb + Ce + Y (339.9-776.1 ppm), all of which are characteristics of A-type granites. The ca. 1.06 Ga granitoids exhibit low (Gd/Yb)N (0.74-1.11), Sr/Y (0.20-0.51), and Y/Nb (0.91-1.14) ratios, high Nb/Ta ratios (14.7-20.5), and heterogeneous epsilon Hf(t) values (-4.52 to + 8.83). These geochemical features indicate an A1-type granite affinity, and suggest that they were primarily generated via partial melting of an ancient crustal source, triggered by the upwelling of hightemperature asthenospheric mantle in a subduction-related slab window setting. In contrast, the ca. 0.82 Ga granitoids have high Y/Nb (1.36-3.00) and Yb/Ta (1.68-2.84) ratios, positive epsilon Hf(t) values (+4.88 to + 10.18), and younger TDM2 ages (0.96-1.16 Ga), indicating an A2-type granite affinity and origination, from partial melting of juvenile crust in a back-arc setting. Integrating these new data with regional geochemical data for magmatic rocks, we propose that the southwestern margin of the Yangtze Block underwent a tectonic transition from a rifting setting (ca. 1.19-1.13 Ga) to multi-stage subduction settings (ca. 1.10-0.90 Ga and ca. 0.90-0.78 Ga).

Abundant stacked sand bodies are developed in the Chang 6 Member (the sixth reservoir unit of the Yanchang Formation) within the Maling-Qiaochuan area of the southwestern Ordos Basin. Through integrated analysis of core observations and well-log interpretations, this study investigates the stacking patterns, spatial distribution characteristics of gravity flow sand bodies and associated depositional environmental changes. The results demonstrate that: (1) Based on the 'lithology-sedimentary structure' classification scheme, seven distinct lithofacies types were identified, including massive sandstone, parallel-laminated sandstone and normal-grained sandstone, which were formed through different gravity-flow depositional processes. (2) These lithofacies assemblages form four principal types of stacked sand bodies with different gravity-flow origins: multi-period thick-layered type (continuous sandy debris-flow deposits), sand-thick and mud-thin type (discontinuous sandy debris-flow deposits), sandstone-mudstone interbedded type (mixed origin from turbidity currents and sandy debris flows) and sand-thin and mud-thick type (primarily late-stage turbidity-current deposits, with contributions from the heads of mud-rich sandy debris flow). (3) The stacked sand bodies exhibit distinct channel features, with the main channel sediments transitioning from multi-period thick-layered sand bodies to sand-thick and mud-thin type and sandstone-mudstone interbedded type. As the semi-deep to deep-lacustrine areas in the Chang 63 to Chang 61 members shrank, the scale of gravity flows diminished. Key factors contributing to this phenomenon include the weakening of seismic and volcanic activities during the Chang 7 to Chang 6 period as the triggering mechanism and the climatic shift from humid to arid-semi-arid conditions caused by the reduced influence of the Carnian Pluvial Event (CPE).

The physicochemical evolution of ore-forming fluids plays a central role in constraining the mineralization processes of skarn-type tungsten deposits, yet reconstructing this evolution remains challenging. The first reported large-scale Neoproterozoic Jianzidong W deposit in the western Yangtze Block, South China, hosts four generations of scheelite (SchI-SchIV), whose mineralogical textures, chemical compositions, and fluid inclusions collectively provide a continuous record of fluid evolution in skarn-type tungsten mineralization. Cathodoluminescence imaging and geochemical data show that SchI (prograde skarn stage) and SchIII (greisen stage) exhibit homogeneous textures with enriched rare earth elements (REEs), and negative Eu anomalies, resembling magmatic fluid inheritance. In contrast, SchII (retrograde skarn stage) and SchIV (quartz-calcite stage) display heterogeneous or incompletely zoned textures with enriched Mo, depleted Sigma REE, and positive Eu anomalies, indicating fluid evolution in an open hydrothermal system. Mo contents and the Eu3+/Eu2+ ratios progressively increase from SchI, SchII, SchIII to SchIV-1, followed by a sharp drop in SchIV-2 to SchIV-3, suggesting a transition from oxidizing to reducing conditions. Fluid inclusions and HO isotope data indicate that SchI-1 and SchI-2 formed from high-temperature (avg. 450 degrees C) magmatic fluids in a relatively closed system, followed by fluid boiling at lower temperatures (avg. 320-350 degrees C), which drove SchI-3 precipitation. Subsequent fluid-rock interaction released Eu and Sr during plagioclase sericitization, forming SchI-2 and SchI-3 characterized by positive Eu anomalies. In an open system, F-rich magmatic fluid mixed with retrograde metamorphic fluid to produce SchI-4 and SchII at similar to 300 degrees C under high fO(2), followed by cooling to similar to 250 degrees C, forming SchIII. Finally, evolved F-rich fluids ascended along fractures, and additional cooling (similar to 180 degrees C) coupled with meteoric water input generated SchIV. These results highlight that progressive cooling, coupled with fluid-rock interaction in an oxidizing environment and localized boiling, were the dominant controls on fluid evolution and scheelite deposition in the skarn-type tungsten mineralization system.

Ultra-deep carbonate oil and gas resources represent a key frontier for future oil and gas exploration and development. Complex fluid activities exert a significant influence on the diagenesis, reservoir formation, and hydrocarbon accumulation processes in ultra-deep carbonate rocks. In the Middle Permian Maokou Formation of the northern Sichuan region, a variety of minerals, predominantly calcite, extensively fill the pores and fractures, yet their origins and the associated fluid evolution processes remain unclear. To address this issue, this study employs petrographic analysis, C-O-Sr isotope characterization, rare earth element (REE) geochemistry, fluid inclusion analysis, and U-Pb geochronology, in conjunction with the burial-thermal evolutionary history. The research focuses on calcite cements occurring in the pores and fractures of the Maokou Formation, aiming to clarify their genesis in the Yuanba area and evaluate their significance for hydrocarbon exploration. The results indicate that the lithology of the Maokou Formation is predominantly composed of bioclastic limestone, bioclastic micritic limestone, and micritic bioclastic limestone. Pores and fractures within the formation are filled with three successive stages of calcite cements: mud-powder crystal calcite (Cal-1) → fine-medium crystal calcite (Cal-2) → coarse crystal calcite (Cal-3). The δ13C, δ18O, and 87Sr/86Sr values of the first-stage cements are comparable to coeval seawater values. The mixing of seawater and meteoric water in the pore space results in increased concentrations of Ca2+ and CO32-, promoting precipitation. Cal-1 formed in the Late Permian–Early Triassic, in response to changes in temperature and pressure due to increased burial depth. The δ18O values of the second-stage cements exhibit a negative shift. Dissolution of Maokou Formation carbonates released Sr2+ and Ca2+ into the formation water, thereby increasing 87Sr/86Sr ratios and returning Ca2+ concentrations to saturation. As temperature and pressure changed with continued burial, Cal-2 precipitated during the Late Triassic–Early Jurassic, as constrained by a U–Pb age of 214.2 ± 4.8 Ma. The third-stage cement is characterized by low δ13C and δ18O values, elevated 87Sr/86Sr ratios, and a pronounced positive Eu anomaly in the REE pattern. Deep hydrothermal fluids carrying substantial concentrations of Ca2+ and CO32- migrated along structural fractures into the Maokou Formation. As temperature and pressure decreased, Cal-3 condensed and precipitated, forming during the Middle Jurassic. Based on the type and abundance of hydrocarbon inclusions in calcite cements, a correlation between reservoir densification and hydrocarbon charging was established. It was determined that densification before hydrocarbon charging is the primary factor contributing to the limited natural gas accumulation in the Maokou Formation of the Yuanba area. The findings suggest that for deep limestone reservoirs lacking or weak dolomitization, early hydrocarbon charging plays a critical role in preserving reservoir quality, ultimately controlling the extent of hydrocarbon enrichment.

The carbonate reservoirs of the Guadalupian series in the Middle Permian are an important target for natural gas exploration in the Sichuan Basin. Episodic Emeishan mantle-plume activity reconfigured the Upper Yangtze depositional architecture: pre-eruptive doming controlled the Roadian-Wordian carbonate-ramp system, whereas volcanic eruption drove a Capitanian transition to a rimmed carbonate platform, generating a SE-NW-trending platform-margin belt along the northern Upper Yangtze Block. Research indicates significant differences in rock types and diagenetic processes on both sides of the platform margin belt, which may be influenced by the potential effects of the Emeishan mantle-plume activity. This study integrates representative wells along the northern Upper Yangtze platform margin, combining detailed petrography with C-O stable-isotope analyses, in situ microscale rare-earth-element determinations, and U-Pb carbonate geochronology to define margin-flanking lithofacies, elucidate the origin and evolution of their contrasting diagenetic signatures, and evaluate their potential linkage to Emeishan mantle-plume activity. The results indicate the following: (1) On both sides of the platform-margin belt along the Capitanian Stage of the Guadalupian Series of the northern edge of the Upper Yangtze region, lithology and diagenetic processes exhibit distinct variations: The inner restricted environment primarily underwent dolomitization, forming MD1 and MD2, while the outer open environment mainly experienced silicification, developing BS and DS. (2) Episodic Emeishan mantle-plume activity induced tectono-sedimentary differentiation within the Guadalupian succession, changing depositional architecture and diagenetic environments; contemporaneous magmatic heating intensified convective dolomitization and upwelling, potentially influencing the differential conditions on both sides of the margin zone. These findings provide a direct exploration template for Guadalupian reservoirs across the Upper Yangtze: forthcoming drilling should prioritize dolostone prospects within the inner platform-margin belt.

The genesis of the Dabaiyang Au-Te deposit on the northern margin of North China Craton remain poorly constrained due to limitations of previous studies that were mainly based on bulk quartz 518O isotope analyses and fluid inclusion microthermometry potentially affected by post-entrapment modification. Here, we presented an integrating study of paragenetic sequence, in-situ trace element and isotopic (534S and 518O) analyses of pyrite and K-feldspar to decipher fluid source and evolution history. The 518O values of pre-ore K-feldspar (8.2 to 9.6 %o) and 534S values of pre-ore pyrite (-5.5 to-0.1 %o) indicate a magmatic source for the ore fluids, with negligible meteoric water input in the pre-ore stage. Trace element compositions of three pyrite generations (Py-1, Py-2a, Py-2b) reveal a two-stage gold enrichment process. The pre-ore stage was characterized by high-temperature, oxidized, and alkaline fluids, where Au was mainly incorporated as invisible gold into the As-rich Py-1. The syn-ore stage involved vigorous fluid boiling and mixing with meteoric water, leading to fluid cooling and the precipitation of visible native gold. The enrichment of gold during this stage was further facilitated by polymetallic Te-rich melts, accounting for the close association between native gold and tellurides. Integrating our results and previously published data, we propose that the Dabaiyang is more appropriately classified as an oxidized intrusion-related gold deposit, likely associated with a concealed Late Triassic granitic intrusion, rather than an epithermal system as previously suggested.

The discovery of extensive layered witherite (BaCO3) deposits in the Early Cambrian strata in South China offers valuable insights into the unique paleo-marine environment of this region. Based on stratigraphy, petrography, geochemistry, fluid inclusions, and pervious published multi-isotope geochemical analysis, we aim to explore the distinct genesis mechanism of the witherite deposits in the Chengkou area of South China and unveil the specific paleo-marine environment during their formation. This study concludes that the wide 87Sr/86Sr ratios (0.708266 to 0.708504) of witherite and barytocalcite (BaCa(CO3)2) support the seawater-derived barium. Negative δ13C values (−15.6 to −12.5‰) indicate the involvement of organic matter during the formation of witherite. The complex vapor-phase (including CH4, H2S, etc.) and HS−-containing liquid-phase compositions in the primary liquid–vapor inclusions of the witherite and barytocalcite imply that the two minerals are formed in sulfur-rich euxinic seawater. The broad homogenization temperatures are generated by thermal re-equilibration of the inclusions, rather than the actual temperatures of the trapped fluids. The salinity range of fluid inclusions in the Bashan witherite deposit (0.2 to 16.2 wt.%) records mixing between moderate-salinity basinal-derived fluids and low-salinity seawater-sourced fluids. We propose that the formation of Chengkou witherite deposits is linked to a sulfate-limited euxinic seawater environment, highlighting the spatiotemporal heterogeneity in Early Cambrian paleo-oceanic sulfate concentrations.

Identifying the source of solid bitumen is a crucial step in oil and gas source correlation. The origin of solid bitumen in the Maokou Formation of the Huayingshan area has always been a subject of debate. This research explores the origin of solid bitumen in the Maokou Formation of Huayingshan through biomarker and carbon isotope analysis of 5 solid bitumen samples and 1 source rock sample. The results show that the solid bitumen originates from a strongly reducing, low-salinity marine environment, with predominant input from bacteria and algae, showing high-overmature stage of maturation. The tricyclic terpane distribution shows C23 tricyclic terpane exceeds C21, and hopanes are dominated by C30H. Regular steranes exhibit an inverted “L” distribution with C28 < C27 < C29. An inversion of carbon isotope type-curves, characterized by δ13Caro < δ13Csat < δ13Cnos < δ13Casp in marl and dolomite limestones, whereas in dolomites, it is δ13Casp < δ13Cnos < δ13Csat < δ13Caro. The hydrocarbon source correlation suggests a strong genetic affinity between solid bitumen in the Maokou Formation reservoirs and source rocks from Maokou Formation I and Longmaxi Formation. Carbon isotope of group compositions type-curves suggest that solid bitumen in the dolomite limestones received more input from the Maokou Formation I, while solid bitumen in dolomite was more influenced by contributions from the Longmaxi Formation. A comprehensive analysis concludes that the inversion is a result of the segmented supply of hydrocarbons from source rocks under pervasive TSR and biodegradation.

This study employs a sequential mediation model to investigate the cognitive mechanisms linking Earth science education to sustainable behavior. Grounded in construal level theory and temporal cognition research, we hypothesize that geological time perception mediates the relationship between Earth science education and temporal construal level, which in turn affects sustainable behavior. Structural equation modeling, based on data from 280 participants, validated the proposed model. It confirmed geological time perception as a second-order construct with four dimensions: time span perception, understanding of geological processes, time depth perception, and continuity of geological change. The results indicated significant indirect pathways. Earth science education influenced the temporal construal level via geological time perception (β = 0.325), and the temporal construal level mediated the relationship between geological time perception and sustainable behavior (β = 0.306). The sequential mediation path (β = 0.215) suggests that Earth science education promotes sustainable behavior by recalibrating temporal cognition and construal processes. This finding illuminates how educational interventions can address the temporal asymmetry in environmental decision-making by developing specific cognitive capacities rather than simply imparting knowledge.

The Cretaceous-Paleogene (K-Pg) extinction is linked to two primary causes: the Chicxulub asteroid impact in Mexico and the Deccan Traps eruptions in India. While substantial geological evidence supporting both events has been found worldwide, to understand their potential interactions, it is crucial to study sites that preserve records of both events simultaneously. The terrestrial K-Pg boundary located in the Sichuan Basin, China (similar to 15,500 km from the Chicxulub Crater and similar to 5,600 km from the Deccan Traps correspond to 66 Ma), preserves evidence of both the Chicxulub impact and the Deccan Traps eruptions, along with the effects of subsequent events on the earlier ones. It offers a new perspective on the K-Pg boundary. Detailed petrological examination and geochemical analyses, including platinum-group element (PGE) and black carbon concentrations, were conducted across a 2 m K-Pg boundary section. The K-Pg boundary layer (similar to 2.5 cm thick) is composed of very fine-grained, brick-red sandstone and exhibits significant enrichments in Ir (9.050 ppb) and Os (10.72 ppb), along with elevated black carbon (1.10 parts per thousand), strongly indicating contributions from the impact. Intriguingly, another PGE anomaly was detected approximately 50 cm below the K-Pg boundary. The strata surrounding the K-Pg boundary display evidence of alteration by acidic and HS--rich fluids. These fluids likely caused the observed downward migration of PGE within the boundary, resulting in two distinct PGE anomalies - one at the K-Pg boundary itself and another approximately 50 cm below. These fluids resulted in the overlying sandstones exhibiting minimal matrix content and bleached the underlying brick-red sandstones. Volcanic gas emissions from the Deccan Traps after the impact are a potential source for these fluids. Our findings support the hypothesis that the most voluminous Deccan eruptions had occurred close to, but not necessarily immediately after, the Chicxulub impact, potentially lasting 100-131 ka. The hiatus after the impact weakens the possibility of a direct causal link between the Deccan eruptions and the impact.

溶蚀作用是四川盆地茅口组储层形成的重要成岩作用之一,为确定川北地区中二叠统茅口组碳酸盐岩岩溶储层发育情况与成因,本次研究通过野外露头、钻井岩心以及薄片观察、同位素地球化学特征分析,对溶蚀作用的发育特征与控制因素展开研究.川北地区茅口组溶蚀作用的发育特征主要表现为晶间溶孔、粒间溶孔(铸模孔)、溶蚀孔、溶洞以及溶蚀缝等不同程度发育,溶蚀孔洞缝方解石充填物可划分为同生—准同生阶段的CC,方解石与表生阶段的CC2方解石,CC1方解石具有高的δ13C值(2.80‰～4.72‰,均值为3.75‰)与δ18O值(-5.30‰～-8.23‰,均值为-6.93‰),且具有与围岩接近的87Sr/86Sr值(0.706 210～0.708 178),形成于同沉积的海水环境中,受到部分大气淡水的影响;相比较下,CC2方解石具有较低的δ13C值(-2.13‰～-0.34‰,均值为-1.12‰)与 δ18O 值(-9.59‰～-7.00％0,均值为-6.56‰),以及较高的 87Sr/86Sr 值(0.708 316～0.711 365),在大气淡水主控下形成,伴有地壳流体的影响.综合溶蚀作用发育与充填物特征将川北地区茅口组溶蚀作用划分为3期:(1)同生期溶蚀作用,流体主要为海水与大气淡水的混合水,受沉积相带控制易发育晶间溶孔、粒内溶孔(铸模孔),充填有CC1方解石;(2)表生期溶蚀,流体为大气淡水与地下水,受古地貌控制主要发育在茅口组顶部,溶蚀孔、溶洞与早期溶蚀缝的大规模发育且伴有CC2方解石与钙泥质的充填;(3)埋藏期溶蚀,主要表现深部热液与酸性流体对构造裂缝与CC2方解石的再溶蚀,导致晚期溶蚀缝的发育,以沥青、黄铁矿、石膏等热液矿物的充填为主.综合各期溶蚀作用的发育规模与充填情况,研究认为川北地区茅口组溶蚀空间的发育主要来源于表生期溶蚀作用,有效溶蚀空间多发育于峰丛洼地微古地貌单元处.

微生物介导碳酸盐矿物沉淀为"白云岩"问题的解决带来了希望.本次研究利用好氧、中度嗜盐细菌,在Mg2+/Ca2+值分别为3,5和7的溶液中合成碳酸盐,记录了每隔24 h溶液中的pH值,并取样分析了溶液中主要阳离子的变化情况.了解溶液pH值和阳离子变化,有利于我们了解微生物作用下碳酸盐矿物形成的过程,对理解微生物作用下碳酸盐的形成机制具有重要意义.实验结果表明,合成的矿物主要为一水碳酸钙、方解石及原白云石.3种溶液的pH值在前4 d均明显降低,溶液整体呈酸性,4 d后溶液pH值降低的趋势减缓,10 d后溶液pH值缓慢上升,呈近中性或弱碱性.Ca2+,Mg2+均呈现先下降后略微上升的趋势,Ca2+,Mg2+后期略微上升可能是由于细菌活性降低后不再消耗Ca2+,Mg2+,溶液中的H+,Na+和K+等阳离子在阳离子交替吸附的作用下替换出了一部分吸附在培养基上的Ca2+和Mg2+所致;3种溶液中,Ca2+的消耗量随着Mg2+/Ca2+值的增大而减小,而Mg2+的消耗量则随着Mgz+/Ca2+值的增大而增大,但这并不意味着高Mg2+/Ca2+有利于原白云石的形成.Sr2+浓度的变化与Ca2+,Mg2+浓度整体趋势一致,但明显与Ca2+浓度变化具有更好的相关性,这可能与Sr2+在进入碳酸盐晶格中时,更容易取代Ca2+而非Mg2+有关.

为明确川北地区中二叠统茅二段碳酸盐岩储层发育机制及控制因素,文中选取典型井及剖面,利用薄片鉴定、阴极发光、扫描电镜、物性分析、高压压汞等手段,对茅二段储层特征及控制因素进行了分析.结果表明:1)茅二段为碳酸盐岩台地沉积,孔渗条件较差,依赖裂缝及成岩作用改造;2)茅口组储层成岩作用复杂,发生多期次溶蚀及白云岩化作用;3)储层受构造活动、沉积及成岩作用等多种因素共同控制.构造演化及古地貌影响了沉积及成岩作用范围,茅口组发育的滩体是储层形成的物质基础,后期岩溶改造叠加白云岩化是储层形成的关键.

四川盆地古生代海相地层沉积厚度巨大.奥陶系碳酸盐岩的碳氧同位素组成受后期成岩作用影响较小,基本保留了原始海洋的同位素组成:δ13 CPDB值分布区间为0.17‰～-6.20‰,δ18 OPDB值分布区间为-4.98‰～-11.07‰,δ18OPDB与δ13CPDB两者不存在明显的线性关系.碳氧同位素对比表明,四川盆地下奥陶统碳氧同位素值与全球下奥陶统的碳氧同位素分布区间基本一致,并且碳同位素值曲线识别了具有全球对比特征的TSICE正漂事件,显示奥陶系碳同位素曲线具有全球可对比性.同时,四川盆地奥陶系桐梓组中期δ13CPDB平均值从—1.62‰负漂为-4.87‰,发生了显著的负漂移事件,分析认为在四川盆地早奥陶世早期由西向东的海退事件导致海洋生产力急速下降是造成δ13CPDB值的负漂移主要原因.桐梓组中上部δ18OPDB大幅度负向偏移,表明桐梓组中期有一个短时期温度升高、盐度降低的过程.研究揭示奥陶系碳氧同位素可以有效的辅助该区的地层划分对比,并且四川盆地早奥陶世发生过显著的海退事件.

以鄂尔多斯盆地环县北地区三叠系延长组长 7 油层组长 72 亚段为研究对象,探讨重力流发育类型、展布特征以及储集性砂体的发育规模.综合对虎 62-45 井、巴 15-19 井、巴 91井长72 亚段岩心录井资料和53 口重点井位测井资料的分析,结果表明:长 72 亚段的重力流主要为浊流和砂质碎屑流两种形式,浊流的沉积构造丰富,薄层的细－粉砂岩与泥岩不规则互层,砂质碎屑流则主要发育含撕裂状泥砾的块状细砂岩;长72 2 小层砂质碎屑流发育略差于浊流,而长72 1 小层则主要发育砂质碎屑流,两个小层的储集性砂体主要发育于砂质碎屑流中,砂体厚度多在5～15 m;以厚层块状砂体为主的砂质碎屑流展布区内油藏发育,油气储集条件要好于以薄层砂泥岩互层为主的浊流.长72 亚段砂质碎屑流砂体的性质和展布特征是其成为储层的主要影响因素,长72 亚段砂质碎屑流砂体储层具有较大的勘探开发潜力,是重力流沉积区油气勘探开发的有效目标.

综合岩心观察、薄片鉴定、碳氧同位素、稀土元素、流体包裹体分析等手段,研究四川盆地元坝地区中二叠统茅口组溶蚀孔洞中方解石充填物类型、流体来源以及形成期次,探讨其储集性能.研究表明:茅口组方解石充填物类型为栉壳状、等轴粒状、亮晶方解石,稀土元素质量分数为(2.425～15.581)×10-6,平均为6.791×10-6;∑LREE/∑HREE为2.782～5.831,平均为4.395;Y/Ho值为35.591～51.534,平均为44.927;δCeN值为0.615～0.864,平均为0.707;δEuN值为0.866～1.385,平均为1.154;稀土元素配分模式图呈现左倾特征;δ13 C值为-2.13‰～-0.34‰,δ18 O值为-9.59‰～-7‰(平均为-8.08‰),δ13 C值与围岩接近,δ18 O值比围岩偏低;流体包裹体显示均一温度主要在80～100℃,盐度(NaCl的质量分数)主要在12.85％～14.15％.方解石主要形成于中三叠世前,形成期次先后为栉壳状、等轴粒状、亮晶方解石.Ce出现负异常,Eu呈正异常的特点,显示受热液影响.δ13 C值低于全球中二叠世的瓜德鲁普阶海水,δ18 O值比围岩更负,说明方解石充填过程中受多种流体的影响,充填时间较早.

为研究川东南地区志留系小河坝组海相致密砂岩储层微观孔隙特征及形成机理,开展了岩石薄片鉴定、阴极发光、电子探针、场发射扫描电镜和高压压汞测试等实验分析.结果表明:①小河坝组致密储层孔隙类型有残余原生粒间孔、粒间溶孔、粒内溶孔、基质孔、晶间孔及微裂缝,其中次生溶孔(粒间溶孔和粒内溶孔)占主导,被溶物质主要为碎屑长石和方解石胶结物;②孔隙发育情况受沉积微相、长石溶蚀作用和下伏烃源岩生烃强度共同影响,离生烃中心越近、长石含量越高的远砂坝砂岩中,次生溶孔最为发育;③双流坝—冷水溪一带微观孔隙最为发育,储层物性相对较好.研究结果为川东南地区致密砂岩气勘探指明了新方向.

通过X射线荧光光谱仪、X射线粉晶衍射分析、热重分析、扫描电镜等表征手段,研究焙烧温度对白云母晶体结构特征、物性变化的影响.结果表明:白云母在25～1 200℃温度范围的加热过程变化主要分为三个阶段:25～500℃,该焙烧温度段对白云母的晶体结构、光学性质、表面形貌影响甚小;600～1 000℃,白云母虽保持片层状晶体结构,但羟基脱出使得其片层内结构进行微调,d002晶面间距由1.010 nm增加至1.021 nm,此温度段内白云母由透明态转为不透明态,色泽由无色变为淡黄色,表面形貌凹凸不平,层面出现皱褶;1 100℃以上,白云母晶体结构完全被破环,形成由少量莫来石、三氧化二铝以及大量非晶态硅氧化合物组成的熔融物,该熔融物不透明,层面疏松,极易脆裂,内含大量微孔隙,白云母物性产生显著变化.

In this paper, the genesis of dolomite in Longwangmiao Formation is analysed through field investigation and geochemical methods, and dolomization model is established, which is very important for the next reservoir prediction in Longwangmiao Formation. According to the crystal size, the Longwangmiao Formation dolomite can be divided into two types: microcrystalline dolomite (MID) and macrocrystalline dolomite (MAD). Both types of dolomite have higher Al content than lime mudstone, indicating that during the deposition process of the Longwangmiao Formation, terrigenous materials are continuously mixed into the sediment, which significantly affects the geochemical characteristics of the Longwangmiao Formation. The rare earth element (REE) composition of the two types of dolomite is consistent with that of lime mudstone (LM), with an obvious 8Ce positive anomaly and no 8Eu anomaly, which is a typical distribution pattern of marine carbonate sediments. The microcrystalline dolomite has a higher Na element content, lower 813C value, and higher 818O value, suggesting that it is formed in a highly saline evaporation environment. Most of the macrocrystalline dolomite has a residual grain texture. The elements, as well as the isotopic geochemical characteristics of the dolomite, are consistent with those of lime mudstone, indicating that macrocrystalline dolomite is formed early and inherits the geochemical characteristics of the precursor limestone. We believe that the dolomitization model of the Longwangmiao Formation is an evaporative concentration + reflux seepage model. In the late sedimentary period of the Longwangmiao Formation, the sea level declined and a large area of lagoon appeared in the restricted and semi-restricted platform. As the evaporation and concentration continued, precursor minerals such as highmagnesium calcite and aragonite mud experienced chemical precipitation. In this process, a large amount of Ca2+ was consumed, resulting in an increase in the Mg2+/Ca2+ ratio. Then, the precursor minerals underwent dolomitization, and microcrystalline dolomite began to form. At the same time, owing to the difference in density between the high-salinity concentrated seawater and the pore water existing in the early limestone, the concentrated seawater flowed back and penetrated downward, causing the dolomitization of the underlying strata, and then the formation of macrocrystalline dolomite. The degree of dolomitization was mainly affected by the development degree of the granule beach and the thickness of the strata.

The tuff layer steadily distributed in the western Yangtze Craton is a regional marker for the EarlyMiddle Triassic (OlenekianAnisian) boundary. Integrated studies of whole-rock geochemistry and zircon geochronology reveal that the parental magma of the tuff is of felsic composition, generated via volcanic eruptions in the continental arc setting along the southwestern margin of the Yangtze Craton at similar to 247 Ma. The syn-depositional zircons in the tuff layers and in the coeval igneous rocks exhibit uniform negative epsilon(Hf)(t) values of approximately -20 to -6, indicating the significant input of crustal materials. Massive crustal assimilation implies a large-scale remelting of the pre-existing continental crust, triggered by the intensive arccontinental collision during that time. This intensive collisional tectonomagmatic event is an important signal for the closing of the eastern Paleo-Tethys branch and points to the initial collision of the Indochina Block and the Yangtze Craton. Xenocrystic zircons in the Precambrian-age offer insight into the early evolution of the southwestern Yangtze Craton, which shows episodic crustal growth and reworking of similar to 2.92.2 Ga, crustal reworking of similar to 1.91.7 Ga, rifting-related tectonomagmatism of similar to 1.61.4 Ga, and crustal growth of similar to 1.10.8 Ga. The older crystallization ages (3.42.5 Ga), lower initial Hf-176/Hf-177 values (0.28050.2813), negative epsilon(Hf)(t) values (-15.7 to -1.6), and two-stage Hf model ages (3.92.8 Ga) of zircons further suggest that an unexposed Archean basement exists beneath the southwestern Yangtze Craton. Significant contributions of mantle-derived materials occur at similar to 1.31.0 Ga, implying that the southwestern Yangtze Craton may not be involved in the Grenvillian-aged continentalcontinental collision orogeny. Comparable age spectrums and Hf isotopic data suggest that the Paleoproterozoic igneous rocks are a non-negligible provenance for Proterozoic metasedimentary in the Kangdian region. (C) 2021 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.