四川盆地东部下寒武统龙王庙组碳、氧同位素组成及古环境意义

在野外沉积特征研究、室内薄片观察的基础上,对四川盆地东部龙王庙组22个碳酸盐岩样品的碳、氧同位素进行测试,在充分论证样品的有效性后,分析研究区龙王庙组碳、氧同位素特征,进而探讨龙王庙组沉积期的古气候及古海洋环境。样品实验数据显示δ13C值分布在-1.533‰~2.619‰,平均为0.046‰;δ18O值分布在-9.916‰~-3.580‰,平均为-7.746‰;碳、氧同位素整体变化趋势与扬子地台其他区域基本相同。古海洋环境恢复表明,龙王庙组沉积期四川盆地东部整体处于海相环境,海水盐度呈先降低、后增高、复又降低的多段式变化;海水温度主要分布在20~30℃,属于温暖或炎热的亚热带气候;在海平面缓慢波动性下降、陆架暴露、生物灭绝的沉积环境影响下,龙王庙组δ13C值具有负漂移的演化趋势。龙王庙组沉积中期的水体深度最浅,古盐度最高,是白云岩最为有利的发育阶段。     

滇东北地区下寒武统龙王庙组白云石化模式研究：来自钙同位素模拟结果

滇东北地区桧溪剖面位于四川盆地南缘外侧,剖面龙王庙组地层白云石化活动强烈,广泛发育泥晶灰岩、砂屑灰岩、泥晶白云岩、云质灰岩和灰质云岩等岩性。剖面3个灰岩-过渡岩性-白云岩旋回中具有混积特征,石英颗粒大量发育。阴极发光下,3个岩性旋回主要呈暗红色,可见石膏。地球化学测试显示：旋回1中灰岩-白云岩碳同位素为-0.78‰～-0.49‰,氧同位素为-9.28‰～-8.96‰,锶同位素为0.709 795 54～0.712 183 18,钙同位素为0.54‰～1.12‰;旋回2中灰岩-白云岩碳同位素为0.37‰～0.41‰,氧同位素为-9.76‰～-9.64‰,锶同位素为0.710 087 11～0.713 741 67,钙同位素为0.63‰～0.81‰;旋回3中灰岩-白云岩碳同位素为-0.03‰～0.23‰,氧同位素为-9.90‰～-9.24‰,锶同位素为0.709 909 34～0.712 376 17,钙同位素为0.56‰～0.94‰;3个旋回中灰岩锶、钙同位素测试结果明显偏低,白云岩锶、钙结果明显偏高。钙同位素对流、缓冲模型模拟结果显示,旋回1白云石化流体Mg²⁺浓...     

西南印度洋脊49.6°E热液区多金属硫化物硫同位素组成特征研究

同位素地球化学特征是海底多金属硫化物成矿作用研究的重要内容之一,是成矿物质来源及成矿介质的性质与条件是探讨矿床成因与时空分布规律的关键所在。在海底多金属硫化物成矿过程中,同位素的分馏机制与示踪特性可有效指示成矿元素的物质来源与迁移演化过程及成矿环境的物理化学变化。     

碳酸盐岩常用主微量元素、同位素分析测试结果差异性探讨: 基于川中下寒武统龙王庙组实例研究*

碳酸盐岩研究中存在多种微量元素、同位素测试方法,为进一步探究各测试手段实际获取地化信息之间是否存在差异?能否进行比对?以川中下寒武统龙王庙组碳酸盐岩样品为例,通过对比研究中常用的主微量元素测试(电子探针[EPMA]、激光剥蚀—等离子质谱[LA-ICP-MS]、溶液法微量[ICP-OES])、氧同位素测定(原位离子探针[in-situ SIMS]、酸溶粉末)结果,揭示讨论各测试结果的差异性,旨在为降低地化信息的多解性提供经验依据。研究发现: (1)各测试手段(EPMA、LA-ICP-MS、ICP-OES)之间的差异性客观存在,但测试结果偏差整体随着所测元素实际浓度的增高而降低。对于主量元素(>10%)各测试结果偏差小于2%;富集元素(>1000 μg/g)各测试结果处于测试误差之内,结果偏差小于6%;微量元素浓度区间(100~1000 μg/g)各测试结果偏差显著增大,并且LA-ICP-MS与ICP-OES结果偏差要小于LA-ICP-MS与EPMA结果偏差,前者偏差幅度由6%增至45%,后者偏差幅度由9.1%增至151%;在低于100 μg/g元素浓度区间,受矿物内非均质性影响LA-ICP-MS与ICP-OES的测试结果可相差几倍。(2)微区原位限定下,EPMA测试结果在邻近检测线区间(100~300 μg/g)与LA-ICP-MS结果偏差逐渐加大,推测此偏差变化是由EPMA结果矫正过程中对低含量元素的矫正补偿机制所造成。(3)in-situ SIMS氧同位素值揭示了矿物微区尺度上的 δ¹⁸O 值差异,但其整体测试结果与传统酸溶法测试的结果存在0.5‰~2.5‰ V-PDB的负偏偏差,推测此偏差可能来自于标样矫正转换误差。(4)实例样品中可见阴极发光特征与Fe、Mn含量无关的现象,故成岩流体判定更需结合岩石学、地化证据探讨。     

碳酸盐岩常用主微量元素、同位素分析测试结果差异性探讨: 基于川中下寒武统龙王庙组实例研究*

碳酸盐岩研究中存在多种微量元素、同位素测试方法,为进一步探究各测试手段实际获取地化信息之间是否存在差异?能否进行比对?以川中下寒武统龙王庙组碳酸盐岩样品为例,通过对比研究中常用的主微量元素测试(电子探针[EPMA]、激光剥蚀—等离子质谱[LA-ICP-MS]、溶液法微量[ICP-OES])、氧同位素测定(原位离子探针[in-situ SIMS]、酸溶粉末)结果,揭示讨论各测试结果的差异性,旨在为降低地化信息的多解性提供经验依据。研究发现: (1)各测试手段(EPMA、LA-ICP-MS、ICP-OES)之间的差异性客观存在,但测试结果偏差整体随着所测元素实际浓度的增高而降低。对于主量元素(>10%)各测试结果偏差小于2%;富集元素(>1000 μg/g)各测试结果处于测试误差之内,结果偏差小于6%;微量元素浓度区间(100~1000 μg/g)各测试结果偏差显著增大,并且LA-ICP-MS与ICP-OES结果偏差要小于LA-ICP-MS与EPMA结果偏差,前者偏差幅度由6%增至45%,后者偏差幅度由9.1%增至151%;在低于100 μg/g元素浓度区间,受矿物内非均质性影响LA-ICP-MS与ICP-OES的测试结果可相差几倍。(2)微区原位限定下,EPMA测试结果在邻近检测线区间(100~300 μg/g)与LA-ICP-MS结果偏差逐渐加大,推测此偏差变化是由EPMA结果矫正过程中对低含量元素的矫正补偿机制所造成。(3)in-situ SIMS氧同位素值揭示了矿物微区尺度上的 δ¹⁸O 值差异,但其整体测试结果与传统酸溶法测试的结果存在0.5‰~2.5‰ V-PDB的负偏偏差,推测此偏差可能来自于标样矫正转换误差。(4)实例样品中可见阴极发光特征与Fe、Mn含量无关的现象,故成岩流体判定更需结合岩石学、地化证据探讨。     

基于自然伽马能谱测井资料的碳酸盐岩层序地层划分及其对古环境恢复的指示意义——以川东北LT1井下寒武统龙王庙组为例

自然伽马能谱测井资料在碳酸盐岩层序地层研究中具有较好的应用效果,Th/U和Th/K曲线的振荡趋势可为层序地层的旋回性识别提供依据。笔者等选取东北地区LT1典型井的自然伽马能谱测井资料为对象进行层序地层分析,结合岩芯碳氧同位素资料,探讨了沉积期古环境和相对海平面升降之间的耦合关系。结果表明,通过对自然伽马能谱测井资料进行INPEFA分析和Demy小波变换分析,可将LT1井下寒武统龙王庙组划分为1个三级层序和6个四级层序。INPEFA处理得到的Th/U_1曲线和Demy小波变换得到的Th/U_3_d8曲线可指示LT1井龙王庙组三级层序的相对海平面变化,Th/U_3_d6曲线与四级层序的相对海平面变化曲线相当。LT1井龙王庙组δ13C变化受三级层序相对海平面变化控制明显,最大海泛面位置对应ROECE碳同位素负漂移事件开始位置。结合龙王庙组δ13C变化和基于自然伽马能谱测井的相对海平面变化分析,认为ROECE事件可能与深部缺氧海水上涌和河流的持续输入以及风暴沉积带入的陆源碎屑物质有关。整体而言,LT1井龙王庙组沉积期古海水温度和古盐度的振荡变化趋势与三级和四级层序的相对海平面变化曲线（Th/U_3_d8和Th/U_3_d6）形态具有一定相关性,说明基于自然伽马能谱测井资料开展碳酸盐岩层序地层划分具有可行性,对沉积古环境恢复具有一定的指导和借鉴意义。     

基于自然伽马能谱测井资料的碳酸盐岩层序地层划分及其对古环境恢复的指示意义——以川东北LT1井下寒武统龙王庙组为例

自然伽马能谱测井资料在碳酸盐岩层序地层研究中具有较好的应用效果,Th/U和Th/K曲线的振荡趋势可为层序地层的旋回性识别提供依据。笔者等选取东北地区LT1典型井的自然伽马能谱测井资料为对象进行层序地层分析,结合岩芯碳氧同位素资料,探讨了沉积期古环境和相对海平面升降之间的耦合关系。结果表明,通过对自然伽马能谱测井资料进行INPEFA分析和Demy小波变换分析,可将LT1井下寒武统龙王庙组划分为1个三级层序和6个四级层序。INPEFA处理得到的Th/U＿1曲线和Demy小波变换得到的Th/U＿3＿d8曲线可指示LT1井龙王庙组三级层序的相对海平面变化,Th/U＿3＿d6曲线与四级层序的相对海平面变化曲线相当。LT1井龙王庙组δ¹³C变化受三级层序相对海平面变化控制明显,最大海泛面位置对应ROECE碳同位素负漂移事件开始位置。结合龙王庙组δ¹³C变化和基于自然伽马能谱测井的相对海平面变化分析,认为ROECE事件可能与深部缺氧海水上涌和河流的持续输入以及风暴沉积带入的陆源碎屑物质有关。整体而言,LT1井龙王庙组沉积期古海水温度和古盐度的振荡变化趋势与...     

鄂西宜昌地区下寒武统水井沱组草莓状黄铁矿SEM图像特征及古环境指示意义：以鄂阳页1井为例

草莓状黄铁矿在页岩中广泛分布,其形态特征及粒径大小等可作为指示氧化还原状态的环境指标。本文以鄂西宜昌地区鄂阳页1井水井沱组富有机质层段及岩家河组样品为研究对象,利用氩离子抛光-场发射扫描电镜技术,结合图像处理软件ImageJ,快速获取SEM图像中草莓状黄铁矿相关参数,并探讨其环境指示意义。结果表明,鄂阳页1井下寒武统剖面样品中黄铁矿赋存形式多样,包括草莓状黄铁矿集合体、团块状黄铁矿、黄铁矿自形晶及有机质中星点状分散的黄铁矿等。其中,草莓状黄铁矿作为最主要的赋存形式,其粒径(D)、微晶粒径(d)、D/d值以及微晶晶型等相关参数在垂向上呈现明显变化。岩家河组草莓状黄铁矿微晶晶型以八面体为主,水井沱组富有机质层段底部以五角十二面体及近球形为主,中部以八面体、立方体为主,上部以立方体、四面体为主,自下而上微晶圆度呈逐渐减小趋势,反映了还原性减弱的过程。水井沱组富有机质页岩中草莓状黄铁矿平均粒径为4.43μm,中下部偏大,上部粒径偏小。草莓状黄铁矿微晶平均粒径为0.338μm,剖面上自下而上呈现由大到小的变化趋势。D/d值在岩家河组样品中偏小,在水井沱组富有机质层段下部最大,上部逐渐减小。综合相...     

川东及其周缘地区下寒武统龙王庙组沉积相

通过野外露头、钻测井、三维地震及区域地质调查等资料的综合研究发现,川东及其周缘地区下寒武统龙王庙组岩石类型以碳酸盐岩(粉晶白云岩、颗粒白云岩、泥晶灰岩和颗粒灰岩)为主,局部发育大套蒸发岩(膏岩和云质膏岩)及碳酸盐岩与碎屑岩的混合沉积;识别出局限台地相、开阔台地相、蒸发台地相和混积台地相4种沉积相类型,以局限台地相最为发育;川东及其周缘地区龙王庙组各沉积相带呈北东—南西向展布,混积台地相分布于研究区西北部,蒸发台地相集中发育在研究区西部华蓥山断裂东侧,局限台地相分布于混积台地相以东到盆地东边界以西的地区,开阔台地相分布于局限台地相以东到广海的部分地区。     

四川盆地磨溪—高石梯地区下寒武统龙王庙组颗粒滩特征及分布规律

以四川盆地磨溪—高石梯地区下寒武统龙王庙组颗粒滩为研究对象,结合钻井、测录井、岩心和薄片等资料,对龙王庙组颗粒滩特征、分布规律和主控因素进行了综合分析。研究区内颗粒滩岩石类型主要有两类:一类为具有明显颗粒结构的颗粒云岩,以砂屑云岩或鲕粒云岩为主;另一类为具有残余颗粒结构的晶粒云岩。颗粒滩主要发育向上变浅、粒度变粗的沉积序列,垂向上,与下部细粒沉积物可构成滩间海—颗粒滩、局限潟湖—颗粒滩等沉积相序;横向上,颗粒滩连续性较好,具有大面积连片分布的特征,自西北—东南向发育程度呈逐渐增大的趋势。进一步分析后认为,海平面的相对变化和沉积水体能量高低决定了龙王庙组颗粒滩的发育特征和叠置样式,不同级次海平面的升降变化使颗粒滩发育层位和发育程度得以定型,而沉积时期的古地貌则最终决定了龙王庙组颗粒滩平面分布的差异性。     

Sedimentary facies and model of shallow water carbonates platform of the Lower Cambrian Longwangmiao Formation in Sichuan Basin

Building the sedimentary model accurately and delineating the spatial-temporal distribution of grain bank are the keys to increase the rate of success in natural gas exploration. Thus,the types and characteristics of sedimentary facies of the Longwangmiao Formation in the Sichuan Basin were studied based on field outcrops,drilling,logging and seismic data. Taking a fourth-order sequence systems tract as a unit,the spatial-temporal distribution characteristics of sedimentary facies within the chronostratigraphic framework were precisely described,and the depositional model of the Longwangmiao Formation was established to reveal the development mechanisms of grain bank and point out the future natural gas exploration. The results showed that: (1)The typical shallow carbonate platform depositional system was developed in the Longwangmiao Formation of the Sichuan Basin and its surrounding areas. Mixed tidal flat,restricted platform(microfacies types including grain bank,dolomitic tidal flat,lagoon,and gypsum lagoon),open platform(microfacies types including grain bank,lime tidal flat),platform margin,and slope-basin were developed from the edge to the interior of the basin;(2)A sedimentary model was established,which was characterized by “one depression,two uplifts,and two grain banks in the form of belts”. The development of grain banks was mainly controlled by palaeo-topography and relative sea-level fluctuation. It was mainly developed in the highstand systems tract of a fourth-order sequence vertically,and distributed as a belt along the platform margin and around the lagoon area horizontally. Our paper pointed out the grain shoal deposits are the material basis for the development of high-quality reservoirs,the results thus provide a sedimentary geological basis for future natural gas exploration of the Cambrian Longwangmiao Formation in the Sichuan Basin.     

四川盆地下寒武统龙王庙组浅水碳酸盐岩台地沉积相特征及模式*

准确建立四川盆地龙王庙组沉积模式和精细刻画颗粒滩时空分布规律,是提高天然气勘探成功率的关键。依据野外露头、钻井、测井和地震等资料,综合分析四川盆地及周缘下寒武统龙王庙组沉积相类型及特征;以四级层序为单元,精细刻画等时地层格架内沉积相时空展布特征,建立沉积模式,揭示颗粒滩发育规律,指出下一步天然气勘探方向。结果表明: (1)四川盆地及周缘龙王庙组发育典型浅水碳酸盐岩镶边台地沉积体系,自盆地西缘向东依次发育混积潮坪、局限台地(颗粒滩、云坪和咸化潟湖等微相类型)、开阔台地(颗粒滩、灰坪等微相类型)、台地边缘和斜坡—盆地等沉积相类型;(2)建立了“一凹两隆,双滩成带”的沉积模式,颗粒滩的发育主要受控于古地貌和相对海平面升降,具体表现为垂向上主要发育于四级层序海退时期,平面上沿台地边缘带和围绕咸化潟湖的相对隆起区呈带状分布。由于颗粒滩是优质储集层发育的有利相带,因此该结果可为四川盆地寒武系龙王庙组下一步天然气勘探提供沉积地质基础。     

四川盆地下寒武统龙王庙组颗粒滩沉积组合及其对储集层的控制作用

基于前人研究成果, 综合四川盆地龙王庙组野外露头、钻测井、岩心及薄片等资料, 对龙王庙组的岩石类型、沉积亚相和岩石物性进行了详细的分析, 探讨了龙王庙组颗粒滩沉积组合的特征、分布规律及其对储集层发育的控制作用。结果表明： （1）四川盆地龙王庙组可以识别出4种主要的岩石类型, 垂向上主要发育3种与颗粒滩相关的水体向上变浅的沉积组合： 多期颗粒滩垂向叠置、颗粒滩—台坪（混积潮坪）、滩间海—颗粒滩（—台坪）;（2）颗粒滩沉积组合分布受控于古地貌和海平面升降;平面分布主要受控于古地貌, 多期颗粒滩垂向叠置组合主要发育在川中地区, 颗粒滩—台坪（混积潮坪）组合主要发育在川北、川西南地区, 滩间海—颗粒滩（—台坪）组合主要发育在川东、川东南地区;垂向分布主要受控于海平面升降, 与所处层序地层的位置有密切关系, 滩间海—颗粒滩组合多发育于层序中下部, 颗粒滩—台坪（混积潮坪）, 多期颗粒滩垂向叠置组合发育于层序中上部;（3）多期颗粒滩垂向叠置组合最有利于储集层发育, 其次是颗粒滩—台坪（混积潮坪）组合, 滩间海—颗粒滩（—台坪）组合储集层物性较差。     

Depositional combination of carbonate grain banks of the Lower Cambrian Longwangmiao Formation in Sichuan Basin and its control on reservoirs

Rock types, sedimentary subfacies and grain bank properties of the Longwangmiao Formation are studied in detail by outcrop, drilling and logging data, core, thin section and physical property of the Longwangmiao Formation in the Sichuan Basin. The characteristics, development and distribution of grain bank depositional combinations of the Longwangmiao Formation in Sichuan Basin and their control on reservoir development are discussed. The results show that: （1）four main rock types can be identified in the Longwangmiao Formation in Sichuan Basin. Vertically, three upward shallowing depositional combinations associated with carbonate grain bank can be identified: multi-stage vertical overlapping of grain banks, grain bank-tidal flat（mixed tidal flat）, interbank-grain bank（-tidal flat）; (2）the distribution of depositional combinations of grain banks is controlled by paleogeomorphy and sea level fluctuation;and the horizontal distribution is mainly controlled by paleogeomorphy, the vertical overlapping of multi-stage grain banks is mainly developed in the central Sichuan Basin, grain bank-tidal flat（mixed tidal flat）mainly develop in northern and southwestern Sichuan Basin, and interbank-grain bank（-tidal flat）mainly develop in the eastern and southeastern Sichuan Basin;vertically, they are mainly controlled by sea level changes, and have close relationship with their locations in the sequence stratigraphy, and interbank-grain bank（-tidal flat）mostly develop in the middle and lower parts of the sequence, multi-stage vertical overlapping of grain banks and grain bank-tidal flat（mixed tidal flat）develop in the upper part of the sequence; (3）multi-stage vertical overlapping of grain banks is the most favorable for reservoir development, followed by grain bank-tidal flat（mixed tidal flat）combination, and interbank-grain bank（-tidal flat）combination has the poor reservoir physical properties.     

四川盆地下寒武统龙王庙组岩相古地理特征和沉积模式

在系统吸收前人研究成果的基础上,通过露头、岩心和薄片观察,结合测井和区域地质资料,探讨了四川盆地龙王庙组岩相古地理特征及沉积模式。研究认为:四川盆地及周缘在寒武系龙王庙组沉积时期为远端变陡的缓坡环境,自西向东依次发育近岸潮坪—内缓坡—中缓坡—外缓坡相带。其中四川盆地主体位于内缓坡,它又可划分为浅水内缓坡、局限内缓坡和开阔内缓坡三个古地理环境,发育颗粒滩、滩间海、正常湖、局限湖和潮坪等5种亚相。在纵向上龙王庙组沉积期经历了上下两个海侵—海退的短期旋回。古地貌较高的浅水内缓坡主要发育上旋回,以颗粒滩和滩间海亚相为主,沉积了较厚层的砂屑白云岩、鲕粒白云岩、细晶白云岩、粉晶白云岩等。局限内缓坡和开阔内缓坡的下旋回发育了2套完整的湖—台坪组合,岩性以泥晶灰岩为主。上旋回普遍发生了白云石化,水体能量总体较弱;其中在局限内缓坡由于水流不畅、环境局限,以上旋回发育膏盐岩为特征。四川盆地及周缘缓坡台地的沉积特征和沉积模式的主控因素有三个:即古构造控制了沉积体系和沉积相类型;海平面升降控制了沉积物的垂向叠置和演变;古地貌和水体能量控制了沉积物类型和沉积微相分异。据此预测了安岳—南充—剑阁一带为有利储层的分布区。     

四川盆地及邻区下寒武统龙王庙组颗粒滩沉积特征与空间分布

通过对区域地质调查剖面资料和钻井资料的研究,结合对部分野外剖面与钻井岩心的系统观察和取样分析,发现四川盆地及邻区下寒武统龙王庙组的颗粒滩主要由颗粒石灰岩(白云岩)和晶粒白云岩构成;颗粒滩以未暴露浅滩为主,发育向上变浅和向上变深2类垂向序列。川中古隆起和黔中古隆起北部地区的颗粒滩的横向规模大、层位稳定性和连续性最好,其余地区颗粒滩多表现为点滩且规模较小。研究区龙王庙期总体上为西浅东深,西南缘、西北缘和北缘为古陆环抱,盆内呈“一隆两坳”的古地理格局。颗粒岩在古地貌高地具有广覆式“五线一带”的平面分布样式。川中古隆起、黔中古隆起北部地区是颗粒滩发育最有利的地区,东北部和东南部的水下岛链区是优质颗粒滩带发育的潜在区。古隆起发育演化对颗粒滩和有利储集相带具有明显的控制效应,次一级海平面升降变化影响滩体的垂向叠置样式和横向连续性。     

Origin and Distribution of Grain Dolostone Reservoirs in the Cambrian Longwangmiao Formation, Sichuan Basin, China

Dolostones in the Cambrian Longwangmiao Formation have become one of the most significant gas exploration domains in China. Over a trillion cubic meters of gas reservoirs have been discovered in the Gaoshiti-Moxi area; however, the origins and distribution of the dolostone reservoirs are not well understood. This work discussed the geology and geochemistry of the dolostone reservoirs in the Longwangmiao Formation to determine their origin and distribution. Two understandings are acquired: firstly, a carbonate ramp provided excellent conditions for grain beach deposition, while the presence of a hypersaline lake was favorable for the contemporaneous dolomitization of grain beach deposits. Petrographic and geochemical evidence further confirm that the Longwangmiao dolostone was formed during the contemporaneous stage. Secondly, the reservoir characteristics indicate that the grain beach sediments provide material basis for the development of the Longwangmiao dolostone reservoirs. Reservoir dissolution simulation experiments show that the porosity of the reservoirs was formed by dissolution during contemporaneous and burial stages. The dissolution pores formed during the contemporaneous stage were controlled by sequence interfaces. The large scale dissolution vugs formed during the burial stage subsequently spread along the pre-existing porosity and fracture zones. This study therefore identified that the development of grain dolostone reservoirs in a shallow water ramp under arid climatic conditions generally met the following conditions: (1) reefal beach deposits lay a foundation for reservoir development; (2) superficial conditions are an important determining factor for reservoir porosity; and (3) burial conditions provide environment for porosity preservation and modification.