New Bradoriid Arthropods from the Early Cambrian Balang Formation of Eastern Guizhou, South China

The Early Cambrian Balang Formation is comprised of mudrock and shale, which was deposited in a shelf environment in the eastern part of Guizhou, south China. The Balang Fauna, which consists of seven phyla, occurs in the middle and upper parts of the Balang Formation. Arthropods are important constituents of the Balang Fauna and include a great number of trilobites, large bivalved arthropods, and newly-discovered well-preserved bradoriid fossils. The bradoriids present include three genera and four species ： Comptaluta inflata （Cheng, 1974） emend Hou et al., 2002; Comptaluta kailiensis sp. nov., and Alutella elongeta sp. nov, Aluta sp. This faunal assemblage in the Balang Formation is distinguished from the Tsunyiella Chang, 1964, Songlinella Yin, 1978 and Kunmingella Hou, 1956 assemblage which occurs in the Niutitang and Mingxinsi formations of the Yangtze Platform in middle region of Guizhou and which is earlier than the Balang Formation in age. However, this assemblage resembles the Comptaluta Opik, 1968 assemblage from the Early Cambrian Heilinpu Formation in Wuding County, Yuanan Province and from the Ordian Stage of the Cambrian of Australia. The great abundance of Comptaluta Opik, 1968 and overall taxonomic diversity of the Comptaluta Opik, 1968 assemblage set it distinctly apart from theAlutella Kobayashi et Kato, 1951 and Aluta Hou, 1956 assemblages of the Balang Formation. Alutella Kobayashi et Kato, 1951 and Aluta Hou, 1956 also occur in the Early Cambrian Niutitang Formation of the Yangtze Platform of Guizhou. Individual Bradoriids from the Balang Formation are characterized by large size （〉3 mm）. The discovery of new Bradoriid assemblages not only expands the group＇s geographical range and assemblage affinities, but also indicates that Bradoriids migrated eastward from shallow-water to deeper-water environments during the Early Cambrian, indicating that they were capable of life in deeper-water, and adaptation to a new ecological setting.

Fossil Association from the Lower Cambrian Yanjiahe Formation in the Yangtze Gorges Area,Hubei,South China

Apart from previously reported Small Shelly Fossils （SSFs）, a macroscopic fossil assemblage, comprising abundant algae, cone-shaped tubular fossil forms, and probable impressions of a megascopic metazoan, comes from the Lower Cambrian Yanjiahe Formation in the Yangtze Gorges area of western Hubei Province, south China. The visible fossils are preserved in thinlaminated siltstone or muddy siltstone intercalated between 8-15 ram-thick carbonate deposits, probably representing sedimentary settings of a constrained local depression in the shallow water carbonate platform during the Early Cambrian Meishucunian Stage. The macroscopic fossil association provides significant fossil evidence about the evolution of life from the late Precambrian to the ＇Cambrian explosion＇ interval.

Trace Fossils from Lower Cambrian Wusongger Formation in Xiaoerbulake Outcrop,Kalpin Area,Xinjiang

Based on the analysis of trace fossils collected from the typical outcrop of the Lower Cambrian Wusongger Formation in the Kalpin area, ten ichnospecies of six ichnogenus were identified in the upper member of the Wusongger Formation, with most of them being found for the first time. The trace fossils are described seriatim. The ichnospecies are mainly represented by such common trace fossils as Ophiomorpha nodosa, Helminthopsis hieroglyphica, Helminthopsis ichnosp., Planolites beverleyensis, Planolites vulgaris, Planolites montanus, Palaeophycus striatus, Palaeophycus curvatus, Cochlichnus anguineus and Rituichnus elongatum. The trace fossils are of high diversity and low abundance, and can be diagnosed as the Cruziana ichnofacies. They can be interpreted as having formed in a shallow water environment.

A New Ichnogenus Kailidiscus Produced by Attachment from the Middle Cambrian Kaili Formation in Taijiang, Guizhou Province, China

Over 190 specimens of an attachment ichnofossil Kailidiscus （n. ichnogen.） have been found in the Kaili Bitoa, a Burgess Shale-type biota, from the middle Kaili Formation （early Middle Cambrian） in Taijiang County, Guizhou Province, southern China. Kailidiscus is an epichnia with a circular to oval attachment platform, on which there is a carbonaceous film probably formed by the body of the living organism. Structures such as a marginal furrow, an inner and outer marginal ride, many convex fold-ridges, and a large caved peripheral furrow on the attachment platform may be the result of basal tissues of a sessile organism that wrinkled to increase the attachment＇s surface area. The Kailidiscus organism may have been a sessile cnidarian attached to the muddy seafioor. Kailidiscus organisms lived in relatively quiet water, and were buried by a sudden influx of sediment.

Research on carbon and oxygen isotopes in phosphorus-bearing rock series of the Late Neoproteroic-Early Cambrian Taozichong Formation in Qingzhen City, Guizhou Province, Southwest China

In the study of the phosphate-bearing stratum at the bottom of the Cambrian system, the authors found that there occurred carbon isotope negative anomalies in the Taozichong section phosphate-bearing stratum in Qingzhen, Guizhou Province; they can be correspondingly compared with other synsedimentary carbon isotope negative anomalies both at home and abroad. The results showed that there occurred three negative anomalies of carbon isotopes in the Neoproterozoic-Early Cambrian Taozichong Formation, indicating that the temporal palaeo-oceanographical environment changed significantly, in which there happened two times of intensive carbon isotope variation, corresponding to creature extinction. Meanwhile, it is believed that the carbon isotope negative anomalies in phosphorites were caused by the ascending water mass of ocean current with the negative carbon isotopic composition of deep-ocean hydrothermal deposits.

Fluid charging and hydrocarbon accumulation in the Cambrian Longwangmiao Formation of Moxi Structure,Sichuan Basin,SW China

The multi-stage minerals filled in pore space were sequenced, and the charging stages of fluid and hydrocarbon were reconstructed based on the observation of drilling cores and thin sections, homogeneous temperature testing of fluid inclusions, Laser Raman composition analysis and isotope geochemical analysis. The Cambrian Longwangmiao Formation in the study area went through 5 stages of fluid charging, in which 3 stages, mid-late Triassic, early-mid Jurassic and early-mid Cretaceous, were related to oil and gas charging. Especially the oil and gas charging event in early-mid Cretaceous was the critical period of gas accumulation in the study area, and was recorded by methane gas inclusions in the late stage quartz fillings. The ^(40) Ar-^(39) Ar dating of the 3 rd stage methane inclusions shows that the natural gas charging of this stage was from 125.8±8.2 Ma. Analysis of Si, O isotopes and ^(87) Sr/^(86) Sr of the late stage quartz indicates that the fluid source of the quartz was formation water coming from long term evolution and concentration of meteoric water, but not from deep part or other sources, this also reflects that, in the critical charging period of natural gas, the Cambrian Longwangmiao Formation in Moxi structure had favorable conservation conditions for hydrocarbon accumulation, which was favorable for the formation of the Longwangmiao large natural gas pool.

Microfossils from the Chert in the Lower Cambrian Shuijingtuo Formation at Miaohe, Zigui, Hubei Province

This paper reports for the first time on the microfossils discovered in the black cherts of the basal part of the Lower Cambrian Shuijingtuo Formation at Miaohe village, Zigui County, Hubei Province, all of which were observed in thin sections. Nine genera, 9 species and 3 indeterminate species (including a new species) are described. According to these microfossils, the conclusion is made that the microfossil zone may be equivalent to the small shelly fossil assemblage zones 2—3 of the Meishucun stage. They have provided another important line of evidence for the correlation of the Sinian-Cambrian boundary strata with those of the adjacent areas.

Grading evaluation and prediction of fracture-cavity reservoirs in Cambrian Longwangmiao Formation of Moxi area,Sichuan Basin,SW China

By using core, thin section, well logging, seismic, well testing and other data, the reservoir grading evaluation parameters were selected, the classification criterion considering multiple factors for carbonate reservoirs in this area were established, and the main factors affecting the development of high quality reservoir were determined. By employing Formation MicroScanner Image(FMI) logging fracture-cavity recognition technology and reservoir seismic waveform classification technology, the spatial distribution of reservoirs of all grades were predicted. On the basis of identifying four types of reservoir space developed in the study area by mercury injection experiment, a classification criterion was established using four reservoir grading evaluation parameters, median throat radius, effective porosity and effective permeability of fracture-cavity development zone, relationship between fracture and dissolution pore development and assemblage, and the reservoirs in the study area were classified into grade I high quality reservoir of fracture and cavity type, grade II average reservoir of fracture and porosity type, grade Ⅲ poor reservoir of intergranular pore type. Based on the three main factors controlling the development of high quality reservoir, structural location, sedimentary facies and epigenesis, the distribution of the 3 grades reservoirs in each well area and formation were predicted using geophysical response and percolation characteristics. Follow-up drilling has confirmed that the classification evaluation standard and prediction methods established are effective.

Sedimentary environment and petrological features of organic-rich fine sediments in shallow water overlapping deposits: A case study of Cambrian Yuertus Formation in northwestern Tarim Basin, NW China

Taking the Cambrian Yuertus Formation outcrop profiles in the Aksu-Keping-Wushi areas of northwestern Tarim Basin as examples, the depositional environments of organic rich fine sediment were analyzed by examining the outcrop profiles macroscopically and microscopically. The study reveals that:(1) The lower part of the Yuertus Formation consists of organic-rich fine sediment or thin rhythmic interbeds of organic-rich fine sediment and siliceous sediment, the formation transforms to terrigenous diamictic grain shoal and inverse grading carbonate rocks upward.(2) The thin limestone interbedded with dark shale rhythmically has inverse grading.(3) The thin-bedded siliceous rock has metasomatic residual granular texture, stromatolithic structure and cementation fabric in vugs.(4) There are iron crust layers at the top of the shallowing diamictic grain shoal, beneath which exposed karst signs, such as karrens, dissolved fissures, sack-like vugs, near surface karst(plastic) breccia, breccia inside the karst system and terrigenous clastic fillings, can be seen.(5) Both the outcrops and seismic profiles show that organic-rich fine sediments above the unconformities or exposed surfaces are characterized by overlapping. The organic-rich fine sediment of the Cambrian Yuertus Formation was deposited in the anoxic-suboxidized restricted gulf lagoon environment, and its formation was controlled by high paleoproductivity and poor oxygen exchange jointly, then a shallow-water overlapping sedimentary model has been established. The results will help enrich and improve the sedimentary theory of organic-rich fine sediments.

The influence factors of gas-bearing and geological characteristics of Niutitang Formation shale in the southern margin of Xuefeng Mountain ancient uplift: A case of Well Huangdi 1

In order to evaluate the geological characteristics and gas-bearing factors of Niutitang Formation within the Lower Cambrian of northern Guizhou,the Huangping area located at the southern edge of the ancient uplift belt of Xuefeng Mountain was selected as the target area,and Well Huangdi 1 was drilled for the geological survey of shale gas.Through geological background analysis and well logging and laboratory analysis such as organic geochemical test,gas content analysis,isothermal adsorption,and specific surface area experiments on Well Huangdi 1,the results show that the Niutitang Formation is a deep-water shelf,trough-like folds and thrust fault.The thickness of black shale is 119.95 m,of which carbonaceous shale is 89.6 m.The average value of organic carbon content is 3.55%,kerogen vitrinite reflectance value is 2.37% and kerogen type is sapropel-type.The brittle mineral content is 51%(quartz 38%),clay mineral content is 38.3%.The value of porosity and permeability are 0.5%and 0.0014 mD,which the reservoir of the Niutitang Formation belongs to low permeability with characteristics of ultra-low porosity.The gas content is 0.09‒1.31 m^3/t with a high-value area and a second high-value area.By comparing with the geological parameters of adjacent wells in the adjacent area,the accumulation model of“sediment control zone,Ro control zone,structure controlling reservoir”in the study area is proposed.Therefore,deep-water shelf-slope facies,Ro is between high maturity-early stage of overmaturity and well-preserved zones in the Niutitang Formation in this area are favorable direction for the next step of shale gas exploration.

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

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

汉中地区构造演化及寒武系页岩气形成地质条件研究

近年来陕南地区页岩气勘探取得了一定的成果,与其同属扬子板块北缘的汉中地区也被认为具有较好的页岩气资源前景。本文利用野外地质调查、二维地震、岩石学及有机地球化学等资料,对汉中地区构造演化及寒武系页岩气地质条件开展研究。结果表明,汉中地区经历了南华纪—三叠纪海相演化、三叠纪末—白垩纪陆内演化和新生代断陷盆地三个演化阶段,寒武系牛蹄塘组和石牌组为海陆过渡相沉积,其中暗色泥岩有机质类型以Ⅱ1型和Ⅱ2型为主,TOC含量0.45%~2.79%,Ro为0.61%~1.21%,整体属于中等—好的成熟烃源岩,具备良好的生烃潜力;且牛蹄塘组灰黑色粉砂质泥岩中有机质较为丰富,石英等脆性矿物及黏土矿物含量较高,微裂缝及孔隙发育,有利于页岩气生成、赋存以及后期开发。综合分析认为汉中地区寒武系具备良好的页岩气资源前景,且东部地质条件优于西部。

塔里木盆地寒武系盐下白云岩成藏条件分析与勘探部署方向

塔里木盆地寒武系盐下具有优质的生储盖组合,是盆地级重大战略接替领域,但由于埋深大、层系古老,寒武系盐下勘探面临烃源岩、沉积储层与油气保存等基础地质方面诸多认识问题。本文在前人研究基础上,通过野外露头、钻井分析与区域地震大剖面解释,重新认识寒武系盐下烃源岩、沉积储层、盖层与油气保存条件,结合已钻井分析,指出寒武系盐下有利勘探方向,优选有利勘探区带。结果表明:1)下寒武统玉尔吐斯组烃源岩分布受控于前寒武纪裂坳体系,主要分布在北部坳陷及周缘、塔西南地区,总面积约26.8×10^(4) km^(2)。2)寒武系盐下发育肖尔布拉克组内—中缓坡丘滩体、吾松格尔组礁后滩两套储层。肖尔布拉克组内—中缓坡丘滩体沿塔南古陆周缘分布,面积4.5×10^(4) km^(2);吾松格尔组礁后滩发育在轮南—古城台缘带内侧,面积5.3×10^(3) km^(2)。3)中寒武统膏盐岩盖层发育膏盐湖、膏云坪、泥云坪3个相带,由巴楚隆起—阿瓦提凹陷膏盐湖中心向四周呈环带状展布,总面积大约25×10^(4) km^(2)。4)基于已钻井分析,提出近源、规模优质储盖组合与古隆起背景是寒武系盐下勘探突破的方向。优选塔中北斜坡、古城—肖塘南、温宿周缘、轮南地区4个Ⅰ类有利区与麦盖提斜坡1个Ⅱ类有利区,总面积5.4×10^(4) km^(2)。研究成果对于塔里木盆地寒武系盐下勘探部署具有一定的指导意义。

四川盆地“槽-隆”控制下的寒武系筇竹寺组页岩储层特征及其差异性成因

四川盆地寒武系筇竹寺组是继五峰组-龙马溪组后页岩气勘探开发的重要接替层位,目前在德阳-安岳裂陷槽中心和槽缘部署的Z201井和WY1井页岩气勘探取得良好效果,但裂陷槽内筇竹寺组页岩储层发育特征仍不清楚。以槽内中心Z201井和槽缘WY1井为重点,结合其他页岩气勘探开发资料,系统分析了研究区筇竹寺组页岩各小层矿物特征、有机地化特征、储层及储集空间特征、含气性特征。研究结果表明:①筇竹寺组可划分为8个小层,页岩整体以脆性矿物为主,总有机碳含量(TOC)普遍大于1%,为优质烃源岩,且槽内TOC高于槽缘,具备良好的生气条件。②筇竹寺组页岩有机孔与无机孔均发育,槽内孔隙发育更好,具有极高的含气量。1,3,5和7小层黑色页岩储层品质较好,5小层储层品质最优。③德阳-安岳裂陷槽控制了筇竹寺组页岩储层发育,槽内Z201井钻遇的筇竹寺组页岩储层优于槽缘WY1井。④乐山-龙女寺古隆起控制筇竹寺组页岩有机质演化程度,古隆起内筇竹寺组有机质热演化成熟度普遍低于古隆起外,隆起区适中的热演化程度具备大规模富气的条件。筇竹寺组页岩储层各项条件较好,是未来页岩气勘探开发的主要接替区域。

四川盆地南部下寒武统筇竹寺组页岩孔隙结构特征与页岩气赋存模式

近年来,四川盆地南部地区(以下简称川南地区)下寒武统筇竹寺组页岩气勘探开发取得了实质性的突破,但是,关于筇竹寺组页岩气储层孔隙结构特征及其对页岩气赋存模式影响的研究还较为薄弱。为此,以川南地区W207井筇竹寺组页岩为例,以总有机碳含量(TOC)不小于1.0%为界,将筇竹寺组页岩划分出4个高有机碳页岩层段(H1—H4层),并基于大视域扫描电镜、流体注入法孔隙定量表征、三维分子结构建模与分子模拟等方法,研究了不同富有机质层段页岩孔隙特征,并着重分析了H3层页岩孔隙发育特征与页岩气赋存模式。研究结果表明:(1)筇竹寺组页岩纵向上孔隙发育差异较大,其中H3层页岩孔隙系统最为有利,发育粒缘缝—有机质纳米连通孔隙—有机质基质分子内孔隙3级孔隙网络,其矿物粒缘缝与有机质纳米孔隙提供了较大的游离气储集空间,页岩有机质分子结构中普遍发育微孔,提供了较大的吸附空间;(2)微孔对总吸附量的贡献随压力增高而降低,但在30.0 MPa时仍贡献了56%以上的总吸附气量;(3)高温高压下(30.0 MPa、70℃),页岩中游离气甲烷含量占总含气量的57%,当压力由30.0 MPa降低至16.5 MPa,游离气贡献总开采气量超过80%;(4)粒缘缝、有机质纳米连通孔隙和有机质基质分子内孔隙良好的配置关系为页岩气富集及开发提供了良好的连通体系,远离风化壳的超压层段有利于页岩孔隙发育。结论认为,川南地区筇竹寺组H3层页岩孔隙系统发育,具备页岩气高产地质条件,是筇竹寺组下一步重点关注层段,在此基础上寻找远离风化壳、孔隙发育的超压页岩储层是筇竹寺组选区选层的关键。

地温梯度在塔里木盆地古生界热演化研究中的应用

塔里木盆地古生界烃源岩热史研究,特别是对超深古老烃源岩热演化认识存在较大争议,热演化阶段评价方法一直是困扰烃源岩热史研究的关键问题。调研结果表明,塔里木盆地寒武系古地温梯度变化在2.95~3.6℃/hm之间,按照生烃温度门槛值65℃计算,分别需要上覆地层厚度2203~1806 m,相差397 m,即2.58℃,温度差值较小。因此认为,塔里木盆地寒武系古地温梯度变化较小,可以忽略每期地温梯度取值上的差别,厚度可能是决定温度的主要因素;地层沉积与残留厚度可比较准确地获得,误差主要取决于剥蚀厚度的恢复。通过可靠获取的地层厚度、古地温梯度和剥蚀厚度等参数,以及烃源岩生烃图版,对塔里木盆地寒武系玉尔吐斯组烃源岩热演化阶段进行了评价;界定了关键期环满加尔坳陷的有效烃源岩及其分布,对玉尔吐斯组有效烃源岩及其规模生烃能力进行了预测和划分,并预测和划分了晚期成藏的有利区域。不同阶段有效烃源岩及其规模生烃量是每期成藏富集的关键,利用该方法避免了成熟度判识缺少可靠温标的问题,为塔里木盆地深层—特深层石油勘探和开发以及晚期成藏有利区的选择提供了重要的科学依据。

塔里木盆地西北部震旦系—寒武系不整合面成因——来自沉积学的证据

【目的】塔里木盆地西北部阿克苏地区广泛发育震旦系—寒武系平行不整合面,目前对其形成机制还存在争议。【方法】以沉积学方法为手段,基于上震旦统奇格布拉克组顶部的沉积相及其岩溶现象,通过详细的野外观察和镜下鉴定,对上述不整合面的成因开展研究。【结果】阿克苏地区奇格布拉克组顶部主要发育于台地边缘和斜坡环境。台地边缘包括颗粒滩和台缘礁,岩相为厚层—块状鲕粒白云岩、中—厚层状砂屑白云岩以及块状叠层石礁白云岩。斜坡环境包括的岩相有滑塌角砾白云岩、浊积岩以及薄层状粒泥白云岩。震旦纪晚期,阿克苏地区东部的沉积水体更深,岩溶发育程度也明显强于西部,垂向上以潜流带为主。此外,寒武纪早期沉积的玉尔吐斯组保持了与奇格布拉克组顶部相一致的沉积趋势,两者自西向东均表现为水体加深的地层序列。【结论】该不整合面由震旦纪末期台缘构造活动诱导的掀斜运动形成,导致阿克苏西部发生抬升,并形成了向东流动的大气淡水水文系统,使得东部台缘带岩溶作用强烈。该研究可为该区域震旦系白云岩储层的油气勘探提供参考。

塔里木盆地中寒武统沙依里克组岩相古地理特征

沙依里克组是塔里木盆地寒武系油气勘探中的重要层位,沉积相的精细刻画依然是目前制约该层位油气勘探取得突破的关键因素。本次研究在大量岩心观察、230块岩石薄片鉴定分析的基础上,总结了研究区内10种典型的岩相组合类型,并识别4种典型地震相带特征,进而分析了沙依里克组发育的沉积相类型及其分布特征。结果表明:(1)塔里木盆地中寒武统沙依里克组发育蒸发台地、局限台地、开阔台地、台地边缘、斜坡相及盆地相6种沉积相,进一步可划分为7种亚相及15种微相;(2)结合地层厚度展布、地震资料,编制了中寒武统沙依里克组岩相古地理图,建立了碳酸盐岩台地到斜坡–盆地的沉积相模式。对沙依里克组岩相古地理的深入研究,可进一步明确蒸发岩类盖层与盐间白云岩储层之间的良好配置关系,为盐间勘探领域新突破提供理论支撑。

川中地区北部下寒武统沧浪铺组一段风暴岩特征及沉积地质意义

川中地区北部下寒武统沧浪铺组风暴岩发育,但对该风暴岩沉积以及该区早寒武世沉积环境、古地理和沉积古地貌的研究较为薄弱。通过详细岩心观察及镜下薄片鉴定,研究了沧浪铺组风暴沉积序列和沉积模式,并揭示其地质意义。研究区沧浪铺组发育砾屑层、粒序段、平行层理和丘状交错层理等风暴沉积构造,可划分出5个风暴沉积序列,即:序列Ⅰ由砾屑段(A)、平行层理段(C)和丘状交错层理段(D)组成,在正常浪基面之上沉积;序列Ⅱ由平行层理段(C)、丘状交错层理段(D)和水平层理泥岩段(E)组成,位于风暴浪基面附近;序列Ⅲ由底冲刷面和砾屑段(A)和粒序段(B)构成,于正常浪基面和风暴浪基面之间;序列Ⅳ由粒序段(B)和平行层理段(C)组成,距离风暴中心远,沉积环境更靠近风暴浪基面附近;序列Ⅴ由底冲刷面和砾屑段(A)构成,位于平均海平面与正常浪基面之间且靠近正常浪基面。川中地区北部风暴岩的发现证实,沧浪铺组一段为陆棚—斜坡—台地边缘沉积,指示上扬子板块在沧浪铺组沉积期处于低纬度地区,这为岩相古地理恢复提供了约束;同时风暴作用形成连片分布的颗粒滩,有效提升储集相带的规模,有助于对颗粒滩相带的分布进行预测。

混合沉积特征精细刻画:以江苏徐州寒武系馒头组为例

江苏徐州地区寒武系馒头组发育极具特色的陆源碎屑组分与碳酸盐组分混合沉积现象。本研究以寒武系馒头组一套典型的混合沉积序列为例,依据剖面实测与镜下特征,对该序列中的混合沉积组合类型开展了系统的岩石学研究;通过分析不同沉积环境中的混合沉积特征,建立了陆表海近岸背景下陆源碎屑组分与碳酸盐组分混合沉积模式,探讨了各种混合沉积组合类型的混积成因类型、混积过程及主控因素等。结果表明:徐州地区寒武系馒头组混合沉积序列中主要发育含砂鲕粒灰岩、含内碎屑砂质灰岩、灰质细砂岩、含灰粉砂岩等11种混合沉积组合类型;混合沉积序列整体为陆表海海侵背景下次级海平面频繁波动且伴随多期次风暴作用的产物,主要表现为海侵作用下由近岸的混积潮坪逐渐演化为混积局限台地;混合沉积主要为相混合与间断混合,局部发育原地混合与母源混合。气候、陆源输入程度、海平面变化、碳酸盐产率是形成相混合的主控因素,同时也受到生物活动、水动力条件的调控;多期次风暴作用在主导间断混合形成的同时,一定程度上会促进相混合与母源混合的发育;在各因素叠加影响下,研究区具有多种混积成因类型组合发育的特征。厘清各种混积成因类型的分布与混积过程可为华北板块寒武纪古环境恢复与沉积演化提供参考,并为“深时”陆表海台地混合沉积相关研究提供典型范例。