Sedimentary Features and Paleogeographic Evolution of the Middle Permian Trough Basin in Zunyi,Guizhou,South China

Based on detailed field surveys,numerous sections and drillcores as well as analyses of lithofacies and sedimentary facies,sedimentary differentiation in the Middle Permian Zunyi(northern Guizhou,South China)trough basin was studied in detail.Caused by activities of the Emeishan mantle plume,the regional extensional setting and the extinguishing of carbonate production factories were shown from Guizhou to Yunnan.Three types of sedimentary enironments were developed in the study area:platform,slope,and basin.In this work,we established a sedimentary model for the study area,identified 14 syndepositional faults,and created the detailed reconstruction of the trough basin via a sedimentological investigation.It is found that the paleogeographic evolution of the study area can be divided into six stages:(1)a pre-rifting stage,(2)rapid rifting and subsidence,(3)stable rifting and subsidence,(4)the second stage of rifting and subsidence,(5)silicification,and(6)regional uplift and denudation.The sedimentary features and paleogeographic evolution of the Maokou Formation in Zunyi show that the platform,slope,and basin sedimentary features coexisted.In addition,the extensional setting and extinguishing of carbonate production factories were important preconditions for the evolution of the platform region in the study area,and the activity of syndepositional faults also played an important role in the paleogeographic evolution of this area.

Petroleum Potentials of the Nigerian Benue Trough and Anambra Basin: A Regional Synthesis

A review on the geology and petroleum potentials of the Nigerian Benue Trough and Anambra Basin is done to identify potential petroleum systems in the basins. The tectonic, stratigraphic and organic geochemical evaluations of these basins suggest the similarity with the contiguous basins of Chad and Niger Republics and Sudan, where commercial oil discovery have been made. At least two potential petroleum systems may be presented in the basins: the Lower Cretaceous petroleum system likely capable of both oil and gas generation and the Upper Cretaceous petroleum system that could be mainly gas-generating. These systems are closely correlative in temporal disposition, structures, source and reservoir rocks and perhaps generation mechanism to what obtains in the Muglad Basin of Sudan and Termit Basin of Niger and Chad Republics. They are very effective in planning future exploration campaigns in the basins.

Petrologic perspectives on tectonic evolution of a nascent basin(Okinawa Trough) behind Ryukyu Arc: A review

Okinawa Trough is a back-arc, initial marginal sea basin, located behind the Ryukyu Arc-Trench System. The formation and evolution of the Okinawa Trough is intimately related to the subduction process of the Philippine Sea Plate beneath the Eurasian Plate since the late Miocene. The tectonic evolution of the trough is similar to other active back-arcs, such as the Mariana Trough and southern Lau Basin, all of which are experiencing the initial rifting and subsequent spreading process. This study reviews all petrologic and geochemical data of mafic volcanic lavas from the Okinawa Trough, Ryukyu Arc, and Philippine Sea Plate, combined with geophysical data to indicate the relationship between the subduction sources （input） and arc or back-arc magmas （output） in the Philippine Sea Plate-Ryukyu Arc-Okinawa Trough system （PROS）. The results obtained showed that several components were variably involved in the petrogenesis of the Oki-nawa Trough lavas：sub-continental lithospheric mantle underlying the Eurasian Plate, Indian mid-oceanic ridge basalt （MORB）-type mantle, and Pacific MORB-type mantle. The addition of shallow aqueous fluids and deep hydrous melts from subducted components with the characteristics of Indian MORB-type mantle into the mantle source of lavas variably modifies the primitive mantle wedge beneath the Ryukyu and sub-continental lithospheric mantle （SCLM） beneath the Okinawa Trough. In the northeastern end of the trough and arc, instead of Indian MORB-type mantle, Pacific MORB-type mantle dominates the magma source. Along the strike of the Ryukyu Arc and Okinawa Trough, the systematic variations in trace element ratios and isotopic compositions reflect the first-order effect of variable subduction input on the magma source. In general, petrologic data, combined with geophysical data, imply that the Okinawa Trough is experiencing the＂seafloor spreading＂process in the southwest segment,＂rift propagation＂process in the middle seg-ment, and＂crustal extension＂process in the northeast segment, and a nascent ocean basin occurs in the southwest segment.

Development and exploration practice of the concept of hydrocarbon accumulation in rifted-basin troughs: A case study of Paleogene Kongdian Formation in Cangdong sag, Bohai Bay Basin

Based on the merged 3 D seismic data, well logging, formation testing, analysis and testing data, the structural evolution, sedimentary reservoirs, thermal evolution of source rocks were investigated of Paleogene Kongdian Formation in the trough area of Cangdong sag, Bohai Bay Basin. A conventional-unconventional hydrocarbon accumulation pattern in the trough area of rifted basin was revealed. The reservoir forming elements in the trough area of Cangdong sag have a zonation feature in terms of reservoirs and source rocks. There are two types of reservoir forming models, primary trough and reformed trough. The formation and evolution of trough controlled the orderly distribution of conventional oil to unconventional oil in the trough. Particularly, structural reservoirs occur in the upper part of the trough, stratigraphic-lithologic reservoirs are likely to form in the delta front deposits at the outer ring of trough, the middle ring transitional belt is the favorable site for tight oil reservoirs, while the fine grain deposits zone in the inner ring is shale oil and gas exploration area. The study has pointed out the new domains and directions for searching reserves in the secondary exploration of mature oilfields.

Brittle deformation in the Afikpo Basin (Southeast Nigeria): Evidence for a terminal Cretaceous extensional regime in the Lower Benue Trough, Nigeria

This paper deals with the regional and structural framework of the Cretaceous rocks in the Afikpo Basin located in the southeastern part of the Lower Benue Trough. Results from regional tectonics are presented together with those of the microtectonic analysis of microfaults in the Owutu-Afikpo-Adadama area in the basin. The Owutu-Afikpo-Adadama ridge at the north-central part of the basin marks the boundary between the Late Cenomanian-Turonian-Conianian sediments and the Campanian-Maastrichtian sandstones. This ridge trends N45oE on average and is faulted in three main directions, namely: (1) N-S normal faults; (2) NE-SW strike-slip faults; and (3) NW-SE strike-slip faults. The faulted rocks along these brittle discontinuities are mainly cataclastics with internal fracture cleavage and sigmoidal quartz mosaics that are reminiscent of extensional deformation. The cataclasites often bear slickenside striations. The NE-SW and NW-SE strike-slip faults are the results of the youngest brittle events on the Owutu-Afikpo-Adadama ridge. These faults were reactivated after deposition of the Campanian-Maastrichtain sediments (post-depositional faults) and, therefore, are post-Maastrichtain. Microfault analysis of these fault trends suggests an extensional regime that prevailed in the Lower Benue Trough. These results are of significance because this event is least poorly understood and less documented in contrast to the Cenomanian and Santonian events that affected the older Cretaceous strata in this region.

Analysis on the basement constitution of the southern Okinawa Trough

Based on the data of seismic reflection, seismic refraction and magnetism collected in the research area and geology obtained from adjacent areas, this paper deals with the issue of basement constitution of the southern part of the Okinawa Trough. In the shelf basin of the East China Sea, Taiwan folded belt and Ryukyu Islands folded belt which surround the trough, outcrop Later Paleozoic, Mesozoic and Eogene strata. In the southern trough, multichannel seismic reflection data indicate that the overlying strata are composed of Neogene and Quaternary deposits, and the acoustic basement consists of Eogent and even older strata. Seismic refraction profiles show that there are Eogene and Mesozoic velocity layers with longitudinal velocities of 4.7 - 5.3 km/s and 6.3 km/s respectively beneath the Quaternary-Miocene Layers. Qualitative analysis and forward and reversed calculation of magnetic data show that the magnetic basement is mainly formed by metamorphic rocks, the Yanshanian neutral-acid magmatic rocks and the Himalayan neutral-basic magmatic rocks being the next components, and the magnetic basement is mostly corresponding to the acoustic basement. Comprehensive analyses demonstrate that the basement of the southern Okinawa Trough is mainly formed by Eogene system and Mesozoic and Upper Paleozoic groups metamorphosed in varying degrees, and the basic magmatic rocks of Himalayan epoch have been formed in some parts of the basin.

四川盆地德阳-安岳凹槽形成机理及灯影组沉积新格局

四川盆地德阳—安岳凹槽两侧陡坎带震旦系灯影组天然气勘探不断取得新突破,是盆地内天然气增储上产的重要领域。为了明确该凹槽的形成机理、形成期次及沉积新格局,进一步指导灯影组气藏的深化勘探,采用最新大连片三维地震成果、结合钻井等资料,分析了各期陡坎之间、陡坎与台缘带之间的空间展布关系,探索了陡坎的演化规律,进一步明确了天然气的勘探方向。研究结果表明:①德阳—安岳凹槽陡坎总体表现为侵蚀谷特征,同沉积小断层的作用不明显;②灯影组二段(以下简称灯二段)发育Ⅰ、Ⅱ两个陡坎,灯影组四段(以下简称灯四段)发育一个陡坎,分别在桐湾Ⅰ和Ⅱ、Ⅲ幕侵蚀作用形成,这些陡坎与灯二段、灯四段台缘带无关;③灯二段沉积时期,受控于基底垒堑格局,发育由南向北进积的4~5排台缘带,呈北东向展布,其中蓬莱地区发育两个大型台缘带,台缘带丘滩体被陡坎Ⅱ截断,叠加岩溶作用形成优质储层。结论认为:①高石梯—磨溪地区灯四段与灯二段的陡坎叠合区发育灯四段陡坎型台缘带,而在灯四段槽上带,丘滩体仍呈北东向发育,表明该地区受陡坎Ⅱ与北东向古地貌双重因素控制;②蓬莱地区陡坎Ⅱ坡度变小,对灯四段台缘带控制作用减弱直至消失,主要发育2排北东向展布的缓坡型台缘带,即蓬莱①、②台缘带,蓬莱地区可作为今后天然气勘探重点关注目标区。

Tectonics and Petroleum Potential of the East China Sea Shelf Rift Basin

There are two Cenozoic sedimentary basins in the East China Sea. They are the East China Sea shelf basin and the Okinawa Trough basin. The former can be divided into a western and an eastern rift region. The development of the shelf basin underwent continental-margin fault depression, post-rift and then tectonic inversion stages. Available exploration results show that the distribution of source rocks is controlled by the basin architecture and its tectonic evolution. In the Xihu depression, mudstones and coals are the main source rocks. The eastern rift region has good geological conditions for the formation of large oil and gas fields.

克拉玛依克百断槽火山岩岩石组合、层位归属及地质意义:来自古66井的约束

克百断槽始于克拉玛依市北的克北断裂,NE向延伸并被大侏罗沟断裂、盆缘断裂、克-百断裂围限。火山岩储层是该断槽内的主要储层,其层位时代无据、层序不清、归属不明。笔者通过对克百断槽古66井242.14~800.18 m井段详细的岩心编录、测井曲线岩电识别及关键层位火山岩锆石U-Pb年代学研究,结果表明:古66井242.14~800.18 m井段是被两层陆源粗碎屑岩(标志层)分隔的3套火山岩建造,于玄武安山岩中获得(304±3)Ma和(303±2)Ma的LA-ICP-MS锆石U-Pb年龄,其岩石组合、时代、层序、地层厚度均与井北缘哈山一带哈拉阿拉特组建组剖面C_(2)h^(1)~C_(2)h^(3)岩段总体可对比。古66井所处的克百断槽是一个四周被断层围限的相对独立火山岩型储层断槽油气藏,这一油气藏新类型丰富了西准噶尔盆内油气藏类型。同时,该断槽具有向南西延伸的构造条件、储层类型和圈闭样式,因而是后续扩大油气勘探的新靶区。

川东—川北地区二叠系茅口组沉积演化及其油气地质意义

近年来,四川盆地二叠系茅口组的勘探思路和布井原则由原来的“占高点、沿长轴”转变为以寻找滩相孔隙型规模储层为目标,并取得了新突破,使其成为了勘探热点层系,这就需要详细的沉积演化研究来支撑。川东—川北地区是茅口组构造—沉积分异最为明显,也是勘探潜力较大的区域。对茅口组386口钻井的测井资料进行系统梳理,并利用野外剖面和钻井取心进行沉积相分析,结合测井曲线与沉积相,分析研究区茅口组的沉积演化。研究认为,川东—川北地区茅口组一段到茅口组二下亚段总体为碳酸盐缓坡,地层厚度和沉积相总体受川中古隆起的影响,局部发育低能滩;茅二上亚段到茅三段转变为具有镶边性质的碳酸盐台地,地层厚度和沉积相带展布转变为北西—南东向,自西向东依次发育台地相、台缘带、斜坡和陆棚相,台缘带发育高能滩相。研究区茅口组沉积期相对海平面总体经历了两次升降过程,对应地层分别为茅一段到茅二下亚段和茅二上亚段到茅三段。受区域海平面升降、区域构造活动以及碳酸盐台地类型的控制,茅一段到茅二下亚段缓坡发育具有岩溶和云化的滩相储层;茅二上亚段到茅三段海槽内发育潜在烃源岩,是非常规油气勘探潜在有利区,而海槽西侧则发育具重要勘探价值的规模性台缘带高能滩。

Balanced Cross Section for Restoration of Tectonic Evolution in the Southwest Okinawa Trough

On the basis of the multi.channel seismic data and the other data, using 2DMove software, the tectonic evolution in three seismic profiles was restored since Pliocene. The tectonic restoration results show that： （1） the initial active center lay in the west slope and then was transferred to east and south via trough center during the evolution process; （2） several main normal faults controlled the evolution of the southern Okinawa Trough; （3） since Late Pliocene, the southern Okinawa Trough has experienced two spreading stages. The early is depression in Early-Middle Pleistocene and the late is back-arc spreading in Late Pleistocene and Holocene, which is in primary oceanic crust spreading stage.

Investigation on the Deposition in an Excavated Trough at the East Shore of Jiaozhou Bay, China

Based on field investigations, this paper analyzes three types of harbour basinns and navigation channel excavated on seabed in Jiaozhou Bay, get a general rule of deposition for excavated trough, it found that pollution is one of crucial factors resulting in the deposition of the excavated trough in the east shore of Jiaozhou Bay. With these results, it predicted the annual deposition thickness for the excavated trough and disclosed the fact that it can't be deposited deadly during one storm. At the same time, with two-dimensional numerical model, it studied the effects of the excavated trough and the reclamation near shore on tidal cureent and said that the excavated trough can decrease the current velocity passing through the trough about 10- 15%, but only limited inside and near the trough and there are no effect on other regions; reclamation can cut off the pollution sources and no obvious effect on the currents of the Jiaozhou Bay. Connecting the deep trough and Cangkou tidal channel with a new excavated trough can improve the current conditions on the deep trough in some degree, but not great.

四川盆地开江—梁平海槽东南台缘带走滑断裂特征及其控藏作用

开江—梁平海槽周缘二叠系—三叠系礁滩型气藏是四川盆地天然气勘探开发的重点领域,但深层(>4500m)碳酸盐岩储层致密,制约了天然气藏的高效勘探与开发。基于重新处理的三维地震资料,开展走滑断裂的地震识别,研究走滑断裂的构造特征,并结合钻井资料分析走滑断裂控藏作用与天然气富集规律。结果表明:开江—梁平海槽地区发育一系列北西向的走滑断裂带,具有纵向分层、平面分段特征。剖面上走滑断裂多表现为直立型断裂与花状断裂多层叠置,平面上断裂组合以斜列、侧列为主,形成线性构造、雁列构造、花状构造、马尾状构造等多种构造类型。走滑断裂位移小、成熟度低,经历震旦纪末—早寒武世、前二叠纪、二叠纪—三叠纪等3期走滑断裂活动,具有连接生长机制与继承性发育的特征。走滑断裂带裂缝发育,断裂及其相关溶蚀作用控制了优质储层的发育,可导致碳酸盐岩渗透率增长超过1个数量级、孔隙度增长超过1倍。走滑断裂不仅沟通海槽内的二叠系烃源岩,形成侧向运移优势通道,而且可垂向连通深部烃源岩,形成断裂输导、复式成藏的多个含气层。开江—梁平海槽周缘台缘带及台内与走滑断裂有关的深层碳酸盐岩气藏的勘探开发潜力巨大,是值得深入探索的有利新领域。

页岩气勘探新领域:四川盆地开江—梁平海槽二叠系海相页岩气勘探突破及展望

近期,中国石油部署于四川盆地东部地区(下文简称川东地区)的风险探井——大页1H井,经测试在二叠系吴家坪组三段深水陆棚相页岩测试获32.06×10^(4)m^(3)/d的高产工业气流,开辟了页岩气勘探开发新领域。为了进一步明确四川盆地二叠系海相页岩气的勘探方向和资源潜力,基于大页1H井钻录试井资料,以开江—梁平海槽内二叠系吴家坪组海相页岩为研究对象,开展了有机地球化学、储层特征、脆性矿物含量和含气性等含油气地质条件研究,指出了该新领域页岩气的勘探开发前景。研究结果表明:①开江—梁平海槽在吴家坪组沉积时期为深水陆棚相沉积环境,槽内沉积了一定厚度、分布稳定的富有机质(TOC>2%)页岩;②吴家坪组具有良好的页岩气富集成藏地质条件,其中吴家坪组三段(下文简称吴三段)最佳,大页1H井吴三段有机碳含量平均值高达9.83%,有机质内部发育不同程度的有机质孔,孔隙发育,平均孔隙度6.40%,为优质储层;③大页1H井吴三段页岩平均脆性指数达85%,可压裂性好,平均含气量高达10.39 m^(3)/t,页岩总含气量高;④川东地区吴家坪组海相页岩具有良好的页岩气勘探开发潜力,其中吴家坪组埋深4500 m以浅面积超过1400 km^(2),估算地质资源量约4500×10^(8)m^(3),可供勘探区内吴家坪组埋深5000 m以浅面积超过2880 km^(2)。结论认为,大页1H井的突破开启了四川盆地开江—梁平海槽二叠系海相页岩气规模增储上产的新篇章,进一步拓展了四川盆地页岩气的工作对象,对夯实四川盆地天然气资源基础和保障国家能源安全具有重要意义。

川北地区二叠系大隆组烃源岩地球化学特征及沉积环境

通过对川北地区上二叠统大隆组3条野外剖面进行系统采样和地球化学特征分析,从沉积背景、热液活动与上升流、古气候和古盐度、水体环境等4个方面分析了烃源岩的沉积环境,并对有机质富集模式和勘探潜力进行了探讨。研究结果表明:(1)川北地区二叠系大隆组烃源岩岩性主要为泥质、硅质泥灰岩,有效厚度为10~40 m,有机质丰度高、类型好,TOC平均值为4.58%,以Ⅱ2型为主,生烃潜力大,平均热解生烃潜量为5.90 mg/g。盆地边缘广元地区长江沟剖面和西北乡剖面处于成熟阶段,Ro值分别为0.72%和1.06%,盆地东部大两乡剖面平均T_(max)值为604℃,达过成熟阶段,广元—梁平海槽大隆组生气量达432.38×10^(12)m^(3),常规天然气资源量为1.70×10^(12)m^(3),页岩气资源量达万亿方级,是一套生气潜力较大的海相优质烃源岩。(2)研究区大隆组优质烃源岩形成于水体缺氧半局限循环的大陆边缘环境,经历了海槽发育雏形期和海槽发育扩展期2期水体环境的演变,其中,雏形期呈现缺氧—局部厌氧—缺氧的非硫化夹硫化环境,有机质不发育;扩展期为贫氧—缺氧—主体厌氧—缺氧环境,热液活动与上升流导致生物繁盛,火山喷发的酸性气体与半封闭水体环境共同造就了长时期大范围的厌氧硫化静海环境,有利于有机质的富集与保存,在西北乡和长江沟等斜坡—陆棚区表现出较高的TOC值,弱滞留硫化环境中TOC值最大,中等滞留硫化环境次之,强滞留硫化环境中TOC值最小。(3)研究区大隆组页岩气和源于大隆组热解气的长兴组—飞仙关组优质气藏为主要勘探方向。

四川盆地开江—梁平海槽东侧三叠系飞仙关组鲕滩储层特征及控制因素

通过岩心观察、微观薄片鉴定、扫描电镜等资料,在层序划分基础上对四川盆地开江—梁平海槽东侧飞仙关组的储层特征及控制因素进行了研究。研究结果表明:(1)铁山坡—普光地区飞仙关组储层以鲕粒云岩和细粉晶白云岩为主,渡口河—七里北地区以(含砾屑、砂屑、豆粒)鲕粒白云岩为主,鲕粒岩原始结构组分保存更好。(2)研究区储层具有多期次发育特征,铁山坡—普光地区储层在ssq1,ssq2,ssq3层序均有分布,具有发育早、厚度大、分布面积广的特征,Ⅰ,Ⅱ,Ⅲ类储层均发育;渡口河—七里北地区储层发育在ssq2,ssq3层序,发育较晚、厚度小、分布面积有限,以Ⅱ,Ⅲ类储层为主。(3)研究区沉积古地貌及海平面升降控制了鲕滩储层发育的期次、厚度等,在ssq1沉积中晚期海平面开始下降时,古地貌高地开始发育鲕滩储层,厚度大,白云石化作用明显。(4)研究区内陡坡型和缓坡型台缘斜坡带,水体能量的强弱控制了鲕滩沉积物类型,为成岩期溶蚀作用和白云石化作用奠定了物质基础,进而控制了储层的物性和规模。

二连盆地洼槽区非常规油气富集模式及勘探潜力

向湖盆中心和深层寻找油气勘探新领域已成为未来主要发展方向。二连盆地剩余油气资源量达8亿吨,主要分布于各富油凹陷洼槽区,以非常规资源形式富存,页岩油潜力巨大。本文通过对富油凹陷洼槽区非常规油气地质特征、成藏富集机理和成藏模式开展研究,总结提升断陷小湖盆洼槽区非常规油气地质理论认识。研究表明:二连盆地多个洼槽区发育互层型页岩油聚集,富集于洼槽区边缘,存在腾二期(120 Ma)未致密先成藏和赛汉期(105 Ma)边致密边成藏(先致密后成藏)两期成藏过程;高充注动力富集区,砂体规模控制页岩油富集程度,低充注动力洼槽区内甜点储层发育及规模控制页岩油富集程度;二连盆地夹层型页岩油存在两种富集机理,即“储层主控”和“生烃主控”。据此,构建了二连盆地斜坡带-洼槽区“常非共存、有序分布、满洼汇聚、差异富集”的全油藏系列成藏模式,研究成果坚定了深入湖盆内部寻找烃源灶边缘互层型页岩油及烃源灶内夹层型页岩油的勘探信心。

开江—梁平海槽演化阶段与构造沉积特征

四川盆地开江—梁平海槽及其周缘地质资源丰富,分布有普光、龙岗等一系列大型气藏群,勘探开发潜力巨大。目前,针对海槽的发育时期、形成演化尚无统一观点,进一步明确其发育起始时期、演化阶段对推进海槽周缘油气勘探及地质研究具有重要意义。文中依据海槽周缘勘探最新进展,利用野外露头、钻井、测井及三维地震资料,综合分析区域构造演化与沉积充填特征,探讨海槽演化阶段及各阶段构造动力和沉积机制差异。研究表明:1)开江—梁平海槽内部可识别出3套典型的深水沉积,在四川盆地北部总体呈西北宽、东南窄的北西—南东向发育,海槽内部至周缘台地相区发育完整的深水—浅水沉积相序组合;2)海槽发育始于中二叠世晚期,持续发育于晚二叠世,在长兴期达到高峰,延续至早三叠世逐渐消亡,表现出多阶段继承性演化的特征,可分为3期构造沉积演化,即中二叠世海槽雏形萌芽期、晚二叠世海槽发育高峰期、早三叠世海槽充填消亡期;3)不同演化阶段的构造动力和沉积机制存在差异,与萌芽期横向迁移的空间变化模式不同,高峰期以纵向加积为主;4)环开江—梁平海槽周缘是海相碳酸盐岩大中型气田分布的主要区带之一,海槽纵向多产层发育,勘探开发潜力巨大。

一种省水、节能兼具船闸和升船机功能的通航设施

现有通航设施通常指船闸或升船机,船闸通行效率高,但耗水较多,升船机不耗水,但通行效率低,结构复杂。因此,针对现有通航设施的局限性,本文提出一种新型水力升降机,应用于通航设施,可最大限度省水节能且具有良好通行效率,该通航设施采用竖井内升降机(母船)承载通航船舶(子船)的模式实现升降,子船停泊在母船甲板上的池内,当母船升降至池内水位与上下游水位齐平时,池内船舶便与上下游船舶进出交换,达到上下游船舶通航的目的。该通航设施可兼具船闸和升船机功能,具有良好的通用性和适用性。

四川盆地及邻区上二叠统—下三叠统海槽的深水沉积特征

四川盆地及邻区广元-旺苍、城口-鄂西、开江-梁平海槽是上二叠统—下三叠统飞仙关组(P_3—T_(?))的深水碳酸盐沉积区。该区上二叠统上部大隆组是硅质岩、硅质泥岩、硅质灰岩组合,含放射虫、有孔虫等化石,厚12．5～29．0 m,为海槽裂陷期凝缩沉积。三叠系飞仙关组下部为远洋沉积的暗色泥岩、微晶碎屑灰岩和重力流沉积的浊积岩、角砾灰岩组成的深水碳酸盐沉积,厚50．0～300．0 m,是裂陷期后的海槽充填沉积。海槽相区沉积在晚二叠统世末达到最大海泛面沉积了大隆组。海平面缓慢下降期沉积了补偿充填性质的飞仙关组深水碳酸盐岩。海槽相区上二叠统一下三叠统飞仙关组构成了一个完整的三级层序。深水沉积物的有机碳平均值高达6．21%,是良好的烃源岩。但在海槽相区上二叠统不发育生物礁,飞仙关组缺乏鲕粒岩。