Coupling relationship and genetic mechanisms of shelf-edge delta and deep-water fan source-to-sink:A case study in Paleogene Zhuhai Formation in south subsag of Baiyun Sag,Pearl River Mouth Basin,China

The coupling relationship between shelf-edge deltas and deep-water fan sand bodies is a hot and cutting-edge field of international sedimentology and deep-water oil and gas exploration.Based on the newly acquired high-resolution 3D seismic,logging and core data of Pearl River Mouth Basin(PRMB),this paper dissected the shelf-edge delta to deep-water fan(SEDDF)depositional system in the Oligocene Zhuhai Formation of Paleogene in south subsag of Baiyun Sag,and revealed the complex coupling relationship from the continental shelf edge to deep-water fan sedimentation and its genetic mechanisms.The results show that during the deposition of the fourth to first members of the Zhuhai Formation,the scale of the SEDDF depositional system in the study area showed a pattern of first increasing and then decreasing,with deep-water fan developed in the third to first members and the largest plane distribution scale developed in the late stage of the second member.Based on the development of SEDDF depositional system along the source direction,three types of coupling relationships are divided,namely,deltas that are linked downdip to fans,deltas that lack downdip fans and fans that lack updip coeval deltas,with different depositional characteristics and genetic mechanisms.(1)Deltas that are linked downdip to fans:with the development of shelf-edge deltas in the shelf area and deep-water fans in the downdip slope area,and the strong source supply and relative sea level decline are the two key factors which control the development of this type of source-to-sink(S2S).The development of channels on the continental shelf edge is conducive to the formation of this type of S2S system even with weak source supply and high sea level.(2)Deltas that lack downdip fans:with the development of shelf edge deltas in shelf area,while deep water fans are not developed in the downdip slope area.The lack of“sources”and“channels”,and fluid transformation are the three main reasons for the formation of this type of S2S system.(3)Fans that lack updip coeval deltas:with the development of deep-water fans in continental slope area and the absence of updip coeval shelf edge deltas,which is jointly controlled by the coupling of fluid transformation at the shelf edge and the“channels”in the continental slope area.

Deep-water Fan Systems and Petroleum Resources on the Northern Slope of the South China Sea

The shallow shelf delta/strand arenaceous-pelitic deposit region in the north of the Pearl River mouth basin, sitting on the northern continental shelf of the South China Sea, has already become an important oil production base in China. Recent researched has revealed that a great deal of deep-water fans of great petroleum potentiality exist on the Baiyun deep-water slope below the big paleo Pearl River and its large delta. Based on a mass of exploration wells and 2-D seismic data of the shallow shelf region, a interpretation of sequence stratigraphy confirmed the existence of deep-water fans. The cyclic falling of sea level, abundant detrital matter from the paleo Pearl River and the persistent geothermal subsidence in the Baiyun sag are the three prerequisites for the formation and development of deep-water fans. There are many in common between the deep-water shelf depositional system of the northern South China Sea and the exploration hotspots region on the two banks of the Atlantic. For example, both are located on passive continent margins, and persistent secular thermal subsidence and large paleo rivers have supplied abundant material sources and organic matter. More recently, the discovery of the big gas pool on the northern slope of the Baiyun sag confirms that the Lower Tertiary lacustrine facies in the Baiyun sag has a great potentiality of source rocks. The fans overlying the Lower Tertiary source rocks should become the main exploration areas for oil and gas resources.

Deep-water Depositional Features of Miocene Zhujiang Formation in Baiyun Sag,Pearl River Mouth Basin

Eleven lithofacies and five lithofacies associations were indentified in the Miocene Zhujiang Formation on the basis of detailed core analysis. It could he determined that three depositional types developed, namely submarine fan, basin and deep-water traction current. Six microfacies were further recognized within the fan, including main channels in the inner fan, distributary channels in the middle fan, inter-channels, levees and the outer fan. The lower Zhujiang Formation, mainly sandstone associations, was inner fan and inner-middle fan deposits of the basin fan and the slope fan. The middle part, mainly mudstone associations, was outer fan deposits. With the transgression, the submarine fan was finally replaced by the basinal pelagic deposits which were dominated by mudstone associations, siltstone associations, and deep-water limestone associations. During the weak gravity flow activity, the lower channels, the middle-upper outer fans and basin deposits were strongly modified by the deep-water traction current. The identification of the deep-water traction deposition in Miocene Zhujiang Formation would be of great importance. It could be inferred that the deep- water traction current had been existing after the shelf-break formation since the Late Oligocene （23.8 Ma） in the Baiyun sag, influencing and controlling the sediment composition, the distribution, and depositional processes. It would provide great enlightenment to the paleo-oceanic current circulation in the northern South China Sea.

Control effects of the synsedimentary faults on the basin-marginal fans in the central part of the deep-water area of early Oligocene Qiongdongnan Basin, South China Sea

The synsedimentary faults and basin-marginal fans located in the central part of the deep-water area of the early Oligocene Qiongdongnan Basin have been investigated using seismic profiles,boreholes,and well-log data.Through the formations of the characterized paleogeomorphology,such as transverse anticlines,fault ditches,and step-fault belts,the synsedimentary faults are known to have controlled the development position,distribution direction,and extension scales of the basin-marginal fans.For example,at the pitching ends of two adjacent faults,transverse anticlines developed,which controlled the development positions and distributions of the fans.During the early Oligocene,the faults controlled the subsidence center,and fault ditches were formed at the roots of the faults.In the surrounding salient or low salient areas,which were exposed as provenance areas during early Oligocene,the fault ditches acted as the source channels and determined the flow paths of the clastics,where incised valley fills were obviously developed.The fault ditches which developed in the sedimentary basins were able to capture the drainage systems and influenced the distributions of the fans.The large boundary faults and the secondary faults generated two fault terraces and formed step-fault belts.The first fault terrace caused the clastics to be unloaded.As a result,fans were formed at the entrance to the basin.Then,the second fault terrace caused the fans to move forward,with the fans developing in a larger extension scale.The results obtained in this study will potentially be beneficial in the future prospecting activities for reservoirs and coalmeasure source rocks in the basins located in the deep-water areas of the South China Sea.

Petroleum geology controlled by extensive detachment thinning of continental margin crust: A case study of Baiyun sag in the deep-water area of northern South China Sea

The relationships between crustal stretching and thinning,basin structure and petroleum geology in Baiyun deep-water area were analyzed using large area 3D seismic,gravity,magnetic,ocean bottom seismic(OBS),deep-water exploration wells and integrated ocean drilling program(IODP).During the early syn-rifting period,deep-water area was a half-graben controlled by high angle faults influenced by the brittle extension of upper crust.In the mid syn-rifting period,this area was a broad-deep fault depression controlled by detachment faults undergone brittle-ductile deformation and differentiated extension in the crust.In the late syn-rifting period,this area experienced fault-sag transition due to saucer-shaped rheology change dominated by crustal ductile deformation.A broad-deep fault depression controlled by the large detachment faults penetrating through the crust is an important feature of deep-water basin.The study suggests that the broad-deep Baiyun sag provides great accommodation space for the development of massive deltaic-lacustrine deposition system and hydrocarbon source rocks.The differentiated lithospheric thinning also resulted in the different thermal subsidence during post-rifting period,and then controlled the development of continental shelf break and deep-water reservoir sedimentary environment.The high heat flow background caused by the strong thinning of lithosphere and the rise of mantle source resulted in particularities in the reservoir diagenesis,hydrocarbon generation process and accumulation of deep-water area in northern South China Sea.

A global satellite survey of density plumes at river mouths and at other environments: Plume configurations, external controls, and implications for deep-water sedimentation

The U. S. National Aeronautics and Space Administration(NASA) has archived thousands of satellite images of density plumes in its online publishing outlet called 'Earth Observatory' since 1999. Although these images are in the public domain, there has not been any systematic compilation of configurations of density plumes associated with various sedimentary environments and processes. This article, based on 45 case studies covering 21 major rivers(e.g., Amazon, Betsiboka, Congo [Zaire], Copper, Hugli [Ganges], Mackenzie, Mississippi, Niger, Nile, Rhone, Rio de la Plata, Yellow, Yangtze, Zambezi, etc.) and six different depositional environments(i.e., marine, lacustrine, estuarine, lagoon, bay, and reef), is the first attempt in illustrating natural variability of configurations of density plumes in modern environments. There are, at least, 24 configurations of density plumes. An important finding of this study is that density plumes are controlled by a plethora of 18 oceanographic, meteorological, and other external factors. Examples are: 1) Yellow River in China by tidal shear front and by a change in river course; 2) Yangtze River in China by shelf currents and vertical mixing by tides in winter months; 3) Rio de la Plata Estuary in Argentina and Uruguay by Ocean currents; 4) San Francisco Bay in California by tidal currents; 5) Gulf of Manner in the Indian Ocean by monsoonal currents; 6) Egypt in Red Sea by Eolian dust; 7) U.S. Atlantic margin by cyclones; 8) Sri Lanka by tsunamis; 9) Copper River in Alaska by high-gradient braid delta; 10) Lake Erie by seiche; 11) continental margin off Namibia by upwelling; 12) Bering Sea by phytoplankton; 13) the Great Bahama Bank in the Atlantic Ocean by fish activity; 14) Indonesia by volcanic activity; 15) Greenland by glacial melt; 16) South Pacific Ocean by coral reef; 17) Carolina continental Rise by pockmarks; and 18) Otsuchi Bay in Japan by internal bore. The prevailing trend in promoting a single type of river-flood triggered hyperpycnal flow is flawed because there are 16 types of hyperpycnal flows. River-flood derived hyperpycnal flows are muddy in texture and they occur close to the shoreline in inner shelf environments. Hyperpycnal flows are not viable transport mechanisms of sand and gravel across the shelf into the deep sea. The available field observations suggest that they do not form meter-thick sand layers in deep water settings. For the above reasons, river-flood triggered hyperpycnites are considered unsuitable for serving as petroleum reservoirs in deep-water environments until proven otherwise.

陆架边缘三角洲-深水扇源汇耦合关系及成因机制——以珠江口盆地白云南洼古近系珠海组为例

基于珠江口盆地新采集处理的三维地震资料、钻测井和岩心资料,精细解剖白云南洼古近系渐新统珠海组陆架边缘三角洲-深水扇(简称“洲-扇”),以揭示陆架边缘到深水扇沉积复杂的耦合关系和成因机制。研究结果表明,珠海组四段—一段沉积时期,研究区“洲-扇”沉积体系规模具有先增大后减小的规律,珠海组三段—一段沉积早期深水扇发育,珠海组二段沉积晚期平面分布规模最大。依据顺物源方向洲-扇发育程度的不同,划分出“有洲有扇、有洲无扇、无洲有扇”3种不同类型的洲-扇耦合关系。(1)“有洲有扇”型的陆架区发育陆架边缘三角洲,其下倾方向的陆坡区深水扇发育,强物源供给和相对海平面下降是主控该类型洲-扇系统发育的两大关键因素,而陆架边缘水道的发育有利于在弱物源供给及相对海平面上升时期仍能形成该类型源汇系统。(2)“有洲无扇”型的陆架区发育陆架边缘三角洲,其下倾方向的陆坡区却不发育深水扇,缺“源”、少“渠”和流体改造是形成该类型的3大主要原因。(3)“无洲有扇”型的陆坡区发育深水扇,但溯源其上倾方向陆架区不发育陆架边缘三角洲,陆架边缘的流体改造和陆坡区渠道通畅(水道发育)两者相互耦合共同控制其形成。

Thermal-history reconstruction of the Baiyun Sag in the deep-water area of the Pearl River Mouth Basin, northern South China Sea

The Baiyun Sag, located in the deep-water area of the northern South China Sea, is the largest and deepest subbasin in the Pearl River Mouth Basin and one of the most important hydrocarbon-accumulation depression areas in China. Thermal history is widely thought to be of great importance in oil and gas potential assessment of a basin as it controls the timing of hydrocarbon generation and expulsion from the source rock. In order to unravel the paleo-heat flow of the Baiyun Sag, we first analyzed tectonic subsidence of 55 pseudo-wells constructed based on newly interpreted seismic profiles, along with three drilled wells. We then carried out thermal modeling using the multi-stage finite stretching method and calibrated the results using collected present-day vitrinite reflectance data and temperature data. Results indicate that the first and second heating of the Baiyun Sag after 49 Ma ceased at 33.9 Ma and 23 Ma. Reconstructed average basal paleo- heat flow values at the end of the rifting periods are -57.7- 86.2 mW/m2 and -66.7-97.3 mW/m2, respectively. Following the last heating period at 23 Ma, the study area has undergone a persistent thermal attenuation phase, and basal heat flow has cooled down to ～64.0-79.2 mW/m2 at present.

珠江口盆地深水扇识别和油气成藏关键要素

近年来在层序地层学理论的指导下,在珠江口盆地白云凹陷的地震剖面上识别出各种层序界面,并进一步识别出大量深水扇沉积体,这些深水扇体由众多的盆底扇、斜坡扇、低位楔和下切水道构成。盆底扇和斜坡扇多期叠加,平面上成朵叶状,并与下切水道相连。综合分析白云深水扇的成藏条件,得出控制深水扇成藏的关键要素有两点(1)由断层、不整合面、横向连通的砂体以及流体底辟带组成的发达的输导格架,特别是能与深水扇相连的断层与流体底辟带,是深水扇油气成藏的关键所在;(2)油气运移的动力,盆地模拟结果表明,白云凹陷曾经历了三个地层压力演化旋回,超压的累积和释放对深部烃源岩的排烃并向深水扇体中运移起到了重要作用。

南海珠江深水扇系统的沉积构造背景分析

从深水扇系统的观点出发,主要基于对最近所采集的穿越整个白云凹陷的700余公里长电缆深反射（深达14 s）地震资料综合解释,结合南海大洋钻探的成果,对南海珠江深水扇系统沉积的构造背景特征进行了综合分析.研究发现：白云主凹在早中新世-中中新世期间（即大约距今25～10 Ma）是一个因坳陷期盆地基底的持续沉降及其相关断裂活动而形成的南海北部陆缘上的斜坡内盆地;白云主凹这个“斜坡内盆地”有别于世界上其它位于被动大陆边缘背景中（如西非近海、巴西近海、墨西哥湾）的斜坡内盆地;海平面变化、沉积物通量变化、构造活动等地质营力都在斜坡内盆地的构造背景上对南海珠江深水扇系统在不同时期产生了不同程度的重要影响.简言之,斜坡内盆地成就了南海珠江深水扇系统.这为以后进一步全面深入研究南海珠江深水扇系统的形成机制、演化过程、结构特征等有着重要意义.

珠江口盆地白云深水扇特征及油气成藏主控因素

揭示中国南海北部珠江口盆地白云深水扇的时空展布和油气成藏规律.无论在理论上、还是在向深海进军的油气勘探实践上都具有十分重要的意义.以层序地层学理论为指导的地震剖面精细解释,在白云凹陷北部陆坡区发现了大量深水扇沉积体,它由众多的盆底扇、斜坡扇、低位楔和下切水道构成.盆底扇和斜坡扇多期叠加,平面上成朵叶状,并与下切水道相连.研究表明,白云深水扇成藏的主控因素包括:(1)白云凹陷具有适合油气生成的活跃烃源岩;(2)拥有包括断层、不整合面、连续分布的砂体以及流体底辟带在内的发达的输导网络;(3)低水位期发育的深水扇体与其上覆的高水位期泥岩共同形成了有利的储盖组合;(4)超压的累积和释放对深部烃源岩的排烃起到了重要作用.因此,白云深水扇具有良好的成藏条件,是珠江口盆地深水勘探的有利目标.

南海北部白云凹陷深水区SQ13.8深水扇砂体识别与分布研究：以SF-5为例

珠江口盆地白云凹陷在继"白云运动"之后,在13.8 Ma发生了一次大规模的海退事件,海平面下降至陆架坡折带附近,三角洲向盆地方向推进最远,十分有利于深水扇的发育。通过深水陆坡区B6井及陆架边缘多口井的井震标定,结合钻井、测井分析,系统总结出具有厚度较大(20～40 m)、以泥质粉砂岩为主的斜坡扇储层,对应低频、短轴、强振幅的地震反射特征,在负极性显示的地震剖面上,表现为强波谷地震响应。层序地层格架分析认为工区处于SQ13.8"陆架边缘三角洲—沉积过路区—斜坡扇"的沉积环境,并在层序格架的约束下,通过合成地震记录建立井-震关系,对斜坡扇区第5套砂层组(SF-5)进行储层识别与追踪解释,确定SF-5砂层为主体分布在陆架坡折带外侧陆坡区的丘状体,平面形态似帚状或朵叶状,具有斜坡扇的特征,其优质储层主要分布在工区的中部-西部地区,呈NW-SE方向条带状展布。

南海珠江深水扇系统的微观内幕结构研究

本文首次探索在以二维地震资料为主的条件下开展深水扇系统的微观内幕研究。结果表明:在珠江口盆地白云凹陷中的南海珠江深水扇系统中能较好地由浅至深识别出多套地层(尤其是浅部地层)中存在的多种类型的深切谷、峡谷、水道,各有不同地质成因机制。能识别的典型扇体微观结构类型包括丘形体、席状体、水道化沉积及朵叶体等,往往分别指示某些特殊的沉积环境,并且最可能构成潜在的深水油气圈闭的良好储层。在二维地震资料条件下容易识别的深水扇系统微观内幕结构类型比较有限,在空间上追踪典型微观内幕结构也相对比较困难,但是若能全面认识区域构造及沉积背景,综合利用相关资料减少对地震反射结构解释的多解性,就有望对扇体的微观内幕结构进行深入剖析,深化对扇体的地质认识,从而指导油气勘探。

珠江口盆地白云凹陷珠江组深水牵引流沉积特征及其地质意义

研究深水牵引流对古大洋环流重建、陆坡位置判断及沉积矿产和能源资源勘探具有重要意义。珠江口盆地白云凹陷中新统珠江组取心段发育丰富的、与远洋低密度浊流和半远洋-远洋悬移沉积有明显区别的深水牵引流沉积,产物包括平行层理细砂岩、双泥岩纹层、双向交错层粉-细粒砂岩、波状层理和脉状层理灰质粉-细粒砂岩、波状层理和脉状层理抱球虫灰岩、透镜状沙纹层理粉砂岩等岩石相类型。珠江组深水牵引流沉积的发现具有重要地质意义,由其可以推测自渐新世末(23.8Ma)白云凹陷陆架坡折带形成之后就开始存在沿着陆架坡折带活动的深水牵引流,并可能影响和改变沉积物的物质组成和区域分布,这将为南海北部古大洋洋流循环重建起到重要启示作用。

白云凹陷珠江组深水扇砂岩储层特征及控制因素

通过薄片鉴定,扫描电镜、物性和孔隙结构分析,对珠江口盆地白云凹陷珠江组深水扇储层特征、控制因素和分布规律展开研究。该深水扇沉积体系的储层主要为一套碎屑流沉积的灰色中-粗粒长石岩屑砂岩和中-细粒岩屑长石砂岩,储集空间以原生粒间孔为主,次为粒间溶孔和裂缝等,具有排驱压力及中值压力小,孔喉半径大、配位数高和分选好等好的孔隙结构,多数属于中-高孔高渗型储层。储层发育主要受陆架坡折带和沉积相控制,后者包括沉积微相、砂岩粒度和砂体发育规模在内的三要素。由于深水扇砂体较早地进入超压旋回,仅经历了相当于中等埋藏深度的早成岩阶段A→B期的成岩改造,对储层发育的影响不大,因此,储层预测可以砂体成因类型和发育规模为主要依据,以深水扇内扇和中扇分流水道为最有利的勘探开发目标。

珠江口盆地白云凹陷中新统珠江组物源及其研究意义

南海北部陆坡深水区3Ma以来碎屑物质来源具多样性、复杂性和变化性。利用砂岩和异源生屑灰岩岩石学及泥岩稀土元素地球化学特征研究了珠江口盆地白云凹陷中新统珠江组深水扇的物源。结果表明,珠江组砂岩岩屑主要为变质岩屑和火山岩屑,并含较多深成岩屑。阴极射线下,石英以发蓝紫色—褐色光为主,长石主要发亮蓝色光。异源生屑灰岩为陆坡钙屑碎屑流沉积,来自于神狐暗沙隆起中新统碳酸盐台地。泥岩∑REE与燕山褶皱带燕山期中酸性火山岩较接近,分配模式与上地壳基本一致,并与燕山中酸性火山岩和花岗岩较接近。渐新世末,南海运动使南海海盆第二次海底扩张,并使陆架坡折带由白云凹陷南侧跳跃到凹陷北侧。该构造事件在青藏高原邻近盆地和中国东部盆地都有反映,反映可能发生了青藏高原隆升事件,使珠江组物源向西拓展。珠江期虽然存在活跃的深水牵引流,但珠江组原始物质仍应源自古珠江携带的华南沿海燕山褶皱带的中酸性火山岩、花岗岩和内陆古老的沉积—变质岩。

白云凹陷珠江组深水扇成岩作用与成岩相分析

根据铸体薄片、扫描电镜、镜质体反射率等分析资料,对珠江口盆地白云凹陷荔湾地区珠江组深水扇砂岩储层成岩作用及成岩相进行了系统研究。确定对储层起破坏作用的成岩作用主要有压实、胶结和自生矿物充填作用,起建设性成岩作用的主要有溶蚀作用。综合成岩方式的组合类型和演化序列,认为深水扇砂岩储层成岩演化主体仅进入中成岩阶段A—B期。在建立成岩演化模式的基础上,对成岩相组合特征进行了分析,划分出胶结—弱压实—弱溶蚀相、弱压实—弱胶结—强溶蚀相和中等压实—弱胶结—中等溶蚀相等3种主要成岩相类型,其中以弱压实—弱胶结—强溶蚀相砂体的物性为最好。

珠江口盆地荔湾井区珠江组深水扇沉积特征

珠江口盆地白云凹陷荔湾深水区为油气勘探有利区域,通过岩石学和古生物组合特征研究,认为该区珠江组下部属于典型的深水扇沉积,可划分为早期盆地扇和晚期斜坡扇两种类型,两类深水扇都以发育颗粒流、砂质碎屑流及低密度浊流等顺坡重力流沉积为主,同时夹有少量内波和等深流等深水牵引流改造沉积。砂质碎屑流为两类深水扇水道砂体的主要沉积类型,发育有逆-正粒序层理、平行层理和水平层理,粒序层内可见各种丰富的液化变形和生物逃逸构造,而水平层内发育有更多的生物钻孔和扰动现象。两类深水扇的沉积构造和古生物特征有明显差异,其中盆地扇水道砂岩中普遍含硅质小砾石,水道间泥岩中含有较多保存完好的抱球虫化石,斜坡扇水道砂岩以富含炭泥屑为典型特征,水道间泥岩含有更丰富的颗石藻和抱球虫化石,其中部分抱球虫和颗石具有遭受海底溶蚀作用的现象,指示斜坡扇相对盆地扇有更大的水体深度。平面上两类深水扇具有相似的重力流沉积的分带性,都具有自陆架坡折向盆地方向由颗粒流沉积逐渐向砂质碎屑流和近源高密度浊流、远源低密度浊流等单向演化的特点。

珠江口盆地白云凹陷深水扇沉积相特征

珠江口盆地深水扇的发现为中国油气勘探中的重大突破,并以其宏大的规模、典型的结构及巨大的勘探前景引起国内外的关注。在区域地质背景研究基础上,通过白云凹陷X-1气田岩石学特征、地球化学特征和地球物理特征研究,识别出该盆地内深水扇沉积体,将深水扇划分为内扇、中扇和外扇三个亚相和水道颗粒流、碎屑流、水道间、近源和远源浊流等微相。对各微相作了较为详细的描述,结果表明水道砂质碎屑流微相是最有利于优质储集砂体发育的沉积微相。在此基础上提出深水扇理想沉积模式。

珠江口盆地荔湾3-1气田珠江组深水扇沉积相分析

根据已钻井取芯段岩相分析,从荔湾3-1气田珠江组深水扇沉积体系中划分出巨厚层和厚层块状砂岩相、厚层正粒序砂岩相、厚层逆粒序砂岩相、平行—板状斜层理砂岩相、滑塌变形砂岩相、薄层砂岩夹层相、薄层(粉)砂岩与泥岩互层相、厚层粉砂岩相、厚层泥岩相和层状深水灰岩相等10种岩相类型和识别出砂岩相组合、泥岩相组合、(粉)砂岩与泥岩互层相组合、粉砂岩相组合和深水灰岩相组合等5种岩相组合类型,在此基础上,从珠江组深水扇沉积体系中进一步识别出内扇主水道、中扇分支水道、水道间、天然堤—溢岸、外扇和盆地等微相类型,将珠江组下部确定为以砂岩相组合为主的盆底扇内扇和斜坡扇内-中扇沉积组合,其中内扇主水道和中扇分支水道是最有利储层发育的沉积微相。中、上部确定为以泥岩相组合为主的外扇和盆地沉积组合,具有随海侵扩大,深水扇最终被远洋所取代的沉积演化特征。