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.

Status and Trends in Research on Deep-Water Gravity Flow Deposits

Deep-water gravity flows are one of the most important sediment transport mechanisms on Earth. After 60 years of study, significant achievements have been made in terms of classification schemes, genetic mechanisms, and depositional models of deep-water gravity flows. The research history of deep-water gravity flows can be divided into five stages： incipience of turbidity current theory; formation of turbidity current theory; development of deep-water gravity flow theory; improvement and perfection of deep-water gravity flow theory; and comprehensive development of deep-water gravity flow theory. Currently, three primary classification schemes based on the sediment support mechanism, the rheology and transportation process, and the integration of sediment support mechanisms, rheology, sedimentary characteristics, and flow state are commonly used.Different types of deep-water gravity flow events form different types of gravity flow deposits. Sediment slump retransportation mainly forms muddy debris flows, sandy debris flows, and surge-like turbidity currents. Resuspension of deposits by storms leads to quasi-steady hyperpycnal turbidity currents （hyperpycnal flows）. Sustainable sediment supplies mainly generate muddy debris flows, sandy debris flows, and hyperpycnal flows. Deep-water fans, which are commonly controlled by debris flows and hyperpycnal flows, are triggered by sustainable sediment supply; in contrast, deep-water slope sedimentary deposits consist mainly of debris flows that are triggered by the retransportation of sediment slumps and deep-water fine-grained sedimentary deposits are derived primarily from fine- grained hyperpycnal flows that are triggered by the resuspension of storm deposits. Harmonization of classification schemes, transformation between different types of gravity flow deposit, and monitoring and reproduction of the sedimentary processes of deep-water gravity flows as well as a source-to-sink approach to document the evolution and deposition of deep-water gravity flows are the most important research aspects for future studies of deep-water gravity flows study in the future.

Microfacies of Deep-water Deposits and Forming Models of the Chinese Continental Scientific Drilling-SKII

Extensive transgression of lake water occurred during the Cretaceous Qingshankou Stage and the Nengjiang Stage in the Songliao basin, forming widespread deep-water deposits. Eleven types of microfacies of deep-water deposits have been recognized in the continuous core rocks from the SKII, including mudstone of still water, marlite, dolostone, off shale, volcanic ashes, turbidite, slump sediment, tempestite, seismite, ostracoda limestone and sparry carbonate, which are divided into two types： microfacies generated due to gradually changing environments （Ⅰ） and microfacies generated due to geological events （Ⅱ）. Type Ⅰ is composed of some special fine grain sediments such as marlite, dolomite stone and oil shale as well as mudstone and Type Ⅱ is composed of some sediments related to geological events, such as volcanic ashes, turbiditie, slump sediment, tempestite, seismite, ostracoda limestone. The formation of sparry carbonate may be controlled by factors related to both environments and events. Generally, mudstone sediments of still water can be regarded as background sediments, and the rest sediments are all event sediments, which have unique forming models, which may reflect controlling effects of climatics and tectonics.

Deep-water gravity flow deposits in a lacustrine rift basin and their oil and gas geological significance in eastern China

The types,evolution processes,formation mechanisms,and depositional models of deep-water gravity flow deposits in a lacustrine rift basin are studied through core observation and systematic analysis.Massive transport of slide and slump,fluid transport of debris flow and turbidity currents are driven by gravity in deep-water lacustrine environment.The transformation between debris flow and turbidity current,and the transformation of turbidity current between supercritical and subcritical conditions are the main dynamic mechanisms of gravity flow deposits in a lake basin.The erosion of supercritical turbidity current controls the formation of gravity-flow channel.Debris flow deposition gives rise to tongue shape lobe rather than channel.Deep-water gravity flow deposits are of two origins,intrabasinal and extrabasinal.Intrabasinal gravity flow deposits occur as single tongue-shape lobe or fan of stacking multiple lobes.Extrabasinal gravity-flow deposits occur as sublacustrine fan with channel or single channel sand body.However,the nearshore subaqueous fan is characterized by fan of stacking multiple tongue shape lobes without channel.The differential diagenesis caused by differentiation in the nearshore subaqueous fan facies belt results in the formation of diagenetic trap.The extrabasinal gravity flow deposits are one of the important reasons for the abundant deep-water sand bodies in a lake basin.Slide mass-transport deposits form a very important type of lithologic trap near the delta front often ignored.The fine-grained sediment caused by flow transformation is the potential"sweet spot"of shale oil and gas.

Sedimentary Processes and Depositional Characteristics of Coarse-grained Subaqueous Fans along Steep Slopes in a Lacustrine Rift Basin:A Case Study from the Dongying Depression,Bohai Bay Basin,China

Coarse-grained subaqueous fans are vital oil and gas exploration targets in the Bohai Bay basin,China.The insufficient understanding of their sedimentary processes,depositional patterns,and controlling factors restricts efficient exploration and development.Coarse-grained subaqueous fans in the Yong′an area,Dongying Depression,are investigated in this study.These fans include nearshore subaqueous fans,and sublacustrine fans,and their sedimentary processes,depositional patterns and distribution characteristics are mainly controlled by tectonic activity and paleogeomorphology.Nearshore subaqueous fans developed near the boundary fault during the early–middle deposition stage due to strong tectonic activity and large topographic subsidence.Early sublacustrine fans developed at the front of the nearshore subaqueous fans in the area where the topography changed from gentle to steep along the source direction.While the topography was gentle,sublacustrine fans did not develop.During the late weak tectonic activity stage,late sublacustrine fans developed with multiple stages superimposed.Frequent fault activity and related earthquakes steepened the basin margin,and the boundary fault slopes were 25.9°–34°.During the early–middle deposition stage,hyperpycnal flows triggered by outburst floods developed.During the late deposition stage,with weak tectonic activity,seasonal floods triggered hyperpycnal flows,and hybrid event beds developed distally.

Diversity of depositional architecture and sandbody distribution of sublacustrine fans during forced regression: A case study of Paleogene Middle Sha 3 Member in Dongying Sag, Bohai Bay Basin, East China

Currently, the differences in gravity flow deposits within different systems tracts in continental lacustrine basins are not clear. Taking the middle submember of the third member of Paleogene Shahejie Formation(Sha 3 Member) in the Shishen 100 area of the Dongying Sag in the Bohai Bay Basin as an example, the depositional architecture of sublacustrine fans during forced regression and the impact of the fourth-order base-level changes on their growth were investigated using cores, well logs and 3D seismic data. Sublacustrine fans were mainly caused by hyperpycnal flow during the fourth-order base-level rise, while the proportion of slump-induced sublacustrine fans gradually increased during the late fourth-order base-level fall. From rising to falling of the fourth-order base-level, the extension distance of channels inside hyperpycnal-fed sublacustrine fans reduced progressively, resulting in the transformation in their morphology from a significantly channelized fan to a skirt-like fan. Furthermore, the depositional architecture of distributary channel complexes in sublacustrine fans changed from vertical aggradation to lateral migration, and the lateral size of individual channel steadily decreased. The lobe complex's architectural patterns evolved from compensational stacking of lateral migration to aggradational stacking, and the lateral size of individual lobe steadily grew. This study deepens the understanding of depositional features of gravity flow in high-frequency sequence stratigraphy and provides a geological foundation for the fine development of sublacustrine fan reservoirs.

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.

Evolution and controlling factors of the gravity flow deposits in the Miocene sequence stratigraphic framework,the Lower Congo-Congo Fan Basin,West Africa

To understand the evolution of the Miocene gravity flow deposits in the Lower Congo-Congo Fan Basin,this paper documents the Miocene sequence stratigraphic framework,the depositional characteristics and the controlling factors of the gravity flow system.Based on the establishment of high-resolution sequence stratigraphic framework,lithofacies characteristics and sedimentary units of the gravity flow deposits in the region are identified by using seismic,well logging and core data comprehensively,and the sedimentary evolution process is revealed and the controlling factors are discussed.The Miocene can be divided into four 3 rd-order sequences(SQ1-SQ4).The gravity flow deposits mainly include siliciclastic rock and pelite.The main sedimentary units include slumping deposits,mass transport deposits(MTD),channel fills,levee-overbank deposits,and frontal lobes.In the Early Miocene(SQ1),mainly gull-wing,weakly restricted to unrestricted depositional channel-overbank complexes and lobes were formed.In the early Middle Miocene(SQ2),W-shaped and weakly restricted erosional-depositional channels(multi-phase superposition)were subsequently developed.In the late Middle Miocene(SQ3),primarily U-shaped and restricted erosional channels were developed.In the Late Miocene(SQ4),largely V-shaped and deeply erosional isolated channels were formed in the study area.Climate cooling and continuous fall of the sea level made the study area change from toe of slope-submarine plain to lower continental slope,middle continental slope and finally to upper continental slope,which in turn affected the strength of the gravity flow.The three times of tectonic uplifting and climate cooling in the West African coast provided abundant sediment supply for the development of gravity flow deposits.Multistage activities of salt structures played important roles in redirecting,restricting,blocking and destroying the gravity flow deposits.Clarifying the characteristics,evolution and controlling factors of the Miocene gravity flow deposits in the Lower Congo-Congo Fan Basin can provide reference for deep-water petroleum exploration in this basin.

3D anatomy and flow dynamics of net-depositional cyclic steps on the world’s largest submarine fan:a joint 3D seismic and numerical approach

Supercritical flows are ubiquitous in natural environments;however,there is rare 3D anatomy of their deposits.This study uses high-quality 3D seismic datasets from the world’s largest submarine fan,Bengal Fan,to interpret 3D architectures and flow processes of Pliocene undulating bedforms that were related to supercritical flows.Bengal undulating bedforms as documented in this study were developed in unconfined settings,and are seismically imaged as strike-elongated,crescentic bedforms in plan view and as rhythmically undulating,upstream migrating,erosive,discontinuous reflections in section view.Their lee sides are overall 3 to 4 times steeper(0.280 to 1.19°in slope)and 3 to 4 times shorter(117 to 419 m in length)than their stoss flanks and were ascribed to faster(high flow velocities of 2.70 to 3.98 m/s)supercritical flows(Froude numbers of 1.53 to 2.27).Their stoss sides,in contrast,are overall 3 to 4 times gentler(0.120 to 0.270 in slope)and 3 to 4 times longer(410 to 1139 m in length)than their lee flanks and were related to slower(low velocities of 2.35 to 3.05 m/s)subcritical flows(Froude numbers of 0.58 to 0.97).Bengal wave-like features were,thus,created by supercriticalto-subcritical flow transformations through internal hydraulic jumps(i.e.,cyclic steps).They have crests that are positive relative to the surrounding region of the seafloor,suggesting the predominant deposition of draping sediments associated with net-depositional cyclic steps.Turbidity currents forming Bengal wave-like features were,thus,dominated by deposition,resulting in net-depositional cyclic steps.Sandy deposits associated with Bengal net-depositional cyclic steps are imaged themselves as closely spaced,strike-elongated high RMS-attribute patches,thereby showing closely spaced,long and linear,strike-elongated distribution patterns.

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.

断陷湖盆陡坡带扇三角洲—滑塌扇复合扇体的沉积演化及油气地质意义——以中非地区Melut盆地A凹陷白垩系为例

【目的】扇三角洲—深水滑塌扇组成的复合扇体作为断陷盆地陡坡带重要的粗粒沉积体系和油气储层,其展布范围、演化期次、成藏模式等一直是湖盆沉积和成藏研究的热点。【方法】以中非地区Melut盆地A凹陷高精度三维地震和钻测井资料为基础,采用岩心观察、层序划分、地震反射特征与地震属性分析等方法,对扇三角洲—滑塌扇复合扇体的沉积特征与演化规律进行了研究。【结果与结论】发现研究区复合扇体的沉积相类型包括扇三角洲和重力流成因的滑塌扇,滑塌扇具有两类形貌特征,第一类为受坡折控制的线状供源滑塌扇,第二类为受较陡地形坡度控制的单点供源多级滑塌扇。白垩系研究层段刻画出五期扇体,单期复合扇体内部具有退积特征,多期复合扇体具有“先进积、后退积”的垂向演化特征,其中下白垩统Renk组沉积末期复合扇体规模最大,达到148 km^(2)。复合扇体演化主要受幕式构造活动、古地貌和物源供给,以及相对湖平面变化的影响,构造活动强烈、物源供给充足、短轴构造隆升幅度大的时期,复合扇体规模更大,相对湖平面下降初期和上升初期滑塌扇最为发育。提出A凹陷早白垩世和晚白垩世发生沉积格局转换的新认识,明确了断陷期陡坡带扇三角洲-滑塌扇复合扇体的勘探潜力,指导了勘探部署。

石英脉型钨多金属矿床的扇状成矿实例及找矿模型

石英脉型钨矿床是中国数量最多的钨矿床类型,但保有储量消耗迅速,迫切需要创新找矿模型,指导找矿突破。文章结合二十余年的找矿实践,通过详细分析扇状成矿矿床实例,构建了石英脉型钨矿床新的找矿模型。该模型强调赋矿裂隙为岩浆动力成因,在花岗岩体顶部呈扇状分布型式,岩浆期后热液恰在裂隙张开时充填其中而形成扇状成矿系统;提出“就岩找矿”、“就矿找矿”、“就矿找岩”的地质、地球化学和地球物理标志,指导矿床尺度的勘查工程部署。截至目前,该模型已在广东禾尚田钨锡矿床、广西珊瑚钨锡矿床、广西社垌钨钼矿床、江西盘古山钨铋矿床等获得了验证,找矿成效显著。

鄂尔多斯盆地二叠系盒8段河流扇沉积模式及勘探意义

根据野外露头及岩心的分析化验资料,在源-汇系统分析的基础上,对鄂尔多斯盆地二叠系盒8段的古气候环境及沉积相特征进行了详细研究。研究结果表明:(1)鄂尔多斯盆地二叠系盒8段Sr/Cu的值多大于10,V/Cr值多小于2.0,地层厚度差小于30 m,未出现明显的突变,古沉积坡度为0.5°~1.0°,古地貌开阔平缓且无明显坡折带,沉积水体较浅,是在古气候干旱、古地形平缓的背景下,受阶段性洪水作用主导的事件沉积。(2)盒8段沉积期,盆地不存在大面积汇水区,沉积体系中河流并未进入湖泊水体,而是向东南流出盆地或是消失在内陆干旱地区,全盆地以洪泛平原沉积为主,表现为河道与泛滥平原交互分布的沉积格局,形成了河流扇沉积模式。(3)湖水进退往复,洪水期与枯水期间歇发育,洪水期多期次决口河道接力搬运使得粗粒级砂岩向湖盆长距离延伸,枯水期发育厚层泥质沉积可作为区域性盖层,形成了良好的储盖组合,勘探潜力大。

中新世以来上印度扇水道-堤岸体系几何学特征及演化

以中新世以来上印度扇水道-堤岸体系为研究对象,利用高精度二维地震资料开展地震精细解释与几何学分析,刻画水道-堤岸体系几何学特征及时空演化过程,探讨中新世以来上印度扇发育演化主要期次及特征。结果表明,中新世以来上印度扇水道-堤岸体系可划分为中新世、上新世及更新世至今三大期次,整体表现出“单期水道-侧向迁移-扁长型”到“多期水道-垂向叠置-厚窄型”的演化特征。深入探讨中新世以来上印度扇水道-堤岸体系的几何学特征及演化可为重力流水道的沉积构型样式研究提供新的例证,并为深海油气勘探开发提供参考。

多翼离心风机叶轮内油性粒子沉积特性的数值研究

为了揭示多翼离心风机内部油性粒子沉积分布规律,减少风机内粒子沉积,采用Fluent离散相模型描述粒子运动,同时结合临界速度模型和用户自定义函数(UDF)建模油性粒子在壁面上的沉积,模拟研究了多翼离心风机内油性粒子的运动轨迹和沉积特性,并探究了颗粒直径对沉积分布的影响。结果表明:油性粒子沉积主要分布在叶片压力面,且靠近出口尾缘段尤为严重;由于进气条件不稳定,整机下内部流场更为紊乱,沉积情况也更为严重;大直径粒子受惯性力主导更容易沉积在叶片表面。针对油性粒子沉积分布规律及成因,提出了切割叶片减小叶片出口安装角从而减少叶轮内油性粒子沉积的方法。对于切割后的叶片,叶轮出口处流动分离区域减小,叶片尾缘段涡量减小,通过数值模拟和实验研究发现,叶轮内油性粒子沉积率分别下降了30.75%和30.66%,两者吻合良好,证实了提出的减小叶轮油性粒子沉积方法的有效性。

基于沉积过程分析的扇三角洲沉积模式研究:以滦平盆地桑园剖面下白垩统西瓜园组为例

洪水类型与流量变化是影响扇三角洲地貌形态与沉积特征的主要因素,但不同类型洪水作用下扇三角洲沉积单元发育规律研究薄弱。论文以滦平盆地桑园剖面下白垩统西瓜园组为例,通过剖面测量和岩相划分,恢复了沉积流体类型、沉积过程及其沉积响应单元,建立了不同洪水作用下扇三角洲沉积模式。根据岩相组合将该剖面的主控沉积过程解释为碎屑流、洪流与片流3种洪水,分别对应于碎屑流建造期、洪流建造期与片流建造期。结合沉积过程与砂砾岩沉积形态特征,将目的层解释为8种沉积单元,具体包括扇三角洲平原环境的陆上碎屑流舌状体、洪流主控辫状河道和扇三角洲前缘的水下碎屑流舌状体、高密度浊流水道、牵引流水下分流河道、高密度浊流朵体、水下片流朵体及滑塌体。在扇三角洲碎屑流建造期,发育多期垂向上叠置的、向湖盆进积的碎屑流舌状体;在洪流建造期,平原中形成洪流主控辫状河道,而进入湖盆后洪流转化为高密度浊流,发育高密度浊流水道与朵体;在片流建造期,则以水下快速沉积形成的水下片流朵体为特征。洪水期扇三角洲前缘沉积物快速沉积和沉积物坡失稳易于形成滑塌体,而间洪期则以平原上辫状河道和前缘中低流态水下分流河道的发育为特征。基于洪水类型及其沉积过程的扇三角洲沉积规律的研究,深化了对其砂体形态与结构规律的认识。

扇三角洲流体类型转换及控制因素分析——以青海希里沟扇三角洲为例

【目的】扇三角洲广泛发育于沉积盆地边缘及内部,具有规模庞大、类型多样、生储盖配置良好等特点,蕴藏着巨大的油气资源勘探潜力。然而,其流体类型转换和控制因素、沉积过程与特征仍尚不清晰。【方法】以青海希里沟扇三角洲为研究对象,基于野外露头和探槽剖面的精细刻画描述,综合利用14C测年、粒度分析等方法,对希里沟扇三角洲不同时期沉积物粒度、结构、沉积构造等方面特征进行研究。【结果与结论】通过野外露头探槽剖面的精细刻画描述共划分出9类岩相及7种垂向组合序列,识别出碎屑流、片状洪流和牵引流共3种流体类型。根据AMS14C定年标定沉积界面、沉积物粒度、结构等方面特征,将希里沟湖三角洲划分为SI、SII和SIII共3个阶段,其中SI期为碎屑流粗粒沉积期,SII为片状洪流改造沉积期,SIII期为牵引流改造沉积期。通过沉积物粒度敏感组分分析,在希里沟湖扇三角洲平面识别出3期朵叶。结合希里沟三角洲沉积地形坡度和青海湖15 ka以来孢粉浓度变化,证实了希里沟扇三角洲流体类型转换受控于沉积坡度与气候的变化,明确了扇三角洲上平原以碎屑流主导,发育碎屑流主水道、片状洪流沉积为主要的构型单元,扇三角洲下平原以片状洪流主导,发育以辫状水道、辫流坝以及洪漫沉积为主要的构型单元,扇三角洲前缘以牵引流主导,发育以水下分流河道、河口坝以及席状砂为主要的构型单元。

叠覆堆积过程中泥石流偏移的实验研究

泥石流堆积扇经过多期叠覆堆积,其在空间和时间分布上有随机性,存在主流偏移和堆积摆动等各向异性现象,给合理规划与利用泥石流滩地带来困难。本文在野外调查四川平武县碓窝梁子沟堆积扇的基础上,开展室内水槽模型实验,结合3D扫描技术和基底压力传感器,探讨泥石流在叠覆堆积过程中的阶段性流态变化以及主流偏移的成因和发展。实验发现:(1)泥石流密度差异导致不同的偏移形式,高密度泥石流易出现层面整体偏移;低密度泥石流易形成插入式的叠覆堆积。(2)泥石流多期堆叠过程中偏移行为并不一定是沿地势更低处,而是取决于后期来流的性态。(3)泥石流偏移角度和距离依赖于流体密度、流速和堆积体几何特征,可以建立以上述参数为变量的堆积偏移角度与偏移距离的计算公式。本研究成果可以为了解泥石流堆积扇的形成机制、致灾范围和演化趋势提供依据。

Platform Evolution in an Oligo-Miocene Back-arc Basin:An Example from the Central Iran Basin

The Qom Formation is the most important hydrocarbon reservoir target in Central Iran.The Qom platform developed in a back-arc basin during the Oligo-Miocene due to the closing of the Tethyan Seaway.This formation consists of a variety of carbonate and non-carbonate facies deposited on a platform ranging from supratidal to basin.A combination of tectonic and eustatic events led to some lateral and vertical facies variations in the study area.Six third-order depositional sequences and related surfaces were identified regarding vertical facies changes in the studied sections of this Oligo-Miocene succession.According to all results and data,this succession was initially deposited during the Chattian upon a distally steepened ramp of siliciclastic-carbonate composition,including the Bouma sequence.Then,from the late Chattian to the Aquitanian,the platform changed into a homoclinal carbonate ramp with a gentle profile.With respect to tectonic activity,this phase was a calm period during the deposition of the Qom Formation.Finally,a drowned carbonate platform and a rimmed shelf emerged during the Burdigalian,terminated by the continental deposits of the Upper Red Formation.Regarding all geological characteristics,three main tectono-eustatic evolutionary phases have been recognized in the Qom back-arcbasin.