Sedimentary Facies Architectures of Third-Order Sequences from Early to Middle Triassic in Nanpanjiang Basin

There are complex and regular changes on sedimentary facies from the Early to the Middle Triassic in the Nanpanjiang basin. After the obvious drowned event of carbonate platforms in the transitional period between Permian and Triassic, carbonate platforms have evolved into the ramp type from the rimmed-shelf type. The differentiation of sedimentary facies becomes dearer in space, which are marked by the changes from an attached platform to a turbidity basin and several isolated platforms in the basin. The striking characteristics are the development of oolitic banks on isolated platforms in Nanning and Jingxi and the reef- and bank-limestones in the margin of the attached platform in the Early Triassic. Despite the difference of the time-span and the architectnre of fades succession of third-order sedimentary sequences, the process of the third-order relative sea-level changes reflected by the sedimentary facies succession of the third-order sequences is generally synchronous. Therefore, six third-order sequences could be discerned in the strata from the Early to the Middle Triassic in the Nanpanjiang basin. Using two types of facies changing surfaces and two types of diachronisms in stratigraphic records as the key elements, the sedimentary facies architectures of the third-order sequences that represent sequence stratigraphic frameworks from the Early to the Middle Triassic in the Nanpanjiang basin could be constructed.     

地震和测井资料联合反演储层物性参数的方法

为了充分利用测井资料较高的纵向分辨率及其反映井壁周围物性直接准确的特点和地震资料良好的横向可追踪性，针对厚储层和薄储层地震—地质模型分别提出了利用测井和地震资料联合反演纵横波速度和密度参数的方法。理论模型的计算结果表明，反演方法是切实可行的     

Morphologies and emplacement mechanisms of the lava flows of the Faroe Islands Basalt Group,Faroe Islands,NE Atlantic Ocean

The Palaeogene Faroe Islands Basalt Group (FIBG) comprises three eruptive sequences or formations, all emplaced into a subaerial environment during the development of the extensive continental flood basalt province that stretches from East Greenland through the Faroe Islands and into the Faroe-Shetland Basin. The Beinisvørð Formation, having a tabular-classic facies architecture, is composed of a sequence of simple flows each comprising a single sheet lobe. The Beinisvørð Formation is overlain by the distinctly contrasting Malinstindur Formation that has a compound-braided facies architecture. The Enni Formation occurs at the top of the sequence and consists of a mixture of simple and compound flows with tabular-classic and compound-braided facies architectures, respectively. Surface and internal characteristics of the sheet lobes of the Beinisvørð and Enni formations indicate emplacement through inflation, which is more obvious for the tube-fed compound flows of the Malinstindur and Enni formations. The difference between the simple and compound flow sequences of the FIBG is, most likely, linked to the manner in which the lava was supplied during the eruption and the eruptive style of the volcanic system. The sheet lobes were erupted over laterally extensive areas from fissure systems which had a continuous supply of lava, which contrasts with the tube-fed compound flows which were erupted in a gradual, piecemeal manner from point-sourced, low shield volcanoes with limited areal extents.     

阵发性洪水条件下辫状河型冲积扇构型研究:以准噶尔盆地西北缘现代白杨河冲积扇为例*

白杨河冲积扇是由阵发性洪水期的碎屑流沉积物与间洪期辫状河沉积物组成的复合型冲积扇,其构型与碎屑流扇的构型和河流型扇的构型有很大的不同。本研究选取准噶尔盆地西北缘干旱气候下发育的现代白杨河冲积扇作为解剖实例,对103个天然剖面和9个人工大型探槽进行了详细测量,在沉积微相及不同级别的沉积构型的观测和分析的基础上,分析了阵发性洪水条件下间歇性辫状河型冲积扇体的地貌单元的演化过程和沉积构型特征,研究不同流态的阵发性洪水条件下各种建造和改造机制,明确受阵发性洪水控制的间歇性辫状河型冲积扇的沉积特征,建立了其沉积构型模式。认为: 在洪水期,阵发性洪流(碎屑流)形成席状化的片流(或片洪)沉积,在洪退期,随着洪水强度的减弱,又转变为辫流沉积,而在间洪期,仍有持续的辫状流体(牵引流)在限制性的水道中流动,并对洪水期的碎屑流沉积物进行改造,形成了限制性的(条带状的)辫状河道沉积,2个时期的沉积物在时空上频繁叠置,形成了一种更加复杂的沉积构型。该模式对油田地下冲积扇砂砾储集层的成因识别、预测及对比具有一定的参考价值。     

Diagenetic signatures of stratal surfaces in the Upper Jurassic Fulmar Formation, Central North Sea, UKCS

Sedimentation rate and changes in relative sea level affect early diagenetic cementation along key stratal surfaces within the deeply buried Upper Jurassic Fulmar Formation, South Central Graben, UKCS. As a result of the bioturbated nature of the shallow marine strata, variations in ichnofabrics and cross-cutting relationships between trace fossils are important in identifying and correlating stratal surfaces. Two transgressive and two regressive surfaces/sequence boundaries were studied, using petrographical, mineralogical and geochemical techniques. Cements, including early diagenetic pyrite framboids, grain-rimming apatite, microcrystalline dolomite and ankerite, occur at, above and immediately below both transgressive and forced regressive surfaces/sequence boundaries. Breaks or subdued rates of sedimentation associated with both types of surfaces meant that the sediment package resided within early diagenetic zones for prolonged periods of time, enhancing diagenetic reactions at and below the surfaces. The distribution of ankerite, despite being a deep-burial cement, was primarily controlled by concentrations of bioclasts that are particularly abundant at transgressive surfaces. The diagenetic character of the forced regressive surfaces/sequence boundaries is more complex than that of the transgressive surfaces, both in terms of mineralogy and paragenesis. This is attributed to the superimposition of diagenetic assemblages as a result of erosion, re-sedimentation and sediment by-passing. Although the diagenetic signature of the surfaces has been modified by dissolution/replacement reactions during deep burial, early diagenetic signatures can still be distinguished.     

河流相砂体识别预测及古气候响应: 以渤中坳陷石南地区明下段为例

河流相砂体的识别预测及其发育演化对古气候变化的响应是当前河流相沉积研究的热点。基于地震沉积学方法,采用三步走的河流相砂体识别预测方法(井震结合建格架→90°相位调整标岩性→切片属性辨砂体),在渤海湾盆地渤中坳陷石臼坨凸起南部(石南)新近系明化镇组下段(简称“明下段”)识别出了顺直和蜿蜒河道砂、河道—堤坝复合体、点砂坝、河口坝、牛轭湖和决口扇6种河流相砂体。依据明下段泥岩颜色,结合藻类种属记录和孢粉记录分析,认为石南地区明下段沉积早期到中期经历了干湿交替→湿润主导的湿润化气候演变; 而明下段沉积中期到晚期经历了湿润主导→干旱主导的干旱化气候演变。润湿化气候演变使得明下段沉积中期河流相砂体宽度和单层厚度减小、弯曲度增大,且带状孤立河道砂体更发育; 而干旱化气候演变使得明下段沉积晚期流相砂体宽度和单层厚度增大、弯曲度减小,且带状河道—溢岸复合带和河口坝砂更发育。研究成果可为其他断陷盆地河流相砂体识别、预测提供参考,对指导构造活动相对较弱的湖盆萎缩期油气勘探实践具有一定的实践价值。     

开发尺度的曲流河储层内部结构地震沉积学解释方法

曲流河地层内部结构复杂,岩性界面具有穿时性,传统的地震相分析法不能满足油藏开发地质研究中对储层内部结构精细解释的需要,急需探索有效的地震解释方法。采用基于探地雷达的露头探测、点坝复合体三维正演模拟和实际地震资料相结合的方法,分析了地震资料频率和地层厚度对曲流河内部结构地震反射特征的影响,研究了利用地层切片解释曲流河沉积结构的原理和方法,建立了开发尺度的曲流河内部结构地震沉积学解释技术。研究发现:(1)高频地震资料中地震反射能够反映曲流河侧积复合体边界,而低频地震资料中反射同相轴与岩性界面一致;(2)不同厚度的点坝侧积单元地震反射特征存在差异,造成反射剖面的多解性。同时指出曲流河内部结构地震沉积学解释的技术关键:(1)发挥地震资料平面与剖面信息的相互约束和补充;(2)将地质体作为三维空间发育的成因体,利用其平面与剖面特征的成因联系指导解释;(3)级次化解释方法,在不同级次上采用针对性的解释方法。将该方法应用于墨西哥湾新近系地震沉积学解释,实现了曲流河点坝复合体内部结构的三维刻画。     

Unique vs. non-unique stratal geometries: Relevance to sequence stratigraphy

The sequence stratigraphic architecture includes a complex array of stratal geometries with different degrees of stratigraphic significance. The ‘non-unique’ variability of the sequence stratigraphic framework (i.e., stratal geometries which are not diagnostic for the definition of systems tracts and bounding surfaces) is irrelevant to the workflow of sequence stratigraphy. What is relevant is the observation of the ‘unique’ stratal geometries that are diagnostic for the definition of units and surfaces of sequence stratigraphy. In downstream-controlled settings, these unique stratal stacking patterns relate to the forced regressive, normal regressive, and transgressive shoreline trajectories. Multiple controls interact during the formation of each type of stacking pattern, including accommodation, sediment supply, and the energy of the sediment-transport agents. This interplay explains the non-unique variability, but does not change the unique criteria that afford a consistent application of sequence stratigraphy. The distinction between unique and non-unique stratal geometries is critical to the sequence stratigraphic methodology. Failure to rationalize the non-unique variability within the context of unique stratal geometries is counterproductive, and obscures the simple workflow of sequence stratigraphy. This is the case with uncalibrated numerical modeling, which may overemphasize non-unique or even unrealistic stratigraphic scenarios. While useful to test the possible controls on stratigraphic architecture, modeling requires validation with real data, and plays no role in the sequence stratigraphic methodology.     

Architecture and sedimentology of the Kerinitis Gilbert‐type fan delta,Corinth Rift,Greece

The Kerinitis Delta in the Corinth Rift, Greece, is a footwall derived, coarse‐grained, Gilbert‐type fan delta deposited in the hangingwall of a linked normal fault system. This giant Gilbert‐type delta (radius 3·8 km, thickness > 600 m) was supplied by an antecedent river and built into a brackish to marine basin. Although as yet poorly dated, correlation with neighbouring deltas suggests that the Kerinitis Delta was deposited during a period of 500 to 800 ka in the Early to early Middle Pleistocene. Facies characterizing a range of depositional processes are assigned to four facies associations (topset, foreset, bottomset and prodelta). The dominantly fluvial topset facies association has locally developed shallow marine (limestone) and fluvial‐shoreface sub‐associations. This delta represents a subsidence‐dominated system in which high fault displacement overwhelmed base‐level falls (creation of accommodation predominantly ≥ 0). Stratal geometries and facies stacking patterns were used to identify 11 key stratal surfaces separating 11 stratal units. Each key stratal surface records a landward shift in the topset breakpoint path, indicating a rapid increase in accommodation/sediment supply. Each stratal unit records a gradual decrease in accommodation/sediment supply during deposition. The cyclic stratal units and key stratal surfaces are interpreted as recording eustatic falls and rises, respectively. A 30 m thick package of foresets below the main delta records the nucleation of a small Proto‐delta probably on an early relay ramp. Based on changes in stratal unit geometries, the main delta is divided into three packages, interpreted as recording the initiation, growth and death of the controlling fault system. The Lower delta comprises stacked, relatively thin, progradational stratal units recording low displacement on the young fault system (relay ramp). The Middle delta comprises vertically stacked stratal units, each recording initial aggradation–progradation followed by progradation; their aggradational component increases up through the Middle delta, which records the main phase of increasing rate of fault displacement. The Upper delta records pure progradation, recording abrupt cessation of movement on the fault. A major erosion surface incising basinward 120 m through the Lower and Middle delta records an exceptional submarine erosion process (canyon or delta collapse).     

有效厚度拟合定量恢复原始地层超覆点位置

地层超覆点的迁移是层序地层分析和海平面变化曲线编制的重要依据。受构造抬升、海平面下降或二者共同作用影响,地层超覆点在沉积后常被剥蚀。如何恢复其原始沉积时的位置,至今尚无定量方法提出。基于地层厚度自盆地边缘向盆地中心依次增大,或先增大、后减小的分布特点,采用指数与线性相结合的分段函数模型,利用未剥蚀区地层厚度数据拟合外推恢复原始地层超覆点位置。该方法适用于被动大陆边缘、大型三角洲沉积区及坳陷型盆地,应用于巽他陆架晚新生代地层分析,取得满意效果.