塔河油田奥陶系中统一间房组沉积特征及储集特征

运用沉积地质及层序地层对塔河油田南部奥陶系中统一间房组发育的一套碳酸盐岩进行分析,结果表明:从岩石组合特征上可分为上下两段,下段为(砂)砾屑灰岩 藻鲕灰岩 鲕粒灰岩,底栖生物丰富;上段为海绵礁灰岩 藻粘结灰岩,生物骨架灰岩及斑状砾屑灰岩.纵向上,构成了一个建滩沉积序列和一个造礁沉积序列,沉积环境为台地浅滩-台内礁.沉积微相为开阔碳酸盐台地,包括海绵礁、浅滩及滩间;储渗空间以溶蚀孔隙、溶蚀孔洞、溶蚀洞穴和裂缝等为主.塔河油田南部一间房组碳酸盐岩经历的海西早期岩溶也叠加了加里东中期第一幕岩溶的影响,(准)同沉积期加里东中期第一幕岩溶,对一间房组酸盐岩储集性改善具重要意义.     

塔里木盆地奥陶系鹰山组台内滩的特征与分布

塔里木盆地早奥陶世晚期进入伸展转向挤压的区域构造背景,造成台缘带挠曲下沉与台内地貌起伏,有利中下奥陶统鹰山组台内滩的发育。钻井资料表明鹰山组台内滩以中高能砂屑滩为主,台内滩主要分布在鹰山组上部,纵向上多旋回叠置,横向呈透镜状尖灭。通过井—震标定,鹰山组台内滩在地震响应上多具有平缓顶底面的丘状外部形态,内部多出现高频杂乱...     

塔中地区晚奥陶世镶边台地沉积演化

通过大量岩芯、薄片、测井、地震等资料的对比分析,建立了塔中地区上奥陶统良里塔格组层序地层格架,并研究了沉积相演化、分布规律。晚奥陶世塔中地区为开阔台地、台地边缘组成的沉积型镶边台地。良里塔格组层序可划分出海侵体系域、高位体系域,共10个准层序组。前者包括准层序组1～4,为退积、加积准层序组,岩性以泥晶灰岩类为主、夹颗粒灰岩,局部发育生物灰岩。后者包括准层序组5～10,为加积、进积准层序组,岩性为颗粒灰岩、生物礁灰岩夹泥晶灰岩。海侵体系域时期,沉积范围逐步覆盖研究区,开阔台地与台地边缘的沉积范围相对稳定,开阔台地以滩间海、台内洼地等低能沉积亚相为主,台地边缘丘、滩沉积范围逐步扩大,出现镶边沉积特征。高位体系域时期,台地边缘沉积范围基本具有继承性,发育2～7期礁（丘）-滩的沉积旋回,形成礁滩复合体镶边特征;开阔台地大范围内为较低能滩间海沉积,局部发育2～4期丘（礁）-滩沉积旋回。该时期,台地边缘与开阔台地沉积地貌出现明显的高低分异,镶边台地成熟、定型。     

Mesozoic deltaic system along the western margin of the Indian plate: lithofacies and depositional setting of Datta Formation,North Pakistan

Over 1 km thick Mesozoic sedimentary sequence is exposed over a wide area in the Upper Indus basin of north Pakistan along the western margin of the Indian Plate. The Mesozoic sequence is comprised of clastic facies in the lower part, while carbonate facies are dominant in the upper part. About 200 m thick mixed sequence of interbedded sandstone, siltstone, clay, and carbonaceous shale represents the lower Jurassic Datta Formation in the Salt and Trans Indus Ranges in North Pakistan. The Datta Formation constitutes important reservoir horizons in a number of oil fields in the western Himalayan foreland basins where it is encountered at a depth of about 4 km in various wells. The Datta Formation is described from different parts of the range front to understand the internal architecture of various sedimentary facies and their depositional system. The thickness and lithofacies assemblages of the Datta Formation change in different parts of the range front as well as in subsurface of the Upper Indus basin. The Datta Formation represents a coarsening upward deltaic sequence in most parts of the basin. On the basis of lithological variations and sedimentary structures, a number of depositional facies have been recognized which include channel belt facies, floodplain/abandoned channel facies, swamp facies, and lagoonal facies. Further north, in the Kalachitta and Hazara regions, the siliciclastic facies change to more complex assemblages of interbedded bauxite, silcrete, marl, and some limestone. These sediments represent deposition in a delta-plain setting of a fluvial-dominated delta with northwestward flowing channels.     

Depositional environments in an extensive tide-influenced delta plain, Middle Devonian Gauja Formation, Devonian Baltic Basin

The Middle Devonian Gauja Formation in the Devonian Baltic Basin preserves tide‐influenced delta plain and delta front deposits associated with a large southward prograding delta complex. The outcrops extend over 250 km from southern Estonia to southern Lithuania. The succession can be divided into 10 facies associations recording distributary channel belts that became progressively more tide influenced when traced southwards towards the palaeo‐shoreline, separated by muddy intra‐channel areas where deposition was characterized by crevasse splays, delta plain lakes, abandoned channel deposits and tidal gullies. Tidal currents influenced deposition over the entire delta plain, extending up to 250 km from the contemporary shoreline. Tidal facies on the upper delta plain differ from those on the lower delta plain and delta front. In the former case, deposition from river currents was only occasionally interrupted by tidal currents, e.g. during spring tides, resulting in mica and mudstone drapes, and distinctive graded cross‐stratification. The lower delta plain was dominated by tidal facies and tidal currents regularly influenced deposition. There was a change from progradation to aggradation from the lower to the upper part of the Gauja Formation coupled with a vertical decrease in tidal influence and a decrease in coarse‐grained sediment input. The Gauja Formation contrasts with established models for tide‐influenced deltas as the active delta plain was not restricted by topography. The shape of the delta plain, the predominant southward (basinward)‐directed palaeocurrents, and the thick sandstone succession, show that although tidal currents strongly influenced deposition at bed scale, rivers still controlled the overall morphology of the delta and the larger‐scale bedforms. In addition, there are no signs of wave influence, indicating very low wave energy in the basin. The widespread tidal influence in the Devonian Baltic Basin is explained by changes in the wider basin geometry and by local bathymetrical differences in the basin during progradation and aggradation of the delta plain, with changes in tidal efficiency accompanying the change in basin geometry produced by shoreline progradation.     

Reef geometries, erosion surfaces and high-frequency sea-level changes, upper Miocene Reef Complex, Mallorca, Spain

The upper Miocene Reef Complex of Mallorca is a 20-km prograding unit which crops out in sea cliffs along the southern side of the island. These vertical and exceptionally clean outcrops permit: (i) identification of different facies (lagoon, reef front, reef slope and open platform) and their geometries and boundaries at different scales, ranging from metre to kilometre, and (ii) construction of a 6-km-long high-resolution cross-section in the direction of reef progradation. This cross-section shows vertical shifts of the reefal facies and erosion surfaces linked to a general progradational pattern that defines the accretional units. Four hierarchical orders of magnitude (1-M to 4-M) of accretional units are identified by consideration of the vertical facies shifts and by which erosion surfaces are truncated by other erosion surfaces. All these orders show similar patterns: horizontal beds of lagoonal facies in the upper part (landward), reefal and slope facies with sigmoidal bedding in the central part, and open-platform facies with subhorizontal bedding in the lower part (basinwards). The boundaries are erosion surfaces, horizontal over the lagoon facies, dipping basinwards over the reef-front facies and connecting basinwards with their correlative conformities over the reef-slope and open-platform facies. The four orders of accretional units are interpreted in terms of four (1-M to 4-M) hierarchies of sea-level cycles because (i) there is a close relation between the coral growth and the sea surface, (ii) there are vertical shifts in the reefal facies and their relation to the erosion surfaces, and (iii) there was very little tectonic subsidence in the study area during the late Miocene. Additionally, all these units can be described in terms of their position relative to the sea-level cycle: (i) the reefs prograde on the open-platform sediments during low stands of sea-level; (ii) aggradation of the lagoon, reef and open-platform facies dominates during sea-level rises, and the lagoonal beds onlap landwards upon the previous erosion surface; (iii) reefal progradation occurs during high stands of sea-level; and (iv) the 2-M sea-level fall produces an off-lapping reef and there is progradation with downward shifts of the reefal facies and erosion landward on the emerged (older) reefal units (A-erosion surfaces); the 3-M and 4-M sea-level falls produce only erosion (B-and C-erosion surfaces). Although precise age data do not exist at present, some speculations upon the frequency of these Miocene relative sea-level cycles can be made by comparisons with Pleistocene cyclicity. There is a good correlation between the Miocene 2-M cycles and the 100-ka Pleistocene cycles. Consequently, the 1-M cycles can be assigned to a fourth order in relation to previously proposed global cycles and the 2-M to fifth-order cycles. All these accretional units could be defined as ‘sequences’, according to the definition as commonly used in sequence stratigraphy. However, they represent higher than third-order sea-level cycles, but are not parasequences. The term subsequence, therefore, is suggested to define ‘a part of a sequence bounded by erosion surfaces (mostly subaerial) and their correlative conformities basinwards'. A hierarchy of subsequences can be established.     

四川宣汉盘龙洞上二叠统长兴组沉积相与岩石地层精细划分

盘龙洞剖面长兴组与普光气田同属于川东北的碳酸盐台地边缘相礁滩相层序,其岩石地层和沉积相研究结果对于认识普光气田、龙岗气田的储层发育和分布规律具有很好的参考作用。根据对薄片的仔细观察分析以及对相关地层的认识,对剖面长兴组的结晶白云岩地层进行了原岩恢复。根据古生物面貌及岩石组构特征,将盘龙洞剖面长兴组自下而上划分四段:下生屑岩段、礁灰岩段、上生屑岩段、微生物岩段。下生屑岩段包括了下部含小型有孔虫的深水陆棚相泥晶灰岩、以及上部含腕足类和棘皮类的浅水陆棚相生屑泥粒岩。礁灰岩段厚达108m,由海绵骨架岩和障积岩组成。上生屑岩段厚约45.3m,已经白云石化为细晶白云岩,导致前人往往误划分为蒸发台地相。仔细观察后仍然可以进行原岩恢复,主要由生屑泥粒岩、粒泥岩组成,含棘皮类、有孔虫、粗枝藻、等组成的群落。微生物岩段厚约8.7m,不仅地层以不规则薄层状为特征,而且含有特征的微生物群落。与普光6井、湖北利川见天坝长兴组剖面对比后发现,它们有相似的沉积层序:下部的深水相灰岩、中部的生物礁岩、上部的开阔台地相或相似环境的生屑灰岩。这应代表台缘礁滩相带的典型层序,可作为认识台缘礁滩相储层的基础。前人研究未能识别长兴组顶部的微生物岩段。这直接导致了二叠系—三叠系界线的无法正确确定。本文提出可以把微生物岩段作为一个岩石地层单位对待,可以作为确定二叠系—三叠系界线的标志层,把界线放在微生物岩段的中部。     

The clayey—carbonate sedimentation cycle and carbonate platform formation: evidence from the linok formation, the middle riphean of the turukhansk uplift, siberia

Using the Linok Formation as an example, spatiotemporal relationships between siliciclastic and carbonate systems in the epeirogenic-type basin and an initial stage of the carbonate platform development are considered. Clayey-carbonate rocks of the Linok Formation correspond to the middle part of the upper Middle Riphean, up to 1.4 km thick terrigenous-carbonate cycle occurring at the base of the Turukhansk Uplift section. The formation is subdivided into the lower clayey-calcareous (18–43 m), middle, mainly argillite (40–75 m), and upper carbonate (120–220 m) subformations. The analysis of facies associations revealed that the formation was deposited as a symmetrical transgressive-regressive rock succession representing a common stratigraphic sequence. Rocks from the lower and middle subformations correspond to the agradational development of the distal and relatively deep part of the basin with mixed clayey-calcareous sedimentation, whereas the upper subformation reflects the processes of formation and expansion of the carbonate platform. It is shown that the platform development initiated in the external area of the basin, from where fine-grained sediments expanded to the internal deep-water zones. It is assumed that progradation of the platform at the initial stage of its development was characterized by diffused patterns     

四川盆地北部长兴组生物礁地震响应特征与分布规律

井下钻探结果和地震资料表明四川盆地北部上二叠统长兴组生物礁发育,通过对典型井长兴组岩性与电性资料的分析,明确了生物礁的岩性与储层发育特征。根据井下生物礁及围岩岩性与电性资料并结合过井地震剖面反射波的几何特征,建立台地边缘生物礁的地震正演数值模型,通过对比生物礁模型地震正演记录与实际生物礁地震剖面,建立针对研究区台地边缘生物礁的地震响应特征模式。依据生物礁的地震响应特征对该地区连片二、三维地震测线开展地震相分析,通过已有钻井地震相与沉积相对应关系分析,指出了长兴组生物礁在该地区的分布规律。四川北部地区地震相与沉积相带具有良好的对应关系,存在环台棚-海盆相的台地前缘斜坡-台地边缘生物礁相-开阔台地相沉积体系,地震剖面上生物礁的外部形态呈丘状或透镜状,内部为杂乱反射特征;礁盖白云岩具有亮点反射特征,生物礁底界面出现上凸或者下凹反射现象,生物礁的上部地层具有披覆反射结构,四川盆地北部地区长兴组台地边缘生物礁相在台棚-海盆相东、西两侧沿北西向呈条带状展布,分布面积大于2000km~2,生物礁气藏勘探潜力巨大。     

四川盆地仪陇-平昌地区二叠系长兴组地震沉积学研究

为明确四川盆地仪陇-平昌地区长兴组地震相及沉积特征,运用地震岩性学和地震地貌学的综合分析技术,开展井-震结合及礁体三维识别研究,以阐明长兴组生物礁滩储集体的展布特征。研究结果表明,仪陇-平昌地区长兴组主要为四个沉积区带,开阔台地相对应平行-亚平行席状中弱断续地震相、台地边缘相对应平行-亚平行丘状或透镜状中弱地震相、台地前缘斜坡相对应前积席状弱地震相,海盆相对应平行-亚平行席状中强地震相,可细分为台缘礁、台内礁和台内滩亚相;30 Hz振幅调谐体切片揭示海盆岸线为北西向展布,25 Hz调谐体切片对于海盆线西侧的台缘带礁体和台内礁滩体反应明显;生物礁滩体的平面展布特征、发育规模受控于长兴组沉积期西南高、东北低的古地貌形态,台缘礁生长发育的有利区域为台地相带两排北西向凸起带。     

New SHRIMP geochronology for the Western Fold Belt of the Mt Isa Inlier: developing a 1800 – 1650 Ma event framework ∗

The integration of detrital and magmatic U – Pb zircon SHIRMP geochronology with facies analysis has allowed the development of a chronostratigraphic framework for the Leichhardt and Calvert Superbasins of the Western Fold Belt, Mt Isa Inlier. This new event chart recognises three supersequences in the Leichhardt Superbasin: the Guide, Myally and Quilalar Supersequences. The Guide Supersequence spans the interval ca 1800 – 1785 Ma and includes the Bottletree Formation and the Mt Guide Quartzite. Sequence relationships suggest that this sedimentary package represents an asymmetric second-order cycle, recording a thickened transgressive suite of deposits and a comparatively thin second-order highstand. The overlying Myally Supersequence spans the interval ca 1780 – 1765 Ma and includes the Eastern Creek Volcanics and syndepositional Lena Quartzite, and the Myally Subgroup. This package represents a second-order supersequence cycle in which mafic volcanism was initiated during a phase of east – west extension. Following the cessation of volcanism, transgression led to the deposition of the Alsace Quartzite and deeper water Bortala Formation. An increase in the rate of sediment supply over accommodation resulted in progradation and deposition of the Whitworth Quartzite and redbed playa facies of the Lochness Formation as accommodation closed. The Quilalar Supersequence spans the interval ca 1755 – 1740 Ma. Sequence analysis in the eastern part of the Leichhardt River Fault Trough identifies a transgressive suite of facies at the base of this supersequence. Black shales from the upper part of the transgressive deposits characterise the condensed section for this supersequence. Facies analysis indicates that deposition took place in a series of storm-, tide- and wave-dominated shelfal marine depositional systems. Although there are no new depositional age constraints for the younger Bigie Formation, field relationships suggest that it is coeval with, or immediately preceded, the ca 1710 Ma Fiery magmatic event. Therefore, a separate supersequence is defined for the Bigie Formation, the Big Supersequence, even though it may be more genetically related to the Fiery magmatic event. The Big Supersequence, together with the ca 1690 Ma Prize Supersequence, comprise the Calvert Superbasin. The evolution of the Leichhardt and Calvert Superbasins are temporally and spatially related to magmatism. In particular, the new maximum depositional ages for the Guide and Myally Supersequences refine the age of the Eastern Creek Volcanics to ca 1780 – 1775 Ma. The new age for the Weberra Granite is within error of the age for the Fiery Creek Volcanics, indicating that they are both part of the ca 1710 Ma Fiery event. New ages for the Sybella Granite confirm that magmatism associated with this magmatic event is refined to 1680 – 1670 Ma, and is followed by deposition of the Gun Supersequence. Combining the new geochronological constraints with previous work now provides a detailed stratigraphic event framework between 1800 and 1575 Ma for the Western Fold Belt of the Mt Isa Inlier, and allows detailed comparisons and correlations with the Eastern Fold Belt and other Proterozoic terranes.     

西秦岭中志留统“硅、灰、泥岩”型层控铀矿的沉积特征及控矿条件

本文详细研究了西秦岭南带中志留统“硅、灰、泥岩”型层控铀矿含矿岩系的沉积相类型及特征,查明了本区中志留世各期的岩相古地理特征。着重讨论了铀矿田内控矿的地质条件。     

Platform margins, reef facies, and microbial carbonates; a comparison of Devonian reef complexes in the Canning Basin, Western Australia, and the Guilin region, South China

Devonian reef complexes were well developed in Western Australia and South China, but no detailed direct comparison has been made between reef building in the two regions. The regions differ in several respects, including tectonic, stratigraphic and palaeoceanographic–palaeogeographic settings, and the reef building styles reflect minor differences in reef builders and reef facies. Similarities and differences between the two reef complexes provide insights into the characteristics of platform margins, reef facies and microbial carbonates of both regions. Here we present a comparison of platform margin types from different stratigraphic positions in the Late Devonian reef complex of the Canning Basin, Western Australia and Middle and Late Devonian margin to marginal slope successions in Guilin, South China. Comparisons are integrated into a review of the reefal stratigraphy of both regions. Reef facies, reef complex architecture, temporal reef builder associations, 2nd order stratigraphy and platform cyclicity in the two regions were generally similar where the successions overlap temporally. However, carbonate deposition began earlier in South China. Carbonate complexes were also more widespread in South China and represent a thicker succession overall. Platforms in the Canning Basin grew directly on Precambrian crystalline basement or early Palaeozoic sedimentary rocks, but in South China, carbonate complexes developed conformably on older Devonian siliciclastic strata. Pre-Frasnian reef facies in South China had more abundant skeletal frameworks than in Canning Basin reefs of equivalent age, and Famennian shoaling margins containing various microbial reefs may have been more common and probably more diverse in South China. However, Late Devonian platform margin types have been documented more completely in the Canning Basin. Deep intra-platform troughs (deep depressions containing non-carbonate pelagic sediments — Nandan-type successions) that developed along syndepositional faults characterize Devonian carbonate platforms in South China, but have no equivalent on the Lennard Shelf, Canning Basin where inter-reef areas were more shallow. The South China platform-to-depression pattern was generally continuous from the Lower to Upper Devonian, indicating that many pre-Devonian tectonic features continued to exercise considerable effect through deposition. Localized, fault-controlled subsidence was an important factor in both regions, but similarities in 2nd order aggradation–progradation cycles suggest that eustasy was also an important control on the larger scale stratigraphic development of both regions.     

Anatomy of a cyclically packaged Mesoproterozoic carbonate ramp in northern Canada

Carbonates in the upper member of the Mesoproterozoic Victor Bay Formation are dominated by lime mud and packaged in cycles of 20–50 m. These thicknesses exceed those of classic shallowing-upward cycles by almost a factor of 10. Stratigraphic and sedimentological evidence suggests high-amplitude, high-frequency glacio-eustatic cyclicity, and thus a cool global climate ca. 1.2 Ga.The Victor Bay ramp is one of several late Proterozoic carbonate platforms where the proportions of lime mud, carbonate grains, and microbialites are more typical of younger Phanerozoic successions which followed the global waning of stromatolites. Facies distribution in the study area is compatible with deposition on a low-energy, microtidal, distally steepened ramp. Outer-ramp facies are hemipelagic lime mudstone, shale, carbonaceous rhythmite, and debrites. Mid-ramp facies are molar-tooth limestone tempestite with microspar-intraclast lags. In a marine environment where stromatolitic and oolitic facies were otherwise rare, large stromatolitic reefs developed at the mid-ramp, coeval with inner-ramp facies of microspar grainstone, intertidal dolomitic microbial laminite, and supratidal evaporitic red shale.Deep-subtidal, outer-ramp cycles occur in the southwestern part of the study area. Black dolomitic shale at the base is overlain by ribbon, nodular, and carbonaceous carbonate facies, all of which exhibit signs of synsedimentary disruption. Cycles in the northeast are shallow-subtidal and peritidal in character. Shallow-subtidal cycles consist of basal deep-water facies, and an upper layer of subtidal molar-tooth limestone tempestite interbedded with microspar calcarenite facies. Peritidal cycles are identical to shallow-subtidal cycles except that they contain a cap of dolomitic tidal-flat microbial laminite, and rarely of red shale sabkha facies or of sandy polymictic conglomerate. A transect along the wall of a valley extending 8.5 km perpendicular to depositional strike reveals progradation of inner-ramp tidal flats over outer- and mid-ramp facies during shoaling. The maximum basinward progradation of peritidal facies coincides with a zone of slope failure that may have promoted the development of the stromatolitic reefs.The sea-level history of the Victor Bay Formation is represented by three hectometre-scale sequences. An initial flooding event resulted in deposition of the lower Victor Bay shale member. Upper-member carbonate cycles were then deposited during highstand. Mid-ramp slumping was followed by late-highstand reef development. The second sequence began with development of an inner-ramp lowstand unconformity and a thick mid-ramp lowstand wedge. A second transgression promoted a more modest phase of reef development at the mid-ramp and shallow-water deposition continued inboard. A third and final transgressive episode eventually led to flooding of the backstepping ramp.Overall consistent cycle thickness and absence of truncated cycles, as well as the high rate and amount of creation of accommodation space, suggest that the periodicity and amplitude of sea-level fluctuation were relatively uniform, and point to a eustatic rather than tectonic mechanism of relative sea-level change. High-amplitude, high-frequency eustatic sea-level change is characteristic of icehouse worlds in which short-term, large-scale sea-level fluctuations accompany rapidly changing ice volumes affected by Milankovitch orbital forcing. Packaging of cyclic Upper Victor Bay carbonates therefore supports the hypothesis of a late Mesoproterozoic glacial period, as proposed by previous workers.     

陆表海台地沉积充填模式及内克拉通碳酸盐岩勘探新启示

内克拉通陆表海盆地是古老碳酸盐建造形成的重要场所。除其顶部风化壳岩溶储层外,广泛分布的内幕非岩溶改造的白云岩勘探长期未受到足够的重视。近年来,随着深层、超深层勘探技术的进步,内幕陆表海白云岩陆续获得油气勘探新发现,但其预测难度远比镶边台地中的礁滩"移动靶"更大。为更好地揭示这类未经岩溶改造的白云岩储层的宏观发育分布规律,本文研究了鄂尔多斯盆地奥陶系马家沟期和四川盆地雷口坡期陆表海台地的高精度岩相古地理和沉积充填模式。结果表明:陆表海台地一般形成于温室期低纬度干燥气候下的稳定内克拉通盆地,与盐湖伴生的台地潮坪广泛分布是其标志性的沉积特征,微环境可进一步划分为潮上带泥云坪、上潮间带云坪、上潮间带微生物席、下潮间带席状潮缘滩、上潮下带灰云质澙湖、下潮下带膏云质澙湖;虽然内克拉通陆表海台地是一个相对静态的沉积环境,其沉积建造并非平板一块,海平面的升降变化往往会在相对平坦的陆表海内引起大幅度的相带迁移,造成潮上带、潮间带、潮下带频繁交互;相带频繁往复迁移过程中,潮间带的晶粒/颗粒/微生物白云岩受到盐湖、古隆起或潮坪岛的制约,形成大面积分布的席状富孔白云岩透镜体;陆表海沉积层序结构为典型的向上变浅序列,主要发育潮坪进积楔和潮坪岛拼嵌两种沉积充填模式,这两种模式形成的席状白云岩透镜体在层序结构和厚度都能很好地对比,通常延伸都在100km以上,甚至可跨越整个陆表海台地,是一个能够媲美台缘礁滩相的油气勘探新领域。     

From platform to basin: the evolution of a Paleocene carbonate margin (Eastern Desert, Egypt)

In this study, progradation and the subsequent retrogradation of a late Paleocene isolated carbonate platform (Galala Mountains, Eastern Desert, Egypt) is demonstrated by variations of distinct facies associations from the platform margin in the north to the hemipelagic basin in the south. A combination of a sea-level drop and tectonic uplift at around 59 Ma (calcareous nannofossil biozone NP5) favored the initiation of the carbonate platform. From this time onwards, the facies distribution along the platform–basin transect can be subdivided into five facies belts comprising nine different facies associations. Their internal relationships and specific depositional settings are strongly coupled with the Maastrichtian–Paleocene seafloor topography, which resulted from local tectonic movements. Patch reefs and reef debris were deposited at the platform margin and the horizontally bedded limestones on the upper slope. Slumps and debris flows were stored on the lower slope. In the subhorizontal toe-of-slope facies belt, mass-flow deposits pass into calciturbidites. Further southwards in the basin, only hemipelagic marls were deposited. Between 59 and 56.2 Ma (NP5–NP8), the overall carbonate platform system prograded in several pulses. Distinct changes in facies associations from 56.2 to 55.5 Ma (NP9) resulted from rotational block movements. They led to increased subsidence at the platform margin and a coeval uplift in the toe-of-slope areas. This resulted in the retrogradation of the carbonate platform. Furthermore the patch-reef and reef-debris facies associations were substituted by the larger foraminifera shoal association. The retrogradation is also documented by a significant decrease in slump and debris-flow deposits on the slope and calciturbidites at the toe of slope.     

元坝地区长兴组典型沉积相及各相带物性特征

元坝气田是四川盆地继普光气田之后所发现的又一大型海相气田,其中,晚二叠世长兴组是元坝气田的主力产层。研究以不同相带钻井为代表,经过岩芯观察、地震资料、测井解释及样品的孔渗数据分析,对元坝地区长兴组所发育的各种沉积相带特征及各沉积相带的物性特征进行对比研究,结果表明:(1)开阔台地、台地边缘浅滩、台地边缘生物礁、台地边缘斜坡及陆棚相在元坝地区长兴期均有发育;(2)在元坝西北部,越靠近台地边缘,其生物礁建隆越明显;(3)长兴组主要可划分出两期成礁旋回,则均发育于长二段;(4)东南部台地边缘斜坡相带窄,坡度陡,西北部则相反;(5)台地边缘暴露浅滩相物性最好,通常形成良好的孔隙型储层;台地边缘生物礁相、台地边缘浅滩相及开阔台地相物性次之,通常形成孔隙-裂缝复合型储层;而斜坡-陆棚相只形成裂缝型储层。     

Platform and off-platform carbonates of the Upper Cambrian of western Maryland, U.S.A.

Upper Cambrian carbonates in western Maryland are comprised of platform facies (Conococheague Limestone) west of South Mountain and basin facies (Frederick Limestone) east of South Mountain. Conocheague platform carbonates contain interbedded non-cyclic and cyclic facies. Non-cyclic facies consist of cross-stratified grainstones, thrombolitic bioherms, and graded, thin-bedded dolostones. These were deposited in shallow, subtidal shelf lagoons. Cyclic facies are composed of repeated sequences of cross-stratified grainstone; ribbon-rock; wavy, prism-cracked laminite; and planar laminated dolostone. The cyclic facies are shallowing-upward cycles produced by lateral progradation of tidal flats over shallow, nearshore subtidal environments. Cyclic and non-cyclic facies are interbedded in the Conococheague in a layer cake fashion, but no higher-order cyclicity can be found. The Frederick Limestone is dominated by monotonously thick sequences of graded, thin-bedded limestones, interbedded with massive peloidal grainstones and beds of breccia up to 10 m thick in the lower Frederick. The breccias contain transported megaclasts of Epiphyton-Girvanella boundstones. The basal Frederick was deposited in a slope-to-basinal setting east of a rimmed shelf. An Epiphyton-Girvanella marginal reef along the shelf edge was the source of the blocks in the breccias. The upper Frederick Limestone formed on a carbonate ramp.     

新疆英吉沙南克孜勒陶组沉积特征及沉积相

英吉沙南阿克巴西麻扎尔一带的中泥盆统克孜勒陶组，下未见底，与上覆上泥盆统考库亚组之间呈整合接触．从剖面特征分析，自下而上可划分出海岸相及混积陆棚相(包括生物礁、风暴岩)，为一典型的进积沉积体系．各相段中沉移特征明显，沉积构造十分发育，特别是上部具有点礁性质的生物礁不仅礁核、礁翼清晰，而且定殖、拓殖、泛殖、统殖等4阶段特征明显．该剖面为研究滨浅海相沉积的良好剖面。     

达县-宣汉地区长兴组-飞仙关组礁滩相特征及其对储层的制约

通过对普光2井、普光6井和毛坝3井等钻井资料以及地震剖面的详细研究,可知长兴组—飞仙关组生物礁相在地震剖面上,形态为透镜状,具有透镜体、中强变振幅、杂乱影像特征。岩性为灰色障积海绵礁灰岩、灰色障积海绵礁白云岩、灰色骨架海绵礁灰岩、灰色骨架海绵礁白云岩等组成。滩相在地震剖面上表现为透镜体、中强变振幅、不连续影像特征,其岩性主要为浅灰色厚块状亮晶鲕粒白云岩、亮晶含砾鲕粒白云岩、亮晶含豆粒鲕粒白云岩、亮晶生屑白云岩及亮晶砂屑白云岩等。两者在空间上相伴生,沿着台地边缘分布,形成台地边缘礁滩相带,该相带控制了达县—宣汉地区储层的岩性、储集性及其空间分布。