南海珠江口盆地深水区混合沉积类型及其形成机制

珠江口盆地是研究深水沉积过程和南海油气勘探的热点区域。利用地震、测井和钻井岩屑等资料,发现珠江口盆地深水区晚渐新世至中中新世期间,发育混合沉积体系。该混合沉积体系岩相主要表现为碳酸盐岩与硅质碎屑以不同比例的混合堆积,垂向岩相变化存在突变式、渐变式和交互式三种递变类型。根据地震反射以及岩相特征,混合沉积体系可划分为4个沉积阶段:第1阶段主要为原位混合沉积,形成渐变式或突变式混合沉积;第2阶段为相缘混合,产生渐变式混合沉积层系;第3、4阶段为间断混合,形成交互式混合沉积。在硅质碎屑沉积为主的背景下,混合沉积由于碳酸盐碎屑的加入,可能会形成潜在的油气储层,对今后深水油气勘探有一定的启示意义。     

加利福尼亚湾南部裂谷盆地西缘全新世-晚更新世非热带碳酸盐沉积物和构造史

研究人员利用高分辨率地震反射剖面和浅海振动岩心及上升海相阶地沉积物测年结果重建墨西哥加利福尼亚湾南部全新世至晚更新世温带至亚热带碳酸盐构造史和沉积形式。研究区位于拉巴斯附近 ,此处碳酸盐形成于构造活动活跃的加利福尼亚裂谷盆地西部狭窄陆架边界断层。地质背景的非热带特征体现在 :1生物碎屑碳酸盐胶结作用不明显 ;2其成分以红藻石 (珊瑚红藻 )、珊瑚、软体动物为主。形成于袋形小海湾和红藻石生物礁的无边缘碳酸盐平地表面积达 2 0 km2 ,厚度达 16 m,构成主碳酸盐生成地。全新世碳酸盐沉积速率是根据地震和岩心数据推断的 ,在…     

南海涠洲岛区现代沉积环境和沉积作用演化

涠洲岛区沉积环境的演化导致陆源碎屑沉积作用转化为礁源和陆源的混合沉积作用,并将向纯礁源碳酸盐沉积作用方向转化;其主要控制因素是陆源碎屑供应量.陆源沉积和礁源沉积之间可以互相制约,沉积环境和沉积作用可以互为因果.文中还指出涠洲岛区的沉积组分特征和南海北部礁坪沉积组分随纬度变化的规律.     

南海表层沉积类型与沉积作用若干特征

根据底质的粒度分析结果，编制了南海表层沉积类型图，把南海的表层沉积划分为１２种主要的类型，它们的展布与水深线的走势大体一致。大陆架表层沉积物主要由现代沉积，再造沉积，残留沉积和少量残余沉积组成，半沉海一深海沉积中生物碎屑的组成和含量往往成为确定沉积类型的重要因素，受碳酸盐溶解作用的影响，随着水深增大，钙质与硅质生物碎屑含量呈相互消长的关系，沉积类型因而不同。     

渤海莱州湾凹陷KL油田沙河街组混积背景下的沉积特征与沉积演化

渤海湾盆地莱州湾凹陷KL油田地区古近系沙河街组发育了陆源碎屑岩和碳酸盐岩的混合沉积构造,国内外学者在莱州湾凹陷地区已做了一些岩相古地理方面研究工作,但KL油田地区的混合沉积研究至今未涉及。由于KL油田地区钻遇沙河街组沙三下亚段的井较少(迄今全地区钻遇沙三下亚段井9口),本文充分利用有限的钻井资料,结合岩心资料、分析化验资料、单井沉积相解剖以及地震相分析,对渤海湾盆地莱州湾凹陷KL油田地区碳酸盐岩台地混合沉积特征以及沉积演化模式进行了较为深入的探讨。研究表明,KL油田古近系沙河街组主要以扇三角洲沉积体系为主,混积岩主要发育在沙河街组沙三下亚段,而沙三下亚段发育三种不同的沉积环境:KL-1井区发育辫状河三角洲,中部KL-4井区发育滨浅湖混积滩坝,东部KL-9井区在I油组处于潍北凸起物源供给区,发育了扇三角洲。沙三下亚段沉积时期,沉积物在碳酸盐岩台地上进行混合沉积,狭义上表现为混积岩,主要类型包括:泥质灰岩、含泥灰岩、灰质粉砂岩;广义上表现为混积层系,主要类型包括:含陆源碎屑一碳酸盐混积岩、含碳酸盐一陆源碎屑混积岩、碳酸质一陆源碎屑混积岩。     

澳大利亚Northern Carnarvon盆地Brigadier组碳酸盐岩混积沉积特征及沉积模式

Northern Carnarvon盆地晚三叠世—早侏罗世发育一套海相Brigadier组碳酸盐岩,但其岩性特征、沉积相类型、分布规律和沉积模式尚不清楚。研究认为,Brigadier组沉积时期构造稳定、基底坡度小、气候温暖潮湿、海洋生物种类繁多、海平面整体上升,具有利于混积沉积发育的地质背景。Brigadier组具有明显的混积沉积特征,盆地东南部Brigadier组岩性为三角洲砂泥岩,盆地西北部岩性为纯碳酸盐岩,ODP多口钻井钻遇生物礁滩沉积,整体呈现从东南向西北岩性由碎屑岩变成碳酸盐岩的特征。研究认为Brigadier组混合沉积形成的主要原因是碎屑物源输入的停止和水动力的减弱,导致碳酸盐岩沉积与砂泥岩沉积出现混合,Brigadier组混合沉积为典型的相混合成因类型。     

意大利Maiella碳酸盐平台上始新世—渐新世与陆架边缘进积和出露有关的高海面和低海面沉积物

意大利Ｍａｉｅｌａ碳酸盐平台上始新世—渐新世与陆架边缘进积和出露有关的高海面和低海面沉积物ＡｄａｍＶｅｃｓｅｉ等１．高水位期与低水位期沉积物与硅质碎屑体系不同，低纬度碳酸盐陆架更偏爱在海平面高水位期时将沉积物输送至其邻近斜坡上和盆地内，这个时候在透光...     

南沙海域礼乐盆地中生界油气资源潜力

位于南沙东部海域的礼乐盆地是一大型的中、新生代叠置盆地,其特有的地质背景及巨厚的中生代地层显示了其与南沙海域其他新生代沉积盆地的差异。盆地内发育的厚度超过4 000 m的中生代海相地层,主要包括了上侏罗统—下白垩统的滨—浅海相含煤碎屑岩或半深海相页岩、上三叠统—下侏罗统三角洲—浅海相砂泥岩和中三叠统深海硅质页岩等3套地层,展示出盆地具有良好的油气生成潜力。而早期位于华南陆缘、现今位于南沙东部海域的礼乐盆地中生界,完全具备了形成油气藏的基本石油地质条件,具有较为良好的油气资源潜力,其中生界油气资源勘探具有非常重要的意义,将成为我国海域油气勘探的一个重要新领域。     

南海表层沉积类型与沉积作用若干特征

根据底质的粒度分析结果，编制了南海表层沉积类型图。把南海的表层沉积划分为１２种主要的类型，它们的展布与水深线的走势大体一致。大陆架表层沉积物主要由现代沉积、再造沉积、残留沉积和少量残余沉积组成。半深海—深海沉积中生物碎屑的组成和含量往往成为确定沉积类型的重要因素。受碳酸盐溶解作用的影响，随着水深增大，钙质与硅质生物碎清含量呈相互消长的关系，沉积类型因而不同。     

南海北部表层沉积物中黏土和碎屑矿物组成及其地质意义

以X-射线衍射仪和偏光显微镜为主要手段,对南海调查区表层底质沉积物中黏土和碎屑矿物组分进行分析和研究,结果表明黏土矿物主要有伊利石、蒙皂石、高岭石和绿泥石,其组合特征在不同区域表现出明显的差异。碎屑成分主要由生物壳(钙质和硅质)、轻矿物(石英、长石为主)和含量低但种类多的重矿物组成。一般认为物质来源是调查区沿岸风化岩石遭受进一步剥蚀后细小组分通过水动力搬运沉积而成的。钙质和硅质生物壳分布受南海碳酸盐补偿深度(CCD)的控制。     

High-resolution sequence stratigraphy of clastic shelves VI: Mixed siliciclastic-carbonate systems

High-frequency sequences composed of mixed siliciclastic-carbonate deposits may exhibit either vertical or horizontal changes between siliciclastics and carbonates. Vertical facies shifts occur between systems tracts and define a ‘reciprocal sedimentation’ pattern, typically consisting of transgressive/highstand carbonates and forced regressive/lowstand siliciclastics, although variations from this rule are common. Mixed systems with lateral facies change, usually typifying transgressive and/or highstand systems tracts, may exhibit proximal siliciclastics and distal carbonates or vice-versa, although variations may also occur along depositional strike. The marked variability of mixed siliciclastic-carbonate sequences makes the definition of a universal sequence stratigraphic model impossible, as the composition and geometries of systems tracts may change considerably, and sequence stratigraphic surfaces and facies contacts may vary in terms of occurrence and physical expression. However, some resemblance exists between siliciclastic sequences and mixed sequences showing lateral facies changes between siliciclastics and carbonates. In particular, these mixed sequences display 1) a stratal architecture of the clastic part of the systems tracts that is comparable to that of siliciclastic deposits, 2) a dominant role of the inherited physiography and of erosional processes, rather than carbonate production, in shaping the shelf profile, and 3) a local lateral juxtaposition of siliciclastic sandstones and carbonate bioconstructions due to hydrodynamic processes. These observations are helpful in predicting the location of porous and potential sealing bodies and baffles to fluid flow at the intra-high-frequency sequence scale, and ultimately they are useful for both petroleum exploration and production.     

Stratigraphic framework of sediment-starved sand ridges on a mixed siliciclastic/carbonate inner shelf; west-central Florida

Seismic reflection profiles and vibracores have revealed that an inner shelf, sand-ridge field has developed over the past few thousand years situated on an elevated, broad bedrock terrace. This terrace extends seaward of a major headland associated with the modern barrier-island coastline of west-central Florida. The overall geologic setting is a low-energy, sediment-starved, mixed siliciclastic/carbonate inner continental shelf supporting a thin sedimentary veneer. This veneer is arranged in a series of subparallel, shore-oblique, and to a minor extent, shore-parallel sand ridges. Seven major facies are present beneath the ridges, including a basal Neogene limestone gravel facies and a blue-green clay facies indicative of dominantly authigenic sedimentation. A major sequence boundary separates these older units from Holocene age, organic-rich mud facies (marsh), which grades upward into a muddy sand facies (lagoon or shallow open shelf/seagrass meadows). Cores reveal that the muddy shelf facies is either in sharp contact or grades upward into a shelly sand facies (ravinement or sudden termination of seagrass meadows). The shelly sand facies grades upward to a mixed siliciclastic/carbonate facies, which forms the sand ridges themselves. This mixed siliciclastic/carbonate facies differs from the sediment on the beach and shoreface, suggesting insignificant sediment exchange between the offshore ridges and the modern coastline. Additionally, the lack of early Holocene, pre-ridge facies in the troughs between the ridges suggests that the ridges themselves do not migrate laterally extensively. Radiocarbon dating has indicated that these sand ridges can form relatively quickly (1.3 ka) on relatively low-energy inner shelves once open-marine conditions are available, and that frequent, high-energy, storm-dominated conditions are not necessarily required. We suggest that the two inner shelf depositional models presented (open-shelf vs. migrating barrier-island) may have co-existed spatially and/or temporally to explain the distribution of facies and vertical facies contacts.     

A unique lacustrine mixed dolomitic-clastic sequence for tight oil reservoir within the middle Permian Lucaogou Formation of the Junggar Basin,NW China: Reservoir characteristics and origin

The middle Permian Lucaogou Formation in the Jimusaer Sag of the southeastern Junggar Basin, NW China, was the site of a recent discovery of a giant tight oil reservoir. This reservoir is unusual as it is hosted by lacustrine mixed dolomitic-clastic rocks, significantly differing from other tight reservoirs that are generally hosted by marine/lacustrine siliciclastic–calcitic sequences. Here, we improve our understanding of this relatively new type of tight oil reservoir by presenting the results of a preliminarily investigation into the basic characteristics and origin of this reservoir using field, petrological, geophysical (including seismic and logging), and geochemical data. Field and well core observations indicate that the Lucaogou Formation is a sequence of mixed carbonate (mainly dolomites) and terrigenous clastic (mainly feldspars) sediments that were deposited in a highly saline environment. The formation is divided into upper and lower cycles based on lithological variations between coarse- and fine-grained rocks; in particular, dolomites and siltstones are interbedded with organic-rich mudstones in the lower part of each cycle, whereas the upper part of each cycle contains few dolomites and siltstones. Tight oil accumulations are generally present in the lower part of each cycle, and dolomites and dolomite-bearing rocks are the main reservoir rocks in these cycles, including sandy dolomite, dolarenite, dolomicrite, and a few dolomitic siltstones. Optical microscope, back scattered electron, and scanning electron microscope imaging indicate that the main oil reservoir spaces are secondary pores that were generated by the dissolution of clastics and dolomite by highly acidic and corrosive hydrocarbon-related fluids.     

Late Quaternary siliciclastic/carbonate sedimentation model for the Capricorn Channel,southern Great Barrier Reef province,Australia

A model is presented for hemipelagic siliciclastic and carbonate sedimentation during the last glacial–interglacial cycle in the Capricorn Channel, southern Great Barrier Reef (GBR). Stable isotope ratios, grainsize, carbonate content and mineralogy were analysed for seven cores in a depth transect from 166 to 2892 m below sea level (mbsl). Results show variations in the flux of terrigenous, neritic and pelagic sediments to the continental slope over the last sea level cycle.During the glacial lowstand terrigenous sediment influenced all the cores down to 2000 mbsl. The percentages of quartz and feldspar in the cores decreased with water depth, while the percentage of clay increased. X-ray diffraction analysis of the glacial lowstand clay mineralogy suggests that the siliciclastic sediment was primarily sourced from the Fitzroy River, which debouched directly into the northwest sector of the Capricorn Channel at this time. The cores also show a decrease in pelagic calcite and an increase in aragonite and high magnesium calcite (HMC) during the glacial. The influx of HMC and aragonite is most likely from reworking of coral reefs exposed on the continental shelf during the glacial, and also from HMC ooids precipitated at the head of the Capricorn Channel at this time. Mass accumulation rates (MARs) are high (13.5 g cm^? 3 kyr^? 1) during the glacial and peak at ~ 20 g cm^? 3 kyr^? 1 in the early transgression (16–14 ka BP). MARs then decline with further sea level rise as the Fitzroy River mouth retreats from the edge of the continental shelf after 13.5 ka BP. MARs remain low (4 cm^? 3 kyr^? 1) throughout the Holocene highstand.Data for the Holocene highstand indicate there is a reduction in siliciclastic influx to the Capricorn Channel with little quartz and feldspar below 350 mbsl. However, fine-grained fluvial sediments, presumably from the Fitzroy River, were still accumulating on the mid slope down to 2000 mbsl. The proportion of pelagic calcite in the core tops increases with water depth, while HMC decreases, and is present only in trace amounts in cores below 1500 mbsl. The difference in the percentage of HMC in the deeper cores between the glacial and Holocene may reflect differences in supply or deepening of the HMC lysocline during the glacial.Sediment accumulation rates also vary between cores in the Capricorn Channel and do not show the expected exponential decrease with depth. This may be due to intermediate or deep water currents reworking the sediments. It is also possible that present bathymetry data are too sparse to detect the potential role that submarine channels may play in the distribution and accumulation of sediments.Comparison of the Capricorn Channel MARs with those for other mixed carbonate/siliciclastic provinces from the northeast margin of Australia indicates that peak MARs in the early transgression in the Capricorn Channel precede those from the central GBR and south of Fraser Island. The difference in the timing of the carbonate and siliciclastic MAR peaks along the northeast margin is primarily related to differences in the physiography and climate of the provinces. The only common trend in the MARs from the northeast margin of Australia is the near synchronicity of the carbonate and siliciclastic MAR peaks in individual sediment cores, which supports a coeval sedimentation model.     

Provenance-related characteristics of beach sediments around the island of Menorca, Balearic Islands (western Mediterranean)

The island of Menorca, one of the Balearic Islands (Spain) located in the western Mediterranean, is characterised by a contrasting geology and landscape with two major geographic domains: (1) a southern region called Migjorn, comprised of Late Miocene calcarenites and limestones, and (2) a northern region known as Tramuntana, which is composed of folded and faulted Palaeozoic, Mesozoic and Tertiary (Oligocene) siliceous and calcareous rocks. Both domains are lined by numerous pocket beaches exhibiting a high variety of surficial sediment assemblages. Grain-size and compositional analyses revealed that cliff erosion and nearshore Posidonia oceanica meadows are the main sources of sediments consisting mostly of medium- to coarse-grained carbonate sands of marine biogenic origin, with variable amounts of terrigenous rock fragments and quartz. Based on distinctly different contributions of bioclastic material, biogenic carbonates and quartz, 320 sediment samples from 64 beaches were grouped into different facies associations dominated by either (1) biogenic sands, (2) biogenic sands with terrigenous contributions or (3) terrigenous sands with quartz. Nevertheless, there is a marked regional variability in sediment texture and composition. Thus, variable mixtures of carbonate and siliciclastic sediments characterise the beaches of the northern region, whereas the beaches of the southern region are composed mostly of carbonate sands of marine biogenic origin. An exception is the central sector of the south coast, which is enriched in quartz sand (~10 %); this can be related to outcrops of quartz-rich basement rock and also to rocks exposed in some northern drainage basins captured by southern streams since the Plio-Quaternary.     

莱州湾凹陷南部地区浅层沙三下亚段混积岩岩石学特征及成岩作用

通过对莱州湾凹陷区域构造地质背景、岩石学特征、沉积环境等分析,认为莱州湾凹陷南部地区古近系沙三下亚段的地层埋藏浅,广泛发育湖相碳酸盐岩与陆源碎屑岩的混合沉积,混合沉积特征主要为结构混合和互层混合。考虑到混积岩成分和成因的复杂性,本文在岩心、壁心观察、铸体薄片鉴定、荧光薄片鉴定和扫描电镜分析的基础上,对莱州湾凹陷南部地区混积岩样品进行了X-射线衍射分析和岩石有机质中碳氢氧元素分析,分析了碳酸盐岩和陆源碎屑岩混积的岩石学特征。结果显示:莱州湾凹陷南部地区浅层沙三下亚段混积岩中陆源碎屑平均含量为60.5%,碳酸盐矿物含量为28.2%,属于碳酸盐质陆源碎屑岩,混积岩主要为泥灰岩、灰质砂岩和砂质白云岩。其中,碎屑矿物主要以细-粉砂级石英为主,碳酸盐矿物主要为泥晶方解石;粘土矿物组合主要为伊蒙混层,其次为伊利石、高岭石和绿泥石;且三者呈均匀混合的特征。同时通过铸体薄片、扫描电镜和储层流体包裹体观察,综合分析成岩作用表明,埋藏浅的沙三下亚段混积岩储层主要经历了压实、压溶作用、溶蚀作用、胶结交代作用,其中胶结交代作用较强,而研究区压实、压溶作用对比渤海湾盆地大部分埋藏较深的古近系地层都弱,储集空间以原生粒间孔为主,其次为粒内溶蚀孔和微缝。压实、压溶作用弱和溶蚀作用强是研究区沙三下亚段储层物性好的主要原因。     

The lost Devonian sequence - Sequence stratigraphy of the middle Bakken member,and the importance of clastic dykes in the lower Bakken member shale,North Dakota,USA

The Late Devonian to Early Mississippian Bakken Formation in the Williston basin of North Dakota, USA, shows a tri-partite subdivision: a middle mixed carbonate-siliciclastic member is sandwiched in-between two black siliciclastic mudstones, the lower and upper Bakken member shales. However, the transition from the lower shale member to the middle member does not represent a gradual coarsening but contains in places several millimeter - to centimeter-thick siliciclastic mudstones and carbonates that consist of three facies: (1) a glauconitic carbonate-rich siliciclastic mudstone, (2) a carbonate mud-to wackestone, and (3) an echinoderm wacke-to packstone with shell fragments. These three facies are present in many (all?) of the cores close and directly in the basin center in Mountrail County, North Dakota. At least one of these three facies is present in all 23 cores included in this study.This thin carbonate unit at the transition between the lower and the middle Bakken members is interpreted as representing the remnants of the transgressive systems tract. It is assumed that relative sea-level fell before deposition of the middle Bakken member establishing a proximal coarse-grained to distal fine-grained depositional transect that successively migrated into the basin. During the subsequent transgression, the siliciclastic input was low to absent, and the entire sedimentary system switched to depositing carbonates. The proximal to distal transect during this time showed coarse-grained packstones (and grainstones?) close to the shoreline, and a fining outwards towards the distal parts of the basin. This transgression also eroded what remained of the regressive and most of the subsequent transgressive sediments, leaving only the thin carbonate layer behind. Evidence for the regression, even though no sediment is directly preserved along the lower to middle Bakken member contact, comes from the fill of clastic dykes that cut through the lower Bakken member shale. The fill of the clastic dykes is partly siliciclastic and partly carbonate and not similar to any of the surrounding sediment. This indicates that these dykes must have originated before the middle Bakken member was deposited, yet the overlying sediment must have been carbonate at some point and siliciclastic another time. As it is not present anymore, this sediment must have been entirely removed by erosion.The here presented model suggests that the Bakken Formation reflects two entire sea-level oscillations. The first encompasses the lower Bakken member shale and the siliciclastic regressive portion of the lowstand only preserved as infill of the clastic dykes. The subsequent transgression deposited the carbonates now blanketing the lower to middle Bakken member transition, and the highstand and subsequent regression plus lowstand are represented by the middle Bakken member. The transgressive surface and therewith the onset of the topmost Bakken transgression is marked by the transition from the middle to the upper Bakken shale member.     

Filling the gap: A 60 ky record of mixed carbonate-siliciclastic turbidite deposition from the Great Barrier Reef

Late Pleistocene to Holocene margin sedimentation on the Great Barrier Reef, a mixed carbonate-siliciclastic margin, has been explained by a transgressive shedding model. This model has challenged widely accepted sequence stratigraphic models in terms of the timing and type of sediment (i.e. carbonate vs. siliciclastic) deposited during sea-level oscillations. However, this model documents only hemipelagic sedimentation and the contribution of coarse-grained turbidite deposition, and the role of submarine canyons in this process, remain elusive on this archetypal margin. Here we present a new model of turbidite deposition for the last 60 ky in the north-eastern Australia margin. Using high-resolution bathymetry, 58 new and existing radiometric ages, and the composition of 81 turbidites from 15 piston cores, we found that the spatial and temporal variation of turbidites is controlled by the relationship between sea-level change and the variable physiography along the margin. Siliciclastic and mixed carbonate-siliciclastic turbidites were linked to canyons indenting the shelf-break and the well-developed shelf-edge reef barriers that stored sediment behind them. Turbidite deposition was sustained while the sea-level position allowed the connection and sediment bypassing through the inter-reef passages and canyons. Carbonate turbidites dominated in regions with more open conditions at the outer-shelf and where slope-confined canyons dominated or where canyons are generally less abundant. The turn-on and maintenance of carbonate production during sea-level fluctuations also influenced the timing of carbonate turbidite deposition. We show that a fundamental understanding of the variable physiography inherent to mixed carbonate-siliciclastic margins is essential to accurately interpret deep-water, coarse-grained deposition within a sequence stratigraphic context.     

Siliciclastic influx and burial of the Cenozoic carbonate system in the Gulf of Papua

An extensive carbonate system in the Gulf of Papua (GoP), developed in the late Oligocene–middle Miocene, was buried by huge influx of siliciclastics originated from Papua New Guinea. Major episodes of siliciclastic influx in the carbonate system are related to tectonic activity in the fold and thrust belt during the Oligocene Peninsular Orogeny, late Miocene Central Range Orogeny, and late Pliocene renewed uplift and exhumation of peninsular region. Siliciclastics did not influence the carbonate deposition during the late Oligocene–middle Miocene, since they were accumulated in the Aure Trough, proximal foreland basin protecting the carbonate system. The most significant burial of the carbonate system started during the late Miocene–early Pliocene in the result of the Central Range Orogeny. However, the largest influx was related to the renewed uplift of the Papuan Peninsula during the early late Pliocene. The shelf edge prograded ∼150 km and formed more than 80% of the modern shelf. This high siliciclastic influx was also enhanced by the “mid” Pliocene global warmth period and intensified East Asian monsoons at 3.6–2.9 Ma. Although many publications exist on carbonate–siliciclastic mixing in different depositional environments, this study helps understand the carbonate–siliciclastic interactions in space and time, especially at basinal scale, and during different intervals of the carbonate system burial by siliciclastic sediments.