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1.
台湾峡谷HD133和HD77柱状样的沉积构成和发育背景 总被引：1，自引：0，他引：1
分别对南海东北部台湾峡谷内水深3 280 m的HD133和峡谷外水深3 378 m的HD77重力活塞柱状样进行了沉积物粒度、古生物和碳酸钙含量分析,利用AMS14C同位素测年和沉积速率初步认定是属于MIS3a以来的沉积。按沉积物粒度和碳酸钙含量可将两支柱状样划分为3套沉积层段:上部层段1和下部层段3均以粉砂质黏土为主,夹薄层粉砂,深水底栖有孔虫含量高,碳酸钙低于10%,代表受重力流作用较弱的正常深海沉积;中部层段2发育一套以中-细粒为主的厚砂层,含大量浅水底栖有孔虫,碳酸钙含量可高达60%,AMS14C测年出现倒置现象,表明主要为浅水重力流沉积。柱状样的沉积构成响应同期海平面变化,特别表现在深水砂层沉积的两大控制因素:在时间上,低海平面时期大量浅水和陆源碎屑物质直接输送到陆坡之下的深水区,形成富砂的层段2;在空间上,峡谷水道是重力流的物质输送通道,地形优势使得重力流携带物优先在水道中发生沉积,造成HD133柱的含砂量明显高于HD77柱状样。 相似文献
2.
深水重力流与底流交互作用研究进展 总被引：9，自引：0，他引：9
重力流和底流是深水环境下的两大基本流动体制,对二者交互作用的研究是当前沉积学研究的前缘和薄弱环节.底流及底流改造沉积物在岩芯上具有上部侵蚀面、双泥层、牵引流成因的各种层理等识别标志;底流成因的漂积体在剖面上呈现透镜状单元、迁移性特征及波状发射等地震反射特征.本文通过综述重力流与底流交互作用的研究成果,认为依据某段地质时期内深水盆地中主导沉积机制的不同,将重力流与底流的交互作用分为以下4种表现形式:①底流对前期重力流沉积进行改造;②重力流对前期底流沉积进行改造;③重力流与底流交互主导同一地区的沉积以及④底流与重力流同时作用于沉积物.相对海平面变化、气候(冰期～间冰期)变化、构造活动、地形地貌等因素,主要通过影响重力流与底流机制的相对强度大小,控制深水重力流与底流交互作用的进行.中国南海具有重力流与底流交互沉积的优越地质条件,发育有单向迁移水道、沉积物波等特色沉积记录.加强现今海流观测,对于南海底流循环格架的建立意义重大. 相似文献
3.
中建海底峡谷具有分段性,但分段的关键地貌特征、各段沉积充填及其控制因素缺乏精细描述和系统论证.综合利用高分辨率二维和三维地震资料,结合水深地貌数据,对中建海底峡谷地貌及沉积特征进行了详细分析,总结了其南北段沉积过程的主控因素.中建海底峡谷呈NW向顺直展布于广乐隆起与西沙隆起之间,以华光礁附近的地貌高点为拐点被分为南北两段.中建海底峡谷北段沉积体系包括重力流沉积（水道、席状沉积、滑塌体）和底流沉积（漂积体、环槽、谷槽）,南段以重力流水道和海底扇为主.北段沉积体系受底流和重力流交互作用控制,底流自中中新世开始出现,改造重力流水道,使其出现侧向迁移或翼部不对称现象,上新世以后重力流作用减弱,底流作用增强,沉积物波和漂积体广泛发育;峡谷南段水道表现出侵蚀-沉积-废弃的沉积旋回,未见底流沉积现象.相对海平面变化导致碳酸盐生产率变化影响物源供应,从而控制水道沉积演化,碳酸盐台地的“高位溢流”作用决定水道在高水位时发育. 相似文献
4.
在台湾峡谷水深3284 m处全长699 cm的HD133柱状样中共识别出1个厚沙层（厚127 cm）和8个薄沙层（单层厚度8-15 cm）,这些沙层中含大量浅水底栖有孔虫,反映其为来自浅水区的陆源物质以重力流方式形成的沉积物。然而,单用重力流无法对这些沙层的成因作出合理的解释：该样中的厚沙层以中沙为主,平均粒径范围1-2Φ,薄沙层以粉沙-细沙为主,平均粒径范围3-4Φ;沙层的分选系数小于2.5,局部接近于1,分选好-极好,长石/石英比值低,具有很高的结构成熟度和成分成熟度;在粒度特征上,其频率分布曲线为单峰,累积概率曲线为2-3段式,在C-M图上厚沙层的样点落在牵引流区域;特别是在垂向序列上,沙层顶底呈突变接触;以上特征均表现为明显的牵引流特征。此外,在柱状样中发现含有太平洋深层水所特有的底栖有孔虫Bulimina aculeata、Planulina wuellerstorfi、Eggerella bradyi种类,且大量生物壳呈棱角状破碎,表明该样在沉积过程中受到太平洋深层水的入侵,这些证据支持了前人关于研究区内可能发育活跃的底流作用的推断。综合分析认为HD133柱状样中的沙层是重力流和底流交互作用的产物。 相似文献
5.
深水沉积是近年来我国海域油气勘探重点之一,利用高精度二维和三维地震剖面的精细解剖,揭示了南海西北陆缘区深水沉积体系类型及其内部构成特征.这些深水地区除堆积正常深海-半深海泥岩外,还发育大量深水重力流沉积,包括块体流沉积、深水峡谷、沉积物波等大型沉积体.研究表明,南海西北陆缘区发育4类陆坡, 即进积型、滑塌型、水道化型、宽缓渐变型陆坡.不同陆坡类型具有不同地貌形态,发育不同的沉积体类型.大型块体流沉积主要发育于滑塌型和水道化型陆坡,沉积物波主要发育于宽缓渐变型陆坡下部及深海中央峡谷长昌段的周缘地区.由于南海西北陆缘自晚中新世以来形成向东开口的喇叭形变深的地貌形态,导致在盆地中央形成了独特的与陆坡走向一致的深海峡谷体系——中央峡谷.该峡谷的沉积充填不仅包括来自于西部峡谷头部的浊积水道沉积,还包括来自于北部陆坡的块体流沉积,特别是来自于滑塌型陆坡的块体流沉积.中央峡谷体系构成了西北陆缘区多源汇聚的深水沉积物输送系统,同时也是南海西北陆缘深水区重要的油气储层发育层系. 相似文献
6.
在南海西北部首次发现中建南峡谷群,目前对其地质信息尚未开展相关研究.综合利用水深地形数据和二维多道地震资料,主要分析中建南峡谷群的地形地貌特征、平面展布与分段性特点,精细刻画峡谷沉积充填结构及演化特征,再进一步讨论峡谷形成的控制因素.中建南海底峡谷群分布于中建阶地与中建北海台之间,它是由西侧的一条主轴峡谷和东侧的多条小型分支峡谷组成,整体呈SE-S-SE走向,以走向转折拐点为起点,将峡谷分为三段式:北段、中段和南段,北段以侵蚀作用为主,中段和南段主要受侵蚀作用、沉积作用,东南部的峡谷口外主要受沉积作用.研究区晚中新世?第四纪时广泛分布峡谷沉积体系,包括半深海相、三角洲相、峡谷/水道充填相、滑塌相、块体搬运复合沉积和浊积扇相.揭示了该海底峡谷群的发育和演化主要受海平面变化、沉积物源供给和重力流、底流作用的控制.通过对该峡谷群的地形地貌和沉积演化特征的分析,将对海洋地质灾害、南海深水沉积体系研究及油气资源勘探有重要的科学意义. 相似文献
7.
南海海槽是全球大地震发生频率最高的地区之一,该地区增生楔上斜坡盆地内的重力流沉积记录了多分支断层及大地震活动历史.利用国际综合大洋钻探计划(IODP)314-316航次岩心-地震-综合测井资料,在详细分析南海海槽增生楔上斜坡盆地内重力流沉积特征基础上,阐明了其对多分支断层和大地震活动的响应机制.研究结果表明,南海海槽增生楔上斜坡盆地内依次充填了楔形块体流、峡谷和表层块体流沉积:楔形块体流形成于多分支断层活动早期,表现出北厚南薄的楔形特征,反映了多分支断层的持续活动的特征,沉积物中富含的粗颗粒泥质角砾岩反映了早期多分支断层剧烈活动的特征;峡谷系统由密集峡谷,大型块体流和轴向峡谷组成,主要受到多分支断层耦合造成斜坡变陡、区域地层孔隙流体压力增大和盆地不均衡抬升的影响;表层块体流位于盆地顶部,由多期次弱振幅块体流叠加组成,现今海底表面表现为大量“马蹄形”的垮塌地形,这些相对短期内广泛分布的块体流应该是由地震引起的地表震动触发的.斜坡盆地内重力流沉积特征反映了多分支断层活动历史以及大地震的发生过程:即1.95~1.55 Ma,多分支断层形成初期活动剧烈,逆冲活动造成了断层上盘沉积物垮塌,楔形块体流沉积在斜坡盆地底部;1.55~1.07 Ma,多分支断层西部耦合,导致斜坡盆地出现东高西低的构造格局以及盆地西部区域楔体和断层处能量的集聚;1.07 Ma至今,断层处能量间断释放,引发多次大地震. 相似文献
8.
洪水型重力流是重力流沉积学的研究热点,以往研究认为洪水型重力流具有紊流支撑的流体性质,对于其流体性质转化及其沉积记录的识别不够深入。近年研究揭示重力流沉积过程中可形成多种过渡型流体,具有特殊流体转换机制和沉积特征。通过调研国内外最新文献,系统介绍了过渡型流体基本特征、沉积机制方面的研究进展,并讨论了其对洪水型重力流沉积研究的启示及地质意义。研究结果表明：在少量黏土矿物影响下,沉积物重力流流体的性质即可由紊流向层流转化,形成特殊的过渡型流体。转化过程主要取决于黏土矿物含量和类型控制的流体内聚力和流速控制的紊流应力二者之间的相互作用。过渡型流体可以产生大型流水沙纹（large current ripple）、砂质纹层—泥质纹层间互形成的低幅度沙波（low amplitude bed wave）等独特的底床类型。尽管实验研究揭示了过渡型流体可能形成的沉积底床特征,针对洪水型重力流沉积记录中过渡型流体的解释仍十分缺乏,尤其是过渡型流体转换机制及其沉积响应仍亟待深入探索。过渡型流体的沉积底形是研究洪水型重力流沉积动力机制的重要载体,可为深入理解洪水型重力流沉积过程提供新视角,同时可能具有更广泛的沉积学研究价值。 相似文献
9.
中国南海西北次海盆西北陆缘洋陆过渡区深水沉积体系特征 总被引：2，自引：0，他引：2
高分辨率二维地震资料显示中国南海西北次海盆西北陆缘（水深1 000 m及以下）发育如下深水沉积体系:珠江口盆地南部隆起区缓坡带（水深约1 000~1 500 m、坡度<1.2°）出露神狐南海山,该海山附近发育“海山相关等深流沉积体系”,可能受南海中层水循环（自西向东）底流控制;神狐南海山以南水深约1 500~2 500 m的陆坡区（坡度>2°）普遍发生坡移,发育“重力流滑塌体系”和“峡谷体系”,鲜见等深流沉积;下陆坡区（水深>2 500 m,坡度稍缓<2°）滑塌现象明显减少,主要发育“峡谷体系”以及“席状等深流沉积体系”,席状等深流沉积体系可能受分散的、流速较低的南海深层水循环底流控制。地震沉积记录显示,神狐南海山附近等深流侵蚀特征最早出现于晚中新世早期,其后至现今该区较稳定发育等深流沉积/侵蚀的加积序列,说明南海西北次海盆西北陆缘的稳定底流沉积/侵蚀可追溯至晚中新世早期。 相似文献
10.
南海北部珠江口盆地重力流与等深流交互作用沉积特征、过程及沉积模式 总被引：2，自引：0，他引：2
通过地震及钻孔资料对南海北部珠江口盆地重力流及等深流沉积进行了研究。南海北部重力流及等深流沉积类型多样,包括峡谷、单向迁移水道、堤岸、朵叶及漂积体。单向迁移水道迁移方向分别为北东向和南西西向,为重力流与等深流交互作用形成。漂积体有大型长条状漂积体、限制型漂积体和陆坡席状漂积体,岩性为粘土、泥质粉沙。南海北部陆坡水深200~1200m范围内发育北东向迁移水道及小规模的漂积体,而水深约1200~3000m内则以朵叶及大规模的漂积体为主,见少量南西西向迁移水道。其中,漂积体多分布于峡谷、水道及朵叶的两侧,为等深流改造堤岸、朵叶等"细粒"沉积物而成。 相似文献
11.
The canyon mouth is an important component of submarine‐fan systems and is thought to play a significant role in the transformation of turbidity currents. However, the depositional and erosional structures that characterize canyon mouths have received less attention than other components of submarine‐fan systems. This study investigates the facies organization and geometry of turbidites that are interpreted to have developed at a canyon mouth in the early Pleistocene Kazusa forearc basin on the Boso Peninsula, Japan. The canyon‐mouth deposits have the following distinctive features: (i) The turbidite succession is thinner than both the canyon‐fill and submarine‐fan successions and is represented by amalgamation of sandstones and pebbly sandstones as a result of bypassing of turbidity currents. (ii) Sandstone beds and bedsets show an overall lenticular geometry and are commonly overlain by mud drapes, which are massive and contain fewer bioturbation structures than do the hemipelagic muddy deposits. (iii) The mud drapes have a microstructure characterized by aggregates of clay particles, which show features similar to those of fluid‐mud deposits, and are interpreted to represent deposition from fluid mud developed from turbidity current clouds. (iv) Large‐scale erosional surfaces are infilled with thick‐bedded to very thick‐bedded turbidites, which show lithofacies quite similar to those of the surrounding deposits, and are considered to be equivalent to scours. (v) Concave‐up erosional surfaces, some of which face in the upslope direction, are overlain by backset bedding, which is associated with many mud clasts. (vi) Tractional structures, some of which are equivalent to coarse‐grained sediment waves, were also developed, and were overlain locally by mud drapes, in association with mud drape‐filled scours, cut and fill structures and backset bedding. The combination of these outcrop‐scale erosional and depositional structures, together with the microstructure of the mud drapes, can be used to identify canyon‐mouth deposits in ancient deep‐water successions. 相似文献
12.
J.R.L. Allen 《Sedimentary Geology》1980,26(4):281-328
Sand waves are large flow-transverse bedforms coupled to oscillatory boundary-layer currents of tidal origin. Like the much smaller ripple-marks generated by short-period wind waves, sand waves are observed to grow more asymmetrical with increase in the time—velocity asymmetry of the governing currents, that is, with increase in the steady component of flow (mass-transport strictly related to wave-motion) relative to the periodic component. Wind-wave ripple-marks owe their origin directly to a mass-transport component dependent on bed-curvature, which arises naturally wherever a sufficiently powerful oscillatory flow is imposed on a deformable grain boundary. This curvature-related current, flowing from troughts to crests on the bed, drifts grains mobilized by the periodic component into transverse bands. Sand waves may also owe their origin and growth to an unstable interaction within tide-generated oscillatory boundary layers between the mobile bed and a curvature-related mass-transport.Sand-wave internal structure apparently depends on the strength and degree of asymmetry of the governing currents. Relatively symmetrical forms associated with currents of low asymmetry are expected to contain comparatively small, intricately related herring-bone or climbing cross-bedding sets. Relatively asymmetrical currents shape sand waves with one side so steep that large-scale flow separation is inevitable. The predominant structure is then expected to be long avalanche bedding broken into sets by mud drapes and bioturbated zones representing periods of gentle flow, and/or by erosional discontinuities recording tidal reversals. The expected structures have parallels in the stratigraphic record and amongst modern sand waves. 相似文献
13.
Deep-water sediment wave fields, bottom current sand channels and gravity flow channel-lobe systems: Gulf of Cadiz, NE Atlantic 总被引：4，自引：0，他引：4
Edward L. Habgood Neil H. Kenyon Douglas G. Masson rey Akhmetzhanov Philip P. E. Weaver Joan Gardner† Thierry Mulder‡ 《Sedimentology》2003,50(3):483-510
Abstract A study of the seafloor of the Gulf of Cadiz west of the Strait of Gibraltar, using an integrated geophysical and sedimentological data set, gives new insights into sediment deposition from downslope thermohaline bottom currents. In this area, the Mediterranean Outflow (MO) begins to mix with North Atlantic waters and separates into alongslope geostrophic and downslope ageostrophic components. Changes in bedform morphology across the study area indicate a decrease in the peak velocity of the MO from >1 m s?1 to <0·5 m s?1. The associated sediment waves form a continuum from sand waves to muddy sand waves to mud waves. A series of downslope‐oriented channels, formed by the MO, are found where the MO starts to descend the continental slope at a water depth of ≈700 m. These channels are up to 40 km long, have gradients of <0·5°, a fairly constant width of ≈2 km and a depth of ≈75 m. Sand waves move down the channels that have mud wave‐covered levees similar to those seen in turbidite channel–levee systems, although the channel size and levee thickness do not decrease downslope as in typical turbidite channel systems. The channels terminate abruptly where the MO lifts off the seafloor. Gravity flow channels with lobes on the basin floor exist downslope from several of the bottom current channels. Each gravity flow system has a narrow, slightly sinuous channel, up to 20 m deep, feeding a depositional lobe up to 7 km long. Cores from the lobes recovered up to 8·5 m of massive, well‐sorted, fine sand, with occasional mud clasts. This work provides an insight into the complex facies patterns associated with strong bottom currents and highlights key differences between bottom current and gravity flow channel–levee systems. The distribution of sand within these systems is of particular interest, with applications in understanding the architecture of hydrocarbon reservoirs formed in continental slope settings. 相似文献
14.
B. K. LEVELL 《Sedimentology》1980,27(5):539-557
The Lower Sandfjord Formation is a 1.5 km thick late Precambrian sandstone. It is a remarkably homogeneous unit consisting largely (98%) of cross-bedded, texturally and mineralogically mature, coarse or medium sandstone, and is interpreted as a shallow marine deposit. This interpretation is based on the maturity, the exclusively tabular bed geometry, occasional sets of herring-bone cross-bedding and most importantly, the abundance of sheet-like pebble layers only 1–5 grain diameters thick and sometimes overlain by thin siltstone drapes. Various different types of compound cross-bedding, all of which show evidence of reversing currents, are interpreted as sub-tidal sandwaves. These sets range in thickness from 0.5 to 14 m, and in conjunction with the overall abundance of cross-bedding probably indicate strong tidal currents. A tide-dominated current regime is also considered essential to explain the derivation of such large quantities of sand from the contemporary coasts. It is suggested that sand transport offshore took place during the erosional transgression of abandoned delta lobes. However, the predominance of a single, easterly, mode in the palaeocurrent patterns suggests that the tidal currents were reinforced by some other current system. The predominantly unimodal palaeocurrent patterns and the coarse, sand-rich nature of the succession, taken together with the thickness do not superficially seem likely characteristics for a shallow marine sequence. Nevertheless this study appears to demonstrate that such deposits were formed on tidal shelves in at least late Precambrian time. 相似文献
15.
琼东南盆地中央峡谷西段莺歌海组沉积演化及储层预测 总被引：2，自引：0，他引：2
发育于琼东南盆地乐东凹陷、陵水凹陷、松南低凸起的中央峡谷西段,早期充填了厚达700 m的深海重力流沉积.基于两口钻井和两块三维地震资料,对研究区内中央峡谷早期的沉积演化进行了研究.通过分析地震剖面波组特征和对比井震资料,将峡谷充填划分为5个沉积期次;在井震对比的基础上,结合反射特征、地震切片及属性分析,识别出四种主要的沉积类型:水道复合体、水道-天然堤、浊积席状砂、块体流.沉积期次1主要为水道复合体,沉积期次2和3主要为水道-天然堤,沉积期次4主要为块体流和水道-天然堤,沉积期次5主要为块体流和浊积席状砂.峡谷DS1~DS3主要受轴向物源控制,以浊流沉积为主,富砂;DS4~DS5逐渐受北部陆坡物源控制,以块体流沉积为主,富泥.浊流沉积是峡谷内优良的储集体,普遍发育于峡谷充填下部,与上部块体流沉积可以形成良好的储盖组合,具有较好的油气勘探潜力. 相似文献
16.
G Mollenhauer T.I Eglinton R.R Schneider P.M Grootes 《Geochimica et cosmochimica acta》2003,67(12):2157-2171
Radiocarbon stratigraphy is an essential tool for high resolution paleoceanographic studies. Age models based on radiocarbon ages of foraminifera are commonly applied to a wide range of geochemical studies, including the investigation of temporal leads and lags. The critical assumption is that temporal coupling between foraminifera and other sediment constituents, including specific molecular organic compounds (biomarkers) of marine phytoplankton, e.g. alkenones, is maintained in the sediments.To test this critical assumption in the Benguela upwelling area, we have determined radiocarbon ages of total C37-C39 alkenones in 20 samples from two gravity cores and three multicorer cores. The cores were retrieved from the continental shelf and slope off Namibia, and samples were taken from Holocene, deglacial and Last Glacial Maximum core sections. The alkenone radiocarbon ages were compared to those of planktic foraminifera, total organic carbon, fatty acids and fine grained carbonates from the same samples. Interestingly, the ages of alkenones were 1000 to 4500 yr older than those of foraminifera in all samples.Such age differences may be the result of different processes: Bioturbation associated with grain size effects, lateral advection of (recycled) material and redeposition of sediment on upper continental slopes due to currents or tidal movement are examples for such processes.Based on the results of this study, the age offsets between foraminifera and alkenones in sediments from the upper continental slope off Namibia most probably do not result from particle-selective bioturbation processes. Resuspension of organic particles in response to tidal movement of bottom waters with velocities up to 25 cm/s recorded near the core sites is the more likely explanation.Our results imply that age control established using radiocarbon measurements of foraminifera may be inadequate for the interpretation of alkenone-based proxy data. Observed temporal leads and lags between foraminifera based data and data derived from alkenone measurements may therefore be secondary signals, i.e. the result of processes associated with particle settling and biological activity. 相似文献
17.
底流在陆缘深水环境下广泛存在,可对深水沉积过程及砂体分布产生重要影响。前人对重力流与底流的交互作用机制及沉积产物开展了大量研究,但目前有关底流改造型的海底扇储层构型模式仍然研究不够深入。东非鲁伍马盆地是当前重力流—底流交互作用研究的热点地区,文中以其代表性的下始新统海底扇水道体系为例,综合岩心、测井及三维地震资料开展储层构型精细表征,建立重力流—底流交互作用下的海底扇水道体系构型模式。研究表明,目标水道体系内部发育水道、溢岸及朵叶3种构型要素,其中水道可分为水道复合体、单一水道及其内部不同级次的构型单元。底流对细粒物质的搬运可形成非对称的溢岸沉积,导致水道复合体之间呈逆底流侧向迁移叠置样式,其间泥岩隔层容易保存; 单一水道之间呈顺水道纵向迁移或逆底流侧向迁移样式,其中纵向迁移部位水道切叠连通,而侧向迁移部位容易保存泥质侧向隔挡体。受重力流沉积演化的影响,单一水道内部充填由砂泥交互型逐渐演化为富砂型,且在水道弯曲段的轴部砂体最为发育。 相似文献
18.
鲁武马盆地古近系-新近系发育多套超深水、超大型、富含天然气藏的重力流沉积砂体。以始新统砂体为解剖对象,分析区内重力流砂岩储层特征及成因。结果表明砂体以巨厚层状产出于深海泥岩内部,并与周围泥岩截然接触,测井曲线表现出宏观均一性;岩心揭示此类巨厚砂体是由多期单砂体叠置而成,单砂体是由底部高密度颗粒流和顶部低密度浊流两部分组成,且经历过强底流改造。鲁武马河流三角洲强大物源供给决定了区内砂体分布面积和体积规模;深海滑塌、块体搬运等重力流沉积过程控制了沉积体粒序构造和内部结构;海底区域性强底流持续冲刷并携带走单砂体顶部细粒沉积物,残留了底部“干净”的中粗粒砂岩;多期沉积事件和频繁水道迁移决定了砂体纵、横向叠加展布,并最终形成了区内厚度巨大、岩性宏观均一且连通性极好的超大型深水重力流沉积砂岩储层。 相似文献