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…     

印度西海岸卡奇湾外大陆架上的鲕粒和球状粒——推测古海平面振荡

碳酸盐鲕粒和鲕状砂岩通常存在于热带陆架沉积中,反映特殊的环境和海洋条件。大陆架上鲕粒的出现与富碳酸盐沉积的关系得到了很好的证明。据报道从孟买到勒德纳吉里鲕粒的１４Ｃ年龄为距今９～１１ｋａ。从浅海搬运到深海平原后,鲕粒的黄铁矿化和印度西海岸外深海岩心中的搬运鲕粒也有报道。然而,至今没有对卡奇湾外的鲕粒进行详细研究。本文对产自卡奇湾外大陆架表面沉积的鲕粒和球状粒的颜色、外部形态、内部结构、矿物成分和化学特征进行了详细的研究,对推断的古海岸线也进行了讨论。１水深测量大陆架宽约１２０ｋｍ,一般陆坡和坡折…     

渤海湾西北岸全新世埋藏牡蛎礁建造记录中的间断及其解释

渤海湾西北岸沿海平原的众多埋藏牡蛎礁体内部,除正常牡蛎壳堆积层外,还存在一些水平夹层,以往的文献对其成因有多种解释。对渤海湾西北岸埋藏牡蛎礁体中所含水平夹层特征进行了研究,并与江苏海岸南部现代活体牡蛎礁顶部沉积特征进行对比,结果表明渤海湾埋藏礁体中局部范围内分布的水平夹层与江苏海岸活礁体顶部的现代沉积相似,其特征与礁体生长时的局部水动力条件有关;但是,江苏海岸活牡蛎礁顶部的现代沉积特征不同于那些大范围分布于埋藏礁体内的水平夹层的特征,后者的成因尚待进一步研究。礁体剖面记录的垂向层序,在反映环境演化的同时,也反映了礁体生长时的平面特征。     

晚更新世以来台湾浅滩西北近岸沉积特征与古环境演化

对取自台湾浅滩西北部福建东山岛外的浅钻ZK2孔进行了包括AMS14C测年、粒度、微体古生物、碎屑矿物和黏土矿物等分析。结果表明该孔地层中存在两个明显的海相层和其间的两个陆相层,顶部的海相层为全新世高海平面以来形成的被现代潮流作用改造的现代沉积和残留沉积混合体;底部陆相层为MIS4期低海平面时期形成的河流沉积;中间的细粒沉积层又可划分为下部形成于MIS3期的以潟湖、潮坪和盐沼交替出现的海相沉积层,以及上部形成于MIS3期末到盛冰期出露水面之前的陆上沟谷充填沉积;台湾海峡南部在MIS3期之后发生了明显的构造沉降过程,但是在末次盛冰期海峡南部仍然出露水面之上形成了沉积间断面。本文研究内容为今后在台湾浅滩西北边缘到福建东南近岸区深入开展沉积学、地层学及古环境演化研究提供了新的参考。     

西沙海域碳酸盐台地周缘水道沉积体系

高分辨率地震资料显示,南海北部西沙海域碳酸盐台地周缘广泛发育水道沉积体系。礁缘水道底界面表现出强反射特征,内部充填弱-强、连续性好的地震相,可见底部杂乱反射特征;斜坡水道在地震剖面上表现为横向上连续发育的"V"型特征,且下切深度较浅。西沙隆起与广乐隆起之间的南北向低洼地带发育大型深水水道,并且受古地貌高点影响,水道分为南北两个分支。北分支水道可分为5期,且水道迁移现象明显;南分支水道可分为4期,水道以充填强振幅、连续性好的浊流沉积体和弱振幅、杂乱的块体搬运体系(Mass Transport Deposits,MTDs)为特征,每期水道均表现出侵蚀-充填-废弃的旋回性。分析认为西沙碳酸盐台地周缘水道沉积物源来自西沙隆起和广乐隆起的碳酸盐台地和生物礁碎屑及由火成作用产生的火成岩碎屑。西沙-广乐碳酸盐台地水道相互贯通,构成台地-斜坡-深水的水道沉积体系,为碳酸盐岩、生物礁及火山碎屑向台地周缘输送提供了良好的通道。     

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。     

西琛—井礁相沉积碳酸盐矿物及氧、碳稳定同位素特征

本文通过对西琛一井晚中新世以来礁相沉积物类型和有孔虫分布的分析,将纵向沉积序列分为9个相段.讨论了各时期沉积相段的碳酸盐矿物和氧、碳稳定同位素组成的变化及它们之间的关系,为研究礁区沉积环境和成岩作用条件的变化、进行区域性礁相沉积地层的划分与对比提供了依据.     

宫古群岛外陆架和陆坡上受潮流影响的高能环境和与红藻石有关的碳酸盐沉积

宫古群岛外陆架和陆坡上受潮流影响的高能环境和与红藻石有关的碳酸盐沉积ＹｏｓｈｉｈｉｒｏＴｓｕｊｉ宫古群岛位于日本琉球岛弧南部。沉积在开阔陆架和水深９００ｍ陆坡上的沉积物泥质含量低（＜５％），而沉积在潮流受阻水深２０ｍ的浅部陆架区的沉积物泥质含量高（＞...     

有限沉积空间背景中的沉积作用：阿尔伯达省东南部Manyberries油田非海相（白垩系）Mannville群和海相（侏罗系）Ellis群

在阿尔伯达省南部，西加拿大沉积盆地东部远端的有限的沉积空间中沉积了下白垩统Mannville群的非海相地层和上侏罗统Ellis群的海相地层。在Manyberries油田中，油气产层为残留的河间地和混合的山谷充填沉积地层。这些Mannville群沉积物是有限沉积空间背景中非海相沉积作用的一种端元成分。该沉积序列的特征是形成于很长一段时间中的薄层沉积物、许多不整合（有些还很重要）、特征性的复合山谷的切人、不同成熟度及分布范围的古土壤、以及煤的缺失等。     

塔里木盆地塔中隆起南坡上奥陶统礁滩相带的发现及油气勘探意义

从沉积演化研究入手,认为塔中南坡与北坡具有相似的构造和沉积演化背景;建立塔中北坡已发现礁滩相的地震解释模型,对南坡地震资料重新进行了精细解释,识别出塔中隆起南部斜坡具有与塔中隆起北坡相似的坡折带地震反射特征,发育大型台地边缘礁滩相沉积;在地震资料识别出的礁滩相带部署钻探了地质探井,发现了巨厚的海相地层礁滩相沉积,有望找到与塔中北坡坡折带类似的生物礁型亿吨级整装含油气新区带,油气勘探意义巨大。     

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.     

Contrasting facies patterns in subtropical and temperate continental slope sediments: inferences from east Australian late Quaternary records

Studies of latest Quaternary continental slope sediments at two localities on the east Australian margin have revealed markedly different responses to late Quaternary sea level fluctuations. Offshore of Noosa, in the sub-tropics, the sediment is predominantly a mixture of fine metastable carbonate, siliciclastic material, and pelagic carbonate. Important features of the stratigraphy include a siliciclastic-dominated facies deposited relatively slowly during the last glacial lowstand (sedimentation rate ≤8 cm/ka), and a calcareous facies, rich in metastable carbonate, deposited more rapidly during the late post-glacial transgression (sedimentation rates 15–24 cm/ka). Highstand and transgressive sedimentation rates are greater than lowstand rates by a factor of 2.5–6 due to increased shelf carbonate productivity after flooding of the mid-shelf. Off Sydney, in temperate latitudes, continental slope sediment is largely a mixture of fine siliciclastic material and pelagic carbonate. Mean sedimentation rates range from 2 to 5 cm/ka over the last four oxygen isotope stages, with mean glacial/interstadial rates higher than Holocene rates by a factor of ∼1.36. This largely reflects the transfer of siliciclastic mud from the shelf to the slope during sea level regression. In both localities, facies changes on the slope are not related to specific sea level states (e.g. lowstand facies, transgressive facies, etc.), but reflect instead the interaction of changing sea level with shelf morphology.     

Sedimentary facies of the eastern Pacific's northernmost reef-like setting (Cabo Pulmo,Mexico)

Cabo Pulmo, Mexico, is often cited as the eastern Pacific's northernmost coral reef. We investigated sedimentary dynamics to verify whether the system functions sedimentologically as a reef, which would mean that it retained internal sediment in a framework and exported peri-reefal sediment creating clearly identifiable facies dominated by reefal fauna. We mapped distribution of sediments using grab samples, the acoustic ground-discrimination systems QTC View and Echoplus at 50 kHz signal frequency and an IKONOS satellite image. Morphologically, the bay of Cabo Pulmo can be divided into intrusive dikes and rocky hardgrounds in less than 10 m depth and a sandy interior with rocky outcrops sloping to over 40 m. Reefal fauna without lasting framework-building but with production of typically reef-associated carbonate sediments, as well as a patch-reef facies were found on the dikes and hardgrounds. Sediments in the bay were a mixture of carbonates and siliciclastics and were influenced by a seasonal river near the bay's center that imported siliciclastic material. To the north and south sediments had a higher carbonate content, although overall the bay was characterized by > 50% siliciclastics. The shallower subtidal sands were dominated by mollusk fragments, whereas in depths > 30 m planktonic foraminiferal sand was found. Acoustically and optically remote-sensed maps were used to differentiate between the rocky and sandy areas and to identify the presumed off-shelf transport pathway of reef-derived carbonates. Overall, the sedimentary system is characterized by carbonate production, but the coarser reef derived carbonates (coral and reef-dwelling mollusks) are transported off-shelf along a steep depth gradient and little typical peri-reef sediment remains. This transport is likely aided by storms. Since no sediment retaining frameworks are formed, the dikes cannot retain internal sediment, and the reefal fauna was not dominant in sediments throughout the bay, we conclude that Cabo Pulmo sedimentologically functions only in a limited way like a coral reef.     

Distribution of riverine sediment chemistry on the shelf,slope and rise of the Gulf of Papua

The tectonically active islands of the Indo-Pacific Archipelago deliver much sediment to the ocean margins. In the Gulf of Papua on the south coast of Papua New Guinea (PNG), the chemical composition of surface sediment from grab samples indicates that Fly River muds are dispersed to the north and east, where they are joined by sediment plumes from the other large rivers along the south coast of PNG. This is the likely source of terrestrial sediment on the Papuan Plateau and the northern Coral Sea Abyssal Plain. The sediment is transported through submarine troughs and canyons offshore, far to the east of the riverine inputs. Immediately south and 30–50 km offshore from the Fly and Purari deltas is a platform of algal and reef carbonate materials, containing little or no terrestrial surface sediment.     

Sand ridges off Sarasota, Florida: A complex facies boundary on a low-energy inner shelf environment

The innermost shelf off Sarasota, Florida was mapped using sidescan-sonar imagery, seismic-reflection profiles, surface sediment samples, and short cores to define the transition between an onshore siliciclastic sand province and an offshore carbonate province and to identify the processes controlling the distribution of these distinctive facies. The transition between these facies is abrupt and closely tied to the morphology of the inner shelf. A series of low-relief nearly shore-normal ridges characterize the inner shelf. Stratigraphically, the ridges are separated from the underlying Pleistocene and Tertiary carbonate strata by the Holocene ravinement surface. While surficial sediment is fine to very-fine siliciclastic sand on the southeastern sides of the ridges and shell hash covers their northwestern sides, the cores of these Holocene deposits are a mixture of both of these facies. Along the southeastern edges of the ridges the facies boundary coincides with the discontinuity that separates the ridge deposits from the underlying strata. The transition from siliciclastic to carbonate sediment on the northwestern sides of the ridges is equally abrupt, but it falls along the crests of the ridges rather than at their edges. Here the facies transition lies within the Holocene deposit, and appears to be the result of sediment reworking by modern processes. This facies distribution primarily appears to result from south-flowing currents generated during winter storms that winnow the fine siliciclastic sediment from the troughs and steeper northwestern sides of the ridges. A coarse shell lag is left armoring the steeper northwestern sides of the ridges, and the fine sediment is deposited on the gentler southeastern sides of the ridges. This pronounced partitioning of the surficial sediment appears to be the result of the siliciclastic sand being winnowed and transported by these currents while the carbonate shell hash falls below the threshold of sediment movement and is left as a lag. The resulting facies boundaries on this low-energy, sediment-starved inner continental shelf are of two origins which both are tied to the remarkably subtle ridge morphology. Along the southeastern sides of the ridges the facies boundary coincides with a stratigraphic discontinuity that separates Holocene from the older deposits while the transition along the northwestern sides of the ridges is within the Holocene deposit and is the result of sediment redistribution by modern processes.     

Pleistocene progradational growth pattern of the northern Catalonia continental shelf (northwestern Mediterranean)

The Pleistocene sedimentary growth pattern of the northern Catalonia continental shelf is characterized by the vertical stacking of seaward downlapping regressive deposits. These deposits are characterized by a progradational development, with oblique clinoforms of low angle in the middle continental shelf, that become more inclined seaward in the outer continental shelf and shelfbreak. Eustatic sea level fluctuations controlled the development of this sedimentary pattern, whereas sediment supply conditioned the nonuniform progradation along the continental shelf and subsidence due to both sediment loading and tectonics controlled its preservation through and along the continental shelf.     

Regional stratigraphic framework linking continental shelf and coastal sedimentary deposits of west-central Florida

A regional study of the Holocene sequence onlapping the west-central Florida Platform was undertaken to merge our understanding of the barrier-island system with that of the depositional history of the adjacent inner continental shelf. Key objectives were to better understand the sedimentary processes, sediment accumulation patterns, and the history of coastal evolution during the post-glacial sea-level rise. In the subsurface, deformed limestone bedrock is attributed to mid-Cenozoic karstic processes. This stratigraphic interval is truncated by an erosional surface, commonly exposed, that regionally forms the base of the Holocene section. The Holocene section is thin and discontinuous and, north or south of the Tampa Bay area, is dominated by low-relief sand-ridge morphologies. Depositional geometries tend to be more sheet-like nearshore, and mounded or ridge-like offshore. Sand ridges exhibit 0.5–4 m of relief, with ridge widths on the order of 1 km and ridge spacing of a few kilometers. The central portion of the study area is dominated nearshore by a contiguous sand sheet associated with the Tampa Bay ebb-tidal delta. Sedimentary facies in this system consist mostly of redistributed siliciclastics, local carbonate production, and residual sediments derived from erosion of older strata. Hardground exposures are common throughout the study area. Regional trends in Holocene sediment thickness patterns are strongly correlated to antecedent topographic control. Both the present barrier-island system and thicker sediment accumulations offshore correlate with steeper slope gradients of the basal Holocene transgressive surface. Proposed models for coastal evolution during the Holocene transgression suggest a spatial and temporal combination of back-stepping barrier-island systems combined with open-marine, low-energy coastal environments. The present distribution of sand resources reflects the reworking of these earlier deposits by the late Holocene inner-shelf hydraulic regime.     

Ocean current generated sedimentary facies in the Osumi Strait, South of Kyushu, Japan

An investigation of the surface sediments and bedforms in the Osumi Strait, located between Kyushu and Tanegashima, south of Kyushu, Japan, was carried out. The distribution of some characteristics of the surface sediments and bedforms is clarified.In the Osumi Strait, the surface sediments tend to become finer in size, better sorted and lower in specific gravity from southwest to northeast. The bedform distribution shows a systematic change in the same direction. This direction is the same as the direction of sediment transportation and of the current flowing through the Strait. It is considered that these changes in bedforms and sediment properties are formed by the decrease in the energy of the current. The current generating bedforms and sediment distribution is the Osumi Branch Current, one of the branches of the Kuroshio. The sediment transportation is active under the present hydraulic conditions.The sedimentary facies developed in the Osumi Strait is controlled by a unidirectional ocean current. The ocean current is one of the important factors for sedimentary processes where strong ocean current prevails along or near the continental shelf such as around the Japanese Islands.     

厄瓜多尔Oriente盆地南部区块沉积特征

通过构造演化和地层发育特征分析,将厄瓜多尔Oriente盆地南部区块Napo组划分为4个层序。根据岩心中的潮汐层理、羽状交错层理、冲洗交错层理、具有大量贝壳等特征,识别研究区具有潮坪沉积环境。针对其沉积坡度缓,碎屑岩和碳酸盐岩互层沉积的特点,建立了缓坡混积陆棚边缘的沉积相模式,认为Oriente盆地南部区块Napo组发育有海岸平原、潮坪、局限台地和混积陆棚相。相序的垂向组合和平面迁移受海平面升降的控制,指出潮坪砂岩主要出现在各层序的陆架边缘体系域,水下浅滩砂岩出现在海侵体系域。从沉积角度看,潮汐水道砂体是最好的储层砂体。     

Seismic Reflection and Vibracoring Studies of the Continental Shelf Offshore Central and Western Long Island,New York

The ridge-and-swale topography on the continental shelf south of Fire Island, New York, is characterized by northeast-trending linear shoals that are shore attached and shore oblique on the inner shelf and isolated and shore parallel on the middle shelf. High-resolution seismic reflection profiles show that the ridges and swales occur independent of, and are not controlled by, the presence of internal structures (for example, filled tidal inlet channels, paleobarrier strata) or underlying structure (for example, high-relief Cretaceous unconformity). Grab samples of surficial sediments on the shelf south of Fire Island average 98 % sand. Locally, benthic fauna increase silt and clay content through fecal pellet production or increase the content of gravel-size material by contribution of their fragmented shell remains. Surficial sand on the ridges is unimodal at 0.33 mm (medium sand, about 50 mesh), and surficial sand in troughs is bimodal at 0.33 mm and 0.15 mm (fine sand, about 100 mesh). In addition to seismic studies, 26 vibracores were recovered from the continental shelf in state and federal waters from south of Rockaway and Long Beaches, Long Island, New York. Stratigraphic and sedimentological data gleaned from these cores were used to outline the geologic framework in the study area. A variety of sedimentary features were noted in the cores, including burrow-mottled sections of sand in a finer silty-sand, rhythmic lamination of sand and silty-sand that reflect cyclic changes in sediment transport, layers of shell hash and shells that probably represent tempestites, and changes from dark color to light color in the sediments that probably represent changes in the oxidation reduction conditions in the area with time. The stratigraphic units identified are an upper, generally oxidized,nearshore facies, an underlying fine-to medium-sand and silty-clay unit considered to be an estuarine facies, and a lower, coarse-grained, deeply oxidized, cross-laminated preHolocene unit. Grain-size analysis shows that medium-to fine-grained sand makes up most (68-99 %) of the surficial sediments. Gravel exists in trace amounts up to 19 %. Silt ranges between 3 % and 42 %, and clay ranges from 1 % to 10 %.