共查询到19条相似文献，搜索用时 453 毫秒
1.
西沙群岛生物碳酸盐的成因和沉积:来自活体仙掌藻的证据 总被引：1，自引：0，他引：1
A recent island survey reveals that the Xuande Atoll and the Yongle Atoll in the Xisha Islands can be classified into one of two systems: the depleted atoll system and growth atoll system; the survey also indicates that the decreased area of several shoals is an unbearable burden for the Xisha Islands, of which the largest island area is 2.13 km2 and the minimum elevation is 1.4 m. According to a survey on the ecological characteristics of Halimeda in the Laolongtou breaker zone of Shidao Island in the Xisha Islands, the green and white living Halimeda are collected,the isotopic ages of 14 C contained in the Halimeda are shown to be 27 years and 55 years, respectively, and carbonate mainly occurs in five types, i.e., luster, segment, sand, sand grain, and marl in the formation. The Halimeda segments mainly provide the carbonate sediments of long-term biogenic deposits in the reef environment and the annual productivity per area is 60–100 g/m2; the characteristics of the microstructure of the Halimeda are analyzed, the aragonite raphide carbonate is deposited and enriched in the cortexes, medullas and cysts, and the Halimeda generally contain major elements such as C, O, Ca, Cl, Mg, K, Na, S and Al, and are rich in trace elements such as tellurium(Te), rhodium(Rh) and strontium. It is believed that the Halimeda grow slowly,including the biotic community of reef corals in the reef areas, thus they possess an environmental remediation capacity, but it takes much time to remedy the environment, and it is necessary to make the law to protect the diversity and vulnerability of the Xisha marine ecology, the ecology of the reef community and the island environment in a scientific way. As indicated in the survey, under the background of global warming and sea-level rise, the discovery of large amounts of Halimeda in the Laolongtou sea area is significant for the natural increase of the depleted atoll system of the Xuande Atoll, while the Halimeda segments represent the primary form of the fossil Halimeda, of which the species can be identified and preserved in great numbers under geological conditions. The Miocene was discovered in large amounts in the Xichen-1 well, therefore the study on the characteristics and mechanism of Halimeda carbonate sediments plays a pivotal role in the formation and construction of organic reefs in the South China Sea as well as oil and gas exploration. 相似文献
2.
《海洋地质与第四纪地质》1983,(2)
In the geological history,there could be two kinds of geological macroprocessoccured on the Earth’s surface……the spreading of the sea floor and the growthof continent.There are two types of the continental growth.One is the union ofcontinents as a result of the collision of different plates,another is the expansionof continents by the formation of marginal sea.Four models have presented now to explain the mechanism of the formationof a marginal basin.1)The subduction of a spreading ridge.2)The thermal di-apirism.3)The"leaky"transform fault.4)The Oceanization or basaltizationThe author presumes that the marginal basin behind the are was formed by hea-ting, rifting and spreading of the lithosphere in the continental margin area whilethe oceanic slab was subducting under the continental crust.All the above men-tions concerned in the mechanism of the formation of a marginal basin can onlybe used to explain the origin of marginal basins,not to explain the evolution ofa marginal basin after it has been for 相似文献
4.
Sand island or cay is the dominant type of coral reef islands in the South China Sea. This paper gives in detail the sand islands composed of loose accumulational materials on the atoll reef flats in the Xisha Islands, their types, characteristics of morphological structure and evolutional pattern and dynamics. 相似文献
5.
The systems of diurnal tidal wave (K1) and semi-diurnal tidal wave (M2) in the Beibu Gulf are studied with numerical method. Also discussed in this paper are the influences of the Qiongzhou Strait, the bottom friction term, the horizontal turbulent friction term and the inertial (acceleration) term in dynamic equations on the tidal system. The calculated results show that there is an independent left-handed tidal system in the diurnal tidal wave of the gulf, the amphidromic point being roughly located at Taigeli Island; that the semi-diurnal wave constitutes no tidal system, generating a small tidal range in the region near Feizhulong Islands; and that the influence of the tidal wave from the strait on the tidal system of the K1 is not evident, but its effect on the system of the M2 component tide is quite obvious. The bottom friction term, the horizontal turbulent friction term, and the inertial term have effects upon the tidal system in the gulf. 相似文献
6.
《中国海洋工程》1987,(4)
- At the sites of the harbours along the coast of China, especially in the vicinity of the mouth of the Yellow River, the Yangtze River and the Pearl River, the soil strata often consist of recently deposited alluvial sediment. Therefore, under the foundations of harbour engineering structures there are always soft clays of considerable thickness. In this paper, the definition of soft clay is at first given according to the Chinese Foundation Code of Harbour Engineering. Then the physical and mechanical properties of some soft clays at the sites of harbour along the coast of China are summarized. These soft clays are classified into four types according to their physico-mechanical characteristics: very soft clay (mud), soft (muddy) clay, soft (muddy) silty clay and very soft clay (mud) mixed with lumps of sand. It is seen from the collected data that the physico-mechanical characteristics for soft clay of the same type at various sites along the coast of China are very similar, which implies that these soft clays may be formed from the similar geological origin and in similar environmental condition. It is well known that the soft clay with such unfavourable engineering properties as high water content, low shear strength, high compressibility and low permeability, is a rather weak foundation for structures, hence there would be frequently some problems happened during the construction of structure on it. However, these problems more or less can be avoided, provided that the soft clay strata have been explored, tested and analyzed carefully and appropriate measures are taken during construction. The problems usually encountered in the construction on soft clay are deformation and stability. The experiences and lessons learned on these respects in China are illustrated with 10 case histories of different types. 相似文献
7.
It has been found that the sea-surface temperature and the characteristics of atmospheric circulation in the preceding months are closely related to the temperature and ice regime in winter months. This relationship is strikingly reflected over the strong ocean current regions and over the regions with quasi-permanent atmospheric center actions. It has also been shown that the influence of the ocean on the atmosphere is more pronounced over these regions. This relationship may offer a key for long-term forecasting of the sea-ice regime in winter. In addition, because there is an obvious instability, the stabilities of the correlation coefficients are analysed. In consideration of the fact that the formation of weather process changes with the variations of time scale, predictions for longer and shorter time scale processes are discussed separately.In conclusion, some forecasting results obtained and tests made in recent years are given. 相似文献
8.
The evidence for the existence of methane seepages in the northern South China Sea: abnormal high methane concentrations in bottom waters 总被引：1，自引：1，他引：0
The methane concentration of water samples at five stations collected by the CTD rosette water sampler in the areas of southwest Dongsha Islands and the Xisha Trough was analyzed by the gas-stripping method on aboard ship. It shows abnormal high methane concentrations in near bottom water samples at three stations. In the southwest Dongsha Islands area, the methane conc.entration of 4. 25 and 10. 64 nmol/dm3 occurs in near bottom water samples at Stas E105A and El06, respectively. In the Xisha Trough area, the high methane concentrations of 5. 17, 8.48 and 8.70 nmol/dm3 in water depths of 1 750, 1 900 and 2 050 m, respectively, have been observed at Sta. F413. It is believed that the abnormal high methane concentrations are generated from the leakage of methane from sediments. Combining with previous geophysical and geochemical data from these two areas, this was probably related to the submarine gas hydrates decomposition and cold seep system. In May 2007, gas hydrate samples were successfully obtained by the drilling in the Shenhu Sea area located in the southwest Dongsha Islands area. It is called for further drilling surveys to confirm the existence of gas hydrate and cold seep system in the Xisha Trough as early as possible. 相似文献
9.
The southern uplift of the Qiongdongnan Basin is a deepwater area in which no wells have beens drilled. The Miocene-Quaternary strata in the Xisha Islands, which are located 40–100 km to the south, are composed of carbonate reef formations. Paleotectonic and paleogeographic analyses of the basin suggest that the southern uplift experienced favorable geological conditions for the development of carbonate reefs during the Miocene.The high-impedance carbonates have high amplitudes and low frequencies on seismic profiles. The reefs are distributed on paleotectonic highs and are thicker than the contemporaneous formations. A forward model of the variation in carbonate thickness based on lithological and velocity information from wells in nearby regions can simulate the seismic response of carbonates with different thicknesses. We identified several important controlling points for determining the thickness of carbonates from seismic profiles, including the pinchout point,the λ/4 thickness point, and the λ/2 thickness point. We depict a carbonate thickness map in the deepwater area of the southern Qiongdongnan Basin based on this model. The carbonate thickness map, the paleotectonic and paleogeographic background, and the seismic response characteristics of reefs suggest that the carbonates that developed on the southern uplift of the Qiongdongnan Basin during the Miocene were mainly an isolated carbonate platform peninsula and ramp deposits. It consisted of gentle ramp platform, steep slope platform,platform depression, gravity flow, and reef bank facies. 相似文献
10.
《中国海洋工程》1987,(4)
- The influence of salinity gradient on the velocity distributions in the Changjiang Estuary has been studied in consideration of gravitational circulation. It is shown by the results of calculation and analysis that there are two regions with the maximum values of both horizontal salinity gradient and gravitational circulation along the longitudinal direction of the Estuary, and the level of stratification is determined by the intensity of tidal turbulence. Values of Richardson Number and Internal Froude Number which represent the characteristics of salinity stratification in the Estuary have been given, and the relationship between them has been determined. Values of tidal diffusion component and shear diffusion component of the salt flux in the South Channel, the North Channel and the North Passage of the Changjiang Estuary have been calculated. It is shown that both components are closely related to the level of salinity stratification. Finally, the two-dimensional distribution of the vertical diffusion coefficient under salinity stratified conditions is discussed. It can be seen that the distribution of vertical diffusion coefficient is related to that of Richardson Number. 相似文献
11.
本文是西沙群岛棘皮动物研究报告的最后部分,包括海百合纲和总结。研究材料和以前一样是中国科学院海洋研究所采集的标本。西沙群岛珊瑚礁海百合种类不多,数量也很贫乏。共采56个标本,通过研究鉴定,仅包括3种海羊齿(Comatulids)，其中有一种在我国是首次记录。 相似文献
12.
青藏高原隆升、琼东南盆地沉降和西沙岛礁发育之间的耦合关系 总被引：1，自引：0，他引：1
本文基于琼东南盆地15口钻井和西沙石岛岛礁“西科一井”的钻井资料,结合过井地震剖面,系统分析了琼东南盆地沉降（沉积充填）和西沙岛礁生长速率及其变化特征,探讨了青藏高原隆升与琼东南盆地沉降和西沙岛礁发育之间的耦合关系,三者在发育时间和发育过程上表现出高度的一致性,且南海古海水中Sr同位素组成变化也表现出对青藏高原隆升速率变化很好的响应。相对于深水区,浅水区的沉积物堆积速率及其变化能够更好地反映盆地的沉降速率及其变化。琼东南盆地的沉降（沉积物堆积）和西沙岛礁的发育过程均可以分为3个阶段,分别对应于青藏高原的3个隆升期,时间自老到新分别为:23~16 Ma BP、16~5.5 Ma BP、5.5 Ma BP至今。相比而言,岛礁的发育过程与青藏高原的隆升之间的耦合关系更为密切。在青藏高原的快速隆升期,相应发生盆地沉降（沉积充填或沉积物堆积）和岛礁生长速率的加快,同时对应发生了南海海水87Sr/86Sr比值的增大,说明青藏高原隆升可能是影响琼东南盆地乃至整个南海沉降（沉积充填）、岛礁发育和古海水Sr同位素组成变化的主要因素。 相似文献
13.
珊瑚藻科都是海生藻类,其细胞壁中含有大量的碳酸钙,外形犹如动物珊瑚,分枝或不分枝,还有些呈片状或块状。紧贴在基质上,故有珊瑚藻之称。珊瑚藻科通常分两个亚科:藻体的直立部分分节,即钙化的节间(intergenicula)和不钙化的节(genicula)接连相间的,属于有节珊瑚藻亚科(Corallinoideae);藻体不分节而全面钙化,紧贴生长在基质上,有的种类其藻体表面并具各式各样甚至是分枝状的突起的,属于无节珊瑚藻亚科(Melo besioideae)。
由于珊瑚藻类的藻体内含有大量的钙质,同其他的红藻相比较,在进行其形态研究和种类鉴定的工作中就必然会遇到一些额外的困难,需要多作些处理,也即是说,首先需要用各种含酸的去钙剂溶解掉其藻体内的钙质,而后才能进行组织观察或切片,并作出比较正确的种类鉴定。正由于存在着这些困难,早期的藻类学家多偏于根据珊瑚藻的外部形态特征来鉴定其种类。这当然是很不够的,以致造成了珊瑚藻类在分类学研究上的混乱现象。
藻类研究工作者们过去对我国的珊瑚藻类还没有进行过比较系统的研究。通过近几年的调查,我们更加感到这项研究工作是很有现实意义的。我们发现在一些海区,例如山东黄县一带所产的药用海浮石竟全都是块状珊瑚藻类。另外,根据近两年来中国科学院海洋研究所的同志赴我国西沙群岛进行实地调查,带回来的丰富资料完全证实了我们过去的推断,在我国南海诸岛珊瑚礁的造礁过程中除了动物珊瑚外,还有一些珊瑚藻,特别是皮壳状的珊瑚藻类确实是起了相当重要的作用的一一在一些珊瑚环礁迎浪一面的礁缘上,这些珊瑚藻繁生特盛,形成了所谓“藻脊”(algal-ridge)。这同Taylor在马绍尔群岛以及 Womersley和Bailey在所罗门群岛所发现并描述的情况基本上是一致的。本文所用的材料就是中国科学院海洋研究所1956-1958年,特别是近两年来先后在我国西沙群岛进行调查时采获的珊瑚藻标本所鉴定的一部分种类。鉴定工作还在进行中,有关的研究结果今后将陆续发表。 相似文献
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砗磲科(Tridacnidae)的种类全部生活在热带浅水珊瑚礁。它们只分布在印度太平洋动物区系区。1956-1958年中国科学院海洋研究所在西沙群岛获得许多砗磲科的标本；1975年作者参加西沙群岛的考察,又特别注意观察、采集这类动物,得到较多的标本和资料。
砗磲科是双売类中一群高度特化的种类,它的外套膜大、很发达,有大量的单细胞藻虫黄藻(Zooxanthellae)与之共生;外套膜中还有一种特殊的结构叫玻璃体(hyaline organ),它们能聚合光线使虫黄藻大量繁殖作为自身养料的一部分,这一过程 Yonge(1936)取名叫“耕殖”(farm),这种蛤一藻的特殊关系叫互惠共生(Symbiotic mutualism)。
砗磲科贝壳方位的辨识与正常双壳类相反,这是由于它与虫黄藻共生的特殊关系导致外套膜面积增加,以致使这类动物生活时原来在背面的壳顶、铰合部和韧带朝下成为腹面;原来的腹面由于植物耕殖组织(plant farming tissue)的发达而移到背面,也即贝壳的自由端朝上。动物体的软体部也有少量“逆转”,前闭売肌消失,前收足肌移到后面;后闭壳肌和后收足肌相邻移到贝壳中央;足和足丝从贝壳铰合部的对应端——腹斜面的足丝孔伸出,直接在底面固着。
为了叙述方便,确定砗磲科贝壳方位时按以下方法:把壳顶朝下,铰合部与手持者相对,这样铰合部的末端是前端、相反的一方是后端;贝売的游离端朝上为背部,壳顶和足丝孔朝下为腹部,在手持者左面为左売,右面为右売。
根据 Rosewater(1965)的意见砗磲科全世界只有6种,这6种在我国西沙群岛都有分布。 相似文献
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西沙群岛群体放射虫的初步调查 总被引：1，自引：0，他引：1
过去已有不少学者对群体放射虫进行过专门研究报道。这类动物的每个群体虽然系由成百上千个单体放射虫联合组成,但在许多方面却起着独立有机体的作用。它们对外界刺激的反应是以整体的方式进行的,而且一些行为习性相当于简单的多细胞动物。群体放射虫的形状多种多样,其大小变化也很大,群体的长度可由数毫米达数十厘米,甚至超过一米;新近 Swanberg (1979)曾找到长达三米的群体,并且常与大型的浮游动物一起存在。据以往报道,群体放射虫多半居于海洋表层,是海洋浮游生物生态系成员之一,它们以原生动物或小型的甲壳类、海鞘、软体动物的幼虫等为食,同时又是被食者。但作为海洋食物链的构成者,这类原生动物尚未引起人们足够的重视,对它的研究也很少。
我国西沙群岛的群体放射虫过去尚无报道。1974和1975年中国科学院海洋研究所和南海海洋研究所曾进行西沙群岛浮游生物调査采集,本文据该两次调查所获资料进行整理鉴定,对以往中国沿海未记录过的种类加以描述,并对其分布作一初步探讨。
调査范围见图1。标本制片按以往方法。 相似文献
18.
三沙永乐龙洞洞内侧壁礁体矿物和元素组成及其晚更新世以来的形成演化 总被引：1，自引：0，他引：1
三沙永乐龙洞深度在300m左右,是目前全球已知最深的海洋蓝洞,但是对其性质和成因了解极其有限。本研究使用X射线粉晶衍射仪、X射线荧光光谱仪、AMS14C测年等分析测试方法对采自不同深度的洞壁礁体的矿物物相、元素含量和形成年代进行了测定,探讨了洞壁性质和龙洞的演化。研究结果表明:三沙永乐龙洞洞内侧壁矿物均属于碳酸盐矿物,包括文石、高镁方解石和低镁方解石,平均含量分别为49.0%、46.6%、14.3%,它们主要来自钙质生物碎屑;洞内侧壁的主要元素是Ca、Mg、Sr,平均含量分别为36.8%、0.98%、0.48%。三沙永乐龙洞是一个复合体,17m以上岩石年龄晚于7.5cal kaBP,是全新世海平面上升时期形成的现代珊瑚礁体,没有经历过海平面下降引起的成岩作用; 17—35m岩石形成时代早于25cal ka BP,是经历了大气淡水成岩作用的晚更新世喀斯特溶洞,且在高海平面时期于17—23m以浅的空间内广泛发育洞内珊瑚礁。 相似文献
19.
我国西沙群岛海产蓝藻类的种类极为丰富。但迄今为止除黎尚豪报导过西沙群岛永兴岛的陆生习性的27种蓝藻外,尚未见过任何报告。本文为西沙群岛海产蓝藻类研究的第一部分。根据的材料是中国科学院海洋研究所1975年和1976年在西沙群岛采集的,计127号。本文仅报道11种,隶于颤藻科(Oscillatoriaceae)的6属,其中4种在我国为海产蓝藻的新记录。 相似文献