Clay minerals from the sedimentary cover from the Northwest Iberian shelf

The Northern Iberian margin is a typical example of a continental margin subjected to seasonal highly energetic regime (waves and tides) and receiving inputs of continental sediments via riverine discharges. The principal goal of this study has been to use clay minerals as indicators of sedimentary dynamics in the open shelf system. The distributions of clay mineral in the top layer of the sedimentary cover are shown to be related to their continental sources, but also reflect the influences of winter storms and longshore currents in determining the pathways of sediment transport.The mineralogical composition of the material issuing from the rivers is very similar to the general mineralogical composition of the fine fractions of the seabed sediments. Those deposits that are directly influenced by riverine discharges have higher contents of kaolinite (>20%), whereas those that are not have higher contents of illite (>80%). The available data indicate no significant quantities of terrigenous particles are being discharged from the Spanish rias. Therefore, we conclude that physical processes are controlling the clay mineral distributions and that, despite contributions from the Minho River, the main source of fine detrital particles to the shelf region is the Douro River discharge. These particles settle on the middle shelf, below the 60 m isobath. During storm events these particles are re-suspended and advected northwards to the Galician shelf or into deeper domains. Thus the distributions of the clays indicate there is a net transport of fine sediments both northwards and off-shelf.     

Environmental influences on the shell mineralogy ofMytilus edulis

The shells ofMytilus edulis in the Tay estuary, Scotland, show mean aragonite contents of 55%, but in one zone the average aragonite proportion is only 45%. Comparison with data forMytilus edulis from other regions indicates the temperature and salinity are not the only significant determinants of the aragonite/calcite ratio. Elimination of other variables suggests that sewage discharges may influence the mineralogy of the shell secreted byMytilus edulis in the relatively nutrient-enriched areas.     

Cementation in cold-water bryozoan sand, Tasmania, Australia

Cold-water (<3–11°C) carbonate is the predominant sediment on the Tasmanian shelf. Calcitic skeletal grains (bryozoa, foraminifera, echinoderms, etc.) predominate over aragonitic (gastropods, etc.) ones. Non-skeletal grains are mostly micritic intraclasts with some pellets.

Fibrous spherulitic and rhombohedral calcite submarine cements range up to 90% in the bryozoan sand. X-ray analyses show that the bryozoan sand is characterized by a spectrum of calcites (low to high magnesian) and some aragonite.

A uniform spread of Mg concentrations from 0.06 to 2.48 wt.% indicates <3–10°C ambient water temperatures. The Mn (10–360 ppm) and Fe (176–2499 ppm) concentrations increase with increasing Mg values due to the formation of impure CaCO₃ phases. The Sr content in bryozoan sand (bryozoa = 3200 ppm Sr) decreases with increasing rhombohedral calcite cement, as low Mg-calcite precipitating from 3° C sea water would have 1350 ppm Sr. The bryozoan sand grains with fibrous spherulitic calcite cements have high Sr concentrations (4470–7000 ppm), in the same range as in aragonitic (detected only by X-ray analyses) bryozoan sand grains. The spherulitic calcite cements are either pseudomorphs after original aragonite cements or these calcite cements and aragonite were inverted from fibrous spherulitic vaterite, a predominant CaCO₃ polymorph at temperatures <10°C.     

The influence of sea level changes on sediment carbonate mineralogy,Tongue of the Ocean,Bahamas

Large fluctuations occur in the aragonite content of fine silt and clay-sized material sampled by piston cores in Tongue of the Ocean, Bahamas. Electron microscopy reveals that sedimentary sequences with high aragonite content are characterized by abundant aragonite needles. Sedimentary sequences containing small amounts of aragonite but large amounts of low-Mg calcite are dominated by coccoliths. The variation in both mineralogy and grain morphology is interpreted to be related to sea level fluctuations and the consequent presence or absence of sediment contribution (needles) from the adjacent Bahama Banks. These fluctuations are useful chronological indicators in these cores and should be applicable in other areas adjacent to carbonate banks. In particular, the last rise in sea level is clearly marked in all the cores.     

Cumulative subject index volumes 34–38, 1980

The coast of the State of Kuwait is characterized by a relatively wide intertidal flat area. At the north, where it is close to Shatt-al-Arab estuary, the intertidal sediments are mainly fluviomarine, while open marine sediments dominate the southern intertidal flat area. Samples were examined from the intertidal zone of deposition from the fluviomarine and open marine environments.The sediments consist mainly of carbonate minerals (low-Mg calcite, high-Mg calcite, aragonite and dolomite), quartz, feldspars, clay minerals and heavy minerals. The mineralogy of the clay fractions of the sediments is dominated by illite, mixed-layer illite—montmorillonite, montmorillonite, chlorite, kaolinite and palygorskite with only minor amounts of quartz. Heavy minerals are concentrated in the very fine sand fraction and are dominated by opaque minerals, amphiboles, pyroxenes, epidotes, garnet, kyanite and sillimanite. Zircon, tourmaline, andalusite, staurolite and rutile are present in subordinate amounts.Three main sources are suggested for the intertidal sediments of Kuwait: (a) Shatt-al-Arab fluviatile deposits, (b) aeolian dust fallout, and (c) direct chemical and biogenic precipitation from the Gulf water.     

Facies character and geochemical signature in the late Quaternary meteoric diagenetic carbonate succession at the Xisha Islands,South China Sea

The late Quaternary shallow-water carbonates have been altered by a variety of diagenetic processes, and further influenced by high-amplitude global and regional sea level changes. This study utilizes a new borehole drilled on the Yongxing Island, Xisha Islands to investigate meteoric diagenetic alteration in the late Quaternary shallowwater carbonates. Petrographic, mineralogical, stable isotopic and elemental data provide new insights into the meteoric diagenetic processes of the reef limestone. The results show the variation in the distribution of aragonite,high-Mg calcite(HMC) and low-Mg calcite(LMC) divides the shallow-water carbonates in Core SSZK1 into three intervals, which are Unit I(31.20–55.92 m, LMC), Unit II(18.39–31.20 m, aragonite and LMC) and Unit III(upper 18.39 m of core, aragonite, LMC and HMC). Various degrees of meteoric diagenesis exist in the identified three units. The lowermost Unit I has suffered almost complete freshwater diagenesis, whereas the overlying Units II and III have undergone incompletely meteoric diagenesis. The amount of time that limestone has been in the freshwater diagenetic environment has the largest impact on the degree of meteoric diagenesis. Approximately four intact facies/water depth cycles are recognized. The cumulative depletion of elements such as strontium(Sr),sodium(Na) and sulphur(S) caused by duplicated meteoric diagenesis in the older reef sequences are distinguished from the younger reef sequences. This study provides a new record of meteoric diagenesis, which is well reflected by whole-rock mineralogy and geochemistry.     

西菲律宾海沉积物矿物组合及其地质意义

用Ｘ射线衍射法测试了１９８８年取自西菲律宾海３个柱样共５２个沉积物样品的矿物组成。结果表明，沉积物中主要矿物为方解石，石英，斜长石和钾长石，次要矿物为高岭石，绿泥石，角闪石，斜发沸石，水云母，蒙脱石和滑石。划分出两类矿物组合：（１）方解石＋石英＋斜长石＋钾长石，水云母含量高，角闪石，斜发沸石滑石含量低；（２）斜长石＋方解石＋石英＋钾长石，角闪石，斜发沸石和滑石含高，水云母含低。（１）类矿物组合反映     

Mineral composition of sedimentary matter in the Caspian Sea

Data on the mineral composition of sedimentary matter and its fluxes in the sediment system of the Caspian Sea are presented. River runoff, aerosols, particulate matter from sediment traps, and the upper layer (0–1 cm) of bottom sediments are considered. The contents of detrital minerals (quartz, albite, and K-feldspar), clay minerals (illite, chlorite, and kaolinite), and carbonates (calcite, Mg-calcite, dolomite, aragonite, and rhodochrosite) are determined. Gypsum was found in bottom sediments but is absent in the other object of the sediment system.     

南海北部陆架表层沉积物重矿物分布特征及物源意义

该文根据2007～2010年间对南海北部陆架采集的292个表层沉积物样品0．063～0．125mm粒级矿物的鉴定和分析结果,研究了该海域表层沉积物重矿物的分布特征和物质来源．结果表明：该海域矿物组成以轻组分矿物为主,平均质量百分数高达98．49％,重组分矿物的含量较低,平均值为1．51％,最高质量百分数仅为10．38％,共发现了60种重矿物．影响南海北部陆架表层沉积物重矿物的含量和分布的首要因素是水动力条件,其次是物质来源,其他因素如沉积环境、矿物自身的变质程度等也在一定程度上影响其分布特征．根据因子分析的因子荷载分布及南海北部陆架的地形地貌,研究区可划分为4个主要矿物组合区和2个亚区．分析结果表明,华南沿海的众多河流特别是珠江的入海泥沙是南海北部陆架表层沉积物的主要物质来源．海南岛东南部海底峡谷区处于相对稳定的沉积环境,胶结于有孔虫壳内的海洋自生黄铁矿含量丰富．     

Surface sediment carbonate mineralogy and water column chemistry: Nicaragua Rise versus the Bahamas

Periplatform surface sediments were studied for carbonate mineralogy in conjunction with analyses of the water column for carbonate chemistry on the eastern Northern Nicaragua Rise (NNR) in the Caribbean Sea. The results show a strong correspondence between variations and disappearance, with increasing water depth, of metastable carbonate minerals (fine aragonite and magnesian calcite) and their respective saturation levels in the overlying waters. Similar correspondence between variations in sediment proportions of fine aragonite and magnesian calcite and their respective saturation levels has previously been established in the Bahamas. There are, however, significant differences between the two areas. The sharp decrease in aragonite content and the measured aragonite saturation level occur at 4000 m in the Bahamas, compared to 1800 m on the eastern NNR. In both areas, magnesian calcite minima correspond to the in situ PCO₂ maxima in the water column. The magnesian calcite minimum, however, is at 950 m in the Bahamas and 750 m on the eastern NNR. Magnesian calcite disappears in the Bahamas at 3800 m and at 2000 m on the eastern NNR. These results demonstrate the importance of the influence of overlying water chemistry on the preservation of metastable carbonate minerals in off-bank periplatform sediments, and they clearly demonstrate the difference in terms of carbonate preservation between the poorly ventilated waters of the Caribbean Sea and the well-oxygenated waters of the adjacent Atlantic Ocean. They also open the possibility of obtaining paleoceanographic information on the depth of the CO₂ maximum (O₂ minimum) and its separation from the aragonite saturation depth in at least some areas.     

南海北部陆坡九龙甲烷礁冷泉碳酸盐岩沉积岩石学特征

本文对南海北部陆坡九龙甲烷礁采集的两个冷泉碳酸盐岩样品TVG-1和TVG-11进行了矿物学、岩石学和碳氧同位素分析研究。X射线衍射分析（XRD）结果表明,自生矿物主要为文石、白云石和高镁方解石等,碎屑矿物含量较少。TVG-11中存在大量的文石,而TVG-1只保留了已转化为方解石的文石假象,据此可以推断TVG-1的形成要早于TVG-11。扫描电镜（SEM）显微结构特征显示,自生矿物主要是通过细菌的厌氧氧化作用,直接从冷泉中沉淀出来的。碳、氧同位素测试结果显示,碳酸盐岩具有强δ^13C亏损和一定程度的δ^18O富集的特征,TVG-1和TVG-11的δ^13C值分别为-46．22％。和-52．88％,均低于-40%,表明碳源于微生物作用的甲烷厌氧氧化,是指示该海域存在冷泉的重要证据;TVG-1和TVG-11的δ^18O值分别为3．19‰和4．07‰,存在一定程度的δ^18O富集。碳氧同位素和矿物的显微结构特征都说明九龙甲烷礁碳酸盐岩是烃类渗漏微生物作用而形成的自生碳酸盐岩,可能是天然气水合物分解引起的沉积,显示该区存在水合物的可能性很大。     

Glauconite grains in continental shelf sediments around the Korean Peninsula and their depositional implications

Glauconite grains are an important component of the surficial sediments on the Korean continental shelf. Relatively high glauconite contents (>20%) occur near Huksan Island in the Yellow Sea and on the outer shelf of the southern East Sea where they are associated with relict, sandy sediments. By contrast, glauconite grains are rare (<1%) in clay-dominated sediments. The grains can be classified into four major categories: (1) very abundant, green to dark green, spheroidal and lobate grains displaying bulbous and honeycomb exteriors with well-developed surface cracks; (2) dark green, discoidal grains with poorly defined cracks; (3) scarce, moderately dark green, accordion-shaped grains characterized by series of closely spaced, parallel surface ridges; (4) scarce, green to dark green, foraminifer-shaped grains. Microprobe analyses as well as optical microscopy and SEM observations show that most grains are composed of mineral mixtures (e.g., quartz, mica, feldspar) rather than a single mineral species. The mineralogy, morphology, and textural properties suggest that the grains may have formed mainly by replacement of fecal pellets, and the alteration of mica and clays which have filled foraminifera tests. The high potassium contents, rosette-shaped clay structures, and bulbous shapes reflect an “evolved” (mature) stage of glauconitization. Glauconite grains in Korean shelf sediments are presumably relict, and have been produced by the reworking of older glauconitic sediments during the Holocene sea-level transgression. Received: 4 October 1999 / Revision accepted: 18 May 2000     

Recent sediments of the southwestern Barents Sea

The paper is based on textural, mineralogical and chemical studies of surface and subsurface sediments from 80 stations in the southwestern Barents Sea. Dispersed phases are quantitatively insignificant in these oxic shelf sediments and it is argued that the deposits are predominantly terrigenous in origin. A combined analysis of the mineralogy and chemistry of the separated size fractions allows the recognition of petrographic provinces. The patterns of sediment dispersal are discussed. The coarsest components of the Barents Sea sediments are of local origin whereas long-distance transport of finer material is taking place.     

西太平洋某海域锰结核的矿物学及矿物化学研究

锰结核中的矿物是对结核生长环境反映。对结核进行X射线衍射分析表明:结核中锰矿物主要为水羟锰矿,并含有石英、钙十字沸石、斜长石、以及绿脱石、辉石、方解石和少量的蒙脱石、伊利石、角闪石、绿泥石、白云石、锐钛矿等。锰矿物表明该区为氧化环境,且受到火山、热液活动的影响。定量分析结果表明结核各矿物的含量变化很大,说明结核的生长过程中环境发生了变化。电子探针分析结果表明:结核锰矿物的组分含量变化较大,表明结核的元素来源的不稳定性。     

北部湾SO-50柱状沉积物地球化学特征及其物源分析

通过对北部湾SO-50柱状沉积物进行粒度、Sr-Nd同位素、主微量元素及AMS14C分析,结果表明该柱状沉积物可以划分为两段,即上段（0~540 cm,0~3.0 ka BP）和下段（540~571 cm,3.0~3.3 ka BP）,它们反映了不同的物质源区贡献。下段较上段砂含量相对较高,主量元素（除SiO₂外）及稀土元素含量相对减少,87Sr/86Sr与ε_Nd除异常点外,总体变化幅度不大。研究结果显示SO-50柱状沉积物的物质来源比较稳定,具有强烈的陆源特征,下段沉积物的源区主要是琼州海峡东侧原有沉积物的再搬运和台湾岛河流携带沉积物的混合,上段沉积物除了琼州海峡东侧和台湾岛的贡献外,周边陆区海岸侵蚀物的贡献相对加强。根据SO-50柱状沉积物的研究结果表明,北部湾东部泥质区的物质来源除了琼州海峡东侧沉积物和沿岸侵蚀物的贡献外,台湾岛河流携带的沉积物对其影响也应引起重视。     

Clay-mineral suites,sources, and inferred dispersal routes: Southern California continental shelf

Clay mineralogy is useful in determining the distribution, sources, and dispersal routes of fine-grained sediments. In addition, clay minerals, especially smectite, may control the degree to which contaminants are adsorbed by the sediment. We analyzed 250 shelf sediment samples, 24 river-suspended-sediment samples, and 12 river-bed samples for clay-mineral contents in the Southern California Borderland from Point Conception to the Mexico border. In addition, six samples were analyzed from the Palos Verdes Headland in order to characterize the clay minerals contributed to the offshore from that point source. The <2 microm-size fraction was isolated, Mg-saturated, and glycolated before analysis by X-ray diffraction. Semi-quantitative percentages of smectite, illite, and kaolinite plus chlorite were calculated using peak areas and standard weighting factors. Most fine-grained sediment is supplied to the shelf by rivers during major winter storms, especially during El Ni?o years. The largest sediment fluxes to the region are from the Santa Ynez and Santa Clara Rivers, which drain the Transverse Ranges. The mean clay-mineral suite for the entire shelf sediment data set (26% smectite, 50% illite, 24% kaolinite+chlorite) is closely comparable to that for the mean of all the rivers (31% smectite, 49% illite, 20% kaolinite+chlorite), indicating that the main source of shelf fine-grained sediments is the adjacent rivers. However, regional variations do exist and the shelf is divided into four provinces with characteristic clay-mineral suites. The means of the clay-mineral suites of the two southernmost provinces are within analytical error of the mineral suites of adjacent rivers. The next province to the north includes Santa Monica Bay and has a suite of clay minerals derived from mixing of fine-grained sediments from several sources, both from the north and south. The northernmost province clay-mineral suite matches moderately well that of the adjacent rivers, but does indicate some mixing from sources in adjacent provinces.     

东海钙质生物骨屑的矿物学特征

通过电镜、电子探针和X射线等项分析,对东海沉积物中的有孔虫、腹足类、双壳类、苔藓、珊瑚、海胆等骨屑进行了矿物学研究,确定了矿物成分与生物属种的关系,并基于有孔虫壳体化学成分将壳体分为均质壳和异质壳,生物碳酸盐中镁主要富集在方解石及镁方解石中,锶在方解石和镁方解石中的分配系数(D)相似,为0.11—0.14;在文石质骨屑中D=1.09-1.20。碳氧同位素组成与生物属种有明显关系。据一些有孔虫壳体氧同位素偏差值计算的水温来看,本次测定的有孔虫属种的骨屑不能作为理想的骨屑温度计。     

晚更新世末期东海陆架沙海之形成

距今18000a前的海面比现在低约130m。那时东海的大部分、台湾海峡都出露成陆，构成亚洲东部最大的南北向低平原。该低平原在寒冷而又干燥的冬季风作用之下，出现了大面积的沙海环境，或者称为陆架沙海，并构成北半球沙漠带的最东缘。     

Shelf sediments of the Ganges delta with special emphasis on the mineralogy of the western part,Bay of Bengal,Indian Ocean

Shelf sediments at the mouth of the Hooghly River which forms the western part of the Ganges—Brahmaputra delta consist of sands, silts and clays and their various admixtures. The bulk of the sediments consists of moderately sorted fine sand to very fine sand. There is variation in lithology in the vertical and horizontal directions, as revealed from the study of the grab and core samples collected in this area, suggesting growth of the delta in different stages. In most of the samples three populations have been recognised. The grain-size variation has resulted from mixing of a number of different grain-size populations. A detailed study of the heavy minerals indicates that the suite consists of hornblende, tremolite/actinolite, opaques, zircon, pyroxenes (ortho-and clino-), garnet, sillimanite, chlorite, muscovite, biotite, epidote, monazite, kyanite, staurolite, riebeckite, carbonates and glauconite. The assemblage and the distribution patterns suggest two distinct mixed igneous and metamorphic sources for the sediments—the Himalayas to the north, mainly drained by the Ganges—Brahmaputra and their tributaries, and the peninsular shield drained by the Dhamra and other easterly-flowing rivers debouching into the Bay of Bengal. The mineralogy of the core samples in the top and bottom layers does not differ, indicating that the source area remained the same during the time of deposition of the sediments. The mineralogy of the sediments in this area, when compared with the mineralogy of the Deep-Sea Drilling Project site in the Bengal fan situated very far to the south, shows similarity because the sediments of the Ganges are carried to the deep-sea. Depending on the mineral assemblage, the area has been divided into four distinct zones: (1) Hooghly River province, consisting of hornblende, tremolite/actinolite, epidote and garnet; (2) a mixed province characterised by epidote, monazite, zircon, kyanite, staurolite, hornblende, tremolite/actinolite, biotite; (3) Dhamra River province characterised by opaques, sillimanite and orthopyroxene; (4) an offshore province comprising muscovite, chlorite and pyroxene. ILlite and kaolinite are the principal clay minerals in the sediments. The mineralogical, grain size and the lithologic studies of the sediments from the core samples suggest a southward to south-southwestward direction of dispersals of the sediments in the eastern part of the area.     

南海西沙永乐龙洞沉积物组成、来源及其沉积作用

南海永乐龙洞发育于永乐珊瑚礁台地,龙洞深度达300m,为世界之最。沉积物堆积在龙洞的洞壁斜坡、龙洞中部的转折平台以及洞底等部位。使用激光粒度仪、X射线粉晶衍射仪、X射线荧光光谱仪等对采自不同深度的沉积物进行了粒级、矿物物相、元素含量的研究。研究结果表明:龙洞沉积物绝大部分为钙质生物碎屑,以砂粒级碎屑为主,含砾石碎屑、粉砂碎屑,分选和磨圆差;沉积物矿物组成以文石、高镁方解石为主,含少量低镁方解石,其平均含量分别为69%、28%、3%;化学组成以Ca、Mg、Sr为主,平均含量分别为35.5%、0.9%、0.5%,含少量Si、Al、Ti、P、S等元素。该区沉积物来源包括礁坪生物碎屑和东亚季风风尘陆源物质两个方面,以礁坪来源的生物碎屑为主;龙洞沉积作用包括机械捕获作用和垂直沉降作用两种方式,而以机械捕获作用为主。