首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 15 毫秒
1.
基于有孔虫AMS14C年龄年代框架,通过冲绳海槽中南部的OKT12孔沉积物黏土矿物的分析,探讨了16 ka以来冲绳海槽细颗粒沉积物的物源变化及其对源区气候的响应。研究结果显示,10 ka时黏土矿物组成发生明显变化,伊利石、绿泥石含量增加,高岭石、蒙皂石含量减少,指示物源由之前的长江和东海陆架源转变为台湾源。受到海平面上升影响,长江河口和冲绳海槽距离增加,夏季风增强,黑潮增强,既搬运台湾来源物质,又阻碍长江物质跨陆架输运,在这些因素综合作用下,长江物质减少、台湾物质增加。高岭石/（伊利石+绿泥石）和绿泥石/（伊利石+蒙皂石）比值在4 ka以来增加指示全新世晚期台湾源区侵蚀强度发生变化。4 ka前后物源判别显示,OKT12孔沉积物来源由台湾东北部河流变为台湾东南部河流,反映了该时期季风降雨导致源区台湾不同区域的侵蚀差异,可能与ITCZ南移、ENSO活动增强有关。  相似文献   

2.
We analyzed the clay mineral assemblages, content and mineralogical characteristics of Hole U1438A sediment recovered from Amami Sankaku Basin during International Ocean Discovery Program (IODP) expedition 351. The results show that the clay minerals are mainly composed of illite (average 57%), smectite (average 26%), chlorite (average 14%) and minor kaolinite(average 3%). The crystallinity of illite in all samples are good (<0.4 Δ° 2θ), and the chemical indexes of illite in all samples are low (<0.4). Both indicate that illite in Hole U1438A formed in cold and dry climate. By comparing clay mineral assemblages of hole U1438A and the potential sediment sources, we suggest that smectite be mainly derived from the volcanic materials around Amami Sankaku Basin. Illite, chlorite and kaolinite are mainly derived from the Asian dust. The ratios of (illite+chlorite)/smectite show a phased increase over the last 350 ka, which is consistent with the cold and drying trend of the Asian continent since late Pleistocene. The high ratios of (illite+chlorite)/smectite and (illite+chlorite)/kaolinite during glacial period indicate that much more Asian dust was input into the Amami Sankaku Basin, which are responded to the aridity of Asian continent and strengthened east Asian Monsoon during glacial period.  相似文献   

3.
对辽河三角洲大凌河河口湿地地区ZK3钻孔的58个沉积物样品中碎屑矿物和黏土矿物进行鉴定和分析,结果显示:碎屑矿物中轻矿物占比大,平均含量为95.7%,主要包括斜长石(43.89%)、钾长石(28.10%)和石英(22.45%);重矿物平均含量仅为4.3%,主要为普通角闪石(38.03%)、绿帘石(27.51%)和自生重晶石(12.01%)。黏土矿物中伊利石平均含量(50.3%)最高,其次为蒙脱石(24.5%)、绿泥石(12.7%)和高岭石(12.6%),黏土矿物组合为伊利石-蒙脱石-绿泥石-高岭石型。ZK3孔晚更新世以来沉积物的物源有所差异,但总体上来说,除河道和湖相沉积时期物源主要来自大凌河外,其它沉积环境中沉积物主要来自辽河和大辽河,物源相对稳定。黏土矿物组合特征所指示的气候变化过程与本区域的孢粉数据有很好的对应关系:45~31 ka BP处于庐山—大理的间冰期阶段,蒙脱石/(伊利石+绿泥石)比值较大,指示气候温和湿润;31~11 ka BP为大理冰期阶段,蒙脱石/高岭石比值较低,指示气候寒冷干燥;11 ka BP至今为冰后期阶段,随着新仙女木事件(YD)的结束,温度逐渐回升,蒙脱石/(伊利石+绿泥石)比值升高,指示气候温暖湿润。  相似文献   

4.
With the analysis of the sources and formation mechanism of the clay minerals in the sediment core from the Dalianhai lake in the Gonghe Basin,northeastern Tibet-Qinghai Plateau,clay mineral composition proxies,grain-size and carbonate contents have been employed for high-resolution study in order to reconstruct East Asian Summer Monsoon （EASM） over the northeastern Tibet-Qinghai Plateau during the lastdeglacial.The study also extended to establish a relationship between vegetation cover changes and erosion during the last 14.5 ka with pollen record and clay mineral proxies.Smectite/kaolinite and smectite/（illite＋chlorite） ratios allow us to assess hydrolysis conditions in lowlands and/or physical erosion process in highlands of the Gonghe Basin.Before 12.9 Cal ka BP,both mineralogical ratios show low values indicative of strong physical erosion in the basin with a dominant cold and dry phase.After 12.9 Cal ka BP,an increase in both mineralogical ratios indicates enhanced chemical weathering in the basin associated with a warm and humid climate.The beginning of Holocene is characterized by high smectite/（illite＋chlorite） and smectite/kaolinite ratios that is synchronous as with deposition of many peat laminae,implying the best warm and humid conditions specifically between 8.0 to 5.5 Cal ka BP.The time interval after 5.0 Cai ka BP is characterized by a return to high physical erosion and low chemical weathering with dry climate conditions in the basin.Comparing variations of clay mineral assemblages with previous pollen results,we observe a rapid response in terms of chemical weathering and physical erosion intensity to a modification of the vegetation cover in the basin.  相似文献   

5.
对伊豆-小笠原海脊(ODP 782A孔)上新世以来沉积物中黏土矿物的组成、含量及矿物学特征进行了分析,结果表明:黏土矿物以伊利石(42%)和蒙皂石(42%)为主,绿泥石的平均含量为14%,高岭石的含量最低,平均仅为2%。伊利石的结晶度较好,平均为0.25°Δ2θ;化学指数较低,平均为0.31;表明伊利石主要形成于干冷的气候环境。通过将ODP 782A孔黏土矿物组合特征和含量与周边可能源区对比,并结合伊利石和蒙皂石的矿物学参数特征,我们认为蒙皂石主要来源于伊豆-小笠原海脊周边岛弧火山物质;伊利石、绿泥石和高岭石主要来自亚洲大陆风尘。上新世以来(伊利石+绿泥石)/蒙皂石比值总体上呈增加的趋势,并且在5.3~3.6、3.6~1.6、1.6~0 Ma的三个阶段表现出不同的变化特征,该比值与全球深海δ18O值所记录的全球变冷、北太平洋ODP 885/886孔风尘通量和灵台黄土沉积速率,以及日本海U1430站伊利石/蒙皂石比值所指示的亚洲内陆干旱变化的总体变化趋势和阶段性变化的时间点大致同步,表明该比值敏感地响应了全球变冷和亚洲内陆的干旱。上新世以来(伊利石+绿泥石)/高岭石比值表现为高/低交替变化,分别与中国灵台黄土磁化率高/低变化相对应,由于黄土磁化率记录了亚洲内陆干/湿变化,因此该黏土矿物比值敏感地响应了亚洲内陆的古气候变化,因而可以作为可靠的亚洲大陆干/湿变化示踪指标。  相似文献   

6.
通过X射线衍射系统分析了杭州湾地区SE2孔全新世沉积物的黏土矿物组成,结果显示研究层段黏土矿物主要由伊利石、绿泥石、高岭石和蒙脱石组成;伊利石结晶度较好,化学风化指数普遍大于0.5,表明以化学风化为主,且风化趋势自下而上呈递减趋势。通过对比中国东南部主要河流沉积物的黏土矿物组成,认为钱塘江下切河谷全新世沉积物的黏土矿物组成具有较好的物源指示意义: 全新世 Ⅰ 段(即古河口湾和河漫滩)沉积物主要来自钱塘江上游,特征黏土矿物为高岭石,河口外物质贡献不大;Ⅱ 段(即现代河口湾和近岸浅海)沉积物包含较多蒙脱石,表明不仅包括钱塘江上游物质,河口外长江物质也开始进入钱塘江河口。黏土矿物中,高岭石对气候有较好的指示作用:中全新世高岭石含量达到最高值,反映气候最为湿热,化学风化程度最高;晚全新世含量逐渐降低,反映气候逐渐回冷,化学风化强度降低。  相似文献   

7.
Fine-grained fluvial residual channel infillings are likely to reflect systematic compositional changes in response to climate change, owing to changing weathering and geomorphological conditions in the upstream drainage basin. Our research focuses on the bulk sediment and clay geochemistry, laser granulometry and clay mineralogy of Late-glacial and Early Holocene River Meuse (Maas) unexposed residual channel infillings in northern Limburg (The Netherlands). We demonstrate that residual channel infillings register a systematic bulk and clay compositional change related to climate change on a 1–10 k-yr time-scale. Late-glacial and Holocene climatic amelioration stabilised the landscape and facilitated prolonged and intense chemical weathering of phyllosilicates and clay minerals due to soil formation. Clay translocation and subsequent erosion of topsoils on Palaeozoic bedrock and loess deposits increased the supply of smectite and vermiculite within River Meuse sediments. Smectite plus vermiculite contents rose from 30–40% in the Pleniglacial to 60% in the Late Allerød and to 70–80% in the Holocene. Younger Dryas cooling and landscape instability caused almost immediate return to low smectite and vermiculite contents. Following an Early Holocene rise, within about 5000 yr, a steady state supply is reached before 5 ka (Mid-Holocene). Holocene sediments therefore contain higher amounts of clay that are richer in high-Al, low-K and low-Mg vermiculites and smectites compared with Late (Pleni-)glacial sediments. The importance of clay mineral provenance and loess admixture in the River Meuse fluvial sediments is discussed. © 1998 John Wiley & Sons, Ltd.  相似文献   

8.
Core U1359 collected from the continental rise off Wilkes Land, east Antarctica, is analyzed for the clay mineralogy and carbon content. The temporal variation of the clay mineralogical data shows a dominance of illite with chlorite, smectite and kaolinite in decreasing concentration. Clay mineral illite is negatively correlated with smectite which shows enrichment during 6.2–6.8, 5.5–5.8, 4.5 and 2.5 Ma. The mineralogical analyses on the silt size fraction (2–53 μm) of some selected samples were also carried out. The combined result of both the size fractions shows the presence of chlorite and illite in both size fractions, smectite and kaolinite only in clay size fraction (<2 μm) and similarity in the crystallinity and chemistry of illite in both fractions. Similar nature of illite in both fractions suggests negligible role of sorting probably due to the deposition from the waxing ice sheet. During times of ice growth, nearby cratonic east Antarctica shield provided biotite-rich sediments to the depositional site. On the other hand, the presence of smectite, only in the clay size fraction, suggests the effective role of sorting probably due to the deposition from distal source in ice retreat condition. During times of ice retreat, smectite-rich sediment derived from Ross Orogen is transported to the core site through surface or bottom water currents. Poor crystallinity of illite due to degradation further corroborates the ice retreat condition. The ice sheet proximal sediments of U1359 show that in the eastern part of Wilkes Land, the ‘warming’ was initiated during late Miocene.  相似文献   

9.
田旭  徐方建  吴淑壮  张晋  郭晨  董江 《地球科学》2015,40(9):1497-1504
以往针对南海北部陆架沉积物物质来源的诸多研究, 在一定程度上忽略了海南岛物质的影响.基于柱状沉积物样品的岩性、粒度、粘土矿物和AMS14C年代分析, 探讨了琼东南陆架沉积区X2站沉积物的物质来源.结果表明, X2站沉积物可划分为上、下两段, 下段(Ⅰ, 240~120 cm)主要为粘土质粉砂, 上段(Ⅱ, 120~0 cm)主要为粉砂质砂.粘土矿物主要由伊利石和高岭石组成, 含有少量绿泥石和蒙脱石.对比分析显示, 伊利石和绿泥石可能主要来自于珠江和台湾岛; 高岭石可能主要来源于海南岛和珠江, 蒙脱石主要来自于近源的雷琼地区, 即海南岛物源对南海北部陆架西段具有一定的影响.近4 ka以来, X2站沉积物的明显变粗和高岭石含量逐渐增高, 说明海南物质的输入增强, 这可能是由于近4 ka以来的气候变化或者人类活动增强所致.   相似文献   

10.
Clay mineralogy and major-element geochemistry of 35 surface sediment samples collected in 21 major to moderate rivers of Luzon, Philippines are used to evaluate the present chemical weathering process. The clay mineral assemblage consists mainly of smectite (average 86%) with minor kaolinite (9%) and chlorite (5%) and very scarce illite (1%), and does not show strong island-wide differences. The major element results of both bulk and clay-fraction sediments indicate that the formation of clay minerals is accompanied by leaching of Ca and Na first and of Fe and Mn thereafter during the chemical weathering process. A low-moderate chemical weathering degree of bulk sediments and a moderate-intensive degree of clay-fraction sediments are obtained in Luzon rivers based on proxies of chemical index of alteration (CIA) and smectite crystallinity. It is suggested that the majority of andesitic–basaltic volcanic and sedimentary rocks along with the tectonically active geological setting and sub-tropical East Asian monsoon climate are responsible for the predominance of smectite in the clay mineral assemblage.  相似文献   

11.
澄湖SC7孔沉积物粘土矿物特征及其古地理意义   总被引：1，自引：0，他引：1  
苏州澄湖湖底残留有一条NNW—SSE延伸且已被淤平的古河道。通过对湖心区古河道段SC7孔沉积物的粘土矿物XRD分析及与湖底硬粘土（Q3）、湖岸区沉积（Q4）和长江口滩地现代沉积的比较,表明古河道充填沉积中的粘土矿物主要为伊利石,其次为高岭石、绿泥石、蛭石,还有少量蒙皂石及蛭石/绿泥石混层矿物;其中的伊利石和绿泥石含量均明显偏高,高岭石含量则偏低,伊利石结晶度也较高。粘土矿物组合兼具太湖流域地带性粘土矿物和长江口沉积物的特点,表明古河道充填沉积既有来自本流域表层物质和澄湖扩大过程中的湖岸崩积,也受到长江物源的影响。这一沉积过程也说明古河道在最大海侵时涨潮流和洪水引起海水和江水的频繁倒灌,直至淤塞和淹废。  相似文献   

12.
Iheya‐North‐Knoll is one of the small knolls covered with thick sediments in the Okinawa Trough back‐arc basin. At the east slope of Iheya‐North‐Knoll, nine hydrothermal vents with sulfide mounds are present. The Integrated Ocean Drilling Program (IODP) Expedition 331 studied Iheya‐North‐Knoll in September 2010. The expedition provided us with the opportunity to study clay minerals in deep sediments in Iheya‐North‐Knoll. To reveal characteristics of clay minerals in the deep sediments, samples from the drilling cores at three sites close to the most active hydrothermal vent were analyzed by X‐ray diffraction, scanning electron microscope and transmission electron microscope. The sediments are classified into Layer 0 (shallow), Layer 1 (deep), Layer 2 (deeper) and Layer 3 (deepest) on the basis of the assemblage of clay minerals. Layer 0 contains no clay minerals. Layer 1 contains smectite, kaolinite and illite/smectite mixed‐layer mineral. Layer 2 contains chlorite, corrensite and chlorite/smectite mixed‐layer mineral. Layer 3 is grouped into three sub‐layers, 3A, 3B and 3C; Sub‐layer 3A contains chlorite and illite/smectite mixed‐layer mineral, sub‐layer 3B contains chlorite/smectite and illite/smectite mixed‐layer minerals, and sub‐layer 3C contains chlorite and illite. Large amounts of di‐octahedral clay minerals such as smectite, kaolinite, illite and illite/smectite mixed‐layer mineral are found in Iheya‐North‐Knoll, which is rarely observed in hydrothermal fields in mid‐ocean ridges. Tri‐octahedral clay minerals such as chlorite, corrensite and chlorite/smectite mixed‐layer mineral in Iheya‐North‐Knoll have low Fe/(Fe + Mg) ratios compared with those in mid‐ocean ridges. In conclusion, the characteristics of clay minerals in Iheya‐North‐Knoll differ from those in mid‐ocean ridges; di‐octahedral clay minerals and Fe‐poor tri‐octahedral clay minerals occur in Iheya‐North‐Knoll but not in mid‐ocean ridges.  相似文献   

13.
张德玉 《沉积学报》1993,11(1):111-120
根据三个沉积岩芯的研究,马里亚纳海槽和西菲律宾海盆更新世以来的沉积物中粘土矿物明显不同:前者以海槽内基性火山物质蚀变形成的蒙皂石为主,伴随少量铁镁绿泥石和伊利石;后者以来自海盆以西陆上岩石风化形成的伊利石为主,其次为蒙皂石、普通绿泥石和高岭石。这种差别除与物源有关外,主要与两个海盆中的火山活动有关。海槽内粘土矿物也有差异,迷可能与海底热液活动的影响有关。古气候对粘土矿物也有影响,但在海槽则被频繁的火山活动所掩盖。  相似文献   

14.
The clay mineralogy of the Newark Supergroup (Upper Triassic/Lower Jurassic) in the Connecticut Valley was studied by X-ray diffraction analysis. Clay minerals identified in 126 samples are illite, chlorite, smectite, kaolinite, vermiculite, expandable chlorite, mixed-layer illite/smectite, mixed-layer chlorite/smectite, and mixed-layer chlorite/vermiculite. In general, the rocks are illitic with subordinate amounts of chlorite. However, the various lithofacies in the Newark Supergroup are characterized by distinct clay-mineral assemblages. Red beds of floodplain origin contain clays mainly of detrital nature with 2M illite most abundant. Subordinate amounts of chlorite, smectite, vermiculite, kaolinite and mixed-layer illite/smectite are also present. An interstratified chlorite/vermiculite occurs in red mudstone underlying basalt flows. Lacustrine gray beds are generally characterized by the clay-mineral assemblage 1Md illite + chlorite with minor amounts of smectite ane expandable chlorite. An interstratified chlorite/smectite predominates in gray mudstone associated with perennial lake cycles in the East Berlin Formation. Black shales of deeper lacustrine origin contain the assemblage 1Md ifillite + trioctahedral smectite and traces of chlorite. Illite and smectite also occur as mixed-layer phases.In many respects, the distribution of clay minerals in the Connecticut Valley can be likened to the general scheme proposed for the Permo-Triassic basins of Europe and Africa. These display both vertical and horizontal variations in clay-mineral assemblages that reflect the chemical and spatiotemporal evolution of intrabasin depositional and diagenetic environments. Chemical data indicate that magnesium, especially, was concentrated in the black muds of large perennial lakes that intermittently occupied the Connecticut rift valley. Pore waters derived from these sediments played an important role in the development of Mg-rich 2 : 1 and interstratified clay minerals during early diagenesis.  相似文献   

15.
The bar-top sediments at the Tons river deposited mainly from the suspension current during waning stage condition of river are collected to study their provenance on the basis of clay mineralogy, heavy minerals and magnetic properties. The clay mineral assemblages in samples predominantly consist of illite, with minor amounts of kaolinite, smectite and chlorite. The clay minerals are contributed due to (i) weathering and decomposition of shales, argillaceous limestones and pyroclastic deposits of upper Vindhyan Groups and (ii) weathering and erosion of Banda plain of Gangetic alluvium. The low ZTR index for the studied samples indicates poor sediment maturity, rapid erosion in the source region and short transportation of detritus. The transparent heavy mineral assemblages in the sediment samples predominantly consist of garnet, with minor amounts of tourmaline, zircon, hornblende, enstatite, hypersthene, rutile, tremolite, kyanite, sillimanite, andalusite, chlorite, epidote, wollastonite, and staurolite. The heavy minerals are dominantly angular to sub-angular with some rounded to sub-rounded grains. The rounded grains indicate multicyclicity and derivation fromVindhyan sandstones. The angular grains are either contributed due to erosion of primary rocks of Bundelkhand gneissic complex and or various Gangetic alluviums. The magnetic properties from sediment samples indicate that the antiferromagnetic minerals (illite, chlorite and smectite) are more concentrated in clay sized particles and it also indicated mixed source rocks for the bar-top sediment of Tons river.  相似文献   

16.
应用X射线衍射(XRD)对南海北部陆架海域225个站位表层沉积物黏土组分进行分析,结果表明,研究区黏土矿物总体以伊利石和绿泥石为主,高岭石和蒙脱石质量分数少,绿泥石、高岭石与蒙脱石质量分数呈明显的负相关关系。根据南海北部陆架海域表层沉积物中黏土矿物空间分布特征,结合邻近河流的黏土矿物组分以及洋流搬运作用,雷州半岛东部海域伊利石主要来源于广东沿海河流和珠江,绿泥石来自台湾岛,蒙脱石主要由吕宋河流提供,高岭石则由广东沿海河流和海南岛入海河流提供;雷州半岛西部海域伊利石来源于珠江,绿泥石和高岭石由红河提供,蒙脱石可能受广西入海河流携带的沉积物影响。  相似文献   

17.
We employed X-ray diffraction methods to quantify clay mineral assemblages in the Indus Delta and flood plains since ~ 14 ka, spanning a period of strong climatic change. Assemblages are dominated by smectite and illite, with minor chlorite and kaolinite. Delta sediments integrate clays from across the basin and show increasing smectite input between 13 and 7.5 ka, indicating stronger chemical weathering as the summer monsoon intensified. Changes in clay mineralogy postdate changes in climate by 5–3 ka, reflecting the time needed for new clay minerals to form and be transported to the delta. Samples from the flood plains in Punjab show evidence for increased chemical weathering towards the top of the sections (6–< 4 ka), counter to the trend in the delta, at a time of monsoon weakening. Clay mineral assemblages within sandy flood-plain sediment have higher smectite/(illite + chlorite) values than interbedded mudstones, suggestive of either stronger weathering or more sediment reworking since the Mid Holocene. We show that marine records are not always good proxies for weathering across the entire flood plain. Nonetheless, the delta record likely represents the most reliable record of basin-wide weathering response to climate change.  相似文献   

18.
南海北部中新世以来粘土矿物特征及东亚古季风记录   总被引：4，自引：0，他引：4  
应用X射线衍射(XRD)、扫描电子显微镜(SEM) 和X射线能谱(EDS) 分析技术对南海北部ODP1146站中新世以来(~20 Ma) 粘土矿物的组成、结晶学特征、微形貌和化学成分进行了研究, 分析了粘土矿物的物质来源及其记录的东亚季风演化历史.1146站粘土矿物组合的总体特点是以伊利石和蒙脱石为主, 高岭石和绿泥石含量较低.物源分析表明, 1146站蒙脱石主要来自于吕宋岛, 伊利石和绿泥石来自于珠江和台湾(长江), 而高岭石则主要来自于珠江.1146站的粘土矿物不仅被南海周围物源的同时代气候所控制, 而且为相互消长的不同传输作用(表层洋流) 的强度所影响.1146站(伊利石+绿泥石) /蒙脱石比值可以用来作为东亚季风演化的矿物学标志.指标变化显示出东亚冬季风强度和冬季风相对夏季风的强度在15 Ma、8 Ma和3 Ma左右发生了3次显著加强, 结果可以与黄土、北太平洋风尘沉积、南海微体古生物记录等很好对比.青藏高原的阶段性隆升可能促进了东亚季风的这3次加强.   相似文献   

19.
台湾海峡表层沉积物中黏土矿物特征及物质来源   总被引：4，自引：1，他引：3  
利用X射线衍射仪,对比分析台湾海峡及周边表层沉积物的黏土矿物特征,讨论长江、福建和台湾河流对海峡黏土矿物的贡献程度。福建河流（闽江）的黏土矿物以高岭石为主（>40％）,其次是伊利石（30％）和绿泥石,不含蒙脱石;长江和浙闽泥质区的黏土矿物特征是伊利石含量最高（61％～66％）,其次是绿泥石（16％～17％）和高岭石（10％～13％）,少量蒙脱石（6％～9％）。台湾河流（浊水溪）黏土矿物组合为伊利石（>70％）和绿泥石,不含高岭石和蒙脱石为特征。台湾海峡高岭石含量由西向东明显减少,说明高岭石主要来自福建的河流。〖JP2〗台湾海峡50 m等深线以东区域的黏土矿物具有高的伊利石和绿泥石含量,低的蒙脱石和高岭石含量,且伊利石的化学指数和结晶度值都明显低于长江和福建的河流,反映台湾河流的物质来源。在台湾暖流作用下,台湾河流为台湾海峡中北部提供了大量的伊利石和绿泥石。福建近海的黏土矿物主要是由福建河流提供的,但在平潭岛周边海域的黏土矿物可能有长江物质的混合。〖JP〗  相似文献   

20.
Clay mineral assemblages, crystallinity, chemistry, and micromorphology of clay particles in sediments from ODP Site 1146 in the northern South China Sea (SCS) were analyzed, and used to trace sediment sources and obtain proxy records of the past changes in the East Asian monsoon climate since the Miocene, based on a multi-approach, including X-ray diffraction (XRD) and scanning electron microscopy combined with energy dispersive X-ray spectrometry (SEM-EDS). Clay minerals consist mainly of illite and smectite, with associated chlorite and kaolinite. The illite at ODP Site 1146 has very well-to-well crystallinity, and smectite has moderate-to-poor crystallinity. In SEM the smectite particles at ODP Site 1146 often appear cauliflower-like, a typical micromorphology of volcanic smecites. The smectite at ODP Site 1146 is relatively rich in Si element, but poor in Fe, very similar to the smectite from the West Philippine Sea. In contrast, the chemical composition of illite at ODP Site 1146 has no obvious differences from those of the Loess plateau, Yellow River, Yangtze River, and Pearl River. A further study on sediment source indicates that smectite originates mainly from Luzon, kaolinite from the Pearl River, and illite and chlorite from the Pearl River, Taiwan and/or the Yangtze River. The clay mineral assemblages at ODP Site 1146 were not only controlled by continental eathering regimes surrounding the SCS, but also by the changing strength of the transport processes. The ratios of (illite+chlorite)/smectite at ODP Site 1146 were adopted as proxies for the East Asian monsoon evolution. Relatively higher ratios reflect strongly intensified winter monsoon relative to summer monsoon, in contrast, lower ratios indicate a strengthened summer monsoon relative to winter monsoon. The consistent variation of this clay proxy from those of Loess plateau, eolian deposition in the North Pacific, planktonic, benthic foraminifera, and black carbon in the SCS since 20 Ma shows that three profound shifts of the East Asian winter monsoon intensity, and aridity in the Asian inland and the intensity of winter monsoon relative to summer monsoon, occurred at about 15 Ma, 8 Ma, and the younger at about 3 Ma. The phased uplift of the Himalaya-Tibetan plateau may have played a significant role in strengthening the Asian monsoon at 15 Ma, 8 Ma, and 3 Ma.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号