Heavy mineral stratigraphy of sediments from the southern outer shelf of the East China Sea since the last glaciation using fuzzy C-means cluster method

Correspondence analysis and fuzzy C-means cluster methods were used to divide the stratigraphy of heavy mineral assemblages, and the sediment sources and depositional dynamics of the environment reconstructed. The assemblages were taken from marine sediments from the late Pleistocene to the Holocene in Core Q43 situated on the outer shelf of the East China Sea. Based on the variable boundaries of the mineral assemblage at 63 and 228 cmbsf (cm below sea floor), the core might have previously been divided into three sediment strata marked with units I, II and III, which would be consistent with the divided sediment stratum of the core using minor element geochemistry. The downcore distribution of heavy minerals divided the sedimentary sequence into three major units, which were further subdivided into four subunits. The interval between 0 and 63 cmbsf of the core (unit I), which spans the Holocene and the uppermost late Pleistocene, is characterized by a hornblende-epidote-pyroxene assemblage, and contains relatively a smaller amount of schistic mineral and authigenic pyrite. In comparison, the interval between 63 and 228 cmbsf (unit II), is representative of the Last Glacial Maximum (LGM), and features a hornblende-epidote-magnetite-ilmenite assemblage containing the highest concentrations of heavy minerals and opaque minerals. However, the interval between 228 and 309 cmbsf (unit III), which spans the subinterglacial period, is characterized by a hornblende-authigenic-pyrite-mica assemblage. Relative ratios of some heavy minerals can be used as tracers of clastic sediment sources. The lower part of the sediment core shows the highest magnetite/ilmenite ratio and relatively high hornblende/augite and hornblende/epidote ratios. The middle core shows the highest hornblende/augite and hornblende/epidote ratios, and the lowest magnetite/ilmenite ratio. The upper part exhibits a slightly higher magnetite/ilmenite ratio, and also the lowest hornblende/augite and hornblende/epidote ratios. The distribution of the mineral ratio is consistent with stratigraphic division in heavy mineral data using correspondence analysis and fuzzy C-means clustering. Variations in heavy mineral association and mineral ratio in core Q43 revealed changes in provenance and depositional environment of the southern outer shelf of the East China Sea since the late Pleistocene, well corresponding to interglacial and glacial cycles.     

大气冰核对雷暴云电过程影响的数值模拟

利用已有的二维雷暴云起、放电模式模拟了一次雷暴天气,并通过敏感性试验研究了冰核浓度变化对雷暴云动力、微物理及电过程的影响。结果表明：随着大气冰核浓度的增加,雷暴云发展提前,上升气流速度和下沉气流速度均呈现降低的趋势。大气冰核浓度提升有利于异质核化过程增强,冰晶在高温区大量生成,而同质核化过程被抑制,因此冰晶整体含量降低,引起低温区中霰粒含量降低和高温区中霰粒尺度降低。在非感应起电过程中,正极性非感应起电率逐渐减小,负极性非感应起电率逐渐增大。由于液态水含量随大气冰核浓度的增加逐渐降低,高温度冰晶携带电荷的极性由负转变为正的时间有所提前。在感应起电过程中,由于霰粒尺度减小及云滴的快速消耗,感应起电率极值逐渐降低。冰晶优先在高温区生成而带负电,不同大气冰核浓度下的雷暴云空间电荷结构在雷暴云发展初期均呈现负的偶极性电荷结构。在雷暴云旺盛期,随着冰核浓度增加,空间电荷结构由三极性转变为复杂四极性。在雷暴云消散阶段不同个例均呈现偶极性电荷结构,且随着冰核浓度的增加电荷密度值逐渐减小。     

冰晶异质核化对雷暴云电过程影响的数值模拟

引入一种新型冰晶异质核化方案, 基于二维雷暴云模式, 探讨雷暴云电过程对三种异质核化的响应。结果表明: 浸润核化是冰晶生成的最重要异质核化过程, 较高数浓度的冰晶消耗雷暴云内液态水含量, 抑制淞附过程, 导致霰粒子比含水量低, 表现为较强的负极性非感应起电率; 接触核化生成的冰晶量最少, 仅对雷暴云中下层3~5 km处的冰晶有贡献, 同时霰粒子数浓度较低, 导致该方案下的起电过程最弱; 沉积核化主要影响云砧处的冰晶, 有利于提高霰收集云滴的效率, 表现为极高的霰比含水量, 促进低温区非感应起电过程的发生。总体上来看, 三个方案下的电荷结构均由较复杂的多极性发展为偶极性。其中浸润方案中主正电荷区的抬升最明显, 而接触方案过低的冰晶分布高度与沉积方案过高的冰晶分布高度, 都直接导致了次正电荷区更快消散。      

南海东部晚更新世以来的火山沉积特征

对取自南海东部的5个沉积岩芯进行矿物学和地球化学研究。结果表明火山碎屑沉积层可分为2种类型：1种具高SiO2低FeO，TiO，MgO和无色玻璃一普通角闪石组合特征，火山玻璃富含微量元素Cu，Sc，Zr，为酸性火山沉积成因；另1种以火山玻璃相对低含SiO2，高MgO，FeO，TiO2为特征，并与褐色玻璃一普通辉石一磁铁矿组合和高V，Ni的沉积层伴生，属中性火山碎屑沉积。晚更新世以来以深海盆为中心曾发生2～5次火山沉积，其性质、强度、频率和分布随区域性的变化而不同，在晚更新世中期(24．1～73．9ka)达到鼎盛。南部海盆属中性火山沉积，北部海盆为中酸性-酸性火山沉积。北部陆坡区和南沙礁台区基本上未受到影响。火山碎屑沉积物主要来自海底喷发，部分源自菲律宾岛弧。     

东海外缘碎屑矿物的物源解释——基于BP神经网络的判识分区

对取自长江、黄河三角洲和东海 230个表层沉积物样的重矿物资料进行人工神经网络分析.结果表明,东海外缘(外陆架和冲绳海槽)沉积物具有明显的分区特征,并与不同的物源影响密切相关.外陆架、陆坡和西部槽底的碎屑物主要来自长江;冲绳海槽中轴线以东主要受槽底火山和岛坡物源控制;黄河物源扩散的影响局部可达26°20′N线以北的陆架、陆坡和槽底区.     

黄河物源碎屑沉积物的重矿物特征

对取自黄河口附近的黄河干道和分流河道、河口潮间带及水下三角洲不同地貌沉积环境的149个表层样品进行了碎屑矿物学研究。结果表明，近代黄河物源碎屑沉积物与长江物源相比，具有云母-普通角闪石-绿帘石组合，富含云母类矿物，但不同环境的矿物组成由于沉积动力条件的不同而有较大变化，以黑云母／白云母和磁铁矿／钛铁矿比值高以及绿帘石／榍石和闪石类／辉石类比值低为特征。     

冲绳海槽中部表层沉积物的成因矿物学研究

研究样品由“向阳红16号”于1992年6～7月间取自冲绳海槽中部。对表层沉积物中>63μm粒级的石榴石和磁铁矿进行显微镜、扫描电镜能谱分析以及人工神经网络(B-P网络)的应用。研究表明,陆架边缘和槽坡的石榴石、磁铁矿主要来源于东海大陆架;槽底的石榴石部分来源于槽坡,部分属于海底火山或海底热液成因;槽底中北部的磁铁矿主要来源于火山活动,槽底南部的磁铁矿则可能主要来自于岛坡。