通过对杭州湾第四系钻孔的年代地层学、沉积学、古环境学等多学科综合分析,认为 XZK169 孔全新世沉积始于孔深17.35m处(年代约为 10 ~ 9 ka B P), 其下至孔深 86.40 m沉积属晚更新世。整个沉积层中可分出3个海进—海退旋回: 晚更新世早期以陆相沉积为主,出现河湖相—滨海湖泊相—河湖相沉积,气候为温凉干燥—温暖湿润—温凉干燥; 晚更新世中晚期出现河湖相—潮滩 湖相—浅海相—河口湾相沉积,气候为温凉干燥—寒冷干燥—温凉—暖热湿润—温热湿润: 经历了末次冰期侵蚀后,全新世出现浅海相—河口湾相沉积,气候以暖热湿润—温暖湿润为主。约在5 ka B P,杭州湾与长江口分离。

Through the comprehensive analyses on chronostratigraphy, sedimentology, and paleoenvironmentology of the Quaternary bore (XZK169) in Hangzhou Bay, it is proposed that the Holocene sedimentation began from the depth of 17.35 m (about 10-9 ka B P), and the strata below this level to the depth of 86.4 m belong to the Late Pleistocene In the profile, three cycles of transgression regression can be recognized In the early period of Late Pleistocene, mainly continental sediments were developed, river-lacustrine facies, lagoon-lacustrine facies, river lacustrine facies respectively appeared, and the paleoclimate changed from temperament cool arid, warm and moist, to temperament cool arid In the mid ate period of Late Pleistocene, river lacustrine facies, tidal flat and lagoon facies, shallow marine facies, estuary facies appeared and the paleoclimate changed from temperament cool arid, cold and arid, temperament cool, warm hot and moist, to warm and moist After the erosion during the last glaciation, shallow marine estuary facies appeared in the Holocene, and the paleoclimate changed from warm hot and moist, to warm and moist. The Hangzhou Bay separated from the Changjiang River mouth in around 5 ka B P.

综合钱塘江下切河谷SE4孔岩心观察和描述及粒度、孢粉、测年等分析数据,探讨了钱塘江下切河谷晚第四纪沉积环境和古气候演化,揭示了其气候变化机制下沉积响应的具体过程。研究表明SE4孔晚第四纪沉积物自下而上包括河床亚相、河漫滩亚相、古河口湾相、浅海亚相和现代河口湾相5套沉积。研究区晚第四纪以来古植被和古气候演化分为6个阶段:第一阶段植被类型为阔叶树为主的针阔混交林—草原,气候温和偏湿,沉积了河床和河漫滩亚相;第二阶段为落叶栎稍多的针阔混交林,气候温和湿润,沉积了古河口湾相和浅海亚相;第三阶段为针阔混交林,气候温暖湿润,浅海亚相沉积发育;第四至第六阶段植被类型经历了针阔混交林—草原、针阔混交林、针阔混交林—草原的交替,气候经历了温和偏干、温和偏湿、温和偏干的变化,现代河口湾相沉积发育。

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。

对晚第四纪钱塘江下切河谷内SE2孔沉积物重矿物和稀土—微量元素进行系统分析,并与邻区长江沉积物相应特征进行对比。结果显示: (1)晚第四纪钱塘江下切河谷充填物中河床(U5)、河漫滩(U4)和古河口湾(U3)沉积物的重矿物组合为赤褐铁矿—磁铁矿—锆石—白钛石—锐钛矿;微量元素中的铁族元素、大离子亲石元素和高场强元素与平均大陆上地壳(UCC)相近,且大离子亲石元素和大部分高场强元素与北美页岩(NASC)相近,在Th/Co-Cr/Th投点图中靠近钱塘江物源区,远离现代长江沉积物投点区;稀土元素球粒陨石和NASC标准化曲线与钱塘江沉积物特征相似,不同于现代长江沉积物。(2)近岸浅海(U2)和现代河口湾(U1)沉积物的重矿物组合为绿帘石—辉石—角闪石—石榴石—榍石—金红石—电气石;微量元素具有与UCC较为相近或富集的铁族元素,大离子亲石元素和高场强元素相对亏损,且与NASC相比,铁族和高场强元素明显亏损,大离子亲石元素亏损较弱,在Th/Co-Cr/Th投点图中主要落于长江和钱塘江来源沉积物之间;稀土元素在球粒陨石和NASC标准化曲线中,配分模式与现代长江沉积物极为相似。(3)U5、U4和U3单元具有与U1和U2单元不同的沉积物来源: 前者母岩主要为长英质中酸性火成岩,为古钱塘江提供; 而后者沉积物主要来源于中基性物源区,由长江提供,同时上游钱塘江也提供了部分沉积物。可见,长江沉积物自近岸浅海沉积时期开始大量进入到钱塘江下切河谷内,为钱塘江下切河谷的沉积环境演化提供了重要物质基础。

In this paper,the heavy-mineral assemblages and the trace-rare earth elements of Borehole SE2 sediments in the late Quaternary Qiantang River incised valley were analyzed systematically in order to investigate their provenance and evaluate the coupling relationship between the Qiantang River and Changjiang incised valleys. Results indicate that: (1)The sediments of the river bed(U5),flood plain(U4) and ancient estuary(U3) are characterized by a heavy-mineral assemblage of hematite-limonite,magnetite,zircon,leucoxene and anatase;show a similar composition of siderophile,large-ion-lithophile,and high field-strength elements with those of the UCC,and a similarity for large-ion-lithophile elements and most high field-strength elements with those of NASC;plot towards the felsic end members in the Th/Co vs. Cr/Th plot;and bear a different distribution pattern in comparison with the modern Changjiang sediments in the Chondrile-and NASC-normalized rare-earth elements diagram. (2)The sediments of the nearshore shallow sea(U2) and modern estuary(U1) are featured by a heavy-mineral assemblage of epidote,pyroxenite,hornblendite,garnet,sphere,rutile and tourmaline;show a similar composition of siderophile elements,and depleted large-ion-lithophile and high field-strength elements compared to the UCC,and a depleted composition of siderophile,high field-strength and large-ion-lithophile elements in comparison with the NASC;plot between the Changjiang River and Qiantang River end members in the Th/Co vs. Cr/Th plot;and resemble the distribution patterns of the modern Changjiang sediments in the Chondrile-and NASC-normalized rare-earth elements diagrams. (3)The deposits of the U5,U4 and U3 units bear a different provenance with those of the U2 and U1 units, with the former derived from the intermediate-felsic source rocks,i.e. from the Qiantang River drainage area,whereas,the latter mostly originated from intermediate-mafic source rocks,namely from the Changjiang catchment,and secondly from the Qiantang River drainage. The Changjiang-derived sediments began to significantly provide sediments for the evolution of the late Quaternary Qiantang River incised-valley fill since the formation of the nearshore shallow sea(U2).

香港是受台风暴潮影响最严重的地区之一。本项研究是根据近岸及浅海地区沉积物的特性来分析和获取全新世时期的台风暴潮信息。根据沉积结构和构造特征，发现有5种类型的沉积层：粉砂质粘土、砂质粒序层、水平或波状层理层、贝屑富集层和含贝屑粉砂层，其中后4种类型与台风暴潮有关。根据沉积物的磁化率分析，上部深厚的高磁化率层可能与台风暴潮对现代受污染沉积物的改造致使新老沉积物的混合所致。有孔虫分析显示，风暴沉积层中含大量外来有孔虫，而且壳体小，壳径分布与沉积物粒度分布很接近。根据沉积物的成分以及有孔虫壳的破碎程度分析，可推断台风暴潮沉积以悬浮方式搬运为主。风暴层的保存主要与沉积速率和生物扰动有关。

Hong Kong, located on the north coast of the South China Sea, is under the influence of tropical storms. In order to examine storm signatures in the Holocene sediments of Hong Kong, offshore cores made for engineering site investigation and sand search were selected for the present study. Instrumental records of storm events since 1884 were also studied to provide an explanation of forcing mechanism for storm sedimentation. Detailed sedimentological study of four offshore cores, VB1,PV3,PV18 and PEW42, located in eastern, central and western waters of Hong Kong, revealed five types of sedimentary beds: ① structureless silty clay bed; ② graded sand bed; ③ horizontal or wavy laminated bed; ④ shell rich bed which can be subdivided into graded shell bed and ungraded shell bed, and ⑤ structureless shelly silt bed. The graded sand beds, laminated beds and shell rich beds are indicative of the dynamic sedimentary environment during storms. Their sedimentological characteristics are similar to modern storm sequences found in other inner shelves. Under normal conditions, the moderate tidal currents are incapable of transporting and enriching coares grained materials such as sand and shells. However, during extreme storms, both currents and waves were greatly enhanced by strong winds with bottom current velocity reaching over several times above normal. It is only under such conditions that coarse sediment can be mobilized. The foraminiferal content in sediments is found to be particularly useful in indicating the presence of storm deposits through a greater abundance of exotic species in comparison to native species. Because of the low specific gravity of the foraminiferal tests, they are significantly exchanged between different sedimentary facies during extreme storms. At least four storm beds have been identified in the upper 7 m of core VB1 based on the increase in diversity of exotic foraminifera species. However, in the eastern waters of Hong Kong which is located in the open shelf foraminifera are not useful for recognition of an individual storm bed. This is because low sedimentation rate and high post depositional reworking in this area makes the storm deposits totally mixed with the normal, leading to a homogenous foraminiferal distribution like in core DEW42. Magnetic susceptibility is also used to assist the identification of sediment mixing caused by storms. Contaminated and uncontaminated sediments are found to have a high and a low magnetic susceptibility respectively. The high content of contaminated sediment down to a depth of about 2 m confirms that mixing through storm is an important process. Because of this, the dating of surficial sea floor sediment down to a depth of about 2 m is problematical. The well preservation of storm beds in the western waters of Hong Kong is explained by the low rates of bioturbation and the high rate of sedimentation due to the influence of the Zhujiang River. In the eastern waters, the poor preservation of storm beds in core DEW42 is explained by low rate of sedimentation and high rate of bioturbation.