山溪性河流锆石年代学对比及对东部海区物源示踪意义

碎屑锆石年代学常被用于示踪物源、重建源区古地理以及揭示区域构造-沉积演化历史。分析和收集了台湾山溪性河流及大陆东南部中小河流的碎屑锆石U-Pb年龄,探究了山溪性中小河流碎屑锆石年代学的主要控制因素,及对东部海区沉积物源的示踪意义。河流碎屑锆石年龄组成与流域基岩性质比较研究揭示,大陆东南部中小河流碎屑锆石年代学与流域基岩所经历的构造-岩浆活动对应,而台湾山溪性小河流的碎屑锆石年代学与流域沉积岩的构造-沉积演化历史密切相关。中国东南部山溪性中小河流的碎屑锆石年龄组成揭示出三类不同的物源端元:(1)东南沿岸的小河流具有极高的燕山期锆石峰值;(2)东南部中等流域规模的河流以明显的加里东期锆石峰值为特征;(3)台湾西部山溪小河具有较高比例的前寒武纪锆石以及明显的晋宁期和吕梁期峰值年龄。这些物源端元特征的确立为今后示踪末次冰期阶段东海内陆架和台湾海峡的粗粒沉积物来源提供重要参考。     

中晚全新世以来闽江口水下三角洲物质来源及古环境演变

通过对闽江口南侧柱状样沉积物开展高分辨率的粒度、粘土矿物分析及AMS¹⁴C测年,揭示了中晚全新世以来闽江口水下三角洲物质来源及古环境演变。中全新世（7 ka BP—4 ka BP）高海平面时期,梅花水道可能是闽江口南侧陆源物质输运的主要通道,沉积了以砂为主［（58.6±8.7）%］的沉积物,平均粒径为（3.76±0.49）φ,为较高能的沉积环境。期间,增强的浙闽沿岸流携带更多的长江物质沉积到闽江口,导致沉积物中蒙脱石含量增多。然而,到晚全新世（3 ka BP）海平面略有下降,梅花水道衰退,闽江口南侧的水动力条件减弱,形成以粉砂为主［（58.1±4.4）%］的沉积物,平均粒径为（6.30± 0.32）φ。晚全新世浙闽沿岸流有所减弱,闽江口沉积物中的蒙脱石含量明显减少,而来自闽江的高岭石含量增加。     

夏季闽江口和椒江口浮游动物群落结构的比较

根据2008年9月在闽江口水域和2010年8月在椒江口水域的调查资料,对两个河口浮游动物的种类组成、生态类群、优势种和生态适应差异进行分析比较,探讨夏季闽江口海域和椒江口海域浮游动物群落结构的区别及其组成受水团变化的影响。研究结果表明:夏季,椒江口受上升流的影响出现13个暖温带种,导致椒江口(44)水域浮游动物种类数要大于闽江口(36);闽江口海域夏季主要受到台湾暖流的影响,6个优势种全部为亚热带种,椒江口有7个优势种,包括4个亚热带种和3个暖温带种;从适温性上看,闽江口和椒江口均主要以亚热带种为主,椒江口由于上升流的原因出现较多数量的暖温带种,从适盐性上看,椒江口主要以近海种为主,闽江口主要以外海种为主,这是闽江口和椒江口浮游动物生态类群的主要差异;闽江口浮游动物群落结构主要受到台湾暖流和沿岸流的影响,而椒江口主要受到浙江近海上升流和沿岸流的影响,通过对两个河口群落结构的比较和生态适应差异的分析,表明水团是各自浮游动物群落结构的形成过程中的一个重要因素。     

闽江河口表层沉积物重矿物特征与物源示踪

对闽江河口近岸海域的230个表层沉积物样品和闽江20个表层沉积物样品进行重矿物分析,系统地研究了重矿物的分布特征及其物源指示。研究区共鉴定出重矿物27种,主要以普通角闪石、绿帘石、磁铁矿和黑云母为主。根据重矿物组合分布特征,将研究区分为两个矿物组合区,并划分为3个矿物组合亚区。闽江口近岸沉积区(Ⅰ-1区)矿物组合为普通角闪石-磁铁矿-绿帘石,受闽江物质影响很大;近岸混合沉积区(Ⅰ-2区)矿物组合为普通角闪石-磁铁矿-黑云母-绿帘石,受浙闽沿岸流携带物质和闽江物质共同影响沉积形成,闽江物质影响明显减弱;残留沉积区(Ⅱ区)矿物组合为普通角闪石-绿帘石-磁铁矿,主要为受后期改造的晚更新世海侵边界层。     

闽江口拦门沙砂体的演变及其沉积年代

本文介绍了闽江口拦门沙砂体的~(14)C年代、沉积速率、堆积趋势及其变化,从历史的演变规律推测现代闽江口拦门沙砂体堆积的可能发展趋势,指出航道整治的重点地段。     

闽江口及周边海域沉积物输运及资源效应

河流入海泥沙的大部分主要分布在河口、三角洲及近岸陆架地区,发育一系列的粗颗粒沉积体系,是海砂资源重要分布区。本文以福建闽江口为研究对象,初步探讨了沉积物输运过程及海砂资源的形成机制。观测结果表明,闽江河口水体盐度由河口内部向口外海域逐渐增大,水体浊度总体减小;闽江河口附近海域近底部(距离海底25cm)流向表现出一定的旋转流特征,潮周期内余流表现为向海输运,而推移质输运主要发生在涨潮期间,并且潮周期内净向陆输运。表层沉积物粒度分析结果表明,闽江河口水下三角洲前缘表层沉积物主要由粗颗粒物质组成,沉积物类型以砂和砂质粉砂为主,中值粒径小于4Φ;前三角洲地区表层沉积物主要由细颗粒物质组成,中值粒径介于4Φ—6Φ之间。沉积物粒径趋势分析结果表明,闽江入海泥沙经梅花水道和长门水道入海后,在盐淡水混合、径流、潮流的作用下,在闽江河口形成了四个粗颗粒沉积物汇聚区,成为闽江口地区海砂资源的重要分布区;而细颗粒物质在河口羽流和潮流的作用下向偏东方向输运,形成了以黏土质粉砂为主的前三角洲。     

闽江口表层沉积物重金属分布及其潜在生态风险评价

为加强闽江流域的环境治理以及支撑闽江口重金属污染的管控工作,文章基于闽江口14个采样站位的实测数据,综合运用相关性分析、主成分分析和潜在生态风险指数等方法,系统评价闽江口表层沉积物重金属分布及其潜在生态风险。研究结果表明:闽江口表层沉积物重金属含量差异显著,除个别站位的锌和汞外,其他重金属含量均符合第一类海洋沉积物质量标准;影响铅分布的主要因素是工业排污,影响其他重金属元素分布的主要因素是有机质和沉积环境;闽江口表层沉积物重金属潜在生态风险的低风险程度和中风险程度占比分别为71.43%和28.57%,其中琅岐岛的东部和南部为中风险区,琅岐岛的北部和东北部以及川石水道外侧为低风险区;镉和汞为主要潜在生态风险重金属元素,达到较高风险程度,须加强风险监控。     

闽江口历史时期的河床变迁

一、史前时期的河口位置全新世以来海平面数十米的变动,深刻地影响闽江口的发育过程。据报道,现闽江口外水深17米海底,有距今7000—8000年前的沉积物;盆地内广泛发育了厚20—35米(最厚达50—70米)第四系,其上部有一层分布范围广并含盐度较高的地下水(属氯化物重碳酸钠钙型或重碳酸氯化钠型)和浅海微体古生物化石以及少数地点有海生     

闽江口及附近海域渔业资源现存量评析

根据2006年夏季(8月)和冬季(1月)、2007年春季(4月)和秋季(10月)在闽江口及其附近海域利用底拖网作业的渔业资源调查资料,应用传统扫海面积法以及△-分布模型法分析了福建闽江口及其附近海域(25°42′-26°27′N,119°42′-120°15′E)的渔业资源现存量.研究结果表明,闽江口及其附近海域的鱼类、甲壳类的资源密度较高,而头足类资源密度较低.渔业资源密度秋季居首位,约为2569.11kg·km-2,夏季次之,约为1 120.23kg·km-2,而冬、春季资源密度较低,分别为867.16和553.60.29kg·km-2.年平均渔业资源现存量约为4599t,渔业潜在资源量达32451t.渔业资源分布与水温、水深关系较密切.该海域渔业资源已经明显衰退,急需加强渔业资源的管理和保护.     

九龙江口沉积物中重矿物组成及其分布特征

利用1994年海岛调查和1999年执行福建省自然科学基金项目所采集的底质样品，分析研究了九龙江口表层沉积物中0.063～0.125mm粒级的重矿物组分、组合及其分布特征。结果表明，该粒级重矿物计有49种，其优势和特征矿物为磁铁矿、赤铁矿、绿帘石、钛铁矿、褐铁矿、角闪石、锆石、红柱石、黑云母等；重矿物的平均含量为9.38％；依据主要重矿物的含量和分布特征，将九龙江口划分为4个矿物组合区(Ⅰ．河道口门矿物区：Ⅱ．河口北部矿物区；Ⅲ河口南部矿物区；Ⅳ.湾口东部矿物区)，各区的矿物组合类型不仅与物质来源有关，而且受水动力条件和沉积环境的控制。     

Sediment source and environment evolution in Taiwan Island during the Eocene–Miocene

Taiwan Island's outcropping strata can provide important insights into the sedimentary environment and source development of the southeast China margin. This research is based on the Eocene–Miocene strata of the Tsukeng area in the central Western Foothills, northeast shoreline of Taiwan Island and two sites of the East China Sea Shelf Basin(ECSSB), using petrology and detrital zircon U-Pb age for the analysis. Results show that central and northeast Taiwan Island experienced a transformation from continental to marine facies during the Eocene–Miocene, and the sandstone maturity changed with time. Source analysis shows that sediments from the Eocene–early Oligocene strata mainly originated from near-source Mesozoic rocks, whose zircon age is consistent with the igneous rock in the surrounding area and coastal Cathaysia, showing 120 Ma and 230 Ma peaks in the age spectrum diagram. Since the late Oligocene, peaks of 900 Ma and 1 800 Ma are seen, indicating that deposition of matter from the old block began. The sediments could be a mixture of the surrounding Mesozoic volcanic and fewer pre-Cambrian rocks sourced from the coastal river and sporadic old basement in the ECSSB instead of longdistance transportation.     

南海北部深水区渐新-中新世沉积地球化学特征及物源演变

Geochemical and detrital zircon U-Pb dating data for drilled sediments from the Baiyun deepwater area of the northern South China Sea demonstrate a change of sedimentary sources from the Oligocene to the Miocene.Zircon ages of the pre-rift Eocene sequences are dominated by Yanshanian ages with various peak values(110–115 Ma for U1435 and L21; 150 Ma for H1), indicating local sediment supply from the pre-existing Mesozoic magmatic belt. For the Oligocene sediments in the northern part of the basin, the rare earth elements show different distribution characteristics, indicating sediment supply from the paleo-Zhujiang River(Pearl River), as also confirmed by the multimodal zircon age spectra of the Lower Oligocene strata in Well X28. By contrast, a positive Eu anomaly characterizes sediments from the western and southern parts of the basin, indicating potential provenances from intermediate to basic volcanic rock materials. The Baiyun Movement at the end of the Oligocene contributed to a large-scale subsidence in the deepwater area and also a northward retreat of continental shelf break, leading to deepening depositional environment in the basin. As a result, all the detrital zircon ages of the Upper Oligocene strata from Wells X28, L13, and L21 share a similar distribution, implying the possible control of a common source like the Zhujiang River. During the Miocene, whereas sediments in the northern area were mainly sourced from the Zhujiang River Delta, and those in the southern deepwater area continued to be affected by basic volcanic activities, the Dongsha Uplift could have contributed as the main source to the eastern area.     

Early Cenozoic paleontological assemblages and provenance evolution of the Lishui Sag,East China Sea

The East China Sea Shelf Basin generated a series of back-arc basins with thick successions of marine- and terrestrial-facies sediments during Cenozoic. It is enriched with abundant oil and gas resources and is of great significance to the petroleum exploration undertakings. Therein, the Lishui Sag formed fan delta, fluvial delta and littoral-to-neritic facies sediments during Paleocene–Eocene, and the research on its sedimentary environment and sediment source was controversial. This study analyzed the paleontological combination characteristics, and conducted a source-to-sink comparative analysis to restore the sedimentary environment and provenance evolution of the Lishui Sag during Paleocene–Eocene based on the integration of detrital zircon U-Pb age spectra patterns with paleontological assemblages. The results indicated that Lishui Sag was dominated by littoral and neritic-facies environment during time corroborated by large abundance of foraminifera, calcareous nannofossils and dinoflagellates. Chronological analysis of detrital zircon U-Pb revealed that there were significant differences in sediment sources between the east and west area of the Lishui Sag. The western area was featured by deeper water depths in the Paleocene–Eocene, and the sediment was characterized by a single Yanshanian peak of zircon U-Pb age spectra, and mainly influenced from Yanshanian magmatic rocks of South China Coast and the surrounding paleo-uplifts. However, its eastern area partly showed Indosinian populations. In particular, the upper Eocene Wenzhou sediments were featured by increasingly plentiful Precambrian zircons in addition to the large Indosinian-Yanshanian peaks, indicating a possible impact from the Yushan Low Uplift to the east. Therefore, it is likely that the eastern Lishui Sag generated large river systems as well as deltas during time. Due to the Yuquan Movement, the Lishui Sag experienced uplifting and exhumation in the late stage of the late Eocene and was not deposited with sediments until Miocene. Featured by transitional-facies depositions of Paleocene–Eocene, the Lishui Sag thus beared significant potential for source rock and oil-gas reservoir accumulation.     

Geochemistry and zircon U-Pb ages of the Oligocene sediments in the Baiyun Sag,Zhujiang River Mouth Basin

In this study, element geochemistry and zircon chronology are used to analyze the Oligocene sediments in the Baiyun Sag, Zhujiang River Mouth Basin. The experimental results are discussed with respect to weathering conditions, parent rock lithologies, and provenances. The chemical index of alteration and the chemical index of weathering values of mudstone samples from the lower Oligocene Enping Formation indicate that clastic particles in the study area underwent moderate weathering. Mudstone samples exhibit relatively enriched light rare earth elements and depleted heavy rare earth elements, "V"-shaped negative Eu anomalies, and negligible Ce anomalies. The rare earth element distribution curves are obviously right-inclined, with shapes and contents similar to those of post-Archean Australian shale and upper continental crust, indicating that the samples originated from acid rocks in the upper crust. The Hf-La/Th and La/Sc-Co/Th diagrams show this same origin for the sediments in the study area. For the samples from the upper Enping deltas, the overall age spectrum shows four major age peaks ca. 59–68 Ma, 98–136 Ma, 153–168 Ma and 239–260 Ma. For the Zhuhai Formation samples,the overall age spectrum shows three major age peaks ca. 149 Ma, 252 Ma and 380 Ma. The detrital zircon shapes and U-Pb ages reveal that during Oligocene sedimentation, the sediments on the northwestern margin of the Baiyun Sag were supplied jointly from two provenances: Precambrian-Paleozoic metamorphic rocks in the extrabasinal South China fold zone and Mesozoic volcanic rocks in the intrabasinal Panyu Low Uplift, and the former supply became stronger through time. Thus, the provenance of the Oligocene deltas experienced a transition from an early proximal intrabasinal source to a late distal extrabasinal source.     

Distribution and composition characteristics of heavy minerals in surficial sediment of Minjiang Estuary

Heavy minerals with a size range of 0.125～49.250 mm in the surficial sediment of Minjiang Estuary are studied. Thirty-four heavy minerals have been identified, with an average content of 1.92%. Major minerals include magnetite, epidote, hematite, hornblende, ilmenite, and zircon mica. These types are the same as those in the 0.063～0. 125 mm range; however, the average content is lower, which reveals that the heavy minerals in Minjiang Estuary are mainly enriched in the very-fine sand fraction. According to the content and distribution characteristics of the major heavy minerals, Minjiang Estuary can be divided into 4 mineral assemblage zones. In each zone the assemblage of heavy minerals is greatly affected by the hydrodynamic condition and the sedimentary environment. Heavy mineral types also show that detrital matters in Minjiang Estuary are originated from the weathering and erosion of the bedrock in the Minjiang River drainage area.     

Upper Miocene–Pliocene provenance evolution of the Central Canyon in northwestern South China Sea

Provenance studies of the Central Canyon, Qiongdongnan Basin has provided significant insights into paleographic and sedimentology research of the South China Sea (SCS). A suite of geochemical approaches mainly including rare earth elemental (REE) analysis and detrital zircon U–Pb dating has been systematically applied to the “source-to-sink” system involving our upper Miocene–Pliocene Central Canyon sediments and surrounding potential source areas. Based on samples tracing the entire course of the Central Canyon, REE distribution patterns indicate that the western channel was generally characterized by positive Eu anomalies in larger proportion, in contrast to the dominance of negative values of its eastern side during late Miocene–Pliocene. Additionally, for the whole canyon and farther regions of Qiongdongnan Basin, the number of samples bearing negative Eu anomalies tended to increase within younger geological strata. On the other hand, U–Pb geochronology results suggest a wide Proterozoic to Mesozoic age range with peak complexity in Yanshanian, Indosinian, Caledonian and Jinningian periods. However in detail, age combination of most western samples displayed older-age signatures than the eastern. To make it more evidently, western boreholes of the Central Canyon are mainly characterized with confined Indosinian and Caledonian clusters which show great comparability with mafic-to-ultramafic source of Kontum Massif of Central Vietnam, while eastern samples largely bear with distinguishable Yanshanian and Indosinian peaks which more resemble with Hainan Island. Based on geochemistry and geochronology analyses, two significant suppliers and sedimentary infilling processes are generated: (1) the Indosinian collision orogenic belt in central-northern Vietnam, Indochina has ever played significant role in Central Canyon sedimentary evolution, (2) Hainan Island once as a typical provenance restricted within eastern Central Canyon, has been enlarging its influence into the whole channel, even into the farther western regions of Qiongdongnan Basin.

     

闽江口表层沉积物中0.125—0.250mm粒级重矿物的分布与组合特征

着重研究了闽江口表层沉积物中０．１２５－０．２５０ｍｍ粒级的重矿物。结果表明，重矿物计有３４种，平均重量含量为１．９２％，主要矿物为磁铁矿，绿帘石、赤铁矿、角闪石、钛铁矿、锆石、云母等。与０．０６３－０．１２５ｍｍ粒级相比，虽然重矿物的种类相同，但其平均含量却低得多，显示闽江口重矿物富集于极细砂粒级中。     

Role of mangrove in mercury cycling and removal in the Jiulong Estuary

Baseline of mercury in mangrove swamp The mercury content in sediments in the Jiulong Estuary was determined in 1984 and 1985(Table 1). The highest content of mercury in sediments (300×10~(-9)) was found in Ditou, contrast-ing strongly with the low content of 36×10~(-9) in Port Dongzhai in the Hainan Island. Tab1e 1 showsthat the average content of mercury in sediments in the Jiulong Estuary is 140×10~(-9) and the averageof four areas is 72×10~(-9). This value means that these areas have not been heavily contaminated by     

Provenance of Triassic sandstones on the southwest Barents Shelf and the implication for sediment dispersal patterns in northwest Pangaea

Thick Triassic siliciclastic units form major reservoir targets for hydrocarbon exploration on the Barents Shelf; however, poor reservoir quality, possibly associated with variation in provenance, remains a key risk factor in the area. In this study, sandstone dispersal patterns on the southwest Barents Shelf are investigated through petrographic and heavy mineral analysis, garnet and rutile geochemistry and zircon U-Pb geochronology. The results show that until the Early Norian Maximum Flooding Surface, two contrasting sand types were present: (i) a Caledonian Sand Type, characterised by a high compositional maturity, a heavy mineral assemblage dominated by garnet and low chrome-spinel:zircon (CZi) values, predominantly metapelitic rutiles and mostly Proterozoic and Archaean detrital zircon ages, interpreted to be sourced from the Caledonides, and (ii) a Uralian Sand Type, characterised by a low compositional maturity, high CZi values, predominantly metamafic rutiles and Carboniferous zircon ages, sourced from the Uralian Orogeny. In addition, disparity in detrital zircon ages of the Uralian Sand Type with contiguous strata on the northern Barents Shelf reveals the presence of a Northern Uraloid Sand Type, interpreted to have been sourced from Taimyr and Severnaya Zemlya. As such, a coincidental system is inferred which delivered sand to the Northern Barents Shelf in the late Carnian/early Norian. Following the Early Norian Maximum Flooding Surface, a significant provenance change occurs. In response to Late Triassic/Early Jurassic hinterland rejuvenation, supply from the Uralian Orogen ceased and the northern Scandinavian (Caledonian) source became dominant, extending northwards out on to the southwest Barents Shelf. The data reveal a link between reservoir quality and sand type and illustrate how provenance played an important role in the development of clastic reservoirs within the Triassic of the Barents Shelf.