西江―北江及珠江三角洲汇流区全新世 泥炭腐木层时空分布与环境变化     

郑卓  汤永杰  郑艳伟  黄康有  韩子云  宗永强  李平日  谭惠中． 《热带地理》2016,36(3):313-325

西江和北江及珠江三角洲西北部汇流区广泛发育全新世的泥炭-淤泥腐木地层,结合剖面的沉积相特征和14C测年数据,对全新世沉积环境和含腐木地层的分布和环境变化进行探讨,获得以下认识：1）在西江和北江下游海侵北界以上的陆相沉积序列中,厚层泥炭主要形成于中晚全新世（7.5―1.5 cal. ka B.P.）,集中堆积时间为5.0―1.5 cal. ka B.P.;2）珠江三角洲全新世海侵对三角洲边缘区陆相泥炭沼泽的形成起决定性作用,早全新世（约9―7 cal. ka B.P.）三角洲西北端的高速率河口相粉砂黏土沉积为后来的半咸水沼泽发育奠定了淤泥深厚的物质基础,而西江―北江下游陆相洪冲积或河漫滩沉积则在8 cal. ka B.P.左右开始发育,也为之后的水松泥炭沼泽繁盛奠定了基础;3）三水西南一带是中全新世西江―北江下游泛滥平原至古河口湾的过渡区,潮汐流与河流的双重作用是造成三角洲边缘区大面积泥炭沼泽湿地形成的主要原因;4）泥炭湿地生态环境大多在2.0―1.5 cal. ka B.P.前后在西江和北江被高位洪水平流沉积物埋藏,而在三角洲区域多被泛滥平原洪积物覆盖。多数剖面泥炭腐木迁移的原因与三角洲的快速加积作用导致的潮流与河流空间位置平衡被破坏和水文条件改变有关,晚全新世不断增强的人类农业活动和森林破坏与水土流失也是导致三角洲天然沼泽湿地消失的重要原因。  相似文献   

珠江口岛屿全新世沙堤的年代与沉积环境     

万一兴  郑卓  萧一亭  汤永杰  陈聪． 《热带地理》2016,36(3):388-398

通过对珠江口岛屿小型海湾如珠海淇澳岛和澳门黑沙滩一级阶地上的古沙坝/沙丘进行光释光（OSL）年代测定、粒度分析,结果表明,全新世潮间带砂体沉积的底部年代根据光释光测年结果和沉积速率推算,超过9 ka。海岸带形成的古沙坝或风成砂质沉积的光释光测年结果大部分老于新石器文化堆积的器物年代,表明全新世高海面期砂质滨海相沉积的形成先于新石器人类活动遗迹。潮间带砂质滨海相沉积的上覆地层常在6.5 ka左右快速转变为潮上带的风成沉积-人类活动混合堆积,导致文化层中沉积物粒度分选变差,参数波动较大。淇澳岛小沙澳湾9―4.3 ka的滨海相砂质沉积的顶部目前位于海拔＋4.8 m,这一高程可能与构造抬升运动有关。  相似文献   

南亚热带全新世火灾记录的气候变化及人类影响     

马婷  郑卓  满美玲  李杰  彭环环  韩爱艳  黄康有． 《热带地理》2016,36(3):486-494

选取华南沿海丘陵山地3个南亚热带不同地点及海拔的钻孔岩芯进行了微炭屑统计分析,结合孢粉分析结果,揭示全新世以来的植被变化与火灾历史,并探讨火灾事件与季风变化和人类活动的关系。结果表明：从8 000―3 500 cal. a B.P.,3个钻孔的微炭屑浓度均极低,证明该时段森林火灾频率很低,同时高木本含量的孢粉分析结果反映了亚热带阔叶林的繁盛,并指示全新世大暖期湿润和降雨丰沛的气候特征。加上早中全新世南方人口稀少,无“刀耕火种”等大面积农业活动。从3 500 cal. a B.P.开始,多个钻孔显示出微炭屑含量的迅速增加并持续高值,这与华南地区夏季风减弱导致降雨减少、气候变干,以及华南地区人类历史从新石器晚期进入商周时代的转折期密切相关。同时,孢粉指示的阔叶类木本植物含量显著减少,表明火灾对森林破坏逐渐严重。2 000 cal. a B.P.以后,人口出现第一次增长高峰,考古出土的器物证明牛耕和铁器农具开始广泛使用,农业快速发展。这一时期低海拔的GY1和中海拔的LTY钻孔微碳屑含量维持高值,禾本科以及芒萁属等次生植物孢粉含量快速增加。这反映了秦或南越国以后在华南地区较低海拔山地和平原农业活动得到迅速发展。此外,位于海拔1 600 m以上的钻孔GT-2的微碳屑记录显示：高海拔山区在800 cal. a B.P.以后才开始出现频繁的森林火灾,反映人类农业活动和人口增加扩张到高海拔山区。  相似文献   

冷水珊瑚礁研究进展与评述     

赵美霞  余克服． 《热带地理》2016,36(1):94-100

相比浅海暖水珊瑚礁,对深海的冷水珊瑚礁研究相对薄弱。近年来随着水下机器人和深潜器技术的进步,国际上兴起了深海珊瑚礁研究热潮。文章综述了：1）冷水石珊瑚的物种多样性及格局分布特征;2）冷水石珊瑚的生长特征及测量方法;3）冷水珊瑚礁的类型、形成机制与演化过程;4）海洋酸化对冷水珊瑚礁的影响;5）冷水石珊瑚对海洋古环境的记录等。最后提出中国南海冷水珊瑚礁研究展望,建议开展探测南海冷水珊瑚礁的分布,监测珊瑚礁区的生态环境,分析冷水石珊瑚群落特征,探讨冷水珊瑚礁对海洋酸化的响应机制,并利用南海冷水石珊瑚重建南海冷水珊瑚礁的发育历史及所记录的古海洋环境等研究工作。  相似文献   

Dredged marine sediments used as novel supply of filling materials for road construction     

Dongxing Wang  Nor Edine Abriak  Rachid Zentar 《Marine Georesources & Geotechnology》2017,35(4):472-480

The dredged marine sediments are classified as waste and how to deal with such kind of abandoned materials is a great challenge. The main objective of this experimental work is to provide a novel way to reuse dredged sediment as filling materials in road section. The laboratory dewatering test is performed to model the in situ evaporation and dewatering process of untreated and treated sediment with chemical binder. The impact of binder amount and time is discussed on the change of water content influenced by evaporation. To valorize dredged sediments as roadbed materials, a hydraulic binder is incorporated to investigate its effect on the bearing capacity and strength performance. The suitability of stabilized sediment is assessed based on the obtained mechanical results followed by a detailed discussion on the in situ test roads.  相似文献   

Lithostratigraphy and geodynamic evolution of Lower Cretaceous sedimentary depocenter infilling,in Western Saharan Atlas (Algeria)     

Athmane Azil  Rachid Ait Ouali 《Arabian Journal of Geosciences》2017,10(13):283

The Lower Cretaceous series, in the Western Saharan Atlas, shows important detritic deposits, particularly continental to nearshore red sandstones. Lithologically, it is an alternation of red clay and sandstone intercalated with some carbonate levels at the lower part of the series. These series can be subdivided into three lithostratigraphic units corresponding to Valanginian-Hauterivian, Barremian, and Aptian-Lower Albian. The lithostratigraphic analysis used to reconstitute the important subsidence in the Lower Cretaceous period, particularly in the Lower Albian. The Lower Cretaceous series could be considered as a geodynamic model characterized by individualization of independent depocenter filled with different detritic material and separated by Jurassic structures. This new situation appeared in the beginning of Lower Cretaceous (Valanginian-Hauterivian), following the Neocimmeriean tectonic phase, and it is increasing in the Early Albian, where differences of thicknesses are more important and allow the distinction of the depocenter. The biostratigraphic analysis of the clay samples yielded some foraminifera and palynomorphs. Benthic and planktonic foraminifera confirmed the Hauterivian age of the basal formation, also, two dominant forms of palynomorphs were recognized; according to the large stratigraphic distribution of the identified forms, it can be attributed to the Lower Cretaceous.  相似文献   

The giant Imiter silver deposit: Neoproterozoic epithermal mineralization in the Anti-Atlas, Morocco     

Alain Cheilletz  Gilles Levresse  Dominique Gasquet  Moulay Azizi-Samir  Rachid Zyadi  Douglas A. Archibald  Edward Farrar 《Mineralium Deposita》2002,37(8):772-781

The world-class Imiter silver deposit, in the Anti-Atlas Mountains of Morocco, is a Neoproterozoic epithermal vein deposit genetically associated with a felsic volcanic event, and formed within a regional extensional tectonic regime. Rhyolitic volcanism related to ore formation has been dated at 550Dž Ma by ion-probe U/Pb on zircons. The economic silver mineralization is superimposed on an older, discrete base-metal assemblage associated with calc-alkaline granodioritic magmatism. The magmatism is dated at 572LJ Ma by ion-probe U/Pb dating on zircons, and by ⁴⁰Ar/³⁹Ar dating on hydrothermal muscovites. In the Anti-Atlas Mountains, the Precambrian-Cambrian transition appears as an important period for the formation of major, productive precious-metal deposits associated with volcanic events and extensional tectonics. The Imiter silver deposit constitutes a Precambrian analogue to modern epithermal deposits.  相似文献   

Cristallisation fractionnée et contamination crustale dans la série magmatique jurassique transitionnelle du Haut Atlas central (Maroc)Fractional crystallisation and crustal contamination in the transitional Jurassic magmatic series of Central High Atlas (Morocco)     

Rachid Zayane  Abderrahim Essaifi  René C Maury  Alain Piqué  Edgard Laville  Mohamed Bouabdelli 《Comptes Rendus Geoscience》2002,334(2):97-104

The Middle Jurassic plutonism of the Central High Atlas (Morocco) was emplaced in N45° trending anticlinal ridges. It is characterised by various petrographic facies including mafic rocks (troctolites), intermediate rocks (diorites, monzodiorites), and evolved rocks (syenites), together with heterogeneous facies resulting from mixing between acidic and the intermediate magmas. Mineralogical and chemical data show (i) the transitional character of the Jurassic magmatic series of the Central High Atlas and (ii) the implication of continental crust as a contaminant during fractional crystallization. To cite this article: R. Zayane et al., C. R. Geoscience 334 (2002) 97–104.  相似文献   

Nuclear fusion in the deuterated cores of inflated hot Jupiters     

Rachid Ouyed  Prashanth Jaikumar 《Astrophysics and Space Science》2016,361(3):89

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Verification of landslide susceptibility mapping: a case study     

Clemente Irigaray Fernndez  Toms Fernndez Del Castillo  Rachid El Hamdouni  Jos Chacn Montero 《地球表面变化过程与地形》1999,24(6):537-544

A methodology is proposed for mapping susceptibility to landsliding and validating the results. Heavy rains in late 1996 and early 1997 led to a large number of landslids in the Rute sector (Córdoba, Southern Spain), where landslide susceptibility mapping had previously been carried out using a ‘matrix’ method developed with a Geographical Information System (GIS). Analysis of the distribution of the new landslides (or reactivated earlier ones) enabled the methodology to be validated by calculating association coefficients and determining the closeness of the match between subsequent field evidence and the previously defined susceptibility levels. From the data obtained, it can be concluded that the susceptibility mapping effectively explained the spatial distribution of landslides, thus providing valuable information on stability conditions over a widespread area. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献