Foraminiferal evidence of submarine sediment transport and deposition by backwash during the 2004 Indian Ocean tsunami

Micropaleontological analysis of nearshore to offshore sediments recovered from the southwestern coast of Thailand was performed to clarify the submarine processes of sediment transport and deposition during the 2004 Indian Ocean tsunami. The distribution pattern of benthic foraminifers showed seaward migration after the tsunami event. Agglutinated foraminifers, which are characteristic of an intertidal brackish environment, were identified in the post-tsunami samples from foreshore to offshore zones. These suggest that sediments originally distributed in foreshore to nearshore zones were transported offshore due to the tsunami backwash. On the other hand, the distribution pattern of planktonic and benthic species living in offshore zones showed slight evidence of landward migration by the tsunami. This suggests that landward redistribution of sediments by the tsunami run-up did not occur in the offshore seafloor of the study area. Our results and a review of previous studies provide an interpretation of submarine sedimentation by tsunamis. It is possible that tsunami backwashes induce sediment flows that transport a large amount of coastal materials seaward. Thus, traces of paleotsunami backwashes can be identified in offshore sedimentary environments as the accumulation of allochthonous materials. This can be recognized as changes in benthic foraminiferal assemblages.     

中国东部地区城市建设用地变化与利用效益分析

此次研究以中国东部地区87 个城市的建设用地为研究对象, 分析2000-2008 年城市建设用地变化的规律及变化的原因, 并对城市建设用地开展利用效益分类与判定研究。在研究的过程中, 主要应用了聚类分析法和判别分析法, 并利用ArcGIS 9.2, 将建设用地变化情况及影响因子空间化。研究结果表明:①城市建设用地总量增长非常大, 增长速度非常快;②城市建设用地的增长速度呈降低的趋势, 不同阶段差异明显;③城市建设用地变化在省域和区域经济圈内差异明显;④城市建设用地与国内生产总值和固定资产投资的相关性最高, 经济投入的增加与人口的增长推动了东部地区城市建设用地的变化;⑤将城市建设用地利用效益分为5 类, 并且第3 类城市的总数为488 个, 占到样本总体的62.32%, 地均建设用地第二产值对聚类结果的影响最大;⑥对5 类城市建设用地效益进行了判别, 确定了各类别的判别式, 并达到检验的要求。     

西南印度洋中脊富钴结壳的矿物学和地球化学

基于采自西南印度洋超慢速扩张中脊的8块富钴结壳样品,利用XRD、XRF等方法对其进行了矿物学及地球化学组成分析,阐明了该区富钴结壳的矿物物相和元素组成特点,结合主成分分析探讨了该区结壳的成因类型和成矿物质来源。结果表明:该区结壳矿物组成以锰、铁氧化物相为主,其中锰相矿物以水羟锰矿占优势,含少量钡镁锰矿,铁相矿物出现了针铁矿及非晶质-隐晶质相;该区结壳Mn、Fe、Co、Cu、Ni的平均值分别为18.96%、19.71%、0.53%、0.099%、0.47%,它们介于中、西太平洋结壳和大西洋、印度洋结壳的相应的元素含量之间;矿物组成、元素组合、元素比值等皆表明该区结壳属于水成成因,受成岩作用影响微弱,但是未见热液活动的明显影响。     

珠江口盆地多期走滑构造与叠合型拉分盆地:以阳江东凹为例

珠江口盆地的成盆机制和构造演化过程探讨是该地区烃源岩研究中不可缺少的环节,也是大家广泛关注的焦点问题.本文以阳江东凹为例,通过整体与局部相结合的分析方法,从整体上确定了研究区走滑断裂的发育特征和展布框架,明确了区域构造运动与走滑断裂的成因联系;并将整体划分成局部,聚焦于阳江东凹古近纪盆地构造演化阶段逐步分解与精细检验,...     

亚洲—太平洋季风区的遥相关研究

亚洲—太平洋季风区各季风子系统间的相互作用对季风区甚至全球的气候变化都有非常显著的影响。文中根据国内外相关研究,重点分析和评述了在亚洲—太平洋季风区中4种季节内时间尺度的遥相关关系,清楚地揭示了印度夏季风、东亚夏季风和西北太平洋夏季风之间的相互作用。研究发现：（1） 在亚洲季风爆发初期,印度夏季风的爆发相对于中国长江流域梅雨的开始存在相差大约两周的超前关系,形成从印度西南部经孟加拉湾到达中国长江流域及日本南部的遥相关型,即“南支”遥相关型。（2） 在季风盛行期间,长江流域降水明显受热带西北太平洋夏季风的影响,与西北太平洋夏季风降水呈反相关关系,即当季风减弱时,长江流域夏季降水偏多。（3） 与长江流域降水相反,华北雨季（7月第4候—8月第3候）则与西北太平洋夏季风降水呈正相关关系,当西北太平洋夏季风强时,西太平洋副热带高压异常偏北偏东,副高西南侧的异常东南水汽输送在中国华北地区上空辐合,给该地区降水偏多提供了充足的水汽条件。（4） 华北夏季降水同时还与印度夏季风呈正相关关系,在夏季风盛行期间,形成由印度西北部经青藏高原到中国华北地区的西南—东北走向的遥相关型,即“北支”遥相关型。 上述4种遥相关关系,反映了亚洲夏季风季节北推过程中,印度夏季风、东亚夏季风和西北太平洋夏季风子系统之间的关联。     

GEOLOGICAL EVIDENCES OF LATE QUATERNARY ACTIVITY OF MOTUO FAULT IN EASTERN HIMALAYAN SYNTAXIS

Motuo Fault locates at the east of Namjagbarwa Peak in eastern Himalayan syntaxis.Based on the remote sensing interpretation,the previous work,and with the field investigation,this paper obtains the spatial distribution and movement characteristics of Motuo Fault in China,and geological evidences of late Quaternary activity.Two trenches in Motuo village and Dongdi village located in Yalung Zangbo Grand Canyon reveal that the Motuo Fault dislocates the late Quternary stratum and behaves as a reverse fault in Motuo village and normal fault in Dongdi village.Motuo Fault is dominated by left-lateral strike-slip associated with the faulted landforms,with different characteristics of the tilting movement in different segments.The trench at Didong village reveals the latest stratum dislocated is~2780±30 a BP according to radiocarbon dating,implying that Motuo Fault has ruptured the ground surface since late Holocene.The movement of left-lateral strike-slip of Motuo Fault is related to the northward movement process of Indian pate.     

南北半球副热带高压对赤道东太平洋海温变化的响应

本文利用1974年1月到1996年12月重分析(NOAANCEP-NCARCDAS-1)全球500hPa位势高度场资料,及同期赤道太平洋各海区SST资料,研究了南北半球副热带高压的变化特征及其对赤道东太平洋SST变化的响应。结果表明,全球副热带高压的变化及对SST的响应,在南北两个半球有很好的一致性。全球副热带高压强度的变化与超前3个月SST的正相关最为显着。对SST响应最强烈的区域主要在南北纬30°之间的低纬,低纬地区局地SST对副热带高压也有强烈的影响。从10°到30°纬度,对SST的响应分别落后于赤道2～9个月。在中、高纬大气环流的响应表现为波列特征,对暖SST及冷SST的响应波列基本相反,但对暖SST的响应更为显着。海温和副热带高压的月际持续性有明显的季节变化,副热带高压9-10月的相关障碍可能与NinoC区SST8-9月的相关障碍低点有关。     

中国东部海区地球物理调查及重磁场特征

中国海洋地质调查始于20世纪50年代,大致分为创业阶段、起步阶段、发展阶段、全面发展阶段和蓬勃发展阶段,经过多年的地质与地球物理调查,获取了大量的地质地球物理资料。该区磁场强度一般为±200 nT,局部达到±500 nT以上,呈NE、NNE向作带状分布,局部异常走向不一,类型多变。空间和布格重力异常总体走向为NE向,陆区以负异常为主,海区主要表现为正异常,空间重力异常值总体上为-45~+100 mGal,局部异常值可达+200 mGal以上;布格重力异常极小值为-140 mGal,极大值可达+440 mGal,局部地区分布高值异常圈闭。根据重、磁异常的幅值高低、形态展布和区域变化等特征,将重、磁异常各自划分为华北-渤海异常区、山东半岛-北黄海异常区等9个异常区,重磁场特征充分展示了中国东部海区东西分带、南北分块的构造格局。     

Seismic studies of the Brasília fold belt at the western border of the São Francisco Craton, Central Brazil, using receiver function, surface-wave dispersion and teleseismic tomography

The Tocantins Province in Central Brazil is composed of a series of SSW–NNE trending terranes of mainly Proterozoic ages, which stabilized in the Neoproterozoic in the final collision between the Amazon and São Francisco cratons. No previous information on crustal seismic properties was available for this region. Several broadband stations were used to study the regional patterns of crustal and upper mantle structure, extending the results of a recent E–W seismic refraction profile. Receiver functions and surface wave dispersion showed a thin crust (33–37 km) in the Neoproterozoic Magmatic Arc terrane. High average crustal Vp/Vs ratios (1.74–1.76) were consistently observed in this unit. The foreland domain of the Brasília foldbelt, on the other hand, is characterized by thicker crust (42–43 km). Low Vp/Vs ratios (1.70–1.72) were observed in the low-grade foreland fold and thrust zone of the Brasília belt adjacent to the São Francisco craton. Teleseismic P-wave tomography shows that the lithospheric upper mantle has lower velocities beneath the Magmatic Arc and Goiás Massif compared with the foreland zone of the belt and São Francisco craton. The variations in crustal thickness and upper mantle velocities observed with the broadband stations correlate well with the measurements along the seismic refraction profile. The integration of all seismic observations and gravity data indicates a strong lithospheric contrast between the Goiás Massif and the foreland domain of the Brasília belt, whereas little variation was found across the foldbelt/craton surface boundary. These results support the hypothesis that the Brasília foreland domain and the São Francisco craton were part of a larger São Francisco-Congo continental plate in the final collision with the Amazon plate.