A ∼6100 14C yr record of El Niño activity from the Galápagos Islands

Lithostratigrahic and mineralogic analyses of sediments from hypersaline Bainbridge Crater Lake, Galápagos Islands, provide evidence of past El Niño frequency and intensity. Laminated sediments indicate that at least 435 moderate to very strong El Niño events have occurred since 6100 ¹⁴C yr BP (7130 cal yr BP), and that frequency and intensity of events increased at about 3000 ¹⁴C yr BP (3100 cal yr BP). El Niño activity was present between 6100 and 4000 ¹⁴C yr BP (4600 cal yr BP) but infrequent. The Bainbridge record indicates that there has been considerable millennial-scale variability in El Niño since the mid-Holocene.     

The Byers Basin: Jurassic-Cretaceous tectonic and depositional evolution of the forearc deposits of the South Shetland Islands and its implications for the northern Antarctic Peninsula

ABSTRACT

This paper addresses the Jurassic–Cretaceous stratigraphic evolution of fore-arc deposits exposed along the west coast of the northern Antarctic Peninsula. In the South Shetland Islands, Upper Jurassic deep-marine sediments are uncomformably overlain by a Lower Cretaceous volcaniclastic sequence that crops out on Livingston, Snow and Low islands. U-Pb zircon ages are presented for the upper Anchorage Formation (153.1 ± 1.7 Ma) and the Cape Wallace granodiorite of Low Island (137.1 ± 1.7 Ma) as well as ⁴⁰Ar/³⁹Ar ages of 136–139 Ma for Low Island andesites. Data are also presented for a U-Pb age of 109.0 ± 1.4 Ma for the upper volcanic succession of Snow Island. In combination with published stratigraphy, these data provide a refined chrono- and litho-stratigraphic framework for the deposits herein referred to as the Byers Basin. Tentative correlation is explored with previously described deposits on Adelaide and Alexander islands, which could suggest further continuation of the Byers Basin towards the south. We also discuss possible correlation of the Byers Basin with the Larsen Basin, a sequence that shows the evolution of foreland to back-arc deposits more or less contemporaneously with the fore-arc to intra-arc evolution of the Byers Basin.     

Circulations east of Taiwan and in East China Sea and east of Ryukyu Islands during early summer 1985

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中国海洋的珊瑚-珊瑚礁: 南海中央区珊瑚-珊瑚礁生物多样性特征

珊瑚是地球上最古老的原住民,具有近6×108年的发育史,弱势群居、喜温和原地长成是珊瑚的基本特征。作者介绍了珊瑚-珊瑚礁的基本特征,综述了跨十年调查的研究区珍贵照片资料和相关认识,指出中国是全球主要的珊瑚-珊瑚礁国家,地位举足轻重;珊瑚-珊瑚礁作为地球生物多样性的代表,造岛、固礁、护鱼、防护岛岸流失,形成南海四大群岛280余座岛、礁、滩、沙,所构建庞大海洋生态系统是无与伦比的海洋生态资源和寸土寸金的南海海洋国土。提出划分南海珊瑚-珊瑚礁为中央区和周缘区2个分布区,阐述了南海中央区珊瑚-珊瑚礁的基本特征,系统汇集报道了间隔10年2个科考航次调查在浅水礁盘浮潜、至20 m水深浅潜-深潜和礁盘及开展岛、礁、滩、沙地质调查的发现,包括科学定名46种六放石珊瑚和6种八放软珊瑚等成果,同时,收集了西沙、中沙、东沙和南沙群岛海域的相关调查航次珊瑚照片;进一步阐述了单体环礁和复合环礁的特征及分布,并进行了初步对比,指出永乐环礁是南海唯一一个真正的切合达尔文模式的环礁,也是环礁发展到最高阶段的产物,构成现代海洋珊瑚-珊瑚礁形成演化研究最好的天然实验室。     

西沙群岛西科1井晚中新世-上新世生物礁沉积的磁性地层学初步结果

本文对西沙群岛西科1井钻孔岩心晚中新世-上新世生物礁沉积进行了详细的岩石磁学、磁性扫描与磁性地层学研究.结果显示,西科1井生物礁相沉积中的载磁矿物主要是磁铁矿.我们推测,这些磁铁矿的微小颗粒主要来自海水中含有的陆源物质,在生物生长过程中通过珊瑚体或其它寄生生物对海水的过滤与吸附作用保存在生物礁沉积中.进一步的磁性地层学研究及其与地磁极性年表的对比发现,在上新统莺歌海组、上中新统黄流组内部可获得多个年龄控制点,并对莺歌海组和黄流组的底界位置给出了初步制约.其中,莺歌海组记录了C2An.3n和C3n.4n,黄流组记录了C3An.2n至C5n.2n.虽然这一对比方案存在一定不确定性,但是在现阶段生物地层年代及其它年代学资料相对匮乏的情况下,我们认为本项研究的磁性地层学结果能为西沙群岛晚中新世以来的生物礁沉积提供更多可靠的年龄控制点,并为今后的区域地层对比提供磁性地层年代学依据.     

New K–Ar ages for calculating end-of-shield extrusion rates at West Maui volcano,Hawaiian island chain

Thirty-seven new K–Ar ages from West Maui volcano, Hawai‘i, are used to define the waning stages of shield growth and a brief episode of postshield volcanism. All but two samples from shield-stage strata have reversed polarity magnetization, so conceivably the exposed shield is not much older than the Olduvai Normal-Polarity subchron, or about 1.8 Ma. The oldest ages obtained are in the range 1.9–2.1 Ma but have large analytical error. Shield volcanism ended about 1.35 Ma, and postshield volcanism followed soon thereafter, persisting until about 1.2 Ma. Exposed shield-stage strata were emplaced at a rate of about 0.001 km³ per year, a rate smaller than historic Hawaiian magmatic rates by a factor of 100. Stratigraphic accumulation rates are similar to those measured previously at Wai‘anae volcano (O‘ahu) or the upper part of the Mauna Kea shield sequence (Hilo drill core, Hawai‘i). These rates diminish sharply during the final 0.3–0.5 m.y. of the shield stage. Hawaiian shield volcanoes begin waning well before their last 0.5 m.y. of life, then end quickly, geologically speaking, if West Maui is representative.     

南沙群岛西南陆架区条尾鲱鲤资源状况研究

根据2003年南沙群岛西南陆架区春秋两季调查资料,分析南沙群岛西南陆架区条尾鲱鲤的资源现状.结果表明,渔获率有明显的季节变动,秋季（1.76kg/h）高于春季（0.08kg/h）,春季密集分布于91～100m水深,秋季密集分布于71～80m水深.其群体组成也有季节差异,春季的平均体长、平均体重大于秋季,春季优势体长组为101～110mm,秋季优势体长组为91～100mm,渔获中不足1龄鱼占多数,其资源密度及现存资源量分别为12.02kg/km^2 和880.82t,现存资源量只有原始资源量的54.92%,该鱼种资源已接近衰退状态.文中并讨论合理利用该资源的措施.     

南麂列岛潮间带环境本底调查

本文系根据１９９２年８月和１９９３年２月（夏、冬两季）对南麂列岛潮间带的环境本底调查以及对水质、底质、生物样监测结果的资料整理而成。调查结果表明，潮间带水质、底质除个别断面外，均处于良好状态。生物体重金属残留量全部低于全国海岸带调查时统一的标准，生态环境条件较好。     

南沙海域第三纪生物礁层序构成和演化

南沙海域第三纪盆地生物礁油气藏勘探具有巨大的潜力。作者运用层序地层学原理精细解剖不同体系域的生物礁内部构成,建立了高精度的生物礁礁层序地层格架,并逐层进行回剥分析,表明第三系充填沉积为四幕伸展裂陷过程,进而揭示盆地生物礁层序的动态发育过程及不同时期南沙海域含油气盆地的发育状态。     

格列菲列岛的地质地球物理研究

本文是中、韩国际合作项目“黄海地质地球物理场特征研究”的一部分 .具体研究了格列菲列岛的基础地质问题及地球物理场特征 .格列菲列岛是由三个小岛组成的位于黄海中部的一组群岛 ,位于朝鲜半岛布格重力异常正值区 ,莫霍面埋深在 2 9km左右 .三个岛屿主要由安山集块岩构成 .安山集块岩是由大小不同的火成岩碎块和熔岩混合而成 .火成岩的碎块成分主要为石英岩、片岩、片麻岩、玄武岩、安山岩和流纹岩 .主要节理方向为NE10°～NE2 0°,倾角近乎垂直 ;另一组节理为NW70°～NW80° ,倾角也近垂直 .本研究为我们了解这个地区的基础地质情况 ,岩石物性和随后进行的黄海海域典型剖面的地球物理物性反演工作以及地质模型的建立 ,打下重要基础 .