Re-Os and Nd isotopes of black shales at the bottom of the Lower Cambrian from the northern Tarim Platform and their comparison with those from the Yangtze Platform

This paper reports Re-Os and Nd isotopes of black shales at the bottom of Lower Cambrian from the northern Tarim Basin and traces source materials of the black shales through isotopes. The average Re/Os, 187Re/188Os, and 187Os/188Os ratios of the black shales at the bottom of Lower Cambrian from the Tarim Basin are 7.18, 5.6438, and 1.9616, respectively. These isotopic ratios suggest the crustal sources of the black shales. The εNd(0) value is -13.17, the εNd(540 Ma) value is -7.32 and the Nd model ages are 1.535 Ga. These parameters in the black shales are quite consistent with those from the basement rocks. Based on the Re-Os and Nd isotopic characteristics of the black shales, we conclude that the continental crust mainly composed of basement rocks is the source material of the black shales. Through comparison of these isotopic parameters with those from the Yangtze Platform, it is clear that the Re-Os isotopic characteristics in the black shales from the Tarim and Yangtze platforms are quite different, which maybe indicates the differences in depositional settings between two platforms. These Re-Os isotopic data provide us with constraints to analyze the genetic relation between the two platforms.     

青藏高原东南部夏季深对流加热研究

文章利用1948～1999年NCEP／NCAR全球深对流加热率再分析资料和1951～2001年全国160站月平均降水量研究了中国区域夏季深对流加热分布状况，青藏高原东南部夏季深对流加热较强，是潜热释放较多和深对流活动旺盛区域；青藏高原东南部深对流加热率与长江中下游地区降水的相关分析也表明，夏季青藏高原东南部深对流活动对长江中下游地区夏季降水偏多有重要影响，可以为长江中下游地区夏季降水提供水分和能量。     

春季青藏高原感热异常对长江中下游夏季降水影响的初步研究

探讨了春季青藏高原感热的分布特征，对高原地区地-气温差与感热的合成分析表明，长江中下游地区旱涝年春季高原近地层热力结构分布呈显著差异；统计分析与数值模拟试验也证实了春季高原下垫面感热南北非均匀异常分布，对长江中下游地区夏季降水存在着显著影响，即春季高原下垫面感热非均匀异常分布特征可能是长江中下游地区夏季旱涝的“强信号”之一。     

梅雨期区域边界水汽输送模型及其数值试验

通过诊断分析,提出梅雨期中国区域边界水汽输送特征模型,即高原中部区域西边界与低纬南海、西太平洋南边界为水汽输送流入主体,西太平洋东边界为水汽“流出”主体。数值模拟研究表明:1998年洪涝特大暴雨过程6月与7月份水汽输送通道特征存在差异,6月中下旬长江流域暴雨过程以西边界与南边界水汽流共同输送为主体,其中南海西太平洋区域水汽输送显著,7月份水汽输送过程以高原中部区域西边界“水汽流”为主体。因此,高原中部区域西边界与中国区域南边界的水汽输送对长江流域特大暴雨的形成均具有重要的作用。区域边界水汽流的时空特征分析及其理论模型将为长江流域暴雨预报提供科学依据。     

华南上扬子区早-中奥陶世疑源类古环境意义

对上扬子区 7个剖面早—中奥陶世疑源类研究表明 ,这些疑源类组合在分异度及属种组成上呈现有规律的变化 ,这种变化是上扬子区古环境变化的反映。在上扬子区西部 ,近岸碎屑岩相沉积的滇东红石崖组所产疑源类组合分异度低 ,为个体较小、壳饰较简单的分子 ;上扬子区中部 ,以黔北湄潭组为代表的浅海相碎屑岩和灰岩沉积中 ,疑源类分异度较高 ,并出现许多个体较大、壳饰较复杂的分子 ;而在上扬子区东部鄂西宜昌大湾组陆棚相灰岩与泥岩中 ,疑源类分异度继续增高 ,其中个体大、具粗大、长而复杂突起的分子占优势。     

长江口动量系数分布特征研究

基于长江口1996年3月和9月共23个测点实测水流资料,计算了动量系数的时空变化,并应用线性回归法,计算了特征时间段内的平均动量系数,获得了长江口动量系数时空分布的基本特征:时间上,涨潮大于落潮,洪季大于枯季,而大、中、小潮则依次递增;空间上,自口外向口内,北支呈逐渐增大,而南支呈先增大后减小、口门附近最大的基本特征.由动量系数分析了潮流的摩阻特性,为数值模拟合理选取曼宁系数提供参考.     

上扬子区震旦纪南沱冰期后碳酸盐岩帽沉积地球化学特征

通过对贵州铜仁和湖南大庸两地南沱冰碛岩层之上白云岩层的岩石、结构和构造、地球化学等综合研究，认为该白云岩层具有快速沉积所形成的沉积结构和构造，碳同位素特征可与全球同期沉积的碳酸盐岩帽（Cap Carbonate)进行对比；特别是在白云岩中发现有机碳同位素低的沥青结核体，支持了冰期后碳酸盐岩快速沉积是由于海底固态CH4发生脱气作用，导致碳酸盐岩帽快速沉积的观点。     

下扬子区海相油气成藏特征

下扬子区从晚震旦世开始至中三叠世沉积了三套巨厚的海相烃源岩系，即上震旦统一上奥陶统、石炭系一二叠系、下三叠统海相烃源岩。三套烃源岩热演化特点不同，下古生界烃源岩经历了加里东、印支——燕山期构造阶段的热演化，已达过成熟干气阶段；上古生界烃源岩基本处于生油阶段晚期；大部分三叠系烃源岩处于成熟生油阶段，少数处于未成熟阶段。全区海相油气储盖条件发育，配置有利，具有良好的找油气前景。     

长江源雀莫错基性-超基性岩带的基本特征及构造意义

雀莫错基性-超基性岩带为单辉橄榄岩-橄榄辉长岩-辉长岩-辉绿岩组合,橄榄辉长岩单颗粒锆石年龄为31～44Ma,属喜马拉雅期。岩石化学研究表明,镁铁质-超镁铁质岩具有SiO2,K2O,Na2O,TiO2,P2O5含量低的特征,且Na2O>K2O,而贫大离子亲石元素Sr和Ba,以及高场强元素Zr,Nb和不相容元素Rb,具大洋拉斑玄武岩特征。其形成是地幔物质上涌,产生具有大洋性质的拉斑玄武质系列岩浆,并沿贡日-温泉兵站大断裂侵位。     

Sedimentary and Geochemical Characteristics of Sinian Cap Carbonates in the Upper Yangtze Region

A global-scale glaciation occurred at about 600 Ma ago. As a result, the Earth became the “Snowball Earth“. The glaciation came to the end abruptly when atmospheric carbon dioxide increased to such an extent as to be about 350 times the modem level because of subaerial volcanic degassing. The rapid termination of glaciation would have led to warming of the Snowball Earth and extreme greenhouse conditions would have been created. The transfer of atmospheric carbon dioxide to oceans would give rise to the rapid precipitation of calcium carbonate in warm surface seawaters, thus forming the cap carbonate rocks as observed worldwide today. Regionally persisting, thin layers of carbonate rocks directly and ubiquitously overlie Proterozoic glacial deposits almost on every continent, and are commonly referred to as cap carbonates. Their unusual litho- fabrics, stratigraphically abrupt basal and upper-level contacts and strongly negative carbonate isotopic signatures ( δ ^13Cearb. values range from -7.0‰ —0‰) suggest a chemical oceanographic origin, the details of which remain unknown. It is proposed that these enigmatic deposits are related to the destabilization of gaseous hydrate in terrestrial permafrost following rapid postglacial warming and flooding of widely exposed continental shelves and internal basins. The authors carried out studies on the geochemistry, sedimentology and palacontology of the Sinian cap carbonates in Guizhou and Hunan provinces, including the occurrence of cap carbonates of unusual fabrics, strongly negative carbon isotopic signatures, and a lot of bitumen nodules.From the results it is suggested that the cap carbonates were formed from solid methane seepage, and it is in agreement with Kennedy‘‘ s viewpoint (2001) that the cap carbonates resulted from the rapid precipitation of calcium carbonate in response to solid methane seepage.