Composition and Provenance of Sandstones and Siltstones in Paleogene, Huimin Depression, Bohai Bay Basin, Eastern China

This study was conducted to distinguish the compositions and provenance of sandstones and siltstones in the Ek1-Es3 members of Huimin (惠民) depression. The samples have been analyzed for petrographic, major element and selected trace element compositions (including REE). The results show that the sandstones from the first member of Kongdian (孔店) Formation (Ek1) have higher quartz compositions than those from the fourth member (Es4) and the third member (Es3) of Shahejie (沙河街) Formation. The alkali feldspar/plagioclase ratio in the A-CN-K diagrams decreases in the order Ek1>Es4>Es3, which suggests that the Ek1 member had a more alkali feldspar-rich granitoid source and more intense weathering of the source than the Es4 and Es3 members. The mineral distributions in the A-CN-K diagrams also indicate that the sandstones and slltstones in the three members underwent K-metasomatism. Extrapolation of the sandstones and siltstones back to the plaginclase-alkali feldspar line in the A-CN-K diagram suggests a high average plagioclase to alkali feldspar ratio in the provenance (tonalite to granite). In addition, the chemical index of weathering (CIW) and chemical index of alteration (CIA) parameters of the sandstones and siltstones suggest that the weathering of the first cycle material was intense, and the CIW decreases in the order Ek1>Es4>Es3. Trace element ratios suggest all the sedimentary rocks were mostly derived from granitoids. Elemental ratio plots (e.g., Th/Sc vs. Eu/Eu*) of sandstones and siltstones suggest a mix of a granodiorite-tonalite source as a source of the sandstones and siltstones. The sandstones and siltstones of Es3 and Es4 members also contain higher Eu/Eu* and lower Th/Sc ratios than the sandstones and siltstones of Ek1 member. As is consistent with the petrography, it suggests that the sandstones and siltstones of Es3 and Es4 members are derived from a source with less granite and more granodiorite-tonalite than the sandstones and siltstones of Ek1 member.     

良渚遗址物质的Sr-Nd同位素特征、物源及其对古文化消亡的指示意义

良渚文化作为新石器时代晚期的重要文化之一,与中华文明的起源有着重要联系。位于杭州瓶窑镇的良渚古城遗址,则代表了良渚文化发展的巅峰。我们采集了良渚遗址剖面的文化层、上覆黄粉土的土壤样品以及遗址周边地区的河流和钱塘江的沉积物样品,测试分析了它们的Sr-Nd同位素组成。通过对比黄粉土和文化层的同位素组成变化,结合遗址周边环境和前人对长江沉积物、东海沉积物的研究,我们推测,良渚黄粉土物质来源可能是东海、长江沉积物和钱塘江沉积物的混合,良渚文化可能并非消亡于来自周边山体的山洪,而是与海侵或者长江下游洪水泛滥有关。     

华北晚中生代构造演化过程——根据太行山北部盆地沉积记录

太行山北部地区处于燕山山脉和太行山山脉的交汇处,其侏罗纪—白垩纪叠加盆地发育过程记录了东西向盆地向北东向盆地转化过程,对刻画华北晚中生代陆内变形过程及其动力学背景具有重要意义。本文以太行山北部草沟堡盆地和招柏盆地为例,在盆地基本构造格架分析的基础上,通过详细的沉积物物源分析、盆地原型再造等沉积学方法,结合岩浆岩同位素年代学数据,提出太行山北部晚中生代构造演化过程,主要经历四个发展演化阶段,包括中侏罗世晚期近南北向构造挤压与挠曲盆地发育、晚侏罗世近南北向弱伸展作用与壳源火山喷发、晚侏罗世末期—早白垩世早期北西—南东向构造挤压与前陆盆地形成、早白垩世北西—南东向伸展作用与幔源火山作用。构造体制转变本质上是动力学体系的转变,在中晚侏罗世东亚大陆多向汇聚体系之下,太行山北部经历的多期构造叠加和盆地叠置过程折射了蒙古—鄂霍茨克构造体系向滨太平洋构造体系的转化过程。     

黔南地区早石炭世黑色岩系稀土元素地球化学特征及沉积-构造环境分析c

为了深入探讨黔南地区早石炭世黑色岩系沉积-构造环境,笔者对页岩气钻孔CY1井打屋坝组黑色岩系进行了详细采样测试,并重点分析了页岩稀土元素地球化学特征。分析结果表明,该区早石炭世页岩稀土元素总量(ΣREE)为(213.08~308.1)×10^-6,平均值为251.43×10^-6,大于北美页岩的平均值(173. 21×10^-6);w(ΣLREE)/w(ΣHREE)及w(Ce)_N/w(Yb)_N等地球化学参数表明,轻、重稀土元素分异明显;REE分布模式呈平坦状,表现出轻稀土富集、重稀土元素亏损;δEu值为0.53~0.67 < 1,显示中等程度的负Eu异常,Ce异常表现不明显。根据δCe和Ce异常值的变化,反映研究区早石炭世为缺氧还原环境。根据稀土元素组合特征、δEu值的变化及w(La)_N/w(Yb)_N-ΣREE的图解特征,结合区域地质背景,认为黔南地区打屋坝组黑色页岩的物源来自黔中隆起和雪峰山隆起,母岩为沉积岩和花岗岩的混合,沉积区构造环境为被动大陆边缘构造背景。     

中扬子地区江汉盆地古新统沙市组物源——来自碎屑锆石U-Pb年代学及地球化学证据

文章利用LA_ICP_MS分析技术,对江汉盆地西南缘古新统沙市组碎屑岩进行了碎屑锆石的U_Pb年代学研究,获得该区沙市组时期碎屑物源的重要信息。97组协和年龄数据产生了12个年龄峰值,分别为2500 Ma、1870 Ma、995 Ma、850 Ma、708~775 Ma、603~640 Ma、505~553 Ma、408~458 Ma、356 Ma、300 Ma、235 Ma和172 Ma。锆石的年龄峰值主要集中于古元古代、新元古代和早古生代,这些年龄峰值与黄陵隆起和江南造山带中的锆石年龄相同。早中生代年龄峰值也较明显,该年龄通常和大别山的高压和超高压变质岩有关,江南造山带也发育印支期花岗岩。结合该时期岩相古地理特征,认为沙市组主要物源来自黄陵隆起以及扬子板块与大别造山带之间的碰撞带,而南部江南造山带的贡献是次要的。黄陵隆起花岗岩含钾量高,其风化可以给盆地带来丰富的成钾物源。     

山东诸城晚白垩世王氏群恐龙化石层碎屑锆石定年和物源示踪

山东东部诸城晚白垩世王氏群大面积、高密度集群埋藏的恐龙化石是近年研究的热点,但其沉积物源与精确沉积时限目前尚不明确。本文通过对山东诸城王氏群恐龙化石层中6个砂岩样品的碎屑锆石U-Pb定年表明,样品090414-24-D中最年轻的单颗粒锆石年龄(YSG)为77.3 Ma,应代表王氏群恐龙化石层的最大沉积时限(下限),结合前人对王氏群红土崖组的年代学研究表明,其沉积时限应老于73.5 Ma(上限),也说明赋存恐龙化石层的王氏群上部红土崖组为Campanian期沉积;碎屑锆石定年揭示物源的锆石年龄组成分布在100～130 Ma之间,6个样品的年龄主峰值多在110 Ma或120 Ma左右,与下伏的早白垩世青山群火山岩年龄主峰较为吻合。王氏群恐龙化石层砾岩的砾石成分和古水流研究显示,其中3组砾石统计表明砾岩层砾石成分主要由火山岩或火山碎屑岩组成,3组古水流数据表明,诸城地区王氏群红土崖组砾岩层的古流向以南和南东方向为主,尚有1组显示古流向为向北,表明王氏群物源主要来自盆地北侧莱阳和北西侧沂沭断裂带的青山群火山岩,其次为盆地南缘。本研究为诸城王氏群化石层沉积时限的限定和沉积物源的判断,以及胶莱盆地王氏群时期古地理格局的恢复等提供了重要的依据。     

杭州湾潮滩沉积物黏土矿物空间差异与物源指示

通过对杭州湾潮滩沉积物中主要黏土矿物成分及组合类型的研究,分析了杭州湾潮滩沉积物黏土矿物的空间分布特征。借助聚类分析等手段,同时结合杭州湾水动力特征,探讨了研究区黏土矿物的来源和成因。研究结果表明,杭州湾潮滩表层沉积物主要为黏土质粉砂,其余为砂质粉砂。本区沉积物黏土矿物成分复杂,主要为伊利石,其次是高岭石和绿泥石;还有少量蒙皂石和蛭石及1.4 nm过渡矿物。根据其相对含量可分为3种组合类型:Ⅰ型为伊利石-高岭石-绿泥石-蛭石类-蒙皂石型,Ⅱ型为伊利石-绿泥石-高岭石-蒙皂石-蛭石类型,Ⅲ型为伊利石-高岭石-绿泥石-蒙皂石-蛭石类型。在空间上,北岸的蒙皂石和绿泥石平均含量高于南岸,而伊利石、高岭石和蛭石(含1.4 nm过渡矿物)平均含量则低于南岸。高潮滩和中潮滩黏土矿物对比,除了蒙皂石含量高潮滩大于中潮滩外,其他矿物含量均无明显规律。表层沉积物黏土矿物的分布特征与水动力条件和物质来源密切相关,杭州湾北岸乍浦以东潮滩受潮流和长江沿岸流影响明显,沉积物主要为长江和东海源的;南岸由于曹娥江和甬江两条河流的注入,流域物质所占比例明显比北岸高。柱状岩芯样品中各黏土矿物含量自下而上的变化则反映了物源区风化强度的波动特征。     

长江镇江段第四纪沉积物重矿物特征及其指示意义

选取长江下游世业洲的第四纪钻孔资料,研究了重矿物的垂向分布特征,以此探讨长江镇江段第四纪以来的沉积类型以及物源演变。结果显示,该区自中更新世开始接受沉积,依次形成河床相、边滩相、漫滩相、河口三角洲相。重矿物自下而上分为2个组合段,分别对应更新世和全新世。更新世地层以角闪石、蓝晶石、石榴石等作为特征矿物,且不稳定矿物含量高于稳定矿物,表明沉积物以近源居多;全新世特征矿物为辉石和钛铁矿,稳定矿物含量高于不稳定矿物,重矿物种类与现代长江中上游类似,表明此阶段沉积物以远源物质为主。     

鸭绿江盆地鹰嘴砬子组和馒头组的沉积时限及物源:碎屑锆石U-Pb年代学证据

鸭绿江盆地中生界鹰嘴砬子组与古生界馒头组河口段碎屑锆石LA-ICP-MS U-Pb的年代学研究结果表明,采自鹰嘴砬子组的凝灰质粉砂岩(样品HD1-3),其碎屑锆石年龄分布区间为3 259~123Ma。主要年龄峰为2 500 Ma(33%)、1 807 Ma(11%)、282 Ma(11%)、235 Ma(5%)、150 Ma(7%)和126 Ma(5%),最年轻的一组锆石加权平均年龄(126 Ma)限定地层的沉积下限为早白垩世,其沉积物源来自于盆地内部及其邻区古元古代、古生代和中生代岩浆作用的产物。采自馒头组河口段的岩屑长石砂岩(样品SD2-1),其碎屑锆石年龄分布区间为2 350~503 Ma。形成的年龄峰值主要为1 553 Ma(13%)、1 396 Ma(13%)、1 086 Ma(17%)和787 Ma(30%)。最小的锆石年龄(503 Ma)限定地层沉积下限为晚寒武世,其沉积物源主要来自鸭绿江盆地内部及其邻区的中元古代和新元古代岩浆作用的产物。     

Geochemistry of Harappan potteries from Kalibangan and sediments in the Ghaggar River: Clues for a dying river

The ephemeral Ghaggar-Hakra River of northwestern India has always been considered to be the remnant of an ancient perennial glacier-fed river(Vedic Saraswati). The exact reason and timing of major hydrological change of this river remains speculative. The river's purported association with the zenith of the Harappan civilisation remains a conjecture because the timings of its fluvial past are still being debated. In this study we have made an attempt to resolve this issue using geochemical provenance of sediments from some dated horizons in the Ghaggar flood plain and that of the material used in the potteries from the Mature Harappan period(4600-3900 yr BP) at Kalibangan. Sampled sedimentary horizons were dated by radiocarbon and optically stimulated luminescence(OSL) methods. Results of our study from the Ghaggar alluvium indicate that the river did have glacial sources during the early Holocene. However, the data from the potteries suggest that during the Mature Harappan period, the sediments in the Ghaggar as used by the potters did not have a higher Himalayan provenance and hence, were not derived from glaciated Himalayas.These findings imply that during the time of the Mature Harappans the Ghaggar had already become a foothill-fed river.