Late Holocene record of environmental changes,cyclones and tsunamis in a coastal lake,Mangaia, Cook Islands

A 4.3 m‐long peat sequence from the shore of Lake Tiriara, Mangaia, Cook Islands, was analyzed using an ITRAX core scanner equipped with a magnetic susceptibility meter. Variations in the elemental profiles, providing insights into long‐ and short‐term environmental changes over the last 3500 years, are supported by grain size data and diatom assemblages. The scattering ratio (Mo Inc/Mo Coh) was evaluated and found to represent a good proxy for organic matter in peat. X‐Ray Fluorescence (XRF) data were processed by principal component analysis that confirmed the distinction of biogenic and detrital phases, organic matter and elements of marine origin. The record preserved in the peat sequence includes a peatland infilling stage followed by alternating drier and wetter periods. A notable steady increase in clay associated with high counts of detrital elements from 2000–1700 cal yr BP is attributed to increased erosion, which is most probably linked with human colonization and/or more intense chemical weathering linked with a wetter climate. Freshwater gastropods (Melanoides sp.), which were possibly introduced by humans, or are native, occupied the wetland during a period of lower water level about 1000–1100 cal yr BP. Short‐term changes in the elemental profiles are often linked with slight coarsening of the inorganic fraction that is, however, only revealed after grain size analysis. Peaks in marine indicators (Br, Cl, S, and/or Ca) associated with marine‐dominated diatom assemblages most probably represent marine incursions through the underground tunnel in the makatea, a fossilized, uplifted coral limestone rim. While none of the marine event units present characteristics typical of cyclone or tsunami deposits, the concurrent or absent peak of detrital elements (Fe, Si, Rb, Ti, K) attributed to increased erosion of the volcanic cone associated with a cyclone is used to distinguish both types of events, as also suggested by principal component analysis.     

渤海湾盆地西部保定凹陷构造-地层层序与盆地演化

保定凹陷位于渤海湾盆地内冀中坳陷的西部, 西侧以太行山山前断层为界与太行山隆起相隔.凹陷内构造-地层层序的划分, 对研究其构造演化和油气勘探有着重要的意义, 对探讨太行山山前断层的发育特征也有一定的帮助.按照井、震结合的思路, 利用最新的钻井和地震资料, 并结合周缘的地质填图成果, 建立了保定凹陷的地层系统; 根据区域性不整合面的发育特征, 对保定凹陷构造-地层层序进行了划分; 利用平衡剖面技术, 分析了保定凹陷的构造演化.研究发现, 保定凹陷内发育了古近系孔店组底部和新近系馆陶组底部两个区域性角度不整合面, 据此将保定凹陷在纵向上划分为3个构造层: 基底构造层、断陷期构造层和拗陷期构造层.保定凹陷的形成演化经历了基底形成、古近纪断陷、渐新世末反转和新近纪-第四纪拗陷4个阶段, 其中, 古近纪断陷期又可以分为强烈断陷期、持续断陷期和断陷末期.     

山西胡家峪南和沟铜矿床深部矿体定位预测的原生晕指示

系统研究了山西胡家峪南和沟铜矿床深部矿体的原生晕特征。结果表明,矿区深部340~240 m中段矿体原生晕的轴向分带序列为(Mn-W-Sn-Ti-Ag)-(Ni-Co-Mo-Pb-Sb-Zn)-(Hg-As-B-Bi-Cu-Au-V),呈现"反分带"特征;地球化学参数a曲线在340~240 m中段的变化趋势为"降→升";原生晕叠加结构显示在3号矿体尾部(290~240 m中段)出现前、尾晕共存。这些现象都反映在240 m中段以下可能存在隐伏矿体。同时,在侧向上,340~240 m中段主成矿元素Cu质量分数由NE向SW方向显著增加,且在240 m中段出现明显Cu异常,推测隐伏矿体分布在已知矿体的SW侧。综合原生晕特征可以推断,在240 m中段92穿脉,3号矿体SW侧应有隐伏的新矿体发育。依据上述认识圈定出了深部矿体的预测靶区。     

Community diversity of bacteria in digestive tract of mud snail (Bullacta exarata Philippi) and its rearing shoal

ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅｍｕｄｓｎａｉｌＢｕｌｌａｃｔａｅｘａｒａｔａＰｈｉｌｉｐｐｉｉｓｄｅｌｉｃｉｏｕｓａｎｄｎｕｔｒｉｔｉｏｕｓ ,ａｎｄｗｅｌｌ ａｃｃｅｐｔｅｄｂｙｐｅｏｐｌｅ,ｅｓｐｅｃｉａｌｌｙｉｎＺｈｅｊｉａｎｇＰｒｏｖｉｎｃｅ ,Ｃｈｉｎａ ,ｋｎｏｗｎａｓａｎｅｃｏｎｏｍｉｃａｌｌｙｉｍｐｏｒｔａｎｔｍａｒｉｃｕｌ ｔｕｒａｌｓｈｅｌｌｆｉｓｈｓｐｅｃｉｅｓ .Ｉｔｈａｓａｔｔｒａｃｔｅｄｃｏｎｓｉｄｅｒａｂｌｅｍａｒｉｃｕｌｔｕｒｅｉｎｔｅｒｅｓｔａｌｏｎｇｔｈｅｃｏａｓｔｏｆ…     

Pb and Nd isotopic composition of the Jigongshan granite: constraints on crustal structure of Tongbaishan in the middle part of the Qinling–Tongbai–Dabie orogenic belt, Central China

The Qinling–Dabie–Sulu belt is the world's largest ultrahigh pressure (UHP) metamorphic belt. The UHP metamorphism is well dated at 220–245 Ma in the Dabie–Sulu belt but at 507 Ma in the Qinling belt. The Tongbaishan is located between the Qinling orogenic belt to the west and the Dabie–Sulu UHP metamorphic belt to the east. It is the key area for studying the tectonic relation between the Qinling and Dabie–Sulu belts and the diachronous UHP metamorphism. The Jigongshan granitic pluton (t=128 Ma) with a total area of 1200 km², composed of monzogranite, was mostly emplaced into the Tongbai complex, an exposed basement in the Tongbaishan. The Jigongshan granites have SiO₂=69.85–72.35%, K₂O/Na₂O=0.87–1.13, A/CNK=0.91–1.03, Rb/Sr=0.14–0.25 and Th/U=3.3–12. Their REE compositions show strongly fractionated patterns with (La/Yb)_N=14–58 and Eu*/Eu=0.79–1.05. The granites are characterized by low radiogenic Pb isotopic composition. The present-day whole-rock Pb isotopic ratios are ²⁰⁶Pb/²⁰⁴Pb=16.707–17.055, ²⁰⁷Pb/²⁰⁴Pb=15.239–15.326 and ²⁰⁸Pb/²⁰⁴Pb=37.587–37.853, which are similar to that of the continental lower crust. Their _Nd(t) values range from −16 to −20, and depleted-mantle Nd model ages (T_DM) from 1.8 to 2.2 Ga. The above evidence indicates that the magma of the Jigongshan granites was derived from the partial melting of the continental crust. The Pb and Nd isotopic compositions of the Jigongshan granites resemble those of the Dabie core complex in the Dabieshan but are distinct from those of the Tongbai complex in the Tongbaishan. Thus, the Dabie core complex would be the magma source of the Jigongshan granites. The result implies that the Dabie core complex is extended to the west and constitutes the unexposed basement underlaying the Tongbai complex in the Tongbaishan.     

数字填图技术在区域地质调查中应用实例--以民和试点图幅为例

文章根据2002年中国地调局在青海省民和幅进行区域地质调查数字填图技术试点,结合实践,详细介绍了数字填图技术在区域地质调查中从野外到至内以最终阶段成果的PRB过程,证明了区域地质调查填图数字化是切实可行的。     

近40年长株潭生态景观的人为干扰过程分析

以长株潭主城区为研究对象,综合考虑卫星遥感数据、土地利用数据以及地理国情普查数据特点建立长株潭用地类型分类系统,应用土地利用转移矩阵和景观人为干扰测度模型获取主城区用地转移矩阵和人为干扰度指数时空分布,探讨长株潭主城区生态景观与人为干扰之间的关系。结果表明:从土地利用变化角度,1978—2015年长株潭主城区耕地、园林地、建设用地发生了显著变化,耕地总体上呈持续下降趋势,从3 544.67 km~2下降到2 571.18 km~2,园林地呈现先下降后升高的变化趋势,总体下降177.89 km~2;建设用地呈持续上升趋势,从80.56 km~2增加到1 252.85 km~2;在1994—2000年和2010—2015年长株潭主城区土地利用变化两个典型阶段,建设用地的增加主要通过占用耕地和园林地的方式实现。景观人为干扰指数时空分析表明:1978—2015年长株潭主城区景观人为干扰指数高值区主要集中在中心城市和其周边地区,在人类活动的影响下,中心城区以耕地、园林地向建设用地转移为主,周边地区主要以耕地和园林地的相互转移为主;随着城市化进程持续加快,人类活动对主城区生态景观的影响总体呈加强趋势,且受人类活动干扰主要集中在中心城区。     

拉脊山-化隆变质核杂岩构造及其隆升机制探讨

中祁连拉脊山、化隆地区的变质核杂岩是由韧性变形的太古宙、元古宙化隆群变质岩系组成核; 由脆-韧性变形和经受了低压变质的中、上寒武统和岩体组成中间层; 由脆性变形和未变质的下白垩统组成盖层.变质核杂岩的组成与结构显示了对称伸展和隆升的特征.23~ 32Ma是快速隆升的时期.主剥离断层剪切位移量约25~ 27km, 并根据矿物对计算, 变质核杂岩的伸展变质温度约625~ 630℃, 变质深度约20km, 变质压力约为0.63GPa, 属偏低压型区域热流变质作用.从青藏高原热壳、热幔、厚壳的演化历史及构造隆升活动来看, 认为拉脊山、化隆变质核杂岩是地幔热隆引起地壳伸展的典型实例, 是研究青藏高原岩石圈结构和高原隆升的重要窗口.      

青海都兰县三色沟铅锌矿区变质岩原岩恢复

对研究区变质岩的岩石学、地球化学研究表明,金水口群中-深变质岩原岩的为一套以火山岩为主的火山-沉积组合。火山岩主要为晶屑凝灰岩、岩屑凝灰岩、角砾凝灰岩、凝灰质砂岩等,属钙碱性岩系。沉积岩为泥灰岩。火山岩构造环境应属活动大陆边缘。     

鮸状黄姑鱼胚胎和仔鱼发育的实验生态

本实验研究了温度、盐度、 ｐＨ对鮸状黄姑鱼胚胎发育和前期仔鱼存活的影响。结果表明,鮸状黄姑鱼受精卵孵化的温度范围为１５～３０℃,最适孵化温度为２５～３０℃;孵化盐度范围为１５～４５,最适孵化公度范围为１５～２５;ｐＨ值在５．００～８．９９范围内,受精卵孵化率没有显著的差异。鮸状黄姑鱼前期仔鱼存活的适合温度为１５～３０℃,最适温度为２５℃;适合盐度为１５～３５;适合ｐＨ值为５．９９～１０．０１。