武夷山南段前寒武纪浅变质岩系的划分与时代     

张利民 《地层学杂志》1996,20(1):16-22

武夷山南段前寒武纪地层分布较广。从下至上分为楼子坝群、丁屋岭组、南岩组和黄连组。过去因缺乏可靠的微古植物化石证据和同位素地质年龄资料,对其时代归属分歧颇大。为此,作者对该区的前寒武系进行了系统的微古植物取样、分析,参考最近的Nd同位素模式年龄资料,认为:楼子坝群为前震旦系,大致相当于蓟县系与青白口系;丁屋岭组为下震旦统;南岩组和黄连组为上震旦统;江西东南部的"下寒武统炭质板岩"应归入老虎塘组,属上震旦统。  相似文献   

Paleohydrology and paleochemistry of Lake Manitoba,Canada: the isotope and ostracode records   总被引：1，自引：1，他引：0  

William M. Last  James T. Teller  Richard M. Forester 《Journal of Paleolimnology》1994,12(3):269-282

Lake Manitoba, the largest lake in the Prairie region of North America, contains a fine-grained sequence of late Pleistocene and Holocene sediment that documents a complex postglacial history. This record indicates that differential isostatic rebound and changing climate have interacted with varying drainage basin size and hydrologic budget to create significant variations in lake level and limnological conditions. During the initial depositional period in the basin, the Lake Agassiz phase (12–9 ka), ¹⁸O of ostracodes ranged from –16 to –5 (PDB), implying the lake was variously dominated by cold, dilute glacial meltwater and warm to cold, slightly saline water.Candona subtriangulata, which prefers cold, dilute water, dominates the most negative ¹⁸O intervals, when the basin was part of proglacial Lake Agassiz. At times during this early phase, the ¹⁸O of the lake abruptly shifted to higher values; euryhaline taxa such asC. rawsoni orLimnocythere ceriotuberosa, and halobiont taxa such asL. staplini orL. sappaensis are dominant in these intervals. This positive covariance of isotope and ostracode records implies that the lake level episodically fell, isolating the Lake Manitoba basin from the main glacial lake.¹⁸O values from inorganic endogenic Mg-calcite in the post-Agassiz phase of Lake Manitoba trend from –4 at 8 ka to –11 at 4.5 ka. We interpret that this trend indicates a gradually increasing influence of isotopically low (–20 SMOW) Paleozoic groundwater inflow, although periods of increased evaporation during this time may account for zones of less negative isotopic values. The ¹⁸O of this inorganic calcite abruptly shifts to higher values (–6) after 4.5 ka due to the combined effects of increased evaporative enrichment in a closed basin lake and the increased contribution of isotopically high surface water inflow on the hydrologic budget. After 2 ka, the ¹⁸O of the Mg-calcite fluctuates between –13 and –7, implying short-term variability in the lake's hydrologic budget, with values indicating the lake varied from outflow-dominated to evaporation-dominated. The ¹³C values of Mg-calcite remain nearly constant from 8 to 4.5 ka and then trend to higher values upward in the section. This pattern suggests primary productivity in the lake was initially constant but gradually increased after 4.5 ka.This is the sixth in a series of papers published in this issue on the paleolimnology of arid regions. These papers were presented at the Sixth International Palaeolimnology Symposium held 19–21 April, 1993 at the Australian National University, Canberra, Australia. Dr A. R. Chivas served as guest editor for these papers.  相似文献   

新疆第四纪盐类矿产的形成和控制因素——兼论“高山深盆”成盐模式   总被引：1，自引：0，他引：1  

王得林 《新疆地质》1993,(1)

根据袁见齐教授“高山深盆”成盐模式,探讨新疆天山对第四纪盐类矿床的形成和控制作用,阐述了天山地貌、气候、水文特征与盐类矿产的分布规律和特征。认为“高山深盆”并非一定是四周环山的深盆,可以是某一高山与其间深盆或两侧盆地的有机组合。高山的屏障作用造成了垂直的气候分带,在潮湿多雨的山区利于成盐组份的析出并迁移到干旱少雨的闭流深盆中,形成盐类矿床。  相似文献   

安徽大别山区5—8月不同阶段降水时空分布特征     

倪婷  凌新锋  黄勇  汪才军 《气象科技》2021,49(6):897-902

利用2008—2016年中国区域CMORPH（Climate Prediction Center Morphing）多卫星降水数据相融合的、分辨率为0.1°×0.1°的逐时降水量数据集，将每年5—8月分为梅雨前（5月1日至入梅前1日）、梅雨期（入梅当日至出梅当日）和梅雨后（出梅次日至8月31日），分析了大别山区梅雨季节降水的时间和空间演变趋势。大别山区梅雨期间年平均降水量360.3 mm，梅雨前平均降水量279.7 mm，梅雨后平均降水量287.0 mm。梅雨季节主要存在3个降水大值区：山区北侧中段、主峰东南侧和西南侧。从日变化情况来看，梅雨期降水日变化呈现双峰特征，出现峰值的时间分别是09:00、16:00。梅雨前、梅雨后降水日变化呈单峰特征。强降水出现频率的空间分布大值区也随着梅雨前—梅雨期—梅雨后的时间变化逐渐北抬。  相似文献   

祁连山南部地区三叠纪弧后前陆盆地——基于沉积填充与大地构造的证据     

肖安成  余龙  熊光耀  张军勇  张永庶  吴磊  赵海峰  覃素华 《岩石学报》2021,37(8):2385-2400

本文通过对祁连山南部地区三叠纪沉积充填特征的研究,建立了盆地形成过程中沉积充填与区域构造演化的关联。依据沉积充填特征、构造接触关系及区域地质背景,认为祁连山南部地区三叠纪盆地具有弧后前陆盆地的构造属性;综合分析年代学、沉积物性和盆地内部填充单元的差异划分出与柴达木岛弧带和祁连山南部弧后前陆盆地相关的区域大地构造单元。认为早三叠世-中三叠世中期,南部遭受俯冲作用持续向北挤压推覆导致盆地挠曲沉降;中三叠世中期-晚三叠世中期发生弧(东昆仑-柴北缘)-陆(巴颜喀拉地块)碰撞,祁连山南部盆地挠曲沉降增大,其间形成区域性断裂和不整合等盆地记录的地质事件;晚三叠世晚期祁连山南部盆地发生过补偿陆相填充,弧后前陆盆地消亡。  相似文献   

豫西后造山阶段存在变质核杂岩吗？   总被引：2，自引：1，他引：1  

曹高社  赵太平 《地质论评》1997,43(4):365-372

不少学者用变质核杂岩模式解释豫西造山阶段基底隆起和与之相伴的盆岭构造的构造格局。介一本区基底隆起的形态、机制、时限和地壳剥露层次均没有变质核杂岩特征与基底隆起相伴的断陷人舅地也不同于变质核杂岩模式中的半地堑。  相似文献   

太行山南段沟谷杂木林的群落学特征及起源初探   总被引：1，自引：0，他引：1  

刘鸿雁 《地理科学》1995,15(2):188-195

  相似文献   

黄海北部长山群岛海洋农牧化分区探讨   总被引：7，自引：0，他引：7  

张耀光 《地理学报》1991,46(1):47-56

本文采用主成分-聚类分析等定量方法,并通过对长山群岛海域的资源、环境、生产条件等的相似性和差异性分析,将其划分为三个海洋农牧化区域,为海水养殖业的合理布局提供科学依据。  相似文献   

西北旅游落后现状的突破及列车旅游的新思路--兼论"西部之星"旅游列车的产品设计   总被引：1，自引：0，他引：1  

刘睿文  吴殿廷 《地域研究与开发》2006,25(1):88-92

近几年，西北地区的旅游业虽然取得了很大的成绩，但其发展相对于东部地区却显得落后，其主要原因之一就是西北地区的旅游资源过于分散，景点间距过大，由此导致游览行程过长，游览内容单薄，这在客观上影响了游客的选择。而与此同时，在国外，列车旅游早已作为各国旅游业的重要旅游产品为世人所熟知。文章从分析我国西北旅游业发展的现状入手，针对景点分散这一制约我国西部旅游业发展的客观不利因素，肯定了开发旅游列车产品的思路。作者以西北地区为例，结合目前我国旅游专列发展现状，提出开通“西部之星”旅游列车的构想，并进行了初步的设计。  相似文献   

Temperature dependence of large-scale water-retention curves: a case study     

Hui-Hai Liu  G. S. Bodvarsson  J. H. Dane 《Hydrogeology Journal》2006,14(8):1403-1408

A local-scale model for temperature-dependence of water-retention curves may be applicable to large scales. Consideration of this temperature dependence is important for modeling unsaturated flow and transport in the subsurface in numerous cases. Although significant progress has been made in understanding and modeling this temperature effect, almost all the previous studies have been limited to small scales (on the order of several centimeters). Numerical experiments were used to investigate the possibility of extending a local-scale model for the temperature-dependence of water retention curves to large scales (on the order of meters). Temperature effects on large-scale hydraulic properties are of interest in many practical applications. Numerical experiment results indicate that the local-scale model can indeed be applicable to large-scale problems for special porous media with high air entry values. A typical porous medium of this kind is the porous tuff matrix in the unsaturated zone of Yucca Mountain, Nevada, the proposed geologic disposal site for national high-level nuclear wastes. Whether this finding can approximately hold for general cases needs to be investigated in future studies.  相似文献