Isotopic fingerprints on lacustrine organic matter from Laguna Potrok Aike (southern Patagonia, Argentina) reflect environmental changes during the last 16,000 years     

Christoph Mayr  Andreas Lücke  Nora I. Maidana  Michael Wille  Torsten Haberzettl  Hugo Corbella  Christian Ohlendorf  Frank Schäbitz  Michael Fey  Stephanie Janssen  Bernd Zolitschka 《Journal of Paleolimnology》2009,42(1):81-102

A combination of carbon-to-nitrogen ratios (TOC/TN), Rock Eval-analyses, and stable isotope values of bulk nitrogen (δ¹⁵N) and organic carbon (δ¹³C_org) was used to characterize bulk organic matter (OM) of a piston core from the Patagonian maar lake Laguna Potrok Aike (Argentina) for the purpose of palaeoenvironmental reconstruction. Sedimentary data were compared with geochemical signatures of potential OM sources from Laguna Potrok Aike and its catchment area to identify the sources of sedimentary OM. Correlation patterns between isotopic data and TOC/TN ratios allowed differentiation of five distinct phases with different OM composition. Before 8470 calibrated ¹⁴C years before present (cal. yrs BP) and after 7400 cal. yrs BP, isotopic and organo-geochemical fingerprints indicate that the sediments of Laguna Potrok Aike consist predominantly of soil and diatom OM with varying admixtures of cyanobacterial and aquatic macrophyte OM. For a short phase of the early Holocene (ca. 8470–7400 cal. yrs BP), however, extremely high input of soil OM is implied by isotopic fingerprints. Previous seismic and geochronological results indicate a severe lake-level drop of 33 m below present-day shortly before 6590 cal. yrs BP. It is suggested that this lake level drop was accompanied by increased erosion of shore banks and channel incision enhancing soil OM deposition in the lake basin. Thus, isotopic data can be linked to hydrological variations at Laguna Potrok Aike and allow a more precise dating of this extremely low lake level. An isotopic mixing model was used including four different sources (soil, cyanobacteria, diatom and aquatic macrophyte OM) to model OM variations and the model results were compared with quantitative microfossil data.  相似文献   

矿区古风化壳属性与缩小防水煤柱机理     

倪宏革 《煤田地质与勘探》1998,26(2):50-52

对黄淮矿区古风化壳进行了详尽分析和简易分带,重点研究了开采煤上方风化带的工程地质特性,探讨了临界风化带开采缩小防水煤柱的机理。   相似文献   

西藏那曲县北聂荣微地块聂荣岩群中斜长角闪岩——Rodinia超大陆裂解的地质纪录   总被引：7，自引：0，他引：7  

辜平阳  李荣社  何世平  查显锋  于浦生  时超  潘术娟  王轶 《岩石矿物学杂志》2012,31(2):145-154

西藏那曲县北聂荣微地块聂荣岩群中斜长角闪岩原岩恢复为正斜长角闪岩,地球化学特征显示岩石属于拉斑系列基性火山岩,具有轻稀土元素富集、重稀土元素亏损的右倾型稀土元素配分模式。岩石富集大离子亲石元素Rb、Ba及高场强元素Nb、Ta,Sr、Th和U呈现明显的负异常,在构造环境判别图解中样品均投到板内玄武岩区,具有与裂谷火山岩相似的地球化学特征。通过高精度的LA-ICP-MS(激光剥蚀等离子体质谱仪)锆石微区原位U-Pb同位素测年,西藏那曲县北聂荣微地块聂荣岩群片麻状斜长角闪岩中获得863±10 Ma的谐和年龄,为原岩(基性火山岩)的形成时代,说明聂荣岩群形成于新元古代早期。该年龄相当于Rodinia超大陆裂解的地质记录。此外,还获得了2 539~1 006 Ma之间的捕获锆石年龄信息。  相似文献   

Seismic time–frequency analysis as a robust method to estimate the fluid saturation: A case study of carbonates reservoir,Iran     

Javad Jamali  Abdolrahim Javaherian 《Geophysical Prospecting》2021,69(1):236-249

The propagation of seismic waves through a saturated reservoir compresses the fluid in the pore spaces. During this transition, parts of seismic energy would be attenuated because of intrinsic absorption. Rock physics models make the bridge between the seismic properties and petrophysical reality in the earth. Attenuation is one of the significant seismic attributes used to describe the fluid behaviour in the reservoirs. We examined the core samples using ultrasonic experiments at the reservoir conditions. Given the rock properties of the carbonate reservoir and experiment results, the patchy saturation mechanism was solved for substituted fluid using the theory of modulus frequency. The extracted relationship between the seismic attenuation and water saturation was used in time–frequency analysis. We performed the peak frequency method to estimate the Q factor in the Gabor domain and determined the water saturation based on the computed rock physics model. The results showed how the probable fault in the reservoir has stopped the fluid movement in the reservoir and caused touching the water‐bearing zone through drilling.  相似文献   

云南泸水隔界河高黎贡山群层控铅矿床     

胡波 《云南地质》2009,28(2):157-160

矿体受元古界高黎贡山群下亚群第三层的层间破碎带及大理岩双重控制。大理岩破碎带为良好容矿空间,姚家坪岩体提供矿质。  相似文献   

岩体结构面蠕变损伤机理研究     

唐红梅  陈涛  鲜学福 《工程地质学报》2009,17(3):357-362

通过对伯格斯模型和西原模型的分析比较,选取西原模型研究岩体结构面的蠕变损伤特性。在0s情况下,由西原模型推出剪切模量的表达式,以剪切模量为变量定义损伤变量,得到结构面的损伤变量表达式。并以泥岩剪切试验为例,计算了相同正压力作用下的结构面剪切模量和损伤量。结果表明:当0s时,剪切模量、损伤量均随时间趋于稳定,且结构面蠕变的前两个阶段损伤量较小,而当0s时,一段时间后,其损伤量开始突变;剪应力越大,其初始剪切模量越大,随时间降低越快,达到稳定蠕变阶段时降低量也相应越大;剪应力越大,结构面损伤量随时间增长越快,在达到稳定蠕变阶段时,损伤量也越大。  相似文献   

岩质边坡稳定性评价的粗糙集－支持向量机方法     

刘勇健  李彰明  杨雪强 《工程地质学报》2009,17(3):332-338

结合粗糙集和支持向量机两种智能算法,建立了基于粗糙集与支持向量机的岩质边坡稳定性评价模型。首先根据有限的经验数据建立属性决策表,通过属性约算法找出影响边坡稳定性的关键因素;然后将所提取的关键信息训练支持向量机。本文以铁路沿线边坡为例,进行边坡稳定性验算,结果表明算法能有效降低边坡稳定性影响因素集数据维数及支持向量机的复杂程度,提高训练速度和泛化能力。  相似文献   

采动影响下金川二矿区14行风井变形破坏机制探讨   总被引：2，自引：0，他引：2  

马凤山  邓清海  陈德信  卢耀军  丁德民  张亚民  王杰  郭捷 《工程地质学报》2009,17(6)

竖井作为井下开采矿山的咽喉工程,在矿山的安全生产中起着举足轻重的作用.金川二矿区14行主力回风井位于矿体下盘,井深715.5m,穿过的工程围岩有超基性岩、花岗岩、大理岩、辉绿岩等以及F_207断层.该风井于1999年10月开工下掘, 2002年投入使用,2005年3月突然跨塌.本文根据现场调查和数值模拟,分析了风井变形破坏的特征和机制.发现主要有井壁错动开裂、片冒、冒落物冲击井壁等几种破坏形式,并得出在采动影响下最易在以下几个位置发生破坏:(1)井筒上部(0～200m),易出现拉裂破坏和围岩整体剪切滑动;(2)F_(207)断层及其上下接触部位(200～220m),井筒很有可能在此处发生上下错动,从而导致剪切破坏;(3)井筒中部(360～460m),受采动影响较大,可能发生鼓肚子破坏;(4)井筒下部F_(16)断层影响带(井底以上50m),岩体在采动影响下将发生松动,从而导致在结构面穿插部位可能发生冒落.  相似文献   

基于灰色聚类法的下洲隧道围岩分级研究   总被引：1，自引：0，他引：1  

祝艳波 《城市地质》2009,4(4):20-24

在隧道开挖施工过程中,经常会遇到围岩失稳,变形的问题。本文结合了宁德至武夷山高速公路S4合同段下洲隧道工程,利用灰色聚类法对隧道围岩分级进行了分析计算,对比传统分级法与灰色聚类法两种分级结果,并对隧道开挖施工后围岩稳定、支护提出了意见。  相似文献   

Life inhabits rocks: clues to rock erosion from electron microscopy of pisolite at a UNESCO heritage site in Brazil     

Kazue Tazaki  Ryuji Asada  Zara Gerhardt Lindenmayer  Tatsuya Shirotori  Juliana Missiaggia Vargas  Carlos Henrique Nowatzki  Osmar Wöhl Coelho 《International Journal of Earth Sciences》2009,98(1):227-238

Rock erosion is attracting increasing attention from scientists worldwide. The area encompassing the Saint John Baptist Church, Saint John Village, XVII century ruins in Rio Grande do Sul at the UNESCO World Heritage Site is considered a Brazilian treasure. However, the risk of damage to this site from rock erosion has recently increased tremendously. Generally, the rocky construction such as fence, wall and tomb stone, seems strong but is actually extremely sensitive to erosion caused by lichens, fungi, molds and bacteria. Because of biological erosion and massive exposure, the fresh rock is dominated by clays and microorganisms. Water-adsorbing clays and microorganisms influence the mechanisms of the rock erosion. In this study, the formation of bio-clay-minerals in porous structure of pisolite was demonstrated using electron microscopy. Bacterial clay mineralization can deform the rock structure and even produce organic materials. Biological activity could easily corrode rocky constructions around the Saint John Baptist Church site. The rocks are pisolitic laterites possibly formed in Tertiary over the Kretaceous Parana flood Basalts. Samples inhabited by lichens and fungi were collected from a collapsed wall in the ancient church. The zonal reddish-brown pisolites are 4 mm in diameter in a matrix of clays associated with porous and empty spaces. Elemental distribution maps from X-ray fluorescence microscopy show iron-rich spherules of pisolite, whereas the matrix is composed of Al, Si, Mn, and Sr; thus producing goethite and kaolinite. Transmission electron microscopic observation showed that various types of bacteria inhabit the spherule and are associated with clay minerals and graphite. STEM elemental analysis confirmed the bio-clay-mineralization with Al, Si, S, and Fe, around bacterial cells. The results presented here will improve our understanding of nm-scale bio-mineralization and bio-erosion in lateritic rocks. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献