Acidities of confined water in interlayer space of clay minerals     

Xiandong Liu  Xiancai Lu  Evert Jan Meijer  for the Collab 《Geochimica et cosmochimica acta》2011,75(17):4978-4986

The acid chemistry of confined waters in smectite interlayers have been investigated with first principles molecular dynamics (FPMD) simulations. Aiming at a systematic picture, we establish the model systems to take account of the three possible controlling factors: layer charge densities (0 e, 0.5 e and 1.0 e per cell), layer charge locations (tetrahedral and octahedral) and interlayer counterions (Na⁺ and Mg²⁺). For all models, the interlayer structures are characterized in detail. Na⁺ and Mg²⁺ show significantly different hydration characteristics: Mg²⁺ forms a rigid octahedral hydration shell and resides around the midplane, whereas Na⁺ binds to a basal oxygen atom and forms a very flexible hydration shell, which consists of five waters on average and shows very fast water exchanges. The method of constraint is employed to enforce the water dissociation reactions and the thermodynamic integration approach is used to derive the free-energy values and the acidity constants. Based on the simulations, the following points have been gained. (1) The layer charge is found to be the direct origin of water acidity enhancement in smectites because the neutral pore almost does not have influences on water dissociations but all charged pores do. (2) With a moderate charge density of 0.5 e per cell, the interlayer water shows a pKa value around 11.5. While increasing layer charge density to 1.0 e, no obvious difference is found for the free water molecules. Since 1.0 e is at the upper limit of smectites’ layer charge, it is proposed that the calculated acidity of free water in octahedrally substituted Mg²⁺-smectite, 11.3, can be taken as the lower limit of acidities of free waters. (3) In octahedrally and tetrahedrally substituted models, the bound waters of Mg²⁺ show very low pKa values: 10.1 vs 10.4. This evidences that smectites can also promote the dissociations of the coordinated waters of metal cations. The comparison between the two Mg²⁺-smectites reveals that different layer charge locations do not lead to obvious differences for bound and free water acidities.  相似文献   

东吴运动的沉积学响应——以湘鄂西及邻区二叠系茅口组顶部不整合面为例   总被引：2，自引：0，他引：2  

李旭兵  曾雄伟  王传尚  刘安  白云山 《地层学杂志》2011,(3):299-304

湘鄂西及邻区二叠系茅口组顶部广泛发育了岩溶角砾岩,并形成了一个分布范围广阔的不整合面,该不整合面特征在各地存在明显差异,其上覆孤峰组与龙潭组也存在不同程度的缺失。东吴运动为两幕式构造运动,上述现象正是东吴运动Ⅰ幕、Ⅱ幕在不同地区的沉积学响应。  相似文献   

广东连州长兴期含煤地层     

姚兆奇  陈楚震  芮琳  刘陆军 《地层学杂志》2011,(1):55-65

九陂组(亚田煤组)是粤北和湘南晚二叠世重要的含煤地层,其下伏"梅田灰岩"的涵义和(虫筵)化石Gallowayinella meitienensis的层位问题曾长期未得澄清.通过对梅田组剖面的详细工作,建立了下部的Gallowayinella组合和上部的Nanlingella jiaozishanica-Sphaerul...  相似文献   

古沙漠记录的沉积体系及层序地层研究进展——以鄂尔多斯盆地白垩系为例   总被引：2，自引：0，他引：2  

庞军刚  国吉安  李文厚  李卫红 《地层学杂志》2011,(1):95-102

鄂尔多斯盆地白垩纪古沙漠沉积地层主要为冲积扇、湖泊、河流、三角洲及沙漠沉积体系.风成沉积和沙漠沉积、风成沉积体系和沙漠沉积体系等概念有必要予以区分.基准面变化是沙漠和河流、湖泊等其他陆相地层对比的基础.鄂尔多斯盆地志丹群划分为上下两个三级层序单元,反映了两期古沙漠由风成沉积强盛期到衰退期的演化,且每个层序可划分为低位、...  相似文献   

浙江早古生代孢粉型化石的研究   总被引：1，自引：0，他引：1  

颜铁增  何圣策  尹磊明  秦祥熙  张志芳 《地层学杂志》2011,(1)

在浙江西北部早寒武世荷塘组、晚寒武世华严寺组、早奥陶世宁国组、晚奥陶世长坞组和文昌组、早志留世霞乡组、河沥溪组和康山组、中志留世唐家坞组中发现孢粉型化石,孢粉型化石包括疑源类,隐花(陆生)植物孢子类型等,计66属、112种、31未定种。同时讨论了这9个层位孢粉型化石的组合特征、地质时代及其沉积环境。  相似文献   

内蒙古固阳盆地东北缘更新统洪积物地层的发现及研究意义     

蔡雄飞  智铎强  罗中杰  吴义布 《地层学杂志》2011,(2):172-178

关于内蒙古高原的隆升,长期以来研究较少,从更新世的冲、洪积物分布在现今1600～1700m海拔高程的山顶上出发,发现固阳盆地东北缘更新统的洪积物的沉积类型、沉积特点和粗碎屑岩系的组分以及孢粉的资料,无不与内蒙古高原隆升紧密相关.内蒙古高原隆升不是孤立的,而是受青藏高原隆升的控制,它们几乎是同步的或者说紧密相连的.  相似文献   

青藏高原地面有效辐射变化及其对表层土温的影响   总被引：7，自引：6，他引：1  

李韧  赵林  丁永建  沈永平  季国良  刘广岳  杜二计  肖瑶  孙琳婵  刘杨  石伟 《冰川冻土》2011,33(5):1022-1032

利用青藏高原格尔木、狮泉河、昌都日射站及中国科学院冰冻圈观测研究站的观测资料,分析了高原有效辐射的变化,在此基础上结合土壤温度资料讨论了高原北部有效辐射的变化对表层土壤热状况的影响.结果显示：1）青藏高原有效辐射变化因所处的区域不同而异,高原东北部、西部及高原腹地有效辐射总体呈减小的趋势,高原东南部有效辐射呈增大的趋势...  相似文献   

Comparison of Results of Recent Seismic Profiles with Tectonic Models of the North China Craton     

Timothy M Kusky 《中国地质大学学报(英文版)》2011,(2)

The geometry and timing of amalgamation of the North China craton(NCC) have been controversial,with three main models with significantly different interpretations of regional structure,geochronology,and geological relationships.The model of Zhao G C et al.suggests that the eastern and western blocks of the NCC formed separately in the Archean,and an active margin was developed on the eastern block between 2.5 and 1.85 Ga,when the two blocks collided above an east dipping subduc-tion zone.The model of Kusky ...  相似文献   

Distribution of Arsenic in Sewage Irrigation Area of Pearl River Delta,China     

黄冠星  孙继朝  张英  荆继红  张玉玺  刘景涛 《中国地质大学学报(英文版)》2011,(3)

The aim of the present work is to investigate the distribution of arsenic(As) in sewage ir-rigation area,to deduce the migration and transformation mechanism of As in soil and groundwater,and to infer the source of As in soil and groundwater.This study is carried out in a sewage irrigation area of the Pearl River Delta,China.Surface water samples,soil samples,and groundwater samples from sewage irrigation area were analyzed for As and other elements.As contents in water samples were analyzed by hydride gene...  相似文献   

Deposition Process of Dust Microparticles from Aerosol to Snow-Firn Pack on Glacier No. 1 in Eastern Tianshan Mountains, China     

尤晓妮  董志文 《中国地质大学学报(英文版)》2011,(4)

Samples were continuously collected from aerosol, fresh snow, and snow pits on Glacier No. 1 at Urumqi River source in eastern Tianshan (天山) Mountains. The deposition processes and the characteristics of mineral dust microparticles from aerosol to fresh snow, and then evolution to the snow pit were determined. Total dust microparticle concentration in the surface snow and aerosol showed a similar temporal variation trend, which was strongly associated with regional and local at-mospheric circulation in the ...  相似文献