摘要:
为了研究洞穴母岩对洞穴系统及次生沉积物产生的影响,以重庆丰都雪玉洞母岩为研究对象,对其沉积地质特征进行了详细的研究,同时还探讨母岩的沉积地质特征与洞穴发育及次生沉积物特征之间的关联.结果表明,雪玉洞的母岩层位为下三叠统飞仙关组第二段,其沉积相为颗粒滩.母岩的岩性为砂屑灰岩、鲕粒灰岩、砾屑灰岩,夹少量微晶灰岩.母岩和洞穴次生沉积物的主要矿物成分是低镁方解石(LMC,low mag-nesium calcite).母岩较低的Mg/Ca导致洞穴滴水的Mg/Ca也较低,这使得组成次生沉积物的低镁方解石晶体快速侧向生长,并导致方解石晶体纯净、粗大且自形程度高.雪玉洞母岩顶底板岩层沉积期稳定的滩间海沉积环境有助于形成高强度的厚层微晶灰岩从而为洞穴系统的发育提供有效的支撑.这表明洞穴母岩的沉积地质特征会在物质基础的层面对洞穴系统的发育以及洞穴次生沉积物的特征产生显著影响.
Abstract:
The purpose of this work is to explore the effect of parent rock at caves on the cave system and its secondary sediments.Taking the Xueyudong Cave in Fengdu,Chongqing City as an example,we have made a detailed investigation to characterize its sedimentary geology,and study the relationship between sedimentary characteristics of parent rock and development of the cave and its secondary deposits.The results indicate that the parent rock of Xueyudong Cave belongs to the second member of Triassic Feixianguan Formation with main sedimentary facies as grain shoal.The main types of the rock are calcarenite grainstone,oolitic grainstone,calcirudite grainstone with a little micrite sandwiched.The predominant mineral compositions of the parent rock and secondary sediments are low magnesium calcite (LMC).The low Mg/Ca ratio of the parent rock led to a low Mg/Ca ratio of drip water in the cave,resulting in fast sideward growth of calcite crystals in LMC which are pure,coarse and of highly idiomorphic,that constitute the secondary sediments.The interbank,a relatively quiet sedimentary environment when the roof strata of the Xueyudong Cave were deposited,provided a good condition for the formation of thick-bedded limestone with high strength,thus helpful for development of the cave system.It means that the features of sedimentary geology of the parent rock in the cave can produce obvious influence on the evolution of the cave system and its secondary sediments.
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