桂林峰林平原、峰丛洼地残留中生代地层空间展布形成机制探讨

Formation mechanism of the spatial distribution of Mesozoic strata in Guilin peak-forest plain and peak-cluster depression

文章探讨了桂林峰林平原、峰丛洼地内中生代地层空间展布及形成机制,为查清桂林岩溶地貌发育演化过程提供参考。在前人研究基础上,通过调查地层、地貌的空间展布特征,结合区内构造发展史、岩相古地理环境变化及岩溶水文地貌过程等要素,对桂林峰林平原、峰丛洼地内中生代地层空间展布特征、形成机制,进行归纳总结与分析,认为:三叠纪地层和白垩纪地层覆盖于泥盆纪地层之上,中间缺失二叠纪、侏罗纪地层,其原因是中三叠世时期地壳抬升,三叠系上统和二叠系被剥蚀殆尽,在侏罗纪研究区处于剥蚀期,导致两个时期地层缺失;而三叠系、白垩系残余地层分布在泥盆系形成的洼地、谷地、洞穴、山腰及山顶等地,主要是区内在中三叠世、侏罗纪时代古岩溶发育的天坑、洼地、谷地和洞穴等负地形,为晚三叠世和白垩纪沉积提供空间;现代岩溶地貌发育过程中,形成的岩溶负地貌将上覆地层向纵深方向携带,从而形成不同常理的地层接触关系;同时,这些负地形为堆积或沉积在内的三叠纪、白垩纪地层提供了免受剥蚀场所,使其残留至今。

This paper discusses the causes of the spatial distribution of Mesozoic strata in the peak-forest plain and peak-cluster depression in Guilin,and provides references for clarifying the development and evolution of karst landforms in this city.Based on the structural development history,the change of lithofacies palaeogeographical environment and karst hydrogeomorphic processes in the study area,this paper investigates the characteristics of spatial distribution of strata and landforms so as to analyze the spatial distribution and the formation mechanism of the Mesozoic strata in the peak-forest plain and peak-cluster depression.The study shows that the Triassic strata and the Cretaceous strata cover the Devonian strata,and the Permian and Jurassic strata are missing in the middle.During the Middle Triassic,the crust was uplifted and the upper Triassic and Permian strata were completely eroded,and the study area was in the denudation period during the Jurassic period,which resulted in the loss of strata in two periods.Besides,the residual strata of Triassic and Cretaceous distributing in depressions,valleys,caves,mountainsides and mountain tops which formed in Devonian strata,are mainly in negative topography developing in the middle Triassic and Jurassic karsts,such as tiankengs,depressions,valleys and caves These negative landforms provide space for the late Triassic and Cretaceous sediments.During the developing process of modern karst landform,these negative karst landforms carry the overlying strata to the depth,thus forming a relationship different from normal stratum contact.Meanwhile,these negative landforms,as residues till today,provide the place to avoid denudation for their accumulation or sedimentation in the inner Triassic and Cretaceous strata.