湘西要坝洞沉积堆积特征及形成时代

要坝洞在保靖县城北5km,是有旅游和科研价值的洞穴。洞穴发育在保靖-复兴断裂带的裂隙破碎构造控制的白云岩、白云岩化灰岩残体中,是断面陡转缓地段的垂向洞穴,成洞原因与所处的特定地质构造环境有关。在阐述洞穴形成特征的基础上,详细论述了洞穴沉积物及其相关性。洞穴碎屑沉积、次生化学沉积类型齐全,组成高、中、低三个沉(堆)积台面,构成多期(次)沉(堆)积的伴生共存组合体,展示洞穴及其沉积特征和过程。笔者进一步完善了次生化学沉积的成因分类,认为壁流石、钟乳石、石笋、石柱聚集匹配,构成景点,具有旅游观赏价值。同时,选择具有代表性的1号石笋进行同位素测年和综合研究,以其完好的沉积旋回、结构构造特征,显示3～1万a间的冰期气候沉积特征,其冷暖气候转(突)变标志明显。在洞穴及其沉(堆)积综合研究的基础上,根据洞穴沉(堆)积、洞内外新近系、古近系、白垩系的伴生沉积、储存关系,判断要坝洞形成于白垩纪前后。

Sedimentary and Accumulation Characteristics and Formation Age of Yaoba Cave in Baojing County, West Hunan

The Yaoba cave with a great value in tourism and scientific research is situated about 5 km to north of Baojing county.The cave was vertically developed in dolomitite and dolomitized limestone and controlled by a fracture zone in the Baojing-Fuxing area. The formation of the cave is closely related to the special geological tectonic environment. Authors discussed the cave sediments-speleothem in particular and its relativity on the base of cave formation characteristics. The cave has all types of cave sediments including debris sediments and sub-chemical deposits and formed upper, middle and lower three different deposit platforms. These platforms and its accompanying deposits display characteristics of cave shape, deposits and its sediment processes. The study has completed the origin classification for sub-chemical deposits and suggests that the wall flowstones, stalactite, stalagmites and stalacto-stalagmites accumulated together could form scenery spots with great importance in tourism. The No.1 stalagmite with perfect deposit cycle, texture and structure characteristics indicates that the deposit of the glacial stage during 30~10ka BP. On the basis of synthetic study about the cave and its sediments, and combined with the Tertiary and Cretaceous sediments and the relationship between the accompanying deposits, it is concluded that the Yaoba cave was formed during the Cretaceous period