湖南兜率岩溶洞特征及形成发育过程

Characteristics of the Doushuai karst cave in Hunan and its formation and development process

为阐明兜率岩溶洞的形成原因和发育过程,调查了兜率岩溶洞及其周边区域地层岩性和地质构造,测量了溶洞形态及溶蚀堆积物特征;用^(14)C法或U系法对洞内典型堆积物样品进行测年,估算出岩溶堆积物的生长速度,研究结果表明:兜率岩溶洞是完整的独立溶腔碳酸盐岩洞穴;溶洞内石笋发育强烈,石笋的生长速度略快于石钟乳的生长速度,石笋高度为2~26 m,直径在0.5~5 m,生长速度为0.24~0.50 mm·a^(-1);石钟乳长度为3~20 m,生长速度为0.20~0.40·a^(-1);洞内最高石柱高达37 m,最高的二次沉积物可达12 m,直径为0.6 m。兜率岩溶洞的形成是岩石、水流与构造运动共同作用的结果,区域构造产生的断层和裂隙使区内碳酸盐岩石破碎并遭受地下水的溶蚀和侵蚀,在区域缓慢抬升活动过程中形成了兜率岩溶洞;溶洞的发育经历了三个阶段:距今200~78万年的初始形成阶段,距今78~14万年的发展壮大阶段和距今14万年前至今的稳定沉积阶段。溶洞内大多数的溶蚀堆积物产生于14万年以来,少量的新生溶蚀堆积物基本形成于700年以前。在距今1万年左右开始形成二次沉积物。目前,兜率岩溶洞进入稳定沉积晚期。

The Doushuai karst cave,is located at the southern end of the Doushuai island in Dongjiang lake of Hunan Province.it is situated in warm and humid subtropical climate zone with an average annual precipitation of 1,645 mm and a mean annual temperature of 17.1℃.As the landform is dominated by erosive and corrosive geomorphologic types,the area is less than 500 m amsl and is well vegetated.In order to study the formation and evolution of the karst cave,the lithologies and geological structures in the vicinity of the cave were investigated in detail.The cave morphology and the characteristics of cave sediments were measured.Furthermore,14 C and U-system dating methods were used to estimate the growth rate of sediments.The results show that the Doushuai cave is an isolated karst cave with well-developed speleothems such as stalagmites.The growth rates of stalagmites are slightly faster than that of stalactites.The height and diameter of stalagmites vary from 2 to 26 m and from 0.5 to 5 m,respectively,with a growth rate ranging from 0.24 to 0.50 mm·a-1.The lengths of stalactites change from 3 to 20 m with growth rate varying between 0.20 and 0.40 mm·a-1.In the cave,the tallest stalagnate is 37 m in height;and the longest secondary sediment can reach 12 m high with a diameter of 0.6 m.The formation of the Doushuai cave is a combined result of carbonate rocks,geological structures,water flow and regional tectonic movement,in which faults and fissures provide groundwater flow paths that control the erosion and corrosion of carbonate rocks;and regional tectonic movement plays an important role in slowly uplifting the crustal block which lead to the formation of the cave.In this process,the cave have undergone three stages of development:initial formation phase of 2-0.78 million years ago,development phase of 0.78-0.14 million years ago and stable sedimentation phase from 0.14 million years ago to the present.Most of the sediments have been deposited since 0.14 million years ago and a small amount of new sediment was formed nearly 700 years ago.The secondary sediments were produced around 10 thousand years ago.At present,the cave is in the later period of the stable sedimentation stage.The non-stratification of the Doushuai cave is perhaps caused by the slow ascending of the regional crustal block and the collapse of rocks on the cave roof