Characteristics of deposits and the depositional environment in the Shuijinggong cave in Bama, Guangxi

The Shuijinggong cave is located in Niudongtun, Daluo Village at the northwest Bama County, Guangxi, 44 km away from the county (24°18′12.3 " N and 107°00′41.2" E). It is subtropical monsoon climate with an average annual temperature of 20.4 ℃, annual rainfall of 1 560 mm. The major stratum is the Maokou formation (P1m) of the Lower Permian system, and its lithology is light-colored or gray-white, middle-thick-layered or thick-bedded limestone. The next stratum is the Middle Triassic system (T2), and its lithology is dark gray or gray-black of thin mudstone, tuff and siltstone.The Shuijinggong cave is formed in Maokou formation (P1m) of the Lower Permian system, the cave is developed along the bedded structure of limestone and near NS trending fault. The height of the cave entrance is 650 m above sea level and the covering layer on the top of cave is about 100 m to 200 m thick. The total length of cave measures 800 m, the width of cave is 4-40 m, and the height of cave tunnel is 1.5-35 m. Cave temperature is 18.5 ℃ to 19.6 ℃, humidity 95 %.This condition is suitable for the formation of the cave sediments and landscape protection. The Shuijinggong cave is a newly developed cave with good enclosed conditions and better humidity, there is still a large number of recent carbonate sediments developing in the cave. The landscapes of secondary chemical sediment in the cave is very rich including stalactite, stone curtain, stone waterfall, stalagmites, stone column and stone shield and so on. Furthermore, there are the rarest landscapes of cave sediments at home and abroad, such as the soda straw, helictite and cave flower，which are still growing nowadays on the top of cave. The research also aims to make clear the environmental significance of carbon and oxygen isotope records from sedimentary of modern speleothems. The research results have shown that cave sediments in the Shuijinggong cave began to deposit in the late Tertiary period according to sediment character, composition, sedimentary sequence dating, and its sedimentary was mainly travertine gravel. The main formation period of cave landscapes in the Shuijinggong cave with magnificence and grand landscape characters is the Early Pleistocene and the Middle Pleistocene periods. These speleothems in the Shuijinggong cave, determined by 230Th-U dating age, are formed 1 000 ka BP, 520-600 ka BP and 350-400 ka BP, respectively. Climate at the early stage of the Late Pleistocene or the last interglacial period during 125-90 ka BP mainly is warm and humid, and only a small number of stalagmites in cave formed and rarely saved. The sudden change of climatic environment occurred after 90 ka BP is more unsuitable for sediment formation and preservation in cave. The present speleothems, composed of 50-150 cm high, pure white stalagmites and stalactites with exquisitely carved, sculpt fancy, rare cave landscapes, are mainly formed 40 ka BP, 7 500 a BP and 1 450 a BP respectively, according to 230Th-U dating. The cave sediment landscapes formed since the late stages of the late Pleistocene do not only provide abundant tourism resources and value for the Shuijingong cave, but also provides important information for paleo-climate reconstruction in Guangxi.