Karst Caves In Zhangjiajie Sandstone Peak Geopark: Development Patterns And Environmental Significance

Zhangjiajie Sandstone Peak Forest Geopark (29°13’18’’-29°27’27’’N, 110°18’00’’-110°41’15’’E) situated in the Wuling Range between the Yun-Gui Plateau to the northeast and the mountainous area of northwest Hunan Province. It covers a total area of approximately 398 km2. Characterized by the spectacular sandstone landscapes, the study region is also featured by its karst landforms, karst cave in particular. The numerous singular karst caves are attributed to the thick and pure limestone, unique geotectonic position, well-developed fractures, good hydrodynamic condition and the intermittent uplifting processes.This thesis combines geomorphologic, sedimentologic and chronological evidence to characterize the karst caves in this region, correlating these features with distribution characteristics, development patterns and genetic mechanism. Comparative analysis of karst cave and terrace sequences is used to unravel the relative controls played by tectonics and climatic changes, providing significance evidence for the presence of sandstone landfroms and geomorphic history of the study area.Our field investigation revealed that these karst caves with particular patterns usually appear in the specific tectonic settings. Overall, karst caves mainly distribute in the core area of Tianzishan and Yujiazui synclines and controlled by the fracture system. These karst caves emerge majorly in four levels of 200 ~ 400m, 400 ~ 600m, 600 ~ 900m and within 900 ~ 1300m, respectively, of which 200 ~ 400m and 900 ~ 1300m are most favorable for cave development.The typical karst cave, Huanglong Cave, 10 km east of Jundiping village on the north flunk of the Suoxi Valley, is the core sightseeing spot of Zhangjiajie Sandstone Peak Forest Geopark. The cave network ranges from 260 to 400 m a.s.l., with exit standing approximately 5±2m above the present Suoxi River. It is comprised of almost all types of stalactite, stalagmite, stone columns, stone waterfall, and stone. There are four primary layers, aligned approximately east-west direction, with a total length of 13 km, vertical height of 140 m. A 60 cm thick bed of rudimental clayey sand and well-rounded gravels in the uppermost layer is considered to be indicative of an imprint from ancient river deposits. ESR dating of these materials indicates that the cave initially formed more than 463±46 ka ago.When taking the base of the Suoxi catchment, multi-layered karst caves and four distinct levels in the alluvial terraces correspond well with the typical four-level sandstone peak forest landforms along the Suoxi River (developed in middle, middle-lower, and upper reaches of Suoxi River, respectively). The good consistence among these stepped landforms indicate that the warm and moist climate during the middle Mid-Pleistocene (~463 ka) favored karstification processes, which followed by the aggradation of the T4. These agreements demenstrate that the development of the Suoxi River lead to initial incision into the sandstone landform during the middle period of the Middle Pleistocene, following a period of long-term tectonic quiescence. For these reasons, the timing of sandstone landform formation, however, should be constrained to middle Mid-Pleistocene.