南京三台溶洞地貌形成与长江古水面关系初探

据洞穴分布位置与形态分析,南京幕府山临长江一侧水平发育的三大溶洞(头台洞、二台洞和三台洞)及附近不同高程洞穴均为短浅的袋状脚洞,系由长江侧蚀山壁而形成,不具排水功能。同时于山壁发现大量不同于基岩的钙板-角砾混杂堆积,由此推测长江在南京幕府山一段活动历史久远,相应有不同时代的洞穴发育: 老一代洞穴是具有排水功能的地下管道,但已经崩塌并为大量钙板充填; 而崩塌角砾和钙板组成的混杂岩在一些地貌部位构成了新一代洞穴的围岩。对钙板做铀系定年确认,已消亡洞穴的年代至少老于40~50万年; 高位脚洞很可能也老于这个年代,而低位脚洞经长江水流长期侵蚀改造直至最近历史时期。

PRIMARY INVESTIGATION OF THE RELATIONSHIP BETWEEN FORMATION OF SANTAI CAVES IN NANJING AND PALEO-WATER-TABLE OF YANGTZE RIVER

According to the distribution and the shapes,the authors speculate that the main three caverns(Toutaidong,Ertaidong and Santaidong)as well as the caves at the different elevation,all of which are pocket-like and developed in the Mufu Mountain and at riverside of the Yangtze River,could be foot caves.These caves were formed by lateral erosion of the Yangtze River and possess non-drainage function.Meanwhile,the chaotic accumulation that consist of flowstones and breccia and much different from bedrock was discovered,which suggests that the Yangtze River at Nanjing Mufu Mountain has been undergoing a long history of activity,corresponding to the development of the caves at different times: the old cave-generation have collapsed and filled of large amounts of flowstones.The collapse breccia and calcium flowstone are composed of the wall rock of the young cave-generation.The U-series dating for the flowstones confirms that the old cave-generation had been dead at least at the time of 400~500kaB.P.And the caves at higher level are probably older than this age,whereas the caves at lower level have been eroding for a long-term by the Yangtze River until the recent historical period.