试论桂林岩溶洞穴发育的古老性及形成时代探讨

PRELIMINARY DISCUSSION ON THE DEVELOPMENT OF KARST CAVES IN GUILIN AND REDEFINITION OF THEIR FORMING TIME

中、晚三叠世是桂林热带岩溶、岩溶洞穴强烈发育的一个重要时期。早休罗世，气候条件仍然有利，热带岩溶继承发育，但因碳酸盐岩被晚三叠世内陆湖盆堆积物覆盖，一定程度上减低了热带岩溶发育的强度。中侏罗世至白垩世，气候干旱炎热，降雨王少，“三水”活动不强烈，岩溶、岩溶洞穴不发育。晚白垩世，广泛发育内陆湖盆，岩溶作用有一定改善，但因仍处于干旱、炎热环境，湖水浅，堆积迅速，不利于大型洞穴的形成。第三纪是本区热带岩溶、岩溶洞穴强烈继承发育时期。除了利用、改造以前形成的洞穴之外，相应地发育了一些新洞穴。古漓江在此时期形成并强烈深切，地下岩溶相应强烈发育。第四纪以来，主要是反复利用、改造以前形成的岩溶洞穴，使之发育得更加复杂、完善。

Middle—Late Friassic Epoch was an important time for theintensivedevelopment ofkarstand caves in Guilin. In Early Jurassic Epoch，the climate was still favourable for the inheritabledevelopment of tropical karst．But，carbonate rocks were buried by the sediments of Late Trias-sic inland basin，so the density of tropical karst development decreased to certain extent．FromMiddle Jurassic Epoch to Cretaceous Peried，arid and scorching climte，low rainfall and weakactivity of water led to the undevelopment of karst and caves. During Late Cretaceous Epoch，the ka rstification was improved due to the widespread development of inland basin，but thearid and scorching climate，shallow lake and rapid accumulation were still unfavourable for theformation of large-scale caves. Tertiary Peridwas an intensive inheritable development timeof the tropical karst and caves in Guilin. During the Peried，some new caves were preduced be-sides the cavesgenerated by utilizing and reforming the former caves，the palaeoriver of Li wasformed and deeply erosed，underground karst was well developed．Since the Quaternary Peri-od，the former caves were repeatedly used and reformed to produce more complicated and com-plete caves.