한국 단양지역 구낭굴 동굴퇴적층 형성과정과 시기 고찰

A Research on Formation Process and Chronology of Gunag Cave Deposits in Danyang County, Korea

Gunang Cave is located at Yecheon-ri Gagog-myeon in Danyang County in Korea. Gunang Cave deposits are composed of 8 layers, which are stratigraphically consist of 3 lime pans or flowstones and 6 fallen debris-fine earth deposits. Gunag cave were spatially originated by the dissolution of basement carbonates along fractures which belong to the Chosun Supergroup, and cave entrance deposits were formed in response to paleo-air temperature, flow water in cave and surface vegetation coverage. This research aims to revealing cave forming process on the basis of organic geochemical analysis, palynological analysis and AMS dating of cave deposits and organics. Organic constituents of cave fine earth indicates that the fine earth layers were derived from fallen maerials or distant origins, and the distribution and change of organic carbon, nitrogen and sulfur are assumed to be related to the biological activity. The deopositional age of cave sediments, based on AMS and U/Th datings, is interpreted as maximum 200,000 yr B.P and minimum 10,000 yr B.P. The palynological analysis indicates that the palynofloral asseblages are classified into three ; 1)poor palynofloral zone(7-8 layers : GN-Ⅰ), 2)conifer-grass zone(4-6 layers : GN-Ⅱ), and 3) conifer-grass-freshwater algae-spores (1-3 layers:GN-Ⅲ). Lastly it is interpreted that the first layer above first lime pan was assumed to be formed after the neolithic age, while the first lime pan marked at the Pleistocene/Holocene transitional period. The third layer between first lime pan and second lime pan was formed during the last glacial, i.e., from the late paleolithic to middle paleolithic, while the lower layers below the second lime pan had been formed at least during the middle paleolithic.