Speleogenesis of Neobaeng-i cave, Seokpo-myeon, Bonghwa-gun, Gyeongsangbuk-do, South Korea

초록

A cave geological analysis of Neobaeng-i cave (total length: 335 m), Bonghwa-gun, Gyeongsangbuk-do, was conducted to present the epigenic speleogenesis and a conceptual model of the cave. The development of cave passages has been limited to several strata, which consist of limestone-shale couplet and flat pebble conglomerate facies, between meter-scale thick shale beds in the middle member of the Dumugol Formation. Neobaeng-i cave can be classified as a drawdown vadose cave, mainly obeyed by the stratal dip of approximately 30 degrees. It can be also correspond with a branchwork cave controlled by cave water originated from surface point sources although it is atypical because of the immature stage in cave development. Based on the columnar section of strata involving Neobaeng-i cave, 60% and 40% of the total passage has been distributed over 0 similar to 3 m and 3 similar to 9 m intervals, respectively, from the bottom of the section. The most active depth interval for the passage development is 2 similar to 3 m, and it accounts for 24% of the total. This is considered as the 'inception horizon'. The evolutionary process of the cave can be divided into three stages as follows: 1) the stage of the initial unconnected conduit under phreatic-epiphreatic conditions, 2) the stage of the doline formation and passage connection/enlargement, and 3) the stage of current stagnation for cave development. The second stage can be subdivided into three substages: clogged passages in the relatively narrow spots with allogenic sediments, partially flooded passages, and reopened passages. In conclusion, the speleogenesis of Neobaeng-i cave has been strongly affected by the basal geological setting like the alternations of limestone-shale beds and, in the latter period, by the evolution of surface karst landforms and large-scale input of allogenic sediments.

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