정동진 단구 자갈층과 충진 물질의 입도 및 형상 특성에 대한 연구 = A study on the granulometric and clast shape characteristic of gravel terrace deposit at Jeongdongjin area

다국어 초록 (Multilingual Abstract)

Samples from newly exposed outcrop of sedimentary layers forming Jeongdongjin coastal terrace in Gangreung area are collected and analyzed to find the sedimentary environment. The site are located at the gentle hillslope of the terrace surface area. The height of the outcrop is about 8m and the altitude of it`s highest part is 68~73m MSL. The lowest part of this out crop is the partly consolidated sand layer with gravel veneer within it. It is found that this part is not in-situ weathered sand stone through the OSL method. This sand layer is overlain by the gravel layer with sand matrix. The shapes of the gravels from this part are mainly ``platy``, ``elongated``, and ``bladed`` by the index of Sneed and Folk(1958). In addition, mean roundness is not so high. It is sceptical to regard this part as marine sediments which are continuously exposed to erosional processes. The boundary between the lowest sand layer and gravel layer showing the abrupt change in forming material without any mixture or transitional zone, so gravels are seemed to deposited after some degree of consolidation of the lowest sand layer. In addition, the hight of the boundary between layers are changed by the place, so the surface of the partly consolidated sand layer is not flat and has irregularity on topography when it buried by gravels. Main part of this out crop is the poorly sorted coarse gravel(22.4mm) with sand matrix(1.36φ) layer with at least 2m thick covering the relatively fine gravels discussed above. Over 20% of particles have ``very platy``, ``very elongated`` and ``very bladed`` shape and only less than 5% of particles have ``compact`` shape, So this particles are also very hard to be regard as marine gravels which are abraded by marine processes. It can be concluded that this gravel layer formed by fluvial processes rather than coastal processes base on the form of the clast and sedimentary structure. The gravel layer is covered by fine(3~4φ) material layers of psudo-gleization which showing inter-bedding of red and white layers. Chemical composition of matrix and other fine materials should be analyzed in further studies. It is attempted to fine the burial ages of the sediment using OSL method, but failed by the saturation. So it can be assumed that these sediments have be buried over 120ka.

참고문헌 (Reference)

1 김종연, "퇴적물 입자의 점하중강도지수와 마식율의 관계에 대한 연구" 대한지리학회 43 (43): 808-823, 2008

2 이재호, "길안천 백석탄의 포트홀과 퇴적물 특성에 대한 연구" 한국사진지리학회 24 (24): 177-199, 2014

3 김종연, "기반암 하상 하천에서의 퇴적물 특성 변화에 대한 연구-스코틀랜드의 River Etive를 사례로-" 한국지형학회 11 (11): 47-62, 2004

4 이선복, "江陵市 正東津 地域 段丘地形 再考" 한국지형학회 16 (16): 29-42, 2009

5 Coombe, D. E., "The nature and origin of the soils over the Cornish Serpentine" 44 (44): 605-615, 1956

6 Oh, G. H., "The correlation of the marine terrace surface along the eastern and the western coast in the central part of the Korean peninsula" 8 : 1-16, 1981

7 Choi, S. G., "Terrace development and tectonic movement during the late Pleistocene in Korea" Kongju National University Press 2012

8 Bigelow, G. E., "Simulation of pebble abrasion on coastal benches by transgressive waves" 9 : 383-390, 1984

9 Dashtgard, S. E., "Sedimentology and stratigraphy of a transgressive, muddy gravel beach: Waterside Beach, Bay of Fundy, Canada" 53 : 279-296, 2006

10 Sneed, E. D., "Pebbles in lower Colorado River, Texas, a study in clast morphogenesis" 66 : 114-150, 1958

11 Ballantyne, C. K., "Paraglacial slope adjustment and resedimentation following recent glacier retreat, Fabergstølsdalen, Norway" 26 : 255-269, 1994

12 Kim, J. Y., "Palaeoenvironmental implication of the Quaternary gravel sequences on the basis of gravel shape" 4 (4): 41-58, 1990

13 Anthony, E. J., "Morphodynamics of intertidal bars on a megatidal beach, Merlimont, Northern France" 208 : 73-100, 2004

14 Kroon, A., "Morphodynamics of intertidal bar morphology on a macrotidal beach under low-energy wave conditions, North Lincolnshire, England" 190 : 591-608, 2002

15 Bartholoma, A., "Modification of gravel during longshore transport(Bianco beach, Calabria, Southern Italy)" 68 (68): 138-147, 1998

16 Choi, S. G., "Last interglacial marine geomorphic surfaces between Gangneung to Muckho in mid-eastern coast of Korean peninsula" 2 (2): 9-20, 1995

17 Chang, H., "Geomorphic development of intermontane basins in Korea" University of Tsukuba 1987

18 Korean Geological Society, "Geology of Korea" Sigma press 1999

19 Hong, S. C., "Constraining the depositional age of marine terrace sediments along the Eastern coast of Korea using optical dating" Seoul National University 2014

20 Yi, S. B., "Characteristics and depositional environment of paleosol layers developed on top of the terrace in the Jeongdongjin area, East Coast, Korea" 23 (23): 1-24, 2009

21 Folk, R. L., "Brazos river bar: a study in the significance of grain size parameters" 27 : 3-26, 1957

22 PiPujol, M. D., "Analyzing ground-water gley and surface water (pseudogley) effects in paleosols" 51-52 : 77-79, 1998

23 Schumm, S. A., "Abrasion in Place: A Mechanism for Rounding and Size Reduction of Coarse Sediments in Rivers" 1 (1): 37-40, 1973

24 Hwang, M. I., "A geomorphic study of erosion surface along the coast of Cheong-dong area, East coast of Korea" 3 : 1-16, 1968

25 Wentworth, C. K., "A field study of the shape of the river pebbles" 730 : 103-114, 1922