Late quaternary environmental changes of the Hwajinpo and Songjiho lagoons on the Eastern Coast of Korea

Abstract

The Hwajinpo and Songjiho lagoons, located 25 km apart on the mideastern coast of Korea, are known tectonically stable. Two core sediments were obtained from the Hwajinpo lagoon (HJ99) and Songjiho lagoon (SJ99). Lithologic, geochemical and paleontological data include grain size, water content, magnetic susceptibility, soft X-ray of core samples, TOC, TN, C/N, TS, C/S, assemblages of mollusc and palynomorphs remains. Based on multi-proxy data, six main lithological units were identified in both lagoons, indicative of paleoenvironmental changes during the Holocene, as well as the evolutionary histories of each lagoons related to Holocene sea level changes of the East Sea (Japan Sea). The environmental changes of both lagoons are considered mainly due to the lake/sea level fluctuation during the Late Quaternary because the mineral composition analysis does not show any provenance changes. Although the lithologic changes in the both lagoons do not show any temporal similarity, T-R (transgression and regression) trends based on the grain size variation shows simultaneity. T-R diagram presents three cycles clearly since 7,800 14C yr BP. Highstand sea levels (transgressions) are appeared at about 7,400, 5,500, and 2,200 14C yr BP, while lowstand sea levels (regressions) at about 6,500, 4,100, and 1,800 14C yr BP during the Holocene. Especially, the anthropogenic deposits in both lagoons since about 300 cal-yr BP show relatively very high sedimentation rate than previous depositional units. The rapid sedimentation was due to human activities, agricultural reclamation and/or deforestation in both lagoon-catchment areas.