• The Journal of the Petrological Society of Korea
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• v.10 no.2
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• pp.121-131
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• 2001

The combination of geological, structural and satellite image studies is used to make an examination of the Miocene eruptive type in the Eoil Basin, SE Korea. The basin subsided by the NW-SE extension due to NNW dextral shearing during the East Sea opening. Based on geological structures as well as lithofacies and ages of the basin-fills, it is divided into the NE subbasin and the SW subbasin which were abundantly filled with basaltic volcanics and marine sediments without volcanic materials, respectively: Syndeposional synclines and anticlines are characteristically developed in the NE subbasin, which amplitudes decrease away from the adjacent normal faults to make them into a homoclinal structure. The thicker lavas as well as the younger agglomerates and lacustrine sediments, which show circular distributions, are distributed around the axial zones of major synclines. The satellite image shows four remarkable circular structures within the NE subbasin. They are located adjacent to and along the normal faults, and they are laid almost exactly on the axial zones of the synclines as well as on the distribution area of the agglomerates and lacustrine sediments. These facts indicate that the basaltic lava effusion were conducted by the normal faults like a kind of fissure-eruption and its activity was more predominant at the sites in where the synclines are developed. More active effusion of lava became a reason for deeper subsidence to make differential subsidence and syndepositional folding adjacent to and along the normal faults. Hence, we suggest that a nested cauldron structure was formed in the NE subbasin of the Eoil Basin, and that the volcanism made the subbasin to be a lava pond and controlled the process of filling and sedimentation in the subbasin.

• Korean Journal of Ecology and Environment
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• v.55 no.3
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• pp.231-243
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• 2022

Anthropogenic disturbances on freshwater ecosystem are known to degrade biodiversity, especially on fish assemblage. In this study, we have conducted fish surveys to identify impact of a bridge construction on fish assemblages. A total of eight study sites were surveyed in the Danjang and the Dong Stream in southern part of South Korea from June to November in 2021. The fish samplings were carried out five times, using cast-nets(10×10 mm mesh size), scoop-nets(4×4 mm, 5×5 mm mesh size), set-nets (10×10 mm mesh size), and fish traps (3×3 mm mesh size), along with the Stream/River Ecosystem Survey and Health Assessment by the Ministry of Environment of Korea and basic water quality measurement. Also, we applied the species diversity index and length-weight relationship regressions on certain species to identify interspecific growth rate differences in accordance with study sites. As a result, a total of 782 individuals, 23 species and 10 families were collected. The dominant species was Zacco Koreanus and relative abundance was 50.89%. When applying the length-weight relationship regressions on certain species, the 'b' value for Z. Koreanus was lower at the downstream points than at the upstream points of the construction site. In addition, when comparing to the results of the past survey, relative density of demersal fish at the upstream and downstream points decreased from 26% to 1.4%, and from 18% to 6.3%, respectively. In conclusion, it is considered that bridge construction negatively affects the habitat of fishes, especially on demersal fishes. Therefore, appropriate conservation efforts such as installation of silt protector and sand sedimentation pond are needed to alleviate the disturbance in habitat such as occurrence of turbidity and destruction of micro-habitats.