Biostratigraphy and Paleoenvironment in Cheju Sedimentary Basin, Determined by Materials from Exploration Wells Geobuk-1 and Okdom-1

A micropaleontological analysis was made using materials from exploration wells Geobuk-1 (Td: 2 722. 5.m) and Okdom-1 (Td: 2 903.7 m) for the purpose of biostratigraphic and paleoenvironmental interpretation of the Cheju sedimentary basin. Two wells yield relatively abundant microfossils such as dinoflagellates, calcareous nannofossils, pollen and spores. The biostratigraphic and paleoenvironmental settings analyzed by microfossil assemblages seem to be closely related to the framework of the local tectonics, seismostraigraphy,and sedimentang environment of the Cheju basin. The diversity and abundance varied significantly throughout the cores.These changes are considered to be related to sea-level fluctuation. The marine transgression and regression are probably caused by the local tectonic movement rather than the eustatic change of seal level, referred to the global sea-level curve.