Abstract
In Geumgwangdong, Janggi and Yangpo areas of Yeongil district, North Gyeongsang-do, the Tertiary strata have been known since 1924 by Tateiwa, who divided the strata into three groups viz. the Janggi, the Beomgogri and the Yeonil in ascending order. The writers found prominent unconformities in the Janggi Group, and they divided the group into the Lower, the Middle and the Upper parts. The lignite beds are intercalated in the Middle part of the Janggi Group. Each area in Yeongil district is characterized by its own stratigraphy. Geumgwangdong Area: The lower and middle parts of the Janggi Group are found in this area, but not the upper part. An unconformity between these two parts is newly found. The Yeonil Group, therefore, overlies the Middle part of the group, lacking the Beomgogri and the Yeonil Groups. Janggi Area: The lower, middle and upper parts of the Janggi Group are well represented in this area, only lacking the Geumgwangdong Formation in the lower part. Absence of the formation suggests a prominent unconformity between the lower and upper parts of the group. Beomgogri Group and the lower part of the Yeonil Group are well distributed in this area, and unconformities define the boundaries of these groups. Yangpo Area: The strata are poorly represented in this area. Only the lower part of the Janggi group, lacking the Geumgwangdong Formation, and the middle part represented only by the Lower Coal-bearing Formation, are distributed in this area. The Beomgogri Group unconformably covers the Lower Coal-bearing Formation. The Yeonil Group is not found in this area. The so-called felsophyre has been reported to distribute widely on the west and the south, and as the basement rock which is overlain by the Tertiary sediments. However, this igneous rock, which should rather be called generally quartz-feldspar porphyry, intruded all the Tertiary deposits. Basalt and andesite of Quaternary ate found in the three areas. These two types of rocks and all other older rocks are unconformably covered by the diluvium and alluvium. The Quaternary is represented by the old fluviatile and dune deposits containing foraminifers and shell fragments. Almost all the formations of the Janggi Group produce plant fossils. In this study, pollens and spores from the Geumgwangdong Formation and the coal-bearing formations in the middle part of the Janggi Group are analysed. These are spores of 7 genera of Pteriodophyta, pollens of 12 genera of Gymnospermae, pollens of 30 genera of Angyospermae. These spores and pollens are expected to indicate the more accurate ages of the strata. Lignite has been known to occur only in the coal-bearing formations in the middle part of the Janggi Formation, but the better coal beds are found and produced from the Janggi Conglomerate Judging from the development of strata in this district, it may be said that the Janggi area was the center of the depositional basin of the area during Miocene Epoch.