Lacustrine stromatolites and diagenetic history of carbonate rocks of Chinju Formation in Kunwi area, Kyongsangbukdo, Korea

다국어 초록 (Multilingual Abstract)

Lacustrine stromatolites occur in the Chinju Formation near Kunwi area. They are mostly rod-shaped and occur in association with ooids and gypsum crystals. The stromatolites are quite variable in dimension and appear to have formed by growth of microbial colonies on tree trunks and branches submerged within lake water rather than by trapping and binding of sediments by cyanobacteria. As organic parts of the trees were decayed, the core parts within the stromatolites were filled with sediments and cemented by gypsum and calcite. The rod-shaped stromatolites include four microstructures: 1) laminated, 2) clotted, 3) tubular, and 4) a combination of two or more microstructures. The macrostructures of rod-shaped stromatolites are laminated, domal, and thrombolitic. The rod-shaped stromatolites have undergone two stages of diagenesis: 1) shallow lacustrine and 2) meteoric phreatic diageneses. The shallow lacustrine diagenesis involved fracturing and cementation of spherulitic fibrous calcite, prismatic calcite, micritic calcite and fibrous gypsum. The meteoric diagenesis was proceeded by calcitization and silicification of gypsum, equant calcite cementation, dissolution of unstable carbonate components, and fracturing. Petrographic investigation of the stromatolites as well as the host carbonate rocks clearly indicates that the stromatolites grew in hypersaline lakes, where evaporation was high enough for evaporite and carbonate minerals to precipitate under arid climate conditions.