IEG 환경지질연구정보센터

퇴적학/층서학/고생물학/석유지질학 10월29일(금)

Paleoclimatic Signatures From Carbon and Oxygen Isotope Data and The Effect of Diagenesis on the Morphology and Microstructure

of the Stromatolites of the Cretaceous Sinyangdong and Hwasan Formations in the Gyeongsang Basin (Korea)

The Cretaceous Sinyangdong and Hwasan Formations of the Gyeongsang Supergroup in the Gyeongsang Basin, Korea, contain lacustrine stromatolites. Textural examination of the stromatolites shows a characteristic repetitive pattern during their growth. Each cycle is always characterized by basalfibrous calcite gradually changing to a micrite layer, reflecting changes in the hydrological cycle of the paleolakes in which the stromatolites grew. Paleoclimatic changes recorded during their growth are also revealed in the stable isotope results from the stromatolites.

Each stromatolite from both formations shows an opposite geochemical trendduring growth of the stromatolites. Consistent

O enrichment from fibrous calcite to micrite in the Sinyangdong Formation means the paleo-salinity increase due to evaporation of lake water, whereas the coeval decrease in

C suggests the paleo-productivity decrease wasaccompanied by paleo- salinity changes. The stromatolite of the Hwasan Formation shows the depletion of

O and enrichment of

C from fibrous calcite towards the micrite layers. The depletion of

O may well indicate the decrease in paleo-salinity due to dilution from fresh water input. This study alsoshows the meteoric diagenetic effect on the morphology and internal structure of the stromatolites. The corroded surfaces at the end of the cycles suggest that the stromatolites underwent meteoric diagenesis during subaerial exposure and internal structures were strongly modified by leaching. As a result, growth form mostly changed from stratiform to columnar mesostructure. This study strongly implies that diagenesis could make a very significant influence on the morphogenesis of lacustrine stromatolites in the geologic past.

5-6 구두