경상분지 신양동층에 나타나는 스트로마톨라이트를 이용한 고기후 연구

초록

Three units of the lacustrine stromatolites (Sy-1, Sy-2, and Sy-3 upwards) in the Sinyangdong Formation (Gyeongsang Basin) were investigated to delineate the physico-chemical conditions of paleo-lake waters and local paleoclimatic conditions based on the textural and stable isotopic data. The internal structures of the stromatolites show cyclic repetition, which can be divided into three cycles; first-, second-, and third-order cycles. First-order cycle is characterized by carbonate mud-drapes and several corroded surfaces at the uppermost part of the cycle. Second-order cycle always shows gradual change from lower fibrous calcite to overlying microbial micrite. Third-order cycle can be recognized by intervening fibrous calcite and micrite layers within micrite and fibrous layers of the second-order cycles, respectively. Texturally (M2 type), and 3) homogeneous micrite (M3 type). The oxygen isotopic compositions of the fibrous calcite and micrite of the Sy-3 stromatolite are more enriched than those of the Sy-1 and Sy-2 stromatolites. This suggests that paleosalinity of the lakewater in which the Sy-3 stromatolite grew may have been higher. Separate lines of textural evidences for higher salinity can be provided: 1) More frequent occurrence of corroded surfaces by meteoric water is present in Sy-1 and Sy-2 and 2) Sy-3 includes more M1 type micrite. Therefore, textural and geochemical differences between the stromatolites may well reflect the local paleoclimatic fluctuations during the Mid-Cretaceous in Korea.

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