Paleoclimatic Investigation From The Lacustrine Stromatolites Of The Sinyangdong Formation Byeongsang Basin(Korea)

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. Fist-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, micrite can be catagorized by: 1) micrite with clotted texture (M1 type), 2) micritie with filamentous texture (M2 type), and 3) homogeneous micrite (M3 type). The oxygen isotopic compositions of the fibrous calcine 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 stromatiolite grew may have been higher Separate lines of textural evidences for higher salinity can be provided: 1) MOre frequent occurrence of micrite. Therefore, textural and geochemical differences between the stromatolites may well reflect the local paleoclimatic fluctuations during the Mide Cretaceous in Korea.