HR: 0800h
AN: PP11A-0241    [Abstracts]
TI: Combined Textural and Stable Isotopic Data as Proxies for the Mid-Cretaceous Paleoclimate: A Case Study of Lacustrine Stromatolites in the Hayang Group, Gyeongsang Basin, SE Korea
AU: * Nehza, O
EM: odetten@kangwon.ac.kr
AF: Kangwon National University, College of Natural Sciences, Department of geology, Chuncheon, 200-701, Korea, Republic of
AU: Woo, K
EM: wooks@kangwon.ac.kr
AF: Kangwon National University, College of Natural Sciences, Department of geology, Chuncheon, 200-701, Korea, Republic of
AU: Lee, K
EM: kclee@sangji.ac.kr
AF: Sangji University, Department of mineral and mining engineering, Wonju, 220-702, Korea, Republic of
AB: Microbial interference of the prevailing sedimentary dynamics during stromatolite growth, records vital biogeochemical information, which reflects the prevailing local paleoclimatic conditions. Most stromatolite studies focus on the use of stable isotopes and other geochemical parameters for paleoclimate reconstructions. The use of textural data as a proxy has hardly been considered. This study documents the simultaneous geochemical and textural changes in Mid-Cretaceous lacustrine stromatolites (Gyeongsang Basin, SE Korea), deposited in a semi arid-arid setting as proxies for determining the paleoclimatic conditions during their growth. Here fibrous calcite/micrite couplets in the Sinyangdong, Hwasan and Banyawol stromatolites constitute the basic growth cycles and can be divided into first-, second and third-order cycles. Second-order cycles show couplets with gradual textural changes from lower fibrous calcite to upper micrite laminae and three different types of micrite are present. There is further textural division in the microbial micrite laminae of the Sinyangdong stromatolites where one micrite type always directly overlies the fibrous calcite and is followed by a second type of micrite. Sometimes, the first type of micrite evolves into the second, and also shows increasing paleosalinity conditions within the cycle (higher δ¹⁸O values) such that the end of a cycle shows more saline conditions than the beginning of the next cycle. Consistent enrichments in δ¹⁸O and depletion in δ¹³C values towards micrites within the Sinyangdong and Hwasan stromatolite couplets and a concomitant depletion of both isotopes from fibrous calcite to micrite in the Banyawol sample can be observed. The consistent shifts in these isotopes imprinted in the different textural growth fabrics indicate that paleohydrological changes related to paleoproductivity and paleosalinity fluctuations could play a significant role in the formation of these primary lacustrine carbonates. Textural changes shown by the frequency of the growth cycles also corresponds with oxygen and carbon isotopic values and this appears to have been influenced by climate-related paleohydrological changes.
DE: 3344 Paleoclimatology (0473, 4900)
DE: 4900 PALEOCEANOGRAPHY (0473, 3344)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting