MULTIDISCIPLINARY PALEOENVIRONMENTAL ANALYSIS FOR THE MID-CRETACEOUS USING TERRESTRIAL AND MARINE CARBON ISOTOPE RECORDS FROM PACIFIC REGOINS

During the last decade, remarkably synchronized fluctuation patterns of d13C records between pelagic carbonates and terrestrial organic matter have been documented for specific Mesozoic and Cenozoic intervals. This fact has established the importance of carbon isotope stratigraphy of terrestrial organic matter as (1) a means to document temporal d13C variations in the ocean-atmosphere-biosphere system in the geologic past and (2) a tool for chemostratigraphic correlation. Global correlation of different (i.e., carbonate or siliciclastic) sedimentary environments in disparate areas by means of carbon isotope stratigraphy may facilitate precise integration of a variety of paleoenvironmental information, although this point has not been emphasized by previous investigators. This study presents terrestrial and marine d13C records for the mid-Cretaceous from Pacific marginal- and deep-marine sections in order to exemplify the usefulness of carbon isotope stratigraphy as a multidisciplinary tool for paleoenvironmental analysis, and to propose new perspectives on Cretaceous paleoenvironmental researches. Carbon isotope compositions of terrestrial organic matter were examined for a marine siliciclastic succession of the Aptian and Albian Stages in central Hokkaido, northern Japan. Coeval pelagic carbonates from the Mid-Pacific Mountains (DSDP Site 463) were analyzed for d13C and d18O records. The d13C profiles of both sections are characterized by having three discrete positive anomalies at the Early Aptian, Latest Aptian, and Albian-Cenomanian boundary, and correlate well to published data from the other regions. The results from these Pacific sections as well as previous data from the other regions are correlated using d13C profiles in order to integrate paleoenvironmental information such as d18O-based marine temperature fluctuations and carbonate sedimentation patterns. Based on the relationship, discussion is given for a peculiar mode of platform carbonate development in the Pacific compared to the Tethys-Atlantic oceans during the mid-Cretaceous.