中国科学院南京地质古生物研究所机构知识库

A new, 430 m long and mostly continuous Upper Cretaceous section from southern hemisphere low paleolatitudes in the Tethys Himalaya (Guru, Tibet) is presented. The lithology, microfacies and fossil contents of the Guru section indicate a continuous shallowing trend from open oceanic conditions at the slope during the Turonian to shallow marine inner shelf environments in the Maastrichtian, interrupted by short periods of stagnation or slight deepening. Strong variations in sedimentation rates and contents of carbonate, quartz, organic carbon and sulfur appear to reflect a combination of regional and global processes. On regional scale, the patterns of varying elastic sediment supply seem to be related to the fast northward drift of the Indian plate from the temperate climate belt in the Turonian and Coniacian, crossing the arid zone during the Santonian and early Campanian, and passing into the tropical humid belt in the late Campanian. On global scale, similar sedimentary changes as in Guru with a transition from clay-rich Turonian sediments to Coniacian carbonates are found in other regions of the world, suggesting an additional influence of global oceanic and climatic factors. Intervals of omission, erosion and reworking in upper Coniacian and lower Campanian sediments of the Guru section appear to coincide with global sea-level lowstands. Well preserved planktic foraminifera occur over most of the Guru section and provide good biostratigraphic control for correlation of stable carbon and oxygen isotopes with data from the reference section for the boreal and Maastrichtian carbon isotope fluctuations can be related to cyclic variations in carbonate showing detailed correlation of bulk sediment carbon isotopes and comparable trends in oxygen isotopes. The real white chalk in northern Germany at Lagerdorf-Kronsmoor and with the English Chalk reference section, content at Lagerdorf-Kronsmoor which are thought to be driven by long eccentricity. This indicates orbital forcing of both carbonate accumulation and carbon isotope signature, most likely mediated by global sea-level changes. The possibility of detailed delta C-13 correlation from boreal sections of the northern hemisphere to a low-latitude section of the southern hemisphere allows for global correlation with an accuracy not achieved by biostratigraphic methods so far. It further enables linking of microfossil and macrofossil biozones, facilitating precise comparison of shallow and deep water sections, which is essential for the improvement of our understanding of timing, causes and effects of climatic and oceanographic processes.