A MESOZOIC RECORD OF FLUVIAL RESPONSE TO CLIMATIC AND TECTONIC PERTURBATIONS, ORDOS BASIN, NORTH-CENTRAL CHINA

Continental sedimentary basins are a major reservoir of particulate carbon and changes in their physical properties (e.g., subsidence and accumulation rates, river hydrodynamics) have potential influence on the global carbon cycle and climate. Unlike marine systems, terrestrial system (e.g., rivers and lakes) is likely to be more directly influenced by tectonically and climatically induced disturbances in hydrological cycle. However, it is still poorly understood how the architecture of the associated continental stratigraphy record signatures of external forcings and carbon cycling dynamics. The objective of this study is to understand the response of river hydraulics to climatic and tectonic perturbations and determine how these forcings impact particulate carbon storage.

To address these issues, we study the fluvial-lacustrine facies dominated Mesozoic succession of the Ordos Basin in north-central China. During the Mesozoic Era, the Earth has experienced several major glacial cycles and several prominent global climate excursions (e.g., Ocean Anoxic Events; OAEs). Therefore, the Ordos Basin can be used as a natural laboratory for studying how river systems and the carbon cycle respond to climatic change in comparison to the variability observed during “background” climatic intervals. Preliminary study shows that a wide range of fluvial styles are indicated by stratigraphic variations in sandstone architecture. It remains unresolved if this variability is associated with allogenic forcing (e.g., tectonic and climate changes), or manifested as a consequence of autogenic processes. For example, preliminary bulk carbon δ13C measurements through the Early Jurassic interval indicate an invariant isotope record (average of -21 permil VPDB) despite substantial changes in fluvial architecture (i.e., a shift from small, 1 – 3 m thick, isolated sandstones to 5 – 7 m thick, amalgamated sandstones). Paleohydrology reconstruction suggests a minimum of a two-fold increase in paleo-flow depth and increases in both sediment flux and discharge across the Early Jurassic interval, which is consistent with predictions of an enhanced hydrological cycle. Future work will include further characterization of the age and organic carbon geochemistry of the strata in the Ordos Basin.