The Characteristic and Origin of Lacustrine Source Rocks in the Lower Cretaceous, Erlian Basin, Northern China

Abstract

Four lacustrine rift sub-basins in the Erlian Basin, one of the most petroliferous basins in the Northern China, have been analyzed to characterize source rock, to reveal the environmental and ecological changes and to construct depositional models for lacustrine source rocks in different tectonic conditions. The first member of the Tengger Formation of these sub-basins is characterized by widely variable total organic carbon contents, hydrogen indices and visual kerogen compositions. These sub-basins have distinctly different border fault activity and sedimentation rates. These differences resulted in a deep lake with high flux of clastic sediment input in the Aer and Wuli sub-basins, a shallow lake with low clastic in the Naoer and Saihan sub-basins. Such environmental differences corresponded to synchronous distinctions in redox conditions, terrigenous organic matter input and productivity. Total reduced sulfur and Pr/Ph ratios show an oxic environment in the Aer and Wuli sub-basins while an anoxic environment was present in the in the Naoer and Saihan sub-basins. It can be concluded from proportional sterane abundances that the terrigenous organic matter input to the Aer and Wuli sub-basins was higher than that of the Naoer and Saihan sub-bains. The carbon isotopic composition of carbonate present in mudstone samples reflects that the productivity of these sub-basins is distinctly different. The difference in tectonics among these sub-basins caused changes in flux of clastic sediment input to the lakes, which induced changes in the productivity and redox conditions. In Aer and Wuli sub-basins, high flux of clastic sediment input have sustained high productivity and oxic conditions. High productivity account for the deposition of organic rich sediments in oxidized environment after oxidative degradation. In Naoer and Saihan sub-basins, low flux of clastic sediment input leads to redox condition and low productivity. Redox condition substitutes for productivity and becomes the controlling factor of origin of lacustrine source rocks. The synergetic evolution of environments and organisms in the lake systems accounted for the deposition of source rocks with distinctly different characteristics and origin. The models constructed in this paper may have important implications for source rock prediction in other lacustrine rift basins.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015