Genetically linked litho- and organo-facies in meter-scale cycles of lacustrine deposits within the Permian Lucaogou Formation in the Bogda Mountains, Northwest China: Implications for paleoenvironment and organic matter origin

Abstract

A close correlation between lithofacies and organofacies in meter-scale high-order cycles composed of lacustrine sediments enables comparison and refinement of lithofacies-defined cyclostratigraphy. Four lithofacies and four organofacies have been identified in fluctuating profundal high-order cycles in the lower-Permian Lucaogou Formation, southern Bogda Mountains, NW China. The four lithofacies include interbedded and interlaminated coarse siltstone and very fine sandstone, black shale, wackestone and dolostone, and calcareous and dolomitic shales. Four distinctive organofacies have been identified, on the basis of geochemical composition of organic matter and specific biomarker proxies related to organic matter types, rather than to depositional conditions and thermal maturity. The four organofacies are associated with the four lithofacies in the meter-scale high-order cycles, suggesting litho- and organo-facies may be genetically linked and may have been controlled by lake contraction and extension. The study shows that the lithofacies-derived and environment-defined high-order cycles can be delineated and substantiated by geochemical proxies-defined organofacies. This study also demonstrates that a holistic approach combining litho- and organic geochemical data is useful in reconstruction of meter-scale lacustrine cycles in a half-graben.