As part of western Hubei province

Laifeng-Xianfeng area is adjacent to the east of Sichuan Basin

with its Upper Ordovician Wufeng-Lower Silurian Longmaxi Formation dark rock series bearing lower organic abundance.The petrological and mineralogical characteristics of Upper Ordovician Wufeng-Lower Silurian Longmaxi Formations in Laifeng-Xianfeng area

were investigated according to detailed observation of the six outcrop sections and three cores

in combination with polarizing microscope

X-ray diffraction(XRD)

field emission scanning electron microscopy(SEM)and organic carbon content(TOC)analysis.Large amount of clastic particles in silt size are developed in the study area whose mineral components are mainly quartz and clay minerals.Besides

siltstones and shales rich in organic matters are the main rock types in this area

which can be divided into four lithologic sections from the bottom-up including carbonaceous and siltyshales

carbonaceous and argillaceous siltstones

argillaceous siltstones and carbonaceous siltyshales.According to instructionsby petrological and mineralogical characteristics and geochemistry of element

and comparison of shale enrichment conditions with the corresponding formation of Sichuan Basin

it can be figured out that the shorter-term anoxic and reducing environment

rapid change of sea level and smaller rate of deposition

render the thickness and abundance of organic matters of organic-rich shales in the Wufeng-Longmaxi Formations in Laifeng-Xianfeng area with higher bioproductivity to be significantly worse than those of the corresponding formation in Sichuan Basin.