Sedimentary characteristics and their bearings to the source rocks in the Dalong Formation, Jingshan region, Hubei

The Dalong Formation crops out very well as a succession of regressive deposits in the Jingshan region, Hubei. The Formation may be divided, according to sedimentary characteristics, into the outer shelf deposits in the lower part and inner shelf deposits in the upper part. Due to slow regression, the shallow-water organisms especially algae appear massively in the upper part of the Dalong Formation, where the organic matter contents are much higher in the upper part than in the lower part. The frequently upwelling oceanic currents close to the continental slope brought about not only abundant algal spores, a source of high organic matter contents and high productivity, but also more nutrients from the bottom to the surficial waters for the variability of the organisms. The factors cited above are interpreted to be favourable for the formation of the excellent source rocks in the Dalong Formation.