Circumjacent distribution pattern of the Lungmachian graptolitic black shale (early Silurian) on the Yichang Uplift and its peripheral region

Stratigraphic hiatuses of variable time intervals within the Rhuddanian to early Aeronian (Llandovery, Silurian) are identified in the area bordering East Chongqing, West Hubei and Northwest Hunan in central China. Their distribution suggested the existence of a local uplift, traditionally named the Yichang Uplift. The diachronous nature of the basal black shale of the Lungmachi Formation crossing different belts of this Uplift signifies the various developing stages during the uplifting process. The present paper defines the temporal and spatial distribution pattern of the Yichang Uplift, which might be one of the important controlling factors for the preservation and distribution of the shale gas in this region, as it has been demonstrated that the shale gas exploration is generally less promising in the areas where more of the basal part of the Lungmachi Formation is missing. Therefore, better understanding of the circumjacent distribution pattern developed throughout the uplifting process may provide the important guidance for the shale gas exploration. The present work is a sister study to the published paper, Stage-progressive distribution pattern of the Lungmachian black graplolitic shales from Guizhou to Chongqing, Central China. These two studies thus provide a complete Ordovician-Silurian black shale distribution pattern in the Middle and Upper Yangtze, a region with the major shale gas fields in China.