Characteristics and spatial variation of the Lower Cretaceous lithostratigraphy in the Ngangla Ringco area, western Tibet, China

The Low Cretaceous in the Ngangla Ringco area is divided into four formal lithostratigraphic units; they are the Zelong Group, Duoni Formation, Langshan Formation and Jiega Formation. Their spatial distribution, lithological characteristics, sedimentary environments and lateral variation are discussed in the paper. The Duoni Formation is only distributed over the eastern part of the Bangkog-Baxoi stratigraphic area and changes facially and pinches out west of Houchimali, Garze. It possesses stratigraphic relationships and lateral facies change relationships with the Second Member of the Zelong Group. The Langshan Formation is a succession of stable carbonate platform facies sediments, only found in the Bangkog-Baxoi stratigraphic area, northern Ngangla Ringco. The Jiega Formation is marked by active carbonate platform facies sediments with volcanic activity, found only in the Coqen-Xainza stratigraphic area, south-central Ngangla Ringco. The Langshan Formation has a synchronic but heteropic relation with the Jiega Formation.