ON THE DALONG FORMATION FROM TONGLING, ANHUI
Guo Peixia ( IGMR, Nanjing ) Hu Furen, Wu Hungyi, Zhang Mingde ( 321 Geological Team of Anhui Province )
The Dalong Formation is composed mainly of clastic rocks with intercalated limestones and belongs to a lithostratigraphic unit of marine deposits. In Tongling area, it is made up of dark grey and thin beded siliceous shale interbedded with shale and 2-3 limestone thin beds, yielding abundant ammonoids, nautiloids, brachiopods, bivalves, etc. The total thickness is 30m. to 60m. Based on the rock features as well as faunal assemblages, it was considered to be formed in deeper water, lower energy and reduction conditions. According to the principles of lithostratigraphic classification, the upper boundary of the Dalong Formation should be placed just below the whitish grey clay bed which is overlain by the yellow green shale of the basal part of Yinkeng Formation of the Lower Triassic, and its lower boundary in best way should be placed below the bottom of what we called "capping coal limestone". It was shown that, in this area, the contact at the boundary of Permian-Triassic is conformable because a transitional bed containing a mixed fauna of Permian-Triassic has been found, as it is in other localities of South China. Seeing that the Dalong Formation yields not only Pseudo-tilolites assemblage in the upper part but also Anderssonoceras assemblage in the lower, its geological age in Tongling should be Wujiapingian to Changxingian.