THE AGE OF THE XIANGSHAN GROUP IN NINGXIA

The Xiangshan Group may be divided into four subgroups.Trilobite fossils were collected from lenticular limestone bodies in the first and third subgroups.The Xiangshan Group is underlain conformably by the Middle Ordovician Miboshan Group and is in turn ovelain unconformably by the Silurian,Devonian and Carboniferous.Analysis of sedimentary facies sequences indicates that the Xiangshan Group has inseparable genetic relation to the lower Miboskan Formation,which is manifested by the change from the slope facies to abyssal basin facies.So the authors revise the stratigraphic position of the Xiangshan Group and place it in the upper part of the Middle Ordovician.