ON THE PROBLEM OF THE TIME ASSIGNMENT OF THE DOLOMITE IN THE LOWER PART OF THE HUANGLONG FORMATION IN THE JIANGSU-ZHEJIANG-ANHUI REGION

In the Jiangsu-Zhejiang-Anhui region,the disconformities at the base of the dolomite of the Huanglong Formation had always been taken as the boundary between the middle and lower Carboniferous in the light of the study of the Nanjing-Zhenjiang Mountain Range by Prof.J.S.Lee et al.（1930, 1935）.But in the past twenty years,some geologists have changed this assignment.Basing themselves only on corals such as Lithostrotion found in the dolomite in Nanjing and Chaoxian county and considering a transition bed between the dolomite and its overlying crystalline limestone as the “basal conglomerate”,they separate it from the Huanglong Formation,call it the “Laohudong Dolomite”and assign it to the lower Carboniferous.Some people even consider that this dolomite is different from that in the Jiangsu-Zhejiang-Anhui border region in age and that the latter is stratigra- phically high （“diachronous”）,so can be given another name—the“Huashishan Formation” or the “Dinghan Formation”.In doing so,the same dolomite is divided into two parts and the Huanglong Formation,a complete cyclic facies sequence,is split up,and moreover the disconformities at the base of the dolomite of the formation which are of economic significance for mineral exploration disappear. The author considers that the Huanglong Formation and its assignment advanced by Prof.J.S.Lee are correct,according to the law of the unity of opposition in the process of continuous development and development by stages in the organic and inorganic worlds and from data of the biotas,rock facies,depositional cycles and crustal movements.Although early Carbonifer- ous corals are found in the dolomite,solitary ones are few and poorly preserved and of limited distribution.When the underlying Hezhou Formation is absent,they disappear utterly.On the other hand,Fusulinids such as Profu- sulinella contained in the dolomite are widespread.The dolomite is closely related with the overlying crystalline limestone and pure limestone and always possesses a bed of conglomerate at its base.It overlies the Hezhou Formation （C₁~3）,the Gaolishan Formation （D₁~2） or the Wutong Formation（D₃） add there is obviously a disconformity between them.The above-mentioned facts combined with the discontinuous evolution of Fusulinids and brachiopods in the overlying and underlying units and the sudden change in rock facies indicate that all this is not accidental but the manifestation and natural result of the Huainan movement in this region.Therefore,the dolomite of the Huanglong Formation is still of middle Carboniferous age and stratigra- phically corresponds to the Dapu Group in Guangxi.