SEDIMENTARY GEOLOGY AND DYNAMIC SEDIMEN-TOLOGY OF THE DEVONIAN STRATA IN THE WEST QINLING OROGENIC BELT SEDIMENTARY CHARACTERISTICS AND FRAMEWORK OF THE DEVONIAN FORELAND BASIN IN THE NORTHERN BELT OF THE WEST QINLING OROGENIC BELT

The Qinling orogenic belt lying between the North China Plate and Yangtze Plate plays an important part in explaining the formation and evolution of palaeo continents in China.As an important link between the Caledonian and Hercynian tectonic stages,the De-vonian strata in the belt has all along been considered as the key bed to decipher the sedi-mentary and tectonic evolution in the study area.The present paper focuses on the early Hercynian basin framework and tectonic features based on stratigraphy and sedimentology of the Devonian strata in the northern belt of the West Qinling orogenic belt.The Devoni-an strata in this region consist of the Shujiaba and Dacaotan Groups (including two types:red facies and green facies).The former is characterized by the nearshore-shelf-bathyal background deposits,storm deposits and gravity flow deposits,while the latter by the braided and anastomosed deposits(red facies)and lake-subaquenous alluvial fan,deep-lake gravity flow deposits (green facies).These depositional characteristics and infilling se-quences indicate the existance of the foreland;which was formed on the northern margin of the central Qinling microplate due to the southward obduction of the northern Qinling oro-genic belt during early Hercynian stage.