A PRELIMINARY STUDY OF THE CARBONATE SEDIMENTARY FACIES AND GENERAL PALEOGEOGRAPHIC FEATURES OF MIDDLE-LATE DEVONIAN IN NORT HERN GUANGDONG

The Middle-Late Devonian of northern Guangdong is mainly composed of sedimentary rocks of marine carbonate facies.The belt of carbonate facies of tidal flat is the most developed sedimentary facies in this region, it is mainly distributed in the sedimentary rocks in late Middle Devonian and early Late Devonian rocks of Le-chang and Renhua Counties.The belt includes laminated dolomite facies, allochem limestone facies, stromatolithic micrite facies, biocalcarenite facies, biolithite facies, coral reef facies and intraclastic limestone facies, etc.The belt of the partial barrier sea basin facies is found in Late Devonian deposits from Lechang and Renhua Counties to Shaoguan city. It is mainly composed of carbonaceous muddy biolithite facies, sulfide micrite facies and biomechanically disturbed micrite facies. The belt of open sea basin facies, which is a suit of rhythmite that consists of alternation of oncolite limestone facies,micrite facies with siliceous nodules and styliolinida micrite facies, occurs in the western region of Yaoshan anticlinorium in Middle-Late Devonian and in the area from Lechang to Shaoguan in Late Devonian. The belt of slope facies, being a suit of carbonate slumping sedimentary conglomerate, is distributed along the western margin of Yaoshan anticlinorium and the northern margin from Wudianmeihua anticlinorium to Yunkai oldland in early Late Devonian. The belt of trench facies is distributed in the area of Yingde County in Middle-Late Devonian. It is a formation of micrite containing some of tentaculitida, styliolinida and radiolaria with a bed of abyssal mudstone. Separated by the Yaoshan barrier islands and Xueshan barrier islands, the region from Lechang to Shaoguan has been developed into a barrier sea basin.To the western part of Yaoshan barrier islands is the Meihua open sea basin and between Xueshan barrier islands and Yunkai oldland is the Yingde trench.It is worth noticing that the E-W trend of Yingde trench lies exactly on the dividing lines between two tectonic systems of Pre-Devonian in northern Guangdong, which are mutual perpendicular-one being NNW, and the other NEE. So it can be inferred that the Yingde trench was developed on the basis of tectonic rift strap formed in Caledonian movement. The distribution of many pyrites and polymetal ore deposits along either side of Yingde trench shows that the rift strap may be an important zone of mineralization.