Sequence Stratigraphy of Devonian in the Youjiang Basin

Based on key sequence boundary, sedimentary system tracts, in conjunction with bio\|stratigraphy, sequence stratigraphy during the Devonian in the Youjiang Basin has been studied in detail. 17 3rd\|order sequences have been recognized for the first time, 7 sequences in the Lower, 5 sequences in the Middle and 5 sequences in the Upper Devonian, including 10 Ⅰ\|type sequences and 7 Ⅱ\|type sequences, representing 17 3rd\|order relative sea level changes. Moreover, sequences in different sedimentary backgruonds have been correlated and then corresponding seqence stratigaphic framework has also been established. This paper demonstrated that sequence internal architecture and genetic framework within various sedimentary facies zones are obviously different, but they can be correlated and traced because of the same control factor-relative sea level changes. The Devonian transgression in this area extended from south to north overlapped in the formation of the transgression\|type sequences. These sequences were controlled by sea\|level change and tectonic activities. At least three 2nd-order rising sea level stages have been distinguished. During the basin evolution, the late stage of Early and Middle Devonian and the early of Late Devonian correspond to the eustatic change of sea level. During these periods the tectonic, volcanism and sedimentary differentiation might be very strong. Devonian basin can be subdivided into stability and riftplatform. the former distributes in Lochkovian, Pragian, Eifelian, Frasnian and Famenian, and the latter in Emrian and Givetian. In the stability age, sequences can be correlated one by one. But in tectonic area period, sequences are clearly different. The result of research shows that Devonian sequence of stabilized platform area is mainly controlled by sea ieel change and tectonic movement of the globe or the region, and the sequence of the rift trough in the platform is controlled by the basement tectonics of the basin and the episodic subsidence.