Analysis on Controlling Factors of Marine Sequence Stratigraphy Evolution in Pearl River Mouth Basin

Key words: 
• sequence stratigraphy

Abstract: The Pearl River Mouth basin transformed to a kind of quasipassive continental margin basin from a continental rifted lake basin after Nanhai movement, and then a set of continentaloceanic transitional facies formations and marine formations which are now the main oilproduction formation formed in Pearl River Mouth basin. The analysis on controlling factors of these sets of formations is useful to the thirdorder sequence stratigraphy division and correlation, and helpful to understand the type and structure of each sequence. Based on the analysis of marine sequence type and developing models of Zhuhai Formation to Yuehai Formation, the controlling factors of marine sequence stratigraphy evolution in Pearl River Mouth Basin are analyzed according to its configuration. It is considered that the tectonic movement, paleogeographic framework, relative sealevel change and sediment supply are the main controlling factors of marine sequence stratigraphy evolution. But these four factors have different effects at different times. The tectonic movement and paleogeographic framework play an important role to the development of sequence stratigraphy from late Oligocene to early Miocene when the basin framework made a great adjustment. Three important movements happened during the period of marine formation forming: the Nanhai movement and the Baiyun movement made the basin framework changed, and controlled the early depositional filling in the basin; The Dongsha movement made parts of basin serious uplift and denudation. These three movements all formed regional unconformities which make up of  the  secondorder sequence boundaries. The influence of paleogeographic framework on the sequence stratigraphy happened in the early period of marine sequence forming, which include the influence of palaeouplift topography, depression topography during the faultdepression stage and shelf breaks. During the peaceful period without tectonic movement, relative sealevel change and sediment supply become the main controlling factors. There is relative wide and smooth continental shelf in Pearl River Mouth Basin, and different types of sequence formed due to the degree of relative sea level fall. When there is a significantly large fall in sea level, reaching to shelf break, a type 1 unconformity develops, such as sequence boundary SB21、SB13.8 and SB10.5 in Pearl River Mouth Basin. When the sea level falling is of lesser magnitude,not reaching to shelf break, a type 2 unconformity develops, such as sequence boundary SB11.7, SB8.5 and SB6.3.In the early period of marine sequence forming, there are three kinds of sediment supply which are PaleoPearl River delta,Hanjiang delta and Dongsha uplift; but from late stage of Zhujiang Formation, the sediment supply of Paleopearl River delta become the main resources. Whereas the influence area of PaleoPearl River delta and other sediment supplies made the  same sequence present different characters at different places.