Xujiaweizi Rift Lower Cretaceous Yingcheng Group Volcanic Sequence Stratigraphic Features

Sequence stratigraphy is a discipline that is developed on the seismic stratigraphy (Vail, 1987). The concept of sequence stratigraphy is born Since 1950’(Sloss, 1959), which is composed of LST, TST and HST. The theoretical system of sequence stratigraphy has been widely used by geologists after half a century of development. It is also developing from the classical three kinds system tracts to four systems tracts(Catuneanu,2006). Although the schemes of sequence boundary division are different(Catuneanu,2006; Catuneanu,2009).but they have stressed the fact is that the inherent mechanism of sequence genesis and phase distribution is controlled by sea level change(Arimoto,1997; Saydam,2000; Caquineay,2008). The theoretical framework of Chinese modern sequence stratigraphy is mainly composed of continental sequence stratigraphy(Shanley,1994; Liu ZJ,2002;Ji YL,2002) and high resolution sequence stratigraphy (Deng HW,2002). at the moment, the application fields of sequence stratigraphy have been developed from the research of the whole basin layers to a intrabasinal measure detailed study(Xu YX,2001; Chen F,2010; Wang QC,2010). With the development of exploration technology, the division of the sequence is more and more detailed, the control factor research of sequence development is more in-depth. However, with the breakthrough of exploration field, a large number of oil and gas resources are found in the volcanic rocks. Sequence stratigraphy is facing new challenges, how to create a volcanic sequence is our new research hotspot (Fig.1). Yingcheng formation is made up of volcanic and sedimentary rocks in Xujiaweizi depression. volcanic rocks include volcanic lava and pyroclastic rocks that is a direct result of volcanism (Wang PJ,2008). sedimentary rocks include two sections: the one is the normal sedimentary rocks that occurred in the intermittent period of volcanism; the other is composed of weather worn volcanic which transport by water. Scholars(Stewart A L,2006; Busby CJ,2007; Wang P J,2006) have carried out intensive research about the volcanic lithology and lithofacies. But the targeted research of volcanic action filling model has not been carried out. Volcanic eruption and accumulation can take place in the high position. so the volcanic occurrence are not controlled by the accommodation space of water bodies, which is the biggest difference between sedimentary strata. Lead to the base level of