Sequence framework of Jiufotang formation in Luxi depression and its relation to lithologic trap

Key words:  Luxi depression  Jiufotang formation  sequence framework  lithologic trap

Abstract:

According to the comprehensive analysis of seismic, core and logging data, sequence stratigraphy and lithological traps in sequence framework were researched in Jiufotang formation of lower Cretaceous in Luxi depression. TTie results show that Jiufotang formation was divided into a third order sequence and three system tracts based on the recognization of first flooding surface and maxium flooding surface. Subaqueous fan and braided river delta developed in lowstand system tract, subaqueous fan and meandering river delta developed in transgressive system tract, meandering river and braided river deltas and fan-delta developed in highstand system tract，and slump turbidite fan developed in all three system tracts. Sand bodies developed in lowstand and transgressive system tracts had poor reservoir physical properties and were not suitable for development of lithological traps- Sand bodies developed in the front of meandering river delta, braided river delta and fan-della in Wushijiazimiao depression belt and Baoriwendu fault zone had preferable physical properties and could form updip pinchout lithologic traps. And sand bodies of slump turbidite fans had preferable physical properties and couid form sand lentic lithologic traps.