Characteristics of lithofacies and depositional model of Mesozic Dayangshu Basin

Mesozic of Dayangshu Basin can be divided into formations of Longjiang,Jiufengshan and Ganhe,which consist mainly of rocks of volcanic lava,volcanic clastic rock,conglomerate,sandstone,mudstone,shale,amd seam.The lithofacies of volcanic overflow,volcanic eruption,alluvium,lacustrine and their transitional types recognized in Mesozic Dayangshu Basin.There are similarities in the lithofacies distribution,the ithofacies of volcanic overflow and volcanic eruption distributed in west part,the lithofacies of volcanic eruption and alluvium distributed in east part,and the lithofacies of volcanic eruption and lacustrine predominated in middle part.Jiufengshan Formation is the major alluvium and lacustrine lithofacies,and Ganhe Formation is the major volcanic overflow and eruption lithofacies.As a result of the differential volcanic activity intensity and lake scale,the depositional models vary a lot.