UNCONFORMITY FEATURES OF CRETACEOUS BOTTOM IN THE BACK-LAND OF JUNGGAR BASIN

The Junggar basin suffered Hercynian,Indosinian,Yanshan and Himalayan tectonic movements,and formed more unconformities.These unconformities did important roles to the oil and gas migration and accumulation in Junggar basin.The Bottom Cretaceous unconformity is widespread in the backland of Junggar basin.Studying on the rock formation,material ingredient and the electric character feature of it indicates that the unconformity can be divided into three structures,ie. bottom block sandrock upper the unconformity,weathered argilic horizon and semi-weathered leached zone lower the unconformity.The bottom block sandrock is good reservoir,the weathered argilic horizon is a part effective cap formation because of suffering long time weather and leaching,rich Al3+、Fe3+and poor Si4+、Ca2+ in it.The semi-weathered leached zone is also a good reservoir because of suffering long time weather and leaching too,the reservoir's physical property gained great improvement.There are two high quality reserveoir-cap combinations along the Bottom Cretaceous unconformity,and formed a lot of non structure subtle traps.It is one of the most important exploration area in the backland of Junggar Basin.The research will provide useful information for oil and gas exploration in this area.