Research indicates that the high quality oil shale of the fourth mumber developed in a transgression period and belong to sapropelic-humic type of oil shale of lacustrine-bog facies.

• 研究结果表明：油四层形成于水进体系域发育时期，成因类型为湖泊-沼泽相腐泥腐殖型油页岩，油页岩品质较好；