Hade 4 is the first large marine oilfield discovered recently in northern Manjiaer depression of Tarim basin. It was previously regarded as an oilfield formed in Himalayan (Neogene) period. Nevertheless, evidence from fluid inclusions, K/Ar dating of authigenic illite in the reservoir and retrospection of oil-water contact has revealed that the CⅢaccumulation (the major accumulation in the oilfield) was formed in Late Hercynian, whereas the C5 accumulation might be a secondary one formed by vertical adjustment of the CⅢaccumulation in Late Himalayan. Such a conclusion is of significance to the exploration and evaluation of western Manjiaer.