A preliminary study on the buried permian and jurassic in the northern Songliao basin

The fifty odd drilling wells in the northern Songliao Basin revealed that the buried Permian there consisted of, in ascending order, the Dorbod Formation (molasses), the Yixin Formation (relict marine basin), the Lindian Formation(volcanic arc) and the Sizhan Formation (large lacustrine basin), which was a development record of the Hercynian Turkic-type(accretion arc-type) orogen, with the structural line being NEE-striking. The buried Jurassic (main part being Middle Jurassic) Daqing Group was composed of lower clastic rocks and upper altered volcanic rocks, which was a molasses formation of the Yanshanian intra continental rogenesis controlled by rejuvenated fossil (Hercynian) sutures, so that the structural line kept a NEE-striking, and the strata in Inner Mongolia stretched eastwards into central-western Heilongjiang. The molass basin in Songliao area closed in Late Jurassic, but the intermediate-acidic magmatism was still active. Based on new evidence of isotopic data, fossils and tectonic trending, the