Abstract: The thick Mesozoic mudstones are well developed in the Labudalin Basin. The strata with characters of hydrocarbon source rock mainly occur in the middle and lower part of the 1st Member, Shangkuli Formation. A section of the 1st Member of Shangkuli Formation was surveyed at 491 km of the Labudalin-Xiakuli highway, in which tuff was found below thick muddy shale. LA-ICP-MS dating for the tuff sample yields an age of 156.7±1.8 Ma(MSWD=2.0), indicating that the source rocks were formed in Late Jurassic. Therefore it is assigned to Manketouebo Formation. This result adds a dating datum to the Mesozoic chronostratigraphic study in northern Daxinganling Mountains, and provides basic information for source rock strata searching in the volcanic rock-covered regions as well.