In this study, we present detrital zircon U-Pb dating and paleontological data for the newly identified Ayadeng formation in the northern margin of the North China Block (NCB) and Xibiehe formation (molasse) in the Bainaimiao Arc Belt (BAB), which could provide strong evidence indicating the affinity of the BAB and the evolution of the southeast Central Asian orogenic Belt (CAOB). Zircon U-Pb data of siltstone samples and paleontological data indicate the Ayadeng formation dates back to the early Ordovician. Although its location is near the NCB, its zircon grains’s age spectra and paleontology share a closer affinity with those of Tarim and NE Gondwana, as the U-Pb data suggest an age range of 778-1235 Ma, and similar gastropod fossils are found in Tarim and NE Gondwana. The U-Pb ages of meta-sandstone samples in the Xuniwusu formation indicate a shared inheritance with the Ayadeng formation (before 440 Ma), and the U-Pb ages of sandstone samples in the Xibiehe formation are concentrated, with age peaks centered at ca. 420Ma. Fossil corals occur in these two formations, and their sedimentary facies also indicate a collisional setting. Therefore, it is speculated that the BAB rifted from Tarim or NE Gondwana during the Ordovician and became attached to northern NCB between 440-420 Ma as an exotic terrane. During the early Paleozoic, there may have occurred a collision between an arc and a continental block.