Cretaceous great Sanjiang Basin and paleogeographic evolution: Constraint from detrital zircon dating in the Hegang basin

As an important component of the Cretaceous basin groups in the eastern Heilongjiang province, the Hegang basin’s depositional process and substance composition in the source area record a large amount of information about the basin-mountain relationship and paleogeographic evolution. To well constrain the chronological framework of the basin fill, detrital zircon U-Pb dating for the crucial formations has been conducted. Based on compiling the published and our own data, ages for the Lower Cretaceous Chengzihe, Muling, and Dongshan formations are assigned to be 116-111 Ma, 111-107 Ma and 107-105 Ma, respectively, and the lower age limit for the Upper Cretaceous Houshigou Formtion is thought to be ca. 104 Ma. The characteristcs of detrital zircon age distribution reveal that the Cretaceous basin groups have already connected and unified a much larger prototype basin, namely the great Sanjiang basin, during the deposition of the Chengzihe and Muling formations. At that time, the paleogeography featured by a high elevation in the west and a low elevation in the east, and the Lesser Xing’an Range became the main source area for the unified basin. By the deposition of the Houshigou Formation, regional tectonic regime turned to be contraction from extension, resulting in differently uplift in the Jiamusi block and destruction of the great Sanjiang basin. Under effects of erosion and thrusting load from the eastern continental margin, the Lesser Xing’an Range reduced markedly in the elevation and eventually submerged by the water. The regional unconformity under the Houshigou Formation has a tightly relationship with this basin-mountain system adjustment, and its corresponding time span could be less than 1 million years.