New zircon U–Pb age of the Didao Formation in Jixi Basin and its significance for the geology and paleogeography in Jixi and eastern Heilongjiang region in the Early Cretaceous

Abstract

The coal-bearing Jixi Basin of Heilongjiang is a unique Cretaceous basin in Northeast China, depositing non-marine alternated marine strata during transgressions in the Early Cretaceous. However, the ages of the Didao-, Chengzihe- and Muling formations and their relationships to transgressions and regressions have been under debate mainly due to a lack of radiometric constraints and comprehensive study of the fossils. The authors report results of new LA-ICP-MS zircon dating from the tuff of the Didao Formation in its type section (131.5 ± 1.4 Ma), which is the oldest isotopic dating data reported for the Early Cretaceous in eastern NE China. This dating result shows the earliest known volcanic activity happened in the Hauterivian stage, which implies the initial rifting of the Jixi Basin probably in the Hauterivian and caused the first sea staged regression eastward or northeastward in Jixi Basin during the Early Cretaceous. Additionally, a comprehensive study of the plant and dinoflagellate fossils, new dating, and the regional paleogeographic characteristics, indicates a Valanginian-Hauterivian age for the Didao Formation, improving the stratigraphic study of the Didao Formation in accuracy. Moreover, according to the dating in the eastern Northeast China, the four volcanic stages in this region during the Early Cretaceous can be recognized as follows (i) the Didao volcanic stage (ca. 130–132 Ma); (ii) Early Chengzihe-Boli volcanic stage (ca. 119–126 Ma); (iii) Late Chengzihe-Muling volcanic stage (ca. 110–117 Ma); (iv) the Dongshan volcanic stage (ca. 101–108 Ma).