Discussion on the age of the Early Cretaceous amber from the Hailar Basin, NE China

Amber in China is predominantly found from the Cenozoic era, with the oldest-known amber originating from the Middle Triassic Qingyan biota in Guiyang, Guizhou. Chinese Cretaceous amber has been known from Xixia and Neixiang (Henan Province), Guangzhou (Guangdong Province), and the Buir Lake area (Inner Mongolia). Some previous studies have suggested that the amber found at the base of the Yimin Formation in the Yimin Coal Mine in the Hailar Basin (130.9 ± 2.8 Ma, as constrained by detrital zircon U-Pb dating in the original paper) represents the oldest known amber in China at that time. In this paper, detrital zircon U-Pb dating was conducted on the clastic rocks from the Damoguaihe Formation of the Zhalainuoer Coal Mine, Hailar Basin to contest the age of the Buir Lake amber. Our results suggest that the upper part of the Damoguaihe Formation was deposited earlier than 116 Ma (late Aptian), consistent with biostratigraphy and isotopic chronology. Therefore, the age of the amber-bearing Damoguaihe Formation in Hailar Basin should be slightly older than 116 Ma. Amber from the Yimin Formation was discovered from two layers, with the lower layer (the first coal seam) likely near the Aptian–Albian boundary and the upper layer slightly later than 111.7 Ma. Our analyses further confirm that Buir Lake ambers are from the upper Lower Cretaceous Damoguaihe Formation and Yimin Formation, dating to the Aptian–Albian.