A new astronomical time scale for the early Jehol Biota in the Luanping Basin, northeastern China

The Early Cretaceous Jehol Biota in northeastern China significantly increased our understanding of the Meso-zoic terrestrial ecosystem and the origin and evolution of a number of biological groups. The early evolutional phase of the Jehol Biota is best recorded in the Members 2 and 3 of the Dabeigou Formation (D-M2-3) in the Luanping Basin and their equivalent Huajiying Formation in the Senjitu-Sichakou Basin in northern Hebei Province. To date, however, no complete, high-resolution time scale has been established for these early Jehol Biota-bearing strata, hindering our understanding of the origin of the Jehol Biota. Here we carried out a cyclostratigraphic analysis using a high-resolution relative lake level variation record, called "depth ranks" (i.e., a series of numerically ranked sedimentary facies) in the-185-m-thick, continuously lacustrine D-M2-3 in the Yushuxia section, Luanping Basin. Our results suggest that the climate/lake level fluctuations in the Luanping Basin during the development of the early Jehol Biota were strongly paced by orbital cycles, including the 405 kyr and -100 kyr eccentricity and -34 kyr obliquity and -21 kyr precession. By anchoring the 405 kyr-tuned depth ranks to a relatively high-precise zircon U-Pb age of one tuff layer at the base of Member 3 (131.5 +/- 0.4 Ma), we built a high-resolution astronomical time scale, spanning from 132.4 to 130.7 Ma, for the D-M2-3, indicating a -1.7 Myr duration of the early Jehol Biota and an average sedimentation rate of-11 cm/kyr of the D-M2-3 in the Luanping Basin. In addition, we suggest that the periods characterized by warm summer, enhanced hydrological cycle and expanded lake at high obliquity and low precession at eccentricity maximum were most conducive for both development and preservation of the early Jehol Biota.