Timing of the late Jehol Biota: New geochronometric constraints from the Jixi Basin, NE China
Abstract The Jehol Biota is a world-famous Early Cretaceous terrestrial ecosystem in East Asia and has revealed exceptionally well–preserved fossils which provide significant insights into the origin and evolution of birds and feathers, and the early diversifications of mammals and angiosperms. After the long-lived controversies over the timing of the biota varying from Late Jurassic to Early Cretaceous in last century, the lifespan of the early-middle Jehol Biota has been precisely dated from Barremian to early Aptian (ca. 131–120 Ma) by a series of recent radiometric analyses. However, few well–constrained ages are available for the late Jehol Biota, hindering our complete understanding of the evolutionary history of the terrestrial ecosystem. Alternating marine and non-marine deposits of the Chengzihe Formation in eastern Heilongjiang have yielded a non-marine bivalve assemblage of the Jehol Biota, basal angiosperms, and Cretaceous marine index bivalves, which collectively offer crucial and indisputable clues against the prevailing Jurassic time of the biota since 1990s. Here we present the first discovery of tephra layers from the Chengzihe Formation, dated by zircon U-Pb geochronology as ca. 116–111 Ma, providing the first quantitative age calibration for the early angiosperms and the Jehol bivalve assemblage. Therefore, we demonstrate that the duration of the Jehol Biota extends to late Aptian–early Albian, approximately 4–9 Myr younger than the currently accepted age limits.