Interdisciplinary investigations of the Jurassic and Cretaceous terrestrial ecosystems in North China

Abstract

The Mesozoic is a critical period in the Earth's history. It witnessed the biological recovery from the most serve mass extinction event, the first dinosaurs roomed, the first flower bloomed, and how life responded to large-scale tectonic activities. In this thesis, I address four research topics covering amber and fossils from the Jurassic and Cretaceous sediments in North China. Two new amber sites from Inner Mongolia, northern China are found and reported. A brief literature review on Chinese amber localities and their geological setting is provided. The Cretaceous fossil resin deposits worldwide are summarized. U-Pb geochronology and stratigraphic correlation show that the oldest known amber in China is approximately 130 Ma. The findings of the FTIR spectra show that the Hailar amber came from coniferous plants. More research on amber and its possible inclusions in the coal-bearing strata of the Hailar Basin will advance our knowledge of the biological and environmental shifts that occurred in Asia in the Early Cretaceous. The Middle-Late Jurassic Yanliao Biota comprises the earliest known members of many groups of plants, invertebrates, and vertebrates. An updated review of the stratigraphy and the paleontology of these three representatives Daohugou, Reshuitang, and Linglongta beds from the Yanliao area, is presented. Detailed biostratigraphic correlation among these three fossil-bearing beds suggests that the Reshuitang beds may represent a transition between the Daohugou and Linglongta beds. This study further suggests that early crown-group salamanders adapted to different aquatic conditions within a brief period. Two novel 40Ar/39Ar ages of 161.4 ± 0.8 Ma and 161.6 ± 0.6 Ma were obtained above salamander fossil-bearing beds in Reshuitang Village, Lingyuan City, Liaoning, China. The new data establish more precise and accurate age constraints on early salamander evolution and diversification. This study indicates that the Reshuitang fossil beds were deposited slightly later than the well-known Daohugou fossil beds in Inner Mongolia and somewhat earlier than the Linglongta fossil beds in western Liaoning. A Chronostratigraphic framework of the Yanliao Biota is refined by combining a review of previous geochronology with the new results and the biostratigraphic correlation. The Naketa fossil beds in eastern Inner Mongolia outcrop the Lower Cretaceous Jiufengshan Formation that contains the typical EEL (Eosestheria-Ephemeropsis trisetalis-Lycoptera davidi) fossils assemblages of the famous Jehol Biota. The fossil beds herein date to approximately 124-121 Ma (Barremian-earliest Aptian), which agrees with the biostratigraphic correlation. Biostratigraphic and geochronological correlations suggest that the Naketa beds document the middle and late phases of the Jehol Biota and correspond to the upper part of the Yixian to the lower part of the Jiufotang formations.