Stratigraphy and paleoclimate patterns in the Late Eocene to Oligocene strata of Ulantatal, Inner Mongolia, China

• Main Author: Wasiljeff, Joonas
• Other Authors: Dupont-Nivet, Guillaume, University of Helsinki, Faculty of Science, Department of Geosciences and Geography, Doctoral Programme in Geosciences, Helsingin yliopisto, matemaattis-luonnontieteellinen tiedekunta, Geotieteiden tohtoriohjelma, Helsingfors universitet, matematisk-naturvetenskapliga fakulteten, Doktorandprogrammet i geovetenskap, Kaakinen, Anu, Salminen, Johanna
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Helsingin yliopisto 2022
• Subjects: geologia; Antarc*; Antarctica
• Online Access: http://hdl.handle.net/10138/348269

This thesis investigates the aridification of Asian continental interiors and the underlying mechanisms affecting aridity during the Eocene-Oligocene Transition and during the Oligocene. The Eocene-Oligocene Transition, at circa 34 Ma, is widely considered to have been the most dramatic climatic shift of the past 50 million years. In the context of Asian continental environments, the Eocene-Oligocene Transition was associated with increased seasonality, dramatic cooling, turnovers in biota, and drying of the environment. The causal mechanism for environmental cooling is likely linked to geographical reorganization of continents and oceanic currents, decline in atmospheric CO2 and permanent glaciation in Antarctica. On the other hand, Oligocene climate was possibly regulated by recurring glacial-interglacial episodes in response to astronomical forcing and changing summer insolation, inducing variations in sea level, atmospheric and oceanic circulation, concentration of CO2, and temperature. However, responses of Asian terrestrial environments to Oligocene climate dynamics have remained poorly constrained. In this dissertation, lithostratigraphical and sedimentological characteristics, depositional environments as well as paleoprecipitation and weathering regimes were determined in the region of Ulantatal, situated in Inner Mongolia of China. In addition, a high-resolution temporal framework was established for the Ulantatal sediments using magnetostratigraphy in conjunction with biostratigraphical correlation. Ulantatal also hosts profuse micromammalian faunas which had previously lacked a proper temporal framework. It has now proven possible to calibrate these faunas with contemporaneous Mongolian Valley of Lakes mammal paleocommunities, where the ages are constrained by a combination of radiometric dating and magnetostratigraphy. Using the calibrated mammalian faunas in Ulantatal to anchor the magnetostratigraphy, it was possible to infer an age of around 35 to 27 Ma for the Ulantatal deposits. ...