Early Cretaceous lignites from inner-continental Asia as paleoclimate archive

The late Early Cretaceous (Aptian-Albian; 121.4 – 100.5 Ma) is generally considered as a greenhouse interval. During the Aptian-Albian interval, paleo-Asia formed a large landmass in the northern hemisphere, creating widespread inner-continental areas, far away from any marine influence. The Cretaceous is well-known for a diverse dinosaur fauna especially from northern America and central Asia. However, studies focusing on the paleoenvironmental context of these dinosaurs are mostly lacking. The Early Cretaceous dinosaur fauna from Mongolia is no exception. An excellent archive for paleoenvironmental reconstructions are lignites, derived from former wetland ecosystems, providing insights into the paleoclimatic and paleoecological evolution. The lignites from Mongolia show unusual low thermal maturity, making them a promising target for these reconstructions. The lignites studied within this thesis are located within the Choir-Nyalga Basin, in the eastern central part of Mongolia and are assigned to the Khukhteeg Formation. In total, three different opencast lignite mines were investigated: the Tevshiin Govi, the Shivee Ovoo and the New Shivee Ovoo. To investigate the paleoenvironmental conditions of the lignites, classical analytical approaches like coal petrography and bulk-rock geochemistry were combined with palynological analysis. The Tevshiin Govi and Shivee Ovoo site were dominated by forested paleoenvironments. The lignites were derived from peats in topogenous mire settings strongly influenced by fluvial processes. A third study investigated the potential of the Mongolian lignites as a paleotemperature archive, applying the branched glycerol dialkyl glycerol tetraethers biomarker proxy, to reconstruct mean annual air temperatures. Former studies reconstructing inner-continental temperatures, suggested contradictory cool temperatures in the context of the greenhouse interval. In this thesis, new mean annual air temperatures of approximately 15.1 ± 2.6 °C are proposed. These results represent some of the oldest continental biomarker based paleotemperatures to date. In order to contextualize the new calculated temperatures, different climate model setups were applied, suggesting higher CO2 levels above 1000 ppm for the Aptian-Albian in Mongolia.