New insights into Early Cretaceous continental environments and climate based on lignite-bearing strata from central Mongolia

The late Early Cretaceous (121.4 to 100.5 Ma) was characterized by a gradual warming trend superimposed on an already warm greenhouse climate. Whereas the evolution of ocean temperatures during this time interval is relatively well constrained, information on the response of continental interiors to such climatic extremes is limited. Here we report new data from the continental Choir-Nyalga Basin of central Mongolia, which contains thick, lignite-rich successions (Khukhteeg Fm.) bearing an exceptionally well-preserved fossil flora of various pine and redwood species as well as representatives of extinct seed plant lineages. The continuous and often long-lasting accumulation of plant remains results in continental high-resolution archives documenting the palaeoecological conditions prevailing during bog growth.

In order to reconstruct the palaeoenvironmental conditions, a combined approach including brGDGT-based palaeothermometry, coal petrology and palynology is applied, complemented by geochemical measurements (TOC, TS, δ¹³C_org). Due to the limited biostratigraphic resolution of the continental Khukhteeg Fm., stratigraphic trends in δ¹³C_org will be applied for local and super-regional chemostratigraphic correlation. The carbon isotopic composition of the land plant-derived organic matter shows pronounced stratigraphic fluctuations and varies between -20.8 ‰ to -24.4 ‰ (average: -22.4 ‰). The brGDGT data represent the oldest analyses obtained from lignites so far. The new data indicate that the climatic conditions in central paleo-Asia (paleolatitude of ~38°N) during the late Early Cretaceous were characterised by high mean annual air temperatures (ranging between 8 ± 3°C and 10 ± 4°C).