Lake sedimentological and ecological response to hyperthermals: Boltysh impact crater, Ukraine

The Boltysh meteorite impact crater, Ukraine, formed at the Cretaceous-Palaeogene boundary at ca 652Ma. A borehole drilled in the central part of the crater cored a>400m thick high-resolution lacustrine succession that covers the Dan-C2 hyperthermal event associated with a negative carbon isotope excursion. Continuous terrestrial records of past hyperthermals are of limited availability, which makes this record a unique case study of the continental impact of rapid climate warming. This study uses high-resolution sedimentological core log data together with thin-section, X-ray diffraction, microprobe and palynological analyses to: (i) reconstruct lake sedimentological and ecological development across the carbon isotope excursion; and (ii) assess the environmental effect of hyperthermals on terrestrial ecosystems. Based on detailed facies analysis, five gradual stages of lake formation are identified, which show a strong relationship to carbon isotope shifts and associated climatic trends. Initially, sediment supply into the Boltysh lake was controlled by crater morphology. During later lake stages, sediment supply was increasingly controlled by changes in inflow-evaporation ratios which affected seasonal stratification patterns and longer term lake levels. An inferred increase in atmospheric pCO(2) related to the carbon isotope excursion, together with increasing mean annual temperatures, was probably responsible for periodic increases in biological activity of photosynthesising organisms and biomass production. These fluctuations in facies and lake settings largely correspond to orbital-paced moisture availability oscillations. The gradual reduction in sediment supply commencing during early lake formation prior to carbon isotope excursion inception suggest that the Dan-C2 event did not initiate sedimentary changes, but intensified sedimentary response to orbital controlled climate change.