Lake evolution during the Early Danian Dan-C2 hyperthermal, Boltysh impact crater, Ukraine

Lacustrine facies record complex relationships between lake evolution and environmental changes, and therefore preserve a record of climatic conditions at time of lake formation. Lakes which preserve sediments deposited in... [ view full abstract ]

Lacustrine facies record complex relationships between lake evolution and environmental changes, and therefore preserve a record of climatic conditions at time of lake formation. Lakes which preserve sediments deposited in steady state conditions over <1my can provide exceptionally high resolution records of the interactions between the lake system and environmental forcing. This is of particular value when studying the environmental impact of rapid climate change, such as that experienced during hyperthermals. Hyperthermals are recorded as negative carbon isotope excursions (CIEs). Here, we present a complete lacustrine record of the Early Danian Dan-C2 hyperthermal at c. 65.2 Ma from a core drilled in the K-Pg Boltysh impact crater, Ukraine. This borehole allows a detailed facies analysis and reconstruction of lake evolution and associated plant ecosystem in correspondence with rapid climate change.

The Boltysh borehole reveals a c. 400 m thick siliciclastic and organic-rich succession which unconformably overlies impact melt-breccia dated at 65.17 ± 0.64 Ma. Based on detailed core logging, 8 facies associations are identified, including 1) littoral mudstones, 2) siliciclastic shoreline deposits, 3) siliciclastic littoral to sublittoral deposits, 4) mudstone laminites, 5) organic-rich mudstones, and deposits of 6) coarse-grained, 7) fine-grained turbidity currents, and 8) debris flows.
Based on the occurrence of these facies associations 3 major phases of lake evolution are distinguished: 1) an initial pre-CIE rising clastic-dominated lake phase characterised by the presence of coarse-grained density and debris flow deposits, 2) a perennial lake phase during the main phase of the CIE, characterised by alternating packages of deep lake facies (mudstone laminites and organic-rich mudstones) and shallow lake facies (siliciclastic littoral to sublittoral deposits); and 3) a shallow lake during and post-CIE recovery phase, which preserve both littoral facies deposited under both wave-dominated and quiet conditions.

This study provides a detailed record of lacustrine response to rapid climate change during the Dan-C2 hyperthermal, and subsequently allows us to infer lake formation and environmental conditions at different stages during climate warming. The high resolution sedimentary record and palynological analysis will allow us to analyse the effects and timing of short-term and long-term climatic variations and their relationship to the hyperthermal. This has important implications for our understanding of response patterns of ancient terrestrial environments and ecosystems to climate changes, but will also help to better understand environmental changes derived from modern climate warming.