Multiproxy analysis of paleoenvironmental, paleoclimatic and paleoceanographic changes during the early Danian in the Caravaca section (Spain)

Abstract After the Chicxulub impact and mass extinction at the Cretaceous-Paleogene boundary (K-PgB), ecosystems haltingly recovered under unstable conditions. An early Danian (65.9 Ma) perturbation of the carbon cycle known as Dan-C2, which includes two carbon isotopic excursions (CIEs), has been ascribed to inputs of greenhouse gases through large-scale volcanism of the Deccan Traps. However, the relationship between Dan-C2, volcanism and environmental and climatic changes during the early Danian remains ambiguous. Based on stable isotopes, calcium carbonate content, magnetic susceptibility and planktic foraminifera, we present a paleoenvironmental, paleoclimatic and paleoceanographic reconstruction of the early Danian from the Caravaca section, Spain, one of the most complete and continuous K-PgB sections worldwide. The paleobiological response of planktic foraminifera suggests very volatile environmental conditions during the first 230 kyr of the Danian, as reflected in the rapid succession of opportunistic/generalist blooms and episodic high occurrences of aberrant specimens. According to our age model, the Dan-C2 has been identified at the Caravaca section from 65.92 to 65.74 Ma. No evidence of strong carbonate dissolution through ocean acidification was observed in the Dan-C2 interval or the rest of the studied section, excluding the K-PgB clay bed. We find that blooms of highly eutrophic Chiloguembelitria and increases in aberrant planktic foraminifera coincided with a major early Danian eruptive episode of Deccan Traps (Ambelani Formation), occurring before the Dan-C2. Conversely, during both Dan-C2 CIEs, less opportunistic taxa thrived, indicating changes in the upper part of the water column. This study demonstrates that the relationship between marine biota and climate change was very complex and rapidly changing during the early Danian. In addition, we propose that the Deccan volcanism had adverse effects on marine plankton, mostly through strong eutrophication, while an increased water column stratification during the Dan-C2 event resulted in a transient boost in the recovery of ecosystems.