The Dan-C2 hyperthermal event at Gubbio (Italy): Global implications, environmental effects, and cause(s).

The Dan-C2 event is an early Danian, transient (∼100 kyr) hyperthermal episode centered at ∼65.2 Ma, which records shifts in carbon reservoirs and ocean warming in the northwestern and southeastern sectors of the Atlantic Ocean. Here we present and discuss high-resolution biochronostratigraphic and magnetic susceptibility data and geochemical records from the western Tethyan Contessa Highway section (Gubbio, Italy), which provide the first direct evidence of the Dan-C2 event beyond the Atlantic Ocean and point to the supra-regional, possibly global, significance thereof. At Contessa Highway, the Dan-C2 event exhibits stressed ecological responses among calcareous nannoplankton and foraminifera, which highlight marked environmental perturbation affecting the geobiosphere and resulting in enhanced eutrophication of the sea surface waters and carbonate dissolution, as well as lowered oxygen content along the water column and at the sea bottom. As for other early Paleogene hyperthermal events, the cause of the Dan-C2 event might likely to be found in changes, potentially astronomically paced, in the distribution of carbon within surface biosphere reservoirs. However, the role played by the concurrent third and last phase of Deccan volcanism with its huge release of greenhouse gases into the atmosphere would be also taken into account. In addition, here we provide first evidence of a further short-lived (∼38 kyr) hyperthermal event not known up to now and that we term the “Lower C29n” event.