The onset of Deccan main phase eruptions is estimated at the base of chron C29r, ~250 ky before the Cretaceous-Paleogene boundary (KTB or K-Pg or KPB). Lava mega-flows reaching eastern India stratigraphically underlie the KPB, standing testimony for peak volcanism preceding/straddling the KPB mass extinction. High-flux injections of thousands of gigatons of CO₂ and SO₂ into the atmosphere could have resulted in surface ocean acidification on variable timescales. Prolonged carbonate crisis is direct stress for marine calcifying planktic foraminifera, and may have played a critical role in their mass extinction. Initial multi-proxy evidence from Bidart (France) and Gamsbach (Austria) strongly support the acidification hypothesis. The current study aims at tracking the stratigraphic timing and nature of this event through the western Tethys Spanish KPB sections.

Carbonate dissolution intervals are recorded in the topmost ~50 cm at Agost and Caravaca (Spain), ~40 cm in Gamsbach and ~150 cm at Zumaiya (Spain). These correlate with the ~60 cm thick Deccan benchmark interval at Bidart (uppermost Maastrichtian zone CF1). Increased abundance (>40%) of dwarfed Guembelitria (<63μm fraction) in the suspect interval at Bidart, Zumaya and Caravaca associated with pulsed mercury peaks (>20 ppb, background values are <0.1 ppb) suggest high faunal stress and ongoing volcanism. The most expanded known KPB transition at Elles (Tunisia) yields a tentative event onset age of ~ 50 ky pre-KPB. The correlative intertrappean sediments between lava mega-flows in the Krishna-Godavari basin (eastern India) record acute carbonate dissolution and rapid diversity decline in planktic foraminifera. The new findings lend strength to a link between intensified Deccan volcanism and the faunal stress build up in the final ~50 ky, leading up to the KPB mass extinction.