Late Maastrichtian paleoclimatic and paleoceanographic changes inferred from Sr/Ca ratio and stable isotopes

Milankovitch-scale cycles can be recognized in high-resolution δ13C, δ18O, Sr/Ca, mineralogical, and magnetic susceptibility data in hemipelagic sediments that span the last 700 kyr of the Maastrichtian at Elles, Tunisia. Oxygen isotope data reveal three cool periods between 65.50 and 65.55 Ma (21.5–23.5 m), 65.26 and 65.33 Ma (8–11 m), and 65.04 and 65.12 Ma (1.5–4 m), and three warm periods between 65.33 and 65.38 Ma (12–16 m), 65.12 and 65.26 Ma (4–8 m), and 65.00 and 65.04 Ma (0–1.5 m). The cool periods are characterized by small surface-to-deep temperature gradients that reflect intensive mixing of the water column. The surface-to-deep Sr/Ca gradient generally correlates with the oscillating ΔT trend (temperature difference between surface and bottom waters). The carbon isotope composition of planktonic foraminifera indicates a continuous decrease in surface bioproductivity during Late Maastrichtian. Decreasing Δ13C values (difference between the δ13C values of surface and bottom dwelling foraminifera) and the carbon isotope ratios of the planktonic species at the onset of gradual warming at 65.50 Ma reflect a reduction in surface productivity as a result of decreased upwelling that accompanied global warming and possibly increased atmospheric pCO2 related to Deccan Trap volcanism. Time series analysis applied to magnetic susceptibility, δ18O, and Sr/Ca data identifies the 20 kyr precession, 40 kyr obliquity, and 100 kyr eccentricity Milankovich cycles.