TY - JOUR

T1 - Combined cadmium and chromium isotopes record a collapse of bioproductivity across the Cretaceous—Paleogene boundary in the Danish basin

AU - Frederiksen, Jesper Allan

AU - Thibault, Nicolas

AU - Gilleaudeau, Geoffrey J.

AU - Bjerrum, Christian J.

AU - Moreau, Julien

AU - Frei, Robert

PY - 2024

Y1 - 2024

N2 - Cadmium (Cd) isotope signatures (δ114Cd) deduced from modern and ancient marine deposits are often used as a proxy for bioproductivity and for micronutrient cycling, whereas chromium (Cr) isotope signatures (δ53Cr) are used as a potential proxy for oxygenation. The Cretaceous—Paleogene (K/Pg) boundary records one of Earth's five big mass extinctions, which contains geochemical fingerprints of the Chixculub asteroid impact and is coeval with the Deccan Trap volcanism. Here we present for the first time a combined record of Cd and Cr isotopes from the Danish Basin to interrogate the effects on bioproductivity across the K/Pg boundary. The δ114Cd values range between −0.28‰ and 0.27‰ defining an average of 0.05‰ ± 0.24 (2σ, n = 87). Authigenic δ53Cr values range between 0.06‰ and 1.06‰ and define an average of 0.59‰ ± 0.51 (2σ, n = 81). An abrupt jump, across the K/Pg boundary layer, from consistently positively fractionated Cd and Cr isotope signatures recorded in Late Maastrichtian white chalks towards less positively fractionated δ114Cd values and heterogeneous δ53Cr values in the Early Danian carbonates, likely indicates a decrease in surface water bioproductivity. This decrease is accompanied by redox fluctuations in the water column as a consequence of environmental changes either related to the Chixculub impact event and/or to the Deccan volcanic eruptions coeval with this boundary. Assuming an efficient removal of Cd and Cr through consumption and/or adsorption by primary producers, or by incorporation into the skeleton/shells of calcifiers, and using the fractionation factor of Cd into carbonates, we reconstruct surface water conditions during the Late Masstrichtian—Early Danian that are compatible with those of modern oceans, with δ114Cd varying from 0.17 to 0.72‰. Overall, the combined Cr-Cd isotope fluctuations over the K/Pg boundary are consistent with a scenario characterized by climate-induced changes of nutrient availability and concomitant responses of primary production levels, ultimately related to the asteroid impact and to the proceeding volcanic activities that influenced the ocean's chemistry. We anticipate our results to point for further studies of other stratigraphic sections worldwide to reveal an extensive Cd-Cr record for the Cretaceous—Paleogene boundary and its corresponding collapse of bioproductivity and decreasing ocean oxygenation.

AB - Cadmium (Cd) isotope signatures (δ114Cd) deduced from modern and ancient marine deposits are often used as a proxy for bioproductivity and for micronutrient cycling, whereas chromium (Cr) isotope signatures (δ53Cr) are used as a potential proxy for oxygenation. The Cretaceous—Paleogene (K/Pg) boundary records one of Earth's five big mass extinctions, which contains geochemical fingerprints of the Chixculub asteroid impact and is coeval with the Deccan Trap volcanism. Here we present for the first time a combined record of Cd and Cr isotopes from the Danish Basin to interrogate the effects on bioproductivity across the K/Pg boundary. The δ114Cd values range between −0.28‰ and 0.27‰ defining an average of 0.05‰ ± 0.24 (2σ, n = 87). Authigenic δ53Cr values range between 0.06‰ and 1.06‰ and define an average of 0.59‰ ± 0.51 (2σ, n = 81). An abrupt jump, across the K/Pg boundary layer, from consistently positively fractionated Cd and Cr isotope signatures recorded in Late Maastrichtian white chalks towards less positively fractionated δ114Cd values and heterogeneous δ53Cr values in the Early Danian carbonates, likely indicates a decrease in surface water bioproductivity. This decrease is accompanied by redox fluctuations in the water column as a consequence of environmental changes either related to the Chixculub impact event and/or to the Deccan volcanic eruptions coeval with this boundary. Assuming an efficient removal of Cd and Cr through consumption and/or adsorption by primary producers, or by incorporation into the skeleton/shells of calcifiers, and using the fractionation factor of Cd into carbonates, we reconstruct surface water conditions during the Late Masstrichtian—Early Danian that are compatible with those of modern oceans, with δ114Cd varying from 0.17 to 0.72‰. Overall, the combined Cr-Cd isotope fluctuations over the K/Pg boundary are consistent with a scenario characterized by climate-induced changes of nutrient availability and concomitant responses of primary production levels, ultimately related to the asteroid impact and to the proceeding volcanic activities that influenced the ocean's chemistry. We anticipate our results to point for further studies of other stratigraphic sections worldwide to reveal an extensive Cd-Cr record for the Cretaceous—Paleogene boundary and its corresponding collapse of bioproductivity and decreasing ocean oxygenation.

U2 - 10.1016/j.chemgeo.2024.122058

DO - 10.1016/j.chemgeo.2024.122058

M3 - Journal article

VL - 654

JO - Chemical Geology

JF - Chemical Geology

SN - 0009-2541

M1 - 122058

ER -