Isotopic evidence for changes in the zinc cycle during Oceanic Anoxic Event 2 (Late Cretaceous)

Widespread deposition of organic-rich shales during the Late Cretaceous Oceanic Anoxic Event 2 (OAE 2, ca. 94 Ma) occurred during a period of significant global paleo-environmental and geochemical change. It has been proposed that an increase in nutrient input to the ocean during OAE 2 was the key mechanism that generated and sustained high rates of organic-matter burial over time scales of 103-105 yr. Zinc is a bio-essential micronutrient and the proportion of Zn burial in oxic sediments relative to burial in organic-rich continental margin sediments is reflected in its seawater isotope composition. The first Zn-isotope records dating from the Cretaceous are presented here from three coeval carbonate successions: two from Europe (southern England and southern Italy) and one from southern Mexico. The new data show reproducible stratigraphic Zn-isotope patterns in spatially and lithologically diverse carbonate successions. Excursions to lower Zn-isotope values may be linked to the input of magmatic Zn, changes in the proportion of Zn burial into organic-rich sediments, and the liberation of previously buried Zn during an episode of widespread seafloor re-oxygenation during OAE 2 (the Plenus Cold Event).