Intermittent euxinia in the high-latitude James Ross Basin during the latest Cretaceous and earliest Paleocene

Seymour Island, in the James Ross Basin, Antarctica, contains a continuous succession of latest Cretaceous sediments deposited in a shallow marine environment at high latitude, making it an ideal place to study environmental changes prior to the K–Pg mass extinction. We measured major and trace elements and conducted petrographic analysis of two sections from the Maastrichtian–Danian López de Bertodano Formation of Seymour Island. Several lines of evidence point to intermittently anoxic to euxinic conditions during deposition, including the presence of pyrite framboids with a size distribution suggesting syngenetic formation in the water column, and enrichments in several trace elements, including molybdenum, arsenic, copper, zinc, and chromium. Molybdenum enrichments are clearly associated with enrichments in manganese and authigenic iron, suggesting “shuttling” of redox sensitive trace elements across a chemocline that fluctuated across the sediment-water interface. Comparisons with modern systems suggest relatively high-frequency redox variability, possibly over approximately annual timescales, which may be related to the annual cycle of polar sunlight and associated seasonal changes in primary productivity. Glauconitic horizons are associated with more reducing conditions, including at the K–Pg boundary, though this does not appear to be a uniquely euxinic interval; similar degrees of trace element enrichment are seen in other highly glauconitic intervals. While euxinia may have contributed to low diversity in the lowermost ‘Rotularia Units’, redox conditions do not seem to have been the primary control on the transition to a mollusc dominated fauna in the latest Maastrichtian. Redox conditions show little to no response to the eruption of the Deccan Traps or Maastrichtian climatic changes. Instead, intermittent euxinia appears to have been a characteristic feature of this high-latitude environment during the Cretaceous–Paleogene transition.