The Cretaceous deep-sea record of the Santonian–Campanian transition is commonly interrupted by an extensive unconformity (representing <10 Myr of hiatus). The resultant palaeoceanographic gap can now be partly bridged by a recent short core of pelagic ooze from Shatsky Rise (Integrated Ocean Drilling Program (IODP) Site U1348), with precise multidisciplinary age constraints developed herein. New oxygen isotope data from very well-preserved benthic foraminifera, together with accurately compiled comparable benthic data from previous Pacific deep-sea sections, exhibit a large (c. +1‰) early Campanian shift. We propose the Santonian–Campanian climatic transition was not gradual but was the first major cooling step after sustained mid-Cretaceous hothouse conditions.

Supplementary material:

Detailed analytical methods including biostratigraphic notes and Sr isotopic chronology, supplementary figures (locality map; additional geochemical, isotopic and micropalaeontological results; palaeomagnetic results; global Sr isotope compilation and age model; benthic foraminiferal stable isotope compilation), tables of microfossil occurrences and numerical data are available at http://www.geolsoc.org.uk/SUP18598.

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