Kate Littler

A carbon-isotope perturbation at the Pliensbachian–Toarcian boundary: evidence from the Lias Group, NE England

A perturbation in the carbon-isotope record at the time of the Pliensbachian–Toarcian boundary (~ 184 Ma) in the Early Jurassic is reported, based on new data from Yorkshire, England. Two sharp δ 13 C org negative excursions, each with a magnitude of ~ −2.5 ‰ and reaching minimum values of −28.5 ‰, are recorded in the bulk organic-matter record in sediments of latest Pliensbachian to earliest Toarcian age. A similar pattern of negative carbon-isotope excursions has been observed at the stage boundary in the SW European section at Peniche, Portugal in δ 13 C carbonate , δ 13 C wood and δ 13 C brachiopod records. The isotopic excursion is of interest when considering the genesis and development of the later Toarcian Oceanic Anoxic Event (OAE), as well as the second-order global extinction event that spans the stage boundary. Furthermore, the isotope excursion potentially provides a chemostratigraphic marker for recognition of the stage boundary, which is currently achieved on the basis of different ammonite faunas in the NW European and Tethyan realms.

Evidence for global cooling in the Late Cretaceous.

The Late Cretaceous ‘greenhouse’ world witnessed a transition from one of the warmest climates of the past 140 million years to cooler conditions, yet still without significant continental ice. Low-latitude sea surface temperature (SST) records are a vital piece of evidence required to unravel the cause of Late Cretaceous cooling, but high-quality data remain illusive. Here, using an organic geochemical palaeothermometer (TEX86), we present a record of SSTs for the Campanian–Maastrichtian interval (~83–66 Ma) from hemipelagic sediments deposited on the western North Atlantic shelf. Our record reveals that the North Atlantic at 35 °N was relatively warm in the earliest Campanian, with maximum SSTs of ~35 °C, but experienced significant cooling (~7 °C) after this to <~28 °C during the Maastrichtian. The overall stratigraphic trend is remarkably similar to records of high-latitude SSTs and bottom-water temperatures, suggesting that the cooling pattern was global rather than regional and, therefore, driven predominantly by declining atmospheric pCO2 levels.

An emerging palaeoceanographic ‘missing link’: multidisciplinary study of rarely recovered parts of deep-sea Santonian–Campanian transition from Shatsky Rise

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.

A new high-resolution chronology for the late Maastrichtian warming event: Establishing robust temporal links with the onset of Deccan volcanism

The late Maastrichtian warming event was defined by a global temperature increase of ∼2.5–5 °C that occurred ∼150–300 k.y. before the Cretaceous-Paleogene (K-Pg) mass extinction. This transient warming event has traditionally been associated with a major pulse of Deccan Traps (west-central India) volcanism; however, large uncertainties associated with radiogenic dating methods have long hampered a definitive correlation. Here we present a new high-resolution, single species, benthic stable isotope record from the South Atlantic, calibrated to an updated orbitally tuned age model, to provide a revised chronology of the event, which we then correlate to the latest radiogenic dates of the main Deccan Traps eruption phases. Our data reveal that the initiation of deep-sea warming coincides, within uncertainty, with the onset of the main phase of Deccan volcanism, strongly suggesting a causal link. The onset of deep-sea warming is synchronous with a 405 k.y. eccentricity minimum, excluding a control by orbital forcing alone, although amplified carbon cycle sensitivity to orbital precession is evident during the greenhouse warming. A more precise understanding of Deccan-induced climate change paves the way for future work focusing on the fundamental role of these precursor climate shifts in the K-Pg mass extinction.