Conference Agenda

The clumped isotope (Δ₄₇) composition of the fossil calcite and aragonite provides direct information about past seawater temperatures. Its greatest benefits include the independence of the Δ₄₇ thermometry from the oxygen isotope composition of the seawater. A limitation of this proxy is its susceptibility to diagenesis and solid-state reordering caused by the elevated temperatures during sediment burial, altering the original Δ₄₇ signal. Laboratory heating experiments show different Δ₄₇ resetting kinetics for various carbonate components, which are necessary to evaluate in order to choose optimal carbonate archives for paleoclimate reconstructions.

We present clumped and stable isotope data from Cenomanian-Campanian rudists, extinct bivalves widely used for Late Jurassic-Cretaceous paleoclimate studies. The fossils come from regions with different burial temperature histories, the Friuli-Venezia Giulia region (FVG; Italy) and Istria (Croatia). Although the rudist δ¹⁸O values from both regions are not significantly different, the Δ₄₇ temperatures in FVG reach as much as 71-101 °C, suggesting Δ₄₇ signal resetting, while Δ₄₇ temperatures in Istria specimens are much lower. We evaluate the clumped isotope resetting of rudist fossils using two models, which, however, do not conclusively reveal what reordering kinetics pattern rudists follow. This merits caution when using rudist calcite as an archive for past temperatures. The well-preserved Δ₄₇ composition of Istrian rudists indicates temperatures of 34-41 °C, aligning with the higher end of Late Cretaceous paleotemperature reconstructions. Combining Δ₄₇ and δ¹⁸O results yields δ¹⁸O_seawater values of -0.1 to 1.4 ‰, differing from the value of -1 ‰ assumed for ice-free Late Cretaceous oceans.

In this study the stable and clumped isotopes of belemnites are presented from the Albian and Campanian - Maastrichtian interval derived from the chalks of Norfolk, UK. These chalk sediments were deposited on the North Atlantic shelf, part of an extensive relatively shallow epicontinental sea that covered most of northern Europe and beyond. Cathodoluminescence and elemental geochemistry of the belemnites reveals that most of the rostra were well preserved. If interpreted in terms of temperature (using an assumption regarding the δ¹⁸O of seawater), our oxygen isotope record reveals relatively warm temperatures for the Albian, warm temperatures during the Campanian with maximum mean temperatures of ~24 °C, followed by cooling to ~21 °C during Maastrichtian. Clumped isotope palaeothermometry is a method that provides a temperature constraint that is independent of the isotopic composition of the water in which the carbonate formed. Our clumped data also show relatively warm temperatures for the Albian and Campanian - Maastrichtian cooling (from 26 to 20 °C). These clumped isotope data compare favourably with published TEX₈₆ temperatures. Significantly, our data are similar or higher than modelled temperatures, modelled with relatively high CO₂ concentrations.

A large part of the African continent has experienced a significant uplift throughout the Late Cretaceous. This event coincides with a decline of CO2 level, and a global climate cooling. Evidences of this uplift include quantification of sediment volumes in oceanic basins, thermochronological dating, and inland geomorphological observations. In addition, new geochemical data from sediment cores, including clay mineralogy and combined Hf and Nd isotopic composition for which data acquisition is still ongoing, indicates a contrasted and asynchronous response of continental weathering systems to this uplift.
Here we used the modelling framework GEOCLIM to simulate the response of continental weathering and global geochemical cycles to the Cretaceous African uplift. We developed an uplift scenario based on marine sedimentary data around the African continent, and reconstruction of paleo elevation and lithology. This scenario is used as input by GEOCLIM, that computes weathering fluxes (including silicates, petrogenic organic carbon and phosphorus), and the evolution of global carbon cycle (both organic and inorganic part). This framework allows us to quantify pCO2 drawdown and the associated global cooling that may have resulted from this tectonic event.

The Western Interior Seaway (WIS) was a vast epicontinental sea that inundated North America in a series of transgressive-regressive marine cycles from the Early to Late Cretaceous. The WIS has been studied as a classic shallow Cretaceous seaway with a complex stratigraphic record of the interplay between tectonics, climate, sea level, basin evolution, and faunal evolution. However, fundamental questions remain unresolved regarding the WIS, including how seawater temperatures and oxygen isotope compositions (δ¹⁸O_w) varied latitudinally and through time. A robust record of latitudinal temperature gradients (LTGs) could help explain paleoceanography and faunal evolution in the WIS. Previous WIS paleotemperature reconstructions have yielded improbably warm temperatures from poorly constrained δ¹⁸O_w values or focused on specific time intervals or regions. Here, we report carbonate clumped isotopes (𝚫₄₇) measurements from 94 Cretaceous oysters obtained from the Smithsonian’s Cobban collection and the University of Michigan Museum of Paleontology to obtain LTGs from the Aptian to Maastrichtian Stages. This study approximately triples the 𝚫₄₇-derived WIS temperatures and δ¹⁸O_w values published to date. Our measurements yield average seawater temperatures ranging from 23-31 °C and indicate LTGs were minimal from the Aptian to Campanian and increased in the Maastrichtian. Values of Cretaceous δ¹⁸O_w, traditionally assumed to be -1.0‰ Standard Mean Ocean Water (SMOW), varied between -1.0‰ and +0.4‰ SMOW through time. We interpret changes in mean temperatures and LTG as responses to global climate drivers and regional influences, offering insights on basin evolution resulting from sea level fluctuations, tectonics, and paleoceanographic circulation patterns in the WIS.