Timing environmental perturbations across the Cretaceous – Paleogene boundary in the Boreal Realm (N. Denmark)

<p>The Cretaceous-Paleogene boundary (K-PgB) interval of Denmark has been the subject of numerous contributions for understanding this mass extinction, focusing essentially on the famous coastal exposures of Stevns Klint (Sjælland). Although less popular, exposures of the K-PgB are also known in northern Jutland (NW Denmark) and have been the subject of a few contributions on their macro- and microfaunal content. Through an integrated study of the section of Nye Kløv (biostratigraphy and high-resolution stable isotope stratigraphy), we show here that the KPgB interval in northern Jutland presents the double advantage of (1) being continuous across the latest Maastrichtian to early Paleogene (contrary to Stevns Klint sections that bear several discontinuities such as prominent hardgrounds) and (2) bearing well-preserved macro- and microfossil assemblages, and isotopic trends in carbon and oxygen. Bulk carbonate oxygen isotopes delineate with great precision temperatures trends across the KPgB interval with cyclic oscillations that faithfully reproduce trends of the La2010b astronomical solution, hence allowing for an astronomical calibration of the section. The orbital calibration of the KPgB in Nye Kløv points to an age of 66.01 Ma. Our study delineates a Deccan warming optimum at 66.25 Ma corresponding to the deposition of the Kjølby Gaard marl, a distinct marly layer that can be traced throughout the North Sea. A clear shift toward the end-Maastrichtian cooling follows the Deccan warming at 66.1 Ma and precedes a last pulse of warming immediately below the boundary at 66.02 Ma. The earliest Danian is characterized by lower temperatures up until 65.88 Ma, after which temperatures resume to the same range as those of the Deccan warming, albeit with strong oscillations that reflect pacing by the short-eccentricity. This shift toward much warmer temperatures is associated with a first negative excursion in carbon isotopes. A second marked negative excursion in carbon isotopes occurs at 65.65 Ma and taken all-together, the overall warm interval comprising these two carbon isotope excursions reflects the local expression of the Dan-C2 hyperthermal event. Orbital calibration of the Nye Kløv section also allowed us to determine the timing of the recovery in the benthic community in the Boreal Chalk Sea, marked by an increase in skeletal fragments and brachiopod diversity, which occurred at 65.8 Ma, hence in conjunction with the Dan-C2 event.</p>

Reinforcing the North Atlantic backbone: revision and extension of the composite splice at ODP Site 982

Ocean Drilling Program (ODP) Site 982 represents a key location for understanding the evolution of climate in the North Atlantic over the past 12 Ma. However, concerns exist about the validity and robustness of the underlying stratigraphy and astrochronology, which currently limits the adequacy of this site for high-resolution climate studies. To resolve this uncertainty, we verify and extend the early Pliocene to late Miocene shipboard composite splice at Site 982 using high-resolution XRF core scanning data and establish a robust high-resolution benthic foraminiferal stable isotope stratigraphy and astrochronology between 8.0 and 4.5 Ma. Splice revisions and verifications resulted in ∼ 11 m of gaps in the original Site 982 isotope stratigraphy, which were filled with 263 new isotope analyses. This new stratigraphy reveals previously unseen benthic δ18O excursions, particularly prior to 6.65 Ma. The benthic δ18O record displays distinct, asymmetric cycles between 7.7 and 6.65 Ma, confirming that high-latitude climate is a prevalent forcing during this interval. An intensification of the 41 kyr beat in both the benthic δ13C and δ18O is also observed ∼ 6.4 Ma, marking a strengthening in the cryosphere–carbon cycle coupling. A large ∼ 0.7 ‰ double excursion is revealed ∼ 6.4–6.3 Ma, which also marks the onset of an interval of average higher δ18O and large precession and obliquity-dominated δ18O excursions between 6.4 and 5.4 Ma, coincident with the culmination of the late Miocene cooling. The two largest benthic δ18O excursions ∼ 6.4–6.3 Ma and TG20/22 coincide with the coolest alkenone-derived sea surface temperature (SST) estimates from Site 982, suggesting a strong connection between the late Miocene global cooling, and deep-sea cooling and dynamic ice sheet expansion. The splice revisions and revised astrochronology resolve key stratigraphic issues that have hampered correlation between Site 982, the equatorial Atlantic and the Mediterranean. Comparisons of the revised Site 982 stratigraphy to high-resolution astronomically tuned benthic δ18O stratigraphies from ODP Site 926 (equatorial Atlantic) and Ain el Beida (north-western Morocco) show that prior inconsistencies in short-term excursions are now resolved. The identification of key new cycles at Site 982 further highlights the requirement for the current scheme for late Miocene marine isotope stages to be redefined. Our new integrated deep-sea benthic stable isotope stratigraphy and astrochronology from Site 982 will facilitate future high-resolution late Miocene to early Pliocene climate research.