International audienc

No abstract

The Cretaceous/Paleogene (K/Pg) boundary is well-represented across a range of depositional settings in New Zealand. Trends in fossil assemblages and marine lithofacies indicate that the K/Pg event was followed by a pronounced and long-term (~1 Myr) perturbation in climate and ocean conditions. These findings are supported by a TEX86derived sea surface temperature (SST) reconstruction across the K/Pg boundary at mid-Waipara River, north Canterbury. The BAYSPAR calibration indicates that SST was very stable in the uppermost Cretaceous (~20°C), but abruptly warmed by ~4°C in a 25 cm-thick lowermost Paleocene interval. This interval is overlain by a ~2 m thick interval in which SST abruptly cooled by ~10°C and then progressively returned to ~20°C. The basal Paleocene warm interval is associated with an acme in the dinoflagellate species Trithyrodinium evittii and the succeeding cool interval is associated with an acme in Palaeoperidinium pyrophorum. Biostratigraphic correlation of the shelfal mid-Waipara section to the pelagic K/Pg sections in Marlborough reveals that a significant unconformity separates these two acme events, with the T acme event occurring in the earliest Paleocene and the P. pyrophorum acme occurring ~1 Myr later and lasting ~200 kyr. A succession of dinoflagellate acme events within the intervening interval in the Marlborough sections implies unstable climatic and environmental conditions in the lead up to the P. pyrophorum acme and cooling event at ~65 Ma. This event also coincides with a peak in biogenic silica accumulation in the Marlborough sections. We suggest that disruption to biogeochemical pathways at the K/Pg boundary caused long-term climatic cooling in the southern Pacific region.

No abstract

Early to late Holocene sediments from core F80, Fårö Deep, Baltic Sea, are investigated for their palynomorph composition and dinoflagellate cyst record to map variations in sea‐surface‐water salinity and palaeoproductivity during the past 6000 years. The F80 palynomorph assemblages are subdivided into four Assemblage Zones (AZs) named A to D. The transition from the stratigraphically oldest AZ A to B reflects a marked increase in palaeoproductivity and a gradual increase in surface‐water salinity over the ∼1500 years between the Initial Littorina (former Mastogloia Sea Stage) and Littorina Sea Stage. A period with maximum sea‐surface salinity is recorded within the overlying AZ C from 7200 to 5200 cal. a BP, where the process length of Operculodinium centrocarpum indicates that average salinities were probably the highest (∼15–17 versus 7.5 psu today) since the last glaciation. The change from AZ C to D correlates with a shift from laminated to non‐laminated sediments, and the dinoflagellate cyst assemblages suggest that the surface‐ and the deep‐water environment altered from c. 5250 cal. a BP, with less productivity in the surface water and more oxygenated conditions in the deep water. Here we demonstrate that past regional changes in surface salinity, primary productivity and deep‐water oxygenation status in the Baltic Sea can be traced by mapping overall palynomorph composition, dinoflagellate cyst assemblages and variations in the process length of O. centrocarpum in relation to periods of laminated/non‐laminated sedimentation and proportion of organic‐matter in the sediments. An understanding of past productivity changes is particularly important to better understand present‐day environmental changes within the Baltic Sea region.