|Plio-Pleistocene dinoflagellate cyst biostratigraphy and palaeoecology of the eastern North Atlantic and southern North Sea Basin|
De Schepper, S. (2006). Plio-Pleistocene dinoflagellate cyst biostratigraphy and palaeoecology of the eastern North Atlantic and southern North Sea Basin. University of Cambridge: Cambridge. 327, 6 appendices, 23 plates pp.
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VLIZ: Open Repository 259322 [ OMA ]
|Document type: Dissertation|
This study provides an independently calibrated high-resolution dinoflagellate cyst (hereafter ‘dinocyst’) biostratigraphy for Plio-Pleistocene (4.0–0.5 Ma) deposits recovered from eastern North Atlantic Deep Sea Drilling Project (DSDP) Hole 610A. The age model, which is largely tied to marine isotope stratigraphy and magnetostratigraphy, has been revised for the lower part of the hole using new data on the range of the calcareous nannofossil Reticulatosphaera pseudoumbilicus.The present study has yielded a rich and diverse dinocyst record, which includes several range bases and tops within the studied interval. The highest and/or lowest occurrences of 23 species were recognised in DSDP Hole 610A and calibrated to the newly defined age model using graphic correlation. A dinoflagellate cyst biozonation with eleven interval zones and one acme subzone have also been erected.The first signs of intense climatic cooling occur at Marine Isotope Stage (MIS) M2 (3.3 Ma, Pliocene), where ice-rafted debris is recognised in Hole 610A for the first time. Within a short interval spanning this event, dinocysts and the d18O-record from the planktonic foraminifer Globigerina bulloides have been examined from the same samples in order to obtain a directly calibrated dinocyst-based temperature index. Several other environmental indices (e.g. productivity, flux or transport indices) were calculated from the dinocyst record as a means to interpret the palaeoecological variability within MIS M2. Multivariate and cluster analysis were applied to distinguish between cold, warm and intermediate assemblages. Palaeo-autecological data on individual extinct species were also obtained using multivariate analysis.The same palaeoecological techniques have then been applied to the entire Plio-Pleistocene section. A cooling of the climate is reflected by a decrease in the number of species, which starts from c. 3.0 Ma onwards. Heat transport to the north via the North Atlantic Current (NAC) is apparently reflected also in the abundance of Operculodinium centrocarpum sensu Wall and Dale (1996). At around 2.85 and 2.7 Ma, peaks in this species’ abundance may reflect increased NAC heat transport associated with the closure of the Isthmus of Panama.The most significant changes in the dinocyst flora occur in the Gelasian Stage, coincident with the intensification of the Northern Hemisphere glaciations. In this interval, the cool-tolerant Habibacysta tectata is the dominant species, reflecting an important ocean-wide reorganisation. A possible explanation could be the cessation of warm surface-water transport to northern latitudes via the NAC and an associated halt in deep-water production in the Greenland–Norwegian Seas.Biostratigraphical data collected from the North Atlantic has been successfully applied to the Pliocene deposits of the southern North Sea Basin. Here, the Tunnel-Canal Dock (Antwerp, northern Belgium) section yielded diverse dinocyst assemblages. Dinocysts, and also pollen, clearly indicate a Pliocene age from both biostratigraphic and palaeoecological evidence. The study firmly places the Kattendijk Formation within the Zanclean Stage, whereas the Lillo Formation belongs to the Piacenzian Stage of the Pliocene. Additional sequence stratigraphical evidence has placed even more accurate age constraints on these lithostratigraphical units. Palaeoecological information from dinocysts shows that deposition of both Pliocene units occurred in progressively shallowing neritic environments under (warm-)temperate conditions, prior to cooling associated with the onset of the Northern Hemisphere glaciations.Finally, taxonomic progress on dinoflagellate cysts, acritarchs and marine incertae sedis from the eastern North Atlantic and the southern North Sea Basin has resulted in the recognition of numerous new taxa from both regions.