Aptian to Cenomanian dinoflagellate cysts from the Mazagan Plateau

Eighty-eight samples of Aptian to lower Cenomanian sediments of Sites 545 and 547, DSDP Leg 79, from the Mazagan Plateau area (offshore Northwest Africa) were analyzed for palynomorphs. The very rich dinoflagellate cyst assemblages make it possible to narrow shipboard age determinations and to correlate Sites 545 and 547. The distribution of 174 dinoflagellate cyst taxa is tabulated in this study and the biostratigraphic value of selected dinoflagellate cysts is discussed. Additional taxonomic remarks are made about some species. The new dinoflagellate cyst species Aptea almohadensis, Occisucysta hinzü, O. mazaganensis, and the subspecies Maghrebinia perforata (Clarke and Verdier, 1967) Below, 1981 ssp. mirabilis are described.

(Table 1) Dinoflagellate cysts and acritarchs in upper Pliocene and Pleistocene sediments from ODP Hole 151-911A

Pliocene and Pleistocene sediments from Ocean Drilling Program Leg 151, Hole 911 A, drilled on the innermost Yermak Plateau (Eastern Arctic Ocean), were studied for their dinoflagellate cyst content. Three assemblage zones were tentatively defined, characterized by the predominance of few species. The composition of the assemblages changed markedly, even within single assemblage zones, during the last 2.6 to 2.8 m.y., reflecting the variable influence of warmer water from the Norwegian Sea, fluctuations in the influence of cold polar water masses, and the extent of sea-ice cover. Polar to subpolar surface water masses prevailed on the Yermak Plateau during the late Pliocene, when the eastern Arctic Ocean was probably isolated from the Norwegian-Greenland Sea. Intrusions of warmer water are recorded since the latest Pliocene, alternating with colder periods and a prolonged seasonal sea-ice cover. The composition of the dinoflagellate cyst assemblages has also changed considerably since the middle Pleistocene, reflecting the establishment of stronger fluctuations in surface water mass conditions than before at Yermak Plateau.

Dinocyst datum events of several holes in the Norwegian-Greenland Sea

The presence of abundant age-diagnostic dinoflagellate cysts in Ocean Drilling Program (ODP) Hole 913B (Leg 151), Deep Sea Drilling Project Hole 338 (Leg 38) and ODP Hole 643A (Leg 104) has enabled the development of a new biostratigraphy for the Eocene-Oligocene interval in the Norwegian-Greenland Sea. This development is important because the calcareous microfossils usually used for biostratigraphy in this age interval are generally absent in high latitude sediments as a result of dissolution. In parallel with this biostratigraphic analysis, we developed a magnetic reversal stratigraphy for these Norwegian-Greenland Sea sequences. This has allowed independent age determination and has enabled the dinocyst biostratigraphy to be firmly tied into the global geomagnetic polarity timescale (GPTS). The relatively high resolution of this study has enabled identification of dinoflagellate cyst assemblages that have affinities with those from the North Sea and the North Atlantic, which allows regional correlation. Correlation of each site with the GPTS has also allowed comparison of the stratigraphic record preserved in each drill-hole. Hole 913B is the most complete and is the best-preserved record of the Eocene and Oligocene in the Northern Hemisphere high latitudes, and can serve as a reference section for palaeoenvironmental reconstructions of this age interval.