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A diverse and well-preserved dinoflagellate cyst and acritarch record, comprising 35 genera and 104 species of dinoflagellate cyst and 14 acritarch taxa, is presented for the Lower Pliocene through Middle Pleistocene (4.00-0.53 Ma) of eastern North Atlantic Deep Sea Drilling Project Hole 610A. The Pliocene samples contain twice as many dinoflagellate cyst taxa than the Quaternary samples but far lower cyst concentrations. The disappearance of taxa during the latest Pliocene is likely to have been associated with global cooling. Eight biozones and four subzones are established, representing a level of detail that surpasses earlier studies. The zones are based mostly on highest occurrences,as these are most prevalent in the Pliocene and Lower Pleistocene. The subzones,based on both the acme and highest persistent occurrence of Habibacysta tectata, appear regionally useful within the Lower Pleistocene. The lowest occurrence of Impagidinium cantabrigiense is a potential marker for the uppermost Gelasian Stage (Lower Pleistocene). While this biozonation is intended primarily for use in the eastern North Atlantic, elements will be applicable across the higher-latitude North Atlantic where calcareous microfossil zonations have reduced reliability and resolution. Most of the stratigraphically useful taxa are illustrated, and selected species are described informally. [ABSTRACT FROM AUTHOR]

ABSTRACT Detailed investigation of the essentially complete uppermost Miocene through Lower Pleistocene sequence in Deep Sea Drilling Project (DSDP) Hole 603C, western North Atlantic. has revealed the presence of the new dinoflagellate cyst species Lejeunecysta hatterasensis, Lejeunecysta interrupta, Corrudinium devernaliae, and Pyxidinopsis vesiculata, as well as the acritarchs Leiosphaeridia rockhallensis Head new species and Leffingwellia costata new genus and species. Independent magnetobiostratigraphic control of DSDP Hole 603C constrains the ranges of these new species. Lejeunecysta interrupta n. sp. appears to range no higher than lowermost Pliocene at 5.2 Ma. Pyxidinopsis vesiculata n. sp. has a range top at about 4.5 Ma in the Lower Pliocene, Corrudinium devernaliae n. sp. has a well-defined range of 4.7-4.1 Ma within the Lower Pliocene, and Leiosphaeridia rockhallensis n. sp. has a similarly well-defined range of 4.4-3.9 Ma within the Lower Pliocene. The presence of Leiosphaeridia rockhallensis n. sp. in the Ramsholt Member of the Coralline Crag Formation, eastern England, supports an Early Pliocene age for this member. [ABSTRACT FROM AUTHOR]

Abstract: In an attempt to document the palaeoecological affinities of individual extant and extinct dinoflagellate cysts, Late Pliocene and Early Pleistocene dinoflagellate cyst assemblages have been compared with geochemical data from the same samples. Mg/Ca ratios of Globigerina bulloides were measured to estimate the spring–summer sea-surface temperatures from four North Atlantic IODP/DSDP sites. Currently, our Pliocene–Pleistocene database contains 204 dinoflagellate cyst samples calibrated to geochemical data. This palaeo-database is compared with modern North Atlantic and global datasets. The focus lies in the quantitative relationship between Mg/Ca-based (i.e. spring–summer) sea-surface temperatures (SSTMg/Ca) and dinoflagellate cyst distributions. In general, extant species are shown to have comparable spring–summer SST ranges in the past (SSTMg/Ca) and today (SST from World Ocean Atlas 2005, Locarnini et al., 2006), demonstrating that our new approach is valid for inferring spring–summer SST ranges for extinct species. For example, Habibacysta tectata represents SSTMg/Ca values between 10 and 15°C when it exceeds 30% of the assemblage, and Invertocysta lacrymosa exceeds 15% when SSTMg/Ca values are between 18.6 and 23.5°C. However, comparing Pliocene and Pleistocene SSTMg/Ca values with present day summer values for the extant Impagidinium pallidum suggests a greater tolerance of higher temperatures in the past. This species occupies more than 5% of the assemblage at SSTMg/Ca values of 11.6–17.9°C in the Pliocene and Pleistocene, whereas present day summer SSTs are around −1.7 to 6.9°C. This observation questions the value of Impagidinium pallidum as reliable indicator of cold waters in older deposits, and may explain its bipolar distribution. [Copyright &y& Elsevier]