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New Dinoflagellate Cyst and Acritarch Taxa from the Pliocene and Pleistocene of the Eastern North Atlantic (DSDP Site 610)

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New Dinoflagellate Cyst and Acritarch Taxa from the Pliocene and Pleistocene of the Eastern North Atlantic (DSDP Site 610) Journal of Systematic Palaeontology 6 (1): 101–117 Issued 22 February 2008 doi:10.1017/S1477201907002167 Printed in the United Kingdom C The Natural History Museum New dinoflagellate cyst and acritarch taxa from the Pliocene and Pleistocene of the eastern North Atlantic (DSDP Site 610) Stijn De Schepper∗ Cambridge Quaternary, Department of Geography, University of Cambridge, Downing Place, Cambridge CB2 3EN, United Kingdom Martin J. Head† Department of Earth Sciences, Brock University, 500 Glenridge Avenue, St. Catharines, Ontario L2S 3A1, Canada SYNOPSIS A palynological study of Pliocene and Pleistocene deposits from DSDP Hole 610A in the eastern North Atlantic has revealed the presence of several new organic-walled dinoflagellate cyst taxa. Impagidinium cantabrigiense sp. nov. first appeared in the latest Pliocene, within an inter- val characterised by a paucity of new dinoflagellate cyst species. Operculodinium? eirikianum var. crebrum var. nov. is mostly restricted to a narrow interval near the Mammoth Subchron within the Plio- cene (Piacenzian Stage) and may be a morphological adaptation to the changing climate at that time. An unusual morphotype of Melitasphaeridium choanophorum (Deflandre & Cookson, 1955) Harland & Hill, 1979 characterised by a perforated cyst wall is also documented. In addition, the stratigraphic utility of small acritarchs in the late Cenozoic of the northern North Atlantic region is emphasised and three stratigraphically restricted acritarchs Cymatiosphaera latisepta sp. nov., Lavradosphaera crista gen. et sp. nov. and Lavradosphaera lucifer gen. et sp. nov. are formally described. KEY WORDS taxonomy, palynology, marine, Quaternary, Neogene Contents Introduction 102 DSDP Hole 610A 102 Materials and methods 103 Samples 103 Methods 103 Repository 103 Systematic palaeontology 103 Dinoflagellate cysts 103 Division Dinoflagellata (Butschli,¨ 1885) Fensome et al., 1993 103 Subdivision Dinokaryota Fensome et al., 1993 103 Class Dinophyceae Pascher, 1914 103 Subclass Peridiniphycidae Fensome et al., 1993 103 Order Gonyaulacales Taylor, 1980 103 Suborder Gonyaulacineae (Autonym) 103 Family Gonyaulacaceae Lindemann, 1928 103 Subfamily Cribroperidinioideae Fensome et al., 1993 103 Genus Operculodinium Wall, 1967 emend. Matsuoka et al., 1997 103 Operculodinium? eirikianum Head et al., 1989b emend. Head, 1997 103 Operculodinium? eirikianum var. crebrum varietas nov. 103 ∗ Present address: Fachbereich-5, Geowissenschaften, Universitat¨ Bremen, Postfach 330 440, D-28334, Germany. E-mail: sdeschepper@uni-bremen. † de. E-mail: [email protected] 102 S. De Schepper and M. J. Head Subfamily Gonyaulacoideae (Autonym) 106 Genus Impagidinium Stover & Evitt, 1978 106 Impagidinium cantabrigiense sp. nov. 106 Subfamily uncertain 107 Genus Melitasphaeridium Harland & Hill, 1979 107 Melitasphaeridium choanophorum (Deflandre & Cookson, 1955) Harland & Hill, 1979 var. A 107 Acritarchs 109 Genus Cymatiosphaera Wetzel, 1933 ex Deflandre, 1954 109 Cymatiosphaera latisepta sp. nov. 109 Genus Lavradosphaera gen. nov. 111 Lavradosphaera crista gen. et sp. nov. 111 Lavradosphaera lucifer gen. et sp. nov. 113 Discussion 113 Acknowledgements 115 References 115 Introduction The lithology is fundamentally pelagic, comprising cal- careous nannofossil ooze, calcareous mud and calcareous The taxonomy of dinoflagellate cysts for the Pliocene and nannofossil ooze containing biogenic silica. Two litholo- Pleistocene has undergone progressive refinement in recent gical units have been recognised at Site 610. Unit I (0– years (e.g. Versteegh & Zevenboom 1995; Head 1996, 1997, 135 mbsf, 0–2.7 Ma) consists of interbedded calcareous 2003a; Head & Westphal 1999; Head & Norris 2003; De mud and foraminiferal–nannofossil ooze of Quaternary and Schepper et al. 2004; Head et al. 2004). Acritarch tax- Middle Pliocene (Piacenzian) age. Unit II is represen- onomy is less well developed for the Cenozoic, although the ted by two subunits in Hole 610A. Subunit IIA (135– biostratigraphical value of small acritarchs in the Pliocene 165 mbsf; 2.7–3.5 Ma) consists of white siliceous nanno- and Pleistocene is becoming increasingly recognised, espe- fossil ooze of Middle Pliocene age. Only the upper part cially for the higher latitudes of the North Atlantic (e.g. de of Subunit IIB (165–201 mbsf; 3.5–4.0 Ma) is represen- Vernal & Mudie 1989a,b; Head 2003b; Head & Norris 2003). ted in Hole 610A and consists of white to very light grey The present study describes three new dinoflagellate cyst taxa and three new acritarch species from Deep Sea Drilling Project (DSDP) Hole 610A, drilled in the sub- 80˚ polar eastern North Atlantic. It highlights, in particular, the Latitude Longitude DSDP 610A 53˚13’ N 18˚53’ W biostratigraphical value of small acritarchs in the higher lat- DSDP 603C 35˚30’ N 70˚2’ W itudes of the North Atlantic and adjacent seas. The study is ODP 642 67˚13’ N 2˚56’ E part of a larger investigation into the palynology of DSDP ODP 643 67˚43’ N 1˚2’ E ODP 644 66˚41’ N 4˚35’ E Hole 610A (De Schepper 2006). This hole was chosen for ODP 645 70˚27’ N 64˚39’ W ODP 646 58˚13’ N 48˚22’ W the completeness of its sedimentary record, relatively high ODP 963 37˚2’ N 13˚11’ E Baffin Bay sedimentation rates and independent age control (Shipboard Norwegian- Scientific Party 1987; Kleiven et al. 2002). 645 Greenland Sea 643 642 644 DSDP Hole 610A 60˚ Labrador Sea ◦ ◦ DSDP Hole 610A (53 13.297 N, 18 53.213 W; water depth, 646 2417 m) is located approximately 700 km due west of Ireland on the Feni Drift at the south-western edge of the Rockall 610A Trough (Fig. 1). The hole was drilled in 1983 on the crest of North Atlantic Ocean a sediment wave on the Feni Drift, as part of DSDP Leg 94. This major sediment drift is nearly 600 km in length, up to 40˚ 603C 700–1000 m thick and is characterised by rapid sedimenta- 963 tion controlled by bottom currents. It has been accumulating since Oligocene or Miocene time (Shipboard Scientific Party -60˚ -30˚ 0˚ 1987) or possibly as early as the Eocene (Kidd & Hill 1987). DSDP Hole 610A was drilled to a total depth of 201 m Figure 1 Location of Deep Sea Drilling Project (DSDP) Hole 610A in below sea floor (mbsf) and terminated in the Lower Plio- the eastern North Atlantic Ocean and location of other DSDP and cene at about 4.0 Ma (De Schepper 2006; unpublished data). Ocean Drilling Program (ODP) sites mentioned in the text. New Pliocene and Pleistocene dinoflagellates and acritarchs 103 nannofossil ooze of Middle Pliocene and Early Pliocene scope slides were scanned along non-overlapping traverses (Zanclean) age (Shipboard Scientific Party 1987, based on under a 40× objective and acritarchs and dinoflagellate cysts our new time scale). were counted until at least 300 dinoflagellate cysts had been This hole was chosen specifically for its excellent core enumerated (Fig. 2). After reaching this number, the re- recovery (95%), absence of hiatuses and high sedimentation mainder of the slide was searched for rare species using rates (Shipboard Scientific Party 1987). The accumulation a20× objective. Detailed morphological analysis of dino- rate during the Pliocene and Quaternary is high and fairly flagellate cysts and small acritarch species was undertaken constant, with rates approximating 5 cm/kyr (Shipboard Sci- using a 100× objective. entific Party 1987). Moreover, Hole 610A has detailed and Most photomicrographs were taken on a Leica DMR independent age control based on magnetostratigraphy for microscope with a Leica DC300 or DFC490 digital camera. the entire section (Clement & Robinson 1987) and marine Selected photomicrographs were taken on a Zeiss Axioplan isotope stratigraphy for the time interval between 3.6 and 2 microscope with a digital MRc5 Zeiss camera at the Pa- 2.4 Ma (Kleiven et al. 2002). Baldauf et al. (1987) combined laeontology Research Unit of Ghent University, Belgium. the available palaeontological data (nannofossils, planktonic Scanning electron microscopy was also performed there on foraminifera and diatoms) with the magnetostratigraphy for selected samples to elucidate the taxonomy of several small the core. This interpretation has largely been followed, except acritarchs and dinoflagellate cysts. Residue was mounted on for the lower part of the core, where evidence from calcareous a circular glass slide, which was attached to a metal stub nannofossils, dinoflagellate cysts and a reappraisal of the using carbon stickers. Stubs were coated with gold using a magnetostratigraphical datums has led to the construction of Bal-Tec MED 010 Planar-magnetron Sputtering Device. The a new age model (De Schepper 2006; unpublished data). This distance between the stub surface and the gold sputtering age model is adopted in the present study, where it provides head was set at 5.2 cm. A gold coating of about 15 nm was an interpolated age for every biostratigraphical datum. applied. The scanning electron microscope (SEM) used was a JEOL 6400. Pictures were acquired digitally using Noran Vantage software. The ATNTS2004 timescale of Lourens et al. (2004) is Materials and methods used throughout. Samples Repository A total of 102 samples were analysed for biostratigraphy All microscope slides containing holotypes and other figured from the Lower Pliocene through lowermost Middle Pleis- specimens are housed in the Invertebrate Section of the De- tocene of DSDP Hole 610A, covering ca. 170 m (199.11– partment of Palaeobiology, Royal Ontario Museum, Toronto, 28.71 mbsf). One sample from each section of core was taken Ontario, under the catalogue numbers ROMP 57983–57996. between sections 610A-21-6 and 610A-4-1, providing an av- erage sampling interval of ca. 1.5 m. Additional samples were taken for taxonomic purposes at selected intervals in the lower part of the hole. Systematic palaeontology Methods Dinoflagellate cysts Samples of ca. 25–30 cm3 volume were cleaned with a knife Division DINOFLAGELLATA (Butschli,¨ 1885) to remove any modern microbial growth and other contam- Fensome et al., 1993 ination and oven dried at ca. 50◦C. The sediment was then Subdivision DINOKARYOTA Fensome et al., 1993 weighed and one or more Lycopodium clavatum tablets were Class DINOPHYCEAE Pascher, 1914 added to each sample to determine palynomorph concentra- tions.
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