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 ∗ Present address: Fachbereich-5, Geowissenschaften, Universit¨ at Bremen, Postfach 330 440, D-28334, Germany. E-mail: sdeschepper@uni-bremen. de. † E-mail: [email protected]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 (B¨ utschli, 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
Transcript
Journal of Systematic Palaeontology 6 (1): 101–117 Issued 22 February 2008
Stijn De Schepper∗Cambridge Quaternary, Department of Geography, University of Cambridge, Downing Place, CambridgeCB2 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 theeastern North Atlantic has revealed the presence of several new organic-walled dinoflagellate cysttaxa. 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 stratigraphicutility of small acritarchs in the late Cenozoic of the northern North Atlantic region is emphasisedand three stratigraphically restricted acritarchs Cymatiosphaera latisepta sp. nov., Lavradosphaeracrista gen. et sp. nov. and Lavradosphaera lucifer gen. et sp. nov. are formally described.
KEY WORDS taxonomy, palynology, marine, Quaternary, Neogene
Genus Melitasphaeridium Harland & Hill, 1979 107Melitasphaeridium choanophorum (Deflandre &Cookson, 1955) Harland & Hill, 1979 var. A 107
Acritarchs 109Genus Cymatiosphaera Wetzel, 1933 ex Deflandre, 1954 109
Cymatiosphaera latisepta sp. nov. 109Genus Lavradosphaera gen. nov. 111
Lavradosphaera crista gen. et sp. nov. 111Lavradosphaera lucifer gen. et sp. nov. 113
Discussion 113
Acknowledgements 115
References 115
Introduction
The taxonomy of dinoflagellate cysts for the Pliocene andPleistocene has undergone progressive refinement in recentyears (e.g. Versteegh & Zevenboom 1995; Head 1996, 1997,2003a; Head & Westphal 1999; Head & Norris 2003; DeSchepper et al. 2004; Head et al. 2004). Acritarch tax-onomy is less well developed for the Cenozoic, although thebiostratigraphical value of small acritarchs in the Plioceneand Pleistocene is becoming increasingly recognised, espe-cially for the higher latitudes of the North Atlantic (e.g. deVernal & Mudie 1989a,b; Head 2003b; Head & Norris 2003).
The present study describes three new dinoflagellatecyst taxa and three new acritarch species from Deep SeaDrilling Project (DSDP) Hole 610A, drilled in the sub-polar eastern North Atlantic. It highlights, in particular, thebiostratigraphical value of small acritarchs in the higher lat-itudes of the North Atlantic and adjacent seas. The study ispart of a larger investigation into the palynology of DSDPHole 610A (De Schepper 2006). This hole was chosen forthe completeness of its sedimentary record, relatively highsedimentation rates and independent age control (ShipboardScientific Party 1987; Kleiven et al. 2002).
DSDP Hole 610A
DSDP Hole 610A (53◦13.297′N, 18◦53.213′W; water depth,2417 m) is located approximately 700 km due west of Irelandon the Feni Drift at the south-western edge of the RockallTrough (Fig. 1). The hole was drilled in 1983 on the crest ofa sediment wave on the Feni Drift, as part of DSDP Leg 94.This major sediment drift is nearly 600 km in length, up to700–1000 m thick and is characterised by rapid sedimenta-tion controlled by bottom currents. It has been accumulatingsince Oligocene or Miocene time (Shipboard Scientific Party1987) or possibly as early as the Eocene (Kidd & Hill 1987).
DSDP Hole 610A was drilled to a total depth of 201 mbelow sea floor (mbsf) and terminated in the Lower Plio-cene at about 4.0 Ma (De Schepper 2006; unpublished data).
The lithology is fundamentally pelagic, comprising cal-careous nannofossil ooze, calcareous mud and calcareousnannofossil ooze containing biogenic silica. Two litholo-gical units have been recognised at Site 610. Unit I (0–135 mbsf, 0–2.7 Ma) consists of interbedded calcareousmud and foraminiferal–nannofossil ooze of Quaternary andMiddle Pliocene (Piacenzian) age. Unit II is represen-ted by two subunits in Hole 610A. Subunit IIA (135–165 mbsf; 2.7–3.5 Ma) consists of white siliceous nanno-fossil ooze of Middle Pliocene age. Only the upper partof Subunit IIB (165–201 mbsf; 3.5–4.0 Ma) is represen-ted in Hole 610A and consists of white to very light grey
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Latitude Longitude
DSDP 610A 53˚13’ N 18˚53’ WDSDP 603C 35˚30’ N 70˚2’ W
ODP 642 67˚13’ N 2˚56’ EODP 643 67˚43’ N 1˚2’ EODP 644 66˚41’ N 4˚35’ EODP 645 70˚27’ N 64˚39’ WODP 646 58˚13’ N 48˚22’ WODP 963 37˚2’ N 13˚11’ E
North Atlantic Ocean
Baffin Bay
Labrador Sea
Norwegian-Greenland
Sea
Figure 1 Location of Deep Sea Drilling Project (DSDP) Hole 610A inthe eastern North Atlantic Ocean and location of other DSDP andOcean Drilling Program (ODP) sites mentioned in the text.
New Pliocene and Pleistocene dinoflagellates and acritarchs 103
nannofossil ooze of Middle Pliocene and Early Pliocene(Zanclean) age (Shipboard Scientific Party 1987, based onour new time scale).
This hole was chosen specifically for its excellent corerecovery (95%), absence of hiatuses and high sedimentationrates (Shipboard Scientific Party 1987). The accumulationrate during the Pliocene and Quaternary is high and fairlyconstant, with rates approximating 5 cm/kyr (Shipboard Sci-entific Party 1987). Moreover, Hole 610A has detailed andindependent age control based on magnetostratigraphy forthe entire section (Clement & Robinson 1987) and marineisotope stratigraphy for the time interval between 3.6 and2.4 Ma (Kleiven et al. 2002). Baldauf et al. (1987) combinedthe available palaeontological data (nannofossils, planktonicforaminifera and diatoms) with the magnetostratigraphy forthe core. This interpretation has largely been followed, exceptfor the lower part of the core, where evidence from calcareousnannofossils, dinoflagellate cysts and a reappraisal of themagnetostratigraphical datums has led to the construction ofa new age model (De Schepper 2006; unpublished data). Thisage model is adopted in the present study, where it providesan interpolated age for every biostratigraphical datum.
Materials and methods
Samples
A total of 102 samples were analysed for biostratigraphyfrom the Lower Pliocene through lowermost Middle Pleis-tocene of DSDP Hole 610A, covering ca. 170 m (199.11–28.71 mbsf). One sample from each section of core was takenbetween sections 610A-21-6 and 610A-4-1, providing an av-erage sampling interval of ca. 1.5 m. Additional sampleswere taken for taxonomic purposes at selected intervals inthe lower part of the hole.
Methods
Samples of ca. 25–30 cm3 volume were cleaned with a knifeto remove any modern microbial growth and other contam-ination and oven dried at ca. 50◦C. The sediment was thenweighed and one or more Lycopodium clavatum tablets wereadded to each sample to determine palynomorph concentra-tions. Standard chemical treatment was followed: cold 20vol% HCl, cold 48–52% HF, a second 20 vol% HCl treat-ment to remove any fluosilicates and intermediate and fi-nal washes in deionised H2O prior to sieving on a NitexTM
nylon screen at 10 µm. No oxidation or alkali treatmentswere used. Samples from sections 610A-21-6 to 610A-8-1were prepared by M.J.H. at the University of Toronto. Theyreceived 30–45 s of ultrasonic treatment to break up flocs ofamorphogen and were mounted on microscope slides usingcellosize and elvacite. This mounting medium has the ad-vantage of being permanent, but the interface between thecellosize and elvacite was occasionally found to obscure thepalynomorphs. Samples from sections 610A-7-6 to 610A-4-1 were prepared by S.D.S. at the University of Cambridge(England). The resulting residues received no ultrasound andwere mounted using glycerine jelly.
A Leica DMLB microscope equipped with differentialinterference contrast optics was used for analyses. Micro-
scope slides were scanned along non-overlapping traversesunder a 40× objective and acritarchs and dinoflagellate cystswere counted until at least 300 dinoflagellate cysts had beenenumerated (Fig. 2). After reaching this number, the re-mainder of the slide was searched for rare species usinga 20× objective. Detailed morphological analysis of dino-flagellate cysts and small acritarch species was undertakenusing a 100× objective.
Most photomicrographs were taken on a Leica DMRmicroscope with a Leica DC300 or DFC490 digital camera.Selected photomicrographs were taken on a Zeiss Axioplan2 microscope with a digital MRc5 Zeiss camera at the Pa-laeontology Research Unit of Ghent University, Belgium.Scanning electron microscopy was also performed there onselected samples to elucidate the taxonomy of several smallacritarchs and dinoflagellate cysts. Residue was mounted ona circular glass slide, which was attached to a metal stubusing carbon stickers. Stubs were coated with gold using aBal-Tec MED 010 Planar-magnetron Sputtering Device. Thedistance between the stub surface and the gold sputteringhead was set at 5.2 cm. A gold coating of about 15 nm wasapplied. The scanning electron microscope (SEM) used wasa JEOL 6400. Pictures were acquired digitally using NoranVantage software.
The ATNTS2004 timescale of Lourens et al. (2004) isused throughout.
Repository
All microscope slides containing holotypes and other figuredspecimens are housed in the Invertebrate Section of the De-partment of Palaeobiology, Royal Ontario Museum, Toronto,Ontario, under the catalogue numbers ROMP 57983–57996.
Systematic palaeontology
Dinoflagellate cysts
Division DINOFLAGELLATA (Butschli, 1885)Fensome et al., 1993
Subdivision DINOKARYOTA Fensome et al., 1993Class DINOPHYCEAE Pascher, 1914
Subclass PERIDINIPHYCIDAE Fensome et al., 1993Order GONYAULACALES Taylor, 1980
Figure 2 Stratigraphic distribution of new dinoflagellate cyst andacritarch taxa from DSDP Hole 610A and calibration of their ranges tomagnetostratigraphy (Clement & Robinson 1987, for the Piacenzian
Subchron (C2An.2r), early Piacenzian (early Middle Plio-cene).
DIAGNOSIS. A new variety of Operculodinium? eirikianumin which the central body wall comprises a thin (<0.3 µm)pedium and thicker (ca. 2.0 µm or more) luxuria, consistingof radiating, non-tabular septa that form a microreticulum.
OCCURRENCE. Recorded only from the Piacenzian (MiddlePliocene) of Hole 610A (Fig. 2), mostly between samples610A-18-1, 81–86 cm (ca. 3.33 Ma) and 610A-17-2, 108–104 cm (ca. 3.15 Ma) near and within the Mammoth Sub-chron (C2An.2r), in calcareous nannofossil zone NN16, andplanktonic foraminifer zone PL3–6. A highest abundance of13% is reached within this interval. However, specimens dooccur higher in the hole and are considered in place, with ahighest occurrence in sample 610A-15-4, 111–117 cm (ca.2.82 Ma).
DESCRIPTION. Central body wall comprises thin solid pe-dium (less than 0.3 µm, only visible as dark line) and muchthicker luxuria forming microreticulum of erect, sinuous, un-dulating, non-tabular muri of ca. 0.2–0.3 µm wide. Luxuriaat least 2.0 µm thick, with walls up to 3.0 µm thick oftenobserved. Muri enclose polygonal lumina of up to 0.7 µm indiameter. Microreticulum appears radially striate in opticalsection. Solid, granule-bearing processes arise directly fromsurface of microreticulate layer, with little if any structuralmodification of microreticulation beneath process bases. Pro-cesses arise mostly from circular bases. Precingular archeo-pyle (by loss of plate 3′′) is large, with well-defined angles.
DIMENSIONS. Holotype: central body length, 32 µm; cent-ral body width, 29 µm; wall thickness, 3.0 µm; archeopylelength, 20 µm; archeopyle maximum width, 14 µm; max-imum process length, 10 µm. Range (minimum, average andmaximum measurements are given): central body maximumdiameter, 28 (35.9) 42 µm; wall thickness, 2.0 (2.4) 3.0 µm;average process length, 9 (10.3) 12. Nine specimens meas-ured.
ETYMOLOGY. Latin crebrum, thick, pressed together; withreference to the thick wall of this variety.
REMARKS. The greater thickness of the central body wallalone distinguishes this variety from Operculodinium? ei-rikianum var. eirikianum (autonym): the luxuria on Opercu-lodinium? eirikianum var. eirikianum is between about 0.5and 1.0 µm (Head 1997), although thicknesses up to 1.5 µmhave also been recorded (Head et al. 1989b; this study). In ad-dition, the average process length (9–12 µm) appears slightlylonger than for Operculodinium? eirikianum var. eirikianum(5–10 µm in Head et al. 1989b; 4–9.5 µm in Head 1997).Operculodinium? eirikianum var. crebrum differs from Fili-sphaera filifera Bujak, 1984 emend. Head, 1994 in possess-ing processes.
and higher) and to calcareous nannofossil (Takayama & Sato1987) and planktonic foraminiferal biostratigraphy (Weaver & Clement1987). The magnetostratigraphy below the Piacenzian is consideredquestionable (De Schepper 2006). The time scale (including boundaryages) follows Lourens et al. (2004) and calibrated ages are updatedfrom De Schepper (2006). The raw counts of each taxon are given, anda cross (+) indicates the presence of a taxon outside the regular counts.
New Pliocene and Pleistocene dinoflagellates and acritarchs 105
Plate 1 Operculodinium? eirikianum var. crebrum var. nov. All images in bright field, except where indicated. Figs 1–4, Holotype, sampleDSDP 610A-17-5, 109–114 cm, slide 1, O21/4; ROMP 57991. Dorsal view of (1,2) high and slightly lower foci on dorsal surface, (3) mid-focusshowing thick luxuria on central body and (4) lower focus on ventral surface. Central body maximum length, 32 µm. Figs 5–7, Sample DSDP610A-17-5, 109–114 cm, slide 1, U28/2; ROMP 57991. Uncertain view at (5) high focus, (6) mid-focus showing thick luxuria on central body and (7)lower focus. Maximum diameter, 29 µm. Fig. 8, Sample DSDP 610A-17-4, 65–70 cm, slide 1, C29/1; ROMP 57992. Dorsal view of dorsal surfaceand large archeopyle. Central body maximum length, 32 µm, central body maximum width, 30 µm, archeopyle maximum length, 21 µm. Figs9–12, Sample DSDP 610A-17-4, 65–70 cm, slide 1, U34/0; ROMP 57992. Ventral view of (9) ventral surface, (10) mid focus and (11) dorsal surface.
106 S. De Schepper and M. J. Head
AUTECOLOGY. Operculodinium? eirikianum is generallyconsidered a cold-intolerant species found in middle tohigh latitudes (Head 1993, 1997). Operculodinium? eiriki-anum var. crebrum may represent a morphological adapt-ation to relatively warm and stable climates, as revealedby the low amplitude of oscillations in the oxygen isotoperecord, following the well-expressed Marine Isotope StageM2 (Lisiecki & Raymo 2005) around the Mammoth Sub-chron in the eastern North Atlantic. Multivariate analysis ona detailed dataset from a glacial–interglacial cycle around3.30 Ma (Marine Isotope Stage M2) in Hole 610A sug-gests that this variety has an affinity for warmer waters (DeSchepper 2006), although confirmation from other datasets isneeded.
TYPE. Holotype, sample DSDP 610A-5-5, 52–54 cm (44.32mbsf), slide 2, England Finder reference H44/0; ROMP57995; Pl. 2, Figs 1–3. Age: ca. 0.82 Ma, Subchron C1r.1r,just below the Bruhnes/Matuyama boundary, Early Pleisto-cene.
DIAGNOSIS. A small suturocavate Impagidinium specieswith smooth inner wall, spherical to subspherical centralbody and incomplete tabulation. Shagreenate to finely gran-ulate tegillum forms crests locally of even height, but lowertowards apex and higher towards antapex. Crests absent orweakly expressed on dorsal surface along posterior cingularmargin; no crests within sulcus.
OCCURRENCE. Latest Pliocene through Middle Pleistoceneof Hole 610A (Fig. 2), with a lowest occurrence in sample610A-11-1, 49–54 cm, in the Olduvai Subchron (C2n), cal-careous nannofossil zone NN19, planktonic foraminifer zonePL6–N22, at ca. 1.86 Ma. It occurs infrequently and inlow abundance (<3% of total assemblage) until just beforethe Jaramillo Subchron (0.99–1.07 Ma) and from then on-wards becomes more common (3–10%) and peaks (13% insample 610A-5-5, 52–54 cm) at ca. 0.82 Ma just before theBruhnes/Matuyama boundary. It has a highest occurrence inthe highest sample processed from Hole 610A, which is ofMiddle Pleistocene age and dated at 0.53 Ma.
Also recorded from the Early and Middle Pleistocene ofZakynthos Island, Greece and from the Early (post-Jaramillo)and Middle Pleistocene of ODP Site 963, offshore Sicily (M.Papanikolaou, pers. comm.).
DESCRIPTION. Central body small and spherical to subspher-ical, sometimes bearing small, faintly discernible apical pro-tuberance of about 0.5 µm high. Sutural crests partially de-limit gonyaulacoid tabulation. Central body comprises two
wall layers that are closely adpressed except at bases of su-tural crests. Pedium solid, smooth. Tegillum thin (<0.3 µm),solid; has shagreenate to finely granulate outer surface; formssuturocavate crests that may be hollow along entire height(e.g. Pl. 2, figs 10, 16) or hollow only at their base (e.g.Pl. 2, figs 3, 14). Both types may be present on same cyst.Some crests may be entirely solid (e.g. Pl. 2, figs 2, 6) butsuturocavate crests always present. Crests are entire, locallyof even height, but highest on hypocyst, reaching maximumheight at antapex. Epicyst bears lower crests; at apex theyare invariably low and almost half the height of crests at ant-apex. A funnel-like structure may occur at antapex, formedby convergence of cavate crests surrounding antapical plate(Pl. 2, figs 2, 7). Crests incompletely express tabulation, espe-cially in dorsal and ventral areas. On dorsal surface, anteriorcingular margin expressed by a crest, whereas posterior cin-gular margin is not. A crest demarcates boundary betweentwo cingular plates (possibly 3c and 4c) immediately belowarcheopyle. On some specimens both anterior and posteriorcingular margins are vaguely recognisable on ventral surface,where cingulum meets sulcus. Outline of sulcus expressedby crests. No crests present within sulcus, but tabulation oc-casionally traced by faint lineation, including along anteriormargin of posterior sulcal plate. Archeopyle 1P (plate 3′′),with sharp angles and operculum free. Archeopyle approx-imately congruent with plate boundaries.
DIMENSIONS. Holotype: cyst length (including crests),43 µm; cyst width (including crests), 40 µm; central bodylength (excluding crests), 27 µm; central body width (ex-cluding crests), 25 µm; minimum apical crest height, 4 µm;maximum antapical crest height, 12 µm. Range (minimum,average and maximum measurements are given): centralbody maximum diameter, 25 (29.0) 36 µm; maximum dia-meter including crests, 38 (46.8) 54 µm; maximum apicalcrest height, 4 (5.8) 8 µm; maximum antapical crest height,9 (11.7) 15 µm. Nineteen specimens measured.
COMPARISON. Impagidinium japonicum Matsuoka, 1983has crests of equal height in apical and antapical areas. Im-pagidinium velorum Bujak, 1984 has smooth to shagreenate,membranous sutural crests, that are also higher (19–25 µm)and of equal height over the entire cyst.
ETYMOLOGY. Named after the city of Cambridge (Latin,Cantabrigium), where this species was first identified.
AUTECOLOGY. An oceanic cyst, reported from the oceanicrealm in the present study (DSDP Hole 610A) and fromthe deep shelf of the Mediterranean (ODP Site 963 andZakynthos, Greece; M. Papanikolaou, pers. comm.).
The transition from a warm to cold interval at ca.0.82 Ma (MIS 20) in Hole 610A is marked by high numbers ofImpagidinium pallidum Bujak, 1984 and Nematosphaerop-sis labyrinthus (Ostenfeld, 1903) Reid, 1974, the latter
Detail of wall structure (12). Maximum diameter, 33 µm. Figs 13–16, Sample DSDP 610A-17-4, 65–70 cm, slide 1, H33/1; ROMP 57992. Ventralview of (13) ventral surface, (14) mid focus and (15,16) slightly lower foci of dorsal surface. Figs 17, 18, Sample DSDP 610A-17-4, 66–68 cm.Scanning electron microscope (SEM) image. Diameter, 34 µm. Dorsal view (17) of dorsal surface and large archeopyle, with sharp angles. Sameview (18), detail of wall surface and processes bearing granules (height of photomicrograph, 21.5 µm). Fig. 19, Sample DSDP 610A-17-4,66–68 cm. SEM image. Maximum diameter, 37 µm. Dorsal view of dorsal surface showing large archeopyle. Fig. 20, Sample DSDP 610A-17-3,81–87 cm. SEM image. Detail of processes and wall structure. Height of photomicrograph, 17 µm.
New Pliocene and Pleistocene dinoflagellates and acritarchs 107
Plate 2 Impagidinium cantabrigiense sp. nov. All images in bright field. Figs 1–3, Holotype, sample DSDP 610A-5-5, 52–54 cm, slide 2,H44/0; ROMP 57995. Dorsal view of (1) dorsal surface showing 1P archeopyle (plate 3′ ′) and immediately below, a crest demarcating boundarybetween two cingular plates (possibly 3c and 4c), (2) mid-focus, and (3) ventral surface showing absence of crests in sulcal area. Central bodylength (excluding crests), 27 µm. Figs 4–8, Sample DSDP 610A-5-5, 52–54 cm, slide 1, L34/4; ROMP 57996. Left latero-ventral view of (4,5)ventral surface with sulcus and cingulum, (6,7) higher and slightly lower mid foci, with view of antapical funnel-shaped structure and (8) rightlatero-dorsal surface with archeopyle on the right and view of cingular plate, probably 4c. Figs 9–12, Sample DSDP 610A-5-5, 52–54 cm, slide 1,O27/2; ROMP 57996. Ventral view of (9) ventral surface, (10,11) successively lower mid foci and (12) dorsal surface. Central body maximumdiameter, 25 µm. Figs 13–16, Sample DSDP 610A-5–5, 52–54 cm, slide 2, O27/2; ROMP 57995. Uncertain view of (13) high focus, revealing thesuturocavate crests, (14,15) successively lower mid foci and (16) low focus. Central body maximum diameter, 29 µm.
becoming the dominant species in the assemblage. Alsoat this time, Impagidinium cantabrigiense sp. nov. has itshighest recorded abundance for Hole 610A and remainsabundant during the cold phase. Therefore, Impagidiniumcantabrigiense sp. nov. seems related to transitional phasesfrom warm to cold surface waters in open-marine settings,suggesting a preference for cooler conditions.
Subfamily uncertainGenus MELITASPHAERIDIUM Harland & Hill, 1979Melitasphaeridium choanophorum (Deflandre &Cookson, 1955) Harland & Hill, 1979 var. A (Plate 3)OCCURRENCE. Recorded from two adjacent samples inDSDP Hole 610A, at Subchron C2An.2r? (3.23 Ma) and
108 S. De Schepper and M. J. Head
Plate 3 Melitasphaeridium choanophorum var. A. All images in bright field, except where indicated. Figs 1–5, Sample DSDP 610A-17-3,65–70 cm, slide 1, K10/3; ROMP 57993. Dorsal view of (1) dorsal surface and archeopyle, (2) slightly lower focus, (3) mid-focus showing therelatively thick wall and (4,5) slightly lower foci of ventral surface, showing the perforated wall structure. Central body length, 32 µm. Figs 6–11,Sample DSDP 610A-17-3, 65–70 cm, slide 1, M36/0; ROMP 57993. Ventral view of (6–8) successively lower foci on ventral surface, (9) mid focusand (10,11) dorsal surface, revealing the perforated wall structure. Central body length, 27 µm. Fig. 12, Sample DSDP 610A-17-3, 65–70 cm.
New Pliocene and Pleistocene dinoflagellates and acritarchs 109
Subchron C2An.2n (3.20 Ma), both within the Piacenzian(Middle Pliocene) and within calcareous nannofossil zoneNN16 and planktonic foraminifer zone PL3–6 (Fig. 2). Thismorphotype has not been reported previously.
DESCRIPTION. A morphotype of Melitasphaeridium choan-ophorum characterised by a thick (>1.0 µm), perforate cent-ral body wall. Central body spheroidal, with wall consist-ing of thin (<0.3 µm), perforated pedium and thick (1.0–2.0 µm), perforated luxuria that almost form coarse retic-ulum. Perforations approximately circular in outline, withdiameters ca. 1.0–2.0 µm, separated from one another byas much as ca. 1.0 µm. Distribution of perforations slightlyirregular; adjacent perforations sometimes adjoined. Circu-lar perforations of pedium appear contiguous with those ofluxuria. Perforations of pedium were observed under SEM(Pl. 3, fig. 12) and using light microscopy (Pl. 3, fig. 3). Per-forations occasionally interrupt principal archeopyle suture.Processes generally long, slender, hollow, distally open; pro-cess terminations typically aculeate but variable, may includereduced aculeae and may even taper to simple acuminate tips(Pl. 3, figs 17–20). Some specimens have smaller processeswith acuminate endings in addition to normal aculeate pro-cesses (Pl. 3, figs 3, 9, 12). No specimens found bearingprocesses with wide, circular distal platforms and serratededges.
DIMENSIONS. Range (minimum, average and maximummeasurements are given): central body length, 27 (30.3)33 µm; central body width, 24 (28.0) 31 µm; process length,7 (9.9) 12 µm; wall thickness, 1.0 (1.7) 2.0 µm. Seven spe-cimens measured.
REMARKS. Process terminations compare favourably withthe wide range of development illustrated for Melit-asphaeridium choanophorum by Strauss & Lund (1992). Thewall of Melitasphaeridium choanophorum var. A seems un-usually thick for this species. The presence of a perforatedpedium on a chorate dinoflagellate cyst is unknown to usand would seem to compromise any protective function thecyst wall might confer upon its contents. Perhaps the per-forations of the wall are caused by microbial degradation.However, no specimens transitional between Melit-asphaeridium choanophorum var. A and the normal morpho-logy of this species were found, even though both morpho-types were recorded in the same samples. In addition, nospecimens belonging to other species in the two samplescontaining Melitasphaeridium choanophorum var. A werefound to have suffered microbial degradation. Hence, primafacie evidence suggests that the thick wall and perforatedpedium are primary features. However, because microbialdegradation cannot be excluded, these specimens are placedin open nomenclature pending further information regardingthis unusual morphological feature.
Acritarchs
Genus CYMATIOSPHAERA Wetzel, 1933 exDeflandre, 1954
Cymatiosphaera latisepta sp. nov. (Plate 4)
1989b Nematosphaeropsis sp. I. de Vernal & Mudie: 414;pl. 2, figs 9–11.
1997 Nematosphaeropsis sp. I. Versteegh: 335; pl. II, figs5, 6.
ETYMOLOGY. From the Latin latus, broad and the Latinseptum, wall, partition; with reference to the distally expan-ded crests.
TYPE. Holotype, sample DSDP 610A-15-3, 108–113 cm(137.91 mbsf), slide 1, England Finder reference D11/1;ROMP 57994; Pl. 4, figs 1–5. Age: ca. 2.79 Ma, SubchronC2An.1n, Piacenzian (Middle Pliocene).
DIAGNOSIS. Small acritarch with smooth thin-walled spher-oidal central body whose surface bears crests of even heightthat delimit polygonal fields of approximately equal size.Crests thickened at intersections and expanded distally toform flat or slightly invaginated tops, are extremely thin else-where and may have occasional perforations. Crests other-wise solid except for thicker distal parts where small vacuolesare usually present.
OCCURRENCE. Always present in low abundance and re-stricted to the Piacenzian of DSDP Hole 610A (Fig. 2).It has its lowest occurrence in sample 610A-18-1, 81–86 cm, Subchron C2An.3n?, calcareous nannofossil zoneNN16, planktonic foraminifer zone PL3–6 and Marine Iso-tope Stage MG2, at ca. 3.33 Ma. The highest occurrence isin sample 610A-14-3, 124–129 cm, Subchron C2An.1n, cal-careous nannofossil zone NN17/18, planktonic foraminiferzone PL3–6 and Marine Isotope Stage 104, at ca. 2.62 Ma.
In DSDP Hole 607, central North Atlantic, it has asporadic occurrence from Marine Isotope Stage 113, at2.80 Ma (the lowest sample examined) to Marine IsotopeStage 98, at 2.48 Ma (Versteegh 1997).
In DSDP Hole 646B, Labrador Sea, it has an isol-ated lowest occurrence in calcareous nannofossil zone NN16(Piacenzian), it becomes persistently present in the upper partof zone NN16 and has a highest occurrence just above theGauss/Matuyama boundary at 2.58 Ma (Clement et al. 1989;de Vernal & Mudie 1989b; Knuttel et al. 1989).
In the western North Atlantic DSDP Hole 603C, it hasa persistent occurrence within the Piacenzian from near thebase of the Gauss Chron (within Subchron C2An.3n) to nearthe top of the Gauss Chron (within Subchron C2An.1n).
In summary, this species is presently known only fromthe North Atlantic where it is recorded from near the base ofthe Piacenzian into the lower Gelasian. Rare and questionableoccurrences in the Zanclean may require verification.
Scanning electron microscope (SEM) image. Dorsal view of dorsal surface showing archeopyle. Maximum diameter, 28 µm. Figs 13–16, SampleDSDP 610A-17-3, 65–70 cm, slide 1, F21/0; ROMP 57993. Uncertain view of (13,14) high and slightly lower foci on processes and upper wallsurface, (15) mid focus and (16) lower surface. Central body maximum diameter, 29 µm. Figs 17–20, Sample DSDP 610A-17-3, 65–70 cm, slide 1,U48/3; ROMP 57993. Ventral view of (17) ventral surface, (18,19) slightly lower mid foci and (20) dorsal surface with archeopyle. Central bodylength, 31 µm.
110 S. De Schepper and M. J. Head
Plate 4 Cymatiosphaera latisepta sp. nov. All images in bright field, except where indicated. Figs 1–5, Holotype, sample DSDP 610A-15-3,108–113 cm, slide 1, D11/1; ROMP 57994. Uncertain view at (1) upper focus, (2) slightly lower focus, (3) mid focus, (4) lower focus and (5) lowermostfocus. Central body maximum diameter, 18 µm. Figs 6–8, Sample DSDP 610A-17-4, 65–70 cm, slide 1, V34/1; ROMP 57992. Uncertain view at (6)upper focus, (7) mid focus and (8) lower focus. Vacuoles and perforations visible within expanded crest tops (indicated with arrow on figs 6, 7)on membranous crests at and between gonal junctions. Central body maximum diameter, 20 µm. Figs 9–11, Sample DSDP 610A-17-4, 65–70 cm,slide 1, V37/0; ROMP 57992. Uncertain view at (9) upper focus, (10) mid focus and (11) lower focus. Central body maximum diameter, 20 µm. Fig.12, Sample DSDP 610A-15-4, 111–117 cm. Scanning electron microscope (SEM) image, maximum diameter (including crests), 24 µm. Figs 13–15,Sample DSDP 610A-17-6, 9–11 cm, slide 1, D31/2; ROMP 57990. Uncertain view at (13) upper focus showing vacuoles (indicated with arrow) withintops of crest intersections, (14) mid focus and (15) slightly lower focus. Central body maximum diameter, 23 µm. Fig. 16, Sample DSDP 610A-15-1,123–128 cm. SEM image, maximum diameter, 22 µm. Note distally expanded crests and pitted surface at top of some crest intersections.
DESCRIPTION. Small acritarch with thin-walled (<0.3 µm)spheroidal central body, surface subdivided by crests intoabout 22–26 polygonal fields of approximately equal size.Crests of even height, thickened where they intersect one an-other and distally expanded to form flat (T-shaped) or slightly
invaginated (Y-shaped) tops up to 3.0 µm wide. Crests solidexcept that thicker distal parts of crests, especially at distalparts of intersections, commonly have small (ca. 1.0 µm orless) vacuoles and perforations visible under light micro-scope. Between intersections and below distal margins, crests
New Pliocene and Pleistocene dinoflagellates and acritarchs 111
are extremely thin and may have occasional perforations.Central body surface smooth, crest surfaces also smooth, al-though under SEM the tops of crests may show pitting andperforations (Pl. 4, figs 12, 16).
DIMENSIONS. Holotype: maximum diameter (includingcrests), 23 µm; central body diameter, 18 µm; crest height,2.5 µm. Range (minimum, average and maximum measure-ments are given): maximum diameter (including processes),23 (24.1) 26 µm; central body diameter, 18 (18.5) 20 µm;crest height, 2.5 (2.8) 3.0 µm. Eight specimens measured.De Vernal & Mudie (1989a,b) recorded a maximum dia-meter of 25–30 µm, a central body diameter of 15–20 µmand crest height of 4–6 µm.
REMARKS. This species differs from all others of the genusCymatiosphaera in the presence of distally expanded crestsand the typical development of small vacuoles and perfora-tions within the crests, especially at the tops of crest intersec-tions. De Vernal & Mudie (1989b) assigned this species tothe dinoflagellate cyst genus Nematosphaeropsis Deflandre& Cookson, 1955 emend. Wrenn, 1988 (as Nematosphaerop-sis sp. I) in the belief that the wall contained processes linkeddistally by single trabeculae. It now appears that the ‘pro-cesses’ interpreted by de Vernal & Mudie (1989b) are thick-enings of the crests where they intersect and that the single‘trabeculae’ are the expanded distal margins of the crests.These intersections impart a rounded appearance to the lu-men of the reticulation, so adding to the distinctiveness ofthis species. This species also shows no evidence of dinofla-gellate tabulation.
Genus LAVRADOSPHAERA gen. nov.
TYPE. The holotype of Lavradosphaera crista gen. et sp.nov. (Pl. 5, figs 1–4)
DIAGNOSIS. Small spheroidal to subspheroidal acritarchswhose vesicle wall comprises a thin, smooth inner layer,a continuous or discontinuous spongy to cancellous middlelayer and a thin, continuous outer layer. All layers closelyadpressed. Middle and outer layers form crests, ridges orcones or combinations thereof that are spongy to cancellousinternally. Pylome polygonal to rounded–polygonal in shape.
ETYMOLOGY. Named with reference to the Labrador Seawhere the stratigraphical utility of this genus was first estab-lished (de Vernal & Mudie 1989b). The origin of the nameLabrador is widely assigned to Joao Fernandes Lavrador,a Portuguese explorer and landholder (= lavrador in Por-tuguese) in the Azores.
Lavradosphaera crista gen. et sp. nov. (Plate 5)1989 Platycystidia sp. 1. Mudie: pl. 3, figs 9–12.1989a Incertae sedis I. de Vernal & Mudie: 396; pl. 2, figs
8, 9.1989b Incertae sedis I. de Vernal & Mudie: 415; pl. 5, figs
20, 23.
TYPE. Holotype, sample DSDP 610A-17-6, 105–107 cm(161.6 mbsf), slide 17.6h (1), England Finder referenceA32/1; ROMP 57988; Pl. 5, figs 1–4. Age: ca. 3.30 Ma,Subchron C2An.2r?, Piacenzian (Middle Pliocene).
DIAGNOSIS. A species of Lavradosphaera with spherical tospheroidal central body bearing relatively straight intersect-ing crests that subdivide the acritarch into about nine poly-gonal fields of unequal size and shape. Pylome always oc-curs on a large field. Crests are widest at base and narrowdistally to irregular or even spinulose margins. Surface ofcentral body scabrate to granulate and crests have radiallystriate surface. Pylome approximately pentagonal with well-defined angles and thin margin; operculum monoplacate,free.
OCCURRENCE. In DSDP Hole 610A, the lowest occurrenceis in sample 610A-21-5, 33–39 cm near the base of the holeand dated at 3.98 Ma (late Zanclean, Fig. 2). The highestcommon occurrence is in sample 610A-16-4, 112–117 cm(3.00 Ma; mid-Piacenzian), in the lower part of SubchronC2An.1n, calcareous nannofossil zone NN16, planktonic fo-raminifer zone PL3–6 and the Nitzschia jouseae diatom zone.There are four isolated records higher in the hole (Fig. 2),which probably represent reworking. Even if these occur-rences are in place, the highest occurrence (sample 610A-14-5, 78–83 cm, 2.67 Ma; late Piacenzian, where nine specimenswere counted) would still fall within Subchron C2An.1n, incalcareous nannofossil zone NN17, planktonic foraminiferzone PL3–6 and the Nitzschia marina diatom zone. Therange of Lavradosphaera crista extends from the mid- orlate Zanclean to the mid- or late Piacenzian in Hole 610A.
In Baffin Bay, ODP Site 645, recorded rarely andsporadically from both the Upper Pliocene (de Vernal &Mudie 1989a) and middle Upper Miocene through Up-per Pliocene or Lower Pleistocene (Anstey 1992). LabradorSea, ODP Site 646, occurring rarely in the Lower Pliocenebut abundantly in the Middle Pliocene and with a well-defined top about 20 m below the Gauss/Matuyama boundary(Clement et al. 1989; de Vernal & Mudie 1989b). NorwegianSea, ODP Leg 104, from the Upper Miocene through MiddlePliocene with a range top near the top of the Gauss Chron(as Platycystidia sp. 1 in Mudie 1989). Western North At-lantic, DSDP Hole 603C, from the Upper Miocene (Messin-ian) through Middle Pliocene (Piacenzian) with a highestcommon occurrence in the Kaena Subchron, although withrare specimens persisting into the Upper Pliocene or LowerPleistocene that may represent reworking (M.J.H., unpub-lished data).
Lavradosphaera crista has a total known range of UpperMiocene through Upper Pliocene or Lower Pleistocene, witha conspicuous range top in the northern North Atlantic withinSubchron C2An.1n (3.03–2.58 Ma).
DESCRIPTION. Small acritarch whose wall comprises a thin(<0.3 µm) smooth inner layer of spherical to spheroidalshape, a discontinuous coarsely spongy to cancellous middlelayer (3–5 µm) and a thin (<0.3 µm) finely ornamented outerlayer. All layers closely adpressed. Outer layer is raised toform intersecting crests, in which middle layer is developed.Vacuoles within spongy middle layer are variable in dia-meter within an individual specimen and may reach 3.5 µm.Crests run in relatively straight lines over entire vesicle, sep-arating about nine polygonal fields whose size and shapevaries within an individual specimen. Crests widest at baseand narrow distally. Distal margins of crests irregular andundulations are often drawn into points. Surface of cent-ral body is scabrate to granulate, crests have radially striate
112 S. De Schepper and M. J. Head
Plate 5 Lavradosphaera crista gen. et sp. nov. All images in bright field, except where indicated. Figs 1–4, Holotype, sample DSDP610A-17-6, 132–134 cm, slide 17.6j(1), A32/1; ROMP 57987. Oblique apical view at (1) high focus on apical field with polygonal pylome, (2,3)successively lower mid foci revealing the cancellous, spongy crests and (4) lower focus. Maximum diameter (including crests),23 µm. Figs 5–8, Sample DSDP 610A-21-1, 24–30 cm, slide 1, F21/1; ROMP 57983. Apical view at (5) high focus on apical field with polygonalpylome, (6) slightly lower focus, (7) mid focus and (8) lower focus. Maximum diameter (including crests), 18 µm. Figs 9–12, Sample DSDP610A-17-6, 105–107 cm, slide 17.6h(1), N24/0; ROMP 57988. Oblique apical view of (9) upper focus on apical field, showing upper margin ofpylome, (10) mid focus on cancellous, spongy crests and (11,12) lower foci. Maximum diameter (including crests), 19 µm. Figs 13–15, SampleDSDP 610A-17-6, 9–11 cm, slide 17.6a(1), U33/1; ROMP 57989. Antapical view of (13) antapical surface, (14) mid focus and (15) lower focusshowing detached operculum within vesicle. Maximum diameter (including crests), 24 µm. Fig. 16, Sample DSDP 610A-17-4, 66–68 cm. Scanningelectron microscope (SEM) image, maximum diameter, 20 µm. View of large apical field showing polygonal pylome and radial striations oncrests.
surface. Pylome always occurs on a large field, is approx-imately pentagonal with well-defined angles, has thin mar-gins comprising only inner and outer wall layers. Operculummonoplacate and free, occasionally found detached withinvesicle (Pl. 5, fig. 15). Crest present on operculum.
DIMENSIONS. Holotype: maximum diameter (includingcrests), 23 µm; central body diameter, 18 µm; crest height,3.0 µm. Range (minimum, average and maximum meas-urements are given): maximum diameter (including crests),18 (22.1) 26 µm; central body diameter, 12 (15.6) 19 µm;
New Pliocene and Pleistocene dinoflagellates and acritarchs 113
maximum crest height, 3 (3.4) 5 µm. Eighteen specimensmeasured from Hole 610A.
A range in maximum diameter of 12–25 µm has beenrecorded for specimens from the Labrador Sea and BaffinBay (de Vernal & Mudie 1989a,b; and 16 (21) 25 µm with amaximum crest height of 4–5 µm for specimens from BaffinBay (Anstey 1992).
ETYMOLOGY. From the Latin Crista, crest, which refers tocrests on the central body.
REMARKS. The name ‘Poculumoides pyxidatum’ was notvalidly described in Anstey (1992) as it was avowedly not in-tended for effective publication, appearing in an unpublisheddissertation.
COMPARISON. Lavradosphaera crista differs from Lav-radosphaera lucifer in having a middle wall layer that isdiscontinuous and a relatively thin vesicle wall bearing in-tersecting crests that subdivide the acritarch into discretepolygonal fields.
1989a Incertae sedis II of de Vernal & Mudie: 396; pl. 2,figs 4, 5.
1989b Incertae sedis II of de Vernal & Mudie: 415; pl. 5,figs 18, 19.
1989a Acritarch sp. 1 of Head et al.: 441; pl. 7, figs 4, 8, 9,12, 13.
TYPE. Holotype, sample DSDP 610A-19-5, 111–116 cm(179.34 mbsf), slide 1, England Finder reference C18/0;ROMP 57985; Pl. 6, figs 1–5. Age: ca. 3.74 Ma, SubchronC2Ar, Zanclean (Lower Pliocene).
DIAGNOSIS. A species of Lavradosphaera with spherical tospheroidal central body consisting of a thin, smooth, innerwall layer; a thick, continuous, spongy to cancellous middlelayer of irregular thickness; and a thin outer layer. Outer sur-face forms an irregular relief of low, broad-based ridges andcones. Pylome circular to subpolygonal; operculum mono-placate and free.
OCCURRENCE. Possibly restricted to the Zanclean of Hole610A, but no clearly defined range top (Fig. 2). The highestoccurrence is accepted as being in sample 610A-18-5, 80–86 cm (at 3.60 Ma) near the Gilbert/Gauss boundary, with twohigher occurrences in the Gauss Chron possibly reworked.The highest accepted occurrence is within calcareous nan-nofossil zone NN16, planktonic foraminifer zone PL3–6 andthe Nitzschia jouseae diatom zone.
In the Labrador Sea, ODP Site 646, this species rangesfrom Upper Miocene (mid-Tortonian) (Head et al. 1989a) toMiddle Pliocene where it has a highest occurrence about 15 mbelow the Gauss/Matuyama boundary (Clement et al. 1989;de Vernal & Mudie 1989b). In Baffin Bay, ODP Site 645, it isreported from the Upper Pliocene (de Vernal & Mudie 1989a)and from the Upper Miocene or Lower Pliocene throughupper Pliocene or Lower Pleistocene (Anstey 1992). In thenorthern North Atlantic, DSDP Hole 611, it is recorded fromthe Upper Miocene through lowermost Middle Pliocene andwith an isolated higher record in the Upper Pliocene (Mudie1987). In the western North Atlantic, DSDP Hole 603C, from
the Upper Miocene (Messinian) through Middle Pliocene(Piacenzian) with a highest occurrence in Subchron C2An.3n(M.J.H., unpublished data).
Accepted range is from the Upper Miocene (mid-Tortonian) calcareous nannofossil zone NN10 (Head et al.1989a) to lower Piacenzian (Subchron C2An.3n) in DSDPHole 603C (M.J.H., unpublished data), with higher occur-rences possibly representing reworking.
DESCRIPTION. Small acritarch having three closely-adpressed concentric wall layers. Innermost layer is thin(<0.3 µm), smooth and spherical to spheroidal in shape.Middle layer (2.5–5 µm) has loosely spongy to cancellousstructure containing vacuoles of variable size up to ca.4.0 µm. Middle layer much thicker than inner or outer walllayers and varies in thickness over vesicle. Outer layer thin(<0.3 µm) and follows relief of middle layer. Outer surfacefinely ornamented with submicron-size bumps and undula-tions and may have smooth areas and scattered small perfora-tions. It forms irregular relief of low, broad-based ridges andcones. Ridges typically rise into cones where they intersect.Relatively large circular to subpolygonal pylome is usuallyvisible. Thick margins of pylome are covered by outer walllayer, which fuses with inner wall layer. Operculum mono-placate and free, sometimes found detached within vesicle(Pl. 6, fig. 18).
DIMENSIONS. Holotype: maximum diameter (includingcrests), 26 µm; maximum diameter central body, 16 µm;maximum crest height, 5 µm; pylome length, 9 µm; pylomewidth, 7 µm. Range (minimum, average and maximum meas-urements are given): maximum diameter (including crests),19 (23.2) 26 µm; maximum diameter central body, 12 (14.7)17 µm; maximum crest height, 2.5 (4.3) 5 µm. Twenty-threespecimens measured. Pylome length, 7 (8.0) 9 µm; pylomewidth, 4 (5.5) 7 µm; pylome measurements on two specimensonly.
Head et al. (1989a) recorded a maximum diameter of19 (23.1) 30 µm; Anstey (1992) recorded a maximum dia-meter of 18 (23) 27 µm; and de Vernal & Mudie (1989a,b)recorded a size of 15–25 µm.
ETYMOLOGY. Named after the Latin Lucifer, the planetVenus in its appearance as the morning star. The speciesrecalls the small spiked ball, also called a ‘morning star’,that forms the head of a mediaeval weapon.
REMARKS. The name ‘Poculumoides multifastigatum’ wasnot validly described in Anstey (1992) as it was avowedlynot intended for effective publication, appearing in an un-published dissertation.
COMPARISON. Lavradosphaera lucifer differs from Lav-radosphaera crista in having a continuously thick wallwhose surface bears a combination of low ridges andcones.
Discussion
This study formally describes new taxa of dinoflagellate cystsand acritarchs from DSDP Hole 610A and establishes theirstratigraphical ranges in this hole and from additional sitesin the North Atlantic and adjacent seas.
114 S. De Schepper and M. J. Head
Plate 6 Lavradosphaera lucifer gen. et sp. nov. All images in bright field, except where indicated. Figs 1–5, Holotype, sample DSDP610A-19-5, 111–116 cm, slide 1, C18/0; ROMP 57985. Apical view of (1) apical surface showing rounded pylome, (2,3) slightly lower and mid foci,(4,5) antapical surface. Maximum diameter (including crests), 26 µm. Figs 6–8, Sample DSDP 610A-19-5, 111–116 cm, slide 1, D48/0; ROMP57985. Antapical view of (6) antapical surface, (7) mid focus and (8) apical surface showing pylome margin. Maximum diameter (includingcrests), 22 µm. Figs 9–11, Sample DSDP 610A-19-5, 111–116 cm, slide 1, C13/4; ROMP 57985. Lateral view at (6) high focus, (7) mid focus and (8)lower focus showing pylome margin. Maximum diameter (including crests), 25 µm. Fig. 12, Sample DSDP 610A-17-4, 66–68 cm. Scanningelectron microscope (SEM) image showing apical view of rounded pylome. Maximum diameter (including crests), 24 µm. Figs 13–17, SampleDSDP 610A-18-5, 80–86 cm, slide 1, D4/0; ROMP 57986. Antapical view of (13) antapical surface, (14) slightly lower focus, (15) mid focus and(16,17) low foci on pylome margin. Maximum diameter (including crests), 24 µm. Fig. 18, Sample DSDP 610A-19-5, 111–116 cm, slide 1, D42/4;ROMP 57985. Uncertain view at mid focus, with detached operculum inside vesicle. Maximum diameter (including crests), 24 µm. Figs 19–20,Sample DSDP 610A-19-6, 21–26 cm, slide 1, D39/4; ROMP 57984. Apical view of (19) apical surface showing pylome and (20) antapical surface.Maximum diameter (including crests), 20 µm.
New Pliocene and Pleistocene dinoflagellates and acritarchs 115
Operculodinium? eirikianum var. crebrum var. nov. isrestricted to the Piacenzian (Middle Pliocene) of Hole 610Aand it has not been reported from elsewhere. In contrast,Operculodinium? eirikianum var. eirikianum (autonym) isfrequently present in the Upper Miocene and Pliocene of theNorth Atlantic (Head 1997). The thicker wall that character-ises Operculodinium? eirikianum var. crebrum may representa morphological adaptation in response to changing environ-mental conditions in the eastern North Atlantic, but there ispresently no information from other sites to test this interpret-ation and no culturing studies on living cysts have yet elucid-ated the environmental controls on wall thickness in choratedinoflagellate cysts. Whether this taxon is an ecophenotypeor represents an incipient evolutionary branch remains to bedetermined, but the wall thickness seems sufficiently dis-tinctive and stratigraphically restricted to warrant treatmentas a new variety.
The dinoflagellate cyst record of the Late Pliocene(Gelasian) and Pleistocene is marked mostly by the disap-pearance of taxa and few species have their first appearancesin this interval (Williams et al. 2004). Impagidinium cantab-rigiense sp. nov. is an exception at DSDP Hole 610A. Thisspecies has a lowest occurrence in the Olduvai Subchron ataround 1.86 Ma, occurs sporadically to 1.23 Ma, after whichit occurs persistently and becomes an important part of theassemblage shortly before the Bruhnes/Matuyama boundary.Its range top in DSDP Hole 610A has not been establishedbecause it is present in the highest sample at 0.53 Ma. How-ever, records from the Early and Middle Pleistocene of theMediterranean (M. Papanikolaou, pers. comm.) corroboratea latest Pliocene through Middle Pleistocene range.
Melitasphaeridium choanophorum var. A is restricted totwo adjacent samples near the top of the Mammoth Subchron(within the Piacenzian, Middle Pliocene) in Hole 610A. Thiscyst is apparently unique in having a perforated pedium aswell as perforations and depressions in the luxuria of thecentral body surface. Although these features might representpreservational artefacts (borings made by marine microbes),there is no direct evidence from Hole 610A to suggest suchan origin.
Small acritarchs are often abundant throughout Mioceneand Pliocene deep-ocean sediments of the North Atlantic andadjacent seas and many appear to be in situ representatives ofthe oceanic flora. Their taxonomic treatment nevertheless re-mains a significant challenge because of their small size andunknown biological affinities. Small acritarchs have, con-sequently, been neglected until recently in spite of their evid-ent stratigraphical potential (e.g. de Vernal & Mudie 1989a,b;Head 2003b; Head & Norris 2003). Three species are newlydescribed and have stratigraphically restricted distributionsin Hole 610A and elsewhere.
Cymatiosphaera latisepta sp. nov. (= Nematosphaerop-sis sp. I of de Vernal & Mudie 1989b) is one of the fewspecies restricted to the Piacenzian in Hole 610A, east-ern North Atlantic. It occurs relatively abundantly near theGauss/Matuyama boundary in the Labrador Sea ODP, Site646 (Clement et al. 1989; de Vernal & Mudie 1989b). Thisspecies ranges into the lowermost Gelasian of Hole 607, cent-ral North Atlantic (as Nematosphaeropsis sp. I in Versteegh1997).
Lavradosphaera crista gen. et sp. nov. (= incertae sedisI of de Vernal & Mudie 1989a,b) extends from the upper Zan-clean to the Piacenzian of Hole 610A and, elsewhere, it has
a known range of Upper Miocene through Upper Pliocene.It has a well-defined range top in the northern North Atlanticwithin the mid- to upper Piacenzian (upper Middle Pliocene).
Lavradosphaera lucifer gen. et sp. nov. (= incertae sedisII of de Vernal & Mudie 1989a) is possibly restricted to theZanclean of Hole 610A but does not have a well-definedhighest occurrence. Elsewhere in the North Atlantic, it rangesfrom the Upper Miocene at least to lower Piacenzian (lowerMiddle Pliocene).
Acknowledgements
This contribution is based partly on the doctoral researchof S.D.S. who is grateful to the Gates Cambridge Trust forthe award of a Gates Cambridge Scholarship (University ofCambridge) and additional funding from the Dudley StampMemorial Trust (Royal Society) and Philip Lake Fund (De-partment of Geography, University of Cambridge). M.J.H.acknowledges support from a Natural Sciences and Engineer-ing Research Council of Canada discovery grant. Colleaguesat the Palaeontology Research Unit, University of Ghent,are kindly thanked for the use of the SEM and transmittedlight microscopes. S. Louwye and an anonymous reviewerare thanked for their constructive comments.
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