Journal of Systematic Palaeontology 6 (1): 101–117 doi:10.1017/S1477201907002167 Printed in the United Kingdom
Issued 22 February 2008 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 interval 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 Pliocene (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 Samples Methods Repository
103 103 103 103
Systematic palaeontology Dinoflagellate cysts Division Dinoflagellata (B¨ utschli, 1885) Fensome et al., 1993 Subdivision Dinokaryota Fensome et al., 1993 Class Dinophyceae Pascher, 1914 Subclass Peridiniphycidae Fensome et al., 1993 Order Gonyaulacales Taylor, 1980 Suborder Gonyaulacineae (Autonym) Family Gonyaulacaceae Lindemann, 1928 Subfamily Cribroperidinioideae Fensome et al., 1993 Genus Operculodinium Wall, 1967 emend. Matsuoka et al., 1997 Operculodinium? eirikianum Head et al., 1989b emend. Head, 1997 Operculodinium? eirikianum var. crebrum varietas nov.
103 103 103 103 103 103 103 103 103 103 103 103 103
∗ Present address: Fachbereich-5, Geowissenschaften, Universit¨at 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) Genus Impagidinium Stover & Evitt, 1978 Impagidinium cantabrigiense sp. nov. Subfamily uncertain Genus Melitasphaeridium Harland & Hill, 1979 Melitasphaeridium choanophorum (Deflandre & Cookson, 1955) Harland & Hill, 1979 var. A
106 106 106 107 107 107 109 109 109 111 111 113
Acritarchs Genus Cymatiosphaera Wetzel, 1933 ex Deflandre, 1954 Cymatiosphaera latisepta sp. nov. Genus Lavradosphaera gen. nov. Lavradosphaera crista gen. et sp. nov. Lavradosphaera lucifer gen. et sp. nov. Discussion
113
Acknowledgements
115
References
115
Introduction The taxonomy of dinoflagellate cysts for the Pliocene and Pleistocene has undergone progressive refinement in recent years (e.g. Versteegh & Zevenboom 1995; Head 1996, 1997, 2003a; Head & Westphal 1999; Head & Norris 2003; De Schepper et al. 2004; Head et al. 2004). Acritarch taxonomy is less well developed for the Cenozoic, although the biostratigraphical value of small acritarchs in the Pliocene and Pleistocene is becoming increasingly recognised, especially for the higher latitudes of the North Atlantic (e.g. de Vernal & Mudie 1989a,b; Head 2003b; Head & Norris 2003). 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 subpolar eastern North Atlantic. It highlights, in particular, the biostratigraphical value of small acritarchs in the higher latitudes of the North Atlantic and adjacent seas. The study is part of a larger investigation into the palynology of DSDP Hole 610A (De Schepper 2006). This hole was chosen for the completeness of its sedimentary record, relatively high sedimentation rates and independent age control (Shipboard Scientific Party 1987; Kleiven et al. 2002).
The lithology is fundamentally pelagic, comprising calcareous nannofossil ooze, calcareous mud and calcareous nannofossil ooze containing biogenic silica. Two lithological units have been recognised at Site 610. Unit I (0– 135 mbsf, 0–2.7 Ma) consists of interbedded calcareous mud and foraminiferal–nannofossil ooze of Quaternary and Middle Pliocene (Piacenzian) age. Unit II is represented by two subunits in Hole 610A. Subunit IIA (135– 165 mbsf; 2.7–3.5 Ma) consists of white siliceous nannofossil ooze of Middle Pliocene age. Only the upper part of Subunit IIB (165–201 mbsf; 3.5–4.0 Ma) is represented in Hole 610A and consists of white to very light grey
80˚
Latitude
Longitude
DSDP 610A DSDP 603C
53˚13’ N 35˚30’ N
18˚53’ W 70˚2’ W
ODP 642 ODP 643 ODP 644 ODP 645 ODP 646 ODP 963
67˚13’ N 67˚43’ N 66˚41’ N 70˚27’ N 58˚13’ N 37˚2’ N
2˚56’ E 1˚2’ E 4˚35’ E 64˚39’ W 48˚22’ W 13˚11’ E
Baffin Bay NorwegianGreenland Sea
645
643
DSDP Hole 610A 60˚
DSDP Hole 610A (53◦ 13.297 N, 18◦ 53.213 W; water depth, 2417 m) is located approximately 700 km due west of Ireland on the Feni Drift at the south-western edge of the Rockall Trough (Fig. 1). The hole was drilled in 1983 on the crest of 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 700–1000 m thick and is characterised by rapid sedimentation controlled by bottom currents. It has been accumulating since Oligocene or Miocene time (Shipboard Scientific Party 1987) or possibly as early as the Eocene (Kidd & Hill 1987). DSDP Hole 610A was drilled to a total depth of 201 m below sea floor (mbsf) and terminated in the Lower Pliocene at about 4.0 Ma (De Schepper 2006; unpublished data).
642 644
Labrador Sea 646 610A
North Atlantic Ocean 40˚ 603C
963
-60˚
-30˚
0˚
Figure 1 Location of Deep Sea Drilling Project (DSDP) Hole 610A in the eastern North Atlantic Ocean and location of other DSDP and Ocean Drilling Program (ODP) sites mentioned in the text.
New Pliocene and Pleistocene dinoflagellates and acritarchs
103
Materials and methods
scope slides were scanned along non-overlapping traverses under a 40× objective and acritarchs and dinoflagellate cysts were counted until at least 300 dinoflagellate cysts had been enumerated (Fig. 2). After reaching this number, the remainder of the slide was searched for rare species using a 20× objective. Detailed morphological analysis of dinoflagellate cysts and small acritarch species was undertaken using a 100× objective. Most photomicrographs were taken on a Leica DMR microscope with a Leica DC300 or DFC490 digital camera. Selected photomicrographs were taken on a Zeiss Axioplan 2 microscope with a digital MRc5 Zeiss camera at the Palaeontology Research Unit of Ghent University, Belgium. Scanning electron microscopy was also performed there on selected samples to elucidate the taxonomy of several small acritarchs and dinoflagellate cysts. Residue was mounted on a circular glass slide, which was attached to a metal stub using carbon stickers. Stubs were coated with gold using a Bal-Tec MED 010 Planar-magnetron Sputtering Device. The distance between the stub surface and the gold sputtering head was set at 5.2 cm. A gold coating of about 15 nm was 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 used throughout.
Samples
Repository
A total of 102 samples were analysed for biostratigraphy from the Lower Pliocene through lowermost Middle Pleistocene of DSDP Hole 610A, covering ca. 170 m (199.11– 28.71 mbsf). One sample from each section of core was taken between sections 610A-21-6 and 610A-4-1, providing an average sampling interval of ca. 1.5 m. Additional samples were taken for taxonomic purposes at selected intervals in the lower part of the hole.
All microscope slides containing holotypes and other figured specimens are housed in the Invertebrate Section of the Department of Palaeobiology, Royal Ontario Museum, Toronto, Ontario, under the catalogue numbers ROMP 57983–57996.
nannofossil ooze of Middle Pliocene and Early Pliocene (Zanclean) age (Shipboard Scientific Party 1987, based on our new time scale). This hole was chosen specifically for its excellent core recovery (95%), absence of hiatuses and high sedimentation rates (Shipboard Scientific Party 1987). The accumulation rate during the Pliocene and Quaternary is high and fairly constant, with rates approximating 5 cm/kyr (Shipboard Scientific Party 1987). Moreover, Hole 610A has detailed and independent age control based on magnetostratigraphy for the entire section (Clement & Robinson 1987) and marine isotope stratigraphy for the time interval between 3.6 and 2.4 Ma (Kleiven et al. 2002). Baldauf et al. (1987) combined the available palaeontological data (nannofossils, planktonic foraminifera and diatoms) with the magnetostratigraphy for the core. This interpretation has largely been followed, except for the lower part of the core, where evidence from calcareous nannofossils, dinoflagellate cysts and a reappraisal of the magnetostratigraphical datums has led to the construction of a new age model (De Schepper 2006; unpublished data). This age model is adopted in the present study, where it provides an interpolated age for every biostratigraphical datum.
Methods Samples of ca. 25–30 cm3 volume were cleaned with a knife to remove any modern microbial growth and other contamination and oven dried at ca. 50◦ C. The sediment was then weighed and one or more Lycopodium clavatum tablets were added to each sample to determine palynomorph concentrations. Standard chemical treatment was followed: cold 20 vol% HCl, cold 48–52% HF, a second 20 vol% HCl treatment to remove any fluosilicates and intermediate and final washes in deionised H2 O prior to sieving on a NitexTM nylon screen at 10 µm. No oxidation or alkali treatments were used. Samples from sections 610A-21-6 to 610A-8-1 were prepared by M.J.H. at the University of Toronto. They received 30–45 s of ultrasonic treatment to break up flocs of amorphogen and were mounted on microscope slides using cellosize and elvacite. This mounting medium has the advantage of being permanent, but the interface between the cellosize and elvacite was occasionally found to obscure the palynomorphs. Samples from sections 610A-7-6 to 610A4-1 were prepared by S.D.S. at the University of Cambridge (England). The resulting residues received no ultrasound and were mounted using glycerine jelly. A Leica DMLB microscope equipped with differential interference contrast optics was used for analyses. Micro-
Systematic palaeontology Dinoflagellate cysts Division DINOFLAGELLATA (B¨ utschli, 1885) Fensome et al., 1993 Subdivision DINOKARYOTA Fensome et al., 1993 Class DINOPHYCEAE Pascher, 1914 Subclass PERIDINIPHYCIDAE Fensome et al., 1993 Order GONYAULACALES Taylor, 1980 Suborder GONYAULACINEAE (Autonym) Family GONYAULACACEAE Lindemann, 1928 Subfamily CRIBROPERIDINIOIDEAE Fensome et al. 1993 Genus OPERCULODINIUM Wall, 1967 emend. Matsuoka et al., 1997 Operculodinium? eirikianum Head et al., 1989b emend. Head, 1997 Operculodinium? eirikianum var. crebrum varietas nov. (Plate 1) TYPE. Holotype, sample DSDP 610A-17-5, 109–114 cm (160.12 mbsf), slide 1, England Finder reference O21/4; ROMP 57991; Pl. 1, figs 1–4. Age: ca. 3.27 Ma, Mammoth
104
S. De Schepper and M. J. Head
? NN17
C2An.1n
?
E
C2An.1r
GAUSS
PL3 – PL6
C
3.12
C2An.2n 3.21
MAM C2An.2r
C2An.3n
3.33
NN16
O I L P
P I A C E N Z I A N
KAE
3.03
?
?
?
?
NN15
?
C2Ar
G I L B E R T (p a r s)
Z A N C L E A N
?
3.60
0.528 0.637 0.732 0.760 0.798 0.816 0.967 1.011 1.034 1.097 1.174 1.232 1.275 1.304 1.339 1.348 1.381 1.408 1.437 1.466 1.489 1.503 1.556 1.576 1.594 1.620 1.634 1.674 1.700 1.722 1.767 1.779 1.823 1.857 1.911 1.955 1.989 2.010 2.057 2.076 2.104 2.141 2.159 2.190 2.236 2.250 2.297 2.339 2.382 2.421 2.455 2.485 2.505 2.535 2.565 2.617 2.631 2.667 2.688 2.742 2.754 2.793 2.821 2.839 2.870 2.883 2.900 2.928 2.965 2.998 3.028 3.037 3.091 3.149 3.198 3.229 3.266 3.295 3.330 3.421 3.504 3.534 3.604 3.614 3.651 3.671 3.695 3.708 3.735 3.743 3.772 3.792 3.818 3.829 3.851 3.871 3.897 3.919 3.939 3.958 3.978 3.996
Lavradosphaera lucifer gen. et sp. nov.
Lavradosphaera crista gen. et sp. nov.
Cymatiosphaera latisepta sp. nov.
Melitasphaeridium choanophorum var. A Operculodinium? eirikianum crebrum var. nov.
Impagidinium cantabrigiense sp. nov.
Calibrated ages (Ma)
16.0 0 23.4 17.1 18.1 20.0 15.9 20.0 19.0 16.5 18.5 15.8 17.6 33.8 32.5 27.0 33.2 29.4 34.0 35.1 34.0 31.6 34.9 35.9 39.2 35.1 31.4 32.7 31.9 26.7 32.8 35.0 35.1 26.7 37.4 37.7 37.7 36.1 34.4 35.7 28.0 39.6 30.8 39.6 30.8 37.9 38.8 36.7 38.2 32.4 37.8 35.4 37.0 37.2 40.6 42.1 37.3 39.4 41.6 37.4 39.0 38.7 40.1 37.4 40.4 42.2 22.8 38.7 28.5 41.0 36.9 38.5 42.4 36.3 34.9 43.7 40.1 39.7 35.4 40.1 38.2 34.4 43.6 42.5 42.1 45.2 41.8 43.4 43.4 41.1 41.8 42.4 45.4 43.3 39.0 45.7 42.9 43.1 46.3 46.5 47.9 42.3 43.7
9 1 + 4 20 41 9 1 6 11 4 + 2 3 1 + +
+ +
+ +
2 9
1
6 5 + 1 3 1 3 3 2 5 5 2
9
1 1 1 2
1
7 +
+ 6 45 16 1 +
1 1 + 3 1
90 27 + 78 85 28 105 32 170
1
+ 70 152 14 4 7 +
1 16 1 8 1 1 11 +
1 5 2 +
20 8 3
1
+
+
1 + 23
+
Total acritarchs counted
C2r.2r
E N
2.58
28.71 34.62 39.78 41.32 43.39 44.32 52.42 54.49 55.41 58.20 62.19 65.21 67.44 68.92 70.76 71.21 72.95 74.32 75.82 77.31 78.52 79.25 81.97 83.00 83.95 85.29 86.01 88.10 89.46 90.56 92.93 93.51 94.87 95.92 97.59 99.08 100.58 101.50 103.58 104.44 105.66 107.76 108.86 110.16 112.13 112.71 114.69 116.47 118.30 119.95 121.45 122.77 123.67 125.01 126.37 128.47 129.09 131.01 132.10 135.06 135.68 137.91 139.44 140.46 142.14 142.83 143.76 145.26 147.26 149.05 150.69 151.13 153.54 155.61 156.84 158.18 160.12 161.64 163.44 165.22 166.71 167.32 169.43 170.17 173.01 174.52 176.34 177.35 179.34 179.94 182.14 183.65 185.65 186.49 188.15 189.68 191.67 193.28 194.82 196.28 197.76 199.11
Subchron (C2An.2r), early Piacenzian (early Middle Pliocene).
Acritarchs
Total dinoflagellate cysts counted
2.15
C2r.1n
51–53 42–44 48–50 52–54 109–111 52–54 52–54 109–111 51–53 120–122 69–71 71–73 81–86 79–85 113–119 8–13 32–37 19–25 19–24 108–113 79–84 2–7 124–129 77–83 18–23 6–11 18–23 77–83 63–68 23–28 110–115 18–23 5–8 49–54 66–71 65–70 65–70 7–12 65–70 2–5 63–68 123–128 83–88 63–68 110–115 18–24 6–12 34–39 67–72 82–87 82–88 64–69 4–10 78–83 64–69 124–129 36–41 78–83 37–42 123–128 35–41 108–113 111–117 63–68 81–86 1–4 33–38 35–38 83–88 112–117 126–131 20–26 51–56 108–114 81–87 65–70 109–114 111–117 81–86 109–114 108–113 19–24 80–86 3–8 78–83 79–84 111–116 62–67 111–116 21–26 31–36 32–38 31–36 16–22 32–38 35–40 24–30 35–40 39–44 35–41 33–39 18–24
Dry weight (g)
? ?
2.13
REU
NN18
G E L A S I A N
C2r.1r
1.95
4-1 4-5 5-2 5-3 5-4 5-5 6-4 6-5 6-6 7-1 7-4 7-6 8-1 8-2 8-3 8-4 8-5 8-6 8-7 9-1 9-2 9-3 9-4 9-5 9-6 9-7 10-1 10-2 10-3 10-4 10-5 10-6 10-7 11-1 11-2 11-3 11-4 11-5 11-6 11-7 12-1 12-2 12-3 12-4 12-5 12-6 13-1 13-2 13-3 13-4 13-5 13-6 13-7 14-1 14-2 14-3 14-4 14-5 14-6 15-1 15-2 15-3 15-4 15-5 15-6 15-7 16-1 16-2 16-3 16-4 16-5 16-6 17-1 17-2 17-3 17-4 17-5 17-6 18-1 18-2 18-3 18-4 18-5 18-6 19-1 19-2 19-3 19-4 19-5 19-6 20-1 20-2 20-3 20-4 20-5 20-6 21-1 21-2 21-3 21-4 21-5 21-6
Depth (mbsf)
N22
NN19
C1r.2r – C1r.3r C2n
1.78
OLD
Sample (core, section, interval in cm)
Planktonic foraminiferal zones
Calcareous nannofossil zones
Boundary age (Ma)
Polarity chron
Subchron
C1n
Chron
C1r.1r
Stage
1.07
C1r.1n
M AT UY A M A
Series
BRUHNES JAR
P L E I S T O C E N E E A R L Y
P L E I S T O C E N E
0.78
0.99
?
?
M.PLEIST
Dinoflagellate cysts
377 376 355 319 387 326 335 428 348 340 345 720 353 421 385 334 395 360 331 360 318 398 359 387 363 381 437 389 325 384 327 313 333 329 331 322 335 348 359 365 342 329 344 350 363 354 361 342 372 359 335 346 487 332 403 352 352 326 362 335 391 383 336 309 337 332 360 380 343 329 346 358 385 317 369 355 375 353 344 382 366 366 325 364 374 356 362 341 352 376 346 349 413 337 343 331 345 353 330 361 339 336
0 0 0 48 0 0 0 0 0 1 0 0 53 1 0 0 0 38 1 6 39 38 3 9 59 50 68 16 1 0 5 0 269 125 2 44 3 0 26 5 1 78 3 15 3 17 4 1 2 0 25 1 0 31 163 201 40 80 23 550 154 52 250 496 143 1190 210 49 18 412 201 101 948 1419 120 647 734 1159 6 278 987 113 80 104 39 4 30 44 166 60 55 29 61 45 10 13 31 1 18 31 306 16
Figure 2 Stratigraphic distribution of new dinoflagellate cyst and acritarch taxa from DSDP Hole 610A and calibration of their ranges to magnetostratigraphy (Clement & Robinson 1987, for the Piacenzian
DIAGNOSIS. A new variety of Operculodinium? eirikianum in which the central body wall comprises a thin (
