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Decahedrella martinheadii Manum 1997 - a stratigraphicallyand paleoenvironmentally useful Miocene acritarch of the

high northern latitudes

Jens Matthiessen,1 Henk Brinkhuis,2 Niels Poulsen,3 and Morten Smelror4

1Alfred Wegener Institute for Polar and Marine Research, Am Alten Hafen 26, 27568 Bremerhaven, Germany

email: [email protected]

2Paleoecology, Institute of Environmental Biology, Utrecht University, Laboratory of Paleobotany and Palynology,

Budapestlaan 4, 3584 CD Utrecht, The Netherlands


3Geological Survey of Denmark and Greenland, Østervoldgade 10, DK-1350 Copenhagen, Denmark


4Geological Survey of Norway, NO-7040 Trondheim, Leiv Eirikssons vei 39, Norway

email [email protected]

Abstract: The endemic aquatic acritarch Decahedrella martinheadii is confined to the Atlantic sector of the high northern latitudes in

the Miocene and has been previously considered as useful for biostratigraphy and paleoenvironmental interpretations in temperate to

cold water environments. Stimulated by its recovery in Neogene sediments from the Lomonosov Ridge (Central Arctic Ocean) during

IODP Expedition 302, the stratigraphic and biogeographic distribution has been compiled to revise its age range based on the Astro-

nomically Tuned Neogene Time Scale 2004, and to assess its paleoecologic affinities.

The biostratigraphic revision reveals that this species is restricted to the late Middle to Late Miocene. The first appearence is in-

consistent at the various sites but was probably in sediments younger than 13 Ma, whereas the last appearance is a relatively well-con-

strained datum in the Norwegian-Greenland Sea at around 6.2 Ma.

Decahedrella martinheadii was particularly abundant and had its widest biogeographic distribution in the northwestern North At-

lantic Ocean, the Norwegian-Greenland Sea, the Fram Strait and the Central Arctic Ocean in the Late Miocene suggesting that it was

adapted to temperate to cold seasonally ice-covered surface waters. This species evolved during the global cooling after the mid-Mio-

cene thermal optimum, and it became extinct when small-scale glaciations developed in the Northern Hemisphere in the latest Miocene.

Moreover, fundamental reorganisations of the circulation system and the water mass characteristics may have affected the distribution

of this species.

INTRODUCTION

During palynological studies on ODP Legs 104 and 105,

Manum et al. (1989) and Head et al. (1989) recorded a marine

palynomorph with a unique morphology from upper Miocene

sediments in the Norwegian and Labrador seas. This species

was subsequently encountered in a number of biostratigraphic

studies on Miocene to Pliocene sediments from DSDP and ODP

holes in the North Atlantic Ocean and Norwegian-Greenland

Sea (Engel 1992; Poulsen et al. 1996; Channel et al. 1999b;

text-fig. 1; Table 1). Manum (1997) formally described it as the

acritarch Decahedrella martinheadii and concluded that it had a

restricted stratigraphic and biogeographic distribution in the

Northern Hemisphere in the late Middle Miocene to possibly

the earliest Pliocene (see also Poulsen et al. 1996). Since then,

numerous studies confirmed that it is absent in the lower and

middle latitudes as well as the high southern latitudes in the

Neogene (e.g. DeVerteuil and Norris 1996, DeVerteuil 1997;

Louwye and Laga 1998; Santarelli et al. 1998; Wrenn et al.

1998; Hannah et al. 2000; Warny and Wrenn 2002; Munster-

man and Brinkhuis 2004; Piasecki 2005; Udeze and Oboh-

Ikuenobe 2005; Hannah 2006; Louwye et al. 2007; Eidvin et al.

2007). The recent discovery in sediments from Lomonosov

Ridge in the Central Arctic Ocean (CAO) during IODP Expedi-

tion 302 (ACEX – Arctic Coring Expedition; Backman et al.

2006) renewed the interest in this species that appears poten-

tially useful to identify Neogene sediments in the Arctic Ocean.

This is particularly important because of the sparse occurrence

of other microfossil groups and difficulties in interpreting the

magnetostratigraphic record there. Furthermore, previous Neo-

gene age assignments in the CAO based on a combination of

magnetostratigraphy, lithostratigraphy and biostratigraphy

(dinoflagellate cysts, pollen) are questionable because of rare

age-diagnostic species (e.g. Mudie 1985; Aksu and Mudie

1985; Herman et al. 1989; Clark 1996; Mudie et al. 1990;

Grantz et al. 2001). Up to now, only Neogene sediments from

the marginal Arctic Ocean (Beaufort-Mackenzie Basin, Fram

Strait) could unequivocally be dated by dinoflagellate cysts,

pollen and benthic foraminifers (e.g. Bujak and Davies 1981,

1984; Mullen and McNeil 1995; Norris 1997; Poulsen et al.

1996; Grantz et al. 1998; Harrisson et al. 1999; Mc Neil et al.

2001).

In this paper, the stratigraphic range of Decahedrella martin-

headii in IODP Exp. 302 Hole M0002A is described and age as-

signments of previous records are revised because they were not

always calibrated to magnetostratigraphy and/or other inde-

pendent biostratigraphic data, and different geological time

scales were used at the time of publication (e.g. Berggren et al.

1985; Cande and Kent 1992, 1995). The stratigraphic ranges in

the individual holes are calibrated to the Astronomically Tuned

micropaleontology, vol. 55, nos. 2-3, pp. 171-186, text-figures 1-4, plate 1, tables 1-2, 2009 171

Neogene Time Scale 2004 (ATNTS 2004; Lourens et al. 2004)

to assess the potential of D. martinheadii as biostratigraphic

marker. Additionally, the paleoecology of this species is dis-

cussed, based on the biogeographic distribution, and evidence

for paleoenvironmental conditions from sedimentological and

micropaleontological studies on Neogene sediments in the high

northern latitudes.

MATERIAL AND METHODS

In addition to published information, the present paper is based

on new data from ODP Holes 907A and 985A in the Norwe-

gian-Greenland Sea, and IODP Hole M0002A in the CAO (Ta-

ble 1; text-fig. 1). Neogene sequences were drilled at 2 sites in

the CAO (Backman et al. 2006) but only Hole M0002A con-

tains Miocene and Pliocene sediments (text-fig. 2). Deca-

hedrella martinheadii (as Evittosphaerula sp. 2 of Manum et al.

1989) was encountered during the shipboard studies in three

core catcher samples between approximately 76 and 101mbsf

(=meters below seafloor) (Backman et al. 2006). For a

shore-based biostratigraphic study, 2cm sediment slices were

sampled at 10 to 60cm intervals from undisturbed cores, repre-

senting a temporal resolution on the order of 10-30kyrs accord-

ing to the10

Be/9Be isotope stratigraphy (Frank et al. 2008). The

low recovery and core disturbances led to some substantial gaps

in the stratigraphic column.

Shipboard processing of samples was done with a novel method

without any acid treatment but included heavy liquid separation

(Riding and Kyffin-Hughes 2004) and sieving at 20µm.

Shore-based processing included sieving at 125µm to exclude

coarse sand and gravel and subsequent treatment with cold hy-

drochloric (10%) and hydrofluoric acids (38-40%). After each

acid treatment the residue and acid were decanted through a

sieve (polyester mesh PES-6/5/SR, Eckert, Waldkirch, Ger-

many), and sieved with demineralized water. The treatment

with hydrofluoric acid was repeated if minerals were still ob-

172

Jens Matthiessen et al.: Decahedrella martinheadii Manum 1997 - a useful Miocene acritarch of the high northern latitudes

TEXT-FIGURE 1

Geographic locations of records of Decahedrella martinheadii. The paleogeography reflects the Late Miocene (10 Ma) reconstruction based on OSDN

(www.osdn.de). Note that Iceland and possible subaerial exposures of the Greenland Scotland Ridge are not shown. The hypothetical surface circulation

in the Norwegian-Greenland Sea is based on Fronval and Jansen (1996). (NS, Norwegian-Greenland Sea; NA, North Atlantic Ocean; LS, Labrador Sea;

BB, Baffin Bay).

served in the residue. The residues were finally centrifuged at

3500 rpm for 7 minutes prior to preparation of microscope

slides. A part of the homogenized residue was mounted in glyc-

erine gelatine on a glas slide, and the cover slip was sealed with

paraffine wax.

Concentrations were calculated with the marker grain method

(Lycopodium clavatum spores, batch 124961, x = ±2081; v=

±3.3%, Department of Quaternary, Lund University) according

to Stockmarr (1971). One tablet was added to the sample after

treatment with hydrochloric acid. One microscopic slides of

each sample was completely scanned at 200x and 400x magni-

fication to record the presence of aquatic palynomorphs.

All calculated ages refer to ATNTS 2004 (Lourens et al. 2004).

The biostratigraphic ages used in previous studies were

recalibrated to this new Neogene time scale. The nannoplank-

ton zonation is after Martini (1971) and the planktonic

foraminifer zonation after Blow (1969).

All data can be retrieved from the data bank WDC-Mare

(iodp.wdc-mare.org).

Stratigraphic distribution of Decahedrella martinheadii inHole M2A

The study of a larger number of samples from lithological units

1/2 to 1/4 led to a much better recovery of aquatic

palynomorphs compared to the initial low-resolution shipboard

analysis (Backman et al. 2006). In particular, lithostratigraphic

Unit 1/3 of Hole M2A that contained few palynomorphs based

on the shipboard analyses of core catcher samples comprises

now a large number of productive samples (text-fig. 2). The re-

covery of palynomorphs is related to lithological units. Units

1/1 and 1/3 contain palynomorphs whereas Units 1/2 and 1/4

were almost barren. The absence may be related to various fac-

tors including unfavourable environmental conditions or vari-

able preservation.

The shore-based palynological analysis revealed a rather con-

sistent occurrence of D. martinheadii from 74.09 to 112.99

mbsf in Hole M2A (Table 2; text-fig. 2). Both the highest oc-

currence (HO) and lowest occurrence (LO) are located within

productive intervals suggesting that the stratigraphic distribu-

tion is not affected by postdepositional processes such as the se-

lective degradation of particulate organic matter.

The relative abundances of the abundant palynomorphs as well

as the concentrations of D. martinheadii have been calculated

for a selected number of samples (text-fig. 3). The concentra-

tions of D. martinheadii are variable and range from 3 to 419

specimens per gram dry sediment. Decahedrella martinheadii,

Nematosphaeropsis spp. and Impagidinium spp. dominate the

assemblages. The assemblages from the LO of D. martinheadii

to 104 rmcd (revised meter composite depth; O´Regan et al.

2008) are dominated by Nematosphaeropsis spp., whereas the

assemblages upcore to the HO are mainly characterized by an

acme of D. martinheadii.

Based on the initial magnetostratigraphic interpretations

(Backman et al. 2006), D. martinheadii occurred from either

Chron C3n.2r (ca. 4.9 Ma) or Chron C3An.1n (ca. 6 - 6.3) to the

top of Chron C4r.2r (ca. 8.5 Ma) (text-fig. 4; Table 2). How-

ever, Backman et al. (2008) did not use the magnetostrati-

graphy to develop a Neogene age model for the ACEX

composite section but instead adopted the10

Be/9Be stratigraphy

of Frank et al. (2008) that leads to a HO at approximately 5.1

Ma and a LO at 7.8 Ma.

Stratigraphic distribution of Decahedrella martinheadii in thehigh northern latitudes

The stratigraphic range has extensively been discussed by

Manum (1997) based on a compilation of data from DSDP and

ODP holes (Table 1). He concluded that D. martinheadii ap-

pears to be restricted to the Late Miocene in records where the

age control is independent of dinoflagellate cysts. Dino-

flagellate cyst stratigraphy at other sites suggested a first ap-

pearance in the later part of the Middle Miocene (Serravallian)

and a possible last appearance in the earliest Pliocene. However,

Manum (1997) used the published age models and did not cali-

brate the occurrences to the magnetostratigraphy any other

biostratigraphic data, and a common time scale. Moreover, con-

sistent age models have not been proposed for some DSDP and

ODP sites (Engel 1992; Hull et al. 1996; Poulsen et al. 1996;

Spiegler 1996; Wolf-Welling et al. 1996; Goll in Manum 1997;

Winkler et al. 2002). The chronostratigraphy of Site 907 was

initially based on a single hole (Shipboard Scientific Party

1995a; Hull et al. 1996) but could be improved due to multiple

coring during Leg 162 (Jansen et al. 1996). A composite section

was established and was dated by diatom and silicoflagellate

biostratigraphy and magnetostratigraphy (Channell et al.

1999a). Therefore, this site has currently the most continuous

and best-constrained Middle Miocene to recent chrono-

stratigraphy north of the Greenland – Scotland Ridge. The data

set of Manum (1997) can be further updated by new observa-

tions from sites in the Norwegian-Greenland-Sea (Smelror

1998; Channel et al. 1999b; Table 1).

The stratigraphy of D. martinheadii in the individual sites will

be assessed here based on independent age control, in particular

magnetostratigraphy. Relevant information (stratigraphic

range, presence of acmes) of the different sites are shown in

text-figure 4 and additional information data are shortly pre-

sented in the following chapters. Sample information is given as

detailed as possible depending on available published and un-

published data (Table 2).

173

Micropaleontology, vol. 55, nos. 2-3, 2009

TABLE 1

Location of DSDP, ODP and IODP holes marked in figure 1 (1, Anstey

1992; 2, Channel et al. 1999b; 3, Engel; 4, Head et al. 1989; 5, Manum

1997; 6, Poulsen et al. 1996; 7, Smelror 1998; 8, this study).

Norwegian-Greenland Sea

Decahedrella martinheadii has been observed at four sites in

the southern Norwegian-Greenland Sea (Manum et al. 1989;

Manum 1997; Poulsen et al. 1996; Smelror 1998; Channell et al.

1999b; text-figs. 1, 4; Table 1, 2). Manum et al. (1989) initially

recorded D. martinheadii (as Evittosphaerula? sp.2) as abun-

dant in a single sample of ODP Leg 104 Hole 642C from the

Vøring Plateau in the Late Miocene (Sample 642C-15H-1,

79-81cm, 111.79mbsf). In conjunction with the formal taxo-

nomic description, Manum (1997) added new stratigraphic data

to his initial observations and suggested an age range of 7.5 to

6.5 Ma at Site 642 based on a unpublished stratigraphic synthe-

sis by Goll (1996, personal communication in Manum 1997).

This stratigraphic range is updated to 6.5 to 7.2 Ma, based on

the magnetostratigraphy (Bleil 1989) and supported by plank-

tonic foraminifer stratigraphy indicating a late Late Miocene

age (Spiegler and Jansen 1989).

The longest stratigraphic range has been recorded from Hole

907A but the LO is located slightly below a hiatus or condensed

section at 105-110mbsf (~9.5 to ~7.5 Ma; Channell et al.

1999b, fig. 8). At Site 985 the LO can not be well defined be-

cause of drilling-related deformation below 160 mbsf (Channell

et al. 1999b) and is based on linear interpolation between the

base of Chron 3Ar at 154mbsf (Channel et al. 1999a) and a

palynostratigraphic age of younger than Burdigalian (< 16 Ma)

at 290mbsf (Williams and Manum 1999).

North Atlantic Ocean

Engel (1992) described rare D. martinheadii (as Evitto-

sphaerula sp.) from single samples in Holes 408 and 554.

Planktonic foraminifer stratigraphy originally suggested an age

around the Pliocene/Miocene boundary for the single occur-

rence in Sample 408-13-3, 100-104cm (N18-N19, Poore 1979),

whereas coccolith stratigraphy indicate a Late Miocene age

(Bukry 1979; Steinmetz 1979: middle part of NN11). Spiegler

(1986, 1989; unpublished in Engel 1992) revised the planktonic

foraminifer biostratigraphy and placed the single occurrence

into the Late Miocene (N17). The occurrence is furthermore lo-

cated slightly above the change from Neogloboquadrina

atlantica dextral coiling morphotypes to the sinistral morpho-

types between core sections 408-14 and 408-13-CC (Poore

1979). Weaver and Clement (1986) calibrated this coiling direc-

tion change to magnetostratigraphy in Leg 94 holes (Clement

and Robinson 1986) and established an age older than the top of

Chron C3An.2n and younger than the top of Chron C4n.2n

(6.4–7.7 Ma). Engel (1992) assumed an Early Pliocene age

based on dinoflagellate cysts but the bulk of evidence suggest a

Late Miocene age (NN 11, younger than ca. 7.1 Ma) for the oc-

currence of D. martinheadii.

The age assignments based on planktonic foraminifer stratigra-

phy vary from Pleistocene to Late Miocene for the single occur-

rence in Sample 554-7-4, 74-78cm (N16 to N19, Huddelstun

1984; N22, Spiegler 1989 unpublished in Engel 1992) whereas

calcareous nannofossil stratigraphy (Backman 1984) suggest a

Late Miocene age, possibly from the middle part of NN11

(younger than the base of NN11b, < 7.4 Ma). Dinoflagellate

cyst stratigraphy indicate a Late Miocene age (Edwards 1984;

Engel 1992). Huddelstun (1984) recorded the Late Miocene

coiling direction change of N. atlantica between core sections

554A-1-CC and 554A-2-CC, approximately 30m below the ho-

rizon with D. martinheadii. Therefore, a Late Miocene (NN11)

174


TEXT-FIGURE 2

Stratigraphic distribution of samples in Hole M0002A analysed in this

study. Samples containing aquatic palynomorphs and D. martinheadii

are shown separately. The chronostratigraphy is from Frank et al.

(2008).

age for the occurrences in Hole 408 and 554 appears more

likely than an Early Pliocene age (text-fig. 4).

Labrador Sea/Baffin Bay

The stratigraphic range is dated by calcareous nannofossil stra-

tigraphy because the interpretation of the magnetostratigraphy

at Site 646 is hampered by poor recovery and drilling distur-

bances (Clement et al. 1989). Decahedrella martinheadii (as

Genus et spec. indet.) occurs from the base of Hole 646B (NN

10) to the lower part of NN 11 (Head et al. 1989; Knüttel et al.

1989). The magnetostratigraphy would suggest a slightly older

age of the HO than the calcareous nannofossil stratigraphy (8.6

Ma, between the base of Chron C4n.2n and the top of Chron

C4An). However, the HO falls into an interval with a short hia-

tus of 0.5 Ma duration or a change in sedimentation rates related

to seismic reflector doublet R3/R4 (Head et al. 1989). In Site

645 from Baffin Bay, this species occurs probably in coeval de-

posits (Anstey 1992; from Manum 1997).

Fram Strait

Decahedrella martinheadii (as Evittosphaerula? sp.2) occurs at

two sites in the Fram Strait that have a poor age control. The LO

is probably not recorded in Hole 908A because it is located just

above a hiatus at approximately 185mbsf (Poulsen et al. 1996).

Different age models have been proposed for the oldest recov-

ered Neogene sediments in Hole 908A. The initial interpretation

of the magnetostratigraphy suggest a Middle Pliocene age

whereas diatom stratigraphy indicate an age older than Early

Pliocene (Shipboard Scientific Party 1995b). A re-interpreta-

tion of the magnetostratigraphy based on unpublished argu-

ments place the top of the hiatus at the Miocene/Pliocene

boundary (Wolf-Welling et al. 1996; Winkler et al. 2002). The

dinoflagellate cyst stratigraphy might have been the reason be-

cause the basal Neogene deposits at approximately 185.61mbsf

are not older than the late Middle Miocene (Serravallian) and

the correlation of the acme of D. martinheadii to Hole 909C

suggest a Late Miocene (Tortonian-Messianian) age (Poulsen et

al. 1996). The paleomagnetic age datums of Wolf-Welling et al.

(1996) can be tied to chrons down to the base of C2Ar at

130mbsf (4.2 Ma) but the oldest age datum at 164.2mbsf (5.4

Ma) can not unequivocally be related to a chron. Different inter-

pretations of the magnetostratigraphy are possible and the old-

est Neogene sediments might be slightly older than the base of

Chron C3An.1n (6.3 Ma) or the base of Chron C3An.2n (6.7

Ma).

175


TABLE 2

Calculated ages, polarity chrons and nannoplankton zones of the lowest and highest occurrences as well as stratigraphic ranges of acmes of D.

martinheadii in the holes (Source of data: 1, Bleil 1989; 2, Backman et al. 2006; 3, Channel et al. 1999a; 4, Channel et al. 1999b; 5, Frank et al. 2008; 6,

Knüttel et al. 1989; 7, Shipboard Scientific Party 1995b; 8, Shipboard Scientific Party 1995c; 9, Spiegler et al. 1996; 10, Wolf-Welling et al. 1996; 17,

this study).

The HO is equally poorly constrained but an age close to the

base of Chron C3n.4n (5.2 Ma) or Chron C3An.1n (6.3 Ma) is

likely (text-fig. 4; Table 2). The coeval HO of the dinoflagellate

cyst Dapsilidinium pastielsii indicate an age not younger than

the top of NN11 (Poulsen et al. 1996). Therefore, a latest Late

Miocene age is more likely than a Early Pliocene age.

The interpretation of the magnetostratigraphy in the lower part

of Hole 909C is seriously hampered by poor recovery, largely

indeterminate inclinations below 830 mbsf and a lack of

biostratigraphic age control leading to two different age models

(Shipboard Scientific Party 1995c). Wolf-Welling et al. (1996)

used model 2 and added a biostratigraphic datum for the lower

part of the hole (1016.15mbsf, 16.15 Ma). However, this datum

was never defined by either Hull (1996) or Hull et al. (1996) as

it has been stated by Wolf-Welling et al. (1996) and Winkler

(1999). Hull et al. (1996) discussed the biostratigraphy of Site

909 but only stated that Miocene (Aquitanian?-Langhian?)

dinoflagellate cysts (Poulsen et al. 1996) support an earliest

Miocene age for the base of Hole 909C derived from calcareous

nannofossil stratigraphy. The shipboard interpretation of an

earliest Miocene age for the base of Hole 909C was based on

the occurrence of the calcareous nannofossils Helicosphaera

carteri, Coccolithus miopelagicus and Cylicargolithus abi-

sectus in Sample 909C-101R-2, 26cm (1050.16mbsf) to Sam-

ple 909C-102R-CC (ca. 1058mbsf) below a coccolith-free

interval (Shipboard Scientific Party 1995c).

Spiegler (1996) distinguished an upper from a middle Miocene

section in Hole 909C based on the LO of the planktonic

foraminifer Globigerina bulloides that appeared in the Late

Miocene although G. bulloides occurs further downcore in

Sample 909C-103R-2, 3-7cm at 1059.53mbsf. Upper Miocene

sediments range from the HO of D. martinheadii (657.14mbsf)

down to Sample 909C-76R-1, 96-98cm (808.56mbsf) while

middle Miocene sediments continue from Sample 909C-77R-2,

94-97cm (819.74mbsf) to the LO of D. martinheadii

(894.44mbsf). The LO of Orbulina universa in Sample 909C-

89R-1, 97-100cm (934.07mbsf) marks the base of planktonic

foraminifer zone N9 (14.8 Ma) in the Middle Miocene

(Spiegler 1996). The occurrence of Globorotalia scitula in

Sample 151-909C-103R-2, 3-7cm (1059.53mbsf) contradicts

an Early Miocene age for the base of the hole because this spe-

cies occurred for the first time in the Middle Miocene plank-

tonic foraminifer zone N9 (Spiegler 1996). This is supported by

the HO of the dinoflagellate cysts Apteodinium australiense

(section 909C-87R-CC, 916.23mbsf) and Distatodinium

paradoxum (section 909C-81R-CC, 861.78mbsf), which both

became extinct in calcareous nannofossil zone NN5/6 in the

Middle Miocene (Poulsen et al. 1996).

According to the preferred interpretation of the shipboard

magnetostratigraphy (Wolf-Welling et al. (1996) and plank-

tonic foraminifer stratigraphy (Spiegler 1996), the LO of D.

martinheadii is in the Middle Miocene between the base of

Chron C5n.2n at 838.5mbsf (11 Ma) and the LO of the plank-

tonic foraminifer O. universa at 934.07mbsf (younger than 14.8

Ma). Using an age of 14.5 Ma for the LO of O. universa, the LO

of D. martinheadii is estimated at 13 Ma (text-fig. 3; Table 1).

If the LO of G. scitula is taken as base of planktonic foraminifer

zone N9 (14.8 Ma), the LO of D. martinheadii would be much

closer to the base of the Late Miocene (12 Ma). The interpreta-

tion is further complicated by stratigraphic breaks in section

909C-89-R (940mbsf) and at the base of section 909C-87-R

(923.40mbsf) suggested by conspicuous reworking of

palynomorphs (Poulsen et al. 1996). Moreover, a Middle to

Late Miocene age for the base of Hole 909C cannot be ruled out

because meter-scale slump structures below 923.4 mbsf may

represent episodic events caused by rapid sediment accumula-

tion (Shipboard Scientific Party 1995c).

The HO of D. martinheadii at the top of Chron C4An (8.8 Ma;

Shipboard Scientific Party 1995c; Wolf-Welling et al. 1996)

differs considerably from that in Hole 908A reflecting the

poorly constrained chronostratigraphy of both sites.

Biostratigraphy of Decahedrella martinheadii

The compilation of the stratigraphic range of D. martinheadii in

the various DSDP and ODP holes clearly demonstrates the

problems associated with palynostratigraphy in the high north-

ern latitude. A uniform zonation is not available and a number

of formal and informal schemes were published in the past 20

years (see Poulsen et al. 1996). Data banks are also of limited

value because palynomorphs were not included e.g. in the

Ocean Drilling Stratigraphic Network data bank (ODSN,

www.odsn.de). Moreover, the only global compilation of

dinoflagellate cyst datums comprises almost no high northern

latitude Neogene species (Williams et al. 2004). Stratigraphic

work has therefore to rely on heterogeneous data sets that were

calibrated to the geological time scales accepted at the time of

publication. Furthermore, a sound magnetostratigraphy to cali-

brate LOs and HOs is not available for most sites in the high

northern latitudes, because few independent biostratigraphic

data constrain the ages of magnetostratigraphic datums. Despite

these inconsistencies and problems, this study illustrates that

palynomorphs are potentially useful to define biostratigraphic

datums applicable in the high northern latitudes.

Decahedrella martinheadii is apparently an excellent strati-

graphic marker because it is confined at most sites to the upper

Miocene (Table 2; text-fig. 4). The oldest LO in any site is in the

upper Middle Miocene (ca. 13-12 Ma) of Hole 909C in Fram

Strait. Since both magnetostratigraphy and biostratigraphy do

not provide a consistent age model for the lower part of Hole

909C alternate interpretations are possible. The LO cannot be

assessed at other sites because coring terminated in upper Mio-

cene sediments at Site 646 and a hiatus has prevented recovery

of the LO at Site 908. An exclusively upper Miocene occur-

rence of D. martinheadii might be reasonable because the oldest

well-constrained LOs are in the lower upper Miocene of Holes

907A and 985A (Table 2).

In contrast, the highest occurrence is much better defined at

most sites being close to the Pliocene/Miocene boundary. The

variable ages may be caused by different sample intervals

and/or a strongly variable quality of the reference stratigraphy.

The magnetostratigraphy of Holes 646B, 908A, 909C, and

M2A is difficult to interpret (Clement et al. 1989; Shipboard

Scientific Party 1995b,c; Backman et al. 2006), and the10

Be

stratigraphy of Hole M2A (Frank et al. 2008; Backman et al.

2008) is based on relatively few data points and the assumption

of linear sedimentation rates in the Neogene. The considerable

age offsets between the HOs of Holes 908A and 909C that were

drilled less than 50km apart illustrate that the published

magnetostratigraphic and biostratigraphic interpretations (e.g.

Wolf-Welling et al. 1996; Hull et al. 1996) are inconsistent and

certainly require revision. These interpretations are also untena-

ble from a paleoecological point of view: if the HO were

diachronous across the high northern latitudes, D. martinheadii

must have disappeared earlier in the Arctic Ocean than in the

176


Norwegian-Greenland Sea because of a general latitudinal tem-

perature gradient during the Neogene with colder conditions in

the Arctic Ocean than further south. Furthermore, the correla-

tion of the palynomorph assemblages and acmes between holes

908A and 909C appears consistent (Poulsen et al. 1996) but

seems unlikely because the published magnetostratigraphic age

models revealed an offset of ca. 2 Ma for the acmes.

At three sites in the southern Norwegian-Greenland Sea, the

HOs are almost coeval (Table 2; text-fig. 4). It appears plausi-

ble to use the magnetostratigraphically constrained youngest

HO of D. martinheadii in Hole 907A as basic age to define a

last appearance datum. The calculated ages from the adjacent

sites in the Norwegian Sea (642B/C, 985A) support a last ap-

pearance datum in the upper part of NN11 at approximately 6.2

Ma (text-fig. 4). When accepting this datum, the chrono-

stratigraphy of Holes 908A, 909C and M2A must be revised.

An alternate interpretation of the magnetostratigraphy of Hole

908A already suggests a HO at the base of Chron C3An.1n (6.3

Ma). The HO in 909C is associated with the top of a normal po-

larity interval (Shipboard Scientific Party 1995c) that could be

interpreted as Chron C3An.2n (6.4 Ma). In Hole M2A, the al-

ternate magnetostratigraphic interpretation fits much better

than the preferred magnetostratigraphic interpretation (Back-

man et al. 2006) placing then the HO in Chron C3An.1n (ca. 6 -

6.3 Ma). The10

Be/9Be age estimates also agree reasonably well

with a palynomorph datum of 6.2 Ma because Be ages are con-

sidered reliable within an error envelope of ±1 Ma (Frank et al.

2008).

The acmes recorded at the various sites may be further useful

for correlation of holes (cf. Poulsen et al. 1996). These acmes

might have occurred diachronously (cf. Manum 1997) but the

youngest acme which is associated with the HO of D.

martinheadii appears synchronous if we accept the revised age

models of Holes 908A, 909C and M2A in the Fram Strait and

Arctic Ocean.

Paleoecology of D. martinheadii

The restricted biogeographic distribution has previously led to

the interpretation of D. martinheadii as an indicator for cold

conditions and changes in the penetration of polar waters from

the Arctic Ocean into the North Atlantic Ocean (Poulsen et al.

1996; Manum 1997). Since Manum (1997) has published his

compilation, a considerable number of palynological studies

were conducted on Miocene sediments but the few new records

from the Norwegian-Greenland Sea (Smelror 1998; Channel et

al. 1999b) and the CAO (Backman et al. 2006; this study) con-

firm that D. martinheadii is an endemic acritarch in the Atlantic

sector of the high northern latitudes (text-fig. 1). The biogeo-

graphic distribution suggests a broader ecologic adaption than

Manum (1997) has proposed with a preference for cool-temper-

ate to cold waters. Decahedrella martinheadii probably lived

in oceanic surface waters (possibly with a relatively high salin-

ity) as indicated by the co-occurrence of the generally oceanic

to outer neritic genera Impagidinium and Nematosphaeropsis

(Marret and Zonneveld 2003). This species was widely distrib-

uted only during a short time interval in nannoplankton zone

NN11 (text-fig. 4), when it occurred in the entire high northern

latitudes, while older records are only from regions that are to-

day part of the modern cold water domain close to the polar

front.

The absence of D. martinheadii in the high latitude North Pa-

cific Ocean has been caused by the geographic isolation from

177


TEXT-FIGURE 3

Composition of palynomorph assemblages and concentrations of D.

martinheadii (rmcd = revised meters composite depth after O´Regan et

al. 2008).

the Arctic Ocean (text-fig. 1; see also Jakobsson et al. 2008).

The Bering Strait was closed until the late Late Miocene (5.5 –

5.4 Ma, Gladenkov 2006) but a connection might have been

temporarily open across Eastern Siberia in the Miocene

(Polyakova 2001). Moreover, the Arctic Ocean was connected

with the North Atlantic Ocean only via the Fram Strait because

the straits through the Canadian Arctic archipelago did not exist

and the Barents Sea was subaerially exposed (Dixon et al. 1992;

Butt et al. 2002; Torsvik et al. 2002).

Decahedrella martinheadii might have been dispersed in the

Atlantic sector of the high northern latitudes with a surface cir-

culation system that largely resembled the modern one with the

advection of relatively warm waters from the North Atlantic

Ocean to the Arctic Ocean and the export of low salinity, cold

and ice-covered waters from the Arctic Ocean. Head et al.

(1989) already noted the possible coeval occurrence of D.

martinheadii both in the Labrador Sea and in the Norwegian

Sea and the similarities in the composition of assemblages. The

low abundance of warm water species and the regular occur-

rence of Impagidinium pallidum and Habibacysta tectata in the

Labrador Sea indicates temperate to cool surface waters in the

Late Miocene and Early Pliocene and a persistent influence of

subarctic surface waters. These were formed by mixing of arc-

tic (East Greenland Current) and warm temperate (North Atlan-

tic Drift) surface waters, perhaps analogous to the origin of

today´s West Greenland Current. Similarities with other

dinoflagellate cyst assemblages from North Atlantic and Nor-

wegian Sea sites were attributed to a southward flowing

proto-East Greenland Current transporting cold water taxa into

the warm waters (Head et al. 1989). Fronval and Jansen (1996)

suggested that a thermal gradient existed in the southern Nor-

wegian-Greenland Sea since the late Middle Miocene, with

colder currents on the western side and warm currents on the

eastern side (text-fig. 1).

However, the circulation system must have differed somewhat

from the modern situation because of a much restricted ex-

change of deep waters between the Arctic Ocean, Norwe-

gian-Greenland Sea and the North Atlantic Ocean. The Fram

Strait developed since the Early Miocene but a true deep-water

passage might not have existed prior to 7.5 to 5 Ma (Lawver et

al. 1990; Kristoffersen 1990). Moreover, the subsidence of the

Greenland-Scotland Ridge might have controlled the long-term

variation of overflow of Northern Component Water (NCW) to

the North Atlantic Ocean (Wright and Miller 1996; Poore et al.

2006). The production of NCW was weak in the Middle Mio-

cene (16-11.6 Ma) and significantly increased since about 12

Ma (Poore et al. 2006 and references therein). After somewhat

variable conditions in the Late Miocene, a distinct long-term in-

crease occurred after 6 Ma.

Interestingly, these reorganisations of the circulation system

bracket the stratigraphic range of D. martinheadii. In particu-

lar, the extinction was almost coeval with the fundamental

change in the latest Miocene. In Hole M0002A, the HO is lo-

cated between two seismic reflectors in a synthetic seismogram

at 71 and 82mcd, respectively, that may correlate with the base

of reflector LR 6 (Backman et al. 2008). This reflector has been

linked to the formation of the deep Fram Strait (Jokat et al.

1995). The HO at Sites 909 and 907 is located close to seismic

reflectors (Shipboard Scientific Party 1996a, c) that might have

been related to the establishment of a more vigorous exchange

of water masses with the North Atlantic Ocean.

The distinct acmes possibly reflect favourable living conditions

in the high northern latitudes in NN 10 and 11 (text-fig. 4). Al-

though the timing is insufficiently constrained, a distinct suc-

cession of acmes (Nematosphaeropsis spp. to D. martinheadii)

in the Late Miocene may be correlated from the Fram Strait

(Holes 908A, 909C) to the CAO (Hole M2A; text-fig. 3). In

Hole 909C, the acme coincides with a specific deep-water ag-

glutinated benthic foraminifer assemblage that probably indi-

cates an increased flux of marine organic matter (Kaminski et

al. 2006). Thus, these abundance maxima might have been re-

lated to increased plankton production in surface waters, e.g.

during seasonal melting along the sea-ice margins.

The biogeographic distribution also implies a relation to a sea-

sonal sea-ice cover which is evidenced by the coeval occurrence

of low amounts of ice-rafted debris in the sediments (Wolf and

Thiede 1991; Fronval and Jansen 1996; Winkler et al. 2002; St.

John 2008). A year-round sea-ice cover that has been suggested

for the CAO since the Middle Miocene (Darby 2008; Krylov et

al. 2008; Frank et al. 2008) can be ruled out because this would

have led to an extremely low production as in the modern Arctic

Ocean (e.g. Wheeler et al. 1996) leading to low abundances or

absence of aquatic palynomorphs in sediments. Moreover the

co-occurrence of Nematosphaeropsis spp. and Impagidinium

spp. suggests seasonally open waters (cf. Marrett and

Zonneveld 2003).

The discrepancies to these previous reconstructions may be ex-

plained by their lower temporal resolution. The study by Darby

(2008) has with a average sampling interval of about 0.17 Ma a

much higher resolution than those by Krylov et al. (2008) and

Frank et al. (2008) but we used samples at an average sample in-

terval of 60cm in the Late Miocene corresponding to a temporal

resolution of approximately 0.04 Ma according to the age model

of Frank et al. (2008). Therefore, periods with a reduced sea-

sonal extent of the sea-ice cover (interglacials?) may have alter-

nated with periods of a year-round sea-ice cover (glacials?).

Moreover, Frank et al. (2008) stated that two10

Be maxima in

the Late Miocene may be attributed to increased fluxes to the

seafloor during short warmer periods with a reduced sea-ice

cover. Therefore, the Late Miocene CAO might have been char-

acterized by a strong (cyclic?) variability in sea-ice conditions

but a high-resolution study at millenial time-scales is required

to prove or disprove this hypothesis.

Apart from the regional oceanographic conditions, the biologi-

cal evolution of D. martinheadii in the high northern latitudes

might have been linked to the global climate cooling in the Mid-

dle to Late Miocene that is also reflected in high latitude terres-

trial and marginal marine records (e.g. Zachos et al. 2001;

Wolfe 1994; White et al. 1997; McNeil et al. 2001; Polyakova

2001). Climate change may have led to a selection of species

best adapted to deteriorating ecological conditions after the

Middle Miocene climate optimum (e.g. Flower and Kenneth

1994 and references therein). The first appearance of D.

martinheadii might have been associated with an intensification

of glaciations in the late Middle Miocene (Fronval and Jansen

1996 and references therein; Eidvin et al. 1998; Winkler et al.

2002 and references therein). Ice-rafted debris in the Norwe-

gian-Greenland Sea sediments indicates that glaciers possibly

reached sea level around that time (Fronval and Jansen 1996).

This event has been associated with a distinct compression

phase along the margins of the Norwegian-Greenland Sea that

led to an uplift of the land areas (Løseth and Henriksen 2005).

This view is, however, disputed, and other mechanism are re-

178


quired to explain the Late Neogene uplift and the present day

high-amplitude elevation of the Scandes (Smelror et al. 2007).

Regardless the fundamental mechanisms, the uplifted land ar-

eas might have been the nucleation sites for glaciations as has

been suggested for a similar tectonic situation during the

Pliocene (Dahlgren et al. 2005).

The extinction might have been linked to another step in the

global cooling, as documented by a cooling phase on the sur-

rounding continents (Wolfe 1994; White et al. 1997) and the

development of small-scale glaciations around the Norwegian-

Greenland Sea and Northwestern North Atlantic Ocean in the

Late Miocene (7 to 6 Ma, Fronval and Jansen 1996 and refer-

179


TEXT-FIGURE 4

Stratigraphic ranges of D. martinheadii in DSDP, ODP and IODP holes. The age assignments of the stratigraphic range in Hole M0002A is based on (A)

the10

Be age model of Frank et al. (2008) and (B) the alternate magnetostratigraphic interpretation for the HO (Backman et al. 2006) and the10

Be age

model (Frank et al. 2008) for the LO. Alternate ages are given for the stratigraphic ranges in Holes 908A and 909C.The Middle Miocene to early Pliocene

time-scale is from Lourens et al. (2004).

ences therein; ca. 6.2 to 5.5 Ma; Hodell et al. 2001; see also

Winkler et al. 2002; since 7.3 Ma, St. John and Krissek 2002;

Fridleifsson 1995, from Roberts et al. 2007). This event was as-

sociated with a distinct cooling of surface and deep waters

(Fronval and Jansen 1996). The HO of D. martinheadii is ap-

proximately coeval with the increase of ice-rafted debris in

Hole 907A in Chron C3Ar and at Site 642/644 (Fronval and

Jansen 1996) suggesting a causal relationship between the onset

of small-scale glaciations and the extinction. Environmental

conditions might have reached a certain threshold (minimum

temperature, expansion of sea-ice coverage etc.) leading to the

extinction of D. martinheadii. The earlier last occurrences off

East Greenland (Hole 987E) and in the Labrador Sea (Hole

946B) might have been an effect of a earlier substantial cooling

along the path of the East Greenland Current (Wolf and Thiede

1991).

CONCLUSIONS

During shipboard biostratigraphic studies on IODP Expedition

302 sediments from the Lomonosov Ridge in the Central Arctic

Ocean, the acritarch Decahedrella martinheadii has been found

in a few samples from the Neogene section of Hole M2A. Sub-

sequent shorebased studies on a much larger sample set re-

vealed a consistent occurrence in the depth interval between

112 and 74mbsf. This species has been previously recorded

from a number of DSDP and ODP holes in the North Atlantic

Ocean and Norwegian-Greenland Sea (Manum 1997; Smelror

1998; Channel et al. 1999b) and a compilation of the strati-

graphic ranges and calibration to the ATNTS 2004 revealed

that D. martinheadii is restricted to the late Middle to latest

Miocene. Based on the available data the first appearence must

be younger than 13-12 Ma whereas the last appearence can

rather accurately be defined at around 6.2 Ma.

The compilation of the biogeographic distribution basically

confirm previous interpretations of D. martinheadii as a

cool-temperate to cold water oceanic species (Poulsen et al.

1996; Manum 1997; Smelror 1998). It is restricted to the Atlan-

tic sector of the high northern latitudes and is particularly abun-

dant in the cold water domain of the Northwest Atlantic Ocean,

the Norwegian-Greenland Sea, and the Arctic Ocean, probably

associated with a seasonal sea-ice coverage. The biological

evolution of this species might have been linked both to the

global climate deterioration after the mid-Miocene thermal opti-

mum and fundamental reorganisations of the surface and

deep-water circulation and the water mass properties due to the

deepening of the gateways to the Atlantic Ocean. Decahedrella

martinheadii appeared in the Northern Hemisphere when gla-

ciers reached sea level for the first time in the Norwegian and

Greenland seas (Fronval and Jansen 1996) and the export of

deep waters from the Norwegian-Greenland Sea to the North

Atlantic Ocean significantly increased (Poore et al. 2006). The

extinction might have been related to a distinct cooling phase in

latest Miocene when the first small-scale glaciations developed

in the Northern Hemisphere between 7.2 and 6 Ma (Fronval and

Jansen 1996) and to the establishment of a deep water passage

through Fram Strait.

SYSTEMATIC PALEONTOLOGY

Acritarcha

Decahedrella martinheadii Manum 1997

Plate 1, figures 1-12

Evittosphaerula? sp. 2, MANUM et al., 1989, pl.7, figs. 8-10. -

POULSEN et al. 1996, p. 282. - CHANNEL et al. 1999b, p. 153. -

BACKMAN et al. 2006, p. 19.

Gen. et sp. Indeterminate HEAD et al. 1989, p. 440, pl. 4, figs. 1,2,4; pl.

6, figs. 1-3, 6, 7.

Evittosphaerula sp. ENGEL 1992, pl. 7, figs, 12,13.

Decahedrella martinheadii MANUM 1997, pl. 1, figs. 1-13, pl. 2, figs,

1-7, Text-fig. 2.

Taxonomic comments: The specimens recorded from the Arctic

Ocean can undoubtly be assigned to D. martinheadii. The ob-

served specimens fall into the size range of D. martinheadii re-

ported by Manum (1997) but they are usually too distorted to

allow accurate measurements. Specimens from the Arctic

Ocean have been analysed by epifluorescence technique that

has not been applied by Manum (1997). Decahedrella

martinheadii has a pronounced bright yellowish greenish

autofluorescence suggesting a possible photoautotrophic feed-

ing behaviour (cf. Brenner and Biebow 2001).

Thalassiphora? sp. A of Powell and Evittosphaerula sp. 1 of

Mudie (1989, pl. 2, fig. 3) have been questionably synonymized

with Gen. et sp. Indeterminate (now D. martinheadii, Head et

al. 1989) but Poulsen et al. (1996) and Manum (1997) con-

180


PLATE 1Decahedrella martinheadii Manum 1997 from Upper Miocene of IODP Exp. 302 Hole M0002A,

Lomonosov Ridge, Central Arctic Ocean. All photomicrographs are bright field; scale bar indicate 20µm.

1-4 Sample: IODP M0002A-21X1, 38-40cm, Slide 1,

England Finder reference P36/2; four consecutive foci

from high to low focus.


England Finder reference R29/2; three consecutive

foci from high to low focus.


England Finder reference R32; five consecutive foci

from high to low focus.

micropaleontology, vol. 55, nos. 2-3, 2009 181

Jens Matthiessen, Henk Brinkhuis, Niels Poulsen and Morton Smelror Plate 1

cluded that these taxa only superficially resemble D.

martinheadii. Thalassiophora ? sp. A of Powell (Powell 1986a,

p. 120, pl. 5, fig. 4; Powell 1986b, p. 138, pl. 1, fig. 4.) has a dif-

ferent geometric configuration and the field shapes and junc-

tions look different from D. martinheadii (Manum 1997). The

distorted specimen of Evittosphaerula sp. 1 illustrated by

Mudie (1989, pl. 2, fig. 3) has a irregular network of trabeculae

connecting processes rather than a network consisting of polyg-

onal fields. Evittosphaerula sp. A of Matsuoka & Bujak (1988:

p. 43-44, pl. 3, fig. 2) differs from D. martinheadii in having a

irregular network of trabeculae that are gonally wider and

membranous.

ACKNOWLEDGMENTS

This research used samples and data provided by the Integrated

Ocean Drilling Program (IODP). We thank a Walter Hale,

Alex Wülbers and Ursula Röhl for their support during the sam-

pling at the Bremen Core Repository and Anja Bartels for assis-

tance during the processing of the samples. We are grateful to

Stijn de Schepper and Christoph Vogt who kindly commented

on an earlier version of the manuscript. Martin Head and Bindra

Thusu thoroughly reviewed the manuscript and suggested nu-

merous improvements. Funding was partly provided by the

German Research Foundation (DFG-grant Ma3913/1 and 3).

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