Taxonomy and biostratigraphy of middle Eocene
silicoflagellates in the central Arctic Basin
Jonaotaro Onodera1 and Kozo Takahashi2
1
2
Center for Advanced Marine Core Research, Kochi University, B200 Monobe, Nankoku, 783-8502, Japan
Department of Earth and Planetary Sciences, Kyushu University, Hakozaki6-10-1, Fukuoka, 812-8581, Japan
email: [email protected]; [email protected]
ABSTRACT: The silicoflagellate taxa obtained in IODP Expedition 302 (ACEX) were identified and counted in order to establish the
silicoflagellate biostratigraphy in the central Arctic Ocean. These microfossils in the ACEX samples were preserved in the Lithology
Units 1/6 and 2, which are dark silty clay and biosiliceous ooze, respectively. The silicoflagellate skeletons in the ACEX samples are assigned to 56 taxa. Seven taxa were described as new species, which were abundant in Lithology Unit 2. Comparison with several study
cases outside the Eocene Arctic Ocean suggested that the silicoflagellate assemblages in ACEX were unique in Lithology Unit 2. The
dominance of silicoflagellate taxa varied throughout the lithological section. Based on the cluster analysis by Morishita similarity index
Cl, the silicoflagellate assemblages were divided into nine assemblage groups. The silicoflagellate datum event of the first occurrence of
Corbisema hexacantha in the lower part of Lithology Unit 1/6 is regarded. Based on the datum events for silicoflagellate and
palynomorphs, the assigned epoch of Lithology Units 1/6 and 2 is the middle Eocene.
INTRODUCTION
Compared to the studies of the Eocene biostratigraphy in the
southern ocean, these studies in the northern high latitude ocean
have been limited despite the importance. What was holding the
biostratigraphic and paleoceanogrpahic studies in the Arctic
Ocean is the technical difficulty of coring in the packed sea-ice
condition in the central Arctic Ocean (Moran et al. 2006). The
previous studies of the pre-Quaternary sediments in the Arctic
Ocean were conducted based on the piston core samples (Clark
1974, Bukry, 1981a, 1985, Kitchell and Clark 1982, Ling
1985a, Clark et al. 1986, Sims and Ross 1988, Dell’agnese and
Clark 1994, Magavern et al. 1996). However, the IODP Expedition 302 (Arctic Coring Expedition: ACEX) successfully retrieved the middle Eocene sediments in the central Arctic
Ocean in summer 2004 (Backman et al. 2006, 2008). This successful continuous coring made the high resolution studies in
the Eocene Arctic Ocean possible.
In the previous studies in the Eocene Arctic Ocean, the Eocene
sections of USGS Fl-422 piston core contained the siliceous
microfossils, which were composed by diatoms, silicoflagellates,
ebridians, chrysophyte cysts and actiniscidian in the Eocene
(Bukry 1984, Ling 1985a, Dell’agnese and Clark 1994). Silicoflagellates are significant contributor of the siliceous microfossil assemblages in the Eocene Arctic Ocean (Dell’agnese
and Clark 1994, Backman et al. 2006). Silicoflagellate taxonomic systems and biostratigraphy in the Eocene have been
mainly established by the significant studies in DSDP/ODP
core sediments (Bukry 1975, 1976, 1978, 1982, 1987, Bunsen
and Wise 1976, Locker and Martini 1986, Ling 1985b, PerchNielsen 1975, 1976, Desikachary and Prema 1996; Bohaty and
Harwood 2000), and the studies on the materials sampled from
land outcrops or piston cores (Schulz 1928, Glezer 1966/1970,
Perch-Nielsen 1976, Barron et al. 1984, Locker and Martini
1987). The Eocene silicoflagellate taxonomy in the Arctic
Ocean is discussed based on the piston core samples of USGS
Fl-422 by Bukry (1984) and Ling (1985). Based on these studies, the Eocene silicoflagellate biostratigraphy for the north At-
lantic and the Greenland Sea was established by Locker (1996).
The silicoflagellates are one of the valuable age indicators together with palynomorphs in the ACEX study because the calcareous microfossils are barren in the Eocene Arctic sediments
(Backman et al. 2006) and the details of the Eocene diatom
biostratigraphy in the high latitude are in the process of being
established (Scherer and Koc 1996). Therefore, it is expected
that the continuous Eocene sediment core samples from the
Arctic Ocean obtained by the IODP Expedition 302 will be able
to shed light on establishment of silicoflagellate biostratigraphy
with the previous studies by USGS Fl-422 (Bukry 1984, Ling
1985). This paper focuses on the silicoflagellate taxonomy and
the establishment of silicoflagellate biostratigraphic zonation in
the ACEX. Paleoceanographic reconstruction by silicoflagellates is discussed in elsewhere (Onodera et al. 2008).
MATERIALS AND METHODS
Materials
The core samples containing siliceous fossils were retrieved
from Sites M0002 and M0004 on the Lomonosov Ridge in the
central Arctic Ocean by IODP Expedition 302 ACEX in summer 2004 (text-fig. 1; Table 1).The samples from Hole M2A
represent the upper part whereas the samples from Hole M4A
mainly represent the lower part of the relatively continuous sequence from the Cretaceous basement to the Holocene surface
sediments with several major hiatuses (Backman et al. 2008).
The lowest part of the cores at Hole M2A (Cores M2A-61X,
62X) is correlated to Cores M4A-4X and 5X at Hole M4A.
Therefore, by combining the available samples from both sites
it is possible to study as one continuous sequence of the siliceous fossiliferous section belonging to the Eocene. The treated
materials are very dark biosiliceous ooze (Lithology Unit 2) and
dark clayey silt (Lithology Unit 1/6), which are reductive sediments with sub-milimeter scale laminations (Backman et al.
2006; Brinkhuis et al. 2006). A total of 122 sediment samples
from core sections in addition to 29 core catcher samples from
Holes M2A and M4A were processed in order to estimate the
micropaleontology, vol. 55, nos. 2-3, pp. 209-248, text-figures 1-4, plates 1-13, tables 1-3, 2009
209
Jonaotaro Onodera and Kozo Takahashi: Taxonomy and biostratigraphy of silicoflagellates in the middle Eocene Arctic Ocean
TEXT-FIGURE 1
The geography of the Arctic Ocean and the coring sites (white circle) by IODP Expedition 302 Arctic Coring Expedition on the Lomonov Ridge in the
central Arctic Ocean.
number of silicoflagellate and ebridian skeletal individuals. The
samples were ordinarily taken at 20cm interval in each section
for biostratigraphy and oceanographic reconstruction.
species level under a light microscope with x400 magnifications. The skeleton content per sample is estimated by the sum
of skeleton contents in both fractions.
Slide preparation and counts
Skeleton Content (skeletons
(Nc*Sc/S/W)+(Nf*Sf/S/V/W)
The obtained samples were freeze dried, measured for dry
weight, and then were treated with hydrogen peroxide, hydrochloric acid, and Calgon® for dispersing particles such as cohesive clays. In the chemical treatment process, ultra sonic was
applied for 10 seconds in order to disaggregate consolidated
clay particles. After adequately diluting the acid and other
chemicals by decantation several times, the sample solution
was sieved through 45µm mesh, and then both fractions were
filtered through 0.45µm nominal pore size membrane filters.
The filtered volume of the <45µm fine fraction is 1/20 of total
volume of the solution. Dried membrane filters were mounted
with Canada balsam onto glass slides.
The taxonomic identification of silicoflagellate skeletons was
conducted under LM and SEM observations. The photomicrographs presented in Plates 1-13 were taken by Light Microscope Olympus BX-50 and Scanning Electron Microscope
Shimazu SS-550 at the Center of Advanced Instrumental Analysis, Kyushu University. Silicoflagellate skeletons in the prepared slides of coarse and fine fractions were observed at
210
mg
dry
sediments-1)
=
Where Nc and Nf is the number of counted skeleton in coarse
and fine fraction slides, Sc and Sf is counted area in coarse or
fine fraction slide, S filtered area (535.32µm2), W dry weight of
treated sample, and V aliquot size for fine fraction (usually
1/20). Large fragments, which represented greater than one half
of a complete skeleton, were counted as one specimen whereas
small fragments representing less than a half were not counted.
The counted skeleton numbers per slide were essentially greater
than 100 skeletons, and hence the counted skeletons per sample
were greater than 200 as shown in the Appendix Table 1.
The species identification of silicoflagellates is basically based
on the previous taxonomic study (Loeblich et al. 1968, Bukry
1975, 1976, 1978, 1982, 1987, Bunsen and Wise 1976, Locker
and Martini 1986, 1987, Ling 1985a, b, Perch-Nielsen 1975,
1976, 1978, Desikachary and Prema 1996, Locker 1996;
Bohaty and Harwood 2000). The previously unknown species
were newly described as new species. The holotypes of these
Micropaleontology, vol. 55, nos. 2-3, 2009
TEXT- FIGURE 2
Total silicoflagellate contents, the relative abundances of relevant taxa, and the zonation based on the assemblage similarity (lithology figures from
Backman et al. 2006).
new species were deposited in the Micropaleontology Collection of the National Science Museum, Tokyo.
dex Cl (Morishita 1959) was utilized on the abundance data of
whole flora.
Age
The age model for the siliceous fossil bearing interval depends
only on the biostratigraphy, which was mainly defined by
palynomorphs (Backman et al. 2008). In the siliceous fossil
bearing interval, the magnetic polarity stratigraphy is not available due to low contents of magnetic minerals in the samples.
The isotope data for age estimation also have not been obtained
thus far. Thus, the tentative age data for the ACEX samples
were established with limited resources (Backman et al. 2008).
The ages of the siliceous fossil bearing interval were estimated
as the middle Eocene (Backman et al. 2008). For the Eocene
silicoflagellate biostratigraphy, Martini and Müller (1976),
Perch-Nielsen (1978), and Locker (1996) from the adjacent
seas are referred for the present study.
Similarity
In order to categorize the silicoflagellate assemblages into several different assemblage groups, the Morishita’s similarity in-
Cl =
2 å niA · niB
i
( lL + l B) å niL å niB
i
i
niA and niB represent the abundance of species i in the samples A
and B, respectively.
lA =
å n ( n -1)
å n ( å n -1)
iA
iA
iA
i
iA
i
The comparison between the Eocene Arctic assemblages and
the Eocene assemblages in the other seas was based on the presence-absence data of species. The correlation coefficients were
utilized for this estimation.
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Jonaotaro Onodera and Kozo Takahashi: Taxonomy and biostratigraphy of silicoflagellates in the middle Eocene Arctic Ocean
RESULTS
Silicoflagellates were observed, going upward in the section,
from Samples 302-M4A-18X-CC, 14-16cm to M2A-47X-2,
56-58cm to (text-fig. 2). Significantly different silicoflagellate
populations were observed in two separate lithology with the
mean values of 4.5 x103 skeletons mg-1 dry sediments (dry sed
hereafter) in Lithologic Unit 2 and 0.2 x103 skeletons mg-1 dry
sed in Lithologic Unit 1/6, respectively. Among the siliceous
microfossil groups, silicoflagellates are relatively abundant in
the lower part of Unit 2 (Stickely et al. 2008), and the highest
population of the silicoflagellate skeleton is observed in Sample
9X-CC, 7-9cm as 17.2 x103 skeletons mg-1 dry sed. The
silicoflagellates skeleton sizes are usually less than 45µm, and
the mean ratios of skeleton contents between coarse and fine
fraction are 0.017 in Lithologic Unit 2 and 0.015 in Lithologic
Unit 1/6, respectively.
The silicoflagellate assemblages comprised of a total of 56 taxa
in all samples (see Taxonomy section). Genus Dictyocha is usually dominant from Cores 302-M4A-18X to M2A-52X in Lithologic Unit 2. The abundances of genus Corbisema are
generally few to common, and the abundances of genera
Distephanus and Naviculopsis are very rare in Lithologic Unit
2. The changes of dominant taxon in Lithologic Unit 2 are transitional. Dictyocha arctios Ling, Dictyocha deflandrei
Frenguelli ex Glezer, Dictyocha frenguellii Deflandre, and
Dictyocha tessera sp. nov. mainly occurred below Core 56X.
The continuous occurrence of genus Bachmannocena is in between Cores M4A-8X and 11X with rare abundance (<2%).
Dictyocha alaris, which is a new taxon with characteristic skeletal shape and probably an endemic species, is abundant from
Samples M2A-56X-3, 116-118cm to 52X-1, 14-16cm. The
samples from M2A-50X-1, 136-138cm to 47X-2, 56-58cm in
Lithologic Unit 1/6 mainly contain Corbisema spinosa
Deflandre, Corbisema hastata globulata Bukry, Corbisema sp.
cf. C. hexacantha (Schulz) Deflandre, Distephanus crux
(Ehrenberg) Haeckel, and Naviculopsis spp. (text-fig. 2).
Corbisema hexacantha occurred between 302-M2A-49X-4,
76-78cm and 48X-2, 96-98cm. The FO of Corbisema hexacantha was located between Samples M2A-49X-4, 96-98cm
and 49X-4, 76-78cm. The silicoflagellate assemblage above
Sample M2A-48X-2, 96-98cm is composed by genera Dictyocha and Distephanus, which are characteristic and dissimilar
to the hemipelagic silicoflagellate assemblages of the Eocene
Atlantic.
Based on the cluster dendrogram constructed using the results
of similarity indices of Morishita’s Cl, total silicoflagellate assemblages including both the coarse and the fine fractions were
categorized into nine different assemblage groups (text-fig. 3,
Table 2). Each group was numbered for the sake of convenience and briefly explained below. Although occasionary not
perfect in placing the similarity index values into assemblage
groups along the time/depth axis in the Lithologic Unit 1/6 because there are few “outliers” within the “majority’ values, it
was more or less possible to assign the assemblage groups with
progressing in time.
Assemblage characteristic: Dictyocha deflandrei, Dictyocha
tessera, Dictyocha frenguellii, Dictyocha arctios, and Dictyocha carentis are major silicoflagellate taxa in this group (Table
2). Although Dictyocha arctios is usually included in both fractions, Dictyocha arctios in the Core M4A-11X is usually large
(>45µm), and is essentially few in the fine fraction. Dictyocha
tessera is abundant in the fine fraction except for Core
M4A-11X. Dictyocha obliqua is common in the fine fraction
except for the interval from Core M4A-10X-1 to 7X. The large
silicoflagellate Corbisema euhadrotes are observed from Cores
M4A-6X toM2A-60X with rare abundance in total silicoflagellates but common in the coarse fraction (>45µm). Genus
Bachmannocena in this group are observed in the coarse fractions of Core M4A-11X, and are essentially absent in the fine
fractions of the same interval. Genus Naviculopsis is absent.
Group II (Characterized by abundant Dictyocha obliqua)
Interval: from 302-M2A-58X-4, 56-58cm (254.68 mbsf) to
M2A-57X-2, 14-16cm (244.87 mbsf).
Assemblage: Dictyocha obliqua, Dictyocha frenguellii, Dictyocha aspera martinii, Corbisema globulata are major components in this silicoflagellate group (Table 2). Dictyocha obliqua
is usually smaller than 45 µm in their diameters, and is major in
the fine fraction. The silicoflagellates in the coarse fraction
(>45µm) are mainly composed of Corbisema apiculata (mean
abundance of 33% in the silicoflagellates of the coarse fraction),
Dictyocha frenguellii (30%), and Dictyocha aspera martinii
(10%).
Group III (Characterized by abundant Dictyocha alaris)
Interval: from 302-M2A-56X-3, 116-118cm (242.90 mbsf) to
M2A-55X-2, 14-16cm (235.24 mbsf).
Assemblage: Dictyocha alaris, Dictyocha frenguellii, Dictyocha deflandrei, Corbisema globulata, Corbisema apiculata are
major components in this group (Table 2). In the fine fraction,
Dictyocha alaris is abundant (40% in the fine fraction). The major taxa in the coarse fraction (>45µm) are Dictyocha frenguellii
(mean abundance of 45% in the coarse fraction), Dictyocha
alaris (16%), Dictyocha deflandrei (11%), and Corbisema
apiculata (11%). Dictyocha explicata is very rare or absence in
both fractions of this group.
Group IV (Characterized by abundant Dictyocha explicata
with D. alaris)
Interval: from 302-M2A-54X-1, 32-34cm (230.32 mbsf) to
M2A-52X-1, 14-16cm (221.08 mbsf).
Assemblage: Dictyocha alaris, Dictyocha curta, Dictyocha
explicata, Dictyocha aspera s.l. are main components in this
group (Table 2). These taxa are common in the fine fraction of
this group. The silicoflagellates in the coarse fraction (>45µm)
are composed of Dictyocha explicata (mean abundance of 32%
in the coarse fraction), Dictyocha frenguellii (22%), Corbisema
apiculata (16%), and Dictyocha alaris (15%).
Group V (Characterized by abundant Distephanus antiquus)
Group I (Characterized by abundant Dictyocha arctios and
Dictyocha tessera)
Interval: from 302-M4A-11X-4, 48-50cm (302.31 mbsf) to
302- M2A-59X-2, 116-118cm (257.26 mbsf).
212
Interval: from 302-M2A-50X-1, 136-138cm (216.36 mbsf) to
M2A-50X-1, 56-58cm (215.56 mbsf)
Assemblage: Distephanus antiquus, Dictyocha curta, Dictyocha deflandrei, Corbisema apiculata, Naviculopsis spp. are
Micropaleontology, vol. 55, nos. 2-3, 2009
TEXT- FIGURE 3
Cluster analysis based on Morishita’s similarity index Cl (Morishita 1959) for silicoflagellate assemblages in the ACEX samples. The assemblage
groups are represented by capital Greek numbers.
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Jonaotaro Onodera and Kozo Takahashi: Taxonomy and biostratigraphy of silicoflagellates in the middle Eocene Arctic Ocean
TEXT-FIGURE 4
The morphological terminologies of silicoflagellate skeletons based on Bukry (1995).
214
Micropaleontology, vol. 55, nos. 2-3, 2009
main components of this group. Distephanus antiquus is rare to
common in the fine fraction, and is very rare in the coarse fraction because of the tiny skeleton size. The coarse fraction is
mainly composed of Dictyocha deflandrei (mean abundance of
25% in the coarse fraction), Corbisema apiculata (17%), and
Naviculopsis punctilia (8%). Corbisema spinosa and C. sp. cf.
C. hexacantha were observed with very rare abundance in the
Sample 302-M2A-50X-1, 56-58cm, but were absent in other
samples of this group.
TABLE 1
Coring summary of Holes M0002A and M0004A in IODP Expedition
302 Arctic Coring Expedition (Backman et al. 2006).
Group VI (Characterized by abundant Corbisema spinosa and
C. sp. cf. C. hexacantha)
Interval: from 302-M2A-49X-4, 76-78cm (213.92 mbsf) to
M2A-48X-2, 136-138cm (208.36 mbsf); from 302-M2A47X-2, 116-118cm (203.42 mbsf) to M2A-47X-2, 56-58cm
(202.82 mbsf)
Assemblage: Corbisema spinosa and Corbisema sp. cf. C.
hexacantha are significant in this group (Table 2, Text-Fig. 2),
which are very abundant in the fine fraction. Typical C.
hexacantha is very rare in total assemblage of this group. The
FO of Corbisema hexacantha is located between 302-M2A49X-4, 76-78cm (213.92 mbsf) and 302-M2A-49X-4, 56-58cm
(213.72 mbsf). In the coarse fraction (>45µm), Corbisema
apiculata is abundant (mean abundance of 28% in the coarse
fraction), Naviculopsis spp. (8%), and Corbisema hastata
globulata (7%).
Group VII (Characterized by abundant Corbisema triacantha)
Samples: 302-M2A-48X-2, 96-98cm (207.96 mbsf), M2A47X-3, 56-58cm (204.32 mbsf)
Assemblage: Corbisema triacantha and Distephanus crux,
Distephanus crux parvus are major taxa in this group (Table 2).
In the coarse fraction, Distephanus quinarius is also common.
In the sample 302-M2A-48X-2, 96-98cm, Corbisema sp. cf. C.
hexacantha is included with very rare abundance (Table 2), although it is hard to recognize the rare abundance of this taxon
during the Group VII interval in text-figure 2.
Group VIII (Characterized by abundant Distephanus crux
parvus)
Samples: from 302-M2A-48X-2, 14-16cm (207.14 mbsf) to
M2A-48X-1, 36-38cm (205.86 mbsf)
Assemblage: The high abundance of Distephanus crux parvus
and common occurrence of Corbisema hastata globulata are
the characteristics of this group (Table 2). Corbisema triacantha and Corbisema apiculata are very rare or absent.
Distephanus crux parvus and Corbisema hastata globulata are
usually observed in the fine fraction. The large skeletons collected in coarse fraction are nearly absent.
Group IX (Characterized by Corbisema globulata and C.
apiculata)
Samples: 302-M2A-49X-5, 14-16cm (210.16 mbsf), M2A49X-4, 96-98cm (214.12 mbsf), M2A-47X-4, 136-138cm
(206.63 mbsf), M2A-47X-4, 56-58cm (205.83 mbsf), and
M2A-47X-3, 116-118cm (204.92 mbsf).
Assemblage: Corbisema globulata and Corbisema apiculata
are major taxa in this group (Table 2).
The silicoflagellate floral similarity between the ACEX samples
versus previously studied data from the Nordic Seas suggested
significant correlations for the samples from Lithologic Unit 1/6
but no significant correlation for the samples from Lithologic
Unit 2 (Table 3).
DISCUSSION
The silicoflagellate biostratigraphy
The Paleogene silicoflagellate biostratigraphy has mainly been
established in the open ocean sediments by Deep-Sea Drilling
Project (DSDP) and Ocean Drilling Program (ODP). Therefore,
the establishment of global biostratigraphic correlation is based
on the premise that the studying samples were influenced by
open ocean waters. In the Arctic area, the opening of the Norwegian-Greenland Sea by the sea-floor spreading along the mid
Atlantic-Gakkel Ridge, and the local tectonic uplift in the Siberia has an important factor for the sea water exchanges between
the Eocene Arctic Ocean and the seas around the Arctic Ocean
(Kitchell and Clark 1982, Akhmetiev and Beniamovski 2004).
The most significant biostratigraphic event of silicoflagellates is
the FO of Corbisema hexacantha in Lithologic Unit 1/6. The
FO of Corbisema hexacantha is initially defined in the north
western Atlantic as 44.1 Ma in the middle Eocene (Bukry 1978,
Locker 1996). In this study, the typical Corbisema hexacantha
in this study is very rare whereas Corbisema sp. cf. C.
hexacantha, probably intermediate form between Corbisema
spinosa and C. hexacantha, is abundant as mentioned above.
Therefore the age of FO of Corbisema hexacantha in this study
may be older than 44.1 Ma in the Atlantic. The older age for the
occurrence interval of Corbisema sp. cf. C. hexacantha is suggested by the biostratigraphy of palynomorphs (Backman et al.
2008). However, the rare occurrences of dinoflagellate fragments found in Core M2A-49X are probably suggesting the
Miocene (Sangiorgi et al., this volume). The some “outliers” of
cluster analysis in Lithologic Unit 1/6 may also suggest the
some turbid condition of Lithologic Unit 1/6 sediments. Although the age estimation is slightly meager, it is considered
that the FO event of Corbisema hexacantha and the FAO of
Corbisema sp. cf. C. hexacantha are basically valid for this
study by the following reasons: 1) the silicoflagellate assemblages of the adjacent horizons below and above of the FO show
significant similarity to the Atlantic and the Norwegian Sea assemblages (Bukry 1978, Martini and Müller 1976) as shown in
Table 3, indicating that both water masses of the Arctic and the
Atlantic/Norwegian Sea were linked in surface of water column
(see more elaborate discussion on this further below); 2) the FO
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Jonaotaro Onodera and Kozo Takahashi: Taxonomy and biostratigraphy of silicoflagellates in the middle Eocene Arctic Ocean
is located above the boundary between Lithologic Units 1/6 and
2, implicating that the oceanographic conditions are within the
same unit (Unit 1/6). Therefore, the samples below the FO of
Corbisema hexacantha can be assigned to the Dictyocha
spinosa Subzone of Naviculopsis foliacea Zone (Bukry 1977;
1981b) (=Corbisema spinosa Zone (Locker 1996)), which is
the latest early to middle Eocene in the Atlantic open waters
(Bukry 1978), although Corbisema spinosa in Lithologic Unit 2
shows very sporadic occurrence with rare abundance (Text-Fig.
2). Corbisema spinosa was observed in Sample
302-M4A-15X-CC, 24-26cm with very rare abundance. Because of the opal diagenesis below Core M4A-15X, the FO of
Corbisema spinosa in the ACEX samples cannot be confirmed.
The base of siliceous fossil bearing interval in Lithologic Unit 2
is definitely younger than the FO datum of Corbisema spinosa,
which is 50.5 Ma (Locker 1996). The datum between Cores
M4A-12X-CC and 15X-CC is the FO (49.2 Ma) of the freshwater fern Azolla spp. (Backman, et al. 2006). Therefore, the base
of siliceous fossil bearing interval is estimated to be between
50.5 Ma and 49.2 Ma. Gleser (1996) correlated the Eocene
silicoflagellate zonations in the northeastern Caspian Basin to
the co-occurring nannoplanktons and the oceanic
silicoflagellate zonation by Bukry (1981). The Lithologic Unit
2 in Dictyocha spinosa Subzone (= Corbisema spinosa Zone) is
probably correlated to the Dictyocha secta Zone and the lower
subzone of Distephanus antiquus in the northeastern Caspian
Basin (Gleser 1996). However, the taxa commonly occurred
both this study and the northeastern Caspian Basin are not so
much. This is probably related to the limited or completely interrupted water connections between the Arctic Sea and the
Caspian Basin via the Western Siberian Sea in the middle
Eocene (Akhmetiev and Beniamovski 2004).
The studied samples above the FO of Corbisema hexacantha
can be assigned to the Corbisema hexacantha Zone (Locker,
1996) of the middle Eocene. The reliable age for the top of siliceous fossil bearing interval has not been available. However,
the palynomolphs in Core M2A-46X-CC suggests the middle
Eocene around 44.5 Ma within the Corbisema hexacantha Zone
of the middle Eocene (Backman et al. 2006). Hence, the overall
interval of siliceous fossil bearing section of the ACEX samples
is the middle Eocene.
The characteristics of silicoflagellates assemblages in
Lithologic Units 1/6 and 2
The silicoflagellate assemblages of this study are unique especially in Lithologic Unit 2 compared to those from the previous
studies conducted in the other Eocene sediments outside the
Arctic Ocean. The previously reported Paleogene silicoflagellate assemblages are usually consisted of genera Corbisema, Dictyocha, Naviculopsis, Bachmannocena, and
Distephanus (Perch-Nielsen 1985). Outside of the Eocene Arctic Ocean, the occurrences of genera Bachmannocena,
Naviculopsis, and Distephanus are common (Martini and
Müller 1976, Barron et al. 1984, Perch-Nielsen 1976). The
silicoflagellate assemblages of Lithologic Unit 2, however, do
not usually contain such genera as Naviculopsis, Distephanus,
and Bachmannocena. In addition to the difference in
silicoflagellate generic composition, many previously unknown
silicoflagellate taxa are conspicuously included in Lithologic
Unit 2 (text-fig. 2). Because the middle Eocene Arctic Ocean
was in the semi-closed environments (Brinkhuis et al. 2006),
the silicoflagellate assemblage in middle Eocene Arctic Ocean
might be different from the oceanic assemblages. Glezer (1996)
pointed out that the more reliable biostratigraphic correlation
216
within the provincial scale should be based on the taxonomic
similarity of zonal assemblages rather than on the simple datum
planes, because the provincial water mass environments are
controlled by not only global but also regional factors. Therefore, the variation of the characteristic assemblages of this study
is warranted to be useful for deciphering distribution of the corresponding water masses of the upper water column around the
Lomonosov Ridge during the middle Eocene. The characteristic
assemblage groups of this study should be correlated to other
Arctic Eocene sediments which may be cored in future.
The silicoflagellate assemblages from Lithologic Unit 1/6 contain all genera found outside of the Arctic Ocean. The absence-presence data suggest the significant similarity of the
upper part of Lithologic Unit 2 as well as Lithologic Unit 1/6,
except for Core 302-M2A-48X which can be attributed to the
unusual assemblage of Group VIII (Table 3), with the outside of
the Arctic basin. Frequent temporal changes of silicoflagellate
assemblage groups belonging to Lithologic Unit 1/6 are probably due to the relatively variable water mass conditions and turbid influences of cores. The silicoflagellate assemblages
abruptly changed from Lithologic Unit 2 into Unit 1/6. These
temporal trends suggest the change from the endemic assemblage to common assemblage in both silicoflagellates from
Lithologic Units 2 to 1/6. This may suggest the upper water
mass condition became similar between the Arctic Ocean and
the northern Atlantic.
TAXONOMY
The silicoflagellate skeletons in the ACEX samples were morphologically distinguished into 55 taxa. The descriptions on
each taxon occurred in this study are listed in alphabetical order
as shown below. The morphological terminologies of silicoflagellate skeletons are mainly based on Bukry (1995) (text-fig.
4).
Class CHRYSOPHYCEAE
Order SILICOFLAGELLATA Borgert 1891
Genus Arctyocha Bukry 1985
Arctyocha bukryi Desikachary and Prema 1996
Plate 1, figures 1-3
Arctyocha sp. A. BUKRY 1985, p. 130, pl. 9.1, figs. 1-3
Arctyocha bukryi DESIKACHARY and PREMA 1996, p. 59, pl. 10, fig.
1.
Remarks: It is similar to Dictyocha pentagona (Schulz) Bukry
and Foster but is distinguished from it by the complete absence
of supporting spines. This taxon is first found in the late Cretaceous sediments from the core CESAR 6 in the Alpha Ridge
(Bukry 1985). In this study, this taxon is usually observed in the
Cores M4A-47X-3, 36-38cm, and sporadically observed
throughout the siliceous microfossil interval.
Genus Bachmannocena (Ehrenberg) Ehrenberg, 1843
Bachmannocena apiculata (Schulz) Bukry 1987
Plate 1, figures 4-9
Mesocena oamaruensis apiculata SCHULZ 1928, p. 240, fig. 11.
Septamesocena apiculata (Schulz) BACHMANN 1970, p. 13.
Mesocena apiculata (Schulz) BUKRY 1975, p. 856, pl. 5, figs. 6-9.
Mesocena apiculata apiculata (Schulz) BUKRY 1978, p. 786, pl. 2, fig.
19.
Bachmannocena apiculata (Schulz) BUKRY 1987, p. 403, pl. 1, fig. 1.
Micropaleontology, vol. 55, nos. 2-3, 2009
Remarks: Bachmannocena apiculata is identified by a simple
equilateral rounded triangle ring with strait or slightly convex
sides, and short radial spines at the ring corners.
Bachmannocena oamaruensis (Schulz) Bukry 1987
Plate 13, figures 10, 11
Mesocena oamaruensis SCHULZ 1928, p. 240, figs. 10a, b.
Bachmannocena oamaruensis (Schulz) BUKRY 1987, p. 404, pl. 1, fig.
6; pl. 2, fig. 1.
Remarks: The ring is quadrangular or triangular without radial
spines.
Bachmannocena quadrangula (Ehrenberg ex Haeckel) Bukry
1987
Plate 13, figure 12
Mesocena quadrangula EHRENBERG ex HAECKEL 1887, p. 1556.
Mesocena elliptica quadrangula (Ehrenberg) BACHMANN and
ICHIKAWA 1962, p. 167, pl. 1, figs. 1, 2, 4, 6, 8.,
Bachmannocena quadrangula (Ehrenberg ex Haeckel) BUKRY 1987,
p. 405.
Remarks: Bachmannocena quadrangula is identified by the
quadrangular ring with radial spines. Some skeletons have other
struts inside of the ring.
Genus Corbisema Hanna 1928
Corbisema apiculata (Lemmermann) Hanna 1931
Plate 2, figures 1-4
Dictyocha triacantha var. apiculata LEMMERMANN 1901, pl. 10,
figs. 19, and 20.
Corbisema apiculata (Lemmermann) HANNA 1931, p. 198, pl. D, fig.
2.
Dictyocha apiculata (Lemmermann) FRENGUELLI 1940, p.44, fig.
12h.
Corbisema triacantha var. apiculata (Lemmermann) EISENACK
1954, p. 74, fig. 7.
For more synonyms, see Desikachary and Prema (1996).
Remarks: The basal ring usually forms equilateral triangle with
slightly rounded corners. One radial spine is located at each
corner. Three sides of basal ring are straight or slightly indented
at the contact point with apical strut. Each apical strut arises
from the middle point of basal ring side, and joins at the skeleton center in the apical view. Basal pikes (= “Supporting
spines”) are sometimes visible. The dimensions on the basal
ring diameters in ACEX samples range from 40 to 90mm [N =
20]. Similar taxa are Corbisema sp. cf. C. apiculata and
Corbisema euhadrotes. The differences from these similar taxa
are in the indented basal ring sides and the angular basal ring
corners.
Corbisema sp. cf. C. apiculata (Lemmermann) Hanna 1931
Plate 2, figures 5-7
cf. Dictyocha triacantha var. apiculata LEMMERMANN 1901, pl. 10,
figs. 19, and 20.
cf. Corbisema apiculata (Lemmermann) HANNA 1931, p. 198, pl. D,
fig. 2.
cf. Dictyocha apiculata (Lemmermann) FRENGUELLI 1940, p.44, fig.
12h.
cf. Corbisema triacantha var. apiculata (Lemmermann) EISENACK
1954, p. 74, fig. 7.
Remarks: The skeletons classified under this taxon have some
minor morphological differences compared to typical Corbisema apiculata skeletons as follows: The basal ring triangle is
not equilateral, and the length of three apical struts is not the
same; and the direction of radial spines is variable.
Corbisema euhadrotes sp. nov.
Plate 2, figures 8-13
Dictyocha triacantha var. archangelskiana SCHULZ 1928 (in part), p.
282, fig. 78.
Derivation of Name: The specific name euhadrotes was taken
from the Greek words eu and hadrotes meaning beautiful and
thickness or fullness, respectively.
Holotype: Plate 2, fig. 8; Sample IODP302-M2A-61X-2,
76-78cm; Slide MPC-02680 (Micropaleontology Collection,
National Science Museum, Tokyo), England finder M31/4
Type locality: Hole IODP302-M2A, 264.87 mbsf, Lomonosov
Ridge, central Arctic Ocean
Description: Corbisema euhadrotes has the equilateral triangular skeleton. The triangular ring with rounded corners is relatively large and robust while the radial spines at each corner of
the triangular ring are thin. Each side of the triangular ring is
slightly concave to the center at the mid points of the sides.
Three apical struts arising from each mid point of the sides of
the basal ring meeting at one contact point at the center of the
triangular ring. The large pikes are observed at each mid point
of the basal ring side in most skeletons. The surface ornamentation on the skeleton is readily visible for the triangular skeleton,
apical struts, and supporting spines. The surface texture of the
radial spines is relatively smooth in most skeletons.
Dimensions: 65-80µm [N = 30] for the basal ring diameter
Occurrence: This taxon consistently occurs between 2A-57X-2,
76-78 and 56X-3, 36-38, and between 4A-6X-3, 96-98 and
2A-60X-1, 76-78 in the early middle Eocene to middle middle
Eocene.
Remarks: The ring morphology of Corbisema euhadrotes resembles to that of Corbisema apiculata (Lemmermann) Hanna
or Corbisema archangelskiana (Schulz) Frenguelli. However,
the skeletons of Corbisema euhadrotes are relatively robust and
round at each triangle corner, compared to those of Corbisema
apiculata (Lemmermann) Hanna. Many specimens lost the radial spines by breakage and some forms without radial spines
resemble to Corbisema archangelskiana. According to the original description (Schulz 1928), however, C. archangelskiana
(with one exception; see below) has, triangular to rectangular
corners without any spines. The corners of C. euhadrotes also
appear to be septate. One specimen illustrated as C.
archangelskiana by Schulz (1928) cannot be any longer accepted as C. archangelskiana since it has radial spines and it
does not fit with the original description (Bukry 1976,
Perch-Nielsen 1976).
Corbisema sp. cf. C. geometrica sensu Bukry 1975
Plate 3, figures 1, 2
cf. Corbisema geometrica geometrica BUKRY 1975, p. 860, pl. 1, fig. 6
(only).
Remarks: In general, Corbisema geometrica has the central
plate as the apical structure. Bukry (1975) suggested that the
specimen, which had just simple juncture of three apical bars,
was also identified as Corbisema geometrica. This taxon is dis-
217
Jonaotaro Onodera and Kozo Takahashi: Taxonomy and biostratigraphy of silicoflagellates in the middle Eocene Arctic Ocean
TABLE 2
The mean abundances of major taxa in total silicoflagellates of each group. The symbol “+” represents the presence as mean abudance of <1% in total
silicoflagellates.
tinguished from typical Corbisema triacantha by the large dimensions of the skeleton and short radial spines.
Corbisema hastata hastata (Lemmermann) Bukry 1976
Plate 3, figures 3-5
Dictyocha triacantha var. hastata LEMMERMANN 1901, p. 259, pl.
10, fig. 16.
Corbisema hastata (Lemmermann) FRENGUELLI 1940, p.62, figs.
12b, and 12c.
Corbisema hastata hastata (Lemmermann) BUKRY 1976, p. 907, pl. 4,
figs. 9-16.
Remarks: The lobate and isosceles basal ring, and short radial
spine at each corner of the basal ring are main characteristics of
Corbisema hastata hastata (Bukry 1976). The skeletons having
round corners and smaller dimensions are classified as
Corbisema hastata globulata.
Corbisema sp. cf. C. hastata hastata (Lemmermann) Bukry 1976
Plate 3, figure 6
cf. Dictyocha triacantha var. hastata LEMMERMANN 1901, p. 259,
pl. 10, fig. 16.
cf. Corbisema hastata (Lemmermann) FRENGUELLI 1940, p.62, figs.
12b, and 12c.
Remarks: The shape of basal ring is not completely conformable to the typical form of Corbisema hastata hastata. The skeleton sizes of this confer taxon are larger than Corbisema
hastata hastata.
Corbisema hastata cunicula Bukry 1976
Plate 3, figure 7
218
Corbisema hastata cunicula BUKRY 1976, p. 905, pl. 3, figs. 8-15.
Remarks: The characteristics of Corbisema hastata cunicula are
having the unscalloped long sides of basal ring, smaller basal
ring, and long spines (Bukry, 1976). The skeleton size in the
original description is 15-22µm as the internal diameter. Relatively large specimens rarely occurred in the ACEX samples
(Pl. 2, Fig. 6: the internal diameter 35µm).
Corbisema sp. cf. C. hastata cunicula Bukry 1976
Plate 3, figures 8, 9
cf. Corbisema hastata cunicula BUKRY 1976, p. 905, pl. 3, figs. 8-15.
Remarks: Equilateral triangular basal ring and the supporting
spines, which extend perpendicular to the basal ring plane, are
significant characteristics of this taxon. The sides of basal ring
are straight or slightly convex. The characteristic supporting
spines are located under or near the contact point between basal
ring and apical struts. Basal ring diameter ranges from 45 to
60µm. The flat side is like C. hastata cunicula Bukry but the
spines are too short.
Corbisema hastata globulata Bukry 1976
Plate 2, figures 10-13
Corbisema hastata globulata BUKRY 1976, p. 907, pl. 4, figs. 1-8.
Corbisema globulata (Bukry) LOCKER and MARTINI 1987, p. 43, pl.
1, figs. 3-4.
Remarks: The lobate and isosceles basal ring, and short spine at
each corner of the basal ring are characteristics of Corbisema
hastata globulata (Bukry 1976). The rounded and normal trian-
Micropaleontology, vol. 55, nos. 2-3, 2009
TABLE 3
The Pearson’s correlation coefficients for silicoflagellate assemblages between the ACEX samples and those of other regions of the middle Eocene. The
underlined values represent the significant correlations (p <0.05).
gular basal ring is different from that of Corbisema hastata
hastata. The skeleton dimensions in our samples (35-45µm as
the internal diameter) are larger than the original description
(15-25µm as the internal diameter).
angular side, therefore the skeleton ring forms rounded triangle
or hexagonal. The abundance of typical C. hexacantha in this
study is very rare. The skeleton was counted in conjunction with
Corbisema sp. cf. hexacantha.
Corbisema hastata minor (Schulz) Bukry 1975
Corbisema sp. cf. C. hexacantha (Schulz) Deflandre 1950a
Plate 3, figures 14-19
Plate 4, figures 1, 2
Dictyocha triacantha var. apiculata f. minor SCHLUZ 1928, p. 249, fig.
29b; GLEZER 1970 (in part), p. 245, pl. 6, figs. 2-4; pl. 31, fig. 4-6.
Corbisema hastata (Lemmermann) FRENGUELLI 1940, p.62, figs.
12b, and 12c.
Corbisema hastata (Lemmermann) LING 1972, p. 155, pl. 24, fig.5.
Corbisema hastata minor (Schulz) BUKRY 1975, p. 854, pl. 1, fig. 10.
cf. Dictyocha hexacantha SCHULZ 1928, p. 255, fig. 43
cf. Dictyocha deflandrei f. hexagona FRENGUELLI 1940, p.65, fig.
14g.
cf. Corbisema hexacantha (Schulz) DEFLANDRE 1950a, p. 136, 193,
figs. 183-187.
Remarks: The skeletal dimensions of this taxon (20-30µm of
basal ring diameter) are smaller than that of Corbisema hastata
globulata and Corbisema hastata hastata (30-50µm).
Remarks: The skeletons classified under this taxon have the characteristic that the accessory spine arose from the apical strut between
the basal plane and the apical plane. This may be the intermediate
type from a typical Corbisema spinosa to a typical C. hexacantha.
This intermediate type form is abundant in the samples from Core
M2A-48X and 49X. The aberrant skeletons are sporadically observed in the older sediment samples.
Corbisema hexacantha (Schulz) Deflandre 1950a
Plate 3, figure 20
Dictyocha hexacantha SCHULZ 1928, p. 255, fig. 43
Dictyocha deflandrei f. hexagona FRENGUELLI 1940, p.65, fig. 14g.
Corbisema hexacantha (Schulz) DEFLANDRE 1950a, p. 136, 193,
figs. 183-187.
Remarks: The accessory spines are extended outside of the ring
arising from the juncture point between basal ring and apical
strut. The juncture point is slightly off outside of the straight tri-
Corbisema regina Bukry in Barron et al. 1984
Plate 4, figure 3
Corbisema triacantha var. minor (Schulz) LING 1972, p. 158, pl. 24,
figs. 20-23.
Corbisema regina BUKRY in BARRON et al. 1984, p. 150, pl. 2, figs.
5-13.
219
Jonaotaro Onodera and Kozo Takahashi: Taxonomy and biostratigraphy of silicoflagellates in the middle Eocene Arctic Ocean
Aberrant skeletons of Corbisema spp.
Remarks: The non-equilateral triangular basal ring and the apical plate are characteristics of this taxon.
Corbisema spinosa Deflandre 1950b
Plate 4, figures 4-8
Corbisema spinosa DEFLANDRE 1950b, p. 193, figs. 178-182.
Dictyocha spinosa (Deflandre) GLEZER 1970, p. 256, pl. 10, figs. 6-8.
Remarks: Accessory spine extends along the apical plane or
obliquely upward from the contact point between the apical
strut and the apical bar. Under the light microscope observation, the focal point of the accessory spine of Corbisema
spinosa is different from that of the radial spines. This is different from the focal point of the accessory spines of Corbisema
hexacantha, which is nearly equal to the radial spines.
Corbisema triacantha (Ehrenberg) Hanna 1931
Plate 4, figures 9-11
Dictyocha triacantha EHRENBERG 1844, p. 80.
Dictyocha trigona ZITTEL 1876, p. 83, pl. 2, figs. 6, 6a.
Corbisema triacantha (Ehrenberg) HANNA 1931, p. 198, pl. D, fig. 1.
Corbisema hastata sensu FRENGUELLI 1940, p.65, fig. 12b.
Corbisema trigona (Zittel) DEFLANDRE 1950a, p. 132, fig. 130.
Dictyocha crux f. trigona BACHMANN in ICHIKAWA et al. 1967, p.
157, pl.4, figs. 1-17.
Remarks: This taxon has equilateral triangular basal ring with
slightly rounded corners, and radial spines of moderate length.
The sides of basal ring are straight or slightly indented at arising
points of the apical struts.
Plate 4, figures 12-15; Plate 5, figure 1-7
Remarks: Basal triangular ring is usually defective or irregular.
Often parts of their skeletons are not connected and thereby
forming an incomplete triangular shape. Based on the number
of three apical struts, the aberrant skeletons are categorized under the genus Corbisema.
Genus Dictyocha Ehrenberg 1837
Dictyocha acuta Bukry 1987
Plate 5, figure 8
Dictyocha acuta BUKRY 1987, p. 414, pl. 6, figs. 1-3.
Remarks: This taxon is distinguished from D. byronalis by
canted bar, asymmetrical strut junctions, angular ring, and longer minor-axis spines. It is also distinguished from D. stapedia,
D. fibula angusuta, and D. concava by canted bar (Bukry 1987).
Dictyocha alaris sp. nov.
Plate 5, figures 9-14; Plate 6, figure 1
Derivation of Name: The specific epithet alaris (Latin, of
wings) stems from the wing-like feature of the part of the skeleton extended off the basal plane.
Holotype: Plate 5, Figure 10; Sample IODP302-M2A-53X-2,
56-58cm; Slide MPC-02681 (Micropaleontology Collection,
National Science Museum, Tokyo), England finder T30/1
PLATE 1
Scale bar for all LM photographs = 50µm.
1-3 Arctyocha bukryi Desikachary and Prema, (1, 2:
IODP302-M4A-11X-CC; 3: IODP302-M2A-47X-3,
36-38cm),
10,11 Bachmannocena oamaruensis Schulz, (10:
IODP302-M4A-11X-CC; 11: IODP302-M4A-12XCC),
4-7 Bachmannocena apiculata apiculata Bukry,
IODP302-M4A-11X-CC,
12 Bachmannocena quadrangula Ehrenberg ex Haeckel,
IODP302-M4A-11X-CC.
8,9 Bachmannocena sp. cf. B. apiculata apiculata Bukry,
IODP302-M4A-11X-CC
220
Jonaotaro Onodera and Kozo Takahashi
micropaleontology, vol. 55, nos. 2-3, 2009
Plate 1
221
Jonaotaro Onodera and Kozo Takahashi: Taxonomy and biostratigraphy of silicoflagellates in the middle Eocene Arctic Ocean
Type locality: Hole IODP302-M2A, 227.08 mbsf, Lomonosov
Ridge, central Arctic Ocean
Description: The quadrangular ring is bent off the horizontal
plane. In most skeletons, one radial spine and two sides of the
quadrangular ring are slanted off the plane on which the remainder of the basal ring and radial spines are located. In some
small-sized specimens, the slanted radial spine is nearly perpendicular to the horizontal plane formed by other spines and the
basal ring. The side of quadrangular ring is straight or slightly
curved. The apical strut arises from each mid point of quadrangular ring side and extending one apical bar, which acts as a
nodal point between the base skeleton and the part slanted off
the base plane. The radial spines are straight or slightly curved.
The length of radial spine is nearly equal or longer than the diameter of quadrangular ring. There is no basal pike at each side.
Surface ornamentation of the skeleton is observed on the all
parts of the skeleton.
Dimensions: 13-37µm for the major axis (on the horizontal
plane) diameter of the quadrangular ring; 6-40µm for the radial
spine [N = 25].
Occurrence: The FO: M4A-6X-3, 96-98; The LO:
M2A-51X-2, 117-118; Consistent occurrences are noted between Samples M2A-58X-2, 96-98 and M2A-51X-2, 117-118.
This taxon is abundant above the occurred interval of Dictyocha
arctios and ebridian Ammodochium lomonosovi.
Remarks: The specimens without the part of skeleton slanted
off the horizontal plane are classified as Dictyocha explicata.
Dictyocha explicata consistently concurrently occurred to-
gether with Dictyocha alaris. Dictyocha alaris may look like
Dictyocha elongata Glezer in the apical view with the apical
structure towards the observer, but completely different with respect to the side numbers of basal ring skeleton, numbers of apical struts, and the apical windows.
Dictyocha arctios Ling 1985a
Plate 6, figures 2-11
Dictyocha arctios LING 1985a, p. 82, pl. 10, fig. 12-15.
Remarks: The long apical spine arising from the apical strut
junction or the short apical bar is the significant characteristic of
this taxon (Ling 1985a).
Dictyocha aspera aspera s.l. (Lemmermann) Bukry 1987
Plate 7, figures 1-4
Dictyocha fibula aspera LEMMERMANN 1901, pl. 10, figs. 27, 28.
Dictyocha aspera (Lemmermann) BUKRY and FOSTER 1973, p. 826,
pl. 2, figs. 4-6.
Dictyocha aspera aspera (Lemmermann) BUKRY 1975, p. 854, pl. 2,
figs. 2-4.
Dictyocha aspera aspera s.l. (Lemmermann) BUKRY 1987, pl. 7, fig.
10.
Remarks: The apical bar is located along the short axis of the
quadrangular ring.
Dictyocha sp. cf. D. aspera aspera (Lemmermann) Bukry 1987
Plate 7, figures 5, 6
cf. Dictyocha fibula aspera LEMMERMANN 1901, pl. 10, figs. 27, 28.
cf. Dictyocha aspera (Lemmermann) BUKRY and FOSTER 1973, p.
826, pl. 2, figs. 4-6.
PLATE 2
Scale bar for all LM photographs = 10µm.
1-4 Corbisema apiculata (Lemm.) Hanna, (1, 2: Sample
IODP302-M2A-54X-CC; 3: IODP302-M2A-53XCC; 4: IODP302-M4A-4X-CC),
5-7 Corbisema sp. cf. C. apiculata, (5: IODP302-M2A47X-3, 36-38cm; 6, 7: IODP302-M2A-61X-CC)
222
8-13 Corbisema euhadrotes, sp. nov., (8: IODP302-61X-2,
76-78cm (Holotype); 9: IODP302-M4A-4X-CC; 10:
IODP302-M2A-61X-CC; 11-13: IODP302M2A-62X-1, 116-118cm).
Jonaotaro Onodera and Kozo Takahashi
micropaleontology, vol. 55, nos. 2-3, 2009
Plate 2
223
Jonaotaro Onodera and Kozo Takahashi: Taxonomy and biostratigraphy of silicoflagellates in the middle Eocene Arctic Ocean
cf. Dictyocha aspera aspera (Lemmermann) BUKRY 1975, p. 854, pl.
2, figs. 2-4.
cf. Dictyocha aspera aspera s.l. (Lemmermann) BUKRY 1987, pl. 7,
fig. 10.
Remarks: The basal ring of this taxon is rounded and thus forming nearly a circle compared to the quadrangular basal ring of a
typical Dictyocha aspera aspera.
Remarks: The shape of the basal ring is oblong or rounded
rather than quadrate. In some cases, the apical bar transverses
over the basal ring, as in the case of the apical structure of
Dictyocha frenguellii.
Dictyocha deflandrei Frenguelli ex Glezer 1966
Plate 7, figures 15, 16; Plate 8, figures 1-5
Dictyocha deflandrei FRENGUELLI 1940, p.65, figs. 14a, d.
Dictyocha deflandrei FRENGUELLI ex GLEZER 1966, p. 262, pl. 12,
figs. 13, 16: pl. 32, fig. 4.
Dictyocha sp. cf. D. aspera martinii Bukry 1975
Plate 7, figures 7-9
cf. Dictyocha aspera martinii BUKRY 1975, p. 854, pl. 2, figs. 5-8.
Remarks: Dictyocha aspera martinii is distinguished from D.
aspera aspera by the apical strut spines. It is distinguished from
other taxa having apical strut spines, such as D. frenguellii,
Corbisema hexacantha, and D. spinosa, by its transverse apical
bar. The apical bar of the skeleton in the ACEX sample is usually slightly oblique to the short axis of the quadrangular ring.
Remarks: The apical plate is nearly square or oblong. The skeletal dimension in ACEX samples varies from 25 to 50µm in the
basal ring diameter with a wider range of size, compared to the
dimension range from 20 to 30µm in the original description.
Dictyocha deflandrei lobata Bukry 1978
Plate 8, figures 6, 7
Dictyocha deflandrei lobata BUKRY 1978, p. 785, pl. 1, figs. 11-17.
Dictyocha curta Ling 1985a
Plate 7, figures 10-12
Remarks: Two lobate forms are in each side of the basal ring.
The apical strut arises from the indented point of the basal ring
side. In some skeletons, apical plate is very small.
Dictyocha curta LING 1985a, p. 83, figs. 18-21.
Remarks: Each radial spine of this taxon is located at the mid
point of the side of the quadrate basal ring (not located at the
ring corners). The apical struts arise from the basal ring corners.
Dictyocha sp. cf. D. elongata Glezer 1960
Plate 8, figure 8
cf. Dictyocha elongata GLEZER 1960, p. 131, 132, pl. 2, figs. 16-20.
Dictyocha sp. cf. D. curta Ling 1985a
Plate 7, Figures 13, 14
Remarks: Two radial spines of typical Dictyocha elongata situate along the long axis but those of D. sp. cf. elongata do not.
cf. Dictyocha curta LING 1985a, p. 83, fig. 18-21.
PLATE 3
Scale bar for all photographs = 10µm.
1,2 Corbisema sp. cf. C. geometrica sensu Bukry 1975,
IODP302-M2A-55X-CC
3-5 Corbisema hastata hastata (Lemm.) Frenguelli, (3:
IODP302-M2A-61X-CC; 4: IODP302-M4A-4X-CC;
5: IODP302-M4A-11X-CC),
6 Corbisema sp. cf. hastata hastata (Lemmermann)
Bukry, IODP302-M4A-11X-CC,
7 Corbisema hastata cunicula Bukry, IODP302M2A-47X-3, 36-38cm,
8,9 Corbisema sp. cf. C. hastata cunicula Bukry, (8:
IODP302-M4A-11X-CC; 9: IODP302-M2A-51X-2,
117-118cm),
224
10-13 Corbisema hastata globulata Bukry, (10, 13:
IODP302-M2A-61X-CC; 11, 12: IODP302-M4A4X-CC),
14-19 Corbisema hastata minor (Schulz) Bukry, (14, 15, 18:
IODP302-M4A-11X-CC; 16: IODP302-M2A-47XCC; 17: IODP302-M2A-48X-CC; 19: IODP302M2A-53X-CC),
20 Corbisema hexacantha (Schulz) Deflandre,
IODP302-M2A-48X-CC.
Jonaotaro Onodera and Kozo Takahashi
micropaleontology, vol. 55, nos. 2-3, 2009
Plate 3
225
Jonaotaro Onodera and Kozo Takahashi: Taxonomy and biostratigraphy of silicoflagellates in the middle Eocene Arctic Ocean
The ring side of typical D. elongata is slightly wide in the middle part but this characteristic is not seen on D. sp. cf. elongata.
It is also distinguished from Corbisema hastata cunicula by the
asymmetrical ring form of this taxon.
Dictyocha explicata sp. nov.
specimens with quadrangular ring whose one corner and a radial
spine are significantly slanted off the horizontal plane are identified as Dictyocha alaris.
Dictyocha fibula s.l. Ehrenberg 1839
Plate 9, figures 2-5
Plate 8, Figures 9-13, Plate 9, Figure 1
Dictyocha fibula EHRENBERG 1839, p. 129.
Derivation of Name: The specific name explicata was derived
from the Latin word meaning spread out.
Holotype: Plate 8, Figure 10, sample IODP302-M2A-52X-1,
36-38cm, slide MPC-02682 (Micropaleontology Collection,
National Science Museum, Tokyo), England finder N19/1
Type locality: Hole IODP302-M2A, 221.30 mbsf, Lomonosov
Ridge, central Arctic Ocean
Description: The quadrangular skeleton is nearly square. The
sides of square skeleton are straight or slightly indented at the
center of ring side. The four very long radial spines are straight
or slightly curved. The apical strut arises from the center of
each quadrangular ring side and connected to the apical bar
along the major axis. Apical struts and bar are nearly
“H-shaped” in plan view. The pikes are absent on all sides. The
skeletal ornamentation is observed on the all part of the skeletal
surface.
Dimensions: 33-41µm in the basal ring diameter of either major
or minor axis; 27-52µm in the length of radial spine [N = 25].
Occurrence: Continuous and common occurrences of this taxon
are recognized in the interval between 4A-11X-4, 48-50 and
4A-11X-1, 88-90, and in the interval between 2A-54X-1, 32-24
and 2A-51X-2, 117-118.
Remarks: Dictyocha pygmaea (Ciesielski) Shaw and Ciesielski
1983 resembles to this taxon with respect to the square shaped
ring and the long radial spines, but differs in the nearly equal
length of radial spines and absence of supporting spines. The
Remarks: In the fibuloidal Dictyocha, the skeletons having apical bar and no accessory spines are identified as D. fibula in a
broad sense in this study.
Dictyocha frenguellii Deflandre 1950b
Plate 9, Figures 6-13; Plate 10, Figures 1, 2
Dictyocha fibula forma DEFLANDRE 1940, p. 598, fig. 2.
Dictyocha frenguellii DEFLANDRE 1950b, p. 194, figs. 188-193.
Remarks: The distal ends of the apical bars transversely extend
out of the basal ring perimeter. It is distinguished from other
Dictyocha taxa by the unique apical structure.
Dictyocha minyrotatilis sp. nov.
Plate 10, figures 3-9
Dictyocha frenguellii var. carentis f. incerta GLEZER 1960 p. 132, pl. 3,
figs. 5, 6 (Nom. Nud.)
Dictyocha frenguellii var. carentis f. incerta GLEZER 1964, p. 52, pl. 1,
figs. 15, 16
Dictyocha sp. cf. D. carentis incerta (Glezer) LING 1985a, p.83, pl. 10,
figs. 16, 17; pl. 13, figs. 1-3.
Derivation of Name: The specific name is taken from a Greek
adjective mini and a Latin noun wheel.
Holotype: Plate 10, Figure 3, sample IODP302-M4A-10X-2,
14-16cm, slide MPC-02683 (Micropaleontology Collection,
National Science Museum, Tokyo), England finder O23/2
Type locality: IODP-302 Site M0004 Hole A, 294.71-294.73
mbsf, the Lomonosov Ridge in the central Arctic Ocean
PLATE 4
Scale bar for all LM photographs = 50µm.
1,2 Corbisema sp. cf. C. hexacantha (Schulz) Deflandre,
IODP302-M2A-48X-CC,
3 Corbisema regina Bukry in Barron et al., IODP302M4A-11X-CC,
4-8 ?Corbisema spinosa Deflandre. 4, IODP302M2A-48X-4, 14-16cm; 5-7, IODP302-M2A-48X-CC
(7, side view); 8, IODP302-M2A-49X-2, 14-16cm),
226
9-11 Corbisema triachantha (Ehrenberg) Hanna, (9:
IODP302-M2A-47X-3, 36-38cm; 10, 11: IODP302M4A-11X-CC),
12-15 Aberrant skeletons of Corbisema spp., (12, 13:
IODP302-M4A-11X-CC; 14: 302-M2A-55X-CC;
15: IODP302-M2A-48X-CC).
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micropaleontology, vol. 55, nos. 2-3, 2009
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Jonaotaro Onodera and Kozo Takahashi: Taxonomy and biostratigraphy of silicoflagellates in the middle Eocene Arctic Ocean
Description: The ring is quadrate or circular, and is small. The
axes defined by the short radial spines with equal length are orthogonal. Each apical strut arises from the mid point between
two radial spines on the side of basal ring. The apical struts arising from the basal ring usually intersect in the center in the apical view and sometimes form an apical plate. The skeletons
rarely have apical bar in stead of apical plate.
Dimensions: 15-20µm in basal ring diameter; 2-5µm in radial
spine length [N = 10]
Occurrence: The siliceous fossil bearing interval of Holes
IODP 302-M2A and M4A, which is in the middle Eocene, contain this taxon with few to common abundances ( Text-Fig. 2).
The common abundances are recorded in Core 302-M4A-10X.
Remarks: The small ring with small apical plate or bar, and the
equally short radial spines are the characteristics of this taxon.
The skeletons in ACEX samples resemble to Dictyocha
frenguellii var. carentis f. incerta Glezer 1964 and D. sp. cf. D.
carentis incerta (Glezer) Ling. Dictyocha frenguellii carentis
incerta is the same morphology as this taxon. However, this
taxon is not assigned to the subspecies of D. frenguellii (Bukry
1976, Perch-Nielsen 1976, Ling 1985a). Dictyocha sp. cf. D.
carentis incerta (Glezer) Ling, and Dictyocha cf. D. carentis
(Glezer) Perch-Nielsen (pl.4, fig. 6 only) are the similar taxa.
However, D. minyrotatilis usually has an apical plate or apical
bar whereas D. sp. cf. D. carentis incerta has not (Ling 1985a).
The radial spine lengths of Dictyocha cf. D. carentis (Glezer)
Perch-Nielsen are not equal each other. Dictyocha minyrotatilis
is also distinguished from D. curta because the radial spines of
D. minyrotatilis extend from the ring corner whereas those of
D. curta originate from the middle part of nearly strait side of
the ring.
Dictyocha obliqua Glezer 1964
some skeletons. The apical structure is characterized by broad
bar or apical plate. In some skeletons, accessory spines extend
from the apical struts or corners of the apical plate. The diameter of basal ring ranges from 20 to 30µm [N = 15].
Dictyocha precarentis Bukry 1976
Plate 10, figure 15
Dictyocha precarentis BUKRY 1976, p. 894, pl. 6, figs. 6-13; pl. 7, figs.
1-3.
Remarks: The basal ring is nearly square. The radial spines with
the same length are septate and are axially aligned. The length
of four equal apical struts and an apical bar appear the same or
nearly equal in the apical view.
Dictyocha stellula sp. nov.
Plate 11, figures 1, 2
Derivation of Name: The specific name stellula is a dimunitive
of the Latin word meaning star.
Holotype: Plate 11, Figure 1, Sample IODP302-M4A-7X-2,
36-38cm, Slide MPC-02684 (Micropaleontology Collection,
National Science Museum, Tokyo), England finder P31/3.
Type locality: Hole IODP302-M4A, 280.38 mbsf, Lomonosov
Ridge, central Arctic Ocean
Description: The pentagonal basal ring is small and robust. Apical strut arises from each corner of the basal ring and forms apical plate or broad apical bar. Radial spines are indistinct.
Supporting spines are absent.
Dimensions: 18-20µm in basal ring diameter [N = 5].
Dictyocha obliqua GLEZER 1964, p. 57, pl. 2, fig. 10.
Occurrence: The taxon is continuously observed between Sections 302-M4A-10X-4 and M2A-61X-3 with rare abundances (
text-fig. 2).
Remarks: Basal ring is oval rather than quadrate. Major axis and
minor axis are intersecting slightly off the perpendicular angle.
Polar radial spines in the major axis are off the straight line in
Remarks: The characteristics of this taxon are the same as the
description of Dictyocha sp. cf. rotundata in the Paleogene Arctic sediments by Ling (1985a). The similar taxa, which are D.
Plate 10, figures 10-14
PLATE 5
Scale bar for all LM photographs = 50µm.
1-7 Aberrant skeletons of Corbisema spp., (1, 3, 4:
IODP302-M4A-11X-CC; 2: IODP302-M2A-61XCC; 5-7: IODP302-M2A-48X-CC),
8 Dictyocha acuta Bukry, IODP302-M4A-4X-CC,
228
9-14 Dictyocha alaris, sp. nov., (9: IODP302-M2A55X-CC; 10: IODP302-M2A-53X-2, 56-58cm
(Holotype); 11, 13: IODP302-M2A-51X-2,
117-118cm; 12: IODP302-M2A-53X-2, 14-16cm;
14: IODP302-53X-CC).
Jonaotaro Onodera and Kozo Takahashi
micropaleontology, vol. 55, nos. 2-3, 2009
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229
Jonaotaro Onodera and Kozo Takahashi: Taxonomy and biostratigraphy of silicoflagellates in the middle Eocene Arctic Ocean
rotundata and the subspecies D. rotundata secta Glezer, have
circular basal rings (Glezer 1962).
Holotype: Plate 11, Figure 9, sample IODP302-M4A-7X-1,
96-98cm, slide MPC-02686 (Micropaleontology Collection,
National Science Museum, Tokyo), England finder L16/1
Dictyocha tessera sp. nov.
Type locality: IODP-302 Site M0004 Hole A, 279.46-279.48
mbsf, the Lomonosov Ridge in the central Arctic Ocean
Plate 11, figures 3-8
Dictyocha sp. cf. D. rotundata LING 1985a, p.84, pl. 11, figs. 9-12.
Derivation of Name: The specific name tessera was taken from
the Latin word meaning small square.
Description: The skeleton is small and robust. Basal ring is triangular. Apical strut arises from each corner of the basal ring
and join together. Radial spines and supporting spines are absent.
Holotype: Plate 11, Figure 3, Sample IODP302-M2A-61X-1,
136-138cm, Slide MPC-02685 (Micropaleontology Collection,
National Science Museum, Tokyo), England finder H33/1.
Dimensions: 14-20µm in basal ring diameter [N = 10].
Type locality: Hole IODP302-M2A, 263.96 mbsf, Lomonosov
Ridge, central Arctic Ocean
Description: The skeleton is small and robust. Basal ring is usually quadrate. Apical strut arises from each corner of the basal
ring and forms apical plate. Radial spines and supporting spines
are absent.
Dimensions: 14-20µm in basal ring diameter [N = 20].
Occurrence: Dictyocha micula is sporadically observed between 302-M4A-10X-4 and M2A-61X-3 with rare abundance.
Remarks: The similar taxon, which is Dictyocha elata var. media f. reducta Glezer, has circular basal ring (Glezer 1964). Although this taxon may be described as species rather than
subspecies based on the skeleton morphology, the occurrence
interval is the same as D. tessera, and the abundance of D.
tessera micula is sporadic and very rare. Therefore, this taxon in
this study is described as the subspecies of D. tessera.
Dictyocha transitoria Deflandre 1932a
Occurrence: Dictyocha tessera is continuously observed between Sections and 302-M4A-10X-4 and M2A-61X-3 (text-fig.
2).
Remarks: The characteristics of this taxon are the same as the
description of Dictyocha sp. cf. rotundata in the Paleogene
Arctic sediments by Ling (1985a). The similar taxa, which are
D. rotundata and the subspecies D. rotundata secta Glezer,
have circular basal rings (Glezer 1962).
Plate 11, figure 10; Plate 13, figures 15-17
Dictyocha transitoria DEFLANDRE 1932a, p. 500, figs. 32, 33.
Remarks: The quadrangular basal ring with rounded corners has
only two radial spines, which are aligned along the major axis.
The apical struts originate from four corners of the basal ring.
The apical bar is located along the shorter axis.
Dictyocha variabilis (Hanna) Ciesielski 1975
Plate 11, figure 11
Dictyocha tessera micula ssp. nov.
Plate 11, figure 9
Derivation of Name: The subspecies name micula is taken from
Latin meaning little.
Distephanus valiabilis HANNA 1931, p. 200, pl. E, figs. 4-7. [nom.
nud.]
Dictyocha valiabilis (Hanna) CIESIELSKI 1975, p. 660, pl. 7, figs.
12-15.
PLATE 6
Scale bar for all photographs = 10µm.
1? Dictyocha alaris, sp. nov., IODP302-M2A-55X-5,
56-58cm,
2-11 Dictyocha arctios Ling, (2, 3, 6: IODP302-M4A4X-CC; 4, 5, 7, 8: IODP302-M2A-61X-CC;
230
9:IODP302-M2A-53X-CC; 10: IODP302-M4A7X-2, 36-38cm; 11: IODP302-M2A-55X-CC),
Jonaotaro Onodera and Kozo Takahashi
micropaleontology, vol. 55, nos. 2-3, 2009
Plate 6
231
Jonaotaro Onodera and Kozo Takahashi: Taxonomy and biostratigraphy of silicoflagellates in the middle Eocene Arctic Ocean
Remarks: The five apical struts, which arise from the relatively
small pentagonal basal ring, make one juncture on the apical
plane.
Remarks: The relatively large dimensions, and the quadrate
basal ring and apical ring are characteristics of this taxon.
Aberrant skeletons of Dictyocha spp.
Plate 12, figures 6-8
Plate 11, Figures 12-17
Remarks: The skeletons, which have four or more apical struts
and no apical ring, are categorized in this group.
Genus Distephanus Stöhr, 1880 (nom. cons.)
Distephanus crux parvus (Ehrenberg) Bukry 1982
Dictyocha crux f. parva BACHMANN in ICHIKAWA et al. 1967 (in
part), p. 156, pl. 4, figs. 14, 15, 19, 29-31.
Distephanus crux parvus (Bachmann in Ichikawa et al.) emended,
BUKRY 1982, p. 433, pl. 4, fig. 7.
Remarks: The ovate or rounded quadrangular basal ring, and
apical ring without apical pikes are characteristics of this subspecies in D. crux group. The skeleton having apical pikes on
the apical ring is distinguished as Distephanus mesophthalmus
(Ehrenberg) Dumitricâ (Bukry 1982).
Distephanus antiquus Glezer 1964
Plate 11, figures 18-20
Distephanus antiquus GLEZER 1964, p. 57, 58, pl. 2, figs. 6-9.
Remarks: The six straight apical struts arise from the basal ring
perpendicular to the hexagonal basal ring. The apical ring size
is nearly equal to or slightly smaller than the basal ring size.
The pentagonal form is rarely observed.
Distephanus crux scutulatus Bukry 1982
Distephanus crux (Ehrenberg) Haeckel 1887
Remarks: The characteristics of this taxon are in the elongated
basal ring, and significantly dissimilar major and minor spine
lengths. This taxon is distinguished from D. crux parvus by the
straight sides of the basal ring and generally smaller apical ring,
and from D. longispinus (Schulz) by spines that are shorter than
the maximum ring length (Bukry 1982).
Plate 12, figure 1
Dictyocha crux EHRENBERG 1840, p. 207.
Distephanus crux (Ehrenberg) HAECHEL 1887, p. 1563.
Dictyocha crux crux GLEZER 1970, p. 279, pl. 18, figs. 1-11, pl. 19;
figs. 1-6.
Distephanopsis crux (Ehrenberg) DUMITRICA 1978, p. 213. pl. 3, figs.
5-12.
Remarks: The apical strut characteristically arises from off the
middle point of the basal ring side. When the apical strut arises
from the middle point, the skeleton is classified as Distephanus
crux lockerii.
Distephanus crux lockerii Amigo 1999
Plate 12, figures 2-5
Distephanus crux lockerii AMIGO 1999, p. 75, pl. 1, figs. 12-15.
Plate 12, figure 9
Distephanus crux scutulatus BUKRY 1982, p. 433, pl. 4, figs. 7.
Distephanus crux subsp. 1
Plate 12, figures 10, 11; Plate 13, figure 1
Remarks: The elongated basal ring, lobate sides of the basal
ring, and similar length of four radial spines are the characteristics of this taxon. The supporting spines are absent or rarely visible in some skeletons. The apical ring is relatively small. The
dimensions are 65-110µm in the basal ring diameter and are significantly larger than those of other Distephanus crux subspecies. The taxon occurred between M2A-48X-2, 96-98cm and
M2A-47X-2, 56-58cm.
PLATE 7
Scale bar for all LM photographs = 10µm.
1-4 Dictyocha aspera aspera (Lemm.) Bukry, IODP302M2A-51X-2, 117-118cm,
5,6 Dictyocha sp. cf. D. aspera aspera, IODP302-M2A51X-2, 117-118cm,
7-9 Dictyocha aspera martinii Bukry, (7, 9: IODP302M2A-61X-CC; 8: IODP302-M4A-4X-CC),
232
10-12 Dictyocha curta Ling, (10: IODP302-M2A-61X-1,
56-58cm; 11: IODP302-M2A-61X-CC; 12:
IODP302-M4A-4X-CC),
13,14 Dictyocha sp. cf. D. curta Ling, IODP302-M2A61X-CC,
15,16 Dictyocha deflandrei Frenguelli ex Glezer, (15:
IODP302-M4A-4X-CC; 16: IODP302-M2A53X-CC).
Jonaotaro Onodera and Kozo Takahashi
micropaleontology, vol. 55, nos. 2-3, 2009
Plate 7
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Jonaotaro Onodera and Kozo Takahashi: Taxonomy and biostratigraphy of silicoflagellates in the middle Eocene Arctic Ocean
Distephanus quinarius Locker and Martini 1989
Plate 13, figures 2, 3
Distephanus quinarius LOCKER and MARTINI 1989, p. 568, pl. 4, fig.
1.
Remarks: Distephanus quinarius is distinguished from other
pentagonal Distephanus skeletons by the relatively large skeletal dimensions.
Dictyocha biapiculata var. constricta (Schulz) DEFLANDRE 1932b,
p.79, fig. 1.
Naviculopsis constricta (Schulz) FRENGUELLI 1940, p.61, fig. 11a,
11b.
Naviculopsis biapiculata var. constricta (Schulz) GLEZER 1966, p.
257, pl. 17, fig. 4.
Remarks: The basal ring is slightly constricted around the juncture area of the apical band.
Naviculopsis eobiapiculata Bukry 1978
Distephanus sp. cf. D. speculum (Ehrenberg) Haeckel 1887
Plate 13, figures 11, 12
Plate 13, figures 4, 5
Dictyocha speculum EHRENBERG 1839, p. 129.
Distephanus speculum (Ehrenberg) HAECKEL 1887, p. 1565.
Remarks: Apical ring diameter is smaller than the basal ring diameter. It is identified as D. antiquus Glezer if the apical ring
diameter of the skeleton is similar to the basal ring diameter.
Aberrant skeletons of Distephanus spp.
Plate 13, figure 6
Remarks: The aberrant skeletons with apical window are categorized in this group.
Genus Naviculopsis Frenguelli, 1940
Naviculopsis aspera (Schulz) Perch-Nielsen, 1976
Naviculopsis biapiculata (Lemmermann) LING 1972, p. 181, pl. 30,
figs. 3, 4.
Naviculopsis regularis (Carnevale) LING 1972, p. 188, pl. 31, fig. 3.
Naviculopsis biapiculata (Lemmermann) s.l. DUMITRICA 1973, p.
847, pl. 1, figs. 5, 9.
Naviculopsis biapiculata (Lemmermann) s.l. PERCH-NIELSEN 1975,
p. 689, pl. 12, figs. 18, 20, 21.
Naviculopsis eobiapiculata BUKRY 1978, p. 787, pl. 4, figs. 9-16.
Neonaviculopsis eobiapiculata (Bukry) DESIKACHARY and PREMA
1996, p.118, pl. 29, figs. 6, 8, 9, 11, 12.
Remarks: The skeleton is relatively large and elongated. The
long radial spine is greater than 1/2 of the basal ring diameter.
The contact points between basal ring and radial spines are
rounded rather than angular compared to that of N. biapiculata
(Desikachary and Prema 1996).
Naviculopsis punctilia Perch-Nielsen 1976
Plate 13, figures 7, 8
Plate 13, figures 13, 14
Dictyocha navicula aspera SCHULZ 1928, p. 245, figs. 20a, b.
Naviculopsis aspera (Schulz) PERCH-NIELSEN 1976, p. 35, figs. 8, 9,
31, 34, 35.
Naviculopsis punctilia PERCH-NIELSEN 1976, p. 36, figs. 1, 32.
Remarks: The walls from the flat basal ring sides arise and connect at center of the skeleton as the apical band.
Remarks: This taxon has four apical struts supporting the apical
bar. The basal ring diameter is slightly longer than the length of
radial spine. The apical bar is slightly oblique to short axis.
Naviculopsis constricta (Schulz) Frenguelli 1940
ACKNOWLEDGMENTS
Plate 13, figures 9, 10
We thank the co-chief scientists Dr. Jan Backman and Dr. Kate
Moran, who materialized the ACEX, and the ACEX scientists
together with the captains and crew of the IODP Expedition 302
Dictyocha navicula var. biapiculata f. constricta SCHULZ 1928, p. 246,
fig. 21.
PLATE 8
Scale bar for all LM photographs = 10µm.
1-5 Dictyocha deflandrei Frenguelli ex Glezer, (1, 2:
IODP302-M4A-11XCC; 3: IODP302-M4A-4X-CC;
4: IODP302-M2A-51X-2, 117-118cm; 5: IODP302M2A-55X-CC),
6,7 Dictyocha deflandrei lobata Bukry, (6: IODP302M4A-11X-CC; 7: IODP302-M4A-4X-CC),
234
8 Dictyocha sp. cf. D. elongata Glezer, IODP302M4A-4X-CC,
9-13 Dictyocha explicata, sp. nov., (9, 11: IODP302M2A-53XCC; 10: IODP302-M4A-52X-1, 36-38cm
(Holotype); 12: IODP302-M2A-53X-1, 116-118cm;
13: IODP302-51X-2, 117-118cm; 3: IODP302M2A-53XCC),
Jonaotaro Onodera and Kozo Takahashi
micropaleontology, vol. 55, nos. 2-3, 2009
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Jonaotaro Onodera and Kozo Takahashi: Taxonomy and biostratigraphy of silicoflagellates in the middle Eocene Arctic Ocean
ACEX. Drs. David Bukry and Francesca Lozar was fully appreciated on the valuable pre-review, help, and suggestions. We
thank Dr. Dimitrios Zafiropoulos who assisted us for the new
taxonomic names in the classic languages. The SEM photography was performed using Shimazu SS-550 at the Center of Advanced Instrumental Analysis, Kyushu University. We
appreciate valuable comment by two reviewers for this manuscript. This research was partially supported by JSPS Research
Fellow to JO as well as JSPS B Project No. 17310009, JSPS B2
No. 10480128, B1 No. 13440152, and B2 No. 15310001 to KT.
A part of this research has been supported by Prof. Tatsuro
Matsumoto Scholarship Funds.
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———, 1975b. Coccolith and silicoflagellate stratigraphy, northwestern
Pacific Ocean, Deep Sea Drilling Project Leg 32. In: Larson, R. L.,
Moberly, R., et al., Initial Reports of the Deep Sea Drilling Project
32, 677-701. Washington, DC: U. S. Government Printing Office.
———, 1976. Cenozoic silicoflagellate and coccolith stratigraphy,
South Atlantic Ocean, Deep Sea Drilling Project Leg 36. In:
Hollister, C. D., Craddock, C., et al., Initial Reports of the Deep Sea
Drilling Project 35, 885-917. Washington, DC: U. S. Government
Printing Office.
———, 1977. Coccolith and silicoflagellate stratigraphy, South Atlantic
Ocean, Deep Sea Drilling Project Leg 39. In: Supko, P. R.,
Perch-Nielsen, K., et al., Initial Reports of the Deep Sea Drilling
Project 39, 825-839. Washington, DC: U. S. Government Printing
Office.
PLATE 9
Scale bar for all LM photographs = 10mm.
1 Dictyocha explicata, sp. nov., IODP302-M2A53XCC,
2-5 Dictyocha fibula s.l. Ehrenberg, (2: IODP302M2A-51X-2, 117-118 cm; 3: IODP302-M2A61X-CC; 4, 5: IODP302-M2A-47X-3, 36-38 cm),
236
6-13 Dictyocha frenguellii Deflandre, (6-8: IODP302M2A-51X-2, 117-118 cm; 10: (side view) 302-M2A53X-CC; 9, 11: IODP302-M2A-55X-CC; 12:
IODP302-M2A-61X-CC; 13: 302-M4A-4X-CC).
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micropaleontology, vol. 55, nos. 2-3, 2009
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Jonaotaro Onodera and Kozo Takahashi: Taxonomy and biostratigraphy of silicoflagellates in the middle Eocene Arctic Ocean
———, 1978. Cenozoic silicoflagellate and coccolith stratigraphy,
northwestern Atlantic Ocean, Deep Sea Drilling Project Leg 43. In:
Benson, W. E., Sheridan, R. E., et al., Initial Reports of the Deep
Sea Drilling Project 44, 775-805. Washington, DC: U. S. Government Printing Office.
———, 1981a. Cretaceous Arctic silicoflagellates. Geo-Marine Letters
1, 57-63.
———,1981b. Synthesis of silicoflagellate stratigraphy for Maestrichtian to Quaternary marine sediment. In: Warme, J. E., Douglas,
R. G., and Winterer, E. L., The Deep Sea Drilling Project—a decade
of progress, 434-444. Tulsa, OK: SEPM (Society of Economic Paleontologists and Mineralogists). Special Publication 32.
———, 1982. Cenozoic silicoflagellates from offshore Guatemala,
Deep Sea Drilling Project Site 495. In: Aubouin, J., von Huene, R.,
et al., Initial Reports of the Deep Sea Drilling Project 67, 425-445.
Washington, DC: U. S. Government Printing Office
———, 1984. Paleogene paleoceanography of the Arctic Ocean is constrained by the middle or late Eocene age of the USGS core Fl-422;
evidence from silicoflagellates. Geology, 12: 199-201.
———, 1985. Correlation of late Cretaceous Arctic silicoflagellates
from Alpha Ridge. In: Jackson, H. R., Blasco, S. and Mudie, P. J.,
Eds., Initial Geological Report on CESAR-The Canadian Expedition to Study the Alpha Ridge, Arctic Ocean, 125-135. Ottawa: Geological Survey of Canada Paper. 84-22.
———, 1987. Eocene siliceous and calcareous phytoplankton, Deep
Sea Drilling Project Leg 95. In: Poag, C. W., Watts, A. B., et al., Initial Reports of the Deep Sea Drilling Project 95, 395-415. Washington, DC: U. S. Government Printing Office.
———, 1995. Silicoflagellates and their geologic applications. Washington, DC: U. S. Geological Survey. Open-file Report 95-260, 27
pp. .
BUKRY, D. and FOSTER, J. H., 1973. Silicoflagellate and diatom stratigraphy, Leg 16, Deep Sea Drilling Project. In: van Andel, T. H.,
Heath, G. R., et al., Initial Reports of the Deep Sea Drilling Project
16, 815-871. Washington, DC: U. S. Government Printing Office.
BUNSEN, K. E. and WISE, S. W. Jr., 1976. Silicoflagellate stratigraphy,
Deep Sea Drilling Project, Leg 36. In: Barker, P. F., Dalziel, I. W. D.,
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CIESIELSKI, P. F., 1975. Biostratigraphy and paleoecology of Neogene
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CLARK, D. L., 1974. Late Mesozoic and early Cenozoic sediment cores
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CLARK, D. L., BYERS, C. W. AND PRATT, L. M., 1986. Cretaceous
black mud from the central Arctic Ocean. Paleoceanography, 1:
265-271.
DEFLANDRE, G., 1932a. Sur la systématique des Silicoflagellés. Bulletin de la Société botanique de France, 79: 494-506.
———, 1932b. Sur quelques Protistes siliceux d’un sondage de la mer
Caspienne. Bulletin de la Societe francaise de microscopie, 7: 78-81.
———, 1940. Sur une structure reticule méconnue du squelette des
Silicoflagellidées. Comptes rendus hebdomadaires des séances de
l’académie des sciences, 211: 597-599.
———, 1950b. Contribution a l’étude des silicoflagellidés actuels et
fossiels (suite et fin). Microscopie, 2: 117-142.
———, 1950c. Contribution a l’étude des silicoflagellidés actuels et
fossiels (suite et fin). Microscopie, 2: 191-210.
DELL’AGNESE, D. J. and CLARK, D. L., 1994. Siliceous microfossils
from the warm Late Cretaceous and Early Cenozoic Arctic Ocean.
Journal of Paleontology, 68: 31-47.
PLATE 10
Scale bar for all LM photographs = 10µm.
1,2 Dictyocha frenguellii Deflandre, (1: IODP302M2A-55X-CC; 2: IODP302-M2A-51X-2, 117-118
cm),
3-9 Dictyocha minyrotatilis sp. nov., (3: IODP302M4A-10X-2, 14-16cm (Holotype); 4: IODP302M4A-4X-CC; 5, 6: IODP302-M2A-47X-CC; 7:
238
I O D P 3 0 2 -M 2 A - 6 1 X - C C ; 8 , 9 : IO D P302M4A-6X-1, 36-38 cm),
10-14 Dictyocha obliqua Glezer, (10: IODP302-M2A55XCC; 11-14: IODP302-M2A-61X-CC),
15 Dictyocha precarentis Bukry, IODP302-M2A61X-CC,
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DESIKACHARY, T. V. and PREMA, P., 1996. Silicoflagellates
(Dictyochophyceae). Bibliotheca Phycologica, 100, pp. 298.
———, 1940. Consideraciones sobré los sílicoflagelados fósiles.
Revista del Museo de La Plata, ser. 2, 2. (Paleontologia), 7. 37-112.
DUMITRICÃ, P., 1973. Paleocene, late Oligocene and post-Oligocene
silicoflagellates in southwestern Pacific sediments cored on DSDP
Leg 21. In: Burns, R. E., Andrews, J. E., et al., Initial Reports of the
Deep Sea Drilling Project 21, 837-883. Washington, DC: U. S. Government Printing Office.
GLESER, Z. I., 1996. Problems of Eocene siliceous phytoplankton
zonation (exemplified by the Caspian Eocene deposits). Stratiraphy
and Geological Correlation, 4: 392-402.
———, 1978. Badenian silicoflagellates from Central Paratethys. In:
Brestenska, E., Ed., Chronostratigraphie und Neostratotypen, Miozän der Zentralen Paratethys 6: 207-230.
EHRENBERG, G. C., 1839. Über die Bildung der Kreidefelsen und des
Kreidemergels durch unsichtbare Organismen. Abhandlungen der
Königliche Akademie der Wissenschaften zu Berlin, 1838: 59-148.
———, 1840. 274 Blätter von ihm selbst ausgeführter Zeichnungen von
ebenso vielen Arten. Bericht über die zur Bekanntmachung
Geeigneten Verhandlungen der Königlich Preussischen Akademie
der Wissenschaften zu Berlin, 1839: 197-219.
———, 1844. Mittheilung über zwei neue Lager von Gebirgsmassen
aus Infusorien als Meeres-Absatz in Nord Amerika und eine
Vergleichung derselben mit den organischen Kreide-Gebilden in
Europa and Afrika. Bericht über die zur Bekanntmachung
Geeigneten Verhandlungen der Königlich Preussischen. Akademie
der Wissenschaften zu Berlin, 1844: 57-97.
EISENACK, A., 1954. Mikrofossilien aus Phosphoriten des
samländischen Unteroligozäns und über die Einheitlichkeit der
Hystrichosphaerideen. Palaeontographica, 105 Abt. A: 49-95, Lief.
3-6.
FRENGUELLI, J., 1935. Variaciones de Dictyocha ficula en el Golfo de
San Matias (Patagonia septentorional). Anales del museo argentino
de ciencias naturares ”Bernardino Rivadavia” 38, Protistologia, 4:
265-281.
———, 1962. K voprosu o filogeneze kremnevykh zhgutikovykh
vodorosley. Paleontologicheskii Zhurnal, 1962: 146-156.
———, 1964. Novye Kremnvye zhgutikovya vodorosli Paleogene
SSSR, Silicoflagellatae fossiles novae URSS. Novosti Sistematiki
Nizshikh Rastenii (= Novitates systematicae plantarum non
vascularium), 46-58. Moscow: Academia scientiarum URSS.
———, 1970. Silicoflagellatophyceae. In: Gollerbakh, M. M., Ed.,
Cryptogamic plants of the U. S. S. R, no. 7, 1966. Jerusalem: Program
for Scientific Translations Ltd., 363 pp.
GRADSTEIN, F. M., OGG, J. G., and SMITH, A. G., Editors, 2004. A
Geologic Time Scale 2004. Cambridge: Cambridge University Press,
589 pp.
HAECKEL, E. H. P. A., 1887. Report on the Radiolaria collected by H.
M. S. Challenger during the years 1873-1876. Report on the scientific
results of the voyage of H. M. S. Challenger during the years
1873-1876, 18: 1-1803.
HANNA, G. D., 1931. Diatoms and silicoflagellates of the Kreyenhagen
Shale. Mining in California, 27: 187-213.
ICHIKAWA, W., SHIMIZU, I. AND BACHMANN, A., 1967. A. Fossil Silicoflagellates and their associated uncertain forms in Iida Diatomite, Noto Peninsula, Central Japan. Science Reports of Kanazawa
University, 12: 143-172.
KITCHELL, J. A. and CLARK, D. L., 1982. Late Cretaceous-Paleogene
paleogeography and palercirculation: Evidence of north polar
PLATE 11
Scale bar for all LM photographs = 10µm.
1,2 Dictyocha stellula, sp. nov., (1: IODP302-M4A7X-2, 36-38cm (Holotype); 2: IODP302-M4A11X-CC),
3-8 Dictyocha tessera, sp. nov., (3: IODP302-61X-1,
136-138cm (Holotype); 4, 8: IODP302-M2A-61X-1,
(8, side view) 56-58cm; 7: IODP302-M4A-4X-CC; 5,
6: IODP302-M2A-61X-CC),
9 Dictyocha tesssera micula, ssp. nov., IODP302M4A-7X-1, 96-98cm (Holotype),
10 Dictyocha transitoria Deflandre, IODP302-M4A4X-CC,
240
11 Dictyocha valiabilis (Hanna) Ciesielski, IODP302M2A-47X-CC,
12-17 Aberrant skeletons of Dictyocha spp., (12: IODP302M2A-51X-2, 117-118cm; 13: IODP302-M2A-53XCC; 14: IODP302-M4A-11X-CC; 15: IODP302M4A-4XCC; 16: IODP302-M2A-55X-CC; 17:
IODP302-M2A-61X-CC),
18-20 Distephanus antiquus Glezer, (18: IODP302-M4A4X-CC; 19: IODP302-M2A-53X-CC; 20: IODP302M2A-54X-CC),
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upwelling. Palaeogeography, Palaeoclimatology, Palaeoecology,
40: 135-163.
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and ebridians. Bulletins of American Paleontology, 62: 135-229.
———, 1985a. Early Paleogene silicoflagellates and ebridians from the
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———, 1985b. Paleogene silicoflagellates and ebridians from the
Goban Spur, northeastern Atlantic. In: Graciansky, P. C. de, Poag, C.
W., et al., Initial Reports of Deep Sea Drilling Project 80, 663-668.
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LOCKER, S., 1996. Cenozoic siliceous flagellates from the Fram Strait
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LOCKER, S. and MARTINI, E., 1986. Silicoflagellates and some
sponge spicules from the southwest Pacific, Deep Sea Drilling Project, Leg 90. In: Kennet, J. P., von der Borch, C. C., et al., Initial Reports of the Deep Sea Drilling Project 90, 887-924.Washington, DC:
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———, 1987. Silicoflagellaten aus einigen russischen PaläogenVorkommen. Senckenbergiana Lethaea, 68: 21-67.
———, 1976. New silicoflagellates and a silicoflagellate zonation in
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———, 1978. Eocene to Pliocene archaeomonads, ebridians, and
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Perch-Nielsen, K., Eds., Plankton stratigraphy, 811-846. Cambridge: Cambridge University Press.
PLATE 12
Scale bar for all LM photographs = 50mm.
1 Distephanus crux (Ehrenberg) Haeckel, IODP302M2A-47XCC,
9 Distephanus crux scutulatus Bukry, IODP302M2A-47X-CC,
2-5 Distephanus crux lockerii Amigo, (2-4: IODP302M2A-47X-CC; 5: IODP302-M2A-47X-3, 36-38 cm),
10,11 Distephanus crux ssp. 1, IODP302-M2A-47X-3,
36-38 cm.
6-8 Distephanus crux parvus (Backmann in Ichikawa et
al.) Bukry, IODP302-M2A-47X-CC,
242
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SANGIORGI, F., BRINKHUIS, H. and DAMASSA, S. P., 2009.
Frigusphaera gen. nov.: A new organic-walled dinoflagellate cyst
genus from the ?early Miocene of the central Arctic basin.
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Ruddiman, W. F., et al., Proceedings of the Ocean Drilling Program, Scientific Results 151, 75-99. College Station, TX: Ocean
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norddeutschen Kreide. Zeitschrift der Deutschen Geologischen
Gesellschaft, 28: 75-86.
PLATE 13
Scale bar for all LM photographs = 50mm.
1 Distephanus crux ssp. 1, IODP302-M2A-47X-3,
36-38cm,
2,3 Distephanus quinarius Locker and Martini,
IODP302-M2A-47X-CC,
4,5 Distephanus sp. cf. D. speculum (Ehrenberg)
Haeckel, (4: IODP302-M4A-4X-CC; 5: IODP302M2A-47X-3, 36-38cm),
6 Aberrant skeleton of Distephanus sp., IODP302M2A-47X-CC,
7,8 Naviculopsis aspera (Schulz) Perch-Nielsen ,
IODP302-M2A-49X-CC,
244
9,10 Naviculopsis constricta (Schulz) Frenguelli, (9:
IODP302-M2A-47X-5, 36-38cm; 10: IODP302M2A-50X-CC),
11,12 Naviculopsis eobiapiculata Bukry, (11: IODP302M2A-49X-CC; 12: IODP302-M2A-50X-CC),
13,14 Naviculopsis punctilia Perch-Nielsen, IODP302M2A-50X-1, 14-16cm,
15-17 Dictyocha transitoria Deflandre, IODP302-M2A49X-CC.
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APPENDIX 1
The contents (no. of skeletons mg-1) of major silicoflagellate skeletons at Holes IODP 302-M0002A and M0004A. The symbols “+” and “-” represent the low content with <1
skeletons mg-1 and no data in Core M0004A-11X, respectively. The only total skeleton counts were conducted for several samples in Core M0004A-11X.
246
Micropaleontology, vol. 55, nos. 2-3, 2009
APPENDIX 1, continued
The contents (no. of skeletons mg-1) of major silicoflagellate skeletons at Holes IODP 302-M0002A and M0004A. The symbols “+” and “-” represent the low content with <1
skeletons mg-1 and no data in Core M0004A-11X, respectively. The only total skeleton counts were conducted for several samples in Core M0004A-11X.
247
Jonaotaro Onodera and Kozo Takahashi: Taxonomy and biostratigraphy of middle Eocene silicoflagellates in the central Arctic Basin
APPENDIX 1, continued.
The contents (no. of skeletons mg-1) of major silicoflagellate skeletons at Holes IODP 302-M0002A and M0004A. The symbols “+” and “-” represent the low content with <1
skeletons mg-1 and no data in Core M0004A-11X, respectively. The only total skeleton counts were conducted for several samples in Core M0004A-11X.
248