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Microfossil Biostratigraphy and Paleoenvironments of the Upper Pliocene KuwaeFormation, Northeast JapanSource: Paleontological Research, 18(3):150-168.Published By: The Palaeontological Society of JapanDOI: http://dx.doi.org/10.2517/2014PR015URL: http://www.bioone.org/doi/full/10.2517/2014PR015

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Paleontological Research, vol. 18, no. 3, pp. 150–168, July 1, 2014© by the Palaeontological Society of Japandoi:10.2517/2014PR015

Microfossil biostratigraphy and paleoenvironments of the upper Pliocene Kuwae Formation, Northeast Japan

TAKASHI GOTO1, TOSHIAKI IRIZUKI2, YUKIO YANAGISAWA3 AND HIROKI HAYASHI2

1Department of Materials Creation and Circulation Technology, Interdisciplinary Graduate School of Science and Engineering, Shimane Univer-sity, 1060 Nishikawatsu-cho, Matsue, Shimane 690-8504, Japan (e-mail: [email protected])2Department of Geoscience, Interdisciplinary Graduate School of Science and Engineering, Shimane University, 1060 Nishikawatsu-cho, Matsue,Shimane 690-8504, Japan3Institute of Geology and Geoinformation, Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST),C7, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8567, Japan

Received September 24, 2013; Revised manuscript accepted December 28, 2013

Abstract. Microfossils abundantly occur in the upper part of the Pliocene Kuwae Formation in the Sakaistratigraphic section, Tainai City, northern Niigata Prefecture. We clarified the biostratigraphy and recon-structed the vertical paleoenvironmental changes based on microfossils such as ostracodes, diatoms and plank-tonic foraminifers. As a result, the sequence in the Sakai section was divided into three parts based on lithologyand correlated with the Neodenticula koizumii-N. kamtschatica diatom zone (NPD 8, 3.5–2.7 Ma). At least thelower and middle parts of the study sequence were assigned to the horizon below the datum of the rapidincrease of N. koizumii (D85, 3.1–3.0 Ma). An index fossil planktonic foraminiferal species, Globorotalia inflata(s.l.), was abundantly found only in the middle to upper part of the study interval. This interval belonged tothe No. 3 G. inflata bed, which has been used as a biozone in the Sea of Japan side during the Pliocene. Fourostracode bioassociations were identified using R-mode cluster analysis. Based on ostracode analysis, theKuwae Formation in the present study section was shown to have benn deposited in the sublittoral to upperbathyal zone and at least one cycle of water depth change was found. In addition, one new ostracode species,Hemicythere sakaiensis sp. nov., was described in this study.

Key words: biostratigraphy, diatom, Kuwae Formation, No. 3 Globorotalia inflata bed, ostracode

Introduction

The Sea of Japan is an enclosed marginal sea betweenthe Eurasian continent and the Japanese Islands (Figure1). It is now connected to the East China Sea through theTsushima Strait to the southwest, the Okhotsk Seathrough the Soya Strait to the north, and the PacificOcean through the Tsugaru Strait to the northeast. TheTsushima Current is a branch of the warm KuroshioCurrent. It flows into the Sea of Japan through theTsushima Strait. From the late Pliocene to early Pleisto-cene, 41-kyr glacial-interglacial cycles became clear andpaleobathymetry changed cyclically. The inflow of awarm-water current to the Sea of Japan through thesouthern entrance was limited because a land bridge wasintermittently formed during the periods of lower sealevel (Tada, 1994; Kitamura and Kimoto, 2004).

Plio-Pleistocene deposits were widely distributed on

the Sea of Japan side of central and northeastern Japan.They contain the cool-temperate Omma-Manganji mol-luscan fauna, which has been studied to reconstructpaleoenvironments (e.g. Otuka, 1939; Ogasawara, 1986,1994; Chinzei, 1991; Amano et al., 2000). The upperPliocene Kuwae Formation, which is the objective of thepresent study, is distributed in Shibata and its neighbor-ing Tainai cities, northern Niigata Prefecture, centralJapan (Figure 1). Several paleontological studies havebeen so far conducted on this formation. Amano et al.(2000) inferred that a warm-water current had flowedinto the Sea of Japan during the deposition of the middleto upper parts of the Kuwae Formation in Shibata Citybased on fossil molluscan assemblages. Watanabe et al.(2003) and Miwa et al. (2004) established diatom andplanktonic foraminiferal biostratigraphies, respectively,in the Tainai section, Tainai City, where the continuoussequence aged at 3.55–2.5 Ma is well exposed (Watanabe

Microfossils from the Kuwae Formation 151

et al., 2003; Inoue et al., 2003). Miwa et al. (2004)showed nine zones with abundant occurrence ofGloborotalia inflata (s.l.) in the No. 3 G. inflata bed,which was used as a biozone in the Sea of Japan side dur-ing the Pliocene (Maiya et al., 1976).

Yamada et al. (2005), Irizuki et al. (2007), and Irizukiand Ishida (2007) studied fossil ostracodes from theTainai section, which is the same locality as that in thestudy of Miwa et al. (2004). They showed cyclic changesin fossil ostracode assemblages based on several quanti-tative analyses, suggesting global eustatic changes. Irizukiet al. (2007) and Irizuki and Ishida (2007) also suggestedthat temperate intermediate water was present at thedeposition of the Kuwae Formation and that a cold-watermass such as Japan Sea Intermediate Water and JapanSea Proper Water in the present day had not been devel-oped at that time.

The aims of this paper are to report the microfossilassemblages and to discuss the paleoenvironment fromthe Pliocene Kuwae Formation distributed in the Sakai

section near the Tainai section, central Japan. This studywill contribute to delineate spatiotemporal changes inpaleoenvironments in the Sea of Japan side, centralJapan, in the future. We also describe one new ostracodespecies, Hemicythere sakaiensis sp. nov.

Geology of the study area

The Kuwae Formation in the Sakai section is exposedalong a valley formed sporadically in low hills (Figure2). This section is approximately 17 m in thickness, andmainly consists of fine- to medium-grained sandstonecontaining many shell fragments. Based on the lithofa-cies, it is divided into three parts (Figures 2, 3). In thelower part, an approximately 20 cm-thick lenticular tuffbed is intercalated in the fine- to medium-grained sand-stone approximately 1 m above the base, and trace fossilssuch as Teichichnus are abundantly found in the lowerpart. In the middle part, hummocky cross stratification isdeveloped 8–9 m above the base. Trace fossils such as

Figure 1. Maps showing locations of the study area in Niigata Prefecture, Northeast Japan. TWC: Tsushima Warm current.

Takashi Goto et al.152

Rosselia are found in the entire section; however, theyare concentrated only in the middle part. In the upperpart, sandy siltstone is developed in the lower portion,and bioturbation is abundantly found in the uppermostpart. Strikes and dips show nearly N-S and 3–4°E,respectively.

Materials and methods

We examined three types of microfossils: diatoms,planktonic foraminifers, and ostracodes. In total, 36 sed-iment samples for microfossil analyses. Of these, fiveRosselia samples (2R, 8R, 18R, 23R, and 28R, indescending order), which are infilled with finer muddysediments, were collected only for diatom analysis fromthe study section. The sediment sample interval wasapproximately 50 cm (Figure 3). Fossil diatoms andplanktonic foraminifers were used for biostratigraphy.Fossil ostracodes were analyzed to infer the depositionalenvironment.

DiatomsWe used the method described by Akiba (1986) to pre-

pare diatom slides. Approximately 1 g of sediment wassoaked in distilled water to prepare a solution. A 0.5-ccaliquot of the suspended solution was placed on a coverglass. An 18 × 18 mm cover glass and Pleurax mountingmedium were used to prepare the slides. Fifty diatomvalves were counted for each slide at ×600 magnificationusing a binocular microscope. One hundred diatomvalves were counted for samples 1, 2 and Rosselia sam-ples 18R, 23R, and 28R. Only 30 diatom valves werecounted for Rosselia sample 8R. The diatom valvesfound by additional scans in an 18 × 5 mm area of thecover glass were marked as present (+). We used the dia-tom biostratigraphy for the northwestern Pacific of Akiba(1986) and Yanagisawa and Akiba (1998). The ages ofdiatom biohorizons were corrected using a methoddescribed by Watanabe and Yanagisawa (2005) and werecalibrated based on a geomagnetic polarity time scalereported by Gradstein et al. (2004). Furthermore, bioho-rizon numbers tentatively proposed by Yanagisawa and

Figure 2. Locality of the study area and section. a, localities of the Sakai and Tainai sections; b, detail of sample sites and route mapof the Sakai section.


Kudo (2011) are used in this paper.

Planktonic foraminifers and ostracodes80 g of dried sediment samples was weighed and dis-

aggregated by the sodium sulfate and naphtha method(Maiya and Inoue, 1973). These processes were repeateduntil all fragment rocks were disaggregated. After wetsieving using a 200-mesh sieve screen (opening size:0.075 mm), the residues were dried. Then, they weredivided using a sample splitter, and approximately 200specimens were picked up from residues coarser than

0.125 mm under a stereoscopic microscope. The numberof ostracode specimens refers to both valves and cara-paces. One carapace was counted as two valves.

Results

DiatomsFossil diatoms were contained in all 36 samples; how-

ever, they were poorly preserved. They were composedof Pliocene pelagic, reworked Miocene, nonmarine, andother marine diatoms (Appendix 1). In particular, many

Figure 3. A columnar section with sample horizons of the Kuwae Formation in the Sakai section.


nonmarine diatoms were present although the study sec-tion consists exclusively of marine deposits (Figure 4).Thalassionema nitzschioides was the most dominanttaxon. Coscinodiscus marginatus, Actinocyclus ingens,Paralia sulcata, Stephanopyxis spp., and Aulacoseiraspp. were also abundant. Of the nonmarine diatoms,Aulacoseira was the most dominant taxon. Pliocaenicus,Cyclotella, and Stephanodiscus were also abundant. Thepercentage of nonmarine taxa was >30% in samples 28,7, 6, 5, and 2. Twenty-five reworked Miocene diatomtaxa were contained in the samples. Among them A.ingens and Denticulopsis spp. were abundant (20–30% insamples 27, 22, 4, and 2).

Index species such as Neodenticula kamtschatica, N.koizumii, Shionodiscus oestrupii, Thalassiosira antiqua,and T. convexa var. aspinosa were found in the studyinterval. N. kamtschatica and N. koizumii intermittentlyoccurred in the interval from samples 31 to 2 and fromsamples 31 to 6, respectively (Appendix 1). In particular,N. kamtschatica was abundant in samples 23, 20, 18, and 17.

The planktonic foraminifer G. inflata (s.l.)The planktonic foraminiferal species group Globoro-

talia inflata (s.l.) in the present study is composed of G.orientalis Maiya, Saito et Sato and G. inflata praeinflataMaiya, Saito et Sato sensu Miwa et al. (2004). This spe-cies grouop was found in the interval from samples 14 to6. This interval was divided into two parts at the bound-ary of sample 11. The lower part from samples 14 to 12was characterized by a high relative abundance of >50%,with the maximum abundance in sample 12. Sample 11had a relatively low abundance. The upper part fromsamples 10 to 6 was characterized by a high relativeabundance of >25% in most samples. G. inflata (s.l.) wasabsent or rarely present in the other horizons (Figure 4).

OstracodesMore than 170 ostracode species were found from 31

sediment samples (Appendix 2, Figure 5). Cythere sp.,Schizocythere kishinouyei, Cytheropteron sawanense,and Cytheropteron miurense were very abundant. They

Figure 4. Stratigraphic distribution of the planktonic foraminifer Globorotalia inflata (s.l.) and diatoms.


Figure 5. Fossil ostracodes from the Kuwae Formation in the Sakai section. RV: right valve, LV: left valve. 1, Acanthocythereis dunel-mensis (Norman), RV, adult, sample 5; 2, Aurila tsukawakii Ozawa and Kamiya, RV, adult, sample 4; 3, Cornucoquimba moniwensis(Ishizaki), RV, adult, sample 5; 4, Cornucoquimba cf. tosaensis (Ishizaki), RV, adult, sample 12; 5, Cornucoquimba sp., LV, juvenile, sample9; 6, Cythere sp. 1, RV, adult, sample 11; 7, Cythere sp. 2, RV, juvenile, sample 06; 8, Cytheropteron carolae Brouwers, LV, adult, sample 9;9, Cytheropteron miurense Hanai, RV, adult, sample 17; 10, Cytheropteron sawanense Hanai, RV, adult, sample 14; 11, Cytherura? sp. 1, RV,juvenile, sample 22; 12, Cytherura? sp. 2, RV, juvenile, sample 19; 13, Finmarchinella hanaii Okada, RV, adult, sample 4; 14, Finmarchinellacf. japonica (Ishizaki), RV, adult, sample 28; 15, Hemicythere kitanipponica (Tabuki), RV, adult, sample 4; 16, Loxoconcha subkotoraformaIshizaki, LV, juvenile, sample 25; 17, Neonesidea sp., LV, juvenile, sample 22; 18, Robertsonites tabukii Yamada, RV, adult, sample 23; 19,Schizocythere kishinouyei (Kajiyama), RV, adult, sample 4; 20, Semicytherura kazahana Yamada, RV, adult, sample 26; 21, Semicytherurasubslipperi Ozawa and Kamiya, RV, adult, sample 12; 22, Semicytherura sp. 1, RV, adult, sample 27. Scale bars are 0.2 mm.


inhabit shallow water areas in a temperate zone (e.g.Ikeya and Itoh, 1991; Irizuki and Ishida, 2007; Iwataniand Irizuki, 2008). Several deep-water taxa such asAcanthocythereis dunelmensis, C. carolae, andRobertsonites tabukii were concentrated in the intervalfrom samples 10 to 5. To reconstruct the vertical changesin paleoenvironments, we conducted quantitative analy-ses using 31 samples containing >150 specimens.

Diversity, equitability, and total number of ostracodesWe used H(S), Eq., and the number of ostracodes as

ecological indices (Figure 6). H(S) is a diversity indexand was calculated on the basis of the Shannon-Wiener

function [H(S) = ], where S is the total number

of species and pi is the proportional abundance of the ithspecies. Eq. is a measure of species equitability and wascalculated using the equation provided by Buzas andGibson (1969) (Eq. = eH(S)/S). These indices are gener-ally used to clarify the structure of fossil assemblages.

As a result, the H(S) index indicated entirely large val-

ues. However, it showed slightly smaller values in theupper part (samples 7 and 1). Small Eq. values wereobserved in the upper part (samples from 9 to 5 except 6and 1). Two peaks of the total number of ostracodes werefound at around sample 26 and sample 12.

R-mode cluster analysisThe relative abundance of 22 dominant ostracode taxa

containing more than 80 individuals as a total numberwere selected for R-mode cluster analysis (Figure 5). ThePaleontological Statistics (PAST) program (Hammer,2013) was used for R-mode cluster analysis using Horn’smodification of Morishita’s overlap index as a similarity(Morishita, 1959; Horn, 1966) and the unweighted pairgroup method with arithmetic average (UPGMA) as aclustering method. As a result, these dominant taxa wereclassified into the four bioassociations, namely I, II, III,and IV (Figures 7, 8).

Bioassociation I was composed of 17 taxa (Aurila tsu-kawakii, Cornucoquimba moniwensis, Cornucoquimbacf. tosaensis, Cornucoquimba sp., Cythere sp. 1, Cythere

Figure 6. Temporal changes of mud content, total number of total ostracodes per 1 g dried sediment sample, the species diversity (H(S))and the equitability (Eq.) in the Sakai section.

p pi ii

S

ln1


sp. 2, C. miurense, C. sawanense, Cytherura? sp. 2, Fin-marchinella hanaii, Finmarchinella cf. japonica, Hemi-cythere kitanipponica, Loxoconcha subkotoraforma, S.kishinouyei, Semicytherura kazahana, Semicytherurasubslipperi, and Semicytherura sp. 1). C. moniwensis,Cythere sp. 1, C. miurense, C. sawanense, Fin-marchinella cf. japonica and S. kishinouyei were thedominant taxa in this bioassociation. C. moniwensis wasreported from Sendai Bay in the Tohoku area in mild tocool temperate zones (Ikeya and Itoh, 1991; Irizuki andIshida, 2007). The genus Cythere is a representativephytal taxon living in the tidal zone (e.g. Tsukagoshi andIkeya, 1987). C. miurense lives in shallow seas in warmto mild temperate waters (Irizuki and Ishida, 2007). C.sawanense lives in mild to cool temperate waters (Ikeyaand Itoh, 1991; Irizuki and Ishida, 2007). S. kishinouyeilives in coastal sandy bottoms in warm to mild temperatewaters (Iwatani and Irizuki, 2008) and is mainly distrib-uted at <80 m depths in the Sea of Japan (off Oki Islands,Noto Peninsula, and Tsugaru Peninsula; Ozawa, 2003).Thus, they are components of the upper to middle sub-littoral zone in several temperate ranges around Japan.

Bioassociation II was composed of three taxa (A.dunelmensis, C. carolae, and R. tabukii). A. dunelmensisis the second most dominant species and is a circumpolarspecies living in water temperatures <6–8°C in high lat-

itude areas of the Northern Hemisphere (North Atlantic,Arctic, and Northern Pacific seas) (Cronin and Ikeya,1987). Although it was thought that A. dunelmensis couldonly live in shallow waters in the relatively cold zonesof northern areas, it has been reported that this specieslives in the upper to middle bathyal zones in the JapanSea Intermediate-Proper Water of the Recent Sea ofJapan off Honshu, where the water temperature isapproximately 0–5°C (Ishizaki and Irizuki, 1990; Ozawa,2003; Ozawa and Kamiya, 2005; Irizuki et al., 2007). Italso lives at >20 m depths and is most abundant at awater depth of 100 m in Alaska Bay or Arctic Siberia(Brouwers, 1993; Stepanova et al., 2003). Cytheropteroncarolae lives in the mid-outer sublittoral and upperbathyal zones in Alaska Bay (Brouwers, 1994). Severalspecies in the genus Robertsonites (R. hanaii, R. tabukii,and R. tsugaruana) occur at >150 m depths in the Sea ofJapan, and the water mass at this depth is characterizedby temperatures <5°C (Yamada, 2003; Ozawa, 2003;Ozawa and Kamiya, 2005; Irizuki et al., 2007). Thus,this bioassociation evidences deep and cold waters.

Bioassociation III was composed of only one species,Cytherura? sp. 1. This taxon has not been identified atthe species level until now. Therefore, the paleoenviron-ment for this bioassociation remains unknown.

Bioassociation IV was composed of only one species,Neonesidea sp. Species in the genus Neonesidea arecommon on algae in the intertidal and littoral zones (e.g.Hanai et al., 1977). Thus, this bioassociation indicatesthe shallowest waters of all the bioassociations.

Biostratigraphy

Almost all samples of this section except for theuppermost two samples can be assigned to the N.koizumii–N. kamtschatica Zone (NPD 8, 3.5–2.7 Ma)based on the cooccurrence of both species. Furthermore,the lower half of this section from samples 31 to 17 couldbe placed below the rapid increase of N. koizumii (D85,3.1–3.0 Ma) because N. kamtschatica is more dominantthan N. koizumii in this interval. However, the paucity ofage-diagnostic Neodenticula species hinders determiningwhether the upper interval of this section from sample 18to 2 is placed below the biohorizon D85. Although theuppermost two samples lack index species, they can beprobably assigned to NPD 8 because no erosional sur-faces were observed in the study section and the thick-ness above D85 was only 9 m.

Depositional environment and correlation

Vertical changes in the relative abundance of the first22 dominant ostracode taxa were arranged on the geolog-

Figure 7. Dendrogram of R-mode cluster analysis basedon the index of overlap (Horn, 1966). I, II, III, and IV are ostra-code bioassociations.


ical column (Figure 8).The lower part was mainly characterized by species of

bioassociation I, and species of bioassociation II wererarely found from samples 30 to 28. Therefore, the lowerpart was suggested to have been deposited in mild to cooltemperate waters in the upper to middle sublittoral zone.

The middle to upper part was characterized by anincrease in the relative abundance of species of bioasso-ciation II. Species of bioassociation I were abundant inthe middle part; however, they were relatively few insamples 9 to 7 in the upper part, which indicated a com-bination of higher mud content and smaller H(S), Eq.,and total number of ostracodes. Species of bioassociationII had large peaks in this interval. Several peaks of R.tabukii were found in samples 20, 16 to 14, 9 to 7, and5. A. dunelmensis was abundantly found in samples 10to 4 but was rare in other horizons. Thus, the middle toupper part was estimated to have been deposited in mildto cool temperate waters in the sublittoral to upperbathyal zone. In particular, sample horizons from 9 to 7in the upper part were assigned to the maximum waterdepth (upper bathyal zone). Sample 5 in the upper partshowed relatively high abundance of C. miurense and S.kishinouyei of bioassociation I, and A. dunelmensis andR. tabukii of bioassociation II. Therefore, this horizonwas characterized by a mixture of several taxa inhabiting

different water depths, suggesting that the depositionalenvironment was nearshore but deep.

The uppermost part (samples 4 to 1) was characterizedby a decrease in the species of bioassociation II and anincrease in the species of bioassociation I, suggesting adecrease in water depth upward. Neonesidea sp., a spe-cies of bioassociation IV, shows its maximum abun-dance. Thus, the depositional environment again becamethe shallowest sea.

The result of R-mode cluster analysis of ostracodeassemblages therefore indicated that the Kuwae Forma-tion in the Sakai section was deposited in the upper sub-littoral to upper bathyal zones with at least one cycle ofwater depth change.

Figure 9 shows the correlation between relative abun-dance of G. inflata (s.l.) and diatoms in the Tainai andSakai sections. In the Tainai section, Watanabe et al.(2003) proposed that nonmarine and reworked Miocenediatoms were transported by rivers from hinterland andthat the relative frequency of these diatoms was relatedto the amount of terrigenous clastic supply. In addition,they suggested that their cyclic fluctuations probably cor-relate with orbital obliquity cycles of approximately41 kyr because one cycle includes approximately severaltens of thousands years. Nonmarine and reworked Mio-cene diatoms in the Sakai and Tainai sections seem to

Figure 8. Vertical changes of percentages of ostracode species in each bioassociation (I, II, III, and IV) in the Sakai section.


indicate cyclic fluctuation. Thus, this cyclic fluctuationmay correlate with orbital obliquity cycles of approxi-mately 41 kyr (Figure 4).

Based on the diatom biostratigraphy in the presentstudy, we inferred that the interval yielding G. inflata(s.l.) between samples 15 and 5 can be correlated withany combination of zones 1 and 2 or zone 3 of the No.3 G. inflata bed shown by Miwa et al. (2004) in theTainai section (Figure 9). If the diatom biohorizon D85would be situated around sample 17, the latter case ismore reasonable than the former one. According toIrizuki et al. (2007), zone 3 of the No. 3 G. inflata bed

was inferred to have been assigned to MIS G19 (approx-imately 3.0 Ma).

Conclusions

1. In total, 36 sediment samples for microfossil analy-ses from the study section. Of these, five Rosselia sam-ples were collected only for diatom analysis.

2. The study interval is correlated to the N. koizumii–N. kamtschatica zone (NPD 8, 3.5–2.7 Ma), and at leastthe lower to middle part is placed below the rapidincrease of N. koizumii (D85, 3.1–3.0 Ma).

Figure 9. Diagram showing comparison between the Sakai and the Tainai sections on the basis of planktonic foraminifers and diatoms.D80 and D85 show diatom datums (Yanagisawa and Akiba, 1998).


3. The result of R-mode cluster analysis of fossil ostra-code assemblages indicates that the Kuwae Formation inthe Sakai section was deposited in the sublittoral to upperbathyal zone with at least one cycle of water depthchange.

4. Nonmarine and reworked Miocene diatoms in theSakai section indicated a cyclic fluctuation, perhaps thesignal of orbital obliquity cycles of approximately 41 kyr.

5. The horizon of occurrences of G. inflata (s.l.) can becorrelated with any combination of zones 1 and 2 or zone3 of the No. 3 G. inflata bed in the Tainai section.

Systematic description

by T. Goto and T. Irizuki

One species belonging to the genus Hemicythere is

newly described. All specimens used in this study aredeposited in the Department of Geoscience, Interdisci-plinary Graduate School of Science and Engineering,Shimane University (DGSU).

Order Podocopida Sars, 1866Suborder Cytherocopina Baird, 1850Superfamily Cytheroidea Baird, 1850

Family Hemicytheridae Puri, 1953Genus Hemicythere Sars, 1925 in Sars (1922–1928)

Hemicythere sakaiensis sp. nov.Figures 10, 1–5

Etymology.—After Sakai, which is the type locality ofthis species.

Types.—Holotype: female LV, DGSU no. CO0291

Figure 10. Scanning electron micrographs of Hemicythere sakaiensis sp. nov. 1a–d, holotype, female left valve, sample 31, DGSUno. CO0291; 1a, lateral view; 1b, internal view; 1c, closeup view of hingement; 1d, closeup view of muscle scars; 2a, b, paratype, femaleright valve, sample 31, DGSU no. CO0292; 2a, lateral view; 2b, internal view; 3a, b, paratype, male left valve, sample 26, DGSU no. CO0293;3a, lateral view; 3b, internal view; 4, paratype, (A 1 instar) left valve, sample 26, DGSU no. CO0294; 5, paratype, (A 1 instar) right valve,sample 26, DGSU no. CO0295.


(Figures 10, 1a–d). Paratypes: female RV, DGSU no.CO0292 (Figures 10, 2a–b); male LV, DGSU no.CO0293 (Figures 10, 3a–b); juvenile (A 1 instar) LV,DGSU no. CO0294 (Figure 10, 4); juvenile (A 1 instar)RV, DGSU no. CO0295 (Figure 10, 5).

Type locality and horizon.—The upper PlioceneKuwae Formation in the Sakai section, Tainai City,northern Niigata Prefecture, central Japan, sample 31.(Lat. 38°02 39 N, Long. 139°47 28 E)

Diagnosis.—Carapace large size, subrectangular andheavily calcified, nearly rounded anterior margin. Robustmarginal rim.

Measurements.—Length = 0.74 mm, height = 0.41 mm(holotype; female LV, DGSU no. CO0291): length =0.74 mm, height = 0.39 mm (paratype; female RV, DGSUno. CO0292): length = 0.70 mm, height = 0.37 mm (para-type; male LV, DGSU no. CO0293): length = 0.59 mm,height = 0.33 mm (paratype; juvenile LV, DGSU no.CO0294): length = 0.62 mm, height = 0.33 mm (para-type; juvenile RV, DGSU no. CO0295).

Description.—Valve moderate to large in size, subrect-angular in lateral view, and highest at anterior cardinalangle. Dorsal margin nearly straight in left valve. Ventralmargin straight. Anterior margin broadly rounded,slightly extended below. Posterior margin concave in itsupper half, and lower half protruding into a caudal pro-cess. Surface ornamented with reticulation except forposterior area, eye tubercle and subcentral tubercle.Robust marginal rim present in anterior. Ventral ridgedistinct, running along ventral margin. One robust ridgeprominent in the posterior area, starting from posterodor-sal corner, running obliquely downward, and connectingto ventral ridge at posterior one-third of valve length.Weak oblique ridge present in the anterocentral area,starting from mid-anterior margin and connecting to sub-central tubercle. Marginal infold broadly anteriorly andposteriorly. Hingement holamphidont with anteriorstepped subround socket, subround tooth, weak andfinely crenulated bar and curved elongate socket. Hinge-ment in right valve complementary. Frontal muscle scarsconsisting of two subround scars. Adductor muscle scarsconsisting of vertical row of four scars: upper three dis-tinctly subdivided and lower one elongate. Sexual dimor-phism not distinct but present. Males more slender thanfemales.

Occurrence.—This species was recorded in 24 sam-ples (2, 3, 5–8, 10, 12–16, 18, 20–24, 26–31) from theKuwae Formation in the Sakai section.

Remarks.—This species closely resembles and is prob-ably related to Caudites japonicus Ishizaki, 1971 fromAomori Bay, northeastern Japan, in the general outline ofthe valves, but differs from the latter in having a distinctoblique ridge in the posterior area. Hanai et al. (1977)

thought that C. japonicus belonged to the genusHermanites but with a question mark. Okubo (1979,1980) suggested that C. japonicus be placed in the genusAmbostracon. Caudites has three frontal scars and aninner lamella with a peculiar secondary fusion (vanMorkhoven, 1963). Hermanites has probably V-shapedor crescent frontal scars (van Morkhoven, 1963). Hazel(1962) established the genus Ambostracon but he couldnot describe frontal scars. Valicenti (1977) mentionedthat Ambostracon has three frontal scars. As C. japonicusof Ishizaki (1971) and the present new species have twofrontal scars, they are not placed in the genera mentionedabove. On the basis of the number of frontal scars andother features of the carapace, the new species and C.japonicus are possibly assignable to the genus Hemi-cythere.

Acknowledgments

We are grateful to Katsura Yamada (Shinshu Univer-sity) for her advice and discussions. Our thanks are alsoextended to Yuki Najima for his helping our planktonicforaminiferal analysis. We thank Den-ichi Nakamura forpermission to collect samples even though private prop-erty. We also thank Thomas M. Cronin and an anony-mous reviewer who provided constructive comments toimprove the manuscript. This study was partly supportedby a Grant–in Aid for Scientific Research (C) from theMinistry of Education (No. 22540476 to T. Irizuki).

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Appendix 1. Occurrence list of fossil diatoms from the Kuwae Formation in the Sakai section. Species with asterisks indicate reworkedMiocene diatoms. Sample numbers with “R” are Rosselia samples.

Sample number 1 2R 2 3 4 5 6 7 8R 8 9 10 11 12 13 14 15 16 17 18 18R 19 20 21 22 23 23R 24 25 26 27 28R 28 29 30 31

Abundance(number of scanned lines) 9.8 3.5 9.7 4.2 4.5 4.2 6.8 19.5 6 11.1 8.9 6.8 2.7 5.7 10.8 10.5 6.9 9.8 4.2 2.5 4.5 6.7 5.8 5 4.9 10.1 3.3 6.9 9.2 12.2 12.8 6.2 2.5 14.6 9.7 8.2

Marine diatoms* Actinocyclus ellipticus

Grunow1 2

* A. ingens f. ingens (Rattray)Whiting et Schrader

6 6 10 2 5 1 4 2 2 2 + 3 1 2 3 2 1 2 3 1 1 6 4 2 5 3 6 5 4 1 3 3 2

* A. ingens f. nodus (Baldauf)Whiting et Schrader

1

* A. ingens f. planus Whiting etSchrader

1 1

A. octonarius Ehr. + 1 1 1 1 1 1 1 1 1 1 1 +A. sp. A 1 2 2 1 1 1 1 1 1 1 2Actinoptychus senarius(Ehr.) Ehr.

1 1 3 + 1 1 1 + 3 2 3 2 + 5 3 4 2 2 1 3 2 1 1 6 3 3 4

Arachnoidiscus sp. 1 1Auliscus sp. +

* Azpeitia endoi (Kanaya)P. A. Sims et G. A. Fryxell

1 1 1 + 1 + 1 1 1 2 1 +

A. nodulifera (A. W. F.Schmidt) G. A. Fryxellet P. A. Sims

1 2 2 1 2 2 1 3 2 1 3 1 1 + 1 + 1 1 2 2 1 2

Bacillaria sp. + 1 1 + +* Cavitatus jouseanus

(Sheshukova) D. M. Williams+ + + + +

* C. miocenicus (Schrader)Akiba et Yanagisawa

+ 1 + + 1 + + +

Cocconeis spp. 2 3 1 4 3 2 3 + 9 2 1 1 1 10 6 5 2 2 1 2 2Coscinodiscus marginatusEhr.

3 3 7 1 5 1 1 6 4 9 5 4 2 5 3 4 3 11 + + 1 2 8 1 3 1 1 4 5 3

C. radiatus Ehr. 1 1Delphineis angustata (Pant.)G. W. Andrews

+

D. surirella (Ehr.) G. W.Andrews

1 1

* Denticulopsis lauta (Bailey)Simonsen

1

* D. hyalina (Schrader)Simonsen

+

* D. dimorpha var. dimorpha(Schrader) Simonsen

+

* (Closed copula) + + 1* D. praedimorpha var. minor

Yanagisawa et Akiba1 + + + 1 1

* (Closed copula) 2 1 1 1 1 1 +* D. praedimorpha var.

praedimorpha Barronex Akiba

+ 1 1 + + +

* (Closed copula) 1 1 + 1 1 1 2 1 1* D. praedimorpha var. robusta

Yanagisawa et Akiba* (Closed copula) 1* D. simonsenii Yanagisawa

et Akiba+ 2 1 1 + + + + + 1 + + 1 + 1 1 1 1 1 + 1 1

* D. vulgaris (Okuno)Yanagisawa et Akiba

1 + + 1 1 + + + 1 1 1 1 1 1 + + 1 + + 2 + + +

* D. katayamae Maruyama + 1 + +


Appendix 1. Continued.

Sample number 1 2R 2 3 4 5 6 7 8R 8 9 10 11 12 13 14 15 16 17 18 18R 19 20 21 22 23 23R 24 25 26 27 28R 28 29 30 31

Abundance(number of scanned lines) 9.8 3.5 9.7 4.2 4.5 4.2 6.8 19.5 6 11.1 8.9 6.8 2.7 5.7 10.8 10.5 6.9 9.8 4.2 2.5 4.5 6.7 5.8 5 4.9 10.1 3.3 6.9 9.2 12.2 12.8 6.2 2.5 14.6 9.7 8.2

* S-type girdle view ofD. simonsenii group

+ 2 1 + 1 + 1 1 1 1 1

Diploneis spp. 1 2 1 1 + 2 + 1 2 3 1 1 2Grammatophora spp. + + + + + + 1 + + + + + 1 + + + + + + + 1 + + +Hyalodiscus obsoletusSheshukova

1 + 1 +

* Ikebea tenuis (Brun) Akiba 1 1 +Neodenticula kamtschatica(Zabelina) Akiba etYanagisawa

+ + 1 11 19 3 2 8 16 + 1 1 +

N. koizumii Akiba etYanagisawa

1 1 1 + 1 3 4 3 1 + 5 + +

Nitzschia cf. extinctaKozurenko et Sheshukova

+ 1 +

* N. heteropolica Schrader 1Paralia sulcata (Ehr.) Cleve 4 2 9 4 1 18 5 2 11 3 11 12 5 2 3 3 4 8 3 11 4 12 17 8 6 4 2 21 6 2 2 3Proboscia alata (Brightw.)Sundstöm

1 + 1

P. barboi (Brun) Jordanet Priddle

2 3 1 1 1 3 2 3 + 1 3 1 2 3 3 1 1 +

* Pseudodimerogrammaelliptica Schrader

+

Rhaphoneis amphiceros Ehr. 1Rhizosolenia hebetata f.hiemalis Gran

2 1 + 1 1 1 1 2 1 1

* R. miocenica Schrader 1 1 1R. styliformis Brightw. 1 3 1 1 1 1Rouxia californica Perag. + + + + + + + +Shionodiscus oestrupii(Ostenf.) Proshk.-Labr.

1 1 2 + 1 1

Stellarima microtrias (Ehr.)Hasle et P. A. Sims

1 1 1 1 1

* Stephanogonia hanzawaeKanaya

1 1 1 1 1 +

Stephanopyxis spp. 6 3 4 4 1 1 2 3 3 3 4 16 4 1 1 3 1 5 2 9 1 6 6 1 5 9 3 5 1 2 12 + 5 4 3* Thalassionema hirosakiensis

(Kanaya) Schrader8 2 + 1 2 1 + 1 1 1 1 1 2 3 1 + + 2 + + 2 2 2

T. nitzschioides (Grunow)H. Perag. et Perag.

43 23 23 26 19 16 6 7 13 6 13 14 12 20 20 27 41 27 14 10 25 23 13 16 16 17 13 16 17 13 14 23 3 18 21 20

* T. schraderi Akiba +Thalassiosira antiqua(Grunow) Cleve-Euler

1 1 + 1 2

T. convexa var. aspinosaSchrader

2 4 4 2 + 1 1 2 5 1 + 2

* T. grunowii Akiba etYanagisawa

1 1 1

* T. cf. temperei (Brun)Akiba et Yanagisawa

+

T. spp. 1 1 4 1 1Thalassiothrix longissimaCleve et Grunow

+ +

* Triceratium condecorumBrightw.

1

Non-marine diatomsActinocyclus? sp. 1 1 1Aulacoseira spp. 24 7 16 9 10 22 14 17 3 6 9 6 3 1 7 3 2 + 1 4 5 5 6 2 8 2 9 9 14 26 9 2Cyclotella spp. 2 1 2 2 1 2 1 1 +Discostella spp. 1Mesodyction spp. 1 1Pliocaenicus spp. 1 1 1 + 1 1 1 5 9 6 1 2 +Stephanodiscus spp. 1 1 1 1 2 2 1 1Amphora sp. spp.Epithemia sp. 1 + 1Eunotia sp. + 1 1Navicula spp. 1 1Synedra sp. 1Total number of valvescounted

100 50 100 50 50 50 50 50 30 50 50 50 50 50 50 50 50 50 50 50 100 50 50 50 50 50 100 50 50 50 50 100 50 50 50 50

Resting spore of Chaetoceros 8 19 18 8 8 6 11 5 2 6 10 8 5 20 9 10 27 14 22 14 30 10 23 13 19 7 68 14 12 8 12 12 1 9 10 21


Appendix 2. Occurrence list of fossil ostracodes from the Kuwae Formation in the Sakai section.

sample No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Acanthocythereisdunelmensis(Norman)

9 15 9 18 17 21 8 4 2 3 2 6 8 3 4 4 2 3 1 1 2 2 4 3

AcanthocythereistsurugasakensisTabuki

1 1 2

Acanthocythereis spp. 2 4 1 2 3 1

Amphileberis sp. 1

Argilloecia hanaiiIshizaki

1

Aurila cf. corniculataOkubo

3 4 1 1 8 2 3 2 1 3 4 2 2 6 1 3 3

Aurila cf. hataiiIshizaki

1 3 3 4 5 3 4 4

Aurila tsukawakiiOzawa and Kamiya

1 10 9 5 2 1 2 6 9 4 7 4 1 3 9 5 2 1 5 2 9 10 13 3 8 4 1 3 4

Aurila spp. 4 1 1 2 1 1 3 2 4 1 1 2 1 2 1 6 1 1

Baffinicythereishizakii Irizuki

2

BaffinicytherereticulataIrizuki

15 1 3 3 1 2 1 1 1 1 1 7 7 2 9 4 4 1 3 1 4 1

BaffinicythererobusticostataIrizuki

4 1 1 3 3 2 1 1

Baffinicythere spp. 3 4 1 1 3 4 2 4 1

Bicornucythere sp. 1

Buntonia sp. 1

Callistocythere cf.japonica Hanai

1

CallistocythereundulatifacialisHanai

1

Callistocythere cf.undulatifacialisHanai

2 1 5 3 1 7 4 2 1 4 4 3 5 2 2 5 7 4 1 3 7 3

Callistocythere aff.undulatifacialis Hanai

1

Callistocythere sp. 1 1

Callistocythere sp. 2 1 1 1 1 2 1 1 1 4

Callistocythere sp. 3 1 1 1 1

Callistocythere spp. 1 2 1 1 1 1 1

ChejudocytherehigashikawaiIshizaki

1 1

Cletocythereisrastromarginata(Brady)

1 2 1 1 1 1 1

Cletocythereis sp. 1

Cluthia sp. 2 1 1 1 1 2 1 6 1 2 1 1 2 1 1 2 1 1

Coquimba sp. 1 1 2

Cornucoquimbamoniwensis (Ishizaki)

8 5 4 7 6 11 6 12 17 9 10 14 13 15 7 8 1 9 6 3 9 4 4 8 7 4 14 11 3 4

Cornucoquimba cf.moniwensis(Ishizaki)

3

Cornucoquimba cf.tosaensis (Ishizaki)

1 3 5 3 2 5 4 3 2 6 5 7 1 2 8 7 1 7 7 5 6 10 4 3 3 3 1 5 7

Cornucoquimba sp. 4 5 2 5 7 3 14 8 4 3 6 5 2 2 7 5 4 2 4 8 5 2 2

Cornucoquimba spp. 1 1 4 2 4 2 1 1 1 2 1 4 1 2

Cythere sp. 1 4 14 12 3 4 9 9 19 15 19 12 12 18 12 23 27 13 18 14 14 19 11 13 15 10 12 13 11 18 9 14

Cythere sp. 2 2 14 5 3 14 15 11 8 11 1 7 12 6 9 5 6 3 2 5 3 2 2 2 3 2 3 3 3

Cythere spp. 3 1

Cytherelloidea sp. 1

Cytheromorpha sp. 1 1

Cytheropteroncarolae Brouwers

1 6 13 12 14 7 3 3 3 5 5 5 1 4 2 4 1 2 4 2 1

Cytheropteron aff.carolae Brouwers

2 1

Cytheropteronmiurense Hanai

6 12 7 8 17 10 3 4 8 6 7 4 5 11 12 9 9 13 5 9 12 12 11 2 6 9 5 9 1 9 9

Cytheropteron aff.miurense Hanai

2 3

Cytheropteronsawanense Hanai

11 11 20 9 5 6 1 5 9 6 4 6 11 5 12 11 4 8 8 10 10 15 15 11 12 4 13 5 13 7

Cytheropteronsubuchioi Zhao

1

Cytheropteron aff.subuchioi Zhao

2 2 1 5 2 4 1 7 1 5 1 2 2 1 1 8 1



sample No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Cytheropteronyajimai Tabuki

1 1 1 2 3 1 3

Cytheropteron spp. 1 1 1 2 3 1 1 1 1 1 1 1 2 1 1

Cytherura? sp. 1 26 9 8 7 5 3 3 4 2 2 1 1 5 4 4 1 1 2 2 4 2 6 2

Cytherura? sp. 2 15 1 7 2 1 4 4 3 8 5 6 5 5 4 8 5 7 1 5 8 10 7 3 4 5 3 10 5 1

Cytherura? sp. 3 1 3 4 2 1 3 1 7 3 1 1 1 6 1 1 2 3 5 1

Cytherura? sp. 4 10 1 1 1 1 2

Elofsonella spp. 1 1 2 3 1

Eucytheruraneoalae (Ishizaki)

2 3 4 1 1 2 2 1 1 2 1 2 2 1 1 2 4 5 1 1 4 2

Eucytherura sp. 1 2 1 2 1 4 3

Eucytherura sp. 2 1 1 3 5 1 1 3

Eucytherura sp. 3 2

Eucytherura sp. 4 2

Eucytherura spp. 1 1 1 1 2 1 5 1

Falsobuntoniahayamii (Tabuki)

4

Falsobuntonia spp. 1 3 3 1 1 1 3 2 1 2 2 1 4 2 1 1 1 1 1

Finmarchinellahanaii Okada

6 3 4 15 4 3 1 2 2 4 9 5 8 6 11 12 6 6 11 4 7 5 13 19 11 8 6 5 8 7 6

Finmarchinella cf.japonica (Ishizaki)

2 12 12 9 9 3 3 1 5 6 6 9 14 10 8 12 12 7 5 11 3 5 12 10 12 6 7 6 5 8 12

Finmarchinella cf.uranipponicaIshizaki

2 1

Hanaiborchellamiurensis (Hanai)

5 3 2 3 2 1 1 1 1 1 1 1 1 1 3 1 1 3 2 1 1 1

Hanaiborchellatriangularis (Hanai)

2 1 1 3 1 1 2 1 1 1 3 1 1 1 2

Hemicytherekitanipponica(Tabuki)

7 4 5 2 4 4 4 1 3 5 2 3 6 3 6 3 4 4 4 2 4 2 1 2 5 3

Hemicythere aff.kitanipponica(Tabuki)

1 2 1 1 2 5 1

HemicythereorientalisSchornikov

1 1 2

Hemicythererobusta sp. nov.

2 2 2 3 1 3 7 3 5 1 2 1 4 7 3 1 4 4 9 2 4 2 4 3

Hemicythere sp. 1 2

Hemicythere sp. 2 1 1 2 2 1

Hemicythere spp. 1 1 1 1 1 1

Hemicytherura cf.cuneata Hanai

4 1 2 2 1 3 1 1 1 9 5 8 5 5 6 3 2 2

Hemicytherura cf.kajiyamai Hanai

2 3 3 2 2 5 2 1 3 2

Hemicytherura sp. 1 1 2 2 1 1

Howeina cf.higashimeyaensisIshizaki

1 1 1

Howeina aff.higashimeyaensisIshizaki

1

Howeinaneoleptocytheroidea(Ishizaki)

3 3 1

Howeina spp. 1

Kangarina sp. 1 2 2 1 4 2 2 1 2 5 4 1 1 2 2 1 1 2 5 4 3 3 4

Krithe spp. 1 2 11 3 1 2 4 9 1 3 12 7 4 7 1 2 1 1

Kotoracythere sp. 1 4 5 1 4 1 1 3 2 4 4 1 1 1 2 1

Laperousecytherecronini Irizukiand Yamada

1

Laperousecythere cf.cronini Irizukiand Yamada

1

Laperousecytheresasaokensis (Irizuki)

1 1 1 1 1 4 3 1 1 4 3 1 3

Laperousecytheresp. 1

3 2 1 1 1 2 1 2 3 4 2 1 2 2 1 1 2


2 1 3


1 1 1 1 2

Laperousecytherespp.

1 1 2 1 1

Loxoconchaepeterseni Ishizaki

2 1 1 1 1



sample No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Loxoconchakamiyai Ozawa

1 2 2 2 1 1 1 2 1 1 3 3 4 1 1

LoxoconchasubkotoraformaIshizaki

4 4 6 2 5 7 11 9 4 8 9 3 11 9 7 5 8 5 5 7 8 5 6 9 7 2 5 7 6 4 3

Loxoconcha aff.subkotoraformaIshizaki

3 1 1 1 2 1 1

LoxoconchauranouchiensisIshizaki

1

Loxoconcha vivaIshizaki

1 1 1 1 1

Loxoconcha sp. 1

Loxoconcha spp. 1 1 1 1 1

LoxocorniculumkotoraformumIshizaki

2 1 1 4 2 1 1 3 3 2 4 2 1 1 1

Loxocorniculummutsuense Ishizaki

2

Microcythere sp. 1 1 1

Munseyella cf.chinzeii Zhou

2 1 2 2 3 3 5 2 6 1 5 2 2 1 3 2 1 1 2

Munseyella aff.chinzeii Zhou

2

Munseyellahatatatensis Ishizaki

5 2 1 1 1 1 1 3 2 1 2 1 2 3 2 4 1 1 1

Munseyellahokkaidoana (Hanai)

1 1 1 1 2 1 2 2 4 5 2 2 1 1 2

Munseyella cf.hokkaidoana (Hanai)

1

Munseyellajaponica (Hanai)

2 1 1 1 1 1 1

Munseyella aff.japonica (Hanai)

1

Neomonoceratinatsurugasakensis(Tabuki)

3 1 1 2 1

Neonesidea sp. 13 10 8 5 2 5 1 1 4 3 2 1 1 1 4 1 2 5 5 2 6 4

Nipponocytherebicarinata (Brady)

1

Normanicytherejaponica Tabuki

1 1 2 1 1 1 1 1 1 2

Pacambocythere sp. 1 2 1 2 2 1 2

Paijenborchellahanaii Tabuki

1 1 2 1 1 1 1 1 1 4 2 1 1 3

Paijenborchella spp. 1

Palmenellalimicola (Norman)

6 1 2 2 4 2 1 1 1 1 3 1 1 1 1 2

Palmoconcha sp. 1 1 3 1 4 1 2 4 1

Palmoconcha sp. 2 1

Paracypris sp. 1

Paracytherideaechinata Hu

3 1

Paracytheridea spp. 3 4 1 1 4 2 2 5 1 2 3 2 2 2 3 1 2 1 1

Paradoxostoma sp. 2

Parakrithella aff.pseudadonta (Hanai)

2 1

Parakrithella sp. 1 2 1 4 3 3 2

Patagonacythere sp. 1

PectocytheredaishakaensisTabuki

4 3 2 3 1 1 2 1 1 1 2

Pectocythere sp. 2 2 1 3 1 2 3 2 1 1 2 3 1 1 4 1 8 2

Pontocytheresubjaponica (Hanai)

1 1 1 1 1 1

Pontocythere sp. 1

Pontocythere spp. 1 1 2 1 5 2 2 2 1 2 1 2 3 1 3 1 2 3 1 1 1

Propontocypris sp. 1 2

Robertsoniteshanaii Tabuki

6 1 1

Robertsonitesirizukii Yamada

1 1 1 2 1 3

Robertsonitestabukii Yamada

5 7 1 11 3 24 14 19 9 2 4 7 11 5 14 2 12 5 2 4 4 3

Robertsonites sp. 1 1 1 1

Robustaurila sp. 1

Robustaurila spp. 1 1 3 2 2 1 1 1



sample No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Schizocytherekishinouyei(Kajiyama)

4 8 10 15 26 14 7 4 5 8 10 13 19 11 7 14 11 6 5 2 12 6 16 17 25 10 12 10 7 8 10

Sclerochilus sp. 1

Semicytherurakazahana Yamada

5 4 4 1 3 4 4 3 3 2 1 5 4 2 6 4 11 5 5 8 4 9 4 5 5

SemicytherurasubslipperiOzawa and Kamiya

9 8 2 2 2 2 4 3 5 3 5 2 1 3 5 6 2 5 8 5 13 7 6 4 2 5 2 2

Semicytherurasubundata (Hanai)

4 2 3 4 1 2 2 2 1 6 4 2 2 2

Semicytherura cf.subundata (Hanai)

2 2

Semicytherura sp. 1 16 6 11 7 2 1 1 5 7 5 2 3 4 4 4 4 8 2 4 13 6 12 12 12 8 8 2 8 9 7

Semicytherura sp. 2 2 3 1 1 2 1 1 1 1 1 4 3 3 3

Semicytherura sp. 3 1 1 1 1 1 1 1 1 1 3 1 1 1 2 1

Semicytherura sp. 4 1 1 1 1 1 3 1 1

Semicytherura sp. 5 1 1 1 1 1

Semicytherura sp. 6 1 1 1 3 2 2

Semicytherura sp. 7 1 3 2 1 1 1 1

Semicytherura sp. 8 1 2 2 1

Semicytherura spp. 1 1 2 1 1 1 1 1 2 2 1 2 1 1

Spinilebelis sp. 1

Sagmatocythere sp. 1 3 3 1 1 1 2 2 1 4 1 3

Sagmatocythere sp. 2 1

Trachyleberisscabrocuneata(Brady)

1

Trachyleberis cf.scabrocuneata(Brady)

2 2 1

Trachyleberis spp. 1 2 1 1 1 2 1 1

Typhlocythere sp. 1 1 3 1 4 1 1 1 1 1 1 1 2 4 1 2 1 1

Urocythereis?gorokuensis Ishizaki

1

Urocythereis? sp. 1 1 2 3 1 2 1 1 4 1 3 5 3 1 8 9 3 1 4 3 2 4 1 5

Urocythereis? sp. 2 2 1 1 4 5

Urocythereis? sp. 3 1

Urocythereis? sp. 4 3 2 1 3

Urocythereis? sp. 5 1 1

Xestoleberis hanaiiIshizaki

2 1 1 2 3 5 2 1 1 1 3

XestoleberisopalescentaSchornikov

1 1

XestoleberissagamiensisKajiyama

1

Xestoleberissetouchiensis Okubo

1 1 1 2 2 1

Xestoleberis cf.setouchiensis Okubo

1

Xestoleberis spp. 1 2 1 1 1

Gen. et sp. indet 1

No. of species 43 55 63 54 53 60 43 48 51 55 58 51 61 49 54 50 45 49 45 51 59 53 63 57 50 50 62 62 58 54 54

No. of specimens 196 213 239 175 190 193 173 193 221 213 183 181 245 170 195 225 170 188 162 155 212 179 256 250 213 177 188 193 189 175 165

Mud contents 62.91 65.49 50.34 47.08 63.45 70.34 71.03 71.03 74.89 65.75 46.95 39.93 54.74 59.83 67.78 44.09 45.19 39.79 36.56 33.86 39.16 36.71 31.55 34.88 34.30 34.44 36.10 40.79 38.56 42.33 42.00

Total ostracodes (/g) 13.1 85.2 63.7 70.0 76.0 51.5 13.8 25.7 88.4 113.6 97.6 144.8 131.2 136.0 78.0 30.0 4.3 75.2 64.8 49.6 56.5 71.6 51.2 50.0 28.4 141.6 100.3 102.9 50.4 93.3 88.0

Diversity 3.30 3.62 3.75 3.61 3.44 3.71 3.24 3.44 3.45 3.65 3.75 3.63 3.68 3.47 3.55 3.50 3.48 3.53 3.55 3.57 3.67 3.66 3.74 3.63 3.49 3.59 3.86 3.77 3.67 3.70 3.64

Equitability 0.63 0.68 0.68 0.69 0.59 0.68 0.59 0.65 0.61 0.70 0.73 0.74 0.64 0.66 0.65 0.65 0.72 0.70 0.77 0.70 0.66 0.74 0.67 0.66 0.66 0.73 0.76 0.68 0.68 0.75 0.71

formation, northeast japan microfossil biostratigraphy and … · 2017-02-07 · abstract....

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