16. Radiolarians from Sites 794, 795, 796, and 797 (Japan Sea)

Pisciotto, K. A., Ingle, J. C , Jr., von Breymann, M. T, Barron, J., et al., 1992Proceedings of the Ocean Drilling Program, Scientific Results, Vol. 127/128, Pt. 1

16. RADIOLARIANS FROM SITES 794, 795, 796, AND 797 (JAPAN SEA)1

Joanne M. Alexandrovich2

ABSTRACT

Japan Sea ODP Leg 127 shipboard radiolarian biostratigraphic data are compiled and improved. The sequence of biostrati-graphic events determined in sediments above the opal-A/opal-CT transition is illustrated graphically with depth-depth plots.The absence of biostratigraphic indicators from the North and subtropical Pacific and differences between the compositions ofthe Japan Sea and Pacific radiolarian assemblages suggest that the planktonic populations of the Japan Sea have been partiallyisolated from the Pacific since the late Miocene. Subtropical fauna in sediments younger than ~1.8 Ma at Site 797 record theoccurrence of a paleo-Tsushima current. These same fauna record larger volumes of the paleo-Tsushima current, or warmerintervals during the colder glacial climate regime at Site 794. The variability of Pleistocene assemblage composition andpreservation shows that radiolarian dissolution has played a large part in determining what is preserved. Preliminary taxonomicevaluations are made, and the stratigraphic and paleoceanographic implications of radiolarian species are discussed.

INTRODUCTION

Previous studies of Japan Sea radiolarian paleontology were lim-ited to samples obtained with piston cores which span the last severalhundreds to thousands of years (e.g., Morley et al., 1986; Oba et al,1991), Miocene through Pleistocene sediments cored at four sitesduring Leg 31 of the Deep Sea Drilling Project (DSDP) (Ling, 1975),and Miocene and Pliocene deposits found on Japan (e.g., Nakasekoet al., 1965; Nakaseko, 1969). Piston cores from the Japan Sea containstratigraphic sections that can be sampled at a rather high stratigraphicresolution, and Japan Sea Leg 31 cores contain relatively long records,but display sediment disturbances due to drilling problems (Karig,Ingle, et al., 1975). One of the principal objectives of Ocean DrillingProgram (ODP) Japan Sea Leg 127 was to use the coring techniquesof the advanced hydraulic piston corer (APC) and extended corebarrel (XCB) to recover more complete stratigraphic sections thatimprove upon the recovery rates of DSDP Leg 31 sediments forpaleontological and paleoceanographic study (Tamaki, Pisciotto, Al-lan, et al., 1990). Indeed, the sedimentary sections obtained duringLeg 127, contain the longest, most continuous, records of radiolarianpaleontology from the Japan Sea.

Radiolarians are found in sediment samples from Leg 127 sitesthat are as old as middle Miocene in age (Tamaki, Pisciotto, Allan, etal., 1990). The radiolarian assemblages in these samples display widevariability in both abundance and preservation. Younger (Pleistocene)assemblages show the highest variability in both preservation andabundance. Many Pleistocene samples are barren, and the dominanttaxa in the assemblages from these samples change dramatically. Theoldest radiolarians are found in sediments where opal-CT comprisesthe dominant siliceous phase and where diatoms are no longer pre-served except in dolomitic nodules. Radiolarians are not found insediments below the level of the diagenetic change from opal-CT toquartz. Radiolarians found in opal-CT sediments are not very abun-dant and rather poorly preserved, but were not completely obliteratedfrom the opal-CT sediments because certain taxa dissolved relativelyslowly and became coated and preserved by opal-CT precipitates. Thedetails of radiolarian preservation within the opal-CT sediments fromJapan Sea Leg 127 sites await further investigation.

' Pisciotto, K. A., Ingle, J. C , Jr., von Breymann, M. T., Barron, J., et al., 1992. Proc.ODP, Sci. Results, 127/128, Pt. 1: College Station, TX (Ocean Drilling Program).

Department of Geological Sciences, Columbia University and Lamont-DohertyGeological Observatory, Palisades, NY 10964, U.S.A. (Present address: Department ofGeology, Florida Atlantic University, Boca Raton, FL 33431, U.S.A.)

The intent of this study is to document radiolarian biostratigraphyand differences in assemblages among samples from the sedimentsof the Leg 127 Japan Sea sites in order to determine the sequence ofradiolarian biostratigraphic events recorded in the cores and thepaleoceanographic significance of assemblages with respect to thegeologic history of the basin. Questions that concern how radiolarianassemblages reflect changes in sill depths, sources of nutrients, sur-face- and deep-water circulation, and the degree of isolation of theJapan Sea from the Pacific are addressed. Because distinctive preser-vational differences are observed among samples, these aspects of theradiolarian assemblages are examined in detail. Although there havebeen several thorough taxonomic studies of Japan Sea radiolarians,the taxonomy of Japan Sea radiolarians is still rather limited withrespect to the diversity displayed by the Leg 127 assemblages. There-fore while summarizing the radiolarian paleontology and stratigraphyoutlined in the Leg 127 shipboard reports (Tamaki, Pisciotto, Allan,et al., 1990), preliminary taxonomic evaluations are made on somedominant taxa and known stratigraphic indicators of Japan.

SAMPLE PREPARATION AND DATA COLLECTION

Samples were taken from Holes 794,795, and 797 during Leg 127for radiolarian paleontological analysis. The 10-cm3 sample plugstaken from sediments above the opal-A/opal-CT transition were driedand weighed. They were subjected to treatment with 10% hydrogenperoxide, and if calcium carbonate material was present in the sam-ples, with HC1. Sodium pyrophosphate was added to the samples,which were then washed several times over a 63-µm sieve. Residuesof the sample-washing procedure were then settled onto glass slidesusing the standard technique of Moore (1973), and after drying underheat lamps, cover slips (24 × 50 mm) were mounted to the slides usingseveral drops of Canada Balsam. Slides were cured by heating on ahotplate. Although contamination of Leg 127 radiolarian samples bythe frustules of large diatoms was obvious and troublesome duringthe slide-making procedure, samples were not treated with sodiumcarbonate or sodium hydroxide to break down and wash out thediatoms because this sample preparation step would probably alterthe preservation of radiolarians in these samples as well.

Because of several complicating factors including limited time andthe aggravating occurrence of Coscinodiscus marginatus in radiolarianslides made from samples stratigraphically below the opal dissolutiontransition zone (White and Alexandrovich, this volume), complete strat-igraphic analyses that include total slide scans and tabulations of allimportant and identifiable radiolarian species were not performed for thisstudy. Therefore, the stratigraphy presented here (Table 1) represents a

291

J. M. ALEXANDROVICH

summation of the stratigraphy presented in the Leg 127 Initial Reports(Tamaki, Pisciotto, Allan, et al., 1990), with some additional refinementof events. The refinement consists of a reduced sample-spacing uncer-tainty for several datum levels. This was accomplished by using Leg 127shipboard radiolarian stratigraphy to identify the interval (core) wherethe stratigraphic event was found. Samples from that core were thenscanned for the presence or absence of the indicator species, and therefined datum level is recorded in Table 1. Entire radiolarian slides fromsamples located stratigraphically above the opal dissolution transitionzone (White and Alexandrovich, this volume) were scanned in order toobserve preservational differences. Abundance and preservation in thesesamples are recorded (Tables 2, 3, and 4) following preservation andabundance guidelines outlined in the radiolarian section of the "Explana-tory Notes" of Tamaki, Pisciotto, Allan, et al. (1990, p. 49). During slidescanning, the occurrence of distinctive features of the assemblages orspecimens were observed. Samples from Hole 794Athat contain warm-water assemblages are tabulated in Table 5. Radiolarian species areidentified using previously established names and descriptions, and allradiolarian species discussed in this report are listed in the Appendix, withseveral important stratigraphic, preservation, and paleoceanographic in-dicators illustrated in the plates.

Because many opaline sponge spicules are larger than 63 µm, theyare commonly observed in samples prepared for radiolarian paleon-tological analysis. Sponge spicules are quite abundant in samplesprepared from Leg 127 sediments, and are also indicative of thedegree of dissolution certain radiolarian assemblages have been sub-

jected to (Alexandrovich and White, this volume). There is one typeof opaline sponge spicule from Japan Sea Leg 127 sediments whichis noteworthy in this report on radiolarians. Sterraster sponge spicules(PI. 1, Figs. 1, 2, and 3) are quite common in Leg 127 Japan Seasediments and in radiolarian samples. This type of sponge spicule wasobserved in radiolarian samples analyzed during Leg 127, but waslargely ignored because it is not a radiolarian and represented aseemingly unimportant unknown. In several instances, however, thismicrofossil was found concentrated in sediments that were termed"bioclastic oozes" by the Leg 127 sedimentologists, but the bioclastscould not be positively identified during Leg 127. The "bioclast"microfossil is positively identified here as a long-ranging (back to atleast the Jurassic) sterraster sponge spicule belonging to the familyGeodiidae, which has a broad latitudinal distribution and can be foundin a variety of water depths (R. M. Finks, pers. comm., 1991). Becausesterraster sponge spicules that are greater than 63 µm are somewhatcommon in radiolarian samples, this sponge spicule has been errone-ously identified and classified as a radiolarian by several workers(Spumellina incertae sedis Form A and B by Benson, 1966; Hatainaovata by Huang, 1967).

RADIOLARIAN PRESERVATION

Records of the preservation of Leg 127 Japan Sea radiolarianassemblages are very variable, reflecting several conditions of sedi-ment deposition and sediment diagenesis. For this reason, the material

Table 1. Radiolarian biostratigraphy of Leg 127 sites by ODP sample designation and depth (m below seafloor). LO and FO refer to the last-occurrenceand first-occurrence datum levels of the species, respectively. Depth interval is caused by sample spacing.

FO L. sp. cf. L. grande

LO C. cabrilloensis

LO S. robusta

LO D. acquilonius

FO D. acquilonius

LO L. sp. aff. T. redondoensis

F0 T. davisiana

LO T. japonica

FO S. langii

LO S. sp. cf. S. acquilonarium

LO T. akitaensis

FO T. akitaensis

FO L. sp. aff. T. redondoensis

LO B. bramlettei

LO S. peregrina

LO T. redondoensis

LO 5. japonica

FO T. iµponica

LO L. nipponicum

LO S. delmontensis

LO T. anthopora

LO T. mammillaris

LO S. wolfii

LO L. tochigiensis

LO C. telrapera

Hole 794A

1H-4,60-62-1H-5,44-575.1-6.553H-6,60-62-3H-CC24.4-25.84H-6,59-62-4H-CC33.89-35.35H-4,59-61-5H-5,58-6040.39-41.88

7H-CC-8H-CC63.8-73.38H-CC-9H-CC73.3-82.89H-3,59-61-9H-4,59-6176.89-78.3910H-CC-11H-CC92.3-101.810H-CC-11H-CC92.3-101.8

15H-CC-16X-CC139.8-149.510H-CC-11H-CC92.3-101.812H-CC-13H-CC111.3-120.818X-CC-19X-1,60-62168.5-169.118X-CC-19X-1,60-62168.5-169.120X-CC-21X-CC187.9-197.520X-CC-21X-CC187.9-197.53821X-CC-22X-CC197.5-207.225X-CC-26X-CC236.2-24626X-CC-27X-CC246-255.727X-CC-28X-CC255.7-265.428X-1,60-62-28X-2,60-62256.3-257.8

Hole 794B

5R-CC-6R-CC338.3-347.8

Hole 795A

2H-CC-3H-CC18.8-28.34H-CC-5H-CC37.8-47.312H-4, 70-72-12H-5, 70-72109.5-11110H-CC-11H-CC94.8-104.3

17H-CC-18H-CC151.9-162.416H-4,74-76-16H-CC147.54-151.811H-CC-12H-CC104.3-113.819H-CC-20X-CC171.9-181.615H-CC-16H-CC142.3-151.816H-CC-17H-CC151.8-151.930X-CC-31X-CC279.1-288.834X-CC-35X-CC317.6-327.2

38X-CC-39X-CC356.2-365.935X-CC-36X-CC327.2-336.9

Hole 795B

2R-CC-3R-CC384.7-394.4

7R-CC-8R-CC432.8-442.47R-CC-8R-CC432.8^t42.4

7R-CC-8R-CC432.8^42.4

Hole 796A

1H-CC-2H-CC3.2-12.75H-CC-«H-CC41.2-50.710X-CC-11X-CC78.3-88.18H-CC-9H-CC58.7-68.418X-CC-19X-CC155.8-165.3

10X-CC-11X-CC78.3-88.19X-CC-10X-CC68.4-78.312X-CC-13X-CC97.7-117.210X-CC-UX-CC78.3-88.1

Hole796B

5R-CC-6R-CC59.5-69.19R-CC-10R-CC97.9-252.7

6R-CC-7R-CC69.1-78.8

9R-CC-10R-CC97.9-252.7

Hole 797B

3H-CC^H-1,118-12024.9-26.084H-CC-5H-CC34.4-43.95H-CC-6H-CC43.9-53.48H-CC-9H-3,118-12072.4-76.5817H-CC-18H-CC157.9-166.413H-CC-14H-CC119.9-129.412-6,117-119-12H-CC109.57-110.411H-CC-12H-CC100.9-110.416H-CC-17H-CC148.4-157.916H-CC-17H-CC148.4-157.9UH-CC-12H-CC100.9-110.423X-CC-24X-CC214.3-22422X-CC-23X-CC204.8-214.3

18H-CC-19H-CC166.4-175.9

20X-CC-21X-CC185.5-195.225X-CC-26X-CC233.7-243.424X-CC-25X-CC224-233.7

RADIOLARIANS FROM SITES 794, 795, 796, AND 797

Table 2. Late Pliocene and Pleistocene age Hole 794A radiolarian samples with estimates of radiolarianabundance and preservation.

Core, section,interval (cm)

127-794A-

1H-1,53-551H-2, 60-621H-3, 60-621H-4, 60-621H-5, 55-571H-CC2H-1,60-622H-2, 60-622H-3, 60-622H-4, 60-622H-5, 60-622H-6, 60-622H-7, 60-622H-CC3H-1, 60-623H-2, 60-623H-3, 60-623H-4, 60-623H-5, 59-613H-6, 60-623H-7, 60-623H-CC4H-1,59-614H-2, 59-614H-3, 59-624H-4, 59-614H-5, 59-614H-6, 59-624H-7, 58-604H-CC5H-1, 60-635H-2,62-655H-3, 60-635H-4, 59-615H-5, 58-605H-6, 63-655H-CC6H-1, 59-616H-2, 59-616H-3, 71-746H-4, 62-646H-5, 59-616H-6, 59-616H-CC7H-1,60-627H-2, 60-627H-3, 60-627H-4, 60-627H-5, 60-627H-6, 60-627H-CC8H-1, 60-628H-2, 60-628H-3, 60-628H-4, 60-628H-5, 59-618H-6, 60-628H-CC9H-1, 59-619H-2, 59-619H-3, 59-619H-4, 59-619H-5, 59-619H-6, 59-619H-7, 59-619H-CC

10H-1, 60-6210H-2, 60-6210H-3, 60-6210H-4, 60-62

Depth(mbsf)

0.532.103.605.106.556.807.408.90

10.4011.9013.4014.9016.4016.3016.9018.4019.9021.4022.8924.4025.9025.8026.3927.8929.3930.8932.3933.8935.3835.3035.9037.4238.9040.3941.8843.4344.8045.3946.8948.5149.9251.3952.8954.3054.9056.4057.9059.4060.9062.4063.8064.4065.9067.4068.9070.4071.9073.3073.8975.3976.8978.3979.8981.3982.8982.8083.4084.9086.4087.90

Age(Ma)

0.0150.0600.1030.1460.1880.1950.2120.2550.2980.3410.3840.4270.4690.4670.4840.5270.5700.6130.6550.6990.7420.7390.7560.8000.8440.8890.9330.9771.0241.0211.0401.0881.1351.1821.2291.2781.3221.3401.3881.4391.4841.5301.5771.6221.6411.6971.7581.8191.8801.9411.9982.0222.0832.1442.2052.2662.3282.3852.4092.4702.5162.5612.6072.6532.6992.6962.7152.7612.8062.852

Slide weight(g)

6.005.494.198.18

10.44

10.165.599.938.41

10.179.065.79

8.487.97

11.128.644.878.71

10.97

12.237.928.367.358.50

10.4214.66

10.7216.8315.5015.7512.9615.91

8.9414.1315.9712.8211.8119.59

10.9813.8410.9210.879.388.38

7.7812.9510.026.525.468.48

6.5911.247.799.22

12.669.408.91

10.849.516.71

15.16

RadiolariansAbundance

BarrenRareRareFewBarrenFewRareBarrenFewBarrenFewRareFewCommonRareRareBarrenBarrenRareRareBarrenFewFewFewCommonCommonRareAbundantFewBarrenBarrenRareRareBarrenRareFewFewBarrenBarrenFewBarrenBarrenRareBarrenRareRareFewFewCommonFewCommonCommonAbundantAbundantFewAbundantAbundantAbundantCommonAbundantCommonAbundantAbundantAbundantAbundantAbundantCommonAbundant

Preservation

PoorModerateGood

ModeratePoor

Moderate

ModerateModeratePoorModerateModerateModerate

PoorModerate

GoodModerateModerateModerateModerate to poorModerate to poorGoodModerate

PoorPoor

ModerateModerateGood

Moderate

Moderate

ModeratePoorModerate to poorModerateGoodPoorModerateModerateModerateModerateModerateGoodGoodModerateModerateGoodModerateModerateModerateGoodGoodModerateModerateGood

Commentsa

High IR*

**High IR*

D, *

2 IR, trissocyclidsDD, *D, * 2 IR

D2IRHigh IR2IRD

D****D, *

**

*

*

fff,2IR

ff

*

a f indicates presence of floaters, D indicates sample comes from a dark layer, * indicates presence of sand-sized grains,and 2IR indicates that radiolarians are present with two states of refractive index (IR).

293

J. M. ALEXANDROVICH

Table 3. Late Pliocene and Pleistocene age Hole 795A radiolarian samples with estimates ofradiolarian abundance and preservation.


127-795 A-

1H-CC2H-CC3H-CC4H-CC5H-CC6H-CC7H-CC8H-CC9H-CC

10H-CC11H-CC12H-1,70-7212H-2, 70-7212H-3, 70-7212H-4, 70-7212H-5, 70-7212H-6, 70-7212H-CC13H-1, 74-7613H-2, 74-7613H-3, 74-7613H-4, 74-7613H-5, 74-7613H-6, 74-7613H-7, 51-5313H-CC14H-2, 73-7514H-3, 73-7514H-4, 73-7514H-5, 73-7514H-6, 73-7514H-7, 51-5314H-CC15H-1,73-7515H-2, 73-7515H-3, 73-7515H-4, 73-7515H-5, 73-7515H-6, 73-7515H-7, 51-5315H-CC16H-1,73-7516H-2, 73-7516H-3, 73-7516H-4, 74-7616H-CC17H-CC

Depth(mbsf)

9.3018.8028.3037.8047.3056.8066.3075.8085.3094.80

104.30105.00106.50108.00109.50111.00112.50113.80114.54116.04117.54119.04120.54122.04123.21123.30125.53127.03128.53130.03131.53132.81132.80133.53135.03136.53138.03139.53141.03142.31142.30143.03144.53146.03147.54151.80151.90

Age(Ma)

0.1940.3920.5900.7800.9501.1201.2901.4601.6301.7611.8841.8931.9121.9321.9511.9711.9902.0072.0162.0362.0552.0752.0942.1142.1292.1302.1592.1782.1982.2172.2362.2532.2532.2622.2822.3012.3202.3402.3592.3762.3762.3852.4052.4242.4442.4992.500

Slide weight(g)

13.019.90

11.058.199.82

11.66

15.8512.5815.3511.2213.9310.5215.51

12.2713.8811.8813.4513.1616.25

8.859.726.846.889.979.17

11.14

9.4212.1211.7211.73


RareRare to fewAbundantRareAbundantFew-RareFewRareRareFewCommonFewFewFewFewCommonCommonFewCommonFewFewCommonCommonCommonCommonCommonCommonAbundantAbundantAbundantAbundantAbundantCommonAbundantFewRareFewCommonFewAbundantAbundantFewCommonCommonCommonCommon

Preservation

GoodModerateGoodModerateGoodModeratePoorModeratePoorModerateModerateModerateModerateGoodGoodModerateModerateModerateModerateGoodModerateModerateModerateGoodGoodModerateModerateModerateModerateGoodModerateModerateGoodGoodGoodGoodPoorGoodModerate to goodGoodModerateGoodModerateModerateModerateGoodGood

Commentsa

*2IR

ff,2IRf, 2IR

ff, 2IRf, 2IRfff

2IRfffff

ffff, 2IRfff

ff

f

a f indicates presence of floaters, * indicates presence of sand-sized grains, and 2IR indicates that radiolarians are presentwith two states of refractive index (IR).

obtained from these sediments provides an excellent opportunity tostudy the preservation of radiolarians. The preservation of radiolarianassemblages from Japan Sea Leg 127 sediments represents severalrather extreme examples of preservation state. The radiolarians fromthe deeper, opal-CT sediments are rather poorly preserved, however,the state of poor preservation of radiolarians found in the opal-CTsediments is quite different from other states of poor preservationfound in sediments of the Japan Sea from above the opal-A/opal-CTtransition, because they were preserved by coatings of opal-CT.Radiolarians from the Miocene and Pliocene diatomaceous sedimentsare relatively well preserved, and display few visible signs of disso-lution; however, their preservation and abundance records are some-what obscured because they are outnumbered in the radiolarian slidesby high abundances of the diatom Coscinodiscus marginatus. ThePleistocene radiolarian assemblages in Japan Sea ODP Leg 127sediments are in general the most poorly preserved; however, there isa small minority of samples from sediments younger than the opal

dissolution transition zone which contain well-preserved, abundantradiolarian assemblages (Tables 2, 3, and 4).

Observations on and comparisons between the preservation of radio-larians in the late Pliocene and Pleistocene samples from Sites 794,795,and 797 reveal that certain types of radiolarians from Japan Sea sedimentsare solution resistant. The two types of most dissolution-resistant radio-larians include morphotypes (PI. 1, Figs. 4 and 5, and PI. 2, Fig. 2) oftrissocyclids (Goll, 1968), and a radiolarian identified as Peripyramisspecies (PI. 2, Fig. 3, and PI. 4, Fig. 5). In samples where only these specieswere found, tests displayed visible signs of dissolution (PI. 1, Fig. 4),which made identifications of species impossible, but confirmed thenotion that concentrations of these species in samples are indicators ofhigh levels of dissolution. The dissolution-resistant trissocyclids of theJapan Sea are very similar in form to the spyrid radiolarians identified asdissolution-resistant forms by Holdsworth and Harker (1975), whichsupports the hypothesis that trissocyclid radiolarians are solution-resis-tant forms. It is interesting to note that collosphaerids, which were also

294


Table 4. Late Pliocene and Pleistocene age Hole 797B radiolarian samples with estimates of radiolarianabundance and preservation.


127-797B-

1H-CC2H-1,118-1202H-2,118-1202H-3, 131-1332H-4,118-1202H-5,118-1202H-6, 118-1202H-CC3H-1,117-1193H-2,117-1193H-3,117-1193H-4,117-1193H-5,111-1133H-6,117-1193H-CC4H-1,118-1204H-2, 118-1204H-3, 118-1204H-4,118-1204H-5,118-1204H-6,118-1204H-CC5H-1,118-1205H-2,118-1205H-3,118-1205H-4,118-1205H-5,118-1205H-6,118-1205H-CC6H-1,115-1176H-2,118-1206H-3,118-1206H-4,110-1126H-5,118-1206H-6, 118-1206H-CC7H-1,118-1207H-2,118-1207H-3,117-1197H-4,117-1197H-5,117-1197H-6, 117-1197H-CC8H-1,118-1208H-2,118-1208H-3,118-1208H-4,118-1208H-5,118-1208H-6, 118-1208H-CC9H-1,118-1209H-2,118-1209H-3,118-1209H-5,118-1209H-6, 118-1209H-CC

10H-1,118-12010H-2,118-12010H-3,118-12010H-4, 118-12010H-5,118-12010H-6,118-12010H-CC11H-1, 118-12011H-2, 118-12011H-3, 118-12011H-4, 118-12011H-5, 118-12011H-6, 118-12011H-CC

Depth(mbsf)

5.907.088.58

10.1111.5813.0814.5815.4016.5718.0719.5721.0722.5124.0724.9026.0827.5829.0830.5832.0833.5834.4035.5837.0838.5840.0841.5843.0843.9045.0546.5848.0849.5851.0852.5853.4054.5856.0857.5759.0760.2762.0762.9064.0865.5867.0868.5870.0871.5872.4073.5875.0876.5879.5881.0881.9083.0884.5886.0887.5889.0890.5891.4092.5894.0895.5897.0898.58

100.58100.90

Age(Ma)

0.1300.1560.1890.2220.2550.2870.3200.3380.3640.3970.4300.4630.4950.5290.5470.5730.6060.6390.6720.7050.7380.7560.7820.8150.8480.8810.9140.9470.9650.9901.0241.0571.0901.1231.1561.1741.2001.2331.2651.2981.3251.3641.3821.4081.4411.4741.5071.5401.5731.5911.6171.6501.6831.7491.7821.8001.8241.8541.8841.9141.9441.9751.9912.0152.0452.0752.1052.1362.1762.182

Slide weight(g)

6.918.16

11.4110.316.65

11.25

7.024.858.856.747.029.62

5.026.497.056.845.898.25

7.248.488.887.22

11.6311.79

10.109.125.107.866.06

13.02

11.889.337.477.018.639.22

8.4911.7212.118.60

10.138.75

8.7513.709.29

10.688.29

11.7311.7216.537.927.93

11.66

8.079.10

10.2410.689.468.57


CommonRareRareRareRareCommonBarrenRareRareCommonBarrenCommonRareRareRareCommonAbundantCommonAbundantCommonCommonRareBarrenRareCommonFewRareRareCommonRareCommonCommonAbundantRareRareAbundantFewRareCommonCommonRareRareAbundantAbundantRareRareAbundantRareCommonCommonRareRareRareRareFewCommonCommonAbundantFewCommonCommonFewFewCommonCommonFew-AbundantFewCommonCommon

Preservation

ModeratePoorModerateModerateModerateModerate

ModerateModeratePoor

ModerateModeratePoorGoodPoorPoorPoorGoodPoor to moderateModerateModerate

PoorModeratePoorPoorModerateGoodPoorModerateModerateModerateModerateModerateGoodModerateGoodModerateModerateModeratePoorGoodGoodPoorModerateGoodModerateModerateGoodModerateModeratePoorPoorModerateModerateModerateModerateModerateModerateModerateModerateModerateModerateModerateModerateModeratePoorModerateModerate

Commentsa

2IR** 2 I R2IR2IR*

D,2IRf,2IRf, *f,D2IRf, *

High IRf, High IR, trissocyclidsf, High IRff, *High IRf, D trissocyclids

f, *f, D High IR2IRf, High IR*High IR*

f, *f, *f, Df

f, *

f, **

f

*

*

*

2IR

fHigh IR2IRf, trissocyclids

295

J. M. ALEXANDROVICH

Table 4 (continued).


12H-1,117-11912H-2, 117-11912H-3,117-11912H-4,113-11512H-5, 117-11912H-6,117-119

12H-CC13H-1,118-12013H-2,118-120

Depth(mbsf)

102.70103.57105.07106.53108.07109.57

110.40111.58113.08

Age(Ma)

2.2182.2362.2662.2962.3272.357

2.3732.3972.427

Slide weight(g)

6.806.667.459.775.297.40

7.408.88


AbundantAbundantAbundantAbundantAbundantAbundant

CommonAbundantCommon

Preservation

GoodModerate to poorGoodModerate to poorGoodGood

GoodGoodModerate

Comments8

fff, trissocyclids

f

trissocyclids

a f indicates presence of floaters, D indicates sample comes from a dark layer, * indicates presence of sand-sized grains, and 2IR indicates that radiolarians are present with two states of refractive index (IR).

found concentrated with trissocyclid radiolarians in the dissolvedassemblages described by Holdsworth and Harker (1975), were notfound in any samples from the Leg 127 sites. Because collosphaeridradiolarians may be indicative of more oligotrophic conditions, theabsence of them from Japan Sea sediments suggests that the JapanSea has always been highly productive. Also, because collosphaeridslive in colonies that can grow quite large, it is possible that the absenceof collosphaerid radiolarians from Japan Sea sediments is due toOceanographic conditions unsuitable for the survival of these species,such as high levels of grazing and/or a well-mixed water column.

Another important preservational indicator of radiolarians ofLeg 127 sediments is the radiolarian refractive index. Although itis not clear what changes in the refractive index of radiolariansrecord, samples from Leg 127 that contain radiolarians with highindices of refraction, typically also contain radiolarians that showvisible signs of dissolution. Differences in refractive index areeasily observed in radiolarians. Radiolarians with a high index ofrefraction appear ghostly because their index of refraction is closerto that of Canada Balsam (PI. 1, Fig. 8), whereas radiolarians witha normal or lower index of refraction appear darker. Typically,when radiolarians in a sample display two states of index ofrefraction (e.g., PI. 1, Fig. 6), reworking may be inferred becauseolder radiolarians commonly have a lower index of refraction.However, the occurrence of two states of index of refraction withina sample does not necessarily imply that reworking has occurred.In fact, some single test radiolarian specimens within Japan Seasamples with assemblages that displayed two refractive indexstates also display two states of index of refraction.

Close inspections of specimen that display two states of refractiveindex (IR) revealed that although the fossils are still relatively complete,the high-IR portions of some of the tests are slightly thinner, indicatingthat the change to a higher index of refraction accompanies and probablyprecedes dissolution. Because many radiolarians from samples thatdisplay two states of IR display obvious signs of dissolution such aspitting, thinning of connecting bars, reduction of lattice "lace," etc., butdo not necessarily display high IR values, it is likely that dissolutionoccurs after deposition of the radiolarians either at the sediment/waterinterface or within the sediment column. Because skeletal thinning willmake the skeletons of radiolarians more fragile, radiolarians that startdissolving within the water column are more likely to become fragmenteddue to the rigors of transport and deposition than are those that begandissolving within the sediments.

Reworking

The distribution of reworked radiolarians in sediments cored duringLeg 127 is a good indicator of sediment transport and tectonically induceddeposits. Reworking of radiolarians was lowest in the sediments of Site794, and was more common at Sites 795 and 797 (Tamaki, Pisciotto,Allan, et al, 1990). Relatively low amounts of reworked radiolarians wereidentified in Site 796 sediments; however, the presence of sands and

sediment slumping obscures the radiolarian record at this site. Forthis reason no additional samples were processed from Site 796 coresfor this study. Radiolarian reworking is confirmed in Pliocene andPleistocene sediments where Miocene forms are identified and alsoin sediments where there are abundant fragmented radiolarians (PI.2, Figs. 1 and 2). Commonly, older reworked radiolarians appearthickened and have a lower index of refraction than the rest of theradiolarians in the assemblage. The most common reworked radio-larians were usually species from the genera Stichocorys or Cyrto-capsella (PI. 2, Fig. 4). Some cycladophorid radiolarians most likeAnthocorys akitaensis looked suspiciously reworked in several sam-ples due to slightly lower apparent index of refraction.

RADIOLARIAN STRATIGRAPHIC INDICATORS OFJAPAN SEA SEDIMENTS

Because of their continuous nature, the sites cored during Leg 127can be used to construct a reference section for radiolarians from Japan.Therefore, an objective of this radiolarian paleontology and stratigraphystudy is to precisely identify the sequence of radiolarian biostratigraphicevents of the Japan Sea. Once the radiolarian stratigraphy is clearlyestablished and age models for Leg 127 sediments are refined, theradiolarian stratigraphy can be used to help decipher the depositionalhistory of basins of the Japan Sea where radiolarians are found. However,the identification of stratigraphic datum levels in Leg 127 Japan Seasediments is complicated by poor preservation in the youngest and oldestsediments recovered, by radiolarian sample contamination by the diatomCoscinodiscus marginatus in Miocene and Pliocene sediments, by in-complete inventories and taxonomies of Japan Sea radiolarian species,and by evolutionary changes throughout the sections examined.

The radiolarian stratigraphy of the Japan Sea is also hard to tiedirectly to standard zonations from other parts of the Pacific becausePacific indicator species do not occur or occur sporadically in thesediments recovered on Leg 127. The radiolarian stratigraphy from theLeg 127 sites can be tied to the radiolarian zonations set up for middleMiocene to Pliocene sedimentary deposits of Japan by Nakaseko andSugano (1973). This zonation is very useful because the boundaries ofthe zones are defined by only a few species and the ranges of 36 taxathat range between the middle Miocene and Pliocene are traced throughthese zones. Although indicator species from several genera such asDidymocyrtis, Calocycletta, or Lithopera were not found in the Leg127 sediments, the fact that they are present in deposits on Japan allowsfor some correlation with radiolarian assemblages assigned to NorthPacific zonations.

Radiolarian zonations set up for Japan Sea sediments (Nakasekoand Sugano, 1973, Tamaki, Pisciotto, Allan, et al., 1990) will not beused to describe the Leg 127 sites examined in this study, because thestratigraphic resolution of the zonations is rather low, and the poorpreservation of the late Pliocene and Pleistocene sediments prohibitsthe exact determination of zonal boundaries. Instead, radiolarianstratigraphy determined in this study is used to examine the correla-

296


Table 5. Samples from Hole 794A containing subtropical radiolarians.


127-794A-

1H-4, 60-621H-5, 55-572H-2, 60-624H-4, 59-614H-5, 59-614H-6, 59-625H-1,60-636H-1,59-616H-2, 59-617H-1, 60-62

Depth(mbsf)

5.106.558.90

30.8932.3933.8935.9045.3946.8954.90

Age(Ma)

0.1460.1880.2550.8890.9330.9771.0401.3401.3881.641

Slide weight(g)

8.1810.445.597.358.50

10.4210.728.94

14.1310.98


RareRareFewFewCommonCommonFewFewFewRare

Preservation

PoorModerateModerateModerateModerateModerate to poorModerateModerateGoodModerate

Comments3

**

#

a * indicates samples containing sand-sized grains.

tions and relative timing of the events among Japan Sea Sites 794,795, and 797. Although Ling (1975) examined radiolarians in DSDPLeg 31 sediments and documented the levels of several biostrati-graphic events, no previous studies exist in which radiolarian first-occurrence (FO) and last-occurrence (LO) event stratigraphy fromJapan Sea or marine sediments from Japan are tied to a paleomagnetictime scale. In addition, most of the radiolarian datum levels identifiedin Japan Sea sediments have not been assigned ages in studies ofPacific sediments. Therefore, radiolarian stratigraphy cannot be usedto define and refine age models for the Japan Sea Leg 127 sites. TheLeg 127 Japan Sea sites can, however, be used as reference sections,and radiolarian datum levels can be assigned ages by interpolatingbetween age control points of other chronological indicators identi-fied in the cores.

Before radiolarian biostratigraphic events can be dated, the se-quence and relative reliability of the events must be documented. Thisis achieved by plotting the 25 first- or last-occurrence events identifiedin the Japan Sea Leg 127 sediments (Table 1) on depth-depth plots (Fig.1). In these plots, the sample-spacing uncertainty of the datum levelsis represented by boxes, and unreliable or diachronous radiolariandatum levels are identified when they violate apparent lines of corre-lation between the stratigraphic sections. Lines of correlation are notindicated in Figure 1 because many of the radiolarian datum levels havenot been researched in detail and appear to be out of sequence at someof the sites. The best correlation of the radiolarian datum levels fromLeg 127 sites occurs between Sites 794 and 797; however an offset ofthe correlation is found below the F0 of Theocalyptra davisiana andthe opal dissolution transition zone (Fig. 1). This offset could beindicative of problems in the identification of the LO of Lipmanellasp. aff. L. redondoensis, a relative decrease in the sedimentation rateat Site 797, or, an increase in the sedimentation rate at Site 794 in theyounger sediments. The gaps in the depth-depth plots between Site 795and Sites 794 and 797 suggest that the sedimentation rate in the intervalcorresponding to the range of Lipmanella sp. aff. L. redondoensis (175and 300 m below seafloor) at Site 795 is significantly higher.

The depth-depth plots that compare the radiolarian stratigraphy ofLeg 127 Sites 794,795, and 797 illustrate that further biostratigraphicanalysis is warranted. Until taxonomic uncertainties are resolved anda clear homotaxial pattern is discerned between the three sites, anyconclusions about the correlation of the stratigraphic records of thesesites is tentative. This preliminary stratigraphic analysis includesillustrations of 14 Japan Sea radiolarian stratigraphic indicators in theplates, and observations on several of these indicator species whichare discussed in the following.

The identification of the LO of Clathrocyclas cabrilloensis (PL 5,Figs. 7, 8,9, and 10) is complicated by both close affinities with otherCycladophorid morphotypes (PL 5, Figs. 4, 5, and 6) and the poor

preservation of the Pleistocene assemblages. Despite this, the mor-phological definition followed for this species is rather robust, andthe stratigraphic level of this LO event correlates well among the threesites (Fig. 1).

Because the LO of Stylacontarium acquilonius (PL 3, Fig. 2)occurs within the cyclical Pleistocene sediments that exhibit a largevariability in preservation, the reliability of this datum level may besuspect. Because it is a rather abundant species, however, its lastoccurrence is somewhat reliable and appears to correlate among Sites794,795, and 797. The LO of the hypothesized ancestor of Stylacon-tarium acquilonius, Stylacontarium sp. cf. 5. acquilonarium, is dis-tinguished from its descendant mainly by the shape of the corticalshell. Because the differences between these two species are verysubtle, it is likely that this lineage is equivalent to the species Styla-tractus yatsuoensis as described by Nakaseko (1969). The similaritiesbetween Stylacontarium acquilonium and Stylatractus yatsuoensiswere noted previously by Ling (1975).

The LO of Sphaeropyle robusta (PL 3, Fig. 7) and the FO of itsdescendant, Sphaeropyle langii (PL 3, Fig. 3), were used as zonalboundary markers for the shipboard reports. Although there areevolutionary intergrades between these two radiolarians in Japan Seasediments, the first morphotypic appearance of S. langii can be easilyidentified and appears to correlate nicely among sites. The LO of S.robusta may not be a reliable stratigraphic indicator because it dis-plays very low abundances in the Pleistocene sediments.

The F0 of Theocalyptra davisiana (PL 1, Fig. 6, and PL 4, Fig. 8)is closely associated with the late Pliocene opal dissolution transitionzone (ODTZ). Near the base of the range of Theocalyptra davisiana,ancestral forms and morphotypical intergrades are abundant; there-fore, in the Japan Sea, the F0 of Theocalyptra davisiana is a morpho-typic first appearance. The datum level is probably reliable andsynchronous within the Japan Sea sediments, although the occurrenceof morphological intergrades deserves more attention.

The LO of Stichocorys peregrina as determined during Leg 127correlates well between Sites 794 and 797. However, the estimatedage for the event is approximately 1 Ma younger in these Japan Seasites than at Pacific sites, and the range of this event is not consistentwith the ranges of the species in the North Pacific. Reworking of thisspecies in the sediments complicates the selection of the level of thislast occurrence event.

Sethocyrtis japonica (PL 3, Fig. 9), Theocorys redondoensis (PL 3,Fig. 5), and Lipmanella sp. aff. Theocorys redondoensis (PL 3, Fig. 4)appear to be closely related and may possibly share a common evolu-tionary lineage. Reynolds (1980) suggested that Sethocyrtis japonicais the ancestor of Theocorys redondoensis. In their overlapping ranges,an intergradation of morphotypes was observed. The complicatedevolutionary relationships of these species may explain the apparent

297

J. M. ALEXANDROVICH

50

Site 794 (mbsf)

100 150 200 250 300 50

Site 797 (mbsf)

100 150 200 250 300

Iir>

2CO

|5

<i>

0

50

100

150

200

250

300

350

400

450

500

0

50

100

150

200

250

300 J

. FO L sp. cf. L grade

| LO C. cabrilloβnsis

LO S. robusta

V J.O S. aquilonius•JLO 7. japonica

F0 7 davisianaI LO fi sp cf. S. acquilonarium

.LO L sp. aff. L rβdondoβnsisFO S.langii

FO L sp. aff. L. redondoensis

" • FO 7. japonica

I LO S. japonica

• LO L nipponicurr,

5 0 :

100:

g 150:

1^200-

<D

250-

300:

350-

400 J

LO 7 anthopora E l LO L tochigiensis

LO 7 mammilaris

I FO L sp. cf. L grade

g LO C. cabrilloensis

LO S. robusta\ LO S. aquilonius

LO 7. akteensi

LO 7 japonicaF0 7 davisiana

I LO S. sp cf. S. acquilonarium'LO L sp. aff. L redonαoensis

MFO S.langii

H F0 T. akitaensis

FO L sp. aff. L redondoensis

• FO 7. japonica

| LO S. japonica

• LO L nipponicurr,

Site 794 (mbsf)

50 100 150 200

I

F0 L sp. cf. L. gradeLO C. cabrilloβnsisI LO S. robusta

LO S. aquilonius

LO 7. japonica•lilFO 7 davisiana

• LO L sp. aff. L redondoensisFO S. /anfif//

• LO S spcf. S. acquilonarium• LO S. peregrine

I LO S. japonica• FO L sp. aff. L redondoensis

π LO L nipponicurr,• FO 7. japonica

Figure 1. Depth-depth plots comparing the location of radiolarian biostratigraphic events at Leg 127 Sites 794,795, and 797. The shaded areas denotethe opal dissolution transition zone of White and Alexandrovich (this volume), and box sizes represent sample-spacing uncertainties of the datumlevels. LO and F0 refer to the last-occurrence and first-occurrence datum levels of the species, respectively.

diachroneity of the LO of S. japonica (Fig. 1) because it may not bean extinction event but rather a pseudo-extinction event, which is moredifficult to define.

PALEOCEANOGRAPHIC IMPLICATIONS OFJAPAN SEA RADIOLARIANS

There are many interesting forms of radiolarians found in the Leg127 Japan Sea sediments. Many of these have specific ecologicaltolerances and affinities which can be used to make paleoclimatic and

paleoceanographic interpretations. Some Japan Sea radiolarians haveundergone morphological changes through time, and can be used todelineate evolutionary histories. A number of noteworthy radiolarianspecies and lineages with interesting paleoceanographic and evolu-tionary implications are illustrated and described as follows.

Radiolarian Evidence of a Paleo-Tsushima Current

Shipboard analyses indicated that radiolarians species with sub-tropical affinities are not present or are not common in three of the

298


sites cored on Leg 127 (Sites 794, 795, and 796), but are common incore-catcher samples from Core 127-797A-8H and above. DuringLeg 127, Sample 127-796A-6H-CC was the only sample from a siteother than Site 797 observed to contain a warmer water assemblage.The subtropical faunal indicators include Tetrapyle octacantha (PI. 4,Figs. 1 and 2), Didymocyrtis tetrathalamus (PI. 4, Fig. 3), a speciesbelonging to the genus Euchitonia (PL 4, Fig. 7), and Spongastertetras. Shore-based observations indicate that subtropical species areabsent from all samples from Hole 795A (Table 3) and are commonin samples containing preserved radiolarians from Hole 797B. Thefirst occurrence of these warmer water radiolarian taxa was recordedbetween Samples 127-797B-9H-6, 118-120 cm, and 127-797B-9H-CC, and the sporadic occurrences of these taxa found in samples fromHole 794A are recorded in Table 5.

Presently Site 797 is situated beneath the Tsushima current (an armof the warm Kuroshio). The occurrence of warm-water (subtropical)fauna in all samples with preserved radiolarians younger than approxi-mately 1.8 Ma from Hole 797B (Table 4) indicates that the Tsushimacurrent probably flowed into the Japan Sea through much of thePleistocene. However, because the abundance of Tsushima currentindicators goes to zero in the Hole 797B barren samples, there mayhave been intermittent flow of the Tsushima current since this time. Inaddition, because Tetrapyle octacantha is present in low abundance inthe cooler glacial period (Morley et al., 1986), its presence in the Hole794A samples may record the increased influence of the Tsushimacurrent. These conclusions largely contradict the supposition of Obaet al. (1991) that warmer water from the Tsushima current did not enterthe Japan Sea until approximately 10,000 yr ago, but is in agreementwith Matoba (1984), who indicated that there was intermittent influxof the Tsushima current since late Pliocene time. If there was a landbarrier at the Tsushima Strait throughout most of the Pleistocene (Obaet al., 1991; and Iijima and Tada, 1990), then the occurrence ofsubtropical radiolarian fauna throughout the Pleistocene would implythat temperatures over Site 797 were much warmer than at the northernsites. It is not likely that warm temperatures could be solely responsiblefor the persistence of subtropical radiolarians at Site 797, because theinflux of the Tsushima current into the Japan Sea is presently respon-sible for the temperate climate of the region.

Cycladophorid Radiolarians

Several described taxa compose the Cycladophorid radiolarians inthe Leg 127 Japan Sea sediments. These species include Theocalyptradavisiana (PI. 1, Fig. 6, and PI. 4, Fig. 8), Cycladophora robusta,Clathrocyclas cabrilloensis, and Anthocorys akitaensis (PI. 5). Manymorphological intergrades were observed in addition to these species,and identification at the species level was hindered by the abundanceand diversity of Cycladophorid forms. Cycladophora robusta (PI. 5,Figs. 11 and 12), a probable ancestor of Theocalyptra davisiana, ispresent in Miocene samples, but its stratigraphic range was notdetermined. If Cycladophora robusta had an ecological niche similarto its probable descendant Theocalyptra davisiana, the high abun-dances of Cycladophora robusta observed in samples suggests thatcold conditions with a stable upper layer (Morley and Hays, 1983)persisted throughout the entire interval of its range. The fluctuationsin the abundance of this radiolarian could imply that these conditionsalso fluctuated.

Radiolarian Productivity and Paleoclimatic Indicators

In general, except for the Tsushima current indicators found inPleistocene samples from Sites 797 and 794, samples examined fromthe Japan Sea Leg 127 sites contain cool-water radiolarian assem-blages. The consistent occurrence of Spongodiscid radiolarians suchas Spongotrochus glacialis is indicative that upwelling has persisted

in the Japan Sea since the late Miocene. In addition, the negativeevidence of the lack of collosphaerid radiolarians in the assemblages,as discussed previously, also indicates that productivity in the JapanSea was high. There are many other radiolarians found in the Leg 127Japan Sea sediments that can be used to record fluctuations in watermass properties, such as the species Larnacantha polyacantha, Theo-calyptra davisiana, Stylochlamydium venustum, and Tetrapyle octa-cantha, which define the paleoceanographic factors determined byMorley et al. (1986) from an 80,000-yr-long record from core RC12-379 in the Japan Sea. These same radiolarian factors can be used todescribe the radiolarian assemblages at Site 797, but will probablynot be very useful at the other sites (Sites 794, 795, and 796) due tothe lack of the important species Tetrapyle octacantha.

Radiolarians from Japan Sea PleistoceneLight and Dark Cycles

An interesting feature of the Leg 127 Japan Sea sediments is theoccurrence of distinct light- and dark-color banding. The controls ofthese Pleistocene light and dark cycles are not well understood andare probably dependent on many factors such as tectonics, sea level,Northern Hemisphere glaciations, deep-water oxygen content, cli-mate, and productivity. Shipboard analyses indicated that the mostdistinctive feature of the radiolarian assemblages observed in thecyclical Pleistocene sediments of the Japan Sea is high variability inpreservation and assemblage composition. Therefore, observations ofthe details of radiolarian preservation and species composition fromthe light and dark cycles were made. The occurrence of nonradiolarianmaterial such as sand-sized grains and sponge spicules was also noted.

Radiolarian paleontological samples were not taken for the spe-cific study of light and dark layers and were not obtained at theresolution required to quantify changes in radiolarian assemblagesthat occur on the time scales of the cycles. By noting if samples fromHoles 794A and 797B processed for radiolarians came from darklayers by an examination of the core photos (Tables 2 and 4), apreliminary analysis of the relationship between radiolarian assem-blages and sediment banding could be made. No obvious correlationis found between radiolarian assemblage composition or preserva-tion and light and dark color banding. However, because mostdistinctive dark layers were not sampled, the conclusion that radio-larian assemblage changes can not be related to the light and darkcolor banding of Leg 127 Japan Sea sediments can not be made.Although no properties observed in radiolarian samples correlatedirectly with light and dark color banding, it is possible that thevariability in the abundance of Theocalyptra davisiana could becorrelated to the light and dark cycles. If the correlation of light anddark layers of Japan Sea sediments to the global benthonic oxygenisotope record is correct (Tada, this volume), Theocalyptra dav-isiana stratigraphy could also be correlated to the cyclicity of lightand dark layers because Theocalyptra davisiana records from otherdeep sea cores have been correlated to records of δ 1 8 θ (Hays et al.,1976, and Morley and Hays, 1979).

Changes in Japan Sea Sill Depths and Isolation ofEvolutionary Lineages

Much more work needs to be performed to determine the evolu-tionary history of radiolarian assemblages found in Japan Sea sedi-ments. Even with an incomplete understanding of these histories, thepaleontological records of radiolarian assemblages from Japan SeaODP Sites 794, 795, and 797 suggest that radiolarians have beeninfluenced by the changing oceanography of the Japan Sea. Theisolation of this marginal basin is illustrated by the lack of strati-graphic indicator species found in the sediments of the North Pacific(such as species found by Sakai, 1980). The sporadic occurrence (with

299

J. M. ALEXANDROVICH

common abundances) of radiolarians such as Lamprocyrtis hetero-poros, and Eucyrtidium matuyamai and the occurrence of severalstratigraphic indicators found outside the Japan Sea suggest thatalthough there was communication between the Japan Sea and thePacific throughout the Miocene and Pliocene, the water mass presentin the Japan Sea must have had properties unique to this marginalbasin and mixing with the Pacific was limited.

Tectonic changes as well as climatic changes of the Japan Sea haveplayed a very important role in shaping the late Pliocene and Pleisto-cene Leg 127 radiolarian assemblages. Subtropical radiolarians inJapan Sea sediments record the influence of the sill at the TsushimaStrait, and the opal dissolution transition zone reflects communicationwith the Pacific at the Tsugaru Strait (White and Alexandrovich, thisvolume). The fact that many of the Miocene and Pliocene depositsstudied on Japan contain radiolarian species common in the NorthPacific (e.g., Nakaseko and Sugano, 1973), whereas most sedimentsof this age recovered during Leg 127 are lacking these same species,implies that the intra-arc deep-sea basins (Iijima and Tada, 1990)where these sediments were deposited had a more extensive connec-tion with the waters of the North Pacific than did the major basinswithin the Japan Sea and that the presence of the islands of Japanformed a significant barrier between the Pacific and the Japan Sea.

SUMMARY

Radiolarians from the Japan Sea Leg 127 sediments are diverseand many interesting morphotypes are found. There are 25 relativelyreliable biostratigraphic events found in these sediments, and becausethere are many forms of radiolarians present in these samples thathave not been identified, more events are likely to be found. Depth-depth plots of the radiolarian datum levels from Sites 794, 795, and797 show that additional stratigraphic evaluation is needed to refinethe stratigraphic resolution of the radiolarian datum levels and corre-lations between sites.

Sediments of the Leg 127 sites provide excellent material for studyof the controls of radiolarian preservation because several states ofpreservation are observable in the assemblages. The differing statesof radiolarian preservation in the Japan Sea sediments record severaldifferent processes. Radiolarian assemblages from sediments in theJapan Sea with high indices of refraction suggest that dissolutionprobably occurred after deposition, either on the seafloor or withinthe sediment column, whereas concentrations of dissolution-resistantforms and/or radiolarian fragments suggest that dissolution probablyoccurred during deposition.

Compositional and preservational changes of radiolarians foundin the Leg 127 sediments resulted from the unique Oceanographicconditions in the Japan Sea and can be used to trace fluctuations ofthe paleo-Tsushima current, and the dissolution of radiolarian teststhat may be related to changes in productivity, dissolved siliconconcentration, and tectonics. Faunal changes observed in the Site 797and 794 sediments indicate that the Japan Sea has been influenced bythe Tsushima current as early as the late Pliocene or early Pleistocene(~1.8 Ma). The absence of biostratigraphic events recorded in thePacific suggests that sill depths played an important role in determin-ing the species composition of the radiolarian assemblages.

Because the evolutionary taxonomy of radiolarians found in theJapan Sea sediments is rather poorly developed, the cores from theLeg 127 sites provide a wealth of material for further study. Qualita-tive observations of the Leg 127 radiolarian assemblages revealed thatthere are many interesting morphological changes observable inradiolarian lineages, but evolutionary relationships between morpho-types are complex. There are a number of very unusual, as well asless distinctive, forms of radiolarians that have unknown speciesaffiliations present in the samples, and large fluctuations in the ratiobetween spumellarian and nassellarian radiolarians may be an impor-tant paleontological record. Future studies that quantify the radiolar-

ian paleontology of sediments obtained during Leg 127 are sure toreveal many interesting facts.

ACKNOWLEDGMENTS

Funding for this research was provided by the JOI U.S. ScienceSupport Program. The laboratory assistance of Elaine Stock, andmanuscript reviews by Joe Morley, Dick Casey, and Jim Ling aregreatly appreciated.

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Bailey, J. W., 1856. Notice of microscopic forms found in the Sea ofKamtschatka—with a plate. Am. J. Sci., 22:1-6.

Benson, R. N., 1966. Recent Radiolaria from the Gulf of California [Ph.D.dissert.]. Minnesota Univ.

Campbell, A. S., and Clark, B. L., 1944. Miocene radiolarian faunas fromSouthern California. Spec. Pap.—Geol. Soc. Am., 51:1-76.

Dreyer, F., 1889. Morphologische Radiolarien studein, I, Die Pylombildungenin vergleitschend—anatomisher und entwicklungsgeschichlicher Bezei-hung bei Radiolarien und Bei Protisten Uberhaupt, nebst System undBeschreibung neuer und des bis jetzt bekannten pylomatischen Spumel-larien. Jena. Z. Naturwiss., 23:1-138.

Ehrenberg, C. G., 1862. fiber den Tiefgrund-Verhaltnisse des Oceans amEingange der Davisstrasse und bei Island. K. Preuss. Akad. Wiss. BerlinMonatsber., 1861:275-315.

Goll, R. M., 1968. Classification and phylogeny of Cenozoic Trissocyclidae(Radiolaria) in the Pacific and Caribbean basins. Part I. /. Paleontoi,42:1409-1432.

Haeckel, E., 1887. Report on the Radiolaria collected by H.M.S. Challengerduring the years 1873-1876. Rep. Sci. Results Voy. Challenger, Zooi,18:1-1803.

Hays, J. D., 1965. Radiolaria and late Tertiary and Quaternary history ofAntarctic Seas. In Llano, G. A. (Ed.), Biology of the Antarctic Seas II. Am.Geophys. Union, Antarct. Res. Sen, 5:125-184.

, 1970. Stratigraphy and evolutionary trends of Radiolaria in NorthPacific deep-sea sediments. In Hays, J. D. (Ed.), Geological Investigationsof the North Pacific. Mem.—Geol. Soc. Am., 126:185-218.

Hays, J. D., Imbrie, J., and Shackleton, N. J., 1976. Variations in the Earth'sorbit: pacemaker of the ice ages. Science, 194:1121-1132.

Holdsworth, B. K., and Harker, B. M., 1975. Possible indicators of degree ofRadiolaria dissolution in calcareous sediments of the Ontong-Java Plateau.In Andrews, J. E., Packham, G., et al., Init. Repts. DSDP, 30: Washington(U.S. Govt. Printing Office), 489-497.

Huang, T., 1967. A new Radiolarian from the Somachi Formation, Kikai-Jima,Kagoshima Prefecture, Japan. Trans. Proc. Paleontoi. Soc. Jpn., 68:177-184.

Iijima, A., and Tada, R., 1990. Evolution of Tertiary sedimentary basins ofJapan in reference to opening of the Japan Sea. J. Fac. Sci., Univ. Tokyo,22:121-171.

Karig, D. E., Ingle, J. C, Jr., et al., 1975. Init. Repts. DSDP, 31: Washington(U.S. Govt. Printing Office).

Kling, S. A., 1973. Radiolaria from the eastern North Pacific, Deep SeaDrilling Project, Leg 18. In Kulm, L. D., von Huene, R., et al., Init. Repts.DSDP, 18: Washington (U.S. Govt. Printing Office), 617-671.

Ling, H. Y., 1975. Radiolaria: Leg 31 of the Deep Sea Drilling Project. InKarig, D. E., Ingle, J. C , Jr., et al., Init. Repts. DSDP, 31: Washington (U.S.Govt. Printing Office), 703-760.

Lombari, G., and Lazarus, D. B., 1988. Neogene Cycladophorid radiolariansfrom North Atlantic, Antarctic, and North Pacific deep-sea sediments.Micropaleontology, 34:97-135.

Matoba, Y, 1984. Paleoenvironment of the Sea of Japan. In Oertli, H. J. (Ed.),Benthos '83: Proc. 2nd Int. Conf. Benthic Foraminifer a, 409-414.

Moore, T. C , Jr., 1973. Method of randomly distributing grains for micro-scopic examination. J. Sediment. Petrol, 43:904-906.

Morley, J. J., and Hays, J. D., 1979. Cycladophora davisiana: a stratigraphictool for Pleistocene North Atlantic and interhemispheric correlation. EarthPlanet. Sci. Lett, 44:383-389.

, 1983. Oceanographic conditions associated with high abundances ofthe radiolarian Cycladophora davisiana. Earth Planet. Sci. Lett., 66:63-72.

Morley, J. J., Heusser, L. E., and Sarro, T., 1986. Latest Pleistocene andHolocene Palaeoenvironment of Japan and its marginal sea. Palaeogeogr.,Palaeoclimatol., PalaeoecoL, 53:349-358.

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Nakaseko, K., 1963. Neogene Cyrtoidea (Radiolaria) from the Isozaki Forma-tion in Ibaraki Prefecture, Japan. Sci. Rep. Osaka Univ., 12:165-198.

, 1969. Neogene Radiolaria in Japan. Proc. 1st Inter. Conf. Plank-tonic Microfossils, 2:468-474.

-, 1972. On some species of the genus Thecosphaera from theNeogene formations, Japan. Sci. Rep., Coll. Gen. Educ, Osaka Univ.,20:59-70.

Nakaseko, K., Iwamoto, H., and Takahashi, K., 1965. Radiolarian stratigraphyin the oil and gas bearing Tertiary and Upper Cretaceous formations, Japan.Contrib. from Govt. of Japan to Econ. Comm, for Asia and the Far EastThird Pet. Symp., 1-13.

Nakaseko, K., and Sugano, K., 1973. Neogene radiolarian zonation in Japan.Jpn.Mem., 8:23^1.

Nigrini, C. A., 1977. Tropical Cenozoic Artostrobiidae (Radiolaria). Micropa-leontology, 23:241-269.

Oba, T, Kato, M., Kitazato, H., Koizumi, I., Omura, A., Sakai, T, andTakayama, T, 1991. Paleoenvironmental changes in the Japan Sea duringthe last 85,000 years. Paleoceanography, 6:499-518.

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Date of initial receipt: 9 May 1991Date of acceptance: 27 September 1991Ms 127/128B-134

APPENDIX

Systematic Species List

Radiolarians species discussed and figured in the plates of this report arelisted below in alphabetical order. References to original and nominal descrip-tions and some taxonomic notes are provided.

Anthocorys akitaensis Nakaseko, 1969(PI. 5, Figs. 1,2, and 3)

Botryostrobus bramlettei (Campbell and Clark, 1944) Nigrini, 1977

Clathrocyclas cabrilloensis Campbell and Clark, 1944(PI. 5, Figs. 7, 8, 9, and 10)

Cycladophora robusta Lombari and Lazarus, 1988(PI. 5, Figs. 11 and 12)

Cyrtocapsella tetrapera Haeckel, 1887(PI. 2, Figs. 4 and 5)

Didymocyrtis tetrathalamus (Haeckel, 1887) Sanfilippo and Riedel, 1980(PI. 4, Fig. 3)

Euchitonia species(PL 4, Fig. 7)

Remarks. Specimens identified as belonging to the genus Euchitoniaprobably belong to the species Euchitonia elegans, Euchitonia furcata, orEuchitonia triangulum.

Eucyrtidium matuyami Hays, 1970

Lamprocyrtis heteroporos (Hays, 1965) Kling, 1973

Larnacantha polyacantha Campbell and Clark, 1944(PL 4, Fig. 5)

Remarks. This species is equivalent to Phorticium pylonium Haeckel,used in faunal analyses of Robertson (1975), and Morley et al. (1986).

Lipmanella sp. aff. Theocorys redondoensis Reynolds, 1980(PL 3, Fig. 4)

Lithatractus tochigiensis Nakaseko, 1969(PL 3, Fig. 10)

Lychnocanium nipponicum Nakaseko, 1963(PL 3, Fig. 8)

Lychnocanium sp. cf L. grande Campbell and Clark, 1944(PL 3, Fig. 1)

Peripyramis species(PL 2, Fig. 3, and PL 4, Fig. 5)

Remarks. It is hard to identify radiolarians belonging to this genus to thespecies level, due to the effects of dissolution. Species that may be representedin this category include Peripyramis circumtexta Haeckel, 1887 and Plec-topyramis pacifica Nakaseko, 1963.

Sethocyrtis japonica Nakaseko, 1963(PL 3, Fig. 9)

Remarks. This species actually belongs to the genus Theocorys (Reynolds,1980), however the genus name Sethocyrtis has been retained in order to avoidconfusion in discussions between this species and the spumellarian T. {The-cosphaera) japonica.

Sphaeropyle langii Drey er, 1889(PL l,Fig. 7, and PL 3, Fig. 3)

Sphaeropyle robusta Kling, 1973(PL 3, Fig. 7)

Spongaster tetras Ehrenberg 1862

Spongotrochus glacialis Popofsky, 1908(PL 4, Fig. 4)

Stichocorys delmontensis (Campbell and Clark, 1944) Sanfilippo andRiedel, 1970

Stichocorys peregrina (Riedel, 1953) Sanfilippo and Riedel, 1970

Stichocorys wolfii Haeckel, 1887

Stylacontarium acquilonius (Hays, 1970) Kling, 1973(PL 3, Fig. 2)

Stylacontarium sp. cf. S. acquilonarium (Kling, 1973) Reynolds, 1980

Stylatractus universus Hays, 1970

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Stylochlamydium venustum (Bailey, 1856) Haeckel, 1887(PI. 4, Fig. 6)

Tetrapyle octacantha Muller, 1858(PI. 4, Figs. 1 and 2)

Theocorys redondoensis (Campbell and Clark, 1944) Kling, 1973(PI. 3, Fig. 5)

Thecosphaera akitaensis Nakaseko, 1972

Thecosphaera japonica Nakaseko, 1972(PI. 3, Fig. 11)

Theocalptra davisiana (Ehrenberg, 1862) Riedel, 1958(PI. 1, Fig. 6, and PL 4, Fig. 8)

Tholospyris anthopora (Haeckel, 1887) Goll, 1968

Tholospyris mammillaris (Haeckel, 1887) Goll, 1968(PL 3, Fig. 6)

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100 µm

5 8Photographs presented in the following plates were taken using a 35-mm camera mounted on a beam splitter on a Wild M20microscope. All figures are at the same scale (2.5 cm = 100 µm). EF refers to the England Finder location (Riedel and Foreman, 1961)of the specimen on the sample slide. Samples are kept at the Department of Geology, Florida Atlantic University.

Plate 1. Sterraster sponge spicules and radiolarian indicators of dissolution. 1-3. Sterraster sponge spicules: (1) Sample 127-794A-1H-3,60-62 cm, EFT51/1; (2)Sample 127-797B-26X-5, 108-110 cm, EF L47/4; (3) Sample 127-794A-1H-5, 55-57 cm, EF F40. 4,5. Trissocyclid radiolarians: (4) Highly dissolved trissocyclidradiolarian representing the only radiolarian recovered from Sample 127-794A-lH-3,60~62cm,EFM43;(5) 127-797B-10H-4,118-120cm,EFO39. 6. Theocalyptradavisiana. These two specimen show two states of index of refraction of the same species in Sample 127-795 A-12H-1,70-72 cm, EF Q40/3. Top left has low index ofrefraction and bottom right has high index of refraction. 7. Sphaeropyle langii. Partially dissolved or juvenile specimen missing cortical shell from Sample127-795A-12H-5, 70-72 cm, EF L35/3. 8. Spongodiscid radiolarians displaying high index of refraction from Sample 127-797B-4H-1, 118-120 cm, EF W44/3.

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J. M. ALEXANDROVICH

100 µm

•

Plate 2. Radiolarian indicators of dissolution and reworking. 1,2. Two views of an unidentified nassellarian radiolarian, present in high abundance, but found onlyas broken specimens indicating disturbance and reworking. Both figures are from Sample 127-794A-4H-6, 60-62 cm: (1) EF U46/2; (2) EF M37/3. The presence ofhigh numbers of trissocyclid radiolarians (Fig. 2) in this sample is another indicator that this sample has been subjected to high levels of dissolution. 3. Highly dissolvedspecimen of the species Peripymmis circumtexta or Circumtexta pacifica, and sponge spicules in Sample 127-795 A-12H-2,70-72 cm, EF V25/4. 4,5. Cyrtocapsellatetrapera: (4) found as an indicator of reworking in Pleistocene Sample 127-797B-7H-2,118-129 cm, EF P48/1; and (5) within its actual stratigraphic range in Sample127-794B-5R-CC,EFV13.

304


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100µm

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Plate 3. Japan Sea radiolarian stratigraphic indicators. 1. Lychnocanium sp. cf L grande. Sample 127-797B-2H-5, 118-120 cm, EF M52. 2. Stylacontariumacquilonius. Sample 127-794A-7H-6, 60-62 cm, EF Q31. 3. Sphaewpyle langii. Sample 127-794A-11H-3, 60-62 cm, EF H2/3. 4. Lipmanella sp. aff. Theocorysredondoensis. Sample 127-794A-19X-2, 60-62 cm, EF R40/4. 5. Theocorys redondoensis. Sample 127-794A-19X-1, 60-62 cm, EF Y43. 6. Tholospyris mammi-laris. Sample 127-794A-29X-1,60-62 cm, EFX29/3. 7. Sphaewpyle robusta. Sample 127-797B-23X-5,108-110cm, EF S4. 8. Lychnocaniumnipponicum. Sample127-797 A-26X-5,108-110 cm, EF G33/3. 9. Sethocyrtisjaponica. Sample 127-794A-28X-2,60-62 cm, EF Z47/4. 10. Lithatractus tochigiensis. Sample 127-794A-29X-1, 60-62 cm, EF V35/3. 11. Thecosphaera japonica. Sample 121-195A.-12H-1, 70-72 cm, EF R49.

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J. M. ALEXANDROVICH

100 µm

Plate 4. Japan Sea radiolarian paleoceanographic indicators. 1, 2. Tetrapyle octacantha: (1) Sample 127-794A-6H-2, 59-61 cm, EF X47/2; (2) Sample127-797B-7H-3, 117-119 cm, EF Y43/4. 3. Didymocyrtis tetrathalamus. Sample 127-797B-8H-4, 118-120 cm, EF T45. 4. Spongotrochus glacialis.Sample 127-795A-19H-4, 73-75 cm, EF H41/3. 5. Larnacantha polyacantha on left and Peripyramis species on right. Sample 127-795A-15H-1, 73-75cm, EF C33/2. 6. Stylochlamydium venustum. Sample 127-797B-8H-1, 118-120 cm, EF R20/1. 7. Euchitonia species. Sample 127-794A-3H-2, 60-62cm, EF X16. 8. Theocalyptra davisiana. Sample 127-794A-6H-1, 59-61 cm, EF WI 1.

306


100µm

10

1112

Plate 5. Synchronopticon of Cycladophorid radiolarians showing some of the variability of these forms in Japan Sea sediments. Horizontal level of the top of each photorepresents relative age of radiolarian (youngest at top, oldest at bottom. Ages listed with samples are calculated using the age model listed in Tamaki et al. (1990) and summarizedin White and Alexandrovich (this volume). 1-3. Anthocorys akitaensis: (1) age = 0.29 Ma, Sample 127-797B-2H-5, 118-120 cm, EF N21; (2) age = 3.3 Ma, Sample127-797B- 17H-7,118-120 cm, EF J25/4; (3) age = 5.3 Ma, Sample 127-797B-26X-5,108-110 cm, EF L47/4. 4-6. Unidentified Cycladophorid radiolarians: (4) age = 1.4Ma, Sample 127-794A-6H-2,59-61 cm, EF H26; (5) age = 2.7 Ma, Sample 127-794A-9H-6,59-61 cm, EF S13/4; (6) age = 5 Ma, Sample 127-794A-17H-6,60-62 cm, EFT25/1. 7-10. Clathrocyclas cabrilloensis: (7) age = 1.2 Ma, Sample 127-794A-5H-5,58-60 cm, EF Q26; (8) age = 1.1 Ma, Sample 127-797B-6H-4,110-112 cm, EF T15/4;(9)age=2.9Ma,Samplel27-794A-10H-6,60-62cm,EFK13;(10)age=3.8Ma,Samplel27-797A-20X-4,108-110cm,EFQ26/4. 11,12. Two specimens of Cycladophorarobusta from Sample 127-794A-28X-2,60-62 cm, age = 7.2 Ma: (11) with lace, EF W47; (12) without lace, EF X34/2.

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Documents

16. Radiolarians from Sites 794, 795, 796, and 797 (Japan Sea)