Pleistocene Radiolaria from Leg 119 Site 738 B ( Sections 1 H 1-1 H 2 ) : Systematics and Biostratigraphy

This paper presents a record of radiolarian species from the sections (1H1-1H2) Leg 119 Site 738B of Southern Ocean region. Well diversified taxa of typical Antarctic assemblage are present in the sections. Thirty species were identified and illustrated from twenty-nine samples. On the basis of appearance, disappearance and abundance of taxa, viz. Omega and Psi zones are established and systematics of stratigraphically important species is described. These zones are equivalent to NR1 and NR2 of Upper Quaternary.


Introduction
The study area lies in the southern part of Kerguelen Plateau at latitude 62˚42.54'Sand longitude 82˚47.25'E(Figure 1).The identified species shows well preserved Antarctic assemblage collected at a water depth of 2252.5 mbsf.Twenty-nine samples from two sections (1H1-1H2) were used for this study.The total length of studied samples is 2.850 m (Figure 2).The Leg 119 site 738B consists of nanno fossil ooze, calcareous chalk and limestone.[1] began the study on radiolarian bearing sediments in the Southern Ocean and described twenty species from the Antarctic sector of the Indian Ocean.[2] reported some species of radiolaria from Indian Ocean sector of Antarctica.[3] studied the radiolaria from the Wilhelm II Coast of Antarctica and Kerguelen Island.[4] worked on the B.A.N.Z.Antarctic Research Expedition and collected sediment samples to carry out detail study on radiolaria.[5] described Antarctic radiolarian species from the Super family Liosphaericae.[6][7][8][9][10][11][12][13][14][15][16][17] established Neogene radiolarian biostratigraphy along with illustrations and descriptions of important taxa.[18][19][20][21][22] carried out the detailed study on Antarctic Neogene radiolarian biostratigraphy.[23] proposed radiolarian biostratigraphy of late Tertiary Antarctic Seas of the Southern Ocean Region.[24] marked radiolarian zones of Quaternary and Upper Tertiary deposits of middle Asia.[25][26][27][28][29][30][31][32][33] worked on biostratigraphy and paleoclimate of the Antarctic re-gion.[34] established Pliocene-Pleistocene radiolarian biostratigraphy and paleoclimatic history from the samples collected near the Antarctic and subtropical convergence of the Southern Ocean region.[35] studied the bottom sediments of the Bellingshausen Basin in the Antarctic Sea.[36][37][38] established Neogene biostratigraphy of Falkland Plateau and Weddell Sea.[39] did the study on radiolarian biostratigraphy and magnetostratigraphy of siliceous microfossils from Antarctic sediments.[40] identified two new genera and seventeen new species from the Neogene sediments of the Kerguelen plateau.[41] carried out work on the biochronology and magnetostratigraphy of the Antarctic sediments.[42] established radiolarian from Eocene to Recent biostratigraphy, biogeography, diversity, and history of Southern Ocean.[43] carried out detail study on Neogene radiolaria from ODP Legs 119 and 120.[44] worked on sections of ODP Site 745 in the Kerguelen Plateau and placed the last occurrence datum of Stylatractus universus.[45] reported Antarctic Neogene radiolaria from ODP Leg 119 and described environmental control of radiolarian diversity, evolutionary rates and taxa longevities.[46,47] identified and described 83 radiolarian taxa and established two Pleistocene zones of Tasman region.[48] worked on radiolarian assemblage proxies for productivity in the 0 -6 Ma on DSDP Site 532 and ODP Site 1084.49] carried out the work on radiolarian paleo-productiv-[ ity variation from the ODP Site 1084 in late Pleistocene.[50,51] described 71 radiolarian species and established one radiolarian zone i.e. lower and upper Chi from the Pleistocene sediments of South East Indian area of the Antarctic continental margin.[52,53] described 45 radiolarian species and proposed the placement of NR1 and NR2 zonal boundary at a shallow depth of 6.63 mbsf from Southern Ocean region.

Methodology
Twenty nine samples from two sections (1H1-1H2) of Leg 119 Site 738B were used to carry out the present study.Sediment samples of about 3 -4 g were disaggregated in dilute Hydrogen peroxide (H 2 O 2 ) for 1 -2 hour followed by heating to just below the boiling point.One teaspoonful of Calgon (Hexametaphosphate) was added to further boil and disaggregate the sediment samples for 1 -2 hours and complete the treatment.The samples were sieved through a 63 micron mesh sieve and dried.The strewn slides were prepared by using an eye dropper and Canada balsam as a mounting medium.Generally, minimum 2 -3 slides (of cover slip size 22:22 mm) were examined for taxonomic and stratigraphic work, depend-ing on their abundance i.e. generally between 950 -1000 individual radiolarians.

Systematic Palaeontology
The classification of the subclass Radiolaria followed here is that of [54][55][56][57].Remarks on observed morphological features and their modifications have been added for many taxa.Species within a genus and genera within a family are arranged alphabetically.Characteristic morphological features for each new species and those given in open nomenclature are described.The synonymy for each taxon is incomplete and consists of references of interest to the present study.The distribution of each species is estimated as percentage of the total number of radiolaria present in the slides of each sample.The following scheme was followed to note the distribution-VA = Very Abundant (>50%); A = Abundant (20% -50%); C = Common (5% -20%), F = Few (0.5% -5%), R = Rare (<0.5%), but more than single specimen; + = Very Rare (single specimen), − = absent) and preservation G = Good, M = Moderate and P = Poor are indicated for each sample in Table 1.The microphotographs of all the idenified species are illustrated in Plate I. t Abundance: Rare Distribution: [4] considered this species as a cosmopolitan, [58] showed its distribution in the Southern Ocean region.
Distribution: [46] reported its presence from rare to abundant in Tasman region.[51] showed its distribution and taxonomy of the Southern Ocean region.
Spongopyle sp.(Pl.I, Figure 22) Description: Spongy, biconvex shell.Shape more or less circular, central part thickened and having dense spongy mass compared to marginal part.Mantle and radial spines absent.Pylome distinct and funnel shaped.
Abundance: Rare to Common Range: Miocene to Recent [14] Neogene and Oligocene?[7,12] Distribution: [4] reported its occurrence in the Antarctic region while [59] reported it in the sub-Antarctic region.[60] Considered as a cosmopolitan species.[46] also reported its presence from rare to abundant in the Pleistocene sediments of Tasman region.
Abundance: Rare Range: Pleistocene to Recent (Chen, 1975a) Distribution: [4,13] reported this species from Antarctic and sub polar regions.[46] reported its presence from rare to abundant from Tasman region.[58] showed its distribution and taxonomy from Southern Ocean region.
Prunopyle sp.(Pl.I, Figure 16) Description: Two concentric shells connected by numerous radial bars.Pores small, circular.Cortical shell thick and bears small spines, pylome large and having spines.
Abundance: Few to Rare Distribution: [58] showed its widespread distribution near the Antarctic region.[50] also showed its presence from very rare to few in the Southern Ocean region.
Abundance: Few to Rare Range: Pliocene to Recent [7,12,23] reported L. nautiloides to be endemic to the present day Antarctic fauna.
Abundance: Few to Abundant Range: [14] reported its range from Pleistocene to Recent whereas [7] assigned it from the Pliocene-Pleistocene. [12] reported its range from Pliocene to Recent from the Antarctic region.
Abundance: Few to Common Range: [14] reported its occurrence from Miocene to Recent, whereas [7,12] reported its presence from Pliocene to Recent.
Distribution: [46] showed its presence from rare to abundant in the Pleistocene sediments of Tasman region.
Abundance: Rare Range: Pliocene to Recent [8] Distribution: [51] reported its occurrence in the Southern Ocean region.
Abundance: Very Rare Genus Cinclopyramis Haeckel, 1879 Cinclopyramis sp.(Pl.I, Figure 13) Description: Pyramidal shell, thorax consisting of six to eight longitudinal bars joined by the transverse bars, network double quadrangular to rectangular pores, increasing in size distally, surface smooth and covered by mantle.
Abundance: Rare Range: [7] reported its occurrence from Oligocene to Recent while [14] reported its presence from Miocene to Recent.
Distribution: [4] considered this species as a cosmopolitan species.[46] reported its distribution from rare to common in the Tasman region.
Abundance: Very rare Range: Oligocene [59] Remark: In the studied samples, it occurs as a reworked form.
Abundance: Rare Distribution: [4] considered it as a cosmopolitan species and showed its greater abundance in the high latitudes than at lower latitudes.[51] reported its occurrence in the Southern Ocean.
Abundance: Rare Remark: On the margin of upper and lower part of thorax a prominent shoulder and well developed abdomen present.

Conclusion
Leg 119 Site 738B of sections 1H1-1H2 shows the typical assemblage of Antarctic radiolaria in Upper Pleistocene (0 -0.8 Ma).Thirty radiolarian taxa were identified and their taxonomy notes of stratigraphically important taxa were given.Two radiolarian zones namely Omega and Psi were recognised on the basis of the first and the last common occurences of Upper Quaternary and are equivalent to NR1 and NR2 respectively.Further, the zonal boundary is marked at a depth of 0.15 mbsf.

Figure 1 .
Figure 1.Showing the position of study area of Leg 119 Site 738 B.

Table 1 . Occurrences of radiolarian species in the samples ((a) to (d)).
) d) Showed its distribution and taxonomy of the Southern Ocean region.