Evolutionary changes in the biometry of the fossil radiolarian Stichocorys peregrina lineage in the eastern equatorial and eastern North Pacific

Marine Micropaleontology 90–91 (2012) 13–28

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Evolutionary changes in the biometry of the fossil radiolarian Stichocorys peregrina lineage in the eastern equatorial and eastern North Pacific Shin-ichi Kamikuri ⁎ Center for Advanced Marine Core Research, Kochi University, Kochi 783-8502, Japan

a r t i c l e

i n f o

Article history: Received 17 December 2011 Received in revised form 9 April 2012 Accepted 15 April 2012 Keywords: S. peregrina lineage evolutionary morphologic changes Miocene Pacific biostratigraphy

a b s t r a c t Stichocorys peregrina (Riedel) contributes to paleoceanography as a valuable stratigraphic tool for correlation of deep-sea siliceous sediments in world oceans and as a paleoceanographic indicator. This paper documents the evolutionary morphologic changes of the S. peregrina lineage from the middle Miocene to late Pliocene in the eastern equatorial and eastern North Pacific (IODP Site U1335 and ODP Site 887, respectively). The size and shape changes show that there are at least two geographical variations in the S. peregrina lineage. In the eastern equatorial Pacific, two significant morphological shifts took place about 11.0 and 7.0 Ma, but the morphology remained relatively stable from 7.0 to 3.0 Ma. Coincident with morphological changes in the S. peregrina lineage were changes in biogenic productivity. These changes suggest that there is a close correspondence between major paleoceanographic events in the late Neogene and evolutionary changes of the S. peregrina lineage in the low latitudes. In the high latitudes, the ratio of the third segment to fourth segment in width and height showed a maximum from 9.5 to 8.0 Ma, and decreased stepwise at about 8.0 and 6.5 Ma. However, the radiolarian data in the high latitudes do not show a clear relationship between the paleoceanographic events and size variation of this lineage. The evolutionary transition from Stichocorys delmontensis to S. peregrina can be used as a primary biostratigraphic marker in the low latitudes. However, it is not easy to use the evolutionary transition for biostratigraphic correlation and age determination in the high latitudes, because there is no obvious change in the ratio of the third to fourth segment widths that can be used to distinguish S. delmontensis from the descendant S. peregrina. © 2012 Elsevier B.V. All rights reserved.

1. Introduction Stichocorys peregrina (Riedel) is one of the most important species for the correlation of deep-sea sediments in world oceans (e.g., Johnson and Nigrini, 1985; Sanfilippo et al., 1985; Spencer-Cervato et al., 1993; Lazarus et al., 1995; Sanfilippo and Nigrini, 1998; Haslett, 2004), and contributes to paleoceanography as a paleoceanographic indicator (e.g., Sancetta, 1978; Casey et al., 1983; Romine, 1985; Romine and Lombari, 1985; Molina-Cruz, 1997; Lazarus et al., 2006; Kamikuri et al., 2007; Sono et al., 2009). Stichocorys peregrina evolved from Stichocorys delmontensis (Campbell and Clark), and became extinct without leaving any descendants (Sanfilippo et al., 1985). The evolutionary transition from S. delmontensis to S. peregrina and the last appearance of S. peregrina define the bases of the tropical radiolarian zones RN9 (S. peregrina Interval Zone) and RN12 (Pterocanium prismatium Interval Zone), respectively. The evolutionary transition in the low latitudes is placed at 7.0 Ma when S. peregrina became more abundant than S. delmontensis (Riedel and Sanfilippo, 1971; Sanfilippo and Nigrini, 1998; Kamikuri et al., 2009). Stichocorys peregrina is common to abundant in deep-sea sediments of at least

the North Pacific from the late Miocene to late Pliocene (Sancetta, 1978; Romine, 1985; Sanfilippo et al., 1985; Oseki and Suzuki, 2009). Stichocorys peregrina is separated into two morphotypes: a low-latitude morphotype and a high latitude morphotype (Kling, 1973; Sanfilippo et al., 1985). The geographical boundary is placed at about 20° (Sanfilippo et al., 1985). Casey et al. (1983) attempted to reconstruct the paleoceanographic history of the North Pacific during the late Neogene based on the geographic distribution of the S. peregrina lineage (S. delmontensis and S. peregrina). Despite the biostratigraphic and paleoceanographic importance of the S. peregrina lineage, some questions still remain to be solved. Holdsworth (1975) noted that the wholly intergradational specimens make it difficult to pin down the evolutionary transition in the low latitudes, and the typical S. peregrina morphotype appears to originate earlier. Nigrini and Sanfilippo (2001) introduced these questions as problems that should be solved. In this study, I quantitatively investigate variations of the S. peregrina lineage in space and time, and discuss the correspondence between the morphological changes and paleoceanographic events during the late Neogene. 2. Neogene paleoceanographic change

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The Neogene is a time of transition in the nature of the oceanclimate system (e.g., Lyle et al., 2008; Zachos, et al., 2008). The deep-

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sea sediments have allowed researchers to study the long-term paleoceanographic history. Miller et al. (1991) interpreted planktic–benthic foraminiferal δ18O covariance to reflect continental ice growth events, and noted several increases in global ice volume during the Miocene as “Mi” events. The global cooling trend was interrupted by three warming events, which are called “climatic optima” (Barron and Baldauf, 1990). Following climatic optimum 3, the Antarctic ice sheets expanded again at about 7.0 Ma in the latest Miocene (Billups, 2002). The Pliocene is characterized by a transition from warm global temperature in the early Pliocene (Dowsett et al., 1996; Sloan et al., 1996; Billups et al., 1998) to the onset of the Northern Hemisphere glaciation in the late Pliocene (Shackleton et al., 1984; Ruddiman and Raymo, 1988; Maslin et al., 1995). This onset appears as a series of long-term increases in ice volume that started at about 4.6 Ma (Billups et al., 1998; Haug and Tiedemann, 1998; Ravelo and Wara, 2004). The onset of the Northern Hemisphere glaciation in the subarctic North Pacific is marked by an abrupt decline of diatoms (Haug et al., 1995; Rea et al., 1995), an abrupt increase in ice-rafted debris (Krissek, 1995; Maslin et al., 1995), increased density stratification of the upper ocean, and abrupt changes in sea-surface temperature (SST) that have been interpreted as an increase in the seasonality of SST (Haug et al., 2005). In the tropical Pacific Ocean, a massive increase in carbonate dissolution occurred in the earliest late Miocene (Lyle et al., 1995). The late Miocene “carbonate crash” was associated with high bioproductivity (Theyer et al., 1985; Kamikuri et al., 2009). The high bioproductivity has also been identified in the global ocean as spanning from the latest Miocene to the early Pliocene (Barron, 1998; Dickens and Owen, 1999; Diester-Haass et al., 2002; Grant and Dickens, 2002; Cortese et al., 2004), and was called the “biogenic bloom” by Farrell et al. (1995).

diatomaceous silty clay (Rea et al., 1993). The samples were placed in a solution of hydrogen peroxide and hydrochloric acid, and gently washed over a 63-μm sieve to collect the residues. The preparation procedures are the same as those in Kamikuri et al. (2007) and Pälike et al. (2010). The S. peregrina lineage (S. delmontensis and S. peregrina) was identified from 33 samples at Sites U1335 (1335A-2HCC to 10H-2, 105–107 cm; 17.82 to 98.51 m) and from 23 samples at Site 887 (887C-13H-2, 20–22 cm to 26H-2, 20–22 cm; 104.50 to 228.0 m). I focused my attention on specimens of this lineage with four (or more) segments along the transverse line, using a transmitted light microscope at a magnification of 200×. Those specimens whose positioning was inclined to the plane of focus or whose shell was broken have been excluded from the measurements. The specimens were projected on a 20-inch monitor used for measurements of the following thirteen parameters with the image analysis software Scion Image® for Windows: width of the first to fourth segments (WS1 to WS4), height of the second to fourth segments (HS2 to HS4), width of strictures between the segments (WL2 to WL4), diameter of pores on the third segment (PD), ratio of WS3 to WS4 (WS3/WS4), ratio of HS3 to HS4 (HS3/HS4), and ratio of WL2 to WL3 (WL2/WL3) (Fig. 2). Thirty specimens per sample were measured for Site U1335, while 16 to 30 specimens per sample were measured for Site 887 because of the relatively low abundance of the lineage in the latter site. A total of 1646 specimens were examined in this study. Magnetostratigraphy was used for dating the sedimentary record of Sites U1335 (Pälike et al., 2010) and 887 (Barron et al., 1995), with linear interpolation between chron boundaries. Herein the geologic time scale (GTS) 2004 (Ogg and Smith, 2004) was employed.

3. Materials and methods 4. Results Samples were obtained from IODP Site U1335 (5° 18.735′ N, 126° 17.002′ W, water depth 4328 m) in the equatorial Pacific, and ODP Site 887 (54° 21.921′ N, 148° 26.765′ W, water depth 3630 m) in the high latitudes of the eastern North Pacific (Fig. 1). Sites U1335 and 887 are located under the North Equatorial Current and the Alaska Current, respectively. In the modern ocean, biogenic silica fluxes to the sea-floor sediments are comparatively high in these two areas. The sediments obtained from Site U1335 are predominantly nannofossil ooze with radiolarians (Pälike et al., 2010), and those from Site 887 consist of

4.1. Morphological variations in the S. peregrina lineage in the eastern equatorial Pacific Ocean (IODP Site U1335) In this study, a total of thirteen items were measured for the S. peregrina lineage (Figs. 3–9). The WS1 shows a maximum from

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WS3/WS4: ratio of WS3 to WS4 HS3/HS4: ratio of HS3 to HS4 WL2/WL3: ratio of WL2 to WL3 Fig. 2. Schematic diagram of a Stichocorys specimen showing the position of the measurements.

S. Kamikuri / Marine Micropaleontology 90–91 (2012) 13–28

12.5 to 11.0 Ma, a minimum from 11.0 to 9.5 Ma, and a slightly leftward shift (reduction) since 7.0 Ma (Fig. 3). The pattern of change is similar in the WS2, WS3 and WL2, showing two local minima from 11.0 to 9.5 Ma and from 7.0 to 3.0 Ma, showing two local maxima from 12.5 to 11.0 Ma and from 9.5 to 7.0 Ma (Fig. 3). The general change of the WS4 and HS4 becomes a gradual increase throughout the investigated time range (Figs. 3, 4). The WL4, HS2 and PD are very conservative through this lineage, showing little change and no apparent directional trends (Figs. 3, 4). The WL3 decreases near

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11.0 Ma, increases again near 9.5 Ma, and is relatively stable from 9.5 to 3.0 Ma (Fig. 3). The HS3 gradually increases in size after 11.0 Ma, and rapidly decreases near 7.0 Ma (Fig. 3). Previous studies have shown wide variation in size and shape of the third and fourth segments. To investigate the variation in size and shape, I calculated the ratio of WS3 to WS4 (WS3/WS4) and of HS3 to HS4 (HS3/HS4) (Figs. 7, 8). The WS3/WS4 showed a maximum from 12.5 to 7.0 Ma with a local minimum in the earliest late Miocene from 11.0 to 9.5 Ma (Fig. 7), decreased dramatically near 7.0 Ma, and

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Fig. 3. Changes through time in mean width of WS1, WS2, WS3, WS4, WL2, WL3, WL4, and in mean height of HS2 and HS3 for the S. peregrina lineage at Site U1335. Horizontal bars indicate ± 1 standard deviation unit. Vertical dotted lines are the mean values.

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pore diameter (μm)

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Fig. 4. Changes through time in mean height of the fourth segment (HS4), and in mean length of the pore diameter of the third segment (PD) for the S. peregrina lineage at Site U1335. Horizontal bars indicate ± 1 standard deviation unit. Vertical dotted lines are the mean values.

was relatively constant in the latest late Miocene. It showed a minimum in the Pliocene. The pattern of change is similar in the HS3/ HS4 (Fig. 8). In other words, the third segment became smaller in size as compared with the fourth segment from 11.0 to 9.5 Ma and from 7.0 to 3.0 Ma (Figs. 7, 8). The WL2/WL3 is a simple index for evaluating the morphology of the third segment (Fig. 9). This index equals one if the third segment is a cylinder, and approaches zero when the third segment is conical. The index indicates that the third segment approached a more conical shape through the studied interval (Fig. 9). Although this reduction (conicality) was gradual, the rate was not constant. The rate of reduction accelerated in the earliest late Miocene (about 11.0 Ma), decelerated in the middle late Miocene, accelerated again in the latest late Miocene (about 7.0 Ma), and remained low in the Pliocene. 4.2. Morphological variations in the S. peregrina lineage in the eastern North Pacific Ocean (ODP Site 887) The WS1, WS2, and HS2 show relatively high values from 10.6 to 8.0 Ma, and gradually decrease from 8.0 to 7.0 Ma (Fig. 5). The WS3, WS4, HS3, and HS4 showed relatively high values from 10.6 to 9.6 Ma, and gradually decreased after 6.0 Ma (Figs. 5, 6). The WL3 and WL4 became relatively large from 10.6 to 9.6 Ma, reached a minimum from 9.6 to 8.0 Ma, and became stable after 8.0 Ma (Fig. 5). The WL2 and PD remained virtually unchanged during the study interval (Figs. 5, 6). The WS3/WS4 increased near 9.5 Ma, decreased near 8.0 Ma, and was constant in the latest late Miocene and Pliocene (Fig. 7). The HS3/HS4 increased near 9.5 Ma, decreased near 7.0 Ma, and increased again in the Pliocene (Fig. 8). The mean values of WL2/WL3 increased gradually and slightly from 7.5 Ma (Fig. 9). 5. Discussion Shell size changes of marine plankton in time and space are related to several properties of the ambient seawater such as temperature, salinity, nutrients, carbonate saturation, dissolved silica, light attenuation, oxygen, and productivity. Schmidt et al. (2006) reviewed the patterns and outlined the causes of size changes geographically and through time in coccolithophorids, foraminifers and radiolarians. They stated that test sizes of planktic foraminiferal species became large gradually through the Neogene, and are smaller in subpolar and temperate areas than in subtropical and tropical areas of the modern ocean. Although radiolarian ecology is similar to that of planktic foraminifers, most modern radiolarians have a relatively constant shell size and/or do not show systematic variations (except for

wall thickness) with geography or environment (Hays, 1965; Kellogg, 1975a; Schmidt et al., 2006). Only a few examples of radiolarian shell size gradients exist (Moore, 1969; Bjørklund, 1977; Granlund, 1986; Cortese and Bjørklund, 1997; Matul and Abelmann, 2005). The main feature through the Neogene is highly variable size patterns in radiolarians, but they do not show a noticeable systematic trend (Kellogg, 1975b; Kellogg and Hays, 1975; Caulet, 1986; Lazarus et al., 1986; Motoyama, 1997; Schmidt et al., 2006). However, the number of lineages studied is too few, when compared with the high diversity of radiolarians, to clarify general trends about the size variation of radiolarians in time and space.

5.1. Comparison of the S. peregrina lineage between the low and high latitudes The genus Stichocorys is composed of several joined segments, and is characterized by the conical upper half and the lower cylindrical half. The S. peregrina lineage can be subdivided into two morphotypes geographically based on the shape and size variations: a low-latitude morphotype having a thin-walled shell with a smooth surface (Plates 1–3), small-sized pores (Fig. 4), small first and second segments (Fig. 3), large third and fourth segments (Figs. 3, 4), and the obviously conical third segment (Fig. 9); a high-latitude morphotype having a relatively thick-walled shell with a rough surface (Plates 1–3), large-sized pores (Fig. 6), large first and second segments (Fig. 5), relatively small third and fourth segments (Figs. 5, 6), and the typically inflated third segment (Fig. 9). Previous studies have shown at least two geographical variations in the overall shape of S. peregrina (Kling, 1973; Pisias and Moore, 1978; WestbergSmith and Riedel, 1978; Sanfilippo et al., 1985). The boundary of the geographical distribution was placed at about 20° in both hemispheres (Sanfilippo et al., 1985). Casey et al. (1983) stated that there are also size and shape differences between the low and high latitude forms of S. delmontensis as well as S. peregrina. The present data supports this opinion. The size and shape differences with latitude in the S. peregrina lineage existed throughout the studied intervals. The noticeable trend might have been influenced by the environments of the ambient seawater, because the latitudinal gradient of environmental conditions such as water temperature and/or salinity was already formed in the North Pacific Ocean in at least the late Miocene (Savin et al., 1985). The hypothesis should be verified by additional information on the size and shape variations of the S. peregrina lineage in the middle latitudes and in the western North Pacific.

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Fig. 5. Changes through time in mean width of WS1, WS2, WS3, WS4, WL2, WL3, WL4, and in mean height of HS2 and HS3 for the S. peregrina lineage at Site 887. Horizontal bars indicate ± 1 standard deviation unit. Vertical dotted lines are the mean values.

5.2. Temporal variation of the S. peregrina lineage Previous studies have suggested variations through time in the size and shape of the third and fourth segments (Kling, 1973; Pisias and Moore, 1978; Westberg-Smith and Riedel, 1978; Sanfilippo et al., 1985). Figures 7 and 8 show that the third segment became smaller in width and height than the fourth segment from 11.0 to 9.5 Ma in the low latitudes. In addition, the increase in conicality of the third segment was initiated at about 11.0 Ma (Fig. 9).

The first and second segments were also relatively small in this short interval (Fig. 3). These morphologic changes coincided in timing with the carbonate crash in the earliest late Miocene (Fig. 10). The carbonate crash occurred with the increase in bioproductivity and the late Miocene cooling event Mi6. Although it is difficult to identify a specific selective factor driving the morphologic changes, the changes near 11.0 Ma might be related to the paleoceanographic environmental changes such as high bioproductivity and/or cooling.

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Fig. 6. Changes through time in mean height of the fourth segment (HS4), and in mean length of the pore diameter of the third segment (PD) for the S. peregrina lineage at Site 887. Horizontal bars indicate ± 1 standard deviation unit. Vertical dotted lines are the mean values.

The rapid, gradual decreases of the third segment in size as compared with the fourth segment and the shape changes took place at the onset of cooler conditions and high bioproductivity (biogenic bloom) in the latest late Miocene (Fig. 10). Following the acquisition of the conical and small third segment in the S. peregrina lineage, the ratios remained relatively low during the return of warmer conditions in the early Pliocene. In the high latitudes, the ratio of third segment to fourth segment in width and height (WS3/WS4 and HS3/HS4) showed a maximum from 9.5 to 8.0 Ma with a local minimum near 9.0 Ma, and decreased stepwise at about 8.0 and 6.5 Ma (Figs. 7, 8). The width of the third segment as compared with the fourth segment (WS3/WS4) increased about 0.7 myr earlier than the beginning of climatic optimum 3 (Fig. 10). The local minimum took place about 0.6 myr earlier than a temporary cooling in climatic optimum 3 (Fig. 10). The decrease in the width and height of the third segment as compared with the fourth segment was initiated about 1.0 myr earlier than the late Miocene cooling event following climatic optimum 3, and the slight increase in width and height occurred at the same time as the return of warmer conditions in the early Pliocene. Although these morphologic trends seem to be similar to the general patterns in the oxygen isotope curve of benthic foraminifera, these data did not suggest an agreement in their timing. In the high latitudes, primary bioproductivity showed a temporary increase near 9.0 Ma and the broad increase from 7.0 to 3.0 Ma (Fig. 10; Barron,

1998). These bioproductivity changes were not associated with the morphologic changes. In summary, there is a close correspondence between major paleoceanographic events and the evolutionary changes of the S. peregrina lineage in the low latitudes. However, the radiolarian data in the high latitudes show the lack of a clear relationship between the paleoceanographic events and the size and shape variations of the S. peregrina lineage. Stichocorys peregrina disappeared at 6.7 Ma at Site 192 in the western North Pacific (Motoyama, 1996), 3.3 Ma at Site 887 in the eastern North Pacific (Morley and Nigrini, 1995; Kamikuri et al., 2007), and 2.7 Ma at Sites 845 and 1241 in the equatorial Pacific (Moore, 1995; Kamikuri et al., 2009). It seems that the reduction in their geographic distribution started in the late Miocene and occurred dramatically within a short interval (0.6 myr) in the late Pliocene. This notable event might be related to global cooling and/or the initiation of Northern Hemisphere glaciation in the North Pacific in the late Miocene. 5.3. Evolutionary transition from S. delmontensis to S. peregrina The evolutionary transition (ET) from S. delmontensis to S. peregrina has provided useful biohorizons for biostratigraphic correlation and age determination in the North Pacific Ocean (e.g., Johnson and Nigrini, 1985; Moore, 1995; Weber and Pisias, 2006; Kamikuri et al., 2009).

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S. Kamikuri / Marine Micropaleontology 90–91 (2012) 13–28

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Fig. 8. Ratio of the HS3 to HS4 (HS3/HS4) for the S. peregrina lineage. Horizontal bars indicate ± 1 standard deviation unit. Rectangles indicate 95% confidence intervals. Vertical dotted lines are the mean values.

The ET defines the base of Zone RN9 (S. peregrina Interval Zone) in the low latitudes and the base of the S. peregrina Zone in the middle latitudes, and is placed within the Lipmanella redondoensis Zone in the high latitudes. The ET takes place at the stratigraphic level at which S. peregrina becomes more abundant than S. delmontensis (Sanfilippo and Nigrini, 1998), and was calibrated at an age of 7.0 Ma in the low latitudes (Sanfilippo and Nigrini, 1998; Kamikuri et al., 2009) and 8.2 Ma in the middle and high latitudes (Reynolds, 1980; Motoyama and Maruyama, 1998; Kamikuri et al., 2004, 2007). Stichocorys peregrina is distinguished from the ancestor S. delmontensis by having the fourth segment as wide as or wider than the third segment (Sanfilippo et al., 1985). Holdsworth (1975) discussed some difficulties with regard to the identification of S. peregrina and the ancestor S. delmontensis, and stated that the evolutionary transition is a most unsatisfactory datum for the Neogene radiolarian biostratigraphy. In this study, I identified S. delmontensis and S. peregrina based on the data of morphologic analysis as mentioned above, and calibrated the percentage of each species within the total abundance of S. delmontensis and S. peregrina. Figure 11 shows that the occurrence of S. peregrina exceeded that of S. delmontensis in two stratigraphic intervals throughout the studied interval at the two sites. At Site U1335 in the eastern equatorial Pacific, the ET can be placed near 11.0 and 7.0 Ma. In this study, I call the first event which occurred near 11.0 Ma as the pre-ET, because the second event near 7 Ma corresponds in

timing to the ET indicated by previous studies. The two ETs were also recognized at Site 289 in the western equatorial Pacific. Fig. 6 of Romine and Lombari (1985) showed that S. peregrina first appeared in the middle Miocene, and exceeded S. delmontensis in relative abundance in the early late Miocene and latest Miocene. Although it may be a problem to identify the ET from S. delmontensis to S. peregrina and the lower limit of Zone RN9 in a sedimentary sequence, the ET is easily distinguished from the pre-ET by the appearance of the typical S. peregrina morphotype. Figures 12 and 13 show that the third segment of S. peregrina became shorter and pronouncedly conical, and the fourth segment was longer and pronouncedly wider than the third segment since the latest Miocene (7.0 Ma). Kamikuri et al. (2009) did not show the pre-ET during the early late Miocene at Sites 845 and 1241 in the eastern equatorial Pacific. In the course of that earlier study, I encountered some S. peregrina which have a less conical third segment but assigned them to “Stichocorys spp.”. Theyer et al. (1978) calibrated an age of 6.4 Ma (7.0 Ma for GTS2004) for the first appearance of S. peregrina in the low latitudes. These studies seem to indicate that the first appearance of the typical S. peregrina morphotype is definable and recognizable. Hence the ET can be used as a primary biostratigraphic marker in low latitudes. At Site 887 in the subarctic Northeast Pacific, S. delmontensis and S. peregrina co-occur throughout much of the studied interval (Fig. 11). Stichocorys peregrina appeared at 15.0 Ma at Site 887 (Kamikuri et al.,

WL2/WL3

WL2/WL3 0.3

0.5

0.6

0.7

0.8

0.9

0.3 3

Site U1335

4

4

5

5

6

6

7 8

Age (Ma)

Age (Ma)

3

0.4

0.4

0.5

0.6

0.7

0.8

0.9

Site 887

7 8

9

9

10

10

11

11

12

12

Fig. 9. Ratio of the WL2 to WL3 (WL2/WL3) for the S. peregrina lineage. Horizontal bars indicate ±1 standard deviation unit. Rectangles indicate 95% confidence intervals. Vertical dotted lines are the mean values.

20

S. Kamikuri / Marine Micropaleontology 90–91 (2012) 13–28

2a 1a

1b

4a

4b

5a

8a 7a

2b

7b

5b

3a

3b

6a

6b

9a

9b

8b 100 µm

Plate 1. Stichocorys delmontensis (Campbell and Clark) in the eastern equatorial Pacific. Figs. 1a–9b. Stichocorys delmontensis: 1a, b, U1335A-4HCC, V34/1; 2a, b, U1335A-4HCC, B16/ 3; 3a, b, U1335A-5HCC, E26/0; 4a, b, U1335A-5HCC, G24/1; 5a, b, U1335A-5HCC, V24/2; 6a, b, U1335A-6H-2, 105–107 cm, J29/3; 7a, b, U1335A-6H-2, 105–107 cm, X39/1; 8a, b, U1335A-5HCC, Y18/1; 9a, b, U1335A-6H-2, 105–107 cm, Z38/1.

2007), and the overlapping range of the two species covers a considerable time interval from 15.0 to 3.3 Ma. The first ET (pre-ET) occurred by at least 10.5 Ma. Although S. peregrina was more abundant than S.

delmontensis from 10.5 to 9.6 Ma at Site 887, S. delmontensis occurred more abundantly than S. peregrina after this event from 9.6 to 8.0 Ma. The next ET can be placed near 8.0 Ma, where S. peregrina becomes

S. Kamikuri / Marine Micropaleontology 90–91 (2012) 13–28

1a

2b

2a

1b

21

3a

4a

4b

5a

3b

6a

5b

6b

100 µm

7a

7b

8a

8b

9a

9b

Plate 2. Stichocorys peregrina (Riedel) in the eastern equatorial Pacific. Figs. 1a–9b. Stichocorys peregrina: 1a, b, U1335A-3HCC, L48/0; 2a, b, U1335A-3H-4, 105–107 cm, F18/0; 3a, b, U1335A-3H-4, 105–107 cm, S39/4; 4a, b, U1335A-3H-4, 105–107 cm, H35/0; 5a, b, U1335A-3H-4, 105–107 cm, E36/3; 6a, b, U1335A-3H-4, 105–107 cm, W37/1; 7a, b, U1335A-3H4, 105–107 cm, S31/0; 8a, b, U1335A-3HCC, D48/0; 9a, b, U1335B-4HCC, W22/0.

more abundant than S. delmontensis. The second ET, which occurred near 8.0 Ma, could be interpreted as the ET indicated by previous studies in the middle latitudes (Reynolds, 1980; Motoyama, 1996;

Kamikuri et al., 2004). Wolfart (1981) showed that the ET from S. delmontensis to S. peregrina was placed near the middle/late Miocene boundary at Site 469 in the middle latitude of the Northeast

22

S. Kamikuri / Marine Micropaleontology 90–91 (2012) 13–28

1b 100 µm

1a

4a

4b

7a

10a

7b

10b

2a

5a

8a

11a

2b

5b

3a

3b

6a

6b

9a

9b

12a

12b

8b

11b

Plate 3. Stichocorys delmontensis (Campbell and Clark) and Stichocorys peregrina (Riedel) in the eastern North Pacific. Figs. 1a–6b. Stichocorys delmontensis: 1a, b, 887C-22H-3, 20–22 cm, D29/1; 2a, b, 887C-23H-7, 20–22 cm, H47/4; 3a, b, 887C-25H-5, 100–122 cm, O23/1; 4a, b, 887C-22H-3, 20–22 cm, C20/0; 5a, b, 887C-23H-7, 20–22 cm, B38/1; 6a, b, 887C-25H-5, 100–122 cm, K30/0. Figs. 7a–12b. Stichocorys peregrina: 7a, b, 887C-22H-5, 20–22 cm, Y25/0; 8a, b, 887C-22H-5, 20–22 cm, Y14/4; 9a, b, 887C-22H-3, 20–22 cm, H41/3; 10a, b, 887C-22H-1, 20–22 cm, S36/4; 11a, b, 887C-22H-3, 20–22 cm, E27/3; 12a, b, 887C-22H-3, 20–22 cm, P32/0.

S. Kamikuri / Marine Micropaleontology 90–91 (2012) 13–28

23

Polarity

4

3

n

Site U1335 (low latitude)

r

C2

Site 849

r

Productivity events low high latitude latitude

third segment ← conical

Site 887 (high latitude) third segment

WS3/WS4 ← small

← conical

WS3/WS4 ← small

Last occurrence

Event D

n

Last occurrence

C2A r

Site 588/590 3 2

n

Pliocene warming

C3

6

Glaciation

r n

C3A r n

7

Biogenic bloom

5

Stichocorys peregrina Lineage

Climatic events

δ18 O (‰) 5

Glaciation

Pliocene Early Late

4

Oxygen isotope

C1 n

2 3

Chron

Epoch Pleistocene

0 1

Early M L

Time (Ma)

ATNTS2004

Event C Decrease of WS3/WS4 and HS3/HS4

Decrease of WS3/WS4 and HS3/HS4

Decrease of WS3/WS4 and HS3/HS4

Decrease of WS3/WS4 and HS3/HS4

Event B

9

n

Climatic optimum 3

C4 r n

C4A

Mi 7

r

10

Mi 6

n

C5

11

Climatic optimum 2 Mi 5

12 13

Middle

r n

C5A

Carbomate crash

8

Miocene Late

C3B r

Event A

Mi 4

r

Fig. 10. Major paleoceanographic changes and morphologic changes for the S. peregrina lineage since the middle Miocene. Climatic records are the oxygen isotope stratigraphy (Kennett, 1986; Mix et al., 1995), isotope events (Barron and Baldauf, 1990; Miller et al., 1991), and productivity events (Farrell et al., 1995; Lyle et al., 1995; Barron, 1998).

Pacific. The ET, which was indicated by Wolfart (1981), seems to correspond to my first ET (pre-ET) near 10.5 Ma. The second ET from S. delmontensis to S. peregrina was not recognized in sediments at Site 469 because of some hiatuses. These data indicate that it is difficult to discriminate between the ET and pre-ET in sedimentary sequences in the middle and high latitudes, especially if there are some hiatuses in the upper Miocene. Figures 12 and 13 show that, beyond the minor changes in the ratio of third to fourth segment widths, there is no obvious tendency that can be used to distinguish S. delmontensis from the descendant S. peregrina in the high latitudes. The histogram of WS3/WS4 for the S. peregrina lineage (S. peregrina + S. delmontensis) also does not show a clear bi-modal but more of a uni-modal distribution throughout the studied interval (Fig. 14). It might not be easy to use the ET for biostratigraphic correlation and age determination in the high latitudes.

5.4. Evolutionary pattern Norris (2000) reviewed speciation models for pelagic environments, including allopatry, parapatry, vicariance, depth parapatry/ sympatry, and seasonal parapatry/sympatry. He stated that it seems likely that vicariant and allopatric models for speciation are far less important than sympatric/parapatric speciation. Lazarus et al. (1986) and Motoyama (1997) also analyzed the size variation in detailed studies of some tropical radiolarian lineages and the Cycladophora davisiana lineage, and stated that the pattern would be of a sympatric/parapatric speciation (transition). The biostratigraphic and geographic distributions of S. delmontensis and S. peregrina are relatively well known. In the North Pacific Ocean, the S. peregrina lineage was widespread and common from low to high latitudes except for the western North Pacific (e.g., Sancetta, 1978; Lombari, 1985; Romine, 1985; Sanfilippo et al., 1985; Spencer-Cervato

relative abundance (%) 0

20

40

60

80

relative abundance (%) 100

0

3

3

Site U1335

4

S. peregrina S. delmontensis

4

5

Age (Ma)

Age (Ma)

60

80

100

Site 887 S. peregrina S. delmontensis

6 ET

8

7 8

ET

9

9

10

10 pre-ET

11

40

5

6 7

20

pre-ET ?

11 12

Fig. 11. Changes through time in relative abundance of specimens of the S. peregrina lineage. ET, evolutionary transition.

24

S. Kamikuri / Marine Micropaleontology 90–91 (2012) 13–28

WS3/WS4 0.8

0.9

1.0

1.1

WS3/WS4 1.2

0.8

1.3

1.8

1.0

1.1

1.2

1.3

1.8 Site U1335

1.7

7.3~9.4 Ma

1.6

1.6

1.5

1.5

1.4

9.8~10.9 Ma

1.3 11.3~12.2 Ma

HS3/HS4

HS3/HS4

1.7

0.9

1.4

1.2

1.1

1.1

1.0

1.0

3.2~6.6 Ma

3.4~7.9 Ma 9.7~10.6 Ma

1.3

1.2

0.9

Site 887

8.0~9.5 Ma

0.9

Fig. 12. Scatter plot of HS3/HS4 vs. WS3/WS4 for the S. peregrina lineage. Each point represents one mean value.

clear relationship between the paleoceanographic events and size variation of this lineage. (3) The evolutionary transition (ET) from S. delmontensis to S. peregrina can be used as a primary biostratigraphic marker in the low latitudes. However, it is not easy to use the ET for biostratigraphic correlation and age determination in the high latitudes, because there is no obvious discriminator, beyond the minor changes in the ratio of the third to fourth segment widths, that allows S. delmontensis to be distinguished from the descendant S. peregrina. (4) The morphologic changes of the S. peregrina lineage should be assigned to a sympatric/parapatric transition.

et al., 1993; Morley and Nigrini, 1995; Shilov, 1995; Oseki and Suzuki, 2009). Since they have had continuous geographic co-occurrence throughout the North Pacific, the observed pattern in morphologic changes (anagenetic evolution) of the S. peregrina lineage should be assigned to a sympatric/parapatric transition. However, it is not certain whether the high latitude morphotype of S. peregrina migrated toward lower latitudes and changed to the low latitude morphotype from 8.0 to 7.0 Ma or whether each morphotype changed independently in each water mass in the latest late Miocene.

6. Conclusions I quantitatively investigated variations of S. peregrina and the ancestor S. delmontensis from the middle Miocene to late Pliocene at IODP Site U1335 in the eastern equatorial Pacific and ODP Site 887 in the eastern North Pacific and reached the following conclusions. (1) The S. peregrina lineage can be subdivided into two morphotypes geographically based on shape and size variations. Previous studies have shown at least two geographical variations in the overall shape of S. peregrina. The present data indicated that there are also size and shape differences between the low and high latitudes in S. delmontensis as well as S. peregrina. The noticeable trend might have been influenced by the environment of the ambient seawater. (2) There is a close correspondence between major paleoceanographic events in the late Neogene and evolutionary changes of the S. peregrina lineage in the low latitudes. However, the radiolarian data in the high latitudes did not show a

7. Systematic descriptions 7.1. Stichocorys delmontensis (Campbell and Clark) Plate 1, Figs. 1–9; Plate 3, Figs. 1–6. Eucyrtidium delmontense Campbell and Clark, 1944, p. 56, pl. 7, Figs. 19–20. Stichocorys delmontensis (Campbell and Clark), Riedel and Sanfilippo, 1970, p. 530, pl. 14, Fig. 6; 1971, p. 1595, pl. 1F, Figs. 5–7, pl. 2E, Figs. 10, 11; 1978, p. 74, pl. 9, Fig. 10; Sanfilippo and Riedel, 1970, p. 451, pl. 1, Fig. 9; Kling, 1971, p. 1087, pl. 2, Fig. 4; 1973, p. 638, pl. 11, Figs. 8–10; Moore, 1971, p. 742, pl. 13, Fig. 7; Goll, 1972, p. 960, pl. 34, Figs. 1–3, pl. 35, Fig. 1; Petrushevskaya and Kozlova, 1972, p. 546, pl. 25, Figs. 11, 12; Dinkelman, 1973, p. 783, pl. 9, Fig. 1; Ling, 1973, p. 781, pl. 2, Fig. 12; 1975, p. 730, pl. 11, Fig. 9; Sanfilippo et al., 1973, pl. 6, Fig. 3; 1985, p. 681, Figs. 23.1a, 1b; Johnson and von der Borch, 1974, p. 549, pl. 8, Fig. 13; Nigrini, 1974,

WS3/WS4

WS3/WS4 0.8

0.9

1.0

1.1

1.2

0.8

1.3

0.8

0.9

1.0

1.1

1.2

1.3

0.8 Site U1335

Site 887

0.7

WL2/WL3

WL2/WL3

11.3~12.2 Ma

9.8~10.9 Ma

0.6

0.7

8.0~9.5 Ma

3.4~7.9 Ma 9.7~10.6 Ma

0.6

7.3~9.4 Ma 3.2~6.6 Ma

0.5

0.5

Fig. 13. Scatter plot of WL2/WL3 vs. WS3/WS4 for the S. peregrina lineage. Each point represents one mean value.

S. Kamikuri / Marine Micropaleontology 90–91 (2012) 13–28

3.18 Ma 3.74 Ma 4.21 Ma 4.40 Ma

10 0 10

n=30

0 10

n=30

0 20

n=30

3.45 Ma 10

5.04 Ma 5.69 Ma 5.95 Ma 6.16 Ma 6.60 Ma 7.28 Ma 7.40 Ma 7.93 Ma 8.41 Ma 8.80 Ma 8.84 Ma

4.05 Ma

10

9.04 Ma 9.44 Ma 9.76 Ma 9.94 Ma 10.33 Ma 10.89 Ma 11.31 Ma 11.78 Ma 11.84 Ma 11.89 Ma 11.95 Ma 12.00 Ma 12.02 Ma 12.05 Ma 12.11 Ma 12.16 Ma

10

n=18

0

n=30

5.02 Ma

10 0 10

n=30

0 10

n=30

0

n=30

0 10

n=30

0 10

n=30

0 10

n=30

0 10

n=30

0 10

n=30

0 10

n=30

0 10

n=30

0 10

n=30

0

n=30

10

n=28

0

5.48 Ma

10

n=26

0

6.17 Ma

10

10

n=16

0 10

6.39 Ma

6.90 Ma

n=24

0 10

n=30

0

7.11 Ma

10

n=30

0

7.32 Ma

10

n=30

0

7.52 Ma

10

n=30

0

7.67 Ma

10

8.90 Ma

n=30

0

0

4.56 Ma

25

0 10

n=30

0 10

n=30

0 10

n=30

0 10

n=30

0 10

n=30

0 10

n=30

0 10

n=30

0 10

n=30

0 10

n=30

0 10

n=30

0 10

n=30

0 10

n=30

0 10

n=30

0 10

n=30

0 10

n=30

0 10

n=30

0

n=30

10

n=30

0

7.89 Ma

10

n=30

0 10

8.00 Ma 8.27 Ma 8.64 Ma

n=30

0 10

n=30

0 10

n=30

0 10

8.78 Ma 8.90 Ma 9.02 Ma

n=30

0 10

n=30

0 10

n=30

0

9.47 Ma

10

n=30

0 10

9.67 Ma 9.80 Ma

0.7

0.8

0.9

1.0

1.1

1.2

1.3

1.4

1.5

n=30

0 10

10.08 Ma

0.6

n=30

0 10

10.63 Ma

n=30

0 10

n=30

0 0.6

0.7

0.8

0.9

WS3/WS4

1.0

1.1

1.2

1.3

1.4

1.5

WS3/WS4

Fig. 14. Histogram of WS3/WS4 for the S. peregrina lineage.

p. 1068, pl. 7, Fig. 4; Chen, 1975, p. 462, pl. 20, Fig. 10; Foreman, 1975, p. 622, pl. 9, Figs. 5–7; Westberg-Smith and Riedel, 1978, pl. 3, Figs. 1–5; Sakai, 1980, p. 711, pl. 8, Fig. 3; Wolfart, 1981, p. 499, pl. 1, Figs., 10, 11; Morley, 1985, p. 412, pl. 7, Fig. 2; Funakawa, 1993, pl. 1, Fig. 9, pl. 2, Fig. 14; Morley and Nigrini, 1995, p. 82, pl. 6, Fig. 5; Shilov, 1995, p. 109, pl. 4, Figs. 3, 4; Motoyama, 1996, p. 258, pl. 5, Fig. 3; Chen et al., 2003, Fig. 2c; Yamamoto and Kawakami, 2005, Fig. 10.16; Kamikuri et al., 2009, p. 742, Fig. 10.Q; Oseki and Suzuki, 2009, p. 186, Fig. 25; Sawada et al., 2009, pl. 1, Figs. 12, 13; Shinzawa et al., 2009, p. 129, pl. 3, Fig. 15. Remarks: In the low latitudes, the shells are relatively thin-walled with a smooth outline. The fourth segment width increases gradually more than the third segment from the middle to late Miocene. The third segment is inflated annular in the middle Miocene, but conical

in the late Miocene. In the high latitudes, the shells are thick-walled with a moderately rough outline. The third segment is typically inflated annular rather than conical, and the ratio of the third segment height to the fourth segment was approximately constant. This ratio was relatively smaller, and the first and second segments and the pore diameter are larger in the high-latitude morphotype than in the low-latitude morphotype.

7.2. Stichocorys peregrina (Riedel) Plate 2, Figs. 1–9; Plate 3, Figs. 7–12. Eucyrtidium elongatum peregrinum Riedel, 1953, p. 812, pl. 85, Fig. 2.

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Stichocorys peregrina (Riedel), Sanfilippo and Riedel, 1970, p. 451, pl. 1, Fig. 10; Riedel and Sanfilippo, 1971, p. 1595, pl. 1F, Figs. 2–4, pl. 8, Fig. 5; 1978, p. 74, pl. 9, Fig. 11; Kling, 1971, p. 1087, pl. 2, Fig. 13; 1973, p. 638, pl. 4, Fig. 27, pl. 11, Fig. 29, pl. 13, Figs. 9, 10; Moore, 1971, p. 742, pl. 13, Figs. 9, 10; Goll, 1972, p. 961, pl. 36, Figs. 1–3; Petrushevskaya and Kozlova, 1972, p. 547, pl. 25, Fig. 25; Dinkelman, 1973, p. 784, pl. 9, Figs. 2, 3; Johnson and von der Borch, 1974, p. 549, pl. 8, Fig. 12; Nigrini, 1974, p. 1068, pl. 7, Fig. 5; Foreman, 1975, p. 622, pl. 9, Figs. 1–4; Petrushevskaya, 1975, p. 582, pl. 14, Fig. 16; Pisias and Moore, 1978, p. 847, pl. 3, Figs. 1–3; Westberg-Smith and Riedel, 1978, p. 22, pl. 3, Figs. 6–9; Sakai, 1980, p. 711, pl. 8, Figs. 1, 2; Wolfart, 1981, p. 499, pl. 1, Figs., 6–8; Molina-Cruz, 1982, p. 995, pl. 1, Figs. 1–4; Weaver, 1983, p. 678, pl. 6, Figs. 3, 9; Morley, 1985, p. 412, pl. 7, Fig. 1A, B; Sanfilippo et al., 1985, p. 682, Fig. 23.2; Caulet, 1986, p. 853, pl. 6, Fig. 4; Funakawa, 1993, pl. 1, Fig. 10, pl. 2, Fig. 15; Morley and Nigrini, 1995, p. 81, pl. 6, Figs. 2, 3; Motoyama, 1996, p. 258, pl. 5, Fig. 2; Yamamoto and Kawakami, 2005, Fig. 10.17; Kamikuri et al., 2009, p. 742, Fig. 10.P; Oseki and Suzuki, 2009, p. 186, Fig. 26; Sawada et al., 2009, pl. 1, Figs. 12, 13; Shinzawa et al., 2009, p. 129, pl. 3, Fig. 16; Sono et al., 2009, p. 149, pl. 3, Figs. 18–20. Remarks: This species has an upper, conical part of the shell composed of four segments rather than three, and the fourth segment is as wide as or wider than the third segment (Sanfilippo et al., 1985). In the low latitudes, the shells are relatively thin-walled with a smooth outline. The fourth segment height increases more than the third segment from the late Miocene to late Pliocene. The conicality of the third segment also increases from the late Miocene to late Pliocene. In the high latitudes, the shells are thick-walled with a moderately rough outline. The third segment is typically inflated annular rather than conical, and the ratio of the third segment height to the fourth segment height is approximately constant. The first and second segments and the pore diameter were larger in the highlatitude morphotype than the low-latitude morphotype. Acknowledgments Ted Moore (University of Michigan) is warmly thanked for valuable comments on earlier versions of this manuscript. I thank Noritoshi Suzuki (Tohoku University) and Kaoru Ogane (National Museum of Nature and Science) for discussions. The author is grateful to Simon Haslett (University of Wales) and Paulian Dumitrica for reviewing the manuscript. I am also grateful to Heiko Pälike (University of Southampton), Hiroshi Nishi (Tohoku University), and the other scientists and crew members of Leg 320 of JOIDES Resolution for their support and prompt attention to my requests. This work was financially supported by a Grant-in-Aid for Research Fellowships of the Japan Society for the Promotion of Science for Young Scientists (number 20·1155) to the author. References Barron, J.A., 1998. Late Neogene changes in diatom sedimentation in the North Pacific. Journal of Asian Earth Sciences 16, 85–95. Barron, J.A., Baldauf, J.G., 1990. Development of biosiliceous sedimentation in the North Pacific during the Miocene and early Pliocene. In: Tsuchi, R. (Ed.), Pacific Neogene Events: Their Timing, Nature and Interrelationship. University of Tokyo Press, pp. 43–63. Barron, J.A., Basov, I.A., Beaufort, L., Dubuisson, G., Gladenkov, A.Y., Morley, J.J., Okada, M., Olafsson, G., Pak, D.K., Roberts, A.P., Shilov, V.V., Weeks, R.J., 1995. Biostratigraphic and magnetostratigraphic summary. In: Rea, D.K., Basov, I.A., Scholl, D.W., Allan, J.F. (Eds.), Proceedings of the Ocean Drilling Program, Scientific Results, 145. Ocean Drilling Program, College Station, TX, pp. 559–575. Billups, K., 2002. Late Miocene through early Pliocene deep water circulation and climatic change viewed from the sub-Antarctic south Atlantic. Palaeogeography, Palaeoclimatology, Palaeoecology 185, 287–307. Billups, K., Ravelo, A.C., Zachos, J.C., 1998. Early Pliocene climate: a perspective from the western equatorial Atlantic warm pool. Paleoceanography 13, 459–470. Bjørklund, K.R., 1977. Actinomma haysi, n. sp., its Holocene distribution and size variation in Atlantic Ocean sediments. Micropaleontology 23, 114–126.

Campbell, A.S., Clark, B.L., 1944. Miocene radiolarian faunas from Southern California. Geological Society of America Special Paper 51, 1–76. Casey, R.E., Wigley, C.R., Perez-Guzmán, A.M., 1983. Biogeographic and ecologic perspective on polycystine radiolarian evolution. Paleobiology 9, 363–376. Caulet, J.P., 1986. Radiolarians from the Southwest Pacific. In: Kennett, J.P., von der Borch, C.C., et al. (Eds.), Initial Reports of the Deep Sea Drilling Project, 90. U.S. Government Printing Office, Washington, pp. 835–861. Chen, P.-H., 1975. Antarctic radiolaria. In: Hayes, D.E., Frakes, L.A. (Eds.), Initial Reports of the Deep Sea Drilling Project, 28. U.S. Government Printing Office, Washington, pp. 437–513. Chen, M., Wang, R., Yang, L., Han, J., Lu, J., 2003. Development of east Asian summer monsoon environments in the late Miocene: radiolarian evidence from Site 1143 of ODP Leg 184. Marine Geology 201, 169–177. Cortese, G., Bjørklund, K.R., 1997. The morphometric variation of Actinomma boreale (Radiolaria) in Atlantic boreal waters. Marine Micropaleontology 29, 271–282. Cortese, G., Gersonde, R., Hillenbrand, C.-D., Kuhn, G., 2004. Opal sedimentation shifts in the world ocean over the last 15 myr. Earth and Planetary Science Letters 224, 509–527. Dickens, G., Owen, R.M., 1999. The latest Miocene–Early Pliocene biogenic bloom: a revised Indian Ocean perspective. Marine Geology 161, 75–91. Diester-Haass, L., Meyers, P., Vidal, L., 2002. The late Miocene onset of high productivity in the Benguela Current upwelling system as part of a global pattern. Marine Geology 180, 87–103. Dinkelman, M.G., 1973. Radiolarian stratigraphy: Leg 16, Deep Sea Drilling Project. In: van Andel, T.H., Heath, G.R. (Eds.), Initial Reports of the Deep Sea Drilling Project, 16. U.S. Government Printing Office, Washington, pp. 747–813. Dowsett, H., Barron, J., Poore, R., 1996. Middle Pliocene sea surface temperatures: a global reconstruction. Marine Micropaleontology 27, 113–125. Farrell, J.W., Raffi, I., Janecek, T.R., Murray, D.W., Levitan, M., Dadey, K.A., Emeis, K.-C., Lyle, M., Flores, J.-A., Hovan, S., 1995. Late Neogene sedimentation patterns in the eastern equatorial Pacific Ocean. In: Pisias, N.G. (Ed.), Proceedings of the Ocean Drilling Program, Scientific Results, 138. Ocean Drilling Program, College Station, TX, pp. 717–756. Foreman, H.P., 1975. Radiolaria from the North Pacific, Deep Sea Drilling Project, Leg 32. In: Larson, R.L., Moberly, R. (Eds.), Initial Reports of the Deep Sea Drilling Project, 32. U.S. Government Printing Office, Washington, pp. 579–676. Funakawa, S., 1993. Late Miocene radiolarian fossils from eastern Hokkaido, Japan. News of Osaka Micropaleontologists, Special Volume 9, pp. 293–311. Goll, R.M., 1972. Leg 9 synthesis, radiolaria. In: Hays, J.D. (Ed.), Initial Reports of the Deep Sea Drilling Project, 9. U.S. Government Printing Office, Washington, pp. 947–1058. Granlund, A.H., 1986. Size and shape patterns in the recent radiolarian genus Antarctissa. Marine Micropaleontology 11, 243–250. Grant, K.M., Dickens, G.R., 2002. Coupled productivity and carbon isotope records in the southwest Pacific Ocean during the late Miocene–early Pliocene biogenic bloom. Palaeogeography, Palaeoclimatology, Palaeoecology 187, 61–82. Haslett, S.K., 2004. Late Neogene–Quaternary radiolarian biostratigraphy: a brief review. Journal of Micropaleontology 23, 39–47. Haug, G.H., Tiedemann, R., 1998. Effect of the formation of the Isthmus of Panama on Atlantic Ocean thermocline circulation. Nature 393, 673–676. Haug, G.H., Maslin, M.A., Sarnthein, M., Stax, R., Tiedemann, R., 1995. Evolution of northwest Pacific sedimentation patterns since 6 Ma (Site 882). In: Rea, D.K., Basov, I.A., Scholl, D.W., Allan, J.F. (Eds.), Proceedings of the Ocean Drilling Program, Scientific Results, 145. Ocean Drilling Program, College Station, TX, pp. 293–315. Haug, G.H., Ganopolski, A., Sigman, D.M., Rosell-Mele, A., Swann, G.E.A., Tiedemann, R., Jaccard, S.L., Bollmann, J., Maslin, M.A., Leng, M.J., Eglinton, G., 2005. North Pacific seasonality and the glaciation of North America 2.7 million years ago. Nature 433, 821–825. Hays, J.D., 1965. Radiolaria and late Tertiary and Quaternary history of Antarctic Seas. Antarctic Research Series 5, 125–184. Holdsworth, B.K., 1975. Cenozoic radiolaria biostratigraphy: Leg 30: tropical and equatorial Pacific. In: Andrews, J.E., Packham, G. (Eds.), Initial Reports of the Deep Sea Drilling Project, 30. U.S. Government Printing Office, Washington, pp. 499–538. Johnson, D.A., Nigrini, C.A., 1985. Time-transgressive Late Cenozoic radiolarian events of the equatorial Indo-Pacific. Science 230, 538–540. Johnson, D.A., von der Borch, C.C., 1974. Radiolaria from the eastern Indian Ocean, DSDP Leg 22. In: Sclater, J.G. (Ed.), Initial Reports of the Deep Sea Drilling Project, 22. U.S. Government Printing Office, Washington, pp. 521–576. Kamikuri, S., Nishi, H., Motoyama, I., Saito, S., 2004. Middle Miocene to Pleistocene radiolarian biostratigraphy in the Northwest Pacific Ocean, ODP Leg 186. The Island Arc 13, 191–226. Kamikuri, S., Nishi, H., Motoyama, I., 2007. Effects of late Neogene climatic cooling on North Pacific radiolarian assemblages and oceanographic conditions. Palaeogeography, Palaeoclimatology, Palaeoecology 249, 370–392. Kamikuri, S., Motoyama, I., Nishi, H., Iwai, M., 2009. Evolution of Eastern Pacific Warm Pool and upwelling processes since the middle Miocene based on analysis of radiolarian assemblages: response to Indonesian and central American seaways. Palaeogeography, Palaeoclimatology, Palaeoecology 280, 469–479. Kellogg, D.E., 1975a. Character displacement in the radiolarian genus, Eucyrtidium. Evolution 29, 736–749. Kellogg, D.E., 1975b. The role of phyletic change in the evolution of Pseudocubus vema (radiolaria). Paleobiology 1, 150–160. Kellogg, D.E., Hays, J.D., 1975. Microevolutionary patterns in Late Cenozoic radiolaria. Paleobiology 1, 150–160. Kennett, J.P., 1986. Miocene to early Pliocene oxygen and carbon isotope stratigraphy in the southwest Pacific, Deep Sea Drilling Project Leg 90. In: Kennett, J.P., von der

S. Kamikuri / Marine Micropaleontology 90–91 (2012) 13–28 Borch, C.C., et al. (Eds.), Initial Reports of Deep Sea Drilling Project, 90. U.S. Government Printing Office, Washington, pp. 1383–1411. Kling, S.A., 1971. Radiolaria: Leg 6 of the Deep Sea Drilling Project. In: Fischer, A.G., Heezen, B.C. (Eds.), Initial Reports of the Deep Sea Drilling Project, 6. U.S. Government Printing Office, Washington, pp. 1069–1117. Kling, S.A., 1973. Radiolaria from the eastern North Pacific, Deep Sea Drilling Project Leg 18. In: Kulm, L.D., von Huene, R. (Eds.), Initial Reports of Deep Sea Drilling Project, 18. U.S. Government Printing Office, Washington, pp. 617–671. Krissek, L.A., 1995. Late Cenozoic ice-rafting records from Leg 145 sites in the North Pacific: Late Miocene onset, late Pliocene intensification, and Pliocene–Pleistocene events. In: Rea, D.K., Basov, I.A., Scholl, D.W., Allan, J.F. (Eds.), Proceedings of the Ocean Drilling Program, Scientific Results, 145. Ocean Drilling Program, College Station, TX, pp. 179–195. Lazarus, D., Scherer, R.P., Prothero, D.R., 1986. Evolution of the radiolarian speciescomplex Pterocanium: a preliminary survey. Journal of Paleontology 59, 183–220. Lazarus, D., Spencer-Cervato, C., Pianka-Biolzi, M., Beckmann, J.P., von Salis, K., Hilbrecht, H., Thierstein, H., 1995. Revised chronology of Neogene DSDP Holes from the world ocean. Ocean Drilling Program, Technical Note, 24. Ocean Drilling Program, Texas A&M University, College Station, Texas. Lazarus, D., Bittniok, B., Diester-Haass, L., Meyers, P., Billups, K., 2006. Comparison of radiolarian and sedimentologic paleoproductivity proxies in the latest Miocene– recent Benguela Upwelling System. Marine Micropaleontology 60, 269–294. Ling, H.Y., 1973. Radiolaria: Leg 19 of the Deep Sea Drilling Project. In: Creager, J.S., Scholl, D.W. (Eds.), Initial Reports of the Deep Sea Drilling Project, 19. U.S. Government Printing Office, Washington, pp. 777–797. Ling, H.Y., 1975. Radiolaria: Leg 31 of the Deep Sea Drilling Project. In: Karig, D.E., Ingle Jr., J.C. (Eds.), Initial Reports of the Deep Sea Drilling Project, 31. U.S. Government Printing Office, Washington, pp. 703–761. Lombari, G., 1985. Biogeographic trends in Neogene radiolaria from the Northern and Central Pacific. In: Kennett, J.P. (Ed.), The Miocene Ocean: Geological Society of America, Memoir, 163, pp. 291–303. Lyle, M., Dadey, K., Farrell, J.W., 1995. The Late Miocene (11–8 Ma) eastern Pacific carbonate crash: evidence for reorganization of deep-water circulation by the closure of the Panama Gateway. In: Pisias, N.G. (Ed.), Proceedings of the Ocean Drilling Program, Scientific Results, 138. Ocean Drilling Program, College Station, TX, pp. 821–838. Lyle, M., Barron, J., Bralower, T.J., Huber, M., Lyle, A.O., Ravelo, A.C., Rea, D.K., Wilson, P.A., 2008. Pacific Ocean and Cenozoic evolution of climate. Reviews of Geophysics 46, 1–47. Maslin, M.A., Haug, G.H., Sarnthein, M., Tiedemann, R., Erlenkeuser, H., Stax, R., 1995. Northwest Pacific Site 882: the initiation of Northern Hemisphere glaciation. In: Rea, D.K., Basov, I.A., Scholl, D.W., Allan, J.F. (Eds.), Proceedings of the Ocean Drilling Program, Scientific Results, 145. Ocean Drilling Program, College Station, TX, pp. 315–325. Matul, A., Abelmann, A., 2005. Pleistocene and Holocene distribution of radiolarian Amphimelissa setosa Cleve in the North Pacific and North Atlantic: evidence for water mass movement. Deep Sea Research II 52, 2351–2364. Miller, K.G., Wright, J.D., Fairbanks, R.G., 1991. Unlocking the ice house: Oligocene– Miocene oxygen isotopes, eustacy and margin erosion. Journal of Geophysical Research 96, 6829–6848. Mix, A.C., Pisias, N.G., Rugh, W., Wilson, J., Morey, A., Hagelberg, T.K., 1995. Benthic foraminifer stable isotope record from Site 849 (0–5 Ma): local and global climatic changes. In: Pisias, N.G. (Ed.), Proceedings of the Ocean Drilling Program, Scientific Results, 138. Ocean Drilling Program, College Station, TX, pp. 371–388. Molina-Cruz, A., 1982. Radiolarians in the Gulf of California: Deep Sea Drilling Project Leg 64. In: Curray, J.R., Moore, D.G. (Eds.), Initial Reports of the Deep Sea Drilling Project, 64. U.S. Government Printing Office, Washington, pp. 983–1002. Molina-Cruz, A., 1997. Closing of the Central American Gateway and its effects on the distribution of Late Pliocene radiolarians in the eastern tropical Pacific. Tectonophysics 281, 105–111. Moore, T.C., 1969. Radiolaria: change in skeletal weight and resistance to solution. Geological Society of America Bulletin 80, 2103–2108. Moore, T.C., 1971. Radiolaria. In: Tracey Jr., J.I., Sutton, G.H. (Eds.), Initial Reports of the Deep Sea Drilling Project, 8. U.S. Government Printing Office, Washington, pp. 727–775. Moore, T.C., 1995. Radiolarian stratigraphy, Leg 138. In: Pisias, N.G. (Ed.), Proceedings of the Ocean Drilling Program, Scientific Results, 138. Ocean Drilling Program, College Station, TX, pp. 191–232. Morley, J.J., 1985. Radiolarians from the Northwest Pacific, Deep Sea Drilling Project Leg 86. In: Heath, G.R., Burckle, L.H. (Eds.), Initial Reports of the Deep Sea Drilling Project, 86. U.S. Government Printing Office, Washington, pp. 399–422. Morley, J.J., Nigrini, C., 1995. Miocene to Pleistocene radiolarian biostratigraphy of North Pacific Sites 881, 884, 885, 886 and 887. In: Rea, D.K., Basov, I.A., Scholl, D.W., Allan, J.F. (Eds.), Proceedings of the Ocean Drilling Program, Scientific Results, 145. Ocean Drilling Program, College Station, TX, pp. 55–91. Motoyama, I., 1996. Late Neogene radiolarian biostratigraphy in the subarctic Northwest Pacific. Micropaleontology 42, 221–262. Motoyama, I., 1997. Origin and evolution of Cycladophora davisiana Ehrenberg (Radiolaria) in DSDP Site 192, Northwest Pacific. Marine Micropaleontology 30, 45–63. Motoyama, I., Maruyama, T., 1998. Neogene diatom and radiolarian biochronology for the middle-to-high latitudes of the Northwest Pacific region: calibration to the Cande and Kent's geomagnetic polarity time scale (CK 92 and CK 95). Journal of Geological Society of Japan 104, 171–183. Nigrini, C., 1974. Cenozoic radiolaria from the Arabian Sea, DSDP Leg 23. In: Davies, T.A., Luyendyk, B.P. (Eds.), Initial Reports of the Deep Sea Drilling Project, 26. U.S. Government Printing Office, Washington, pp. 1051–1121.

27

Nigrini, C., Sanfilippo, A., 2001. Cenozoic radiolarian stratigraphy for low and middle latitudes with descriptions of biomarkers and stratigraphically useful species. Ocean Drilling Program, Technical Note, 27. Ocean Drilling Program, Texas A&M University, College Station, Texas. Norris, R.D., 2000. Pelagic species diversity, biogeography, and evolution. Paleobiology 26, 236–258. Ogg, J.G., Smith, A.G., 2004. The geomagnetic polarity time scale. In: Gradstein, F.M., Ogg, J.G., Smith, A.G. (Eds.), A Geologic Time Scale. Cambridge University Press, pp. 63–86. Oseki, S., Suzuki, N., 2009. Miocene to Pleistocene paleogeographic distributions of polycystine radiolarians in the North Pacific. News of Osaka Micropaleontologists, Special Volume 14, pp. 183–238. Pälike, H., Nishi, H., Lyle, M., Raffi, I., Gamage, K., Klaus, A., the Expedition 320/321 Scientists, 2010. Expedition 320/321 summary. In: Pälike, H., Lyle, M., Nishi, H., Raffi, I., Gamage, K., Klaus, A., the Expedition 320/321 Scientists (Eds.), Proceedings of the Integrated Ocean Drilling Program 320/321. Integrated Ocean Drilling Program Management International, Inc, Tokyo, pp. 1–141. Petrushevskaya, M.G., 1975. Cenozoic radiolarians of the Antarctic, Leg 29, DSDP. In: Kennett, J.P., Houtz, R.E. (Eds.), Initial Reports of the Deep Sea Drilling Project, 29. U.S. Government Printing Office, Washington, pp. 541–675. Petrushevskaya, M.G., Kozlova, G.E., 1972. Radiolaria, Leg 14, Deep Sea Drilling Project. In: Hayes, D.E., Pimm, A.C. (Eds.), Initial Reports of the Deep Sea Drilling Project, 14. U.S. Government Printing Office, Washington, pp. 495–648. Pisias, N.G., Moore, T.C., 1978. Cenozoic radiolarians from Deep Sea Drilling Project Leg 40. In: Bolli, H.M., Ryan, W.B.F. (Eds.), Initial Reports of the Deep Sea Drilling Project, 40. U.S. Government Printing Office, Washington, pp. 845–856. Ravelo, A.C., Wara, M.W., 2004. The role of the tropical oceans on global climate during a warm period and a major climate transition. Oceanography 17, 32–41. Rea, D.K., Basov, I.A., Janecek, T.R., Palmer-Julson, A., 1993. Proceedings of the Ocean Drilling Program, Initial Reports, 145. Ocean Drilling Program, College Station, TX, http://dx.doi.org/10.2973/odp. proc.ir.145.1993. Rea, D.K., Basov, I.A., Krissek, L.A., the Leg 145 Scientific Party, 1995. Scientific results of drilling the North Pacific transect. In: Rea, D.K., Basov, I.A., Scholl, D.W., Allan, J.F. (Eds.), Proceedings of the Ocean Drilling Program, Scientific Results, 145. Ocean Drilling Program, College Station, TX, pp. 577–595. Reynolds, A., 1980. Radiolarians from the western North Pacific, Leg 57, Deep Sea Drilling Project. In: von Huene, R., Nasu, N. (Eds.), Initial Reports of the Deep Sea Drilling Project 56/57 (Part 2). U.S. Government Printing Office, Washington, pp. 735–769. Riedel, W.R., 1953. Mesozoic and Late Tertiary radiolaria of Rotti. Journal of Paleontology 27, 805–813. Riedel, W.R., Sanfilippo, A., 1970. Radiolaria, Leg 4, Deep Sea Drilling Project. In: Bader, R.G., Gerard, R.D. (Eds.), Initial Reports of the Deep Sea Drilling Project, 4. U.S. Government Printing Office, Washington, pp. 503–575. Riedel, W.R., Sanfilippo, A., 1971. Cenozoic radiolaria from the western tropical Pacific, Leg 7. In: Winterer, E.L., Riedel, W.R. (Eds.), Initial Reports of the Deep Sea Drilling Project, 7 (part 2). U.S. Government Printing Office, Washington, pp. 1529–1672. Riedel, W.R., Sanfilippo, A., 1978. Stratigraphy and evolution of tropical Cenozoic radiolarians. Micropaleontology 24, 61–96. Romine, K., 1985. Radiolarian biogeography and paleoceanography of the North Pacific at 8 Ma. In: Kennett, J.P. (Ed.), The Miocene Ocean: Geological Society of America, Memoir, 163, pp. 237–272. Romine, K., Lombari, G., 1985. Evolution of Pacific circulation in the Miocene: radiolarian evidence from DSDP Site 289. In: Kennett, J.P. (Ed.), The Miocene Ocean: Geological Society of America, Memoir, 163, pp. 273–290. Ruddiman, W.F., Raymo, M.E., 1988. Northern Hemisphere climate regimes during the past 3 Ma: possible tectonic connections. Philosophical Transactions of the Royal Society of London, Series B 318, 411–430. Sakai, T., 1980. Radiolarians from Sites 434, 435, and 436, Northwest Pacific, Leg 56, Deep Sea Drilling Project. In: von Huene, R., Nasu, N. (Eds.), Initial Reports of the Deep Sea Drilling Project 56/57 (Part 2). U.S. Government Printing Office, Washington, pp. 695–733. Sancetta, C., 1978. Neogene Pacific microfossils and paleoceanography. Marine Micropaleontology 3, 347–376. Sanfilippo, A., Nigrini, C., 1998. Code numbers for Cenozoic low latitude radiolarian biostratigraphic zones and GPTS conversion tables. Marine Micropaleontology 33, 109–156. Sanfilippo, A., Riedel, W.R., 1970. Post-Eocene “closed” theoperid radiolarians. Micropaleontology 16, 446–462. Sanfilippo, A., Burckle, L.H., Martini, E., Riedel, W.R., 1973. Radiolarians, diatoms, silicoflagellates and calcareous nannofossils in the Mediterranean Neogene. Micropaleontology 19, 209–234. Sanfilippo, A., Westberg-Smith, M.J., Riedel, W.R., 1985. Cenozoic radiolaria. In: Bolli, H.M., Saunders, J.B., Perch-Nielsen, K. (Eds.), Plankton Stratigraphy. Cambridge Univ. Press, Cambridge, pp. 631–712. Savin, S.M., Abel, L., Barrera, E., Hodell, D., Keller, G., Kennett, J.P., Killingley, J., Murphy, M., Vincent, E., 1985. The evolution of the Miocene surface and near-surface marine temperatures: oxygen isotopic evidence. In: Kennett, J.P. (Ed.), The Miocene Ocean: Geological Society of America, Memoir, 163, pp. 49–82. Sawada, T., Shindo, R., Motoyama, I., Kameo, K., 2009. Geology and radiolarian biostratigraphy of the Miocene and Pliocene Series exposed along the Koitogawa River, Boso Peninsula, Japan. Journal of Geological Society of Japan 115, 206–222. Schmidt, D.N., Lazarus, D., Young, J.R., Kucera, M., 2006. Biogeography and evolution of body size in marine plankton. Earth-Science Reviews 78, 239–266. Shackleton, N.J., Backman, J., Zimmerman, H., Kent, D.V., Hall, M.A., Roberts, D.G., Schnitker, D., Baldauf, J.G., Desprairies, A., Homrighausen, R., Huddlestun, P., Keene, J.B., Kaltenback, A.J., Krumsiek, K.A.O., Morton, A.C., Murray, J.M., Westberg-Smith, J.,

28

S. Kamikuri / Marine Micropaleontology 90–91 (2012) 13–28

1984. Oxygen isotope calibration of the onset of ice-rafting and history of glaciation in the North Atlantic region. Nature 307, 620–623. Shilov, V.V., 1995. Miocene–Pliocene radiolarians from Leg 145, North Pacific. In: Rea, D.K., Basov, I.A., Scholl, D.W., Allan, J.F. (Eds.), Proceedings of the Ocean Drilling Program, Scientific Results, 145. Ocean Drilling Program, College Station, TX, pp. 93–116. Shinzawa, M., Kamikuri, S., Motoyama, I., 2009. Radiolarian fossils from the Miocene series in the Hobetsu area, southern central Hokkaido, Japan. News of Osaka Micropaleontologists, Special Volume 14, pp. 293–311. Sloan, L.C., Crowley, L.C., Pollard, D., 1996. Modeling of middle Pliocene climate with the NCAR GENESIS general circulation model. Marine Micropaleontology 27, 15–61. Sono, A., Suzuki, N., Yoshimura, E., Kano, H., Takeda, K., 2009. Radiolarian faunal changes in the mid-latitudinal North Pacific over the past 6.4 m.y. (ODP Leg 198 Site 1210, Shatsky Rise). News of Osaka Micropaleontologists, Special Volume 14, pp. 143–181. Spencer-Cervato, C., Lazarus, D., Beckmann, J.-P., von Salis Perch-Nielsen, K., Biolzi, M., 1993. New calibration of Neogene radiolarian events in the North Pacific. Marine Micropaleontology 21, 261–293. Theyer, F., Mato, C.Y., Hammond, S.R., 1978. Paleomagnetic and geochronologic calibration of latest Oligocene to Pliocene radiolarian events. Marine Micropaleontology 3, 377–395. Theyer, F., Mayer, L.A., Thomas, E., 1985. The equatorial Pacific high-productivity belt: elements for a synthesis of Deep Sea Drilling Project Leg 85 results. In: Mayer, L.,

Theyer, F. (Eds.), Initial Reports of Deep Sea Drilling Project, 85. U.S. Government Printing Office, Washington, pp. 971–985. Weaver, F.M., 1983. Cenozoic radiolarians from the Southwest Atlantic, Falkland Plateau region, Deep Sea Drilling Project, Leg 71. In: Ludwig, W.J., Krasheninnikov, V.A. (Eds.), Initial Reports of the Deep Sea Drilling Project, 71. U.S. Government Printing Office, Washington, pp. 667–686. Weber, M., Pisias, N., 2006. Data report: radiolarian biostratigraphy, ODP Leg 202, Site 1237. In: Tiedemann, R., Mix, A.C., Richter, C., Ruddiman, W.F. (Eds.), Proceedings of the Ocean Drilling Program, Scientific Results, 202. Ocean Drilling Program, College Station, TX, pp. 1–29. Westberg-Smith, M.J., Riedel, W.R., 1978. Accuracy of radiolarian correlations in the Pacific Miocene. Micropaleontology 24, 1–23. Wolfart, R., 1981. Neogene radiolarians from the eastern North Pacific off Alta and Baja California, Deep Sea Drilling Project Leg 63. In: Yeats, R.S., Haq, B.U. (Eds.), Initial Reports of the Deep Sea Drilling Project, 63. U.S. Government Printing Office, Washington, pp. 473–506. Yamamoto, Y., Kawakami, S., 2005. Rapid tectonics of the late Miocene Boso accretionary prism related to the Izu–Bonin arc collision. The Island Arc 14, 178–198. Zachos, J.C., Dickens, G.R., Zeebe, R.E., 2008. An early Cenozoic perspective on greenhouse warming and carbon-cycle dynamics. Nature 451, 279–283.