Ecology, morphology, stratigraphy, and the paleoceanographic significance of Cycladophora davisiana davisiana. Part II: Stratigraphy in the North Atlantic (DSDP Site 609) and Labrador Sea (ODP Site 646B)

ELSEVlER

Marine Micropaleontology

25

( 1995) 67-86

Ecology, morphology, stratigraphy, and the paleoceanographic significance of Cycladophora davisiana davisiana. Part II: Stratigraphy in the North Atlantic (DSDP Site 609) and Labrador Sea (ODP Site 646B) P.F. Ciesielski n, K.R. Bj@-klund b aDepartment of Geology, university of Florida, 1112 Turlington Hall, Gainesville, FL 3261 I. USA ’ University of Oslo. Paleontological Museum, Sarsgate I, 0562 Oslo 5, Norway Received

10 May 1994; accepted after revision 18 November

1994

Abstract

Upper Pliocene and Pleistocene abundance lhrctuations of the radiolarian Cycladophora dauisiana (Ehrenberg) rfaoisiana (Petrushevskaya) are documented from North Atlantic (Site 609) and Labrador Sea (Site 646B) to provide the first long-term correlation of its abundance fluctuations to oxygen isotope stages 1-I 14. Also examined are temporal and regional fluctuations in abundances C. d. duuisiana and the global dispersal routes of the species. The first occurrence of C. d. dauisiana in the eastern North Atlantic Ocean (Site 609) occurred between 2.586 and 2.435 Ma (oxygen isotope stages 109.66-102.19). During the early Matuyama Chron, prior to oxygen isotope stage 63, C. d. dauisiana abundances were less than 1% and never greater than 12%, while abundances of greater than 5% are found in stages 6571-73, 74, and 83-84. The initial major abundance peak (35.7%) of C. d. dauisiuna was noted near the stage 63/62 boundary. Abundance peaks of greater than 15%, between oxygen isotope stages 35 and 63, are limited to stages 63.02, 58.07, 55.0754.26, and 50.76-50.22. These represent the only such abundance peaks detected during the first N 1.5 million years of the species within the North Atlantic. The character of C. d. dauisiana abundance fluctuations in Site 609 changes after oxygen isotope stage 35; average abundances are greater (7.7% vs. 4.3%) and abundance maxima of more than 15% are more frequent. Many, but not all, peak abundances of C. d. davisiana occur in glacial stages (e.g., 8, 14, 18,20,26,30,34,50,54, and 58). Increased abundances of the species are also noted in weak interglacial stages (e.g., stages 3, 23, 39, and 41), and significant cool periods of robust interglacial periods (e.g., late stage 11f . Sample spacing is adequate in some stages to note some rapid changes in abundance near stage transitions (e.g., stages 415, 25126, 62/63). The sample density in Holes 609 and 611 and the upper portion of 646B is sufficient to detect a synchroneity of many abundance maxima and minima among sites. Some abundance peaks are undetected in one or more of the two holes, warranting further sampling to obtain a more accurate record of regional abundance fluctuations. Prior to stage 36, few ages of Hole 611 peaks are the same as those in the more precisely dated Hole 609. The highest abundances of C. d. dauisiana were noted in Labrador Sea Hole 646B where the earliest known occurrence of the species is documented (3.08-2.99 Ma). C. d. dauisiana is inferred to have evolved in the Labrador Sea (or Arctic), and migrated next through the Arctic into the North Pacific (2.62-2.64 Ma, stage 114) before migrating into the Norwegian Sea (2.63-2.53 Ma) and North Atlantic (2.59-2.44 Ma, stages 109-102). Additional migration of C. d. dauisiana into the southern South Atlantic (Site 704) occurred much later (2.06 Ma, stage 83).

0377.8398/95/$09,50 0 1995 Elsevier Science B.V. AI1 rights reserved SSDfO377-8398(94)00027-l

68

P. F. Ciesielski,

K. R. Bj@rklund/Murine

1. Introduction and objectives 1,l. Introduction The radiolarian species Cycladophora davisiana (Ehrenberg) dauisiana (Petrushevskaya) is a cosmopolitan species which comprises less than 5% of Holocene sediments, except within the Sea of Okhotsk and nearby areas of the northwest Pacific (Morley and Hays, 1979) where it accounts for up to 37.6% of the assemblage. In modern sediments of the tropical and subtropical Atlantic Ocean, the species rarely exceeds 1% of the radiolarian assemblage (Bjorklund and Ciesielski, 1994). During the Pleistocene and Pliocene, however, this species has a higher abundance in the high latitudes of both hemispheres, particularly during glacial stages when it may account for as much as 70.33% of the assemblage. High abundances of C. d. davisiana ( > 20%) in high latitude Pleistocene sediments were proposed to reflect paleoceanographic conditions similar to those of today’s Sea of Okhotsk (Robertson, 1975; Morley and Hays, 1979; Morley, 1983)) where its abundance is linked to the formation of a low-salinity surface layer with a strong temperature minimum at its base. These conditions provide a stable subsurface environment for this species. This water structure is most likely produced by intense freezing of sea ice in winter and subsequent summer melting. Variations in the relative abundance of C. d. davisiana have been used as a stratigraphic tool for the study of high latitude sediments by calibrating abundance fluctuation patterns with oxygen isotope stages, paleomagnetic records and cross-calibration with 14C ages and other stratigraphic datums. Pleistocene abundance fluctuations of the species were documented from the Antarctic-Subantarctic (Hays et al., 1976; Cooke, 1978; Abelmann and Gersonde, 1988), North Atlantic (Morley and Hays, 1979; Morley, 1987), northwest Pacific (Robertson, 1975; Morley et al., 1982), Bering Sea (Morley and Robinson, 1986), and in the tropical Atlantic (Morley, 1980; Bjorklund and Jansen, 1984). Such documentation led to use of its abundance fluctuation patterns as a substitute high-resolution stratigraphic framework for high latitude Pleistocene sections lacking key calcium carbonate microfossils and the associated oxygen isotope record. Calibration of the relative abundance fluctuations of C. d. davisiana with oxygen isotope records reveal synchroneity within

Micropaleontology

25 (1998) 67-86

the Subantarctic and North Atlantic (Hays et al., 1976; Morley and Hays, 1979). Although direct calibration to oxygen isotope stages has not been made in the northwest Pacific and Bering Sea, relative abundance fluctuations appear synchronous within each of these regions and between them for the last 50,000 years (Morley et al., 1982; Morley and Robinson, 1986). Most previous studies of the temporal abundance fluctuations of C. d. davisiana are of the late Pleistocene ( <4.50,000 yr B.P.). Morley’s study ( 1987) of DSDP Holes 611 and 61 IA is the only examination of older abundance fluctuations in the North Atlantic documenting such variations to 1.66 Ma and has an average spacing (sample interval) of approximately 7000 yr. Morley ( 1987) also presented abundance variations of the species from northwest Pacific DSDP Site 580 almost back to 2.64 Ma (our calculation based on information in Morley, 1985; 1987) at approximately 6000year-increments. In these, the only late PliocenePleistocene sections with a detailed C. d. davisiana record, ages are based upon interpolation between paleomagnetic datums. Unfortunately, few published records of temporal fluctuations in C. d. davisiana are directly calibrated to oxygen isotope stages and none are linked to records older than isotope stage 12 (Morley et al., 1982). 1.2. Objectives Previous studies have shown that temporal abundance fluctuation patterns of C. d. dauisiana in the latest Pleistocene are distinctive and apparently synchronous over large areas, allowing them to be used as surrogates to identify specific glacial-interglacial oxygen isotope stages. The primary objective herein is to examine the longer term abundance variations of this species in one of only a few sections calibrated to oxygen isotope stages l-l 14 (DSDP Site 609) to document the nature and precise timing of such variation. The intent of this study is to extend the usefulness of the C. d. davisiana stratigraphy in sections with oxygen isotope records beyond isotope stage 12 to the limit of the identified oxygen isotope stages (stage 114). An additional objective is to determine the northern applicability of C. d. davisiana stratigraphy by examining its abundance variations in ODP Site 646B which is partially calibrated to the oxygen isotope record through stage 16. Finally, the C. d. davisiana records

P.F. Ciesielski, K.R. Bj@rklund/Marine Micropaleontology 25 (1995) 67-86

of Holes 609 and 646B are compared with the only other long record of North Atlantic fluctuations of this species from DSDP Site 611 (Morley, 1987). Although Holes 611 and 6llA lack an oxygen isotopic record; the ages of C. d. duvisiuna maxima ( > 15%) and some minima are calculated for comparison with Holes 609 and 646B. Records of all three sites are compared for: ( 1) differences in the initial appearance of the species, (2) possible synchroneity of abundance fluctuations, (3) differences in the magnitude of abun-

69

dance fluctuations, and (4) production of a composite of major C. d. duvisiana abundance peaks. While the regional stratigraphic characteristics of C. d. duuisiunu abundance fluctuations are the subject of this contribution, Part III of this series will attempt to interpret the paleoceanographic significance of this North Atlantic-Labrador Sea record.

60’

GREENLAND

60

30’N E

Fig. 1. Map showing the locations of the studied sections, Hole 609 in the North Atlantic and Hole 646B in the Labrador Sea, and the general oceanic surface circulation of the region. Shown also are sections in the North Atlantic discussed herein, including: DSDP Sites 607, 609 and 611; aswell as. Vema piston cores V27-114, V27-116, and V29-179.

P. F. Ciesielski, K. R. Bj@rklund / Marine Micropaleontology

70

2.5 (1995) 67-86

Table 1 Samples, age, percentage C. d. dwisiona and isotope stages in DSDP Site 609 and ODP Site 646B Site 609 samples

Site 646B samples

Age

% C. d.

Stage

Site 609 samples

I-l, 96-99

0.000 0.005 0.007 0.029 0.032 0.045 0.052 0.060 0.072 0.080 0.083 0.095 0.104

0.00

1.02 1.43 1.58 3.15 3.23 3.60 3.81 4.09 4.87 5.12 5.16 5.37 5.55

4-3, 5G52 4-4,50-52

0.108AI.143 (0.125) 0.128 0.135 0.162 0.175 0.189 0.190 0.218 0.220 0.243 0.245 0.257 0.259 0.282 0.285 0.309 0.313 0.313 0.327 0.343 0.350 0.361 0.374 0.376 0.415 0.428 0.435 0.456 0.457 0.478 0.4784.520 (0.499)

1.60

6-1,4OA2W

8-5,5&52 8-6,50-52 S-CC. 0-2# 9- 1.40-42W

I-1,40-42W l-1,52-54 l-2,52-54 l-3,96-99 2-1,95-98 I-3.52-54 l-5,96-99 2-3.95-98 l-4,40-42W

l-4,52-54 I-CC, 12-15 l-5.52-54 1-cc, &2# 2-5,95-98 2-cc, 2-4 2-l,52-54 3-1, loo-102 2-2,4OA2W 2-2,50-52 z-3.50-52 3-3, 100-102 2-4,50-52 3-5, loo-102 2-5,48-50 3-cc, O-2 2-6,4@42W 2-6,50-52 4-1,96-99 2-7,40-42# 2-cc, O-2# 3-1,51-53# 4-3, 9G99 3-2.5 l-53# 4-5, 10-13 3-3,4M2#W 3-3,51-53# 3-4.51-43 5-1,99-102 3-5.48-50 3-6,48-50 5-3,5&53 5-4, 3-6 3-cc, &2#

4-1,5&52# 4-2,4OA2#W 4-2,50-52# 6-1, 106-109

1.40 1.30 25.70 29.18 27.33 23.30 23.33 8.00 15.90 2.20 17.00 4.20

0.526 0.534 0.535

6.70 9.30 6.60

6.21-5.61 (5.92) 5.97 6.08 6.52 6.76 6.99 7.01 7.52 7.56 7.98 8.01 8.22 8.26 8.65 8.70 9.17 9.27 9.28 9.66 10.16 10.46 10.95 11.20 il.23 Il.86 12.04 12.22 12.60 12.61 13.00 12.9913.91 (13.45) 14.05 14.25 14.26

0.530

21.00

14.42

2.33 5.00 3.10 3.00 4.20 0.00 8.90 17.67 0.00 37.33 9.50 47.67 17.30 1.80 10.67 3.60 3.20 4.40 25.67 0.00 8.00 13.00 10.10 0.00 19.00 0.00 0.00 40.67 35.67 18.90

Site 646~ samples

6-4, 106-109 4-5.4&42W 6-6, 106-109 5-1,50-52# 5-2,5&52# 5-3,40-42W 5-3,5&52 5-4, 5&52 5-5,49-51 5-6,48-50 5-w, 0-2#

6-1,50-52 6-2, N-52 6-3,48-50 6-4,4&42W 6-4,48-50 6-6, S&52 9-1,97-100 6-X50-52 6-7,4749 6-E, 0-2# 7-1,40_42W 7-1,50-52 7-2,52-54 9-3,97-100 7-3, SO-52 9-5,97-100 7-4,52-54 7-5,40-42W 7-5,50-52 9-cc, O-3 7-6,5O-52 7-K, &2# 10-l. 97-100 8-1,4749# 8-2,4OA2W 8-2, SO-52 8-3,50-52 S-4,5&52 lo-3,97-loo 8-5,4&42W

Age

% C. d.

Stage

0.548 0.589 0.605 0.611 0.636 0.646 0.673 0.690 0.690 0.699 0.713 0.742 0.75M.756 (0.753) 0.762

15.80 9.30 18.33 9.00 0.00 5.90 0.00 8.40 5.00 0.00 41.60 0.00 0.00

14.59 15.43 15.73 15.83 16.26 16.43 16.89 18.02 18.04 18.27 18.67 19.97 20.44-20.73 (20.59) 20.94

0.762 0.778 0.795 0.812 0.813 0.830 0.847 0.851 0.868 0.869 0.875 0.876 0.885 0.886 0.92 1 0.93 1 0.944 0.958 0.959 0.969 0.975 0.986 0.987 0.991 1.004 1.005 1.018 1.034 1.048 1.048

4.80 1.20 0.00 18.90 12.20 0.00 42.00 0.60 4.30 15.50 17.00 11.10 4.00 70.33 2.90 2.33 2.20 14.50 16.00 0.00 5.80 0.60 23.85 5.60 10.50 5.10 0.00 6.80 0.00 15.20

20.97 21.62 22.32 23.15 23.19 24.08 _ 24.92 25.10 25.92 25.96 26.22 26.25 26.67 - 26.70 28.41 - 28.86 29.41 30.15 30.21 _ 30.69 31.00 31.55 -31.58 31.78 32.36 32.40 33.22 33.98 - 34.53 34.57

1.049 1.059 1.065-l .074 (1.071) 1.079

37.80 3.70 4.40

34.60 35.09 35.48-35.82 (35.65) 36.04

10.40

6.50

P. F. Ciesielski, K.R. Bj@rklund/Marine Micropaleontology 25 (1995) 67-86

Site 609

Site 646B

samples

samples

Age

% C. d.

Sage

Site 609

Site 646B

samples

samples

71

Age

% C. d.

Stage

9-1,x-52

I.080

3.10

36.08

l4-3,50-52

I .762

0.90

9-2, So-52

1.091

0.00

l4-4,5&52

I.776

1.30

69.63 70.24

I.099

58.33

36.62 _ 36.91

14-5,40--42W

I.787

0.20

70.78

9-3,40_42w

1.110

0.20

37.50

14-5,50-52

I .?88

0.00

9-3.50-52

1.111

0.00

14-6,54-56 14-CC, 16-18#

I.799

5.70 3.60

70.83 71.38

IO-5,97-100

I.113

0.00

37.70 - 37.61

g-4,5&52

1.135

9-5,4042W

1.160

0.00 12.70

38.72 39.86

15-1,4&42W 15-1.50-52 15-2.48-50 15-3,45+7

IO-6,6&63

1.802 1.803 1.804 1.812

9-5,5&52

1.162

0.00

39.95

9-6,5&52

1.180

1.20

40.87

9-cc,

I.188

0.30

15-4,4CM2W

IO-I, 4OA2W

1.190

9.30

41.29 41.38

IO-l, 50-52#

1.191

5.30

41.45

15.5,5&52

I.858

lo-2,5@52

1.212

0.00

15.6,4@42W

1.867

IO-3,5&52

I .240

0.00

42.49 43.94

15.6,5&52

IO-4,5&52

1.256

0.00

44.11

15.cc,

0-2#

lo-5,4&42W

1.216

3.50

45.65

IO-5,50-52

I .277

4.50

IO-6,5@52

1.288

11-1,5&52#

71.53

9.70 10.10

71.57 71.59

3.60

71.90

6.60 9.80

72.24 73.07

6.30

73.19

0.00 12.00

74.04 74.73

1.867

7.40

74.75

1.887

0.00

75.65

16.1,40_42W

1.898

4.30

76.08

45.70

16-1,5C-52

1.899

3.30

76.15

5.90

46.22

16-2.50-52

1.923

0.00

77.54

1.324

0.30

48.00

16.3,50-52

0.00

78.86

I l-2, 5&52#

I .358

0.90

49.47

16-4.50-52

1.957 1.986

I 1-3,4&42W

1.376

29.60

50.22

16.5,5&52

2.016

0.00 0.00

79.59 81.70

I l-3,5&52 I l-4. 50-52

1.377 1.391

29.80 3.60

50.76 51.38

16-6.50-52 16-E, &2#

2.003 2.049-2.067

0.00 9.60

82.75 83.50-84.40

I 1-5,4&42w

I .409

12.50

17.1.40-42W

(2.058) 2.072

7.20

84.31

11-5.50-52

1.411

0.60

52.19 52.27

17-1.50-52

2.073

0.00

84.66

I 1-cc,

I.443

3.00

17-2.50-52

2.103

0.00

86.22

12-1.50-52

I .450

17.40

53.91 54.26

2.137

0.00

87.47

12-2,4@-42W

1.468

20.60

55.07

17-3.50-52 17-4,4&42W

2.155

0.90

88.64

12-2,5@-52 12-3, 50-52

1.470 I.491

10.90

55.15

17-4,50-52

2.157

0.00

88.69

0.90

56.10

17-5,5&52

2.176

0.00

89.45

12-4,4&42W

I.508

1.30

51.07

17-6,5&52

2.197

0.00

90.40

12-4, 52-54

1 SO9

1.20

57.16

17xX.

2.223

0.00

91.85

12-5,5&52 12-6. 40-42W

1.521 1.543

55.30

58.07

18-1,5Ck52

2.245

0.00

2.80

58.75

l8-CC. 21-23#

2.262-2.337

0.00

92.75 93.61-97.37

12-6.53-55 12-w. o-2#

I .544 I.563

2.70 2.10

58.80 59.68

19-1,49-51# 19.2,49-5 I #

2.336 2.368

0.00 0.00

97.32 98.82

13. I, 5%52#

I .567

8.40

59.94

19-cc,

2.58s2.435 (2.507)

0.00

109.34-102.19 (105.77)

13.2,5&52# l3-3,50-52 13.4,48-50

I.579 1.598

60.61 61.62 62.26

20-I. 49-5 I 20-2,49-5 I

2.586

1.611

0.00 0.00 0.00

20-3,49-5

I

2.595 2.614

0.00 0.00 0.00

109.66 110.17 III.37

13-5, 4@42w

1.626

35.70

63.02

20-4,49-5

1

2.638

0.00

112.24

13-5,48-50

1.627

0.00

112.82

0.00

I 1

0.00

1.662

20-5,49-5 20-6,49-5

2.652

13.6,53-55

63.07 64.48

2.668

0.00

I 13.66

13.cc.

1.681

6.90

65.44

20-cc,

0-2#

2.681

0.00

I 14.26

l4# 14-1, SO-52

I .694

66.18 68.04 68.08

2.782

0.00

1.730 1.731

0.00 0.20 0.00

22-1,32-34

14.2,40-42W 14-2, 5&52

22-2,5&52

2.799

0.00

_ _

c-2#

o-2#

15.4,49-5

I .822 1

G2#

1.843 I .846

(83.95)

(95.49)

(2.299)

12..

4-6#

Key to symbols after sample interval: W = Samples counted by Westberg-Smith et al. ( 1987); # = Sample with some stage and age uncertainty it is not in composite section of Ruddiman et al. (1989) or Raymo et al. (1989).

because

P. F. Ciesielski, K. R. Bj@rklund/ Marine Micropuieontolo~_v 25 (I 9Y5) 67-86

72

2. Physical oceanographic 611, and 609

setting of Sites 646B,

Site 6463 is the more northerly site addressed herein and lies in the central Labrador Sea north of the westernmost terminus of Eirik Ridge at 345 1 m. The site is located southwest of the southern tip of Greenland at 58”1256’N and 48”22.15’W, today situated beneath the subpolar West Greenland Current (Fig. 1) . Site 609 (49”52.67’N, 24”14.29’W, 3884 m) is located along the eastern flank of the Mid-Atlantic Ridge and is strongly influenced by the diffuse eastern extension of the North Atlantic Current (Fig. 1) . The site is in the region of maximum glacial-interglacial sea surface temperature change during the late Pleistocene (Ruddiman and McIntyre, 1984). These late Pleistocene glacial-interglacial temperature variations were a consequence of major fluctuations of the North Atlantic Polar Front, bringing the site under the influence of both cold polar (glacial), and much warmer (interglacial) North Atlantic surface waters. The C. d. dauisiana records of Holes 646B and 609 are compared with a similar record obtained by Morley (1987) from Holes 611 and 61 IA (52’50.47’N, 30”18.58’W, 3203 m) and Morley and Hays (1979) from piston cores V27-114 (55”03’N, 33”04’W, 2532 m), V27- 116 (52O50’N, 30”2O’W, 3202 m) and V29179 (44”01’N, 24”32’W, 3331 m). Hole 611 and nearby piston cores V27- 114 and V27- 116 were

obtained from under the axis of the North Atlantic Current, whereas, V29-179 is from the northern limb of the North Atlantic Current at the northern edge of the subtropical gyre (Fig. I ).

3. Material and methods 3.1. Taxonomy The taxonomy of Cycludophora dauisiana (Ehrenberg) davisiana (Petrushevskaya) has been discussed carefully in Petrushevskaya ( 1967)) Morley ( 1980) and in Bjorklund and Ciesielski ( 1994). The reader is referred to the latter report for a more detailed taxonomic treatment. It is important to note that counts were carried out only on the classical morphotype of C. d. davisiana with well-developed “shoulders” at the junction of the thorax and the third segment, that is to say that C. d. cornutoides was not included [see plate I in Bjorklund and Ciesielski ( 1994), and plate 1 (fig. 6a-b) and plate 2 (fig. 2a-b) in Morley ( 1987) 1. 3.2. Sample preparation and census The non-calcareous, coarse-elastic fractions of > 45 pm were separated from bulk sediment using routine laboratory procedures (Go11 and Bjorklund, 197 1, 1974). The coarse fraction was mounted as simple

80

0.0

0.2

0.4

0.6

AGE IN tIlLLIONS

0.8

1.0

112

OF YEARS

Fig. 2. Fluctuations in percent of Cvchdophoru dauisianu dmisiana VS.age, from 0 to 1.11Ma, in Hole 646B. Oxygen isotope stage assignments are cited for selected samples. Samples barren of opal are designated by black squares.

P. F. Ciesielski, K. R. Bj@rklund/Murine Micropaleontology 25 (I 995) 67-86

%C. 0

20

d

davisiana 40

60

0.0

0.5

g Q

1.0

73

lated in Hole 646B samples through 1.11 Ma (Table 1; Fig. 2). However, counts were not made in older sediments because additional occurrences were very sparadic. Unfortunately, due to no core recovery, C. d. davisiana was not recorded between 0.636 and 0.830 Ma (stage 16.26 to N 24). Sporadic occurrences of C. d. davisiana in Hole 6468, prior to 1.1 Ma, were recorded as relative abundances, according to the criteria of Go11 and Bjarklund ( 1989). and cited in Fig. 3 with their ages. 3.3. Age model and isotopic stage assignments

e 8 s 0

1.5

? ;

Colmm

1901.78

t s Q

2.0

Conmn 2.25

2.5

Dotiant 2.53-2.51

3.0

fTrace

3.08-2.99

Fig. 3. Fluctuations in percent of Cycludnphora daoisiana daoisianu in Hole 646B. between 0 and I. 1I Ma, and earlier sporadic relative abundances of the species between 1.1 I Ma and the initial occurrence of the species.

strewn slides in Canada Balsam under a 22X50 mm cover glass. In each sample, C. d. dauisiana was counted as a percentage of the total radiolarian assemblage and tabulated in Table 1. For the most part, counts of C. d. davisiana are based upon counts of 300 or more radiolarians per strewn slide, a number which has been accepted and recommended by Imbrie and Kipp ( 197 1) for extracting data to be used in the development of paleotemperature equations. The Hole 609, C. d. daoisiana record was constructed by combining our census data of 129 samples with an additional census of 33 samples by WestbergSmith et al. ( 1987), identified by a ‘ ‘W” after samples in Table I. The percentage of this species was calcu-

Ages for the upper Pliocene-Pleistocene (2.730.007 Ma) of Site 609 were determined on the basis of an orbital “tuning” of the Site 609 carbonate record to the TP607 oxygen isotope record of North Atlantic Site 607 (location in Fig. I ) by Ruddiman et al. ( 1989) and Raymo et al. ( 1989). Sample ages were derived by interpolation between the published ages of samples calibrated to the TP607 record (Ruddiman et al., 1989, table 3A; Raymo et al., 1989, table 2A). The interpolation points are separated by 30 cm, equivalent to approximately 4 100 years. Ages of two samples, older than the stage boundary age assignments, are interpolated between the oldest oxygen isotope age (2.73 Ma) and the top of the Kaena Subchron (2.92 Ma) as identified by Clement and Robinson ( 1987). Some Hole 609 samples, identified by a “#” in the sample column of Table 1, could not be tied directly into the composite depth model of Raymo et al. ( 1989) and Ruddiman et al. ( 1989) due to splicing problems. Ages of these samples were determined by calculating their sub-bottom depth up and down from the closest portion of the composite section and then calculating the age and oxygen isotope stage position from the composite section. Sample depths determined from extrapolation up and down to composite intervals generally varied little. Given the sedimentation rate of 7.3 cm/ 1000 years, the potential error of these samples is small and most likely within the oxygen isotope stage assigned herein. Some core catcher samples with the “#” designation have a wider range of potential ages, Table 1 presents the full age and oxygen isotope stage uncertainty of these samples. Two separate oxygen isotope stage and age assignments are cited in Table 1 for core catcher samples with splicing problems, representing the

74

P. F. Ciesielski, K.R. Bj@rklund/ Marine Micropaleontology 25 (1995) 67-86

Table 2 C. duuisiam dauisiana abundances Age

% C. d. dauisiana

(Ma)

646B

0.029 0.032 0.045 0.052 0.060 0.080 0.095 0.220 0.245 0.259 0.282 0.343 0.428 0.457 0.478 0.499 0.504 0.530 0.548 0.605 0.658 0.713 0.730 0.812 0.816 0.846 0.863

611

of > 15% in Holes 646B, 611, and 609 Actual

Approx.

Age

% C. d. dauisiann

609

stage

stage

(Ma)

6468

25.70

3.15 3.23 3.60 3.81 4.09 5.12 5.37 7.56 8.01 8.26 8.65 10.16 12.04 12.61 13.00 13.45

29.18 27.33 23.30 23.33 15.90 17.00 17.67 37.33 47.67 17.30 25.67 19.00 40.67 35.67 18.90

13

23 21.00 15.80 18.33

14.42 14.59 15.73 16

43 41.60

18.67

18.90

23.15

19

47 55 42.00 28

23 24 25

uncertainty of assignments based upon interpolation from closest samples (above and below) in the composite section. Raymo et al. (1989, table 7) cited ages for midpoints of late Pliocene oxygen isotopic stages 62-l 16. Based upon these ages and the calibration of Hole 609 to TP607, we have assigned the isotopic stages to each of the Hole 609 late Pliocene samples examined herein. Ages for stage boundaries are from Martinson et al. ( 1987) for stages l-8 and from the SPECMAP time scale of Imbrie et al. ( 1984) for stages 9-16. We follow the revision of Ruddiman et al. ( 1989) to the SPECMAP age for the stage 16/17 boundary (680 ka). Use of the younger (659 ka) date of SPECMAP resulted in a designation of mid-interglacial stage 17.47 to Sample 6095-2, SO-52 cm, a sample barren of all siliceous microfossils and with common ice-rafted detritus. Using the stage 16/17 boundary age of Ruddiman et

0.869 0.875 0.886 0.896 0.923 0.933 0.959 0.987 1.03 1.048 I.049 1.05 1.09 1.10 1.18 1.28 1.34 1.376 I.377 1.42 1.450 1.468 1.50 1.527 1.56 1.61 1.626

611

609

Actual

Approx.

stage

stage

25.96 26.22 70.33

26 27 28 28

30 30 45 16.00

30.2 1

23.85

31 33

27 15.20 37.80

34.57 34.60

40 32

34 36 36 41 45 48

58.33 65 53 22 29.60 29.80

50.22 50.76

17.40 20.60

54.26 55.07

55.30

58.07

45

52

38

56

47 28

59 61-62 63.02

al. ( 1989), this clearly glacial sample is assigned to glacial stage 16, supporting an older age for this boundary. Further results are in keeping with SPECMAP ages for stage 17 / 18 and 18 / 19 boundaries rather than those of Black et al. (1988) which compress stage 18 and upper 19 with the BrunheJMatuyamalower boundary. Additional assignments of samples to oxygen isotopic stages 19-64 and 64-l 16 are interpolated from stage mid-point ages given by Ruddiman et al. (1989) and Raymo et al, (1989). Oxygen isotope stage assignments of datums within Hole 607 are based upon the TP607 record of Ruddiman et al. ( 1989) and Raymo et al. ( 1989), with stage boundary assignments made as cited for Hole 609. In Hole 646B, ages and oxygen isotope stages through 0.782 Ma and upper oxygen isotope stage 16 are based upon the composite depth record of the hole by Srivastavaet al. ( 1987) and the corresponding com-

P. F. Ciesielski,

M -

o’.o

K. R. L?j)rklund / Marine

Micropuleontr)lo~~

S C. davisima Opal barren

0.2

0.8

0.6

0.4

AGE IN HILLIONS

1.2

Fig. 4. (a) Fluctuations

25 ( 1995) 67-86

1.4

in percent of Cyludophoru

OF YEARS

I .8

2.0

AGE IN tIlLLIONS

OF YEARS

1.6

dulGunu

dmisiunu

2.2

2.4

in Hole 609 vs. age (O-l.2 Ma). All peak

ae numbered by their oxygen isotope stage assignment. (b) Fluctuations in percent of Cvcladophoru

( I .2-2.4 Ma) All

1.0

occurrences exceeding 5%

du~ri.siunu dulisiunu

in

Hole 609 vs. age

peak occurrences exceeding 5% are numbered by their oxygen isotope stage assignment, with the exception of the stage

88.64 sample which represents the first abundance of -

I %.

posite depth of oxygen isotope events 1.1 through 2 1.3

as defined by Aksu et al. ( 1989, table 2). To make the stage event ages similar to those used in Hole 609, isotopic events I. l-7.5 were assigned ages according to Martinson et al. ( 1987), and events 8.2-21.3 according to the SPECMAP time scale of Imbrie et al. ( 1984). Additionally, events 16.22, 17.10, 20.23, 21.10, and 21.30 were assigned ages to conform with revisions required by stage boundary age changes by Ruddiman et al. ( 1989). Samples 646B-9- 1, 97-100 cm through 646B- I O-6,60-63 cm (Table 1) are below the oxygen isotopic record of the site. Ages for the eight samples in this interval were calculated by interpolation between the following points: oxygen isotope event

21.30, the top and base of the Jaramillo Subchron, and the LAD G. infzatu datum which has an age of I .97 Ma in well dated sites. Since the depths of these samples are from only slightly beneath the Jaramillo Subchronozone to oxygen isotope event 2 I .30, the ages are well constrained. Estimates of their approximate oxygen isotope stage position are given in Tables 1 and 2. Hole 611 lacks an oxygen isotope record, however, ages for C. d. duuisiana maxima ( > 15%) and some minima are calculated for comparison with Holes 609 and 646B. To compare the two records we have assigned ages to the numbered ( * I-’ 12) and unnumbered abundance intervals of Morley ( 1987). These ages (Table 2 for ages of peaks > 15%) are based upon

(4 60 L” u 50 uf 3 2 40 d 2

30

I” 2 20 2 C! = 10 w 0 2

4

6

8

10

12

OXYGEN

14

16

ISOTOPE

18

20

22

24

STAGES

I 26

28

(W

30

32

34

36

38

40

42

OXYGEN

44

46

ISOTOPE

48

50

52

54

56

58

STAGES

OXYGEN ISOTOPE STAGES Fig. 5. (a) Fluctuations in percent of Cycludophoru dmisiana dulGsiunu in Hole 609 relative to oxygen isotope stages I to 29. Stage boundaries are represented by vertical lines with glacial stages stippled. Samples barren of opal are designated by black squares. (b) Fluctuations in percent of C,ycladophora duoisianu dmisiunrr in Hole 609 relative to oxygen isotope stages 30 to 59. Stage boundaries are represented by vertical lines with glacial stages stippled. Samples barren of opal are designated by black squares. (c) Fluctuations in percent of Cvcludophoru du~isruna duvisinnu in Hole 609 relative to oxygen isotope stages 60 to 89. Stage boundties are represented by vertical lines with glacial stages stippled. Samples barren of opal are designated by black squares.

P. F. Ciesielski, K. R. Bjprklund /Marine Micropaleoniolog~ 25 (I 995) 67-86

interpolation from the paleomagnetic record with no direct calibration to oxygen isotope stages. A notational system, similar to that of Prell et al. ( 1986) through stage 21, has not yet been presented to designate oxygen isotope events within stages 22- 116 until more records of older stages are available. A system is adopted here to designate the relative intra-stage position of samples within oxygen isotope stages lI 16 of Holes 609 and 646B. Stage numbers in the tables are followed by a decimal indicator representing the proportional time between stage boundaries (e.g., 38.30 = three-tenths of the time between stages 38 and 39). Intra-stage fractions increase with age in keeping with increasing stage numbers with age. With this SYStern it should be possible lo add new abundance peaks to any data set, and the old datum points should still maintain their validity.

4. Results: Temporal fluctuations of C. d. davisiana in the North Atlantic-Labrador Sea (Table 1; Figs. 2-6) 4.1. Labrador Sea, Hole 646B The percentage of C. d. daoisiana was determined from twenty-nine samples (Table 1; Figs. 2 and 3) with direct calibration to oxygen isotope stages I-16. Among oxygen isotope stages l-l 6, only stages 2 and I 1 were unsampled. Two samples were barren of radi-

2.50,

, 0

10

,

20

I

30

% Cycladophora

77

olaria (stages 1.02 and 16.26) and the remaining twenty-seven samples have an average of 23.27% C. d. dauisiana. The average percentage of this species in stages 1-l 6 exceeds that previously recorded at lower latitudes in the North Atlantic for the same period (Morley and Hays, 1979; Morley, 1987). Percentages of C. d. davisiana exceed 15% in portions of stages 3, 4, 5-8, 10, and 12-15; whereas, lower values were observed in portions of stages 4-6, and 9-10. An interval of no core recovery occurs in Hole 646B between oxygen isotope stage 16.26 (0.636 Ma) and N 0.85 Ma, accounting for the lack of samples analyzed in this interval. Direct oxygen isotope stage calibration is absent below 0.636 Ma (stage 16.26), however, we estimate the base of the no recovery zone to be in stages 24 to 25. This estimate is based upon interpolation from the paleomagnetic record of Hole 646B and the occurrence of a C. d. davisiana peak (42%) just below the dissolution zone that we correlate to late stage 25+arly stage 26 in Hole 609. Below the no recovery zone between stages 16-24, C. d. davisiana is present consistently until 1.10 Ma in all but two (0.97 and 1.05 Ma) of seven examined samples where its absence is due to silica dissolution. In the remaining five samples between 0.85 and 1.10 Ma, C. d. dauisiana percentages are high (23.8570.33%), except at 0.93 Ma where only 2.3% occur. Estimated oxygen isotope stages for values in excess of 20% are stages 24,26,3 1, and 36. Biogenic silica is sparse in Hole 646B between lo5,97-IO0 cm and 23-1, 97-100 cm, 1.10 and -2.60

I

40

I

50

I

60

1

70

80

davisiana davisiana

Fig. 6. Percent C~ycladophoradatGunu dauisiana in Hole 609 versus benthic S’*O values (Ruddiman et al.. 1989; Raymo et al., 1989) in Hole 607 from age equivalent horizons. Calibration of the both sites was done on the basis of an orbital “tuning” of the Site 609 carbonate record to the TP607 oxygen isotope record of North Atlantic Site 607 (see Methods section) by Ruddiman et al. ( 1989) and Raymo et al. ( 1989).

---.

Core

40

0

42

60

46

46

40

Core 611-6

0

Core 20

20

611-5

10

6

6

4

2

40

611-2

16

16

14

12

20

Core

x

<,

i

'1

F

20

o

56

56

52

50

3 .. '3 ._ '. '. ... -130K

40

611-3 60

-

26 -

26

24- 2

22

20

Core 611.7 40

0

Core

0

40

i

..,

_

,.

,

a-.,

.

.-

,,>-w_-._>

_,“,._

.~..~___.__.__

_.

__

0

5

'6

5

_

< ,_1. _,,’

20

..__

611-4

Fig. 7. Temporal fluctuations of the abundance of Qcladuphora da~:isinna duuisiano as a percent of the radiolarian assemblage in North Atlantic ODP Hole 6 I 1 (from Morley, 1987) and piston cores V27- 116, V27-114, and V29-179 (from Morley and Hays, 1979). Note that the following C. d. dmisiuna peaks occur in the designated oxygen isotope stages: *f, *g, and *h in stage 6; * i,, *i,, ‘j, and ‘kin stage 7; and “I, ‘m, and *n in stage 8.

36

32

611A-1

P. F. Ciesielski, K.R. Bj)rklund/Marine

Ma, respectively; therefore, percentages of C. d. dauisiana were not counted. Three samples within this interval contain radiolaria and C. d. dauisiana. The species is common in 16-CC and 20-3, 101-104 cm, 1.74 and 2.34 Ma, respectively, and is very dominant in the radiolarian assemblage at 21-CC, 2.51 Ma (Fig. 3). Trace occurrences are found in 23-CC (2.49 Ma) and within 25-CC of the Gauss Chronozone. The deepest trace occurrence in Hole 646B at N 3.08-2.99 Ma is the oldest recorded occurrence of the species in the world’s oceans. 4.2. North Atlantic, Hole 609 Percentages of C. d. davisiana were determined in 162 samples between 0.0002 and 2.80 Ma, with an average sample spacing of 17,000 years. Sample intervals, percentage of C. d. davisiana, ages, and oxygen isotope stage positions are given in Table 1. The percentage C. d. dauisiana fluctuations are plotted from the present to 1.2 Ma (Fig. 4a), and from 1.2 to 2.4 Ma (Fig. 4b). Furthermore, the percentage of C. d. dauisiana is plotted versus oxygen isotope stage boundaries, stages 1 to 29 (Fig. 5a), stages 30 to 59 (Fig. 5b), and stages 60 to 89 (Fig. 5~). The FAD of C. d. dauisiana is located in DSDP Hole 609-19-CC, 4-5 cm. Some uncertainty occurs in the age of this first occurrence because the core-catcher sample is not placed in the composite section of Raymo et al. ( 1989). Thus, estimates of its age and stage position range from 2.580 to 2.435 Ma and oxygen isotope stages 109.34-102.19 based on the range of sub-bottom depth uncertainty. An age of 2.5 1 Ma and oxygen isotope stage designation of 105.82 is assigned for the first occurrence of the species as a mean value of the uncertainty. Prior to this initial occurrence Cycladophora daoisiana cornutoides is found, a species that also overlaps with C. d. davisiana and probably is its ancestor. C. d. davisiana is found only in traces between its initial occurrence at 2.51 Ma (stage 105.82; 19-CC, 2-4 cm) and 2.155 Ma (stage 88.64), when it reached 0.9% of the total fauna. The observed abundance fluctuations of C. d. davisiana (Figs. 4 and 5) reveal changes in the frequency and magnitude of abundance maxima through time. During the early Matuyama Chron, prior to oxygen isotope stage 63, C. d. daoisiana abundances are low.

Micropaleontology 25 (1995) 67-86

79

Only once during this period, at 1.867 Ma (stage 74.73), have we evidence for the species exceeding 10% of the assemblage. Near the stage 63/62 boundary (stage 63.02), the initial major abundance peak (35.7%) of C. d. dauisiana was noted at 1.626 Ma. Prior to the initial major abundance peak in oxygen isotope stage 63, C. d. dauisiana is often less than 1% and never greater than 12% of the radiolarian assemblage. In the Matuyama Chronozone prior to stage 35, observed abundance peaks of greater than 15% are limited to oxygen isotope stages 63.02, 58.07, 55.0754.26, and 50.76-50.22. Thus, during the first N 1.5 million years of the species presence within the North Atlantic ( -2.51-1.05 Ma), only four abundance peaks were noted in excess of 15%. The abundance fluctuation pattern of C. d. davisiana changes character after oxygen isotope stage 35; average abundances are greater (7.7% vs. 4.3%) and abundance maxima of more than 15% are more frequent. Between oxygen isotope stages 109 and 35, four abundance maxima of greater than 15% were noted, whereas, no fewer than nine such events occurred between 1.049 Ma (stage 34.60) and the present. The relationship of C. d. davisiana abundances fluctuations to oxygen isotope stages may be observed in Fig. 5. Many, but not all, peak abundances of C. d. davisiana occur in glacial stages (e.g., 8, 14, 18, 20, 26, 30, 34, 50, 54, and 58). Increased abundances of the species are also noted in weak interglacial stages (e.g., stages 3, 23, 39, and 41)) and significant cool periods within robust interglacial stages (e.g., late stage 11) . Sample spacing is adequate in some stages to note some rapid changes in abundance near stage transitions (e.g., stages 4/5,25/26,62/63). Additional insight on the relationship between glacial-interglacial conditions and abundance variations C. d. davisiana can be seen in Fig. 6. Fig. 6 is a plot of the percent of C. d. dauisiana in Hole 609 versus the benthic oxygen isotope values of equivalent stage positions in Hole 607. Occurrences of the species as 10% or more of the assemblage occurred when benthic S”O values exceed modern values. Most high abundance of the species occurred when benthic S”O values exceeded 3.7 and the majority of high abundances coincide with #*O values of more than 4.0. Reference to the oxygen isotopic records of Site 607 (Ruddiman et al., 1989; Raymo et al., 1989) reveal that most peak

80

P. F. Ciesielski, K.R. Bj@rklund/Marine

occurrences occurred during glacial stages of transitions between glacial and interglacial stages. 4.3. North Atlantic, Hole 61 I the Cycladophoru duuipatterns in Hole 611 based upon an examination of samples taken at approximately 30-cm intervals ( N 7000 year sample spacing). Lacking a Hole 611 oxygen isotope stratigraphy, ages of abundance fluctuations were determined by interpolation between paleomagnetic boundaries, assuming constant sedimentation rates. The concept of constant sedimentation rates is obviously an oversimplification as it is most likely that the glacial-interglacial cycles produce large short-term fluctuations in the sedimentation rate. However, the ages provide a first-order age estimate with an accuracy that is acceptable for our study. Morley’s ( 1987) percentage abundance curve of Cycladophora dauisiana daoisiana in Hole 611, between 0 and N 1.66 Ma, is reproduced in Fig. 7. A closer examination and correlation of the Hole 611 abundance curve with the peak correlations among Holes 611,609 and 646B is provided in the discussion. Morley

(1987)

presented

siana dauisiana abundance

5. Discussion 5.1. Regional comparison and correlation of C. d. davisiana records A comparison of the Site 609 C. d. davisiana record with Site 611, the only other existing lengthy record of such fluctuations in the North Atlantic, reveals many apparently concurrent abundance fluctuations. The C. d. davisiana record in oxygen isotope stages l-9 is represented in more detail in Hole 6 11 and may be confidently correlated to the nearby C. d. duuisiana records of V27-114 and V27-116 (Morley and Hays, 1979) which is reproduced in Fig. 7. The largest abundance peak in this interval ( “b) of these piston cores and Site 611 represents the later portion of the last glacial period (stage 2)) when the percentage of C. d. davisiana is -55-42% between 55” and 53”N. In Holes 609 and 646B, stage 2 was unsampled; however, high abundances (29-23%) of C. d. davisiana were found throughout stage 3 to earliest stage 4 (0.0290.060 Ma) in both sites. These high abundances rep-

Micropzleontolo~y

2.5 (I 995) 67-86

resent in part the ‘d maximum of Morley and Hays (1979) near the stage 314 boundary. The high values in Sites 609 and 646 in stage 3 reveal a more extensive dominance of elevated C. d. duuisiana values than the previous records of Morley and Hays (1979) who show a long period of increase in its abundance from a mid-stage 3 minimum ( ‘c) up to the stage 2 maximum. Six samples were examined from oxygen isotope stage 5 in Holes 646B and 609. As shown by Morley and Hays ( 1979), C. d. dauisiana abundances were low during substages 5a, 5b, and 5c (their *e,, *ez, *e,) A C. d. davisiuna maximum ( 15.90%) in stage 5.12 of Hole 609 represents a maximum not well represented between the stage 5 *e, minimum and the stage 5 boundary in previous North Atlantic piston cores of Morley and Hays ( 1979). Most other characteristics of the C. d. dauisiana record in stage 5 are represented, including: their *e, minimum (substage 5a) in stage 5.16 (2.2%), substage 5b maximum (17.0%) in stage 5.37, *e2 minimum (substage 5c) in stage 5.55 (4.2%)) and *e3 minimum (substage 5e) in stage 5.92-5.97 (2.33-1.66%). Only the substage 5d maximum of Morley and Hays ( 1979) is unrepresented, otherwise their stage 5 abundance patterns appear reproducible in Holes 609 and 646B. All four samples from oxygen isotope stage 6 have C. d. davisiana abundances of less than 5%. Only a portion of stage 6 was previously tied directly to the C. d. davisiana record of the North Atlantic (V29- 179, Morley and Hays, 1979). A C. d. duvisiuna maximum ( *f) is identified in upper stage 6 in this core; whereas, a minimum ( ‘g) and maximum ( *h) were inferred in middle and lower stage 6 based upon comparison of North Atlantic C. d. davisiana record with a similar record in the Subantarctic core RC 1 l- 120 (Morley and Hays, 1979). Neither the *f nor *h C. d. duuisiana maxima of Morley and Hays ( 1979) were noted in our upper and lower stage 6 samples. In oxygen isotope stage 7, Morley and Hays ( 1979) identified three C. d. duuisiana minima (ii, iZ, and k) and one significant maximum (j) in Subantarctic core RC 1 l- 120. They recognized these same events in North Atlantic core V27-116 which lacks direct oxygen isotope calibration. Our four samples from stage 7 have relatively low percentages of C. d. davisiana, except near mid-stage in Hole 646B, where they are 17.7%. This peak probably represents the small maximum between the *i, and ‘i, minima of Morley and Hays

I? F. Ciesielski, K.R. Bj@rklund /Murine Micropaleontology

( 1979) which may be assigned here to oxygen isotope event 7.3 of Prell et al. ( 1986). Morley and Hays (1979) revealed a prolonged period of high C. d. davisiana abundances ( lO-30% in oxygen isotope stage 8 of Vema 27-l 16). Peak abundances in upper to middle stage 8 are assigned to maximum “I and are separated from a lower stage 8 maximum ( *n) by a brief minimum ( 'm) .We also recognize a C. d. dauisiana maximum (37.3%) just below the stage 7/8 boundary (stage 8.01) that declines rapidly into the base of stage 7 (stage 7.98) just as is recognized between their * 1maximum and *k minimum. High abundances between 9.5 and 47.5% in Holes 609 and 646B (stages 8.01-8.65) are correlated to the North Atlantic maximum ‘1 of Morley and Hays ( 1979). A single low abundance minimum in stage 8.7 of Hole 609 most likely represents the abundance minimum *m of Morley and Hays ( 1979). The basal stage 8 maximum *n is unrepresented in our sections. No previous direct calibration of C. d. davisiana records has been made to oxygen isotope stages older than upper stage 9 (Morley and Hays, 1979). C. d. duvisiana percentages are low in stage 9 of Holes 609 and 646B, except in the upper portion of the stage in Hole 646B (stage 9.17, 10.7%) within event 9.1 of Prell et al. ( 1986), the cooler portion of this major interglacial period. Peaks of C. d. davisiana greater than 10% in oxygen isotope stages 9-l 1 cannot be correlated to the few records of this interval in theNorth Atlantic or elsewhere (Site 611 of Morley, 1987, and Morley et al., 1982) lacking oxygen isotope stage calibration. A C. d. davisiana maximum of 18.9% in Hole 609 (stage 12.99-13.91) is probably correlative to a peak of 23% in Hole 611 where Morley ( 1987) designates maximum * 1 ( - 23%, Table 2). Our assigned age for this maximum in Hole 611 (0.504 Ma) falls within the age uncertainty of the Hole 609 maximum (0.4780.520 Ma, stage 12.99-13.91). A major abundance of C. d. davisiana in Hole 646B (40.7-35.7%) seen in stages 12.6 1 and 13.00 is interpreted as a portion of the abundance maximum extending from the Labrador Sea to the North Atlantic between mid-stage 12 and midstage 13. Following a lower stage 13-upper stage 14 minimum, seen in the more detailed record of Hole 609, higher percentages of C. d. davisiana are noted in midstage 14 of Holes 646B (stage 14.42, 21%) and 609

25 (1995) 67-86

81

(stage 14.59, 15.8%). The Hole 611 maximum ‘3 ( - 43%) of Morley ( 1987)) with an estimated age of 0.658 Ma, reveals no similar peak abundances in Holes 646B and 609, if * 3 is within stage 16. The largest abundance of C. d. dauisiana in Hole 609 (41.6%) occurs in stage 18.67 (0.713 Ma). This very significant abundance peak in the North Atlantic, is in the zone of no recovery in Hole 646B and apparently unsampled in Hole 611. Another maximum ( 18.9%) occurs in Hole 609 in stage 23.15. This maximum is tentatively correlated to the Hole 611 peak *4 of Morley ( 1987) where -55% are recorded. Morley’s minimum *5 in Hole 6 11 has an estimated age of 0.848 Ma and is probably correlative to minimas of C. d. davisiana in Hole 609 in upper stage 24 or upper stage 25. The major C. d. duuisiana maximum of 42% in Hole 646B has an estimated age of 0.847 Ma, appears to be unrepresented in Holes 609 and 6 I 1 samples, and is tentatively assigned to stage 24. Morley ( 1987) found two additional C. d. davisiana maxima between *5 and the top of the Jaramillo Subchron. These peaks, ‘6 ( - 28%) and an undesignated peak between *6 and * 7 ( - 30%)) have respective ages of 0.863 and 0.896 Ma. Given some inaccuracy in ages due to fluctuating sedimentation rates, these peaks in Hole 611 may be correlative with Hole 609 maxima in stages 25.96-26.22 and a Hole 646B maximum (70.3%) with an estimated age of 0.886 Ma. The 70% abundance peak in Hole 646B and the Hole 611 peak between ‘6 and ‘7 we tentatively assign to lower stage 26 or stage 27. Within the Jaramillo Subchron of Hole 611, Morley ( 1987) assigned notational identifiers *7, *8., and *9 to a C. d. davisiana maximum and two minima. An additional undesignated maximum also occurs between “7 and *8. We assign an age of 0.923 Ma to the ‘7 maximum ( - 30%), however, find no corresponding peak in the Hole 609 stage 28.41 (0.921 Ma) or in Hole 646B at 0.931 Ma. Based on calibrations of the C. d. dauisiana record above and below this event, it is most probably a short duration event undetected in Holes 609 and 646B but evident in stage 28. The undesignated maximum ( -45%) of Morley (1987), between his *7 and ‘8 maxima, is assigned an age of 0.933 Ma, or approximately age-equivalent with the stage 28/29 boundary (0.934 Ma). Either this is a distinct peak not represented in Hole 609 or variable Jaramillo sedimentation rates in Hole 6 I 1 may make it

82

P. F.

Ciesielski,K.R. Bj@rklund/Murine Micropcrleontol(~R.v 25 (I 995) 67-86

slightly older, in which case it may be age-equivalent with an increase in the percentage of C. d. daoisiana in Hole 609 within stage 30.15 and 30.21 (14.5-16.0%, 0.958-0.959 Ma). C. d. daoisiana values are low (O5.8%) in lower stage 30and uppermost stage 3 1 within the lowermost Jaramillo of Holes 609 and 646B. This interval is correlative to C. d. dauisiana minima ‘8 ( - 5%) and ‘9 (8%) which are assigned ages of 0.955 and 0.980 Ma, respectively. In Hole 611 Morley ( 1987) noted ten C. d. davisiana abundance peaks between the base of the Jaramillo and the top of the Olduvai Subchron. Morley gave notational designations to only two abundance peaks ( * 11 and * 12) and one abundance minimum ( * IO). Ages calculated for the first three of these maxima suggest they occur between lower stage 33 and mid-stage 36. The peak ( - 27%) at 1.03 Ma in Hole 611 most likely coincides with increasing C. d. davisiana abundance noted near the stage 33134 boundary in Hole 609. A very significant abundance peak ( - 40%) in Hole 6 11 at 1.05 Ma is suggested to represent the stage 34.6 peak (37.8%) in Hole 609. The - 1.09 Ma abundance peak ( - 32% in Hole 611) was probably unsampled in Hole 609, however, may be age-equivalent to a - 1.1 Ma peak of 58.33% in Hole 646B which we infer to be in lower stage 36. Accordingly, the * 10 abundance minimum of Morley ( 1987)) between the Hole 611 maxima at - I .05 and 1.09 Ma, would represent a Hole 609 minimum in stage 35. Prior to stage 36 C. d. davisiana abundance maxima are less frequent in Holes 609 and 611, which should make inter-hole correlation more certain. In Hole 6 1I, seven significant abundance maxima occur between 1.09 Ma and the top of the Olduvai Subchron. The C. d. davisiana record of Hole 609 (Figs. 4 and 5; Table 1) reveals six abundance maxima of greater than 10% during the age-equivalent interval (stage 36-64). In spite of few abundance peaks and the almost equal sample spacing per section (49 in Hole 611 and 40 in 609)) few of the Hole 611 peaks (as estimated based on the assumption of constant sedimentation rates between the base of the Jaramillo Subchron and the top of the Olduvai Subchron) are the same age as those in the more precisely dated Hole 609. Some undetected variations in Hole 611 sediment accumulation rates may account for some mismatch in abundance peak ages, therefore at present, correlations between sites in these intervals are tentative. Morley’s * 1 I peak

(-65%)at - 1.18 Ma may represent our C. d. davisiana maximum ( 12.7%) at 1.160 Ma (stage 39.86). Morley’s * 12 abundance peak at - 1.28 Ma ( - 53%) is most likely a peak undetected in Hole 609, probably in stage 45.Two Hole 61 I abundance peaks with estimated ages of 1.34 Ma (22%) and 1.42 Ma (45%) each may be slightly older and represent significant Hole 609 maxima between 1.376 and 1.377 Ma (29.6% and 29.8%, stage 50) and between 1.450 and 1.468 Ma ( 17.4-20.6%, stages 54-55). Two additional abundance maxima in Hole 611 at - 1.50 Ma (38%) and 1.56 Ma ( - 47%) likely occur in glacial stages 56,58, or 60. The younger of these is possibly the major stage 58 peak (55.3%) noted in Hole 609. The oldest Hole 611 abundance peak ( 28%) centered between approximately 1.60-l .61 Ma is probably the oldest major C. d. davisiana peak in Hole 609 (35.7% with a more precisely determined age of 1.626 Ma, stage 63.02). In and prior to stage 64, C. d. davisiana never exceed 12% in Hole 609. In this older portion of the record, abundances of greater than 5% are found in stages 65 (6.9%), stage71-74 (12%), and 83-84 (7.2-9.6%). 5.2. The$rst occurrence of C. d. davisiana world ocean

in the

In the following section we will review the first occurrences of C. d. daoisiana from the literature. As three subspecies of C. d. dauisiana have been described, the possibility for not discriminating between them is possible, a fact that will greatly alter and falsify the true first occurrence of C. d. davisiana. However, the authors of the articles we have cited are aware of this problem, and their species concept of C. d. davisiana is not questioned. Having now reviewed temporal fluctuations in the abundance of C. d. davisiana in the North Atlantic-Labrador Sea an examination is made of the regional differences in the initial occurrences of the species and its probable early dispersal throughout the world’s oceans. Unless indicated otherwise, the initial occurrences of C. d. davisiana discussed here are based on sections with paleomagnetic control. In the Norwegian Sea, the initial C. d. davisiana was noted only in Hole 644A below the Gauss/Matuyama boundary but above the base of the hole which terminated above the Kaena Subchron. Applying the sedimentation rate between the base of the Olduvai and

P. F. Ciesielski, K.R. Bj#rklund/Marine

Gauss/Matuyama boundary to the level of initial occurrence we assign an age uncertainty to this event of 2.61-2.53 Ma. Our examination of Labrador Sea Hole 646B places the initial occurrence of C. d. dauisiana lower in the Gauss Chronozone than previously noted elsewhere in the world (Fig. 3). Two interpretations are offered for the first occurrence of the species in this section. First, an age calculated based upon the assumption of a constant sedimentation rate between the Gauss/Matuyama boundary and the Gauss/Gilbert results in an age range of 2.99 to 3.08 Ma (range represents the exact depth of only partially recovered core 25). The alternate interpretation recognizes the presence of the upper boundary of the Kaena Subchronozone in core 23 as shown by Clement et al. ( 1989). Because the depth of the Kaena is undisclosed by Clement et al. ( 1989)) an exact age estimate is not possibly but is older than 2.92 Ma. South of the Labrador Sea, in North Atlantic Hole 609, the initial occurrence of C. d. duuisiana is between 2.435 and 2.586 Ma. Calibration to the oxygen isotope stage boundaries of Raymo et al. (1989) places this event between stages 102 and 109, very nearly the same age as in Norwegian Sea Hole 644A. Abelmann and Gersonde (1988) reported on the abundances fluctuations of C. d. dauisiana in piston cores from the southeast Atlantic sector of the Subantarctic. They found the first significant abundance of the species to occur at approximately the Gauss/Matuyama boundary (2.47 Ma) with some rare occurrences shown (Abelmann and Gersonde, 1988; Fig. 4) slightly below this boundary but with no specified age. Recently we re-examined the range of C. d. daoisiana from Meteor Rise Site 704. In Hole 704A the initial occurrence of C. d. duuisiana is in sample 17-4, 3032 cm (unpubl. data). According the oxygen isotopic record of Hole 704A (Hodell and Venz, 1992), the initial C. d. dauisiana occurred at 2.06 Ma, within OXYgen isotope stage 83. In the southwestern Atlantic sector of the Subantarctic, Weaver ( 1983) also found the initial occurrence of C. d. duuisiana at approximately the Gauss/Matuyama boundary. Further to the south in Antarctic waters of the Atlantic sector of the Southern Ocean, Lazarus (1987) reported an age of 2.7 Ma for the initial occurrence of C. d. dauisiana in ODP Leg 113 sections. Examination of his range charts reveals this age as a maximum age

Micropaleontology 25 (1995) 67-86

83

including the range of age uncertainty. In the six sites he examined, the FAD of C. d. dauisiana was not documented in enough detail to propose an age of 2.7 Ma, as is done in his table 5. A more correct statement for the age would be < 2.7 Ma. Caulet ( 199 1, table 7)) in his study of ODP Leg 119 sections from the Antarctic of the Indian Ocean, reported the FAD of C. d. davisiana to be between 2.47 and 2.53 Ma in Hole 745. However, due to opal dissolution in parts of this section, the first occurrence of the species might not have been recorded correctly, and Caulet (1991) states that the FAD of C. d. dauisiana probably is slightly younger than 2.6 Ma. The initial C. d. duvisiana was calibrated to a third section with an established oxygen isotopic record by Raymo et al. ( 1992). In eastern equatorial Pacific ODP Hole 677, the datum as defined by Alexandrovich ( 1989) is identified within oxygen isotope stage 114 (2.63 Ma). From mid-latitude North Pacific sites, Morley ( 1985) examined radiolarian assemblages from DSDP Leg 86. According to the data presented by Morley (1985) the FAD of C. d. duoisiuna in the examined sites occur between the magnetic Matuyama/Gauss (2.47 Ma) and the top of Kaena (2.92 Ma) boundaries. We calculate the ages of the FAD of C. d. duuisiana to be 2.62 Ma and 2.63 Ma for Sites 577 and 579. respectively. In addition, using the reported depth of the initial C. d. duuisiana in Site 580 (Morley, 1987), we calculated an age of 2.64 Ma for this datum. The age for the same datum at Site 578 is 2.39 Ma and younger than other sites in the region. In conclusion, an age of 2.63 Ma seems to be the best estimate for the FAD of C. d. duuisiana in the mid-latitude North Pacific. Hays et al. (1988, abstract only) reported that C. d. dauisiana first evolved in the North Pacific and then at approximately 2.6 Ma migrated throughout the world’s oceans. On the basis of this analysis of well dated sections, the origination center of C. d. dauisiana appears instead to have been in the Labrador Sea (3.08-2.99 Ma). Slightly prior to the species migration into the Norwegian Sea (2.63-2.53 Ma) and the North Atlantic (2.58-2.43 Ma, stages 109-102) it had spread throughout the North Pacific to the equator (2.62-2.64 Ma, stage 114). Although the initial occurrence of the species is not as well constrained in the high latitudes of the Southern Ocean, C. d. dauisiana appears to have migrated into this region by 2.47 to 2.53 Ma.

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The migration history of C. d. davisiana out of the Labrador Sea appears to have been first through the Arctic and Bering Sea into the North Pacific and southward into the South Atlantic and Indian Ocean sectors of the Southern Ocean. Migration of C. d. dauisiana throughout the Arctic between 3.08 and 2.99 Ma would have not been impeded by the extensive ice conditions of the late Pleistocene. Raymo et al. ( 1992) concluded that oxygen isotope data are compatible with significant deglacation of Antarctica around 3.0 Ma and numerous studies have inferred much warmer conditions within the Arctic region during the middle Pliocene (Carter et al., 1986; Matthews and Ovenden, 1990; Funder et al., 1985; Brouwers et al., 1991). Indeed, the Arctic may have been the evolutionary center of C. d. dauisiana, however, supporting evidence is lacking in the sparse silica poor Arctic record. Following the migration of C. d. dauisiam as far as the equatorial Pacific, it spread first into the Norwegian Sea and then into the North Atlantic. Further southward migration through the Atlantic and introduction of the C. d. davisiana into the Antarctic can not be ruled out, however, its initial appearance at South Atlantic Site 704 (2.06 Ma, stage 83) is the youngest noted. Apparently the species was either delayed in its southward migration to the site from the North Atlantic or was later introduced from the Subantarctic South Atlantic.

6. Conclusions An examination of the occurrence and abundance fluctuations of the radiolarian C. d. davisiana in Labrador Sea Hole 646B and North Atlantic Hole 609 provides the initial long-term correlation of its abundance fluctuations to oxygen isotope stratigraphy. From a comparison of the records from these sites and the previously studied Site 611 (Morley, 1987) the following conclusions are made: ( 1) C. d. dauisiana appeared earlier in the Labrador Sea than in the North Atlantic. In the Labrador Sea (Site 646B) its initial occurrence was prior to the Kaena Subchron (3.08-2.99 Ma) but was rare until its first common occurrence in the Labrador Sea at 2.49 Ma. (2) The first occurrence of C. d. dauisiana in the North Atlantic (Site 609) was slightly later, between 2.586 and 2.435 Ma (stages 109.34-102.19).

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(I 99.5) 67-86

(3) The highest abundances of C. d. davisiana were noted in the Labrador Sea Hole 646B where the earliest known occurrence of the species is documented (3.082.99 Ma). C. d. davisiana is inferred to have evolved in the Labrador Sea (or Arctic), and migrated next through the Arctic into the North Pacific (2.62-2.64 Ma, stage 1 14) before migrating into the Norwegian Sea (2.63-2.53 Ma) and North Atlantic (2.59-2.44 Ma, stages 109-102). Additional migration of C. d. dauisiana into the southern South Atlantic (Site 704) occurred much later (2.06 Ma, stage 83). (4) During the early Matuyama Chron, prior to oxygen isotope stage 63, C. d. dauisiana abundances were low. Only once during this period, at 1.867 Ma (stage 74.73)) is there evidence for the species exceeding 10% of the assemblage. Near the stage 63162 boundary (stage 63.02), the initial major abundance peak (35.7%) of C. d. dauisiana was noted at 1.626 Ma. Prior to the initial major abundance peak in stage 63, C. d. dauisiana is often less than 12% of the radiolarian assemblage. In older portions of the record, abundances of greater than 5% are found in stage 65, stages 71-73 (five samples), stage 74, and stages 83-84 (two samples) (5) Observed abundance peaks of greater than 15% in the Matuyama Chronozone between oxygen isotope stages 35 and 63 are limited to stages 63.02, 58.07, 55.07-54.26, and 50.76-50.22. These represent the only such abundance peaks detected during the first - 1.5 million years of the species within the North Atlantic ( -2.51-1.05 Ma). (6) The character of C. d. dauisiana abundance fluctuations in Site 609 changes after oxygen isotope stage 35; average abundances are greater (7.7% vs. 4.3%) and abundance maxima of more than 15% are more frequent. (7) Many, but not all, peak abundances of C. d. dauisiana occur in glacial stages (e.g., 8, 14, 18, 20, 26, 30, 34, 50, 54, and 58). Increased abundances of the species are also noted in weak interglacial stages (e.g., stages 3, 23, 39, and 41)) and significant cool periods of robust interglacial stages (e.g., late stage 11) . Sample spacing is adequate in some stages to note some rapid changes in abundance near stage transitions (e.g., stages 4/5,25/26, and 62163). (8) The sample density in Holes 609 and 611 and the upper portion of 646B is sufficient to detect a synchroneity of many abundance maxima and minima

P. F. Ciesielski, K.R. Bj#rklund /Marine Micropaleonrology 25 (I 995) 6746

between sites. For example, a major abundance of C. d. duuisiunu in Hole 646B (40.7-35.7%), seen in stages 12.6 1 and 13.0, is interpreted as a portion of an abundance peak extending from the Labrador Sea to the North Atlantic between mid-stage 12 and mid-stage 13. Some abundance peaks are undetected in one or the other of the two holes. warranting further sampling to obtain a more accurate record of regional abundance fluctuations. Prior to stage 36 few of the ages of Hole 61 1 peaks are the same as those in the more precisely dated Hole 609.

Acknowledgements This work was begun while PFC held a Fulbright-Hays Research Fellowship (F-HRF) at the Paleontological Museum, University of Oslo, during the 19901991 academic year. Additional work was conducted when KRB held a fellowship from the Norwegian Research Council for Sciences and the Humanities (NAVF) during a 1992-1993 sabbatical to the Department of Geology, University of Florida. We acknowledge support of our home institutions during our sabbatical years. The financial support we received from F-HRF (PFC) and NAVF (KRB) is acknowledged and made this work possible. Further support from Mobil Exploration Norway, Inc. (Stavanger, Norway) is much appreciated. Furthermore we thank Susan M. Case-Ciesielski for drafting and editorial assistance. Drs. Stanley A. Kling (Leucadia, CA) and Hsin-Yi Ling (Northern Illinois University) are thanked for critical review of the manuscript. For further information, the authors can also be contacted via INTERNET, their e-mail addresses are [email protected] and kjell.bjorklund@ t0yen.uio.m~. respectively.

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