deep sea drilling project hole 552a · 6.15 2-2,64 6.21 2-2, 70 6.26 2-2, 75 6.32 2-2, 81 6.41 2-2,...

37. HISTORY OF PLIO-PLEISTOCENE CLIMATE IN THE NORTHEASTERN ATLANTIC,DEEP SEA DRILLING PROJECT HOLE 552A1

H. B. Zimmerman, Union CollegeN. J. Shackleton, Cambridge UniversityJ. Backman, University of Stockholm

D. V. Kent, Lamont-Doherty Geological ObservatoryJ. G. Baldauf, U. S. Geological SurveyA. J. Kaltenback, Marathon Oil Co.

andA. C. Morton, British Geological Survey, Key worth2

ABSTRACT

DSDP Hole 552A, cored with the HPC on Hatton Drift, represents an almost complete and undisturbed sedimentsection spanning the late Neogene and Quaternary. Lithologic, faunal, isotopic, and paleomagnetic analyses indicatethat the section represents the most complete deep sea record of climatic evolution hitherto recovered at high latitudes inthe northern hemisphere. A glacial record of remarkable resolution for the late Pliocene and Pleistocene is provided byoxygen and carbon isotope ratios in benthic foraminifers. In the upper part of the section, the whole of the standardoxygen isotope record of the past million years is well preserved. The onset of ice-rafting and glacial-interglacial alter-nations occurs at about 2.4 m.y. ago.

INTRODUCTION

The introduction of the hydraulic piston corer (HPC)by the Deep Sea Drilling Project (DSDP) has provided,for the first time, the ability to retrieve virtually undis-turbed sections of Neogene sediment from the deep ocean.In HPC Hole 552A, we obtained an almost complete re-cord of the inception of glaciation and subsequent vari-ation of Plio-Pleistocene climate in a high latitude regionof the North Atlantic (Figs. 1, 2). In this chapter wesummarize the sedimentologic, faunal, geochemical, pale-omagnetic, and isotopic data generated by examinationof this core.

A relatively high rate of sediment accumulation atHPC Hole 552A provided an unusual and detailed Plio-Pleistocene record with good resolution and minimal bio-turbation. In contrast, relatively few conventional pistoncores, such as core V28-239, contain a complete record ofglacial stratigraphy because bioturbation and low ratesof accumulation obscure the fine-scale resolution of de-tailed features of the climatic record.

In Hole 552A deposition is fashioned by the interplayof two climatically controlled processes: the influx ofnoncarbonate material transported primarily by ice-raft-ing and bottom currents and the changing production ofcalcareous microfossils in the surface waters (carbonatedissolution is of little importance at the water depths of

1 Roberts, D. G., Schnitker, D., et al., Init. Repts. DSDP, 81: Washington (U.S. Govt.Printing Office).

2 Addresses: (Zimmerman) Union College, Schenectady, New York; (Shackleton) GodwinLaboratory for Quaternary Research, Cambridge University, Cambridge CH2.3 RS, UnitedKingdom; (Backman) Department of Geology, University of Stockholm, Stockholm, S-10691, Sweden; (Kent) Lamont-Doherty Geological Observatory, Palisades, NY 10964; (Baldauf)U.S. Geological Survey, Menlo Park, CA 94025; (Kaltenback) Marathon Oil Company, Den-ver Research Center, Littleton, CO 80160; (Morton), British Geological Survey, Key worthNG12 5GG, United Kingdom.

this site). The section is thus characterized by a strikingalternation of biogenic ooze and terrigenous muds. Auniform rate of sedimentation is certainly unlikely withso dramatic a variation in the nature of the sediments.Although depositional processes are variable, the corenevertheless exhibits a remarkably complete stratigraphicrecord.

METHODS

All cores from Hole 552A were extremely well preserved (see Site552 chapter) with the exception of Core 6 (24-29 m sub-bottom). Be-cause of severe disturbance, Core 6 was excluded from all analyses.

Total carbonate content was determined by the "Karbonate Bom-be" technique (Müller and Gastner, 1971). In this procedure, a sampleis powdered, weighed, and treated with 6N HC1 in a closed cylinder.The resulting CO2 pressure is proportional to the CaCO3 content ofthe sample. Application of an appropriate calibration factor to the ma-nometer reading yields percent CaCO3. For sediments rich in CaCO3,error is generally as low as 1%. Repeated analyses show that an accu-racy of ± 2°7o is obtained for samples with CaCO3 content below 10%.Analyses were made on the whole sediment and on the coarse fraction(CF) after screening at 74 µm (Table 1, Fig. 3).

Following carbonate determination, the remaining acid-insolublefraction of selected samples was examined petrographically (Morton,this volume). Cores 1 through 10 were examined for major composi-tional variation. A closely spaced sample set for Cores 1 and 2 was ex-amined for the abundance of volcanic glass. A small number of sam-ples were also analyzed for heavy mineral content, following separa-tion from the light minerals by gravity-settling in bromoform (sp. grav.2.80).

Organic geochemical and visual kerogen analysis was performedon selected samples covering two glacial-interglacial cycles from nearthe top and bottom of the section. Sedimentary organic matter wasevaluated by Rock-Eval pyrolysis, determination of organic phospho-rous, and pyrolysis/mass spectrometry (Figs. 4, 5). A complete de-scription of these methodologies and results is given in Kaltenback etal. (this volume).

Diatom biostratigraphy in the Plio-Pleistocene section was estab-lished by Baldauf (this volume). Values of species abundance were basedon the average number of diatom frustules observed per field of view(at least 450 fields of view per sample; 0.5 mm2 at 500 ×) .

861

H. B. ZIMMERMAN ET AL.

65°

60° N

35° 30° W 25° 20° 15° 10° 5°

Figure 1. Location map for Hole 552A (56°02.56'N, 23°13.88'W; water depth: 2311 m).

Samples for paleomagnetic analysis were taken approximately ev-ery 25 cm; we avoided sediment section that showed any sign of distur-bance. Only orientation with respect to the vertical axis was preservedso that the inclination component was used to infer polarity at thishigh-latitude site. Natural remanent magnetization (NRM) was mea-sured on a two-axis cryogenic magnetometer (Goree and Fuller, 1976)both before and after alternating-field demagnetization at 10 to 30 mT.NRM intensities are typically of the order 10'2 A/m in the upper 45 mof the section, decreasing to about 10~3 A/m in the lower part. Inclina-tions are generally well grouped near to the expected dipole valve (71 de-grees, positive for normal and negative for reversed) for the latitude ofthe site. A reliable record of the geomagnetic field was obtained to thebase of the Gauss normal magnetochron (Fig. 6). The lower boundaryof the Olduvai subchron is obscured by disturbance at the break be-tween successive cores, while the Mammoth subchron is unclear, prob-ably lying in a slightly disturbed section at the top of Core 11.

Stable oxygen and carbon isotope analyses were made at intervals ofapproximately 10 cm from well below the first ice-rafting layer throughto the recent sediment (Figs. 7-9). The sample was dispersed by shak-ing for a few hours in distilled water, and sieved on a 150 µm screen.The portion retained was dried at 60°C and weighed; the fine fractionwas settled for 24 hr., dried, and weighed; the residue was retained fornannofossil studies (Backman, this volume). Three species were uti-lized for stable isotope analysis: Globocassidulina subglobosa, Uvi-gerina peregrina, and Planulina wuellerstorfi. Standard techniques foranalysis were used: reaction with 100% orthophosphoric acid at 50°C,removal of water, and isotopic analysis in a VG Isogas 903 triple col-lector mass spectrometer. Overall analytical uncertainty during the timethese measurements were made was ±0.07‰ (0-18) and ±0.05‰ (C-13) (both 1-sigma valves). A more complete description of these tech-niques and tables of analytical results and calibrations are given inShackleton et al. (1984) and Shackleton and Hall (this volume).

LITHOLOGIC DESCRIPTION

Hole 552A is located at a water depth of 2311 m onthe Hatton Sediment Drift at the base of the westernflank of Rockall Plateau (Site 552 chapter, Figs. 1, 2).The drift sediments are thought to have been depositedunder bottom currents flowing northeastward unparal-lel to the slope. According to McCave et al. (1980), thisflow consists of Iceland-Scotland Overflow Water whichhas rounded the southern end of the plateau after hav-ing passed over Feni Drift in the Rockall Trough.

The uppermost sediments are Plio-Pleistocene in ageand are characterized by alternating beds of foraminif-eral-nannofossil ooze and calcareous marls and mud.These extend from the seafloor to a basal contact definedby the lowermost marl in this unit (Section 552A-9-4;43.6 m sub-bottom), which is also defined by the base ofhigh magnetic intensity. This part of the section wascontinuously cored with the HPC; with the exception ofCore 6 (24-29 m sub-bottom), most of the cores wereundisturbed, as indicated by the well-defined stratigraph-ic contacts and sedimentological details.

One of the most striking characteristics of this unit isthe cyclicity of color and carbonate content (Fig. 7A,B). Color cycles are clearly coupled with carbonate con-tent, the lighter shades correlating with high carbonatevalues. In this part of the North Atlantic, variation in

862

PLIO-PLEISTOCENE CLIMATE

Table 1. Calcium carbonate data, Hole 552A. Table 1. (Continued).

Depth (m)

0.080.160.210.31 ]0.390.490.61 ]0.69 ]0.80 ]0.91 ]1.00 11.101.19 ]1.291.42 11.521.611.711.791.90 ]2.01 12.15 12.19 ]2.30 ]2.412.49 12.60 12.71 12.80 12.95 ]3.02 13.10 13.20 13.31 13.45 13.50 13.59 13.70 ]3.79 ]3.89 13.99 14.05 1

Core-Section(level in cm)

------

I, 7I, 15[,20[, 30I, 38[, 48I, 60[, 68[, 79

-1,90-1, 99-1, 109-1, 118-1, 128-1, 141-2, 1-2, 10-2,20-2, 28-2, 39-2, 50-2, 64-2,68-2,79-2, 90-2, 98-2, 109-2, 120-2, 129-2, 144-3, 1-3, 9-3, 19-3, 30-3, 44-3, 49-3, 58-3, 69-3, 78-3, 88,CC (4),CC (10)

4.29 2-1, 284.41 2-1, 404.50 2-1, 494.60 2-1, 594.70 2-1, 694.81 2-1, 804.91 2-1, 904.99 2-1, 985.11 2-1, 1105.20 2-1, 1195.31 2-1, 1305.40 2-1, 1395.52 2-2, 15.61 2-2, 105.72 2-2, 215.76 2-2, 255.81 2-2, 305.90 2-2, 396.00 2-2, 496.10 2-2, 596.15 2-2,646.21 2-2, 706.26 2-2, 756.32 2-2, 816.41 2-2, 906.50 2-2, 996.61 2-2, 110

CaCO3 (%

808276523434282033373346395141215570678277818361252842352345644250627068634165725050344429334477716075687166848144525372787279889191918787

CF (%)

4462514123

27161829193427

231735303843

46

2527181815143245424150

3438253739252122251724223238

3431333744

2328542426363512161619

15

CFCaCO3 (%)

8590846669

56627764797469

771782867887

92

798553916687182717781

8480808692696566765765718686

8788898593

74696092869396981009897

90

Depth (m)

6.716.816.917.027.117.207.317.397.517.617.697.797.928.018.098.218.308.408.528.558.618.688.758.818.898.989.029.119.219.319.419.489.589.699.799.879.9810.0610.1810.3010.3710.5510.6810.7510.8410.8810.9811.1411.2411.3411.3911.4411.5011.6411.7311.8411.9712.0412.1312.2012.3312.4512.5012.5812.6412.7512.8512.9412.98


2-2, 1202-2, 1302-2, 1402-3, 12-3, 102-3, 192-3, 302-3, 382-3, 502-3, 602-3, 682-3, 782-3, 912-3, 1002-3, 1082-3, 1202-3, 1292-3, 1392-4, 12-4,42-4, 102-4, 172-4, 242-4, 302-4, 382,CC (8)3-1, 13-1, 103-1, 203-1, 303-1, 403-1, 473-1, 573-1, 683-1, 783-1, 863-1, 973-1, 1053-1, 1173-1, 1293-1, 1363-2, 43-2, 173-2, 243-2, 333-2, 373-2, 473-2, 633-2, 733-2, 833-2, 883-2, 933-2, 993-2, 1133-2, 1223-2, 1333-2, 1463-3, 33-3, 123-3, 193-3, 323-3,443-3, 493-3, 573-3, 633-3, 743-3, 843-3, 933-3, 97

CaCO 3 (%)

83464632151223342934427844424444453367887649818888906949666627768264427779717980857964312525491423342422152640233328313(ash)452983898477664342

CF (%)

21151322211229

152419222820192216101916105

1416362214202111131324274635285054

434117211435242123

2312132110162419152115543736342916

CFCaCO3 (%)

8880

33

2948

6057714869697265606487838065

8191958573758567767876749286808788

877656416685594767

5067607256677357106076969295917770

863


Table 1. (Continued). Table 1. (Continued).

Depth (m)

13.1513.1913.2213.3013.4013.4713.5413.6313.7513.7813.9514.0214.1114.2114.3114.4214.5214.6014.7214.8014.9015.1215.2015.3015.4015.5215.6215.7015.7915.9216.0116.1016.1916.3016.4116.5116.6216.7116.7816.8916.9617.0217.1017.2017.3017.3917.4917.6017.7117.8117.8617.9118.0218.0618.1318.2018.3118.4218.5218.6118.6818.7118.8118.8918.9819.0219.0919.2019.31


3-3, 1143-3, 1183-3, 1213-3, 1293-3, 1393-3, 1463-4, 33-4, 123-4, 243-4, 273,CC (15)4-1, 14-1, 104-1, 204-1, 304-1, 414-1, 514-1, 594-1, 714-1, 794-1, 894-1, 1114-1, 1194-1, 1294-1, 1394-2, 14-2, 114-2, 194-2, 284-2, 414-2, 504-2, 594-2, 684-2, 794-2, 904-2, 1004-2, 1114-2, 1204-2, 1274-2, 1384-2, 1454-3, 14-3, 94-3, 194-3, 294-3, 384-3, 484-3, 594-3, 704-3, 804-3, 854-3, 904-3, 1014-3, 1054-3, 1124-3, 1194-3, 1304-3, 1414-4, 14-4, 104-4, 174-4, 204-4, 304,CC (8)4,CC (17)5-1, 15-1, 85-1, 195-1, 30

CaCO 3 («7o)

48101740577162491818485270591814736164798067767578774137332187910196060603616184504964885510707962474918360695228113453512863375674

CF (%)

6

91528

463527191624311622216273243413335

4341

272428

16181334

394033115192425

50402820395031

251064138351071831221940163361

CFCaCO3 (%)

17

236787

9182905550808260742738536583868883

8586

4949

483412850(?)

8586805923443775

68898217898479

804533(?)86888756387784807287717782

Depth (m)

19.4019.5619.6119.7219.8019.9119.9720.1220.2020.3020.4320.5220.5920.7020.8120.9221.0321.1121.2321.3221.4121.4921.5821.7121.8221.9322.0222.1022.2022.3222.4322.5322.6122.6922.8122.9123.0123.1123.2023.3123.4323.5223.6322.6723.7123.8123.9123.9524.0329.0829.1929.2929.3929.4929.6129.7229.8229.9029.9930.0930.2130.3230.4230.5230.6130.7230.8130.9231.01


5-1, 395-1, 555-1, 605-1, 715-1, 795-1, 905-1, 965-1, 1115-1, 1195-1, 1295-1, 1425-2, 15-2, 85-2, 195-2, 305-2, 415-2, 525-2, 605-2, 725-2, 815-2, 905-2, 985-2, 1075-2, 1205-2, 1315-2, 1425-3, 15-3,95-3, 195-3, 315-3, 425-3, 525-3, 605-3, 685-3, 805-3, 905-3, 1005-3, 1105-3, 1195-3, 1305-3, 1425-4, 15-4, 125-4, 165-4, 205-4, 305-4, 405,CC (4)5,CC (12)7-1, 77-1, 187-1, 287-1, 387-1, 487-1, 607-1, 717-1, 817-1, 897-1, 987-1, 1087-1, 1207-1, 1317-1, 1417-2, 17-2, 107-2, 217-2, 307-2, 417-2, 50

CaCO3 (%;

7256363362918983755916312668109344323416986857031354539416484634716374854774917452941219728584365456827278898479525383837254153028155917

) CF (%)

43351825293836444135242483194354618164451495724

401317532815371017303142311511145

64241391736

513744393036393039544328331713132812

CFCaCO3 (%)

85715677789693918889717535775486585862657992878964

427377749060793756637886393378240

98089922557

8589949596877585939277620475728435

864



Depth (m)

31.1031.1931.2831.3931.5431.5931.7031.8231.8831.9632.0232.1232.2232.3132.3832.5432.5932.6832.8332.8732.9933.1233.2033.3233.4633.5233.5733.6733.7734.0334.0934.1934.3134.4334.5034.5834.6934.7934.8834.9935.1135.2035.3235.4635.5235.6135.6835.8135.9236.0136.1136.2136.3136.4136.5236.6136.6636.8136.9637.0237.0937.1837.3137.4137.5337.6137.7237.7937.87


7-2, 597-2, 687-2, 777-2, 887-2, 1037-2, 1087-2, 1197-2, 1317-2, 1377-2, 1457-3, 17-3, 117-3, 217-3, 307-3, 377-3, 537-3, 587-3, 677-3, 827-3, 867-3, 987-3, 1117-3, 1197-3, 1317-3, 1457-4, 17-4, 67,CC (6)7,CC (16)8-1,28-1, 88-1, 188-1, 308-1, 428-1, 498-1, 578-1, 688-1, 788-1, 878-1, 988-1, 1118-1, 1198-1, 1318-1, 1458-2, 18-2, 108-2, 178-2, 308-2, 418-2, 508-2, 608-2, 708-2, 808-2, 908-2, 1018-2, 1108-2, 1158-2, 1308-2, 1458-3, 18-3, 88-3, 178-3, 308-3, 408-3, 528-3, 608-3, 718-3, 788-3, 86

CaCO3 (%

54848446337858789858466521346408177775824858990898988898860186866667172838081617363715579889290888990878787868789845355532961587279496886

) CF (%)

3029444021124940

3746251791714373229169394450

402937393343225222936393939

242425233833

3733283629273121263414143114

2615

26121633

CFCaCO3 (%)

8690886974479796

929183500

728685877641929696

98959695697758084

78868990

858186899896

98989810096979794979694776367

7672

84728789

Depth (m)

37.9538.0138.1338.2138.2938.4238.5238.6138.7138.8138.9038.9739.0639.1639.3439.4839.6539.7539.9540.0040.0740.1740.2840.4040.4840.5640.6640.7840.9040.9641.0741.1841.2841.3541.3841.4741.5541.6141.6941.7941.8641.9841.9942.0642.1442.1842.2842.3942.4942.5842.6942.7942.9543.0743.1643.1843.2843.4043.5043.5643.6643.7743.9244.0244.1244.2644.3244.4344.53


8-3, 948-3, 1008-3, 1128-3, 1208-3, 1288-3, 1418-4, 18-4, 108-4, 208-4, 308-4, 398.CC (6)9-1, 59-1, 159-1, 339-1, 479-1, 649-1, 749-1, 949-1, 999-1, 1069-1, 1169-1, 1279-1, 1399-1, 1479-2, 59-2, 159-2, 279-2, 399-2, 459-2, 569-2, 679-2, 779-2, 849-2, 879-2, 969-2, 1049-2, 1109-2, 1189-2, 1289-2, 1359-2, 1479-2, 1489-3, 59-3, 139-3, 179-3, 279-3, 389-3, 489-3, 579-3, 689-3, 789-3, 949-3, 1069-3, 1159-3, 1179-3, 1279-3, 1399-3, 1499-4, 59-4, 159-4, 269,CC (13)10-1, 110-1, 1110-1, 2510-1, 3110-1, 4210-1, 52

CaCO 3 (%)

79683862974907985788331777385814633847858878056868581683529808464246282818255155223212744929092929090939090906788786078898786838593919289

CF (%)

13201431114236333447341237312619202646

304129223545363220354037211444

172223622

221926

2528363434242026272719142050263731352423323017

CFCaCO3 (%)

90784945093?

909389915488889294478685

7792897110092877146408385704060

9290625858

302473

971001009810098971009194988564929388929068979397100

865



Depth (m)

44.6144.7344.8344.8844.9345.0445.0845.2345.3045.4945.5445.6345.7245.8245.9646.0346.1346.2346.3446.4246.5346.5846.6446.7246.8046.8846.9647.0447.1247.2247.3147.4347.5547.6347.7347.8547.9348.0648.1348.2343.2548.4748.5448.6748.7648.7848.9049.0149.0749.2149.2949.4149.5149.5949.7149.8049.8850.0050.1150.1850.3150.4150.5550.6450.7050.8550.9150.9851.0951.24


10-1, 6010-1, 7210-1, 8210-1, 8710-1, 9210-1, 10310-1, 10710-1, 12210-1, 12910-1, 14810-2, 310-2, 1210-2, 2110-2, 3110-2, 4510-2, 5210-2, 6210-2, 7210-2, 8310-2, 9110-2, 10210-2, 10710-2, 11310-2, 12110-2, 12910-2, 13710-2, 14510-3, 310-3, 1110-3, 2110-3, 3010-3, 4210-3, 5410-3, 6210-3, 7210-3, 8410-3, 9210-3, 10510-3, 11210-3, 12210-3, 13410-3, 14610-4, 310-4, 1610-4, 2510-4, 2710-4, 3910.CC (8)11-1,611-1,2011-1,2811-1, 4011-1, 5011-1, 5811-1,7011-1,7911-1, 8711-1,9911-1, 11011-1, 11711-1, 13011-1, 14011-2,411-2, 1311-2, 1911-2,3411-2,4011-2,4711-2, 5811-2, 73

CaCO 3 (%)

90929492899192919292899091838790919292898990929391929289929188929393929492939293929292939087949083909290899184899292939393929391919192918990

CF (%)

111622

2119

2825213434463645253439322224

273224

282619151815182723223023264030

31191923191827192515222521192016162218212614151814

2512

CFCaCO3 (%)

10097

98100

96979893959193929695949697100

989698

1009998100971001009910010099100989898

9885100959810079981001009898841009810010010097939797948897

9993

Depth (m)

51.4351.5351.6651.6851.7951.8952.0552.1452.2452.3352.3852.4852.5852.7552.8752.9853.0953.2353.3553.5553.6753.7853.9054.0254.0754.2054.3354.4054.5554.6354.7554.8554.9155.0855.2355.3655.4955.5555.6655.7555.8355.9556.0856.1956.2956.4156.5356.6856.7956.9557.0457.0857.1757.3357.4657.5957.7557.7857.9157.9858.1658.1958.3058.3958.5458.6658.7458.7858.8658.96


11-2, 9211-2, 10211-2, 11511-2, 11711-2, 12811-2, 13811-3, 411-3, 1311-3, 2311-3, 3211-3, 3711-3, 4711-3, 5711-3, 7411-3, 8611-3,9711-3, 10811-3, 12211-3, 13411-4, 411-4, 1611-4, 2711-4, 3911,CC(8)12-1, 612-1, 1912-1, 3212-1, 3912-1, 5412-1,6212-1, 7412-1, 8412-1, 9012-1, 10712-1, 12212-1, 13512-1, 14812-2, 412-2, 1512-2, 2412-2, 3212-2, 4412-2, 5712-2, 6812-2, 7812-2, 9012-2, 10212-2, 11712-2, 12812-2, 14412-3, 3,12-3, 812-3, 1612-3, 3212-3, 4512-3, 5812-3, 7412-3, 7712-3, 9012-3, 9712-3, 11512-3, 11812-3, 12912-3, 13812-4, 312-4, 1512-4, 2312-4, 2712.CC (5)12.CC (15)

CaCO3 (%)

92939493919291919292939394959493959392929392959488939592939294949494919091939293939392939493929191908788899493949394909189879291958793959192

CF (%)

151079111617151526

261517

10968811711171413771069121313111215131221111918171816249811

1111101314

9799999

791110

CFCaCO3 (%)

959695969696949710099

9410096

969793961009788947684958891931009696100981001009810010095100959810097979510010088

100959796100

93100100100100100100

10010010096

866


- i

Hatton /0f h\/×^lA'," ,

I j

50 km

Figure 2. Position of Hole 552A on the western flank of Rockall Pla-teau. Sediments of the Gardar and Hatton drifts are stippled. Sub-bottom information generalized from Site 552 chapter (this vol-ume).

the carbonate content is controlled by glacial-intergla-cial depositional regimes (Ruddiman and Mclntyre, 1976);coccoliths and foraminifers are deposited two to threetimes more rapidly during interglacials (a function ofsurface water productivity), whereas noncalcareous ter-rigenous sediments are deposited more rapidly underglacial climatic conditions as a result of ice-rafting.

Biogenous ConstituentsThe calcareous oozes occur in shades of white and

light gray and are somewhat mottled by bioturbation.Laminated structures are rare, although an occasionalthin layer (< l cm thick) of foraminiferal "sand" mayresult from winnowing by bottom currents. The carbon-ate content of the interglacial calcareous oozes fluctu-ates between 70 and 90%, attaining a consistent value of95% in the underlying late Pliocene preglacial oozes be-low 44 m (Fig. 3).

Carbonate content is clearly correlated with the coarsefraction (>74 µm) content. Even a cursory examinationof the sediment reveals that the largest proportion of thecoarse fraction of the interglacial stages consists of fora-miniferal tests (Fig. 3). Except for the low-carbonatespikes during glacial episodes, most of the coarse frac-tion is of high carbonate content. It is interesting to notethat during interglacial stages the coarse fraction compo-nents (foraminifers) form 40 to 60% of the total sedi-ment, whereas in the preglacial late Pliocene oozes, thecoarse fraction makes up generally less than 20% of thesediment.

The interplay between these three curves—carbonatepercent, coarse fraction percent, and carbonate percentof the coarse fraction (Fig. 3)—reflects the variation ofthe calcareous components produced under the rapidlychanging climatic regimes of the past 2.4 m.y. The lowcarbonate-low productivity segments of the carbonatecurve most probably reflect the prevalence of sea ice anddownwelling within the broadly cyclonic circulation ofsurface water in the Rockall-Greenland sector of the gla-cial North Atlantic. Under interglacial conditions the

return of the warm North Atlantic Drift stimulates anincrease in biologic productivity. The spikes of low coarsefraction carbonate associated with the glacial stages sug-gest particularly intense cold periods during which sea-ice cover may have been so extensive that surface pro-ductivity in this area was effectively eliminated for peri-ods of time long enough to be recorded in this section.

There is also a positive correlation between biogenicsilica and total carbonate content (Baldauf, this volume).Biosiliceous productivity thus corresponds to that of thecalcareous microfossils. Biogenic silica, however, onlybecomes abundant where carbonate content exceeds 90%.Sponge spicules occur commonly in sediments with car-bonate values as low as 80%; the more delicate diatomsand radiolarians, however, only occur in sediments ofhigher carbonate content. The correspondence of dia-tom and calcareous microfossil abundance suggests thatplanktonic productivity of both is controlled by similarclimatically induced environmental factors in the sur-face ocean.

A particularly distinct interval of biosiliceous disso-lution, occurring between 8 and 33 m sub-bottom (0.44-1.8 m.y., Fig. 9; Baldauf, this volume), does not allow acomplete correlation of siliceous/calcareous planktonicproductivity. Although occasional samples within thisinterval contain well-preserved diatom flora, the majori-ty of samples are barren of diatoms. This barren inter-val has probably resulted from a complex of environ-mental factors affecting productivity and preservation.An interval which may be similar was recorded by Schra-der and Fenner (1976) in the Norwegian Sea (DSDP Leg38). At these sites, the barren interval was also punctu-ated by occasional samples with an abundant assem-blage of temperate diatoms. It is suggested that theseoccurrences of abundant diatom content represent iso-lated episodes of warmth during which the North Atlan-tic Drift is able to penetrate into the Norwegian Sea.

Organic carbon content (Kaltenback et al., this vol-ume) also has a cyclical variability. Interglacial carbon-ate oozes have organic carbon contents of 0.06-0.08%,whereas in the glacial muds the organic carbon valuesare in the 0.14-0.20% range (Fig. 4). Analysis by Rock-Eval pyrolysis also reveals that organic carbon contentof glacial sediments contains a higher proportion of re-sidual or reworked carbon (commonly termed "highlyoxidized, residual nonsource," Fig. 5). The higher levelsof organic carbon, therefore, reflect an influx of re-worked organic matter during glacial climates, undoubt-edly a result of lower sea levels and increased erosion ofthe continents and continental shelves.

Sediments enriched in organic phosphorus often char-acterize organic material of pelagic origin. Interglacialorganic material of these sediments is enriched in phos-phorus (c/p < 25), whereas in glacial sediments organicphosphorus was not detected. Relatively high levels oforganic phosphorus also characterize the late Pliocenecalcareous oozes deposited prior to the inception of gla-ciation. These high values of organic phosphorus con-sidered together with the low values of residual carbonsuggest a predominately marine origin for the organicmaterial of the interglacial sediments.

867


Carbonate (%)

0 20 40 60 80 100

Coarse fraction (%) Carbonate of coarse fraction (%)

20 40 60 80 100 0 20 40 60 80 100

Figure 3. Percent carbonate, coarse fraction (>74 µta), and coarse fraction carbonate plotted on a depth scale,Hole 552A, Cores 1-5 and Cores 7-12.

Because of the difficulty in measuring such smallamounts of organic material, samples from only two cli-matic cycles were examined. We note that, with respectto organic matter, there is apparently little difference be-tween a glacial-interglacial cycle occurring early or latein the Plio-Pleistocene sequence.

Terrigenous ComponentsThe bulk of the noncarbonate fraction of these sedi-

ments is concentrated in the glacial sequences. XRD analy-

sis indicates that the clay composition is almost totallysmectite in the interglacial oozes, whereas the glacialmuds contain the predominately terrigenous clays—il-lite, kaolinite, and chlorite. This observation reinforcesthe suggestion that sediments of the glacial stages origi-nate primarily from continental sources related to lowersea levels and increased rates of continental erosion.

The terrigenous coarse fraction is arkosic in composi-tion (Morton, this volume); the presence of feldspar withpolycrystalline and strained monocrystalline quartz and

868


Carbonate (%)

.0 20 40 60 80 100 0

Coarse fraction (%)

20 40 60 80 100

Carbonate of coarse fraction (%)

0 20 40 60 80 100

Figure 3. (Continued).

869


100

90 -

80

70

60

O 50

u

40 -

30 -

20

10

2-

-

i i i

o

A

A

O

1

o

A

0A

O

A

Section 2-2 to 2-4

Section 8-2 to 8-3

o ° A

8

1 I I.02 .04 .06 .08 .10 .12 .14

Organic carbon (%)

.16 .18 .20

Figure 4. Percent calcium carbonate plotted against organic carbonfor two climatic cycles (Hole 552A, Cores 2 and 8).

metamorphic rock fragments suggests a source largelyof metamorphic basement. The occurrence of basaltgrains also indicates some contribution from nearby ex-posed lavas. Heavy mineral constituents similarly sug-gest a mixed metamorphic-basaltic terrane (Morton,

this volume). The most immediate single source forthese sediment grains is Greenland, which satisfies thecriteria of possessing both extensive tracts of metamor-phic basement and large areas of exposed basalt. Thesheltered position of Site 552 on the upper reaches ofthe Hatton Drift serves to eliminate other potentialsource areas to the east. Given the presence of scatteredlarge pebbles (Site 552 chapter), ice-rafting is the mostlikely process of sediment transport for these sands andsilts.

Pyroclastic input is sporadic; it is a consistent but rel-atively minor constituent in the lower part of the se-quence (Cores 5 to 9), disappears in Cores 3 and 4, andis present again in Cores 1 and 2 (Morton, this volume).Most of the pyroclastic material is glassy, varying be-tween slightly to highly vesiculated; both clear and browntypes occur in variable proportions. Minor componentsof pyroclastic origin include augite, plagioclase, andopaque grains. These constituents of volcanic ash aresimilar to those of DSDP Site 404 (Harrison et al.,1979) and also to ashes of Plio-Pleistocene age at DSDPSite 346 on the Icelandic Plateau (Sylvester, 1976).

It is generally accepted that the volcanic ash of Plio-Pleistocene age in the North Atlantic and Norwegian-Greenland Sea originated from eruptions on Iceland (Rud-diman and Glover, 1972; Sylvester, 1976; Harrison et al,1979; Donn and Ninkovitch, 1980). The explosive na-ture of the volcanism is ascribed to the interaction of themagma with water, in this case with glacial meltwater, inthe manner described by Heiken (1975).

.30

.28

.26

.24

.22

.20

.18 -

.16 -

a .14

δ

.12

.10

.08

.06

.04

.02

Figure 5.Cores

1 1 !

Hole 552A

O Section 2-2 to 2-4A Section 8-2 to 8-3

-

-

_

-

-

-

-

I I 1

1 1

/

IInterglacial ^

1 1

1

' o

A o

l

1 1

/ A1lo_oo .

-1 /AD A A*,. ^

//-**

i i

1

y Glacial

_

Transitional

-

-

10 20 30 40 50 60Residual carbon %

70 80 90 100

Percent organic carbon plotted against residual carbon for two climatic cycles (Hole 552A,2 and 8).

870


STABLE ISOTOPE STRATIGRAPHY

Oxygen Isotope Record: Hole 552A, Cores 1-5

In Figures 6 and 7A, the oxygen isotope, paleomag-netic, and carbonate data for the upper five cores areshown together with the oxygen isotope record of pistoncore V28-239 (Shackleton and Opdyke, 1976). We haveused V28-239 here because, although it is known to in-clude changes in accumulation rate, it contains an almostcomplete record of Plio-Pleistocene climatic cycles. Acomparison of DSDP Hole 552A with V28-238, whichrecords an almost uniform accumulation rate, may befound in Shackleton et al. (1984). Correlation of the iso-topic stage boundaries reveals marked variations in ac-cumulation rate in DSDP Hole 552A, a not unexpectedresult considering the lithological variations that are evi-dent.

We have erected isotopic stage boundaries for Hole552A by comparisons of the curves and paleomagneticcontrol points. For this part of the section, the globaloxygen isotopic record is relatively well known. Hole552A is clearly correlative with the Pacific record andcomplete to the extent of preserving every isotope stage.Shackleton and Opdyke (1973; 1976) recognized 23 iso-topic stages in the late and middle Pleistocene. Throughcomparison of Hole 552A with the Pacific records, wehave extended this numbering system to at least intergla-cial stage 25, which is defined as including the base ofthe Jaramillo subchron at 0.98 m.y. ago.

Late Pliocene Onset of Ice-rafting

The climatic record is less well known below the iso-topic stages established for the middle and late Pleisto-cene. In Figure 8, the oxygen isotope data for the lowerpart of the sequence in Hole 552A is compared with theoxygen isotope data from piston core V28-179 (Shackle-ton and Opdyke, 1977), which covers a benthic oxygenisotope record back to 3.5 m.y. To facilitate compari-son, the plotting scale for both records has been adjust-ed at the indicated magnetostratigraphic boundaries; anapproximate age scale is thus obtained.

Comparison between these two records is good con-sidering the low accumulation rate, bioturbation, andrelatively coarse sampling interval in V28-179. The am-plitude of variation, however, is substantially greater in

Hole 552A than in V28-179. Since the accumulationrate of V28-179 was only about 0.55 cm/k.y., climaticextremes lasting only a few thousand years should be se-verely degraded by bioturbation.

Nannofossil extinction levels have been determinedquantitatively for both cores and their ages estimated(Backman and Shackleton, 1983). Using these ages, theaverage accumulation rate over the pre-ice-rafting inter-val in Hole 552A is estimated at approximately 1.7 cm/k.y. This is surprisingly close to the average for the up-per Pleistocene (1.8 cm/k.y.), although the rate has cer-tainly varied over the intense climatic fluctuations repre-sented by the alternating oozes and muds.

Paleomagnetic and nannofossil stratigraphies of thesequence in Hole 552A give identical estimates for theage of the first major northern hemisphere glacial event—2.37 m.y. Back to about 2.4 m.y. there is a remarkablecorrespondence between the carbonate and oxygen iso-tope records of Hole 552A (Fig. 7B). It is evident thatboth parameters are causally related to glaciation. More-over, the coincidence of the first isotopic event with thedramatic influx of ice-rafted debris at 2.4 m.y. is clear ev-idence that this late Pliocene episode is related to a north-ern hemisphere occurrence, rather than to an Antarcticclimatic event.

Comparison of the isotopic composition of benthicforaminifers at this level of the first glacial maximumwith values in glacial stages in the upper part of the se-quence show that the initial event represents a truly gla-cial interval with an ice volume similar to maxima of themiddle and late Pleistocene. Although the section inHole 552A may preserve a significant record of deep-water temperature variability in addition to the ice vol-ume signal, the glacial event at 2.4 m.y. must certainlyhave been more severe than was recognized by Shackletonand Opdyke (1977). Almost a million years prior to thePliocene/Pleistocene boundary (Backman et al., 1983),this glacial occurrence must represent the major environ-mental event of the late Neogene of the northern hemi-sphere.

Ice-rafted debris is absent prior to 2.4 m.y. This agefor the initiation of major ice-rafting in the North Atlan-tic is considerably later than 3.0-3.2 m.y. determined byBerggren (1972) and Poore (1981). Their observations,however, were made on cores recovered by conventional

10 12

0.73 0.91

'30 '40 50

Core

'θOm

1.66 2.47 2.92 3.40 m.y. ago

Figure 6. Magnetic record for Hole 552A, Cores 1-12. Demagnetized inclinations are shown only for apparently undisturbed parts ofthe cores. Time scale from Berggren et al., in press. (B = Brunhes; M = Matuyama; J = Jaramillo; CM = Cobb Mountain; O= Olduvai; R = Reunion; K = Kaena; G/G = Gauss/Gilbert.)

871


1

2

3

4

5

6

7

8

g

10

11

I 12

§13Q

14

15

16

17

18

19

20

21

22

23

24

A

_

-

-

-

—

-

-

-

-

-

-

-

-

-

Core

(

1

2

3

4

5

Value

) 5 10

p

i

j

J7 0.73

£

H CM

E

i i

Carbonate (%)

20 40 60 80 100

δ 1 8 θ (‰) Core V28-2390 -1.0 -2.0

Figure 7. Summary of percent carbonate and oxygen isotope data for Hole 552A correlated with oxygen isotope record of V28-239 (Shackleton and Opdyke, 1976). Records of both cores are plotted linearly with depth. Proposed oxygen isotope stageboundaries, paleomagnetic data, and color value (light [10]-dark [1]) are also indicated. A. Cores 1-5. B. Cores 7-12.

rotary drilling in which the sediments were greatly dis-turbed. Backman (1979) has re-dated the inception of ice-rafted sediments at DSDP Sites 111 and 116 at 2.5 m.y.ago. Prell (1982) and Hodell et al. (1983) presented evi-dence of isotopic variability around 3.2 m.y. ago; Prellinterpreted this as representing a brief excursion in icevolume. The record preceding the initial glacial event atHole 552A indicates that although there was considerableclimatic variability somewhere, such glaciation as mayhave occurred prior to 2.5 m.y. ago did not give rise toice-rafting in the northeastern Atlantic.

Carbon Isotope Record

A water mass forming at the surface has the 1 3C con-tent of surface water and a high content of dissolved oxy-gen. During its passage through the deep reaches of theocean, the water mass "ages"; dissolved oxygen is uti-lized by the oxidation of particulate organic matter sink-

ing from the sea surface, and dissolved CO2 becomes iso-topically lighter as a consequence of the addition of thisisotopically light carbon (Kroopnick, 1980; Shackletonand Hall, this volume).

Carbon isotope records of Hole 5 52A and piston coreV28-179 are compared in Figure 9. The data are plottedon the same isotopic scale, and the same species-depen-dent correction factors have been applied (Shackleton etal., 1984). In today's ocean there is an observed differ-ence of a little over l%o between the two areas, reflectingthe fact that the deep ocean is ventilated (younger watermass) in the North Atlantic. It is clear from the persistentoffset in values that the water mass bathing Hatton Driftwas younger than that of the deep Pacific throughout theinterval studied. Moreover, since the high-frequency vari-ability was approximately the same prior to the major cli-matic event at 2.4 m.y. ago as after, the 1 3C variabilitywas not forced by climatic cyclicity.

872


B Core Value Carbonate (%)0 5 10 0 20 40 60 80 100 5

518O (‰)

4518O (%o)Core V28-2390 -1.0 -2.0

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

10

11

12

45

46

47

48

49

50

51

52

53

54

55

56

57

58

59

Figure 7. (Continued).

CONCLUSIONS

DSDP Hole 552A was cored with the HPC on HattonDrift and obtained an almost complete and undisturbedsediment section spanning the late Neogene and Quater-nary. Lithologic, faunal, isotopic, and paleomagnetic anal-yses indicate that the section represents the most com-plete deep sea record of climatic evolution hitherto re-covered in the high latitude northern hemisphere. Onthe basis of the foregoing studies, the following conclu-sions seem warranted:

15

20

I I I I > I

1. The climate-ocean system, expressed as lithologicparameters, clearly shows a cyclic mode of variation.The gross lithology is a sequence of alternating whitepelagic-calcareous ooze and dark muds rich in ice-rafteddebris. Composition of the acid-insoluble coarse frac-tion and geographic position of Hole 552A suggest Green-land as the most probable origin of the ice-rafted debris.

2. The cyclic nature of the sediments extends to theincluded organic material. The glacial muds, with a rel-atively high content of organic carbon of a reworkedcharacter, reflect the lowered sea levels and increased con-

873


Core V28-179 benthics

DB DP I I DS DT

mQα. 4

Hole 552A benthics

1.4 1.6 1.8 2.0 2.2 2.4 2.6Age (m.y.)

2.8 3.0 3.2 3.4 3.6

Figure 8. Oxygen isotope data of Hole 552A (Cores 7-12) plotted on an age scale of linear adjustment between magnetic reversals. The oxygenisotope record for Pacific core V28-179 (Shackleton and Opdyke, 1977) is plotted at the same age scale for comparison; time control isshown — 1.66 m.y., top Olduvai N subchron; 2.47 m.y. ago, base Matuyama R chron; 2.92 m.y., top Kaena R subchron; 3.40 m.y., baseGauss N chron. Nannofossil extinction horizons determined for both cores: DT, Discoaster tamalis; DS, D. surculus; DP, D. pentaradiatus;DB, D. brouweri. Horizontal lines indicate the present position of O18 equilibrium.

Hole 552A

Core V28-179 —

J L I I I J I I L • I • I • I1.4 1.6 1.8 2.0 2.2 2.4 2.6

Age (m.y.)

2.8 3.0 3.2 3.4 3.6

Figure 9. Carbon isotope records for Hole 552A (Cores 7-12) and Pacific core V28-179. Both records are plotted on the same 13C and agescales.

874


tinental erosion of glacial episodes. The enhanced levelsof organic phosphorus in organic material of the inter-glacial stages suggest a pelagic-marine source.

3. The carbonate and coarse fraction data reflect thevariation of the calcareous components produced underthe rapidly changing climatic regimes of the past 2.4 m.y.Spikes of low coarse fraction carbonate may indicate par-ticularly intense cold periods with extensive ice cover andresulting low productivity in the northeastern Atlantic.In the opposite sense, episodes of particular warmth aresuggested by isolated occurrences of temperate diatoms.

4. In the upper part of the section, DSDP Hole 552Apreserves the whole of the standard oxygen isotope re-cord of the past million years. We have extended the iso-tope stage stratigraphy to interglacial stage 25 which in-cludes the base of the Jaramillo subchron at 0.98 m.y.ago.

5. Oxygen isotope analysis of the sequence togetherwith nannofossil and magnetostratigraphic time controlindicate that the first major glacial event, as representedby coincident ice volume and ice-rafting horizons, oc-curs at 2.37 m.y. ago, well before the Pliocene/Pleisto-cene boundary. These data do not support the notion ofsignificant northern hemisphere glaciation prior to 2.5m.y. ago.

6. The carbon isotope record shows that Hole 552Ahas been bathed by a water mass with characteristics sim-ilar to those of present-day North Atlantic Deep Waterat least since 3.5 m.y. ago and that quasi-cyclic alterna-tions in the intensity of its production were occurringduring the Pliocene prior to the onset of extensive glaci-ation in the northern hemisphere.

ACKNOWLEDGMENTS

The authors would like to thank the staff at DSDP for the oppor-tunity to participate on Leg 81 and for their encouragement to com-plete this study. The good fellowship and stimulating collaboration ofthe shipboard scientific party will serve as a model for future cruises.Our sincere thanks to the captain and crew of The D/V Glomar Chal-lenger for a job well done under the trying circumstances of the NorthAtlantic.

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Backman, J., 1979. Pliocene biostratigraphy of DSDP Sites 111 and116 from the North Atlantic Ocean and the age of northern hemi-sphere glaciation. Stockholm Contrib. Geol., 32:113-137.

Backman, J., and Shackleton, N. J., 1983. Quantitative biochronolo-gy of Pliocene and early Pleistocene calcareous nannofossils fromthe Atlantic, Indian and Pacific Oceans. Mar. Micropaleontol., 8:141-170.

Backman, J., Shackleton, J. J. and Tauxe, L., 1983. Quantitative nan-nofossil correlation to open ocean deep sea sections from the Plio-Pleistocene boundary at Vrica, Italy. Nature, 304:156-158.

Berggren, W. A., 1972. Late Pliocene-Pleistocene glaciation. In Laugh-ton, A. S., Berggren, W. A., et al., Init. Repts. DSDP, 12: Wash-ington (U.S. Govt. Printing Office), 953-963.

Berggren, W. A., Kent, D. V., and Van Couvering, J., in press. Neo-gene geochronology and chronostratigraphy. J. Geol. Soc. Lon-don.

Donn, W. L., and Ninkovitch, D., 1980. Rate of Cenozoic explosivevolcanism in the North Atlantic Ocean inferred from deep sea cores.J. Geophys. Res., 85:5455-5460.

Goree, W. S., and Fuller, M., 1976. Magnetometers using RF-drivensquids and their application in rock magnetism and Paleomagne-tism. Rev. Geophys. Space Phys., 14:591-608.

Harrison, R. K., Knox, R. W. O'B., and Morton, A. C , 1979. Petrog-raphy and mineralogy of volcanogenic sediments from DSDP Leg48, southwest Rockall Plateau, Site 403 and 404. In Montadert,L., Roberts, D. G., et al., Init. Repts. DSDP, 48: Washington(U.S. Govt. Printing Office), 771-785.

Heiken, G., 1975. An atlas of volcanic ash. Smithsonian Contrib. EarthScL, 12:1-101.

Hodell, D. A., Kennett, J. P., and Leonard, K. A., 1983. Climaticallyinduced changes in vertical water mass structure of the VemaChannel: Evidence from Deep Sea Drilling Project Holes 516A,517, and 518. In Barker, P. F., Johnson, D. A., et al., Init. Repts.DSDP, 72: Washington (U.S. Govt. Printing Office), 907-920.

Hodell, D. A., Williams, D. F., and Kennett, J. P., in press. Reorgani-zation of deep vertical water mass structure in Vema Channel at3.2 Ma: faunal and isotopic evidence from DSDP Leg 72. Geol.Soc. Am. Bull.

Kroopnick, P., 1980. The distribution of 13C in the Atlantic Ocean.Earth Planet. Sci Lett., 49:469-484.

McCave, I. N., Lonsdale, P. F., Hollister, C. D., and Gardner, W. D.,1980. Sediment transport over the Hatton and Gardar ContouriteDrifts. J. Sediment, Petrol., 50:1049-1062.

Müller, G., and Gastner, M., 1971. The "Karbonate-Bombe," a sim-ple device for the determination of the carbonate content in sedi-ments, soils, and other materials. N. Jb. Miner, Mh., 10:466-469.

Poore, R. Z., 1981. Temporal and spatial distribution of ice-raftedmineral grains in Pliocene sediments of the North Atlantic: Impli-cations for late Cenozoic climatic history. SEPM Spec. Publ., 32:505-515.

Prell, W. L., 1982. A reevaluation of the initiation of northern hemi-sphere glaciation at 3.2 m.y.: New isotope evidence. Geol. Soc.Am., (95th Ann. Mtg.), p. 592 (Abstract with program).

Ruddiman, W. F., and Glover, L. K., 1972. Vertical mixing of ice-raft-ed volcanic ash in North Atlantic sediments. Geol. Soc. Am. Bull.,83:2817-2836.

Ruddiman, W. F., and Mclntyre, A., 1976. Northeast Atlantic paleo-climatic changes over the past 600,000 years. Mem. Geol. Soc.Am., 145:111-146.

Schrader, H. J., and Fenner, J., 1976. Norwegian diatom biostratigra-phy and taxonomy. In Talwani, M., Udintsev., G., et al., Init Repts.DSDP, 38: Washington (U.S. Govt. Printing Office), 921-1098.

Shackleton, N. J., Backman, J., Zimmermann, H. B., Kent, D. V,Hall, M. A., Roberts, D. G., Schnitker, D., Baldauf, J. G., Des-prairies, A., Homrighausen, R., Huddlestun, P., Keene, J. B.,Kaltenback, A. J., Krumsiek, K. A. O., Morton, A. C , Murray, J.W., and Westberg-Smith, J., 1984. Oxygen isotope calibration ofthe onset of icerafting in DSDP Site 552A: History of glaciation inthe North Atlantic region. Nature, 307:620-623.

Shackleton, N. J., and Opdyke, N. D., 1973. Oxygen isotope and pa-leomagnetic stratigraphy of equatorial Pacific core V28-238: Oxy-gen isotope temperatures and ice volumes on a 105 year and 106

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Date of Acceptance: January 30, 1984

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deep sea drilling project hole 552a · 6.15 2-2,64 6.21 2-2, 70 6.26 2-2, 75 6.32 2-2, 81 6.41 2-2,...

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