6. a new late neogene time scale: application to …the sediments recovered during leg 138 provide a...

Pisias, N.G., Mayer, L.A., Janecek, T.R., Palmer-Julson, A., and van Andel, T.H. (Eds.), 1995Proceedings of the Ocean Drilling Program, Scientific Results, Vol. 138

6. A NEW LATE NEOGENE TIME SCALE: APPLICATION TO LEG 138 SITES1

N.J. Shackleton,2 S. Crowhurst,2 T. Hagelberg,3 N.G. Pisias,3 and D.A. Schneider4

ABSTRACT

The sediments recovered during Leg 138 provide a remarkable opportunity to improve the geological time scale of the lateNeogene. We have developed new time scales in the following steps. First, we constructed age models on the basis of shipboardmagnetostratigraphy and biostratigraphy, using the time scale of Berggren, Kent, and Flynn (1985). Second, we refined these agemodels using shipboard GRAPE density measurements to provide more accurate correlation points. Third, we calibrated a timescale for the past 6 m.y. by matching the high-frequency GRAPE density variations to the orbital insolation record of Berger andLoutre (1991); we also took into account δ 1 8 θ records, where they were available. Fourth, we generated a new seafloor anomalytime scale using our astronomical calibration of C3A.n (t) at 5.875 Ma and an age of 9.639 Ma for C5n.ln (t) that is based on anew radiometric calibration (Baksi, 1992). Fifth, we recalibrated the records older than 6 Ma to this new scale. Finally, we recon-sidered the 6- to 10-Ma interval and found that this could also be partially tuned astronomically.

INTRODUCTION

In geology, the phrase "time scale" denotes the formal frameworkthat is used to assign ages to geological deposits or to events in thegeological record. It is often hard for a nongeologist to appreciateeither the importance of the development of geological time scales orthe difficulties that arise in generating and applying them. In thischapter, we focus on three types of "time scale." First, we have a timescale for variations in the geometry of the Earth-sun orbital system.We have used that published by Berger and Loutre (1991). Berger(1988) reviewed the history of studies of the Milankovitch theory inrelation to climate in the geological past, and Berger and Loutre(1992) reviewed the accuracy of recent computations. Second, wegenerate a time scale for variations in sediment density (reflectingchanges in the ratio of opal to calcite) that is based primarily on Sites849, 850, and 851, with records from Sites 846 and 847 providingimportant information; this time scale will probably be applicable toa large area of the equatorial Pacific Ocean. Third, we use this torecalibrate a section of the magnetic polarity time scale that is usedglobally to assign ages to rock sequences for recording an identifiedsequence of magnetic field reversals.

In another chapter (Shackleton et al., this volume), we use the timescale of this study to calibrate part of the oxygen isotope time scale(Shackleton and Opdyke, 1973; Imbrie et al., 1984). Finally, we applyour new time scale to the extensive series of biostratigraphic datums,determined by our colleagues, to refine the Neogene biostratigraphictime scale (Shackleton et al., biostratigraphic summary, this volume).The results of major synthetic studies on the geological time scale(Berggren, Kent, and Flynn [1985] and Berggren, Kent, and VanCouvering [1985]; Harland et al. [1990]) are usually presented interms of age calibration of chronostratigraphic boundaries defined instratotype sections. The geological literature is muddled by the factthat the word "age" has a specialized meaning: "sensu stricto thechronostratic division of rank between epoch and chron..." (quotedfrom the glossary in Harland, 1978) that we do not make use of here.In this chapter, we are concerned with the numerical ages expressedin an astronomical unit (years) and calibrated through slower astro-nomical cycles.

1 Pisias, N.G., Mayer, L.A., Janecek, T.R., Palmer-Julson, A., and van Andel, T.H.(Eds.), 1995. Proc. ODP, Sci. Results, 138: College Station, TX (Ocean Drilling Program).

2 University of Cambridge, Godwin Laboratory, Free School Lane, Cambridge, CB23RS, United Kingdom.

3 College of Oceanography, Oregon State University, Corvallis, OR 87331, U.S.A.4 Woods Hole Oceanographic Institution, Woods Hole, MA 02543, U.S.A.

The first statistically convincing demonstration that the imprint ofvariations in EartiYs orbital geometry can be detected in deep-seasediment records of climatic variability was that of Hays et al. (1976).The major advance that led to this work was the application of a reliableinitial time scale through the simultaneous application of magnetostra-tigraphy and oxygen isotope stratigraphy in equatorial Pacific OceanCore V28-238 (Shackleton and Opdyke, 1973), and indeed, prelimi-nary spectral analysis indicated that the validation of the Milankovitchhypothesis was imminent. The advantage of the cores examined byHays et al. (1976) was the relatively high sedimentation rate of about4 cm/k.y., which ensured that the evidence for precession could bedetected. By contrast, Core V28-238, having a sedimentation rate ofless than 2 cm/k.y., barely preserves a precession signal.

Imbrie et al. (1984) published a time scale for the past 800 k.y. onthe basis of a stack of oxygen isotope records from a number of cores.The major part of this calibration has held up to subsequent scrutiny,but the lowest part, which was dependent on two cores having lowsedimentation rates, has undergone major revision (Shackleton et al.,1990; henceforth, SBP90). This revision was only possible becausethe Ocean Drilling Program (ODP) visited DSDP Site 504 again andresampled it as Site 677 using the advanced piston corer (APC). Site677 has a consistent sedimentation rate of about 4 cm/k.y. There islittle doubt that sedimentation rate is the chief limitation on thereliable detection of orbital signals in deep-sea sequences. Leg 138was planned so as to core a number of sites in the high productivityarea of the eastern equatorial Pacific Ocean, where scientists alreadyknew that high sedimentation rates could be anticipated, and wherepervasive evidence of lithological cyclicity was also known (vanAndel et al., 1975). Thus, an excellent opportunity was presented forextending the astronomical time scale.

PAST RESEARCH

The first steps toward astronomical calibration of the pre-Brunhestime scale were those of Pisias and Moore (1981), who had access toonly relatively low-resolution data from a piston core. A major ad-vance was made by Ruddiman et al. (1986) and Raymo et al. (1989),while working on DSDP Site 607 in the North Atlantic Ocean. Thesescientists showed that a long interval, now known to extend at leastto 3 Ma, existed during which climatic variability was concentratedat the frequency of changes in obliquity (period 41 k.y.). Making onlyminor adjustments to the time scale based on linear interpolationbetween observed magnetic reversals, and using published ages forthe last few reversals of Earth's magnetic field, these researchersdeveloped a time scale that extended to about 2.4 Ma. This major

73

NJ. SHACKLETON ET AL.

achievement was possible because of the careful work that had beendone to develop a complete and continuous section for Site 607(Ruddiman, Kidd, Thomas, et al., 1987) and by the large amount oflaboratory work that had been invested in that site.

Both Hilgen (1991a, henceforth H91) and SBP90 found evidencethat this pioneering work, in fact, had led to incorrect conclusions.Hilgen's work was focused on the sequence of sapropels preserved inPliocene rocks in southern Italy; he obtained an astronomically cali-brated age for the Matuyama/Gauss boundary on the basis of matchingthese sequences with the astronomical eccentricity and precessionsignals. Soon after, Hilgen (1991b, henceforth H91) extended hiscalibration to the base of the Pliocene and gave ages for magneticreversals back to Thvera Subchron (H91). SBP90 worked on plank-tonic and benthic δ 1 8 θ records from ODP Site 677 in the easternequatorial Pacific Ocean, covering the past 2.6 m.y. These workersidentified three points where Ruddiman et al. (1986) had interpreted asa single obliquity cycle a section of record that actually spanned twoobliquity cycles. Other researchers subsequently have confirmed thisinterpretation by examining GRAPE density records from the Atlantic(Herbert et al., 1992) and through a new high-resolution δ 1 8 θ recordfrom the Indian Ocean (Bassinot, pers. comm., 1992). Since that time,a number of scientists have provided new estimates of the age of thelast few magnetic reversals (largely based on high precision 40Ar/39Ardating) that support the new calibrations. For the Brunhes/Matuyamaboundary, Izett and Obradovich (1991), Tauxe et al. (1992), Spell andMcDougall (1992), Baksi et al. (1992), and Hall and Farrell (1993) allobtained ages supporting the new astronomically calibrated age of0.78 Ma. For the Jaramillo Subchron, Glass et al. (1991), Spell andMcDougall (1992), and Tauxe et al. (1992) found support for the newage (although Obradovich and Izett [1992] obtained values nearer theconventional age). Obradovich and Izett (1992) obtained age estimatesfor Cobb Mountain and for the base of the Olduvai to support theastronomical calibration. Walter et al. (1991) also obtained an agewithin the Olduvai Subchron at Olduvai Gorge to support the astro-nomical calibration of the base of the normal subchron. Walter et al.

(1992) obtained ages in the Gauss that support the new calibration, andMcDougall et al. (1992) showed that age determinations in the Gilbert(that had previously appeared anomalous), in fact, were in good agree-ment with the H91 time scale for the early Pliocene. Finally, Wilson(1993) demonstrated that if seafloor spreading rates are examined withhigh precision, they prove to be less variable when estimated using theastronomical time scale than when using other published time scales.

MAGNETOSTRATIGRAPHY OF LEG 138 SITES

The time scale used during Leg 138 was based on the version of theseafloor spreading magnetic anomaly time scale derived by Berggren,Kent, and Flynn (1985). In turn, this represented a new age calibrationof the anomaly sequence created by LaBrecque et al. (1977), whichwas based on the classic South Atlantic profile of Heirtzler et al.(1968). Berggren, Kent, and Flynn (1985) used as age control pointseight anomalies having ages that range from 3.40 to 84.0 m.y.; theyassumed linear spreading on their profile between these controls. Re-cently, Cande and Kent (1992) (henceforth CK92) introduced threesignificant modifications to this time scale. First, they generated a morereliable baseline anomaly sequence by re-evaluating a suite of SouthAtlantic profiles, instead of relying on the single profile of Heirtzler etal. (1968). Second, they restacked high-resolution profiles from otherareas onto this improved South Atlantic sequence. Third, they used acubic-spline, instead of a linear interpolation, to estimate the ages ofanomalies between their calibration points; this is important from ageophysical standpoint, because it avoids introducing artificial instan-taneous plate accelerations at the control point ages. CK92 also docu-mented some additional reversals that were not included in the schemeof LaBrecque et al. (1977). Finally, CK92 introduced a minor improve-ment to the nomenclature, which we use in this chapter, alongside thefamiliar Pliocene-Pleistocene terminology. We have used the standard

South Atlantic Ocean profile of CK92 as our guide to the relativespatial and temporal spacing of reversals during the Neogene.

Among the 11 sites drilled during Leg 138, eight (844, 845, 848,850, 851, 852, 853, and 854) provided segments of useful magneto-stratigraphy. Taken together, these provide a complete coverage of thepolarity transitions of the last 13 m.y. since C5AB.n (t). For thepurpose of calibration, reversals located in sediments having a highersedimentation rate are more valuable. In this sense, Site 851 is par-ticularly valuable for events between the present and C3n.ln (theCochiti Subchron). Site 852 preserves a good record to the top ofC5.2n, except for the interval between C3A.nl and C4A.nl, wherewe rely on Site 853. Site 848 also preserves a record to the base ofC5r. 1 n. For the oldest part of the record, we rely primarily on Site 845,which extends to C5AB.n (t). The depths of the reversals in each siteare given in the appropriate site chapter, with a few exceptions.Schneider (this volume) has reinterpreted the data for Core 138-844C-6H; we have accepted this new version. Schneider (this vol-ume) has also improved the data from Site 845 by analyzing discretesamples. Again, we have used this revised data set. We accept theGauss/Gilbert boundary in Hole 850B (plotted in error, p. 841, Fig.22 of Mayer, Pisias, Janecek, et al., 1992). Data for Hole 85 ID areprovided by Meynadier et al. (this volume).

BIOSTRATIGRAPHY

Remarkably high resolution was achieved in the shipboard biostra-tigraphy for all the major microfossil groups. Initially, age models weredeveloped on the basis of the compilation given in the "ExplanatoryNotes" chapter (Shipboard Scientific Party, 1992). A small number ofdatum levels were redated (within the framework of the Berggren,Kent, and Flynn [1985] time scale) on the basis of the excellentmagnetostratigraphy in Sites 844 and 845. This more-or-less self-consistent set of datum levels provided the basis for the age modelsdeveloped in the site chapters and in Shackleton et al. (1992).

The objective of this chapter is to develop a more accurate timescale than has hitherto been available, by using the obvious cycliccharacter of the GRAPE density records as a monitor of the responseof the fertile equatorial circulation system to forcing by variations inEarth's orbital geometry. The gamma-ray attenuation porosity evalu-ator (GRAPE) density tool is used aboard JOIDES Resolution toobtain automatic high-resolution records of sediment density; thesedata are discussed in Hagelberg et al. (this volume). In this region,sediment density varies with carbonate content, which in turn isclosely linked to surface productivity. Since it was obvious at an earlystage that this study would entail significant changes to the time scaleused aboard JOIDES Resolution, biostratigraphic datum levels wereused mainly to maintain the stratigraphic correlation between sites asthe "tuning" was performed. Procedurally, this was done by recalcu-lating the age for each datum level as the ages of the magnetostrati-graphic boundaries were estimated again. Subsequently (Shackletonet al., this volume), we created a new set of best estimates for the agesof all useful biostratigraphic datums, based on the combined evidenceofalltheLeg 138 sites. Here, it is appropriate to remark that publishedestimates for a good proportion of the datums used were based onsparse data. This means that it is difficult to evaluate an age model formany of the sites because of apparent conflicts among age estimatessuggested by data from different fossil groups. Ultimately, the mostrigorous test of our age models will come, on the one hand, from thestatistical evaluation of the patterns of density variability that theypredict (Hagelberg et al., this volume) and, on the other, from furtherradiometric dating of the magnetic reversal sequence.

OXYGEN ISOTOPE STRATIGRAPHY

To maintain internal consistency in this study, we have attemptedto develop a time scale that is based almost entirely on characteristicevents in the GRAPE density records. We have not directly used the

74

NEW LATE NEOGENE TIME SCALE

standard δ 1 8 θ chronology in the upper part. As these data emerged,we have had access to the benthic 518O records of Sites 846 and 849(Mix et al., this volume) and to the planktonic δ 1 8 θ records of Sites847 (Farrell et al., this volume) and 851 (Ravelo et al., this volume)for the Pleistocene, as well as to the benthic δ 1 8 θ record of Site 846(Shackleton et al., this volume) for the Pliocene. Our aim has been togenerate a GRAPE-based time scale for the Pleistocene that wouldnot be in conflict with a δ18O-based time scale, where that is available.Thus, we have used as control points features that are visible in theGRAPE density records. Initially, we utilized the same procedurethroughout, correlating GRAPE density maxima to insolation max-ima and GRAPE density minima to insolation minima. However,Farrell et al. (this volume) show that in the Pleistocene section of Site847, age differences between our time scale based on GRAPE densityand one based on δ 1 8 θ stratigraphy do arise, although they seldomexceed a few thousand years. Thus, we have in addition developedmodified time scales for the past million years in which the ages forGRAPE density events have been shifted away from the ages of inso-lation maxima and minima to generate time scales that are closer tothose suggested by the δ 1 8 θ data.

In Tables 1 to 11, we present age models that are probably close toa true δ 1 8 θ time scale through the past million years; we also present(Table 12) the alternative age models for the upper part that weredeveloped independent of the δ 1 8 θ data. These may be regarded asviable alternative age models. Although age models based solely onGRAPE density might be expected to be less reliable than those basedon δ 1 8 θ stratigraphy, one cannot assume that the current δ 1 8 θ timescale is perfect in every detail.

TUNING METHODS

It was a strength of the investigation by Hays et al. (1976) that theywere able to document variance in the bandwidth of each of the threeorbital variables (eccentricity, obliquity, and precession) in three in-dependent paleoclimate proxies (δ 1 8 θ, radiolarian-based sea-surfacetemperature, and percentage Cycladophora davisiana) using an agemodel for their cores that was entirely independently generated. Ingeneral, this is difficult to achieve, especially in a situation such as theeastern equatorial Pacific Ocean, where sedimentation rate clearlyvaries with climate, perhaps over a wide range. Thus, we have notattempted to demonstrate independently for each segment of time ineach site that a statistical likelihood exists for the variability observedto be associated with orbital forcing. However, spectra on untunedsections of GRAPE density record consistently suggest concentrationof power at orbital frequencies.

In a similar manner, Imbrie et al. (1984) did not attempt to dem-onstrate in advance that each of the records they used in their compi-lation contained the orbital imprint. Instead, they reasoned that thetime scale that they generated gave rise to a sufficiently high coher-ency between δ 1 8 θ and orbital insolation that the time scale wasprobably largely correct. Procedurally, Imbrie et al. (1984) used astrategy based on digital filters. To do this, one must develop an initialtime scale, filter one orbital bandwidth (for example, obliquity), andnote such small changes in the age model as may be needed tomaintain a constant phase relationship between the filtered signal andthe calculated obliquity record. The disadvantage of the method isthat it is difficult to apply if sedimentation rates are extremely vari-able. In the case of the Leg 138 sites, it was already clear that this isso (Shackleton et al., 1992). For this reason, we chose to work entirelyin the time domain, comparing GRAPE density with a target recordderived from the orbital data.

This was also the strategy used by SBP90 for Site 677 (indeed thesame strategy also had its place in the study of Imbrie et al. [1984] asconsiderable uncertainty regarding the appropriate "first guess" chro-nology existed when that work started). However, in the case of thework on Site 677, a reasonable tuning target already existed; SBP90used the simple ice sheet model of Imbrie and Imbrie (1980) to

Table 1. Age model for Site 844.

Age(Ma)

0.0000.0880.1270.1400.1740.1840.2470.3540.4790.5090.5790.6140.6280.6590.7170.7370.7830.9901.0701.7701.9502.6003.0533.1313.2243.3373.6114.1924.3224.4784.6044.7844.878

Depth(mcd)

0.000.581.481.632.072.353.274.396.436.787.768.438.508.809.319.60

10.0911.8312.6318.1019.1522.2023.7523.9524.4024.5025.4526.9527.4027.9028.4029.0529.35

Age(Ma)

4.9815.2325.8756.1226.2566.5546.9197.0727.4067.5337.6188.0278.6318.9459.1429.2189.4829.5439.639

10.02210.54810.69310.99111.37311.98812.63612.92913.25214.07014.95015.83017.060

Depth(mcd)

29.9031.3035.1036.8537.8538.7041.0041.8043.1544.4044.9549.9553.7256.7558.0058.9060.6061.9562.4067.1373.0175.2781.7493.65

116.77134.68148.04160.48189.45219.98258.05308.30


Age(Ma)

0.0000.4101.9613.0533.1313.2243.3373.6114.1924.3224.4784.6044.7844.8784.9815.2325.8756.1226.2566.5556.9197.0727.4067.5337.6188.0278.174

Depth(mcd)

0.0012.3243.0353.8854.9855.9857.3859.8865.5666.6268.5169.7671.5972.0473.2975.9787.4990.2293.0096.31

101.44103.18108.04110.12111.02119.29120.53

Age(Ma)

8.2058.6318.9459.1429.2189.4829.5439.6399.7759.815

10.83910.94310.99111.37311.42811.84111.98812.60512.63712.70512.75212.92913.08313.25215.83016.450

Depth(mcd)

120.82129.71136.74140.01141.43145.08146.70147.74150.34150.78164.94166.03166.78174.17175.78183.65187.06204.91206.26208.13209.57215.54220.07226.07275.23309.10

produce a target record that embodied the same time constants relat-ing ice volume and summer insolation at 65 °N that have been docu-mented for the late Pleistocene. In the case of GRAPE density (or theunderlying variable, the ratio of calcite to biogenic opal), we do nothave a model linking the forcing and the response. Therefore, we havesimply used the calculated record of summer insolation at 65 °N as thetuning target. We have throughout assumed that no phase lag existedbetween insolation and GRAPE density and that high density (highpercentage of CaCO3) is associated with high Northern Hemispheresummer insolation. This phase relationship may be approximatelyvalid for the most recent past; in the Pacific Ocean, a low percentage

75


Table 3. Age Model for Site 846. Table 4. Age model for Site 847.

Age(Ma)

0.0000.0390.0880.1270.1480.1710.1840.2200.2400.2470.2780.2900.3100.3260.3330.3540.3880.4050.4220.4460.4790.5090.5150.5230.5440.5790.6140.6280.6590.6810.6920.7170.7370.7720.7830.8630.8840.9080.9360.9780.9991.0291.0501.0921.1141.1361.2151.2431.3171.3371.3581.3791.4001.4311.4731.4931.5131.5281.5471.5671.6061.6451.6641.6971.7081.7821.8321.8751.9261.9471.968L986

Depth(mcd)

0.001.803.705.966.767.387.948.769.609.94

11.0411.2611.8412.3612.6613.4415.0415.7016.2617.0618.7819.9020.1420.3820.9622.1222.8823.3824.4225.3825.7226.2626.9228.1628.7432.1833.2634.3435.1435.9836.5637.4637.9239.8040.8042.1244.6845.1447.1247.7448.8649.5450.6452.1453.0653.5854.5854.9255.2255.8057.2458.2859.1860.9661.7264.0265.8867.7270.2471.2072.3673^62

Age(Ma)

2.0232.0862.0972.1182.1402.1902.2112.2332.2552.2782.3052.3482.3772.4112.4222.4382.4772.4902.5212.5342.5472.5692.5922.6372.6832.7072.7412.7542.7762.7982.8352.8532.8762.9042.9262.9492.9943.0423.0633.0853.1353.1563.1773.1983.2313.2883.3283.3713.4013.4223.4643.4963.5163.5263.5783.6143.6543.6803.7093.7303.7513.7813.8023.8243.8673.9183.9604.0144.0344.0894.1104.131

Depth(mcd)

74.8879.0079.5080.0680.7482.6083.8884.5485.5686.4887.4889.2690.1691.6292.2292.6494.9495.5496.5297.6898.7899.56

100.36102.43104.43105.37107.27108.27109.39110.13111.61112.53113.63115.21115.83117.61119.57121.71122.55123.81125.49126.37127.05127.75128.49129.91131.39133.51134.51135.51138.05139.13139.59140.01142.99144.03145.27145.79146.69147.51147.99148.93149.48150.14151.32152.70154.30156.88157.46159.02159.52160.22

Age(Ma)

4.1544.1824.2044.2254.2464.2724.2964.3194.3394.3614.4124.4514.4914.5374.5624.5954.6294.6534.6764.6984.7224.7444.7704.8124.8664.8964.9194.9404.9845.0115.0335.0775.1015.1275.1485.1705.2245.2645.3005.3425.3925.4145.4355.4575.5075.5285.5495.5695.5875.6245.6435.6615.6805.7005.7215.7525.7725.7945.8155.8645.8875.9816.0606.0996.1746.2156.2676.2896.3096.3306.3496.383

Depth(mcd)

161.02161.78162.34163.00163.60164.74165.50166.04167.08167.74169.66170.88172.02174.22175.26177.24179.20180.12181.26182.82183.78184.96186.64187.88190.14191.40192.38193.46194.64195.26195.73196.87197.41198.31199.41200.77202.53204.65206.79208.41210.07211.71212.57213.43215.83216.57217.97218.93220.21223.25224.15225.05226.03226.89227.23229.01230.79232.05235.61237.49238.31242.07247.42249.76252.88253.38255.14255.50255.92258.80260.12262.35

Age(Ma)

6.4046.4236.4436.5016.5356.5407.0807.0907.1177.1637.2047.2257.3157.3707.4047.4747.4967.7407.8787.9217.9468.0138.0808.3018.3128.3228.3738.4148.4348.4708.5478.6398.6828.7328.7768.7868.8338.9268.9909.0849.1339.1559.1999.2919.4209.4659.4899.5119.5359.5579.6269.6629.7049.7359.7549.7989.8229.8479.8929.9139.985

10.37210.69310.98711.21211.37713.32613.48015.83518.067

Depth(mcd)

262.79263.59263.91265.35266.61266.73280.34281.16282.60284.86286.98287.75290.05292.70294.54296.84297.34301.84304.84305.74306.39307.49308.74310.54310.79311.19312.24312.94313.29313.79314.59315.69316.29317.59318.29318.49318.64320.94322.65324.30325.10325.40326.60328.05330.15330.65331.05331.40331.75332.10333.00333.40333.85334.45334.70335.40335.90336.25336.74336.99338.29343.29346.54353.39357.04359.94394.97400.00423.80460.00

of CaCO3 is associated with interglacial-to-glacial transitions andgood carbonate preservation with glacial-to-interglacial transitions(e.g., Ninkovich and Shackleton, 1975; Keir and Berger, 1985; Le andShackleton, 1992). Whether this phase relationship is appropriate tothe equatorial high productivity belt in the eastern Pacific Ocean, andwhether the same phase relationship is appropriate for the older partof the record, is not yet known. Although the uncertain phase contrib-utes a significant source of potential error in our time scale, it onlyentails, at a maximum, a few thousand years of systematic error in theuncertainty of the age estimates.

Age(Ma)

0.0000.0390.0880.1160.1270.1480.1710.1840.2200.2400.2470.2780.2900.3080.3260.3330.3490.3880.4050.4220.4460.4630.4790.4840.5090.5440.5790.6140.6360.6590.6810.6920.7170.7370.7720.7830.8240.9080.9781.0001.0501.0721.2051.2151.2431.2721.2831.3071.3271.3371.3791.4001.4311.4931.5281.5671.6061.6971.7181.7501.8111.8321.8751.9041.9471.9582.0032.0232.0422.0522.0972.118z. i y

2.140

Depth(mcd)

0.001.793.013.814.114.755.996.737.458.178.839.499.79

10.2910.7711.1311.8113.1913.7714.0514.5115.1915.7116.0516.6917.4518.2319.0919.5920.3321.2721.4722-2322.6923.3924.2925.1528.1529.6130.4331.5332.6737.5138.1539.0939.7740.5141.0741.7342.4143.8144.7545.5747.5548.5949.8350.8953.0955.1555.8757.6558.7961.2561.9363.7164.6766.1566.8368.1568.5970.0770.5570 8371.17

Age(Ma)

2.2112.2332.2552.2782.3052.3482.3902.4222.4382.4772.5212.5472.5692.5922.6142.6372.6832.7072.7292.7542.7762.7862.7982.8352.8762.9042.9262.9372.9492.9692.9943.0193.0303.0413.0633.0853.1113.1353.1563.1773.1983.2313.2523.2713.2883.3083.3283.3483.3593.3913.4013.4223.4433.4643.4963.5163.5783.6043.6333.6543.6893.7203.7503.8243.8673.8963.9183.9393.9604.0144.0344.0554 0724.089

Depth(mcd)

73.3374.0374.9975.5176.1377.4378.9179.6980.3982.3983.5784.4984.8585.9186.7787.2588.8389.4789.8991.1191.4791.7992.4593.9394.8395.4196.3396.9797.2397.7598.3199.0799.4199.69

100.11100.63101.29102.12102.82103.42103.92104.66105.72106.28106.68107.48107.94108.68108.96109.72110.06110.80111.44111.84112.62113.10114.94115.74116.84117.38118.28119.40120.00122.14123.32124.10124.60125.06125.72126.84127.26127.98128 26128.62

Age(Ma)

4.1104.1314.1544.1824.2044.2254.2464.2964.3194.3394.3614.3764.4124.4334.4914.5374.5624.5834.6064.6294.6534.6984.7224.7444.7704.8214.8474.8664.8964.9194.9404.9624.9845.0335.0555.0775.1015.1075.1485.1705.2245.2455.2645.3005.3205.3425.3925.4145.4355.5075.5285.5495.5695.5875.6035.6245.6435.6805.7215.7525.7725.7835.7945.8155.8365.8645.8875.9095.9296.0036.3006.700

Depth(mcd)

129.10129.54130.14130.70131.28131.94132.52133.82134.40135.42136.00136.80137.76138.02139.88141.86143.44144.26146.68148.70151.60155.60156.70157.30158.70159.90161.80163.50166.20167.20167.80168.30169.00170.80171.30172.50173.80174.10174.50176.60178.30179.30180.20181.70182.60183.70185.30185.90186.90189.50190.30191.10192.20192.80193.80194.60196.20198.50199.30200.10201.50202.00202.20204.10205.20206.00206.70207.50208.90211.00230.21251.01

Procedurally, the process of tuning the GRAPE density data maybe idealized as follows. We must, however, emphasize that in realitya considerable number of iterations exist for each step. The work wasperformed on three-dimensional LOTUS 1-2-3 spreadsheets. Foreach site, the starting point was the composite section of continuousGRAPE density record generated by splicing segments of data fromamong the holes available and shown by Hagelberg et al. (1992;Chapter 5, Fig. 6) and by Shackleton et al. (1992; Chapter 6, Fig. 1).

76


Age Depth Age Depth(Ma) (mcd) (Ma) (mcd)

0.000 0.00 2.614 31.180.039 0.68 2.637 31.340.056 1.02 2.695 31.740.088 1.44 2.766 32.360.127 1.76 2.864 32.900.171 2.46 2.892 33.180.184 2.64 2.937 33.400.247 3.12 2.969 33.600.278 3.68 2.994 33.680.290 3.80 3.030 33.860.326 4.16 3.054 33.920.349 4.70 3.231 34.520.372 5.20 3.252 34.660.388 5.52 3.318 34.960.405 5.64 3.359 35.240.422 5.96 3.433 35.640.446 6.52 3.440 35.700.479 7.20 3.475 35.820.504 7.64 3.516 35.920.526 7.88 3.537 36.020.579 8.98 3.578 36.380.614 9.30 3.654 36.800.628 9.64 3.689 37.000.659 10.36 3.730 37.160.681 10.80 3.781 37.380.717 11.34 3.867 37.640.737 11.70 3.918 37.920.772 12.20 4.110 38.680.783 12.46 4.154 38.840.863 13.80 4.204 39.120.908 14.86 4.334 39.640.925 15.16 4.361 39.840.978 15.76 4.491 40.700.999 16.02 4.537 41.041.061 16.96 4.583 41.481.092 17.84 4.606 42.081.215 19.66 4.744 44.281.272 20.60 4.770 44.801.307 21.04 4.821 45.281.347 21.48 4.847 45.701.379 21.86 4.880 46.201.400 22.44 5.004 47.641.431 22.88 5.170 49.441.493 23.50 5.224 50.401.528 23.82 5.342 52.951.567 24.28 5.528 56.451.606 24.44 5.549 57.151.664 24.96 5.680 59.851.718 25.52 6.099 65.051.750 25.70 6.330 67.651.799 26.28 6.575 70.851.821 26.50 7.406 81.051.875 27.00 7.533 82.001.916 27.30 7.618 82.251.958 27.50 8.027 84.402.003 27.74 8.174 84.702.052 28.08 8.631 87.602.086 28.42 8.945 89.702.097 28.60 9.142 91.002.140 28.76 9.218 91.952.245 29.20 9.482 94.202.293 29.32 9.543 94.602.325 29.44 9.639 94.752.377 29.82 9.775 95.202.411 30.06 9.815 95.402.438 30.14 10.839 102.802.490 30.44 10.943 103.352.500 30.52 10.991 103.652.534 30.70 11.270 105.602.604 31.08


Age Depth Age Depth Age Depth Age Depth(Ma) (mcd) (Ma) (mcd) (Ma) (mcd) (Ma) (mcd)

0.000 0.02 2.521 71.10 4.513 126.32 6.554 261.410.039 1.16 2.534 71.72 4.537 127.62 6.575 263.500.088 2.76 2.547 71.98 4.562 129.62 6.596 265.600.116 3.60 2.569 72.30 4.595 132.42 6.621 271.550.127 4.02 2.592 73.04 4.641 135.22 6.647 273.750.148 4.74 2.614 73.50 4.653 135.62 6.669 275.250.171 5.58 2.637 74.08 4.698 137.52 6.690 275.750.184 6.12 2.650 74.54 4.722 140.62 6.711 276.200.220 7.22 2.683 74.94 4.744 143.02 6.742 276.950.240 8.02 2.707 75.80 4.770 145.12 6.762 277.400.247 8.34 2.729 76.44 4.788 145.82 6.784 277.700.278 9.00 2.741 76.64 4.812 146.52 6.803 278.250.290 9.34 2.754 77.12 4.821 146.92 6.880 280.750.308 9.72 2.776 77.98 4.847 147.72 6.912 281.500.326 10.10 2.798 78.32 4.866 148.22 6.933 282.000.349 11.30 2.823 78.80 4.896 149.02 6.954 283.050.388 12.46 2.853 79.58 4.919 149.92 6.976 284.650.405 12.98 2.876 80.16 4.940 150.45 6.999 285.300.422 13.22 2.904 80.78 4.962 151.40 7.026 285.840.446 13.90 2.926 81.38 4.984 152.50 7.070 286.690.463 14.34 2.937 81.84 5.011 154.80 7.117 288.640.479 14.82 2.949 81.96 5.033 155.60 7.141 290.440.526 16.48 2.969 82.50 5.055 156.80 7.163 291.240.579 17.50 2.994 83.12 5.077 157.80 7.204 293.640.636 18.76 3.019 83.68 5.101 158.60 7.280 295.140.681 20.24 3.030 84.16 5.127 160.10 7.315 296.490.737 21.92 3.041 84.46 5.148 160.40 7.357 298.340.783 23.00 3.063 85.02 5.170 162.00 7.404 300.640.805 23.24 3.085 85.58 5.190 162.80 7.449 302.240.853 24.56 3.135 86.76 5.224 164.05 7.474 302.990.874 25.28 3.156 87.42 5.264 166.60 7.496 303.440.908 26.16 3.177 87.96 5.282 167.50 7.623 306.340.936 26.86 3.198 88.66 5.300 168.45 7.774 306.390.957 27.36 3.252 90.36 5.320 171.85 7.784 306.740.978 27.62 3.271 90.88 5.342 174.00 7.807 307.890.999 28.26 3.288 91.36 5.392 177.20 7.830 308.441.050 29.44 3.298 91.72 5.414 179.45 7.878 309.941.072 30.54 3.318 92.14 5.435 180.65 7.928 311.541.092 30.92 3.348 92.92 5.457 181.35 7.946 312.291.114 31.56 3.359 93.34 5.479 182.75 7.972 312.941.136 32.06 3.370 93.62 5.507 183.55 7.993 313.391.187 33.20 3.391 93.98 5.528 184.75 8.032 314.091.215 33.76 3.401 94.52 5.549 185.70 8.144 316.141.263 35.32 3.422 95.00 5.587 188.45 8.164 316.391.283 36.20 3.443 95.46 5.603 190.25 8.186 317.091.337 37.94 3.464 95.94 5.624 191.45 8.208 318.191.369 39.50 3.496 97.12 5.643 193.00 8.235 318.991.389 39.90 3.537 98.04 5.661 193.90 8.258 320.341.400 40.08 3.567 98.76 5.680 195.45 8.279 320.891.431 40.56 3.587 99.66 5.721 197.50 8.301 321.841.463 41.28 3.595 99.96 5.752 199.70 8.322 322.791.493 41.78 3.614 100.28 5.772 201.75 8.351 324.291.528 42.72 3.633 100.78 5.794 204.40 8.434 325.641.567 43.82 3.654 101.32 5.815 209.45 8.470 326.641.586 44.30 3.689 102.53 5.836 211.10 8.489 326.931.606 44.88 3.709 103.05 5.864 214.80 8.508 327.281.645 45.62 3.730 103.73 5.887 215.75 8.547 327.931.664 46.22 3.751 103.91 5.909 216.45 8.588 328.831.697 46.68 3.781 104.81 5.929 216.75 8.600 329.431.718 47.88 3.802 105.85 5.951 217.25 8.661 330.231.739 48.28 3.824 106.23 5.981 218.05 8.682 330.681.760 48.90 3.845 106.95 6.043 223.40 8.732 331.431.782 49.24 3.867 107.51 6.060 225.95 8.796 332.731.811 50.18 3.896 108.17 6.080 228.15 8.816 333.331.832 50.66 3.918 108.75 6.099 229.45 8.926 335.131.854 51.54 3.939 109.35 6.121 230.30 8.947 335.481.916 53.92 3.960 109.87 6.138 231.05 8.968 335.83I.947 54.48 4.014 111.39 6.154 232.56 8.990 336.331.958 55.38 4.034 111.83 6.174 234.31 9.062 337.882.003 57.22 4.055 112.47 6.195 235.11 9.155 339.732.023 57.94 4.072 112.85 6.215 237.16 9.199 340.532.052 59.24 4.089 113.43 6.239 238.16 9.218 341.282.097 60.88 4.110 113.99 6.267 240.06 9.397 344.132.129 61.42 4.131 114.49 6.289 240.96 9.465 345.232.140 61.82 4.154 115.21 6.309 241.61 9.511 346.082.211 63.20 4.204 116.59 6.330 243.06 9.583 347.482.233 63.68 4.215 116.99 6.349 243.86 9.682 348.632.278 64.72 4.246 117.81 6.383 245.56 9.704 348.982.305 65.58 4.272 118.67 6.404 246.21 9.815 350.082.325 65.92 4.296 119.39 6.423 247.26 10.548 360.982.348 66.56 4.319 120.03 6.443 248.51 10.693 364.332.367 66.88 4.339 121.05 6.461 249.71 11.212 379.072.388 67.46 4.412 123.25 6.480 250.91 11.420 384.722.428 68.44 4.451 124.02 6.501 254.21 11.600 387.422.462 69.68 4.491 125.42 6.535 259.21

For Sites 846 to 852, this was later replaced by the stacked record,generated by Hagelberg et al. (this volume). This stacked record isbased on the same depth scale as the original spliced record, with datafrom all the other holes at the site stacked onto it and averaged toprovide a record having a higher signal-to-noise ratio. This GRAPEdensity record was placed first on a low-resolution time scale. Thistime scale was based on the age models in Shackleton et al. (1992)modified on the basis of a smooth conversion to the CK92 magne-tostratigraphic time scale. The GRAPE density time series then wascompared on the same age scale with the orbital insolation record.



Age(Ma)

0.0000.0390.0560.0880.1270.1480.1710.2200.2400.2470.2780.2900.3080.3260.3330.3490.3720.3880.4050.4220.4460.4630.4790.5040.5260.5790.6280.6590.6810.6920.7170.7370.7490.7720.8050.8240.8630.8840.9080.9780.9991.0291.0501.0721.0921.1361.1661.1871.2051.2241.2431.2631.2831.3171.3371.3581.3791.4001.4631.4731.4931.5041.5281.5471.5671.6061.6971.7391.7501.8111.8321.9041.9161.9581.9862.003

Depth(mcd)

0.000.751.031.652.313.213.894.775.115.455.875.996.536.696.957.437.858.338.678.919.419.71

10.2910.5110.8511.5912.5313.6914.1114.3114.7315.0915.3715.6316.2716.6117.5717.9918.5119.6519.9320.5320.8721.8122.1923.1723.6923.9724.1924.5724.9125.0725.4526.2926.8127.3127.5527.9729.2529.3729.5129.8930.3730.8531.1731.9133.2934.5534.7335.9136.3537.7338.1938^9339.3139.69

Age(Ma)

2.0232.0522.0972.1182.1292.1402.1902.2012.2112.2222.2332.2552.2782.3052.3162.3252.3362.3772.3902.4112.4222.4382.4772.4902.5342.5582.5802.6042.6252.6502.6612.6832.7072.7292.7542.7982.8352.8532.8642.8762.9262.9372.9492.9692.9812.9943.0193.0413.0633.0853.1113.1353.1563.1773.1983.2143.2313.2523.2623.2713.2883.3283.3383.3483.3593.3913.4013.4223.4333.4433.4643.4963.5163^5373.5673.595

Depth(mcd)

40.0940.7341.6941.9742.1542.4543.2943.4543.7143.9344.0544.6545.0945.7546.1746.4546.7548.2748.5949.4149.6549.8950.3150.6351.2951.8152.4352.9153.3953.9354.2154.4955.1955.4756.3357.3358.0558.5558.7958.9560.2360.5960.7961.2561.6161.7362.2362.8163.0563.5364.1164.6565.4166.0166.2566.5366.7967.2367.4567.6768.0168.8569.0169.1569.4169.9170.1370.6171.0371.1571.6172.4972.8773.2974.1974.89

Age(Ma)

3.6143.6333.6543.6893.7093.7303.7513.7813.8023.8243.8353.8553.8673.8963.9183.9393.9604.0344.0554.0724.0894.1104.1314.1544.2044.2254.2464.2724.2964.3194.3394.3614.4124.4514.4704.4904.5134.5374.5624.5834.6064.6294.6534.6984.7444.7704.8124.8664.9005.0115.0555.1015.1275.1595.1705.2245.2645.2705.2825.3005.3105.3205.3425.3635.3705.4105.4145.4355.4575.4795.5075.5495 5695.5875.6145.624

Depth(mcd)

75.3175.7176.1776.9977.4978.1778.4379.0579.6380.1580.4980.7181.0181.5982.1382.6183.1584.4784.8785.1585.6586.0386.3986.7987.3987.4187.7788.4588.9389.3290.2291.3292.2393.1593.5494.4694.9396.0697.2497.8299.97

101.09102.50106.10107.20108.90110.30112.20114.30115.30116.70118.30119.70120.60121.10122.60124.40124.90125.30126.70128.80129.10131.50133.80134.20134.70134.80136.30137.40138.70139.80141.10142.30143.90144.20144.70

Age(Ma)

5.6435.6615.6805.7005.7215.7525.7625.7945.8155.8365.8645.8935.9095.9295.9515.9816.0036.0226.0236.0596.1216.1746.1906.1956.2156.2676.2896.3096.3306.3366.3736.3836.4046.5016.5756.6476.6906.7116.7626.8036.9546.9997.0267.0707.1107.1207.1417.1637.2047.2387.2577.2807.3157.3807.4047.4287.4497.4747.4967.5257.6457.6507.7407.7637.8087.8307.8557.8787.9557.9557.9727.9938.0328.0698.0908.144

Depth(mcd)

146.20146.80148.10148.90150.20152.00155.20158.00159.30160.50161.40163.10164.30165.10166.50168.00170.60172.20172.80175.50178.70181.80182.40182.50184.90188.50189.40190.40191.10191.30191.60192.10193.10198.50210.50220.91225.11226.01227.11228.11233.21235.11236.41237.50239.40239.90240.70242.00245.80246.70247.60248.80250.20253.00253.90255.20256.20257.30258.00258.90259.00259.20262.40263.50265.60266.30266.90268.10268.20268.50269.10270.40271 60273.10273.90275.60

Age(Ma)

8.1868.1888.1978.2588.3018.3228.3738.4348.4708.4898.5088.5258.5478.5678.5888.6618.6828.6858.7558.7768.7968.8338.8518.8728.8908.9268.9909.0029.0319.1079.1339.1559.1999.2219.2519.2699.2919.3059.3159.3819.3979.4209.4439.4659.4899.5119.5359.6269.6629.6779.6829.7359.7779.7989.8699.9639.985

10.07010.27010.37010.40010.49010.51010.52010.69310.72510.75710.84311.15411.41311.54711.950

Depth(mcd)

277.70277.80277.10279.60281.50282.60285.40287.90289.20289.80290.70291.20291.80292.30293.00296.00296.80296.90297.40297.80298.80300.30301.10302.10303.40304.90306.20306.70307.00310.30310.80311.40312.31312.91313.61314.11314.81315.41315.71316.71317.21318.01318.71319.51320.11321.01322.11324.51326.21326.41326.81328.01329.71330.21332.21334.91335.81336.01345.51345.71347.01350.61351.41355.31363.51364.71364.91368.11382.71393.51393.91407.31

Age control points then were added so as to align prominent groupsof density maxima with groups of insolation peaks. We found thatsections having about 0.8-m.y. duration were conveniently viewed.Each of the sites containing orbital scale variability over a chosentime interval was first tuned in this fashion independently. Next,records were compared with each other and, if necessary, with otherlower-resolution sites containing magnetostratigraphic data. Because

aboard the ship we had observed close similarities among the GRAPEdensity records of sites even when widely separated, we have as-sumed throughout this exercise that changes in percentage carbonate(as reflected in the GRAPE density records) in reality did occursynchronously over wide areas of the Pacific Basin. Many previousstudies have been based successfully on this hypothesis (Arrhenius,1952; Hays et al, 1969; Vincent, 1981; Farrell and Prell, 1991).

78



Age(Ma)

0.0000.0390.0650.0880.1270.1480.1710.1840.2200.2400.2470.2780.3080.3260.3490.3880.4050.4220.4460.4790.4790.5100.5230.5440.5790.6140.6280.6360.6590.6810.7170.7370.7830.8050.8240.8630.8840.9080.9250.9780.9991.0501.0721.0921.1141.1361.1661.2051.2151.2431.2631.2831.3171.3371.3791.4001.4311.4631.4931.5671.5951.6061.6451.6641.6971.7181.7501.8111.8321.8541.8751.904

Depth(mcd)

0.000.S21.441.842.482.782.983.163.844.004.264.664.885.225.726.526.706.907.508.269.66

10.2810.5410.8211.3011.6211.8012.0012.6613.1814.2414.5415.3015.7015.9016.6016.9217.6017.9018.8019.1219.8020.3020.9821.5421.8822.4023.1023.3223.5624.1424.6025.1825.6026.3226.9427.4627.9628.7829.8230.2230.4230.9631.3231.6431.8032.8433.7034.0034.3434.7035.00

Age(Ma)

1.9161.9471.9582.0032.0232.0412.0522.0972.1182.1292.1402.1902.2112.2332.2782.2932.3052.3162.3252.3362.3772.3902.4112.4382.4652.4772.4902.5342.5472.5692.5922.6142.6372.6502.6612.6842.7072.7182.7292.7542.7662.7762.7982.8352.8532.9042.9262.9372.9492.9692.9943.0193.0303.0413.0633.0853.0953.1113.1353.1563.1773.1983.2313.2523.2713.2883.3083.3183.3283.3483.3593.370

Depth(mcd)

35.4835.8036.1436.8037.2837.8438.0638.7439.0039.1239.5440.2440.5840.9442.0442.2242.3642.4842.6842.9644.7445.1245.5846.0046.4246.6046.9247.5647.8048.0248.5249.0049.2649.6049.8450.0450.3650.6251.0051.8252.2452.4452.7253.3653.8054.6855.2455.6855.8456.1456.5056.9857.4457.5857.9458.4258.4858.6459.0859.5859.9060.2860.8061.2061.6661.8662.3862.6262.9063.1263.3263.50

Age(Ma)

3.3913.4013.4223.4433.4643.4753.4963.5163.5373.5673.6043.6233.6543.6893.7203.7643.7813.7923.8133.8243.8353.8453.8673.8843.8963.9183.9393.9604.0044.0344.1104.1544.2044.2254.2464.2724.3194.3394.3614.4124.4514.4914.5134.5374.5624.5834.5954.6414.6654.6984.7224.7444.7704.8124.8354.8664.8784.9194.9404.9624.9975.0435.0875.1155.1595.1705.1905.2245.3205.3425.3925.414

Depth(mcd)

63.8064.2064.5665.1665.3665.7666.0866.4866.7867.3267.9468.5669.0869.7270.2670.8471.0271.3071.5071.6471.9072.0872.2672.5872.7473.0473.3873.7074.3874.7275.8077.0877.5077.9678.4479.0879.9280.5681.3682.2883.0484.0884.6484.9685.6285.8486.4287.7288.7489.6390.1890.6891.6492.4993.1293.9394.5995.4196.0096.8498.0899.38

100.94101.86102.81103.21103.56104.13107.41107.93109.09110.67

Age(Ma)

5.4355.4575.4795.5075.5285.5495.5875.6035.6245.6435.6615.6805.7005.7215.7525.7725.7945.8155.8365.8645.8875.9095.9295.9515.9665.9816.0036.0436.0606.1216.2156.2676.2896.3096.3836.4046.4236.4616.5016.5186.5356.5546.5756.5966.6216.6406.6696.6906.7116.7426.8036.8226.8396.8806.9546.9766.9997.0707.1177.1417.1637.2047.2387.2577.2807.3337.3807.4047.4497.4747.4967.519

Depth(mcd)

111.29111.81112.98114.37115.07116.16118.36119.03119.88120.45121.38122.42122.88123.73124.64125.99127.88129.07130.91131.85132.47133.27133.80134.38134.87135.28135.78136.89137.69139.84146.86149.76150.67151.28153.76154.41155.18157.49158.94160.55163.85165.30167.00168.20174.65177.20178.85179.65180.75181.45183.40183.95184.85186.20188.25189.70190.25193.50195.45196.70197.55199.05199.90200.35200.90202.75203.95204.90205.75206.90207.45208.85

Age(Ma)

7.5417.5657.5927.6117.6507.6917.7407.7637.7847.8077.8307.8557.8787.8997.9217.9727.9938.0698.1448.1868.2088.2358.2478.3018.3518.3738.3948.4348.4708.5088.5478.6618.6828.7048.7558.7768.8168.8338.8728.8908.9078.9268.9478.9909.0189.0629.0849.1999.2699.2809.3489.3979.4209.4439.4659.4899.5119.6269.6829.7359.7989.8479.8929.9139.9399.963

10.02210.69311.21211.42012.000

Depth(mcd)

209.85210.40211.85212.65214.35216.60218.30219.35220.50221.50222.15223.10223.95225.55226.00228.30229.50231.46233.81234.86235.36235.91236.16236.26238.46239.26239.91242.11243.91244.51245.96249.11249.46249.81251.26252.61254.41255.31258.01258.76259.41260.06260.81262.30263.20265.25265.85269.50271.50271.80272.00273.35274.00274.55275.20275.75276.50279.70282.50284.30286.25287.65289.10289.70290.35291.40293.05323.54346.08353.48370.63

Mayer (1991) showed how one may calculate a record of percent-age carbonate from a GRAPE density record, and Hagelberg et al.(this volume) show carbonate records derived by this method for theLeg 138 sites. We chose to work with untransformed GRAPE densitydata because analytical uncertainty (and, hence, any measure of sig-nificance) is uniform across the density range, whereas it is not uni-form across the percentage range. For logistical reasons, we initiallyworked with the spliced records as displayed in Hagelberg et al.(1992; Fig. 5); when a stacked record for a site (Hagelberg et al., thisvolume) became available, this was used instead. Consequently, not

all the records were worked on at the same degree of smoothing. Ingeneral, working with the stacked and smoothed records was easier.For the plots that are shown in this chapter as Figures 1A through IF,all the GRAPE density data were smoothed in the time domain.

RESULTS

In this section, we discuss the results of tuning the Leg 138 sitesin 1-m.y. sections, starting from the most recent increment. The out-come is reported in the series of Tables 1 through 11 that lists depth-

79

N.J. SHACKLETON ET AL.

Table 9. Age model for Site 852. Table 10. Age model for Site 853.

Age(Ma)

0.0000.0390.0560.0880.1270.1710.1840.2200.2400.2470.2780.3080.3260.3490.3880.4220.4460.4790.5100.5790.6140.6280.6590.6810.7120.7170.7720.7830.8240.8630.9080.9570.9781.0501.0921.1141.1661.2051.2431.2831.3371.3791.4001.4311.4931.5281.5671.6061.6451.6641.7501.8111.8321.8541.8751.9471.9581.9862.0232.0422.0752.0972.1402.1902.2332.2782.3052.3362.3772.3902.4382.4772.5342.5582.5922.604

Depth(mcd)

0.000.530.731.111.652.172.232.372.572.652.933.113.233.614.054.374.615.115.656.316.496.776.957.518.098.178.859.059.49

10.0910.6511.1711.2912.1712.9713.2513.9714.2514.7515.3515.9116.5716.8717.2117.8718.1918.6119.1719.5919.7920.7321.3921.5721.7121.9122.5122.6522.9323.3523.5724.0924.4524.8125.3325.6925.9926.4326.7327.2527.4327.8528.3729.1729.3729.6729.75

Age(Ma)

2.6372.6832.7182.7292.7662.7982.8352.8532.8642.8762.8922.9042.9152.9262.9492.9692.9943.0193.0413.0633.1113.1313.1463.1983.2313.2523.2623.2713.3183.3333.3383.3483.3703.3913.4013.4113.4223.4433.4753.4963.5163.5373.5483.5673.6143.6803.7513.7813.8023.8243.8843.9183.9604.0344.1414.2044.2254.2464.3194.3394.4124.4514.4704.4914.5374.5834.6064.6294.6764.6984.7444.7584.7704.8124.8354.878

Depth(mcd)

30.1530.5730.9531.1531.9532.2532.6133.0333.1533.2533.4133.6333.8133.9134.3534.4534.7334.8535.2935.4736.0936.2536.5137.1137.3537.5337.5937.7738.2338.3938.4538.5738.7938.9139.1139.2539.3939.6940.0540.2140.3540.5140.7140.8341.2341.6542.0942.5542.7942.9543.6543.9344.5345.1546.0746.5146.7546.9747.7748.3149.2149.8150.0350.3350.7751.3151.7951.8752.5553.1153.6754.1154.3354.8755.1755.87

Age(Ma)

4.9194.9404.9844.9975.0555.0875.1155.1595.2005.2245.2645.3205.3425.3635.3925.4355.4575.4795.5075.5285.5495.5875.6435.6805.7215.7325.7525.7835.8255.8645.9095.9515.9816.0036.0606.0806.1226.1956.2156.2396.2896.3836.4046.4806.5016.6216.6696.7426.9337.4047.4747.5197.7407.7637.8077.8557.8997.9217.9468.0278.1448.1648.1748.6358.9459.1429.2189.4829.5439.6399.7759.815

10.02210.54810.57610.830

Depth(mcd)

56.3756.7157.4757.6158.5759.1559.7560.8161.2561.5562.1563.2163.7764.1164.3365.1365.3965.8166.1766.4766.9367.3768.1168.5969.3569.5370.1570.4971.0771.6972.4172.9773.5974.0775.3775.8176.2777.9178.2378.6779.4780.5380.8581.6781.9783.9184.4185.2189.8395.5396.0596.7599.4999.95

100.85101.71102.59103.17103.51105.02107.66107.96108.32114.36116.60117.30118.10119.04119.40119.64120.34120.50122.40127.60127.86128.30

age pairs for recognizable GRAPE events at each site. Figures lAtoIF show GRAPE density for Sites 846 to 854 vs. age for each ageinterval; each panel covers 2 m.y. For each site, vertical lines showthe positions of all age control points. To aid in comparison, all theGRAPE density data for Figure 1 were interpolated at 1-k.y. intervalsand smoothed in the time domain using a Gaussian filter having a totalwidth of 5.9 k.y. Where the reconstructed sedimentation rate falls

Age(Ma)

0.0000.4730.6810.7800.9901.0701.7701.9502.6003.0543.1273.2213.3253.6124.1884.3204.4524.6214.801

Depth(mcd)

0.221.772.472.953.854.197.808.57

12.1815.2315.7416.3316.8918.8222.3023.5325.2426 0827.41

Age(Ma)

4.8855.0045.2405.8756.2566.5547.0727.3187.3517.4067.5337.6188.0278.1738.2058.6358.645

Depth(mcd)

28.1528.9631.5038.5743.5546.5254.1655.5656.3156.5558.3059.0465.6068.4069.0075.0675.20


Age(Ma)

0.0000.7800.9901.0701.7701.9502.6003.0533.1313.2243.3373.6113.7405.8756.1226.2566.555

Depth(mcd)

0.004.085.355.82

10.6111.4816.6817.6817.8217.9518.1519.0819.5019.9321.1121.9123.03

Age(Ma)

6.9197.0727.4067.5337.6188.0278.1748.2058.6318.9459.1429.2189.4829.5439.639

Depth(mcd)

25.2727.5730.7232.6933.2339.7841.7542.3043.7845.4046.5547.3348.8549.4849.80

below about 5 m/m.y., as it does at several points in Site 848, the dataare further smoothed; these intervals are not useful for tuning.

We show the results of tuning sections of individual holes fromSites 850, 851, and 852 in Figures 2 to 8 for two reasons. First, it isonly by referring to the individual holes that one can assess the exactrelationship between the GRAPE density and paleomagnetic stratig-raphies. Second, these figures display the strengths and limitations ofour tuning approach more clearly than Figure 1 does.

The interval from zero to 2 Ma (Fig. 1 A) was surprisingly difficultto tune, considering the amount of work that has been devoted to thestudy of Pleistocene climate. Examination of Figure 1A shows aconvincing degree of correlation among the sites, but the relationshipwith the orbital data is not at all obvious. Here, we do not quantify thecorrelation among sites, but note that Hagelberg et al. (this volume)demonstrate by empirical orthogonal function (EOF) analysis that ahigh proportion of the variability in all the sites is explained by thefirst EOF.

Figure 2 shows the data for the interval 0 to 1 Ma from Holes85 IB, 851C, 85ID, and 85IE separately, tuned with GRAPE densityextremes correlated to insolation extremes. In this interval, the matchbetween GRAPE density and the orbital record is fairly poor. Asregards tuning to the orbital record is concerned, we emphasize againthat in this interval we have been guided by the objective of creatinga time scale based on features in the GRAPE density record that is notgrossly inconsistent with a δ18O-based time scale. By contrast, inFigure 1, the GRAPE density data for Site 851 are shown using thecontrol points in Table 8, so that for the past million years the GRAPEdensity extremes are no longer all exactly aligned with insolation

80


Table 12. Age-depth control points for the interval 0 to IMa derived by

correlating GRAPE density and orbitally controlled insolation without

regard to the established δ 1 8 θ time scale.

Table 13. Coherency between June insolation at 65° N (Berger and

Loutre, 1991) and stacked GRAPE density for sites 849, 850 and 851

estimated over 1 m.y. intervals (Fig. 9).

Age

(Ma)

Site 8440.0000.7800.9901.070

Site 8450.0003.610

Site 8460.0000.0330.0560.1260.1480.1730.2180.2410.2620.2900.3110.3330.3540.3860.4080.4620.4730.4840.5040.5150.5280.5770.5980.6200.6480.6920.7120.7870.8630.8840.9080.9360.9780.999

Site 8470.0000.0560.0820.1030.1260.2190.2620.2900.3110.3330.3540.3720.4080.4620.4840.5280.5770.6480.6920.7120.7490.7870.8240.9080.9781.000

Site 8480.0000.0560.0820.1140.1480.173

Depth

(mcd)

0.0010.0411.8312.36

0.0059.88

0.001.823.045.986.767.388.529.069.94

11.8412.0612.6613.4414.7015.9817.7218.7819.4419.9020.1420.3822.1222.3223.3824.4225.7226.0628.7432.1833.2634.3435.1435.9836.56

0.001.112.733.474.117.658.839.79

10.2911.1311.8112.2313.7715.1916.0517.4518.2320.3321.4721.7122.6924.2925.1528.1529.6130.43

0.000.681.021.442.142.46

Age

(Ma)

0.2180.2410.2620.3110.3540.4080.4620.4840.5280.5650.6090.6480.6810.7100.7490.7870.8630.9080.9250.9780.999

Site 8490.0000.0560.0700.0820.1260.1480.1730.2180.2410.2770.2900.3330.3540.3860.3970.4080.4620.4840.5280.5650.5770.6310.6810.6920.7490.7870.8050.8530.8740.9080.9360.9570.9780.9991.050

Site 8500.0000.0560.0820.1260.1480.1730.2180.2620.2900.3330.3540.3720.4080.4250.4450.4620.4840.5040.5280.5770.598

Depth

(mcd)

2.803.123.444.104.705.646.527.427.888.689.30

10.0810.8011.0811.8612.7013.8014.8615.1615.7616.02

0.021.582.763.184.025.105.587.048.348.929.72

10.4611.3012.0612.4612.9813.9015.2216.5417.1017.5018.7620.2420.3821.9223.0023.2424.5625.2826.1626.8627.3627.6228.2629.44

0.001.031.392.313.213.894.535.456.016.957.437.858.679.079.419.71

10.3910.5110.8511.5912.11

Age

(Ma)

0.6310.6810.6920.7120.7490.8050.8240.8630.8840.9080.9780.9991.029

Site 8510.0000.0560.0820.1030.1260.1480.1730.2180.2620.2900.3330.3540.3720.4080.4250.4620.4840.5040.5280.5550.5770.6480.6920.7120.7490.7870.8050.8240.8630.8840.9080.9250.9780.999

Site 8520.0000.0560.1260.1960.2620.2900.3540.4080.4620.4840.5770.6480.6920.7490.7870.8240.8630.9080.9570.978

Site 8530.000.780.99

Site 8540.000.780.99

Depth

(mcd)

12.7914.1114.3114.8115.0916.2716.6117.5717.9918.5119.6519.9320.53

0.001.161.621.982.482.782.983.764.264.885.365.706.066.707.027.508.489.029.289.509.94

12.6613.5014.1414.5415.3015.7015.9016.6016.9217.6017.9018.8019.12

0.000.731.652.312.633.033.614.214.675.496.316.957.858.499.059.49

10.0910.6511.1711.29

0.222.953.85

0.004.085.35

Interval(Ma)

0-l a

0-l b

1-22-33^44-55-66-7

COH41k.y.

0.870.890.780.890.860.740.610.42

COH23k.y.

0.630.910.960.960.970.920.940.90

COH 19k.y.

0.380.780.940.900.970.910.920.91

a O-based time scale from Tables 6, 7, and 8.b GRAPE-based time scale from Table 12.

extremes. From a statistical standpoint, the tuning illustrated in Figure2 leads to an acceptable coherency between GRAPE density andorbital insolation, whereas the tuning illustrated in Figure 1 does not(Table 13). The fact that neither version of the time scale for theinterval from 0 to 1 Ma leads to high coherency for both GRAPEdensity and δ 1 8 θ has the unfortunate consequence that we cannotobtain statistically useful information on the phase relationship be-tween these two parameters.

Between 1 and 2 Ma, the situation is slightly clearer (Fig. 3). Inthis time interval, δ 1 8 θ records are dominated by 40-k.y. obliquitycycles (Pisias and Moore, 1981; Ruddiman et al., 1986). Severalsegments of GRAPE density variability show evidence of 40-k.y.cycles over this interval; see, for example, Sites 847 and 852 in Figure1A. The individual holes of Site 851 do not show the 40-k.y. cyclesso clearly (Fig. 3), and it would not have been possible to develop thetime scale on the basis of only this site.

Moving to the interval between 2 and 4 Ma shown in Figure IB,the tuning operation became easier. For intervals between 2.0 and 2.6Ma, we have been guided by the δ 1 8 θ record of Site 846 (Shackletonet al., this volume). Correlating this record to that of Site 677 (SBP90)implies a strong obliquity signal in the GRAPE density, especiallybetween 2.4 and 2.6 Ma. In some sites, the precession cycles between2.1 and 2.3 Ma are recognizable. The good magnetostratigraphicrecord for Site 851 (Fig. 4) provides a tie to the astronomical calibra-tion of SBP90 in Site 677, and it is only for the section older than 2.6Ma that we are seeking a tuning that is independent of previous work.Thus, the marked similarity between GRAPE density variations andthe orbital record between 2.5 and 3.0 Ma in several sites, as well asthe conspicuous precession cycles in the interval from 3.0 and 3.2 Maand between 3.7 and 4.0 Ma, are particularly important for carryingthe tuning operation back through the Gauss. It is appropriate toremark that our starting point was the assumption that since the timescale developed by Cande and Kent (1992) was calibrated astronomi-cally at 2.6 Ma, it would prove to be nearly correct. We were awarethat this time scale diverges from H91 in the Gilbert Chron, butimagined (wrongly, as it turns out) that this disagreement would beresolved in favor of smooth seafloor spreading and, hence, in favor ofthe time scale of Cande and Kent (1992). The data for the individualholes of Sites 850 and 851 for the interval 3 to 4 Ma are shown inFigures 5 and 6. From 3.0 to 3.5 Ma, the tuning is exceptionally clear;however, with the data from several sites to work with, the tuning to4 Ma also is reliable.

The interval from 4.0 to 6.0 Ma is shown in Figure 1C. Again, theprecession signal is well recorded in several of the sites. Between 4.0and 4.4 Ma, Site 846 shows a clear precession signal, and both Sites846 and 847 appear to record the interval between 4.6 and 5.0 Ma,during which the insolation record shows strong precession cyclesflanking an interval dominated by obliquity. Of course, this pattern isa reflection of eccentricity maxima flanking a broad interval of loweccentricity. The significance of this is that although uncertainties inthe astronomical calculations mean that the exact temporal relation-


I I I I I I I l I I I I I M I N I M I . I l l I I I I ,1 I I I I I I I I I I I I I I I I I

848

849

850

Ins.

851

852

846

847

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0Age (Mα)

Figure 1. A. GRAPE density vs. age for Sites 846, 847, 848, 849, 850, 851, and 852, 0 to 2 Ma. For each site, the upper part has been constructed from the stackedrecords, making use of data from all holes at the site, while the older parts of the sections have been based on the shipboard splice. Vertical lines above the datafor each site show the age control points from Tables 1 to 11. For this figure, all data sets have been smoothed in the time domain with the same filter (see text).B. GRAPE density vs. age for Sites 846, 847, 848, 849, 850, 851, and 852, 2 to 4 Ma. C. GRAPE density vs. age for Sites 846, 847, 848, 849, 850, 851, and 852,4 to 6 Ma. D. GRAPE density vs. age for Sites 846, 847, 848, 849, 850, 851, and 852, 6 to 8 Ma. E. GRAPE density vs. age for Sites 846, 847, 848, 849, 850, 851,and 852, 8 to 10 Ma. F. GRAPE density vs. age for Sites 846, 847, 848, 849, 850, 851, and 852, 10 to 12 Ma.

ship between a particular precession peak and a particular obliquitymaximum may be unknown, the timing of the eccentricity record isprobably reliable (Berger et al., 1992).

Between 5 and 6 Ma, GRAPE density variations are more erratic,but even so, there appear to be intervals having large-amplitudevariations associated with precession. These large jumps in meandensity value adversely affect the results of bandpass filtering of thedata. Their origin is partly the episodes during which laminatedsediments accumulated (Kemp and Baldauf, 1993). It is difficult toput bounds on possible sedimentation rate excursions associated withthese events and, in some details, the tuning is speculative in thoseparts of the record associated with accumulation of laminated sedi-ments. At about 5.8 Ma, we were assisted in correlating sites byfeatures in the bulk sediment δ13C record that could be correlatedamong sites (Shackleton and Hall, this volume).

STATISTICAL EVALUATION

To present a straightforward statistical evaluation of the timescales that have been generated, we constructed a synthetic westerntransect record by simply averaging the GRAPE density estimate ateach 0.001-Ma age increment at Sites 849, 850, and 851. Figure 9shows cross-spectral analyses of this record vs. the 65°N insolation

record of Berger and Loutre (1991) in million-year segments. It isapparent from Figure 9 that tuning has resulted in coherency esti-mates in the precession band of more than 0.9 in every time intervalexcept 0 to 1 Ma. Coherency estimates are given in Table 13. In everytime interval, coherency with precession is greater than coherencywith obliquity; coherency with obliquity ranges from a low of 0.61 inthe 5- to 6-Ma interval to 0.89 in the 2- to 3-Ma interval. Phase plotsare not shown because we tuned by assuming a zero phase lag be-tween insolation and GRAPE density; however, note that in no caseare the phase estimates for either precession or obliquity significantlydifferent from zero, other than the phase against obliquity in the rangeof from 3 to 4 Ma, where GRAPE density lags insolation by 50 ± 20°(6 ± 2 k.y.) in the obliquity band. In the interval from 0 to 1 Ma,coherency is acceptable for the age models in which GRAPE densityextremes are exactly aligned with insolation extremes (Table 12), butnot for the δ 1 8 θ age models given in the upper parts of Tables 1 to 11.

Coherency between the geological data and the orbital target in theprecession band is the fundamental method by which a time scale maybe evaluated. There are two reasons for this. First, the modulation onthe precession signal is very much stronger than that on the obliquitysignal, so that the test of coherency is more valuable. Second, the mod-ulation on the precession signal arises directly from the orbital eccen-tricity record for which the calculations are the most robust (Berger et

82

B


I I I I ; I I I I I I I I I I I I

848

849

850

Ins.

851

852

846

847

2.0 2.2 2.4 2.6 2.8 3.0Age (Mα)

3.2 3.4 3.6 3.8 4.0

Figure 1 (continued).

al., 1992), whereas the modulation on the obliquity signal (1) does nothave a clearly defined and independent origin, (2) appears in theseries expansion through the interference between several terms withperiods close to 41 k.y. (Berger and Loutre, 1991; Table 7), and (3)thus is sensitive to extremely small errors in their estimation.

Two studies (Pisias, 1983, and Brüggemann, 1992) showed thathigh coherencies cannot be generated by "tuning" a randomly varyingtime series to the orbital signal (although Neeman [in press] reacheda different conclusion). Thus, it seems unlikely that the very highcoherencies shown in Figure 9 could have been obtained had therenot been a close coupling between changing solar insolation andEast Pacific Ocean paleoceanography. Moreover, Hagelberg (1993)showed that, although estimated coherency is reasonably robust withrespect to small errors in time scale, the reduction in coherencyresulting from time-scale error is frequency dependent, with the co-herency at precession frequencies showing the highest degradation.Thus, the very high coherencies in the precession band shown inFigure 9 constitute strong evidence that our time scale is close tocorrect. It must be pointed out that the high coherencies shown byImbrie et al. (1984) for a stacked δ 1 8 θ record covering the past 0.78Ma did also imply that the chronology was close to correct; thisremains true, despite the fact that we now think that it was correct onlyover 75% of the interval covered (SBP90).

The high coherencies shown in Figure 9 also indicate that thephysical linkage between changing solar insolation and paleoceanog-raphy has remained strong through the whole Pliocene, suggestingthat it may be amenable to modeling. On the other hand, it must be

said that it is important in the future to test the validity of the calibra-tions that we have obtained beyond the range of overlapping with H91in an area that experienced less violent fluctuations in sedimentationrate. The reason is that one property of a convincing age model is thatit should not generate physically unreasonable changes in sedimenta-tion rate; one of the findings of Leg 138 was that in the easternequatorial Pacific, sedimentation rates are extremely variable so thatit is difficult to specify what is, in fact, a physically unreasonablechange. In addition, the hole-to-hole comparisons made by Hagelberget al. (this volume) show that a significant proportion of the apparentvariability in sedimentation rate either persists over only small dis-tances on the seafloor or else is an artifact of distortion during coring.

It is a striking feature of both the records from the MediterraneanBasin, studied by Hilgen (1991a, 1991b), and those from the easternAtlantic Ocean, studied by Tiedemann (1992), that good evidence canbe seen for a 100-k.y. eccentricity cycle in their data. Indeed, theground-breaking study by Hilgen (1991a) was possible only becausehe was able to place his records in the context of the 400- and 100-k.y.eccentricity cycles and so could to develop an astronomically cali-brated time scale without working systematically back from the pres-ent. It is evident from Figures 1 and 9 that this approach is notpossible in the GRAPE density records recovered during Leg 138. Noconsistent 100-k.y. signal is present, and coherency between insola-tion and GRAPE density is only marginally significant in the eccen-tricity frequency band. Figure 1 shows that there is considerablelow-frequency variability in GRAPE density; presumably, this masksany eccentricity signal that might otherwise have been present.

83


I I I

848

849

850

Ins.

851

852

846

847

4.0 4.2 4.4 4.6 4.8 5.0Age (Wo)

5.2 5.4 5.6 5.8 6.0


DISCUSSION: CALIBRATIONS OF THE MAGNETICPOLARITY TIME SCALE FROM 0 TO 6 M.Y.

To obtain the most reliable ages for Pliocene magnetostratigraphy,we examined the critical intervals hole by hole. This enabled us toevaluate the quality of each estimate. In Figures 2 to 5, we show themagnetic declination and tuned GRAPE density vs. age for each holein Sites 850 and 851 over the interval from 3 to 4 Ma. For the Kaenaand Mammoth subchrons, the boundaries are clearly related to theGRAPE stratigraphy, and the estimates are consistent (Table 14).Initially, we were unable to obtain a clear calibration for the base ofthe Gauss, but careful examination of the data for Holes 850A and850B (Fig. 5) shows clear precession cycles; by correlating the holesof Site 851 to those of Site 850, we obtain a consistent calibration.

In the Gilbert interval, Site 852 provides the vehicle for transfer-ring our time scale to the paleomagnetic record; in addition, a recordof the Cochiti occurs in Site 851. Figures 7 and 8 show the GRAPEdensity and magnetic declination data for the individual holes of Site852 over the intervals from 4 to 5 Ma and from 5 to 6 Ma. In theserecords, the age control points derive from correlation to Sites 849,850, and 851, rather than direct correlation to the orbital record; forthis reason, we show in Figures 7 and 8 the stacked GRAPE densityrecords of Sites 849, 850, and 851, as well as the orbital insolation, sothat the tuning process may be followed. The interpolated ages ofeach of the reversals in each hole are given in Table 15.

The top of the Nunivak is a problematic area because the 65°Norbital signature is structureless where the GRAPE data show evidentstructure; here, we may have difficulties with the accuracy of the

astronomical solution. If this is the correct explanation, we would beled to conclude that the eccentricity values were not so low as thosegiven in the calculations of Berger and Loutre (1992). Such a conclu-sion would not necessarily be in conflict with the observation that themain eccentricity periods are known rather accurately so that thetiming of eccentricity maxima is reliably known at ages where thetiming of obliquity maxima is less well known.

Table 16 provides mean estimates for the ages of the magneticreversals in Sites 850,851, and 852 that arise from the tuning discussedabove. These estimates are compared (1) with those that, until recently,have been regarded as "standard" (Berggren, Kent, and Flynn (1985)and Berggren, Kent, and Van Couvering (1985); (2) with those givenby CK92; and (3) with the earlier tuned ages of SBP90 and H91.

It is apparent from Table 16 that ages for the Kaena and Mammothintervals agree well with both Hilgen's estimates and those of CK92.At the base of the Gauss, our estimate agrees with that of Hilgen(1991a); both estimates are significantly older than those of CK92.The age obtained here, 3.594 Ma, is a little younger than that reportedby Shackleton et al. (1992). The reason is that we reevaluated theGRAPE density record of Site 850, which has the higher sedimenta-tion rate across this interval, and identified the complete sequence ofprecession cycles in this critical interval. We then mapped the Site 851holes into this record. The result (Figs. 5 and 6) is convincing.

On average, our age estimates are a few thousand years greaterthan those given by Hilgen (1991a). Hilgen's estimates were based onan assumed lag of 4 k.y. between precession extremes and the mid-points of the equivalent lithological bed, whereas we have not as-sumed any lag between insolation and GRAPE density extremes.

D


848

849

850

Ins.

851

852

846

847

7.0Age (Mα)


Pending a more sophisticated evaluation of the response of the re-spective paleoceanographic systems to orbital forcing, we concludethat differences between our estimates and H91 are negligible. Fromthe Cochiti to the base of the Thvera subchrons, our estimates also arenear those given by Hilgen (1991b), although, because they werecalibrated in more slowly accumulating sediment, our estimates forthe ages of these reversals are not so precise as those for the reversalsin the Gauss. However, it is now clear that this time scale providestrue accuracy through a sufficient amount of the Pliocene that onemust recalibrate the magnetic anomaly time scale of CK92 to take intoaccount the significant deviations that become evident by the base ofthe Gauss.

From the Thvera to C3A.ln (t), tuning was difficult as a result ofthe exceptionally wide ranges in sedimentation rate in several sites.However, we attempted it for two reasons. First, this is a key toextending the work of Hilgen (1991b) into the Miocene: it is neces-sary to cover the interval of the Messinian salinity crisis by workingin extra-Mediterranean sediments. Second, the young side of C3 A iswidely used as a calibration point when developing time scales for theseafloor magnetic anomaly sequence. In the interval from 5 to 6 Ma,GRAPE density and orbital insolation are highly coherent in theprecession band, but only weakly coherent in the obliquity band (Fig.9F); moreover, in our solution, no discrete concentration of varianceis observed in the 41-k.y. band. The δ 1 8 θ record developed for Site846 does not show a strongly coherent 41 -k.y. signal either; it remainspossible that either a different tuning of the data investigated here ora record of different components of the climate system might lead tohigher coherencies than those we have obtained here.

RECALIBRATING THE MIOCENE TIME SCALE

One will recall that CK92 calibrated the distance scale for the SouthAtlantic Ocean anomaly sequence on the basis of a control age at 2.6Ma and another at 14.8 Ma (and of course others through the past 100Ma). The age of 2.6 Ma for the Gauss/Matuyama boundary was basedon astronomical calibration (SBP90), while the remaining have beenbased on radiometric age determinations. Clearly, for several years tocome, there will be two sections to the anomaly time scale: an uppersection that is calibrated in detail by astronomical tuning, and a lowersection that is developed by interpolation between a limited number ofcontrol points that are based on radiometric dates. A possible procedureat this juncture would be to insert one new age control in the latestMiocene and retain the remaining points as used by CK92. However,when South Atlantic spreading rates are estimated on this basis, ageophysically unexpected oscillation in spreading rate is generated(Fig. 10). Therefore, we have inserted an additional control point onthe basis of the new determination by Baksi (1992) for C5 (t), 9.66 ±0.05 Ma. For ease of use, we have adopted the value of 9.64 Ma for thisboundary, which is the closest age within the uncertainty limits thatenables GRAPE density to be matched directly to the insolation record.We have used 5.875 Ma for C3A(t). Table 17 gives the ages of reversalboundaries estimated from Table 2 in CK92 by fitting a cubic-spline inthe same manner as they adopted. If one uses these new figures forevents younger than 14.8 Ma together with those given by CK92 forolder events, this does not generate a significant discontinuity at 14.8Ma; we suggest that this time scale is probably more nearly correct asregards its depiction of changes in spreading rate during the late


848

849

850

Ins.

851

852

846

9.0Age (Mα)

9.2 9.4 9.6 9.8 10.0


Neogene (Fig. 10) than that of CK92. Because South Atlantic spread-ing rates clearly did change significantly during the late Miocene, itis highly likely that future tuning will modify this picture. Thesefuture modifications may undermine the basis for using a cubic-splinefit to predict the ages of the seafloor anomalies, but in the meantime,we recommend that the ages in Table 17, together with those in CK92,Table 6, for ages greater than 14.8 Ma, be used for Miocene calibra-tions. We are aware that the control age at 14.8 Ma may also bequestioned (Baksi and Farrar, 1990) but prefer here to devise a solu-tion that limits the adjustments recommended to that part of the timescale over which we have contributed new data.

DISCUSSION: MIOCENE AGES

Our objective was to generate an accurate, high-resolution timescale for the past 6 m.y. for Leg 138 sites. Several factors limit thebackward extension of this type of time scale. First, the quality of ourdata deteriorates. It is not yet clear to what extent our composite depthsections are complete representations of the sediment column wherethe extended core barrel (XCB) was used instead of the APC. Second,both the quality of the GRAPE density data and the fidelity of itsrelationship to percentage carbonate deteriorates in more lithifiedsediments. Third, sedimentation rates are not so favorable in themid-portion of the late Miocene sequence. Fourth, Berger and Loutre(1991) did not claim accuracy for their astronomical reconstructionsprior to about 5 Ma and, indeed, it has already been suggested thatmodifications in the calculations may be required (Berger and Loutre,1992). Fortunately, the chief basis for tuning is the characteristic

Table 14. Ages for reversals in the mid-Pliocene, estimated for Sites 850and 851.

Event

C2n.lr(t)C2n.lr(o)C2n.2r(t)C2n.2r(o)C2n(o)C3n.ln(t)C3n.ln(o)

Hole850A

3.0433.1333.2243.3333.595N.D.N.D.

Hole850B

3.0483.1333.2193.3293.596N.D.N.D.

Hole85 IB

3.0443.1243.2303.3273.5944.1944.322

Hole851C

N.D.3.1323.2223.3313.5924.208N.D.

Hole85 IE

3.0493.1313.2333.3353.5914.2084.320

Mean

3.0463.1313.233a

3.3313.594

****

Event

Kaena (t)Kaena (o)Mammoth (t)Mammoth (o)Gauss (o)Cochiti (t)Cochiti (o)

a At C2n.2r(t), the GRAPE density signal is much clearer at Hole 85IE than at the otherholes, so that we have taken the estimate for that hole, rather than the mean, (t) =termination and (o) = onset. ** See Table 15.

modulation of the precession signal by eccentricity, while the mostlikely modification to the calculated record would be in the timing ofthe obliquity cycles with respect to the precession cycles.

On the positive side, several of the Leg 138 sites have goodmagnetostratigraphy, all have good biostratigraphy, and the GRAPEdensity records show considerable promise. Thus, we have aimed todevelop partially tuned age models for the interval between 6 and 10Ma. Their chief practical utility is that they enable us to proposedetailed correlation among sites wherever the GRAPE data permitsit; they also enable us to propose calibrated sedimentation rates overintervals that display orbital frequency variability; and finally, theyenable us to evaluate the changing response to orbital forcing. Wehave made some use of bulk sediment δ13C data (Shackleton and Hall,this volume) as an additional tool for correlation between sites.

86


848

849

850

I I

851

852

846

10.0 10.2 10.4 10.6 10.8 11.0Age (Mα)

11.2 11.4 11.6 1 1.5 12.0


Table 15. Ages for reversals in the Gilbert, estimated for Site 852.

Event

C3n.ln(t)C3n.ln(o)C3n.2n(t)C3n.2n(o)C3n.3n(t)C3n.3n(o)C3n.4n(t)C3n.4n(o)C3A.ln(t)C3A.ln(o)C3A.2n(t)

Hole852B

4.1974.307N.D.4.6214.7804.8824.9805.2405.8706.1066.275

Hole852C

4.194N.D.4.4804.6184.7854.8754.9755.2245.8926.1106.277

Hole852D

4.1944.3164.4784.6314.7774.8774.9775.2315.885N.D.6.283

Mean

4.1992a

4.316a

4.4794.6234.7814.8784.9775.2325.8826.1086.278

Event

Cochiti (t)Cochiti (o)Nunivak (t)Nunivak (o)Sidufjall (t)Sidufjall (o)Thvera (t)Thvera (o)Epoch 5 (t)

Table 16. Ages of the magnetic reversals of the past 6 m.y., according toSBP90, H91, CK92, and this study.

1 at C3n.ln(o) and (t), the mean is based on Sites 851 and 852. (t) = termination and (o)= onset.

The interval between 6 and 8 Ma is shown in Figure ID. Between6 and 7 Ma, several sites show variability that is readily tuned to theinsolation record, and some preliminary tuning has been performed.Note that the GRAPE density minimum between 6.5 and 6.6 Ma canbe traced from Site 853 with a complete paleomagnetic record, throughSite 852 with a similar GRAPE density record, to the extreme repre-sented by Site 850, where this interval is marked by a 20-m-thicksequence of laminated sediment.

In the interval from 8 to 10 Ma shown in Figure IE, further workwill be required to ensure the continuity of the records recovered withthe XCB system, but it may be possible ultimately to generate a

Event

Cln (o)Clr.ln(t)Clr.ln(o)Clr.2n (t)Clr.2n(o)C2An.ln(t)C2An.ln(o)C2An.2n (t)C2An.2n (o)C2An.3n (t)C2An.3n (o)C3n.ln(t)C3n.ln(o)C3n.2n (t)C3n.2n (o)C3n.3n (t)C3n.3n (o)C3n.4n (t)C3n.4n (o)C3An.ln(t)C3An.ln(o)C3An.2n (t)

SBP90

0.780.991.071.771.952.60

H91

2.59/623.043.113.223.333.584.184.294.484.624. HO4.S94<•>K

5.23

CK92

0.7800.9841.0491.7571.9832.6003.0543.1273.2213.3253.5534.0334.1344.2654.4324.6114.6944.8125.0465.7055.9466.078

This study

3.0463.1313.2333.3313.5944.1994.3164.4794.6234.7814.8784.9775.2325.882a

6.108a

6.278a

Event

B/MJaramillo (t)Jaramillo (o)Olduvai (t)Olduvai (o)Gauss (t)

Mammoth (o)Gilbert (t)Cochiti (t)Cochiti (o)Nunivak (t)Nunivak (o)Sidufjall (t)Sidufjall (o)Thvera (t)Thvera (o)C3A.nl (t)C3A.nl (o)C3A.n2 (t)

1 These values are regarded as tentative; we recommend using the figures in Table 17 untila more secure calibration is obtained for events in the late Miocene, (t) = termination;(o) = onset.

87


Hole 851 D

1.5 >

I 0.5 0.6

Age (Ma)0.4 0.5 0.6

Age (Ma)

Figure 2. GRAPE density and magnetic declination for Holes 85 IB, 851C, 85 ID, and 85 IE for the interval 0 to 1 Ma, with orbital tuning target. Age control pointsare marked on the GRAPE density record. Declinations have been rotated arbitrarily for ease of comparison; the original data are shown in the site chapters inMayer, Pisias, Janecek, et al. (1992).

continuous tuning to 10 Ma. In the meantime, we have made somepreliminary correlations to the orbital record so that in correlating aparticular maximum in the GRAPE density record from one site toanother we use an age corresponding to an insolation maximum. Itwas on this basis that we adopted the value of 9.639 Ma for C5n.ln(t), which is consistent with the estimate of 9.66 ± 0.05 Ma given byBaksi (1992), while permitting the tentative tuning close to that ageshown in Figure IE.

Beyond 10 Ma, no orbital estimates were available to us, althoughin fact, the calculations of Berger and Loutre (1991) have been ex-tended back in time (Berger, pers. comm., 1993). We have made someuse of GRAPE density as well as biostratigraphy to correlate the othersites to Site 845, for which a good magnetostratigraphy is available toC5AB.n (t) at a recalibrated age of 13.252 Ma. Below that, we havenot attempted here to improve on the shipboard age models, whichwere based exclusively on biostratigraphy. In Tables 1 to 11, we iden-tify those age control points that are based on magnetostratigraphy orbiostratigraphy, rather than on GRAPE density.

SEDIMENTATION RATES

The high sediment accumulation rates along the equator are themost obvious geological indication of the characteristics of the physi-cal oceanography of the region, and scientists have long known thatthe paleoceanographic history could be partly sought simply by ex-amining the history of changing sedimentation rates. The work of vanAndel et al. (1975) elegantly exploited and reviewed the material thatwas available up to the time of DSDP Leg 17. Perhaps the moststriking scientific achievement during Leg 138 was the production ofthe high quality biostratigraphy and magnetostratigraphy that enabledus to generate refined sedimentation rate history (Mayer, Pisias, andShipboard Scientific Party [1992] and Shackleton and Shipboard

Scientific Party [1992]). The main feature of that result was theremarkably high sedimentation rates that prevailed over an interval ofabout 3 m.y. in the equatorial Pacific Ocean during the early Plioceneand latest Miocene.

Figure 11 shows the sedimentation rate picture that emerges fromthe more refined time scales developed in this chapter. For each site,sedimentation rate has been estimated over 0.2-m.y. intervals cen-tered at each 0.1 Ma in age (Tables 18 to 28). This presentationeffectively damps out any sedimentation rate variability that may beattributed to the result of Milankovitch-scale processes. Both theonset of the interval of enhanced sedimentation rates at about 7.5 Maand its termination at about 4.5 Ma are surprisingly rapid. We suggest(1) that it is hardly likely that such dramatic changes in the easternPacific Ocean could occur without repercussion in other parts of theglobal climate system and (2) that efforts should be made to identifyrelated changes in other regions with a view to identifying the cause.Certainly, analogous changes have been reported in the equatorialIndian Ocean (Peterson and Backman, 1990) as well as in the westernequatorial Pacific (Berger et al., 1993).

SUMMARY

A consistent set of high-resolution age models for the Leg 138sites is presented; these were provided to the Shipboard ScientificParty for use in preparing other chapters in this volume. For the past6 m.y., these are fully orbitally tuned, providing a secure, absolutetime scale for the seafloor anomaly scale, for the oxygen isotoperecord, for the seismic stratigraphy of the Pacific Ocean, and, ofcourse, for all those aspects of climatic and Oceanographic variabilitythat transfer the astronomical record of varying solar insolation intoquasi-cyclic sedimentological variability. For the period prior to 6Ma, the absolute time calibration becomes less secure, but we have


Age (Ma)

Figure 3. GRAPE density and magnetic declination for Holes 851B, 851C, and

85IE for the interval from 1 to 2 Ma, with orbital tuning target. Age control

points are marked on the GRAPE density record. Declinations have been

rotated arbitrarily for ease of comparison; the original data are shown in the

site chapters in Mayer, Pisias, Janecek, et al. (1992).

defined a new magnetic polarity time scale based on astronomical

tuning to the base of the Pliocene together with the anomaly distance

scale given by CK92 and a new calibration by Baksi (1992) for the

young side of C5n.

ACKNOWLEDGMENTS

We thank the crew of J01DES Resolution for enabling the Leg 138

Shipboard Scientific Party to return with such a magnificent legacy

of material and our colleagues aboard the ship for sharing nine weeks

of exciting, hard work for the benefit of a generation of Pacific-loving

paleoceanographers. The labor-intensive job of tuning all the GRAPE

density records would have been impossible without the support of

NERC through Grant GST/02/554, and we are especially grateful for

their contribution to the cost of a Sun SPARCstation as soon as the

need for this became apparent. We thank Fritz Hilgen and Andre

Berger for their helpful reviews of the submitted manuscript, and Ted

Moore and Jan Backman in particular for valuable discussions at

several stages in its progress.

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Shackleton, NJ., Crowhurst, S., Pisias, N., Hagelberg, T, Schneider, D., Mix,A., and ODP Leg 138 Shipboard Scientific Party, 1992. An astronomicallycalibrated Pliocene time scale based on Leg 138 GRAPE density records.GEOMAR Rep., 15:260. (Abstract)

Shackleton, NJ., and Opdyke, N.D., 1973. Oxygen isotope and paleomagneticstratigraphy of equatorial Pacific core V28-238: oxygen isotope tempera-tures and ice volumes on a I05 year and I06 year scale. Quat. Res. N.Y.,3:39-55.

Shackleton, NJ., and Shipboard Scientific Party, 1992. Sedimentation rates:toward a GRAPE density stratigraphy for Leg 138 carbonate sections. InMayer, L., Pisias, N., Janecek, T., et al., Proc. ODP, Init. Repts., 138 (Pt.1): College Station, TX (Ocean Drilling Program), 87-91.

Shipboard Scientific Party, 1992. Explanatory notes. In Mayer, L., Pisias, N.,Janecek, T., et al., Proc. ODP, Init. Repts., 138 (Pt. 1): College Station, TX(Ocean Drilling Program), 13—42.

Spell, T.L., and McDougall, I., 1992. Revisions to the age of the Brunhes-Matuyama boundary and the Pleistocene geomagnetic timescale. Geophys.Res. Lett., 19:1181-1184.

Tauxe, L., Deino, A.D., Behrensmeyer, A.K., and Potts, R., 1992. Pinningdown the Brunhes/Matuyama and upper Jaramillo boundaries: a reconcili-ation of orbital and isotopic time scales. Earth Planet. Sci. Lett., 109:561—572.

Tiedemann, R., 1992. Astronomic tuning of the high-resolution benthic recordsfrom ODP Sites 658 and 659 for the last 5 million years vs. non-linearclimate dynamics. GEOMAR Rep., 15:282. (Abstract)

van Andel, T.H., Heath, G.R., and Moore, T.C., Jr., 1975. Cenozoic history andpaleoceanography of the central equatorial Pacific Ocean. Mem.—Geol.Soc. Am., 143.

Vincent, E., 1981. Neogene carbonate stratigraphy of Hess Rise (central NorthPacific) and paleoceanographic implications. In Thiede, J., Valuer, T.L., etal., Init. Repts. DSDP, 62: Washington (U.S. Govt. Printing Office),571-606.

Walter, R.C., Deino, A., Renne, P., and Tauxe, L., 1992. Refining the Plio-Pleis-tocene GPTS using laser fusion 40Ar/39Ar tephrochronology: Case studiesfrom the East African Rift. Eos (Suppl), 73:629. (Abstract)

Walter, R.C., Manega, P C , Hay, R.L., Drake, R.E., and Curtis, G.H. 1991.Laser-fusion 40Ar/39Ar dating of Bed 1, Olduvai Gorge, Tanzania. Nature,354:145-149.

Wilson, D.S., 1993. Confirmation of the astronomical calibration of the mag-netic polarity timescale from sea-floor spreading. Nature, 364:788-790.

Date of initial receipt: 5 February 1993Date of acceptance: 27 July 1993Ms 138SR-106

90


Table 17. Ages for magnetic anomalies between C3An.ln (t) and C5Bn.ln(t), derived by re-calibrating the distances in CK92 Table 2 with C3An.ln(t) at 5.875 Ma and C5n.ln (t) at 9.639MAMa Ma.

Anomalystudy

C3An.ln(t)C3An.ln(o)C3An.2n (t)C3An.2n (o)C3Bn (t)C3Bn (o)C4n.ln(t)C4n.ln(o)C4n.2n (t)C4n.2n (o)C4r.ln(t)C4r.ln(o)C4An (t)C4An (o)C4Ar.ln(t)C4Ar.ln(o)C4Ar.2n (t)C4Ar.2n (o)C5n.ln(t)C5n.ln(o)C5n.2n (t)C5n.2n (o)C5r.ln(t)C5r.ln(o)C5r.2n (t)C5r.2n (o)C5An.ln(t)C5An.ln(o)C5An.2n (t)C5An.2n (o)C5Ar.ln(t)C5Ar.ln(o)C5Ar.2n (t)C5Ar.2n (o)C5AAn (t)C5AAn (o)C5ABn (t)C5ABn (o)C5ACn (t)C5ACn (o)C5ADn (t)C5ADn (o)C5Bn.ln(t)

Berggrenet al.

(1985)

5.355.535.685.896.376.506.706.786.857.287.357.417.908.218.418.508.718.808.92N.D.N.D.10.4210.5410.5911.0311.0911.5511.7311.8612.1212.4612.4912.5812.6212.8313.0113.2013.4613.6914.0814.2014.6614.87

CK92

5.7055.9466.0786.3766.7446.9017.2457.3767.4647.8928.0478.0798.5298.8619.0699.1499.4289.4919.5929.7359.777

10.83410.94010.98911.37811.43411.85212.00012.10812.33312.61812.64912.71812.76412.94113.09412.26313.47613.67414.05914.16414.60814.800

Thisstudy

5.8756.1226.2566.5556.9197.0727.4067.5337.6188.0278.1748.2058.6318.9459.1429.2189.4829.5439.6399.7759.815

10.83910.94310.99111.37311.42811.84111.98812.09612.32012.60512.63712.70512.75212.92913.08313.25213.46613.66614.05314.15914.60714.800

Note: N.D. = not determined.

2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3.0

Age (Ma)

Figure 4. GRAPE density and magnetic declination for Holes 85 IB, 851C, and

85IE for the interval from 2 to 3 Ma, with orbital tuning target. Age control

points are marked on the GRAPE density record. Declinations have been

rotated arbitrarily for ease of comparison; the original data are shown in the

site chapters in Mayer, Pisias, Janecek, et al. (1992).

91


Table 18. Accumulation rates (mcd scale) estimated in overlapping 0.2m.y. intervals for Site 844 (from Table 1).


Age(Ma)

0.00.10.20.30.40.50.60.70.80.91.01.11.21.31.41.51.61.71.92.02.12.22.32.42.52.62.72.82.93.03.13.23.33.43.53.63.73.83.94.04.14.24.34.44.54.64.74.84.95.05.15.25.35.45.55.65.75.85.96.06.16.26.36.46.56.66.76.86.97.07.17.27.37.47.57.67.77.87.98.08.18.28.38.4

Depth(mcd)

0.001.532.583.825.146.688.169.16

10.2311.0711.9312.8613.6514.4315.2115.9916.7717.5518.8619.3819.8520.3220.7921.2621.7322.2022.5422.8823.2323.5723.8724.2824.4724.7225.0725.4125.6825.9426.2026.4526.7126.9827.3227.6527.9928.3828.7529.1029.4730.0130.5631.1231.7032.2932.8833.4734.0734.6635.2835.9936.6937.4337.9838.2638.5538.9939.6240.2540.8841.4241.9142.3242.7243.1344.0844.8345.9547.1748.4049.6250.4151.0351.6552.28

Rate(m/m.y.)

12.911.512.814.315.112.410.49.68.59.08.67.87.87.87.87.87.55.55.04.74.74.74.74.74.13.43.43.43.23.63.02.23.03.53.12.62.62.62.62.63.13.43.33.73.83.63.64.55.55.65.75.95.95.95.95.96.16.67.17.26.44.12.93.65.46.36.35.95.24.54.04.06.88.59.4

11.712.212.210.07.06.26.26.2

Age(Ma)

8.58.68.88.99.09.19.29.39.49.59.69.79.89.9

10.010.110.210.310.410.510.610.710.810.911.011.111.211.311.411.511.611.711.811.912.012.112.212.312.412.512.612.712.812.913.013.113.213.313.413.513.613.713.813.914.014.114.214.314.414.514.614.714.814.915.015.115.215.315.415.515.715.815.916.016.116.216.316.416.516.616.716.816.917.0

Depth(mcd)

52.9053.5355.3556.3257.1057.7358.6959.4360.0761.0062.2263.1564.3965.6266.8668.0069.1270.2471.3672.4773.8275.4277.5979.7682.0285.1488.2691.3794.6798.42

102.18105.94109.70113.46117.10119.87122.63125.39128.16130.92133.68137.60142.16146.72150.77154.63158.48162.18165.72169.26172.80176.35179.89183.43186.97190.49193.96197.43200.90204.37207.84211.31214.78218.25222.14226.47230.80235.12239.45243.77252.43256.75260.91265.00269.08273.17277.25281.34285.42289.51293.59297.68301.76305.85

Rate(m/m.y.)

6.27.49.68.77.17.98.56.97.9

10.710.810.912.312.311.911.311.211.211.212.314.718.921.722.126.931.231.232.035.337.637.637.637.637.032.027.627.627.627.627.633.442.445.643.139.538.537.836.235.435.435.435.435.435.435.334.934.734.714.734.734.734.734.736.841.143.343.343.343.343.343.342.441.240.940.940.940.940.940.940.940.940.940.9

AgeMa

0.00.10.20.30.40.50.60.70.80.91.01.11.21.31.41.51.61.71.81.92.02.12.22.32.42.52.62.72.82.93.03.13.23.33.43.53.63.73.83.94.04.14.24.34.44.54.64.74.84.95.05.15.25.35.45.55.65.75.85.46.06.16.26.36.46.56.66.76.86.97.07.17.27.37.47.57.67.77.87.98.08.18 2

Depth(mcd)

0.003.006.019.01

12.0214.1016.0818.0620.0422.0224.0025.9827.9629.9431.9233.9035.8837.8639.8441.8243.4244.4145.4046.4047.3948.3949.3850.3751.3752.3653.3554.5455.7256.9257.9558.8759.7860.7561.7362.7163.6864.6665.6366.4467.5768.7369.7270.7471.6772.3173.4974.5675.6377.1978.9880.7782.5684.3586.1587.7788.8789.9891.8493.4994.5995.7096.9498.3599.76

101.17102.36103.59105.04106.50107.95109.58110.83112.68114.70116.72118.74119.91120.77122.80

Ratem/m.y.

30.030.030.025.420.319.819.819.819.819.819.819.819.819.819.819.819.819.817.912.99.99.99.99.99.99.99.99.99.9

10.911.811.911.29.79.19.49.79.89.89.89.78.99.7

11.410.810.09.77.99.1

11.310.713.116.817.917.917.917.917.113.611.114.817.613.811.111.813.314.114.113.012.113.414.614.615.414.415.519.420.220.215.910.114.520.6

AgeMa

0.08.48.58.68.78.88.99.09.19.29.39.49.59.69.79.89.9

10.010.110.210.310.410.510.610.710.810.911.011.111.211.311.411.511.611.711.811.912.012.112.212.312.412.512.612.712.812.913.013.113.213.313.413.513.613.713.813.914.014.114.214.314.414.514.614.714.814.915.015.115.215.315.415.515.615.715.815.916.016.116.216.316.4

Depth(mcd)

0.00124.89126.98129.06131.25133.49135.73137.65139.31141.09142.56143.95145.56147.32148.91150.61151.96153.34154.72156.10157.49158.87160.25161.64163.02164.40165.58166.95168.89170.82172.76174.96177.15179.06180.96182.87185.02187.41190.30193.19196.09198.98201.87204.77207.99211.19214.56217.63220.67224.22226.99228.89230.80232.71234.61236.52238.43240.33242.24244.15246.05247.96249.87251.78253.68255.59257.50259.40261.31263.22265.12267.03268.94270.84272.75274.66279.05284.52289.98295.44300.91306.37

Ratem/m.y.

20.920.921.422.222.420.817.917.216.314.315.016.916.716.515.213.613.813.813.813.813.813.813.813.812.812.816.519.319.320.722.020.519.119.120.322.726.428.928.928.928.928.930.632.132.832.230.633.031.623.319.119.119.119.119.119.119.119.119.119.119.119.119.119.119.119.119.119.119.119.119.119.119.119.131.549.354.654.654.654.6


Hole 850 A

3.4 3.5 3.6Age (Ma)

Figure 5. GRAPE density and magnetic declination for Holes 850A and 850Bfor the interval from 3 to 4 Ma, with orbital tuning target. Age control pointsare marked on the GRAPE density record. Declinations have been rotatedarbitrarily for ease of comparison; the original data are shown in the sitechapters in Mayer, Pisias, Janecek, et al. (1992).

3.4 3.5 3.6Age (Ma)

Figure 6. GRAPE density and magnetic declination for Holes 85 IB, 851C, and85 IE for the interval from 3 to 4 Ma, with orbital tuning target. Age controlpoints are marked on the GRAPE density record. Declinations have beenrotated arbitrarily for ease of comparison; the original data are shown in thesite chapters in Mayer, Pisias, Janecek, et al. (1992).

93

N.J. SHACKLETON ET AL.

4.4 4.5 4.6

Age (Ma)

Figure 7. GRAPE density (middle) and magnetic declination (below) for Holes852B, 852C, and 852D for the interval from 4 to 5 Ma, with orbital tuning target.Age control points are marked on the GRAPE density record. Above: stackedGRAPE density records of Sites 849, 850, and 851 for the same interval.Declinations have been rotated arbitrarily for ease of comparison; the originaldata are shown in the site chapters in Mayer, Pisias, Janecek, et al. (1992).

5.4 5.5 5.6Age (Ma)

Figure 8. GRAPE density (middle) and magnetic declination (below) for Holes852B, 852C, and 852D for the interval from 5 to 6 Ma, with orbital tuning target.Age control points are marked on the GRAPE density record. Above: stackedGRAPE density records of Sites 849, 850, and 851 for the same interval.Declinations have been rotated arbitrarily for ease of comparison; the originaldata are shown in the site chapters in Mayer, Pisias, Janecek, et al. (1992).

94


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Figure 9. Cross-spectral analysis of average GRAPE density for Sites 849, 850, and 851 vs. summer insolation at 65°N.A. 0 to 1 Ma (from Tables 6, 7, and 8). B. 0 to 1 Ma (from Table 12). C. 1 to 2 Ma. D. 2 to 3 Ma. E. 3 to 4 Ma. F. 4 to 5Ma. G. 5 to 6 Ma. H. 6 to 7 Ma. The time series were sampled at 3-k.y. intervals and cross-spectra calculated for 80 lags.Dashed line = insolation spectra; dash-dotted line = GRAPE spectra; solid line = coherency; dotted line = 80% confidencelimit for coherency. Arrows at the top of the figure identify prominent peaks in insolation variance associated with obliquity(41 k.y.) and precession (23 and 19 k.y.).

95


Table 20. Accumulation rates (mcd scale) estimated in overlapping 0.2 m.y. intervalsfor Site 846 (from Table 3).

Age(Ma)

0.00.10.20.30.40.50.60.70.80.91.01.11.21.31.41.51.61.71.81.92.02.12.22.32.42.52.62.72.82.93.03.13.23.33.43.53.63.73.83.94.04.14.24.34.44.54.64.74.84.95.05.15.25.35.45.55.65.75.85.96.0

Depth(mcd)

0.004.398.30

11.5515.5119.5622.5825.8929.4733.9836.5940.1644.1946.6750.6453.9357.0261.1764.6968.9674.1079.5883.2187.2991.1595.86

100.73105.10110.21114.98119.84124.31127.79130.35134.48139.22143.63146.41149.43152.21156.21159.28162.24165.59169.21172.45177.53182.90187.53191.57195.01197.39201.75206.79210.67215.49221.28226.89233.07238.8324336

Rate(m/m.y.)

41.535.836.040.135.431.634.540.435.630.938.032.532.236.331.936.238.438.947.053.145.638.639.742.847.946.247.449.448.146.639.830.233.444.345.735.929.029.033.935.330.131.634.934.341.652.250.043.437.429.133.747.044.643.553.157.058.959.75 1 . 454.9

Age(Ma)

6.16.26.36.46.56.66.76.86.97.07.17.27.37.47.57.67.77.87.98.08.18.28.38.48.58.68.78.88.99.09.19.29.39.49.59.69.79.89.9

10.010.110.210.310.410.510.610.710.810.911.011.111.211.311.411.511.611.711.811.912.0\2.\

Depth(mcd)

249.80253.20255.73262.71265.33268.24270.76273.28275.80278.32281.69286.77289.67294.32297.41299.26301.10303.14305.30307.28308.90309.72310.53312.70314.10315.22316.76318.53320.30322.83324.56326.62328.20329.82331.22332.66333.81335.44336.84338.48339.78341.07342.36343.57344.59345.60346.70349.04351.37353.61355.23356.85358.59360.36362.15363.95365.75367.55369.34371.14372.94

Rate(m/m.y.)

49.229.647.548.027.727.225.225.225.229.442.239.937.838.724.718.419.421.020.718.012.28.114.917.812.613.316.617.7

2 1 . 52 1 . 3

19.018.216.015.114.212.913.915.115.214.712.912.912.511.110.110.617.223.322.919.316.216.817.617.818.018.018.018.018.018 018.0

Age(Ma)

12.212.312.412.512.612.712.812.913.013.113.213.313.413.513.613.713.813.914.014.114.214.314.414.514.614.714.814.915.015.115.215.315.415.515.615.715.815.916.016.116.216.316.416.516.616.716.816.917.017.117.217.317.417.517.617.717.817.918.0

Depth(mcd)

374.73376.53378.33380.13381.92383.72385.52387.31389.11390.91392.71394.50397.39400.20401.21402.22403.23404.24405.26406.27407.28408.29409.30410.31411.32412.33413.34414.35415.36416.37417.38418.39419.40420.41421.43422.44423.45424.85426.48428.10429.72431.34432.96434.59436.21437.83439.45441.07442.69444.32445.94447.56449.18450.80452.43454.05455.67457.29458.91

Rate(m/m.y.)

18.018.018.018.018.018.018.018.018.018.018.023.428.519.110.110.110.110.110.110.110.110.110.110.110.110.110.110.110.110.110.110.110.110.110.110.112.115.116.216.216.216.216.216.216.216.216.216.216.216.216.216.216.216.216.216.216.216.2

96


ET3

30

25

20

15

% 1 0

Without C5n (t) control

This work

Cande and Kent (1992)

10 15 20 25

Age (Ma)

Figure 10. South Atlantic Ocean spreading rates derived by applying a cubic-spline function to the distances in CK92 (Table 2).

Line A uses our calibration for C3An (t) in addition to those used in CK92; Line B, our preferred solution, includes an additional

calibration at C5n.ln (t).

Table 21. Accumulation rates (mcd scale) estimated in overlapping 0.2m.y. for Site 847 (from Table 4).

Age(Ma)

0.00.10.20.30.40.50.60.70.80.91.01.11.21.31.41.51.61.71.82.02.12.22.32.42.52.62.72.82.93.03.13.23.33 A

Depth

(mcd)

0.003.357.05

10.0713.6016.4618.7521.7124.6527.8630.4333.6937.3340.9144.7547.7650.7353.3857.3366.0570.1473.0076.0279.1583.0186.2289.2892.5395.3398.49

101.01103.96107.16Ilθ!θ3

Rate(m/m.y.)

35.333.632.732.025.726.329.530.828.929.134.536.137.134.329.928.133.042.341.534.729.430.835.035.331.431.530.229.828.427.430.730.3

Age(Ma)

3.53.63.73.83.94.04.14.34.44.54.64.74.84.95.05.15.25.35.45.55.65.75.85.96.06.16.26.36.46.56.66.7

Depth(mcd)

112.72115.62118.68121.45124.19126.55128.87133.92137.44140.27146.05155.69159.41166.37169.59173.75177.54181.70185.52189.25193.61198.89202.74207.17210.91217.27223.74230.21235.41240.61245.81251.01

Rate(m/m.y.)

28.029.829.127.625.523.423.131.331.743.077.166.853.450.936.939.839.839.937.740.548.245.741.440.950.564.164.758.352.052.052.0

97


100 Table 22. Accumulation rates (mcd scale) estimated in overlapping 0.2m.y. intervals for Site 848 (from Table 5).

Figure 11. Sedimentation rates from Tables 18 through 28. Estimates areplotted at 0.1-m.y. intervals; each estimate plotted represents the mean for the0.2-m.y. interval centered on that age, derived by interpolating a depth pointevery 0.1 Ma from the table. Note that the values given are probably greaterthan the true in-situ sedimentation rates by about 10%, and somewhat more inthe intervals recovered by the XCB (Hagelberg et al., 1992; Fig. 3; Harris etal., this volume).

AgeMa

0.0O.I0.20.30.40.50.60.70.80.')1.01.11.21.31.41.51.61.71.81.92.02.12.22.32.42.52.62.72.82.93.03.13.23.33.43.53.63.73.83.94.04.14.24.34.44.54.64.74.84.95.05.15.25.35.45.55.6

Depth(mcd)

0.001.542.763.905.607.579.17

11.0912.7414.6716.0417.9619.4420.9522.4423.5624.4225.3326.2927.1827.7228.6129.0129.3529.9830.5231.0631.7832.5533.2233.7134.0834.4134.8835.4635.8836.5037.0437.4437.8238.2438.6439.1039.5040.1040.7741.9243.5845.0846.4347.5948.6849.9752.0454.0455.9258.20

Ratem/m.y.

13.811.814.218.317.817.617.917.916.516.417.015.015.013.19.98.89.49.27.27.16.43.74.95.95.46.37.47.25.84.33.54.05.25.05.25.84.73.94.04.14.34.35.06.39.1

14.115.814.312.611.211.916.820.319.420.820.9

AgeMa

0.05.75.85.96.06.16.26.36.46.56.66.76.86.97.07.17.27.37.47.57.67.77.87.98.08.18.28.38.48.58.68.78.88.99.09.19.29.39.49.59.69.79.89.9

10.010.110.210.310.410.510.610.710.810.91 1.011.111.2

Depth(mcd)

0.0060.1061.3462.5863.8265.0666.1967.3168.5669.8771.1672.3873.6174.8476.0777.2978.5279.7580.9881.7582.2082.6883.2183.7384.2684.5584.8685.5086.1386.7787.4088.0688.7389.4090.0690.7291.7292.6593.5094.3294.6994.9595.3296.0196.7497.4698.1898.9099.63

100.35101.07101.80102.52103.12103.71104.41105.11

Ratem/m.y.

15.712.412.412.411.811.311.912.813.012.612.312.312.312.312.312.312.310.06.14.65.05.35.34.13.04.86.36.36.36.56.66.76.76.68.39.68.98.35.93.23.25.37.17.27.27.27.27.27.27.27.26.66.06.47.0

98



Table 24. Accumulation rates (mcd scale) estimated in overlapping 0.2m.y. intervals in Site 850 (from Table 7).

Age(Ma)

0.00.10.20.30.40.50.60.70.80.91.0.1.2.3.4.5.6.7.8.92.02.12.22.32.42.52.62.72.82.93.03.13.23.33.43.53.63.73.83.94.04.14.24.34.44.54.64.74.84.95.05.15.25.35.4.5

Depth

(mcd)

0.023.126.619.5512.8315.5617.9620.8123.1925.9528.2831.1533.4636.7540.0841.9744.7146.8549.8253.3157.1060.9362.9965.4267.7570.5973.2175.5578.3680.6983.2585.9388.7291.7694.4697.21100.04102.82105.76108.28111.00113.73116.48119.50122.89125.79132.72137.78146.17149.18153.86158.57163.17168.45178.02183.35

Rate(m/m.y.)

32.932.231.130.125.726.226.125.725.526.025.928.033.126.123.124.425.632.336.438.129.422.423.825.927.324.825.825.724.526.227.329.128.727.227.928.128.627.326.227.227.428.932.031.449.260.067.257.038.547.046.549.474.374.559.5

Age(Ma)

5.65.75.85.96.06.16.26.36.46.56.66.76.86.97.07.17.27.37.47.57.67.77.87.98.08.18.28.38.48.58.68.78.88.99.09.19.29.39.49.59.69.79.89.910.010.110.210.310.410.510.610.710.810.91 1.011.1

Depth(mcd)

189.91196.45205.84216.16219.69229.49235.62241.32246.09254.05266.55275.96278.16281.22285.32287.94293.41295.91300.45303.53305.81306.37307.54310.64313.51315.33317.79321.79325.08327.14329.43330.95332.85334.71336.55338.64340.57342.59344.18345.88347.68348.92349.93351.34352.82354.31355.80357.29358.77360.26362.18364.52367.37370.21373.05375.89

Rate(m/m.y.)

65.579.798.669.266.679.759.152.363.7102.3109.658.126.335.833.640.539.935.238.126.814.28.6

21.429.923.421.432.336.526.721.819.117.118.818.519.720.119.718.016.517.515.211.212.114.514.914.914.914.914.917.021.325.928.428.428.4

Age(Ma)

0.00.10.20.30.40.50.60.70.80.91.01.11.21.31.41.51.61.71.81.92.02.12.22.32.42.52.62.72.82.93.03.13.23.33.43.53.63.73.83.94.04.14.24.34.44.54.64.74.84.95.05.15.25.35.45.55.65.75.85.96.0

Depth

(mcd)

0.001.854.416.298.5710.4711.9914.4416.1718.3419.9522.3724.1325.8727.9729.7531.8033.3835.7037.6539.6241.7343.4445.6348.9850.7852.8354.9957.3759.5661.8563.8666.2968.2670.1172.5775.0077.2679.5781.6983.8685.8587.3489.0092.0294.6699.41106.15109.90114.30115.20118.26121.93126.70134.57139.53144.04148.90158.37163.63170.25

Rate(m/m.y.)

22.022.220.820.917.119.820.919.518.920.220.917.519.219.419.118.119.521.419.620.419.119.527.725.819.221.022.722.922.421.522.222.019.121.524.523.522.922.121.420.817.415.823.428.337.057.452.540.826.519.833.742.263.264.147.346.971.673.659.470.0

Age(Ma)

6.16.26.36.46.56.66.76.86.97.07.17.27.37.47.57.67.77.87.98.08.18.28.38.48.58.68.78.88.99.09.19.29.39.49.59.69.79.89.910.010.110.210.310.410.510.610.710.810.911.011.111.211.311.411.511.611.711.811.9

Depth(mcd)

177.62183.10189.95192.91198.45214.12225.53228.03231.38235.15238.92245.43249.60253.75258.12258.96260.98265.23268.13270.62274.21278.17281.46286.51290.32293.49297.01298.96303.82306.62310.00312.34315.20317.31320.56323.82327.22330.27333.10335.85337.43342.18345.57347.01351.01359.10363.77366.51370.79375.48380.17384.63388.80392.97393.77395.67399.00402.32405.65

Rate(m/m.y.)

64.361.749.142.5106.0135.469.629.235.637.751.453.441.642.626.114.331.335.826.930.437.836.241.744.334.933.427.334.038.330.928.626.024.926.832.533.332.229.427.921.731.740.724.127.260.563.837.035.144.946.945.743.141.724.913.526.133.333.3

99


Age Depth Rate Age Depth Rate(Ma) (mcd) (m/m.y.) (Ma) (mcd) (m/m.y.)

0.0 1.40 6.1 139.10 50.10.1 3.43 17.3 6.2 145.74 59.50.2 4.86 13.9 6.3 151.01 42.70.3 6.22 15.9 6.4 154.29 39.50.4 8.05 19.3 6.5 158.90 74.70.5 10.09 17.2 6.6 169.23 106.40.6 11.49 18.3 6.7 180.18 70.40.7 13.74 20.6 6.8 183.31 32.90.8 15.61 18.2 6.9 186.76 35.00.9 17.37 17.6 7.0 190.30 40.01.0 19.13 19.1 7.1 194.75 43.01.1 21.18 19.4 7.2 198.91 34.31.2 23.01 18.5 7.3 201.60 29.21.3 24.89 19.6 7.4 204.75 30.51.4 26.94 19.9 7.5 207.70 37.21.5 28.88 16.9 7.6 212.19 46.11.6 30.31 13.9 7.7 216.92 45.01.7 31.66 16.2 7.8 221.20 43.31.8 33.55 16.5 7.9 225.58 42.41.9 34.96 16.1 8.0 229.68 34.32.0 36.76 19.1 8.1 232.43 27.42.1 38.78 18.2 8.2 235.17 19.12.2 40.40 17.6 8.3 236.25 25.32.3 42.30 24.7 8.4 240.24 40.62.4 45.34 23.8 8.5 244.38 35.92.5 47.07 16.8 8.6 247.42 26.82.6 48.70 16.0 8.7 249.74 31.32.7 50.26 20.3 8.8 253.69 47.02.8 52.76 21.7 8.9 259.14 44.72.9 54.61 19.3 9.0 262.63 36.13.0 56.62 19.6 9.1 266.36 34.53.1 58.53 18.5 9.2 269.53 27.53.2 60.31 18.2 9.3 271.86 19.53.3 62.17 19.2 9.4 273.44 21.33.4 64.16 19.9 9.5 276.13 27.73.5 66.16 18.6 9.6 278.98 34.93.6 67.87 18.8 9.7 283.11 36.63.7 69.91 17.5 9.8 286.31 31.13.8 71.38 14.4 9.9 289.33 30.63.9 72.79 14.7 10.0 292.43 36.34.0 74.32 14.3 10.1 296.59 43.54.1 75.66 15.7 10.2 301.13 45.44.2 77.47 19.6 10.3 305.68 45.44.3 79.58 23.0 10.4 310.22 45.44.4 82.06 23.6 10.5 314.76 45.44.5 84.31 22.5 10.6 319.30 45.44.6 86.56 26.8 10.7 323.83 44.44.7 89.68 28.4 10.8 328.18 43.54.8 92.25 26.8 10.9 332.52 43.54.9 95.03 29.6 11.0 336.87 43.55.0 98.16 31.7 11.1 341.22 43.55.1 101.37 27.8 11.2 345.56 40.05.2 103.73 26.8 11.3 349.21 36.05.3 106.73 29.7 11.4 352.77 33.25.4 109.66 36.5 11.5 355.85 30.25.5 114.02 46.2 11.6 358.80 29.65.6 118.90 44.3 11.7 361.76 29.65.7 122.88 46.6 11.8 364.72 29.65.8 128.22 50.3 11.9 367.67 29.65.9 132.94 37.5 12.0 370.636.0 135.71 30.8

Table 26. Accumulation rates (mcd scale) estimated in overlapping (m.y. intervals for Site 852 (from Table 9).

Age Depth Rate Age Depth Rate(Ma) (mcd) (m/m.y.) (Ma) (mcd) (m/m.y.)

0.0 0.00 5.5 66.08 15.30.1 1.27 11.5 5.6 67.54 14.40.2 2.29 8.9 5.7 68.96 15.90.3 3.06 9.4 5.8 70.72 16.50.4 4.16 12.1 5.9 72.27 16.40.5 5.48 11.3 6.0 74.00 18.80.6 6.42 11.9 6.1 76.03 19.90.7 7.87 14.1 6.2 77.99 17.80.8 9.23 13.4 6.3 79.59 14.00.9 10.55 11.6 6.4 80.79 11.81.0 11.56 12.6 6.5 81.95 13.91.1 13.07 13.3 6.6 83.57 14.01.2 14.21 12.3 6.7 84.75 15.21.3 15.53 13.3 6.8 86.61 21.41.4 16.87 12.0 6.9 89.03 20.11.5 17.93 11.0 7.0 90.64 14.11.6 19.08 11.1 7.1 91.85 12.11.7 20.18 10.9 7.2 93.06 12.11.8 21.27 9.7 7.3 94.27 12.11.9 22.12 9.1 7.4 95.48 10.92.0 23.09 11.8 7.5 96.45 11.42.1 24.48 11.6 7.6 97.75 12.72.2 25.41 9.4 7.7 98.99 14.82.3 26.35 10.5 7.8 100.70 18.12.4 27.52 11.7 7.9 102.61 19.12.5 28.69 11.0 8.0 104.52 20.32.6 29.72 10.3 8.1 106.67 20.72.7 30.76 12.7 8.2 108.66 16.52.8 32.27 14.0 8.3 109.98 13.12.9 33.56 12.4 8.4 111.29 13.13.0 34.76 12.0 8.5 112.60 13.13.1 35.95 11.8 8.6 113.91 11.23.2 37.13 10.5 8.7 114.83 8.23.3 38.05 9.8 8.9 116.28 6.23.4 39.09 10.9 9.0 116.80 4.43.5 40.24 10.1 9.1 117.15 5.63.6 41.11 7.7 9.2 117.91 6.23.7 41.77 8.3 9.3 118.39 4.23.8 42.77 10.0 9.4 118.75 3.83.9 43.78 10.5 9.5 119.15 4.04.0 44.87 9.7 9.6 119.54 4.04.1 45.72 8.1 9.7 119.96 4.54.2 46.48 9.2 9.8 120.44 6.64.3 47.56 12.9 9.9 121.28 8.84.4 49.06 14.3 10.0 122.20 9.54.5 50.42 13.0 10.1 123.17 9.84.6 51.67 13.6 10.2 124.16 9.94.7 53.14 15.3 10.3 125.15 9.94.8 54.72 15.0 10.4 126.14 9.94.9 56.14 14.7 10.5 127.13 8.85.0 57.66 16.5 10.6 127.90 4.75.1 59.43 18.0 10.7 128.08 1.75.2 61.25 17.0 10.8 128.255.3 62.83 16.15.4 64.48 16.2




Age(Ma)

0.00.10.20.30.40.50.60.70.80.91.01.11.21.31.41.51.61.71.81.92.02.12.22.32.42.52.62.72.82.93.03.13.23.33.43.53.63.73.83.94.04.14.24.3

Depth(mcd)

0.220.550.881.201.531.862.202.563.043.463.894.344.865.385.896.416.927.447.938.368.859.409.96

10.5111.0711.6212.1812.8513.5214.2014.8715.5516.2016.7617.3918.0718.7419.3519.9620.5621.1621.7722.4123.34

Rate(m/m.y.)

3.33.33.33.33.33.54.24.54.34.44.85.25.25.25.25.25.04.64.65.25.65.65.65.65.66.16.76.76.76.86.76.06.06.66.76.46.16.06.06.06.27.9

10.8

Age(Ma)

4.44.54.64.74.84.95.05.15.25.35.45.55.65.75.85.96.06.16.26.36.46.56.66.76.86.97.07.17.27.37.47.57.67.77.87.98.08.18.28.38.48.58.6

Depth(mcd)

24.5725.4825.9826.6627.4028.2528.9329.9931.0732.1733.2834.3935.5136.6237.7338.9040.2041.5142.8243.9944.9945.9847.2048.6750.1551.6253.1054.3254.8955.4656.5257.8558.8860.3661.9663.5665.1767.0068.9170.3471.7573.1674.57

Rate(m/m.y.)

10.77.05.97.17.97.78.7

10.710.911.111.111.111.111.111.412.313.113.112.410.810.011.113.514.714.714.713.59.05.78.2

11.911.812.515.416.016.017.218.716.714.214.114.1

Age(Ma)

0.00.10.20.30.40.50.60.70.80.91.01.11.21.31.41.51.61.71.82.02.12.22.32.42.52.62.72.82.93.03.13.23.33.43.53.63.73.83.94.04.14.34.44.54.34.44.54.64.7

Depth(mcd)

0.000.521.051.572.092.623.143.664.204.815.416.036.717.398.088.769.45

10.1310.7611.8812.6813.4814.2815.0815.8816.6816.9017.1217.3417.5617.7617.9218.0818.3618.7019.0419.3719.5119.5319.5519.5719.6119.6319.6519.6119.6319.6519.6719.69

Rate(m/m.y.)

5.25.25.25.25.25.25.35.76.06.16.56.86.86.86.86.86.55.57.28.08.08.08.08.05.15.22.22.22.11.81.62.23.13.43.32.30.80.20.20.20.20.20.20.20.20.20.20.2

Age(Ma)

4.84.95.05.15.25.35.45.55.65.75.85.96.06.16.26.36.46.56.66.76.86.97.07.17.27.37.47.57.67.77.87.98.08.18.28.38.48.58.68.78.99.09.19.29.39.49.59.6

Depth(mcd)

19.7119.7319.7519.7719.7919.8119.8319.8519.8719.8919.9120.0520.5321.0021.5822.0722.4522.8223.3123.9224.5425.1526.4927.8328.7829.7230.6632.1833.1234.5436.1437.7539.3540.7642.2142.6342.9843.3243.6744.1445.1745.7246.3047.1547.8048.3849.0449.67

Rate(m/m.y.)

0.20.20.20.20.20.20.20.20.20.20.83.14.85.25.34.43.74.35.56.26.29.7

13.411.49.49.4

12.312.311.815.116.016.015.114.39.43.83.53.54.14.95.35.77.17.56.26.26.5

101

6. a new late neogene time scale: application to …the sediments recovered during leg 138 provide a...

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