14. EOLIAN AND SILICA DEPOSITION IN THE CENTRAL NORTH ...€¦ · Core LL44-GPC3 (30°N, 158°W) by Janecek and Rea (1983), and DSDP Site 464 (40°N, 174°E) by Rea and Harrsch (1981)

Rea, D.K., Basov, I.A., Scholl, D.W., and Allan, J.F. (Eds.), 1995Proceedings of the Ocean Drilling Program, Scientific Results, Vol. 145

14. EOLIAN AND SILICA DEPOSITION IN THE CENTRAL NORTH PACIFIC:RESULTS FROM SITES 885/8861

Hilde Snoeckx,2 David K. Rea,2 Charles E. Jones,2 and B. Lynn Ingram3

ABSTRACT

Sediments recovered at Ocean Drilling Program Sites 885/886 (central North Pacific Ocean at 44°41'N, 168°14'W and44°41'N, 168°16'W, respectively) record eolian deposition during the Cenozoic and late Mesozoic. We constructed a record ofeolian MAR, which is a proxy for aridity/humidity of the climate in the continental source area. Eolian fluxes are low during theLate Cretaceous through Eocene, reflecting humid conditions in the source area. During the Oligocene, more arid climatesprevailed at the source area, as indicated by increased eolian accumulation. The "Diatom Dump", an interval of enhanced silicadeposition mainly apparent in the northwest Pacific, is reflected in the record at Sites 885/886 by two- to fivefold higher opal fluxescompared with younger and older sediments. Increased eolian deposition starting at 3.5 Ma and culminating at 2-2.6 Ma arecoincident with the onset of Northern Hemisphere glaciation. Sites 885/886 lie 10° north of sites examined previously for thehistory of eolian deposition in the central North Pacific and therefore allow enhanced understanding of the latitudinal variation ofthe wind system.

INTRODUCTION

One of the objectives of Ocean Drilling Program (ODP) Leg 145was to investigate the history of Cenozoic and Late Cretaceous atmo-spheric circulation provided by eolian sediments in the North Pacific.For that purpose, Sites 885 and 886 were drilled 1 km apart at44°41'N, 168°16'W and 168°14'W, respectively, at about 5700 mwater depth (Fig. 1). The sites are underneath the northern edge of thelow-productivity zone of the central gyre. More importantly, they arelocated downwind from Asia, presumed to be the main source area fordust throughout the Cenozoic (Rea et al., 1985;Kyteetal, 1993;Nakaiet al., 1993). Also, their location is sufficiently far removed from thecontinent to preclude influence of riverine input and ice-rafted debris.

The flux of windblown particles transported to the ocean is mainlydependent on the availability of deflatable material and therefore aproxy of humid-arid continental climate conditions (Prospero, 1981;Rea et al., 1985; Pye, 1989).

Earlier studies in the north Pacific Ocean covering the Cenozoicand late Mesozoic were performed on data from Deep Sea DrillingProject (DSDP) Site 576 (32°N, 164°E) by Janecek (1985), pistonCore LL44-GPC3 (30°N, 158°W) by Janecek and Rea (1983), andDSDP Site 464 (40°N, 174°E) by Rea and Harrsch (1981). This lastsite provided only a discontinuous record of eolian influx because ofthe low recovery and long hiatuses (Rea and Harrsch, 1985).

Whole Cenozoic records of eolian deposition were obtained fromDSDP Site 576 and piston Core LL44-GPC3. During the Late Creta-ceous and the Paleocene, eolian mass accumulation rates (MARs) atthese sites were low, corresponding to warm and wet climates. Duringthe middle to late Eocene the records of DSDP Site 576 and CoreLL44-GPC3 show a decrease in eolian MARs that may be the resultof a more humid climate in the eolian source region and/or the passageof those sites from one wind belt to another (Leinen and Heath, 1981;Janecek and Rea, 1983; Rea, 1994). Accumulation rates at those siteswere found to be low in the Oligocene which contradicts the notionof drier climates in the Oligocene than in the Paleocene and Eocenesuggested by other climatic data (Janecek, 1985).

1 Rea, D.K., Basov, I.A., Scholl, D.W., and Allan, J.F. (Eds.), 1995. Proc. ODP, Sci.Results, 145: College Station, TX (Ocean Drilling Program).

2 Department of Geological Sciences, University of Michigan, 1006 C.C. LittleBuilding, Ann Arbor, MI 48109-1063, U.S.A.

3 Department of Geology and Geophysics, University of California, Berkeley, CA94720, U.S.A.

The record obtained at Sites 885/886, which are the northernmostsites studied thus far for their eolian signal, provides an opportunityto establish longitudinal transects and to make comparisons with datafrom farther to the south, such as at DSDP Site 576 and in CoreLL44-GPC3.

METHODS

Sample Strategy

The eolian record for Sites 885/886 was determined from samplesfrom Holes 885A, 886B, and 886C. Samples were taken over theentire length of the sediment column of Holes 885 A and 886B and thebottom of Hole 886C (Cores 7H and 8H). The three holes, as well asHole 886A, were placed on a common depth scale based on themagnetic susceptibility record, using the chemostratigraphy and dustrecords as independent controls (Dickens et al., this volume). Therecords for Holes 885 A and 886B largely overlap, and drilling in Hole886C extended the record to basement and provided a comfortableoverlap of 8 m with Hole 886B. Samples from Holes 886B and 886Cwere analyzed at a spacing of four samples per 1.5-m section. Hole885 A was analyzed with a sample frequency of two samples per sec-tion to provide a control; because of stratigraphic ambiguity in the top10 m of Hole 886B (Dickens et al., this volume), the sample frequencywas increased to four samples per 1.5-m section in the top 12.6 mbsf.

Extraction of the Eolian Component

The eolian component of the sediments was isolated using amodified version of the extraction procedure detailed by Rea andJanecek (1981). The procedure calls for the removal of calciumcarbonate by acetic acid. Because Sites 885/886 are beneath thecalcite compensation depth, we did not expect to find CaCO3 in thesediment. Amorphous Fe and Mn oxides and hydroxides, as well aszeolites were removed with a buffered sodium citrate and sodiumdithionite solution. The increased accumulation of hydrothermal ma-terial at the bottom of Hole 886C (Dickens and Owen, this volume)required repeated applications of this procedure. Parallel analyses oflow oxy-hydroxide samples from the same site do not indicate addi-tional clay loss after repeating this step. Opaline silica in the Rea andJanecek (1981) method is removed by sodium carbonate. However,this digestant is inadequate in removing all of the biogenous silica forsediments at these sites. Therefore, opal was dissolved by the harshersodium hydroxide. Unlike Hovan's (in press) experience with equa-

219

H. SNOECKX, D.K. REA, C.E. JONES, B.L. INGRAM

60°N

50°

40°

//

-1/ •

1bO

\

' E 180°

Sites 885/886

North Pacific

i i i i

150° 120°W

\

\ -VI

\

Figure 1. Map of the North Pacific Ocean showing Sites 885/886.

torial Pacific samples, we did not observe a quantifiable leaching ofthe crystalline silicate component. Different clay mineralogy and arelatively greater amount of dissolution-prone neoformational miner-als in the low-dust equatorial sediments may explain the difference.The extraction procedure does not remove volcanic ash. We took carenot to sample ash layers but samples younger than 2.6 Ma may con-tain minute amounts of disseminated ash. Results of the extractionmethod are tabulated in Table 1.

Siliceous Component

To the extent that sediments at Sites 885/886 are a two-compo-nent system of biogenous silica and eolian dust (i.e., above -54meters composite depth [mcd]), the amount of opal can be estimatedby the difference:

wt% opal = 100 - wt % dust.

Calculated amounts of opal are presented in Table 1.

Mass Accumulation Rate Calculations

The mass accumulation rate (MAR) is the product of the linearsedimentation rate (LSR) and the dry bulk density of the sample. Theflux of the windblown component and of opal is the product of thepercentage by weight of the respective component and the total sedi-ment MAR. For example,

eolian MAR [g/(cm2 • k.y.)] = % extracted x LSR (cm/k.y.)× DBD (g/cm3).

The MAR of the eolian and biogenous component was calculatedbased on assumptions related to depth, age, and dry bulk density ofthe sample as outlined below. All data are tabulated in Table 1. Theaccuracy of the MARs strongly depends on the accuracy of thestratigraphy. In view of the assumptions described here, care shouldbe taken in interpreting the eolian flux. Changes in eolian MAR ofless than 10%-20% above 52 mcd (or 8.5 Ma) and of 50%-100% inthe older sediments are geologically not significant.

Dry Bulk Density

Dry bulk density was calculated from onboard physical propertiesmeasurements (Rea, Basov, Janecek, Palmer-Julson, et al., 1993). One10-cm3 sample was taken per section. The index properties (wet-bulkdensity, grain density, water content, porosity, and dry-bulk density)were determined from measurements of wet and dry weights and dryvolume (Rea, Basov, Janecek, Palmer-Julson, et al., 1993). We calcu-lated dry bulk densities by interpolation between these known values.

Composite Depth Scale

The eolian record for Sites 885/886 is a composite based on therecord of three holes. Therefore, it was necessary to place all sampleson a common depth scale, termed meters composite depth. To this end

a composite depth scale was established (Dickens et al., this volume).Because of stratigraphic ambiguity in the top of Hole 886B, no com-posite depths are calculated for the interval between 0 and 10.25 mbsf.The composite depth scale for Sites 885/886 stretches the sedimentcolumn for each hole, by approximately 8% in the case of Hole 886Bto 10% for the top 10 m and 40% below 10 m in the case of Hole 885A.No stretching was done in Hole 886C for the depth interval studied.The use of a composite depth scale, therefore, may increase the LSRand would therefore lead to exaggerated MARs. The eolian record forSites 885/886 has been assembled from segments of the three holes:between 0 and 10.25 mcd in samples from Hole 885A, from 10.25 to60 mcd in samples from Hole 886B, and from 60 mcd to basement insamples from Hole 886C. This composite record ensures that the errorin the LSR caused by stretching or compression is minimal and negli-gible compared with the uncertainties in the time scale.

Age Model

The time scale adopted by the Leg 145 scientific party was con-structed by Cande and Kent (1992). The age model (Fig. 2) for theupper 52 mcd is based on the magnetic reversal stratigraphy (Rea,Basov, Janecek, Palmer-Julson, et al., 1993) and radiolarian stratig-raphy (Morley and Nigrini, this volume). In general, radiolarian eventssupport the magnetic reversal stratigraphy (Fig. 2). The age modelbased on these two stratigraphies is reliable to 8.5 Ma.

Below 53 mcd, the sediment column is devoid of identifiablemicrofossils except for occasional fish remains. As a consequence,the sedimentation rate drops to a level too low for reliable magneto-stratigraphy. The age of the oldest sediment is constrained by the ageof the basement, which is 80 ± 1 Ma (Keller and Duncan, this vol-ume). The Cretaceous/Tertiary (K/T) stratum was placed in Core 145-886C-8H between 130 and 145 cm, which corresponds to 63.25-63.4mcd (Kyte and Zhou, this volume). A time resolution of three strata,which are 56.5 and 15 m.y. apart, respectively, inhibits the study of anyclimatic or geologic signals for this period. To improve the time reso-lution, the Sr-isotope stratigraphy determined from ichthyoliths wasused as an alternative dating method (Ingram, this volume). All strati-graphic data considered for the age model are presented in Table 2.

Sr Isotopes and Fish Teeth: A Tartar RemovalExperiment

The Sr-isotope seawater curve recorded by ichthyoliths promises toprovide a useful relative dating method for red-clay sites, where datingtraditionally has been difficult. Previous work on fish teeth showedthat, although they can retain 87Sr/86Sr signatures that are close to theprimary marine signal (Staudigel et al., 1985), several samples did infact yield 87Sr/86Sr ratios that were significantly different from whatwould be expected from their stratigraphic ages. We picked fish teethfrom eight samples from Hole 886C for Sr isotopic analysis. The maingoal of this pilot study was to determine whether the main source oferror in ichthyolith analyses resides in the Fe-Mn oxide coatings com-monly found on fish teeth, in the incomplete cleaning of samples, or inthe preservation of the fish teeth themselves.

Fish teeth handpicked from sieved sediment samples were washedwith distilled water. To remove any transition-metal oxide coatings,all samples were subjected to the reductive dissolution techniquedescribed by Mehra and Jackson (1960) and Rea and Janecek (1981).Two mL of 0.3 M sodium citrate and 0.25 mL of 1.0 M sodiumbicarbonate were added to each beaker and heated to near-boiling.Then, approximately 0.05 g of sodium dithionite was added and thecapped Teflon perfluoralkoxy (PFA) beakers were placed in an ultra-sonic bath for 30 min. Because of the very small sample size, just oneapplication of this treatment appeared to remove all visible Fe-oxidecoatings. Before this treatment, samples from greater depths (Table 3)appeared under a binocular microscope to be heavily coated with Feoxides and to have their hollow cores also filled with oxides. After the

reductive dissolution, all fish teeth except for two exceptionally largespecimens (~l mm in length) became translucent such that it wasdifficult to see them against their semitranslucent Teflon background.No sign of oxide staining or residual clay minerals was present oneither the outside or inside of any tooth. The two large teeth, one ofwhich had been bored and appeared to be (bio?)corroded (Table 3),were too large to be translucent; nevertheless they showed no sign ofoxide staining on the outside surfaces. Because of the translucence ofthe teeth, it was necessary to use a pipette under the binocular micro-scope to avoid losing the fish teeth while decanting the reductivesolution. The samples were then rinsed twice using 7 mL of ultrapurewater and placed in the ultrasonic bath for 30 minutes. This rinsingwas intended to remove as much as possible of the Sr associated withboth the Fe oxide coatings and with the reagents used for the reductivedissolution. The fish teeth were then transferred to fresh acid-cleanedTeflon beakers, dissolved in 0.2 mL 3 M ultrapure nitric acid, andloaded onto SrSpec columns with a resin bed volume of 0.07 mL.Major elements were eluted with 1 mL 3 M nitric acid, and thepurified Sr was collected in 1 mL of water. The Sr was loaded onto Resingle filaments with a TaCl5 solution and 5% phosphoric acid andanalyzed on a VG Sector multicollector thermal ionization massspectrometer in multidynamic analysis mode. Samples were normal-ized to 86Sr/88Sr = 0.1194; total procedural blanks were < 40 pg. Thesample details and Sr isotopic results are presented in Table 3.

It seems possible that the somewhat scattered results of Staudigelet al. (1985) are caused by the variable inclusion of contaminant Srassociated with the Fe-Mn oxide coatings. Our results support thelikelihood that fish teeth retain a primary marine 87Sr/86Sr signature.However, despite this important result, the data presented in Table 3should still be viewed with some caution. For example, the Ir anomalywas located about 30 cm above interval 145-886C-8H-2, 10-15 cm(Kyte, this volume), thus dating this sample as older than the K/Tboundary. However, the 87Sr/86Sr ratio of the fish teeth from this levelwould indicate an age of approximately 33 Ma, based on a comparisonwith the seawater Sr-isotope record. It would require a lowering of themeasured ratio by roughly 0.000080 to be consistent with a latestCretaceous age. In addition, a sample taken from interval 145-886C-7H-6, 10-15 cm, and analyzed by Ingram (this volume) has yielded a87Sr/86Sr ratio 0.000080 higher than the ratio measured in this work.Fish teeth from this level do not have visible coatings; our cleaningprocedure, therefore, is less likely to have removed any contaminatingSr associated with any oxide phases. The fact that intervals 145-886C-8H-2,10-15 cm, and -7H-6,10-15 cm yielded ratios that appear to betoo high may indicate that there may be some contamination associatedwith a residual amount of the reductive dissolution reagents. Becausethe fish teeth were transferred to fresh beakers, this potential contami-nation, which was not removed by the double water rinses, may beeither associated with material on the fish tooth surfaces or with ma-terial left in the tiny conical cavities of the fish teeth. Any future workon fish teeth should include more rigorous rinsing, perhaps with a pureammonium chloride solution or acetic acid (cf. Bertram et al., 1992).

Backtrack and Paleolatitude (Paleoposition)

Because wind patterns may change in time and space, it is funda-mental to the interpretation of the eolian signal to know the paleo-position of Sites 885/886. The backtrack path (Fig. 3) was drawn afterthe model proposed by van Andel et al. (1975) and modified by Prince(1978). The same model was used by Leinen and Heath (1981) forpiston Core LL44-GPC-3.

RESULTS

Eolian Abundance

The eolian dust record shows very good agreement among thedifferent holes (Fig. 4) and presents an independent test for the com-posite depth scale (Dickens et al., this volume).

EOLIAN AND SILICA DEPOSITION

> i u B °r rT

20

30

40 60Age (m.y.)

80

50

60

70

80

* hiatus

hiatus?

I i I2 4 6 8LSR (m/m.y.)

10

Figure 2. A. Age-depth model for Sites 885/886 based on magnetic reversalstratigraphy (Rea, Basov, et al., 1993), radiolarian stratigraphy (Morley andNigrini, this volume), Sr-isotope stratigraphy (Ingram, this volume; this paper),Ir anomaly (Kyte and Zhou, this volume), and Ar/Ar dating (Keller andDuncan, this volume). Open circles represent paleomagnetic reversals; dia-monds represent ichthyoliths (fish teeth), the open square represents the Iranomaly that indicates the Cretaceous/Tertiary boundary; and the closed squarerepresents basement. Solid thick lines represent the depth range of radiolarianevents. Also shown are lithologic units from Rea, Basov, Janecek, Palmer-Julson, et al. (1993), as modified by Dickens et al. (this volume). B. Linearsedimentation rates calculated from the age-depth model.

Three major lithologic units are recognized in Sites 885/886 (Fig.5) (Rea, Basov, Janecek, Palmer-Julson, et al., 1993). The boundariesof the units described here have been adjusted to the composite depthscale according to Dickens et al. (this volume). Unit I, between 0 and23.75 mcd, consists mainly of clay with diatoms; Unit II, between23.75 and 53 mcd, of diatom ooze and clayey diatom ooze; and UnitIII of clay and hematitic clay (Rea, Basov, Janecek, Palmer-Julson, etal., 1993). A reinterpretation of Unit III suggests subdivision at 62mcd into Subunit IIIA, which is predominantly clay, and Subunit IIIB,which consists mainly of distal hydrothermal Fe-Mn precipitates(Dickens et al., this volume). The abundance of extracted eolianmaterial in Unit I is 40%-55% (Fig. 5) in the top 18 mcd and de-creases gradually to 20% toward the bottom of this unit. A sharpplunge in the percentage of eolian material occurs at approximately16 mcd (Fig. 5). This anomalous interval is also present in the geo-chemical record (Dickens et al., this volume). Unit II is marked bytwo lithologies: diatom ooze above 48 mcd and clayey diatom oozebelow. Within the diatom ooze interval, there are two levels in eolianabundances: above 35 mcd eolian abundance is low (10% or less)whereas below 35 mcd, abundance varies from 10% to 20% (Fig. 5).In the clayey diatom ooze (between 48 and 55 mcd) the eolian com-ponent varies from 20% to 45% (Fig. 5). Subunit IIIA contains 25%to 40% dust, whereas the amount of extracted material decreases tonearly nil toward the basement in Subunit IIIB (Fig. 5).

Opal Abundance

As expected, the record of opal is the mirror image of the eolianrecord (Figs. 5 and 6). The amount of biogenic silica is roughly equalto the windblown sediment in the top 18m of the sediment column,


Table 1. Data from Sites 885/886.

Core, sectioninterval (cm)

145-885A-1H-1,30-351H-1, 55-601H-1, 105-1101H-1, 130-1351H-2, 30-351H-2, 55-601H-2, 105-1101H-3, 30-351H-3 , 55-601H-3, 105-1101H-3, 130-1352H-1,30-352H-1,55-602H-1, 105-1102H-1, 130-1352H-2, 30-352H-2, 53-582H-2, 105-1102H-2, 130-1352H-3, 30-352H-3, 55-602H-3, 105-1102H-3, 130-1352H-4, 30-352H-4, 105-1102H-4, 130-1352H-5, 30-352H-5, 55-602H-5, 105-1102H-5, 130-1352H-6, 30-352H-6, 55-602H-6, 105-1102H-6, 130-1353H-1,30-353H-1, 105-1103H-2, 30-353H-2, 105-1103H-3, 30-353H-3, 105-1103H-4, 30-353H-4, 105-1103H-5, 30-353H-5, 105-1103H-6, 30-353H-6, 105-1103H-1, 30-354H-1, 30-354H-1, 105-1104H-2, 30-354H-2, 105-1104H-3, 30-354H-3, 105-1104H-4, 30-354H-4, 105-1104H-5, 28-334H-5, 105-1104H-6, 30-354H-6, 105-1104H-1,30-355H-1,30-355H-1, 105-1105H-2, 30-355H-2, 105-1105H-3, 30-355H-3, 105-1105H-4, 30-355H-4, 105-1105H-5, 30-355H-5, 105-1105H-6, 30-355H-6, 105-1105H-1, 30-356H-1, 30-356H-1, 105-1106H-2, 30-356H-2, 105-1106H-3, 30-356H-3, 105-1106H-4, 30-356H-4, 105-1106H-5, 30-356H-5, 105-1106H-6, 30-356H-6, 105-1106H-1,30-35

Depth(mbsf)

0.300.551.051.301.802.052.553.303.554.054.304.905 . 1 5

5.655.906.406.637.157.407.908 .158.658.909.40

10.1510.4010.9011.1511.6511.9012.4012.6513.1513.4014.4015.1515.9016.6517.4018.1518.9019.6520.4021.1521.9022.6523.4023.9024.6525.4026.1526.9027.6528.4029.1529.8830.6531.6032.1532.9033.4034.1534.9035.6536.4037.1537.9038.6539.4040.1540.9041.6542.4042.9043.6544.4045.1545.9046.6547.4048.1548.9049.6550.4051.1551.78

Depth(mcd)

0.350.711.401.712.402.743.474.474.605.005.255.655.916.466.737.277.528.018.238.67

9.429.77

10.4311.7612.321.35

13.8514.7315.0715.7616.1016.7917.1120.0021.1222.6023.3524.1024.8525.6026.3527.1017.8528.6029.3530.1029.4530.2030.9531.7032.4033.0633.7134.3635.0035.8236.8737.4838.1739.2039.9540.7441.6942.7243.6644.5545.4446.3447.2348.1949.2150.1050.6051.4452.3853.1553.8254.5055.1755.6659.0462.4063.1569.7970.38

Age(m.y.)

0.060.110.220.270.380.440.550.710.740.810.870.971.011.101.161.281.331.431.481.571.621.731.811.962 .172.262.412.492.622.672.722.762.832.863.163.283.433.513.613.743.863.984.114.234.364.484.614.504.624.754.874.995.105.215.325.425.565.735.835.956.126.246.376.536.706.867.017.167.297.407.527.647.757.818.058.849.47

10.0210.5811.1321.3630.4064.1565.5477.8478.94

LSR(m/m.y.)

6.36.36.36.36.36.36.36.36.34.14.14.17.54.84.84.84.84.84.84.84.84.84.34.36.66.66.66.66.66.69.69.69.69.69.69.69.69.66.06.06.06.06.06.06.06.06.06.06.06.06.06.06.06.06.06.06.06.06.06.06.06.06.06.06.06.06.06.08.18.18.18.18.18.1

.2

.2

.2

.2

.2

.20.40.40.50.50.5().5

DBD(g/cm3)

0.470.470.460.460.450.440.450.480.490.500.500.510.510.500.490.470.470.470.490.510.520.510.490.450.420.420.440.440.430.420.390.380.370.370.360.370.410.410.360.330.320.310.300.290.300.320.370.390.300.310.340.380.400.390.390.420.430.390.420.520.560.430.390.370.380.380.350.370.450.490.480.460.430.410.390.420.440.450.490.570.580.490.440.450.450.42

Eolian(wt%)

45.647.951.052.448.152.348.936.938.950.552.554.050.849.445.647.040.445.545.040.649.850.140.448.040.147.041.331.443.238.514.722.9

24.222.419.518.913.210.010.0

8.69.48.05.25.33.53.34.24.24.85.74.6

18.012.68.7

18.516.212.09.7

17.220.523.212.117.114.110.19.7

11.214.425.135.030.928.127.134.645.750.844.546.742.446.037.630.622.5

6.14.9

Eolian MAR(mg/[cm2 k.y.])

13414114815013514513911111910310711119511810710791

10410599

1251218492

11013111992

123106568493857870755222201718149977

1079

1211432920474228255470602838322321255299

13611699901623272428291077511

Opal(wt%)

54.452.149.047.651.947.751.163.161.249.547.546.149.250.654.453.059.654.555.059.450.249.959.652.059.953.058.768.656.86 1 . 5

85.377.173.875.877.680.581.186.890.190.091.490.692.094.894.796.596.795.895.895.294.395.482.087.491.381.583.888.090.382.879.576.887.982.985.989.990.388.885.674.965.069.171.972.965.454.349.2

Opal MAR(mg/[cm2 k.y.])

1601531421371451321451891871019795

18912112812113412412814512512112499

165148169201162170323

261

270290319342195178178171166167169186216224170178191216196203216207216206229

270199205183197206193198311

258

30

27


Table 1 (continued).


145-886B-1H-1, 30-351H-1,55-601H-2, 30-352H-1, 30-352H-1 , 55-602H-1, 105-1102H-1, 130-1352H-2, 30-352H-2, 55-602H-2, 105-1102H-3, 30-352H-3, 55-602H-3, 105-1102H-3, 130-1352H-4, 30-352H-4, 55-602H-4, 105-1102H-4, 130-1352H-5, 30-352H-5, 55-602H-5, 105-1102H-5, 130-1352H-6, 30-352H-6, 55-602H-6, 105-1102H-7, 30-352H-7, 55-603H-1,30-353H-1,55-603H-1, 105-1103H-1, 130-1353H-2, 30-353H-2, 55-603H-2, 105-1103H-2, 130-1353H-3, 30-353H-3, 55-603H-3, 105-1103H-3, 130-1353H-4, 30-353H-4, 55-603H-4, 105-1103H-4, 130-1353H-5, 30-353H-5, 55-603H-5, 105-1103H-5, 130-1353H-6, 30-353H-6, 55-603H-6, 105-1103H-6, 130-1354H-1,30-354H-1,55-604H-1, 105-1104H-1, 130-1354H-2, 30-354H-2, 55-604H-2, 105-1104H-2, 130-1354H-3, 30-354H-3, 55-604H-3, 105-1104H-3, 130-1354H-4, 30-354H-4, 55-604H-4, 105-1104H-4, 130-1354H-5, 30-354H-5, 55-604H-5, 105-1104H-5, 130-1354H-6, 30-354H-6, 55-604H-6, 105-1105H-1,30-355H-1,54-595H-1, 105-1105H-1, 130-1355H-2, 30-355H-2, 54-595H-2, 105-1105H-2, 130-1355H-3, 30-355H-3, 54-595H-3, 105-1105H-3, 130-1355H-4, 30-35

Depth(mbsf)

0.300.551.502.102.352.853.103.603.854.355.105.355.856.106.606.857.357.608.108.358.859.109.609.85

10.3511.1011.3511.6011.8512.3512.6013.1013.3513.8514.1014.6014.8515.3515.6016.1016.3516.8517.1017.6017.8518.3518.6019.1019.3519.8520.1021.1021.3521.8522.1022.6022.8523.3523.6024.1024.3524.8525.1025.6025.8526.3526.6027.1027.3527.8528.1028.6028.8529.3530.6030.8431.3531.6032.1032.3432.8533.1033.6033.8434.3534.6035.10

Depth(mcd)

10.4010.6511.2711.6312.3312.6913.3913.7414.4514.7015.2015.4515.9516.2016.7016.9517.4517.7018.2018.4520.4020.6521.1521.4021.9022.6223.2723.6024.2524.5825.2425.5526.0526.3026.8027.0527.5527.8028.3028.5529.0529.3029.8030.3030.5431.0531.3031.8032.0432.5532.8033.3033.5434.0534.3034.80

Age(m.y.)

1.962.002.102.152.262.312.422.472.582.612.662.692.742.772.822.852.902.922.983.003.203.233.283.313.363.443.503.543.643.693.803.853.933.984.064.104.184.234.314.354.434.474.564.644.684.774.814.894.935.015.065.145.185.265.315.39

LSR(m/m.y.)

4.36.66.66.66.66.66.66.66.69.69.69.69.69.69.69.69.69.69.69.69.69.69.69.69.69.69.69.66.06.06.06.06.06.06.06.06.06.06.06.06.06.06.06.06.06.06.06.06.06.06.06.06.06.06.06.0

DBD(g/cm3)

0.480.480.510.530.540.520.500.470.450.450.470.480.490.490.500.500.510.520.520.530.540.550.560.570.560.530.520.520.510.490.480.450.430.450.460.480.490.490.480.460.450.430.420.410.400.410.410.420.430.430.430.420.420.420.420.410.410.390.370.340.330.320.320.330.330.330.320.320.310.310.310.320.320.310.260.260.260.270.290.300.340.360.400.420.430.440.44

Eolian(wt%)

45.846.443.545.751.550.749.950.646.043.446.745.744.340.545.044.953.448.247.848.650.148.847.248.052.451.145.946.744.341.836.041.939.242.643.544.037.240.836.540.540.533.134.015.115.723.839.532.025.326.825.817.219.918.311.723.119.411.914.07.57.46.38.38.57.06.45.64.14.42.93.75.25.03.73.92.54.96.85.4

12.96.1

14.014.912.810.611.39.6


81112126132140121130114121174137139596193

157130104110106708174479277445015151216171413118

57

10107648

11102412303632

30

Opal(wt%)

54.253.656.554.348.549.350.149.454.056.653.354.355.759.555.055.146.651.852.251.449.951.252.852.047.648.954.153.355.758.264.058.160.857.456.556.062.859.263.559.559.566.966.084.984.376.260.568.074.773.274.282.880.181.788.376.980.688.186.092.592.693.791.791.593.093.694.495.995.697.196.394.895.096.396.197.595.193.294.687.193.986.085.187.289.488.790.4


112174169171178204189199179255277269335327299240276307302305336324328353305319329309191183182179180184183183182179183182181182178152150151154168159192186204220234234

223




5H-4, 54-595H-4, 105-1105H-4, 130-1355H-5, 30-355H-5, 54-595H-5, 105-1105H-5, 130-1355H-6, 30-355H-6, 54-595H-6, 105-1105H-6, 130-1355H-7, 30-355H-7, 54-596H-1,30-356H-1,54-596H-1, 130-1356H-2, 30-356H-2, 54-596H-2, 105-1106H-2, 130-1356H-3, 30-356H-3, 54-596H-3, 105-1106H-3, 130-1356H-4, 30-356H-4, 54-596H-4, 105-1106H-4, 130-1356H-5, 30-356H-5, 54-596H-5, 105-1106H-5, 130-1356H-6, 30-356H-6, 54-596H-6, 105-1106H-6, 130-1356H-7, 30-356H-7, 55-607H-1,30-357H-1, 55-607H-1, 105-1107H-1, 130-1357H-2, 30-357H-2, 55-607H-2, 105-1107H-2, 130-1357H-3, 30-357H-3, 55-607H-3, 105-1107H-3, 130-1357H-4, 30-357H-4, 55-607H-4, 105-1107H-4, 130-1357H-5, 30-357H-5, 55-607H-5, 105-1107H-5, 130-1357H-6, 30-357H-6, 55-607H-6, 105-1107H-6, 135-1407H-7, 30-357H-7, 55-60

145-886C-7H-1,30-357H-1, 103-1087H-1, 130-1357H-2, 30-357H-2, 55-607H-2, 130-1357H-3, 30-357H-3, 55-607H-3, 105-1107H-3, 130-1357H-4, 30-357H-4, 55-607H-4, 105-1107H-4, 130-1357H-5, 30-357H-5, 55-607H-5, 105-1107H-5, 126-1317H-6, 30-357H-6, 55-607H-6, 105-1107H-6, 130-1357H-7, 30-35

Depth(mbsf)

35.3435.8536.1036.6036.8437.3537.4038.1038.3438.8539.1039.6039.8440.1040.3441.1041.6041.8442.3542.6043.1043.3443.8544.1044.6044.8445.3545.6046.1046.3446.8547.1047.7047.8448.3548.6049.1049.3549.6049.8550.3550.6051.1051.3551.8552.1052.6052.8553.3553.6054.1054.3554.8555.1055.6055.8556.3556.6057.1057.3557.8558.1558.6058.85

54.6055.3355.6056.1056.3557.1057.6057.8558.3558.6059.1059.3559.8560.1060.6060.8561.3561.5662.1062.3562.8563.1063.60

Depth(mcd)

35.0435.5535.8036.3036.5437.0537.1037.8038.0438.5538.8039.3039.5439.8040.0441.2541.7541.9942.5042.7543.2543.4944.0044.2544.7544.9945.5045.7546.2546.4947.0047.2547.8547.9948.5048.7549.2549.5050.8551.1951.8852.2252.8553.1053.6053.8554.3554.6055.1055.3555.5055.5755.9056.0956.6456.9657.5958.0658.6558.8659.2859.4359.6559.78

53.5653.9454.0854.3454.4754.8755.1555.2955.7556.0056.5056.7557.2557.5058.0058.2558.7558.9659.5059.7560.2560.5061.00

Age(m.y.)

5.435.515.555.645.685.765.775.895.936.016.056.146.186.226.266.466.546.586.676.716.796.836.926.967.047.087.177.217.287.317.377.407.477.497.557.597.657.687.847.898.428.709.229.439.84

10.0510.4610.6611.0811.2811.4011.4722.0022.5123.9924.8326.5227.7829.3529.9231.0331.4332.0332.37

9.8010.1210.2310.4510.5510.8911.1211.2411.6122.2723.6124.2825.6226.2827.6228.2929.6330.1931.6332.3033.6438.6845.47

LSR(m/m.y.)

6.06.06.06.06.06.06.06.06.06.06.06.06.06.06.06.06.06.06.06.06.06.06.06.06.06.06.06.08.18.18.18.18.18.18.18.18.18.18.18.1.21.21.21.21.21.21.21.21.21.21.21.20.40.40.40.40.40.40.40.40.40.40.40.4

1.21.21.21.21.21.21.21.21.20.40.40.40.40.40.40.40.40.40.40.40.40.10.1

DBD(g/cm3)

0.450.430.420.390.380.370.370.370.370.400.410.450.470.460.420.410.420.430.420.410.400.390.380.370.350.350.370.380.420.440.450.460.470.470.460.460.450.450.450.440.450.450.460.470.520.560.630.660.650.640.600.580.570.580.580.590.570.550.520.510.520.540.570.55

0.360.380.440.580.650.690.690.690.660.640.600.580.560.560.550.540.510.490.510.520.570.600.64

Eolian(wt%)

19.513.212.710.510.09.7

10.310.912.616.410.018.624.917.216.89.1

15.615.315.312.512.99.33.86.18.79.6

12.112.98.6

14.317.824.034.732.632.428.629.125.123.721.134.544.443.142.744.440.946.442.442.532.736.132.531.729.435.135.337.63 1 . 530.826.436.732.137.235.5

43.140.538.443.241.242.140.238.036.831.631.732.534.733.432.533.128.530.233.435.334.936.739.2


5334322523222324283925507048422239

39313122

91419

273029516689

13212412310710792

76192424242828353434252623

76,::

66

77

e7

191920303235343230

877777755

7722

Opal(wt%)

80.586.887.389.590.090.389.789.187.483.690.081.475.182.883.290.984.484.784.787.587.190.796.2

91.390.487.987.191.485.782.276.065.367.467.67 1 . 4

70.974.976.378.965.555.656.957.355.6


217225219211205201200198195200225221212229209222213217214218210215219209194

194202314307305284248257256268262274277284

3630323235




8H-1,30-358H-1,55-608H-1, 105-1108H-1, 130-1358H-2, 30-358H-2, 55-608H-2, 105-1108H-2, 130-1358H-3, 30-358H-3, 55-608H-3, 105-1108H-3, 130-1358H-4, 30-358H-4, 55-608H-4, 105-1108H-4, 130-1358H-5, 30-358H-5, 55-608H-5, 105-1108H-6, 30-35

Depth(mbsf)

64.1064.3564.8565.1065.6065.8566.3566.6067.1067.3567.8568.1068.6068.8569.3569.6070.1070.3570.8571.60

Depth(mcd)

62.2562.5063.0063.2563.7564.0064.5064.7565.2565.5066.0066.2566.7567.0067.5067.7568.2568.5069.0069.75

Age(m.y.)

63.8764.3365.2665.7266.6567.1168.0468.5069.4369.8970.8271.2972.2172.6873.6074.0774.9975.4676.3877.77

LSR(m/m.y.)

0.50.50.50.50.50.50.50.50.50.50.50.50.50.50.50.50.50.50.50.5

DBD(g/cm3)

0.590.560.530.530.520.510.510.510.520.520.510.500.490.480.480.480.470.470.460.45

Eolian(wt%)

26.825.526.525.228.726.319.421.116.513.89.27.37.26.87.77.87.79.7

3.0


8777

756442222222221

Opal(wt%)


Note: DBD = dry bulk density, LSR = linear sedimentation rate, and MAR = mass accumulation rate.

120°E 150° 180° 150° 120°W

55°N

45=

Figure 3. Present location of ODP Sites 885/886, DSDP Site 576, and pistonCore LL44-GPC3. Lines are pale-backtrack paths. Plate rotation model is fromvan Andel et al. (1975). K/T = Cretaceous/Tertiary boundary.

and increases to approximately 80% toward the bottom of Unit I (Fig.6). Opaline silica is the dominant component in Unit II, occupying atleast 80% of the sediment for most of the unit (Fig. 6). Below 46 mcd,opal becomes less important in the total sediment makeup (Fig. 6). Nomicrofossils suitable for biostratigraphy were found below 53 mcd(Rea, Basov, Janecek, Palmer-Julson, et al., 1993). Onboard measure-ments of DBD and porosity indicate an increase in DBD of 0.16-0.31g/cm3 and a decrease in porosity of 6-11% between Samples 145-885A-6H-3, 74 cm and -6H-4, 74 cm, between 145-886B-7H-2, 69cm and -7H-3, 69 cm, and between 886C-7H-1, 109 cm and -7H-2,69 cm (Rea, Basov, Janecek, Palmer-Julson, et al, 1993). Opalinesilica-bearing sediments are usually characterized by lower DBD andhigher porosity than opal-free sediments. Based on those two param-eters, the transition from fossil-bearing to barren sediments is brack-eted between 54 mcd and 54.5 mcd. A visual examination of smear-slides from samples in this interval shows the presence of some bio-genic opal debris in samples shallower than 54.1 mcd but none insamples below 54.3 mcd.

Mass Accumulation Rates: the Time Frame

The age model, based on the stratigraphic data (Table 2), is de-picted as an age-depth plot in Figure 2A. The plot shows steep slopesin Units I and II, indicating fast sedimentation rates (Fig. 2B). Unit Iextends back to approximately 3.55 Ma, whereas Unit II extends backto about 11 Ma. The LSRs between 0 and 2.6 Ma average 5 m/m.y.,

10 20 30 40Extracted component (wt%)

50 60

Figure 4. Abundance (in weight percent) of the extracted eolian component ofsediments at Sites 885/886. The record for Hole 885A is represented by opencircles connected by a solid line, the record for Hole 886B is represented bysolid circles connected by a long-dashed line, and the record for Hole 886C isrepresented by open squares connected by a short-dashed line. All sampleswere placed on a composite depth scale. Note excellent correspondence ofrecords from different holes.

and increase to approximately 6.5 m/m.y. from 2.6 to 7.25 Ma (Fig.2B). There is a distinct decrease in LSR toward the bottom of Unit II,equivalent to the time interval between 8.5 and 11 Ma (Fig. 2B). Abreak in the age-depth relationship at 55 mcd marks the boundarybetween Units II and III and may indicate a hiatus occurring betweenapproximately 11 and 20 Ma based on 87Sr/86Sr stratigraphy (Fig. 2A).A hiatus at this depth was suggested by Dickens et al. (this volume).Ichthyoliths allowed us to determine the age-depth relationship for

225


Table 2. Stratigraphic control data, Sites 885/886.

Magnetic reversal

Brunhes/MatuyamaTermination JaramilloOnset JaramilloTermination OlduvaiOnset OlduvaiMatuyama/GaussGauss/GilbertTermination C4n.lnOnset C4n.2nTermination C4An

Radiolarian event

LO S. acquiloniumLO S. umiversusLO L. heteroporosFO C. davisiana davisianaFO L. heteroporosT S. delmontensis-S. peregrinaFO S. acquiloniumLO L. nipponica magnacornuta

LO S. acquiloniumLO S. umiversusLO L. heteroporosFO C. davisiana davisianaFO L. heteroporosT S. delmontensis-S. peregrinaFO S. acquiloniumLO L nipponica magnacornuta

Ir anomaly

Ar/Ar dating

Paleomagnetostratigraphy

Core, section, interval (cm)

Biostratigraphj

145-885A-1H-1, 115 and -1H-2, 115145-885A-1H-1, 115 and -1H-2, 115145-885A-1H-1. 115 and -1H-2, 115145-885A-2H-5. 115 and -2H-6, 115145-885A-5H-2, 115 and -5H-3, 115145-885A-5H-5, 115 and -5H-6, 115145-885A-5H-6, 115 and -6H-1, 115145-885A-6H-1, 115 and -6H-2, 115

145-886C-1H-1, 114 and -1H-2, 114145-886C-1H-2, 114 and -1H-3, 114145-886C-1H-4, 114 and -2H-1, 114145-886C-3H-1, 114 and -3H-2, 114145-886C-5H-3, 98 and-6H-l, 114145-886C-6H-3, 112 and -6H-4, 114145-886C-6H-4, 114 and -6H-5, 114145-886C-6H-5, 114 and -6H-CC

Depth(mbsf)

1.15-2.651.15-2.651.15-2.65

11.75-13.2535.75-37.2540.25-41.7541.75^3.7543.75^5.25

1.14-2.642.64-4.145.64-7.94

17.44-18.9439.28^15.9448.92-50.4450.44-51.9451.94-54.3

Sr-isotope stratigraphy

145-885A-6H-1, 125-130145-885A-6H-2, 50-55145-885A-6H-4, 50-55145-885A-6H-4, 125-130145-885A-6H-5, 50-55145-885 A-7H-CC*

145-886B-7H-2, 47-52145-886B-7H-3, 135-140145-886B-7H-4, 47-52145-886B-7H-4, 125-130145-886B-7H-4, 135-140145-886B-7H-5, 120-125145-886B-7H-6, 140-145145-886B-7H-7, 47-52145-886B-7H-7, 64-69

145-886C-6H-4, 135-140145-886C-6H-7, 60-65145-886C-7H-2, 135-140145-886C-7H-3, 11-16145-886C-7H-3, 135-140145-886C-7H-4, 135-140145-886C-7H-5, 120-125145-886C-7H-6, 10-15145-886C-8H-1, 135-140145-886C-8H-2, 10-15145-886C-8H-4, 30-35145-886C-8H-4, 45-50145-886C-8H-4, 135-140145-886C-8H-5, 120-125145-886C-8H-6, 75-80

145-886C-8H-1.130 and-8H-1,145

Basement

43.8544.6047.6048.3549.1052.10

51.2753.6754.2755.0555.1756.5258.2258.7758.94

50.3054.4057.1557.4158.6560.1761.5261.9065.1565.4068.6068.7569.6071.0072.05

65.1-65.25

52.30

Depth(mcd)

4.885.716.209.55

10.5214.5823.7545.9851.2552.01

1.54-3.671.54-3.676.56-8.10

14.86-16.9141.83-43.7847.35-49.3449.34-51.5751.57-53.24

1.14-2.642.64-4.145.84-9.30

15.29-16.9937.9^4.63

47.51^49.0449.04-50.5450.54-52.90

51.6952.6455.2955.9059.6870.70

53.0255.3755.5556.0556.1457.8759.4659.7459.82

48.9053.0054.9055.0456.0557.5758.9259.3063.3063.5566.7566.9067.7569.1570.20

63.25-63.40

70.95

Age(m.y.)

0.7800.9841.0491.7571.9832.6003.5537.2457.8928.529

0.40.551.72.96.57.557.728.8

0.40.551.72.96.57.557.728.5

5.75.9

21.319.430.279.0

6.511.311.124.021.527.830.731.331.2

5.86.1

11.011.021.028.534.032.865.033.668.571.572.576.574.5

66

80

Source

1111111111

222222

2

2

2222

2

333333

33

333333

33343

343444334

5

6

Notes: mcd = meters composite depth. LO = last occurrence, FO = first occurrence, T = species transition. 1 = Rea, Basov, et al. (1993); 2 = Morley and Nigrini (this volume); 3 =Ingram (this volume); 4 = this paper; 5 = Kyte and Zhou (this volume); 6 = Keller and Duncan (this volume). * = this sample is listed as 145-885A-7H-CC. However, Core 7H hasno core catcher. We assume this sample is 145-885A-6H-CC.

the time interval between approximately 20 and 34 Ma, equivalent tothe depth interval between 56 to 60 mcd (Fig. 2A). The LSRs between-34 and 63 Ma, represented by 1.5 m of sediments and a 0.75-m coregap (Dickens et al., this volume), are low, and occurrences of hiatusesare likely (Fig. 2A). However, the possibility of resolving this part ofthe sediment record using the seawater Sr- isotope curve is smallbecause 87Sr/86Sr ratios do not vary much in this time interval. Thedifference in slope in the age-depth plot between Units I and II com-pared with Subunit IIIA attests to biogenous sedimentation as the

driving force in the rate of sedimentation (Fig 2A). In Subunit IIIB,however, hydrothermal sedimentation may be the controlling factor.Sedimentation rates between the K/T boundary and the basementaverage 0.5 m/m.y. An exponential increase in LSR toward the base-ment is predicted by the hydrothermal activity model for the first 15m.y. (Dickens and Owen, this volume). An exponential best fit curvethrough the 87Sr/86Sr ages in Core 886C-8H yields ages that are1.8-2.2 m.y. younger than those obtained by linear regression be-tween the K/T boundary and the basement. There is no significant dif-


Subunit NIBHydrothermal deposits

10 20 30 40 50Extracted component (wt%)

60

Figure 5. Record of eolian abundances at Sites 885/886 with lithostratigraphyon right-hand side. The eolian record has been assembled from data obtainedin the top 10.25 mcd in Hole 885A, between 10.25 and 60 mcd in Hole 886B,and between 60 mcd and basement (at 70.95 mcd) in Hole 886C. Lithologicunits are from Rea, Basov, Janecek, Palmer-Julson, et al. (1993), as modifiedby Dickens et al. (this volume).

ference in the eolian MAR. In view of the uncertainties of the 87Sr/86Srstratigraphy determined on ichthyoliths (see above) and the samplingresolution of the fish teeth, we prefer the linear interpolation approach.

Several unexpected values in the LSRs are emphasized in Figure2. Suspect high LSRs occur between 0.984 and 1.049 Ma, between2.6 and 3.553 Ma, and between 7.245 and 7.892 Ma. These values area consequence of closely spaced "age-picks." Although not necessar-ily wrong, these high LSRs lead to anomalously high MARs com-pared to MARs calculated from LSRs averaged over more widelyspaced "age-picks."

Eolian Mass Accumulation Rates

Eolian fluxes were low, that is less than 10 mg/(cm2 148 k.y.) formost of the history of the sites (Fig. 7). A slight increase in eolianMARs at the end of the Cretaceous is probably the result of LSRaveraging and not indicative of paleoclimate in the Late Cretaceousand Paleocene. Eocene sediments occur in negligible amounts. Duringthe Oligocene and earliest Miocene, eolian sediments were deposited,but fluxes remained low (10 mg/[cm2 148 k.y.]) (Fig. 7). The firsteolian deposition of note occurs at approximately 11 Ma (Figs. 7 and8). Eolian accumulation for most of the late Miocene fluctuates around30 mg/(cm2148 k.y.). An exception in this trend is the sudden spike ineolian MARs between 7.8 and 7.2 Ma (Fig. 8), a consequence in partof the presence of a large eolian component but probably caused moreso by elevated LSRs. Eolian fluxes are very low (less than 10 mg/[cm2

148 k.y.]) in the early Pliocene, at the high tide of the "Diatom Dump"(Fig. 8). At -3.5 Ma, fluxes increased rapidly to reach maxima inexcess of 120 mg/(cm2148 k.y.) between 2.6 and 2.0 Ma. Fluxes in theyounger sediments vary from -90 to 100 mg/(cm2 148 k.y.) in the earlyPleistocene and from -130-150 mg/(cm2 148 k.y.) for the last 1 m.y.

10 -

20 -

30

ë. 40

iΦQ

50

60

70 -

80

- Unit 1 " WC^7 Clay with diatoms # β

- Unit II; Diatom ooze

- Clayey diatom ooze ^ " * ^ .

. f *" Subunit III A- Clay

- Subunit III B" Hydrothermal deposits

Unit IVI Basalt

i i i i i i i i i i i i i i i i i i i

_

-

i i i i i i i i i"

40 50 60 70Opal (wt%)

80 90 100

Figure 6. Record of opal abundances at Sites 885/886. The opal record hasbeen assembled from data obtained in the top 10.25 mcd of Hole 885A, andbetween 10.25 and 55 mcd of Hole 886B. The sediment column is barren ofsiliceous microfossils below -54 mcd, (i.e., in Subunits IIIA and HB). Litho-logic units are from Rea, Basov, Janecek, Palmer-Julson, et al. (1993), asmodified by Dickens et al. (this volume).

50 100 150

Eolian MAR (mg/[cm2*ky])

200 2 4 6 8 10LSR (m/m.y.)

Figure 7. Mass accumulation rates (MAR) of eolian sediment at Sites 885/886during the past 80 m.y. Linear sedimentation rates (LSR) shown for reference.

227


Table 3. Fish teeth Sr-isotopic results.

Core, section,interval (cm)

Depth(mbsf)

Depth(mcd) Notes

Visibleoxides ± 2s

145-886C-6H-4, 100-1056H-7, 60-657H-3, 11-167H-6, 10-158H-2, 10-158H-4, 30-358H-4, 45-508H-6a, 75-808H-6b, 75-80

NBS 987(analyzed twice)

Long-termNBS 987 average

50.3054.4057.4161.9065.4068.6068.7572.0572.05

48.9053.0055.0459.3063.5566.7566.9070.2070.20

2 teeth8 teeth7 teeth7 teeth8 tiny teeth1 big tooth4 teeth1 big bored tooth9 tiny teeth

NoNoNoNoYesYesYesYesYes

0.708949 ± 450.708926 ± 240.708846 ± 130.707965 ± 170.707939+ 170.707749 ± 150.707698 ± 150.707617 ±200.707809 ± 17

0.710246 ± 17

0.710248 ±18

2 -

CD6 -

8 -

10 -

12 I I 1 1 1 1 1 • I 1 1 1 1 I 1 1 1 1 1

1 | 1 | 1 | | l | 1

• •

•(

•i

ll

LJ 1 1

1 1

1 1

1 1

1 1 1 1

1 1

1 1

1 1

50 100 150Eolian MAR (mg/[cm2*ky])

200 2 4 6 8LSR (m/m.y.)

10

Figure 8. MAR of eolian sediment at Sites 885/886 during the past 11 m.y.Eolian fluxes increased markedly in the late Pliocene, corresponding to theonset of Northern Hemisphere glaciation. Increased fluxes between 2.6 and3.5 Ma and between 7.2 and 7.8 Ma are probably artifacts of the linearsedimentation rate. LSR shown for reference.

Opal Mass Accumulation Rates

The oldest sediments with an identifiable siliceous microfossilassemblage are approximately 9 m.y. old (Joe Morley, pers. comm.,1994). Based on changes in DBD and porosity of the sediment, thevisual examination of smearslides (see above), and our age model,which is partly based on ichthyolith-ages, we determine the age of theoldest opal-bearing sediment between 10 and 10.5 Ma (Fig. 9). Opaldeposition remained low during the first 2 m.y but it was well under-way at 8 Ma. The abrupt rise in opal MAR at 8 Ma may be an artifactof the exceptional LSRs mentioned above (Fig. 9). The details in theopal record are LSR driven. The failure to distinguish the interval ofincreased silica deposition clearly between approximately 6 and 3Ma, as seen in all other Leg 145 sites, (especially the somewhatpuzzling low accumulation between 5 and 3.5 Ma) may be caused bythe choice of the "master section" for the composite depth for thisinterval. Dickens et al. (this volume) suggest that the composite depth

Opal MAR (mg/[cmz*ky])2 4 6 8LSR (m/m.y.)

Figure 9. MAR of opal at Sites 885/886 during the past 11 m.y. Opal fluxes dur-ing the Pliocene "silica dump" are 1.5 to 2 times higher than fluxes during thePleistocene. The height of the flux between 2.6 and 3.5 Ma and the rapid increasein opal flux at 7.8 Ma are artifacts of the LSR, shown for reference.

at about 30 mcd may be -1.5 m too short because of compressioncaused by drilling through soft diatom ooze. However, the overallpicture clearly shows 1.5-2 times higher opal fluxes during the lateMiocene and early Pliocene than in the period after 2.6-2 Ma. Theremay be a stepwise(?) increase in opal MAR at about 1 Ma from 120to 160 mg/(cm2 148 k.y.) in the late Pleistocene.

DISCUSSION

The record of eolian fluxes at Sites 885/886 at a location that is12°-14°N of DSDP Site 576 and piston Core LL44-GPC3 (Fig. 3)provides an excellent addition to the knowledge of paleoclimategathered from those well-studied records.

As in Sites 885/886, much of the time scale for Core LL44-GPC3has been derived based on different, uncommon tools, whose usehave lead to different interpretations. In presenting the depositionalhistory for this red clay core we have used the time scale published byJanecek and Rea (1983). The stratigraphy is based largely on fishteeth (Doyle and Riedel, 1979) along with magnetic reversal stratig-raphy down to the Maruyama/Gauss boundary (Prince et al., 1980).Leinen and her co-workers (including Rea et al., 1985; Doh et al.,1988; and Leinen, 1989) show a somewhat different stratigraphy, alsobased on ichthyoliths. This version has accumulation peaks in thelower and middle Miocene part of the section. Kyte et al. (1993) havegenerated a third age-model for this core based on the assumption thatcobalt accumulates at a constant rate in the sediments throughout theTertiary, and on the discovery of the Ir anomaly associated with theCretaceous/Tertiary boundary at a depth of 20.6 mbsf (Kyte andWasson, 1986). The presence of three age models in the literature forthe same core points out the need for a reliable stratigraphic tool withwhich to date the pelagic clays of the abyssal oceans.

All three sites have records which extend back into the Late Creta-ceous. During the Late Cretaceous and the Paleocene eolian MARs atDSDP Site 576 and in Core LL44-GPC3 were low (Fig. 10), corre-sponding to warm and wet climates (Janecek, 1985). Furthermore,


0 6 12

0 200 400 600Eolian MAR (mg/[cm2*k.y]) LSR (m/m.y) Eolian MAR (mg/[cmz*k.y]) LSR (m/m.y) Eolian MAR (mg/[cmz*ky]) LSR (m/m.y.)

Figure 10. A. MAR of eolian sediment at DSDP Site 576 (32°N, 164°E) during the past 75 m.y. (Janecek, 1985); B. MAR in piston Core LL44-GPC3 (30°N,158°W) during the past 70 m.y. (Janecek and Rea, 1983); C. MAR at Sites 885/886. LSR shown for reference.

during the middle and late Eocene, the records show a further decreasein eolian MARs (Fig. 10). This decrease was interpreted as the resultof a more humid climate in the eolian source region and/or the passageof those sites from one wind belt to another (Leinen and Heath, 1981;Janecek and Rea, 1983; Rea, 1994). Our results show no exception:accumulation during the Cretaceous is low, and (nearly) nonexistentduring the later part of the Paleocene and during the Eocene. BecauseODP Sites 885/886 are situated north of the other sites, and becausethe Pacific Plate moved northward (Fig. 3), the movement of Sites885/886 from one wind belt to another should have occurred earlier.The record at Sites 885/886 does not provide evidence for this event.Low accumulation rates at DSDP Site 576 (Janecek, 1985) during theOligocene contrast with our results. Higher eolian fluxes during thetime interval between -20 and 34 Ma suggest drier conditions in thesource area. The onset of this interval may be coincident with theappearance of ice-rafted debris in the Southern Ocean at about 34 Maand glaciological evidence for ice cover on Antarctica (Crowley andNorth, 1991). The age resolution provided by the fish teeth does notallow precise determination of the onset of this interval. The beginningof the Neogene is characterized by a doubling of the eolian accumula-tion (from very low to low) in Core LL44-GPC3 (Janecek and Rea,1985) and at DSDP Site 576. This increase is thought to reflect theinitiation of deposition from the westerlies at those sites as they movedunder its influence (Janecek and Rea, 1985). If a similar increase influx is present at Sites 885/886, it remains unresolved within theresolution of the Sr-isotope stratigraphy.

Eolian accumulation increases at 11 Ma, shortly before sedimentsbegin to contain microfossils. Accumulation of the biogenic silicaincreases rapidly after 8 Ma, which would be over 1 m.y. earlier thanat the other Leg 145 sites, in which the kick off to the "Diatom Dump"occurs at 6-7 Ma (Rea and Snoeckx, this volume). An earlier onset ofincreased silica deposition may reflect the sensitivity of a marginalarea to changes in and expansion of the high-productivity zone of theNorth Pacific. It is clear that a silica shift did occur at Sites 885/886and although fluxes are smaller than at the other Leg 145 sites, they

signify at least a fivefold increase compared with older sediments and1.5-2 times the accumulation in younger sediments.

The flux of the windblown sediments increases from 3.5 Ma on toreach the highest eolian MARs during the late Pliocene and Pleisto-cene. A similar pattern was observed in Core LL44-GPC3 (Janecekand Rea, 1985) and at DSDP Site 576 (Janecek, 1985); it reflects thedrying of the Asian source region before and after the onset of North-ern Hemisphere glaciation at 2.6 Ma.

CONCLUSIONS

The sediment column of Sites 885/886 records the history ofeolian deposition for much of the Cenozoic and latest Late Creta-ceous. The record contains hiatuses between 11 and 20 Ma andprobably also in the Eocene and Paleocene.

Eolian fluxes were low in the Late Cretaceous and early Cenozoicas a consequence of the humid conditions thought to have prevailedat that time.

The flux of windblown sediments during the Oligocene reflectsthe drier climate conditions in the source area. The increased aridityis coincident with the expansion(?) of Antarctic glaciation and ageneral cooling and drying of the Northern Hemisphere.

The "Diatom Dump," an interval of increased opal accumulation inthe late Miocene to middle Pliocene, extends areally to Sites 885/886.Although fluxes are smaller than at the other Leg 145 sites, they signifya two- to fivefold increase to fluxes before and after the event.

A fivefold increase in eolian MARs beginning at 3.5 Ma testifiesto the arid conditions that dominated continental climate at the onsetof Northern Hemisphere glaciation.

ACKNOWLEDGMENTS

We thank everyone on Leg 145 for the company and the learningexperience during the cruise. This manuscript was reviewed byWilliam Balsam and John King whose useful suggestions greatly


improved this manuscript. We also like to acknowledge the help ofJoe Morley with biostratigraphic data. We also thank Karen Boven,Angela Walker, and Pamela Warner for help in the lab. This researchwas supported by the U.S. Science Support Program of the JointOceanographic Institutions.

REFERENCES*

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Dole, P.S., and Riedel, W.R., 1979. Cretaceous to Neogene ichthyoliths in agiant piston core from the central North Pacific. Micropaleontology,25:337-364.

Hovan, S.A., in press. Late Cenozoic atmospheric circulation intensity andclimatic history recorded by eolian deposition in the eastern equatorialPacific Ocean, Leg 138. In Pisias, N.G., Mayer, L.A., Janecek, T.R.,Palmer-Julson, A., and van Andel, T.H. (Eds.), Proc. ODP, Sci. Results,138: College Station, TX (Ocean Drilling Program).

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Janecek, T.R., and Rea, D.K., 1983. Eolian deposition in the northeast PacificOcean: Cenozoic history of atmospheric circulation. Geol. Soc. Am. Bull,94:730-738.

Kyte, RT, Leinen, M., Heath, G.R., andZhou, L., 1993. Cenozoic sedimentationhistory of the central North Pacific: inferences from the elemental geochem-istry of Core LL44-GPC3. Geochim. Cosmochim. Acta, 57:1719-1740.

Kyte, F.T., and Wasson, J.T., 1986. Accretion rate of extraterrestrial matter:iridium deposited 33 to 67 million years ago. Science, 232:1225-1229.

Leinen, M., 1989. The pelagic clay province of the North Pacific Ocean. InWinterer, E.L., Hussong, D.M., and Decker, R.W. (Eds.), The Geology ofNorth America (Vol. N): The Eastern Pacific Ocean and Hawaii. Geol.Soc. Am., 323-335.

Leinen, M., and Heath, G.R., 1981. Sedimentary indicators of atmosphericcirculation in the Northern Hemisphere during the Cenozoic. Palaeo-geogr., Palaeoclimatol, PalaeoecoL, 36:1-21.

Mehra, O.P., and Jackson, M.L., 1960. Iron oxide removal from soils and claysby a dithionite-citrate system buffered with sodium bicarbonate. ClaysClay Miner., Proc. Conf, 7:317-327.

Nakai, S., Halliday, A.N., and Rea, D.K., 1993. Provenance of dust in thePacific Ocean. Earth Planet. Sci. Lett., 119:143-157.

Prince, R.A., 1978. Southward motion of the Hawaiian hotspot between 42and 25 MYBP. Geol. Soc. Am. Abstr. Progr, 10:474.

Prince, R.A., Heath G.R., and Kominz, K., 1980. Paleomagnetic studies of thecentral north Pacific sediment cores: stratigraphy, sedimentation rates, andthe origin of magnetic instability. Geol. Soc. Am. Bull. (Pt. 2), 91:1789-1835.

Prospero, J.M., 1981. Eolian transport to the world ocean. /« Emiliani, C. (Ed.),The Sea (Vol. 7): The Oceanic Lithosphere: New York (Wiley), 801-874.

Pye, K., 1989. Processes of fine particle formation, dust source regions, andclimatic changes. In Leinen, M., and Sarnthein, M. (Eds.), Paleoclimatol-ogy and Paleometeorology: Modern and Past Patterns of Global Atmo-spheric Transport: Boston (Kluwer Acad. Publ.), 3-30.

Rea, D.K., 1994. The paleoclimatic record provided by eolian deposition inthe deep sea—the geologic history of wind. Rev. Geophys., 32:159-195.

Rea, D.K., Basov, I.A., Janecek, T.R., Palmer-Julson, A., et al., 1993. Proc.ODP, Init. Repts., 145: College Station, TX (Ocean Drilling Program).

Rea, D.K., and Harrsch, E.C., 1981. Mass accumulation rates of the non-authigenic inorganic crystalline (eolian) component of deep sea sedimentsfrom Hess Rise, Deep Sea Drilling Program Sites 464, 465, and 466. InThiede, J., Vallier, T.L., et al., Init. Repts. DSDP, 62: Washington (U.S.Govt. Printing Office), 661-668.

Rea, D.K., and Janecek, T.R., 1981. Mass-accumulation rates of the non-authigenic inorganic crystalline (eolian) component of deep-sea sedimentsfrom the western mid-Pacific Mountains, Deep Sea Drilling Project Site463. In Thiede, J., Vallier, T.L., et al., Init. Repts. DSDP, 62: Washington(U.S. Govt. Printing Office), 653-659.

Rea, D.K., Leinen, M., and Janecek, T.R., 1985. A geological approach to thelong-term history of atmospheric circulation. Science, 227:721-725.

Staudigel, H., Dole, P., and Zindler, A., 1985. Sr and Nd isotope systematicsin fish teeth. Earth Planet. Sci. Lett., 76:45-56.

van Andel, T.H., Heath, G.R., and Moore, T C , Jr., 1975. Cenozoic history andpaleoceanography of the central equatorial Pacific Ocean: a regionalsynthesis of Deep Sea Drilling Project data. Mem.—Geol. Soc. Am., 143.

Abbreviations for names of organizations and publications in ODP reference lists followthe style given in Chemical Abstracts Service Source Index (published by AmericanChemical Society).

Date of initial receipt: 4 April 1994Date of acceptance: 19 September 1994Ms 145SR-123

230

Documents

14. EOLIAN AND SILICA DEPOSITION IN THE CENTRAL NORTH ...€¦ · Core LL44-GPC3 (30°N, 158°W) by Janecek and Rea (1983), and DSDP Site 464 (40°N, 174°E) by Rea and Harrsch (1981)