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26. MASS-ACCUMULATION RATES OF THE NON-AUTHIGENIC INORGANIC CRYSTALLINE(EOLIAN) COMPONENT OF DEEP-SEA SEDIMENTS FROM HESS RISE,

DEEP SEA DRILLING PROJECT SITES 464, 465, AND 4661

David K. Rea and Eileen C. Harrsch, Oceanography Program, Department of Atmospheric and Oceanic Science,The University of Michigan, Ann Arbor, Michigan

ABSTRACT

The mass-accumulation rate (MAR) of the non-authigenic, inorganic, crystalline component of deep-sea sedimentsfrom the Pacific aseismic rises apparently reflects influx of eolian sediment. The eolian sediment usually is dominatedby volcanic material, except during glacial times. Sediments from Hess Rise provide a discontinuous record of eolianMARs. During Albian to Cenomanian time, the influx of volcanic material was fairly high (0.35-0.6 g/cm2/103 yr),recording the latest stages of the Albian volcanism that formed Hess Rise. From the Campanian through the Paleocene,influx of eolian sediment was low, averaging 0.03 g/cm2/103 yr. None of the four Hess Rise drill sites show evidence ofthe Late Cretaceous volcanic episode recorded at many sites now in the equatorial to subtropical Pacific. Pliocene toPleistocene samples record a peak in volcanic influx about 4 to 5 m.y. ago, which has been well documented elsewhere.The several-fold increase in eolian accumulation rates elsewhere which are correlated with the onset of severe northern-hemisphere glaciation 2.5 m.y. ago is not obvious in the Hess Rise data.

INTRODUCTION

Background and ObjectivesDSDP Leg 62 was planned to investigate the paleo-

environment of the North Pacific Ocean. Hess Rise waschosen as the location for three drill sites, because itscrestal parts lie near or above the calcite compensationdepth, thus greatly increasing the chance of encounter-ing well-preserved sections of calcareous biogenic sedi-ment. It was hoped that sediments from Hess Rise andthe Mid-Pacific Mountains would provide the basis fora detailed reconstruction of the Pacific oceanic environ-ment from the present back to middle Cretaceous time.

The North Pacific aseismic rises (Hess, Shatsky, andthe plateau level of the Mid-Pacific Mountains) are alsoamong the best places for studying the history of eoliandeposition. These areas probably have always beenabove the region of nepheloid-layer transport of fine-grained sediments below about 4500 meters. Second,these sites are far from continental margins, and thusbeyond the realm of hemipelagic deposition. Further-more, the rises have been south of the polar front (sub-polar convergence) during Pleistocene nonglacial andglacial intervals (CLIMAP, 1976), and thus are notlikely to have been subject to deposition by ice-rafting.

If these three sediment sources can be discounted,then the most significant remaining non-authigenic,inorganic, crystalline materials are the dust grains car-ried by the winds. Eolian dust may come from distantcontinents or local volcanoes, and the mass-accumula-tion rates presented below record changes in both sup-ply rate and transport efficiency; we are unable to deter-mine which factor is dominant from accumulation-ratedata alone. The mineralogy of the Hess Rise sediments

Initial Reports of the Deep Sea Drilling Project, Volume 62.

(Valuer and Jefferson, this volume) suggests that mostof the presumably eolian component is of volcanicorigin.

Geologic SettingHess Rise is a triangular elevation bounded by the

Mendocino Fracture Zone on the south, the EmperorTrough on the northeast, and the Emperor Seamountsto the west (Fig. 1). Site 464 is on the deeper, northernextension of the rise (39°51.6'N, 173°53.3'E; 4637 mdeep). Sites 465 (33°49.2'N, 178°55.1'E; 2161 m deep)and 466 (34°11.5'N, 179°15.3'E; 2665 m deep) are onthe higher, south-central portion of the rise near MellishBank.

The sections cored at these three sites are illustratedin Figure 2. At Site 464, Sub-unit IA is 18.8 meters ofclayey radiolarian ooze of Pleistocene to early Plioceneage; Sub-unit IB is 17.3 meters of lower Pliocene andupper Miocene siliceous clay that contains somevolcanic glass. Below, there is a rather abrupt change tothe underlying brown clays of Unit II. These clays are52.9 meters thick and range in age from early Mioceneto late Cretaceous (Doyle and Riedel, this volume). UnitIII consists of 218.6 meters of red-brown chert and nan-nofossil limestone of Albian and Cenomanian age.Because the recovery from this unit was essentially allchert pieces, there were no subsamples taken for ouranalysis. Basalt comprises the 0.16 meters of Unit IV.

Drilling in two holes at Site 465 encountered threelithologic units (Fig. 2). Unit I is 276 m of nannofossiland foraminifer-nannofossil ooze of Pleistocene toCenomanian age. Lacunae representing Pliocene toPaleocene time, late Campanian to Santonian time, andSantonian to early Cenomanian time occur within UnitI. The Paleocene to upper Campanian section is thebest-preserved record of the Cretaceous/Tertiary boun-dary recovered to date from the Pacific Ocean (Site 465

661

D. K. REA, E. C. HARRSCH

40°

10°

170° 180° 170° 160°

Figure 1. Track line of the Glomar Challenger during DSDP Leg 62, showing the location of the Hess Rise drill sites.

report, this volume). Below the oozes at Site 465 is 135.7meters of laminated limestone of early Cenomanian tolate Albian age which constitutes Unit II. Unit III is 64.3meters of trachyte.

Site 466 was drilled about 50 km northeast of 465,and a similar stratigraphic section was found (Fig. 2).

Sub-unit IA is 84 meters of Pleistocene to upper Eocenenannofossil ooze, Sub-unit IB is 161.5 meters of middleEocene to Turonian cherty nannofossil ooze; this sub-unit contains rounded pebbles of alkali basalt and ofhematite in the Campanian section (Site 466 report, thisvolume). Lacunae separate early Pliocene from late

662

MASS-ACCUMULATION RATES, SITES 464, 465, 466

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Eocene sediments and middle Eocene from earlyMaastrichtian sediments. Unit II is composed of 66.5meters of Turonian to upper Albian olive-gray nan-nofossil chalk and limestone, containing pyritic clay inthe upper part. Drilling at Site 466 did not penetratevolcanic basement.

METHODS

There are two parameters which describe the rate of deposition ofsediment: one, the linear sedimentation rate (LSR), or the length perunit time, undergoes an apparent reduction in value (van Andel et al.,1975) as the weight of the overlying sediment compacts the sedimentand reduces its porosity; the second parameter, a measure of the dry-mass flux called the mass-accumulation rate (MAR), eliminates thecompaction problem and allows comparison of samples from dif-ferent depths. To determine the MARs in units of g/cmVlO3 yr, wefirst determined the dry weight of the sediment per unit wet volume.The product of this value, the dry-bulk density, and the LSR yields themass-accumulation rate. To determine the inorganic MAR, we cal-culated the product of the weight percent of the non-authigenic, in-organic, crystalline component and the MAR of the sedimentarysection.

The non-authigenic, inorganic, crystalline component was isolatedby extracting the calcareous, opaline, and oxide-hydroxide portionsof the sediment. Details of the laboratory methods are given by Reaand Janecek (this volume).

Tables 1,2, and 3 are a summary of the dry-bulk densities, porosi-ties, MARs, LSRs, and inorganic MARs at each Hess Rise site.Figures 3 to 6 are plots of the inorganic MARs versus age.

Values that seemed to indicate an important change in MAR werererun, as were widely discrepant points. We achieved agreementwithin 5% of the originally determined value with each replicate, anindication of the precision of our procedures.

MASS-ACCUMULATION RATES

Site 464

The LSR determined for the Pliocene siliceous claysof Unit I is 11.3 m/m.y. (site 464 report, this volume).For our calculations, we have assumed that this rate isvalid down to the top of the brown clays of Unit II. Theage span of the brown clays is broad and gives a LSR ofless than 1 m/m.y. for Unit II. This section is almostcertainly characterized by discontinuous sedimentation(Doyle and Riedel, this volume), so we have not in-cluded it in our calculations of the inorganic MAR.

During the Pliocene, the MAR of the non-authigenic,inorganic, crystalline component of sediments at Site464 was moderately high, fluctuating between 0.2 and0.4 g/cm2/103 yr (Table 1; Figs. 3 and 6).

Site 465

At Site 465, we were able to calculate MARs of theeolian component for materials of Pleistocene toPliocene, Paleocene to Maastrichtian, and Cenomanianto Albian age (Table 2; Fig. 4). The first two cores atthis location were somewhat disturbed and gave evi-dence of Paleogene to Neogene reworking (Site 465report, this volume).

Linear sedimentation rates are unusually low for thethree samples of youngest nannofossil ooze, about 1m/m.y., and ages of these sediments are not well deter-mined. We suspect that a significant part of the Plio-Pleistocene section has been lost (or was never depos-ited). Sedimentation rates for the entire section aregiven in the Site 465 report (this volume).

The MARs of the eolian component of the Plio-Pleistocene sediments at Site 465 are artificially low(0.002 to 0.009 g/cm2/103 yr), roughly two orders ofmagnitude lower than values for sediments of the sameage at other Hess Rise sites (Table 2). The percentage ofthe eolian component at Site 465 (2-8%) is, however,similar to that at Site 466 (2-18%) (Tables 2 and 3).Near the Cretaceous/Tertiary boundary, the MAR ofthe eolian component is also very low, averaging 0.016and ranging up to 0.057 g/cm2/103 yr.

Samples from the organic-matter rich section of theCenomanian to Albian laminated limestone showmoderately high values for the accumulation of non-authigenic, inorganic, crystalline components, but someof these values may be in error. We were unable toremove all the organic material from our samples fromthese intervals, although treatment with H2O2 seemed toremove most of it. Furthermore, the laminated lime-stones apparently were emplaced by down-slope trans-port from Mellish Bank (Site 465 report, this volume),so the inorganic MARs from this unit may represent

Table 1. Data generated for the calculation of MAR values for the non-authigenic, inorganic, crystalline,eolian (NICE) component of sediments recovered at DSDP Site 464.

Sample(interval in cm)

464-2-2, 40-442-5, 41-453-2, 80-843-5, 80-844-2, 110-1144-4, 120-1225-2, 134-1385-4, 134-1386-2, 22-246-4, 22-247-2, 130-1327-5, 130-1328-2, 68-709-1, 82-849-6, 82-8410-1, 50-5210-3, 50-52

Sub-bottomDepth

(m)

5.419.92

15.3119.8125.1128.2134.8537.8543.2346.2353.8158.3162.6970.8378.3380.0183.01

Age(m.y.)

2.422.823.293.694.164.435.02

——

—

Porosity(%)

83.579.585.982.882.683.682.968.469.970.579.081.779.581.680.081.474.1

Dry-BulkDensity(g/cm3)

0.440.540.370.460.460.430.450.840.800.780.550.480.540.490.520.490.69

LSR(cm/103 yr)

1.131.131.131.131.131.131.13

—

—

MAR(g/cm2/103 yr)

0.4970.6100.4180.5200.5200.4860.508

——

—

NICE(%)

61.4833.0749.6559.5866.3347.5273.2769.2166.2173.1849.5949.9858.5764.6870.3655.6160.73

NICE MAR(g/cm2/lθ3 yr)

0.3050.2020.2080.3100.3450.2310.372

——

——

—

Note: Rates for sediments below Core 5, Section 2 (the brown clays) are uncertain.

664


0.2

MAR (g/cm"/10° yr)

Figure 3. Mass-accumulation rates of the non-authigenic, inorganic,crystalline, eolian (NICE) component of deep-sea sediments fromDSDP Site 464. See text.

more than just eolian materials. Data from the lowerpart of the laminated limestone of Unit II are not com-plicated by organic carbon and show high MARs for theinorganic component, averaging about 0.6 g/cm2/103

yr, and reaching a maximum of 1.14 g/cm2/103 yr just

above the basal trachyte (Table 2). These values aresimilar to or somewhat higher than those from mid-Cretaceous sediments at Site 463 and elsewhere in thePacific (Rea and Janecek, this volume.)

Site 466

At Site 466, the most-complete Plio-Pleistocene sec-tion of the three Leg 62 drill sites on Hess Rise wascored. Lower in the section, we were able to analyze afew samples from Eocene, Campanian, and Albianmaterials. Linear sedimentation rates are from the 466Site report (this volume).

The upper Cenozoic section (Table 3; Figs. 5 and 6)shows generally high, although fluctuating values forsediments about 3.8 to 5.8 m.y. old. The average MARfor the eolian component during this interval is 0.22g/cmVIO3 yr. The mid-Pliocene to recent average MARis 0.095 g/cm2/103 yr and shows relative peaks at 1.4and 0.2 m.y. The (reworked) Eocene materials in Cores8 through 10 display a low eolian component, averaging

Table 2. Data generated for the calculation of MAR values for the non-authigenic, inorganic, crystalline, eolian (NICE) component of sedimentsrecovered at DSDP Site 465.


465-1-1, 76-782-2, 64-662-5, 64-663-1, 60-623-3, 60-624-2, 48-504-4, 48-505-2, 95-975-5, 95-976-2, 28-306 A 28-3010-2, 30-3210-5, 30-32

465A-1-1, 132-1343-2, 18-203-5, 18-209-2, 47-499-5, 50-5210-2, 87-9111-2, 100-10411-4, 70-7412-2, 25-2915-2, 10-1215-4, 10-1216-2, 10-1216-4, 10-1217-2, 13-1518-1, 125-12719-2, 112-11420-2, 15-1721-4, 4-626-1, 65-6627-1, 78-7928-29-30-31-32-33-34-36-.37-.38-39-

, 19-20, 26-27, 36-38, 5-7, 59-60, 94-95, 94-95

I, 90-91>, 77-78, 75-76, 115-116

40-1, 45^t6

Sub-bottomDepth

(m)

0.773.157.65

11.1114.1121.9924.9931.9636.4640.7943.7978.8183.31

40.3359.6964.69

116.98121.51126.88136.51139.21145.26173.61176.61183.11186.11192.64201.76212.63221.16

33.55277.16286.79

29.70305.27314.87324.06336.10343.95353.45373.91383.28391.26401.16409.96

Age(m.y.)

1.02.54.0

55565757575858596566

5864.56669696969697070707070707070708098.599.5

100100100100100100101101101101102102

Porosity( * )

54.862.459.759.758.455.553.852.050.649.755.357.356.3

52.460.956.570.256.654.8a

52.2a

55.055.555.353.754.953.047.9a

57.2a

52.8a

54.854.914.613.713.911.419.450.830.930.723.442.441.9a

40.138.535.05

Dry-BulkDensity(g/cπw)

1.200.991.06

(

.07

.10

.18

.22

.27

.31

.33

.18

.13

.16

.26

.03

.15).79.10.203

.26a

.191.171.181.231.201.241.38a

1.13a

1.25a

1.201.192.262.292.282.352.141.301.831.842.031.531.54a

1.571.631.72

LSR(cm/lθ3 yr)

0.100.100.100.800.800.800.800.800.800.800.800.700.70

0.300.300.804.204.204.204.204.204.204.204.204.204.204.204.204.204.200.704.504.504.504.504.504.504.504.504.504.504.504.504.504.50

MAR(g/cm2/lθ3 yr)

0.1200.0990.1060.8560.8800.9440.9761.0161.0481.0640.9940.7910.812

0.3780.3090.9203.3184.6205.0405.2924.9984.9144.9565.1665.0405.2085.7964.7465.2505.0400.833

10.17010.30510.26010.5759.6305.8508.2358.2809.1356.8856.9307.0657.3357.740

NICE(%)

7.693.602.1092.880.280.311.390.430.580.7071.320.500.22

2.210.890.590.650.950.630.120.430.231.170.410.350.620.510.570.330.361.012.84b

2.64b

2.10b

14.90b

2.39b

6.63b

2.20b

2.19b

2.18b

7.7510.986.476.6314.69

NICEAfter Removal of

Organic Matter(%)

——

——

—————

—

—

———

0.753—

0.3330.026

——————

NICE MARAfter Removal ol

NICE MAR Organic Matter(g/cm2/lθ3 yr) (g/cm2/103 yr)

0.009 —0.004 —0.002 —0.025 —0.002 -0.003 —0.014 —0.004 —0.006 -0.007 —0.013 —0.004 —0.002 —

0.008 —0.003 —0.005 —0.020 —0.044 —O.O32a —0.006a —0.022 —0.011 —0.057 —0.021 —0.017 —0.032 —0.029a —0.027a —0.017a —0.018 —0.008 —0.289b 0.0760.272b —0.215b —1.576b —0.23 l b —O.388b —0.182b 0.0270.181b 0.00210.199b —0.534 —0.761a —0.457 —0.486 —1.137 —

a Samples that had undergone some drying (artifically lowered porosity values, and therefore larger MARs).b Samples with a high organic-matter content (artificially high NICE and NICE MAR values).

665


50-

>70

ε

90 -

110

-

1

s1/11

i

1 1 1

NICE component

-

-

i i i i i

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

MAR (g/cm2/103yr)


about 0.04 g/cm2/103 yr. A single high value (0.43g/cm2/103 yr) was obtained for upper Campaniansediments where the alkalic basalt pebbles were found(Core 12; Site 466 report, this volume). Upper Albiansediments, probably emplaced by turbidity currents,

have a moderate to high MAR for the non-authigenic,inorganic, crystalline component, averaging 0.36g/cm2/103 yr. These higher values are similar to Albianinorganic MARs from Site 463 (Rea and Janecek, thisvolume), and somewhat lower than those rates calcu-lated for Site 465.

DISCUSSION

The record of accumulation of eolian material onHess Rise is far from complete, a result of large gaps inthe depositional record and of very low recovery in thecherty Cretaceous sequences. Enough data do exist,however, to provide some insight into eolian MARs dur-ing Pleistocene to Pliocene time, Paleocene throughCampanian time, and early Cenomanian to late Albiantime.

Accumulation rates of the non-authigenic, inorganic,crystalline component of the deep-sea sediments onHess Rise were moderately high during the late Ceno-zoic. At Sites 464 and 466, the MARs of this componentare about 0.3 and 0.2 g/cm2/103 yr, respectively. Theeolian MARs at Site 465 are unusually low, because ofinaccuracies in dating the apparently incomplete Plio-Pleistocene section there (Site 465 report, this volume).

Details of the Plio-Pleistocene accumulation ratesfor the eolian component are shown in Figure 6. Datafrom Site 464, on northern Hess Rise, show fluctuating

Table 3. Data generated for the calculation of MAR values for the non-authigenic, inorganic, crystalline,eolian (NICE) component of sediments recovered at DSDP Site 466.


466-1-1, 31-341-2, 110-1121^, 40-431-5, 110-1122-1, 20-232-2, 65-672-4, 63-652-6, 65-673-2, 67-683-3, 67-683-5, 99-1014-1, 10-134-2, 58-605-1,20-235-2, 65-6754, 65-676-1, 20-236-2, 130-1326-4, 130-1326-6, 130-1327-1, 50-537-2, 50-527-3, 30-337-5, 50-528-2, 62-648-5, 62-649-2, 65-6794, 65-6710.CC12-1, 82-8413-2, 45-4713-5, 45-4715-2, 82-84154, 82-8416-2, 64-6617-1, 94-9629-1, 20-2230-1, 50-5234-1, 51-5235-1, 62-63

Sub-bottomDepth

(m)

0.322.614.917.118.21

10.1613.1416.1619.6821.1824.527.1129.0936.7138.6641.6646.2148.8151.8163.8156.0157.5158.8162.0167.1371.6376.6679.6684.194.3396.9699.96

124.33127.33133.65141.95255.21265.01293.52303.13

Age(m.y.)

_

0.30.60.91.01.01.41.72.03.03.23.33.43.83.94.04.34.54.74.95.05.05.05.0

3739.54046.549707070.270.9718181

100100.5101.5102

PorosityW

62.863.759.662.861.664.461.763.562.160.958.962.357.558.460.459.459.561.559.163.161.067.064.361.054.244.952.455.946.655.662.355.856.958.552.658.046.545.234.149.2

Dry-BulkDensity(g/cm3)

0.990.961.070.991.020.941.010.971.001.041.091.001.121.101.051.071.071.021.080.981.030.870.951.031.211.461.261.171.411.181.001.171.141.101.261.111.421.451.751.35

LSR(cm/lθ3 yr)

1.201.201.201.201.201.201.201.201.201.201.201.201.204.104.104.104.104.104.104.104.104.104.104.100.200.200.200.200.204.304.304.304.304.302.802.802.802.802.802.80

MAR(g/cm2/lθ3 yr)

1.1841.1521.2851.1881.2200.9411.2171.1641.2001.2481.3071.1991.3444.5184.3054.3874.4034.1824.4444.0184.2323.5673.8794.2230.2420.2920.2520.2340.2285.0744.3005.0314.9024.7303.5283.1083.9764.0604.9003.780

NICE(<Fo)

6.8218.075.735.626.496.238.15

11.679.536.078.162.297.893.644.724.035.224.384.238.524.984.544.849.525.706.042.835.14

23.108.481.100.320.641.131.331.687.918.747.829.99

NICE MAR(g/cm2/lθ3 yr)

0.0810.2080.0740.0670.0790.0590.0990.1360.1140.0760.1070.0270.1060.1640.2030.1770.2290.1830.1880.3420.2110.1620.1880.4020.0140.0180.0070.0120.0530.4300.0470.0160.0310.0530.0470.0520.3140.3550.3830.378

666


10

30

(m.y

.) o

Ag

e

7n/ U

90

110

-

IIIs

- i

-

-

NICE component

-

-

i i i i

0.2 0.3 0.4

MAR (g/cm2/103yr)

0.5


values from Pliocene sediments about 2.4 to 5.0 m.y.old. The MAR pattern at Site 464 apparently containsno unique information; it broadly conforms to thegeneral pattern of higher eolian MARs 4 to 5 m.y. ago,and relatively lower values about 3 m.y. ago, that can beseen in the data from Site 466 (Fig. 6) and from Site 463(Rea and Janecek, this volume).

Site 466 contains the most complete record of thethree Hess Rise Plio-Pleistocene sections drilled duringLeg 62. We sampled this section in greater detail thanthe others, hoping to learn more about the periodicvolcanism and the climatic changes of the late Cenozoic.Smear slides of these sediments show as much as 5%volcanic glass, and traces of clay minerals and zeolites.Between about 3.8 and 5.4 m.y. ago, the accumulationof eolian material averaged about 0.22 g/m2/103 yr.More recently at Site 466, the average has been about0.1 g/m2/103 yr (Table 3; Fig. 6). The accumulationmaximum of the eolian component between roughly 4and 5 m.y. ago also occurs at Site 463 (Rea and Janecek,this volume), and ash layers of this age are commonthroughout the world's oceans (Kennett and Thunell,1977). Both circum-Pacific (Kennett et al., 1977) andmid-plate (Rea and Scheidegger, 1979) volcanic activitywere relatively high during the early Pliocene, and this

ai 5

<

DSDP Site 464NICE Component

DSDP Site 466NICE component

0.2 0.3 0.4 0.1 0.2

MAR (g/cm2 /103 yr)

0.3 0.4 0.5

Figure 6. Details of Plio-Pleistocene eolian MARs from DSDP Sites464 and 466. See text.

appears to be the direct cause of the high MARs 4 to 5m.y. ago at Site 466.

Between 3.8 m.y. ago and the present, the eolianMAR at Site 466 has been about 0.1 g/cm2/103 yr anddisplays relative lows at 3 and 1 m.y. ago, with highervalues 1.5 to 2 and about 0.2 m.y. ago (Fig. 6). This pat-tern is different from that calculated for the other twolocations in the North Pacific where appropriate dataexist. About 2200 km east of Site 466, and at a similarlatitude, a large-diameter piston core of red clay (LL44-GPC3; 30.3 °N, 157.8°W) reveals a similar MAR for theeolian component, but shows a pattern of roughly five-fold increase in that MAR value since the late Miocene(Leinen et al., 1979). At Site 463, 1400 km south of Site466, there has also been a five-fold increase in the eolianMAR since late Miocene time, although the actualvalues of inorganic MAR are almost an order ofmagnitude less than at Site 466 (Rea and Janecek, thisvolume). The absence of the upper Miocene at Site 466precludes an evaluation of this anticipated relative in-crease in eolian MARs.

During the Maastrichtian to early Campanian, themass-accumulation rate of non-authigenic, inorganic,crystalline material on Hess Rise was very low; MARsaveraged less than 0.02 and about 0.04 g/cm2/103 yr forSites 465 and 466, respectively. Smear-slide and carbon-ate-percent data from Site 310, on central Hess Rise(Larson, Moberly, et al., 1975), also suggest a very lowaccumulation rate of eolian material during this sameperiod.

This low MAR for the eolian component on HessRise is in marked contrast to MAR data for the sametime from drill sites to the south. At Site 463, in thewestern Mid-Pacific Mountains, the eolian MAR forlower Maestrichtian materials is about 0.2 g/cm2/103 yr(Rea and Janecek, this volume). In the Nauru Basin, atSite 462, it is even higher, averaging 0.6 g/cm2/103 yrfor the interval 69 to 77 m.y. ago (Rea and Thiede, inpress). Many other sites in the central Pacific containmore-qualitative data recording an increase in volcanicactivity during Campanian to Maastrichtian time (Site61, Leg 7, Winterer, Riedel, et al., 1971; Sites 196, 198,and 199, Leg 20, Heezen, MacGregor, et al., 1973; Site313, Leg 32, Larson, Moberly, et al., 1975; Sites 315and 316, Leg 33, Schlanger, Jackson, et al., 1976).There seems little doubt that many of the volcanic

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edifices now lying in the equatorial and subtropicalPacific were created during this period of eruptive ac-tivity (c/. Winterer, 1976).

Cores from Sites 465 and 466 show large MARs ofthe non-authigenic, inorganic, crystalline component inthe lower Cenomanian and upper Albian laminatedlimestone and chalk turbidites (Figs. 4 and 5). Some ofthe MAR values from the Cenomanian samples of Site465 are large because of their high organic-matter con-tent, but the underlying Albian materials are notorganic-matter-rich and display an average inorganicMAR of about 0.6 g/cm2/103 yr (Table 2). At Site 466,this value is 0.35 g/cm2/103 yr (Table 3).

Hess Rise basement is Albian, as indicated by drillingresults at Site 464 and 465 (Site 464 and Site 465 reports,this volume), so indications of Albian volcanism are tobe expected. Mellish Bank, the shallowest, southernportion of Hess Rise is underlain by trachyte, a late-stage differentiate of alkalic basalt, suggesting thatvolcanism may have continued in this region longer thanit did farther north.

Mass-accumulation rates of this component averagedabout 0.27 g/cm2/103 yr at Site 463 in the Mid-PacificMountains (Rea and Janecek, this volume) during Al-bian time. Data from the Line Islands (Winterer, Ew-ing, et al., 1973) and the Nauru Basin (Rea and Thiede,in press) also reflect a moderate amount of mid-Cretaceous volcanism. Albian to Cenomanian volcan-ism apparently was a common phenomenon in the cen-tral Pacific (Winterer, 1976).

SUMMARY

Samples from three drill sites on Hess Rise weretreated chemically to remove the calcareous, opaline,and authigenic fractions of the sediment. The remainingfraction is presumed to represent the influx of eolianmaterial to Hess Rise, except for the mid-Cretaceouslimestone turbidites. Variations in the mass-accumula-tion rate of this component appear to reflect fluctu-ations in the influx of volcanogenic material, exceptperhaps during the late Cenozoic glacial ages. As aresult of long hiatuses and very low recovery in somesections, only a discontinuous record of eolian influxcan be constructed (Figs. 3, 4, and 5).

Ash layers just above the trachyte basement at Site465 record the waning of Albian volcanism that con-structed Hess Rise; MARs of the inorganic componentfor the late Albian and early Cenomanian may reflectbottom transport of material as well as eolian influx andare reasonably high—0.6 g/cmVlO3 yr at Site 465, and0.35 g/cmVl03 yr at Site 466, somewhat farther fromthe possible source region on Mellish Bank. This mid-Cretaceous volcanism on Hess Rise appears to be partof an episode of volcanic activity that spanned much ofthe west-central Pacific.

Mass-accumulation rates of the eolian componentwere very low from the Paleocene through the Campa-nian, averaging roughly 0.03 g/cm2/103 yr at Sites 465and 466. Low MARs for the Paleocene volcanic compo-nent have been found in sediments at Site 462 in theNauru Basin (0.06 g/cm2/103 yr; Rea and Thiede, in

press), but many DSDP sites in the central Pacificrecord a significant influx of volcanic materials duringMaastrichtian to Campanian time. None of the HessRise sites contain evidence for a late Cretaceous vol-canic maximum, indicating that this event was confinedto more southerly locations.

Pliocene and Pleistocene accumulation of eolianmaterials was moderately high at two of the three HessRise sites (0.3 and 0.2 g/cmVl03 yr at Sites 464 and465), but only 0.005 g/cmVl03 yr at Site 465. Thegeneral pattern of Plio-Pleistocene eolian deposition onHess Rise (Fig. 6) reveals a maximum MAR 4 to 5 m.y.ago, a low centered about 3 m.y. ago, and slightlyhigher but fluctuating values since then. The peak at 4to 5 m.y. ago is thought to reflect the Pacific-widevolcanic maximum that occurred in early Pliocene time(Kennett et al., 1977; Rea and Scheidegger, 1979). Datafrom other locations in the Pacific show a several-foldincrease in the eolian MAR during the last 2 or 3 m.y.,associated with the onset of glaciation (Leinen et al.,1979; Rea and Janecek, this volume), but this MAR in-crease is not as clear-cut at Site 466. Perhaps other kindsof data from Site 466, such as the grain size and mine-ralogy of the eolian component, would give more ob-vious information on this topic.

ACKNOWLEDGMENTS

We would like to thank Tom Janecek for assistance with thelaboratory work. Margaret Leinen and Ted Moore reviewed themanuscript, and we appreciate their comments and suggestions.

Portions of the work presented here were supported by NSF GrantOCE-7825341.

REFERENCES

CLIMAP Project Members, 1976. The surface of the ice-age earth.Science, 191:1131-1137.

Heezen, B. C , MacGregor, I. D., et al., 1973. Init. Repts. DSDP, 20:Washington (U.S. Govt. Printing Office).

Kennett, J. P., and Thunell, R. C , 1977. On explosive Cenozoic vol-canism and climatic implications. Science, 196:1231-1234.

Kennett, J. P., McBirney, A. R., and Thunell, R. C , 1977. Episodesof Cenozoic volcanism in the circum-Pacific region. J. Volcanol.Geothermal Res., 2:145-163.

Larson, R. L., Moberly, R., et al., 1975. Init. Repts. DSDP, 32:Washington (U.S. Govt. Printing Office).

Leinen, M., Heath, G. R., and Rea, D. K., 1979. Paleo-eoliata:sedimentary indicators of Cenozoic atmospheric circulation in theNorthern Hemisphere. Geol. Soc. Am. Abs. Prog., 11:465.(Abstract)

Rea, D. K., and Scheidegger, K. F., 1979. Eastern Pacific spreadingrate fluctuation and its relation to Pacific area volcanic episodes./. Volcanol. Geothermal Res., 5:135-148.

Rea, D. K., and Thiede, J., in press. Mesozoic and Cenozoic massaccumulation rates of the major sediment components in theNauru Basin, western equatorial Pacific. In Larson, R. L., Schlan-ger, S.O., et al., Init. Repts. DSDP, 61: Washington (U.S. Govt.Printing Office).

Schlanger, S. O., Jackson, E. D., et al., 1976. Init. Repts. DSDP, 33:Washington (U.S. Govt. Printing Office).

van Andel, Tj. H., Heath, G. R., and Moore, T. C , Jr., 1975. Ceno-zoic History and Paleoceanography of the Central EquatorialPacific Ocean: Geol. Soc. Am. Mem., 143.

Winterer, E. L., 1976. Anomalies in the tectonic evolution of the Paci-fic. In Sutton, G. H., Manghnani, M. H., and Moberly, R.(Eds.), The Geophysics of the Pacific Ocean Basin and its Margin:Washington (Am. Geophys. Union), pp. 269-278.

Winterer, E. L., Ewing, J. I., et al., 1973. Init. Repts. DSDP, 17:Washington (U.S. Govt. Printing Office).

Winterer, E. L., Riedel, W. R., et al., 1971. Init. Repts. DSDP, 7:Washington (U.S. Govt. Printing Office).

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