Winterer, E.L., Sager, W.W., Firth, J.V., and Sinton, J.M. (Eds.), 1995Proceedings of the Ocean Drilling Program, Scientific Results, Vol. 143

26. PALEOLATITUDE INFERRED FROM CRETACEOUS SEDIMENTS,HOLE 865A, ALLISON GUYOT, MID-PACIFIC MOUNTAINS1

William W. Sager2 and John A. Tarduno3

ABSTRACT

We measured the Paleomagnetism of 53 limestone samples recovered from Hole 865A, atop Allison Guyot in the Mid-PacificMountains, to place constraints on the paleolatitude of the edifice near the time of its formation. Most samples were recoveredfrom the bottom of the hole, in a section of Albian (probable early Albian) clayey limestone deposited in a marshy, nearshoreenvironment and intruded by several basaltic sills while soft. Natural remanent magnetization (NRM) intensities displayed a largerange, varying byjnore than five orders of magnitude and generally decreasing upsection. The NRM intensities probably reflectthe concentration of volcanic grains, eroded from a nearby volcanic high and deposited in the sediments. Saturation of isothermalremanent magnetizations in low applied fields and moderate mean destructive field values are consistent with titanomagnetite asthe dominant magnetic grain type in these limestones. Nearly all samples showed stable behavior during alternating field (AF)demagnetization and gave apparently reliable characteristic remanence directions. A mean inclination of-26.8° (95% confidencelimits: -24.4°, -28.7°; k = 75; N = 51) implies a paleolatitude of 14.2° ± 1.3°S. This value is statistically indistinguishable fromthat inferred from the mid-Cretaceous Pacific apparent polar wander path (APWP), suggesting that the paleolatitude is reliable.

INTRODUCTION

The Pacific Plate is almost entirely covered by water; thus, track-ing its past motions and paleolatitudes is challenging because orientedpaleomagnetic samples are difficult to recover from the deep sea.Samples of Cretaceous formations are especially hard to obtain, asthey are typically found deep in the ocean, often covered by youngersediments. Thus, when mid-Cretaceous sediments and basalts werecored from Allison Guyot during Ocean Drilling Program (ODP) Leg143, it allowed us the opportunity to add to the meager subset ofPacific paleomagnetic data of that age.

Hole 865A (18.44°N, 180.44°E) was drilled into the center ofAllison Guyot, located in the west-central Pacific Ocean within theMid-Pacific Mountains province (Sager, Winterer, Firth, et al., 1993).The hole penetrated approximately 871 m into the summit, passingthrough 136 m of Cenozoic pelagic sediments; 702 m of Cretaceouslagoonal-facies, shallow-water platform limestones; and 33 m of inter-fingered platform limestones and basalt sills. Geochemical similaritiessuggest that the sills were intruded as a single event. Furthermore, thedisturbance of surrounding sediments implies that they were uncon-solidated during the intrusion; therefore, the sills are apparently con-temporaneous with the host sediments (Sager, Winterer, Firth, etal., 1993).

Biostratigraphy (Vanneau and Sliter, this volume) and Sr-isotopedata (Jenkyns et al., this volume) suggest that the shallow-waterlimestone section spans much of the Albian stage (97-112 Ma, by thetime scale of Harland et al., 1990). The base of the limestones isprobably lower Albian, whereas the top of the limestones is upperAlbian (Vanneau and Sliter, this volume). These ages agree with40Ar_39Ar racü0metric dates from the drilled basalts (104.8 ± 0.8,111.2 ± 1.2 Ma; Pringle, this volume), as well as basalts dredged fromthe guyot flanks (101.2 ± 0.8 Ma; Winterer et al., 1993).

The Cretaceous shallow-water lithologic succession of Hole 865 Aseems to show the evolution of the edifice from a volcanic island to

Winterer, E.L., Sager, W.W., Firth, J.V., and Sinton, J.M. (Eds.), 1995. Proc. ODP,Sci. Results, 143: College Station, TX (Ocean Drilling Program).

Departments of Oceanography and Geophysics, Texas A&M University, CollegeStation, TX 77843, U.S.A.

Department of Earth and Environmental Sciences, University of Rochester, Roch-ester, NY 14627, U.S.A.

an open-marine atoll (Sager, Winterer, Firth, et al., 1993). The deepest133 m of Cretaceous limestones contains abundant organic matterand appears to have been deposited along the shoreline in the re-stricted, stagnant waters of a swamp. Pyrite is present, implyingreduction, but pervasive bioturbation throughout most of this sectionindicates that the waters contained sufficient oxygen for shallowinfaunal activity. Abundant clay and volcanic grains that occur inthese limestones are probably the product of erosion from nearbyvolcanic outcrops. Progressing upward through the section, the Cre-taceous limestones become progressively "cleaner," with less clayand organic matter. Evidently, the shoreline retreated from the site andthe volcanic outcrops were buried as the edifice evolved into an atollor shallow-water carbonate platform.

METHODS

Fifty-three paleomagnetic samples were taken from Hole 865Acores as 10 to 12 cm3 minicores, 2.5 cm in diameter and typically 2.0to 2.5 cm in length. All but two are from 748 to 866 mbsf (Table 1),within the clay-rich limestones near the bottom of the hole. The mini-cores were drilled perpendicular to the split face of the core (a verticalplane) and were oriented with a mark to indicate the upward direction.

To obtain an indication of variations of magnetic grain concentra-tion, volume magnetic susceptibility was measured for each sampleusing a Bartington MS-2 susceptibility meter having a 36-mm sens-ing loop. This device has a sensitivity of I0"6 S1. Sample remanenceswere measured with a cryogenic magnetometer having an effectivesensitivity limit of approximately 0.005 mA/m. A subset of samplesfirst was treated to detailed, stepwise alternating field (AF) demagne-tization (16-18 steps) and then remagnetized with an isothermalremanent magnetization (IRM) in fields up to 1200 mT using a pulse-magnetizer. These pilot experiments suggested the efficacy of usingAF demagnetization on Hole 865A samples; thus, in the remainder,characteristic remanent magnetization (ChRM) directions were iso-lated using AF demagnetization, typically with 8 to 12 steps in fieldsup to 60 to 80 mT.

Orthogonal-vector and stereonet plots were made of vector end-points of all demagnetization steps of all samples. These plots allowedus to determine which steps defined a ChRM by univectorial decay.To calculate the ChRM direction, we used a linear least-squares linefit to the univectorial segment directions (Kirschvink, 1980), typi-cally with the solution anchored to the origin.

399

W.W. SAGER, J.A. TARDUNO

Table 1. Paleomagnetic data, Hole 865A limestone samples.

Core, section,interval (cm)

143-865A-34R-74R-81R-82R-;82R-;84R-84R-85R-85R-85R-;86R-86R-86R-:86R-:86R-:87R-87R-87R-87R-:88R-88R-88R-:89R-89R-89R-89R-

,37-39, 43^5,98-100

>, 7-9I, 22-24,61-63, 90-92,38-40, 65-67

>, 49-51,127-129, 143-145

., 77-79, 107-109

., 141-143, 40-42,44-46,83-85

.. 11-13,13-15,91-93

., 40-42. 17-19. 85-87, 111-113, 119-121

89R-2, 15-1789R-2. 96-9889R-2, 121-12389R-3, 11-1389R-3, 76-7889R-4, 16-1889R-4, 40-4289R-6, 36-3889R-6, 43-4590R-1,21-2390R-1,31-3390R-1,58-6090R-1,71-7390R-2, 13-1590R-2, 55-5690R-2, 115-11790R-3, 2-490R-3, 63-6591R-3, 78-8091R-4,4_691R-4, 35-3791R-5, 123-12592R-1,33-3592R-1,82-8492R-2, 2-494R-3, 10-1294R-3, 26-28

Depth(mbsf)

294.57680.13748.38758.12758.27777.11777.40786.58786.85787.92797.07797.23798.07798.37798.71805.80805.84806.23806.88815.23816.01816.95824.97825.65825.91825.99826.32827.12827.38827.66828.31829.07829.31831.69831.76832.01832.11832.38832.51833.07833.49834.09834.23834.84844.57845.33845.64847.89847.53848.02848.58865.97866.13

Inc(deg.)

30.4a

-37.1-26.6-18.1

Not stableNot stable-25.3

29.8a

-27.0-33.4-27.8-20.0-29.2-25.2-28.5-32.4-25.8-27.3-32.1-28.9-31.7-29.0-24.5-21.9-19.4-24.5-35.8-27.4-44.4-15.4-20.2-29.1-31.1-29.7-12.9-18.1-23.5-23.1-28.1-24.0-26.1-29.0-37.8-21.8-5.5

-22.8-29.1-30.0-27.6-36.4-28.1-21.7-19.9

MAD(deg.)

3.83.6

12.56.5

6.52.82.41.32.91.31.70.81.82.54.31.91.91.21.12.74.93.13.41.65.34.63.74.23.62.02.33.52.34.72.71.92.41.01.01.62.11.75.11.91.34.41.51.81.23.83.1

N

9546

497

1089977

I08787775699556575688b567917

10879

117

109

I096

AFsteps

10-7010-3030^55-20

7-1510-5010-4010-6020-6010-5010-6010-5020-6010-7015-6010-5015-7015-6010-4020-7015-4010-4015-6012-5020-5010-3015-5020-4010-5020-5010-4020-705-6025-7025-6025-7015-5020-8015-6025-6015-7015-5020-5010-7010-8030-7020-8025-8020-8020-7035-80

Jo

(mA/m)

0.0490.0830.1070.0950.1040.0180.0280.2940.2450.4150.2700.5670.6431.2010.6070.4250.2310.5020.4791.3060.5448.032

136.060145.840246.780178.640193.280136.790131.510441.120273.330174.380197.880

0.8440.7711.2791.5561.2480.6791.7081.4501.5872.0060.3815.6254.6962.3180.9720.6057.3983.312

15.3407.205

J/Jo

0.760.390.180.39

0.320.180.320.180.280.190.270.160.180.170.170.140.180.120.180.290.050.100.040.040.090.180.080.030.030.040.080.300.550.260.290.120.140.090.210.190.140.200.220.200.210.150.160.060.200.090.14

MDF(mT)

702520239

12101219201122

81213148

159

10114

1211131317174577

305025271012132020181219202818194

151817

Susc.(Six I0'5)

-0.8-0.9-0.3-0.1-0.6-0.5-0.3-0.1

0.10.90.30.70.71.10.70.10.30.10.51.30.6

16.7371.6709.9100.9892.2

10611003.61013.5694.1851.5512.3913

2.52.81.621.71.72.84.33.42.71.2

42.37.93.431.14.4

92.359.222.7

Notes: Inc = inclination of characteristic remanence, determined by least-squares line fit; MAD = maximum angle of deflection (Kirschvink, 1980); N = number of steps used for cal-culating least-squares line; AF steps = range of alternating fields for steps used in line fit calculation; Jo = intensity of natural remanent magnetization, in milliamperes per meter;J/Jo = percentage of Jo remaining at highest AF demagnetization step used in line fit calculation; MDF = median destructive field, AF demagnetization field at which 50% of Jo

remained. Susc. = volume magnetic susceptibility. aSample inverted.

Because the cores were drilled with a rotary bit, core fragmentswere twisted off from the country rock as they were drilled and,thus, are azimuthally unoriented. Sample paleomagnetic declinations,therefore, are arbitrary, and only the paleomagnetic inclinations havegeologic significance. To calculate mean paleoinclinations, we mustcorrect for the bias inherent when averaging inclination-only data(Briden and Ward, 1966; Cox and Gordon, 1984). Consequently, weused a maximum-likelihood routine designed to calculate correctedmean inclination values and their confidence limits (McFadden andReid, 1982).

RESULTS

Samples were restricted to the base of the limestone section be-cause recovery was low in much of the hole (typically <5%) and didnot exceed 20%, except in the lower 100 m. Recovery increaseddramatically in the clayey limestones in this part of the hole and isapproximately correlated with the intensity of magnetization of the

samples, probably because the clays and volcanic detritus made thelimestones both less friable and more magnetic.

Natural remanent magnetization (NRM) intensities of the lime-stone samples ranged over five orders of magnitude, from 0.049 to441.120 mA/m, and magnetic susceptibility ranged by a similaramount, from -0.9 × I0"5 to 1061.0 × I0"5 S1 (Table 1; Appendix).NRM intensity correlates well with susceptibility, implying that mag-netic mineral concentration is the primary factor controlling its magni-tude (Fig. 1). NRM intensities of samples above Core 143-865A-85R(786.2 mbsf) were the weakest. Indeed, these samples were difficult tomeasure with the cryogenic magnetometer, owing to their low mag-netizations. Intensities of other samples were typically between 0.2 to15.0 mA/m, except for a zone of highly magnetic limestones in Sec-tions 143-865 A-89R-1 to -4 (824.7 to 830.4 mbsf), which gave valuesfrom 136.060 to 441.120 mA/m (Table 1). Magnetic intensity also cor-relates with color, with weaker limestones being whiter and strongerlimestones being darker greenish-black. The color changes probablyreflect differences in the amount of volcanic material in the sediments,

400

PALEOLATITUDE FROM CRETACEOUS SEDIMENTS

A B Intensity (mA/m) Q

Inclination Susceptibility (10r4S|) M D F

-90 -75 -60 -45 -30 -15 0 10"2 10"

1 10° 10

1 10

2 10

3 0 10 20 30 40 50 60

760

780

)St)

Dep

th (

ml

00

00

o

o

840

860

• • • i • • i | -

L l '-

\':7

•

-

r *' i

r 1 •i•II

i * i j

i j

•J * * "

I 1 :r 1 •:: . . i . . i , . i . . i i . ? i . . :

π π

\ ••

•? •• •••

%

Figure 1. Magnetization properties of Cretaceous limestone samples. A. Paleoinclination of the characteristic remanent magnetization vs. depth. Dashed line showsthe average inclination. B. Natural remanent magnetization (NRM) intensity (solid circles) and volume magnetic susceptibility (open squares) plotted vs. depth;intensity units in mA/m; susceptibility in I0"4 S1. Note that the horizontal scale is logarithmic. C. Median destructive field (MDF) values plotted vs. depth. MDFin milliteslas.

0.2 mA/m-

N r

143-865A-85R-2, 48-50 cm 143-865A-89R-3, 76-78 cm

)0

143-865A-92R-2, 2-4 cm

30

S N

E,Up-i2 mA/m

s N , , 1 1 r

W.Down

W.Down • Horizontalo Vertical

η S

W.Down

Figure 2. Orthogonal vector ("Zijderveld") plots of the behavior of three typical Cretaceous limestone samples during AF demagnetization. Numbers indicate AFdemagnetization steps, in tens of milliteslas.

but may also be related to changes in the environment of depositionand, hence, diagenesis, owing to other factors, such as the influx oforganic material.

Most samples exhibited stable AF demagnetization behavior: lit-tle scatter in direction and univectorial decay toward the origin (Fig.2). The only samples that displayed unstable behavior were weaklymagnetic samples of "clean" limestone in the sections above Core143-865A-85R (786.2 mbsf). AF demagnetization was effective inremoving overprint magnetizations and isolating sample ChRMs(Fig. 2). Many samples showed no significant overprint; those thatdid, exhibited no consistent overprint direction. This suggests that theoverprints were acquired from the environment during handling.

IRM acquisition experiments showed that most pilot samplessaturated in applied fields of 400 mT or less (Fig. 3), implying thattheir magnetizations reside in a low-coercivity magnetic mineral,such as titanomagnetite. Low median destructive field (MDF) values,

25 mT or less, characterize most samples (Fig. 1), suggesting that thisbehavior is the norm. However, a few samples displayed highercoercivities, as shown by larger applied fields needed to bring themto saturation (Fig. 2) and higher MDF values. Only five of 53 samples(9%) had MDF values in excess of 25 mT (Fig. 1). These samples didnot give paleoinclination values any different than the other samples;thus, AF demagnetization was evidently able to isolate the ChRM inthe higher coercivity samples as well.

All but two samples gave negative ChRM inclinations (Table 1),indicating that the limestones were magnetized in the Southern Hemi-sphere during a period of normal geomagnetic polarity. This is con-sistent with their having acquired their magnetizations during theAlbian stage, in the middle of the Cretaceous Quiet Period. The twosamples with positive inclinations (143-865A-34R-1, 37-39 cm, and-85R-1, 3 8 ^ 0 cm) probably do not indicate reversed polarity, butwere likely inverted during handling. Neither exhibits a demagneti-

401

W.W. SAGER, J.A. TARDUNO

J/Jc

• 143-865A-90R-3, 63-65 cm

A 143-865A-92R-1, 82-84 cm

O 143-865A-94R-3, 26-28 cm

200 400 600Applied Field (mT)

800 1000

Figure 3. IRM acquisition curves for three Cretaceous limestone samples. Onthe vertical axis is magnetic intensity normalized by the saturation value; onthe horizontal axis, the applied field in milliteslas. Most samples show lowcoercivity behavior, as the upper two curves, with saturation occurring in fieldsof 200-400 mT; however, a small percentage of samples show a high coercivitybehavior, evidenced by saturation occurring in higher applied fields, as in thelower curve.

Ui/a = -26.8°

10

JS 6 -

N=51 U•i i i i i i

MM4 8 12 16 20 24 28 32 36 40 44

Inclination

Figure 4. Histogram of characteristic remanent magnetization inclinations forHole 865A clayey limestone samples.

zation behavior that would suggest a reversed polarity ChRM over-printed with a normal polarity (Brunhes or Cretaceous Quiet Period)magnetization, as is common for similar, reversely magnetized deep-sea sediments (e.g., Steiner, 1983).

Paleoinclination values display remarkably low scatter (Fig. 4)and although the inclination histogram appears somewhat biasedtoward shallow values, the distribution has a skewness value nearzero (0.06), indicating that it is indistinguishable from a normaldistribution. The grouping implies that these samples recorded thesame paleofield direction, which has been reliably isolated. A meaninclination of -26.8° (95% confidence limits: -24.4° to -28.7°; k =75; N = 51) was calculated. Thus, the limestones imply a paleolatitudeof 14.2°S with 95% confidence limits of approximately ±1.3°.

DISCUSSION

The -14.2° ± 1.3° paleolatitude estimated from the sediments isindistinguishable from that given by the basalts from the same unit(-16.8° ± 3.0°; Sager, Winterer, Firth, et al., 1993). This paleolatitudeimplies that Site 865 has drifted 32.6° northward since the limestoneswere deposited, an amount similar to estimates for Leg 129 sites

Figure 5. Comparison of paleocolatitudes from Hole 865A clayey-limestonesamples and basalt sills (Sager, Winterer, Firth, et al., 1993) with the Pacificapparent polar wander path. The polar wander path is shown by solid squaresconnected by a line. Each pole is identified by its mean age (in Ma) and issurrounded by its 95% confidence ellipse (from Sager and Pringle, 1988;Larson and Sager, 1992; Sager, unpubl. data). Heavy, nearly horizontal arcsshow the locus of paleomagnetic poles inferred from azimuthally unorientedHole 865A mean paleoinclinations (sediments and basalts). The 95% confi-dence limits for the basalt and limestone paleocolatitudes are shown by thecross hatched and stippled bands, respectively.

(29°-37°) located on Jurassic lithosphere, approximately 2800 kmwest of Allison Guyot (Larson et al., 1992; Steiner and Wallick,1992). Few mid-Cretaceous paleomagnetic data exist for the PacificPlate; thus, some uncertainty exists in the polar wander of this period.Published APWP for that period trend more-or-less east to west(Gordon, 1983; Cox and Gordon, 1984; Sager and Pringle, 1988;Sager, 1992; Larson and Sager, 1992; Fig. 5), implying that there waslittle paleolatitude change for the plate during that period (e.g., Larsonet al., 1992). Therefore, we need not have a paleomagnetic pole ofprecisely the same age for comparison. Nevertheless, we determineda pole using paleomagnetic data from seamount magnetic anomalyinversions and DSDPbasalt and sediment cores (Sager, unpubl. data).The result is located at 55.0°N, 326.8°E and has an average age of 105Ma. From this pole, we infer an expected paleolatitude of-11.2° ±2.0°. The confidence limits of both the limestone and basalt paleoco-latitude estimates overlap those of the 105 Ma mean pole, implyingagreement of these data (Fig. 5).

Geological observations from the cores and the low scatter of theirinclinations (Sager, Winterer, Firth, et al. ,1993) are consistent withthe sills having been emplaced within a short time; thus, they shouldrecord only geomagnetic field directions representative of a fewyears, during the period of their cooling. Secular variation studiessuggest that an equatorial site should have a standard deviation ofabout 9° (implying 95% confidence limits of approximately 18°) inpaleolatitude owing to this phenomenon (Harrison, 1980; Cox andGordon, 1984); therefore, the match of the basalt paleolatitude andthe expected paleolatitude is probably fortuitous.

The agreement of the paleolatitude determined from the lime-stones with the expected paleolatitude is somewhat surprising, be-

402

PALEOLATITUDE FROM CRETACEOUS SEDIMENTS

cause many cores of Cretaceous sediments from Pacific DSDP andODP holes have been found to give anomalously shallow inclinations(Tarduno, 1990; Gordon, 1990; Steiner and Wallick, 1992). It ispossible that the 105-Ma reference paleomagnetic pole is biasedtoward lower paleolatitudes, because it is controlled in part by datafrom other Cretaceous DSDP sediment cores and by paleopoles fromthe inversion of seamount magnetic anomalies, which can give shal-low inclinations owing to viscous remanent magnetization overprint(e.g., Gee et al., 1993). Nevertheless, the sediment data used for thereference pole were those that seem to be unbiased by their concor-dance with other Pacific paleomagnetic data (Tarduno, 1990; Gordon,1990). Moreover, basalt core data from a number of DSDP sites alsowere used in the calculation. Thus, a biased reference pole seemsunlikely and the Hole 865A sediment paleolatitude appears reliable.

The causes of inclination shallowing in sediments are not wellunderstood; thus, it is difficult to pinpoint the reason why the Hole865 A limestones give reliable results. One often-cited explanation forinclination shallowing is that it is caused during compaction anddewatering by the rotation of magnetic grains toward the horizontal,either by the physical rotation of elongated magnetic grains or by theirbecoming attached to platelike clusters of clay particles (Blow andHamilton, 1978; Anson and Kodama, 1987). We can imagine severalfactors that might have mitigated compaction effects. Although theHole 865A limestones we measured had variable, but significant,amounts of clay, possibly the nearness to the source rocks preventedinclination shallowing, because the magnetic grains are larger and,thus, less likely to be affected by the clay particles. Alternatively,these carbonate sediments may have resisted compaction by rapidcementation before significant burial. For example, deeply buriedcarbonate sandstones were drilled at sites on Resolution Guyot thathad intact void spaces caused during deposition by trapped air (Sager,Winterer, Firth, et al., 1993). Another possibility is that the heat andhot fluid flow associated with the sill intrusions may have remagne-tized the sediments after much of the compaction had already oc-curred. Without a more thorough study of the petrography of thesesediments, all of these suggestions are speculative.

CONCLUSIONS

Shallow-water limestone samples from Hole 865A displayed awide range of NRM intensity, with a variation over more than fiveorders of magnitude. Higher intensities were found in the clayeylimestones recovered in the 140 m above the bottom of the hole; theseevidently resulted from the influx of volcanic material into the sedi-ments from a nearby volcanic island. These sediments were depositedin a nearshore lagoonal marsh environment, and their magnetic prop-erties seem to be the characteristic of titanomagnetite grains.

Biostratigraphic data give an age of Albian (probably lower Albian)for the measured limestones, whereas an average radiometric age of104.5 ± 0.5 Ma was determined from the cored basalt sills and dredgematerial. Paleoinclination data gave a mean of-26.8° and 95% confi-dence limits of-24.4° to -28.7°. This inclination implies a paleolati-tude of-14.2° ± 1.3°, which is indistinguishable from paleolatitudesinferred from a 105-Ma reference pole (-11.2° ± 2.0°) and from basaltsills that intruded these sediments (-16.8° ± 3.0°). This concordancesuggests that the paleomagnetic results from these limestones were notbiased by compaction-induced inclination shallowing.

ACKNOWLEDGMENTS

We thank the JOI/USSAC science support program for providingfunds for this study. Reviews by Charles Helsley and an anonymousreviewer were appreciated. Craig Jones, of CIRES, at the Universityof Colorado, Boulder, kindly provided a Macintosh program to plotand analyze sample magnetizations; his many hours of programmingand debugging are greatly appreciated. This is Texas A&M Geody-namics Research Institute Contribution No. 94.

REFERENCES*

Anson, G.L., and Kodama, K.P., 1987. Compaction-induced shallowing of thepost-depositional remanent magnetization in a synthetic sediment. Geo-phys. J. R. Astron. Soc, 88:673-692.

Blow, R.A., and Hamilton, N., 1978. Effect of compaction on the acquisitionof a detrital remanent magnetization in fine-grained sediments. Geophys.J. R. Astron. Soc, 52:13-23.

Briden, J.C., and Ward, M.A., 1966. Analysis of magnetic inclination inborecores. Pure Appl. Geophys. 57:47-52.

Cox, A., and Gordon, R.G., 1984. Paleolatitudes determined from paleomag-netic data from vertical cores. Rev. Geophys. Space Phys., 22:42-72.

Gee, J., Staudigel, H., Tauxe, L., and Pick, T, 1993. Magnetization of the LaPalma Seamount Series: implications for seamount paleopoles. J. Geo-phys. Res., 98:11743-11767.

Gordon, R.G., 1983. Late Cretaceous apparent polar wander of the Pacificplate: evidence for a rapid shift of the Pacific hotspots with respect to thespin axis. Geophys. Res. Lett, 10:709-712.

, 1990. Test for bias in paleomagnetically determined paleolatitudesfrom Pacific Plate Deep Sea Drilling Project sediments. J. Geophys. Res.,95:8397-8404.

Harland, W.B., Armstrong, R.L., Cox, A.V., Craig, L.E., Smith, A.G., andSmith, D.G., 1990. A Geologic Time Scale 1989: Cambridge (CambridgeUniv. Press).

Harrison, C.G.A., 1980. Secular variation and excursions of the earuYs mag-netic field. /. Geophys. Res., 85:3511-3522.

Kirschvink, J.L., 1980. The least-squares line and plane and the analysis ofpalaeomagnetic data. Geophys. J. R. Astron. Soc, 62:699-718.

Larson, R.L., and Sager, W.W., 1992. Skewness of magnetic anomalies M0 toM29 in the northwestern Pacific. In Larson, R.L., Lancelot, Y, et al., Proc.ODP, Sci. Results, 129: College Station, TX (Ocean Drilling Program),471-481.

Larson, R.L., Steiner, M.B., Erba, E., and Lancelot, Y., 1992. Paleolatitudesand tectonic reconstructions of the oldest portion of the Pacific Plate: acomparative study. In Larson, R.L., Lancelot, Y, et al., Proc. ODP, Sci.Results, 129: College Station, TX (Ocean Drilling Program), 615-631.

McFadden, PL., and Reid, A.B., 1982. Analysis of paleomagnetic inclinationdata. Geophys. J. R. Astron. Soc, 69:307-319.

Sager, W.W., 1992. Seamount age estimates from Paleomagnetism and theirimplications for the history of volcanism on the Pacific Plate. In Keating,B.H., and Bolton, B. (Eds.), Geology and Offshore Mineral Resources ofthe Central Pacific Basin. Circum.-Pac. Counc. Energy Miner. Resour.,Earth Sci. Ser., 14:21-37.

Sager, W.W., and Pringle, M.S., 1988. Mid-Cretaceous to Early Tertiaryapparent polar wander path of the Pacific Plate. J. Geophys. Res.,93:11753-11771.

Sager, W.W., Winterer, E.L., Firth, J.V., et al., 1993. Proc ODP, Init. Repts.,143: College Station, TX (Ocean Drilling Program).

Steiner, M.B., 1983. Geomagnetic excursion in the late Cretaceous. Geophys.J. R. Astron. Soc, 73:17-25.

Steiner, M.B., and Wallick, B.P., 1992. Jurassic to Paleogene Paleolatitudes ofthe Pacific Plate derived from the Paleomagnetism of the sedimentarysequences at Sites 800, 801, and 802. In Larson, R.L., Lancelot, Y, et al.,Proc ODP, Sci. Results, 129: College Station, TX (Ocean Drilling Pro-gram), 431^146.

Tarduno, J.A., 1990. Absolute inclination values from deep sea sediments: areexamination of the Cretaceous Pacific record. Geophys. Res. Lett.,17:101-104.

Winterer, E.L., Natland, J.H., van Waasbergen, R.J., Duncan, R.A., McNutt,M.K., Wolfe, C.J., Premoli Silva, I., Sager, W.W., and Sliter, W.V., 1993.Cretaceous guyots in the Northwest Pacific: an overview of their geologyand geophysics. In Pringle, M.S., Sager, W.W., Sliter, W.V., and Stein, S.(Eds.), The Mesozoic Pacific: Geology, Tectonics, and Volcanism. Am.Geophys. Union, Geophys. Monogr., 77:307-334.

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: 29 November 1993Date of acceptance: 21 April 1994Ms 143SR-250

403