2. SITE 290

The Shipboard Scientific Party1

130° 135° 140°

145°

Figure 1. Location map and track of Glomar ChallengerLeg 31 for region around Site 290. From map: "Topog-raphy of North Pacific," T. E. Chase, H. W. Menard, andJ. Mammerickx, Institute Marine Resources, Geol. DataCenter, Scripps Institution of Oceanography, 1971. Con-tour depths in kilometers; scale 1:6,500,000.

SITE DATA

Position:Hole 290: 17°44.85'N; 133°28.08'EHole 290A: 17°45.05'N; 133°28.44'E

Water Depth (from sea level): 6062.5 corrected meters (echosounding)

Bottom Felt At: 6071 meters (drill pipe)Penetration:

Hole 290: 255 metersHole 290A: 140 meters

•James C. Ingle, Jr., Stanford University, Stanford, California;Daniel E. Karig, Cornell University, Ithaca, New York; Arnold H.Bouma, Texas A & M University, College Station, Texas; C. HowardEllis, Marathon Oil Company, Littleton, Colorado; Neville S. Haile,University of Malaya, Kuala Lumpur, Malaysia; Itaru Koizumi,Osaka University, Osaka, Japan; Ian MacGregor, University ofCalifornia at Davis, Davis, California; J. Casey Moore, University ofCalifornia at Santa Cruz, Santa Cruz, California; Hiroshi Ujiié,National Science Museum of Tokyo, Tokyo, Japan; TeruhikoWatanabe, University of Tokyo, Tokyo, Japan; Stan M. White,California State University at Fresno, Fresno, California; MasashiYasui, Japan Meteorological Agency, Tokyo, Japan; Hsin Yi Ling,University of Washington, Seattle, Washington.

Number of Holes: 2

Number of Cores:Hole 290: 9Hole 290A: 2

Total Length of Cored Section:Hole 290: 80 metersHole 290A: 19 meters

Total Core Recovered:Hole 290: 38.9 metersHole 290A: 1.9 meters

Percentage of Core Recovery:Hole 290: 48.6%Hole290A: 10%

Oldest Sediment Cored:Depth below sea floor: 255 metersNature: Volcanic conglomerate and brecciaAge: Early Oligocene or late EoceneMeasured Velocity: 3.8 km/sec horizontal

4.21 km/sec vertical

Principal Results: The stratigraphic sequence in Hole 290 con-sists of 90 meters of Quaternary to late Oligocene brownsilt-rich clays overlying 49 meters of late Oligocene nanno-fossil ooze. This transition dates the subsidence of this partof the West Philippine Basin through the CCD. Beneaththese units lie more than 80 meters of early Oligocene orlate Eocene volcanic silts forming the distal edge of a largesedimentary apron lying west of the Palau-Kyushu Ridge.Apron formation probably extended from the late Eoceneto early Oligocene. The basal sediment unit is a late Eoceneor very early Oligocene volcanic breccia, over 30 metersthick, formed by slumping from a local topographic high.Basalt fragments and nannofossils in clasts suggest that thebasement, which was not reached, is of late Eocene age.

BACKGROUND AND OBJECTIVES

BackgroundSite 290 is located in the West Philippine Basin at the

distal edge of a sedimentary apron along the west flankof the Palau-Kyushu Ridge. It is also just to the north-east of the broken topography associated with thebroadly splayed southeast end of the Central BasinFault. At this end, the Central Basin Fault displaces theapron sediments, but does not appear to cause signifi-cant horizontal offset of the Palau-Kyushu Ridge. Base-ment in the site area has a relief of several hundredmeters but until surveying, prior to and following drill-ing, no basement lineation directions were known.

The Palau-Kyushu Ridge, with its asymmetric profileand sediment distribution, has been identified as atypical remnant arc (Karig, 1972). Its geologic historyshould have been that of an active arc system until itbecame abandoned, after which it should display ahistory of quiescence and subsidence. The sediments,

25

SITE 290

west of and derived from the Palau-Kyushu Ridge,should reveal much of its early arc history. Informationfrom similar tectonic settings suggested that theseaprons consist of volcaniclastics, transported by wind,current, and density current mechanisms. Source areasare on the associated remnant arcs or in volcanic centerson the arc flank closest to the apron. As the aprongrows, coarser clastic material oversteps pelagic sedi-ment which comprises a more distal basin facies. Aftervolcanism ceases, sedimentation in the apron areachanges to a much slower accumulation of pelagic clay.

Near Site 290 the pelagic cover over the apronsediments averages 100 meters in thickness, and thickensslightly beyond the distal edge of the apron to 100-150meters, which is representative of most of the WestPhilippine Basin.

Objectives

The objectives at Site 290 were largely tectonic withthe primary goals of determining the age and nature ofthe basin crust and obtaining information concerningthe history of the Palau-Kyushu Ridge. This informa-tion could elucidate the evolution of the Philippine Seaarc complexes. Site 290 was the first in the pattern ofholes designed to test various modes of basin origin,and, as such, was placed as close as possible to both theCentral Basin Fault and the Palau-Kyushu Ridge(Figure 1). Several factors further limited its location.The site had to be placed beyond the edge of thebroadened Central Basin Fault zone to avoid thepossibility of testing an anomalous environment, due tominor later spreading or extrusion. It also had to beplaced near the distal edge of the apron where basementcould be reached in a local trough (Figure 2). DSDPholes on ridges often have shown large unconformitiesin the critical basal sediment section.

Another high-priority objective was to determine theduration of apron formation. This could be done bydating the transition from apron sediments to overlyingpelagic clays, and, hopefully, by locating and dating anunderlying section of calcareous ooze. If the age span ofthis volcanic pulse on the Palau-Kyushu Ridge is similarto that on the Mariana Ridge (Cloud et al., 1956; Traceyet al., 1964), then the concept that the younger inter-vening marginal basins are of extensional origin wouldbe strengthened. Furthermore, the determination of thetiming and duration of arc volcanism and basin exten-sion is necessary to reconstruct evolutionary models ofmarginal basins.

If the West Philippine Basin were of extensionalorigin, then the subsequent aging and cooling of thebasin lithosphere should be reflected in crustal sub-sidence. Identifying and dating points on this curvecould both substantiate extension and aid in dating it.

OPERATIONSPresite Survey

The original location of this site was selected on thebasis of seismic reflection profiles made during the SIOANTIPODES 13 expedition. These records suggestedthat the intersection of the edge of the Central BasinFault, and the volcaniclastic apron lay near 17°N,

6 . 0 --8 .0

Figure 2. Seismic reflection profile ofD/V Glomar Chal-lengers first crossing over Site 290 area. Profile locationis shown in Figure 3.

133°E. Subsequent, recontouring of all available bathy-metric data, together with a desire to avoid structuralcomplexities associated with the Central Basin Fault,necessitated the relocation of Site 290 to the north of theinitially proposed site.

The general area of Site 290 was approached from thesoutheast along bearing 300°T about 19 km (30 miles)north of the Central Basin Fault, and parallel with thisfeature (Figure 3). Reflection records obtained alongthis track illustrated that a major portion of the clasticapron and the underlying basement was masked by avery reflective horizon just below a 70-meter-thick inter-val of transparent sediments. Because of this masking,the ship was slowed to 8 knots, and a detailed presitesurvey was commenced to search for an area of apronbeneath which a basement reflector could be detected.An additional objective of this survey was to locate a sitewithin a topographic low in order to obtain a more com-plete stratigraphic sequence than might be present onthe crest or flank of adjacent highs within the apronarea. Therefore, the predrilling survey was focused onthe distal portion of the apron.

A favorable area of "ponded" apron sediments wassubsequently found between two topographic highs(Figure 2). A relatively thick uppermost transparentlayer suggested slumping of pelagic debris from the ad-jacent highs. A second weak reflector was interpreted asvolcaniclastic apron sediments. A strong and steeplydipping basement reflector was apparent in a minortrough along the south side of the apron "pond" (Figure2), and this subarea was selected as the most promising

26

SITE 290

1 7 ° 2 5 ' H | I L

Figure 3. Glomar Challenger survey tracks in vicinity ofSite 290. The hachured line outlines the basement topo-graphy in the area.

site. During additional passes across this site (Figure 3)both PDR and reflection records indicated the ship wasmoving progressively north across this "pond." Thebeacon was released at 1230 June 18 in a water depth of6062 meters (PDR). An additional pass across andbeyond the beacon site revealed the encroachment oflarge side echos on the seismic record, and it was decid-ed to offset the final drilling site 400 meters south of thebeacon site to 17°44.85'N, 133°28.O8'E.

Drilling Program

The drill pipe made contact with the sea floor at adepth of 6071 meters as opposed to a PDR depth of6062 meters. Hole 290 was spudded and interval coredto a total depth of 255 meters below the sea floor. Cor-ing details are found in Table 1.

An abrupt and dramatic decrease in drilling rate(Figure 4) was noted at 225 meters as a 19.5-meter inter-val was washed following retrieval of Core 7, signalingpenetration of Unit 4 consisting of coarse volcanicdebris (Table 2). After 5 hr of ever-increasing torque,stalled rotation, and sticking pipe, Core 8 was cut from241.5 to 251 meters recovering a well-cemented, veryhard volcanic grit and conglomerate. The very compe-tent nature of the conglomerate suggests that some ofthe core actually came from the interval between 225

TABLE 1Coring Summary, Site 290

Core

Hole 290

Wash1

Wash2

Wash3

Wash4

Wash5

Wash6

Wash7

Wash

89

Total

Hole 290A

Wash1

Wash2

Total

Cored IntervalBelow Bottom

(m)

0.0-23.023.0-32.532.5-70.570.5-80.080.0 99.099.0-108.5

108.5-118.0118.0-127.5127.5 137.0137.0-146.5146.5-156.0156.0 165.5165.5 231.0213.0-222.5222.5-241.5

241.5-251.0251.0-255.0

255.0

0.0-108.5108.5 118.0118.0 130.5130.5-140.0

140.0

Cored(m)

9.5

9.5

9.5

9.5

9.5

9.5

9.5

9.54.0

80.0

9.5

9.5

19.0

Recovered(m)

5.0

8.1

4.5

1.7

4.0

4.1

4.6

6.90.0

38.9

1.9

0.0

1.9

(%)

52.6

85.0

47.4

18.0

35.8

43.0

48.0

72.60.0

20.0

0.0

Remarksa

Decrease in drilling rate

Gradational lithologic contact

Decrease in drilling rate at 165 meters

Decrease in drilling rate at 325 meters50 bbls of mud used

1See Figure 4 for graph of drilling rates and lithologies.

27

to

00

DRILLING RATE(m/min)

LITHOLOGY DENSITY

(g/cc)

ΔWET BULK

— GRAPE"SYRINGE

-GRAPE

SONIC VELOCITY(km/sec)

2.00 3.00 100.00 0.00 1.40 4.40

200-

300-

UNIT 1 -Brown s i l t -rich claysand zeo-l i te-r ichsi l tyclays.

Nannofossils i l t y clayand ash-rich nanno-

_ f ß 5 j_Lc_Lay..

UNIT 3 * * -Clayeynanno-fossil-richash andclay/nanno-fossil-richash.

UNIT 4*** -VolcanicconglomerateT.D. = 255 m + •Hole 290T.D. = 140 mHole 290A

*Unit 2 in Hole 290Aoccurs from 108.5-118 m.

**Unit 3 - not presentin Hole 290A.

***Unit 4 - in Hole 290Aoccurs from 130.5-140 m.

Figure 4. Hole summary diagram, Site 290.

SITE 290

and 241.5 meters. Rounded pieces of this latter unit, in-cluding a broken cobble of diabase, apparently causedbinding of the bit. Coring continued, but pipe stickingand high torque caused the hole to be abandoned at0900 (June 19) after recovery of Core 9.

The predrilling site survey suggested that a thinnersediment cover might be found higher on the buriedflank of a high adjacent to the sediment "pond" drilledat Site 290 (Figure 3). The ship moved 2000 feet east ofthe beacon to Hole 290A (17°45.05'N, 133°28.44'E).Water depth at this hole was the same as at Hole 290.Hole 290A was spudded, and the initial core cut at 108.5to 118 meters below the sea floor. An interval from 118to 130.5 meters was washed, and a second core was cutfrom 130.5 to 140 meters recovering only a fewfragments of the same hard volcanic conglomerate en-countered at the base of Hole 290.

The pipe became stuck in Hole 290A after recovery ofthe second core, due to caving and a bound bit. Pullingon the stuck pipe was hampered by the water depth andlong drill string. An explosive severing tool was rundown the hole three times. Following two unsuccessfulattempts with the tool, the pipe became free just prior tofiring the third charge. The entire drill string wasrecovered with one bumper sub damaged. About 4 litersof foraminifera-bearing volcanic grit, sand, and pebbleswere recovered from the bit and core catcher at the endof the stuck pipe. This latter sediment may represent anuncored interval above the hard volcanic conglomerateand breccia encountered at the base of Hole 290A. Ashort postsite seismic survey was completed beforeheading for Site 291.

LITHOLOGYAt Site 290, drilling and coring achieved a total sub-

surface penetration of 255 meters for Hole 290 and 140meters for Hole 290A. The ages of the sedimentrecovered from both holes range from late Pliocene tothe early Oligocene. Figure 4 establishes the strati-graphic column for the holes, in which four lithologicunits are defined (Table 2).

Unit 1Unit 1 consists of dark yellow-brown to moderate

brown silt-rich clays, locally becoming zeolite-rich siltyclays toward the bottom of Core 290-2. Zeolite-richvolcanic ash interbeds also occur. The brown colors aredue to goethite. The base of the unit was established at90 meters in Hole 290, which is in a noncored intervalbetween Cores 2 and 3. Bedding characteristics are notapparent; however, the vertical color streaking due tocoring disturbance may indicate a preexisting interbed-ding of minor lithologies. At the base of Core 290-2,wedge-shaped laminae occur with alternating yellowand brown colors. Sediment constituents include: zeo-lites (predominately phillipsite, with clinoptilolite);volcanic ash composed of glass, devitrified glass(palagonite), and lithic fragments; minor amounts (to5%) of quartz, feldspar, and heavy minerals (augite).The biogenic content is low, with trace amounts of nan-nofossils and sponge spicules. The microfossils of Core290-1 indicate a late Pliocene age; however, the age ofthis same unit in Core 290-2 could not be determineddue to the lack of indigenous microfossils.

Unit 2Unit 2 is represented in Cores 3 through 5 to 139

meters in Hole 290, and in Core 1 of Hole 290A. In Hole290, this unit may be further divided into two subunits,both of a dark yellow-brown to moderate yellow-browncolor: the dominant subunit is an ash/radiolarian-bearing nannofossil-rich silty clay containing up to 15%-20% nannofossils, 5%-10% volcanic glass andpalagonite, l%-10% radiolarians, 4%-5% zeolites(clinoptilolite), and 40%-70% clay minerals; a secondsubunit (Sample 290-4-1, CC) is a volcanic ash-rich nan-nofossil clay.

Sedimentary features within Unit 2 include: a vagueto locally clear lamination defined by color and somegrain-size variations, scattered areas of semilithified tolithified nannofossil silty claystone, and burrows. Ad-ditionally, the volcanic ash content increases with in-creasing depth in the unit.

TABLE 2Unit Descriptions, Depths, Thicknesses, and Ages, Site 290

1

2

3

4

Unit and Descriptions

Brown silt-rich claysand zeolite-rich silty clays

Ash/radiolarian-bearingnannofossil silty clay,and ash-rich nannofossilclay

Clayey nannofossil-richash, and clay/nannofossil-rich ash

Volcanic conglomerate

Depth (m)

0.0-90.0

90.0-139.0 (290)108.5-118.0 (290A)

139.0-222.5 (290)(apparently absentin 290A)

222.5(?)-251.0(?) (290)130.5-140.0(?) (290A)

Thickness (m)

90(?)

499.5

+83.5(?) (290)

+28.5(?) (290)+9.5(?) (290A)

Age

Late Pliocene

Late Oligocene

Early Oligocene

Early Oligocene(?)

29

SITE 290

The unit as represented in Hole 290A (Core 1, Sec-tions 1 and 2) has the color and lithologic characteristicsof Unit 2, found in Hole 290. The lithology ispredominantly a moderate brown, ash/nannofossil-bearing silty clay with l%-2% zeolites (phillipsite andclinoptilolite), 5%-8% radiolarians, 3%-6% spongespicules, and 8%-10% nannofossils. The age of the unit islate Oligocene.

Unit 3The Unit 3-Unit 2 boundary is defined at 139 meters

in Hole 290, with the base of Unit 3 at 222 meters. Unit3 is apparently absent in the cores from Hole 290A. Theunit shows a color change from moderate browns tolight olive-grays, and an increasing volcanic ash content(up to 50%). The color change first appeared at 139meters and lithologic differences do seem to be present.The lithology is characterized as a clayey nannofossil-rich ash grading down-core into a clay/nannofossil-richvolcanic ash, and local zones of clayey nannofossil oozeand nannofossil volcanic ash. Characteristically thevolcanic ash content increases from approximately 35%at the top, to 50% at the bottom (Sample 7, CC). Locallyin Core 7, the volcanic ash zones have sedimentaryvolcanic ash clasts up to 7 mm in diameter, which are in-terbedded within a nannofossil volcanic ash matrix.Other lithologic characteristics of the unit include: adecrease in radiolarian content down-core; zeolites(phillipsite and clinoptilolite); the presence of traceamounts of palagonite and chlorite; incorporated finegravel (4-5 mm); coarse, medium, and fine sand in theash zones. Microfossils (nannofossils and radiolarians)indicate an early Oligocene age for the unit.

Unit 4

Unit 4 is a characteristic volcanic conglomerate unitwhich was found in Holes 290 and 290A. The upper 70cm (Hole 290, Core 8, Section 1) is an olive-gray subunitwith well graded (2-3 mm) subangular-subroundedclasts. The overall texture is bimodal, and the sorting ispoor. A second subunit, moderate yellow-brown incolor, begins at Sample 290-8-1, 130 cm, and continuesto the bottom of Sample 8, CC.

Megascopically the clasts consist of subangular tosubrounded diabase, weathered or altered volcanics,palagonite, glass, and devitrified glass and chalk. Thereis a definite size increase of the clasts down-core, from adiameter of 0.5 to 1 cm in Hole 290, Core 8, Section 2 toa maximum diameter of 6 cm in Hole 290, Core 8, Sec-tion 5. Elongate clasts show a long axis orientation inthe horizontal plane. Many clasts exhibit a man-ganese^), palagonite, and/or weathering rind. Thematrix is a recrystallized mixture of carbonate(dolomite), zeolites, and dispersed clay. Zeolites andcalcite also occur as amygdaloidal infillings in voidswithin the matrix. The upper portion of the yellow-brown subunit (Sample 290-8-2, 3 cm) appears more"weathered" than the seemingly fresher, more in-durated, lower zone (Sample 290-8-4, 5).

Radiograph studies of the conglomerate in the inter-val from 242 to 249 meters, illustrate that the sedimentcomponents range in size from a gravel through a fine

sand. Most gravel sizes are fine (=6 mm); however, larg-er pebbles up to 37 mm are found. The unit tends to behomogeneous, but does have indistinct to irregularlayering.

At the conclusion of the drilling of Hole 290A, it wasfound that the bit was blocked by a large quantity ofsediment material, which in some degree was unlike thesediment recovered from the two cores. This bit-sediment was a moderate dark-brown color, and a drill-ing residue of clay to granule size is apparent. Thefragments consist of: angular, indurated fragments of ig-neous lithics, and micrite (this material may representfragmental material from the volcanic conglomerate ofCore 290A-2); rounded, soft, clay to granule sizefragments of clay and clayey nannofossil ooze, whichcontains Pliocene foraminifera, Pliocene and Eocenenannofossils, and Cretaceous foraminifera; and isolatedsilty to sand-size grains of quartz, feldspar, glass shards,pyroxenes (augite), and amphiboles.

Conglomerate PetrographyThe clast to matrix ratio ranges from 50:50 to 40:60.

The clasts generally occur in an open framework withsome grain-to-grain contacts noted. In thin sections theclast size ranges from an average of 0.6 mm in Section 1,to an average of 5 mm in Section 5. The clasts are sub-angular to angular, have a moderate to poor sorting,and for the most part consist of manganese(?)-rimmeddevitrified glass (palagonite?). Some of the basalt clasts(Section 5, 140-150 cm) show a dark rim which is a crustof palagonite glass, similar to that found around pillowlavas. This crust or rim superficially resembles aweathering rim or manganese crust. The composition ofother clasts includes: opaque-brown glass with feldsparmicrolites; fresh and altered basaltic fragments withfeldspar laths and pyroxene crystals; crystals of pyrox-ene, olivine and feldspar, and chalk. Early Oligocenenannofossils were recovered from the chalk clasts.

The matrix is composed of a micrite mud (calcite)with zeolite and dispersed clay. Voids (up to 10%) in thematrix are lined with calcite and zeolite crystals. Isolatedmanganese concentrations and Oligocene nannofossilswere found within the matrix.

Lithologic InterpretationsBeginning with the lowermost unit (4) and progress-

ing with decreasing age, the following interpretationsare proposed:

1) The physical nature of the volcanic conglomeratic(Unit 4) is indicative of deposition via submarine gravitytransfer mechanism such as a debris flow. This inter-pretation is supported by the high matrix content, openframework, subangular to subrounded clasts, bimodalsize distribution, and long axis orientation.

a) The lithology and lithologic nature of the clastssuch as: fresh surfaces, manganese(?) or palagonitesurfaces; and varying degrees of alteration can beused to denote similar features of the rocks in theprovenance area. The distinctive clast lithology ofglassy basalts and palagonite are also indicative ofan area of pillow basalts.

30

SITE 290

b) Other characteristics of the unit such as: abruptcolor changes (olive-gray to brown; clast size); ageneral increase in size with increasing depth;sorting of the clasts (moderate to poor with in-creasing depth); and an overall poorly developedgraded bedding may further indicate: (i) normalsize grading or pulsations of a single debris flowand chemical reduction of the uppermost sedimentlayers following deposition; (ii) several pulses orperiods of debris flows with a general decrease inthe fragment size with time: perhaps from differingprovenance areas or over different intervals oftime.

c) Nannofossils found in the matrix and chalklikeclasts are early Oligocene in age and may indicatethe timing of the debris flow and the age of thesource area for the conglomerate.

2) The clayey nannofossil-rich ashes of Unit 3 in-dicate an onset of eruptive volcanism during the earlyOligocene. The nannofossil ooze sediment component isindicative of deposition above the regional carbonatecompensation depth. Sedimentary volcanic clast zonesoccur near the base of the unit and depositional charac-teristics such as interfingering with the finer ash bedsshow these zones may have been involved in a gravitytransfer process concurrent with the ash-nannofossil-clay deposition.

3) Unit 2 illustrates, via a decreasing ash content up-wards in the unit, a lessening of an eruptive volcanic cy-cle for the area. The relative increase in the nannofossilooze content shows either a return to higher productivi-ty in the overlying waters, or less masking of thebiogenous sediment by the pyroclastic deposition. Thepresence of nannofossils indicates deposition above theregional carbonate compensation depth, but below thelysocline.

4) The brown silt-rich clays comprising Unit 1 con-tain some volcanic ash, but are relatively devoid ofmicrofossils, particularly foraminifera and nannofossils.These clays were probably deposited near or below theregional carbonate ccompensation depth after the seafloor subsided. The subsidence may have been con-current with the sedimentation and may have beencaused by motion away from a spreading center.

PHYSICAL PROPERTIESThe nature of the sediment cored from Hole 290, with

regard to physical properties, varies considerably. Core1 was too watery to allow any measurements, whileCores 2-6 were so dry that the cutting operation in-troduced additional microruptures. These microrup-tures had a serious effect on velocity measurements, aswell as on the accuracy of the syringe sampling methodfor density and water content. Cores 7 and 8 were in-durated to such a degree to necessitate band-saw anddiamond-saw cutting.

Bulk Density, Porosity, and Water ContentIn spite of overlap of densities between the upper

three units, a minor increase in average density can beseen between Units 1 and 2, while Units 2 and 3 showa greater difference (Figure 4). The difference between

units, based on porosity and water content, has a similartrend, although not so pronounced. Unit 4 shows an in-crease in bulk density and decrease in porositysuggesting that this unit is acoustic basement. The corecatcher of Core 8 (Unit 4) contained a large piece ofdiabase. GRAPE count calculations indicate a higherdensity than any other sample from Core 8 (Unit 4).

Vane ShearThe sensitive vane adapter, measuring the 0-0.2 tons

per square foot range, was used (see Chapter 1, thisvolume). The tops of Core 2, Sections 5 and 6 gave ashear strength of 0.13 tons per square foot (126.9g/cm2), the top of Core 3, Section 2 yielded a shearstrength of 0.15 tons per square foot (146.5 g/cm2).Further results of the vane shear studies are found inBouma and Moore (this volume).

Sonic VelocityThe sonic velocity increases slightly with depth from

1.6 km/sec at about 120 meters to 1.9 km/sec at 222meters. The velocity increases to 3.1 km/sec in thevolcanic conglomerate present in Core 8 (Table 3 andFigure 4).

Several slabs were cut in the conglomerate inlongitudinal and transverse directions to study possibleanisotropy in sonic velocity. These measurements failedto show any significant difference in the two directionsfor the upper part of Core 8. However, samples from thelower half of Core 8, Section 5 show a discrepancy ofmore than 1 km/sec, being higher in the stratigraphicdirection. A pebble of altered basalt is located in thecenter of a transverse slab and may be the reason for thishigher velocity. Another measurement made on atransverse slab showed a better relationship betweenvertical and horizontal sonic velocities. However, the

Sample(Intervalin cm)

Hole 2904-1, 755-1,305-3, 526-1,36-3, 777-2, 817-3. 5374 1478-1,38-1, 268-5, 126

8-5 1388, CC

Hole 290A

1-2.51-2,5

TABLE 3Sonic Velocity Measurements, Site 290

HoleDepth

(m)

118.7137.3140.5156.0159.8215.3216.5219.0241.5241.8248.1

248.9250.5

110.0110.0

SonicVelocity(km/sec)

1.641.721.731 781.781.891.901.883.093.114.88

4.215.23

1.711.70

Remarks

Chunk of dry weak sediment

In horizontal directionIn vertical directionIn vertical direction, apebble of altered basalt is inthe center of the sampleIn vertical direction

31

SITE 290

velocity was still about 10% higher in the stratigraphicdirection. This difference between the sonic velocities inthe two directions can be ascribed more to inhomo-geneity in the pebble alignment rather than to a realanisotropy in the sonic velocity. The sonic velocity is lessdependent upon direction of a pebble than the fabric ofthe conglomerate.

The diabase sample from Sample 8, CC gave a veloci-ty measurement of 5.2 km/sec.

GEOCHEMICAL MEASUREMENTSAlkalinity, pH, and salinity measurements from Site

290 are summarized in Table 4. Techniques used aredescribed in the Explanatory Notes (Chapter 1, thisvolume).

Alkalinity

The average alkalinity is 2.72 which is higher thanthat of the surface seawater reference of 2.30. The loweralkalinities are found in Unit 3. The overall trend foralkalinity is one of a decrease with increasing depthfrom a high of 3.23 (Core 2, Section 3) to a low of 1.96(Core 7, Section 1). This may be indicated bypostdepositional precipitation in the older sediments.

pH

pH values in the cores were all below that of theseawater reference taken at the site. A definite increasein pH occurs in Unit 3 at 214 meters. The lithology ofCore 7 at this depth is lapilli-size nannofossil volcanicash in a matrix of nannofossil volcanic ash.

Salinity

Five salinity measurements made were taken withfour having the same value as the overlying seawaterreference (35.2°/oo). The highest value of 35.5°/oo camefrom the deepest sample. Little interpretation can bemade from these data, although it may be of significancethat Units 1 and 2 show the same values, while the lowerportion of Unit 3 shows an increase in salinity matchingthe comparative increase in pH and decrease in alkalini-ty.

PALEONTOLOGIC SUMMARY

Introduction

Cores taken at Site 290 contain late Pliocene and lateto early Oligocene calcareous nannoplankton and late

Eocene calcareous nannoplankton and radiolarians. Nodiatoms or silicoflagellates were recovered from any ofthe samples examined, and only one sample was foundto contain foraminifera of early Pliocene age.

A few moderately well-preserved calcareous nan-nofossils diagnostic of a late Pliocene age were found inCore 1 (23-32.5 m) within a brown silty clay despite thefact that these sediments were deposited well below thecalcium carbonate compensation depth. The cored in-terval between 70.5 and 80 meters (Core 2) is barren ofindigenous nannofossils and cannot be dated paleonto-logically. No other fossils were observed in either ofthese upper cored intervals.

Cores 3 and 4 (99-137 m) contain a nannofossil oozewith increasing amounts of volcanic ash downward.Calcareous nannofossils indicate a late Oligocene agefor these sediments, whereas radiolarians suggest a lateEocene age. This discrepancy in age represents a probl-em of arbitrary definition of epoch boundaries usingthese two fossil groups rather than an actual differencein absolute age.2 Radiolarian zonation indicates allsediments in Cores 3 through 7 (99-222.5 m) are lateEocene in age, whereas late Oligocene calcareous nan-nofossils are identified in a hard volcanic ash unit inCores 5 and 6 (137-165.5 m), and early Oligocene speciesare found in Core 7 (213-222.5 m).

Calcareous nannofossils observed in the matrixmaterial and in a few clasts selected from the coarsevolcanic conglomerate recovered from 241.5 to 251meters (Core 8) suggest an early Oligocene age. LateEocene calcareous nannofossils were recovered fromSample 9, CC (255 m).

A composite sample of pebbles and sand retained bythe drill bit when abandoning Hole 290A (Sample 11,CC; 118 m) contained a mixture of Late Cretaceous andPliocene foraminifera, late Oligocene and Neogenecalcareous nannofossils, late Eocene radiolarians, andfish teeth. It is important to note that although only twoabraded and poorly preserved specimens of LateCretaceous planktonic foraminifera {Globotruncana sp.)were recovered in Hole 290A, they represent the oldestfossils recovered to date in the West Philippine Basin.

2Epoch and subepoch boundaries appearing on the Hole SummaryDiagram (Figure 4) for Site 290 were arbitrarily placed solely on thebasis of calcareous nannofossil zonation to facilitate case of definition.

Sample(Intervalin cm)

TABLE 4Summary of Shipboard Geochemical Data, Site 290

Depth BelowSea Floor (m)

Surface seawater reference2-3,0-63-3, 0-65-1, 144-1505-2, 143-1507-1, 138-150Average

73.6102.1138.5140.0214.4

PH

Punch-in

8.267.41

___-

-

Flowthrough

8.267.357.277.417.567.92

7.50

Alkalinity(meq/kg)

2.303.232.832.832.741.962.72

Salinity(°/ o)

35.235.235.235.235.235.5

35.3

LithologicUnit

__ TJnTtT __ JMt^ _

Unit 3

32

SITE 290

This has attendant implications for the age of the adja-cent Palau-Kyushu Ridge from which they were mostlikely derived.

Calcareous NannofossilsThe two samples from Core 1 in Hole 290 contain

only very rare specimens of Discoaster brouweri and D.asymmetricus. The absence of other diagnostic nan-nofossil species places these samples in the late PlioceneCyclococcolithina macintyrei Subzone of Bukry (1973).The sample from Core 2 contains two specimens of theearly Tertiary nannofossil Marthasterites tribrachiatuswhich represent reworking or redeposition in this sam-ple.

Samples from Cores 3, 4, 5, and 6 contain abundant,well-preserved specimens of a diverse late Oligocenefloral assemblage. The presence of Sphenolithus cipero-ensis, S. distentus, and Cyclical'golithus abisectus insamples from Cores 3, 4, and Core 5, Section 1 permitsthe placing of these samples in the Sphenolithus ciperoen-sis Zone as defined by Bukry (1973). The presence ofSphenolithus distentus and the absence of S. ciperoensisin samples from Core 5, Section 1 and Core 6 refersthese samples to the Sphenolithus distentus Zone.

Samples from Core 7 also contain an abundant, well-preserved, diverse assemblage; however, the presence ofReticulofenestra hillae and R. umbilica suggests that thissample can best be assigned to the early OligoceneReticulofenestra hillae Subzone of Bukry (1973).

Core 8 is a conglomerate from which one of the pebbl-es and some of the matrix from Section 5 (140-141 cm)were examined for nannofossils. Specimens of Reticulo-fenestra umbilica were recovered from both theselithologic components. In addition, specimens of Dic-tyococcites scrippsae, Cyclicargolithus ßoridanus, andthe long-ranging species Coccolithus pelagicus wererecovered from the matrix sample. The fossils recovered,while sparse, suggest an early Oligocene age.

All of Core 9 consists of very "soupy" mud, and in allprobability represents a thorough mixing of sedimentsfrom above. Although several species of nannofossilswere recovered, they occur in considerably lower abun-dance than do those present in cores above. Thepresence of Discoaster barbadiensis with the youngerspecies from above suggests a late Eocene age for thissample.

The abundant and diverse nannofossil assemblagerecovered from Core 1 samples of Hole 290A containsSphenolithus ciperoensis, S. distentus, and Cyclicar-golithus abisectus which can be used to recognize the lateOligocene Sphenolithus ciperoensis Zone. Theassemblage from this sample correlates very well withthat recovered from Cores 3, 4 and Core 5, Section 1 inHole 290. Nannofossils recovered from several pebblesretained in the drill bit upon completion of Hole 290Aare also indicative of the Sphenolithus ciperoensis Zone.

ForaminiferaThe only foraminifera found at Site 290 were

recovered from Sample 2, CC (80.0 m). Nevertheless,the fauna is of considerable interest, as species represen-tative of two distinct ages were identified. Two poorlypreserved specimens of the Late Cretaceous genus

Globotruncana were found after an intense search ofmaterial in this sample. The umbilical sides of these testsare filled with secondary calcite making species iden-tification impossible. A second assemblage from thissame sample can be placed within the early PlioceneN19 Zone as defined by Blow (1969). The diagnosticcomponents of this latter assemblage are Globorotaliatumida tumida which has its initial appearance at thebase of Zone N18, Sphaeroidinella dehiscens dehiscenswhich initially appears at the base of Zone N19,Globigerina nepenthes delicatula which ranges into thebasal portion of Zone N19, along with Globigerinoidesobliques and G. extremus which range into the upperpart of Zone N19.

Several species of benthonic foraminifera of probablelate Pliocene were also recovered from Sample 2, CC.Amphistegina sp. and Elphidium aff. E. macellum charac-teristic of subtropical neritic environments are rathercommon and represent evidence of displaced sedimentat the lower bathyal depths at Site 290.

Radiolaria and SilicoflagellatesModerately well-preserved radiolarians were

recovered from Core 7, Section 3 (217 m) in Hole 290and Cores 1 and 2 (100.5-118; 130.5-140.0 m) of Hole290A; abundance ranges from few to abundant. Theassemblages recovered are all assigned to the lateEocene Thyrsocyrtis bromia Zone of Dinkleman (1973).

No silicoflagellates or ebridians were observed.

SUMMARY AND INTERPRETATIONS

SummaryHole 290 sampled 255 meters of pelagic and volcanic

sediments from the distal edge of the apron west of thePalau-Kyushu Ridge which could be divided into fourunits (Figure 4).

Unit 1 (0-90 m): Brown zeolitic, very sparselyfossiliferous to barren. Quaternary to late Oligocene.

Unit 2 (90-139 m): Moderate brown nannofossilooze, zeolitic near top and becoming ash-rich towardbase. Late Oligocene.

Unit 3 (139-225 m): Olive-gray volcanic silt and clay,showing decreasing nannofossil content with depth.Early to late Oligocene.

Unit 4 (225 m—total depth): Volcanic grit and con-glomerate, coarsening downward. Both clasts andmatrix are very late Eocene or very early Oligocene.

Hole 290A was drilled 800 meters northeast of Hole290 in the same water depth, but closer to the edge of alocal basement trough. In this hole, Unit 1 was aboutthe same thickness as in Hole 290, but Unit 2 was only30 meters thick and lay directly on Unit 4, a con-glomerate, which was reached more than 100 metersabove the same contact in Hole 290.

The brown clay of Unit 1 appears to represent thepelagic blanket which overlies the sediment apron onregional reflection profiles. Although these profiles in-dicate an average pelagic thickness near 60 meters in thevicinity of Site 290, local augmentation of sedimentationfrom nearby ridges and perhaps from infrequentturbidity-like influx have increased this thickness inHole 290.

33

SITE 290

Calculated average sedimentation rates for the brownclay in Site 290 and for nearby, more typical sectionsrange from about 2.5 m/m.y. to 3.5 m/m.y. (Figure 5)and are nearly identical with those obtained in the lateTertiary brown clays in the Parece Vela Basin (DSDPSites 53 and 54) (Fisher et al., 1971; Karig, 1971). Thevolcanic ash in Core 2, from 70 to 80 meters, may reflectthe eruptive activity related to the opening of the PareceVela Basin.

If there is no break in deposition between the clay andthe underlying nannofossil ooze, this contact is mostsimply interpreted as reflecting the time at which theregion passed through the local calcium carbonate com-pensation depth.

The upward increase in zeolite content and decreasein volcanic ash is thought to reflect waning volcanic ac-tivity and a decrease in sedimentation rate. Unit 2 thuswould mark the end of the major volcanic pulserepresented by volcaniclastics of Unit 3.

Although only 86 meters of volcanic silts werepenetrated in Hole 290, they undoubtedly represent thedistal facies of the apron west of the Palau-KyushuRidge. The geometry of this unit on reflection recordsand its absence in Hole 290A attest to some form oflateral transport from the vicinity of the Palau-KyushuRidge, but the exact mechanism is not clear.Investigations of similar aprons behind active and rem-nant arcs (Karig, 1970, 1971; Fisher et al., 1971; Burns etal., 1973) indicate that toward the head of the apron, theclastic material coarsens and the age span of the apronsediments increases, chiefly because the apron expandsby overstepping an ooze facies. Thus the initiation of the

AGE (MILLIONS OF YEARS)

100

200

300

' 400)>J

: 500

> 600J1

:

800

900

1000

1100

1S

T.

s!

OC

.PL

MIOCENE

L. M. E.

10 20

-

-

OLIGOCENE

L. E.

30

EOCENE

L.

40

100

200

£ 300400

BOO

600

E.

50

PALEOCENE

L. E.

60 65

MILLIONS OF YEARS

10 20 30

"\s V \\f \

•\ X

40 50 60

^ > .

\

Figure 5. Estimated sedimentation rate for Site 290 basedupon calcareous nannoplankton zonation (Ellis, this vol-ume) and time scale of Berggren (1972). Radiolarianzonation would alternately place the Oligocene-Eoceneboundary above Core 7 (213 m) ultimately affectingestimated rate of sedimentation.

apron occurred before deposition of the oldest apronsediments cored in Hole 290. Application of growthrates observed in other aprons suggests that the durationof the Paleogene pulse of volcanic activity along thePalau-Kyushu Ridge was from the late Eocene to earlyOligocene.

Unit 4, the volcanic conglomerate, probablyrepresents a debris flow, which moved down the adja-cent ridge from the north or east, as implied from thesteep southwesterly dip component defined by the for-mation tops in Holes 290 and 290A and from thetopography defined by the series of profiles across thetrough in which the two holes were located. Thepredominance of angular basalts clasts, the nannofossil-bearing matrix, and a few clasts of manganese-encrustedsediments all suggest that the entire sediment cover andsome basement was involved in the slumping. For thisreason it is assumed that the Eocene-Oligocene age ofboth clasts and matrix is a fair indicator of the localbasement age.

It is impossible to differentiate Unit 4, with a seismicvelocity of about 4 km/sec, from basaltic basement onreflection profiles. Undoubtedly there is some sectionbeneath the breccias at Site 290 which is coeval with theage of the clasts and matrix of Unit 4, but the downwardextrapolation of basement of both ridges flanking thetrough does not permit this section to be very thick(Figure 2).

InterpretationThe most likely age of this part of the West Philippine

Basin is late Eocene, for the reasons outlined above. Itmight be argued that this date represents a later phase ofbasaltic volcanism in the area, but the north-northeast-trending ridges and troughs which comprise the base-ment, seen both in the site survey (Figure 3) and on alater bathymetric compilation in the region, are similarto that seen in actively extending basins. That thesetrends are strongly oblique to the Central Basin Faultsuggests that this fault zone was not a spreading centerat which the basin crust was generated. A more inclusivediscussion of the basin origin is presented in Chapter 42(this volume) where data from all the basin sites are dis-cussed.

The results of Site 290 are also relevant to the historyof the Palau-Kyushu Ridge. Reworked Late Cretaceouspelagic foraminifera, recovered from the bit after com-pletion of Hole 290A, demonstrate that crust of that ageexists somewhere in an area capable of supplyingsediments to the site area. Shallow-water benthonic andpelagic foraminifera of Pliocene age from the samemixed sample suggest that this source is the Palau-Kyushu Ridge, as it is the only sufficiently shallow areaanywhere near the site. It can be surmised that crust ex-isted in the Palau-Kyushu Ridge area during the LateCretaceous, although not necessarily in the form of aridge. The ridge must have existed by the end of theEocene and at least sections of it remained at veryshallow depths until the early Pliocene. The 125-km dis-tance from the crest of the ridge to Site 290 speaks for avery efficient mode of lateral transport, persisting eveninto the depositional regime of the brown clay.

34

SITE 290

REFERENCESBerggren, W., 1972. A Cenozoic time-scale—some im-

plications for regional geology and paleobiogeography:Lethaia, v. 5, p. 195-215.

Blow, W. H., 1969. Late middle Eocene to Recent planktonicforaminiferal biostratigraphy: Internat. Conf. Plankt.Microfossils Proc. 1st, Leiden.

Bukry, D., 1973. Low-latitude coccolith biostratigraphic zona-tion. In Edgar, N. T., Saunders, J. B., et al., Initial Reportsof the Deep Sea Drilling Project, Volume 15: Washington(U.S. Government Printing Office), p. 685-703.

Burns, R. E., Andrews, J. E., et al., 1973. Initial Reports of theDeep Sea Drilling Project, Volume 21: Washington (U.S.Government Printing Office).

Cloud, P. E., Schmidt, R. G., and Burke, H. W., 1956.Geology of Saipan, Mariana Islands: U.S. Geol. Surv.Prof. Paper 280-A.

Dinkleman, M. G., 1973. Radiolarian stratigraphy, Leg 16,DSDP. In van Andel, T. H., Heath, G. R., et al., InitialReports of the Deep Sea Drilling Project, Volume 16:Washington (U.S. Government Printing Office), p. 747-813.

Fischer, A. G., Heezen, B. C , et al., 1971. Initial Reports ofthe Deep Sea Drilling Project; Volume 6: Washington (U.S.Government Printing Office).

Karig, D. E., 1970. Ridges and basins of the Tonga Kermadecisland arc system: J. Geophys. Res., v. 75, p. 239-255.

, 1971. Structural history of the Mariana Island ArcSystem; Geol. Soc. Am. Bull., v. 82, p. 323-344.

., 1972. Remnant arcs: Geol. Soc. Am. Bull., v. 83, p.1057-1068.

Tracey, J. I., Schlanger, S. O., Stock, J. T., Doan, D. B., andMay, H. G., 1964. General geology of Guam: U.S. Geol.Surv. Prof. Paper 403-A.

35

Hmto

APPENDIX ASummary of X-Ray, Grain Size, and Carbon-Carbonate Results, Site 290

Section

290-1-1290-2-3290-2-3

290-24

290-3-1290-3-3290A-1-2

2904-2290-5-1

290-5-3290-6-3290-7-2

290-74

290-8-1290-8-5

Sample DepthBelow SeaFloor (m)

23.774.3*74.3*

75.7-75.8

99.7103.4111.0-111.1

120.3138.0

140.8159.8215.2

218.2

242.3248.0

Lithology

Unit 1Silt-rich Claysand zeolite-rich

Silty clays

Unit 2Ash-radiolarian

•bearingnannofossil-rich

Silty clays

Unit 3Clayey

nannofossil-richAsh and clay-richnannofossil ash

Unit 4Volcanic

Conglomerate

Age

Quaternaryto

lateOligocene

Late

Oligocene

Earlytolate

Oligocene

Very lateEocene orvery earlyOligocene

Bulk SampleMajor Constituent

1

MicaMont.Phil.

Phil.

Calc.

Calc.Clac.Mont.

Phil.Plag.

2

Quar.Plag.Mont.

Plag.

Plag.

Mont.Mont.Plag.

Augi.Calc.

3

Plag.Phil.Plag.

Mont.

Mont.

Plag.Plag.Calc.

Mont.Phil.

2-20µm FractionMajor Constituent

1

Mica

2

Quar.

3

Plag.No Residue AvailableNo Residue Available

Phil.

Plag.

Mont.Plag.Plag.

Plag.

Mont.

Plag.Mont.Mont.

Quar.

Phil.

Phil.Phil.Phil.

No Residue AvailableNo Residue Available

Core 1 Cored Interval: 23.0-32.5 m Site 290 Hole Core 2 Cored Interval: 70.5-80.0 m

FOSSILCHARACTER

CoreCatcher

ixx>f-•---:

LITHOLOGIC DESCRIPTION

5YR 3/4

10YR 4/2

5YR 3/4

Unit 1. Core is intensely deformed in Sections1, 2 and 3, to a drilling breccia in Section 4color is dominately a dark yellow brown(10YR 4/2) with minor moderate brown (5YR 3/4)core generally lithologically consistentthroughout all sections.

SILT-RICH CLAYSmears: 1-70, 3-75, CC

Composition65-71% Clay minerals25-30% Quartz, Feldspar

1 - 3% Fe-oxides1- 5% Zeol i te

1% MicaTr- 2% Volcanic glass

Tr% Heavy mineralsTr% NannofossilsTr% Sponge spiculesTr% Foraminifera

Zeolites (phillipsite, clinoptilolite), plusvolcanic glass, igneous rock fragments, andheavies (apatite ?), pyroxene; also noted weresponge spicules, and Asvmetricius discoasters

Grain Size 1-720.1, 16.9, 83.0

X-ray 1-69 (Bulk)42.658 Mica25.2% Quar18 .U Plag6.1% Chlo4.5% Mont3.6% K-Fe

Note: A O-Section occurred at the top ofSection 1 - Smear sl ides showed theO-Section to be of the DominantLi thology.

Explanatory notes i n chapter 1

FOSSILCHARACTER

CoreCatche

iEOCHEM SAM LE .

LITHOLOGIC DESCRIPTION

5YR 3/2

5YR 3/2and5YR 3/4with5YR 4/4

5YR 3/2with5YR 4/4and5YR 3/4

5YR 3/4

Core is intensely deformed in Section 1 and 2,moderately deformed i n Sections 3 to 6;dominant colors gray brown (5YR 3 /2 ) ; mediumbrown (5YR 3/4) and moderate brown (5YR 4/4)wi th ver t i ca l s t reak ing; minor blebs of l i g h tbrown (5YR 5/6) also occur.

ZEOLITE-RICH (to Zeo l i t i c ) SILTY CLAYSmears: 1-110, 4-80, 6-70, CCTexture74.1* Clay25.8% S i l t

0 . 1 * Sand

Composition55-67% Clay minerals20-25% Zeol i te

5-15% Fe-oxides0-10% Quartz, Feldspar

1% MicronodulesTr% Volcanic glass

ZEOLITIC VOLCANIC ASH (Minor Lith)Smear: 3-78Texture Composition100% S i l t 55% Devit . volcanic glass

45% Zeol i te (low. es t . )

ZEOLITE-RICH VOLCANIC (Palagonite) ASH(Minor L i th )Smear: 6-71Texture Composition65% S i l t 60% Palagonite30% Clay 20% Feldspar5% Si>nd 10% Devit. glass

10% Zeol i te (low. es t . )

Sand and s i l t size grains are mainly aggregatesof c lay ; s i l t f r ac t i on of volcanic ash hasquartz, fe ldspar , microcrysta l l ine feldspaglass; a microphi t ic texture and quenchglasses; zeol i tes coimion ( p h i l l i p s i t e andc l i n o p t i l o l i t e ) .

Grain Size 4-790.1 , 25.8, 74.1

in

X-ray 4-74 (Bulk)60.1% Phil11.8% Plag8.9% Mont8.3% Quar6.1% Mica4.1% Chlo0.8% Clin

P Goet

X-ray 3-77 (Bulk)73.9% Phil8.4% Mont8.2% Plag5.3% Quar4.2% Mica

P Goet

Explanatory notes in chapter 1

ooSite

AGE

ENE

o

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Cored Interval:

LITH0L0GY

i _

J _J _J_

X.J_

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o

oo

oo

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76

70

CC

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99-108.5 m

LITH0L0GIC DESCRIPTION

Unit 2. Core is d r i l l i n g breccia in Section1 with moderate s l i g h t deformation in Sections2 to 3; colors alternate dark yellow brown(10YR 4/2), t o moderate yellow brown (10YR 5/4)

10YR 4/2 in Section 1 , to dominate moderate yellow£ brown (10YR 5/4) i n Sections 2 and 3; some10YR 5/4 minor l i t h i f i c a t i o n to claystone at 145-150 cm

NANNOFOSSIL-RICH SILTY CLAYSmears: 1-16, 1-76, 2-70, CCTexture Composition50-80% Clay 40-71% Clay minerals20-50% S i l t 15-20% Nannofossils

5-10% Volcanic glass4- 5% Zeoli tes1-10% Radiolarians1-5% Micronodules1- 3% Sponge spicules1- 2% Feldspar1-2% Foraminifera0- 3% Palagonite

Minor l i t h o l o g i c variations include: ash-bearing, r a d i o l a r i a n , ash-rich (2%), nanno-

10YR 5/4 f o s s i l - r i c h clay: micronodules noted (5%) at1-76; color variations seem to r e f l e c tchanges i n clay content (increase clay * darkercolorat ion) ; zeolites are p h i l l i p s i t e andc l i n o p t i l o l i t e ; some pyr i te staining.

Carbon Carbonate 1-741.5, 0.0, 12

Carbon Carbonate 3-1431.7, 0.0, 14

Site 290 Hole Core 4 Cored Interval: 118.0-127.5 m

Explanatory notes in chapter 1

FOSSILCHARACTER

CoreCatcher

LITHOLOGIC DESCRIPTION

49

t•

75

10YR 5/4with10YR 4/2and10YR 6/6

Smear: 2-75Texture75% Clay25% S i l t

Top of core is d r i l l i n g breccia with s l i g h tto moderate d r i l l i n g deformation lower;colors dominant moderate yellow brown (10YR 5/4), interlayed with dark yellow orange(10YR 6/6) as laminae; (10YR 6/6) - highervolcanic content.

NANNOFOSSIL RICH SILTY CLAY

Composition62% Clay minerals20% Nannofossils

5-10% Volcanic glass5% Radiolarians2% Zeol i te1% Sponge spicules

VOLCANIC (ASH)-RICH NANNOFOSSIL CLAY(Minor L i th)Smears: 2-49, CCTexture Composition40-85% S i l t 35-70% Clay minerals15-60% Clay 10-20% Nannofossils

10-20% Volcanic glass5-10% Radiolarians3- 5% Palagonite2-10% Feldspar

Basic l i tho logy is nannofossil-rich clay withlocal ash-bearing to r ich and radiolar ian-bearing zones; laminae of dark layers (10YR6/6) higher i n volcanics; scattered Mnnodules

Site 290 Cored Interval: 137.0-146.5 m Cored Interval: 156.0-165.5 m

FOSSILCHARACTER

CoreCatcher

UGEOCHEM SAM LE-

GEO'CHEM~ SAM LE -

LITHOLOGIC DESCRIPTION

10YR 7/4

10YR 7/4

ColorTransition

5Y 5/2

5Y 5/2

Texture (1-100)20-50* S i l t50-80* Clay

Core s t i f f with s l ight deformation, howeverd r i l l i n g has broken or fragmented core;numerous color laminae, burrows, and shear

Site 290 Hole Core 7 Cored I n t e r v a l : 213.0-222.5 m

FOSSILCHARACTER

CoreCatche

GEOCHEM SAM LE"

J-**•*'».

LITHOLOGIC DESCRIPTION

LapilliZone

5Y 5/2

Core is s t i f f with slight deformation;consistent light olive gray (5Y 5/2) colorthroughout core, except for multi-coloredvariations in " lap i l l i " zones.

CLAY/NANNOFOSSIL RICH ASH AND NANNOFOSSIL ASH*Smears: 2-69, 2-110, 4-63, CC

Composition35-45% Volcanic glass20-27% Clay minerals18-25% Nannofossils

12% Zeolite10% Feldspar

3-10% RadiolariansTr- 3% Sponge spiculesTr- 2% Heavy minerals

* L a p i l l i of nannofossil volcanic ash (max.of 7 mm) occur within a matrix of nannofossilvolcanic ash. The clast zone is ungraded;irregular contacts with the volcanic ashand interf inger as mass flow deposit. Nanno-

7 f o s s i l volcanic ash very consistent throughoutand occurs as the matrix of c last zone. Theclasts are rounded, very soft and altered.Zeolites are p h i l l i p s i t e ; radiolariansnoticeable in smear s l i d e s , approaching10% in Section 4.

5Y 5/2

5Y 5/2

Grain Size 2-720.6, 56.6, 42.8

X-ray 2-68 (Bulk)31.1% Mont27.1% Plag25.6% Calc11.8* Phil

3.2% Quar1.2% Anal

Carbon Carbonate 4-741.4, 0.1, 11

Explanatory notes in chapter 1

Site

1 AGE

zUJ

O

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O

ARL

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ZONE

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FOSSILCHARACTER

1 FOR

AMS

| NAN

NOS

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| RAD

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| OTH

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Core 8

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LITHOLOGY

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TS

TS

*TS

TS

TS

'TS»TS

241.5-251.0 m

LITHOLOGIC DESCRIPTION

Section 1. VOLCANIC CONGLOMERATE (Unit 4)o l ive gray (5Y 3/2) to 125 cm moderate yellowbrown (10YR 5/4) to 150 cm. Open framework ofbasal t ic , igneous fragments, dark chert ,black-dark glass, and some zeo l i te /ca lc i te -

5Y 3/2 1 i n e d v o i d s ; clasts (0.2-10 mm) are wellsorted in upper por t ion, moderate to poor inlower; subangular to subrounded fragments

10YR 5/4 in yellow brown matrix.

Section 2. As 125-150 cm in Section 1 withcoarser clasts (1-3 cm) moderate sor t ing;weathering(?) rim noted on large (7 cm) diabasefragment. Faint grading noticed.

Section 3. Moderate yellow brown (10YR 3/4)with darker c lasts; average size 3 mm inc.porp. basalt; glassy basalt , feldspar, alteredvolcanics, palagonite a l l within a zeol i te-micr i te matrix; moderately-well sorted andcoarser towards bottom. Tendency for a closedframework.

Section 4. Coarser than Section 3 with poorsor t ing; maximum size is about 6 cm, average

10YR 5/4 3 mm; closed framework; basalt, chert,weathered volcanics, palagonite fragments.Matrix mud with white zeol i te and ca lc i te .

Section 5. Coarser than Section 4 with increaseof large diabase fragments down section; clastsincluding: highly altered basalt , glass, dia-base some with Mn crust;

Clast l i tho log ies : 40% pumice20% weathered pumice

in Matrix =30% 5% m i n e ™ls includingpyroxene crystals

3% volcanic glass2% diabase

DIABASE* - Fragment (Cobble) (Minor Li th)Thin Section: CCMedium grained, ophi t ic texture; tabularto la th- l ike plagioclase po ik i l i t i ca l lyenclosed by clinopyroxene. Some alterationof clinopyroxene to brown, chlor i t ic material.

*Fragment below conglomerate unit of corewith diabase clasts.

THIN SECTION (DIABASE)Plagioclase 60% (An35-55) (An cores-Ab rims);Pyroxenes 36% (Po ik i l i t i c clinopyroxene);Chlorite 4% (alteration of pyroxene edges)Magnetite-Ilmenite 2%

X-ray 1-77 (Bulk) X-ray 5-52 (Bulk)70.9% Phil 27.8% Plag20.2% Augi 27.0% Calc8.9% Mont 22.8X Phil

21.8% Augi0.6% Quar

Explanatory notes in chapter 1

Site 290 Hole Core 9 Cored Interval: 251.0-255.0 Site 290 Core 2 Cored Interval: 130.5-140.0 m

aer

rbad

FOSSILCHARACTER

CoreCatcher

LITHOLOGIC DESCRIPTION

Five sections of moderate brown (5YR 3/4)SILT-BEARING CLAY. Very soupy and flowed fromliner upon re t r i va l . Core apparently representscaving sediment representative of Core 1 -Hole abandoned due to collapse, after Core 9was taken.

SILT-RICH CLAYSmear: CCTexture86% clay14% S i l t

Composition84% Clay minerals

7-10% Zeolite5% Quartz, Feldspar

1- 2% Nannofossils1- 2% Fe-oxides

5 additional smears show: SILT-BEARING/RICHCLAYTexture85-98% Clay2-15% S i l t

Composition77-86% Iron stained day

minerals12-17% Zeolites ( c l i n o p t i l -

o l i t e and ph i l l ip •si te)

1- 4% Nannofossils1- 2% Quartz, Feldspar

PALEONTOLOGY: Mixture of upper Eocenenannofossils.

FOSSILCHARACTER

CoreCatcher

LITHOLOGIC DESCRIPTION

10YR 5/4VOLCANIC CONGLOMERATE

Color moderate yellow brown (10YR 5/4); clastsaverage 3 mm (up to 2-3 cm) including: basalt,glass, chert(?), altered volcanics, palagonitefragments; subangular to subrounded in amatrix of, dolomitized(?) calc i te(?) , zeolitemud. Unit equivalent to Unit 4 in Core 8Hole 290.

Explanatory notes in chapter 1

Explanatory notes in chapter 1

Site 290 Hole A Core 1 Cored Interval: 108.5-118.0 m

FOSSILCHARACTER

CoreCatche

LITHOLOGY LITHOLOGIC DESCRIPTION

Lithologic material is f irm but is d r i l l i ngbreccia occurs within sections; colors aremoderate brown (5YR 4/4) to moderate brown(5YR 3/4) and generally uniform. No structuresare apparent in the core. Similar to Unit 2in Hole 290 Core 3.

ASH/NANNOFOSSIL-BEARING SILTY CLAYSmears: 2-110, CC

5YR 4/4to5YR 3/4

Texture Composition40-50% S i l t 41-45% Clay minerals50-60% Clay 25% Quartz, Feldspar

10-12% Zeolites8-10% Nannofossils6-10% Volcanic glass

5% Heavy minerals3- 6% Sponge spicules

2% Fe-oxides

The zeolites are ph i l l i p s i t e : some discoasterspresent. May local ly be ash-rich, andzeol i te- r ich.

Carbon Carbonate 2-1041.0, 0 . 1 , 8

X-ray 2-112 (Bulk)

ZI~At Plag19.1% Mont13.5% Phil6.9% Augi3.4% Quar

Explanatory notes in chapter 1

SITE 290

0 cm

25

I—50

100

125

150290-1-1 290-1-2 290-1-3 290-1-4 290-2-1 290-2-2

42

SITE 290

0 cm

— 25

50

— 75

—100

—125

150290-2-3 290-2-4 290-2-5 290-2-6 290-3-1 290-3-2

43

SITE 290

•Ocn

— 50

— 75

—100

— 125

• : • ' • ' , .

H3 \

. • • • • v .

• •

k •

1

^ 1

1

r

r

290-3-3 290-4-1 290-4-2 290-5-1 290-5-2 290-5-3

44

SITE 290

Ocm

— 25

— 50

— 75

—100

— 125

1 150290-6-1 290-6-2 290-6-3 290-7-2 290-7-3 290-7-4

45

SITE 290

-Ocn

— 25

U-50

—100

125

150 290-8-1 290-8-2 290-8-3 290-8-4 290-8-5 290A-1-1

46

>Ocm

— 25

SITE 290

— 75

— 125

150290A-1-2

47