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9. SITE 454: NEAR THE CENTER OF THE MARIANA TROUGH1
Shipboard Scientific Party2
HOLE 454
Date occupied: 5 April 1978
Date departed: 5 April 1978
Time on hole: 20 hours 54 minutes
Position: 18°00.78'N; 144°31.92'E
Water depth (sea level; corrected m, echo-sounding): 3816
Water depth (rig floor; corrected m, echo-sounding): 3826
Bottom felt (m, drill pipe): 3828.5
Penetration (m): 38.5
Number of holes: 1 of 2
Number of cores: 5
Total length of cored section (m): 38.5
Total core recovered (m): 22.51
Core recovery (%): 58.4
Oldest sediment cored:Depth sub-bottom (m): 38.5Nature: vitric mudAge: late PleistoceneMeasured velocity (km/s): 1.52
Basement:Depth sub-bottom (m): not attained
Principal results: Site 454 (SP-4E) is located in a small sediment pondin the shallow, central portion of the Mariana Trough. The site ison what should be the youngest crust west of the back-arc axis ofspreading where there is enough sediment for us to spud-in. Afterpenetrating 38.5 meters of hemipelagic, biogenic, mainly siliceoussediments, we had to abandon the hole when adverse weather con-ditions caused the Glomar Challenger to experience rolls up to13°.
HOLE 454A
Date occupied: 6 April 1978
Date departed: 9 April 1978
Time on hole: 102 hours 36 minutes (includes time waiting on weatherafter Hole 454)
Initial Reports of the Deep Sea Drilling Project, Volume 60.Donald M. Hussong (Co-Chief Scientist), Hawaii Institute of Geophysics, Honolulu,
Hawaii; Seiya Uyeda (Co-Chief Scientist), Earthquake Research Institute, University ofTokyo, Tokyo, Japan; Rene Blanchet, Université de Bretagne Occidentale, Brest, France;Ulrich Bleil, Institut für Geophysik, Ruhr Universitàt, Bochum, Federal Republic of Ger-many; C. Howard Ellis, Marathon Oil Company, Denver Research Center, Littleton, Col-orado; Timothy J. G. Francis, Institute of Oceanographic Sciences, Surrey, United Kingdom;Patricia Fryer, Hawaii Institute of Geophysics, Honolulu, Hawaii; Ki-Iti Horai, Lamont-Doherty Geological Observatory, Palisades, New York; Stanley Kung, Marine Life ResearchGroup, Scripps Institution of Oceanography, La Jolla, California (present address: 416 ShoreView Lane, Leucadia, California); Arend Meijer, Department of Geosciences, University ofArizona, Tucson, Arizona; Kazuaki Nakamura, Earthquake Research Institute, University ofTokyo, Tokyo, Japan; James H. Natland, Deep Sea Drilling Project, Scripps Institution ofOceanography, La Jolla, California; Gordon H. Packham, Department of Geology and Geo-physics, University of Sydney, Sydney, N.S.W. Australia; and Anatoly Sharaskin, VernadskyInstitute of Geochemistry, U.S.S.R. Academy of Sciences, Moscow, U.S.S.R.
Position: 18°00.78'N; 144°31.92'E
Water depth (sea level; corrected m, echo-sounding): 3816
Water depth (rig floor; corrected m, echo-sounding): 3826
Bottom felt (m, drill pipe): 3929.0
Penetration (m): 171.5
Number of holes: 2 of 2
Number of cores: 16
Total length of cored section (m): 142.5
Total core recovered, (m): 40.92
Core recovery (%): 28.7
Oldest sediment cored:Depth sub-bottom (m): 145Nature: bioturbated vitric mudstoneAge: early Pleistocene (0.9-1.6 m.y.)Measured velocity (km/s): 2.1-2.3
Basement:Depth sub-bottom (m): 67Nature: basalts interbedded with sedimentsVelocity range (km/s): 4.2-5.1
Principal results: Drilling of Hole 454A (SP-4E) was begun withoutrepositioning the ship after being forced to abandon Hole 454 andwaiting 20 hours for adverse weather to improve. Total penetra-tion was 171.5 meters with a 41 percent recovery rate. The upper67 meters were vitric mud and ash with abundant radiolarians andnannofossils, underlain by an approximately 10-meter-thick se-quence of massive pillow basalts composed of at least two coolingunits with distinct mineralogies. From 77 to 117 meters, vitricmudstones and tuffs interbedded with apparently thin (less than50-cm each) pillow basalt flows were encountered. Two massive,generally aphyric, fine-grained basalt flows about 12 and 8 metersthick, separated by 2 meters of sediment, overlie the deepest sedi-ment that was recovered from about 139-149 meters beneath thesea floor. These sediments contained nannofossils indicating anage range of 0.9 to 1.6 m.y. These determinations overlap an agerange of 1.4 to 1.9 m.y. from paleomagnetic analysis. The sedi-ments contain several sedimentary cycles of graded bedding overlaminated bedding over bioturbated layers. Below these deepestcored sediments, interbedded spherulitic pillow fragments andmicrolitic basalts were encountered to the bottom of the hole. Thedeeper basalts were very fractured and they repeatedly caved in,eventually causing termination of the hole.
The hole was fully logged from the bottom of the partiallylifted drill string (82 m) to the bottom of the partially collapsedhole (about 150 m below the sea floor). The successful logging per-mitted reliable reconstruction of the interbedded sequences eventhough the core recovery through this region was very poor(< 18%). The large-scale downhole resistivity experiment was suc-cessfully completed after the downhole logging.
Downhole heat flow measurements gave a surprisingly lowvalue of 0.06 HFU, which may represent the cooling effect of seawater circulating into the basement from the drill hole.
BACKGROUND AND OBJECTIVESThe general framework of scientific objectives of
drilling in the Mariana Trough back-arc basin portionof the South Philippine Sea transect (Fig. 1) has been
169
SITE 454
150°
Proposed spreading centers<dashed where no well-defined rift)
Figure 1. Location of Site 454 (O) in the Mariana Trough, plus otherLeg 60 sites ( • ) and sites from previous legs.
discussed in the Background and Objectives chapter forthe Mariana Trough of this volume, so it will not berepeated here.
Holes 454 and 454A, which are at the same location,are in a small sediment pond (Fig. 2) near the center ofthe Mariana Trough. The pond was designated "TargetSP-4E" for site survey and planning purposes. Thedrilling objective was to acquire samples of very youngback-arc basin crust. Thus, the main criterion for thesite selection was to identify a sediment pond of ade-quate dimensions so that we could spud-in the drillstring, and as close as possible to the apparent axis of
spreading in the Trough. The samples were to be sub-jected to petrologic study to determine the relationshipof rock types in this well-developed young portion ofthe basin to the rocks found during its earlier openingstages (Sites 453 and 456), on the island-arc (Sites 457and 458), at mid-ocean ridges, and in other back-arcbasins (e.g., Wood et al., this volume; Fryer et al.; thisvolume).
Spreading rates for the Mariana Trough are variouslyinterpreted to average from 8 cm/y. (Karig, 1971) to 1.5cm/y. (Bibee, 1979). It was therefore important to ob-tain a reliable age determination at Site 454, by paleon-tologic, paleomagnetic, and/or radiometric means, toconstrain the estimates of spreading history in theTrough. In conjunction with age dates for Sites 453 and456, the site provides control over models of episodicand/or asymmetric spreading in the Trough.
Site 454 permits us to focus on the sedimentationhistory of young basin crust which is far from the sub-aerial volcanoes that form the Mariana arc. Sedimenta-tion was influenced only by processes of volcanism andcrustal genesis that have occurred during the past one ortwo million years. During this period the Mariana trench-arc-basin system was tectonically configured much as itis now. At the time we drilled Site 454, for example, weexpected that the high sedimentation rates observed atSite 453, which are presumably functions of the closeproximity of the young Mariana arc volcanoes and theinitial opening phases of the Mariana Trough, wouldnot have occurred at Site 454. We also expected the ig-neous rocks at Site 454 to carry the story of any com-
C\
17°45'
17°30'
143°45'E 144° 144°15' 144°30' 144 °45' 145
Figure 2. Bathymetry of a portion of the Mariana Trough near Site 454. Contour interval is 200 corrected meters. Site 453 is also shown.
170
SITE 454
positional change which has occurred in the back-arcbasin crust, as its potential magma source becomes geo-graphically more removed from the island arc volca-nism. The older portion of the Mariana Trough exhibitsmore chaotic bathymetry than the younger crust, which(at least in our transit area along 17° 15-18° 15 'N) ap-pears symmetric around a graben (Fig. 3). If the con-trast between the older lack of symmetry and theyounger symmetry is a function of the mode of back-arcspreading, are these differences reflected in the com-position of the upper crustal rocks?
Site 454 is located in a region of the Mariana Troughthat is relatively shallow (averaging about 3700 m, Fig.2). Except for a few tiny sediment ponds, which aresmaller than the one we drilled in this axial portion ofthe Trough, the Trough is devoid of sediments. Largelybased on this consideration, the axial-high region wasconsidered the possible axis of spreading in the Troughby some workers. Seismic studies conducted near surveyarea SP-4E by the Hawaii Institute of Geophysics aspart of the IPOD site survey effort show that seismicenergy propagation and crustal structure beneath SP-4Eare normal when compared with the rest of the Trough.High attenuation of energy and abnormal crustal struc-ture are generally found at a crustal spreading center.Natural seismicity levels, magnetic anomaly trends, andbathymetric trends indicated by the site surveys (Fryerand Hussong, this volume) have since led us to suspectthat the axis of spreading may more likely be in thegraben-like deep portion of the Mariana Trough ap-proximately 28 km east of Site 454.
Site 454 is about 130 km west of the active volcanicarc of the Mariana Island, and 100 km east of theeastern edge of the West Mariana Ridge.
OPERATIONSAfter a short post-drilling survey of Site 453, the
Challenger sailed for target site SP-4E. The standardgeophysical profiling system (3.5-kHz and 12-kHz ba-thymetry, 120-cu. in. air gun with single hydrophone ar-ray, and magnetometer) were used for the transit andsurveying.
The small sediment pond that had been chosen forSP4-E prior to Leg 60 had been missed on the earlierChallenger transect (Fig. 3) of the area between Holes452 and 453 (Hussong, this volume), but this time wewere able to locate it on our first pass (Fig. 4) anddropped a 16.0-kHz double-life beacon at 1940 local on4 April, 1978. A short survey of the pond to delineate itsshape, the position of the beacon, and the configurationof a strong seismic reflection occurring above the acous-tic basement and at only 85 milliseconds below the seafloor, was completed by 2212 on 4 April (for results seeGeophysics section, this chapter).
The strong shallow reflector was interpreted poten-tially as either interlayered basalt and sediments or anigneous breccia zone as encountered at Hole 453, so ashort bottom-hole assembly consisting of the core bar-rel, only five drill collars, and one bumper sub, for atotal length of 83 meters, was assembled. This con-
figuration is less desirable for maximum bottom pene-tration because the single bumper sub allows less flex-ibility in drilling procedures, particularly by permittingapplication of less weight to the bit. It is prudent,however, to have as much as possible of the relativelyfragile bottom-hole assembly buried in the sediment be-fore trying to penetrate lithified sediments or crystallinerock. The thin sediment at Site 454 dictated use of theshort bottom-hole assembly. A F93CK bit was selected.
The pipe string was run and bottom felt and cored ata pipe string length of 3828.5 meters at 0720 on 5 April1978. The coring summary is given in Table 1.
After acquiring four sediment cores, the TokyoT-pro.be was run to the bottom of the hole at 29 metersbelow the sea floor. The measurement was unsuccessfuldue to electronic problems with the instrument.
After Core 5, which penetrated to 38.5 meters, thehole was abandoned since worsening weather conditionswere causing the ship to roll regularly 5-6 degrees, withan occasional roll as great as 13 degrees. This motionwas especially undesirable with a portion of the bottom-hole assembly still above bottom.
The weather was not particularly severe (~25-knotwinds), but the wind and seas were coming from the eastwhile a long swell came from the north. The ship had topoint into the wind, thus orienting itself in the troughrelative to the long swell, which caused the excessiveroll.
We pulled out of the hole at 1636 on 5 April. Sevenpipe stands were pulled to get well off the bottom, andthen one stand per hour was pulled to prevent wear onany one section while in contact with the ship.
By the following morning (6 April), conditions hadeased and drilling was resumed. Hole 454A was spuddedat 1218 local time; this hole is charted at the same posi-tion as Hole 454. The coring summary is continued inTable 1. The first 9.5 meters was cored because therewas no recovery of this interval from Hole 454. Subse-quently, we washed down to 38.5 meters, because it didnot seem worthwhile to duplicate the soupy disturbedmaterial obtained from this interval in Site 454. Theheave compensator was used for Cores 5-14 because ofpoor weather and the short bottom assembly.
Basalt was first encountered in Core 4,CC ( — 67 m),matching the 85-millisecond reflector (67 m at 1.57 km/s) observed in the surface seismic records. Interbeddedbasalts and sediments were subsequently cored to a totalpenetration of 171.5 meters.
Recovery dropped severely toward the bottom of thehole as torquing increased (Fig. 5) and pump pressurehad to be raised. The string became stuck during Core14. When the string was finally freed, 30 barrels of mudwas spotted to try to clear the hole. Nevertheless, in-creasing torquing and sticking in the hole, caused by ap-parent collapse of the lower portions of the hole, finallyforced us to pull up at 2335 on 7 April. A final core in-ner barrel, which would have been for Core 17, wasretrieved with a sample from an unknown depth (thehole had filled in to well above the top of the Core 16 in-terval by the time the string was lowered for the last timebefore pulling out).
171
^East
1800Z 1900Z 2000Z 2100Z 2200Z 2300Z OOOOZ 0100Z
Figure 3. Glomar Challenger profiler record over Site 454 and approaching Site 453. Note tilting of fault blocks away from the graben.
0200Z 0300Z
- 9
-10
SITE 454
West North South
Course 081° T Course 180°T
, - • - • • - : • • : .
• ' V •• . . ' • • - t
Figure 4. Challenger air-gun seismic reflection record during the maneuvering over the sediment pond at Site 454. Note the pervasive flat sub-bottom reflection (1^ and R2) and the even deeper, more irregular reflector (R3).
173
SITE 454
Table 1. Coring summary, Site 454.
Date(April
Core 1978)
Depth fromDrill Floor
(m)
Depth belowSea Floor
(m)
LengthCored
(m)
LengthRecovered
(m)Recovery
Hole 45412345
Total
55555
Hole 454A123456789
10111213141516
6666677777777777
08150933105412041524
1305160117131949230602090347050006140750094811151239154018532135
3828.5-3829.03829.0-3838.53838.5-3848.03848.0-3857.53857.5-3867.0
3829.0-3838.53867.0-3876.53876.5-3886.03886.0-3895.53895.5-3905.03905.0-3914.53914.5-3923.53923.5-3932.53932.5-3941.53941.5-3950.53950.5-3959.53959.5-3968.53968.5-3977.53977.5-3986.53986.5-3990.53990.5-4000.0
0.0-0.50.5-10.0
10.0-19.519.5-29.029.0-38.5
0.5-10.038.5-48.048.0-57.557.5-67.067.0-76.576.5-86.086.0-95.095.0-104.0
104.0-113.0113.0-122.0122.0-131.0131.0-140.0140.0-149.0149.0-158.0158.0-162.0162.0-171.5
0.59.59.59.59.5
38.5
9.59.59.59.59.59.59.09.09.09.09.09.09.09.04.09.5
0.0205.968.458.08
22.51
8.224.704.403.654.03.1102.210.100.654.792.151.330.500.111.0
4.0—
62.788.985.0
58.1
86.549.446.338.442.032.70
24.61.17.2
53.223.914.85.52.7
10.5
Total 40.92 28.7
100-
10 20 30 40
Drilling Rate (m/hr.)
140+
50
100
150
•>nn
-
10J
141
T.D. 171.5 m
1.
9l
1 2 T3]
10 20 30 40Drilling Rate (m/hr.)
90 140+
Figure 5. Drilling rates per core, Holes 454 (A) and 454A (B). T.D. =total depth. Core numbers are shown on the figure.
Prior to releasing the bit, the Tokyo T-probe was runto a depth of 3968.5 meters, and an apparently goodmeasurement was obtained.
The bit was then released and the full set of Gearhart-Owen downhole logs were run. This logging includedtemperature, gamma-density, caliper, sonic velocity,gamma-neutron, gamma-induction, XY caliper, andfinally a repeat of the temperature log, in that order.The complete logging program was accomplished from
the bottom of the drill string (approx. 3911.5 m) to thetop of where the hole had filled in (approximately 3977m). Useful logging data were actually obtained con-siderably below the bottom of the drill string. This was ashort interval for such complete logging, but because wehad interbedded sediments and basalts, fairly poorrecovery (29%), and it was our first chance to log, wedecided to make as many measurements as possible. TheGearhart-Owen logging was done from 0700 on 8 Aprilto 0630 on 9 April.
The downhole resistivity experiment was then runfrom 0815 to 1618 on 9 April, also with apparently goodresults (Francis, this volume). At the completion of thiswork the drill string was brought aboard.
The Challenger departed for the next survey target(SP-4D) at 2315 on 9 April 1978.
LITHOLOGY OF SEDIMENTS
At Site 454, two holes were drilled (Holes 454 and454A), penetrating 38.5 meters of sediment in Hole 454and 133 meters of deeper sediments and basalts in Hole454A. As the holes were very close and overlapping, atotal penetration of 171.5 meters was obtained. Basaltwas first encountered at a sub-bottom depth of about 67meters (Core 454A-4).
The drilled sequence has been divided into two units(Fig. 6). Unit I is the sedimentary sequence overlying thebasalts and Unit II contains interbedded sediments andbasalts.
0
50
100
150
_§
αa 3
1,2A1
3
4
5
A2
A3
A4
A5
A6
A7
A8
A9
J R
eco
vere
d
l •
Aid
A12
A13
A14
A15A16
Age
0
LatePleistocene
0.9 my
EarlyPleistocene
*Younger than1.6 m.y. MA
Lithology
-»-
,\ * =
II *
x _ II
II
,\ •
% \
ooαα
J—i D Π D
II * * *
t=> o o σ
Vitric mudSiliceous oozeSiliceous nannofossil ooze
Vitric mud
Silty/sandy ashlayers increasingdownward(biogenic decrease)
Vitric mudstone
+ and silty tuffinterbedded withbasaltic rocks
Cycles: graded,laminated, bioturba-ted
m Biogenic compo-nents extremely
*rare
UN
ITI
UN
IT 1
1
Holes 454 and 454A
Figure 6. Lithologic summary, Site 454. Lithologies for Unit II aregiven only for recovered intervals. See Figure 8 for reconstructionbased on logging data. Symbols are as in introductory chapter Ex-planatory Notes.
174
SITE 454
Unit I: 67 Meters Thick, Late Pleistocene toUppermost Early Pleistocene
It is represented by Cores SP-4F (piston core fromthe Hawaii Institute of Geophysics site survey), 454-1(CC) through 5 and 454A-1 through 4.
Basically, Unit I consists of hemipelagic sediments(mud and vitric mud with volcanic ash) and biogenicsediments (siliceous ooze, siliceous nannofossil ooze,nannofossil ooze).
Mud and volcanic ash are present all through the unit(clayey, silty, and sandy vitric ash). Most of thosesediments contain over 10 per cent of volcanogenic com-ponents. Ash layers increase downward between 15 and57 meters; but sandy ash layers are mainly present above31.7 meters. The color is generally greenish gray toolive-gray. Silty and sandy ash layers are the darkerlithologies.
Sediments rich in biogenic components are lighter incolor (dusky to dark yellowish brown). Among the bio-genic sediments, siliceous ooze (with radiolarians, dia-toms, and sponge spicules) and siliceous nannofossilmarly ooze are dominant. Nannofossil-foraminifer mar-ly ooze is also present. Biogenic sediments are well de-veloped (50% and over) between 0 and 15 meters; theydecrease progressively downward.
Some layers rich in unidentified micronodules werealso encountered (Core SP-4E, Section 454-4-4).
Unit II: 67 to 171.5 Meters, Early Pleistocene
Unit II consists of alternating sediment layers andbasalts (massive lavas and pillow lavas). The sedimentsprobably represent two continuous layers interbeddedwith basalts. They are observed in three cores—Cores 8(Sections 1 and 2), 12, and 13. Lithologically, they aremostly hemipelagic sediments (vitric mudstone and clay-stone) with clayey to silty vitric tuff. Biogenic com-ponents, mainly nannofossils, become extremely re-stricted. A few per cent is usual, but biogenic compo-nents rarely exceed 10 per cent.
In this unit, we find cyclic sedimentary structuressimilar to those observed in cores at Site 453. They con-sist of basal-graded layers, intermediate, thinly lam-inated layers, and upper bioturbated layers. Each cycleis at least 10-20 cm thick (some parts could have beenlost during coring). Upper bioturbated layers (vitricmudstones and claystones) are thicker than the coarsergraded and laminated ones. In Core 8 are several bur-rows filled with fecal pellets. Dendrites (Mn?) occur insome bedding planes (Core 13).
In Core 13 (Section 1, 70 cm) a rather abrupt changein color occurs from moderate to dark greenish grayabove to light olive-gray to light olive-brown below. Insmear slides, the upper darker part is higher in clay con-tent (-90%) and lower in volcanic ash (10-13%), whilethe lower, lighter colored part is higher in ash (-40%),silt (-40%), and unidentified micronodule (-20%)content.
BIOSTRATIGRAPHY
Summary
A Quaternary section penetrated at Site 454 can bedated on the basis of calcareous nannofossils throughthe entire sequence and with radiolarians in the upperpart. Except for Core 1 in Hole 454A, which duplicatesthe interval penetrated by Core 1 in Hole 454, cores inHole 454A continue below the bottom samples in Hole454. In the oldest sediment interbedded with basalts atthe bottom of Hole 454A, the Gephyrocapsa carib-beanica nannofossil subzone can be recognized, in-dicating an age range of 0.9 to 1.6 m.y.
Only impoverished undifferentiated Quaternary for-aminiferal assemblages were recovered from Holes 454and 454A.
NannofossilsThe Holocene and part of the late Pleistocene were
penetrated in Hole 454. A complete section of latePleistocene and much of the early Pleistocene were en-countered in Hole 454A. All of the Holocene andPleistocene nannofossil zones and subzones, except thelowest Emiliania annula Subzone, can be recognized.Each of the sedimentary units recovered from betweenbasaltic layers contains calcareous nannofossil assem-blages with age-diagnostic species. All of the zonesobserved in samples from these two holes can be definedby the presence of the primary zone defining species.
In Hole 454, the Holocene Emiliania huxleyi Zonecan be identified in Sample 1,CC. No sediments wererecovered in Core 2. Cores 3 through 5 can be assignedto the late Pleistocene Emiliania ovata Subzone of theGephyrocapsa oceanica Zone.
Section 1 of Core 1 in Hole 454A contains nan-nofossils indicative of the late Pleistocene Ceratolithuscristatus Subzone of the Gephyrocapsa oceanica Zone.This subzone was not observed in samples from Hole454, presumably because of the lack of recovery in Core2 from that hole.
The late Pleistocene Emiliania ovata Subzone of theGephyrocapsa oceanica Zone can be recognized inSamples 454A-1-2, 90-91 cm through 454A-3,CC.
The early Pleistocene Gephyrocapsa caribbeanicaSubzone of the Crenalithus doronicoides Zone can berecognized in Samples 454A-4-2,82-83 cm through 454A-13-1, 132-133 cm. Samples from 454A-8,CC through454A-13-1, 132-133 cm represent fossiliferous sedimen-tary occurrences between basaltic layers.
According to the geochronologic time scale for nan-nofossil zones presented by Bukry (1975), the lowestfossiliferous sediments penetrated at Site 454 can be noyounger than 0.9 m.y. and no older than 1.6 m.y.
Radiolarians
Well-preserved radiolarians are generally abundantin the upper Quaternary cores of Holes 454 (Cores 1-5)and 454A (Cores 1-4). No radiolarians were seen inolder sediment.
175
SITE 454
Species upon which Nigrini's (1971) Quaternary zo-nation is based are generally very rare, even in the rich-est radiolarian assemblages. The latest zone, Buccino-sphaera invaginata, can be identified only in the smallsample recovered from Core 1 of Hole 454. The Collo-sphaera tuberosa Zone is recognizable in Core 3 of Hole454 and in Core 1 of Hole 454A. Only one deeper sam-ple (Sample 454-4,CC) can be assigned with confidenceto the Amphirhopalum ypsilon Zone.
SEDIMENT ACCUMULATION RATES
The sediment accumulation curve (Fig. 7) has beencalculated in kilograms of water-free sediment per squarecentimeter. The calculation was done in the same way asfor Site 453, except that averaging was not necessaryand the density log was used to determine the propor-tion of sediment interbedded with the basalt in Unit II.The total sediment accumulated at the site in the drilledsection was 7.1 kg/cm2, accumulated from 0.9 to 1.6m.y. B.P.
Because of the short duration of sedimentation, onlya few boundaries could be determined. The results areas follows (the rate for Segment 3 is for the sedimentonly):
Age (m.y.)
1)
2)
3)
Interval
Holocene and latestPleistocene(0-0.3 m.y.)Late Pleistocene(0.3-0.9 m.y.)Early Pleistocene(0.9->1.6 m.y.)
Depth belowSeafloor (m)
0-2.2
2.2-56.6
56.5-141.3
Accumulation(kg/cm2/m.
0.5
6.3
>4.8
Ratey )
The accumulation within Segment 1 is substantiallylower than within Segment 2. The organic content of theupper part of Segment 2 is similar to that in Segment 1,but it decreases at about 17 meters below the sea floor.It is possible that the lower rate of sedimentation of Seg-ment 1 commenced in the later part of the time ofdeposition of Segment 2 and is due to a decrease ofvolcanic activity in the arc in the past 0.3 m.y.
Segment 3 is entirely within the nannofossil subzoneof Gephyrocapsa caribbeanica and commences 10.4meters above the top of the interbedded basalts andsediment of Unit II. The accumulation rate is probablyconsiderably greater than the calculated minimum of4.8 kg/cm2/m.y. The high rate of deposition may bepartly the result of sediment being contributed fromlocal sources as well as the active arc.
LITHOLOGIC SYNTHESIS
Site 454 is located in the central Mariana Trough, onthe western limb of the central high-relief zone 28 kmwest of the suspected spreading axis. Seismic profilesshow that the site is on the western side of a small sedi-ment pond, the surface of which slopes gently to thewest and even more gently to the south. The east andwest flanking ridges are steep, with the western beingthe steeper.
-
Holocene
Late
\ \
Pleistocene
Early
-.1 10
Figure 7. Sediment accumulation (kg/cm2) versus age, Site 454. I iserror bar for depth of zone boundary,of zone boundary.
is upper limit for depth
Only Pleistocene fossil assemblages are recorded inthe drilled succession. Sediment at Site 454 are dividedinto two units, a hemipelagic mudstone associated withabundant but upward decreasing volcanogenic detritus(Unit I) overlying at least two layers (Core 8 and Cores12 and 13) of hemipelagic sediments interbedded withbasalts (Unit II).
In the sediment of Unit II, biogenic components(mainly calcareous nannofossils) are rare, but they con-tain age-diagnostic forms. Several sedimentary cyclesare developed with, from the bottom to top, gradedbedding, laminated bedding, and bioturbated layers.Sediment deformation is minor, even next to basalts.Undisturbed horizontal fine lamination is common, oc-curring in the core samples nearest to underlying basalt(e.g., the lowest sediments above basalts in Section 8-2,at 100 cm, and Section 13-1, at 134 cm). Only a singlenormal fault with 1.5 mm of displacement was observedin the top sample of the upper sediment layer inter-bedded with basalts (Section 8-1, 90-95 cm).
We infer the interlayered basalts to be interbeddedpillows and flows, since we recovered no baked intrusivecontacts, and the level of sediment disturbance wasminor.
Comparison of the downhole Gearhart-Owen densitylogging with wet-bulk density data between Cores 8 and13 allows the lithologic column to be constructed (Fig.8) with the following features:
1) Vitric mudstone samples in Cores 12 and 13 makeup a single, nearly continuous layer that may possiblyinclude a few basalt fragments (isolated pillows?).
2) An additional 50-cm-thick sediment layer occursbetween basalts in the lowest part of Core 11. This layercan be recognized on the logs, but no samples wererecovered in the core.
3) Cores 8, 9 and the upper two-thirds of Core 10contain sediments with basalts (pillows?) no thickerthan 50-cm, the limit of resolution of the density loggingtool. A few basalt fragments were recovered in thesecores. In this interval, sediment densities obtained bylogging range between 1.55 and 1.85; by laboratorymeasurement they give 1.56 for vitric tuff and 2.21 forbasalt.
The occurrence of basalts interbedded with turbiditesediments at Site 454 indicates that a basin existed at thesite when the last flows of Layer 2 were extruded. While
176
SITE 454
Hole 454A
α; O
Figure 8. Comparison of three density logs (overlapped) obtained inHole 454A showing the inferred relationship to interbedded mas-sive basalts, pillowed basalts, and sediments. Cores, recovery, andthe shipboard classification of lithologic units are also indicated.After shore-based investigation, the lithologic units were revised asin Figure 10.
no data exist on the interbedding of sediments in thebasalts on the adjacent ridges, we feel that the ridgesprobably originated before the conclusion of volcanicactivity and therefore may lack interbedded turbidites.
GEOCHEMISTRY
Two samples were taken for pore water chemistry,one each from Holes 454 and 454A. The data arepresented in Gieskes and Johnson (this volume). Thesamples are virtually identical and differ only slightlyfrom sea water; they resemble near-mudline samplesfrom Site 452.
IGNEOUS AND METAMORPHIC ROCKS
Lithology and Downhole Chemical Variations
At Site 454, 20 meters of aphyric to sparesly phyricbasalt in both massive units and pillow sequences, in-terspersed with layers of pumice and sedimentarymaterial, was recovered in Cores 4 through 16. Totalbasalt penetration was about 104.5 meters including in-terbedded sediments. The stratigraphy of the basaltsand sediment layers is shown in Figure 9. The lithologyof the uppermost and lowest portions of the section
Q
3895.5π
3905.0-
3914.5-
3923.5-
3932.5-
3941.5-
3950.5-
3959.5-
3968.5-
3977.5-
3986.5-
3990.5-
nnn n.
o a;_)DC
5
6
7
8
H•••
9
•••
1 nI U
ma
11
12
13
MM
14
^•••
15•H
16
^ ^>s3 Pillow basalt
Massive basalt(showing fractures andvesicularity)
- — — Sediment
Drilling breccia
Density Log
Figure 9. Complete column for the intercalated basalt flow and sedi-ment layer showing depth below the sea surface, core recovery,and lithology of the basalts.
(Cores 4 through 7 and 14 through 16, respectively) wasreconstructed based on the assumption that the propor-tion of material recovered is representative of the trueproportions of materials in the intervals cored. Fromthe interval represented by Cores 8 through 13, the li-thology has been reconstructed using the logging resultsas a guide to the thickness and relative proportions oflayers present. We subdivided the basalts into five unitson the basis of petrographic and lithologic characteris-tics (Fig. 10). These will be described in more detail. Thefirst three are similar in composition and are groupedtogether as a single chemical type, whereas Units 4 and 5form distinct chemical types (Fig. 11).
The first petrographic unit consists of massiveaphyric basalts which probably comprise two coolingunits. The upper cooling units appear to be overlain bypillow basalts of similar compositions. A few smallglassy pillow fragments interspersed with sediments
177
SITE 454
were recovered in the core catcher sample of Core 4.The upper meter or so of Core 5 is distinctly fine-grained, moderately altered basalt which becomes coarserand fresher downward. At the base of Section 5-3, therocks show microdolerite textures. Fracturing is wide-spread, and fracture surfaces and veins are coated orfilled with carbonate (aragonite, as identified in thinsections and occurring on fracture surfaces, Fig. 12),some chlorite, and in one instance, a botryoidal greencoating, probably of green smectite. Aragonite-filledamygdules occur in the middle of Core 5. At the top ofSection 5-4, the average grain size decreases perceptibly.In thin sections, the proportion of very fine grainedspherulitic patches increase and the typical size of ti-tanomagnetites in these patches decreases. This suggeststhe base of the cooling unit is close to this depth. How-ever, it was not recovered. Instead, the next several frag-ments recovered are distinctly coarser grained, less ve-sicular, and rich in olivine. This suggests a second cool-ing unit, although neither its top nor bottom was recov-ered.
Underlying the massive basalt in Core 6, is a gradeddrilling breccia varying from clay-sized to pebble-sizedfragments of pumice, volcanic glass, and coarse-grainedbasalt. This material is described more fully in the sec-tion on sediment lithology. Fragments of medium-grained, olivine-poor basalt were recovered in the lowerpart of Core 6 and are indicated as basaltic Unit 2 inFigure 10.
Below the massive basalt is a zone of interbeddedsediment and pillow basalt (Cores 7,8,9, and the upperpart of Core 10). The basalts in this zone are shown asbasaltic Unit 3 of Figure 10. The density distribution asrevealed by logging in this interval (see Fig. 8) precludesthe presence of thick (larger than 0.5-m) pillow basalt
5
6
7
H
9
10
••
„13
14
15
16
Rec
ove
ry (
%)
-
3-
Lithology
Pillow fragments on top, restis massive, veined basalt
Drilling breccia
Interbedded pillows +sediment (vitric mudstone)
Sediment (vitric mudstone)
Interbedded pillows +sediment (vitric mudstone)
. O . = O « . o o ° 0 θ " = ° O . " .
— Sediment
Sediment (vitric mudstone)
Interlayered pillow fragments+ massive basalt (massive
Pe
tro
gra
ph
icU
nits
Bl
B2
B3
S1
B3
B4SII
B4
SMI
B5
Chemical Units(wood et al.,this volume)
1
2
3
Magnetic Inclination
-12°
1No oriented samples
-31°
-37°
-30°
-13°
Figure 10. Summary of lithologic units and variation with depth inhole of percentage recovery, lithology, composition, and magneticinclination.
layers interspersed with sediment. The pillow fragmentsrecovered are fresh and display spherulitic textures adja-cent to glassy rinds. Olivine appears to be fairly abun-dant in these rocks, but cannot be resolved in handspecimens.
Beneath the sediment/pillow basalt sequence are twomassive basalt flows separated by a thin sediment layer(Cores 10-12). These form Basaltic Unit 4 in Figure 10.No material from the sediment layer was recovered, buta prominent drop in the integrated bulk density (see log-ging section) at a drill hole depth which correlates withthe lower part of Core 11 attests to its presence. Thebasalt of these two flows is predominantly fine-grainedand microvesicular. There are scattered Plagioclasephenocrysts throughout the units, but for the most partthe basalt is aphyric. There are numerous fracturesthroughout these basalts. They contain secondary min-erals—chiefly clays and carbonate. Grain size increasesfrom fine to medium in the lower unit. There is very lit-tle alteration of the basalt despite the presence of nu-merous carbonate veins. Only the base of the lower ba-salt flow (the lower 40 cm) shows moderate alteration toa general brownish gray color. A layer of silty mudstoneshowing signs of bioturbation underlies the lower flow.(See section on sediment lithology, this chapter.)
Interbedded spherulitic pillow fragments and micro-litic basalts (which may have been pillow interiors) makeup the lower portion of the hole (Cores 14-16; BasalticUnit 5 of Fig. 10). The pillow fragments generally showspherulitic texture adjacent to glassy rinds. Some of thepillow fragments contain small olivine phenocrysts. Themore massive basalts are aphyric, slightly altered, andcontain varying amounts of vesicles concentrated inpatches.
BASALT PETROGRAPHY (HOLE 454A)
Unit 1—Upper Massive Basalt Flows (Core 5)
The massive basalts of Core 5 can be subdivided intothree zones based on mineral composition and textureof the rocks.
The upper zone (in Core 5, Section 1) is about 1 meterthick and consists of vesicular microphyric basalt withscarce and small (less than l-to-1.5-mm) micropheno-crysts of olivine and Plagioclase set in an intersertal orsubophitic groundmass. Both types of phenocrysts con-tain rare inclusions of tiny, euhedral crystals of brownspinel. The groundmass is composed of 25-30 per centPlagioclase laths (up to 0.6 mm long; ca. An65), 55-60per cent granular to plumose augite between Plagioclaselaths, 3-5 per cent opaque grains (titanomagnetite), andup to 10 per cent devitrified and partly altered inter-stitial glass.
Round to irregular-shaped vesicles (up to 15% rockvolume) range in size from 0.15-1.6 mm and are filledor encrusted with palagonite and/or smectite. Patchesand irregular veins of these mineraloids also replace theglassy material of the rock groundmass.
The next main zone (Core 5, Sections 2,3 and part of4) is free of phenocrysts and has subophitic, sometimesintersertal texture. It consists of 25-30 per cent plagio-
178
SITE 454
TiO. Sr
130 170 210 2501.0 1.2 50
Zr
70
Ni Cr
100 300 500 P l P x O l C r S p G l
90 100 300 500 700 P GM P GM P GM IncGM- 21 60 3
15 10 Tr 10
3900 r
- 60103
- T r
37
- T r 4439
- 41
_ 25
18
25
23
Tr 252237
5
6
Tr2Tr
2 4
2 2
2 I
Tr
Tr
92
91
7
3222
23
22
27
3
3
10
251215
40
5545
Tr
134
CrSp = chrome-spinel inclusions in olivine (Inc) ancgroundmass (GM)
4000^- TiC>2 in wt.%
Sr, Zr, Ni, Cr in ppm Gl = glass
PI = Plagioclase phenocrysts (P) and groundmass (GM) yes = vesicles
Px = pyroxene phenocrysts (P) and groundmass (GM)
Ol = olivine phenocrysts (P) and groundmass (GM)
Figure 11. Variation with depth in hole of abundance of TiO2, Sr, Zr, Ni, Cr, and major phase mineralogy of basalts.
(Tr = trace (>1%)
Other = opaque minerals and secondary minerals (primarilyclays, carbonate and zeolites)
clase (ca. An65_70), 50-70 per cent augite, 2-5 per centopaque, and 5-7 per cent glassy material. Small sub-angular olivine grains scattered throughout this zoneusually contain tiny spinel inclusions. These inclusionsare also widespread within the Plagioclase laths. Thegrain size of minerals gradually increases downward toabout the bottom of Section 5-3; textures in its lowestparts are microdoleritic. The degree of vesicularity re-mains constant (10-15%). In addition to smectite andpalagonite, carbonate (aragonite) and zeolites fillvesicles and veins within this interval.
At the top of Section 5-4, the proportion of in-terstitial material increases somewhat, indicating thebase of this subzone was being approached. It was notrecovered, however. The rocks in the third subzone (re-mainder of Section 5-4) are considerably different. Theyare denser (2-5% vesicles), more coarse-grained, andenriched in granular olivine crystals (up to 0.6 mmacross; 10-15% rock volume). In addition to olivine,abundant Plagioclase laths (up to 4 mm long; ca.An65_70), pale brown augite (zoned, slightly anomalousinterference colors), and minor opaque minerals, are setin a granular to subophitic matrix containing no morethan 10 per cent glass. Green, extremely fine grained,clay minerals (smectite) are the principal secondary
product after glass. Minute inclusions of brown spinelare rather abundant both in olivine and Plagioclasecrystals.
Unit 2—Medium-grained Basalt(Core 6, Sections 2 and CC)
Several pieces of basalt recovered under the gradeddrilling breccia are fine to medium-grained, vesicular(up to 15%) rocks with aphyric, intersertal or tran-sitional-to-spherulitic textures. These basalts consist ofplumose aggregates of Plagioclase and clinopyroxene (inthe proportion 2:1) cemented by fresh or partly devitri-fied and altered glass. Since the recovery is very small, itis difficult to judge from petrographic data whetherthey represent samples of a chilled massive flow or pil-low fragments with disintegrated glassy margins.
Unit 3—Pillow Basalts Interbedded with Sediments(Cores 8 through 10)
According to logging data, the fragments of pillowbasalts with chilled glassy margins recovered in Cores 8,9, and 10 could have been sampled from several (at leastfour) rather thin (about 0.5-m thick) pillow units in-terbedded with sediments. These rocks are slightly vesic-ular (~3%), microphyric in texture, and contain small
179
SITE 454
Figure 12. Clump of aragonite crystals in vug on stub of basalt; Section 454A-5-3. Holes in rocks are vesicles ~ l mm in diameter. Smooth coatingon vug surface is green smectites.
180
SITE 454
(0.2 to 0.4-mm) euhedral olivine microphenocrysts (upto 5% rock volume) set in a hyaline to spheruliticgroundmass.
Unit 4—Massive Basalt Flow (Cores 11 and 12)
The two separate massive basalt flows (see loggingresults) of this unit are similar petrographically. Theyhave intersertal outer and subophitic inner zones and donot show internal signs of differentiation. The maincomponents of the rocks are Plagioclase laths (50-60%)up to 1.5 mm long (ca. An65), augite (30-40%) up to 1mm long, minor titanomagnetite, and interstitial glass.Rare small grains of olivine can be seen in thin sectionof Sample 454A-11-4, 71-75 cm. Tiny brown spinel in-clusions are common both in olivine and Plagioclasecrystals.
These rocks have high porosity as evidenced by ve-sicles (up to 25%), especially in the upper parts of theflows. Abundant round to irregular vesicles (0.1-7 mm)are encrusted or filled by smectite, zeolite, and car-bonate. Smectite also replaces the interstitial materialforming green colored patches and irregular zones.
Unit 5—Pillow Basalts (Cores 13 Through 16)
Only one rock fragment was recovered in the sedi-ment of Core 13—a small piece of pahoehoe. No thinsection was made from it.
Two distinct textural groups are observed among thebasalt fragments recovered in Cores 14 through 16.
One group consists of microphyric olivine basalts con-taining up to 7 percent olivine microphenocrysts (0.2-0.6 mm; with spinel inclusions) in a slightly porous( — 3% vesicles) spherulitic glassy matrix. In hand speci-mens these usually have well-developed glassy marginsor at least glassy remnants. These rocks resembled theolivine pillow basalts of Unit 3.
The other group of basalts are also olivine micro-phyric (2-3% rock volume), but their groundmass is in-tersertal or sometimes transitional to spherulitic. Themost crystalline basalts consist of ~3 percent olivinegrains (0.1 mm and less in diameter; with spinel inclu-sions), 55-60 percent Plagioclase laths (up to 0.8-1.0mm long), and interstitial glassy materials with abun-dant crystallites of clinopyroxene and dust-like opaquegrains. The more crystalline the rock is, the higher is itsvesicularity (up to 15%).
On the basis of textural characteristics, the rocks ofthe unit could be interpreted as fragments from theouter (the first group) or inner (the second group) zonesof pillows. Unit 5 is thus probably a sequence of pillowbasalts.
Many of the rock samples from this unit are mod-erately altered and have palagonite-smectite aggregatesreplacing glassy material.
ALTERATION
Alteration is moderate to minor in the basalts of Hole454A. The uppermost fine-grained portions of BasalticUnit 1 in Core 5 are gray-brown in color as opposed tothe basic gray of the fresher basalts. One or two pieceshave distinct rinds of this brown-stained material. Frac-
ture surfaces are thinly coated with rust-colored ironoxyhydroxides, locally flecked with black ferroman-ganese oxides. Cracks and vugs in Basaltic Unit 1 arelined with green clays or aragonite. In one thin section,a vein of clear orange isotropic palagonite occurs, lo-cally crossing vesicles lined with radially grown fibrouspalagonite.
The minor "brown-stone" alteration at the top ofCore 5 diminishes with depth. The basalts of Core 11,like those of Core 5, have cracks filled with aragonite(Fig. 12). Green clays with palagonite-like structures canbe seen in thin sections of rocks from Core 11:Aragonite is a common secondary mineral throughoutthese rocks.
Most of the basalts recovered at this site are filledwith tiny (0.5-mm) vesicles (15-2.0%), giving them highporosity (they took a long time to dry after splitting).Glassy intersertal patches which contain these vesiclesare usually altered to pale fibrous clays. Alteration,though minor, is pervasive, and may give the basaltssome of the chemical imprint of sea water.
CHEMISTRY
Wood et al. (this volume) define three chemical unitsamong the Hole 454A basalts (Fig. 10) and report thatthey have most of the characteristics of depleted inter-arc basin tholeiitic basalts. However, trace element dataindicate that they have been hybridized to some extentwith calc-alkalic materials. Wood et al. (this volume) in-fer these to be magmas. It seems to us also possible thatthe basalts may have assimilated sediments of overallcalc-alkalic composition, since such sediments clearlywere supplied to the site throughout the time of erup-tion, and consist of air-fall ashes derived from the Mari-ana arc.
GEOPHYSICS
Examples of the reflection seismic profiles run acrossthe pond at Site 454 by the Glomar Challenger areshown in Figure 4. The pond is approximately 2 kmwide from east to west, and over 5 km wide from northto south. It is surrounded by very steep scarps; the ridgewest of the pond (Fig. 4) has an essentially vertical dropof over 700 meters. A prominent, flat, reflector 85 milli-seconds below the sea floor (Rb Fig. 4) correlates withthe top of the uppermost basalt flow encountered in thedrilling. This reflector, and a similarly pervasive reflec-tor (labeled R2 on Fig. 4) at a depth of about 0.15seconds below the sea floor, are observed on all tra-verses of the pond. An even deeper reflector (R3, Fig. 4)is less distinct and can be seen only intermittently.
A prominent mound stands about 40 meters abovethe sea floor in the middle of the Site 454 pond. It has abasal diameter of about 300 meter:;, but it is too small totell much about its shape or whether it is composedof sediment or rocks. It is larger than the geothermalmounds observed in the Galapagos region (Lonsdale,1977). The mound does not appear to be an almost-buried pinnacle of basement rock because it has little ef-fect on the sub-bottom reflectors Rj and R2. Holes 454and 454A are located within 300 meters of the mound.
181
SITE 454
There are no faults observed in the sediment pond.The sea floor and reflectors Rj and R2 all dip slightly tothe west.
PALEOMAGNETISM
Site 454 is situated on a negative magnetic anomalyadjacent to the western flank of the possible centralanomaly over the axial graben in the Mariana Trough.A magnetic basement age of about 1.2 to 1.6 m.y. (firsthalf of the Matuyama reversed epoch) is inferred fromthis negative anomaly, although correlations with adja-cent tracks have been discouragingly unsuccessful.
Sediments at this site were too disturbed for paleo-magnetic study, except for three mudstone beds inter-layered in the basaltic basement. On the basis of dif-ferences in magnetic inclination, the basalts are sepa-rated into five groups (Fig. 10). Each unit sampled con-tains rocks of distinct magnetic inclination, with the ex-ception of Unit 4. Samples from the upper portion ofUnit 4 have slightly greater inclination than those fromthe lower portion. The three mudstone beds and five ig-neous units all show a negative stable inclination (formore details, see Bleil, this volume).
PHYSICAL PROPERTIES
Compressional wave velocity, wet-bulk density, salt-corrected water content, porosity, acoustic impedance,and thermal conductivity were determined for cores re-covered from Holes 454 and 454A. Measurements aretabulated in Table 2 and plotted against depth in Figure13.
Sonic Velocities
Sonic velocities for the vertical direction were mea-sured in the Hamilton Frame. Velocities in the sedi-ments range from 1.52 to 2.32 km/s, showing no in-crease in depth in the first 40 meters below the sea bed,but progressively increasing with depth when overlainby basalts (Fig. 13). Velocities in the basalts range from3.65 to 5.12 km/s, showing no relationship with depthbut correlating with porosity and density (Figs. 14 and15). It is likely that the higher-velocity basalts comefrom the more massive rocks of the interior of lavaflows.
Densities
Wet-bulk densities were determined both by 2-minuteGRAPE counts and by gravimetric method. The aver-age discrepancy between the two methods is 0.06 g/cm3.As with the sonic velocities, no conspicuous trend withdepth is noticeable in the top 40 meters of the column.The limited number of measurements on the vitric ashesand mudstones intercalated with the basalts, however,showed density increasing with depth (Fig. 13).
COMPARISON OF LABORATORYMEASUREMENTS WITH DOWNHOLE LOGGING
Laboratory measurements of wet-bulk density areplotted on the downhole compensated density log inFigure 16. The depth at which a laboratory value is plot-
ted is derived from its position within the recoveredcore. This can be in error by several meters, particularlywhen the recovery is low. Furthermore, the density log-ging tool averages over a depth range of about 0.3 me-ters, so that small fragments of basalt that are largeenough to measure in the laboratory may not be de-tected. These factors may explain the discrepancy ob-served between downhole and laboratory values at 3942meters in Figure 16. In general, The agreement betweenlaboratory and downhole logged densities is excellent.
Laboratory measurements of sonic velocity are plot-ted on the sonic log in Figure 17. Here the agreement isless good than in the density case. Measurements onbasalt samples are higher, and on sedimentary samplesare lower, than the corresponding downhole values.These discrepancies may be explained by the following:
1) The sonic log determines interval time (1/velocity)over a 2-ft (0.6-m) depth range. However, unlike thedensity log which is pressed against the side of the hole,the sonic tool is free to move with the end of the loggingcable. The heave of the ship will thus induce an up-and-down motion in the sonic tool as it progresses up thehole. The effect of this will be to make the sonic logaverage over a greater depth range than its receiver spac-ing, probably in the range of 1 to 2 meters. Thus, in for-mations consisting of a smaller-scale mixture of hetero-geneous rocks (such as the basalt pillow fragments andvitric mudstones recovered in Cores 8 and 9) the velocitylogged is likely to be an average for the rock types en-countered. Only when homogeneous formations thickerthan 1 to 2 meters are encountered can the sonic logmake an accurate measurement of the in situ velocity ofthe particular rock type. This appears to be the case forthe massive basalt lavas encountered between 3947 and3962 meters below the drill floor (Fig. 17).
2) The sedimentary rock samples measured were vit-ric mudstones and tuffs, which have had porosities inthe range of 60-70%. The recovery of these samples in-volved a reduction in pressure from about 400 bar to 1bar. Since water is much more compressible than rock-forming minerals, the water held in the rocks must (1)have expanded within the rock, thus increasing its po-rosity, and/or (2) have partially escaped from the rock,possibly destroying some of the rock fabric in the pro-cess. In either case, the sonic velocity of the rock is like-ly to have been reduced.
3) Basalt samples selected for measurement in theHamilton Frame were necessarily coherent pieces ofrock which were sawn into parallel-sided slabs. Theporosity of these samples is confined to the vesicles theymight contain. On the scale of the downhole velocitylogging, fissures and cracks are likely to be important.Indeed, there were mineralized fissures and cracks inmany of the recovered cores. Thus laboratory measure-ments of sonic velocity in basalt samples are likely to ex-ceed those observed on a larger scale in situ.
Thermal Conductivity
Many thermal conductivity measurements were madeon the core samples recovered from Holes 454 and454A. The results indicate that the thermal conductivity
182
SITE 454
Table 2. Physical properties measurements, Site 454.
Sample(Interval in cm)
Hole 4543-1, 99-1013-3, 56-584-1, 77-794-3, 122-1254-5, 102-1045-3, 106-1085-5, 106-108
Hole 454A1-1, 77-792-2, 103-1055-2, 49-525-4, 11-136,CC, 18-208-1, 119-1218-2, 20-2210-1, 41-4211-2, 44-4611-4, 37-4312-2, 5-713-1, 6-1013-1, 84-8614-1, 63-6516-1, 81-8316-2, 2-4
Depth(m)
10.9913.5620.2723.7226.5233.0636.06
1.2741.0368.9971.6179.3296.1996.70
113.41123.94126.87132.55140.06140.84149.63162.81163.52
SoundVelocity(vertical)(km/s)
1.531.551.54.52.52.54.52
.52
.534.075.094.261.851.743.714.214.283.652.112.325.124.904.49
GRAPE2-minuteWet-BulkDensity(g/cm3)
1.571.721.551.301.361.331.41
1.432.452.662.511.56
2.212.252.432.201.69
2.482.472.37
WaterContent
(salt-corrected)
56.042.350.760.9
56.6
10.6
9.9
45.915.412.8
15.6
10.0
Porositya
(%)
77.266.873.680.5
78.1
25.1
23.7
69.233.629.0
33.9
23.8
Wet-Bulkb
Density(g/cm*)
1.411.621.491.36
1.41
2.42
2.45
1.552.242.32
2.23
2.44
AcousticImpedance
(g/cm2s × I05)
2.162.512.292.072.072.052.14
2.199.85
13.510.42.892.708.319.77
10.48.143.57
12.712.010.6
RockType
Soft mudFirm mud
Firm clay
Soft mudFirm clay
Mud
BasaltBasaltBasaltVitric ashVitric ashBasaltBasaltBasaltBasaltVitric mu<:Vitric mu:BasaltBasaltBasalt
j* Porosity = salt-corrected water content x wet-bulk density (gravimetric)/1.025.° Gravimetric method.
u
50
100
150
t 1 1 1 1
^ Sonic Velocity* (vertical) (km/s)
•*
-
AA
A
| • •
A
AA
A•_ A
A A
1 1 1
# Wet-Bulk• Density
t * (g/cm3)
•
AA
A
A
AA
A
*
A
# Acoustic• Impedance
• (g/cm2s)
•
-
AA
A
A
AA
A
*
A _
A A
1 1
2.0 3.0 4.0 5.0 1.5 2.0 2.5 5x1Q5 1 0 × 1 05 1 5 x 1 05
Figure 13. Physical properties versus depth, Holes 454 and 454A; = sediments, • = basalts.
of the sediment at Site 454 is generally higher than atSite 453. This difference may be related to the shallowerdepth at Site 454. The rate of increase of thermal con-ductivity with depth was found to be the same as at Site453.
The basaltic samples from the basement in Hole 454Ashowed a fairly uniform thermal conductivity. More de-tails and discussions on the measurements are given inHorai (this volume).
LOGGINGA complete series of downhole logs for Site 454 were
obtained. Preliminary correlation of the logs with other
data are included in the appropriate sections of thischapter.
In addition to the inherent resolution of each of thetypes of logs, two other points should be rememberedwhen making geologic interpretation from the logs:
1) The logging tool will be moving up and down inthe hole in response to the heave of the drilling vessel.This heave is on the order of ± 1 meter during the mod-erate seas encountered during Site 454 logging opera-tions. The heave at the logging tool will be heightened ordamped to an unknown degree as a function of the elas-tic properties of the logging wire and friction in thepipe. The bottom of the drill pipe will also heave with
183
SITE 454
32
30
| 2 8
o£ 26
24
22
A
1 1
A
A
1
-
A
-
1
3920 -
3.5 4.0 4.5Velocity (km/s)
5.0
Figure 14. Comparison of sonic velocities and porosities of basalts,Hole 454A.
2.6
2.4
2.2
1 1
-
A
1
A
A
A
r~
A
A
A
3.5 4.0 4.5Velocity (km/s)
5.0
Figure 15. Comparison of sonic velocities and 2-minute GRAPE den-sities for basalts, Hole 454A.
the ship, but perhaps not in phase with the logging toolbecause of the different elastic properties of the pipeand the logging cable.
2) The bottom of the hole is the level to which thehole caved in after lifting the bit. It is different for dif-ferent shapes and weights of the logging tools, so itshould not be used as a fixed datum.
The logging proved invaluable for reconstructing thestratigraphy of Site 454, where core recovery was notvery good.
HEAT FLOW
Two downhole temperature measurements were at-tempted in Holes 454 and 454A. The measurement con-ducted in soft mud in Hole 454 at a sub-bottom depth of27 meters was unsuccessful.
In Hole 454A, we decided not to attempt any heatflow measurements until the bottom-hole assembly wascompletely buried in order to protect the drill string.Unfortunately, by the time the bottom-hole assemblywas buried the bit was penetrating interbedded basaltand sediments, which made the heat flow measurementimpossible.
3980-
1.50
Sedimentary rocksBasalts
Density (g/cm )2 minute GRAPE
densityGravimetric
densityo
Figure 16. Comparison of laboratory density measurements with down-hole compensated density log, Hole 454A.
After drilling in Hole 454A ended, we made a bottom-hole water temperature measurement using the TokyoT-probe. Later, two lowerings of the Gearhart-Owenlogging tool were made. All these measurements revealeda remarkably small temperature rise in the hole.
The observed low gradient in Hole 454A was prob-ably not due to the effect of thermal disturbance bydrilling and circulation of mud (water), because therewas not enough change in temperature with time afterthe drilling ceased.
If we take the mean of the observed temperature gra-dient (0.2°C/100 m), and interpret it as the geothermal
184
SITE 454
3920
3930
1 Flo
or (
m)
00 CD o
wD
ri
o£3950a>
Dis
tanc
3960
3970
•
-
c
•
-
i
)
A
L
\1
180 150
Sedimentary rock
100Microseconds per FootBasalt A
50
Figure 17. Comparison of laboratory measurements of sonic velocitywith bore-hole compensated sonic log, Hole 454A.
gradient, the apparent heat flow in Hole 454A is cal-culated as: Q = 0.06 HFU.
An entirely different interpretation for the low tem-perature gradient observed in Hole 454A is also possi-ble. It may be that cold sea water was continuouslydrawn into the hole after the drill penetrated into thehighly permeable igneous basement and this artificiallyinduced circulation of sea water cooled the entire hole.For more details, see Uyeda and Horai (this volume).
LARGE-SCALE RESISTIVITY
Hole 454A provided the first opportunity to try thelarge-scale resistivity experiment. Only about 70 metersof open hole was available for logging beneath the endof the drill pipe—too short a distance to provide aproper test of the resistivity experiment. Nevertheless,the results gave values similar to those obtained with theelectrical resistivity log (Francis, this volume).
SUMMARY AND CONCLUSIONSThe major objectives of drilling at Site 454 were to
determine: (1) the age, state and petrologic character-istics of the youngest "drillable" back-arc basin crustformed at a well-developed stage of spreading; and (2)the history of the sedimentary, volcanic, tectonic, andthermal activity in the area of the youngest "drillable"back-arc basin.
Being the youngest back-arc crust also means thatSite 454, of all our Mariana Trough sites, formed at thegreatest distance from the active subaerial volcanos onthe Mariana arc.
The age of the deepest sediments suggests that thefirst basalt flow encountered in Hole 454A, at the age ofthe sediments intercalated between the deeper basaltflows, is 0.9-1.6 m.y. This fits the age of 1.2-1.6 m.y.calculated from the surface magnetic anomaly pattern(Bleil, this volume). Paleomagnetic measurements ofthe three mudstones between the basalt flows, and ofthe five basalt units, all gave stable negative inclinationin agreement with the surface anomaly. The overlapof the ages (1.2-1.6 m.y.) provides a maximum half-spreading rate from the Trough spreading center of1.7-2.3 cm/y., although the accuracy of such an esti-mate is poor because of the short distances and times in-volved. Nevertheless, the spreading rates agree withthose estimated for Site 453, supporting the idea that theback-arc basin spreading is slow and likely originates atthe graben 28 km east of Site 454.
The basalts in Hole 454A show only minor alteration,and are chemically similar to depleted inter-arc basinand mid-oceanic ridge tholeiites. The different flowshave distinct chemical and, to some extent, petrographiccharacteristics. Their chemistry appears to reflect avarying degree of hybridization, possibly caused by mix-ing with calc-alkalic material (Wood et al., this volume).
On the basis of the reflection seismic records and therelief surrounding the pond, we suspect that the inter-bedded basalt and sediment sequence extends far deeperthan we were able to sample. The presence of thick in-terbedded sediments in the upper part of the crust im-plies a very high sedimentation rate in the basin duringits earliest history. If the sediments are derived from air-or water-borne volcanoclastics from island arc volca-nism, interbedded sediments should be thickest in theolder parts of the back-arc basin that formed when thedistance from the volcanics to the spreading center is thesmallest. We have no evidence whether or not this is thecase.
The nature of the 40-meter mound in the center of theSite 454 pond remains a mystery. It could be the top of anarrow pillar of basalt that was extruded after risingthrough the sediments and basalt flows in the pond. Itmight also be a small horst, although there is no othersign of faulting cutting the deposits in the Site 454 basin.It is tempting to speculate that, in light of the high levelof geothermal activity in the Mariana Trough (see chap-ters on Sites 454 and 457), the mound is an oversizedversion of the geothermal mounds in the Galapagosarea. No other direct evidence for active geothermal ac-tivity is apparent at Site 454, but Hobart et al. (1979)found very high and very variable heat flow near thissite. If we are correct that there i:> a considerable thick-ness of interbedded sediment and basalt flows beneathwhere we were able to penetrate, then our cored sectionmight be isolated from nearby geothermal activity.
The very low heat flow measured at Site 454 (0.06HFU) could be representative of a local extreme value,but we prefer to regard it as evidence of cool sea water
185
SITE 454
being drawn into the drill hole and flowing into perme-able beds deep in the hole. It is not caused by drillingdisturbance.
REFERENCESBibee, L. D., 1979. Crustal structure in areas of active crustal accre-
tion [Ph.D. dissert.]. University of California, Sari Diego.Bukry, D., 1975. Coccolith and silicoflagellate stratigraphy, north-
western Pacific Ocean, Deep Sea Drilling Project, Leg 32. In Lar-son, R. L., Moberly, R., et al., Init. Repts. DSDP, 32: Washing-ton (U.S. Govt. Printing Office), 677-701.
Hobart, M. A., Anderson, R. N., and Uyeda, S., 1979. Heat transferin the Mariana Trough. EOS, 60:383.
Karig, D. E., 1971. Structural history of the Mariana Island ArcSystem. Geol. Soc. Am. Bull., 83:323-344.
Lonsdale, P., 1977. Deep-tow observations at the Mounds AbyssalHydrothermal Field, Galapagos Rift. Earth Planet, Sci. Lett.,36:92-110.
Nigrini, C. A., 1971. Radiolarian zones in the Quaternary of theequatorial Pacific. In Funnel, B. M., and Riedel, W. R. (Eds.),The Micropaleontology of Oceans: London (Cambridge Univer-sity Press), pp. 443-461.
186
SITE 454 HOLE 1 CORED INTERVAL: 0.0 to 0.5 r
FOSSIL
CHARACTER
GRAPHIC
LITHOLOGYLITHOLOGIC DESCRIPTION
VITRIC S1 LICEOUS MUD, dark yellowish brown (10YR 4/2),
SMEAR SLIDE SUMMARY
TEXTURE:
Sand
SiltClayTOTAL DETRITAL
COMPOSITION:
Feldspar
Clay
Volcanic glass
Microπodules
Nannofossils
Diatoms
Radiolaπans
Sponge spicules
V i t
M u d
CC
15454055
10
3510
•f
5
5
3G
5
NOTE: Site 454, Core 2, 0.5 to 10.0 m: No Recovery (See Site 454/Hole A/Core 1/
Cored Interval 0.5 to 10.0 m).
SITE
•j
ME
-R
O
UN
IT
i1α.
s
454
,_
IO
ST
RA
ZO
NE
CD
_
s2
•S
1!
CC
§
ai
11
HOLE
FOSSIL
CHARACTER
RA
MS
J
FO
I
SO
NN
4Z
CM
AG
CM
Q
4
AG
AG
AG
AG
FM
CORE
SE
CT
IOrV
1
2
3
4
CC
ME
TE
RS
-
0.5-
1.0-
-
-
--
_—-
-
-
J
3 CORED INTERVAL:
GRAPHICLITHOLOGY
-•tC= =C= =0
—•jr
= 1
_ Λ Λ _ _ T Λ _
P I — _/~\_ _ j " " \
vy-• —\ — —\j•~-KJ~- - v - r -
1— , —*—
:—
_!7.-
J - , - L
- J-*~ 1
_ !- — t —*•
~\ j _[ -L.
_r::.-
— — 1
L J_1
— t ~*•
__ _i.
Ti- -/
-^ ~C—^-
—w~
_ z ^
- > ^ .
—l
-
-
-
-
_
-
1
-‰
J_
_L
_L
- i .-I
J.
_;»- -4
^ 'i, II ^
,_3 •=*!*; J,
o
ILL
ING
ST
UR
BA
N
SQ
DIM
EN
T>
RU
CT
UR
E
" ^
jΛ/^
' m'
0
HO
LO
GIC
MP
LE
#
*
*
#
10.0 to 19.5 m
LITHOLOGIC DESCRIPTION
SILICEOUS MUD, SILICEOUS NANNOFOSSIL OOZE andNANNOFOSSIL OOZE LAYER (2-5/10) with SANDY AND
10YR 4/2 SILTY VITRIC ASH increasing downwards in Section 4, darkyellowish brown (10YR 4/2), moderate yellowish brown(10YR 5/4), olive gray (5Y 4/1), to olive black. The entire
Grayish orange core is very deformed. Sandy layer is graded (3-130 cm).(10YR 7/4) grades .IO10YR4/2 SMEAR SLIDE SUMMARY , 0
foss
il
foss
il
- 10YR4/2 § , • •= l . § 2 S- 10YR 7/4 = 2 2 % J 8 = %- D a r k y e l l o w i s h M S S * z δ < o c i n
brown (10YR 4/4) 1 4 8 1-129 2-4 3-89 3-130
10YR5/4 TEXTURE:- 1 U Y K "" Sand 25 10 5 20 40
Silt 10 40 25 20 60Swirls of all c , a y 6 5 5 0 7 0 6 0 _o f a b o v e TOTAL DETRITAL 50 5 17 15 50
- COMPOSITION:Feldspar 7 5 8 5 10
Moderate yellowish Heavy minerals 1 + 4 - 5brown (10YR 2/2) Clay 42 - -
Volcanic glass - 5 10 5— Rock fragments — — — — 30
, „ . , , Micronodules 30 5 5 5 5- 5 Y 4 / 1 Carbonate unsp. - - 1 - -
- 5Ya2/irPa'Ch iEff"5 ^ 10 ?2 " I1 0 Y R 6 / 4 Radio^ians 15 25 3 5 -10YR4/2 Sponge spicules - 5 1 -
Sand grain with_ Light greenish Iron-hydroxides - - - 45
brown (5YR 4/2)Dusky yellowish SMEAR SLIDE SUMMARYbrown (10YR 2/2) ~ α
—-VOID T l.a S
Dark yellowish | -%$ '*brown I10YR 2/2) ^ g J. •oPatches of darker .2 I f ! {sandv sediment "-S z • « «
S.1 4-81 4-1022 j TEXTURE:
5Y 2/1 >. = Sand 30 40J S Silt 40 40
Dark olive S 2 Clay 30 20
!_ ~\" COMPOSITION:Dark olive qrav \ Feldspar - 5(5Y3/1) Heavy minerals 7
Volcanic glass 50 70Micronodules 3 *-Carbonate unsp. + —Nannofossils 30 20Radiolarians 5
OO
- J
0 00 0
SITE
ME
-R
OC
KU
NIT
181~\8
454
lOS
TR
AT
ZO
NE
ta
a2
1ε
HOLEFOSSIL
CHARACTER
RA
MS
O
SO
NN
<z
AG
FM
AM
a<
AM
A M
A M
FM
CG
CORE
SE
CT
ION
1
2
3
4
5
6
7
CC
ME
TE
RS
-
_0.5-
-
1.0-
-
_
-
-—
-
z
-
:--z
-
--
-
4 CORED INTERVAL:
GRAPHICLITHOLOGY
, _• *• ^— — — — j * ^
1 ^
_.._. ~'. J* *-. _ . jl ^ =
_ _ . 1 * ^ ^
~ - ~ - ~ - • " -
- " - " - " - "
_ . .
*»°»:
J*.. ;
•--:~-7.•-l l
'-'_-7_-'_-:.;.. .
;*.
= M 1.
:—>..érj.L"«*
1^. % " /
" tv// II
u
VOID
_..
'17.-7.-~.-7..
—
- • - ~ - ~ • - ~
, * (
* *
"**
> l>-*
:
• *~.*<*:
VOID
ST
UR
BA
NC
E
hSS
j
All
0
0Λ
0
HO
LO
GIC
MP
LE
•••
19.5 to 29.0 m
LITHOLOGIC DESCRIPTION
MUD, VITRIC MUD with layers or patches of SILTY5 Y 4 " VITRIC ASH, SANDY VITRIC ASH, NANNOFOSSIL
~ Sandv sediment OOZE (3-115 cm), and SILICEOUS NANNOFOSSIL(5Y 2/1) (pushed in OOZE (4-6 cm), mainly olive gray (5Y 4/1), light olivefrom above?) gray (5Y 6/1), olive black (5Y 2/1). Darker litholoαies:5Y 6/1 silty and sandy ash. Very deformed streaks and patches
with coarser and darker sediments. Section 2 very mixed.5Y4/1 Core-Catcher: As above
Moderate°Illowish SMEAR SLIDE SUMMARYbrown (10YR 5/4) 5
S 7 ~
Patches | I 1(5Y4/1) 0 S 0
1 a Nam
Vit
ri
Mic
rm
ud
(10YR 5/4)3-115 4-5 4-6
TEXTURE:Sand ~ 1 5
' ° Y R 7 ' 4 Silt 20 19 25
5Y4/1 and 10YR5/4 5 Λ L , Π I T D 1 T . , ?? 52 iü
and brownish gray COMPOSITION:
Dark yellowish brown Feldspar 4 20 10- (10YR 4/2) streaks Heavy minerals -
Dusky yellowish brown C|aV - - ~(10YR 2/2) in sandy bed Volcanic glass 7 15 5
Rock fragments - 10 -Micronodules 3 18 -
10YR 5/4 and 5Y 6/1 Zeolite - - +Carbonate unsp. 2 2 +Foraminifers 1 - 1
5Y 2/, pale yellowish g l ^ J - ' " 8° + 2
6°brown (1 u b/bl(s arp Radiolarians 2 — 20
o u π a r v Sponge spicules — 1 2
_ Streaked 5Y 5/1 F i s h r e m a l n s + _ -
SMEAR SLIDE SUMMARY_ 10YR 4/2 S
~ 5Y 6/1 to 5Y 4/1 = .a
10YR 2/2 silty layers 3 J |
Silt
yas
h
Sili
cec
San
dy
ash
4-45 4-95 CC-5TEXTURE:
— 5Y 4/1 (fine sediment) Sand - 5 80~~ 5Y 2/1 (sandy) Silt 40 95 20
Clay 60 -
1 0 YR5/4 COMPOSITION:
Feldspar 9 30 10
- 5Y 6/1 with small Heavy minerals ^ ^ 5 -
streaks of coarser and .. . . . ., c o oslightly darker sediment Volcanic glass 7 5 88
Rock fragments - 5 2Micronodules 20 50Zeolite - - -Carbonate unsp. 3 — —
Nannofossils 2 +Diatoms 1Radiolarians 1
5 Y 4 / 1 F ishTmains'" - ' - -
Yellowish grey (5Y 7/2)5Y 4/1 (sandv ash)
SITE 454 HOLE CORED INTERVAL
MUD, VITRIC MUD with layers or patches ofSILTY TO SANDY VITRIC ASH, VITRIC NANNOFOSSILOOZE, light olive gray (5Y 5/2) to moderate olive brown(5Y4/4). Soupy to very deformed.
SITE 454 HOLE 1 CORED INTERVAL:
LITHOLOGIC DESCRIPTION
L _ l I i l l
5Y 4/1 with bands
Medium olivegray (5Y 4/2)Dusky yellow (5Y 6/4)5YR 2/2
10Y 4/2
5YR 2/2
5Y6/4
5YR 2/2
Dark yellowish brown(10YR 4/2) withsandy patchGrayish olive (10Y 4/2)10YR 2/2, sandy10YR 2/2, sandy
Light olive gray(5Y 5/2) (fine)5Y7/2
5Y5/2
10YR 4/2,
10YR 2/2
Pale olive (10Y 6/2)becomes a little
5Y5/2
10YR 4/2
Olive gray(5Y 372)
5Y3/2
MUD AND VITRIC MUD, olive gray (5Y 4/11 to greenisholive (10Y 4/2) with bands, laminae, layers or patches of:SANDY or SILTY VITRIC ASH, dusky brown (5YR 2/2)or dusky yellowish brown (10YR 2/2); SILICEOUSOOZE, 3-82 cm, yellowish gray (5Y 7/2), SILICEOUSNANNOFOSSIL OOZE, VITRIC NANNOFOSSIL OOZE,(Core-Catcher). Foraminifers visible in paler lithologies(S-4). Column changes below Section 3 to more biogeπic
SMEAR SLIDE SUMN
s i l l
Ji s If H i2 5 0 2-100 2-106 3-82
TOTAL DETRITALCOMPOSITION:Feldspar
SMEAR SLIDE SUMMARY
TEXTURE:SandSiltClayTOTAL DETRITALCOMPOSITION:Feldspar
jiol.
iπof
£ i4-77
10108015
5
RadiolarianSponge spic
o _
HOLE A CORE 2 CORED INTERVAL: 38.5 to 48.0 mFOSSIL
CHARACTER
GRAPHICLITHOLOGY
LITHOLOGIC DESCRIPTION
VITRIC MUD, MUD with layers of VITRIC ASH, SILTYVITRIC ASH, one band of NANNOFOSSIL OOZE(4-30 cm). Vitric ash layers are darker. The core issoupy, deformed, or very deformed. All bands are 5GY 4/1from 1-76 to 3-110 cm.Core-Catcher: Crumbly fragments of zeolitic silty vitric ash.
SMEAR SLIDE SUMMARYgreenish gray (5G 6/11Greenish gray(5GY 6/1!
Dark greenishgray (5GY 4/1)
5GY 5/1 If328 3-130
yTOTAL DETRITALCOMPOSITION:Feldspar
10Y 4/2
5GY 6/1
80 73 60
4-11 4-30 CC
30 -5 7i1 _
10Y4/25GY 4/1 sesubconcho,
5GY 4/1 sesubconcho5GY 6/1
imi-lithrfied,idal fracture
imi lithified.dal fracture
RaSpFi!Sil
idiolari<onge sp;h remaicoflage
SITE 454 HOLE A CORED INTERVAL:FOSSIL
CHARACTER
GRAPHICLITHOLOGY
CC
LITHOLOGIC DESCRIPTION
Light olive gray(5Y 5/2) toolive gray(5Y 3/2)
MUD, SILTY VITRIC ASH, VITRIC ASH, WITHLAYERS OF FORAMINIFER-NANNOFOSSIL OOZE,
in grayish orange layers. Darker lithologies with moreabundant brown volcanic glass.
SMEAR SLIDE SUMMARY Φ
Dark yellowishorange (10YR 8/6)Dark greenishgray (BG 4/1)5Y3/2
Brownish black (5YR 2/1)
TEXTURE:SandSiltClayTOTAL DETRICOMPOSITIONQuartzFeldsparHeavy mineralsClay
234
I :yIiSS
Grayish orange5Y5/25Y3/2
oc•sD
SITE 454 HOLE A CORED INTERVAL: 57.5 to 67.0 m
LITHOLOGIC DESCRIPTION
gray (5GY6/11
5Y3/1
MUD, SILTY VITRIC ASH, NANNOFOSSIL VITRICASH and MUD, dark olive gray (5Y 3/1), dark greenishgray (5GY 4/1), grades down to moderate greenish gray(5GY4/1). Very deformed to soupy. Brown volcanic
Core-Catcher: Sedir ..-iih >;!..
SMEAR SLIDE SUMMARY
I|1S1
1-149.5
ClayTOTAL DETRITALCOMPOSITION:
30 74 3570 25 6566 91 81
60-454A-5 3885.5-3895.0 m (67.0-76.5 m, BSF)
Aphyric to sparsely plagioclase-phyric basalt
Fresh to moderately altered aphyric and sparsely-plagioclase phyric
„, « » j> « ffl <δ basalt. Some pieces show yellow (10YR 6/6) alteration on cored
c M c ^ c ^ c ^ c ^ c ^ c ^ surfaces. Many pieces show sworls or "varioles" of acicular plagioclase,o = « 2 3 a .2 3 0 .2 3 S .2 3 « .2 3 a> .2 3 indicating that this is probably a pillowed unit. The length of coherent
1 I | % - 1 S § £ c 1 2 § £ c 1 S S S = 1 S S S g 1 | § " § 1 S i " c pieces is greater sections 2 and 3. ,n Section 4. te×tures are coarser| j | i l l I .0 I I 1 1 I .a I I I I I .Si § 1 I I -ll I i l 2 * I" I • 8 1 * * f S I 1 grained. Alteration is spotty down the core. In Section I.Fe-hydroxides
cm el O <r O w < 1 (3 1 O i β < ė L O C O K < Q T O O C O C O < £ O CC O C/J < Q I O K O C O < £ O CC O 05 < d a r k g r e e n c | a y s p i e c e 8 h a s a t h i n e n c r u s t a t i o n o f p a l e d a y s o π i t s
Q , , ___. | | . . 1 - p—1 . —1 .—- . • 1—- t ! 1—1 —I uppermost fracture surface, and vugs filled with radial zeolites. Piece 7
×\ 1 X T / ~TΛ / ( \ TSTΛ / ~^=~~^ °°'> PfT also has a radial zeolite clump on its top fracture surface in a slightlyI/ J t K I /, \ VL K V - ~ ' o 1 f ‰ scoriaceous zone. In Section 3, zeolites are also scattered throughout.
I ^ ' 1 I ' ' i / i\ i ^ ^ / -TJ- " - Λ Λ / Piece 2B has a crack with Fe-Mn oxides, continued from the lower— /—j 1 ' / I T K Λ I " > • c D T ~—J~ " °° 7T7' ~ fracture surface of 2A. Pieces 6A and 6B have alight olive gray (5Y 5/2)
2 o t / i j / \j 2 T×,k r-•' /o° 2A [ | . ‰T^;;!^^^^3 ^7 ' ——^r / /^^x ^ ". ~7 ' ' M The basalts throughout appear very porous, probably because of
~• r~~^ i / / / i ^ ^-j • . • ' lY\ ~ vesicularity (myriads of tiny, pin-hole vesicles).4 _ ^ J f K / 2 A ^ ^ K ' 3 m \ \ • t . 0 L M • Thin Section Synopsis:
^ =d 2A iX-di "•••"•'. - » p=r— Sections 1-4. Aphyric basalt with texture vary ing from subophitic toδQ 7 , R T V OK^ V ~ o ' f I i - in«erser,al,containing10-15%olivine(Fo8 0.8 5:<0.6mm)inmicro-
= = 2 B _-—• ^ ^ _ ^ Q 1 - * ':.- „ 3 \ \ T diabase, 18-60% plagioclase ( A n 7 0 7 g : < 1.5 mm in fine-grainedA\ i / -—=- ^ V -7^— ',/. '• * ' V ) " basalt; An6 5:0.4-4.0 mm in microdiabase), 45-65% clinopyroxene
6 l \ T K / / I l i 2 B ^ \ \ "-* '" ' ' o (augite: <2.0 mm), 1-5% magnetite (<0.1 mm) and 4-10% devitrified— ^ -1. 3/ ( * , \ j K •.~* o . , ^ S 5 ~ glass. The glass shows patchy alteration to clay or palagonite. Vesi-
( "5 y ( -I f „ _ ^ _ . ' ' ^ I" A i cularity is 2-15% with many vesicles lined or filled with clay minerals,-,[ I i ^^>\ A . ' β * 4 / palagonite, chlorite or carbonate.
5 0 - ' 4 f i J | | '•• i" ' '. M - Rock
I , T
S D U < B L . . . . . ° o ( 3 ! JNRM M D F l n c • s D TvPβ~~g ' -^ ' 1 .' • °o ° y S ? ' 5-1. 133-136cm 1.99×10"3 — -16.2
_ 8 <^ / C^—I Z C " K ° o ' _ 5-2, 49-52 cm — 4.07 2.42 Basalt7 ^ / 5B&V^ K ' ° 5 " 3 ' 7 4 • 7 β c m 2.79x10•3 7.0
9 (—^ J ' r\ L .. I T • . ' « . 5 ^ 11-13 cm — — — 5.09 — Basalt
= 7 ^ / I i = = s I / ; •••— , n f \ i 5 C \ \ ° o " ' — 60-454A-6 3895.0-3904.5 m (76.5-86.0 m, BSF)
iu I , T ) yp
— — - ^ 'j • • o ^ o " Graded cuttings and aphyric basalt
11\_2) 6 Λ2)3 °''• 0 °0 _ Sections 1 and 2 consist mainly of graded drilling cuttings which
. y ZIZHZ •o ^ c>.0 include fragments of pumice, volcanic glass, and fine-grained basalt.LA > / ^ Q C\o*< - The top of the core has minor Holocene carbonate sediments, clearly
1 2 (\\ ' 7 / I 4 C D •. "" /nS'α out of place down the hole. Below 92 cm in Section 2 are 2 pieces of_ / C C ' O" •S?/^ — fine-grained aphyric basalt with about 5% vesicles (0.5-2 mm diameter),
I 1 . ^ ^ ^ 5A A Λ •• \cf" y of generally irregular shape, aligned in roughly parallel streaks along theJ ×T~~* T K . : " 1 ' * / K y " cut surface. Piece 2 is coarser grained than Piece 1 {it is microdiabasic),(_ . K / • 0 . , , ?"j / aphyric, and moderately vesicular. A narrow alteration rind is on Piece
100— / " V * "n * " /^^S 1 — 1. Piece 2 is fresh. Basalt in the Core-Catcher is similar, fine-to14/ i K 8 5B A i •'.? ' / T × ' T medium-grained, and aphyric.
V J / T i L z f - λò T K-7y / ö K p — , o " ^ η . _ J N R M MDF Inc. S D Type
15 f I y 0 ' °o " 3 ) 1 * 6,CC 18-20 cm 4.26 2.45 Basalt
p^s / J7 - = ^ < 1 T "I=*** 9B / / ^ T
— 17B » 9C Uf -^ λ ° - -
I M T r ~ j 1 r S / \o°_ T = ^ • ' 1 " W N " f , J I o _ 60-454A-7 3904.5 3913.5 m (86.0-95.0 m, BSF)
r^ . ' ~ 6B»\ f18 I t K' ^ K° " N o R e verv
^ - ^ ^_ _ I PiPol | | | I | | Lf | | I | I I I I | I I I Logging data indicates that this interval is occupied primarily by
CORE/SECTION 5/1 5/2 5/3 5/4 6/1 6/2 6,CC sediments, but with a few small pillows.
GO
H
_ αi i VΛ
SITE 454 HOLE A CORE 8 CORED INTERVAL: 95.0 to 104.0 m
toLITHOLOGIC DESCRIPTION
VITRIC MUDSTONE with GRADED ANDLAMINATED SILTY VITRIC MUOSTONE ANDTUFF. Grayish olive green (5GY 3/2). Mudstoneall burrowed and mottled. Fecal pellets, well-preserved in burrows (1-115 to 2-25 cm).
1-130 cm: Graded bedded silty sand to mud
SMEAR SLIDE SUMMARY
Fish remainsPyritePalagonite
SMEAR SLIDE SUMMARY
ClayTOTAL DETRITALCOMPOSITION:
II2 2 5
5 5> E
2-30
3 S £ S S S o 60-454A-8 3913.5-3922.5 m (95.0-104.0 m, BSF)c " ° c "^ c " ö c " ° c " ° c " θ c " °
I 1 _ I I •S c á I I e I JE I c £ I 1 c I I | c i & S _ I Aphyricbasal,I of 1 l i I . j I l i I J f 1.2 I ..I I I I I A 1 11 i .1 I I I I of I l.| The piece, recovered in thi5 core are fine-grained, fresh pmow basal,Z ~ S { o ; !c i ™ .§ ra Z £ O 5 O K i : α> ™ .§ " !c » ™ ^ » Z J S S o S Z | « J o ; ; fragments. Some variolitic zones occur next to glass. A few fragmentsS g • α . ü i S • i i § ë • Q . . i . e J> § ra O• .1 U• | g ë••g• .1 .S• jjj § reg .1 .9- j j g g α .2 .S• Jj § g•α ,| .α o have irregularly shaped vesicles (0.5-2 mm). Logging indicates that this
c m i o r 6 á < Q l ò α i ò á i < i O I O E < öT (5 IX O c/5 < £ á IT O <Λ < £ < S c O M < £ (5 CC O w < interval is occupied primarily by sediments, which were not recovered,and by lesser amounts of basalt.
~ ^ ^ ~ 1 Q J/ i ~ / ^ l K K—-g| i f~~Sl / S~l Thin Section Descriptioni ^ X T K ^ – — > 1 / _ y lO^n "°| i ° o - 8-1. 1-3 cm No. 1. Microporphyritic basalt with 4% euhedral olivine(f_/ ' ' 2 Q T Λ PC°1 1 1A P—1 T K \ \ _ i crystals (0.2-0.4 mm) and 93% glass. The glass is devitrified and con-
— Z = f~, 2 ^ /~~l l 1 B 1 ° J O T K X °J \ O T K _ tains variolitic structures. Vesicularity is -3%, small irregular shapedr• , „ 3 (J K '-^ I ° 1 K ^ ^ ^ 1 A P N i vesicles « 5 mm) scattered throughout the rock
~ T ^ - ^ ^~--^ 2 (| y 'θ\J 60-4S4A-9 3922.5-3931.5 m (104.0-113.0 m, BSF)3 (j qrc-<> . ö ^ i ^ – ^ •4 ^ : 4 • = | 3 A ( g ) i c t ; h IB , A • Aph-cbasait
^ 'oßO' β fl ( V-J I «. Three pieces of fine- to medium grained, dark gray to black, aphyric— .- $ó? ΛΛ ff ° \ 3B M ^ l JT~\ " v — pillow basalt fragments were recovered. All are fresh. Piece 3 has a
3 - = — /-r—v ^ " V,o o i \•^| 2 <-X-SJ o ^ I ind V II b t L " d t indi te th
6 <S? 5 λ ° K ° 4 /3(g?| r -j /=S=T] " the interval of this core is occupied primarily by sediments, hence
7 ^ ç > r7—Λ ( ^ T / ° ) r~J^l 1 C 0 « i Thin Section Description= ^ = 6 Jo? S " D 4B T ° I 5A 0 o) 1 S D 4 L0J i Ko . 9-1,5-7cmNo. 2. Microporphyritic basalt with 5% euhedral olivine
** ^ lfi__5J l^^•-\ I \ ° II y — o o crystals (0.1 -0.4 mm) containing brown spinel inclusions and 92%50— 9 £§> = L j l j \új ~T^T ^P=N — devitrified glass. Vesicularity is 3% with round to oval vesicles, some
s—"T i M " ^ ^ 3 /> 5 Cθ3^ *n» t ° K filled with clay minerals, scattered throughout.π S 7 Δ f l i i / •- \& & } I ° [ ^ H •'*^7 "- 1 D ^ - N T Ö ~
10 g/ K /A 0 »; ' K 5 \VJ/ f•/»>i p^r ——
_ r^^ i J^ 5B Λ-^1 [\°°! t ^ ^ 60454A-10 3931.5-3940.5 m (113.0-122.0 m, BSF)7B ^ _ . — T 6 ( \ ^ \ I i j t ^~ 9 \ k
= = 0 U T ßT^j i \ . 1 Aphyric basalt8 <°fP 7 € 3 ) ^ ^ C / ' - j^• Fine-to medium-grained, gray to bluish gray, vesicular, aphyric
9 ' J O T 8 ( g - J 5 C | r ; ' / K 7A^tß ' 3 U σ J × • T " ™ t r i× G°á S"ndI "ec•n^iec^iaπdS.Some sedimentary materialkü^i , ; \\ H Q^T\ ‰/ K was recovered in the interval 20-30 cm. Logging data indicates that
Q ;o o I i >d=-, ! / i — ^ x < u • . , * .u• •./——\• y / /\ 4 i I /7 i -m / Λ it /' l ~~ severa meters at the top ot the iπterva ot this core are pπmaπ y
1 0 M ×K b d f BD£2 T U f *fi] i . sediments•
-―^-^ r—.—. i / i ' / ^Λ Ö Thin Section Description_ \ ° l \ \ I " o — 101,81-84 cm No. 10. Aphyric basalt with interstitial to subophitic
10 \O_0j T fi λ / 7 C ] ° T rr l texture containing 38% plagioclase(An65:<1.5 mm), 22% clino-= q lV/° , " / o . i - pyroxene (augite: <0.6 mm), 1% magnetite, and 7% glass.
1 0 0 ~ n " " U K M 8 ( ^ ^ J N R M M D F lnc• s D T v p e
(„ fl• "N3 ~P\ - 10-1,41-42 cm — — — 3.71 2.24 Basalt-o_P] M I ^ = I \ 1 10-1,51*3 cm 3.85x10'3 — -31.4
1 2 1° o j " σ T i^ . 'I I „ fes " 60-454A-11 3940.5-3949.5 m (122.0-131.0 m, BSF)
^ z r z I ( ° I ' ^ fl —
/3 i ö 9 C f e ( i 4 Aph-icbasal113 (σ * / ^ ~ " ^~^-J T /o) Fine-to medium-grained aphyric vesicular dark gray basalt, generally
V 9 ^ 7A X / i f a ft lacking glassy rinds. The basalts are not significantly altered although~T^T) V J 1 0 A \ ü ° veins of greenish clays are present in Sections 1 and 4, carbonate veins
/ )° "I 1 /-5 1 'ö-T~i ~ ~ ~ in Sections 2-4, and sprays of zeolite and pçehniteR) in Section 3. One[f°y ' 7B\?o° T 1 0 B /vR 17 apparently oxidized vein occurs near the bottom of Section 4; Piece 8B.
— • S^J ^ ^ U Λ — Thin Section Synopsisf " 0 ) I /*°*\ i / 1 8B (°y 11-1,40•44cmNo.4Band 11-4, 71-75cmNo.3.MicroporphyriticV/ ' 7 C > » <! T K 1 1 / ° ° i T = = " to aphyric basalt containing <2% olivine ( F o 8 0 . 8 5 : 0.2-0.4 mm),
1 5 0 _ J I I I_J I I L J I I L J I X—Jl L J N- 1 I I \^-J\ L J I I L J _ l 39-44%, plagioclase ( A n 6 5 . 7 0 : < 1.2 mm), 2225% clinopyroxeneCORE/SECTION 8/1 9/1 10/1 11/1 11/2 11/3 11/4 (augite: <1 mm), 1-2% magnetite «0.1 mm), and 5-22% devitrified
glass. The glass is partially replaced by palagonite and chlorite. Vesi-cularity is 12-25% with round to irregular vesicles scattered throughoutthe rock and filled in part with chlorite or carbonate.
RockJNRM M D F '"'• S D Type
11-2, 44-46cm — — — 4.21 2.32 Basalt <-*11-2,111-113cm 11.3x10'3 — -41.7 — — — 3
*-* 11-4, 24-26 cm 9.85x10"3 — -38.5 — — — m
^ 2 •11"4. 37-43 cm 4.28 Basalt j j j j
\o CΛ
60-454A-12 3949.5-3958.5 m (131.0-140.0 m, BSF) " ^
Aphyric basalt and mudstone
Fine- to medium-grained, fresh to moderately altered, vesicular8 3 $ S> S> S β aphyric basalt, gray t o gray black in color. There are several veins
C 1 • - i l .- £ 1 - S i _ 5 1 > . § ! _ £ 1 f i l led w i t h calcite and green smectite. Piece 17 of Section 1 has aI | c S> S I c a ü S c δ > ü f c S5 ü f c 55 3 ~ c £ 2 I c £ 0.5 cm vein containing calcite and smectite, plus part of a glassyI É 2 E § I ε • s • s g | s • s E g | s . e • ε i i E .£ i g | ε . e p g | £ •g "s g r i n d ™ ° π e s i d e • v « i c l e s a r e b o t h s P h e r i « l a n d '^suianv shaped,
Z ~ S S o ' i Z ^ S i S o ' ^ Z - ü S S o ' ^ Z •a * S 8 'g Z •S I « J j Z ~ | S o ' 5 Z . S S B o ' ^ and filled with a grayish blue (5PB 5/2) secondary mineral. Fractures§ $ α. .1 "§- $i 8 g• o. .1 "S. 6 S " | • | . S • α £ g "& 1. S "S• S 8 g 1 SL » "§• Jj 8 g• I . S € . g 8 ' f ' a » ^ B in Section 2, Pieces 3A and3B contain a dark green (5G 3/2) clayI UlT O m 3 C O i r O w S I Off 0 S < * OK 6 S 3 £ O I O M I I U I O « 5 t OK O. S 3 mineral. Below 90 cm in Section 2, the material recovered is an
olive gray (5Y 3/2) to light olive gray (5Y 5/2) indurated mudstone• •• - _»____ y showing signs of biotuebstion.
1 A C J 1 3 T i f \ «.n/ Thin Section Synopsis~ T ~ ^ ^ J S D / 12-1,100-104 cm No. 12, 12-2,2426 cm No. 3. Intergranular to
— L 7 ) 1 - > - . _ intersertal in 12-1, No. 12, subophitic to interstitial in 12-2, No. 3,\y K yf with <1%olivine, 15-41%plagioclase (An 6 5 : <1 mm), 13-37%clino•rrjO , \ I ' Pyroxene (augite:<0.5mm>, 2% magntitee(<0.2 mm), and 2-15%
1C IY ] K devitrified glass. The glass is partially altered to clay minerals and/or" " ^ ^ ^ I — palagonite. Vesicularity is 15-50% with round to irregular vesicles
2 (a 6 βl ΠΛ SK ' T scattered throughout, partially filled with carbonate, palagonite,— - — JA r \ j | . c | a y m i n e r a l s a n d z e θ | i t e
_ 3 (T>3 r=\ - R k
= 3 B l J N R M MDF Inc. S D Type4 _^3 J " 12-2, 5-7 cm — — — 3.65 2.23 Basalt
_ TFT •^~ T M 12-2,39-41 cm 13.6x10"3 — -29.3
5 B E Q K to50— = / _
7 Q^V K — = = > . 60-454A-13 3958.5-3967.5 m (140,0-149.0 m, BSF)
— g / J i n 6 _^£_ / — Mo basalt recovered. Logging data shows that the interval is' ' —pz— occupied by sediments.
Cf-\ /
II .11 * K ~ /10°: «s ×j _:i ^
- 14S! = -iüCα
i7ëS t -i5o—I I 1 I—I I 1 U I 1 LJ I 1 LJ I 1 LJ I 1 l_l I 1 LJ _
CORE/SECTION 12/1 12/2
454 HOLE A CORE 12 CORED INTERVAL: 131.0 to 140.01
TIM
E-R
OC
KU
NIT
Earl
y P
leis
tocene
BIO
ST
RA
TZ
ON
E
z
J{
FOSSIlCHARACTER
FO
RA
MS
NA
NN
OS
CM
RA
DS SE
CT
ION
1
2
ME
TE
RS
0.5
1.0—
=
GRAPHICLITHOLOGY
IGNEOUSROCKS
DIS
TU
RB
AN
CE
11S
ED
IME
NT
AR
YS
TR
UC
TU
RE
SL
ITH
OL
OG
ICS
AM
PL
E LITHOLOGIC DESCRIPTION
MUDSTONE, color is moderate to dark greenish gray I5YG 6/1 to 5GY 4/1).2-90 to 94 cm: Laminated mudstone2-94 to 100 cm: Bioturbated mudstone2-100 to 103 cm: Laminated, but with burrows parallel to bedding2-103 to 120 cm: Laminated mudstone
SITE 454 HOLE A CORE 13 CORED INTERVAL: 1 4 0 0 t o 1 4 9 0 ,
LITHOLOGIC DESCRIPTION
Moderate to darkgreenish gray(5GY 6/1 to5GY4/1)
MUDSTONE, VITRIC MUDSTONE, and SILTYTUFF,Bioturbation: Some burrows are filled with feca
Mn(?) dendrites occur on some bedding planes atthem (1-78 to 85 cm).One piece of basalt 0-132 to 140 cm) with a gla:embedded in the mudstones at the base of the cc
SMEAR SLIDE SUMMARY s
TOTAL DETRITALCOMPOSITION:FeldsparClayVolcanic glassMicronodulesZeoliteCarbonate unsp.Nannofossils
VITRIC
pellets.
ON tfl*>.
60-454A-14 3967.5-3976.5 m (149.0-158.0 m.BSF) " ^
Aphyric basalt
Vesicular basalt and pillow basalt fragments, all aphyric, were„ „ recovered in this core. The pillow fragments are variolitic. Piece 1
.2 .2 iθ .2 .2 .2 2 has small vesicles in general, evenly distributed throughout the= s g | fe § | j . § 1 j . § 1 felS S . 1 3 r o c k . Pieces 2-7 s h o w an irregular d i s t r i b u t i o n o f vesicles. A l l are
IJ ! 1! 1,11 i I i ill jl 1 A I 1! tiff U\ I 11 t i l l E= — -S f ^ S α l S | l S | | S f l i l • l 8 S | I l | I j l I ! I I ^ .1 ! | j &α I | | Th n Sector. Descri tion
c m I OK 0 & < I á < T 0 « < 1 θ i θ i § < E 0 * O £ < £ O « r O 5 < S r < S f f O < S < £ UCC O £ < M - T ^ N o . V S p l ™ " " olivine (2% F o g g . ^ : 0.2-0.7 mm) phyric
" 1 I (T\ I V T P I I _ , / 7T ' / -, ' 7 " " N " 25% plagioclase (0.2-1.0 mm), 3% magnetite (<.O2 mm), and 23%1 \f , (I / •> ^ 1 / 1 T S • D • T / 1 I / ' gla«.Vesicularity 40% round to oval vesicles.
- /I / ^ 2 l J / / I / , , j IUDF Inc. S D Type
2L°á K; 2~CL T / 3 ^ / 2 L J * M / 2 ® • 14"1•63•65cm — 512 - Basalt
7 7 ^ /• 1 — 60-454A-15 3976.5-3980.5 m (158.0-162.0 m, BSF)
As) ~ *S= /X^-~' C\Z ' ' Aphyric basalt
/ 5 / I / _ Only two pieces of slightly altered vesicular basalt, with surfaces of~ f^\ N• J fragments coated with dusky yellow (5Y 6/4) clays and Fe hydroxides
4 _kL / /-> X,T / - were recovered in this core.
5 /C\ 6 ± d Thin Sectjon D e s c r j p , i o n— IJy / y £\ 15-1, 13-15 cm No. 2). Sparsely microphyric vesicular basalt with 2%
—-—_ j _ euhedral to skeletal olivine (FogggQ: <O.5 mm) crystals containingc f ] j o ( ) brown spinel inclusions. The groundmass is intersertal and contains
(ft J ^ • ~ / J _ 2-3% olivine (<0.2 mm), 18-20% plagioclase (<0.5 mm), 2-3% magnetite5 0 — j < (<.02mm), 22% glass only very slightly altered (1%) to yellow or green
7 Z~β\ ' 9/ J / - clay. Vesicularity is 50-55% with oval shaped vesicles (0.1-0.4 mm)*-—' l• / scattered throughout.
o f β 1 S D 1 0 ^ ' 60-454A-16 3980.5-3990.0 m (162.0-171.5 m BSF)8 l £ J * 'K^ ^ /
11 \ ) Aphyric basaltI ) \ / / —
9 IQJ ' —7-y ' Two types of basalt were recovered in this core. In Section 1, Pieces= = _LJL / " 3,4, and 13-18 are fragments of pillow basalts with glassy margins and/orr~gT~*) / /—s. variolitic textures. In general, they appear less altered than other rocks
1 0 ' ^ y . — in the core. All other pieces in Sections 1 and 2 are coarser grained,βj i S,D / and probably represent pillow interiors. They are olive gray (5Y 4/1)
® M . - with fresher looking patches in the interiors that are dark gray (N4).^-^V , ' The basalts are very porous, the result of a high proportion of pin-hole
~ 14 <$> ~ v e s i c l e s • uniformly dispersed throughout.. Thin Section Synopsis
1 5 >• 16-1,33-36cm No.6;16-1, 111-114cm No. 8, 16-2, 2-4 cm No. 1.TgT / - Pillow basalt contains 5% skeletal to euhedral olivine crystals (Fo 8 5 . 9 0 :
l u u lb_üi_ y 0.1-0.4 mm) with brown spinel inclusions. The groundmass is glassy toO . . spherulitic and contains 3% olivine (<0.1 mm), 47% plagioclase (<0.5 mm)
17 'g-' f and -50-80% glass very slightly altered (1%) to clays. Vesicularity is 15%/ ~ V — (< 0.1 mm) with irregular shaped vesicles concentrated in spherulites.
18 ® « ) ' R"*^ . J N R M MDF Inc. S D Type(\ ' _ 16-1,81-83 em — — — 4.90 2.44 Basalt
"~ 19 \ y j 16-2, 2-4 cm — — — 4 49 — Basalt•p=r• ' . 16-2,14-16cm 8.94x10"3 — - 9 . 3-Q ;
C \ i . ' 60-454A17T /
. . Aphyric basalt/
/ I | I J 1 | 1 I | f I I I I I I —I unknown interval. Fresh portions of the pieces are dark gray (N3)1 5 0 . . . . , c ; i 1 R / 1 ig/2 17/1 • or medium dark gray (N4) with olive gray (5Y 4/1) zones of alter-
CORE/SECTION 14/1 15/1 16/1 16/2 1//1 ation. Both pieces have patches of irregularly shaped vesicles.
SITE 454
Hole 454r -0 cm
•25
:
— 50
—75
—100
— 125
L-150
/:
1,CC 3-1 3-2 3-3 3-4 3,CC 4-1 4-2 4-3 4-5 4-6
197
SITE 454
— 50
Hole 454r—0 cm
— 25
— 75
—100
— 125
1—1504,CC 5-1 5-2 5-3 5-4 5-5 5-6 5,CC
198
SITE 454
Hole 454Ar-0 crrii
h-25
h-50
h-75
h-100
h-125
1—150 1-1 1-2 1-3
-
1-4 1-5 1-6 1-71,CC
2-1 2-2 2-3 2-42,CC
3-1
199
SITE 454
Hole 454A•0 cm
3-2 3-3 3,CC T i T 2 5-1 5-2 5-3 54 T i
200
SITE 454
1—50
Hole 454Ar-0 cm
h-25
h-75
h-100
h-125
1—1506,CC 8-1 8-2 9-1 10-1 11-1 11-2 11-3 11-4 12-1 12-2
201
SITE 454
Hole 454Ar—0 cm
— 25
— 50
- 7 5
—100
— 125
—15016-1 16-2 17-1 SP
4E-1 4E-2 4E-3 4E-4 4E-513-1 14-1
202
