Davies, P. J., McKenzie, J. A., Palmer-Julson, A., et al., 1991Proceedings of the Ocean Drilling Program, Initial Reports, Vol. 133

11. SITE 8181

Shipboard Scientific Party2

HOLE 818A

Date occupied: 8 September 1990

Date departed: 8 September 1990

Time on hole: 4 hr, 56 min

Position: 18°3.767'S, 150°2.533'E

Bottom felt (rig floor; m, drill-pipe measurement): 759.9

Distance between rig floor and sea level (m): 11.26

Water depth (drill-pipe measurement from sea level, m): 748.7

Total depth (rig floor; m): 769.5

Penetration (m): 9.6

Number of cores (including cores with no recovery): 1

Total length of cored section (m) 9.5

Total core recovered (m): 9.6

Core recovery (%): 101.0

Oldest sediment recovered:Depth (mbsf): 9.6Nature: foraminifer micrite ooze with bioclastsAge: Pleistocene

HOLE 818B

Date occupied: 8 September 1990

Date departed: 9 September 1990

Time on hole: 15 hr, 54 min

Position: 18°3.767'S, 150°2.533'E

Bottom felt (rig floor; m, drill-pipe measurement): 756.1

Distance between rig floor and sea level (m): 11.26

Water depth (drill-pipe measurement from sea level, m): 744.8

Total depth (rig floor, m): 1059.0

Penetration (m): 302.9

Number of cores (including cores with no recovery): 32

Total length of cored section (m): 302.9

Total core recovered (m): 314.6

Core recovery (%): 103.9

Oldest sediment recovered:Depth (mbsf): 302.9Nature: chalk with bioclasts and foraminifersAge: late Miocene

Principal results: Site 818 is located on a gently inclined terrace onthe upper slope of the Queensland Plateau southwest of theTregrosse/Lihou/Coringa bank complex. This location was se-lected to penetrate a uniquely thick pile of upper Neogenesediments that accumulated on the terrace. APC drilling fully

1 Davies, P. J., McKenzie, J. A., Palmer-Julson, A., et al., 1991. Proc.ODP, Init. Repts., 133: College Station, TX (Ocean Drilling Program).

2 Shipboard Scientific Party is as given in list of participants preceding thecontents.

recovered a 303-m-thick sequence of periplatform sediments thatrange in age from early Pliocene to Pleistocene. Benthic fora-minifer assemblages indicate that the depositional environmentremained at middle bathyal paleodepths (600-1000 m) through-out this period. The occurrence of platform-derived carbonatesthroughout the sequence implies that banks were producing andthat carbonate has been transported off the Queensland Plateausince the early Pliocene. However, the sequence contains arecord of varying flux of bank-derived carbonate to the upperslope that may be associated with either changes in the rate ofbank productivity and/or the amount of redeposited sedimentsthat accumulated at the site. Based on sedimentation rates, weidentified two periods having significantly modified rates ofcarbonate accumulation that compared with sedimentation ratesfor the past 1.5 m.y. (5.7 cm/k.y.): (1) between 1.5 and 2.42 Ma,a decelerated rate of 2.4 cm/k.y. is half as great, and (2) between2.42 and 2.6 Ma, an accelerated rate of 42 cm/k.y. is more thanseven times greater.

One major sedimentary unit was recovered between the sea-floor and 293.4 mbsf. A second sedimentary unit was barelypenetrated between 293.4 mbsf and the bottom of Hole 818B at302.9 mbsf. The lithologic units defined are as follows:

1. Unit I: depth, 0 to 293.4 mbsf; age, Pleistocene to earlyPliocene. Unit I contains white to light gray homogeneous periplat-form oozes composed of varying proportions of micrite andnannofossils, with minor amounts of bioclasts, foraminifers, andpteropods. The unit has been divided into four subunits on thebasis of compositional changes of pelagic-derived vs. bank-de-rived carbonates, as defined by nannofossil to micrite ratios thatwere determined qualitatively from smear-slide descriptions.

Subunit IA: depth, 0 to 65.4 mbsf; age, Pleistocene. Subunit IAconsists of periplatform ooze that is characterized by a greaterproportion of micritic than nannofossil components and thus is amicrite ooze. The high aragonite content in this interval, withvalues between 44% and 68%, clearly demonstrates the majorcontribution of bank-derived carbonate. Near the base, two layersof floatstone with mud clasts and graded foraminiferal and litho-clastic packstone, interpreted as calciturbidites, occur in associa-tion with slumped sediments.

Subunit IB: depth, 65.4 to 103.4 mbsf; age, late late Pliocene toPleistocene. The periplatform ooze of Subunit IB contains avisibly greater amount of nannofossils and planktonic foraminifersthan the overlying sediments and is predominantly a micritenannofossil ooze. This indicates that the contribution of pelagiccarbonate to the sedimentary deposit during this interval increasedrelative to the bank-derived carbonate. However, the presence ofaragonite in the ooze, as recorded in X-ray diffractograms, impliesthat the carbonate banks continued to be a source of micrite fortransport to the depositional site.

Subunit IC: depth, 103.4 to 198.4 mbsf; age, early late Pliocene.The thick package of sediments comprising Subunit IC containspredominantly micrite ooze. A transition from ooze to chalkoccurs between 150 and 180 mbsf that is associated with celestiteconcretions and burrow fillings.

Subunit ID: depth, 198.4 to 293.4 mbsf; age, early to latePliocene. Subunit ID contains a mixture of ooze and chalk with amicrite component that gradually decreases with depth. The unit ismainly characterized by the occurrence of gravity-flow deposits,which have been interpreted as calciturbidites, and slumps. Phos-phatized benthic and planktonic foraminifers and glauconite grainsare scattered throughout the coarser layers.

417

SITE 818

2. Unit II: depth, 293.4 to 302.9 mbsf; age, late Miocene. Unit IIcontains light gray, well-indurated calcareous chalk with bioclastsand foraminifers. The carbonate content of these sediments rangesbetween 92% and 100%. Throughout Unit II, values show highvariability and fluctuate up to 4%, although the mean value remainsfairly constant. Between 40 and 80 mbsf, a sharp excursion todecreased values occurs with a minimum centered at 52 mbsf (atabout 1.0 Ma). Dilution by noncarbonate material or dissolutionmight have produced the observed decrease. In the same interval,between 45-50 and 90 mbsf, the sediments are characterized bylower porosity, higher bulk density, and higher velocity than adjacentsediments. Variations in physical properties may be related to thecomposition of these carbonate components, neritic vs. pelagic.Interestingly, this anomalous interval has considerable overlap withthe micrite nannofossil ooze of Subunit IB.

The carbonate mineralogy of the Pleistocene sediments isapproximately a 50:50 mixture of calcite and aragonite withdetectable amounts of high Mg-calcite only at very shallow depths.The aragonite content can be as high as 68%, but decreases sharplywithin the upper Pliocene sediments and disappears entirely belowabout 210 mbsf. Dolomite occurs below 80 mbsf with concentra-tions less than 3%.

Interstitial water chemistry succinctly reflects the diageneticreactions occurring within these sediments. With the dissolution ofmetastable carbonates, aragonite, and high Mg-calcite, concentra-tions of Sr2"1" increase steadily, reaching a maximum value at about 70mbsf. As a consequence, the interstitial water is saturated withrespect to celestite (SrSO4) between 75 and 230 mbsf. Distinctivecelestite concretions and burrow fillings were recognized in two coresat about 160 to 170 and 220 mbsf, but microcrystalline celestite maybe present elsewhere within the saturated interval. A downwardtrend toward increasing Ca2+ and decreasing Mg2+ concentrationsrelative to that of chloride is apparently controlled by dolomiteformation. Concentrations of chloride tend to increase with depthand reach values up to 15% greater than seawater. As at Site 817,interstitial water chemistry indicates the presence of a source ofwater with elevated salinity at depth below the sampled section.

Total organic carbon contents of the sediments were low, butvariable, and ranged from 0.05% to 0.45%. Volatile hydrocarbonshaving methane concentrations of up to 10 ppm, ethane concentra-tions of about 1 ppm, and no propane presented no safety problems.

BACKGROUND AND SCIENTIFIC OBJECTIVESSite 818 is located in a water depth of 748 m on an isolated,

gently inclined slope-terrace, 10 km south of the southernedge of the Queensland Plateau, a partially drowned late earlyto middle Miocene, large (150,000 km2) tropical carbonateplatform. The site lies 30 km southwest of Tregrosse Reef, amodern 5100 km2 atoll-type platform, which is characterizedby a 40- to 60-m-deep lagoon rimmed by a barrier reef at sealevel. Tregrosse Reef accounts for one-quarter of the modernQueensland Plateau reef complex near or at sea level today,covers a surface area of about 20,000 km2, and represents theprotracted remnant of the larger Miocene platform. Site 818 islocated on the middle of a slope transect between Sites 814and 813 on the upper slope and Site 817 on the lower slope,along the southwestern margin of the Queensland PlateauMiocene platform or the modern Tregrosse Reef bank system.Site 818 was expected to have received large volumes ofbank-derived material plus pelagic sediments during periodsof bank production, as in the early and middle Miocene, andduring intervals of highstands of sea level, as in the Pliocene-Pleistocene. On the other hand, more pelagic sedimentarysequences within the slope sediments should correspond toperiods during which bank production had substantially de-creased or was totally turned off because of either bankdrowning or bank exposure in relation to variations in sealevel. The Neogene sedimentary sequence in Site 818 thus wasexpected to include a good record of the evolution through

time of the Queensland Plateau carbonate platform system.Because of the sensitivity in terms of carbonate preservationat the seafloor of the metastable bank-derived aragonite andMg-calcite carbonates, we expected to recover periplatformoozes in Site 811 that would record variations through time ofoceanic carbonate saturation states with respect to aragoniteand Mg-calcite in the upper part of the water column that hadoccurred during the Pliocene-Pleistocene. Because of timeconstraints, only the upper part of the sedimentary column,and thus only a late Neogene section, was recovered.

Both distribution of site-survey data and the pre-drillingprognosis are shown in Figure 1A, while a seismic sectionthrough Site 818 is depicted in Figure IB.

Our objectives for drilling at Site 818 were as follows:

1. To determine the age and facies of periplatform andfore-reef sequences on the margin of the Miocene, Pliocene-Pleistocene, and modern carbonate bank platform of theQueensland Plateau.

2. To determine the paleoceanographic signal in theperiplatform ooze.

3. To establish the relationship between fluctuations in sealevel and bank-derived carbonate facies.

4. To determine the diagenetic signal contained withinperiplatform sediments: in particular, to establish the stabilityregimes of Mg-calcite and aragonite, the possible occurrenceof dolomite, and the chemistry of interstitial waters within theplatform margin environment.

OPERATIONS

Transit to Site 818The sea voyage to Site 818 (proposed Site NEA-9A) began

at 0315L (all times given in local time, or L) 8 September 1990and covered 14 nmi, with an average speed of 9.3 kt. A seismicsurvey was run over the site that covered 12 nmi in 2.2 hr, atan average speed of 5.5 kt. A Datasonics beacon was droppedat 0550L, 8 September, but we lost the acoustic signal whilewe were running pipe into the hole with the APC/XCBbottom-hole assembly (BHA). A second beacon, a high-powered Benthos model, was run on taut wire, but this onealso gave an erratic signal and was retrieved. We dropped athird beacon, again a high-powered Benthos model, and againreceived an erratic signal, which led us to suspect that eitherstrong bottom currents were present or that the beacon'spower level was too high for the water depth. A fourthbeacon, a low-powered Benthos model, was run on taut wire.Although this beacon initially gave an erratic signal, it even-tually steadied, and we were finally able to position the shipafter more than 4 hr of effort.

Hole 818AHole 818A was spudded at 1046L, 8 September at

18°3.767'S, 150°2.533'E. A precision depth recorder (PDR)indicated a water depth of 752.1 m from sea level. Wepositioned a bit at a water depth of 748.7 m from sea level,where we shot the first core. From Core 133-818A-1H werecovered 9.6 m of sediment, which indicated that we hadovershot the mud line at least 0.1 m.

Hole 818BHole 818B was spudded at 18°3.767'S, 15O°2,533'E, 1112L,

8 September, with the bit positioned at a water depth of 743.7m from sea level for our first shot. From Core 133-818B-1Hwe recovered 8.59 m of sediment, which placed the mud lineat a water depth of 744.8 m from sea level.

418

SITE 818

18°00'S

18°02'

18°04'

75.2711600

2200 f*~T*

\i<**->—C-

Part A June

/"

' Pa

rt/75^271I 1800

1 Part L J

^*H S

Pi=±=NE

\_ t { Part E

59 \

\ CM ( 5 |

A-9A1 Part M' T

v H y

PartF

r 75.271 Λ2000 |

" • , /

jB

18°06'148°59'E 150°00' 150°02' 150°04' 150°06' 150°07'

B Key Depthreflectors (mbsf)

0

1.0-= "

2.4-

500-

VelocityAge (km/s) Lithology Paleoenvironment

Sedimentationrate (m/m.y.) Comments

Quaternary

[66]

Pliocene toPleistocene

[149]

Pliocene

[265]

latest Miocene

[315]

early Miocene

1.65

1.65

1.65

1.65

2.4

Carbonate sandand mud

Carbonate sandand mud

Carbonate sandand mud

Wackstone/packstone

Rudstone,backstone, and

wackstone

Periplatform ooze

Periplatform ooze

Periplatform ooze

Reef slope

Reef slope

30

30

35

20

25

Figure 1. A. Distribution of site-survey data. B. Pre-drilling prognosis for Site 818.

Section subjectedto cementation

Continuous APC cores (Cores 133-818B-1H through -32H)were taken from 0 to 302.9 mbsf, with 302.9 m cored and 314.6m recovered (103.8% recovery). The BHA was pulled out of the

SITE GEOPHYSICS

JOIDES Resolution separated from the beacon at Holehole and was back on deck at 0240L, 9 September. The beacons 817C at 0110L (JD 250/1510UTC) on 8 September 1990, andwere recovered, and the ship made ready for transit to Site 819. began the 2-hr transit to Site 818 (proposed Site NEA-9A) at

Table 1 contains the coring summary for Site 818. 0318L (JD 250/1718UTC). A magnetometer was towed imme-

419

SITE 818

Table 1. Coring summary, Site 818.

Core no.

Hole 818A1H

Hole 818B1H2H3H4H5H6H7H8H9H

10HIIH12H13H14H15H16H17H18H19H20H21H22H23H24H25H26H27H28H29H30H31H32H

Date Time(Sept. 1990) (UTC)

8

88888888888888888888888888888888

0050

Coring totals

01200135015502200240030503300350041504350435052005450605063006500720074508050825085009150935100510251055112011451210123512551305

Coring totals

Depth(mbsf)

0.1-9.6

0-8.48.4-17.9

17.9-27.427.4-36.936.9-46.446.4-55.955.9-65.465.4-74.974.9-84.484.4-93.993.9-103.4

103.4-112.9112.9-122.4122.4-131.9131.9-141.4141.4-150.9150.9-160.4160.4-169.9169.9-179.4179.4-188.9188.9-198.4198.4-207.9207.9-217.4217.4-226.9226.9-236.4236.4-245.9245.9-255.4255.4-264.9264.9-274.4274.4-283.9283.9-293.4293.4-302.9

Lengthcored(m)

9.5

9.5

8.49.59.59.59.59.59.59.59.59.59.59.59.59.59.59.59.59.59.59.59.59.59.59.59.59.59.59.59.59.59.59.5

302.9

Lengthrecovered

(m)

9.60

9.60

8.399.909.49

10.009.889.929.879.929.979.939.759.459.969.849.569.989.779.859.789.889.989.919.999.929.959.959.859.999.989.949.95

10.07

314.57

Recovery(%)

101.0

101.0

99.9104.099.9

105.2104.0104.0104.0104.0105.0104.0102.099.5

105.0103.0100.0105.0103.0103.0103.0104.0105.0104.0105.0104.0105.0105.0103.0105.0105.0104.0105.0106.0

103.9

Note that times are given in Universal Time Coordinated or UTC, which is 10 hr later thanlocal time, L.

diately after our departure, and continuous bathymetric andmagnetic data were recorded during the Line 5 transit whileheading about 84° along the northern margin of the TownsvilleTrough. The ship arrived at a position of 18°07.010'S and150°00.133'E, about 3.3 nmi south of Site 818, at 0448L (JD250/1848UTC), ready to start the site location survey.

Site 818 lies in approximately 739 m of water on a smallterrace on the upper slope of the southern Queensland Plateauadjacent to the Townsville Trough (Figs. 2 and 3) and about 26km southwest of the edge of the modern Tregrosse Bank. Thesite is 52 km southwest of Site 812 and 34 km east-northeast ofSite 817. It was selected with the aim of determining thecomposition and origin of slope facies immediately seaward ofthe Neogene carbonate platform of southern QueenslandPlateau, thus permitting us to compare it with mixed carbon-ate/siliciclastic slope sites adjacent to the Great Barrier Reef(Sites 819 through 821). The area was first recognized as apotential ODP drilling target from a 1972 BMR sparker line(Line 13/079) and a 1973 Gulf Research and Developmentaquapulse line (Line QP-10; Fig. 3). In 1987, the BMR vesselRig Seismic was used to conduct a site survey at this location(Symonds and Davies, 1988; Feary et al., 1990), and about 67km of 24-channel, 80-in.3 water-gun seismic, magnetic, andbathymetric data were collected on a grid of north-south andeast-west lines (BMR Line 75/59, Figs. 3 and 4). Pre-drillinginterpretation of the seismic data was performed using aLandmark RT interactive seismic interpretation system, while

five structure-contour and four TWT-thickness maps wereproduced (Feary et al., 1990). This mapping showed that thesite is located within a broad, buried channel that trendswest-northwest toward the adjacent platform margin. Orig-inally, we planned to drill Site 818 to 500 mbsf (Feary et al.,1990); however, owing to time constraints during Leg 133, wedecided to focus on the higher-priority, shallower objectives,and the site was drilled to only 303 mbsf.

An important requirement of the Leg 133 site-locationsurveys was that seismic records obtained with the JOIDESResolution be as close as possible in appearance to thosecollected during the 1987 site surveys by the Rig Seismic,thus reducing ambiguity when defining sites and whencomparing the seismic stratigraphy between the two datasets. Accordingly, JOIDES Resolution seismic deploymentsystems were modified (see "Explanatory Notes" chapter,this volume).

The position of Site 818 within the site survey grid wasbased on two intersecting lines that were surveyed using onlya Transit Satellite/dead-reckoning navigation system; coordi-nates thus were not as accurate as those for sites positionedusing the global positioning system (GPS). With this in mind,we designed the site-location survey for this site to confirm theseismic character of the proposed site from JOIDES Resolu-tion seismic data collected along a Rig Seismic line. Because"pin-point" accuracy was not required for drilling location inthis instance, we decided to drop a beacon while collecting

420

SITE 818

PartM PartCSite 818 (appro× Part A PartE

CDP 4100I

1 1.0

Figure 2. Multichannel SSI 80-in.3 water-gun, high-resolution seismic data, BMR Line 75/059, crossing proposed Site NEA-9A (Site 818).

seismic data by predicting the site location ahead of thedisplayed seismic record.

Distribution of regional seismic data in the area around thesite is shown in Figure 3, and tracks of the original Rig Seismicsite survey and the JOIDES Resolution site location surveyare shown in Figure 4. Following a reduction in ship's speed to5 kt, the JOIDES Resolutions single-channel seismic profilingsystem was deployed, and seismic recording began at JD250/1857UTC, 7 September 1990, in choppy seas (BeaufortScale force 3-4), with 1- to 2-m swells. The JOIDES Resolu-tion sailed north across Site 818, and a beacon was dropped atJD 250/1950UTC (Fig. 4). We stopped acquiring seismic dataand retrieved our equipment at JD 250/2009UTC, while dy-namic positioning of the ship over the beacon began at JD250/2100UTC. Following the beacon drop, a mound about 10m high appeared on our echo sounder and seismic profiles(Figs. 5 and 6). This feature had not been seen in the RigSeismic site-survey data, which indicated that our beaconlocation was slightly different from that of the proposed site,although seismic characteristics at depth were similar in boththe Rig Seismic and JOIDES Resolution data. During DPpositioning over the beacon, the ship was offset as far aspossible away from the mound, so that it would cause noproblems while drilling the shallow part of the hole. The finalcoordinates of Hole 818A are 18°03.767'S and 150°02.533'E, ata water depth of 748.7 m (drill-pipe measurement from sealevel).

About 9 km of seismic and magnetic data was collectedduring the site location survey; the ship's track was accuratelypositioned using GPS navigation. Our seismic equipmentoperated well, and fair quality monitor records were obtained(Fig. 5). Because of the compressed nature of these analogrecords, related mainly to the minimum available shot interval

of 9 s, we had difficulty discerning the detailed seismiccharacteristics of the site; however, correlation between seis-mic profiles of the Rig Seismic and JOIDES Resolution overthe site generally was reasonable (Fig. 5). During both thetransit to the site area and the site-location survey, weobtained a good quality 3.5-kHz echo sounder record with upto 40 m of sediment penetration in the vicinity of the site (Fig.6). This profile illustrates the location of Site 818 adjacent tothe carbonate platform and also shows that to the west of thesite, the Queensland Plateau slope has been incised by anumber of canyons up to 130 m deep.

Basement is not clearly defined in either the JOIDESResolution or the Rig Seismic water-gun data across the site;however, it probably lies about 1.0 s two-way traveltime(TWT) below seafloor at the base of a band of strong subhor-izontal reflectors that intersect the first water-bottom multiplejust north of the site (Fig. 4). Site 818 is underlain by four mainseismic units, although we only drilled in the upper three. Theshallowest unit is about 0.23 s TWT (190 m) thick and consistsof variable amplitude, generally discontinuous reflectors. Pre-drilling interpretation (Feary et al., 1990) suggested that thisunit was composed of periplatform carbonate sand and mud,in the form of both channel and mounded facies. It is underlainby a 0.09-s-TWT(75-m)-thick channel-fill unit containing verylow-amplitude, irregular reflectors that were interpreted asalso representing periplatform sediments. The underlying unitis thin at the site (0.05 s TWT; 52 m), but thickens rapidly tothe north and south, forming the walls of the channel. The unitis composed of subparallel, low-amplitude reflectors, whichpre-drilling had been interpreted as platform (reef>slope sed-iments. The top of the basal unit, which is at least 0.65 s TWTthick, may have just been intersected at the site. This unitconsists of interbedded bands of high-amplitude subparallel

421

SITE 818

17°30'S

18°00'

18°30'

Figure 3813,814

149°30'E 150°00'

Track chart showing the distribution of regional seismic data in the area around Site 818. Also shows the locations of Sites 812,and 817, and the simplified bathymetry in meters.

and low-amplitude chaotic reflectors. To the north of the site, theunit contains thick zones of chaotic reflectors, which were thoughtto be platform-derived deposits before drilling. The completeunit was thought to represent platform-slope sediments.

To provide some predictive capability during drilling at Site818, we estimated the reflection-time (TWT)/depth relation-ship below the seafloor using stacking-derived interval veloc-ities from the BMR site-survey seismic lines across the site. InFigure 7, this relationship is compared with similarly derivedTWT/depth relationships for other off-platform sites on theQueensland Plateau (Sites 811, 813, 814, and 817) and forDSDP Site 209 (Andrews, 1973).

LITHOSTRATIGRAPHY

Lithologic UnitsSite 818 is located in 745 m of water on an isolated, gently

inclined slope-terrace, 10 km south of the southern edge ofQueensland Plateau, a partially drowned, Miocene tropicalcarbonate platform. The site is 30 km southwest of TregrosseReef, a modern 5100-km2, atoll-type platform that is charac-terized by a 40- to 60-m-deep lagoon, which is rimmed by abarrier reef at sea level.

In Hole 818B, a 303-m-thick calcareous sedimentary se-quence (having carbonate content values that range between

422

SITE 818

18°00'S

18°02'

18°04'

18°06'

18°08'

75.27112200

PartF

BMRLine 75/59

75.271

1600

^ '

P

art

D

Part A

\l\ * \π \

PartE

.End Line 5/ J D 250/2009 UTC i

(7 Sept. 1990) /

I ?/— CJ CO 1

u>* l-~

PartC

Site 818 PartM

PartL

Beacon dropJD 250/1950 UTC(7 Sept. 1990)

JOIDES Resolution

Line 5 Start seismicJD 250/1857 UTC(7 Sept. 1990)

150°00'E 150°02' 150°04' 150°06'

Figure 4. JOIDES Resolution Leg 133 site location tracks (dotted line) and Rig Seismic 1987 site survey tracks (solid line) around Site818.

94% and 99%, see "Inorganic Geochemistry" section, thischapter; Fig. 8) was cored using the APC. This sequencemostly corresponds to a single 293-m-thick unit (Unit I) thatconsists of mixed pelagic and bank-derived carbonate sedi-ments. Unit I was divided into four subunits on the basis of theproportions of bank-derived material in the sediments. Thecalcareous sediments of Subunits IB and ID generally containmore pelagic components than those of Subunits IA and ICand have been interpreted as representing time intervalsduring which productivity on Tregrosse Bank (and thus off-bank transport) was considerably reduced, either by drowningor by exposure of the shallow bank.

Core 133-818B-32H of Hole 818B terminated in the upperpart of a second lithological unit (Unit II) that consists ofwell-indurated calcareous chalks with bioclasts and foramini-

fers that is differentiated from the nannofossil ooze and chalkscharacteristic of the overlying Subunit ID. Stratigraphic dis-tribution of the units and subunits is summarized in Figure 8;each is discussed in detail next.

Unit I (Cores 133-818B-1H to -31H-CC, 16 cm; depth, 0-293.4mbsf; age, Pleistocene to early Pliocene)

Unit I consists of essentially homogeneous, almost purecarbonate (bulk carbonate values range between 94% and98.5%; see "Inorganic Geochemistry" section, this chapter;Fig. 8), white to light gray ooze having nannofossils andmicrite as its main components. On the basis of variations inthe relative proportions of nannofossils and micrite, a series ofoozes was differentiated between two extreme end-membersof (1) nannofossil ooze and (2) micrite ooze. Intermediate

423

SITE 818

JOIDES Resolution

Line 5 Site 818

BMR Rig Seismic

Site 818 Line 75/059 NParti

2 km 2 km

Figure 5. Comparison of JOIDES Resolution and Rig Seismic 80-in.3 water-gun seismic profiles across Site 818.

cases thus include nannofossil micrite ooze, micrite nannofos-sil ooze, nannofossil ooze with micrite, and micrite ooze withnannofossils. Proportions of bioclasts, foraminifers, andpteropods in these oozes usually reached values ranked onlyas secondary components. On rare occasions, however, theirproportions were high enough to qualify as a major modifier,and thus some of these oozes can be designated micritebioclastic ooze or foraminifer nannofossil ooze.

We based our differentiation of Unit I into four subunitsessentially upon the two end-members of micrite ooze andnannofossil ooze. Micrite is predominant in Subunits IA andIC. These two subunits thus have been interpreted as trueperiplatform oozes, and the sediments consist of a mixture ofsignificant proportions of bank-derived, fine materials (micritesensu lato, mostly as aragonite and Mg-calcite) and, to a lesserextent, of pelagic fine-grained particles, mostly nannofossilsand some planktonic foraminifers. Sediments in Subunits IBand ID are more pelagic (i.e., they contain more nannofossils)in character and have a smaller proportion of bank-derivedmicrite material, based on smear slide estimates, which,however, are qualitative. Our subdivision will need to beconfirmed by more quantitative shore-based analyses. Be-cause of their gradational transitions, subunit boundaries wereselected a priori as core boundaries. The selection of foursubunits in Unit I may be more meaningful when one consid-ers that roughly the same subunits can be distinguished by (1)

bulk-density data (see "Physical Properties" section, thischapter), (2) variations of carbonate content (see "InorganicGeochemistry" section, this chapter), and (3) variability ofsedimentation rates (see "Sedimentation Rates" section, thischapter).

Subunit IA (Cores 133-818B-1H to -7H-CC, 15 cm; depth, 0 to65.4 mbsf; age, Pleistocene)

In addition to abundance of nannofossils, sediments inSubunit IA can be characterized by a large proportion of finecalcareous particles (micrite), which were identified insmear slides. The coarser particles consist of planktonic andbenthic foraminifers, pteropod tests, and bioclasts. SubunitIA also consists of variable white to very light gray micriteooze that ranges from micrite ooze to foraminifer micriteooze with bioclasts, pteropods, and nannofossils to nanno-fossil micrite ooze and rare micrite nannofossil ooze andnannofossil ooze with micrite, bioclasts, and foraminifers.The large proportions of micritic components in these oozes,which mostly correspond to high aragonite content values inthese sediments (ranging between 50% and 70%) and, to alesser extent, to some Mg-calcite, provide good evidencethat sediments in Subunit IA are mostly bank-derived mate-rial that has been exported from Tregrosse Bank. Thus,these sediments can be called periplatform oozes afterSchlager and James (1978).

424

SITE 818

37.5 m

s

Site 818

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Figure 6. Portions of the JOIDES Resolution 3.5-kHz echo sounder profile collected during the transit to Site 818 (A) and the site-location survey (B).

interpreted these sandy foraminiferal ooze layers as calcitur-bidite layers. The upper turbidite layer was deposited on topof contorted ooze, which we interpreted as representing aslump. The lower layer seems to overlie dipping layers that wealso interpreted as a slump. This 3-m-thick turbidite layer andslump package overlies micrite ooze (which we interpreted asperiplatform ooze) down to the base of Subunit I A.

Subunit IB (Cores 133-818B-8H-CC to -11H-CC, 20 cm; depth,65.4 to 103.4 mbsf; age, late late Pliocene to Pleistocene)

At first, sediments in Subunit IB resemble the overlyingoozes of Subunit IA. However, they can be differentiated bytheir larger proportion of pelagic particles, mostly nannofos-sils and planktonic foraminifers. Subunit IB consists of vari-able white to very light gray and light gray micrite nannofossilooze and micrite nannofossil ooze with foraminifers. Valuesof aragonite contents gradually decrease from 45% in theupper part of Subunit IB to 20% at its base, with an averagevalue of 30%, half the average of the aragonite contents inSubunit IA (see "Inorganic Geochemistry" section, this chap-ter). The gradual decrease of aragonite contents with depthmay reflect (besides diagenetic aragonite recrystallization)reduced bank-derived aragonite influx related to the partial orfull exposure of shallow banks during the late late Pliocene,which has been globally recognized as an interval of lowstandsin sea level (Droxler et al., 1988). Values of carbonatecontents increase slightly from 94% in the upper part ofSubunit IB to 97% at its base. As a general observation, thesediments of Subunit IB appear more pelagic than bank-derived in character. Sedimentation rates (2.4 cm/k.y.) inSubunit IB are lower than those in Subunit IA (5.7 cm/k.y.),roughly by a factor of two (see Fig. 10, "SedimentationRates" section, this chapter). Finally, no gravity-flow depos-its have been described in Subunit IB, contrasting with theoccurrence of a few turbidite layers in Subunit IA and in theunderlying Subunit ID (see below).

Subunit IC (Cores 133-818B-12H to -21H-CC, 12 cm; depth,103.4 to 198.4 mbsf; age, early late Pliocene)

Sediments in Subunit IC are mostly micritic and monoto-nous in character. The most common type of ooze in the95-m-thick Subunit IC ranges from white to light gray micriteooze to nannofossil micrite ooze, to intermediate micrite ooze

• Site 818o Site 811

Site 814DSDP 209-sonobuoyDSDP 209-phys. prop., etc

700 -

800

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

Two-way traveltime (s)

Figure 7. Comparison of TWT/depth curve estimated for Site 818 withthose for Sites 811, 814, and 818, and DSDP Site 209 on theQueensland Plateau.

The monotonous periplatform ooze in Subunit IA is inter-rupted toward its base by the occurrence of two distinct layersthat consist of floatstones with mud clasts and graded fora-miniferal lithoclastic packstones. The upper layer is 45 cmthick and extends from Sections 133-818B-6H-2, 115 cm, to-6H-3, 10 cm. The lower one is 40 cm thick and extends fromSections 133-818B-6H-3, 125 cm, to -6H-4, 15 cm. We

425

Description of lithologic unitsand subunits

300-

Foraminifer micrite ooze with bioclasts andpteropods

Micrite ooze,Micrite nannofossil ooze with nannofossil micrite

oozeNannofossil ooze with micrite, bioclasts, and

foraminifersOnly a few turbidite layers, and a major slump

at the base of Subunit IA

Micrite nannofossil oozeMicrite nannofossil ooze with foraminifersNannofossil micrite ooze with foraminifersNo turbidite layer, a possible slump in

the middle of Subunit IBNannofossil micrite oozeNannofossil micrite ooze with foraminifersMicrite ooze with bioclasts, foraminifers, and

nannofossilsMicrite nannofossil ooze with foraminifers and

bioclastsßioclast micrite ooze with foraminifers and

nannofossilsMicrite bioclast ooze with foraminifers and

nannofossilsNo turbidite layer, no slumpsIn the upper half oozes and minor chalksIn the middle oozes and chalks (50%:50%)In the lower half chalks and minor oozesOccurrence ofcelestite between 160-170 mbsf,

andat220mbsfMicrite nannofossil oozeNannofossil micrite oozeMicrite nannofossil ooze with

foraminifersForaminifer bioclast nannofossil oozeThrough Subunit ID, turbidite layers and

slumpsChalks and oozes (50%:50%)

Calcareous chalks with bioclasts andforaminifers

Well -indurated chalks

Interpretationof

depositionalenvironments

Carbonate content bulk sediment (%)

92 93 94 95 96 97 98 99 100

Celestite occurrence

Figure 8. Description and interpretation of lithologic units and subunits for Site 818. Darkness of shading in components columns indicates relative abundance and variations of carbonatecontent in bulk sediments.

SITE 818

with bioclasts, foraminifers, and nannofossils to bioclasticmicrite ooze and nannofossil micrite ooze with foraminifers.Aragonite contents decrease from 20% in the upper part ofSubunit IC to only trace amounts at its bottom. Carbonatecontents vary between 95% and 98%. No clear evidence existsin the entire subunit for redeposited material by gravity flows,although sedimentation rates average 19 cm/k.y., roughly anorder of magnitude higher than average sedimentation rates inthe overlying Subunit IB.

Transition from ooze to chalk was observed in Subunit ICin Cores 133-818B-17H, -18H and -19H, between 150 and 180mbsf. At this ooze/chalk transition, in Cores 133-818B-18Hand -19H, concretions and crystalline veins of celestite (usu-ally associated with burrows) were observed. The lower partof Subunit IC, which corresponds to Cores 133-818B-20H and-21H, is totally chalky.

Subunit ID (Cores 133-818B-22H to -31H-CC, 16 cm; depth,198.4 to 293.4 mbsf; age, early to late Pliocene)

Sediments in Subunit ID appear more pelagic than theoverlying sediments of Subunit IC, although the boundarybetween the two subunits is gradual. Sediments deposited inthe upper part of Subunit ID (Cores 133-818B-22H, -23H, and-24H) usually have a larger proportion of micrite than those inthe lower part, where micrite nannofossil ooze/chalk andmicrite nannofossil ooze/chalk with foraminifers and bioclastsare the most common sediments. Sediments in Subunit ID area mixture of about 50% ooze and 50% chalk, in contrast to thelowermost part of Subunit IC (Cores 133-818B-20H and-21H), where sediments are exclusively chalk. Values ofcarbonate content (ranging between 94% and 97%) are similarto those observed in Subunit IC. Calcite with traces ofdolomite is the only carbonate phase that was determined byX-ray diffraction (see "Inorganic Geochemistry" section, thischapter). Gravity-flow deposits and slumping are the maincharacteristics of Subunit ID.

Four distinct layers, which range from 20 to 130 cm thick,of coarse foraminiferal, lithoclastic, and bioclastic oozeshaving a characteristic sharp base and normal grading wereobserved in Cores 133-818B-22H, -27H, -30H, and -31H.These characteristics are typical features of calciturbidites.Phosphatized benthic and planktonic foraminifers, as well asglauconite grains, are scattered throughout these coarserlayers. Gently to steeply inclined and contorted bedding is themost common sedimentological feature in Subunit ID. Thisbedding appears in each core of Subunit ID, with the excep-tion of Core 133-818B-22H, and has been interpreted asslumps. This slump- and calciturbidite-rich subunit filled mor-phological depressions that were observed in the pseudo-three-dimensional interpretation of the site-survey seismicdata (Feary et al., 1990, page 203), as described in the "SiteGeophysics" section (this chapter).

Unit II (Cores 133-818B-32H to -32H-CC, 20 cm; depth, 293.4to 302.9 mbsf; age, late Miocene)

Drilling in Core 133-818B-32H penetrated the top of litho-logical Unit II, where we recovered a well-indurated, lightgray, calcareous chalk with bioclasts and foraminifers. Thegeneral appearance of this chalk and its brittle response todrilling are different from those of the overlying micritenannofossil ooze/chalks of Unit I. An average carbonatecontent of 97% (which ranged between 96% and 98.5%) and anaverage bulk density (1.9 g/cm3) are higher than the overallaverage carbonate and bulk density values of the overlyingUnit I (see "Inorganic Geochemistry" and "Physical Proper-ties" sections, this chapter). Determinations of calcareousnannofossils and planktonic foraminifers indicate that sedi-

ments in Core 133-818B-32H are upper Miocene (see "Bio-stratigraphy" section, this chapter).

BIOSTRATIGRAPHYTwo holes were drilled at Site 818. Samples from Hole

818B were analyzed for calcareous nannofossils and plank-tonic and benthic foraminifers. The succession at this site isfrom Pleistocene to late Miocene age, with a relatively thicklower Pliocene section. A preliminary biostratigraphic subdi-vision is shown in Figure 9. Calcareous nannofossils indicatethat the Pliocene/Pleistocene contact is within Core 133-818B-10H. The lower/upper Pliocene contact is in Core 133-818B-28H. The sample at the bottom of the hole contains onlypoorly preserved planktonic foraminifers, which indicates anage older than 5.2 and younger than 10.2 Ma.

Benthic foraminifers are well preserved. The assemblagesindicate a middle bathyal paleodepth. Redeposition of shal-lower water materials in most of the samples is suggested byshallower faunal elements.

Calcareous NannofossilsOne sample per core (except for Core 133-818B-32H) from

Hole 818B was examined for calcareous nannofossils. UpperPleistocene through lower Pliocene nannofossils were recov-ered at Site 818. Nannofossils are generally abundant and wellto moderately preserved in the Pleistocene interval. ThePliocene section contains common, poorly preserved nanno-fossils. The biostratigraphy for Site 818 is summarized inFigure 9.

Sample 133-818B-1H-CC contains few Emiliania huxleyi;it was assigned to Zone CN15 (00.275 Ma). The interval fromSamples 133-818B-2H-6, 0 cm, through -5H-CC yieldedcommon to abundant Pseudo emiliania lacunosa and Gephy-rocapsa caribbeanica and thus can be placed in SubzoneCN14a (0.465-0.93 Ma). Only rare specimens of G. carib-beanica are present in the interval from Samples 133-818B-6H-5, 150 cm, through -8H-5, 150 cm. Calcidiscus macin-tyrei is not present in this interval. This indicates SubzoneCN13b (0.93-1.48 Ma). Calcidiscus macintyrei was found inSample 133-818B-9H-6, 0 cm, although discoasters areabsent. This sample was assigned to Subzone CN13a (1.48—1.88 Ma).

The highest occurrences of Discoaster brouweri, D. pent-aradiatus, D. surculus, and D. tamalis are in Samples 133-818B-10H-5, 150 cm, -11H-5, 15 cm; -12H-5, 150 cm, and-20H-CC, respectively. These biohorizons delimit the tops ofSubzones CN12d (1.88 Ma), CN12c (2.29 Ma), CN12b (2.42Ma), and CN12a (2.6 Ma), respectively. The next lowermarker species, Reticulofenestra pseudoumbilica, was foundin Sample 133-818B-28H-CC, which represents the top ofSubzone CNllb (3.51 Ma). Relatively common Discoasterasymmetricus occur down to Sample 133-818B-30H-CC, butnot in the next lower sample at 133-818B-31H-CC; the bottomof Subzone lib (3.88 Ma) thus has been placed between thesesamples. A fairly diverse lower Pliocene assemblage wasfound in Sample 133-818B-31H-CC, but it lacks Amauroli-thus. This suggests an age of Subzone CNlla (3.88-4.24 Ma)for the sample. Two samples examined from Core 133-818B-32H (Samples 133-818B-32H-5, 150 cm, and -32H-CC)yielded poorly preserved assemblages without age-diagnosticspecies.

Planktonic ForaminifersGenerally, planktonic foraminifers are abundant and mod-

erate to well preserved throughout Hole 818B, except for thebottom Sample 133-818B-31H-CC, which contains somepoorly preserved specimens.

427

SITE 818

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14H

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N22-N23

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N21

N18-N19

Figure 9. Biostratigraphy summary for Site 818.

The latest occurrences of Globigerinoides fistulosus (1.6Ma) and Globigerinoides obliquus (1.8 Ma) can be found inCore 133-818B-9H, which delineates the lowest part of thePleistocene. The lower limit of Zone N22-N23, as defined bythe first occurrence of Globorotalia truncatulinoides, wasplaced in Core 133-818B-13H. Typical late Pliocene plank-

tonic foraminifers, such as Globorotalia tosaensis, Globoro-talia limabata, and Neogloboquadrina humerosa, are presentin Cores 133-818B-14H through -22H. This interval can beassigned to Zone N21. The latest occurrences of Globoquad-rina altispira (2.9 Ma) and Sphaeroidinellopsis seminulina (3.0Ma) are in Sample 133-818B-21H-CC. In the next lowercore-catcher sample (133-818B-22H-CC), the first occurrenceof Globigerinoide fistulosus (2.9 Ma) can be found.

The lower part of Hole 818B can be referred to ZoneN18-N19. The dominance of Globoquadrina altispira, Globi-gerinoides obliquus, and Globigerinoides trilobus indicatesthat surface waters were tropical during that time. The highestoccurrence of Globigerinoides nepenthes is in Sample 133-818B-31H-CC, which indicates either that the bottom of thehole is older than 3.9 Ma or that this interval has beenslumped. The planktonic foraminifers in Sample 133-818B-32H-CC were badly preserved. The absence of Globorotaliatumida tumida and the presence of Neogloboquadrina acos-taensis may indicate that this sample is older than 5.2 butyounger than 10.2 Ma.

Benthic Foraminifers

Core-catcher samples examined from Hole 818B containwell-preserved benthic foraminifers. The benthic foraminif-eral assemblages indicate a middle bathyal paleodepth (600-1000 m) for Hole 818B.

Most of the core-catcher samples examined contain middlebathyal species associations that include the depth-indicatorsBulimina mexicana, Cibicidoides bradyi, C. cicatricosus, C.mundulus, C. robertsonianus, Hanzawaia mantaensis, Hoe-glundina elegans, Hyalinea balthica, Lenticulina peregrina,Nuttallides umbonifera, Planulina rugosa, Planulina wueller-storfi, Plectofrondicularia vaughni, Pyrgo murrhina, Sig-moilopsis schlumbergeri, Sphaeroidina bulloides, Uvigerinapigmaea, and U. proboscidea (van Morkhoven et al., 1986).In addition to these taxa, Sample 133-818B-10H-CC containsabundant Bulimina aculeata. This sample yields abundantGlobigerina bulloides, which is an indicator of high produc-tivity. Bulimina aculeata has been found to prefer nutrientabundance and to have great tolerance for high salinities andoxygen deficiency. It has also been correlated to high carbonvalues in certain areas (van Morkhoven et al., 1986).

Most of the samples that were examined included a smallcomponent of transported specimens, such as Amphisteginaspp., Asterigerina spp., Discorbis spp., Elphidium spp., andPlanorbulina spp. In addition, Sample 133-818B-1H-CC con-tains approximately 80% transported specimens, includingAmphistegina spp., Asterigerina spp., Cibicides lobatulus,Discorbis spp., Elphidium spp., abundant miliolids, and Plan-orbulina spp. Similarly, Sample 133-818B-5H-CC containsabout 20% transported specimens.

PALEOMAGNETISM

We were unable to define any reliable magnetic reversals inperiplatform sediments at Hole 818B from shipboard paleo-magnetic measurements. The absence of a resolvable ship-board magnetostratigraphy probably results from relativelyweak magnetization in the pure carbonate sediments. Naturalremanent magnetization (NRM) intensities for most of thecore are near I0 1 mA/m. After alternating field (AF) at 15 mT,these intensities generally were reduced by 50% to 80%. In thelower part of the core, values approach the lower measure-ment limit of the cryogenic magnetometer. Both the NRM andAF inclinations show considerable scatter, part of which maybe attributed to the high water content (]40% by volume, see"Physical Properties" section, this chapter), thus promotingintermittent resetting of the magnetization directions.

428

SITE 818

50 —

100 —

150 —

-Q

Q.ΦO

200 —

250 —

300 —

Φ

ΦΦ IΦ

Φ

Φ

O Nannofossil datum

D Foraminifer datum

Sample spacing

Pleistocene late Pliocene early Pliocene

• • I2 3Magnetic polarity time scale (Ma)

Figure 10. Plot of age vs. depth for Site 818.

A total of 351 oriented discrete samples were collected foranalysis in a shore-based magnetically shielded laboratory totest whether a reliable polarity reversal stratigraphy can beascertained at this site.

Whole-core volume magnetic susceptibility at Hole 818Bshows weak values, except for two zones from 0 to about 10mbsf and from 27 to 35 mbsf. These susceptibility peaks haveno obvious correlation to lithologic changes or depositionalfeatures observed in the core. The upper peak may representeither a biogenic influx or a detrital pulse of ferrimagneticmaterial.

SEDIMENTATION RATES

The sediments at Site 818 provide an excellent biostrati-graphic framework for calculating sedimentation rates. Evenallowing for the relatively large sample spacing, the age-depthplot (Fig. 10) indicates significant fluctuations in sedimenta-tion. Four distinct intervals can be recognized on the sedi-mentation rate curve: the first extends from 0 to about 85 mbsfand spans the last 1.5 m.y. of the Pleistocene. Sedimentationrate for this interval is 5.7 cm/k.y. This interval from 85 to 108mbsf covers the time span from 1.5 to 2.42 Ma; that is, theearliest Pleistocene and the latest Pliocene, and the sedimen-tation rate for this segment is only about 2.4 cm/k.y. The timeinterval from 2.42 to 2.6 Ma is represented by sediments fromabout 108 to 184 mbsf, where the sedimentation rate jumps by

an order of magnitude to about 42 cm/k.y. for this segment.One should view this number with caution, however, becausethe very short time interval used to calculate the rate, even ifincorrect by only a small amount, might introduce a largeerror. The mid-Pliocene and latest early Pliocene—2.6 to 3.88Ma—is represented from about 184 to 279 mbsf, and thesedimentation rate for this interval is approximately 7.4 cm/k.y.

The nature of the sediment does not change radically,except in Core 133-818B-32H at the bottom of the hole.Consequently, the sedimentation rate does not seem to becontrolled primarily by delivery of carbonate—or noncarbon-ate—detritus, although the former seems to vary in thesection. Clearly, the order-of-magnitude increase in sedimen-tation rate during the late Pliocene was not accompanied by anorder-of-magnitude decrease in abundance of pelagic compo-nent in these sediments.

INORGANIC GEOCHEMISTRY

Interstitial WatersInterstitial water samples were taken from Cores 133-

818B-1H to -10H and 133-818B-13H, -16H, -19H, -22H, -25H,-28H, and -31H. Samples were squeezed and analyzed accord-ing to the methods outlined in the "Explanatory Notes"chapter (this volume).

429

SITE 818

Table 2. Interstitial water data, Site 818.

Core, section,interval (cm)

Depth(mbsf) pH

Alkalinity(mM)

Salinity(g/kg)

Calcium(mM)

Magnesium(mM)

Chloride(mM)

Silica(µM)

Strontium(µM)

Sulfate(mM)

Phosphate(µM)

Seawater 0.00 8.20 2.595 35.5 10.64 54.78 546.77 97 29.03 0.00

133-818B-

1H-4, 145-1502H-5, 145-1503H-5, 145-1504H-5, 145-1505H-5, 145-1506H-5, 145-1507H-5, 145-1508H-5, 145-1509H-5, 145-150

10H-5, 145-15013H-5, 145-15016H-5, 145-15019H-5, 145-15022H-5, 145-15025H-5, 145-15028H-5, 145-15031H-5, 145-150

4.4912.9922.4631.9941.4950.9960.4969.9979.4988.99

120.53148.91177.50206.00234.51262.00291.00

7.467.597.307.287.307.317.26

7.727.387.277.247.287.307.247.297.30

3.4883.3234.6996.1796.3736.2896.519

6.6796.4976.4716.2695.7875.0574.4123.4132.862

34.835.036.236.036.0

36.0

36.236.238.038.238.540.240.2

10.039.998.798.328.619.129.97

11.0411.2411.4212.7313.4414.7715.7518.3221.2920.94

52.9453.6154.8254.9754.3053.7753.7051.9752.4552.6152.3952.5053.3453.5353.4651.6850.25

535.21537.14540.03550.62555.43555.43562.17562.17564.09571.79587.20606.45615.11620.89634.36619.92606.45

131661137172185172156148141135141139143137148152185

196211449603662685704716685746716704638601599470217

27.3327.9827.7227.1926.5726.4226.7626.9326.6626.5626.6027.5928.2528.5429.8332.2131.21

1.950.811.301.621.621.301.131.620.971.131.951.621.781.301.300.650.65

100 •

.αE

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Q

150 -

200 -

250 -

30010 20Calcium (mM)

50 51 52 53 54Magnesium (mM)

200 400 600Strontium (µM)

520 560 600Chloride (mM)

640

Figure 11. Calcium, magnesium, strontium, and chloride data as a function of depth, Site 818.

Calcium, Magnesium, and Strontium

Calcium concentrations increase steadily from a seawatervalue of 10.64 to 20.94 mM at 291 mbsf (Fig. 11, Table 2).The profile of interstitial water of Mg2+ decreases in the firstsample from a seawater concentration of 54.8 to 52.9 mM.Below this depth, values increase to 55.0 Mm, then decreaseto 52.0 mM at 70 mbsf (Fig. 11, Table 2). With increasingdepth, Mg2+ concentrations increase to approximately 53mM. Below 262 mbsf, values decrease to 50.25 mM. Stron-tium concentrations increase rapidly from a seawatervalue of 97 to 685 µM at 79 mbsf. Below this depth, valuesslowly decline to a value of 217 µM at 291 mbsf (Fig. 11,Table 2).

When concentrations of Ca2+ and Mg2+ are normalized tosurface-water salinity (Fig. 12), concentrations of Mg2+ de-crease with increasing depth. This loss of Mg2+ is probablyassociated with the formation of minor amounts of dolomite inthe sediments. Calcium is being consumed within the top 75mbsf of the cored interval (Fig. 12), possibly as a result of theprecipitation of authigenic calcite. Below 75 mbsf, concentra-tions of Ca2+ increase as a result of formation of dolomite anddissolution of aragonite. Re-mineralization of aragonite re-leases Sr2+ into the pore fluids.

At Site 818, celestite (SrSO4) was found in Cores 133-818B-18H, -19H, and -29H. The ion molar product of SrSO4 wascalculated using interstitial water data taken at Site 818 (Fig.13). Values greater than approximately 1.7 × 10~6 indicate that

430

SITE 818

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20

Figure 12. Calcium and magnesium concentrations normalized tosurface-water salinity as a function of depth, Site 818.

sedimentary precipitation of celestite should be occurring. Ionmolar product values greater than this were found between 41.5and 234.5 mbsf, yet celestite was found in only two cores in thisinterval. Should our predictions be correct, and celestite werepresent within this interval, only a small amount needs to beprecipitated before pore-water Sr is significantly depleted (Swartand Guizikowski, 1988). Therefore, a portion of the precipitatingSrSO4 may be in quantities undetectable by XRD analysis ascoatings and microcrystalline grains. In the case of Core 133-818B-29H, 140-150 cm, pore fluids are undersaturated withrespect to SrSO4 at the present time; thus, precipitation mayhave taken place at an earlier time, when concentrations of Sr2+

were sufficiently high.Precipitation of celestite has been seen in DSDP cores from

Lord Howe Rise (Baker, 1986; Kennett, von der Borch, et al.,1985), the central equatorial Pacific (Schlanger, Jackson, et al.,1976), in sediments from Leg 101 on the Bahamian Platform(Swart and Guizikowski, 1987), and in numerous other locationswhere active carbonate recrystallization occurs.

50

100

CD

a

150

200

250

3000.00e+0 1.00e-6

Ion molar product [Sr][SO 4 ]2.00e-6

Figure 13. Ion molar product of strontium and sulfate, Site 818. Solidline is the approximate limit for celestite undersaturation in porewaters. To the right of this line celestite will precipitate. Dashed linesare the positions at which celestite was found in the sediments.

Chloride

Chloride values decrease slightly from a seawater value of546.8 to 535.2 mM at 4.5 mbsf (Fig. 11, Table 2). Below thisinterval, values increase with increasing depth until 235 mbsf,where values decrease to 606.5 mM. This increase in Cl—concentration is accompanied by an increase in salinitytoward the bottom of the sampled interval, possibly as a resultof the presence of evaporites at greater depth. An alternativeexplanation is that concentrations of Cl- reflect a relict highsalinity in sediments of Pliocene age.

Alkalinity, Sulfate, pH, and Phosphate

Concentrations of phosphate at Site 818 were low, with anaverage value of about 1.25 µM. The profiles of alkalinity andsulfate mirror each other, which is supporting evidence forsulfate reduction and organic-matter diagenesis at this site

431

SITE 818

Alkalinity (mM)4 5

50

100

Q.CDQ

150

200

250

30026

Alkalinity (mM)o Sulfate (mM)

50 -

Q.

α>Q

250 -

300200

29 30Sulfate (mM)

32 33

400Silica (µM)

600 800

Figure 14. Alkalinity and sulfate data as a function of depth, Site 818.

(Fig. 14 and Table 2). Alkalinity values range from 2.595 mMin seawater to 6.679 mM at 79.5 mbsf. Sulfate values rangefrom 26.20 (seawater) to 32.21 mM.

Silica

Concentrations of silica averaged approximately 150 µMthroughout, except for a high value of 661 µM in Sample133-818B-3H-5, 145-150 cm (Fig. 15 and Table 2). Concen-trations of silica were low as a result of the small amount ofbiogenic silica and quartz in the sediments, as shown by X-raydiffraction (XRD) and micropaleontological analyses.

Carbonate Content and X-Ray Diffraction Data

Samples for XRD analyses were taken from interstitial-water squeeze cakes and physical properties samples. X-rayanalyses at Site 818 indicate that sediments in the top 100 mare composed of equal amounts of aragonite and calcite (Fig.

Figure 15. Silica contents of interstitial water as a function of depth atSite 818.

Table 3. X-ray diffraction data, Site 818.

Core, section,interval (cm)

133-818A-

1H-4, 145-1502H-5, 145-1503H-5, 145-1504H-5, 145-1505H-5, 145-1506H-5, 145-1507H-5, 145-1508H-5, 145-1509H-5, 145-150

10H-5, 145-15013H-5, 145-15016H-5, 145-15019H-5, 145-15022H-5, 145-15025H-5, 145-15028H-5, 145-15031H-5, 145-150

Calcite

(%)

31.842.642.232.341.132.254.857.461.167.085.591.387.597.298.592.6

100.0

Aragonite

(%)

66.055.156.065.258.967.843.941.836.331.312.85.67.01.10.00.00.0

Quartz(%)

2.22.31.82.60.00.01.30.82.70.50.01.44.20.00.04.50.0

Dolomite(%)

0.00.00.00.00.00.00.00.00.01.21.71.71.31.71.52.80.0

432

SITE 818

100 -,

Q.Φ

Q

1 5 0 -f

Dolomite

Quartz

Aragonite

Calcite

200 '-

250 £

30020 40 60 80

Relative concentration (%)100

Figure 16. X-ray diffraction data, Site 818. All data are calculated aspercentages relative to the concentration of calcite.

16, Table 3). High Mg-calcite was detected in one sample from4.49 mbsf. Concentrations of aragonite are approximately 67%near the top of the section and decrease with depth. Below 210m, aragonite is absent. As discussed previously, the disap-pearance of aragonite coincides with an increase in pore-waterconcentrations of Sr, which is indicative of carbonate disso-lution and re-mineralization. Quartz concentrations are low a.tSite 818. Dolomite is absent in the top 80 m of Hole 818B.Below this depth, concentrations of dolomite never exceed3%. Calcite is abundant over the entire sampled interval.Values range from 31.8% to 100%.

Carbonate values at Site 818 vary from 92.2% to 100% (Fig.17A, Table 4). These data possess a high degree of variability,yet when smoothed by a running average for every five points,distinct trends of cyclic carbonate variations can be seen.These variations are either the result of dilution or dissolutionof the carbonate fraction of the sediment. When the data areplotted vs. age (Fig. 17B), the low carbonate event between0.9 and 1.0 Ma (observed in other sites of Leg 133) can be seen

clearly. The high density of points between 2.5 and 2.7 Maresults from the high sedimentation rates determined for thisinterval.

ORGANIC GEOCHEMISTRY

In addition to safety monitoring for hydrocarbons, the mainpurpose of shipboard organic geochemistry studies at Site 818was to assess the amount and type of organic matter preservedin the Pleistocene to lower Pliocene sediments on the slopebetween Queensland Plateau and Townsville Trough.

We determined the total nitrogen, sulfur, carbon, andorganic carbon contents of 11 samples using an NA 1500 CarloErba NCS analyzer.

Volatile Hydrocarbons

Light hydrocarbon gases (Q-C3) in sediments were ana-lyzed routinely as part of the ODP safety and pollution-prevention monitoring program, using the headspace tech-nique and the Carle gas chromatograph. Results of 32 analysesfrom Hole 818B are presented in Table 5.

The sediments at Site 818 contained low concentrations ofhydrocarbon gases and presented no safety problems. Con-centrations of methane in headspace gas ranged between 2 and10 ppm, while only trace amounts of ethane were detected.

Organic Carbon Contents

Total organic carbon (TOC) and total inorganic carboncontents recorded in Hole 818B are presented in Table 6. Weobserved low TOC values (Fig. 18) in these carbonate-richsediments, while total sulfur and nitrogen concentrations werebelow detection limits of the NCS analyzer.

As a consequence of the low organic contents, we wereunable to conduct detailed geochemical characterization ofkerogen types using the Rock-Eval pyrolysis method, asoriginally planned. More detailed shore-based studies (ele-mental analysis and optical investigations of extracted kero-gens) will permit characterization of the organic matter pre-served in the sediments encountered at Site 818.

PHYSICAL PROPERTIES

Physical properties analyzed in cores from this site includebulk density, P-wave velocity, and magnetic susceptibility ofunsplit cores and P-wave velocity, electrical-resistivity forma-tion factor, shear strength, and index properties (includingbulk density, grain density, water content, porosity, and voidratio) of split cores. Our methods are described in detail in the"Explanatory Notes" chapter (this volume).

Bulk Density

Bulk densities for Site 818 were determined from volumeand mass measurements of discrete core samples and fromabsorption of gamma rays by whole-round cores (Figs. 19Aand 19B; Table 7). In Figures 19A and 19B, an illustration ofthe similarity of bulk density determinations using differentmethods is presented. This figure also shows that bulkdensity is not obviously related to lithologic units on thebasis of visual core descriptions. After an initial increase inbulk density was found in the uppermost 10 mbsf, somevariation occurred around a mean of about 1.75 g/cm3 toabout 50 mbsf, where there was a step increase to a mean ofabout 1.8 g/cm3. This was followed by a step decrease atabout 90 mbsf (the three dashed lines above 100 mbsf in Fig.19 outline this high-density layer that straddles the boundarybetween lithologic Subunits IA and IB). From about 90mbsf, the density to a first approximation increases to thebottom of the hole, although some variations about thistrend can be correlated between Hamilton Frame and

433

SITE 818

Table 4. Carbonate data, Site 818. Table 4 (continued).

Core, section,interval (cm)

133-818B-1H-1, 80-821H-2, 80-821H-3, 80-821H-4, 80-821H-5, 80-821H-6, 40-432H-2, 80-822H-3, 80-822H-4, 80-822H-5, 80-822H-6, 80-822H-7, 80-823H-1, 79-813H-2, 79-813H-3, 79-813H-4, 79-813H-5, 79-813H-6, 79-814H-1, 80-834H-2, 80-834H-3, 80-834H-4, 80-834H-5, 80-834H-6, 87-905H-1, 87-905H-2, 87-905H-3, 87-905H-4, 87-905H-5, 87-905H-6, 87-906H-1, 80-836H-2, 80-836H-3, 80-836H-4, 80-836H-5, 80-836H-6, 80-837H-1, 87-897H-2, 87-897H-3, 87-897H-4, 87-897H-5, 83-857H-6, 87-908H-1, 85-888H-2, 85-888H-3, 85-888H-4, 85-888H-5, 85-888H-6, 85-889H-1, 83-859H-2, 83-859H-3, 83-859H-4, 83-859H-5, 83-859H-6, 83-85

10H-1, 100-10310H-2, 100-10310H-3, 100-10310H-4, 100-10310H-5, 100-10310H-6, 100-10311H-1, 98-10011H-2, 101-10311H-3, 101-10311H-4, 99-10111H-5, 99-10112H-1, 100-10312H-2, 100-10312H-3, 100-10312H-4, 100-10312H-5, 105-10912H-6, 100-10313H-1, 101-10313H-2, 100-10313H-3, 100-10313H-4, 100-10313H-5, 100-10313H-6, 100-103

Depth(mbsf)

0.802.303.805.306.807.90

10.0911.5913.0914.5916.0917.5918.6920.1921.6923.1924.6926.1928.2029.7031.2032.7034.2035.7737.7739.2740.7742.2743.7745.2747.2048.7050.2051.7053.2054.7056.7758.2759.7761.2762.7364.2766.2567.7569.2570.7572.2573.7575.7377.2378.7380.2381.7383.2385.4086.9088.4089.9091.4092.9094.8896.4197.9199.39

100.89104.40105.90107.40108.90110.45111.90113.91115.45117.00118.53120.03121.53

Sampletype

PPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPP

Total Inorganiccarbon carbon

(%) (%)

11.5711.43

11.71 11.4511.4511.4311.4411.4711.5811.6511.5011.4311.5911.6811.6711.6611.4711.5611.5011.5511.45

11.76 11.6711.7111.6311.6211.7811.7711.8111.7711.6711.5911.3011.6711.8411.1011.7911.3911.3711.32

11.60 11.3011.4811.5111.5411.4611.5911.4811.2911.7511.5611.5611.6211.6611.3911.6611.6011.7811.54

11.69 11.6311.6911.6711.6111.6811.5511.7511.5011.5911.4911.5411.5211.5211.5411.6611.6811.54

11.69 11.6411.6011.6811.66

Organiccarbon

(%)

0.26

0.09

0.30

0.06

0.05

CaCO3(%)

96.495.295.495.495.295.395.596.597.095.895.296.597.397.297.195.596.395.896.295.497.297.596.996.898.198.098.498.097.296.594.197.298.692.598.294.994.794.394.195.695.996.195.596.595.694.097.996.396.396.897.194.997.196.698.196.196.997.497.296.797.396.297.995.896.595.796.196.096.096.197.197.396.197.096.697.397.1

Core, section,interval (cm)

14H-1, 103-10514H-2, 103-10514H-3, 111-11414H-4, 110-11414H-5, 104-10614H-6, 110-11215H-1, 110-11215H-2, 100-10315H-3, 106-10815H-4, 111-11215H-5, 111-11215H-6, 111-11216H-1, 107-11016H-2, 115-11816H-3, 111-11416H-4, 100-10316H-5, 101-10416H-6, 75-7817H-1, 60-6317H-2, 60-6317H-3, 60-6317H-4, 60-6317H-5, 60-6317H-6, 60-6318H-1, 70-7318H-2, 70-7318H-3, 70-7318H-4, 70-7318H-5,70-7318H-6, 70-7319H-1, 60-6319H-2, 60-6319H-3, 60-6319H-4, 60-6319H-5, 60-6319H-6,60-6320H-1,60-6320H-2, 60-6320H-3, 60-6320H-4, 60-6320H-5, 60-6320H-6, 60-6321H-1, 60-6321H-2, 61-6421H-3, 61-6421H-4,61-6421H-5, 61-6421H-6, 61-6421H-7, 61-6422H-1, 60-6322H-2, 60-6322H-3, 60-6322H-4, 60-6322H-5, 60-6322H-6, 60-6322H-7, 60-6323H-1, 60-6223H-2, 60-6223H-3, 60-6223H-4, 60-6223H-5, 60-6223H-6, 60-6223H-7, 60-6224H-1, 60-6324H-2, 60-6324H-3, 60-6324H-4, 60-6324H-5, 60-6324H-6, 60-6325H-1, 61-6325H-2, 61-6325H-3, 61-6325H-4, 61-6325H-5,61-6325H-6, 61-6325H-7, 60-6326H-1,60-6326H-2, 60-63

Depth(mbsf)

123.43124.93126.51128.00129.44131.00133.00134.40135.96137.51139.01140.51142.47144.05145.51146.90148.41149.65151.50153.00154.50156.00157.50159.00161.10162.60164.10165.60167.10168.60170.50172.00173.50175.00176.50178.00180.00181.50183.00184.50186.00187.50189.50191.01192.51194.01195.51197.01198.51199.00200.50202.00203.50205.00206.50208.00208.50210.00211.50213.00214.50216.00217.50218.00219.50221.00222.50224.00225.50227.51229.01230.51232.01233.51235.01236.50237.00238.50

Sampletype

PPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPP

Total Inorganiccarbon carbon

(%) (%)

11.5511.5711.5611.5111.6111.6311.6711.6511.7111.7411.6011.4911.4611.56

11.82 11.7111.6611.6511.6911.6111.7111.7711.6111.3411.6011.6411.6611.7511.6411.6411.5611.6911.65

11.75 11.7111.4511.6811.6611.6811.7311.6811.6611.6311.6111.3811.6211.6311.5611.6611.5311.5611.4911.61

11.53 11.4611.6211.6111.6311.6511.6011.6611.5711.6111.6411.6311.4811.4911.6011.4611.6011.6011.4011.6611.59

11.66 11.5811.5511.5411.6111.4811.6011.67

Organiccarbon CaCO3

(%) (%)

96.296.496.395.996.796.997.297.097.597.896.695.795.596.3

0.11 97.597.197.097.496.797.598.096.794.596.697.097.197.997.097.096.397.497.0

0.04 97.595.497.397.197.397.797.397.196.996.794.896.896.996.397.196.096.395.796.7

0.07 95.596.896.796.997.096.697.196.496.797.096.995.695.796.695.596.696.695.097.196.5

0.08 96.596.296.196.795.696.697.2

434

SITE 818

Table 4 (continued). Table 4 (continued).

Total Inorganic OrganicCore, section, Depth Sample carbon carbon carbon CaCC>3interval (cm) (mbsf) type (%) (%) (%) (%)

Total Inorganic OrganicCore, section, Depth Sample carbon carbon carbon CaCO3

interval (cm) (mbsf) type (%) (%) (%) (%)

26H-3, 60-6326H-4, 60-6326H-5, 60-6326H-6, 60-6326H-7, 60-6327H-1, 60-6327H-2, 60-6327H-3, 60-6327H-4, 60-6327H-5, 60-6327H-6, 60-6327H-7, 60-6328H-1, 60-6328H-2, 60-6328H-3, 60-6328H-4, 60-6328H-6, 60-6328H-7, 60-6329H-1, 60-6329H-2, 60-6329H-3, 60 63

240.00241.50243.00244.50246.00246.50248.00249.50251.00252.50254.00255.50256.00257.50259.00260.50263.50265.00265.50267.00268.50

PPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPP

11.75

11.6611.5211.5811.5411.4911.5111.4711.6111.5911.6411.5611.7011.4811.4411.3111.5511.5711.4811.5411.5911.63

0.44

97.196.096.596.195.795.995.596.796.597.096.397.595.695.394.296.296.495.696.196.596.9

29H-4, 60-6329H-5, 60-6329H-6, 60-6330H-1, 60-6330H-2, 60-6330H-3, 60-6330H-4, 60-6330H-5, 60-6330H-6, 60-6331H-1, 60-6331H-2, 60-6331H-3, 60-6331H-4, 60-6331H-5, 60-6331H-6, 60-6332H-1, 60-6332H-2, 60-6332H-3, 60-6332H-4, 60-6332H-5, 60-63

270.00271.50273.00275.00276.60278.00279.50281.00282.50284.50286.00287.50289.00290.50292.00294.00295.50297.00298.50300.00

PPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPP

11.54

11.6311.5311.6111.6111.5511.5611.5111.4811.3711.4211.4911.4611.4411.2711.4011.8911.7811.4312.0011.88

0.10

96.996.096.796.796.296.395.995.694.795.195.795.595.393.995.099.098.195.2

100.099.0

350

PP = physical properties sample.

B o

94 96 98

Carbonate (%)

100 94 95 96 97

Carbonate (%)

98 99

Figure 17. A. Raw (solid line) and smoothed (open circles) carbonate data, Site 818 as a function of depth. B. Smoothed carbonate data plottedvs. age, Site 818.

435

SITE 818

Table 5. Volatile hydrocarbon data from headspace analysis at Site 818.

Core, section,interval (cm)

133-818B-1H-4, 145-1462H-5, 145-1463H-5, 149-1504H-5, 145-1465H-5, 145-1466H-5, 145-1467H-5, 140-1418H-5, 145-1469H-5, 140-141

10H-5, 145-14611H-5, 149-15012H-5, 149-15013H-5, 140-14114H-5, 149-15015H-5, 149-15016H-5, 140-14117H-5, 149-15018H-5, 149-15019H-5, 149-15020H-5, 149-15021H-5, 149-15022H-5, 149-15023H-5, 149-15024H-5, 149-15025H-5, 149-15026H-5, 149-15027H-5, 149-15028H-5, 149-15029H-5, 149-15030H-5, 149-15031H-5, 149-15032H-5, 149-150

Depth(mbsf)

5.9515.2425.3934.8544.3553.8563.372.8582.391.85

101.39110.89120.43129.89139.39148.8158.39167.89177.39186.89196.39205.89215.39224.89234.39243.89253.39262.89272.39281.89291.39300.89

Sampletype

HSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHS

Volume(mL)

55555555555555555555555555555555

Gas chromato.

CAR132CAR132CAR 132CAR132CAR 132CAR132CAR132CAR 132CAR 132CAR 132CAR 132CAR 132CAR 132CAR 132CAR 132CAR132CAR 132CAR132CAR132CAR132CAR 132CAR 132CAR 132CAR 132CAR 132CAR 132CAR 132CAR 132CAR132CAR132CAR 132CAR132

Ci(ppm)

23445777

1087

1077786846886454434353

c2(ppm)

00000000

0100000000000000

(Ppm)

00000000000000000000000000000000

HS = headspace sample.

Table 6. Concentrations of total organic carbon, inorganic carbon, total carbon, totalnitrogen, and sulfur in sediments from Site 818.

Core, section,interval (cm)

133-818B-

1H-3, 80-824H-3, 80-837H-3, 87-89

10H-3, 100-10313H-3, 100-10316H-3, 111-11419H-3, 60-6322H-3, 60-6325H-3, 61-6328H-3, 60-6331H-4, 60-63

Depth(mbsf)

3.831.259.7788.4

117145.51173.5202230.51259289

Sampletype

PPPPPPPPPPPPPPPPPPPPPP

Totalorganic

carbon (%)

0.250.10.30.050.050.10.040.050.10.450.1

Totalinorganic

carbon (%)

11.4511.6511.311.6511.6511.711.711.4511.5511.311.45

Totalcarbon

(%)

11.711.7511.611.711.711.811.7511.511.6511.7511.55

Totalnitrogen

(%)

00000000000

Totalsulfur(%)

00000000000

PP = physical properties sample.

GRAPE density measurements and also can be correlatedwith variations in velocity.

P-Wave VelocityP-wave velocities were measured in whole-round cores

using the multisensor track (MST) and in discrete coresamples using the Hamilton frame (Table 8 and Figs. 19Cand 19D). As with densities, some features of velocitystructures at this site can be seen in velocity vs. depth plotsgenerated from different sets of measurements and distin-guish portions of velocity structures at different depths, i.e.,features that do not correlate with lithologic unit boundaries.

As with density, a step increase in velocity occurs at about50 mbsf from values fluctuating at about 1.75 km/s to valuesaveraging around 1.8 km/s. At 90 mbsf, velocity decreasesbefore beginning an approximately linear increase to thebottom of the hole. As was often observed, features ofvelocity structures also were seen in density structures,where variations in one quantity were proportional to vari-ations in another quantity, contrary to the inverse relation-ship suggested by the physics of sound in an isotropicmedium, in which velocity is inversely proportional to thesquare root of density. The explanation of this apparentparadox must lie in the overwhelming influence of increases

436

SITE 818

50 -

100 -

150 -

n

Q.

a200 -

250 -

300

350

1 '

•

•

Verylow

• ' ' i ' ' ' ' i ' ' ' ' i ' ' ' '

Subunit IA

Subunit IB

Subunit IC

Subunit IC

i i

Low ! Moderate ! Highi i

i i

i i i i . i . i i i I ! I i i . . i ,

Table 7. Index properties, Site 818.

0.0 0.5 1.0 1.5Total organic carbon (%)

2.0

Figure 18. Distribution with depth of total organic carbon contents insediments at Site 818.

in bulk and shear moduli that must accompany increases inbulk density.

PorosityPorosity was one of the index properties determined from

discrete core samples, using mass balance and the pycnometer(Table 7). A graph of porosity vs. depth is shown in Figure19E. Similarly, the water content, derived from the same setof index property measurements, also is plotted vs. depth inthis figure. A plot of water content vs. porosity is depicted inFigure 20. Here, we also have the expected close correlationof porosity to dry-water content.

Porosity and water content show a first-order linear de-crease with depth, with a negative excursion between 45 and90 mbsf that coincides roughly with the region of high velocityand bulk density. The boundaries of this low-porosity zone donot coincide with lithologic unit boundaries nor with majorchanges in rates of deposition.

Core, section,interval (cm)

133-818B-

1H-1, 79-821H-2, 79-821H-3, 79-821H-4, 79-821H-5, 79-821H-6, 40-432H-1, 79-822H-2, 79-822H-3, 79-822H-4, 79-822H-5, 79-822H-6, 79-823H-1, 79-823H-2, 79-823H-3, 79-823H-4, 79-823H-5, 79-823H-6, 79-824H-1, 80-834H-2, 80-834H-3, 80-834H-4, 80-834H-5, 80-834H-6, 87-905H-1, 87-905H-2, 79-825H-3, 87-905H-4, 87-905H-5, 87-905H-6, 87-906H-1, 80-836H-2, 80-836H-3, 80-836H-4, 80-836H-5, 80-836H-6, 80-837H-1, 87-907H-2, 87-907H-3, 87-907H-4, 87-907H-5, 83-867H-6, 87-908H-1, 85-888H-2, 85-888H-3, 85-888H-4, 85-888H-5, 85-888H-6, 85-889H-1, 83-869H-2, 85-889H-3, 85-889H-4, 85-889H-5, 85-889H-6, 85-88

10H-1, 101-10410H-2, 101-10410H-3, 101-10410H-4, 101-10410H-5, 101-10410H-6, 101-10411H-1, 98-10111H-2, 101-10411H-3, 101-10411H-4, 101-10411H-5, 101-10411H-6, 101-10412H-1, 101-10412H-2, 101-10412H-3, 101-10412H-4, 101-10412H-5, 105-10812H-6, 101-10413H-1, 101-10413H-2, 101-10413H-3, 101-104

Depth(mbsf)

0.792.293.795.296.797.909.19

10.0811.5813.0814.5816.0818.6920.1921.6923.1924.6926.1928.2029.7031.2032.7034.2035.7737.7739.1940.7742.2743.7745.2747.2048.7050.2051.7053.2054.7056.7758.2759.7761.2762.7364.2766.2567.7569.2570.7572.2573.7575.7377.2578.7580.2581.7583.2585.4186.9188.4189.9191.4192.9194.8896.4197.9199.41

100.91102.41104.41105.91107.41108.91110.45111.91113.91115.46117.01

Bulkdensity(g/cmJ)

1.791.721.731.751.731.731.821.711.821.801.771.771.811.741.791.761.831.781.731.741.781.801.691.861.791.831.811.801.801.771.771.721.881.781.891.811.771.991.811.791.811.821.801.841.751.861.921.941.801.801.821.771.801.781.861.861.761.761.761.801.741.731.771.761.761.771.761.781.771.801.751.711.801.841.74

Graindensity(g/cm3)

2.792.932.722.752.722.772.732.752.652.742.752.802.782.752.752.792.772.732.772.812.762.772.702.772.712.732.752.802.162.662.762.832.752.722.802.782.722.802.752.872.762.742.642.802.732.732.762.782.642.562.562.702.722.842.702.692.702.712.782.692.712.752.682.712.712.562.672.732.662.702.652.842.762.842.63

Porosity(%)

61.766.363.263.562.864.160.762.159.760.061.561.160.363.359.061.758.559.763.361.861.164.660.363.159.963.157.659.060.861.463.359.852.861.755.857.756.658.056.958.758.058.957.556.757.155.750.156.758.258.356.859.859.058.152.654.260.559.159.458.060.760.359.160.859.760.660.058.259.759.860.359.858.758.460.1

Watercontent Void(%)

54.765.259.759.359.261.452.059.050.652.055.354.851.859.250.856.048.852.359.957.354.258.257.953.552.254.848.250.453.055.057.855.640.455.043.548.348.842.647.450.548.749.448.546.050.044.436.442.849.449.846.953.050.850.1 140.9 142.554.352.752.8 149.2 155.5 155.4 152.1 154.8 153.5 153.9 153.6 150.3 152.8 151.7 154.6 155.7 150.4 148.3 154.5 1

•atio

1.611.971.711.741.691.791.551.641.481.501.601.571.521.721.441.611.411.481.721.621.571.83.52.71.49

1.71.36.44.55.59.73.49.12.61.26.37.31.38.32.42.38.43.35.31.33.26.00.31.39.40.32.49.44.39.11.19.53.45.46.38.54.52.45.55.48.54.50.39.48.49.52.49.42.40.50

437

SITE 818

Table 7 (continued).

Core, section,interval (cm)

13H-4, 101-10413H-5, 101-10413H-6, 101-10414H-1, 101-10414H-2, 101-10414H-3, 111-11414H-4, 111-11414H-5, 101-10414H-6, 106-10915H-1, 110-11315H-2, 101-10415H-3, 105-10815H-4, 111-11415H-5, 111-11415H-6, 111-11416H-1, 107-11016H-2, 115-11816H-3, 111-11416H-4, 100-10316H-5, 101-10416H-6, 75-7817H-1, 60-6317H-2, 60-6317H-3, 60-6317H-4, 60-6317H-5, 60-6317H-6, 60-6318H-1, 70-7318H-2, 70-7318H-3, 70-7318H-4, 70-7318H-5, 70-7318H-6, 70-7319H-1, 60-6319H-2, 60-6319H-3, 60-6319H-4, 60-6319H-5, 60-6319H-6, 60-6320H-1, 60-6320H-2, 60-6320H-3, 60-63

20H-4, 60-6320H-5, 60-6320H-6, 60-6321H-1, 60-6321H-2, 60-6321H-3, 60-6321H-4, 60-6321H-5, 60-6321H-6, 60-6322H-1, 60-6322H-2, 60-6322H-3, 60-6322H-4, 60-6322H-5, 60-6322H-6, 60-6322H-7, 60-6323H-1, 60-6323H-2, 60-6323H-3, 60-6323H-4, 60-6323H-5, 60-6323H-6, 60-6323H-7, 60-6324H-1, 60-6324H-2, 60-6324H-3, 60-6324H-4, 60-6324H-5, 60-6324H-6, 60-6325H-1, 60-6325H-2, 60-6325H-3, 60-6325H-4, 60-6325H-5, 60-6325H-6, 60-63

Depth(mbsf)

118.54120.04121.54123.41124.91126.51128.01129.41130.96133.00134.41135.95137.51139.01140.51142.47144.05145.51146.90148.41149.65151.50153.00154.50156.00157.50159.00161.10162.60164.10165.60167.10168.60170.50172.00173.50175.00176.50178.00180.00181.50183.00

184.50186.00187.50189.50191.00192.50194.00195.50197.00199.00200.50202.00203.50205.00206.50208.00208.50210.00211.50213.00214.50216.00217.50218.00219.50221.00222.50224.00225.50227.50229.00230.50232.00233.50235.00

Bulkdensity(g/cm5)

1.731.851.781.771.741.761.771.771.771.771.811.791.79[.761.771.79L.781.80.82

1.771.821.76

:

1.801.811.821.81.79.79.79

1.741.781.74

:

:

.77

.80

.83

.79

.80

.83

.84

.82

.85

.82

.80

.79

.79

.82

.81

.84

.74

.85

.85

.811.791.781.811.79

1

.80

.86

.79

.85

.81

.86

.93

.84

.84

.79

.73

.79

.79

.80

.80

.84

.85

.81

.82

.82

.82

Graindensity(g/cm5)

2.762.612.622.642.552.732.772.752.732.752.712.732.732.772.702.702.712.782.732.772.742.702.782.772.712.712.722.762.712.722.672.742.712.782.622.772.742.742.722.752.862.77

2.702.742.742.752.732.762.522.772.712.892.772.782.742.732.792.712.732.722.782.702.712.702.782.692.702.652.762.662.642.712.672.772.762.792.76

Porosity(%)

60.954.258.558.560.459.361.559.259.258.559.557.558.259.259.457.658.459.657.357.159.559.159.257.258.658.358.456.659.857.560.158.658.658.357.157.656.956.557.156.658.357.8

57.658.560.254.155.153.753.853.653.956.356.959.257.156.757.854.456.253.256.153.948.554.655.257.156.159.157.857.156.956.054.655.155.656.857.3

Watercontent ^

(%) i

56.642.850.751.155.552.755.352.052.351.051.049.150.152.452.349.150.751.347.849.250.352.350.948.049.349.250.247.852.251.152.752.451.149.846.849.447.846.446.646.847.748.1

48.750.552.843.845.342.746.342.242.746.848.251.547.647.949.1 142.9 147.541.746.542.3 134.8 C43.6 144.5 148.4 149.9 150.9 149.4 148.3 148.0 145.2 143.3 145.3 145.6 147.1 147.5 1

/oidatio

1.561.181.411.411.531.461.601.451.451.411.471.351.391.451.461.361.401.48.34.33.47.44

1.451.341.411.40.40.31.49.36.51.41

1.41.40.33.36.32.30.33.31.40.37

.36

.41

.51

.18

.23

.16

.17

.16

.17

.29

.32

.45

.33

.31

.37

.19

.28

.14

.28

.17).94.20.23.33.28.44.37.33.32.27.20.23.25.31.34

Table 7 (continued).

Core, section,interval (cm)

25H-7, 60-6326H-1, 60-6326H-2, 60-6326H-3, 60-6326H-4, 60-6326H-5, 60-6326H-6, 60-6327H-2, 60-6327H-3, 60-6327H-4, 60-6327H-5, 60-6327H-6, 60-6327H-7, 60-6328H-1, 60-6328H-2, 60-6328H-3, 60-6328H-4, 60-6328H-6, 60-6328H-7, 60-6329H-1, 60-6329H-2, 60-6329H-3, 60-6329H-4, 60-6329H-5, 60-6329H-6, 60-6330H-1, 60-633OH-2, 60-633OH-3, 60-6330H-4, 60-6330H-5, 60-6330H-6, 60-6331H-1, 60-6331H-2, 60-6331H-3, 60-6331H-4, 60-6331H-5, 60-6331H-6, 60-6332H-1, 60-6332H-2, 60-6332H-3, 60-6332H-4, 60-6332H-5, 60-63

Depth(mbsf)

236.50237.00238.50240.00241.50243.00244.50248.00249.50251.00252.50254.00255.50256.00257.50259.00260.50263.50265.00265.50267.00268.50270.00271.50273.00275.00276.50278.00279.50281.00282.50284.50286.00287.50289.00290.50292.00294.00295.50297.00298.50300.00

Bulkdensity(g/cm?)

::

1.821.761.811.791.781.811.821.791.811.811.81.80.85.85.85

1.851.861.831.87

:

.87

.86

.81

.81

.89

.90

.85

.88

.88

.85

.82

.83

.85

.89

.85

.87

.88

.86

.97

.92

.85

.95

.95

Electrical-Resistivity

Graindensity(g/cmJ)

2.752.732.762.702.732.722.732.682.952.722.743.172.742.742.732.732.712.722.702.772.722.682.742.692.692.732.752.702.672.702.752.732.712.782.682.742.742.782.742.702.712.91

Porosity(%)

56.257.855.256.858.857.155.856.149.056.556.439.254.055.754.955.154.955.551.956.955.556.154.751.852.855.252.654.555.753.553.954.452.653.254.553.354.547.750.953.149.948.0

Watercontent Void

(%) ratio

46.450.545.648.151.247.845.947.438.4 (47.246.928.7 (42.644.843.744.143.245.139.845.144.046.545.038.939.943.940.142.4 144.5 142.943.243.240.041.842.6 141.0 142.7 133.0 (37.4 141.835.5 1

1.281.371.231.32.43.33.26.28

).96.30.30

).65.17.26.22.23.22.25.08.32.25.28.21.08.12.23.11.20.26.15.17.19.11.14.20.14.20

).91.04.13.00

33.8 0.92

Formation Factor

We measured the electrical-resistivity formation factor atthree intervals in sections from Hole!USA (see Table 9 andFigs. 19F and 20). Formation factor data from the upperm of Hole 818Bship to porositywith depth, but

show an unexpectedandthe

100proportional relation-

water content in its general decreaseine structure of the formation-factor/

depth relationship shows the expected inverseto water conten t (see

relationshipdashed lines of correlation in Fig. 19).

From 50 mbsf, formation factor increases downward to apeak at about 160 mbsf, before decreasing again until 250mbsf. This long-wavelength ^changes in porosity,odlllC HllCl Veil.

We measured818B (Table 10downward to a

variation does not parallelwhich indicate steady decline over

Shear Strengthshear strengthand

deptrbrittle for measuringwith a major change

in the

the

upper section of HoleFig. 19H). Shear strengths increase

L at which the formation becomes toovane shear—approximately coincidingin sediment accumulation rates at 90

mbsf. Some of the fine structure in the shear strength vs.depth function correlates with fine structure in the formationfactor and water content Junctions.

438

SITE 818

A B C D E

Bulk density (g/cm3) Bulk density (g/cm3) Velocity (km/s) Velocity (m/s) Porosity (%)

1.6 1.7 1.8 1.9 2.0 1.6 1.7 1.8 1.9 2.0 1.5 1.6 1.7 1.8 1.5 1.6 1.7 30 40 50 600

70

100-

E

Q.CDQ

200-

300

Water content (%)

20 40

G H I

Formation factor Shear strength (kPa)

1 2 3 4 5 0 10 20 0

Age (Ma)

1 2 3 4

100 -

CΛ_αE

Q

200 -

300

Figure 19. Comparison of velocity with bulk density derived from different sets of measurements, Site 818. A. Bulk density calculatedfrom pycnometer and mass observations of discrete samples from split cores. B. Bulk-density determined from GRAPEmeasurements of whole-round cores. C. Velocity is determined from traveltime and distance measurements of discrete samples fromsplit cores. D. Velocity determined from MST observations of whole-round cores. E. Porosity; least-squares linear regression is ofthe form Y = 61 - 2.7 × 10~2X, where Fis porosity, Xis depth, and the regression coefficient/? = 0.70. Dashed lines highlight detailsthat appear consistently in all sets of observations. F. Water content. G. Electrical resistivity formation factor. H. Shear strength.I. Age-depth curves are derived from paleontological dating of core-catcher samples. The two curves indicate possible depth rangeof dates. Depth ranges are approximately 10 m, the length of a core, which is the sample spacing. Dashed horizontal lines emphasizedetailed features that show up consistently in the various sets of measurements. Subunit designations are after "Lithostratigraphy"chapter (this volume).

439

SITE 818

Table 8. Compressional wave velocity, Site 818. Table 8 (continued).

Core, section,interval (cm)

133-818B-

1H-1, 79-821H-2, 79-821H-3, 79-821H-4, 79-821H-5, 79-821H-6, 40-432H-2, 79-822H-3, 79-822H-4, 79-822H-5, 79-822H-6, 79-822H-7, 79-823H-1, 79-823H-2, 79-823H-3, 79-823H-4, 79-823H-5, 79-823H-6, 79-824H-1, 80-834H-2, 80-834H-3, 80-834H-4, 80-834H-5, 80-834H-6, 87-905H-1, 87-905H-2, 79-825H-3, 87-905H-4, 87-905H-5, 87-905H-6, 87-906H-1, 80-836H-2, 80-836H-3, 80-836H-4, 80-836H-5, 80-836H-6, 80-837H-1, 87-907H-2, 87-907H-3, 87-907H-4, 87-907H-5, 83-867H-6, 87-908H-1, 85-888H-2, 85-888H-3, 85-888H-4, 85-888H-5, 85-888H-6, 85-889H-1, 83-869H-2, 85-889H-3, 85-889H-4, 85-889H-5, 85-889H-6, 85-88

10H-1, 101-10410H-2, 101-10410H-3, 101-10410H-4, 101-10410H-5, 101-10410H-6, 101-10411H-1, 98-10111H-2, 101-10411H-3, 101-10411H-4, 101-10411H-5, 101-10411H-6, 101-10412H-1, 101-10412H-2, 101-10412H-3, 101-10412H-4, 101-10412H-5, 105-10812H-6, 101-10413H-1, 101-10413H-2, 101-10413H-3, 101-10413H-4, 101-104

Depth(mbsf)

0.792.293.795.296.797.90

10.0811.5813.0814.5816.0817.5818.6920.1921.6923.1924.6926.1928.2029.7031.2032.7034.2035.7737.7739.1940.7742.2743.7745.2747.2048.7050.2051.7053.2054.7056.7758.2759.7761.2762.7364.2766.2567.7569.2570.7572.2573.7575.7377.2578.7580.2581.7583.2585.4186.9188.4189.9191.4192.9194.8896.4197.9199.41

100.91102.41104.41105.91107.41108.91110.45111.91113.91115.46117.01118.54

Distance(mm)

29.5027.2429.5128.3028.9727.8029.0730.4629.7030.2228.9129.4028.5928.6728.8528.9828.2328.4127.9327.7528.0228.0830.6429.3329.6028.8628.7628.8628.6829.6529.7829.1129.2029.0729.5928.9929.5930.0230.1329.1129.7428.1529.1928.9528.0228.9828.5828.9828.0227.8028.8928.9828.3425.5727.2327.4126.6225.7527.0327.1927.5827.4527.8028.5429.2829.5427.1428.8528.5027.5428.4528.2927.7128.8627.6228.68

Traveltime(µs)

21.5019.9821.5320.8121.1220.2620.6122.1021.3721.7020.9420.6320.6620.8720.9120.8420.5120.2719.9720.1020.4220.5422.1620.8921.2220.8120.7020.9020.8521.4821.4821.0819.4721.0920.5220.6021.4120.8621.4420.8821.3520.3720.7820.5520.2320.4019.8920.2120.0420.1320.6920.7320.6118.2319.1019.2319.2918.8719.5919.6919.7719.7120.0520.2321.0320.7819.4120.4820.5819.7420.2820.4819.7518.8920.0820.47

Velocity(m/s)

1547155215451539155015601602154915701570156316191569155515621576156215951595157115581550155415911577157215761563155815571564156217231559164115981560163415881580157415701593160115751617164216351593157215841586155916211638163615801566157615761593159015791607157616141601160115711593159615681603176515651592

Core, section,interval (cm)

13H-5, 101-10413H-6, 101-10414H-1, 101-10414H-2, 101-10414H-3, 111-11414H-4, 111-11414H-5, 101-10414H-6, 106-10915H-1, 110-11315H-2, 101-10415H-3, 105-10815H-4, 111-11415H-5, 111-11415H-6, 111-11416H-1, 107-11016H-2, 115-11816H-3, 111-11416H-4, 100-10316H-5, 101-10416H-6, 75-7817H-1, 60-6317H-2, 60-6317H-3, 60-6317H-4, 60-6317H-6, 60-6318H-2, 70-7318H-5, 70-7319H-2, 60-6319H-3, 60-6319H-4, 60-6319H-5, 60-6319H-6, 60-6320H-1,60-6320H-2, 60-6320H-3, 60-6320H-4, 60-6320H-5, 60-6320H-6, 60-6321H-2, 60-6321H-3, 60-6321H-4, 60-6321H-5, 60-6321H-6, 60-6321H-7, 60-6322H-2, 60-6322H-3, 60-6322H-4, 60-6322H-5, 60-6322H-6, 60-6322H-7, 60-6323H-1,60-6323H-2, 60-6323H-3, 60-6323H-4, 60-6323H-5, 60-6323H-6, 60-6323H-7, 60-6324H-1, 60-6324H-2, 60-6324H-3, 60-6324H-4, 60-6324H-5, 60-6324H-6, 60-6325H-1,60-6325H-2, 60-6325H-3, 60-6325H-4, 60-6325H-5, 60-6325H-6, 60-6325H-7, 60-6326H-1, 60-6326H-2, 60-6326H-3, 60-6326H-4, 60-6326H-5, 60-6326H-6, 60-6326H-7, 60-6327H-2, 60-63

Depth(mbsf)

120.04121.54123.41124.91126.51128.01129.41130.96133.00134.41135.95137.51139.01140.51142.47144.05145.51146.90148.41149.65151.50153.00154.50156.00159.00162.60167.10172.00173.50175.00176.50178.00180.00181.50183.00184.50186.00187.50191.00192.50194.00195.50197.00198.50200.50202.00203.50205.00206.50208.00208.50210.00211.50213.00214.50216.00217.50218.00219.50221.00222.50224.00225.50227.50229.00230.50232.00233.50235.00236.50237.00238.50240.00241.50243.00244.50246.00248.00

Distance(mm)

28.4028.2829.0627.8028.2428.1525.9428.7728.9828.9527.5427.1927.4028.4129.5129.1129.5529.1227.6427.9828.7628.0828.4228.1628.5827.7128.8130.8229.4930.5030.0730.4630.1230.4630.4229.2927.5028.3828.9828.2427.4528.8528.9829.4228.6828.9828.3829.6928.5428.8129.3327.5428.8128.5428.9827.5428.6328.6228.9728.1528.7529.2029.5931.0330.0331.2129.9828.5927.6729.4129.0829.9829.3829.1230.2229.5928.1528.99

Traveltime(/*)

19.6520.1820.6420.1020.0020.2718.6920.0120.0420.7619.5918.8319.5020.5320.2720.0619.7719.2219.5920.0120.2019.3118.7619.7420.2519.6820.1421.6920.9321.6020.6321.6721.2021.5921.2019.9419.9220.1319.5919.4318.8119.8320.0320.7720.0820.5419.4320.4720.1119.7420.5918.8319.9119.5519.7318.6619.5219.8719.7519.8319.7420.2120.7921.4620.9121.5121.0320.3119.7420.8820.6520.6920.5920.7021.1220.6519.6320.43

Velocity(m/s)

165515961599157416111579159716421651158116081664160815711661165717131745161415941623167017511631160716091631160415971594165915861608159316251680157316061697166816831664165216081629160316761652161816711619168616541674168317051683164616801622166716481616163616301642161616021601159715991648162215971621162916421614

440

SITE 818

Table 8 (continued). 30

Core, section,interval (cm)

27H-3, 60-6327H-4, 60-6327H-5, 60-6327H-6, 60-6327H-7, 60-6328H-1, 60-6328H-2, 60-6328H-3, 60-6328H-4, 60-6328H-6, 60-6328H-7, 60-6329H-1, 60-6329H-2, 60-6329H-3, 60-6329H-4, 60-6329H-5, 60-6329H-6, 60-6330H-1, 60-633OH-2, 60-6330H-3, 60-6330H-4, 60-633OH-5, 60-6330H-6, 60-6331H-1, 60-6331H-2, 60-6331H-3, 60-6331H-6, 60-6332H-1, 60-6332H-2, 60-6332H-3, 60-6332H-5, 60-63

Depth(mbsf)

249.50251.00252.50254.00255.50256.00257.50259.00260.50263.50265.00265.50267.00268.50270.00271.50273.00275.00276.50278.00279.50281.00282.50284.50286.00287.50292.00294.00295.50297.00300.00

Distance(mm)

28.7629.5029.3729.5030.0429.9829.8530.4631.3629.5530.5530.3830.6931.1229.9829.8130.1329.6832.0430.2529.2429.2929.9030.0729.4228.1629.7729.8129.9129.5930.42

Traveltime(µs)

20.4320.8720.%20.7520.9421.2020.8221.2921.7020.9421.2021.3621.5622.0020.9620.5820.8320.6521.7420.7520.4320.5620.9720.6019.8619.2720.5019.3520.6320.0919.72

Velocity(m/s)

16011603158716141628160016281619163315991633160916081593162216481643163416671658162916201617166216%167916541774164916831772

40

t 50oδ

CL

SEISMIC STRATIGRAPHY

The stratigraphic section at Site 818 was divided into fiveseismic sequences, of which four were drilled (Fig. 21). Eachof the sequences is briefly described next and is correlatedwith lithostratigraphy encountered at the site.

Sequence 1 extends from the seafloor down approximately0.08 to 1.072 s at Site 818. Much of the character of thissequence is obscured by a strong source pulse at the seafloor.Generally, this sequence is characterized by wavy discontin-uous reflectors of various amplitude and frequency. It onlapssequence 2.

Sequence 2 occurs between 1.072 and 1.175 s at Site 818(Fig. 22) and is characterized by wavy reflectors of moderateamplitude and frequency.

Sequence 3 occurs between 1.175 and 1.312 s at Site 818 (Fig.22). The lower boundary is characterized by onlap both to thenorth and south (Fig. 21). Reflectors tend to be subparallel, withlow to high amplitude and moderate frequency.

Sequence 4 occurs between 1.312 and 1.370 s at Site 818(Fig. 22), but thickens both to the north and south (Fig. 21) toform the walls of a channel in which sequence 3 was depos-ited. The sequence is characterized by subparallel, low-amplitude reflectors.

Sequence 5 occurs between 1.370 and 1.420 s at Site 818(Fig. 22). The upper surface is characterized by erosionaltruncation and moderate to low amplitude discontinuousreflectors.

Site 818 was not logged; thus, correlation between seismicsequences and lithostratigraphy encountered at the site isbased on an approximate velocity/depth curve (Fig. 7) con-structed from interval velocities that were derived from thestacking velocities used to process these seismic data. None-

60

7020 40 50

Dry-water content (%)

Figure 20. Dry-water content vs. porosity for Site 818. Data arederived from mass and pycnometer volume measurements of discretesamples from cores. Least-squares linear regression is of the form Y= -43 + 1.6Z, where Tis porosity, X is depth, and the regressioncoefficient R = 0.96.

theless, the sequences correlated well with units identified inthe lithostratigraphy.

Sequences 1 through 3 form a total thickness of approxi-mately 300 m that corresponds to the Pliocene-Pleistoceneperiplatform ooze with minor turbidite beds and slumpedhorizons of lithologic Unit I (Fig. 22). These three sequencesform a broad, mounded, onlapping channel fill. Sequence 4forms the walls of the channel (Fig. 21), which has been cut onthe slope in front of a carbonate platform. The top of sequence4 consists of calcareous chalk.

SUMMARY AND CONCLUSIONS

For a discussion of this site, the reader is directed to the"Summary and Conclusions" section of the "Site 817" chap-ter (this volume).

441

SITE 818

REFERENCES

Andrews, J. E., 1973. Correlation of seismic reflectors. In Burns, R.E., Andrews, J. E., et al., Init. Repts. DSDP.21: Washington(U.S. Govt. Printing Office), 459-479.

Baker, P. A., 1986. Pore-water chemistry of carbonate-rich sedi-ments, Lord Howe Rise, southwest Pacific Ocean. In Kennett, J.P., von der Borch, C. C , et al., Init. Repts. DSDP, 90: Washing-ton (U.S. Government Printing Office), 1249-1256.

Droxler, A. W., Bruce, C. H., Sager, W. W., and Watkins, D. H., 1988.Pliocene-Pleistocene variations in aragonite content and planktonicoxygen-isotope record in Bahamian periplatform ooze, Hole 633A. InAustin, J. A., Jr., Schlager, W., et al., Proc. ODP, Sci. Results, 101:College Station, TX (Ocean Drilling Program), 221-244.

Feary, D. A., Pigram, C. J., Davies, P. J., Symonds, P. A., Droxler,A. W., and Peerdeman, F., 1990. Ocean Drilling Program—Leg133 safety package. Bur. Miner. Res. Aust. Rec, 1990/6.

Kennett, J. P., von der Borch, C. C , et al., 1986. Init. Repts. DSDP,90: Washington (U.S. Govt. Printing Office).

Schlager, W., and James, N. P., 1978. Low-magnesian calcite lime-stones forming at the deep-sea floor, Tongue of the Ocean,Bahamas. Sedimentology, 15:675-702.

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

Swart, P. K., and Guzikowski, M., 1988. Interstitial-water chemistryand diagenesis of periplatform sediments from the Bahamas, ODPLeg 101. In Austin, J. A., Jr., Schlager, W., et al., Proc. ODP, Sci.Results, 101: College Station, TX (Ocean Drilling Program),363-380.

Symonds, P. A., and Davies, P. J., 1988. Structure, stratigraphy,evolution and regional framework of the Townsville Trough andMarion Plateau region—research cruise proposal, project9131.11. Bur. Miner. Res. Aust. Rec, 1988/48.

van Morkhoven, F.P.C.M., Berggren, W. A., Edwards, A. S., etal., 1986. Cenozoic cosmopolitan deep-water benthic foramin-ifera. Bull. Cent. Rech. Explor.-Prod. Elf-Aquitaine, Mem. 11.

Ms 133-111

NOTE: All core description forms ("barrel sheets") and core photographs have been printed oncoated paper and bound separately as Part 2 of this volume, beginning on page 813.

442

SITE 818

Table 9. Electrical-resistivity formation factor data, Site 818. Table 9 (continued).

Core, section,interval (cm)

133-818B-1H-1, 20-201H-1, 70-701H-1, 120-1201H-2, 20-201H-2, 70-701H-2, 120-1201H-3, 20-201H-3, 70-701H-3, 120-1201H-4, 20-201H-4,70-701H-4, 120-1201H-5, 20-201H-5, 70-701H-5, 120-1201H-6, 20-201H-6, 70-702H-2, 20-202H-2, 70-702H-2, 120-1202H-3, 20-202H-3, 70-702H-3, 120-1202H-4, 20-202H-4, 70-702H-4, 120-1202H-5, 20-202H-5, 70-702H-5, 120-1202H-6, 20-202H-6, 70-702H-6, 120-1202H-7, 20-202H-7, 70-702H-7, 120-1203H-1, 20-203H-1, 70-703H-1, 120-1203H-2, 20-203H-2, 70-703H-2, 120-1203H-3, 20-203H-3, 70-703H-3, 120-1203H-4, 20-203H-4, 70-703H-4, 120-1203H-5, 20-203H-5,70-703H-5, 120-1203H-6, 20-203H-6, 70-703H-6, 120-1204H-1, 20-204H-1, 70-704H-1, 120-1204H-2, 20-204H-2, 70-704H-2, 120-1204H-3, 20-204H-3, 70-704H-3, 120-1204H-4, 20-204H-4, 70-704H-4, 120-1204H-5, 20-204H-5, 70-704H-5, 120-1204H-6, 20-204H-6, 70-704H-6, 120-1204H-7, 20-204H-7, 70-705H-1, 20-205H-1, 70-705H-1, 120-120

Depth(mbsf)

0.200.701.201.702.202.703.203.704.204.705.205.706.206.707.207.708.209.499.99

10.4910.9911.4911.9912.4912.9913.4913.9914.4914.9915.4915.9916.4916.9917.4917.9918.1018.6019.1019.6020.1020.6021.1021.6022.1022.6023.1023.6024.1024.6025.1025.6026.1026.6027.6028.1028.6029.1029.6030.1030.6031.1031.6032.1032.6033.1033.6034.1034.6035.1035.6036.1036.6037.1037.1037.6038.10

Seawater(ohms)

2.92.92.92.92.92.93.02.92.82.82.92.92.92.92.92.82.82.82.82.82.82.93.02.92.92.92.92.82.82.82.82.82.82.82.82.92.92.92.82.82.82.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.93.03.02.92.92.9

Sample(ohms)

10.09.29.78.2

10.39.38.57.77.58.67.48.29.98.18.17.37.67.08.2

10.36.46.96.26.68.19.37.17.46.76.87.57.37.98.87.98.38.37.66.76.76.46.67.39.47.67.17.98.07.67.57.3

10.27.07.57.77.96.87.88.06.46.87.56.27.36.96.36.97.37.67.57.97.38.17.3

10.27.1

Formationfactor

3.453.173.342.833.553.212.832.662.683.072.552.833.412.792.792.612.712.502.933.682.292.382.072.282.793.212.452.642.392.432.682.612.823.142.822.862.862.622.392.392.292.282.523.242.622.452.722.762.622.592.523.522.412.592.662.722.342.692.762.212.342.592.142.522.382.172.382.522.622.592.722.432.702.523.522.45

Core, section,interval (cm)

5H-2, 20-205H-2, 70-705H-2, 120-1205H-3, 20-205H-3, 70-705H-3, 120-1205H-4, 20-205H-4, 70-705H-4, 120-1205H-5, 20-205H-5, 70-705H-5, 120-1205H-6, 20-205H-6, 70-705H-6, 120-1206H-1, 20-206H-1, 70-706H-1, 120-1206H-2, 20-206H-2, 70-706H-2, 120-1206H-3, 20-206H-3, 70-706H-3, 120-1206H-4, 20-206H-4, 70-706H-4, 120-1206H-5, 20-206H-5, 70-706H-5, 120-1206H-6, 20-206H-6, 70-706H-6, 120-1207H-1, 20-207H-1, 70-707H-1, 120-1207H-2, 20-207H-2, 70-707H-2, 120-1207H-3, 20-207H-3, 70-707H-3, 120-1207H-4, 20-207H-4, 70-707H-4, 120-1207H-5, 20-207H-5, 70-707H-5, 120-1207H-6, 20-207H-6, 70-707H-6, 120-1208H-1, 20-208H-1, 70-708H-1, 120-1208H-2, 20-208H-2, 70-708H-2, 120-1208H-3, 20-208H-3, 70-708H-3, 120-1208H-4, 20-208H-4,70-708H-4, 120-1208H-5, 20-208H-5, 70-708H-5, 120-1208H-6, 20-208H-6, 70-708H-6, 120-1209H-1, 20-209H-1, 70-709H-1, 120-1209H-2, 20-209H-2, 70-709H-2, 120-1209H-3, 20-209H-3, 70-709H-3, 120-120

Depth(mbsf)

38.6039.1039.6040.1040.6041.1041.6042.1042.6043.1043.6044.1044.6045.1045.6046.6047.1047.6048.1048.6049.1049.6050.1050.6051.1051.6052.1052.6053.1053.6054.1054.6055.1056.1056.6057.1057.6058.1058.6059.1059.6060.1060.6061.1061.6062.1062.6063.1063.6064.1064.6065.6066.1066.6067.1067.6068.1068.6069.1069.6070.1070.6071.1071.6072.1072.6073.1073.6074.1075.1075.6076.1076.6077.1077.6078.1078.6079.10

Seawater(ohms)

3.03.03.03.03.03.03.03.03.03.23.23.23.23.23.23.03.03.03.03.02.92.92.92.92.92.92.92.93.03.03.03.03.03.02.82.82.92.92.92.92.92.92.92.92.93.03.02.82.82.82.82.82.82.82.92.92.92.92.92.82.92.82.82.82.82.82.72.72.72.72.72.72.72.72.72.72.72.7

Sample(ohms)

6.27.36.16.97.27.37.87.47.56.77.36.76.57.07.47.47.47.57.17.56.39.09.88.29.27.08.39.87.78.47.28.77.47.47.07.57.98.27.58.08.88.07.57.78.58.16.97.47.77.27.37.19.58.96.77.86.87.18.17.57.49.99.27.9

10.19.18.7

10.27.96.78.49.38.58.78.07.58.07.4

Formationfactor

2.072.432.032.302.402.432.602.472.502.092.282.092.032.192.312.472.472.502.372.502.173.103.382.833.172.412.863.382.572.802.402.902.472.472.502.682.722.832.592.763.032.762.592.662.932.702.302.642.752.572.612.543.393.182.312.692.342.452.792.682.553.543.292.823.613.253.223.782.932.483.113.443.153.222.962.782.962.74

443

SITE 818

Table 9 (continued). Table 9 (continued).

Core, section,interval (cm)

9H-4, 20-209H-4,70-709H-4, 120-1209H-5, 20-209H-5, 70-709H-5, 120-1209H-6, 20-209H-6, 70-709H-6, 120-120

10H-1, 20-2010H-1, 70-7010H-1, 120-12010H-2, 20-2010H-2, 70-7010H-2, 120-12010H-3, 20-2010H-3, 70-7010H-3, 120-12010H-4,20-2010H-4, 70-7010H-4, 120-12010H-5, 20-2010H-5, 70-7010H-5, 120-12010H-6,20-2010H-6, 70-7010H-6,120-12011H-1, 20-2011H-1, 70-7011H-1, 120-12011H-2, 20-2011H-2, 70-7011H-2, 120-12011H-3, 20-2011H-3, 70-7011H-3, 120-12011H-4, 20-2011H-4,70-7011H-4, 120-12011H-5, 20-2011H-5, 70-7011H-5, 120-12011H-6, 20-2011H-6, 70-7011H-6, 120-12012H-1, 20-2012H-1, 70-7012H-1, 120-12012H-2, 20-2012H-2, 70-7012H-2, 120-12012H-3, 20-2012H-3, 70-7012H-3, 120-12012H-4, 20-2012H-4, 70-7012H-4, 120-12012H-5, 20-2012H-5, 70-7012H-5, 120-12012H-6, 20-2012H-6, 70-7012H-6, 120-12013H-1, 20-2013H-1, 70-7013H-1, 120-12013H-2, 20-2013H-2, 70-7013H-2, 120-12013H-3, 20-2013H-3, 70-7013H-3, 120-12013H-4, 20-2013H-4, 70-7013H-4, 120-12013H-5, 20-2013H-5, 70-7013H-5, 120-120

Depth(mbsf)

79.6080.1080.6081.1081.6082.1082.6083.1083.6084.6085.1085.6086.1086.6087.1087.6088.1088.6089.1089.6090.1090.6091.1091.6092.1092.6093.1094.1094.6095.1095.6096.1096.6097.1097.6098.1098.6099.1099.60

100.10100.60101.10101.60102.10102.60103.60104.10104.60105.10105.60106.10106.60107.10107.60108.10108.60109.10109.60110.10110.60111.10111.60112.10113.10113.60114.10114.65115.15115.65116.20116.70117.20117.73118.23118.73119.23119.73120.23

Seawater(ohms)

2.72.72.72.72.72.72.72.72.72.82.82.82.82.82.82.82.82.82.82.82.82.72.72.72.72.72.72.72.72.72.72.72.72.72.72.72.72.72.72.72.72.72.72.72.72.72.72.72.72.72.72.72.72.72.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.6

Sample(ohms)

7.37.48.57.87.36.76.67.86.89.7

10.19.89.6

10.011.18.69.58.28.67.77.67.78.17.58.37.29.77.07.47.47.47.38.97.77.77.68.47.67.37.67.97.87.78.99.58.27.47.58.89.47.48.97.37.47.27.17.77.57.67.88.07.97.57.97.39.48.48.58.27.38.87.5

10.06.86.97.28.37.8

Formationfactor

2.702.743.152.892.702.482.442.892.523.463.613.503.433.573.963.073.392.933.072.752.712.853.002.783.072.673.592.592.742.742.742.703.302.852.852.813.112.812.702.812.932.892.853.303.523.042.742.783.263.482.743.302.702.742.772.732.962.882.923.003.083.042.883.042.813.623.233.273.152.813.382.883.852.622.652.773.193.00

Core, section,interval (cm)

13H-6, 20-2013H-6, 70-7013H-6, 120-12014H-1, 20-2014H-1, 70-7014H-1, 120-12014H-2, 20-2014H-2, 70-7014H-2, 120-12014H-3, 20-2014H-3, 70-7014H-3, 120-12014H-4, 20-2014H-4, 70-7014H-4, 120-12014H-5, 20-2014H-5, 70-7014H-5, 120-12014H-6, 20-2014H-6, 70-7014H-6, 120-12015H-1, 20-2015H-1, 70-7015H-1, 120-12015H-2, 20-2015H-2, 70-7015H-2, 120-12015H-3, 20-2015H-3, 70-7015H-3, 120-12015H-4, 20-2015H-4, 70-7015H-4, 120-12015H-5, 20-2015H-5, 70-7015H-5, 120-12015H-6, 20-2015H-6, 70-7015H-6, 120-12016H-1, 20-2016H-1, 70-7016H-1, 120-12016H-2, 20-2016H-2, 70-7016H-2, 120-12016H-3, 20-2016H-3, 70-7016H-3, 120-12016H-4, 20-2016H-4,70-7016H-4, 120-12016H-5, 20-2016H-5, 70-7016H-5, 120-12016H-6, 20-2016H-6, 70-7016H-6, 120-12017H-1, 20-2017H-1, 70-7017H-1, 120-12017H-2, 20-2017H-2, 70-7017H-2, 120-12017H-3, 20-2017H-3, 70-7017H-3, 120-12017H-4, 20-2017H-4,70-7017H-4,120-12017H-5, 20-2017H-5, 70-7017H-5, 120-12017H-6, 20-2017H-6, 70-7017H-6, 120-12018H-1, 20-2018H-1, 70-7018H-1, 120-120

Depth(mbsf)

120.73121.23121.73122.60123.10123.60124.10124.60125.10125.60126.10126.60127.10127.60128.10128.60129.10129.60130.10130.60131.10132.10132.60133.10133.60134.10134.67135.10135.60136.10136.60137.10137.60138.10138.60139.10139.60140.10140.60141.60142.10142.60143.10143.60144.10144.60145.10145.60146.10146.60147.00147.60148.10148.60149.10149.60150.10151.10151.60152.10152.60153.10153.60154.10154.60155.10155.60156.10146.60157.10157.60158.10158.60159.10159.60160.60161.10161.60

Seawater(ohms)

2.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.6

Sample(ohms)

7.97.99.37.59.09.6

10.18.07.68.78.09.17.59.67.98.29.79.38.47.57.59.48.78.89.48.38.69.57.38.58.88.17.67.97.37.47.97.37.58.88.38.9

10.29.28.88.79.28.2

11.08.39.28.38.38.69.2

10.29.09.48.29.58.77.98.67.79.58.19.5

10.79.78.18.78.59.49.7

10.38.49.6

10.6

Formationfactor

3.043.043.582.883.463.693.883.082.923.353.083.502.883.693.043.153.733.583.232.882.883.623.353.383.623.193.313.652.813.273.383.122.923.042.812.853.042.812.883.383.193.423.923.543.383.353.543.154.233.193.543.193.193.313.543.923.463.623.153.653.353.043.312.963.653.123.654.123.733.123.353.273.623.733.963.233.694.08

444

SITE 818

Table 9 (continued). Table 9 (continued).

Core, section,interval (cm)

18H-3, 20-2018H-3, 70-7018H-3, 120-12019H-1, 20-2019H-1, 70-7019H-1, 120-12019H-2, 20-2019H-2, 70-7019H-2, 120-12019H-3, 20-2019H-3, 70-7019H-3, 120-12020H-1, 20-2020H-1, 70-7020H-1, 120-12020H-2, 20-2020H-2, 70-7020H-2, 120-12020H-3, 20-2020H-3, 70-7020H-3, 120-12020H-4, 20-2020H-4, 70-7020H-4, 120-12020H-6, 20-2020H-6, 70-7020H-6, 120-12021H-1, 20-2021H-1, 70-7021H-1, 120-12021H-2, 20-2021H-2, 70-7021H-2, 120-12021H-3, 20-2021H-3, 70-7021H-3, 120-12021H-4, 20-2021H-4, 70-7021H-4, 120-12021H-5, 20-2021H-5, 70-7021H-5, 120-12021H-6, 20-2021H-6,70-7021H-6, 120-12021H-7, 20-2021H-7, 70-7022H-1, 20-2022H-1, 70-7022H-1, 120-12022H-2, 20-2022H-2, 70-7022H-2, 120-12022H-3, 20-2022H-3, 70-7022H-3, 120-12022H-4, 20-2022H-4, 70-7022H-4, 120-12022H-5, 20-2022H-5, 70-7022H-5, 120-12022H-6, 20-2022H-6, 70-7022H-6, 120-12023H-1, 20-2023H-1,70-7023H-1, 120-12023H-2, 20-2023H-2, 70-7023H-2, 120-12023H-3, 20-2023H-3, 70-7023H-3, 120-12023H-4, 20-2023H-4,70-7023H-4, 120-12023H-5,20-20

Depth(mbsf)

163.60164.10164.60170.10170.60171.10171.60172.10172.60173.10173.60174.10179.60180.10180.60181.10181.60182.10182.60183.10183.60184.10184.60185.10187.10187.60188.10189.10189.60190.10190.60191.10191.60192.10192.60193.10193.60194.10194.60195.10195.60196.10196.60197.10197.60198.10198.60198.60199.10199.60200.10200.60201.10201.60202.10202.60203.10203.60204.10204.60205.10205.60206.10206.60207.10208.10208.60209.10209.60210.10210.60211.10211.60212.10212.60213.10213.60214.10

Seawater(ohms)

2.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.62.72.82.82.82.82.82.82.82.82.82.82.82.82.82.82.82.82.82.82.82.82.82.82.82.82.82.82.82.82.82.82.82.62.62.62.62.62.62.62.62.62.62.92.92.92.92.92.83.03.03.03.03.03.03.03.03.03.03.03.03.1

Sample(ohms)

9.69.0

10.67.38.9

10.48.6

10.29.58.28.4

10.27.87.37.78.17.47.17.48.58.87.69.97.88.07.27.07.49.87.57.88.49.37.37.58.77.28.37.77.78.89.97.88.97.58.69.87.58.78.27.78.37.37.17.78.59.07.89.27.77.77.87.37.18.46.88.97.98.18.58.37.38.37.68.38.88.27.7

Formationfactor

3.693.464.082.813.424.003.313.923.653.153.233.923.002.812.963.122.852.632.643.043.142.713.542.792.862.572.502.643.502.682.793.003.322.612.683.112.572.962.752.753.143.542.793.182.683.073.502.683.113.152.963.192.812.732.963.273.463.003.542.662.662.692.522.453.002.272.972.632.702.832.772.432.772.532.772.932.732.48

Core, section,interval (cm)

23H-5, 70-7023H-5, 120-12023H-6, 20-2023H-6, 70-7023H-6, 120-12024H-1, 20-2024H-1, 70-7024H-1, 120-12024H-2, 20-2024H-2, 70-7024H-2, 120-12024H-3, 20-2024H-3, 70-7024H-3, 120-12024H-4, 20-2024H-4, 70-7024H-4, 120-12024H-5, 20-2024H-5, 70-7024H-5, 120-12024H-6, 20-2024H-6, 70-7024H-6, 120-12025H-1, 20-2025H-1, 70-7025H-1, 120-12025H-2, 20-2025H-2, 70-7025H-2, 120-12025H-3, 20-2025H-3, 70-7025H-3, 120-12025H-4,20-2025H-4, 70-7025H-4, 120-12025H-5, 20-2025H-5, 70-7025H-5, 120-12025H-6,20-2025H-6,70-7025H-6, 120-12025H-7, 20-2025H-7, 70-7026H-1, 20-2026H-1, 70-7026H-1, 120-12026H-2, 20-2026H-2, 70-7026H-2, 120-12026H-3, 20-2026H-3, 70-7026H-3, 120-12026H-4, 20-2026H-4, 70-7026H-4, 110-11026H-5, 20-2026H-5, 70-7026H-5, 120-12026H-6, 20-2026H-6,70-7026H-6, 120-12026H-7, 20-2026H-7, 70-7027H-1, 20-2027H-1, 70-7027H-1, 120-12027H-2, 20-2027H-2, 70-7027H-2, 120-12027H-3, 20-2027H-3, 70-7027H-3, 120-12027H-4, 20-2027H-4, 70-7027H-4, 120-12027H-5, 20-2027H-5, 70-7027H-5, 120-120

Depth(mbsf)

214.70215.10215.60216.10216.60217.60218.10218.60219.10219.60220.10220.60221.10221.60222.10222.60223.10223.60224.10224.50225.10225.60226.10227.10227.60228.10228.60229.10229.60230.10230.60231.10231.60232.10232.60233.10233.60234.10234.60235.10235.60236.10236.60236.60237.10237.60238.10238.60239.10239.60240.10240.60241.10241.60242.00242.60243.10243.60244.10244.60245.10245.60246.10246.10246.60247.10247.60248.10248.60249.10249.60250.10250.60251.10251.60252.10252.60253.10

Seawater(ohms)

3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.(3.3.3.3.3.3.3.3.3.3.3.3.

)

3.03.03.03.03.03.03.03.3.3.3.3.3.3.3.3.3.13.3.3.3.3.13.13.13.13.13.13.13.03.03.03.03.03.03.33.03.03.03.03.13.13.13.1

Sample(ohms)

9.36.98.09.47.58.47.79.67.68.18.27.77.88.37.98.6

11.27.59.87.76.97.88.19.37.17.37.59.88.17.79.27.98.48.78.27.47.27.07.36.98.57.27.16.97.07.18.07.86.97.87.97.27.89.27.38.27.39.38.08.69.06.58.98.57.38.78.67.28.48.06.77.27.37.47.69.47.57.2

Formationfactor

3.002.232.583.032.422.712.483.102.452.612.652.482.522.682.552.773.612.423.162.482.232.522.703.002.292.352.423.162.612.482.972.552.712.812.652.472.402.332.432.302.832.402.292.232.262.292.582.522.232.522.552.322.522.972.352.652.353.002.582.772.902.102.872.832.432.902.872.402.802.422.232.402.432.472.453.032.422.32

445

SITE 818

Table 9 (continued). Table 9 (continued).

Core, section,interval (cm)

27H-6, 20-2027H-6, 70-7027H-6, 120-12028H-1, 20-2028H-1, 70-7028H-1, 120-12028H-2, 20-2028H-2, 70-7028H-2, 120-12028H-3, 20-2028H-3, 70-7028H-3, 120-12028H-4, 20-2028H-4, 70-7028H-4, 120-12028H-6, 20-2028H-6, 70-7028H-6, 120-12029H-1, 20-2029H-1, 70-7029H-1, 120-12029H-2, 20-2029H-2, 70-7029H-2, 120-12029H-3, 20-2029H-3, 70-7029H-3, 120-12029H-4, 20-2029H-4, 70-7029H-4, 120-12029H-5, 20-2029H-5, 70-7029H-5, 120-12029H-6, 20-2029H-6, 70-7029H-6, 120-12030H-1, 20-2030H-1, 70-7030H-1, 120-12030H-2, 20-2030H-2, 70-7030H-2, 120-12030H-3, 20-203OH-3, 70-70

Depth(mbsf)

253.60254.10254.60255.60256.10256.60257.10257.60258.10258.60259.10259.60260.10260.60261.10263.10263.60264.10265.10265.60266.10266.60267.10267.60268.10268.60269.10269.60270.10270.60271.10271.60272.10272.60273.10273.60274.60275.10275.60276.10276.60277.10277.60278.10

Seawater(ohms)

3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.13.13.13.13.03.03.03.03.03.03.03.03.03.03.03.03.03.03.03.3.3.3.3.3.3.3.3.3.

3.

Sample(ohms)

8.96.77.16.97.08.28.28.58.29.28.38.18.68.88.38.28.88.89.09.18.67.98.37.47.38.09.08.48.98.18.48.68.29.18.88.68.37.48.39.89.69.4

10.08.8

Formationfactor

2.872.162.292.232.262.652.652.742.652.972.682.612.772.842.682.652.842.843.003.032.872.632.772.472.432.673.002.802.972.702.802.872.732.942.842.772.682.392.683.163.103.033.232.84

Core, section,interval (cm)

3OH-3, 120-12030H-4, 20-2030H-4, 70-7030H-4,120-12030H-5, 20-2030H-5, 70-7030H-5, 120-12031H-1, 20-2031H-1, 70-7031H-1, 120-12031H-2, 20-2031H-2, 70-7031H-2, 120-12031H-3, 20-2031H-3, 70-7031H-3, 120-12031H-4, 20-2031H-4, 70-7031H-4, 120-12031H-5, 20-2031H-5, 70-7031H-5, 120-12031H-6, 20-2031H-6, 70-7031H-6,120-12032H-1, 20-2032H-1,70-7032H-1, 120-12032H-2, 20-2032H-2, 70-7032H-2, 120-12032H-3, 20-2032H-3, 70-7032H-3, 120-12032H-4, 20-2032H-4, 70-7032H-4, 120-12032H-5, 20-2032H-5, 70-7032H-5, 120-12032H-6, 20-2032H-6, 70-7032H-6, 120-120

Depth(mbsf)

278.60279.10279.60280.10280.60281.10281.60284.10284.60285.10285.60286.10286.60287.10287.60288.10288.60289.10289.60290.10290.60291.10291.60292.10292.60293.60294.10294.60295.10295.60296.10296.60297.10297.60298.10298.60299.10299.60300.10300.60301.10301.60302.10

Seawater(ohms)

3.13.13.13.13.13.13.13.13.13.13.13.13.13.13.13.03.03.03.03.03.03.03.03.03.03.03.03.03.03.03.03.03.03.03.03.03.03.03.03.03.03.03.0

Sample(ohms)

7.57.67.47.78.27.97.99.18.4

10.39.19.69.58.89.79.59.68.99.88.18.89.49.09.1

10.011.611.59.7

11.17.78.78.68.28.58.68.19.59.48.99.49.89.98.7

Formationfactor

2.422.452.892.482.652.552.552.942.713.322.943.103.062.843.133.173.202.973.272.702.933.133.003.033.333.873.833.233.702.572.902.872.732.832.872.703.173.132.973.133.273.302.90

446

SITE 818

Table 10. Vane shear strength, Site 818. Table 10 (continued).

Core, section,interval (cm)

133-818B-1H-1, 94-951H-2, 94-951H-3, 94-951H-4, 94-951H-5, 94-951H-6, 67-682H-2, 91-922H-3, 91-922H-4, 91-922H-5, 91-922H-6, 91-922H-7, 91-923H-1, 91-923H-2, 91-923H-3, 91-923H-4, 91-923H-5, 91-923H-6, 91-924H-1, 91-924H-2, 91-924H-3, 91-924H-4, 91-924H-5, 91-924H-6, 100-1014H-7, 50-515H-1, 100-1015H-2, 100-1015H-3, 100-1015H-4, 100-1015H-5, 100-1015H-6, 100-1016H-1, 100-1016H-2, 100-1016H-3, 100-1016H-4, 100-1016H-5, 100-1016H-6, 100-1017H-1, 99-1007H-2, 99-1007H-3, 100-1017H-5, 100-1017H-6, 100-1018H-1, 95-968H-2, 95-968H-3, 95-968H-4, 95-%8H-5, 95-968H-6, 95-969H-1, 95-969H-2, 95-969H-3, 95-969H-4, 95-969H-5, 95-%9H-6, 95-%

10H-1, 95-%

Depth(mbsf)

0.942.443.945.446.948.17

10.2011.7013.2014.7016.2017.7018.8120.3121.8123.3124.8126.3128.3129.8131.3132.8134.3135.9036.9037.9039.4040.9042.4043.9045.4047.4048.9050.4051.9053.4054.9056.8958.3959.9062.9064.4066.3567.8569.3570.8572.3573.8575.8577.3578.8580.3581.8583.3585.35

Spring Torquenumber (degrees)

1 161 81 191 191 161 161 341 301 241 181 271 26I 27I 241 281 151 31I 241 9

27[ 16I 14I 14

151 14I 22I 17

36293020

1 397

38444134315221372940322436423750443648283947

Strain(degrees)

20119

1214111813131114111313171118105

121210131115151315131115159

1310151416g

13201415151017131310101412141516

Shearstrength

(kPa)

3.41.74.04.03.43.47.26.45.13.85.75.55.75.15.93.26.65.11.95.73.43.03.03.23.04.73.67.66.26.44.28.31.58.19.38.77.26.6

11.04.57.96.28.56.85.17.68.97.9

10.69.37.6

10.25.98.3

10.0

Core, section,interval (cm)

10H-2, 95-%10H-3, 95-%10H-4, 95-%10H-5, 95-%10H-6, 95-%11H-1, 95-9611H-2, 95-9611H-3, 95-%11H-4, 95-%11H-5, 95-%11H-6, 95-9612H-l,95-%12H-2, 95-%12H-3, 95-%12H-4, 95-%12H-5, 95-%12H-6, 95-9613H-1, 95-%13H-2, 95-%13H-3, 95-%13H-4, 95-%13H-5, 95-%13H-6, 95-9614H-1, 93-9414H-2, 95-9614H-3, 105-10614H-4, 105-10614H-5, 95-%14H-6, 95-%15H-1, 70-7115H-2, 95-%15H-3, 90-9115H-4, 95-9615H-5, 82-8315H-6, 85-8616H-1,97-9816H-2, 104-10516H-3, 95-%16H-4, 93-9416H-5, 94-9516H-6, 94-9517H-1, 94-9517H-2, 94-9517H-3, 94-9517H-5, 94-9517H-6, 95-%18H-1,94-9518H-3, 94-9519H-1, 94-9519H-2, 94-9519H-3, 94-9520H-1, 94-9520H-2, 94-9520H-3, 94-9520H-4, 94-9521H-1, 81-82

Depth(mbsf)

86.8588.3589.8591.3592.8594.85%.3597.8599.35

100.85102.35104.35105.85107.35108.85110.35111.85113.85115.40116.95118.48119.98121.48123.33124.85126.45127.95129.35130.85132.60134.35135.80137.35138.72140.25142.37143.94145.35146.83148.34149.84151.84153.34154.84157.84159.35161.34164.34170.84172.34173.84180.34181.84183.34184.84189.71

Spring Torquenumber (degrees)

:

1 551 331 291 301 351 371 471 501 361 391 441 551 60i 46

351 391 331 67L 50[ 581 54

721 34I 30

40I 57I 45I 511 52

44[ 49I 43I 30

2960726169766139423447573048515142454415794179

Strain(degrees)

1510121415172113141312101920121612152011151011111410131515101220171122151310171713212814111412161310132217121525

Shearstrength

(kPa)

11.77.06.26.47.47.9

10.010.67.68.39.3

11.712.79.87.48.37.0

14.210.612.311.515.37.26.48.5

12.19.5

10.811.09.3

10.49.16.46.2

12.715.312.914.616.112.98.38.97.2

10.012.16.4

10.210.810.88.99.59.33.2

16.88.7

16.8

447

SITE 818

Part M Part CSite 818 (approx) Part A PartE

CDP

000.HHH 270.2100

4100I

CDP

000.HHH

1.5

Figure 21. Part of seismic line 75/59 showing the seismic character of the sequences at Site 818 and their relationship to the carbonate platformthat is represented by the nonreflecting zone at the right hand side of the section.

448

SITE 818

Two-waytraveltime

(s)

1.00

Site 818Seismic

sequence

1.10

1.20

1.30

1.40

Seafloor

Thickness(m)

65

30

130

60

55

Lithologic units(mbsf)

Unit I

Unit II

IA

65.4

IB

103.4

IC

198.4

ID

293.4

30P.9

Figure 22. Correlation chart of seismic sequences (as in Fig. 21) with lithostratigraphy for Site 818.

449