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

14. SITE 8211

Shipboard Scientific Party2

HOLE 821A

Date occupied: 15 September 1990

Date departed: 16 September 1990

Time on hole: 1 day, 13 hr, 40 min

Position: 16°38.793'S, 146°17.376'E

Bottom felt (rig floor; m, drill-pipe measurement): 224.1

Distance between rig floor and sea level (m): 11.35

Water depth (drill-pipe measurement from sea level, m): 212.7

Total depth (rig floor; m): 624.1

Penetration (m): 400.0

Number of cores (including cores with no recovery): 43

Total length of cored section (m): 400.0Total core recovered (m): 382.9

Core recovery (%): 95.7

Oldest sediment recovered:Depth (mbsf): 400.0Nature: lithified silty to sandy calcareous clayey mixed sedimentAge: Pleistocene

HOLE 821B

Date occupied: 16 September 1990

Date departed: 17 September 1990

Time on hole: 13 hr

Position: 16°38.794'S, 146°17.366'E

Bottom felt (rig floor; m, drill-pipe measurement): 222.7

Distance between rig floor and sea level (m): 11.35

Water depth (drill-pipe measurement from sea level, m): 211.6

Total depth (rig floor; m): 388.9

Penetration (m): 165.9

Number of cores (including cores with no recovery): 20

Total length of cored section (m): 165.9

Total core recovered (m): 167.4

Core recovery (%): 100.9

Oldest sediment recovered:Depth (mbsf): 165.9Nature: bioclastic wackestoneAge: Pleistocene

Principal results: Site 821 is located in 212 m of water in Grafton Passage,on the continental slope to the east of Cairns. This site is the proximaland shallowest end-member of a shelf-edge transect aimed at defining•the relationships among changes in sea level, sediment Sequences,and seismic geometries and, in particular, the response of a slope

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.

sequence to rapid global changes in sea level. Hole 821A was coredwith the advanced piston corer (APC) to 145.9 mbsf and the extend-ed-core barrel (XCB) corer to 400 mbsf and had a final averagerecovery of 95%; Hole 821B was cored with the APC to 165.9 mbsf,with 100% recovery. As at Sites 819 and 820, the section to 400 mbsfat Site 821 is an expanded Pleistocene section. Nannofossils indicatean age of 1.27-1.48 Ma for the bottom of the hole. Preservation ofplanktonic foraminifers and nannofossils varies from near pristine inclayey intervals to overgrown in sandy intervals. Benthic foramini-fers indicate a depth range of neritic to upper bathyal for thesequence at Site 821. The pattern of variation in sedimentation ratesat Site 821 is similar to that at Site 820. Middle Pleistocene rates of28.2 cm/k.y. are succeeded by 12.2 cm/k.y. between 0.930 and 0.465Ma, 49.2 cm/k.y. in the succeeding 190 k.y., and 10.2 cm/k.y. from0.275 Ma to the present. However, in comparison to Site 820, thelocus of increased sedimentation had shifted to Site 821 by the latePleistocene, coincident with the aggradation phase of sedimentation.

Drilling at Site 821 has led to the identification of five litho-stratigraphic units. Units I and II are aggradational while Units IIIto V are thought to be progradational.

1. Unit I: depth, 0-145.5 mbsf; age, <0.93 Ma, Holocene tolate Pleistocene. Principal sediment types include mixed sedi-ments of siliceous and bioclastic components, calcareous silts andclays, bioclastic and nannofossil oozes and chalks, bioclasticpackstones, and Halimeda rudstones. With the exception of theuppermost part, the unit is thought to represent a series of rapidlydeposited aggradational packages. It is divided into seven sub-units.

SubunitIA: Depth, 0-16.5 mbsf; age, <0.275 Ma, Holocene tolate Pleistocene. An upward-fining sequence that is a fine to coarsesandy bioclastic/siliciclastic mixed sediment containing largebenthic foraminifers, coralline algae, and bryozoans at the baseand grades upward into clays with bioclasts and nannofossils.

Subunit IB: depth, 16.5-40.3 mbsf; age, <0.465 Ma, latePleistocene. Two facies make up the subunit in ascending order:(1) silt to fine sand mixed sediment with bioclasts and molluscan/bryozoan fragments; sometimes the facies is a coarse sandybioclastic/siliciclastic mixed sediment with large benthic foramin-ifers, Halimeda, coralline algae, and pectinids and other mollusks;and (2) calcareous clayey and silty mixed sediment with somebioclasts.

Subunit IC: depth, 40.3-66.5 mbsf; age, 0.275-0.465 Ma, latePleistocene. An upward-fining sequence composed of clay or siltyfine to medium bioclastic and siliciclastic sands grading upward intoa homogeneous silty bioclastic or nannofossil clay.

Subunit ID: depth, 66.5-88.7 mbsf; age, 0.275-0.465 Ma, latePleistocene. A rhythmic alternation of calcareous silty clays andclayey silts above and below a lithified and dolomitized mixedsediment unit.

Subunit IE: depth, 88.7-99.2 mbsf; age, 0.275-0.465 Ma, latePleistocene. Dolomitized calcareous fine to medium bioclasticsand.

Subunit IF: depth, 99.2-132.1 mbsf; age, 0.275-0.93 Ma, latePleistocene. The basis of the subunit is a poorly sorted fine tocoarse bioclastic sand and bioclastic-nannofossil ooze or chalk.The sequence is repeated three times.

Subunit IG: depth, 132.1-145.5 mbsf; age, 0.475-0.93 Ma, latePleistocene. This subunit is divided into three parts: (1) a lowerlithified Halimeda rudstone with molluscan and bryozoan frag-ments, large benthic foraminifers, and lithoclasts of packstone andwackestone in a mud matrix; (2) calcareous mudstone containing

569

SITE 821

sand-sized siliciclastic grains; and (3) at the top a medium to finesand-sized bioclastic packstone.

2. Unit II: depth, 145.5-172.0 mbsf; age, 0.465-0.93 Ma, latePleistocene. An upward-fining siliciclastic-dominated packstone atthe base and a glauconitic and siliciclastic lithified mudstone at thetop, perhaps representing a hardground. Sedimentation through-out the unit is low (12 cm/k.y.) compared with the units above andbelow. The unit is divided into two subunits:

Subunit IIA: depth, 145.5-156.3 mbsf; age, 0.465-0.93 Ma, latePleistocene. Partially to well-lithified bioclastic packstones areoverlain by lithified chalk/mudstone containing glauconite anddetrital grains.

Subunit HB: depth, 156.3-172.0 mbsf; age, 0.465-0.93 Ma, latePleistocene. Lithified bioclastic/siliciclastic packstones exhibit up-ward-fining textures and are overlain by a 7-m-thick unit ofbioclastic mudstones.

3. Unit HI: depth, 172.0-215.0 mbsf; age 0.465-1.27 Ma, earlyPleistocene. Dolomitized bioclastic wackestone/chalk and bioclas-tic packstone. Sedimentation rates are relatively high (28.2 cm/k.y.). The unit is composed of two subunits.

Subunit IIIA: depth, 172.0-184.3 mbsf; age, 0.465-0.93 Ma,early Pleistocene. The subunit changes from a lithified dolomitizedbioclastic wackestone at the base through a 3-m-thick dolomitizedbioclastic packstone to a nannofossil-rich chalk at the top.

Subunit MB: depth, 184.3-215.8 mbsf; age, 0.93-1.27 Ma,early Pleistocene. At the base, the subunit is composed of 50 cm ofa coarse-grained dolomitized packstone/mixed sediment, which isoverlain by bioclastic and nannofossil chalky wackestones withoccasional dolomitized packstone/mixed sediment intercalations.

4. Unit IV: depth, 215.8-298.8 mbsf; age, between 0.93 and1.48 Ma, early Pleistocene. Thickly bedded subunits of dolomi-tized chalk and bioclastic packstones and wackestones. The unitwas deposited at a rate of 28 cm/k.y. Four subunits have beenrecognized.

Subunit IVA: depth, 215.8-246.3 mbsf; age, 0.93-1.27 Ma,early Pleistocene. A basal dolomitized micritic to nannofossilchalk containing siliciclastics is overlain by 6 m of dolomitizedbioclastic packstone/wackestone that exhibits an upward-finingtexture over the basal 1.5 m.

Subunit IVB: depth, 246.3-279.0 mbsf; age, 0.93-1.27 Ma,early Pleistocene. A coarse to very coarse bioclastic clay at thebase and dolomitized micritic to nannofossil chalk throughout therest of the subunit.

Subunit IVC: depth, 279.0-298.8 mbsf; age, 1.27-1.48 Ma,early Pleistocene. The base of the subunit is defined by a 30-cm-thick dark glauconitic packstone, which is replaced upward by adolomitized micritic to nannofossil-rich chalk.

5. Unit V: depth, 298.8-400.0 mbsf; age, 1.27-1.48 Ma, earlyPleistocene. Dolomitized bioclastic packstones and chalky mixedsediments interbedded with less calcareous sandy, silty, andclayey mudstones. The unit was deposited at an extremely rapidrate. Five subunits have been recognized.

Subunit VA: depth, 298.8-322.0 mbsf; age, 1.27-1.48 Ma, earlyPleistocene. Chalk with bioclasts and siliciclasts.

Subunit VB: depth, 322.0-350.0 mbsf; age, 1.27-1.48 Ma, earlyPleistocene. Upward-coarsening dolomitized bioclastic packstoneand chalk with siliciclastic mudstones.

Subunit VC: depth, 350.0-360.0 mbsf; age, 1.27-1.48 Ma, earlyPleistocene. Dolomitized calcareous silt to medium-grained sands.

Subunit VD: depth, 360.0-377.0 mbsf; age, 1.27-1.48 Ma, earlyPleistocene. Upward-coarsening dolomitized bioclastic pack-stones and chalks with siliciclastic-rich muds.

Subunit VE: depth, 377.0-400.0 mbsf; age, 1.27-1.48 Ma, earlyPleistocene. Dolomitic calcareous silt to medium sand intercalatedwith a central section of clayey to silty mud.

Interstitial water sampling at Site 821 shows that calcium,magnesium, and potassium decrease with depth to 144.8 mbsf.This occurs mainly because of the precipitation of calcite anddolomite and clay diagenesis, that leads to the formation of illite.An increase in strontium throughout much of the hole is due todissolution of aragonite and high-magnesium calcite combinedwith precipitation of low-magnesium calcite and dolomite; de-creases in strontium in the lower part of the core reflect clay

mineral diagenesis and a lower rate of recrystallization of carbon-ates. Alkalinity increases to 11 mbsf and peaks again at 116.35mbsf, coincident with the removal of sulfate. Chlorinity decreasesare tied to salinity changes effected by the precipitation of carbon-ates and the removal of sulfate.

X-ray diffraction analysis indicates that the sediments at Site821 are composed of aragonite, low-magnesium calcite, high-magnesium calcite, dolomite, quartz, kaolinite, albite, and illite.Variations in carbonate content are due to dilution by terrigenousmaterial and may reflect alternations of sea level. Dolomite occursat —10% between 40 and 398.5 mbsf coincident with the depth ofremoval of high-magnesium calcite. As at Sites 819 and 820, it isproposed that high-magnesium calcite provides the magnesiumsource for dolomitization.

Organic carbon at Site 821 was generally low, varying between0.15% and 0.45%. This is thought to be of mixed terrigenous/marine origin above 120 mbsf and of marine origin below thisdepth. Methane concentrations reached a maximum of 74,000 ppmat 220 mbsf, whereas the Ci/C2 ratio varied with depth andtemperature between 3600 and 800, showing no anomalous trend.There were no safety or pollution problems at this site; total ethaneand propane never exceeded 40 ppm, with ethane greater thanpropane above 310 mbsf. Methane and propane above 250 mbsfare of bacterial origin.

Downhole measurements at Site 821 included runs with theseismic stratigraphy logging tool combination and the formationmicroscanner. The velocity, density, and resistivity are stronglycorrelated because of the dominance of porosity in all three logs.Three log units have been identified. Log Unit 1 occurs from the baseof the pipe (65 mbsf) to 210 mbsf and is considered as equivalent tolithologic Units I, II, and III. The resistivity log suggests upward-fining sequences 4- to 14-m thick caused by increases in theproportions of clay and decreases in carbonate. Log Unit 2 occursbetween 210 and 293 mbsf and equates with lithologic Unit IV.Again, the resistivity log exhibits a saw-toothed pattern that suggestsupward-fining sequences 10-to 20-m thick; however, the gamma-raylog correlates positively with resistivity and velocity, suggesting thatclay-rich intervals are low in porosity, perhaps the result of diagen-esis. Between 261 and 270 mbsf, a comparison of velocity andresistivity indicates substantial cementation, which is borne out bythe lithostratigraphic identification of an increase in dolomitization inthe same interval. Log Unit 3 occurs between 293 and 392 mbsf andis considered to be equivalent to lithologic Unit V. Logs indicate fourcycles of upward-coarsening sequences, as indicated by upward-decreasing clay contents and porosity, as seen in the gamma-ray,resistivity, and velocity logs.

Paleomagnetic results from Site 821 must await shore-basedstudies. A large portion of the sediments from the Pleistocenecored sections were found to carry a remanence with a steeplydipping negative inclination. Many of the cores maintained thisremanence direction after AF demagnetization with peak fields of15 mT, the maximum field allowable on the archive half of thecores. Detailed AF demagnetization in peak fields greater than 15mT, together with thermal treatment, will be required to generatea clear magnetic polarity stratigraphy at this site.

BACKGROUND AND SCIENTIFIC OBJECTIVESSite 821 is one of three sites in close proximity that were

occupied in Grafton Passage. For a summary of the back-ground and overall objectives of these sites the reader isreferred to the "Background and Scientific Objectives" sec-tion of the "Site 819" chapter.

Site 821 is located on the inner portion of an upper slopeterrace (Fig. 2, "Site 819" chapter, this volume) adjacent tothe Great Barrier Reef. Of the three sites occupied in GraftonPassage it is the most proximal to the Great Barrier Reef. Thepre-drilling prognosis for this site is shown in Figure 1.

The objectives at this site were as follows:

1. To determine the age and facies of the most proximalportions of the aggradational and progradational units imme-diately in front of the present Great Barrier Reef.

570

SITE 821

0.1

0.2

0.3

0.4

0.5

0.6

0.7

1.0

1.1

1.2

1.3

1.4

1.5

1.6

Keyreflectors

5 0 0 -

Age

Quaternary

(127)

Plioceneand

Pleistocene

(234)

Pliocene

(336)

latestMiocene

toPliocene

Velocity(km/s)

1.54

1.94

1.94

2.05

Lithology

Interbeddedfine-grained

siliciclastic andcarbonatesediments;

possibly somehardgrounds

Siliciclastic sandand mud with

increasingcarbonate

content towardthe top

Siliciclastic sandand mud; low

carbonatecontent

As above

Paleoenvironment

Upper slope

Outer shelfto

shelf edge

Shelf edgefan delta

As above

Sed.rate

(m/m.y.)

63

54

51

Comments

High-resolutionsea levelsignature

fromsiliciclastic/carbonatecouplets

Initiation ofshallow water

carbonatesedimentation

Figure 1. Pre-drilling prognosis for Site 821.

2. To determine the relationship between sea level anddepositional fades to extract the sea-level signature.

3. To determine the timing and factors controlling theinitiation of reef growth on the central Great Barrier Reef.

4. To understand the factors that control the transitionfrom prograding to aggrading depositional geometries.

In addition to the above, a principal objective that appliesequally to all three sites is to define the processes of upper-slope deposition and their relationship with mid-slope pro-cesses and products seen at Site 822.

OPERATIONS

Transit to Hole 821AThe ship moved 1.0 nmi from Site 820 to Site 821 (proposed

Site NEA-1) in 0.95 hr, in dynamic positioning mode at anaverage speed of 1.05 kt. The same Benthos low-powerbeacon used at Sites 819 and 820 was run on the taut wire at0330L (all times in this section given in local time, or L) 15September. The location of Site 821 is 16°38.793'S,146°17.376'E; the precision depth recorder (PDR) indicatedthat water depth at the site is 212.6 m below sea level (mbsl).The bit was positioned 207.6 mbsl, and the first core shot at0429L, 15 September. Core 133-821A-1H recovered 4.39 m ofsediment, and the mud line was estimated at 212.7 mbsl.Continuous APC cores (Cores 133-821A-1H through -16H)

were recovered from 0.0 to 145.9 mbsf, with 145.9 m coredand 149.4 m recovered (102.4% recovery). Core 133-821A-16H hit a layer of coarse-grained bioclastic material, whichshattered the liner.

Cores 133-821A-17X through -43X were taken from 145.9to 400.0 mbsf, with 254.1 m cored and 233.5 m recovered(91.88% recovery). As hole conditions appeared to be excel-lent, we decided to cancel a hole-conditioning trip in theinterest of time. The go-devil was dropped and the bit waspulled to 85.3 mbsf for logging. Logs were run as follows:

1. The induction/density/sonic/caliper/gamma-ray (DUE/HLDT/SDT/MCDG/NGT) logging tool was run into the holeat 1035L, 16 September, where we found 4.5 m of fill on thebottom of the hole. The tool was back out of the hole at 1241L.

2. Owing to the excellent condition of the hole, the forma-tion microscanner/gamma-ray/temperature (FMS/NGT/TCC)logging tool was run. The tool was sent into the hole at 133OL,16 September, where we found 8.4 m of fill at the bottom ofthe hole. This tool was back out of the hole at 1500L.

Hole 821A was filled with heavy mud; we pulled the bit clearof the seafloor at 1710L, 16 September to begin Hole 821B.

Hole 821BThe ship moved 25 m west to Hole 821B at 16°38.794'S,

146°17.366'E. The mud line was estimated to occur at a water

571

SITE 821

depth of 211.6 mbsl. The bit was positioned at 211.5 mbsl tospud the first core at 1825L, 16 September. Core 133-821B-1Hrecovered 9.83 m of sediment, which indicates that the mudline is at 211.6 mbsl. Continuous APC cores (Cores 133-821B-1H through -14H) were taken from 0 to 140.0 mbsf, with140 m cored and 144.8 m recovered (103.4%). APC coringended at the top of a coarse bioclastic interval, where thevibrapercussive corer (VPC) was picked up for our attempt torecover this interval better.

Cores 133-821B-16V to -18V were taken from 140.0 to146.6 mbsf, with 6.6 m cored and 6.6 m recovered (100.0%recovery, using the advance-by-recovery method). As pre-dicted, material in the VPC cores from this interval were lessdisturbed than XCB cores might have been. However, only inCore 133-821B-17V did we actually recover material. There-fore, we picked up the XCB in the hope of obtaining betterrecovery.

Cores 133-821B-19X through -20X were taken from 146.6to 165.9 mbsf, with 19.3 m cored and 15.9 m recovered (88.0%recovery). Hole 821B was filled with heavy mud, and the bitwas pulled out of the hole, arriving on deck at 0619L, 17September.

Table 1 contains the coring summary for Site 821.

SITE GEOPHYSICSA general description of the design and operation of the

joint site location survey for Sites 819,820, and 821 is includedin the "Site Geophysics" section, "Site 819" chapter (thisvolume).

Site 821Following completion of drilling at Hole 820B and separa-

tion from the beacon at JD 257/1559 UTC on 14 September1990, JOIDES Resolution returned to the confirmed globalpositioning system (GPS) position of Site 821 under dynamicpositioning control. The taut-wire beacon was deployed at thesite at JD 257/1656 UTC, and the final coordinates of Hole821A are 16°38.793'S and 146°17.376'E, with a water depth of212.7 m (drill-pipe measurement from sea level).

Site 821 is the most landward or westerly of the three sites(Sites 819,820, and 821) on the upper slope terrace adjacent tothe Great Barrier Reef, being about 5 km west of Site 819 and2 km west of Site 821 (Figs. 2 and 3). It lies about 6 km east ofthe nearest reef (Euston Reef), and was positioned to examinethe most proximal parts of both the topset facies of theprogradational units, and the aggradational units, that underliethe upper slope (Fig. 4; Symonds and Davies, 1988).

There was reasonable correspondence of the major fea-tures at the site on the JOIDES Resolution single channelseismic profiles and the Rig Seismic multichannel seismicprofiles (Figs. 3 and 4), but the detailed seismic characteristicsof the site were difficult to resolve on the Resolution profileowing to the very compressed nature of the record. Basementis not visible on any of the water-gun data across the site;however, normal resolution Gulf Aquapulse seismic data inthe area (Symonds et al., 1983) indicates that it may lie up to4 s TWT (two-way traveltime) below seafloor. The site isunderlain by parallel to subparallel reflectors and no distinc-tive sequence boundaries are present (Fig. 4); however, whenthe sequence boundaries are traced landward from Site 820,the internal character of reflector packages is maintainedthrough Site 821. The upper, aggradational unit is 0.2 s TWT(-170 m) thick, and as at Site 820 its upper part containshigher amplitude reflectors than its lower part. The irregular,disrupted reflector that occurs within this unit at Site 820 doesnot maintain its character to Site 821. The underlying units tobeyond TD represent the topset facies of various prograda-

TaMe 1. Coring summary, Site 821.

Core no.

Hole 821A

1H2H3H4H5H6H7H8H9H

10HUH12H13H14H15H16H17X18X19X20X21X22X23X24X25X26X27X28X29X30X31X32X33X34X35X36X37X38X39X40X41X42X43X

Hole 821B

1H2H3H4H5H6H7H8H9H

10HUH12H13H14H15H16V17V18V19X20X

Date(Sept. 1990)

14141414141414141414141414141414151515151515151515151515151515151515151515151515151515

1616161616161616161616161616161616161616

Time(UTC)

1830184018501920194020052025204021052120214021552210223522552315000500200040010501200140022002450315035004200445052005450650075509001010115513251425152017101825200021252210

08300845090009200945101010351100112511501210124013001320134015051605171017351755

Depth(mbsf)

0-4.44.4-13.9

13.9-23.423.4-32.932.9-42.442.4-51.951.9-61.461.4-70.970.9-80.480.4-89.989.9-99.499.4-108.9

108.9-118.4118.4-127.9127.9-137.4137.4-145.9145.9-155.6155.6-165.2165.2-174.9174.9-184.6184.6-193.9193.9-203.5203.5-212.8212.8-222.5222.5-232.2232.2-241.8241.8-251.4251.4-261.1261.1-270.8270.8-280.4280.4-290.1290.1-299.7299.7-309.4309.4-319.0319.0-328.7328.7-338.3338.3-347.9347.9-357.5357.5-367.2367.2-376.8376.8-386.4386.4-3%. 1396.1-400.0

Coring totals

0-9.59.5-19.0

19.0-28.528.5-38.038.0-47.547.5-57.057.0-66.566.5-76.076.0-85.585.5-95.095.0-104.5

104.5-114.0114.0-123.5123.5-133.0133.0-140.0140.0-140.0140.0-146.6146.6-146.6146.6-156.2156.2-165.9

Coring totals

Lengthcored(m)

4.49.59.59.59.59.59.59.59.59.59.59.59.59.59.58.59.79.69.79.79.39.69.39.79.79.69.69.79.79.69.79.69.79.69.79.69.69.69.79.69.69.73.9

400.0

9.59.59.59.59.59.59.59.59.59.59.59.59.59.57.00.06.60.09.69.7

165.9

Lengthrecovered

(m)

4.399.519.449.91

10.099.569.919.979.999.929.979.949.639.959.557.629.728.828.878.599.559.407.949.779.849.899.789.858.99

10.027.540.329.818.996.879.819.298.699.858.248.78

10.104.24

382.91

9.839.999.629.659.779.869.639.749.797.719.849.949.779.959.760.016.600.006.819.14

167.41

Recovery(%)

99.8100.099.3

104.0106.2100.0104.0105.0105.0104.0105.0104.0101.0105.0100.089.6

100.091.991.488.5

102.097.985.4

101.0101.0103.0102.0101.092.7

104.477.73.3

101.093.670.8

102.096.890.5

101.085.891.4

104.1109.0

95.7

103.0105.0101.0101.0103.0104.0101.0102.0103.081.1

103.0104.0103.0105.0139.0100.0100.0

0.070.994.2

100.9

Note: Times are Universal Time Coordinated or UTC, which is 10 hr differentfrom local time or L.

572

SITE 821

16°00'S

16°30'

17°00'

1 i^Ty

146°00'E 146°30'

Figure 2. Track chart showing the distribution of regional seismic data in the area around Sites 819, 820, and 821; also shown are locations ofSites 822 and 823; simplified bathymetry in meters.

tional units. The foreset facies of these units generally lie tothe east of Site 820. The topsets related to the upper, gentlysigmoidal unit are about 0.06 s TWT (~60 m) thick, andconsist of both high and low amplitude reflectors. The topsetsrelated to the lower, complex sigmoid-oblique progradationalunits are at least 0.14 s TWT (~ 160 m) thick and appear to becomposed of very low amplitude reflectors. These units ex-tend to just beyond TD at Site 821 and lie largely within thefirst water-bottom multiple at the site (Fig. 4).

To provide some predictive capability during the drilling atSite 821, an estimate of the two-way traveltime (TWT)/deρthrelationship below the seafloor was made using stackingderived interval velocities from the BMR seismic lines acrossthe site. In Figure 5, this relationship is compared withsimilarly derived TWT/depth curves for the adjacent Sites 819and 820.

LITHOSTRATIGRAPHY

Site 821 is located in 212 m of water depth in GraftonPassage; the most landward site in a transect of three sites(Sites 819, 820, and 821) on the upper slope east of the presentday Great Barrier Reef. APC drilling of Hole 821A recovereda complete section to 145.9 mbsf; a change to XCB and furtherdrilling to 400 m recovered an almost complete section, withthe exception of the interval between 290.1 and 299.7 mbsf,where only 3.3% was recovered. Hole 82IB was drilled byAPC to 140.0 mbsf, VPC from 140.0 to 146.6 mbsf, andfinished with XCB down to the total depth of 165.9 mbsf.Recovery in this hole was almost complete.

The lithostratigraphy of Site 821 is divided into five units(Fig. 6) based on sharp lithologic changes, usually associatedwith distinct rather thin, fining-upward, coarse siliciclastic

573

SITE 821

End Line 6JD/252/1446UTC(9 Sept. 1990)

16°35'S

16°36'Beacon deployedJD 254/2241 UTC(11 Sept. 1990)

JOIDESResolutionLine 6

16°38'

Beacon deployedJD 257/1656 UTC(14 Sept. 1990)

16°40'

16°42'

Beacon deployedJD 252/1524 UTC(9 Sept. 1990)

16°43'146°12'E 146°14' 146°16' 146°18' 146°20' 146°22'

Figure 3. JOIDES Resolution Leg 133 site location tracks (dotted line) and Rig Seismic 1987 site survey tracks (solid line) around Sites 819, 820,and 821.

beds above the unit boundary. The upper half of Unit Iconsists of fining-upward cycles, each of which is composedof (1) greenish gray calcareous sand; (2) greenish gray calcar-eous silt; and (3) light greenish gray calcareous clay. Thelower half of Unit I is composed of alternations of calcareoussilt and clay, which tend to become chalky with a greenishgray color downward. This lower part also contains interca-lated beds of calcareous silty sand or wackestone. Unit II iscomposed of two sets of dark gray, bioclastic calcareousmudstone or chalk overlying a partially to well lithified, grayto light gray, bioclastic packstone. Unit III is represented bygreenish gray, dolomitized, bioclastic wackestone, chalkywackestone and chalk, with interbeds of lightly greenish graybioclastic packstone. Unit IV consists of considerably dolo-mitized greenish gray chalk intercalated with varying thick-nesses of light greenish gray bioclastic packstone-wacke-stones. Unit V is characterized by coarsening-upward cyclescomposed predominantly of greenish-gray clay and clayey tosandy calcareous mixed-sediment, with subordinate amountsof calcareous sandstone and calcareous mudstone. Scattered

foraminifer tests and molluscan shell fragments occurthroughout the unit.

Lithologic Units

Unü I (Sections 133-821A-1H-1 through -16H-4; depth, 0-145.5mbsf; age, Holocene to late Pleistocene [<0.93 Ma])

This unit consists of three fining-upward cycles in theupper half, and rhythmic alternations of calcareous clay, siltbeds, and calcareous silty sand or wackestone in the lowerhalf. A shallow water-derived Halimeda rudstone defines thebasal part of the unit.

Subunit IA (Sections 133-821A-1H-1 through -2H-5; depth,0-16.5 mbsf. age, Holocene to late Pleistocene [<0.275 Ma])

Subunit IA forms an upward-fining set composed of (1)sand-sized bioclastic-siliciclastic sediment with large benthicforaminifers, coralline algae, bryozoans, etc.; (2) homoge-neous clayey-silt to clay mixed sediment with bioclasts andnannofossils; and (3) clay with bioclasts and nannofossils.

574

NE

JOIDES ResolutionLine 6

B

SW SW

BMR Rig SeismicLine 75/043 Part T

SITE 821

NEO.O-i

S 0.5-

1.0J

mm2 km 2 km

Figure 4. Comparison of JOIDES Resolution and Rig Seismic 80-in.3 water gun seismic profiles across Site 821. A. JOIDES Resolution. B. Rig Seismic.

Subunit IB (Sections 133-821A-2H-5 through -5H-5; depth,16.5-40.3 mbsf; age, late Pleistocene [<0.465 Ma])

Subunit IB forms two upward-fining sets composed of (1)homogeneous silt- to sand-sized mixed sediment with bioclastsand mollusks and/or bryozoan fragments; (2) sandy bioclasticand siliciclastic mixed sediment with large benthic foraminifers,Halimeda interaodes, coralline algae, pectinids and other mol-lusks; and (3) calcareous clay and silt, and mixed sediment.

Subunit IC (Sections 133-821A-5H-5 through -8H-3; depth,40.3-66.5 mbsf; age, late Pleistocene [between 0.275 and0.465 Ma])

Subunit IC also consists of two upward-fining cycles com-posed of (1) sandy silt to fine- to medium-sand with bioclastsand minor siliciclastic material; (2) clayey silt with bioclasts;and (3) homogeneous silty-clay to clay or clayey-silt withbioclasts and nannofossils.

575

SITE 821

I" 300

350

400

450

500

\ ' \ i • r

O Site 819 log• Sites 820-821 seismicπ Site 819 seismic

0.1 0.2 0.3 0.4

Two-way traveltime (s)

0.5 0.6

Figure 5. Comparison of TWT/depth curve estimated for Site 821 withthose for Sites 819 and 820.

Subunit ID (Sections 133-821A-8H-3 through -10H-7; depth,66.5-88.7 mbsf; age, late Pleistocene [between 0.275 and0.465 Ma])

This subunit exhibits a rhythmic alternation of calcareoussilty clay and clayey silt and, in part, lithified and dolomitizedsandy layers of mixed sediment.

Subunit IE (Sections 133-821A-10H-7 through -11H-6; depth,88.7-99.2 mbsf; age, late Pleistocene [between 0.275 and0.465 Ma])

An upward-coarsening dolomitized calcareous bioclasticsand that contains a silty mud bed in the middle of thesubunit.

Subunit IF (Sections 133-821A-11H-6 through -15H-3; depth,99.2-132.1 mbsf; age, late Pleistocene [between 0.275 and0.93 Ma])

Subunit IF is composed of three repeated cycles of inter-bedded, poorly sorted, firm, bioclastic sand or wackestone,and bioclastic-nannofossil ooze or chalk.

Subunit IG (ections 133-821A-15H-3 through -16H-4; depth,132.1-145.5 mbsf; age, late Pleistocene [between 0.465 and0.93 Ma])

The lowermost subunit within Unit I is characterized byupward-fining sediments consisting of (1) partially lithified,Halimeda rudstone, with minor molluscan and bryozoanfragments, large benthic foraminifer tests, and lithoclasts ofpackstone or other sediment types in a mud matrix; (2)calcareous mudstone with sand-sized siliciclastic detritus; and(3) medium to fine sand-sized bioclastic packstones.

Unü II (Sections 133-821A-16H-4 through -19X-5; depth,145.5-172.0 mbsf; age, late Pleistocene [between 0.465 and0.93 Ma])

Two suites of partially to completely lithified bioclasticpackstone are overlain by a bioclastic to calcareous mudstoneor chalk.

Subunit IIA (Sections 133-821A-16H-4 through -17X-CC;depth, 145.5-156.3 mbsf; age, late Pleistocene [between 0.465and 0.93 Ma])

Partially to well-lithified bioclastic packstone is overlain bya 1.5-m-thick bed of firm to partially lithified chalk to calcar-eous mudstone. The uppermost part contains glauconite asdetrital grains as well as infilling foraminifer chambers andmay represent a submarine erosional or nondepositional hard-ground.

Subunit HB (Sections 133-821A-18X-1 through -19X-5; depth,156.3-172.0 mbsf; age, late Pleistocene [between 0.465 and0.93 Ma])

A 7-m-thick bioclastic mudstone bed is underlain by par-tially to entirely lithified bioclastic packstone. The basal 2-mof bioclastic packstone contains abundant siliciclastic detritusand exhibits upward-fining structure.

Unü III (Sections 133-821A-19X-5 through -24X-2; depth,172.0-215.0 mbsf; age, early Pleistocene [between 0.465 and1.27 Ma])

This unit consists of partially dolomitized bioclastic wacke-stone, chalky wackestone, and chalk, with interbedded dolo-mitized bioclastic packstone layers.

Subunit IIIA (Sections 133-821A-19X-5 through -20X-6;depth, 172.0-184.3 mbsf; age, early Pleistocene [between0.465 and 0.93 Ma])

Subunit IIIA is a lithified, dolomitized, bioclastic wacke-stone to chalk in the middle of which is a 3-m-thick, dolomi-tized, bioclastic packstone bed.

Subunit IIIB (Sections 133-821A-21X-1 through -24X-2; depth,184.3-215.8 mbsf; age, early Pleistocene [between 0.93 and1.27 Ma])

Subunit IIIB, a lithified, dolomitized, bioclastic wacke-stone to nannofossil-rich, chalky wackestone, has scatteredintercalations of dolomitized bioclastic packstone or mixedsediment layers. The lowermost 50-cm-thick bed is a coarse-grained mixed sediment.

Unü IV (Sections 133-821A-24X-2 through -32X-CC; depth,215.8-298.8 mbsf; age, early Pleistocene [between 0.93 and1.48 Ma])

This unit comprises extensively dolomitized chalk inter-bedded with bioclastic packstone-wackestone beds of variousthickness.

Subunit IVA (Sections 133-821A-24X-2 through -27X-4;depth, 215.8-246.3 mbsf; age, early Pleistocene [between 0.93and 1.27 Ma])

In Subunit IVA, dolomitized micritic to nannofossil-richchalk with bioclastic and siliciclastic detritus is overlain by a6-m-thick bed composed of dolomitized bioclastic packstoneto wackestone. An upward-fining structure was observed in a1.5-m-thick wackestone layer at the base.

Subunit IVB (Sections 133-821A-27X-4 through -30X-6;depth, 246.3-279.0 mbsf; age, early Pleistocene [between 0.93and 1.27 Ma])

576

SITE 821

160—

180-

200-

240-

320-

Hole821A

Age(Ma)

0.465

0.93

1.27

Unit

IV

Major lithological characteristics

Upward-fining cycles of greenish gray sand;greenish-gray silt-light greenish clay form theupper half of the unit; sand becomes coarseand terrigenous-rich and contains reef-relatedbenthic fossils in the upper two subunits.Alternation of calcareous silt and clay, whichtends to become chalky with a greenish-graycolor downward; beds are silty sand or arewackestone intercalated. The bottommostsubunit also shows an upward-fining set fromrudstone to packstone.

Two sets of a bioclastic calcareous mudstone orchalk overlying a partially to well- lithifiedbioclastic packstone.

Dolomitized bioclastic wackestone-chalk,interbedded with dolomitized bioclasticpackstone.

Extensively dolomitized chalk intercalatedwith bioclastic packstone-wackestone ofvarious thickness.

Upward-coarsening cycles composed of dolo-mitized greenish gray calcareous sandstoneand calcareous mudstone of mixed sediment,containing scattered foraminifer tests andmollusk shell fragments throughout the unit.

Figure 6. Summary chart showing the lithostratigraphy and lithologic characteristics for each unitat Site 821. Age assignment is provided by nannofossil biostratigraphy (See "Biostratigraphy"section, this chapter).

In addition to dolomitized micritic to nannofossil-richchalk, this subunit also contains an upward-coarsening, lesslithified clayey layer with coarse- to very coarse-grainedbioclasts.

Subunit IVC (Sections 133-821A-30X-6 through -32X-CC;depth, 279.0-298.8 mbsf; age, early Pleistocene [between 1.27and 1.48 Ma])

Subunit IVC is a dolomitized micritic to bioclastic chalkwith a 5-cm-interval of planar lamination close to the top. A

30-cm-thick, dark greenish-gray, glauconitic(?) packstone oc-curs at the top.

Unit V (Sections 133-821A-33X-1 through -43X-CC; depth,298.8-400.0 mbsf; age, early Pleistocene [between 1.27 and 1.48Ma])

Unit V is distinctly different in lithologic characteristics fromthe four units above. It is characterized by upward-coarsening,dolomitized, greenish-gray, calcareous mixed sediment, inter-bedded with less calcareous mudstone and silts and sands.

577

SITE 821

Wispy lamination occurs in the middle two silty subunits.Foraminifer tests and mollusk shell fragments are scatteredthroughout the unit.

Subunit VA (Sections 133-821A-33X-1 through -35X-5; depth,298.0-322.0 mbsf; age, early Pleistocene [between 1.27 and1.48 Ma])

Subunit IA consists of upward-coarsening, dark greenish-gray chalk with bioclasts and abundant siliciclastic material.

Subunit VB (Sections 133-821A-35X-CC through -37X-CC;depth, 322.0-350.0 mbsf; age, early Pleistocene [between 1.27and 1.48 Ma])

Upward-coarsening, greenish-gray dolomitized, bioclasticpackstone to chalk with siliciclastic mud comprises Subunit VB.

Subunit VC (Sections 133-821A-38X-1 through -39X-2; depth,350.0-360.0 mbsf; age, early Pleistocene [between 1.27 and1.48 Ma])

This subunit is composed of greenish-gray, dolomitic,calcareous silt to medium-grained mixed sediment: wispylaminations occur at 348.8 mbsf.

Subunit VD (Sections 133-821A-39X-2 through -41X-6; depth,360.0-377.0 mbsf; age, early Pleistocene [between 1.27 and1.48 Ma])

Upward-coarsening, dolomitized, bioclastic packstone tochalk with abundant siliciclastic mud dominates this subunit.Wispy lamination occurs at 368.0 mbsf.

Subunit VE (Sections 133-821A-41X-6 through -43X-CC;depth, 377.0-400.0 mbsf; age, early Pleistocene [between1.27 and 1.48 Ma])

Dolomitic calcareous silt to medium-grained mixed sedi-ment is intercalated with clay and silty mud in the middle ofthe subunit.

Interpretation

Examination of the site-survey seismic data indicates thatUnit V, dominated by upward-coarsening cycles, correspondsto a sequence with progradative geometry (see "Site Geo-physics" section; this chapter). Units I and II correspond to asequence with aggradative geometry. The boundary betweenUnits II and III appears to correspond to the seismic reflectordefining the transition from progradational to aggradationalseismic geometries.

There is a remarkable degree of correlation between thelithologic units shown in Figure 6 and the variations in calciumcarbonate content shown in Figure 7. The mixed lithologiccharacter of Unit V, the generally consistent carbonate facieswithin Units III and IV, and the cyclical variations within UnitsI and II are also seen in the carbonate variations. If the variationsin %carbonate reflect alternations between siliciclastic-rich, ter-restrial-derived and carbonate-rich, marine-derived skeletal sed-iments, then the facies variations may accurately reflect sea-level fluctuations due to glacio-eustatic control.

The Halimeda-dominaieá sediments in Subunit IG (Fig. 8)suggest a tropical environment, while the shape of the carbon-ate curve would indicate deposition during a transgression,which may have occurred before 0.465 Ma. Further system-atic analysis of both the reef-related and inter-reef benthicorganisms among the allochthonous bioclasts or autochtho-nous build-up in these units will provide more relevant paleo-climatic and Paleobathymetric information.

40040 60

Carbonate (%)

100

Figure 7. Graph showing trends in the vertical variation of percentage ofCaCO3 in Hole 821A. Original data are "smoothed" by a five-pointweighted moving average (see "Inorganic Geochemistry" this chapter).

The lithological evidence suggests a hiatus or disconfor-mity between Units I and II. It might explain the apparentdecrease of the sedimentation rate in this part of thesequence (see "Sedimentation Rates" section, this chapter).

BIOSTRATIGRAPHYThe abundance and preservation of calcareous microfossils

varies with the lithological facies at Hole 821 A. Fine-grainedmuds contain abundant, well-preserved specimens, whereas thesandy intervals are characterized by sparse, poorly preservedspecimens. The upper part of the section (Cores 133-821A-1Hthrough -10H) contains abundant, well-preserved planktonic andbenthic foraminifers, whereas the lower part of the hole (Cores133-821A-11H through -43H) generally yield sparse, poorlypreserved specimens, but with several exceptions (Samples133-821 A-17H-CC, -28H-CC, -34H-CC, -38H-CC, and -43H-CC). Although some of the poorly preserved faunas contain fewdepth-indicative benthic foraminifers, preliminary analysis sug-gests that the faunas at Hole 821A vary from neritic (<200 m) toupper bathyal (200-600 m).

The biostratigraphy of Site 821 is summarized in Figure 9.Planktonic foraminifers and nannofossils indicate a Pleistocenesection for all of Hole 821 A. Nannofossils indicate that thebottom of Hole 821A has an age between 1.27 and 1.48 Ma.

578

SITE 821

cm5

1 0 -

15

20 - I

> r•

r~'

rFigure 8. Photograph of the interval between 5 and 20 cm in Section133-821A-16H-4, showing partially lithified Halimeda rudstone com-posed of an abundance of Halimeda internodes in association withskeletal fragments of mollusk shells, large benthic foraminifers, and avariety of encrusting organisms (bryozoans, serpulids, etc.), in addi-tion to lithoclasts of bioclastic packstone and other sediment types. Asmall "rhodolith" in the middle of the photograph may be composedof bryozoa and nonarticulated coralline algae.

Calcareous Nannofossils

Site 821 is the shallowest of the three sites on a slopetransect to the east of the Great Barrier Reef. Site 821, like theother two sites of the transect (819 and 820), yielded anexpanded section of Pleistocene sediments. The bottom of thehole has an age between 1.27 and 1.48 Ma. The sedimentsconsist of highly calcareous mud with varying amounts ofcalcareous sand. Nannofossils are generally abundant andpreservation varies from near pristine in clayey intervals toseverely overgrown in sandy intervals. Only core-catcher

CDQ

u-

2 0 --

4 0 -

6 0 -

8 0 -

100-

120-

-140-

-

160-—

180--

200-_

220-_

240-_

260-

280-

300-

320-

340 -—

360-—

380 -

Hole821A

ore

ü1H2H

3H

4H5H

6H

7H

8H

9H

10H11H

12H13H

14H

15H16H

17X18X

19X20X21X

22X23X

24X25X26X

27X28X

29X30X

31X

32X33X

34X35X

36X37X38X

39X40X

41X42X

>OëDC

•1•1••1I1•j•

i•jij•I1

Age

I1CDK

Nannofossilzone/

subzone

CN15

CN14b

CN14a

(?)

CN13b

Planktonicforaminifer

zone

COCM

ZCMCM

z

Figure 9. Summary of planktonic microfossil data from Hole 821 A.

samples were examined, and from them the following biostra-tigraphy is constructed.

Emiliania huxleyi occurs in the core-catcher samples ofCores 133-821A-1H through -4H and these four cores areassigned to nannofossil Zone CN15, with an age <0.275 Ma.The highest occurrence of Pseudoemiliania lacunosa is inSample 133-821A-14H-CC, and the interval between this andthe previous biohorizon is assigned to Subzone CN14b, withan age range of 0.275-0.465 Ma. The next lower subzone,CN14a, extends to Sample 133-821A-20X-CC, which marksthe upper limit of dominant small Gephyrocapsa with aconcomitant virtual absence of large species of this genus. Theinterval has an age of 0.465-0.93 Ma and is assigned to

579

SITE 821

Subzone CN14a. The next lower, and oldest biohorizonpenetrated, is the highest occurrence of Helicosphaera sellii inSample 133-821A-30X-CC, which has an age of 1.27 Ma andthe interval between the last two biohorizons also is assignedto Zone CN13b. The next lower biohorizon, the highestoccurrence of Calcidiscus tropicus (1.48 Ma) was not pene-trated, thus the cored section below Sample 133-821A-30X-CC has an age from 1.27 to 1.48 Ma.

Planktonic ForaminifersMost core-catcher samples of Hole 821A were examined

for planktonic foraminifers. The upper part of the section(Cores 133-821A-1H through -10H) contains abundant, wellpreserved foraminifers, whereas the lower part of the hole(133-821A-11H through -43H) generally yielded sparse, poor-ly-preserved specimens, except for some samples (133-821A-17H-CC, -28H-CC, -34H-CC, -38H-CC, and 43H-CC).

The presence of Bolliella adamsi in Sample 133-821A-4H-CC, Globigerina rubescens pink in Samples 133-821A-1H-CCthrough -4H-CC, Globigerinoides ruber pink in Sample 133-821A-4H-CC, and Globigerinella calida calida in Samples133-821A-4H-CC and -8H-CC, indicates that the upper part ofthe hole can be referred to the upper Pleistocene. The lowerpart of the hole contains sparse Globorotalia truncatulinoidesspecimens, which indicates that Zone N22-N23 occursthroughout the hole. As at the other sites on this margin, Sites819 and 820, the abundance of foraminifers seems to vary withthe lithological facies. The fine grained muds contain abun-dant, well preserved specimens whereas sandy intervals arecharacterized by sparse, poorly preserved specimens.

Benthic ForaminifersSamples 133-821A-1H-CC through -10H-CC contain abun-

dant, well-preserved benthic foraminifers. Below this, core-catcher samples generally yield benthic foraminifers withmoderate to poor preservation. However, Samples 133-821A-34X-CC, -38X-CC, and -43X-CC contain abundant, well-preserved benthic foraminifers. Although some of the poorlypreserved faunas contain few depth-indicative benthic fora-minifers, preliminary analysis suggests that the faunas at Hole821A fluctuate between neritic (<200 m) and upper bathyal(200-600 m).

Samples 133-821A-2H-CC, -5H-CC, -8H-CC, 20H-CC,-23H-CC, -34X-CC, -38X-CC, and -43X-CC contain the upperbathyal depth indicators Bulimina marginata, Bulimina mex-icana, Cibicidoides cicatricosus, C. dutemplei, C. mundulus,C. pachyderma, C. subhaidingerii, Hanzawaia mantaensis,Hoeglundina elegans, Hyalinea balthica, Sigmoilopsisschlumbergeri, Sphaeroidina bulloides, and U. proboscidea(van Morkhoven et al., 1986). Most of these samples includeat least a small component of transported specimens, such asAmphistegina spp., Discorbis spp., and Planorbulina spp.

Core-catcher samples examined from Cores 133-821A-10Hthrough -17H lack species found exclusively deeper than 200m, yet they contain faunas that can be found deeper than 100m, including the species B. marginata, C. dutemplei, C.pachyderma, C. subhaidingerii, Hoeglundina elegans, Hya-linea balthica, and Sphaeroidina bulloides (van Morkhoven etal., 1986), indicating an outer neritic paleodepth (100-200 m)for this interval. Samples 133-821A-26X-CC and -30X-CClack both upper bathyal and outer neritic markers, and pres-ervation is poor; these samples were tentatively assigned tothe neritic zone.

PALEOMAGNETISMOf the two holes (821A and 821B) drilled at this site,

continuous paleomagnetic measurements were conducted

only at Hole 821A. Cores 133-821A-1H through -16H werecollected using the APC system, whereas Cores 133-821A-17X through -43X were obtained with the XCB system. Allarchive halves of cores from Hole 821A were measured at10-cm intervals with the shipboard pass-through cryogenicmagnetometer both before and after AF demagnetization at 15mT. Whole-core magnetic susceptibilities also were measuredat 10-cm intervals in all core sections using the shipboardBartington pass-through susceptibility meter.

Paleomagnetic data obtained from the sediments in theupper 120 m of the cored section are of acceptable qualityalthough perhaps not completely free of magnetic overprint-ing, and may be used for a preliminary polarity assignment(Fig. 10). However, below 120 m, inclinations are scattered,rendering the data unreliable and uninterpretable. We at-tribute this behavior to drilling disturbances. As a typicalexample of this, in Figure 11 one can see the variations ofmagnetic declination, inclination, and intensity after 15-mTAF demagnetization.

As noted above, inclination data in the upper 120 m of Hole821A are fairly consistent and undisturbed. Inclination excur-sions, such as those observed around the 45-, 55-, 75-, and95-mbsf level probably result from drilling deformation andgas expansion near the tops of these cores. When we ignoredthese variations, inclinations indicated normal polarity wasusually about 30°. These values are in good agreement withthe geocentric axial dipole inclination for Site 821 of 30.9°,implying that demagnetization at 15 mT was fairly effective forisolating a stable remanent magnetization component. As innearby Sites 819 and 820, the origin of this remanence is stilluncertain, owing to the strong geochemical regimes thought tohave affected these sediments.

Available nannofossil data suggest that the upper 130 m orso of the sediments in Hole 821A have an age 0.465 Ma.

CDQ

20 "

40 -

60 "

80

100 -

120

'—1

1

i

. — .

-ere

-

si

—.-»

I' 1

31

r

—

-

> .

-60 0 60Inclination(degrees)

1 102

Intensity(mA/m)

Figure 10. Downhole variation of magnetic inclination (after AFdemagnetization at 15 mT) for the upper 120 m of Hole 821 A.

580

SITE 821

f

150

160

170

180

190

2000 180 360 -60 0 60 10"2 1 102 104

Declination Inclination Intensity(degrees) (degrees) (mA/m)

Figure 11. Example of scattered directional results from XCB cores inHole 821A, 150-200 mbsf interval.

Normal polarity measured to —120 mbsf is consistent withaccumulation during the Brunhes normal chron. We areuncertain if this is a primary or secondary remanence. Thisnormal polarity zone contains at least one short reversedinterval at 35-39 mbsf, which may represent a field excursion.Shore-based analysis of 484 undisturbed, oriented discretesamples should help to locate the Brunhes/Matuyama bound-ary and possibly the Jaramillo subchron, if preserved.

Downhole variation of magnetic susceptibility for the up-per 120 mbsf of Hole 821A is shown in Figure 12. Aspreviously observed for Site 820, various large and smallpeaks seen in the susceptibility data exhibit a strong correla-tion with the NRM and AF 15 mT intensity. The largesusceptibility peaks seen at -10, 35, 65, and -90 mbsfcorrelate well with peaks in the intensity data (Fig. 10). Thesusceptibility peaks, as at Sites 819 and 820, likely representperiods of lower relative sea level and greater input ofterrigenous magnetic minerals.

INORGANIC GEOCHEMISTRY

Interstitial WatersInterstitial fluids were taken from the first 10 cores of Hole

821A and from Cores 133-821A-13H, -17X, -20X, -23X, -26X,-29X, -33X, -35X, -38X, and -41X. Samples from Hole 821Awere analyzed according to the procedures outlined in the"Explanatory Notes" (this volume). These data are listed inTable 2 and Figures 13 and 14.

Calcium, Magnesium, Potassium, and Strontium

The concentration of Ca2+ decreases below surface seawa-ter values (10.36 mM) to a minimum of 2.32 mM at 144.8 mbsf(Fig. 13). Magnesium also decreases in concentration from

Q-α>Q

100 -

12020 40 60

Volume magnetic susceptibility K (10 ~6 cgs)

80

Figure 12. Downhole variation of magnetic susceptibility for the upper120 mbsf of Hole 821A.

54.65 mM at 2.95 mbsf to 5.08 mM at 144.8 mbsf. Whennormalized to Cl", a net loss of 7 mM of Ca2+ and 50 mM ofMg2+ occurs (Fig. 14). This loss of Mg2+ and Ca2+ is mainlythe result of precipitation of authigenic calcite and dolomite.During the alteration of clay minerals, Mg2+ and K+ are alsoincorporated to form illite, according to Equation 1.

l.lAl2Si205(0H)4 + 0.8K+ + 0.5Mg2+

= Ko.8Mgo.5Al2.2Si3.4θ10(OH)2 + 1.8H+

1.2SiO2

0.3H2O. (1)

It may be significant that as protons are produced duringthis reaction, these may cause enhanced dissolution ofhigh-Mg calcite (HMC), thereby releasing Mg2+ to the porefluids.

The concentration of Sr2+ increases rapidly to a maximumof 759 µM at 239.6 mbsf (Fig. 13). Below this depth, the Sr2+

slowly decreases in concentration to 730 µM at 382.7 mbsf.The increase in the concentration of Sr2+ is primarily a resultof the dissolution of aragonite and HMC, combined withprecipitation of low-Mg calcite (LMC) and dolomite. Anincrease in Sr2+ with increasing sub-bottom depth at Site 821was greater than values at both Sites 819 and 820, suggestingthat carbonate dissolution and precipitation processes weremore prevalent at Site 821 than at the previous two sites.Decreases in the concentration of Sr2+ in the lower part ofHole 821A may be a result of the removal of Sr2+ during claymineral diagenesis and of a lower rate of recrystallization inthe carbonate part of the sediments.

581

SITE 821

Table 2. Interstitial water analyses data, 821.

Core, section,interval (cm)

Depth(mbsf) pH

Alk.(mM)

Sal.(g/kg)

er(mM)

Mg.2 + Ca2 +

(mM) (mM)SO 4

2 "(mM)

PO43~

(µM)N H 4

+

(µM)Si K +

(mM)Sr2*(µM)

N a +

(mM)

Seawater133-821A-

1H-2, 145-1502H-5, 145-1503H-5, 145-1504H-5, 145-1505H-5, 145-1506H-5, 145-1507H-5, 145-1508H-5, 145-1509H-5, 145-15010H-5, 145-15013H-5, 145-15017X-5,140-15020X-5, 140-15023X-5, 140-15026X-5, 140-15029X-5, 140-15033X-5, 140-15035X-3, 140-15038X-5, 140-15041X-4, 140-150

2.9511.8521.3530.8540.3549.8559.3068.8578.3587.85116.35144.80182.30210.90239.60268.50307.10323.40355.30382.70

8.12

7.527.407.327.597.337.457.297.487.407.687.877.897.828.11

8.208.238.358.108.33

2.595

6.9%7.1604.8175.0865.0995.2676.0476.1445.3825.8879.0366.3306.3225.745

4.3605.2663.5495.0123.650

35.2

35.835.235.235.234.933.833.533.533.032.032.030.230.230.530.530.232.230.531.530.2

542.01

562.86560.96558.12560.02554.33551.49551.49544.86547.70543.91544.86538.22539.17542.01538.22540.12536.33538.22535.38538.22

53.51

54.6554.1149.3844.4035.4429.7424.8521.2518.4615.587.825.086.965.655.264.747.565.228.716.87

10.53

8.616.257.808.057.696.145.965.514.914.432.912.322.842.842.882.663.293.143.794.03

30.15

26.1923.5424.4721.7318.4415.6513.2911.6911.179.224.040.000.310.000.440.111.600.000.831.33

.10

14.804.202.402.802.001.802.001.801.50.60.60.10.20.40.10.10.20.20.90.40

130

56082595511001599204420582027222925692113304622392233242324062598

2598

0

312170153132168226172176170157141160166160151128134105185136

10.66

9.049.379.799.048.596.086.385.765.155.213.592.683.182.161.791.671.821.441.611.41

93

8286147222329353379412437436489462548651759702612695642730

465.97

486.52484.93487.44494.17500.81509.50515.36514.26522.65522.14535.93526.16522.25527.32519.51526.83520.04522.21514.14517.21

Note: Alk. = alkalinity; Sal. = salinity.

100 -

Q.CD

a

400

200 -

300 -

3 5 7 9Calcium (mM)

5 7 9 11Alkalinity (mM)

20 40Magnesium (mM)

535 555Chloride (mM)

575 300 500 700Strontium (µM)

Figure 13. Concentrations of Ca2+, alkalinity, Mg2+, Cl", and Sr2*, Site 821.

582

SITE 821

Table 3. Percentages of calcite, aragonite,quartz, and dolomite, Site 821.

Table 3 (continued).

Core, section,interval (cm)

133-821A-

1H-1, 95-981H-2, 145-1501H-3, 95-982H-1, 95-982H-3, 95-982H-5, 95-982H-5, 145-1503H-1, 95-983H-3, 95-983H-5, 95-983H-5, 145-1504H-1, 95-984H-3, 95-984H-5, 95-984H-5, 145-1505H-1, 95-985H-3, 96-985H-5, 96-985H-5, 145-1506H-1, 95-986H-3, 95-986H-5, 95-986H-5, 145-1507H-1, 95-987H-3, 95-987H-5, 95-987H-5, 145-1508H-1, 100-1038H-3, 96-998H-5, 96-998H-5, 145-1509H-1, 15-179H-3, 15-179H-5, 15-179H-5, 145-150

10H-1, 22-2410H-3, 22-2410H-5, 22-2410H-5, 145-15011H-1, 20-2311H-3, 20-2311H-5, 20-2311H-7, 20-2312H-1, 17-1912H-3, 17-1912H-5, 17-1913H-1, 15-1713H-3, 15-1713H-5, 15-1713H-5, 145-15013H-7, 15-1714H-1, 10-1114H-3, 3-414H-5, 3-415H-1, 10-1315H-3, 10-1315H-5, 10-1316H-1, 8-1016H-3, 8-1016H-5, 8-1117X-1, 10-1217X-1, 145-15017X-3, 10-1217X-5, 10-1218X-1, 1-218X-2, 9-1018X-3, 9-1018X-5, 9-1019X-1, 2-419X-3, 2-419X-5, 7-820X-1, 11-12

Depth(mbsf)

0.952.953.955.358.35

11.3511.8514.8517.8520.8521.3524.3527.3530.3530.8533.8536.8639.8640.3543.3546.3549.3549.8552.8555.8558.8559.3562.4065.3668.3668.8571.0574.0577.0578.3580.6283.6286.6287.8590.1093.1096.1099.1099.57

102.57105.57109.05112.05115.05116.35118.05118.50121.43124.43128.00131.00134.00137.48140.48143.48146.00147.35149.00152.00155.61157.19158.69161.69165.22168.22171.27175.01

Carbonate(%)

74.2067.7064.7055.5052.5045.0047.1055.6086.5069.5070.2073.6063.5044.3042.9034.2041.5084.1080.4078.6075.4057.4057.6066.1082.4068.1069.0033.7066.4068.0070.9063.1086.1082.7078.1070.0065.6069.7058.3061.0063.0080.8082.5051.3065.1075.2078.6076.9081.4087.1086.5079.9087.6087.6077.7078.5079.6081.6067.3078.1063.3075.2069.7071.5083.0080.3074.9075.8069.5058.9053.6072.10

Core, section,interval (cm)

20X-3, 11-1220X-5, 11-1220X-5, 140-15021X-1, 90-9221X-3, 90-9221X-5, 90-9222X-1, 90-9222X-3, 90-9222X-5, 90-9223X-1, 90-9223X-3, 90-9223X-5, 90-9223X-5, 140-15024X-1, 90-9224X-3, 90-9224X-5, 90-9225X-1, 90-9225X-3, 90-9225X-5, 90-9226X-1, 90-9226X-3, 90-9226X-5, 90-9226X-5, 140-15027X-1, 90-9227X-3, 90-9227X-5, 90-9228X-1, 90-9128X-3, 90-9128X-5, 90-9129X-1, 90-9229X-3, 90-9229X-5, 90-9229X-5, 140-15030X-1, 1-330X-3, 4-630X-5, 5-731X-1, 2-431X-3, 11-1331X-5, 9-1133X-1, 3-533X-3, 3-533X-5, 4-633X-5, 140-15034X-1, 4-634X-3, 4-634X-5, 4-635X-1, 5-735X-3, 5-735X-5, 140-15035X-5, 5-736X-1, 6-836X-3, 6-836X-5, 6-836X-7, 6-837X-1, 5-737X-3, 5-737X-5, 5-738X-1, 5-638X-3, 2-338X-5, 5-639X-1, 5-739X-3, 5-739X-5, 5-740X-1, 10-1140X-3, 10-1140X-5, 10-1141X-1, 10-1141X-3, 10-1141X-5, 10-1141X-5, 140-15042X-1, 90-9242X-3, 90-9242X-5, 90-9243X-1, 89-9143X-2, 90-92

Depth(mbsf)

178.01181.01182.30185.50188.50191.50194.80197.80200.80204.40207.40210.40210.90213.70216.70219.70223.40226.40229.40233.10236.10239.10239.60242.70245.70248.70252.30255.30258.30262.00265.00268.00268.50270.81273.84276.85280.42283.51286.49299.73302.58305.59306.95309.44312.44315.44319.05322.05323.40325.05328.76330.82333.82336.82338.35341.35344.35347.95350.92353.95357.55360.55363.55367.30370.30373.30376.90379.90382.90384.20387.30390.30393.30396.99398.50

Carbonate(%)

37.7043.2067.2069.5085.4076.5046.7072.5085.8061.0057.2067.9051.7033.5063.0083.5076.1078.1067.8059.8071.9053.5053.1063.1068.1070.0075.9073.6068.9046.9077.3074.9065.1060.4054.1069.4072.1062.2046.5075.3065.0059.7072.5037.3027.2037.1048.6059.5059.9059.1061.0049.6063.6068.0044.4053.6068.2062.0065.7039.7039.2031.2044.8050.7047.1071.7053.1047.7034.7034.0029.9057.9071.3072.7047.60

583

SITE 821

100 "

200 -

300 "

400

Table 4. Carbonate content data, Site 821.

-40

Excess Ca? Mg, SO I" and alkalinity (mM)

Figure 14. Changes in the concentration of SC^~, alkalinity, Ca2+, andMg2+ relative to seawater Cl" concentrations as a function of depth forSite 821.

Alkalinity, Sulfate, and Phosphate

The alkalinity increases in Hole 821A to 7.160 mM at11.85 mbsf. It exhibits another peak of 9.036 mM coincidentwith the removal of sulfate at 116.35 mbsf. As at Sites 819and 820, the alkalinity is lower than would be expected fromsulfate reduction, which indicates the presence of precipita-tion reactions involving carbonate. Increases in phosphateand ammonia are considerably lower than expected (see"Inorganic Geochemistry," "Site 820" chapter, this vol-ume).

Salinity and Chlorinity

The chlorinity exhibits a sharp increase in Core 133-821A-1H from seawater values to 542.01 mM. Below thisdepth there is a steady decrease (Fig. 13) reaching 535 mM at355.3 mbsf. The decrease in chlorinity is insufficient to ac-count for the change in salinity (see "Inorganic Geochemis-try," "Site 819" chapter, this volume). Salinity decreases asa result of the precipitation of carbonates and the removal ofsulfate through oxidation of organic material.

Carbonate Content and X-Ray Mineralogy

The carbonate content of the sediment at Site 821 variesbetween 10% and 90% (Table 3). Changes in the amount ofcarbonate occur principally as a result of dilution by terrige-nous materials and are probably related to changes in theposition of sea level.

Core, section,interval (cm)

Depth(mbsf)

Calcite Aragonite Quartz Dolomite

133-821A-1H-4,145-1502H-5, 145-1503H-5, 145-1504H-5, 145-1505H-5, 145-1506H-5, 145-1507H-5, 145-1508H-5, 140-1509H-5, 140-150

10H-5, 140-15013H-5, 140-15017X-5, 140-15018X-2, 9-1320X-1, 148-15021X-3, 90-%23X-3, 140-15024X-3, 90-9426X-5, 140-15029X-6, 140-15030X-3, 4-633X-2, 140-15035X-5, 140-15038X-5, 140-15039X-3, 5-839X-4, 4-640X-3, 10-1341X-5, 140-15042X-3, 90-%43X-2, 90-%

5.9511.8521.3530.8540.3549.8559.3568.8078.3087.80

116.30153.50157.19176.38188.50207.90216.70239.60270.00273.84302.60326.40355.30360.25361.74370.30384.20390.30398.50

36.433.539.033.230.732.125.131.732.032.935.953.541.841.462.531.536.735.950.338.320.943.346.833.131.831.230.252.035.3

51.848.655.344.559.355.343.250.552.649.748.932.935.842.314.342.844.141.228.642.527.934.838.730.830.343.637.431.232.5

11.717.95.7

22.35.3

11.714.310.67.9

14.52.87.69.36.25.6

21.711.917.78.0

16.111.619.114.535.636.924.530.611.817.7

0.00.00.00.04.81.0

17.47.27.52.9

12.36.0

13.110.117.64.17.35.2

13.13.1

39.52.80.00.51.00.61.85.0

14.5

100

200Q .CDQ

300

400

1

HUIptilIpfl

w>.j.+K+l+>*

0 10 20 30 40 50 60 70 80 90 100Mineral (%)

HMC

LMC

Aragonite | Dolomite

Quartz

Figure 15. X-ray mineralogy data for Site 821.

584

SITE 821

Table 5. Volatile hydrocarbon data from headspace analyses, Site 821.

Core, section,interval (cm)

133-821A-

1H-2, 145-1462H-5, 145-1463H-5, 145-1464H-5, 145-1465H-5, 145-1466H-5, 145-1467H-5, 145-1468H-5, 145-1469H-5, 149-150

10H-5, 145-14611H-5, 149-15012H-5, 124-12513H-5, 145-14614H-5, 149-15015H-5, 149-15017X-5, 149-15018X-5, 149-15019X-5, 149-15020X-5, 140-14121X-5, 149-15023X-5, 140-14124X-5, 149-15025X-5, 149-15026X-5, 140-14127X-5, 149-15028X-5, 149-15029X-5, 140-1413OX-5, 148-15031X-4, 149-15032X-CC, 0-133X-5, 149-15034X-5, 149-15035X-3, 140-14136X-4, 149-15037X-5, 149-15038X-5, 140-14139X-5, 149-15040X-5, 149-15041X-4, 140-14142X-5, 149-15043X-2, 149-150

Depth(mbsf)

2.9511.8521.3530.8540.3549.8559.3568.8578.3987.8597.39

106.64116.35125.89135.39153.39163.09172.69182.3192.09210.9220.29229.99239.6249.29258.89268.5278.28286.39290.1307.04316.89323.4333.75345.79355.3364.99374.69382.7393.89399.09

Sample

HSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHS

Volume(mL)

55555555555555555555555555555555555555555

Gas chromato.

CAR132CAR132CAR132CAR132CAR132CAR132CAR132CAR132CAR132CAR 132CAR 132CAR 132CAR132CAR132CAR132CAR132CAR132CAR132CAR132CAR132CAR132CAR132CAR132CAR132CAR132CAR132CAR132CAR132CAR132CAR132CAR 132CAR 132CAR 132CAR132CAR132CAR132CAR132CAR132CAR 132CAR 132CAR 132

Ci(ppm)

1891274444343348

203334

2052150052492935471139839623327378861008492572194946761680853299750808573

502719117

159589106

1823420851161579188937299279461

(ppm)

138

15141611222122149

16201135

167

1068

1698

119

10

c3(ppm)

2489

107

161520121017171337

1811189

12401619341828

C,/C2

2011112565333735213419362228333514277335182439292334043000169317153142130215%15182279130317951149852

1103946

C2/C3

1.52.0.9.6.6.6.4.4.1.2

0.90.91.20.81.00.70.90.60.60.70.70.40.60.40.30.50.4

C!/(C2+C3)

20667

1710217621432104221316402050145318951155137518401375847714

1479507550607912372621328204355243

HS = headspace sample.

Mineralogy

The sediments at Site 821 contain aragonite, LMC, HMC,dolomite, quartz, kaolinite, albite, and illite (Fig. 15 and Table4). Dolomite is particularly abundant (10%) between 40.35 and398.50 mbsf, coincident with the interval in which HMC isabsent. This association lends credence to the speculation thatHMC may provide the source for the Mg2+ needed fordolomitization. Similar associations between the occurrenceof HMC and dolomite were noted at Sites 819 and 820. On thebasis of the calculations of Swart and Guzikowski (1988), onecan estimate that the dissolution of 40% HMC might provideenough Mg2+ to form 16 wt% dolomite. A further source ofMg2+ may be provided by diffusion along concentration gra-dients from the overlying seawater, provided that the dolomiteforms at a shallow depth.

ORGANIC GEOCHEMISTRYIn addition to safety monitoring for hydrocarbons, the main

purpose of the shipboard organic geochemistry studies at Site821 was to assess the amount and origin of the organic matterpreserved in the Pleistocene mixed sediments deposited infront of the present-day Great Barrier Reef. The secondpurpose was the characterization of the propor-tions of different light hydrocarbons generated in the sedi-

ments through biogenic or thermogenic decay of organicmatter.

Samples

Forty-one samples were collected from Hole 821A at10-m intervals over the depth range from 3 to 399 mbsf. Allsediments were analyzed for their composition of lighthydrocarbons (Q-Q) using headspace analyses, and fortotal nitrogen, sulfur, and carbon, using a NA 1500 CarloErba NCS analyzer.

Volatile HydrocarbonsHydrocarbon gases (Q-Q) in sediments were analyzed as

part of ODP's safety and pollution-prevention monitoringprogram, using the headspace technique, the Carle gas chro-matograph (for determination of Q - Q concentrations), andthe NGA gas chromatograph (mainly for determination ofC4-C6 concentrations). The results of 41 headspace analysesfrom Hole 821A are presented in Table 5. In Figure 16, theWSTP-temperature data from Sites 817 and 820 are shownwith the geothermal gradient used at Site 821 for the interpre-tation of the depth-related evolution of the Q/C2 ratio.

The sediments at Site 821 contained high concentrations ofmethane, which represented no safety and/or pollution haz-

585

SITE 821

Geothermal gradient: 57°C/kmQ | r i i i | run

Geothermal gradient: 57°C/km

50

100

150

200

ΦQ 250

300

350

400

450

Site 817WSTP

temperature data Site 820WSTP

temperature data

Regression line usedfor gas monitoring

at Site 821Site 821

15 20 25

Temperature (°C)

30 40

Figure 16. WSTP-temperature data from Sites 817 and 820, geother-mal gradient, and approximate seafloor temperature at Site 821.

ards. The evolution of the Ci/C2 ratio with increasing depthand temperature did not show any anomalous trend (Fig. 17),and the values ranged between 3,600 and 800 (normal trendbetween 19°C and 33°C).

Headspace gas concentrations of methane were low tomoderate (ranged between 3 and 190 ppm) in the sulfatereduction zone (Fig. 18, see also "Inorganic Geochemistry"section and Fig. 14), but increased rapidly below 130 mbsf.The concentrations reached a maximum value at 220 mbsf(74,000 ppm in Sample 133-821A-24X-5, 149-150 cm), andprogressively decreased below this depth. Propane appearedtogether with ethane at 135 mbsf (Fig. 18). Their concentra-tions did not exceed 40 ppm and follow the trend of themethane concentrations. Between 135 and 225 mbsf ethaneconcentrations were higher than the propane concentrations(C2/C3 values progressively decreased between two and one).Between 230 and 310 mbsf C2/C3 = 1, and below this depth thepropane concentrations exceeded ethane (C2/C3 ratio <l) .

The observed coincidence between low sulfate concen-trations and high amounts of methane (> 10,000 ppm) and atrace amount of ethane/propane in the sediments suggests abacterial origin of methane (and ethane/propane?) in thesulfate-free section (between 145 and 250 mbsf) of thesediments at Site 821 (Fig. 19). Below 250 mbsf, the pro-gressive increase of propane content and the decrease ofboth the C2/C3 and Cy(C2+C3) ratio at shallow depth and lowtemperature (Figs. 18 and 19) are factors that seem to

0

10

20

30

ü

CD

1 40ΦQ.

Φ

50

60

70

80

Unusual

Anomalous

10 100 1,000

CVC2

10,000 100,000

Figure 17. Distribution of the Ci/C2 ratio from headspace analyseswith temperature at Hole 821 A. This diagram was compiled for theshipboard safety and pollution-prevention monitoring program.

indicate the beginning of a mixing with thermogenic free-hydrocarbons.

Important variations of the gas concentrations were ob-served between 280 and 310 mbsf corresponding to sharpchanges in the porosity of the sediments (see also "PhysicalProperties" section and Fig. 20): a decrease was observed inthe dolomitized chalks (bottom of Unit IV), and below this capan increase in the more porous chalks (top of Unit V, see also"Lithostratigraphy" section, Fig. 6, this chapter).

Organic Carbon Contents

The total organic carbon (TOC) and total inorganic carboncontents together with the total nitrogen and sulfur concen-trations recorded in Site 821 are presented in Table 6.

The amount of organic carbon at Site 821 varied betweenvery low (<0.25% TOC) and low values, not exceeding 0.45%TOC, and the average values remained relatively constant inthe different lithologic units (Fig. 21).

In the first 140 m, corresponding to the sulfate reductionzone and to lithologic Unit I, the total sulfur concentrations insediments were below the detection limits of the NCS ana-lyzer (Table 6). Below this depth the sulfur content variedbetween 0.1% and 0.6% (average value = 0.2%)

The total nitrogen concentrations in sediments of lithologicUnit I were very low (<0.05%), but increased progressively to0.08% between 120 and 398 mbsf (Fig. 21).

586

SITE 821

Geothermal gradient: 57°C/km

IQ.

Q

Mixing withmigrated

thermogenicgas

300 -

350 -

400100 1,000 10,000

Hydrocarbon gas (ppm)100,000

C,/C,

Figure 18. Distribution with depth of the amounts of hydrocarbon gas in headspace samples at Hole 821 A. Evolutionof CXIC2, C2/C3, and C,/(C2+C3) ratios.

On the basis of the TOC/nitrogen ratios (Fig. 21) marineorganic matter is abundant below 120 mbsf in all the bioclas-tic and mixed sediments encountered at Site 821. There wasmixing of terrestrial organic materials within the autochtho-nous organic matter above the Halimeda rudstone horizon,in the more siliciclastic Pleistocene sediments of Unit I. Asa consequence of the low organic contents, we were unableto conduct detailed geochemical characterization of kerogentypes using the Rock-Eval pyrolysis method, as originallyplanned. More detailed shore-based studies (elemental analysisand optical investigations on extracted kerogens) will permitcharacterization of the short-term fluctuations in the verticaldistribution and preservation of the different components of theorganic matter in the sediments encountered at Site 821.

PHYSICAL PROPERTIES

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

Bulk DensityBulk densities for Site 821 were determined from volume

and mass measurements on discrete core samples and fromabsorption of gamma rays by whole-round cores (Figs. 22 and

587

SITE 821

Geothermal gradient: 57°C/km

,

(mb

si

szQ.

a>Q

u

50

100

150

200

250

300

350

400

Λ en

"I i i i i i ii ij

10°

-

Temperature (c

— 20°

—30°

-

Thermogenic ga

C)

Mixing

s

D

DD

D D

' i i 111 n| i II

Ba<

DDDDα

DD

DD

D

cP

TbD

D

D

i

DD

D

Serial gas

-

-

•

-

-

-

10 100 1,000 10,000 100,000

Figure 19. Evolution with depth and temperature of the Ci/(C2+C3)ratio at Hole 821A.

23A and Table 7). After an initial increase in density withdepth in the upper 100 mbsf, density increases much moreslowly with depth. This increase in density is primarily afunction of decreasing porosity resulting from increasingoverburden with depth (see the discussion of porosity below).

P-Wave Velocity

P-wave velocities were measured on whole round coresusing the multisensor track (MST) and on discrete coresamples using the Hamilton Frame (Table 8 and Fig. 24A). Asindicated in Figure 24, velocity is to some extent correlatedwith shear strength in that major low velocity peaks correlatewith low shear strength peaks while the general increase invelocity with depth parallels the increase of shear strengthwith depth.

Porosity

Porosity was one of the index properties determined fromdiscrete core samples using the mass balance and the pycnom-eter (Table 7). A graph of porosity vs. depth (Fig. 23B) depictsa comparison of the porosity measured for samples from splitcores and from wireline logging. Much of the fine structure aswell as the overall trend of the porosity-depth function is seenin both the wireline log and the core sample measurements,though some differences in detail and in amplitude of varia-tions exist. High-porosity zones tend to be regions wherecalipers indicate that the hole has washed out to larger thannormal size. This change in hole size accentuates the wirelinelog porosity estimates. In addition, Figure 23B exhibits an

apparent correlation of peaks in porosity with lows in calciumcarbonate content. However, Figure 25 indicates that overallthe concentration of calcium carbonate does not correlatewith porosity. In Figure 25, the expected strong correlation ofporosity to bulk density is shown. The degree of correlation isa measure of the internal consistency of our measurements ofdensity and porosity since both quantities are measured on thesame sample, but the density involves both a mass and avolume measurement while the porosity involves only thelatter.

Now that we have accumulated data from several sites, wehave begun to recognize trends in the porosity data. Plots ofporosity vs. depth for Site 815 in Figure 26 show that the generaltrend of porosity vs. depth at Site 815 is best represented by alinear regression of In porosity on In depth. Site 821 is similar toSite 820 in that a linear regression of hi porosity on In depth ismarginally better at describing the data than either the linearregression of porosity on depth or In porosity on depth (Fig.26B). These general trends are summarized in Figure 20, wherewe plotted normal compaction curves for all sites analyzed todate. Sites 820 and 821 have almost identical normal compactioncurves, while Site 819 has a slightly divergent trend. Site 815 ismore divergent, followed by Site 817, which is the most differentfrom Sites 820 and 821. This trend parallels trends in sedimentcomposition, where Site 817 is almost totally carbonate com-pared with a large admixture of terrigenous sediments at theother sites. We are not clear at present why Site 819 differs fromSites 820 and 821.

Electrical-Resistivity Formation Factor

We measured the formation factor (FF) in cores from Hole821A (see Table 9 and Fig. 24D). Peaks in FF correlate withtroughs in sonic velocity as well as with lows in shear strength ina number of cases. This probably is a consequence of the highwater content that controls these three variables to some extent.

Shear Strength

We measured shear strength in the upper section of this hole(Table 10 and Fig. 24Q. A suggestion that shear strength lowscorrelate with peaks in FF and lows in sonic velocity, might beexpected if water content to controlled all three of these variables.

Physical Properties Conclusions

Sediment physical properties at Site 821 allow one to charac-terize the sediments into three basic physical property units.Unit A extends from the seafloor to 40 mbsf and consistspredominantly of calcareous ooze. Physical properties showed anormal compaction trend of soft sediment. Unit B includes theinterval from 40 to 300 mbsf and is composed of calcareousmudstone, chalk, and dolomitized wackestone. The compactiontrend showed a more gentle slope than the Unit A (Figs. 23, 24,and 25). P-wave velocity exhibited a significant amount of thevariation in this unit because of the occurrence of unsaturatedforaminifer ooze. Vane shear strengths exhibited large variationsthat we found correlated with the occurrence of compactedgassy sediments. Unit C, which extends from 300 to 400 mbsf,consists of dolomitized calcareous sandstone and mudstone.Physical properties exhibited a significant amount of variationthrough this unit (Figs. 23 and 25) because of lithology and, forthe most part, were invariant with depth. Two significant bulkdensity troughs were observed at 320 and 360 mbsf (Fig. 23) thatmay result from the occurrence of clay-rich mudstone. Valuesfor the physical properties of this unit remained relativelyconstant throughout the section.

Water content and porosity showed a good inverse corre-lation with bulk density (Fig. 26). WE found that variations inthese properties correlated with changes in sediment compo-sition, especially the amount of clay.

588

SITE 821

45050 55In Porosity

Figure 20. Generalized normal compaction curves for Sites 815,817,819,820, and 821, obtained by linear regression of In porosity on depth.

DOWNHOLE MEASUREMENTS

Log Reliability

Hole size is the most important control on accuracy of logsfrom Leg 133, and hole size at Hole 821A was the mostuniform of any Leg 133 site to-date. Three types of caliperwere obtained: an apparent caliper (Fig. 27) calculated fromthe sonic log (see "Explanatory Notes" chapter, this volume),a caliper (Fig. 27) from the Mechanical Caliper Device (MCD),and a two-axis caliper (Fig. 28) from the Formation Micro-Scanner (FMS). The lithodensity tool caliper was not opera-tional at this site. The FMS caliper is much more reliable thanthe sonic and MCD calipers. Based on correlation of largestcaliper values with anomalously low density values (Fig. 28),we suspect that occasional lowest-density portions of thelithodensity run are unreliable because of insufficient padcontact against the borehole wall. As discussed later, thispattern implies that porosity and Archie m calculations will bein error in these zones (Fig. 29). Most other logs do not requirepad contact and therefore are relatively insensitive to the

changes in borehole size. Two minor exceptions are thespectral gamma-ray and resistivity logs, which are likely to bechanged slightly by post-cruise borehole correction.

As is often the case with ODP holes, the initial sonic logsfrom Hole 821A exhibited a few zones in which cycle skippingcaused unreliable swings in apparent velocity. Reprocessing(see "Explanatory Notes" chapter, this volume) appears tohave removed all unreliable data, and we consider the repro-cessed velocity log of Figure 28 to be of good quality. For theshort interval 376.2-392.8 mbsf at the bottom of the hole,resistivity logs but not sonic logs are available, because theresistivity tool is much lower on the tool string. A pseudosoniclog was generated and used for this interval, based on regres-sion of sonic transit time on logarithm of shallow resistivity forthe overlying interval 333.7-376.1 mbsf (R = -0.86).

The spectral gamma-ray tool is the only tool on the seismicstratigraphic combination that can provide useful formationdata even through pipe. At Hole 821 A, through-pipe spectralgamma-ray logs were obtained for the interval 0-65.3 mbsf;however, we have not undertaken pipe correction of theselogs yet.

Velocity, Resistivity, and Density RelationsVelocity, resistivity, and density are strongly correlated

throughout almost all of the logged interval at Hole 821A (Fig.28). This correlation arises from a porosity dominance of allthree logs. The changes in velocity and density with depth(Fig. 28) generally follow a gradual compaction profile, sug-gesting that mechanical compaction is dominant over diagen-esis in controlling porosity at this site. Similar patterns wereobserved at Sites 814, 817, 819, and 820 (see "Site 814", "Site817", "Site 819", and "Site 820" chapters, this volume).Velocity and density within the open-hole logged interval aresomewhat greater than are normally observed in terrigenousor calcareous sediments of comparable depths. Average ve-locity increases from 1.7 km/s at 70 mbsf to 2.3-2.4 km/s at370-390 mbsf, compared to typical values for these depths of1.55-1.60 and 1.9-1.95 km/s (Hamilton, 1979). Density in-creases very little, from 1.95 g/cm3 at 80 mbsf to 2.1-2.2 g/cm3

at 320-385 mbsf, compared to typical values for these depthsof about 1.64 and 1.98 g/cm3 (Hamilton, 1976). These valuesfor density and porosity at Site 821 are similar to those atnearby Site 820 (see "Site 820" chapter, this volume).

The density log was used to calculate the Archie m (Fig. 29)to assess possible changes in style of pore structure (see "Site817" chapter, this volume). Although the Archie (1942) rela-tionship may not be applicable in this lithology, one canidentify a trend for further study. For example, the density loghas five intervals that may be affected by poor pad contact.These washouts where the density is in error have anoma-lously high values of m. If pore morphology changes withlithology, then m will vary and can be used as an additionalindicator. Velocity and resistivity ratios (Fig. 30) are similarlyuseful in identifying changes in pore morphology and styles ofcementation.

The velocity log has been converted to an integrated travel-time log (Fig. 31), to facilitate depth-to-time conversion forcomparison of Site 821 data with seismic facies. For the un-logged interval between the seafloor and 66.2 mbsf, we used asimple linear interpolation between water velocity at the seafloorand the first log value at 66.2 mbsf. We subjectively estimate anerror of less than 6 ms associated with uncertainties of velocitiesin the top 66.2 mbsf. A checkshot survey at nearby Site 820 (see"Site 820" chapter, this volume) showed <l ms error in a 241 minterval of integrated sonic log. However, it also showed that thelinear interpolation for unlogged shallow sediments led to trav-eltimes that were too slow by 5 ms.

589

SITE 821

Table 6. Concentrations of total organic carbon, inorganic carbon, total carbon, total nitrogen, and sulfur in headspace samples fromSite 821.

Core, section,interval (cm)

133-821A-1H-2, 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, 145-15011H-3, 20-2312H-3, 17-1913H-5, 145-15014H-3, 3-415H-3, 10-1316H-3, 8-1017X-1, 145-15018X-2, 9-1019X-3, 2-420X-5, 140-15021X-3, 90-9222X-3, 90-9223X-5, 140-15024X-3, 90-9225X-3, 90-9226X-5, 140-15027X-3, 90-9228X-3, 90-9129X-5, 140-1503OX-3, 4-631X-3, 11-1333X-5, 140-15034X-3, 4-635X-3, 140-15036X-3, 6-837X-3, 5-738X-5, 140-15039X-3, 5-740X-3, 10-1141X-5, 140-15042X-3, 90-9243X-2, 90-92

Depth(mbsf)

2.9511.8521.3530.8540.3549.8559.3568.8578.3587.8593.1

102.57116.35121.43131140.48147.35157.19168.22182.3188.5197.8210.9216.7226.4239.6245.7255.3268.5273.84283.51306.95312.44323.4330.82341.35355.3360.55370.3384.2390.3398.5

Sample

XRDXRDXRDXRDXRDXRDXRDXRDXRDXRD

PPPP

XRDPPPPPP

XRDPPPP

XRDPPPP

XRDPPPP

XRDPPPP

XRDPPPP

XRDPP

XRDPPPP

XRDPPPP

XRDPPPP

Totalorganic

carbon (%)

0.40.160.320.330.20.420.280.20.230.350.30.290.40.110.060.070.350.260.260.250.190.130.210.260.160.150.20.180.230.170.420.010.260.320.190.230.370.30.230.370.30.35

Totalinorganic

carbon (%)

8.135.668.435.159.656.918.288.519.3877.567.82

10.4610.529.428.089.039.647.078.07

10.258.76.217.569.376.388.188.837.816.497.478.73.267.195.%6.434.434.045.654.086.955.71

Totalcarbon (%)

8.535.828.755.489.857.338.568.719.617.357.868.11

10.8610.639.488.159.389.97.338.32

10.448.836.427.829.536.538.389.018.046.667.898.713.527.516.156.664.84.345.884.457.256.06

Totalnitrogen (%)

0.200.020.020.030.010.030.030.010.020.030.020.020.0200.020.040.040.040.060.050.050.070.060.040.050.060.040.060.060.060.050.060.060.060.060.060.080.080.070.080.070.08

Totalsulfur (%)

0000000000000000.230.030.090.360.170.140.110.070.140.060.240.250.140.430.080.180.070.090.090.230.230.090.370.080.120.140.58

TOC/nitrogen

208

161120149.3

201111151420

328.76.54.353.81.83.56.53.22.5533.82.88.40.14.35.33.13.84.63.73.34.64.34.4

TOC/sulfur

0.03112.90.721.51.31.231.82.60.620.81.30.532.12.30.12.93.50.8214.10.812.93.12.10.6

PP = physical properties sample; XRD = X-ray diffraction sample.

Log-Based Units

Lithostratigraphy at Site 821 is dominated by variations inconcentration of two principal components: carbonate (either nan-nofossils or micrite) and clay minerals. This conclusion is based onsmear-slide descriptions (see "Lithostratigraphy" section, thischapter); it was independently demonstrated at nearby Site 820 bygeochemical logs (see "Site 820" chapter, this volume).

In general, the three porosity-sensitive logs are moderatelywell correlated with the spectral gamma-ray log (SGR in Fig.27), with gamma-ray maxima corresponding to velocity, resis-tivity, and density minima. This pattern implies a substantialeffect of mineralogy on porosity. This pattern is typical inODP of clay-mineral variation. Higher clay-mineral concen-tration is evidenced by higher gamma-ray counts, particularlyif illite (3%-8% potassium; Serra, 1986) is a significant con-stituent of the clays, and clay minerals substantially increasethe porosity of uncompacted (<2 km overburden) sediments.Diagenesis can augment or diminish this correlation betweenhigh clay content and high porosity. Augmentation occurs ifdiagenesis is more extensive in carbonate-rich beds than inclay-rich beds due to higher permeability or local dissolution/

precipitation. Diminishment occurs if there is preferentialprecipitation in clay-rich beds.

The spectral gamma-ray values at Site 821 are similar tothose at Site 819 and 820, which are in turn substantiallyhigher than at previous sites on Leg 133. The potassium inparticular has increased by more than a factor of 10, to valuesranging from 0.5% to 1.0%. Thorium values increased by afactor of three, while the total SGR count was nearly doublethat at Site 817 (see "Site 817" chapter, this volume), withvalues in the range of 30 to 50 API units. These patterns canbe attributed to the much higher clay content and proportion-ately lower carbonate content at Sites 819, 820, and 821, incomparison to earlier Leg 133 sites.

On the basis of log responses, the open-hole logged intervalof Site 821 was divided into three units and several subunits:log Unit 1 from the base of the pipe (65 mbsf) to 210 mbsf, logUnit 2 from 210 to 293 mbsf, and log Unit 3 from 293 mbsf tothe bottom of the logged interval at 392 mbsf.

Log Unit 1 (<65-210 mbsf) includes calcareous mud-stones and chalks corresponding to lithologic Units I, II, andIII (0-215 mbsf; see "Lithostratigraphy" section, this chap-ter). Log Unit 1 is characterized by a smooth compaction

590

SITE 821

50-

100-

150-

Siliciclastic to bioclasticsandy / clayeymixed sediments

Unit!

200-

CL

Q

250

300

350-

400

Halimeda rudstone

Bioclasticmudstone / packstone

Lithified dolomitizedbioclastic wackestone

Unit II

Unit III

Dolomitizedmicritic / bioclastic chalk Unit ' ̂

Dolomitic calcareousmixed sediments

UnitV

Terrigenous

Mixed

Marine

0.5 1.0 1.5Total organic carbon (%)

2.0 0.0 0.1 0.2 0.3Total nitrogen (%)

10 20 30TOC/nitrogen

40

Figure 21. Distribution with depth of concentrations of total organic carbon and nitrogen and of TOC/nitrogen ratio in headspace samples fromHole 821A.

profile for the velocity and resistivity logs as shown inFigure 28. Punctuating this broad pattern is a regular saw-toothed pattern of apparently upward-fining beds, 4- to14-m thick. A sawtoothed pattern is most evident in resis-tivity logs and subtle-to-absent in spectral gamma-ray andpotassium logs (Fig. 27). We attribute this difference to themuch higher signal-to-noise ratio of resistivity than spectralgamma rays or potassium, particularly at the high loggingspeed used for the seismic stratigraphic combination tool.On the basis of patterns seen at Site 820 (see "Site 820"chapter, this volume), where spectral gamma-ray logs had ahigher signal-to-noise ratio than at Site 821, we speculatethat these cycles of upward-increasing porosity were causedby an increase in the proportion of clay minerals and adecrease in carbonate contents.

Log Unit 2 (210-293 mbsf) corresponds with lithologicUnit IV (215-299 mbsf); interbedded dolomitized chalks andbioclastic packstone-wackestone (see "Lithostratigraphy"section, this chapter). Resistivity (Fig. 29) in log Unit 2exhibits a sawtoothed pattern of beds increasing in porosity

up the section, much like log Unit 1, except that the beds areusually thicker (10-20 m). Gamma rays are generally posi-tively correlated with resistivity and velocity in this unit(Fig. 27); this pattern is opposite to that normally observedand indicates that intervals rich in clay minerals are lower inporosity, presumably due to diagenesis. Little or no evi-dence of a compaction pattern occurs in this unit (Fig. 28),again suggesting the importance of diagenesis.

Further evidence for diagenesis in log Unit 2 is shown inFigure 30, where the ratios of velocity and resistivity have beennormalized with respect to seawater, and the resulting ratiosdivided to create the A/B ratio (see "Site 817" chapter, thisvolume). This ratio can be used to identify sections (such as theone from 261 to 270 mbsf) where values have increased as aresult of a substantial relative reduction in resistivity. Previ-ously, this form of response has been associated with dolomiti-zation of porous facies (see "Site 817" chapter, this volume).Shipboard scientists suggested that this dissolution caused in-creased porosity to which the resistivity logs responded, whilecementation may account for the relatively high compressional

591

SITE 821

0

25

50

75

100

125Q .CD

Q

150

175

200

225

250

• ' • * . **i « * * • - * ;

•••r<tT- . *

1.6 1.7 1.8 1.9 2.0

Wet-bulk density (g/cm 3)

2.1 2.2

Figure 22. GRAPE bulk density measurements for Site 821. Datavalues have been averaged at 5-cm intervals.

wave velocity. Thus, we have interpreted this response between261 and 270 mbsf as having been caused by cementation, whichagrees with the increase in dolomitization observed in the cores(see "Lithostratigraphy" section, this chapter).

Log Unit 3 (293 to at least 392 mbsf) corresponds withlithologic Unit V (299-400 mbsf), which consists of coarsen-ing-upward cycles of calcareous sandstone and calcareousmudstone (see "Lithostratigraphy" section, this chapter). Atleast four such cycles are visible in the logs: 362-340 mbsf,340-330 mbsf, 330-318 mbsf, and 318-293 mbsf. The gamma-ray log typically is inversely correlated with resistivity andvelocity in this unit, in contrast to the pattern in Log Unit 2but consistent with the pattern at Site 820 of higher clay-mineral abundance causing higher porosity (see "Site 820"chapter, this volume).

The logs do not directly establish that the cycles in log Unit3 are coarsening upward, but instead that they are decreasingin clay-mineral content and porosity upward. However,within each upward-coarsening be, some tendency exists forthe Archie component m to decrease upward (Fig. 29). Such atrend might be caused by a decrease in the proportion of clayminerals, which should result in the shape of the particlesbeing less platy; this is known to decrease the value of m.These are relatively subtle trends at this site, but they can betaken as an indication of upward-coarsening owing to theoften observed decrease in grain size with increasing contentof platy clay minerals. These log-based upward-coarseningsequences are discussed in more detail in the "Lithostratigra-phy" section (this chapter). A good example of changing styleof cementation can be seen at the top of Log Unit 3 from 295

to 300 mbsf, where the A/B ratio (Fig. 30, described above) ishigh at a point of high velocity and low resistivity, thusindicating that an increase in cementation is probable. Otherzones having a high A/B ratio occur; however, these areassociated with low velocities and thus do not immediatelyindicate an increase in cementation. Post-cruise research isplanned for evaluating these trends in terms of diagenesis andsedimentological processes to produce more comprehensivelithological correlations.

TemperatureThe Lamont-Doherty Geological Observatory (LDGO)

temperature tool was run at the bottom of the seismicstratigraphic tool string. Because the hole temperatureshave been reduced by circulation during coring and by holeconditioning immediately prior to logging, it is not possibleto infer an equilibrium thermal profile from a single tem-perature logging run. Thus, our recorded maximum temper-ature of 28.6°C is a minimum estimate of equilibrium tem-perature.

The temperature tool was run not to estimate heat flow, butin case fluid flow was present. In Figure 32, temperature hasbeen measured as a function of pressure recorded simultane-ously by the tool. Depths shown are approximate and may berevised by up to 5 m by post-cruise merging of Schlumbergertime/depth data with LDGO time/pressure data.

The temperature pattern in Figure 32 exhibits evidence ofthermal lags from a mud-clogged end sub. Mud clogging canoccur when the temperature tool, which is the bottom tool onthe tool string, hits the bottom of a hole that contains stickyclay. The effect on the log is a higher temperature for theupgoing log than for the downgoing log, and a maximumtemperature recording, not at the deepest point in the hole,but somewhat shallower than the deepest point on the upgoinglog. When rigged down after logging, the temperature tool didhave a mud-clogged end sub.

The downgoing log probably has been minimally affected,while the upgoing log is probably somewhat affected by mudclogging. This pattern indicates an approximately linearlyincreasing temperature between the base of pipe and thebottom of the hole. Both logs indicate that through-pipetemperatures are significantly cooler than those of the adja-cent open hole. The extrapolated bottom-water temperature(based on observed sub-bottom thermal gradient) is substan-tially warmer than the observed bottom-water temperature(Fig. 32). This discrepancy might be caused by either upwardflux of pore fluids out of the formation or by bottom watersthat are presently cooler than average; the latter seems morelikely in these shallow waters.

Hole DeviationAt Hole 821A, the hole deviation measured by the FMS

ranges from 0.2° to 1.1° (Fig. 33). Azimuth of this very smalldeviation ranges from south to west.

SEISMIC STRATIGRAPHYFor a discussion, see "Seismic Stratigraphy" section,

"Site 819" chapter (this volume).

SUMMARY AND CONCLUSIONSFor a discussion of this site, see "Summary and Conclu-

sions" section, "Site 819" chapter (this volume).

REFERENCES

Archie, G. E., 1942. The electrical resistivity log as an aid indetermining some reservoir characteristics. J. Pet. Tech., 5:1-8.

Hamilton, E. L., 1976. Variation of density and porosity with depth indeep-sea sediments. J. Sediment. Petrol., 46:280-300.

592

SITE 821

, 1979. Sound velocity gradients in marine sediments. J.Acoust. Soc. Am., 65:909-922.

Serra, O., 1986. Fundamentals of Well Log Interpretation 2: TheInterpretation of Logging Data: Amsterdam (Elsevier).

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 and

Marion Plateau region-research cruise proposal, project 9131.11.Bur. Miner. Res. Aust. Record, 1988/48.

Symonds, P. A., Davies, P. J., and Parisi, A., 1983. Structure andstratigraphy of the central Great Barrier Reef. BMR J. Aust. Geol.Geophys., 8:277-291.

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

Ms 133A-114

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.

Formation microscanner images for this site are presented on microfiche in the back of Part 2.

Caliper 1 (in.11 16 0.1

Fractional porosity0.3 0.5 0.7

4001.6 1.8 2.0 2.2

Bulk density (g/cm 315

Caliper 2 (in.

20 0.3 0.5 0.7Fractional porosity

0.9 20 40 60 80CaCO3 (wt%)

100

Figure 23. A. Bulk density vs. depth at Site 821. The data were obtained from mass and volume measurements of samples taken from split cores.B. Porosity, wireline caliper measurements, and weight percent of carbonate at Site 821. Carbonate contents are derived from measurements ofsamples from split cores as is one of the porosity curves. For the most part, the samples for carbonate analysis were a subsample of the samplesused for determining porosity. The wireline porosity curve and the caliper curves were obtained by wireline logging. The dashed lines indicatecorrelations among the various curves. There is a pattern, by no means perfect, for lows in carbonate to correlate with highs in porosity.

593

SITE 821

Table 7. Index property data, Site 821. Table 7 (continued).

Core, section,interval (cm)

133-821A-1H-1, 95-981H-2, 95-981H-3, 75-782H-1,95-982H-2, 95-982H-3, 95-982H-4, 95-982H-5, 95-983H-1, 95-983H-2, 95-983H-3, 95-983H-4, 95-983H-5, 95-983H-6, 95-984H-1, 95-984H-2, 95-984H-3, 95-984H-4, 95-984H-5, 95-984H-6, 95-985H-1, 95-985H-2, 95-985H-3, 95-985H-4, 95-985H-5, 95-985H-6, 95-986H-1, 95-986H-2, 95-986H-3, 95-986H-4, 95-986H-5, 95-986H-6, 95-987H-1, 95-987H-2, 95-987H-3, 95-987H-4, 95-987H-5, 95-987H-6, 95-988H-1, 95-988H-2, 95-988H-3, 95-988H-4, 95-988H-5, 95-988H-6, 95-989H-1, 95-989H-2, 95-989H-3, 95-989H-4, 95-989H-5, 95-989H-6, 95-98

10H-1, 95-9810H-2, 95-9810H-3, 95-9810H-4, 95-9810H-5, 95-9810H-6, 95-9811H-1, 95-9811H-2, 95-9811H-3, 95-9811H-4, 95-9811H-5, 95-9811H-6, 95-9812H-1, 95-9812H-2, 95-9812H-3, 95-9812H-4, 95-9812H-5, 95-9812H-6, 95-9813H-1, 95-9813H-2, 95-9813H-3, 95-9813H-4, 95-9813H-5, 95-9813H-6, 95-9813H-7, 10-12

Depth(mbsf)

0.952.453.755.356.858.359.85

11.3514.8516.3517.8519.3520.8522.3524.3525.8527.3528.8530.3531.8533.8535.3536.8538.3539.8541.3543.3544.8546.3547.8549.3550.8552.8554.3555.8557.3558.8560.3562.3563.8565.3566.8568.3569.8571.8573.3574.8576.3577.8579.3581.3582.8584.3585.8587.3588.8590.8592.3593.8595.3596.8598.35

100.35101.85103.35104.85106.35107.85109.85111.35112.85114.35115.85117.35118.00

Bulkdensity(g/cm?)

1.771.761.771.721.701.741.951.761.791.771.731.881.881.851.881.871.851.861.831.811.952.012.001.881.901.941.961.931.901.931.921.871.931.911.921.831.941.961.841.811.921.951.941.921.911.921.931.911.932.012.001.991.971.972.042.001.911.921.941.951.991.921.961.951.992.021.991.942.012.012.032.011.972.011.97

Graindensity(g/cm3)

2.772.772.752.782.722.772.692.672.742.742.752.732.772.742.782.802.772.662.812.792.712.732.752.812.782.832.802.563.562.782.872.792.782.822.632.752.802.822.722.692.782.752.582.652.782.742.722.732.732.592.742.772.742.852.852.752.752.772.702.892.732.722.642.592.792.732.802.772.782.702.832.732.652.822.82

Porosity(%)

61.260.559.859.562.561.848.861.658.759.563.459.457.459.256.357.154.755.857.160.649.044.548.657.252.551.352.252.252.151.152.755.651.651.251.647.347.552.254.551.350.650.150.451.249.051.251.947.249.049.147.349.047.948.349.745.549.652.249.048.446.651.849.648.546.447.648.650.946.146.446.146.148.947.948.6

Watercontent

(%)

54.754.453.055.060.657.334.455.750.452.460.247.845.748.944.345.543.344.547.052.234.729.433.145.439.337.237.738.239.037.339.243.937.637.838.036.033.637.643.440.936.935.736.437.835.637.538.134.035.033.532.033.933.233.633.230.536.338.734.834.131.638.234.934.331.231.933.236.730.731.030.430.734.032.233.9

Voidratio

1.581.531.491.471.671.620.951.601.42I Al1.731.461.351.451.291.331.211.261.331.540.960.800.951.341.111.061.091.091.091.051.121.261.071.051.060.900.901.091.201.051.031.001.021.050.961.051.080.890.960.970.900.960.920.940.990.840.981.090.960.940.871.080.980.940.860.910.941.040.860.860.860.860.960.920.95

Core, section,interval (cm)

14H-1, 5-714H-2, 5-714H-3, 5-714H-4, 5-714H-5, 15-1714H-6, 10-1315H-1, 10-1315H-2, 10-1315H-3, 10-1315H-4, 10-1315H-5, 10-1315H-6, 2-416H-1, 8-1116H-2, 8-1116H-3, 8-1116H-4, 8-1116H-5, 8-1117X-1, 8-1117X-2, 8-1117X-3, 8-1117X-4, 8-1117X-5, 8-1117X-6, 8-1118X-1, 3-518X-2, 9-1118X-3, 11-1318X-4, 11-1318X-5, 22-2418X-6, 10-1219X-1, 3-519X-2, 3-519X-3, 3-519X-4, 6-919X-5, 6-919X-6, 6-920X-1, 12-1320X-2, 7-1020X-3, 7-1020X-4, 7-1020X-5, 7-1020X-6, 7-1021X-1, 90-9221X-2, 90-9221X-3, 90-9221X-4, 90-9221X-5, 90-9221X-6, 90-9222X-1, 90-9222X-2, 90-9222X-3, 90-9222X-4, 90-9222X-5, 90-9222X-6, 90-9223X-1, 90-9223X-2, 90-9223X-3, 90-9223X-4, 90-9223X-5, 90-9224X-1, 90-9224X-2, 90-9224X-3, 90-9224X-4, 90-9224X-5, 90-9224X-6, 90-9225X-1, 90-9225X-2, 90-9225X-3, 90-9225X-4, 90-9225X-5, 90-9225X-6, 90-9226X-1, 90-9226X-2, 90-9226X-3, 90-9226X-4, 90-9226X-5, 90-9226X-6, 90-9227X-1, 90-92

Depth(mbsf)

118.45119.95121.45122.95124.55126.00128.00129.50131.00132.50134.00135.42137.48138.98140.48141.98143.48145.98147.48148.98150.48151.98153.48155.63157.19158.71160.21161.82163.20165.23166.73168.23169.76171.26172.76175.02176.47177.97179.47180.97182.47185.50187.00188.50190.00191.50193.00194.80196.30197.80199.30200.80202.30204.40205.90207.40208.90210.40213.70215.20216.70218.20219.70221.20223.40224.90226.40227.90229.40230.90233.10234.60236.10237.60239.10240.6242.70

Bulkdensity(g/cm*)

2.022.101.921.931.972.142.052.002.012.002.071.982.582.142.012.001.991.992.042.122.041.872.171.992.002.041.972.071.932.012.052.042.052.041.972.001.941.972.071.952.121.991.942.052.072.072.142.021.992.032.012.202.032.092.082.072.051.962.002.072.112.071.972.032.072.072.062.092.082.092.072.102.022.122.052.142.18

Graindensity(g/cmJ)

2.772.752.772.812.742.812.772.782.762.772.772.722.692.732.732.752.752.782.752.772.712.712.782.742.722.712.772.712.692.712.752.732.772.752.772.762.722.762.752.762.752.772.762.732.742.732.812.772.722.752.802.762.722.762.742.732.732.792.752.742.832.762.732.732.692.742.732.732.642.732.742.722.772.762.752.732.74

Porosity(%)

47.242.052.052.452.255.545.348.048.144.244.347.836.440.345.545.747.447.244.639.644.841.648.943.047.643.845.343.847.144.743.445.345.445.047.446.948.147.542.348.740.447.450.039.543.341.642.544.545.945.347.533.944.242.042.742.142.648.547.345.142.342.649.847.642.041.843.242.449.441.243.838.046.342.044.741.935.4

Watercontent

(%)

31.525.838.438.737.336.229.232.732.529.328.132.716.923.930.130.532.232.028.923.729.029.430.028.432.328.130.827.733.329.527.729.329.329.132.631.634.032.826.534.324.332.435.824.627.326.025.529.130.929.731.918.728.826.026.726.327.133.931.928.825.826.734.931.726.226.127.426.232.225.327.722.730.725.528.825.020.0

Voidratio

0.890.721.081.101.091.250.830.920.930.790.800.920.570.670.830.840.900.890.800.660.810.710.960.750.910.780.830.780.890.810.770.830.830.820.900.880.930.910.730.950.680.901.000.650.760.710.740.800.850.830.910.510.790.720.750.730.740.940.900.820.730.740.990.910.720.720.760.740.980.700.780.610.860.720.810.720.55

594

SITE 821

Table 7 (continued). Table 7 (continued).

Core, section,interval (cm)

27X-2, 90-9227X-3, 90-9227X-4, 90-9227X-5, 90-9227X-6, 90-9228X-1, 90-9228X-2, 90-9228X-3, 90-9228X-4, 90-9228X-5, 90-9228X-6, 90-9229X-2, 90-9229X-3, 90-9229X-4, 90-9229X-5, 90-9229X-6, 90-9230X-2, 11-133OX-3, 4-530X-4, 5-73OX-5, 5-730X-6, 5-731X-1, 2-431X-2, 9-1131X-3, 11-1331X-4, 11-1331X-5, 9-1133X-1, 3-533X-2, 3-533X-3, 3-533X-4, 5-733X-5, 4-633X-6, 4-634X-1.4-634X-2, 4-634X-3, 4-634X-4, 4-634X-5, 4-634X-6, 4-635X-1, 5-735X-2, 5-735X-3, 5-735X-4, 5-735X-5, 5-736X-1, 6-8

Depth(mbsf)

244.20245.70247.20248.70250.20252.30253.80255.30256.80258.30259.80263.50265.00266.50268.00269.50272.41273.84275.35276.85278.35280.42281.99283.51285.01286.49299.73301.08302.58304.10305.59307.09309.44310.94312.44313.94315.44316.94319.05320.55322.05323.55325.05328.76

Bulkdensity(g/cm*)

2.012.242.122.092.072.172.122.082.122.152.072.102.032.112.112.152.112.112.142.142.082.211.692.222.042.072.272.242.152.162.162.071.941.992.042.052.001.941.972.072.102.312.122.23

Graindensity(g/cm3)

2.782.712.742.762.742.732.702.662.752.742.712.672.902.812.792.802.722.742.722.752.662.742.712.712.662.732.692.712.742.742.722.752.712.752.742.732.732.792.702.732.712.562.712.70

Porosity(%)

45.837.042.741.141.739.740.941.841.338.443.642.132.838.936.838.140.743.040.140.241.346.633.833.743.742.33.33

31.640.339.639.244.649.442.243.344.348.147.248.944.142.333.333.833.7

Watercontent

(%)

30.520.325.925.226.023.024.725.925.022.427.525.919.823.321.822.224.626.523.723.825.527.625.818.428.126.517.716.923.823.222.928.335.227.727.728.432.633.134.227.825.917.319.518.3

Voidratio

0.850.590.740.700.720.660.690.720.700.620.770.730.490.640.580.620.690.750.670.670.700.870.510.510.780.730.500.460.680.660.640.810.980.730.760.800.930.890.960.790.730.500.510.51

Core, section,interval (cm)

36X-2, 6-836X-3, 6-836X-4, 6-836X-5, 6-836X-6, 6-836X-7, 6-837X-1, 5-737X-2, 5-737X-3, 5-737X-4, 5-737X-5, 5-737X-6, 5-738X-1, 5-638X-2, 5-638X-3, 2-338X-4, 2-338X-5, 5-638X-6, 5-639X-1, 5-739X-2, 5-739X-3, 5-739X-4, 5-739X-5, 5-739X-6, 5-740X-1, 10-1140X-2, 10-1140X-3, 10-1140X-4, 10-1140X-5, 10-1140X-6, 10-1141X-1, 10-1141X-2, 10-1141X-3, 10-1141X-4, 10-1141X-5, 10-1141X-6, 10-1142X-1, 90-9242X-2, 90-9242X-3, 90-9242X-4, 90-9242X-5, 90-9242X-6, 90-9243X-1, 89-9143X-2, 90-92

Depth(mbsf)

329.32330.82332.32333.82335.32336.82338.35339.85341.35342.85344.35345.85347.95349.45350.92352.42353.95355.45357.55359.05360.55362.05363.55365.05367.30368.80370.30371.80373.30374.80376.90378.40379.90381.40382.90384.40387.30388.80390.30391.80393.30394.80396.99398.50

Bulkdensity(g/cm?)

2.222.082.162.192.262.122.052.132.082.122.232.222.142.052.252.312.051.901.901.992.072.052.172.312.052.182.112.212.092.202.172.042.132.162.041.972.052.092.242.162.212.232.211.99

Graindensity(g/cm1)

2.712.742.702.732.722.762.912.742.772.772.722.712.562.752.572.702.692.752.892.752.702.742.792.742.732.792.562.692.713.012.692.712.732.872.922.682.772.782.762.752.752.792.622.65

Porosity(%)

34.144.238.734.633.429.646.838.841.745.034.342.838.544.329.733.247.454.243.045.850.945.541.033.842.845.440.842.640.641.040.145.441.540.445.151.942.140.934.939.833.032.532.447.6

Watercontent

(%)

18.727.922.519.317.916.730.622.925.927.818.724.622.628.515.617.331.141.230.230.933.629.523.917.627.127.124.724.624.723.623.429.624.923.729.337.026.625.119.023.218.017.617.732.6

Voidratio

0.520.790.630.530.500.420.880.630.720.820.520.750.630.790.420.500.901.180.750.851.040.840.690.510.750.830.690.740.680.690.670.830.710.680.821.080.730.690.540.660.490.480.480.91

595

SITE 821

Table 8. Compressional-wave velocity data, Site 821.

Core, section,interval (cm)

133-821A-1H-1, 95-981H-2, 95-981H-3, 75-782H-1, 95-982H-2, 95-982H-3, 95-982H-4, 95-982H-5, 95-982H-6, 95-983H-1, 95-983H-2, 95-983H-3, 95-983H-4, 95-983H-5, 95-983H-6, 95-984H-1, 95-984H-2, 95-984H-3, 95-984H-4, 95-984H-5, 95-984H-6, 95-985H-1, 95-985H-3, 95-985H-4, 95-985H-5, 95-985H-6, 95-986H-1, 95-986H-2, 95-986H-3, 95-986H-4,95-986H-5, 95-986H-6, 95-987H-1, 95-987H-2, 95-987H-3, 95-987H-4, 95-987H-5, 95-987H-6, 95-988H-1, 100-1038H-2, 95-988H-3, 95-988H-4, 95-988H-5, 95-988H-6, 95-989H-1, 15-199H-2, 15-199H-3, 15-199H-4, 15-199H-5, 15-199H-6, 15-19

10H-1, 22-2510H-2, 22-2510H-3, 22-2510H-4,22-2510H-5, 22-2511H-1, 20-2311H-2, 20-2311H-3, 20-2311H-4, 20-2311H-5,20-2311H-6,20-2311H-7, 20-2312H-1, 15-1812H-2, 15-1812H-3, 15-1812H-4, 15-1812H-5, 15-1812H-6, 15-1813H-1, 15-1813H-2, 15-1813H-3, 15-1813H-4, 15-1813H-5, 15-1815H-1, 10-1315H-2, 10-1315H-3, 10-1315H-4, 10-1315H-5, 10-13

Depth(mbsf)

0.952.453.755.356.858.359.85

11.3512.8514.8516.3517.8519.3520.8522.3524.3525.8527.3528.8530.3531.8533.8536.8538.3539.8541.3543.3544.8546.3547.8549.3550.8552.8554.3555.8557.3558.8560.3562.4063.8565.3566.8568.3569.8571.0572.5574.0575.5577.0578.5580.6282.1283.6285.1286.6290.1091.6093.1094.6096.1097.6099.1099.55

101.05102.55104.05105.55107.05109.05110.55112.05113.55115.05128.00129.50131.00132.50134.00

Distance(mm)

28.%29.5727.9329.8029.8229.5528.9329.2829.5127.6229.1128.8326.3329.2929.5529.6829.5029.9129.4229.2027.5827.9328.%29.5128.%28.5029.2929.5127.9929.3429.5529.0129.3329.8927.6128.2329.8129.0229.6529.9329.7830.3831.2529.9930.5530.4231.5530.5528.1528.6430.3130.3629.5030.0730.4128.5828.8629.8529.4229.5129.7230.0329.4230.6829.7229.6829.7929.3729.9929.8129.5129.5530.1632.0630.9429.9930.2330.07

Traveltime(µs)

20.9821.5220.3921.7321.8121.4819.3821.3721.3820.1020.5420.1519.0720.%21.2121.2720.%21.4121.1121.2820.1821.3922.4622.7220.2319.9720.5920.7719.7020.5020.6820.7520.5220.8720.8019.7120.5220.1621.0721.4020.3421.0621.7020.8320.9821.1721.7221.4519.5019.9820.8620.8320.4220.5421.0821.8322.0820.5120.2121.8221.7020.5520.9921.1820.3920.5520.0720.4919.8522.7620.1920.3520.8322.4321.2920.3720.5319.84

Velocity(m/s)

156215491555154415381552171615461558156416111632158315831575157715951578157715491554146914401449163216291617161316251628162415861626162615001638165416421593158016701636162716351653162816411610165516371651165616451667163614691464165716611521154216641587164216611643169716311732146216681655164516071647167916781738

596

20 "

40

60

80

100 ~

120 -

140 "

HT ' *"

> • _

- • • • - l r •

. rat ."".""X..

, I i I i I % ' i T". ' 1 i *•"

i i i l i 1 i

-

-

-

-

1500 1600 1700 1800

Velocity (m/s)

1900

100

1501500 1700 1900

Velocity (m/s)

2100 40 80 120

Shear strength (kPa)3 4 5

Formation factor

1.4 1.5 1.6 1.7 1.

Velocity (km/s)

Figure 24. A. MST sonic velocity data Hole 821 A. Raw data values with amplitudes greater than 30 have been averaged in 5-cm intervals. B. Velocity vs. depth for the upper 150mbsf of section at Site 821 determined from Hamilton Frame measurements of samples from split cores and from wireline logging. C. Shear strength vs. depth. D. FF vs. depth. E.Velocity vs. depth. All these data were obtained from split cores. There is a general, though not perfect, correlation of velocity lows with shear strength lows and FF highs that shouldbe consistent with expected relationships between water content and the measured physical properties.

SITE 821

2030 40 50 60

CaCO3 (wt%)70 80 90

1.6

>sity

Por

e

60

50

40

30

?n

-

-

D

I

D

3 DD D

D

D

I

D

*>>

D

1

T_öB

U

i

D ^

a

D

D

Sm

D

D

i ' i

D

D D

-

-

-

D

1.8 2.0 2.2Density (g/cm 3 )

2.4 2.6

Figure 25. Porosity vs. wt% carbonate and porosity vs. bulk density at Site 821. This plot suggests essentially no correlation betweenwt% carbonate and porosity. The linear regression curve is of the form, P = 47.7 - 0.0310 CaCO3, where P - porosity, CaCO3 =wt% carbonate, and the regression coefficient R = 0.06. There is the expected strong linear inverse correlation between porosity andbulk density. The regression curve is of the form P = 137-45D, where P = porosity, D = bulk density, and the regression coefficientR = 0.83. This is a useful check on the internal consistency of our measurements of density and porosity.

598

SITE 821

200

300

400

W

= 58.020 - 3.3528e-2xR2 = 0.549

50 60

Porosity (%)

70 3.7

100

300

400

y= 53.818 -4.2039e-2xR2 = 0.527

π β.

(Fi

he

^

20 40 50

Porosity (%)

70

y= 4.2801 -6.8605e-2xR2 = 0.621

y= 4.3545- 0.10999xR2 = 0.547

3.6 3.8

In Porosity

3.2 3.4 3.6 3.8

In Porosity

4.0 4.2

Figure 26. A. Porosity-depth, In porosity-depth, and In porosity-ln depth plots of data from Site 815. Linear regressions areshown for each plot along with R2 where R is the regression coefficient. For Site 815 a linear regression of In porosity on Indepth describes the actual data marginally better than the other regressions. B. Porosity-depth, In porosity-depth, and Inporosity-ln depth plots of data from Site 821. Linear regressions are shown for each plot along with R2 where R is theregression coefficient. For Site 821, a linear regression of In porosity on In depth describes the actual data marginally betterthan the other regressions.

599

Table 9. Formation factor data, Hole 821A. Table 9 (continued).

Core, section, Depth Seawater Sample Formationinterval (cm) (mbsf) (ohms) (ohms) factor

133-821A-

1H-1,40-40 0.40 2.6 7.1 2.731H-1,80-80 0.80 2.6 7.9 3.041H-1, 130-130 1.30 2.6 8.0 3.081H-2,20-20 1.70 2.6 8.5 3.271H-2,70-70 2.20 2.6 9.8 3.771H-2, 120-120 2.70 2.6 8.0 3.081H-3,20-20 3.20 2.6 8.1 3.121H-3,70-70 3.70 2.6 8.5 3.271H-3, 110-110 4.10 2.6 8.7 3.352H-1,20-20 4.60 2.6 8.2 3.152H-1,70-70 5.10 2.6 7.4 2.852H-1, 130-130 5.70 2.6 7.8 3.002H-2,20-20 6.10 2.6 8.2 3.152H-2,70-70 6.60 2.6 8.2 3.152H-2, 130-130 7.20 2.6 7.5 2.882H-3,20-20 7.60 2.6 7.8 3.002H-3,70-70 8.10 2.6 7.7 2.962H-3, 130-130 8.70 2.6 9.7 3.732H-4, 20-20 9.10 2.6 10.4 4.002H-4, 70-70 ' 9.60 2.6 10.9 4.192H-4, 130-130 10.20 2.6 9.7 3.732H-5, 20-20 10.60 2.6 9.8 3.772H-5,70-70 11.10 2.6 8.1 3.122H-5, 130-130 11.70 2.6 8.3 3.192H-6,20-20 12.10 2.6 8.8 3.382H-6, 70-70 12.60 2.6 8.5 3.272H-6, 130-130 13.20 2.6 8.7 3.353H-1,20-20 14.10 2.6 8.9 3.423H-1,70-70 14.60 2.6 9.4 3.623H-1, 130-130 15.20 2.6 9.3 3.583H-2,20-20 15.60 2.6 9.8 3.773H-2, 70-70 16.10 2.6 9.5 3.653H-2, 130-130 16.70 2.6 9.5 3.653H-3, 20-20 17.10 2.6 9.6 3.693H-3,70-70 17.60 2.6 9.6 3.693H-3, 130-130 18.20 2.6 10.0 3.853H-4,20-20 18.60 2.6 10.4 4.003H-4,70-70 19.10 2.6 9.5 3.653H-4, 130-130 19.70 2.6 9.9 3.813H-5, 20-20 20.10 2.6 9.5 3.653H-5, 70-70 20.60 2.6 10.1 3.883H-5, 110-110 21.00 2.6 10.0 3.853H-6, 20-20 21.60 2.6 10.0 3.853H-6, 70-70 22.10 2.6 9.7 3.733H-6, 130-130 22.70 2.6 9.6 3.694H-1,20-20 23.60 2.6 7.8 3.004H-1,70-70 24.10 2.6 9.4 3.624H-1, 130-130 24.70 2.6 9.8 3.774H-2,20-20 25.10 2.6 9.6 3.694H-2,70-70 25.60 2.6 9.6 3.694H-2, 130-130 26.20 2.6 9.7 3.734H-3,20-20 26.60 2.6 10.2 3.924H-3,70-70 27.10 2.6 9.6 3.694H-3, 130-130 27.70 2.6 10.2 3.924H-4, 20-20 28.10 2.6 10.3 3.964H-4,70-70 28.60 2.6 9.1 3.504H-4, 130-130 29.20 2.6 9.0 3.464H-5,20-20 29.60 2.6 9.2 3.544H-5,70-70 30.10 2.6 9.2 3.544H-5, 130-130 30.70 2.6 8.9 3.424H-6, 20-20 31.10 2.6 8.5 3.274H-6,70-70 31.60 2.6 8.6 3.314H-6, 130-130 32.20 2.6 8.5 3.274H-7, 20-20 32.60 2.6 8.9 3.424H-7,60-60 33.00 2.6 9.8 3.775H-1,20-20 33.10 2.6 10.4 4.005H-1,70-70 33.60 2.6 10.5 4.045H-1, 130-130 34.20 2.6 9.9 3.815H-2, 20-20 34.60 2.6 10.8 4.155H-2,70-70 35.10 2.6 13.1 5.045H-2, 130-130 35.70 2.6 12.9 4.965H-3, 20-20 36.10 2.6 12.8 4.925H-3,70-70 36.60 2.6 12.0 4.625H-3, 130-130 37.20 2.6 10.6 4.085H-4, 20-20 37.60 2.6 10.1 3.88

Core, section, Depth Seawater Sample Formationinterval (cm) (mbsf) (ohms) (ohms) factor

5H-4,70-70 38.10 2.6 9.6 3.695H-4, 130-130 38.70 2.6 10.2 3.925H-5,20-20 39.10 2.6 9.8 3.775H-5,70-70 39.60 2.6 10.0 3.855H-5, 130-130 40.20 2.6 9.8 3.775H-6,20-20 40.60 2.6 9.6 3.695H-6, 70-70 41.10 2.6 9.7 3.735H-6, 130-130 41.70 2.6 10.3 3.966H-1,20-20 42.60 2.6 10.2 3.926H-1,70-70 43.10 2.6 9.9 3.816H-1, 130-130 43.70 2.6 9.90 3.816H-2,20-20 44.10 2.6 10.3 3.966H-2,70-70 44.60 2.6 10.0 3.856H-2, 130-130 45.20 2.6 10.0 3.856H-3,20-20 45.60 2.6 10.5 4.046H-3,70-70 46.10 2.6 10.0 3.856H-3, 130-130 46.70 2.6 10.4 4.006H-4, 20-20 47.10 2.6 10.1 3.886H-4, 70-70 47.60 2.6 10.2 3.926H-4, 130-130 48.20 2.6 10.4 4.006H-5, 20-20 48.60 2.6 11.1 4.276H-5, 70-70 49.10 2.6 10.3 3.%6H-5, 110-110 49.50 2.6 9.8 3.776H-6, 20-20 50.10 2.6 10.0 3.856H-6,70-70 50.60 2.6 9.6 3.696H-6, 130-130 51.20 2.6 9.9 3.817H-1,20-20 52.10 2.6 9.9 3.817H-1,70-70 52.60 2.6 10.4 4.007H-1, 130-130 53.20 2.6 10.2 3.927H-2,20-20 53.60 2.6 10.7 4.127H-2,70-70 54.10 2.6 10.5 4.047H-2, 130-130 54.70 2.6 9.8 3.777H-3,20-20 55.10 2.6 9.6 3.697H-3,70-70 55.60 2.6 10.0 3.857H-3, 130-130 56.20 2.6 10.5 4.047H-4,20-20 56.60 2.6 10.8 4.157H-4,70-70 57.10 2.6 10.4 4.007H-4, 130-130 57.70 2.6 10.5 4.047H-5, 20-20 58.10 2.6 10.7 4.127H-5,70-70 58.60 2.6 10.8 4.157H-5, 130-130 59.20 2.6 10.5 4.047H-6, 20-20 59.60 2.6 10.8 4.157H-6, 70-70 60.10 2.6 10.9 4.197H-6, 130-130 60.70 2.6 10.5 4.048H-1,20-20 61.60 2.6 10.0 3.858H-1,70-70 62.10 2.6 9.5 3.658H-1, 130-130 62.70 2.6 9.8 3.778H-2,20-20 63.10 2.6 9.8 3.778H-2,70-70 63.60 2.6 9.8 3.778H-2, 130-130 64.20 2.6 9.7 3.738H-3, 20-20 64.60 2.6 9.7 3.738H-3,70-70 65.10 2.6 10.5 4.048H-3, 130-130 65.70 2.6 10.3 3.968H-4, 20-20 66.10 2.6 10.4 4.008H-4,70-70 66.60 2.6 10.7 4.128H-4, 120-120 67.10 2.6 10.4 4.008H-5, 20-20 67.60 2.6 11.2 4.318H-5,70-70 68.10 2.6 10.4 4.008H-5, 120-120 68.60 2.6 10.4 4.008H-6,20-20 69.10 2.6 10.2 3.928H-6,70-70 69.60 2.6 11.2 4.318H-6, 120-120 70.10 2.6 10.7 4.129H-1,20-20 71.10 2.6 11.3 4.359H-1,70-70 71.60 2.6 10.9 4.199H-1, 120-120 72.10 2.6 10.4 4.009H-2,20-20 72.60 2.6 9.9 3.819H-2,70-70 73.10 2.6 9.8 3.779H-2, 120-120 73.60 2.6 10.1 3.889H-3,20-20 74.10 2.6 9.8 3.779H-3,70-70 74.60 2.6 9.6 3.699H-3, 120-120 75.10 2.6 10.0 3.859H-4, 20-20 75.60 2.6 10.5 4.049H-4,70-70 76.10 2.6 9.8 3.779H-4, 120-120 76.60 2.6 10.1 3.889H-5,20-20 77.10 2.6 9.9 3.819H-5,70-70 77.60 2.6 10.1 3.889H-6, 20-20 78.60 2.6 10.7 4.12

SITE 821

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

Core, section,interval (cm)

9H-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, 120-12012H-7, 20-2013H-1, 20-2013H-1, 70-7013H-1, 120-12013H-2, 20-20

Depth(mbsf)

79.1079.6080.6081.1081.6082.1082.6083.1083.6084.1084.6085.1085.6086.1086.6087.1087.6088.1088.6089.1090.1090.6091.1091.6092.1092.6093.1093.6094.1094.6095.1095.6096.1096.6097.1097.6098.1098.6099.60

100.10100.60101.10101.60102.10102.60103.10103.60104.10104.60105.10105.60106.10106.60107.10107.60108.10108.60109.10109.60110.10110.60

Seawater(ohms)

2.62.62.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.92.93.13.3.3.2.(3.3.3.3.

Sample(ohms)

10.810.011.511.211.112.212.011.911.411.611.511.911.911.810.811.311.212.712.210.69.89.6

10.010.49.9

10.111.810.811.311.611.110.811.211.610.39.69.8

10.911.111.812.310.911.010.811.713.511.611.711.311.411.310.110.79.6

10.510.59.8

11.112.211.012.1

Formationfactor

4.153.853.973.863.834.214.144.103.934.003.974.104.104.073.723.903.864.384.213.663.383.313.453.593.413.484.073.723.904.003.833.723.864.003.553.313.383.763.834.074.243.763.793.724.034.664.004.033.903.933.903.483.453.103.393.393.773.583.943.553.90

Core, section,interval (cm)

13H-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, 120-12013H-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, 120-12014H-4, 20-2014H-4, 70-7014H-4, 120-12015H-1, 20-2015H-1, 70-7015H-1, 120-12015H-2, 70-7015H-2, 120-12015H-3, 20-2015H-3, 70-7015H-3, 120-12015H-4, 20-2015H-4, 70-7015H-4, 120-12016H-1, 20-2016H-1, 70-7016H-1, 120-12016H-2, 70-7016H-2, 120-12016H-3, 20-2016H-3, 70-7016H-3, 120-12016H-4,20-2016H-4,70-7017X-1, 20-2017X-1, 70-7017X-1, 120-12017X-2, 20-2017X-2, 70-7017X-2, 120-12017X-3, 20-2017X-3, 120-12017X-4, 20-2017X-4, 120-12017X-5, 20-2017X-5, 70-7017X-5, 120-12017X-6,20-2017X-6, 70-7017X-6, 120-120

Depth(mbsf)

111.10111.60112.10112.60113.10113.60114.10114.60115.10115.60116.10116.60117.10117.60118.60119.10119.60120.10120.60121.10122.60123.10123.60124.10128.10128.60129.10130.10130.60131.10131.60132.10132.60133.10133.60137.60138.10138.60139.60140.10140.60141.10141.60142.10142.60146.10146.60147.10147.60148.10148.60149.10150.10150.60151.60152.10152.60153.10153.60154.10154.60

Seawater(ohms)

3.3.3.3.3.3.3.3.3.3.3.13.13.03.03.03.03.03.03.03.03.03.03.03.03.03.03.03.03.03.03.03.03.13.13.03.03.03.03.03.03.03.03.03.03.03.03.03.03.03.03.03.03.03.03.03.03.03.03.03.03.0

Sample(ohms)

11.611.211.114.011.712.012.211.610.610.69.7

10.011.612.310.811.210.89.4

10.39.8

10.09.6

10.210.013.112.511.911.711.111.912.112.713.512.013.011.111.912.413.015.916.114.414.917.617.515.714.013.812.816.114.311.811.513.011.412.011.811.913.013.814.8

Formationfactor

3.743.613.584.523.773.873.943.743.423.423.133.233.874.103.603.733.603.133.433.273.333.203.403.334.374.173.973.903.703.974.034.234.353.874.333.703.974.134.335.305.374.804.975.875.835.234.674.604.275.374.773.933.834.333.804.003.933.974.334.604.93

601

SITE 821

Table 10. Vane shear strength data, Hole 821 A.

ShearCore, section, Depth Spring Torque Strain strengthinterval (cm) (mbsf) Number (degrees) (degrees) (kPa)

5768679

141412101917221916212119211517101627273441394851474152104261655852465437865415252839445358704862779

2650482915552263552425384245192720

133-821A-

1H-1, 92-931H-2, 92-931H-3, 72-732H-1,92-932H-2, 92-932H-3, 92-932H-4, 92-932H-6, 89-903H-1, 89-903H-2, 89-903H-3, 90-913H-4, 90-913H-5, 90-913H-6, 90-914H-1, 90-914H-2, 90-914H-3, 90-914H-4, 90-914H-5, 90-914H-6, 90-915H-1, 81-825H-2, 90-915H-3, 90-915H-4, 90-915H-5, 90-915H-6, 90-916H-1, 91-926H-2, 91-926H-3, 91-926H-4, 91-926H-5, 91-926H-6, 91-927H-1, 91-927H-2, 91-927H-3, 91-927H-4, 91-927H-5, 92-937H-6, 92-938H-1, 91-928H-2, 91-928H-3, 91-928H-4, 91-928H-5, 91-928H-6, 91-929H-1, 91-929H-2, 91-929H-3, 91-929H-4, 91-929H-5, 91-929H-6, 91-92

10H-1, 91-9210H-2, 91-9210H-3, 91-9210H-4, 91-9210H-5, 91-9210H-6, 91-9211H-1, 88-8911H-2, 88-8911H-3, 88-8911H-4, 88-8911H-5, 88-8911H-6, 88-8912H-1, 94-9512H-2, 94-9512H-3, 94-9512H-4, 93-9412H-5, 93-9412H-6, 96-9713H-1, 96-9713H-2, 96-9713H-4, 96-9713H-5, 96-9713H-6, 96-9714H-1, 96-97

0.922.423.725.326.828.329.82

12.7914.7916.2917.8019.3020.8022.3024.3025.8027.3028.8030.3031.8033.7135.3036.8038.3039.8041.3043.3144.8146.3147.8149.3150.8152.8154.3155.8157.3158.8260.3262.3163.8165.3166.8168.3169.8171.8173.3174.8176.3177.8179.3181.3182.8184.3185.8187.3188.8190.7892.2893.7895.2896.7898.28

100.34101.84103.34104.83106.33107.86109.86111.36114.36115.86117.36119.36

44444444444444444444444444444444444444444444444444444444444444444444444444

51012129

12111212121620171619182015151417232615142117181621131217161122171616161316211715111719151515181517131312101818189

161316161516161613151018

5.98.37.19.57.18.3

10.716.716.714.311.922.620.226.222.619.025.025.022.625.017.820.211.919.032.132.140.448.846.457.160.755.948.861.811.950.072.577.369.061.854.764.244.0

102.364.217.829.733.346.452.363.069.083.357.173.791.610.730.959.557.134.517.865.426.274.965.428.529.745.250.053.522.632.123.8

602

SITE 821

Figure 27. Comparison of porosity-sensitive logs (resistivity, velocity, and bulk density) to logs sensitive to clay-mineral content (SGR gammaray and potassium). Calipers shown are from the mechanical caliper device (solid line) and sonic caliper (dashed line); both are less reliable thanthe calipers of Figure 28.

603

SITE 821

0.

R

5

<•s1

<

ΛV

S\V

<

—;r

— E1

3ilc

• 1

- •

m m

•c-Mi •

1 f

• m

- I

esistivity (oh

TIJI L

M-PHD-PH

l

t

j * >

\\

< '

•i

"%

IF

>

•A

m m)

5.0

Depth

(mbsf)

100

150

200

250

300

350

Velocity(km/s)

1.5 3.0

it

>

• =—-r

*

Λ

>r5

•M•

— ^

•a

> -

Density(g/cm 3)

1.5 2.5

••H B

—

r

•M•

β

•

1

si

i

<

<<

m

J *

<

>

ito

•

>

.j

fr

<

i

}

%

S

)

i

f

Caliper(in.)

10 2

<-

~J

I's

I

{<^\

• >

• • —i

/

i

b

i

JJf

JjJ

j i

)

>

t

11-

>

0

Figure 28. Porosity-sensitive logs obtained by the seismic stratigraphic tool string at Hole 821A. The calipers shown are from the FMS. Densitylows are probably artifacts caused by poor pad contact in washed-out intervals.

604

SITE 821

Figure 29. Site 821 logs of FF (from the ratio of formation resistivity to fluid resistivity), porosity (from the density log), the Archie componentm relating FF to porosity, and the parameter "Thin R," which responds to thin-bed effects.

605

SITE 821

Figure 30. Velocity and resistivity logs for Hole 821A, plotted as ratios to each other and to water to highlight changes in pore geometry.

606

SITE 821

Velocity(km/s)

1.5 2.5

I3 v_

\\mM

«•

%

£IP

>

—•sM••i

I

~ ^ i

1

—«•

I i -

E

S rr

— = •

*: •

">

P

— • -

•HPM

^ - ,

—―̂

Jppt

Depth(mbsf)

50

100

150

200

250

300

350

0

\

Λ\\

\

Integrated traveltime(ms)

\

\

\

\

\\

\\

\

\

\

\

\

\

\

\

400

\

\

\

\

\

Figure 31. Velocity log, and the integrated two-way traveltime function that it implies, for matching of core-based information from Site 821with the seismic sections across the site.

607

SITE 821

10

30

cp

50

70

— Seafloor

Pipe down —100 m b s f -

r— Pipe up

200 mbsf - J

300 mbsf —\

400 mbsf —'

18 22 26Temperature (°C)

30

Figure 32. Temperature log as a function of pressure (or depth) forSite 821.

Depth(mbsf)

100

150

200

250

300

350

Azimuth (degrees)

90 180 270

Deviation (degrees)

0 1 2

Figure 33. Hole deviation and its azimuth at Hole 821 A.

608

SITE 821

10

11

12

13

14

15

16

17

Hole 821 A: Resistivity-Sonic-Natural Gamma Ray Log Summary

SPECTRAL GAMMA RAY RESISTIVITY

*8

0

0

TOTALAPI units

COMPUTEDAPI units

100

100

0.5

0.5

FOCUSEDohm m

SHALLOWohm m

5

5

URANIUM10 ppm

I ___THORIUM Il~ö ppm 15~|

10CALIPER

in. 20 0.5

DEEPohm m 5 200

TRANSIT TIMEµs/ft 100 -2

POTASSIUMppm 2

250-

3 0 0 -

3 5 0 -

- 1 0 0

-150

609

SITE 821

Hole 821 A: Resistivity-Sonic-Natural Gamma Ray Log Summary (continued)

SPECTRAL GAMMA RAY RESISTIVITY

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

II> - - I πrOC LU oLU CD X

O fiLU LU SS

er o er

0

0

10

TOTAL

API units

COMPUTED

API units

CALIPER

In.

100

100

20

0.5

0.5

0.5

FOCUSED

ohm m

SHALLOW

ohm m

DEEP

ohm m

5

5

5

TRANSIT TIME

200 µs/ft 100

URANIUM

10 ppm 0

THORIUM

" ö " ""fiprn""' ~~iY

POTASSIUM-2 ppm 2

II0- <

üJW

400 -

4 5 0 -

500-

550-

^= -

-200

-250

-300

610

SITE 821

Hole 821 A: Resistivity-Sonic-Natural Gamma Ray Log Summary (continued)

i = EL!

er

550-

SPECTRAL GAMMA RAY

TOTALAPI units

COMPUTED"~APfünis"

100

RESISTIVITY

FOCUSED0.5

100 0.5

ohm m

SHALLOWohm m

CALIPER10 in.

DEEP20 0.5 ohm m

URANIUM10 ppm

I THORIUM I 3l~ö ppm 15~] m

TRANSIT TIME POTASSIUM5 200 µs/tt 100 -2 ppm 2 α $

11IIα. <LU LU

36

37

38

39

40

41

42

43

600 —

\ „

f

- 3 5 0

- 4 0 0

611

SITE 821

Hole 821 A: Density-Natural Gamma Ray Log Summary

SPECTRAL GAMMA RAY

TOTAL

0

0

20

API units

COMPUTED

API units

CALIPERin.

100

100

10BULK DENSITY

1.5 g/cm 3I

2.5DENSITY CORRECTION-0.1 g/cm a o.15 0

•

PHOTOELECTRICEFFECTbarns/e" 7

I!CD Q

10

11

12

13

14

15

16

17

2 5 0 -

300—

3 5 0 -

- 5 0

- 1 0 0

-150

612

SITE 821

Hole 821 A: Density-Natural Gamma Ray Log Summary (continued)

SPECTRAL GAMMA RAY

TOTAL

API units 100

óc UJLU o

« 8 t8 £ 8

18

0

20

COMPUTED

API units

CALIPERIn.

100'

10 1.5BULK DENSITY

g/cm 3 TsiDENSITY CORRECTION

-0.1 g/cm 3 0.15 0

PHOTOELECTRICEFFECTbarns/e* 7

SR

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

4 0 0 -

450 —

500—

550-

- 2 0 0

- 2 5 0

- 3 0 0

613

SITE 821

Hole 821 A: Density-Natural Gamma Ray Log Summary (continued)

SPECTRAL GAMMA RAY

TOTAL

API units 100

COMPUTED

10 API units ioo|LUer8

ooLU

er

)— LL

LU yo er 20

CALIPERin. 10 1.5

BULK DENSITYg/cm 3 2.5

DENSITY CORRECTION-0.1 g/cm 3 0.15 0

PHOTOELECTRICEFFECTbarns/e - 7

£80. <LU LUQ (O

550-

600 —

- 3 5 0

- 4 0 0

614