Collot, J.-Y., Greene, H. G., Stokking, L. B., et al., 1992Proceedings of the Ocean Drilling Program, Initial Reports, Vol. 134

6. EXPLANATORY NOTES1

Shipboard Scientific Party2

In this chapter, we have assembled information that willhelp the reader understand the basis for our preliminaryconclusions and also help the interested investigator selectsamples for further analysis. This information concerns onlyshipboard operations and analyses described in the site re-ports in the Initial Reports volume of the Leg 134 Proceedingsof the Ocean Drilling Program. Methods used by variousinvestigators for shore-based analysis of Leg 134 data will bedetailed in the individual scientific contributions published inthe Scientific Results volume.

AUTHORSHIP OF SITE CHAPTERSThe separate sections of the site chapters were written by

the following shipboard scientists (authors are listed in alpha-betical order, no seniority is necessarily implied):

Site Summary (Collot, Greene)Background and Objectives (Collot, Greene)Seismic Stratigraphy (Fisher)Operations (Foss, Stokking)Lithostratigraphy (Goud, Quinn, Reid, Riedel, Taylor)Biostratigraphy (Akimoto, Martinez-Rodriguez, Perembo,

Riedel, Staerker)Structural Geology (Meschede, Pelletier)Paleomagnetism (Roperch, Stokking, Zhao)Sediment and Fluid Geochemistry (Martin)Igneous Petrology (Baker, Briqueu, Coltorti, Hasenaka)Igneous Geochemistry (Baker, Briqueu, Coltorti, Hasenaka)Physical Properties (Ask, Leonard)Downhole Measurements (Chabernaud, Hobart, Kram-

mer, Menger)Summary and Conclusions (Collot, Greene)Core Descriptions (Shipboard Scientific Party)Following the final site chapter are summary core descrip-

tions ("barrel sheets" and igneous rock visual core descrip-tions) and photographs of each core.

SURVEY AND DRILLING DATAGeophysical survey data collected during Leg 134 fall into

two categories: (1) magnetic and bathymetric data acquiredduring transits from Australia to Vanuatu and from Vanuatu toFiji, and (2) data collected between sites. These data arediscussed in the "Underway Geophysics" chapter (this vol-ume), along with a brief description of all geophysical instru-mentation and acquisition systems used, and a summarylisting of Leg 134 navigation. The survey data used for finalsite selection, including both data collected during site sur-veys prior to Leg 134 and on short site location surveys duringLeg 134, are presented in the "Seismic Stratigraphy" sectionof the individual site chapters in this volume. During the Leg134 JOIDES Resolution surveys, single-channel seismic, 3.5-

1 Collot, J.-Y., Greene, H. G., Stokking, L. B., et al., 1992. Proc. ODP,Init. Repts., 134: College Station, TX (Ocean Drilling Program).

Shipboard Scientific Party is as given in the list of participants precedingthe contents.

and 12-kHz echo sounder, and magnetic data were recordedacross the planned drilling sites to aid site confirmation priorto dropping the beacon.

The single-channel seismic profiling system used two 80-in.3 water guns as the energy source and a Teledyne streamerwith a 100-m-long active section. These data were recordeddigitally on tape using a Masscomp 561 super minicomputer,and were also displayed in real time in analog format on twoRaytheon recorders using a variety of filter settings (common-ly 30-140 Hz) and two different scales (commonly 1- and 2-ssweeps and 50 traces/in.).

Bathy metric data collected using the 3.5- and 12-kHzprecision depth recorder (PDR) system were displayed on twoRaytheon recorders. The depths were calculated on the basisof an assumed 1463 m/s sound velocity in water. The waterdepth (in meters) at each site was corrected for (1) thevariation in sound velocity with depth using Matthews' (1939)tables, and (2) the depth of the transducer pod (6.8 m) belowsea level. In addition, depths that refer to the drilling-platformlevel are corrected for the height of the rig floor above thewater line, which gradually increased from 10.89 to 11.41throughout the cruise (see Fig. 1).

Magnetic data were collected using a Geometries 801proton precession magnetometer and were then displayed ona strip chart recorder and recorded on magnetic tape for laterprocessing.

Drilling CharacteristicsBecause water circulation downhole is open, cuttings are

lost onto the seafloor and cannot be examined. Informationconcerning sedimentary stratification in uncored or unrecov-ered intervals may be inferred from seismic data, wireline-logging results, and from an examination of the behavior of thedrill string as observed and recorded on the drilling platform.Typically, the harder a layer, the slower and more difficult it isto penetrate. A number of other factors may determine therate of penetration, so it is not always possible to relate thedrilling time directly to the hardness of the layers. Bit weightand revolutions per minute, recorded on the drilling recorder,also influence the penetration rate.

Drilling DeformationWhen cores are split, many show signs of significant sediment

disturbance, including the concave-downward appearance oforiginally horizontal bands, haphazard mixing of lumps of differ-ent lithologies (mainly at the tops of cores), and the near-fluidstate of some sediments recovered from tens to hundreds ofmeters below the seafloor. Core deformation probably occursduring cutting, retrieval (with accompanying changes in pressureand temperature), and core handling on deck.

SHIPBOARD SCIENTIFIC PROCEDURES

Numbering of Sites, Holes, Cores, and SamplesDrilling sites are numbered consecutively from the first site

drilled by the Glomar Challenger in 1968. A site number refers

65

SHIPBOARD SCIENTIFIC PARTY

Seafloor

Sub-bottom top

DRILLED(BUT NOT

CORED AREA)

Sub-bottom bottom -

Y/\ Represents recovered material

BOTTOM FELT: distance from rig floor to seafloor

TOTAL DEPTH: distance from rig floor to bottom of hole(sub-bottom bottom)

PENETRATION: distance from seafloor to bottom of hole(sub-bottom bottom)

NUMBER OF CORES: total of all cores recorded, includingcores with no recovery

TOTAL LENGTHOF CORED SECTION: distance from sub-bottom top to

sub-bottom bottom minus drilled(but not cored) areas in between

TOTAL CORE RECOVERED: total from adding a, b, c, and d indiagram

CORE RECOVERY (%): equals TOTAL CORE RECOVEREDdivided by TOTAL LENGTH OF COREDSECTION times 100

Figure 1. Diagram illustrating terms used in the discussion of coringoperations and core recovery.

to one or more holes drilled while the ship was positionedover one acoustic beacon. Multiple holes may be drilled at asingle site by pulling the drill pipe above the seafloor (out ofthe hole), moving the ship some distance from the previoushole, and then drilling another hole. In some cases, the shipmay return to a previously occupied site to drill additionalholes.

For all ODP drill sites, a letter suffix distinguishes eachhole drilled at the same site. For example, the first hole drilledis assigned the site number modified by the suffix A, thesecond hole takes the site number and suffix B, and so forth.Note that this procedure differs slightly from that used byDSDP (Sites 1 through 624), but prevents ambiguity betweensite- and hole-number designations. It is important to distin-guish among holes drilled at a site, because recovered sedi-ments or rocks from different holes usually do not come fromequivalent positions in the stratigraphic column.

The cored interval is measured in meters below seafloor(mbsf); sub-bottom depths are determined by subtracting thedrill-pipe measurement (DPM) water depth (the length of pipefrom the rig floor to the seafloor) from the total DPM (from therig floor to the bottom of the hole; see Fig. 1). Note thatalthough the echo-sounding data (from the precision depthrecorders) are used to locate the site, they are not used as abasis for any further measurements.

The depth interval assigned to an individual core beginswith the depth below the seafloor that the coring operationbegan and extends to the depth that the coring operationended for that core (see Fig. 1). For rotary coring (RCB andXCB), each coring interval is equal to the length of the joint ofdrill pipe added for that interval (though a shorter core may beattempted in special instances). The drill pipe in use variesfrom about 9.4 to 9.8 m. The pipe is measured as it is added tothe drill string and the cored interval is recorded as the lengthof the pipe joint to the nearest 0.1 m. For hydraulic pistoncoring (APC) operations, the drill string is advanced 9.5 m, themaximum length of the piston stroke.

Coring intervals may be shorter and may not necessarily beadjacent if separated by drilled intervals. In soft sediments,the drill string can be "washed ahead" with the core barrel inplace, without recovering sediments. This is achieved bypumping water down the pipe at high pressure to wash thesediment out of the way of the bit and up the annulus betweenthe drill pipe and the wall of the hole. If thin, hard, rock layersare present, it is possible to get "spotty" sampling of theseresistant layers within the washed interval and thus to have acored interval greater than 9.5 m. In drilling hard rock, acenter bit may replace the core barrel if it is necessary to drillwithout core recovery.

Cores taken from a hole are numbered serially from the topof the hole downward. Core numbers and their associatedcored intervals in meters below seafloor usually are unique ina given hole; however, this may not be true if an interval mustbe cored twice, because of caving of cuttings or other holeproblems. Maximum full recovery for a single core is 9.5 m ofrock or sediment contained in a plastic liner (6.6 cm internaldiameter) plus about 0.2 m (without a plastic liner) in the corecatcher (Fig. 2). The core catcher is a device at the bottom ofthe core barrel that prevents the core from sliding out whenthe barrel is being retrieved from the hole. For sediments, thecore-catcher sample is extruded into a short piece of plasticliner and is treated as a separate section below the last coresection. For hard rocks, material recovered in the corecatcher is included at the bottom of the last section. In certainsituations (e.g., when coring gas-charged sediments whichexpand while being brought on deck) recovery may exceed the9.5-m maximum.

66

EXPLANATORY NOTES

Fullrecovery

Sectionnumber

1

•Top

Partialrecovery

Partialrecoverywith void

Sectionnumber

7~cc"

Core-catchersample

Emptyliner

Top

Sectionnumber

1

2

3

4

~cc~

Voi

d

77:

If

£

T

Top

Core-catchersample

Core-catchersample

Figure 2. Diagram showing procedure used in cutting and labelingcore sections.

A recovered core is divided into 1.5 -m sections that arenumbered serially from the top (Fig. 2). When full recovery isobtained, the sections are numbered from 1 through 7, withthe last section possibly being shorter than 1.5 m (rarely, anunusually long core may require more than 7 sections). Whenless than full recovery is obtained, there will be as manysections as needed to accommodate the length of the corerecovered; for example, 4 m of core would be divided into two1.5-m sections and one 1-m section. If cores are fragmented(recovery less than 100%), sections are numbered serially andintervening sections are noted as void, whether shipboardscientists believe that the fragments were contiguous in-situ ornot. In rare cases a section less than 1.5 m may be cut in orderto preserve features of interest (e.g., lithological contacts).

By convention, material recovered from the core catcher isplaced below the last section when the core is described, andlabeled core catcher (CC); in sedimentary cores, it is treatedas a separate section. The core catcher is placed at the top ofthe cored interval in cases where material is only recovered inthe core catcher. However, information supplied by thedrillers or by other sources may allow for more preciseinterpretation as to the correct position of core-catcher mate-rial within an incompletely recovered cored interval.

Igneous rock cores are also cut into 1.5-m sections that arenumbered serially; individual pieces of rock are then eachassigned a number. Fragments of a single piece are assigned asingle number and individual fragments are identified alpha-betically. The core-catcher sample is placed at the bottom ofthe last section and is treated as part of the last section ratherthan separately. Scientists completing visual core descriptionsdescribe each lithologic unit, noting core and section bound-aries only as physical reference points.

When, as is usually the case, the recovered core is shorterthan the cored interval, the top of the core is equated with thetop of the cored interval by convention in order to achieve

consistency in handling analytical data derived from the cores.Samples removed from the cores are designated by distancemeasured in centimeters from the top of the section to the topand bottom of each sample removed from that section. Incurated hard-rock sections, sturdy plastic spacers are placedbetween pieces that did not fit together in order to protectthem from damage in transit and in storage; therefore, thecentimeter interval noted for a hard-rock sample has no directrelationship to that sample's depth within the cored interval,but is only a physical reference to the location of the samplewithin the curated core.

A full identification number for a sample consists of thefollowing information: leg, site, hole, core number, core type,section number, piece number (for hard rock), and interval incentimeters measured from the top of section. For example, asample identification of "134-827A-5H-1, 10-12 cm" wouldbe interpreted as representing a sample removed from theinterval between 10 and 12 cm below the top of Section 1,Core 5 (H designates that this core was taken during hydraulicpiston coring) of Hole 827A during Leg 134.

All ODP core and sample identifiers indicate core type. Thefollowing abbreviations are used: R = rotary core barrel(RCB); H = hydraulic piston core (HPC; also referred to asAPC, or advanced hydraulic piston core); P = pressure coresampler; X = extended core barrel (XCB); B = drill-bitrecovery; C = center-bit recovery; I =in-situ water sample; S= sidewall sample; W = wash-core recovery; and M =miscellaneous material. APC, XCB, RCB, and W cores werecut on Leg 134.

Core Handling

SedimentsAs soon as a core is retrieved on deck, a sample is taken

from the core catcher and given to the paleontological labo-ratory for an initial age assessment. The core is then placed onthe long horizontal rack, and gas samples may be taken bypiercing the core liner and withdrawing gas into a vacuumtube. Voids within the core are sought as sites for gassampling. Some of the gas samples are stored for shore-basedstudy, but others are analyzed immediately as part of theshipboard safety and pollution-prevention program. Next, thecore is marked into section lengths, each section is labeled,and the core is cut into sections. Interstitial water (IW) andorganic geochemistry (OG) samples are then taken. (Thepractice of taking OG samples was discontinued during Leg134; the sections taken will be returned to the cores.) Inaddition, some headspace gas samples are scraped from theends of cut sections on the catwalk and sealed in glass vials forlight hydrocarbon analysis. Each section is then sealed at thetop and bottom by gluing on color-coded plastic caps—blue toidentify the top of a section and clear for the bottom. A yellowcap is placed on the section ends from which a whole-roundsample has been removed and the sample code (e.g., IW) iswritten on the yellow cap. The caps are usually attached to theliner by coating the end liner and the inside rim of the cap withacetone, and then the caps are taped to the liners.

The cores then are carried into the laboratory, where thesections are again labeled using an engraver to permanentlymark the full designation of the section. The length of the corein each section and the core-catcher sample are measured tothe nearest centimeter; this information is logged into theshipboard CORELOG database program.

Whole-round sections from APC and XCB cores are nor-mally run through the multisensor track (MST). The MSTincludes the gamma-ray attenuation porosity evaluator(GRAPE) and compressional wave (P-wave) logger devices,

67

SHIPBOARD SCIENTIFIC PARTY

which measure bulk density, porosity, and sonic velocity, andalso includes a meter that determines the volume magneticsusceptibility. At this point, whole-round samples for physicalproperties (PP) and structural analysis are taken. In well-lithified sedimentary cores, the core liner is split and the tophalf removed so that the whole-round core can be observedbefore choosing the samples. Relatively soft sedimentarycores are equilibrated to room temperature (approximately 3hr) and thermal conductivity measurements are performed onthem.

Cores of soft material are split lengthwise into working andarchive halves. The softer cores are split with a wire or saw,depending on the degree of induration. Harder cores are splitwith a band saw or diamond saw. The wire-cut cores are splitfrom the bottom to top, so investigators should be aware thatolder material could have been transported up the core on thesplit face of each section.

The working half of the core is sampled for both shipboardand shore-based laboratory studies. Each extracted sample islogged into the sampling computer database program by thelocation and the name of the investigator receiving the sample.Records of all removed samples are kept by the curator atODP. The extracted samples are sealed in plastic vials or bagsand labeled. Samples are routinely taken for shipboard phys-ical properties analysis. These samples are subsequently usedfor analyses of total carbonate (by coulometer) and organiccarbon (by CNS elemental analyzer) and the data are reportedin the site chapters.

The archive half is visually described. Smear slides aremade from samples taken from the archive half and aresupplemented by thin sections taken from the working half.Most archive sections are run through the cryogenic magne-tometer. The archive half is then photographed with bothblack-and-white and color film, a whole core at a time.Close-up photographs (black and white) are taken of particularfeatures for illustrations in the summary of each site, asrequested by individual scientists.

Both halves of the core are then put into labeled plastictubes, sealed, and transferred to cold-storage space aboardthe drilling vessel. At the end of the leg, the cores aretransferred from the ship in refrigerated airfreight containersto cold storage at the Gulf Coast Repository at the OceanDrilling Program, Texas A&M University, College Station,Texas.

Igneous and Metamorphic Rocks

Igneous and metamorphic rock cores are handled differ-ently from sedimentary cores. Once on deck, the core catcheris placed at the bottom of the core liner and total corerecovery is calculated by shunting the rock pieces togetherand measuring to the nearest centimeter; this information islogged into the shipboard core-log database program. Thecore is then cut into 1.5-m-long sections and transferred intothe lab.

The contents of each section are transferred into 1.5-m-long sections of split core liner, where the bottom of orientedpieces (i.e., pieces that clearly could not have rotated top tobottom about a horizontal axis in the liner) are marked with ared wax pencil. This is to ensure that orientation is not lostduring the splitting and labeling process. The core is then splitinto archive and working halves. A plastic spacer is used toseparate individual pieces and/or reconstructed groups ofpieces in the core liner. These spacers may represent asubstantial interval of no recovery. Each piece is numberedsequentially from the top of each section, beginning withnumber 1; reconstructed groups of pieces are assigned thesame number, but are lettered consecutively. Pieces are

labeled only on external surfaces. If the piece is oriented, anarrow is added to the label pointing to the top of the section.

The working half of the hard-rock core is then sampled forshipboard laboratory studies. Records of all samples are keptby the curator at ODP.

The archive half is visually described, then photographedwith both black-and-white and color film, one core at a time.Both halves of the core are then shrink-wrapped in plastic toprevent rock pieces from vibrating out of sequence duringtransit, put into labeled plastic tubes, sealed, and transferred tocold-storage space aboard the drilling vessel. As with the otherLeg 134 cores, they are housed in the Gulf Coast Repository.

SEDIMENT CORE DESCRIPTION FORMSSediment core description forms (Fig. 3), or "barrel

sheets," summarize data obtained during shipboard analysesof each sediment core. The following discussion explains theODP conventions used in compiling the core descriptionforms and the exceptions to these procedures adopted by Leg134 scientists. Barrel sheets for each core are included in theback of this volume.

Core DesignationCores are designated using leg, site, hole, core number,

and core type as previously discussed (see "Numbering ofSites, Holes, Cores, and Samples" section, this chapter). Inaddition, the cored interval is specified in terms of metersbelow seafloor (mbsf). On Leg 134, these depths were basedon the drill-pipe measurements, as reported by the SEDCOcoring technician and the ODP Operations Superintendent.

Paleontological DataMicrofossil abundance, preservation, and zone assign-

ment, as determined by the shipboard paleontologists, appearon the core description form under the heading "Biostrat.Zone/Fossil Character." The chronostratigraphic unit, basedon paleontological results, is shown in the "Time-Rock Unit"column. The zonations and terms used in reporting fossilabundance and preservation are discussed in the "Biostratig-raphy" section of this chapter.

Paleomagnetic, Physical Properties, and Chemical DataColumns are provided on the core description form to

record paleomagnetic results (normal and reversed polarityintervals), physical properties values (wet-bulk density, graindensity, porosity, water content, and compressional velocity),and chemical data (percentages of total carbonate determinedfrom coulometer analyses and of organic carbon by gaschromatography). Additional information on shipboard proce-dures for collecting these data appears in the "Paleomag-netism," "Physical Properties," and "Inorganic Geochemis-try" sections of this chapter.

Graphic Lithology ColumnThe lithological classification scheme of Mazzullo et al.

(1987) was used in a slightly modified form on Leg 134. Theclassification adopted is outlined in the "Sedimentology"section of this chapter. The only significant modifications arethe division of volcaniclastic sediment into two types, pyro-clastic and epiclastic, and the division of fine pyroclasticsediment into "fine ash" and "coarse ash." Sediment typereflecting the classification system is graphically representedon the core description forms using the symbols illustrated inFigure 4. "Fine ash" and "coarse ash" are represented bydifferent symbols, but no new symbol is introduced for themodification made in the epiclastic sediment classification.Instead, the symbolic designation for epiclastic sediments on

68

EXPLANATORY NOTES

SITE HOLE CORE CORED INTERVAL

H

E-R

OC

K

2

PREG =M =p =

BIOSTRAT. ZONE/

FOSSIL CHARACTERco

MIN

IFE

R

<DC

oLL

CO

OF

OS

SII

zz<z

CO

)LA

RIA

N

D<CC

CO

o1—<Q

ESERVATION:GoodModeratePoor

ABUNDANCE:A =C =F =R =Tr =X =

AbundantCommonFrequentRareTrace

Very rare

CO

DM

AG

NE

LU

<

!3I

cc

. P

RO

PE

co>Q_

cm/s

]

^ -

|

Φ

10OCOCOΦQ.

Eoo

Ĵ•σ

cc

-§•2_-

ite

nt

oo

1>II

i> N

rosi

t

oQ.II

- θ -

Eio/E

sit\

cΦT3

ain

σ>II

0.

oσ,

ityjl

kd

jw

et-

bi

n

IIST

RY

LUX

ü

gczo-9cσof i

CO

σ>o

>tal

üO

Φ

ra

1cπoIICO

oüccü

ON

I—üUJco

1

2

3

4

5

6

7

CC

coLUHLU

0.51

1.01

-

_-

--

-

-

z-_:

—__----:

-_----

—

-

--_~-

—--~-

-

1 1 1

1

GRAPHICLITHOLOGY

σ>

CO

mbo

CO

σ>oo

:lit

h

§"σ>o

key

ΦΦ

CO

CDQ;

ING

DIS

"

ii

EQ

coLUCC—1

5T

RU

CT

I

DLUco

σ>

CO

o.αECO

o><Φ

See

LE

S

<co

PP

OG

IW

#

LITHOLOGIC DESCRIPTION

^ — Physical properties whole-round sample

"^—Organic geochemistry sample

Smear-slide and thin-section summary (%):Section, depth (cm)M = minor lithologyD = dominant lithology

" ^ — Interstitial water sample

*

SHIPBOARD SCIENTIFIC PARTY

PELAGIC SEDIMENTSCalcareous

Nanno-foram orNannofossil Ooze Foraminiferal Ooze foram-nanno ooze

SILICICLASTIC SEDIMENTS

Clay/claystone

mmSand/silt/clay

i

• i

• i

• i

• i

-•

-•

-i-

i•

i i•

• i

i i

• i

• i

• i

i • i

• i

• i

• i

i

• i

• i

i • i

-i

-•

-i

-•

•

Silt/siltstone

Calcareous ooze Nannofossil chalk Foraminiferal chalk Sand/sandstone Silty sand/sandy silt Silty clay/clayey silt

a a a a a a ai a a a a a a ia a a a a a ai a a a a a a ca a a a a a ai a a a a a a ta a a a a a al a a a u a a i

• • • • • i i

• • i i i •

Nanno-foram or

foram-nanno chalk

|' 1 ' | ' |' | ' j ' |1 1 1 1 1 11 1 • 1 • 1 '4-1.4 ' 1 -1 ' 1 ' 1 ' 1 ' 1 ' 1 ' 1It 1 1 1 1

i ' i! i! i! i! i!fc

Calcareous chalk

9-D-O-D-D-O-DH

Limestone

Sandy clay/

clayey sand Gravel Conglomerate

NERITIC SEDIMENTSBoundstone Grainstone Packstone

B

B

B—TB—HJ—t«— m — E E — I D -MI—OD—rXr—TJE—m—no—m—si—rxi—m—rx—m—m—m—

3 CB Θ aΘ no Θ

3 DE r=i rxΘ tn Θ

3 [XJ ( 3 EXr=i rwi r=i

Breccia

itWackestone Mudstone Floatstone Rudstone

r LQJ \=i ππB BΣ B

3 El Q B2B El B

3 OS B BS= i πm r =

LXI 1X1 LXJ LKDE rxi rxi

I 1 31 Im m m

an [xi si ex

HI—an—[3—SΣ D LÜJ LSJ Grm rm πnQ rfl] DH G

rm rm rm0 US E ] Grm rm ππ

VOLCANICLASTIC SEDIMENTS

Volcanic ash/tuff Coarse ash/tuff Volcanic lapilli Volcanic breccia

*////* =11//* *

* ^ / / *// ="=/ / = H ^ I I ^ ^ W *

A ^A ^A A4 A * ^ ^ k» 4 4 ft '•H>•> »**. » * < * * . < i ^ ^ i i

»>•» *»>. Λ * > * *

> v v> V ^ ^ v

7 < 4 t V

Drilling disturbance symbols

Soft sediments

Slightly disturbed

Moderately disturbed

Highly disturbed

Soupy

Hard sediments

Slightly fractured

Moderately fractured

Highly fragmented

Drilling breccia

>

>

X×X

Sedimentary structures

F

C

-rrt

\ \

Δv

X

77

00

l< l

Interval over which primary sedimentarystructures occur

Fining-upward sequence

Coarsening-upward sequence

Reduction of particle abundance

Planar laminae

Cross-laminae (including climbing ripples)

Wavy laminae/beds

Wedge-planar laminae/beds

Cross-bedding

Graded interval (normal)

Graded interval (reversed)

Graded bedding (normal)

Graded bedding (reversed)

Scoured contact with graded beds

Flaser bedding

Lenticular bedding

Convoluted and contorted bedding

Current ripples

Sharp contact

Gradational contact

Scoured, sharp contact

Cross-stratification

Slump blocks or slump folds

Contorted Slump

Mud/desiccation cracks

Scour

Imbrication

Clastic dike

Water-escape pipes

Veins

O

-AH

-II-X

8

6aò

EXPLANATORY NOTES

Load casts

Isolated mud clasts

Isolated pebblescobles/dropstones

Ash or pumice pods

Ash layer

Micro fault (normal)

Micro fault (thrust)

Macro fault

Fracture

Mineral-filled fracture

Injection

Probable compactionfracture

Tension gashes

Concretions/nodules

Vugs

Bioturbation, minor(60% surface area)

Discrete Zoophycostrace fossilFossils, general(megafossils)

Shells (complete)

Shell fragments

Wood fragments

Cylindrichnus tracefossil

Sagarites

Figure 5. Symbols used for drilling disturbance and sedimentary structures on core description form shown in Figure 3.

71

SHIPBOARD SCIENTIFIC PARTY

Sedimentary Structures

Observed sedimentary structures, including fining-upwardand coarsening-upward sequences are indicated in the "Sed-imentary Structure" column of the core description forms. Akey to symbols used on Leg 134 is given in Figure 5. Originalsedimentary structures may have been destroyed in cores thathave been severely disturbed by drilling.

Samples

The position of samples taken from each core for analysisis indicated by symbols in the "Samples" column in the coredescription form, as follows:

" * " = smear-slide samples;" # " = location of thin sections, except igneous rock

clasts;" T S " = thin sections of igneous rock clasts;"IW" = whole-round interstitial water geochemistry

samples;" O G " = frozen whole-round samples for organic geo-

chemistry. (This process was discontinuedduring Leg 134, as directed by ODP, aftersome OG samples had been removed from thecores. They did not appear in photos, but willbe replaced in the cores.)

" P P " = whole-round physical properties samples;" L E O " = whole-round personal samples (taken by J. N.

Leonard).

Sample position for routine physical properties measure-ments is indicated by a circled dot in the "Physical Proper-ties" column, accompanied by one or more of the followingsymbols:

p = wet-bulk density (g/cm3);grn = grain density (g/cm3);Φ = porosity (%);w% = water content (%);Vp = P-wave velocity (km/s);Vs = shear (S-wave) velocity.

Sample position for routine geochemical analyses of totalcarbonate is indicated in the "Chemistry" column by a dot.The value on the left side of the column indicates percentageof carbonate, and the value on the right side of the columnindicates total organic carbon (TOC).

Shipboard paleontologists generally base their age deter-minations on core-catcher samples, although additional sam-ples from other parts of the core may be examined whenrequired. The sample locations are shown in the appropriatecolumn by letter codes indicating the abundance and preser-vation of the fossils.

Lithologic Description

The lithologic description that appears on each core de-scription form consists of a brief summary of the major andminor lithologies observed in the core. Sedimentary structures,color, and composition of each lithology are described and,where appropriate, their distribution in the core is indicated.

Sediment color was were determined by comparison withthe Geological Society of America Rock Color Chart (MunsellSoil Color Chart, 1975) immediately after the cores were splitand while they were still wet, to minimize alteration due toexposure to air.

The thickness of sedimentary beds and laminae is de-scribed using the terminology of McKee and Weir (1953): very

thick bedded (>IOO cm thick), thick bedded (30-100 cmthick), medium bedded (10-30 cm thick), thin bedded (3-10cm thick), and very thin bedded (1-3 cm thick). In caseswhere there are thin or very thin beds of a minor lithology, adescription including occurrence information is included inthe text, but the beds may be too thin (

EXPLANATORY NOTES

100

Ratio of siliciclastic to volcaniclastic grains1:1

çθσ>o

1 60

40

Volcaniclasticsediments

Siliciclasticsediments

Mixed sediments

Neriticsediments

Pelagicsediments

40

60

1:1 1:1 >1:1Ratio of pelagic to neritic grains

100

Figure 6. Diagram of granular-sediment classification scheme (modi-fied from Mazzullo et al., 1987).

neritic grains with a higher proportion of neritic than pelagicgrains. Siliciclastic sediments are composed of >60% siliciclasticand volcaniclastic grains with a higher proportion of siliciclasticthan volcaniclastic grains. Volcaniclastic sediments are com-posed of >60% siliciclastic and volcaniclastic grains with ahigher proportion of volcaniclastic than siliciclastic grains.Mixed sediments are composed of 40% to 60% siliciclastic andvolcaniclastic grains, and 40% to 60% pelagic and neritic grains.

Classification of Granular Sediment

A granular sediment is classified by designating a principalname and major and minor modifiers. The principal name of agranular sediment defines its granular-sediment class; majorand minor modifiers describe the texture, composition, fabric,and/or roundness of the grains themselves (Table 1).

/. Principal Names

Each granular-sediment class has a unique set of principalnames, which are outlined below.

For pelagic sediment, the principal name describes composi-tion and degree of consolidation using the following terms:

1. Ooze: unlithified calcareous and/or siliceous pelagic sedi-ments;

2. Chalk: partially lithified pelagic sediment predominantlycomposed of calcareous pelagic grains;

3. Limestone: lithified pelagic sediment predominantlycomposed of calcareous pelagic grains;

4. Radiolarite, diatomite, and spiculite: partially lithifiedpelagic sediment predominantly composed of siliceous radio-larians, diatoms, and sponge spicules, respectively;

5. Chert: lithified pelagic sediment predominantly com-posed of siliceous pelagic grains.

For neritic sediment, the principal name describes textureand fabric using the following terms (after Dunham, 1962;

Embry and Klovan, 1971). Note that the suffix "-stone" doesnot signify lithification.

1. Boundstone: components organically bound during dep-osition;

2. Grainstone: grain-supported fabric, no mud, grains 64 mm in diameter.2. Volcanic lapilli: pyroclasts between 2 and 64 mm in

diameter; when lithified, lapillistone is used.3. Volcanic ash: pyroclasts

SHIPBOARD SCIENTIFIC PARTY

Table 1. Outline of granular-sediment classification scheme (modified from Mazzullo etal., 1987).

Sedimentclass

Pelagicsediment

Neriticsediment

Siliciclasticsediment

Volcaniclasticsediment

Mixedsediments

Majormodifiers

1. Composition ofpelagic and neriticgrains present inmajor amounts

2. Texture of clasticgrains present inmajor amounts

1. Composition ofneritic and pelagicgrains present inmajor amounts

2. Texture of clasticgrains present inmajor amounts

3. Degree of lithification

1. Composition of allgrains present inmajor amounts

2. Grain fabric(gravels only)

3. Grain shape(optional)

4. Sediment color(optional)

5. Degree of lithification(optional)

1. Composition of allgrains present inmajor amounts

2. Texture of clasticgrains present inmajor amounts

3. Degree oflithification(optional)

1. Composition ofneritic and pelagicgrains present inmajor amounts

2. Texture of clasticgrains present inmajor amounts

Principalname

1. Ooze2. Chalk3. Limestone4. Radiolarite5. Diatomite6. Spiculite7. Chert

1. Boundstone2. Grainstone3. Packstone4. Wackestone5. Mudstone6. Floatstone7. Rudstone

1. Gravel, breccia,conglomerate

2. Sand3. Silt4. Clay

Pyroclastic:1. Volcanic breccia2. Lapilli3. Coarse ash/tuff4. Fine ash/tuff

Epiclastic:1. Volcanic

conglomerate2. Ig-lithic breccia3. Volcanic sand4. Volcanic silt

1. Mixed sediments/mixed sedimentaryrock

Minormodifiers

1. Composition ofpelagic and neriticgrains present inminor amounts

2. Texture of clasticgrains present inminor amounts

1. Composition ofneritic and pelagicgrains present inminor amounts

2. Texture of clasticgrains present inminor amounts

1. Composition of allgrains present inminor amounts

2. Texture and compositionof siliciclasticgrains present asmatrix (for coarse-grained clasticsediments)

1. Composition of allvolcaniclasts presentin minor amounts

2. Composition of allneritic and pelagicgrains present inminor amounts

3. Texture of clasticgrains present in minoramounts

1. Composition ofneritic and pelagicgrains present inminor amounts

2. Texture of clasticgrains present inminor amounts

types present in major (>25%) and minor (10%-25%) propor-tions. In addition, major modifiers can be used to describedegree of lithification, grain fabric, grain shape, and sedimentcolor. The nomenclature for major and minor modifiers isoutlined below.

Composition of pelagic grains can be described with themajor and minor modifiers diatom(-aceous), radiolarian, spic-ule(-ar), siliceous, nannofossil, foraminifer(-al), and calcare-ous. The terms siliceous and calcareous are generally used todescribe sediments composed of siliceous or calcareous pe-lagic grains of uncertain origins.

Composition of neritic grains can be described with thefollowing major and minor modifiers:

1. Ooid (or oolite): spherical or elliptical nonskeletal parti-cles smaller than 2 mm in diameter, having a central nucleussurrounded by a rim with concentric or radial fabric.

2. Bioclast (or bioclastic): fragment of skeletal remains.Specific names such as molluscan or algal can also be used.

3. Pellet (or pelletal): a grain composed of micrite, gener-ally lacking significant internal structure and often ovoid inshape, usually of fecal origin.

4. Intraclast: reworked carbonate-rock fragment or rip-upclast.

5. Pisolite: spherical or ellipsoidal nonskeletal particle, com-monly >2 mm in diameter, with or without a central nucleus butdisplaying multiple concentric layers of carbonate.

6. Peloid (or peloidal): micritized carbonate particle ofunknown origin.

7. Calcareous, dolomitic, aragonitic, sideritic: these mod-ifiers should be used to describe the mineralogic compositionof neritic grains.

Texture of siliciclastic grains is described by the modifiersgravel(-ly), sand(-y), silt(-y), and clay(-ey). Composition ofsiliciclastic grains can be described in terms of mineralogy andprovenance using the following modifiers:

1. Mineralogy: using modifiers such as quartz, zeolitic,lithic (for rock fragments), or calcareous (for detrital clasts ofcalcium carbonate).

2. Provenance, or source of rock fragments (particularly ingravels, conglomerates, and breccias): using modifiers such asvolcanic, sed-lithic (contains clasts or grains of clastic rock),

74

EXPLANATORY NOTES

Table 2. Udden-Wentworth grain-size scale for siliciclastic sediments

(Wentworth, 1922).

Millimeters

1 'A

1 /ft

1 /I A

1 /T*

1.641/1281/256

40961024

8416

A

3.362.832.361 001.581.411.191 000.840.710.59

0.420.350.30n T>0.2100.1770.149n nc

0.1060.0680.074π ΠA"11;

0.0630.0440.037

0.01560.00780 00390.00200.000960.000490.000240.000120.00006

Micrometers

420350300'yen

210177149fJK

1068874E l l

834437

15.67.83 92.00.960.490.240.120.06

Phi (Φ)

-20-12-10

g

- 4i

-1.75-1.5-1.25

1 0-0.75-0.5-0.25

0 00.250.50.75i n

1.251.51.75

2.252.52.75

3.253.53.75

4.254.54.75

6.07.08 09.0

10.011.012.013.014.0

Wentworth size class

Boulder (-8 to - 1 2 0 )

Cobble (-6 to -8 0)

Pebble (-2 to - 6 0 )

Granule

Very coarse sand

Coarse sand

Medium sand

Fine sand

Very fine sand

Coarse silt

Medium silt

Fine siltVery fine silt

Clay

C

IT;

3

calcareous sed-lithic (contains clasts or grains of calcareousrock), basaltic, etc.

Volcaniclastic grain composition is described by the mod-ifiers ig-lithic (rock fragments), vitric (glass and pumice),volcanic sed-lithic (contains clasts or grains of volcaniclasticrock), and crystal (mineral crystals), or by modifiers describ-ing the composition of lithic grains and crystals (e.g., feldsparor basaltic).

Sediment fabric can be described by the major modifiersgrain-supported, matrix-supported, and imbricated. Gener-ally, fabric descriptors are applied only to gravels, conglom-erates, and breccias.

Degree of consolidation is described using the followingmajor modifiers: "unlithified" designates soft sediment that isreadily deformable under the pressure of a finger, "partiallylithified" designates firm sediment that is incompletely lithi-fied, and "lithified" designates hard, cemented sediment thatmust be cut with a saw.

Grain shapes are described by the major modifiersrounded, subrounded, subangular, and angular. Sedimentcolor is determined with the Munsell Chart, a standard color-comparator, and can be employed as a major modifier.

Mixed sediments are described using major and minormodifiers indicating composition and texture.

Figure 7. Ternary diagram showing principal names for siliciclasticsediments (from Shepard, 1954).

X-ray Diffraction (XRD) Analysis

A Philips ADP 3520 X-ray diffractometer was used for theX-ray diffraction (XRD) analysis of bulk samples. CuKαradiation with a Ni filter was used with a tube voltage 40 kVand a tube current 35 mA. Bulk samples were ground using theSpex 8000 Mixer Mill or with an agate mortar and pestle, andpressed into a sample holder. Samples were scanned from 2°to 70° (2θ) in 0.02° by 1-5 steps.

BIOSTRATIGRAPHY

Chronological FrameworkFour microfossil groups were examined for biostrati-

graphic purposes on Leg 134: calcareous nannofossils, plank-tonic foraminifers, benthic foraminifers, and radiolarians. Ageassignments are made on the basis of core-catcher samples;however, additional samples were studied when a core-catcher sample was found to be inconclusive or otherwiseunrepresentative of the core in its entirety.

The general correlation between the biostratigraphic zonesand the magnetic polarity reversal record is based on thescheme of Berggren et al. (1985a, 1985c). Sample positionsand the abundance, preservation, and age or zone for eachfossil group are recorded on barrel sheets for each core.

Calcareous Nannofossils

Sediments recovered from Leg 134 are all of Cenozoic age.The calcareous nannofossil zonations used in this study includethe schemes of Okada and Bukry (1980) and Martini (1971).

Smear slides were prepared for each sample using NorlandOptical Adhesive #61 as a mounting medium. The calcareousnannofossils were examined in smear slides by standard lightmicroscopy techniques (plane-polarized light, phase-contrast,and cross-polarized light) at a magnification of approximately1000 ×.

Calcareous nannofossils often show signs of both signifi-cant etching and overgrowth; more dissolution-resistant formsadd secondary calcite provided by dissolution-prone morpho-types. The following descriptive categories have been createdto record the various states of preservation observed:

75

SHIPBOARD SCIENTIFIC PARTY

G = good (little or no evidence of dissolution and/orsecondary overgrowth of calcite, diagnostic characteristicsfully preserved);

M = moderate (dissolution and/or secondary overgrowthpartially alter primary morphological characteristics, butnearly all specimens can be identified at the species level);

P = poor (severe dissolution, fragmentation, and/or sec-ondary overgrowth with primary features largely destroyed;many specimens cannot be identified at the species and/orgeneric level).

Abundance estimates of the nannofossils in the smearslides were made on optimum density areas of the slide, thatis, areas where most of the field was covered with samplematerial without appreciable piling of specimens or othermaterial. Smear slides were examined at a magnification of1000 × and the relative abundances of individual nannofossilspecies in a given sample were estimated using the methodproposed by Hay (1970). Six levels of abundance are recordedas follows:

H = highly abundant (101-1000 specimens per field of view);V = very abundant (11-100 specimens per field of view);A = abundant (1-10 specimens per field of view);C = common (1 specimen per 2-10 fields of view);F = few (1 specimen per 11-100 fields of view);R = rare (1 specimen per 101-1000 fields of view);

Estimates of the percentage of nannofossils present in thesediment were made from smear slides using the followingscale:

A = abundant (>50%);C = common (between 10% and 50%);F = few (between 1% and 10%);R = rare (IO specimens per field of view);C = common (1-10 specimens per field of view);F = few (1 specimen per 2-10 fields of view);R = rare (1 specimen per >IO fields of view);B = barren (no planktonic foraminifers).

The state of preservation of planktonic foraminifers isdescribed as follows:

G = good (little or no fragmentation, overgrowth, and/ordissolution);

M = moderate (some signs of fragmentation, overgrowth,and/or dissolution);

P = poor (severe fragmentation, heavy overgrowth, and/ordissolution).

Larger Benthic ForaminifersThe larger benthic foraminifers were used to determine the

ages of neritic carbonate sediments by applying the T-letterzonation scheme as proposed by Adams (1984). For identifi-cation of species, specimens were mounted at various orien-tations in lakeside cement and thin-sectioned to reveal internalstructures.

Paleoenvironmental AnalysisIn addition to biostratigraphic applications, microfossils

were used for paleobathymetric estimates. Where applicable,relative paleodepth evaluations were made using both plank-tonic and benthic foraminifers.

Smaller Benthic ForaminifersSmaller benthic foraminifers were used primarily as pa-

leoenvironmental indicators of both the paleodepth and theearly geochemical conditions at the water-sediment inter-face. Approximately 10 cm3 of sediment sample was usedfrom each core catcher. Carbonate-sand samples were dis-aggregated in boiling water with added detergent (Calgon);siltstone samples were disaggregated in a weak solution ofhydrogen peroxide and Calgon. The residues were washedon a 63 -µm sieve and dried under a heat lamp. Smallerbenthic foraminifers were examined from the >125-µmfraction. The conventions for describing abundance andpreservation of benthic foraminifers are similar to thoseapplied to planktonic foraminifers.

Paleobathymetric interpretations of smaller benthic fora-minifers were primarily based on Akimoto's (1990) depthzonations. Where applicable, additional information was ob-tained from planktonic foraminifers applying the depth zona-tion of Keller (1985). Bathymetric ranges are as follows:sublittoral (0-150 m) is divided into upper (0-30 m), middle(30-80 m), and lower (80-150 m) parts; bathyal is divided intoupper (150-500 m), middle (500-2000 m), and lower (2000-3000 m) parts; and abyssal indicates a depth >3000 m.

PALEOMAGNETISMPaleomagnetic studies performed aboard the JOIDES Res-

olution during Leg 134 included routine measurements ofnatural remanent magnetism (NRM) and of magnetic suscep-tibility of sedimentary and volcanic material. Because cores

76

EXPLANATORY NOTES

are commonly affected by secondary magnetizations, alternat-ing field (AF) demagnetizations were also performed system-atically. Where magnetic cleaning successfully isolates pri-mary component of remanence, paleomagnetic inclinationsare used to assign a magnetic polarity to the stratigraphiccolumn. With the assistance of biostratigraphic data, polarityreversal zones are correlated with the magnetic polarity timescale of Berggren et al. (1985b) (see "Biostratigraphy" sec-tion, this chapter). In addition, magnetic logging involving themeasurement of in-situ susceptibility and total magnetic fieldwas performed during Leg 134.

Remanent Magnetization Measurements

The JOIDES Resolution maintained two magnetometersfor measurement of magnetic remanence during Leg 134, aMolspin spinner magnetometer and a 2-G Enterprises (model760R) pass-through cryogenic superconducting rock magne-tometer. An AF demagnetizer (model 2G600) capable ofalternating fields up to 20 mT is on-line with the cryogenicmagnetometer. Both the cryogenic magnetometer and the AFcoils are encased in a Mu-metal shield, and an automatedsample-handling system moves the core sections through theAF coils and the magnetometer sensor region. The cryogenicmagnetometer, AF demagnetizer, and sample-drive systemare controlled by a multiserial communication board (FAST-COM 4) in an IBM PC AT-compatible computer. Measure-ments using the cryogenic magnetometer were controlled by amodified version of a University of Rhode Island BASICprogram. Prior to drilling, we conducted various calibrationexperiments to establish the accuracy of the basic measure-ment apparatus and to check the operation of the processingsoftware. In particular, we investigated the possible inversionof the orientation of axes reported during Leg 133 andmodified the software controlling the cryogenic magnetometeraccordingly.

The superconducting quantum interference device(SQUID) sensors in the cryogenic magnetometer measuremagnetization over an interval approximately 20 cm long. Thewidths of the sensor region suggest that as much as 150 cm3 ofcore contributes to the output signal. The large volume of corematerial within the sensor region allows accurate determina-tion of remanence for weakly magnetized samples despite therelatively high background noise related to the motion of theship. The cryogenic magnetometer is incapable of measuringarchive halves with magnetizations greater than 1 A/m; inten-sities of this magnitude exceed the sensing range of thecryogenic magnetometer.

The output from the cryogenic magnetometer during con-tinuous measurement assumes a uniformly magnetized coreand provides reliable directional data when an interval largerthan the sensing region is measured. Tests conducted duringLeg 131 indicate that in cases where the core is not uniformlymagnetized, either through natural processes or artifacts(voids in the core or differential rotation of segments withinthe core liner), the values of declination, inclination, andintensity should be treated with caution.

Remanence measurements of sediments and rocks wereperformed by passing continuous archive-half core sectionsthrough the cryogenic magnetometer. NRM measurementswere taken at intervals of either 5 or 10 cm along the core, andafter AF demagnetization at 5, 10, and 15 mT. The maximumAF demagnetizing field allowed by the Information HandlingPanel for archive-half sections is 15 mT or the median destruc-tive field, whichever is lower. In some cores, this field isinsufficient to remove secondary remanences and isolate theprimary component of remanence required for magneto-stratigraphy and plate history. Therefore, at least one discreteshipboard paleomagnetic sample was taken from each section

and from each representative lithology. These samples weredemagnetized using either a Schonstedt GSD-1 AF demagne-tizer capable of fields up to 100 mT or a Schonstedt thermaldemagnetizer.

Discrete samples in soft sediment were taken usingoriented standard plastic sampling boxes (7 cm3). In order toreduce the deformation of the sediment, the core was cutusing a thin stainless steel spatula before pressing the plasticsampling boxes into the sediment. Minicores were drilledfrom lithified sedimentary rocks and igneous rocks using awater-cooled nonmagnetic drill bit attached to a standarddrill press.

During AF demagnetization of the discrete samples withthe GSD-1 AF demagnetizer, we noticed that several samplesacquired spurious magnetizations above 40 mT. A few testswere made after demagnetization along each positive andnegative axis and the spurious magnetizations were shown tobe the sum of two types: an anhysteretic remanence (ARM)produced along the axis of demagnetization and a sample-dependent component of gyromagnetic origin (GRM) that wasproduced mostly orthogonal to the axis of demagnetization.The acquisition of gyromagnetic remanence during staticthree-axis AF demagnetization is often not recognized bypaleomagnetists and is often confused with ARM acquisition.Detailed descriptions on how to recognize these spuriousmagnetizations have been given by Dankers and Zijderveld(1981) and Roperch and Taylor (1987).

Perturbations Produced by Drilling

Interpretations of measurements with the pass-throughcryogenic magnetometer often are difficult because of me-chanical disturbances, such as twisting of unconsolidatedsediments during XCB or RCB coring. A persistent problem isthe pervasive overprint produced by drilling, as noted onprevious legs. Exposure to large magnetic fields on the rigfloor and contamination by rust have often been suggested assources for these spurious magnetizations. During Leg 115,Schneider and Vandamme (Shipboard Scientific Party, 1988)suggested that one particular source of remagnetization wasthe remanent field of the core barrel.

We performed several tests to establish the nature ofspurious magnetizations observed in cores recovered on Leg134. Low-coercivity sediments at all sites showed strongNRM intensities and steep negative inclinations when archivehalves were measured using the cryogenic magnetometer.Discrete samples taken from the center of the working-halfsections did not show as strong an overprint, which suggestedthat the intensity of the overprint decreased radially from theedge to the center of the core. Three discrete samples weretaken and demagnetized to test this hypothesis: one from thecenter of the core, one from the edge, and one from inbetween (Fig. 8). The primary magnetization in the sampletaken from the center was isolated by AF demagnetization at5 mT. Isolation of the primary component of remanence in thesample taken from the outer edge of the core, however,required AF demagnetization at 15 mT. This drilling-inducedoverprint may be considered a viscous remanence or may becompared to a strong-field (10-15 mT) isothermal remanentmagnetization. Cores recovered using both rotary and pistondrilling are affected by this overprint, the intensity of which isdependent upon the magnetic mineralogy of the recoveredmaterial.

Magnetic Susceptibility Measurements

Whole-core magnetic susceptibility measurements weremade on all APC and selected XCB and RCB cores using aBartington Instruments magnetic susceptibility meter (modelMSI) with an MS1/CX 80-mm whole-core sensor loop set at

77

SHIPBOARD SCIENTIFIC PARTY

Table 3. Shipboard pore-fluid analytical methods.

-YDown Down Down

Section 134-827A-9H-2,83-85 cm

(Edge)

Section 134-827A-9H-2,83-85 cm(Middle)

Section 134-827A-9H-2,83-85 cm(Center)

Figure 8. Orthogonal projections of alternating field (AF) demagneti-zation data from three specimens from Core 134-827A-9H. Opencircles correspond to projection onto the vertical plane and solidcircles are projections onto the horizontal plane. All three sampleswere demagnetized using the same AF steps.

0.47 kHz. The susceptibility meter is part of the multisensortrack (MST) which also contains a GRAPE and P-wave logger(see "Physical Properties" section, this chapter).

The general trend of the susceptibility data curve was usedto characterize the magnetic material contained within thecored sediment. The susceptibility response is a function ofthe mineralogy (on Leg 134, predominantly magnetite) as wellas the shape and volume of the magnetic particles within therocks. Because magnetic susceptibility is a temperature-de-pendent property, the cores were permitted to equilibratethermally (2-4 hr) prior to the analysis on the MST.

Downhole Magnetic MeasurementsTwo magnetic logging tools compatible with Schlumberger

and ODP requirements have been manufactured by a researchgroup from France (LETI-CEA) and the oil industry (Total-CFP). One is a susceptibility tool and the other measures thetotal field. The susceptibility tool consists of a cylinder, 60 mm indiameter and 2.7 m long, that contains the sensor (mutualinductance bridge with two main coils) and electronic circuits.The volume of rocks measured is approximately equivalent tothat of a cylinder 0.5 m in radius and 1.5 m in length. Thetotal-field instrument measures the resonance frequency of pro-tons placed in a magnetic field. The resolution of the sensor is0.01 nT.

Analysis

Salinity

Alkalinity

pH

Chlorinity

Potassium

Sodium

Calcium

Magnesium

Ammonia

Phosphate

Silica

Technique

Goldberg refractometer

Gran titration

TRIS-BIS buffers

Mohr titration

Atomic emission spectrometry

Atomic emission spectrometry/calculated

EGTA titration/atomic absorptionspectrometry

EDTA titration/atomic absorptionspectrometry

Colorimetry

Colorimetry

Colorimetry

Units

None

Millimolar (mM)

apmH

Millimolar (mM)

Millimolar (mM)

Millimolar (mM)

Millimolar (mM)

Millimolar (mM)

Micromolar (µM)

Micromolar (µM)

Micromolar (µM)

a See Gieskes and Gamo (in press).

The total measured field is the sum of the field of internalorigin from the earth's core, the external field that resultsprimarily from solar activity, and the field produced by theinduced and remanent magnetizations of the rocks measured.The induced contribution was calculated from the susceptibil-ity data. The diurnal variations of the earth's magnetic fieldwere recorded by a reference station operated on EspirituSanto Island, about 50 km from the drill sites.

The effect of variations of the external field can thereforebe determined and subtracted from downhole measurements.A qualitative interpretation of the in-situ magnetostratigraphycan be made following guidelines from theoretical investiga-tions of magnetic fields in boreholes (Pozzi et al., 1988).

SEDIMENT AND FLUID GEOCHEMISTRY

Inorganic GeochemistrySediment and pore-fluid samples were measured for a

variety of chemical components during Leg 134 in order to (1)document diagenetic processes that alter pore-fluid chemistryand (2) identify the fluids that may be flowing or may haveflowed through the sediments. Diagenesis and fluid flow aretwo important processes at convergent margins because of thecombination of high concentrations of chemically reactivesedimentary components, such as volcanic ash, and largeamounts of tectonic deformation. The types of pore-fluid mea-surements are listed in Table 3 and the sediments were measuredfor their organic and inorganic carbon contents. The inorganiccarbon contents are plotted against depth in the "Lithostratig-raphy" section of each site chapter in this volume.

Pore-Fluid ChemistryPrevious drilling (Mascle et al., 1988; Shipboard Scientific

Party, 1991) indicates that structural and lithologic boundariesmay control the hydrology at convergent margins. The resultsat Sites 827 and 828 indicate that structural features arealsoimportant in the New Hebrides Island Arc, and that onesample collected every third core (about every 30 m) would beinsufficient to observe subtle changes in the pore-fluid chem-istry. All subsequent sites were thus sampled more frequently,at a maximum density of one per every second core (about

78

EXPLANATORY NOTES

Table 4. Leg 134 sample dilutions from alkalinity measurements. Table 4 (continued).

Hole

832B

Core, section,interval (cm)

Depth(mbsf)

Sample volume(cm3)

Acid volume(cm3)

Dilution(total/sample)

827 A

827B

828A

828B

829A

829B

829C

83OA

830B

83OC

1H-4, 145-1503H-4, 145-1506H-4, 145-1509H-2, 145-15013H-2, 135-140

2R-3, 145-1505R-2, 140-15011R-1, 135-15014R-2, 0-30

1H-2, 145-1503H-3, 145-1506H-3, 145-1509H-5, 145-150

1R-3, 135-150

1R-1, 146-1503R-2, 145-1505R-5, 145-1507R-1, 145-15012R-5, 140-15014R-4, 135-15016R-4, 135-150

2H-2, 145-150

1H-2, 145-1501H-4, 145-1502H-2, 145-1503H-6, 135-140

1H-3, 145-1503H-4, 145-1505H-1, 145-150

4R-1, 100-1106R-1, 134-1508R-1, 134-15010R-2, 0-1912R-2, 0-18

12R-2, 28-53

6.025.350.970.090.8

122.1149.5205.9236.3

3.018.446.976.9

94.4

1.515.338.552.3

104.9124.1143.4

3.5

369.8

26.8

4.522.536.4

78.598.4

117.8141156.8

341.2

4.85044.85044.85044.85044.8504

4.85044.85044.85044.8504

4.85044.85044.85044.8504

4.8504

4.85044.85044.85044.85044.85044.85044.8504

4.8504

4.85044.85044.85044.8504

4.85044.85044.8504

4.85044.85044.85044.85044.8504

4.8504

831A 1H-2, 145-150

831B 5R-3, 145-150

832A

135.4

4.8504

4.8504

1.0700.9001.3461.0270.196

.2206

.1856

.2775

.2117

.0404

Not recorded0.0990.0570.106

.0204

.0118

.0219

Sample spilled0.7420.4770.194

1.440

0.3940.5470.3460.2080.8060.6850.474

0.435

0.4430.5410.3300.480

0.2820.1600.188

0.1400.1420.1660.1540.134

.1530

.0983

.0400

.2969

.0812

.1128

.0713

.0429

.1662

.1412

.0977

.0897

.0913

.1115

.0680

.0990

.0581

.0330

.0388

.0289

.0293

.0342

.0317

.0276

0.093

0.248

0.244

1.0192

1.0511

1.0503

1H-3, 145-1504H-3, 145-1506H-3, 145-1508H-2, 144-15010H-3, 143-15016H-3, 145-15019H-1, 145-15024H-2, 145-150

9R-2, 140-15015R-2, 58-6817R-1, 10-2019R-1, 140-15023R-2, 16-3128R-2, 135-15030R-4, 138-15032R-2, 135-15034R-1, 135-15037R-3, 130-15042R-2, 0-1345R-1, 130-15047R-1, 130-15049R-CC, 0-2061R-2, 130-15063R-6, 0-20

1H-3, 145-1503H-3, 145-150

4.523.042.059.577.0

117.5142.5180.7

222.9280.0300.3319.5358.2407.8428.0445.8462.9494.7540.4569.0588.3611.2723.6747.3

4.523.5

4.85044.85044.85044.85044.85044.85044.85044.8504

4.85044.85044.85044.85044.85044.85044.85044.85044.85044.85044.85044.85044.85044.85044.85044.8504

4.85044.8504

0.353.295.506.604.601.464.415.179

0.6350.1040.0980.0920.0900.1130.1080.1030.1060.1080.1080.1070.0990.0960.0750.089

0.799.094

.0728

.2670

.3105

.3307

.3301

.3018

.2917

.2431

.1309

.0214

.0202

.0190

.0186

.0233

.0223

.0212

.0219

.0223

.0223

.0221

.0204

.0198

.0155

.0183

.1647

.2255833A

every 20 m). In many lithologies, however, limited corerecovery dictated a smaller sampling density. The first sam-ples taken at each site were 5-cm lengths of the whole-roundcore, but the length of samples increased to 35 cm as thesediments became more indurated with depth. The amount offluid obtained per centimeter of core is plotted against depth in

HoleCore, section, Depth

interval (cm) (mbsf)Sample volume

(cm3)Acid volume

(cm3)Dilution

(total/sample)

833A 6H-1, 145-1508H-1, 145-15010H-4, 145-15013H-1, 145-15016H-2, 140-15021X-2, 140-15023X-2, 0-1026X-1,92-102

833B 5R-2,90-10114R-3, 140-15016R-1, 140-15018R-1, 141-15020R-1, 140-15022R-2, 0-1025R-1, 95-10527R-1, 136-15029R-1, 117-13131R-2, 135-15033R-1, 112-12546R-3, 135-15063R-2, 0-15

40.755.568.979.595.6

144.9162.8191.2

118.2207.2223.5242.3261.4280.8309.2328.9348.1369.1386.3494.5656.4

4.85044.85044.85044.85044.85044.85044.85044.8504

4.85044.85044.85044.85044.85044.85044.85044.85044.85044.85044.85044.85044.8504

0.9350.8110.7510.52440.1860.1280.1580.117

0.1090.1140.10.0930.0770.0810.0850.0830.0910.0780.0850.0720.074

.1928

.1672

.1548

.1081

.0383

.0264

.0326

.0241

.0225

.0235

.0206

.0192

.0159

.0167

.0175

.0171

.0188

.0161

.0175

.0148

.0153

the site chapters. This value is only a qualitative estimate ofthe fluid contained within the sediment because the corediameters vary depending on the coring technique and be-cause pore fluids were not extracted from those parts of thecore that were disturbed by drilling.

After the cores were brought on deck, each sample wascollected before the end caps were sealed with acetone. Thesamples were cleaned, by scraping with a stainless steelspatula, of material that appeared to be contaminated by thefluids used as drilling mud, particularly in fractures and alongthe outside edge of the sample. The whole-round sampleswere squeezed in high-pressure stainless steel presses (Man-heim and Sayles, 1974). The maximum pressure used wasabout 30,000 pounds per square inch (psi) (2.11 × 107 kg/m2)and pressure was applied until no additional fluid was ob-tained. The samples were squeezed as soon as possible afterrecovery but they generally had equilibrated to room temper-ature prior to the squeezing procedure. Because in-situ tem-peratures varied from 2° to ~50°C, the change in temperaturemay produce some artifacts (Sayles et al., 1973; Gieskes,1973, 1974), but overall trends and concentration variations inneighboring cores should not be altered. All samples werefiltered through 0.45 -µm Gelman acrodisc disposable filtersand subsequently subdivided for both shipboard work as wellas for future work in shore-based laboratories.

The procedure for each analysis (Table 3) is described byGieskes and Gamo (in press) and references therein. Thealkalinity was titrated using Baker "Ultrex" ultrapure HC1because the alkalinity samples from Legs 112 and 131 werefound to be contaminated by high concentrations of iodine inthe acid (Gieskes and Gamo, in press). Table 4 shows thevolumes of sample and acid used for each titration and thedilution caused by addition of acid to the sample. The alka-linity samples were sealed in polyethylene tubes immediatelyfollowing the titration and thus should be useful for anysubsequent chemical analysis.

Sediment ChemistryInorganic carbon contents were routinely measured in

splits of the samples that had been used for the physicalproperties studies and this value was used to calculate thepercentage by weight of CaCO3 in the samples. The measure-ments were made using a Coulometrics 5011 coulometerequipped with a System 140 carbonate carbon analyzer.Depending on carbonate content, 15 to 70 mg of ground and

79

SHIPBOARD SCIENTIFIC PARTY

weighed sediment was reacted in a 2-N HC1 solution. Theliberated CO2 was titrated in a monoethanolamine solutionwith a color indicator, whereas the change in light transmit-tance was monitored with a photo-detection cell.

Organic GeochemistryShipboard organic geochemistry was measured during Leg

134 in order to monitor volatile hydrocarbon concentrations forsafety reasons. Hydrocarbon concentrations appear to charac-terize fluids within décollement zones (Gieskes et al., 1990a,1990b) and thus the hydrocarbon concentrations were also usedas tracers for flow of deep-seated fluids. The sedimentaryorganic carbon component was measured to provide an initialcharacterization of the content of organic matter.

Elemental AnalysesTotal nitrogen, carbon, and sulfur concentrations were

measured on oven-dried samples of the sediment residuesfrom the physical properties measurements using a NA 1500Carlo Erba NCS analyzer. The bulk samples plus vanadiumpentoxide were combusted at 1000°C in an oxygen atmos-phere, converting organic and inorganic carbon into CO2 andsulfur into SO2. These gases along with nitrogen were thenseparated by gas chromatography and measured with athermal conductivity detector (TCD). The total organiccarbon (TOC) content of the sediments was calculated bysubtraction of the inorganic carbon content from the totalcarbon content. Because of the low organic carbon contentsand difficulty with the instrument, the Rock-Eval procedurewas not used.

Gas AnalysesGases were extracted from bulk sediments utilizing head-

space sampling techniques (Emeis and Kvenvolden, 1986). A~5-cm3 plug of sediment was taken as the core arrived ondeck, utilizing a No. 4 cork borer. The sample was placedimmediately in a glass vial that subsequently was sealed witha septum and metal crimp and than heated to 70°C and kept atthis temperature for 45 min.

Each gas sample was expanded into a gas-tight syringeand injected into an HP 5890A NGA gas chromatograph forflame ionization detection (FID) and TCD analyses. The gaschromatographic system employs a steel column (6 in. × 1/8in.) packed with Poropak T, a steel column (3 ft × 1/8 in.)with a 13X molecular sieve, a steel column (6 ft × 1/8 in.)packed with 80/100 mesh Hayesep R(AW), and a DB1 (1-mmfilm thickness, J&W). Appropriate automatic valve switch-ing, controlled by a HP 3392 integrator that also recordedand integrated the count rates, provided a rapid determina-tion of oxygen, nitrogen, carbon dioxide, and hydrocarbonsfrom methane to hexanes. The separation on the FID linewas carried out isothermally at 40°C at a flow rate of 2.24cm3/min. Helium was used as carrier gas. All gas concentra-tions are reported in parts per million (ppm).

IGNEOUS ROCKS

Core Curation and Shipboard SamplingIn order to preserve important features and structures,

core sections containing igneous rocks were examined prior tosplitting with a diamond saw into archive and working halves.During core handling and splitting, care was taken to ensurethat the core orientation was preserved by marking theoriginal base of individual pieces. Each piece was numberedsequentially from the top of each core section and labeled atthe top surface. Pieces that could be fitted together wereassigned the same number, but were lettered consecutively

(e.g., 1A, IB, and 1C). Plastic spacers were placed onlybetween pieces with different numbers. The presence of aspacer, therefore, may represent a substantial interval of norecovery. If it was evident that an individual piece had notrotated about a horizontal axis during drilling, an arrow wasadded to the label pointing to the top of the section. As pieceswere free to turn about a vertical axis during drilling, azi-muthal orientation of a core was not possible.

After the core was split, the working half was sampled forshipboard physical properties, magnetic studies, X-ray fluor-escence, X-ray diffraction, and thin-section studies. Nonde-structive physical properties measurements, such as magneticsusceptibility, were made on the archive half of the core.Where recovery permitted, samples were taken from eachlithologic unit. Some of these samples were minicores. Thearchive half was described on the visual core description formand was photographed before storage.

Visual Core DescriptionsVisual core description (VCD) forms were used in the

documentation of the igneous rock cores (see VCD formsfollowing the core barrel sheets in the back of this volume).The left column is a graphic representation of the archive half.A horizontal line across the entire width of the columndenotes a plastic spacer. Oriented pieces are indicated on theform by an upward-pointing arrow to the right of the piece.Shipboard samples and studies are indicated in the columnheaded "shipboard studies," using the following notation: XD= X-ray diffraction analysis; XF = X-ray fluorescence analy-sis; TS = petrographic thin section; PP = physical propertiesanalysis; and PM = paleomagnetic analysis.

To ensure consistent and complete documentation, thevisual core descriptions were entered into the computerizeddatabase HARVI. The database is organized into separatedata sets for fine-grained rocks and coarse-grained rocks.Each record is checked by the database program for consist-ency and is printed in a format that can be directly pasted ontothe barrel sheet for subsequent curatorial handling.

When describing sequences of rocks, the core was subdi-vided into lithologic units on the basis of changes in petrog-raphy, mineral abundances, rock composition, and rock clasttype. For each lithologic unit and section, the followinginformation was recorded in the database system:

1. The leg, site, hole, core number, core type, and sectionnumber.

2. The unit number (consecutive downhole), position in thesection, number of pieces of the same lithologic type, the rockname, and the identity of the describer.

3. The dry color of the rock and the presence and characterof any deformation.

4. The number of mineral phases visible with a hand lensand their distribution within the unit, together with the follow-ing information for each phase: (1) abundance (volume per-cent), (2) size range in millimeters, (3) shape, (4) degree ofalteration, and (5) further comments.

5. The groundmass texture: glassy, fine-grained (5 mm). Rela-tive grain size changes within the unit were also noted.

6. The presence and characteristics of secondary mineralsand alteration.

7. The abundance, distribution, size, shape, and infillingmaterial of vesicles (including the proportion of vesicles thatare filled by alteration minerals).

8. The structure, including any layering and noting whetherthe flow is massive, pillowed, thin or sheetlike, brecciated, or ahyaloclastite.

80

EXPLANATORY NOTES

9. The relative amount of rock alteration: fresh (2 hr)and 30 drops of polyvinyl alcohol binder into an aluminumcap. A modified Compton scattering technique based on theintensity of the Rh Compton peak was used for matrixabsorption corrections (Reynolds, 1967).

Replicate analyses of rock standards show that the majorelement data are precise within 0.5% to 2.5%, and are consid-ered accurate to —1% for Si, Ti, Fe, Ca, and K, and between3% and 5% for Al, Mn, Na, and P. The trace-element data areconsidered accurate between 2% and 3% or 1 ppm (whicheveris greater) for Rb, Sr, Y, and Zr, and between 5% and 10% or1 ppm for the others, except for Nb, Ba, and Ce. Precision isalso within 3% for Ni, Cr, and V at concentrations >IOO ppm,but 10% to 25% at concentrations

SHIPBOARD SCIENTIFIC PARTY

Table 5. Leg 134 XRF analytical conditions.

Element

SiO2TiO2A12O3Fe 2 O 3 *MnOMgOCaONa2OK 2OP 2 O 5

RhNbZrYSrRbZnCuNiCrFeVTiO2CeBa

Line

KαKαKαKαKαKαKαKαKαKα

K-CKαKαKαKαKαKα.KαKαKαKαKαKαLαLß

Crystal

PET(002)LiF(200)PET(002)LiF(200)LiF(200)TLAPLiF(200)TLAPLiF(200)Ge(ll l)

LiF(200)LiF(200)LiF(200)LiF(200)LiF(200)LiF(200)LiF(200)LiF(200)LiF(200)LiF(200)LiF(220)LiF(220)LiF(200)LiF(220)LiF(220)

Detectora

FPCFPCFPCFPCKrSCFPCFPCFPCFPCFPC

ScintScintScintScintScintScintScintScintScintFPCFPCFPCFPCFPCFPC

Collimator

CoarseFineCoarseFineFineCoarseCoarseCoarseFineCoarse

FineFineFineFineFineFineFineFineCoarseFineFineFineFineCoarseCoarse

Peakangle

(°)

109.1086.16

144.4957.5363.0344.88

113.1854.73

136.66141.00

18.6021.3922.5423.8325.1526.6041.8145.0248.6469.3885.73

123.2086.16

128.35128.93

Backgroundoffset

(°)

00000

±0.800

-1.2000

0±0.35±0.35±0.40±0.41±0.60±0.40±0.40±0.60±0.50

-0.40 + 0.70-0.50±0.50±1.50±1.50

Total count time

Peak

4040

1004040

20040

20040

100

10020010010010010060606060406040

100100

(s)

Background

00000

4000

20000

020010010010010060606060406040

100100

Note: *Total Fe as Fe 2θ3 All elements analyzed under vacuum on goniometer 2 at generator settings of 60 kVand 50 mA.

a FPC = flow proportional counter using P l o gas; KrSC = sealed Krypton gas counter; Scint = Nal scintillationcounter.

ical caliper device (MCD), and phasor dual-induction tool(DIT). This tool combination measures compressional wavevelocity and provides indicators of the two variables that mostoften control velocity: porosity, as indicated by density orresistivity, and clay content, as indicated by the naturalgamma-ray tool.

The FMS tool string included not only the FMS but also ageneral purpose inclinometer tool (GPIT) that spatially orientsthe FMS resistivity image of the borehole wall. The tool stringalso contained a natural gamma-ray tool (NGT) to allow depthcorrelation of the FMS data with other logs.

The geochemical combination for Leg 134 consisted of theNGT, aluminum clay tool (ACT), and gamma spectrometry tool(GST). This tool combination measures the relative concentra-tions of 12 elements: silicon, calcium, aluminum, iron, titanium,sulfur, hydrogen, chlorine, potassium, thorium, uranium, andgadolinium.

Log data are recorded at 0.5-ft (0.15-m) intervals for thestandard Schlumberger logging strings. The FMS and bore-hole televiewer logging strings record data on millimeter-scalevertical intervals.

Logs

A brief description of logging tools run during Leg 134 ispresented here. A detailed description of logging tool princi-ples and applications is provided in Schlumberger (1989),Serra (1984, 1989), and Timur and Toksoz (1985).

Electrical Resistivity

The dual induction tool provides three different measure-ments of electrical resistivity, each with a different depth ofinvestigation. Two induction devices (deep and medium resis-tivity) send high-frequency alternating currents through trans-mitter coils, creating magnetic fields that induce secondary(Foucault) currents in the formation. These ground-loop cur-

rents produce new inductive signals, proportional to theconductivity of the formation, which are recorded by thereceiving coils. Measured conductivities are then converted toresistivity. A third device (spherically focused resistivity)measures the current necessary to maintain a constant voltagedrop across a fixed interval. Vertical resolution is around 2 mfor the medium and deep resistivity devices and about 1 m forthe focused resistivity.

Water content and salinity are by far the most importantfactors controlling the electrical resistivity of rocks. To thefirst order, resistivity responds to the inverse square root ofporosity (Archie, 1942). Other factors influencing resistivityinclude the concentration of hydrous and metallic minerals,vesicularity, and the geometry of interconnected pore space.

Sonic Velocity Measurements

The LSS tool uses two acoustic transmitters and two receiv-ers to measure the time required for sound waves to travel oversource-receiver distances of 2.4,3.0, and 3.6 m. The raw data areexpressed as time required for a sound wave to travel through0.31 m of formation (µs/ft); these traveltimes are then convertedto sonic velocities. First arrivals for the individual source-receiver paths are used to calculate the velocities of the differentwaves traveling in the formation (compressional, shear, etc.).Only compressional wave velocity is determined during dataacquisition, but waveforms are recorded for post-cruise deter-mination of shear-wave velocities and refining the compressionalwave velocities. The vertical resolution of the tool is 0.61 m.Compressional wave velocity is dominantly controlled by poros-ity and lithification; decreases in porosity and increases inlithification cause the velocity to increase.

Natural Gamma-Ray Tool

The NGT measures the natural radioactivity of the formation.Most gamma rays are emitted by the radioactive isotope ^K and

82

EXPLANATORY NOTES

by the radioactive elements of the U and Th series. Thegamma-ray radiation originating in the formation close to theborehole wall is measured by a scintillation detector. The ele-mental abundances of K, U, and Th are determined by analyzingthe gamma-ray spectrum using five discrete energy windows.

Because radioactive elements tend to be most abundant inclay minerals, the gamma-ray curve is commonly used toestimate the clay or shale content. There are rock matrices,however, for which the radioactivity ranges from moderate toextremely high values as a result of the presence of volcanicash, potassic feldspar, or other radioactive minerals.

Mechanical Caliper Device

The MCD provides a basic two-dimensional caliper log ofthe borehole by means of a bowspring-mounted measure-ment system. The hole diameter log is used to detectwashouts or constrictions. Borehole diameter significantlyaffects many of the other logging measurements, and thehole diameter is an important input to log correction rou-tines. This caliper tool is subject to sticking when formationmud gets into its mechanical parts, resulting in bimodal(fully open or nearly fully closed) readings. In contrast, themeasurement of hole diameter produced by the HLDT ismuch more reliable. Consequently, on Leg 134 the MCD toolwas used primarily to provide centralization and associatedimproved log quality for the sonic log rather than to measurehole diameter.

High-Temperature Lithodensity Tool

The HLDT uses a 137Ce gamma-ray source and measuresthe resulting flux at fixed distances from the source. Undernormal operating conditions, attenuation of gamma rays iscaused chiefly by Compton scattering (Dewen, 1983). Forma-tion density is extrapolated from this energy flux by assumingthat the atomic weight of most rock-forming elements isapproximately twice the atomic number. A photoelectriceffect index is also provided. Photoelectric absorption occursat energies below 150 keV and depends on the energy of theincident gamma ray, the atomic cross section, and the natureof the atom. Because this measurement is almost independentof porosity, it can be used directly as an indicator of matrixlithology. The radioactive source-and-detector array ispressed against the borehole wall by a strong spring arm. Theextension of this spring arm measures hole diameter. Exces-sive roughness of the hole will cause some drilling fluid toinfiltrate between the detector array and the formation. As aconsequence, density readings may be artificially low. Ap-proximate corrections can be applied by using the caliperdata. The vertical resolution is about 0.30 m.

Compensated Neutron Porosity Tool (CNT)

A radioactive source mounted on the CNT sonde emitshigh-energy neutrons (4 MeV) into the formation, where theyare scattered and slowed by collisions with atomic nuclei.When the neutrons reach a low energy level (0.025 MeV) theyare captured by atomic nuclei such as hydrogen, chlorine,silicon, and boron. The scattering cross section is the quantitythat describes the rate at which neutrons are slowed. Becausethe scattering cross section for hydrogen is about 100 timeslarger than for any other common element in the crust, mostenergy dissipation is caused by collisions with water mole-cules. Therefore, a change in the number of neutrons detectedat a receiver may be related to porosity. In practice, an arrayof detectors is used to minimize borehole or drilling fluideffects. Because water is present both in pores and as boundwater (e.g., clay minerals), porosity measurements made in

the presence of hydrous minerals overestimate the true poros-ity. The vertical resolution of the tool is theoretically about0.25 m, but a low signal-to-noise ratio degrades this potentialresolution.

Gamma Spectrometry Tool

The induced spectral gamma-ray tool consists of a pulsedsource of 14-MeV neutrons and a gamma-ray scintillationdetector. A surface computer performs spectral analysis ofgamma rays resulting from the interactions of neutrons emit-ted by the source with atomic nuclei in the formation (Hert-zog, 1979). Characteristic sets of gamma rays from six ele-ments dominate the spectrum, permitting calculation of sixelemental yields: calcium, silicon, iron, chlorine, hydrogen,and sulfur. The tool normalizes their sum so that the yields donot reflect the actual elemental composition. Instead, ratios ofthese yields are commonly used in interpreting the lithology,porosity, and salinity of the formation fluid. Shore-basedprocessing is used to derive elemental composition from thisand the other logs.

Aluminum Clay Tool

Aluminum abundance as measured by the ACT is deter-mined by neutron-induced gamma-ray spectrometry usingcalifornium as the radioactive source. By placing Nal detec-tors both above and below the neutron source, contributionsfrom natural gamma-ray activity can be removed. Calibrationto elemental weight percent is performed by taking irradiatedcore samples of known volume and density and measuringtheir gamma-ray output while placed in a jig attached to thelogging tool (generally after logging).

Formation Microscanner

The FMS produces high-resolution microresistivity im-ages or structural maps of the borehole wall that can be usedfor detailed sedimentological or structural interpretationsand for determining fracture and breakout orientations. Thetool consists of 16 electrode "buttons" on each of fourorthogonal pads that are pressed against the borehole wall.The electrodes are spaced about 2.5 mm apart and arearranged in two diagonally offset rows of eight electrodeseach. The focused current that flows from the buttons isrecorded as a series of curves that reflect the microresistiv-ity variations of the formation. Onboard or shore-basedprocessing convert the current intensity measurements intocomplete, spatially oriented images. Further processing canalso provide measurements of dip magnitude and directionor azimuth of bedding surfaces.

Applications of the FMS images include detailed correla-tion of coring and logging depths, orientation of cores, map-ping of fractures, faults, foliations, and formation structures,as well as determining strikes and dips of bedding. The FMScan also be used to measure stress in the borehole throughbreakout delineation. In an isotropic, linearly elastic rocksubjected to an anisotropic stress field, breakouts form in thedirection of the least principal horizontal stress. An importantlimitation is the restriction to a hole diameter of less than 37cm (14.5 in.). Thus, little useful information can be obtainedfrom seriously washed-out sections of hole.

General Purpose Inclinometer Tool

The GPIT provides a measurement of borehole inclination,the orientation of the tool with respect to the earth's magneticfield using a three-component magnetometer, and tool motionusing an accelerometer. It is run with the FMS to providespatial orientation of the borehole wall images.

83

SHIPBOARD SCIENTIFIC PARTY

Borehole Televiewer (BHTV)The BHTV produces an ultrasonic acoustical image of the

borehole wall. A transducer emits ultrasonic pulses that arereflected at the borehole wall and then are received by thesame transducer. The amplitude and traveltime of the re-flected signal are determined and stored in the loggingcomputer. The 360° rotation of the transducer and theupward motion of the tool produces a complete map of theborehole wall. The amplitude depends on the reflectioncoefficient of the borehole fluid-rock interface, the positionof the BHTV tool in th