1. INTRODUCTION: OBJECTIVES, STRATEGY, OPERATIONS,SHIPBOARD ANALYTICAL PROCEDURES, AND EXPLANATORY NOTES OF

DEEP SEA DRILLING PROJECT LEG 54

Bruce R. Rosendahl,1 Roger Hekinian,2 James H. Natland;3 Nick Warren,4

Nikolai Petersen,5 William Roggenthen,6 and Louis Briqueu2

BACKGROUND, OBJECTIVES, AND STRATEGY

The Pacific phase of IPOD ocean crust drilling wasinitiated with Leg 54, the region targeted for study bythe Ocean Crust Panel being survey area PT-4 (Figure 1)(and Plate 1 [in back pocket]) north of the Siqueirosfracture zone on the western flank of the East PacificRise (EPR). The original purpose of this leg was toestablish a type section for fast-spreading, nonriftedcrust by direct sampling with stratigraphic control. Weanticipated that this section would serve, in part, as astandard of comparison for other type sections, such asthe Mid-Atlantic Ridge (MAR).

To achieve the stated objective, we devised anelaborate strategy for the selection and chronologic se-quencing of holes and an array of tests to choose thelocation of the multiple re-entry type area site (Figure2). An important part of this strategy was to locate aspot where a deep re-entry hole could be drilled severalhundred meters into normal, fast-spreading oceaniccrust. However, by the time we had terminated drillingat only a few holes, the vagaries of nature had made itabundantly clear that the strategy for Leg 54, indeed itsoriginal purpose, was as yet technologically unrealistic.The main difficulty was the intensely fractured state ofthe basaltic crust, effectively limiting penetration to adepth at which frictional binding of the drill stembecame so great that continued drilling became impossi-ble, and/or resulted in obliteration of the core bit. Eventhe fact that 30-meter holes into basement were ob-tained is a tribute to the dedication, expertise, and per-sistence of the drillers, not a lessening of nature's con-trariness. Similar difficulties had been experienced onLeg 34 on the Nazca plate, but we had hoped that suc-cessful deep crustal drillings in the Atlantic on Legs 37

1 Department of Geology, Duke University, Durham, NorthCarolina.

2 Centre Océanologique de Bretagne, Brest, France.3 Deep Sea Drilling Project, Scripps Institution of Oceanography,

La Jolla, California.4 Department of Geology, University of California, Los Angeles,

California.5 Institut für Allgemeine und Angewandte Geophysik, Ludwig-

Maximilians-Universitat, Munich, Federal Republic of Germany.6 Department of Geological and Geophysical Sciences, Princeton

University, Princeton, New Jersey (now at: South Dakota School ofMines and Technology, Department of Geology, Rapid City, SouthDakota).

and 45 had "taught" us how to drill oceanic crust. Ex-perience, however, proved woefully inadequate to dealwith the difficulties encountered on Leg 54. These dif-ficulties necessitated an on-the-spot re-evaluation of thegoals of Leg 54 and the development of an appropriatestrategy, both of which were based upon what could belearned from low-penetration, single-bit holes. Also, anunscheduled drilling program on the flanks of theGalapagos spreading center (GSC), supplemental tothat in survey area PT-4, was set up.

As perceived by the scientific party, it was no longerpossible to establish a type section for fast-spreadingcrust, but we could drill a transect of relatively shallow,single-bit holes that would span the same geologicalperiod as covered by one successful deep hole. By doingso, we would still be able to answer important questionsregarding (1) temporal variations and timing of eruptiveevents at the EPR and their relationship to postulatedaxial magma reservoirs; (2) the cause of the apparentlygreater extent of basalt fractionation observed in EPRdredged rocks than in MAR basalts; (3) magnetizationpolarities of drilled rocks and their comparison toresults in the Atlantic; and (4) the relation of physicalproperties to the degree of alteration, weathering,crystallinity, and fracturing. Moreover, by allowing thetransect to cross an off-ridge volcanic lineament, wehoped to learn something about the chemical, magnetic,and physical nature of the transition from EPR fabric totransverse volcanic and structural features. The abovestrategy and objectives formed the framework for thedrilling program in survey area PT-4.

The Galapagos program originated as a DSDP direc-tive while en route to our sixth site in area PT-4. The ob-ject of the directive was to conduct "drilling trials alongthe Galapagos Spreading Center" for the sake of the"overall [Deep Sea Drilling] Project and IPOD-JOIDES plans," and to this end we were given specifictargets in the Galapagos area. The main purpose of thisprogram was to determine whether a proposed two-legdrilling program in the Galapagos area was feasible, inlight of the difficulties encountered in area PT-4, and, ifso, what modifications should be made to that program.The directive required the location and drilling of sup-posed geothermal area south of the Galapagos spread-ing axis. This area contained several groups of smallsedimentary mounds and cones no larger than theGlomar Challenger herself, which we thought had beenformed by localized hydrothermal activity, perhaps

10°N -i— 1 1 r π 1 1 1- — T •

SIQUEIROS FRACTURE ZONE

105°W 104°W

Figure 1. Leg 54 drill sites on the western flank of the East Pacific Rise. Inset: Location of Leg 54 principal target areas in the eastern Pacific.

LEG 54 OBJECTIVES

Test for Suitability ofPT-4 Area for Multiple

Re-entry (via pilot-holes)

Test for Suitabilityat Alternative Site(e.g.. Anomaly 5)

ContingencyProgram

Multiple Re-entryat Alternative Site

Alternative AreaSingle-Bit Program//Single-Bit Programv

Figure 2. Flow diagram of the original recommended drilling strategy for Leg 54.The stippled boxes indicate the program we eventually carried out, but by thepathway shown by heavy arrows.

along basement faults and fissures. Other targets onolder crust were given, which were to be drilled as timeallowed.

Although most members of our scientific party wereunfamiliar with the mounds area, and we had virtuallyno survey data to find them, we accepted the Galapagoschallenge and devised a set of scientific objectives andstrategies compatible with both the purpose of theGalapagos diversion and the goals of ocean crust drill-ing. The objectives pertained to: (1) the origin of theGalapagos mounds and their relationship to hydrother-mal circulation patterns in young crust, (2) the internalstratigraphy and constitution of the mounds and thephysicochemical nature of basement beneath and be-tween the mounds, and (3) Galapagos equivalents of theEPR objectives listed above. The strategy entailedlocating the mounds' field with a high-frequency, fast-sweep profiling system and deploying a beacon as closeto an individual mound as possible. The Edo re-entrysonar scanning tool would then be used to position theship for spud-in accurately over a mound. Once amound had been drilled, we would move north-southfrom the beacon and establish a minitransect of holesacross one or more mound chains. A site would also beplaced on a known heat-flow maximum far removedfrom the transect area to provide additional insight into

the nature and diversity of sea-floor hydrothermal ac-tivity.

The inadequacy of onboard Galapagos survey datadeserves special mention, because it played a critical rolein the drilling program we devised. There had not been asite survey in the Galapagos area (as there had been atthe EPR area), and it was by pure accident that we hadany relevant literature aboard at all. This literature con-sisted of a paper by Sclater and Klitgord (1973) contain-ing a small ( 4 x 5 in.) general bathymetric map of thearea and a few reflection profiles, and a first-draft pre-print of a paper later published by Lonsdale (1977) deal-ing with deep-tow observations in the mounds locality.This latter manuscript, along with its figures, consti-tuted the sum total of information we possessed on thesupposed geothermal area prior to drilling. We used thisinformation to find the mounds and to identify the spe-cific parts of the mounds' field drilled. One other criti-cal factor was the severe time restriction imposed byhaving to include a 13-day round trip between the Si-queiros and Galapagos areas within a cruise alreadyconsiderably shortened by termination at Long Beach,rather than Mexico, for necessary dry-docking. In all,Leg 54 had 19 days of operations (drilling and steaming)in its target areas, out of a 50-day cruise. At the end ofour Galapagos drilling a cruise extension of five days

B. R. ROSENDAHL ET AL.

for additional operations was granted at the urgent ap-peal of the Leg 54 shipboard party. We used this exten-sion to return to the Siqueiros area and continue ourprogram there. In our 19 days of operations we drilled18 holes at 11 sites.

Even though the EPR and GSC drilling programsshared many of the same hard-rock objectives, eachprogram stands alone with respect to its achievementsand scientific appeal. In a very real and practical sensethe programs are as different from each other as anytwo crustal drilling legs, and for this reason we treateach as a separate entity within this volume. Moreover,since each program consists mainly of transects of holesclosely related in terms of purpose, operations, and re-sults, we have elected not to assign chapters to individu-al sites. Instead, the Site Reports are grouped into twochapters under EPR and Galapagos headings. We thinkthe above conventions will result in a more readable andconcise volume.

OPERATIONS

The Glomar Challenger left Cristobal, Panama, onthe morning of 30 April 1977, to begin transit throughthe Panama Canal. Because of a malfunction first in theNo. 4 generator, and then the electrical circuitry for thestern thrusters, our departure from Panamanian waterswas delayed until 2030 hours, 1 May. We arrived in SanPedro, California, on the morning of 18 June 1977.

During Leg 54, the ship traveled 6333 nautical miles,occupied 11 sites, attempted to drill 18 holes, and suc-cessfully penetrated basement at 13 localities. Waterdepths ranged from 2617 to 3834 meters. Total penetra-tion was 1282 meters, of which 847 meters of materialwas cored and 461 meters recovered. Basement penetra-tion totaled 324.5 meters, but only 66 meters of basaltwas recovered. Coring data for Leg 54 are given in Ta-ble 1. Sites 419 through 423 and 426 through 429 weredrilled in the Siqueiros area (within survey area PT-4)and Sites 424 and 425 on the flanks of the Galapagos rift(Figure 1).

By using the official starting date of 25 April 1977 forLeg 54, the time distribution was as follows: 4.6 days inport including 0.7 day of downtime, 32.6 days in transit,and 17.8 days on site (Figure 3). The on-site time break-down was 8.6 days for coring, 6.1 days for pulling pipe,1.5 days for ship positioning, 0.4 day of mechanicaldowntime, 0.2 day of drilling, 0.1 day for a stuck drillpipe, and 0.9 day of miscellaneous time (Figure 4).

We had our share of "ups and downs," successes andfailures, agreements and disagreements. On the positiveside, Leg 54 occupied more sites and drilled more base-ment holes than any previous IPOD leg. We drilled theyoungest basement of any DSDP leg and proved thatsuccessful spud-in was possible where sediment coverwas as thin as 29 meters. In addition, Leg 54 establishedthe practicality of locating and drilling Challenger-sizedstructures on the sea floor. In the success column, wealso list the attitude, understanding, and diligence of theLeg 54 drilling crew, to whom this volume is informallydedicated. On the negative side, our deepest penetrationinto basement and average bit life were less than thoseachieved on any previous crustal drilling leg, andaverage hole conditions were the worst ever encoun-tered. Moreover, the percentage of on-site time devotedto actual drilling was a meager 1.1 per cent and our ratioof in-transit time to days on station was almost 2:1.

In view of the large number of holes, the extremelyunfavorable conditions at the holes, and inherentdangers of spudding into basement with minimal sedi-ment cover, Leg 54 was remarkably free of mechanicalbreakdowns. The most serious operational failure oc-curred prior to any drilling and involved the inoperativestate of the blower shaft on the gel pump. The gel hadbeen expected to improve hole conditions significantlyby aiding in the removal of drilling chips; consequently,there was some consternation when this ability appearedlost for the remainder of the leg. However, toward theend of the cruise an alternative pumping system wasjury-rigged and gel was used on Site 428. There was nonoticeable improvement in drilling conditions. The only

TABLE 1Coring Summary, Leg 54

Hole

419419A420420A421422423424424A424B424C425426427428428A429429A

Total

Date (1977)

8-9 May9 May10-11 Mayll-12May12-13 May14-15 May15-16 May23-24 May24 May25 May25 May26-27 May3 June4-5 June6-7 June7-8 June9 June9-10 June

Latitude

08°55.96'N08°55.47'N09° 00.10'N09°00.50'N09°01.41'N09°10.59'N09°08.81'N00°35.63'N00°35.33'NOO°35.82'N00°35.93'N01°23.68'N08°47.28'N08°06.79'N09°02.77'N09°02.77'N09°02.01'N09°02.01'N

Longitude

105°41.17'W105°41.22'W106°06.77'W106°06.32'W106°03.68'W105°16.27'W105°06.57'W86°07.82'W86°07.81'W86°07.82'W86°07.82'W86°04.22'W

104°15.27'W104°36.35'W105°26.14'W105°26.14'W106°46.35'W106°45.87'W

WaterDepth(m)

327432743381338233393247316126852708270526992850

_38343295328634063426

Penetration(m)

35.046.0

147.063.0

114.073.053.576.034.046.534.5

110.00.0

174.576.5

115.031.052.5

Numberof

Cores

51

1714

108836390

116713

103

Cored(m)

35.08.0

147.06.0

38.073.053.576.034.046.516.581.5

0.098.554.552.5

5.021.5

847.0

Recovered(m)

21.644.74

95.076.05

11.2246.9727.9836.4513.1329.30

7.8143.42

0.0057.2636.3416.374.672.95

461.37

Recovery(%)

625965

1003064524839634753

05867319314

54

BasementPenetration (m)

00

28.70

19.1823.515.538.545.0114.5

3.028.5

028.515.552.50

021.5

334.39

BasementRecovery (m)

001.2201.639.560.878.458.452.350.485.600

12.512.14

12.6002.95

68.81

Note: Average recovery in basement = 20.6%.

LEG 54 OBJECTIVES

IN PORT(4.6 DAYS; 7.3%)

IN PORT DOWNTIME(0.7 DAY; 1.3%)

START: 25 April 1977FINISH LEG: 18 June 1977TOTAL TIME: 53.7 Days

Figure 3. Total time distribution, Leg 54.

STUCK PIPE (0.6%)

MECHANICALDOWNTIME (1.9%)

OTHER (5.3%)

POSITIONING (8.5%)

TOTAL TIME ON SITE: 17.8 daysTOTAL SITES: 11TOTAL HOLES: 18

Figure 4. On-site time breakdown, Leg 54.

other serious breakdown involved the diaphragm andclutch lining in the make-up drum for the drawworks re-quiring 5 hours to repair while on Site 421.

Ship positioning and weather were generally excellentthroughout Leg 54 and probably played an importantrole in reducing on-site mechanical failures. The ship-board positioning computer was almost trouble-free, al-though beacon failures occurred at Sites 419 and 426.

INSTRUMENTATION, EQUIPMENT,AND PROCEDURES

X-Ray Fluorescence (XRF) Chemical AnalysesDuring Leg 54, the equipment and technique used to

perform chemical analyses onboard Glomar Challengerwere the same as those on previous crustal drilling legs(Legs 37, 45, 46, 47, 51, 52, and 53). The instruments in-cluded an XRF unit, a furnace, a motor-driven crusher,a balance, and two cooling systems. The general proce-dures to perform chemical analyses and description ofthe equipment are given in Bougault (1977) and Melson,Rabinowitz, et al. (1978). The routine analytical workconsisted of making glass disks for major elements andpowdered disks pressed with wax for trace elements.The matrix effect in the glass pellets is eliminated byusing a mixture of Li2B4O7 (3.5 g) and La2O3 (0.5 g).The elements (as oxides) analyzed during Leg 54 were:SiO2, A12O3, Fe2O3 (total Fe as Fe2O3), MgO, CaO,K2O, and TiO2. The standards used during this leg werethe following: W-l, BCR1, PCC1, DTS1, G2, GST1,GH (Nancy), and VBR (Nancy).

Equipment and Technical ProblemsDuring Leg 51, the restricted sample holder was

changed to one with a six-position compartment device.Toward the end of Leg 53 a complementary safety de-vice (conceived by the marine technician group) wasadded on the sample chamber of the XRF unit. The de-vice prevents the operator, who previously had notturned off the high-voltage knob, from being exposed toX-ray irradiation. The unit consists of a solenoid ac-tivated by a lever, which mechanically locks the samplechamber door whenever the high-voltage switch is on. Acompression spring in the solenoid retracts the lockingarm only if the generator is off or in standby position.(Details of the system are described in the LaboratoryOfficer notebook of Leg 53.) Direct access to the X-raytube is prevented should it be necessary to replace theX-ray tube, and the mechanical lock mounted on theside of the sample holder has first to be removed.

Limitations of Leg 54 Shipboard XRF AnalysesThe shipboard XRF instrument was not fully opera-

tional during the early part of Leg 54 and ceased opera-ting altogether after drilling Hole 424. Difficulties wereencountered with both the auxiliary (Newman) coolingsystem unit and the X-ray spectral lines discriminator.The cooling unit eventually was made to function, de-spite its high-temperature environment (sea-water tem-perature was high). The role of the sinusoidal amplifierof the XRF equipment is to regulate and modify the im-pulse received when the crystal is positioned at the cor-rect angle of diffraction for a specific energy level, aswell as to regulate the discriminative channels and thehigh voltage readout. Even during the first part of thecruise, the sinusoidal amplifier did not furnish the pro-per signal impulses to the discriminator. Hence, thevarious energy levels characterizing each analyzed ele-ment had to be changed accordingly. This made the

B. R. ROSENDAHL ET AL.

chemical analyses obtained under such conditions bothdifficult to acquire and unreliable. To minimize thelimits of uncertainty, it was necessary to change the dis-criminator settings and increase the voltage of the gas-eous flux above the maximum voltage recommended bythe manufacturers. By changing the discriminator set-tings, interference was increased between the analyzedenergy level of the spectrum and that of the higher orderlevel. For example, to obtain the intensity Kα of Fe, wehad to increase the voltage to 2200 volts, thereby gener-ating noticeable instability for this element.

Nonetheless, we were able to measure some of themajor oxides with adequate precision, particularly CaO,K2O, and TiO2. Total Fe, calculated as Fe2O3, alsocould be obtained, but with less precision. The analyti-cal results for the other major oxides, such as SiO2,A12O3, and MgO, were even less satisfactory, and traceelements were impossible to determine. After comple-tion of the cruise, the rocks recovered on Leg 54 were re-analyzed on the beach by L. Briquieu. These revisedanalyses form the basis for discussions in the Site Re-ports and are those listed on the Site Report basalt de-scription forms.

Paleomagnetics

Equipment on board ship used in the paleomagneticstudy of recovered material includes a Digico spinnermagnetometer with its associated Digico M16V com-puter and a Schonstedt geophysical specimen demagne-tizer (Model GSD-1). A portable magnetic susceptibilitybridge (Geophysics Specialty Co., Model MS-3) wasalso used.

The primary goal of the paleomagnetic investigationswas to determine the original magnetic remanence direc-tion acquired by the igneous material upon cooling.This type of remanence is a thermal remanent magneti-zation, but it is often not the only kind of remanencewhich may be present in the rock. During the intervalbetween cooling and measurement in the laboratory, therock may acquire secondary remanences such as chemi-cal and viscous magnetizations. To eliminate these sec-ondary directions and to establish the "stable direc-tion," a program of stepwise AF demagnetization wasemployed. Because the AF demagnetizer is a uniaxialmodel, each specimen was successively demagnetizedalong the three principal axes of the specimens at each de-magnetization step. Peak AF fields as high as 1000 Oewere employed, although fields at which stable direc-tions were reached are commonly much lower. In orderto characterize the igneous samples more fully, the sus-ceptibilities were measured and the Königsberger ratiocalculated from the relationship:

e ='NRM

X × H (1)

We determined a sample's "stable" direction by ex-amining its change in inclination upon progressive de-magnetization. If during this process the inclinationreached a value that did not change materially for sever-al steps, this was termed the "stable" direction. Changein declination was also considered but was not used asthe determining parameter. As a measure of inherentstability, the median demagnetizing field (MDF) wasfound for each sample. This is the AF field necessary toeliminate half of the original intensity of magnetization(see Figure 5).

Because the rock samples can be oriented solely withrespect to the vertical axis, only the inclinations can bedetermined as absolutes. Declinations are relative valuesand are referred to the face of the split core.

The low latitudes at which the sites were drilledcreated some problems in the determination of polarity;inclinations expected at the latitudes of the Siqueirossurvey area PT-4 are only about 18°. Therefore, some

where JNRM is the volumetric NRM intensity, x is thesusceptibility, and H is the magnitude of the earth'sfield at this location (H = 0.36 Oe).

Figure 5. Example of the determination of the median de-magnetizing field (MDF) and stable magnetic inclina-tion of the natural remanent magnetization (NRM).The inclination is given in absolulte values, the decli-nation in relative values.

10

LEG 54 OBJECTIVES

attempts were made to orient the cores using differencesbetween low-value demagnetization steps to ascertainviscous remanences most likely associated with thepresent-day field. This procedure also assists in deter-mining the declinations.

In summary, the shipboard measurements included:(1) determination of NRM and subsequent directionsafter demagnetization to establish the "stable" direc-tions (inclinations) for each sample, (2) determinationof intensities before and after demagnetization, and (3)measurement of susceptibilities and calculation of Kön-igsberger Q ratios. These data are given on the basaltdescription forms in the Site Reports.

Physical Properties: Introduction

The physical properties of recovered cores provide abase line for interpreting geophysical data obtainedfrom ocean-bottom and shipboard surveys. A chief ob-jective of Leg 54 was to compare core properties andsurvey properties. The goal of the leg was to character-ize the normal fabric of young ocean crust near the EPRDetailed presite surveys had been made and a re-entryhole was planned. As already described, this objectivecould not be met because of the impossibility of drillinga re-entry hole and even of making any deep single-bitholes.

Although the primary objective was lost, the low re-covery still enabled us to make detailed shipboard stud-ies on the recovered samples. Sound velocities, bulkdensities, grain densities, water content, porosities, andshear strength were measured in sediments and basalts.Additional velocity, grain, and bulk-density measure-ments were made post-cruise on a number of samples atUCLA (Warren and Rosendahl, this volume).

These primary data are presented in the Site Reports,this volume. Generally, more accurate data were ob-tained for the basalt than for the sediments. The rocksamples consist chiefly of fragments of very dense, hardbasalts. At three sites where sills or thick flows were en-countered, drilling was good and fairly continuous sam-pling was possible.

For the basalts, Birch-law systematics and the effectof average iron content are clearly visible in the ship-board velocity-density data. The data also show veloci-ty, density systematics within basalt units (which in turnmay be used to correlate with grain-size), cooling rates,and magnetics.

Sediments were generally soft oozes at all sites, andfrequently the cores were moderately to highly dis-turbed. The physical properties of the sediments werevery uniform except at the Galapagos sites. There, theforaminifer and nannofossil oozes were interbeddedwith iron and magnesium-rich green muds which showedhigher densities and velocities than the pelagic sedimentsin the Siqueiros PT-4 locales.

Techniques

Density Measurements

Gamma-Ray Attenuation PorosityEvaluator (GRAPE)

Densities and porosities of materials can be deter-mined by measuring their attentuation of a beam ofgamma rays. The equipment and technique for doingthis by the onboard gamma-ray absorption instrumenthave been fully described in earlier reports (Boyce,1976).

On this leg the GRAPE was used conventionally.Continuous logs of the sediment cores were made rou-tinely. Some 2-minute GRAPE counts were made ofsediment minicores.

Only one section of basalt was logged continuously.Two difficulties were encountered in trying to log therock cores. First, the cores were seldom continuous and,typically, consisted of loose fragments of very fresh ba-salts with very little glass. Therefore, they were not ob-viously characteristic of an in-situ rock column. Second,we found the cores were iron-rich basalts (up to 15 percent Fe as Fe2O3), so that grain densities for many of thesamples were over 3.00 g/cm3.

Because bulk and grain densities were abnormallyhigh, we found that the densities determined by theGRAPE were significantly off from values determinedby weight and volume measurements on minicores thatwere carefully prepared for the velocity measurements.Use of the "standard" grain density values assumed forreducing raw data to density and porosity often gavenegative porosities. It was clear that porosities and den-sities had to be determined more accurately than couldbe done by using the standard program. GRAPEingwhole sections or whole rough rocks yielded neither realinformation about in situ densities nor accurate data onrock densities themselves. Therefore, wet- and dry-bulkdensities were determined using weight and volume mea-surements on the carefully prepared minicores.

Two-minute GRAPE counts were made on the mini-cores for later reduction to densities. On some samples,grain density and porosity estimates were made usingwet and dry weight data from the same minicore. Thiscould be done with considerable accuracy for cut andlapped minicores which could be weighed both wet anddry; samples from Site 425 were dealt with in this way.Assuming salt corrections, the grain density of the sam-ple could be solved from

where 0 ' is the true porosity and K is defined by

„ wet weight - dry weight , ,, . . .K = % :—r̂ —— (no salt corrections).

dry weight

11

B. R. ROSENDAHL ET AL.

Velocity Measurements

Compressional velocities (V) were measured at zeroconfining pressure on water-saturated samples. A scal-ing wave technique for measuring velocity, which tookadvantage of the shipboard Tektronix 485 oscilloscope,was set up. This was both easier and faster than thestandard method, as well as being inherently more accu-rate. Visual detection of the onset of an acoustic signalwas facilitated and the uncertainty of measuring its arri-val time reduced. The method required the addition of avoltage-controlled frequency and sweep-generator and afrequency counter to the ship's regular velocity measur-ing system. Both of these additional instruments wereavailable onboard ship.

We shall briefly describe the idea underlying themethod. A scaling wave is a gated sinusoidal wavewhich is visually displayed on the oscilloscope alongwith the acoustic signal itself. The starting time for thescaling wave {t = 0) is set to coincide with the arrivaltime of an acoustic wave through the Hamilton Framesample holder, with no sample.

When a sample is placed in the holder, the arrival ofthe acoustic signal is further delayed from t = 0 bysome interval t. By simply adjusting the frequency, thescaling wave can be stretched or compressed exactly likea Gerber scale to divide this delay time t by an integralnumber of waves. The travel time is then given by

t = N/f (3)

where N is the number of cycles and/is the frequency.The velocity V is then

V = L/t = L N/f (4)

where L is the sample length. (Operational instructionsfor using the scaling-wave technique are described in theAppendix.)

In the case of basalts, minicore samples were madefor accurate velocity and density measurements. Thegeneral procedure involved splitting and taking mini-cores from rocks directly after they were brought infrom the drilling platform. The minicores were thenplaced in 10 bottles filled with sea water and capped andreturned to their location in the section until curatorialwork was completed. This kept these samples fully satu-rated. The rough end of the minicore was later sawedoff and used for thin sections. A polishing block wasbuilt and used to lap the ends of the minicores to paral-lel (usually to less than ±0.02 mm). Velocities, magnet-ics, and bulk densities were then determined on thecores.

Because most of the sediments were very soft, theirvelocities were usually determined on the split cores stillin the liners.

The length L of the basalt minicore was measuredwith a caliper. The lengths of the split sediment coreswere measured directly off the micrometer wheel on theHamilton Frame, and standard core liner corrections ofL (liner) = 2.56 mm and t (liner) = 1.18 ̂ ts were used inreducing the data.

Using brass, aluminum, and plexiglas standards, thesystem was checked and calibrated frequently during theleg by one of two methods. Either standards, such asaluminum and lucite, were measured simply as if theywere samples, or the system was calibrated to one of thestandards and then the other standards were measured.This calibration was done by first placing the standardinto the Hamilton Frame. A scaling wave frequency waschosen and the visual start of the scaling wave was thenadjusted so that there were exactly N cycles in the scal-ing wave to the start of the acoustic signal.

Assuming the true velocity of the standard to be cor-rect, the travel time of the acoustic signal through thestandard was of course known. This gave "zero" errorfor the velocity measurement of the chosen standard,and other standards or samples could be measuredrelative to it.

Table 2 shows some calibration data. The values de-termined for the velocities seldom varied more than±0.5 per cent from the "true" values.

Other Measurements

a) Shear strengths:These were measured using the hand-held Torr-vane

gauge.b) Water content:Water content, bulk densities, and porosities were de-

termined for the sediments using 3-cm3 syringe samples.Procedures were routine, as described by Boyce (1976).These measurements were also used to estimate graindensity (p) for comparison with that assumed (Pgc) inthe inversion of the GRAPE data (Pgc = 2.7 g/cm3).

Grain densities can be calculated from the water con-tent (C), and the porosity (Φ) by the equation

Po =

where g is the grain density. Equation 1 assumes no saltcorrections and a water density of 1.00. Salt correctionsand sea-water density can be included, resulting in equa-tion (6).

A, = 1-025( Φ \ /0.965 - c\\p.989 - Φ/\ C j (6)

where C and Φ are the directly calculated (non-salt cor-rected) water content and porosity, respectively.

A computer program was written to calculate graindensities on shipboard using Equation (6). The averagevalue calculated was close to Pgc. This is discussed in theSite Report section on physical properties of sedimentsfrom the EPR sites.

EXPLANATORY NOTES

Organization of the Volume

This volume is divided into an introductory chapter(Part I), site survey reports and regional geophysics(Part II), site reports (Part III), paleontologic andbiostratigraphic studies (Part IV), sedimentologic

12

LEG 54 OBJECTIVES

TABLE 2Shipboard Velocity Calibrations

Standard

Aluminum

DistiUedwater

Lucite

Brass

Temperature (°C)

25

Number ofMeasurements

11

1111

1111

55

1

1

111

True Velocity

6.295

1.498

2.745

4.529

AverageMeasured Velocity

6.2906.2796.1666.3526.3216.2716.2956.2986.2926.289

1.4971.490

2.7312.743

4.5544.5514.522

Δ(%)

-0.07-0.2-2.1+1.0+0.41-0.39

_+0.04-0.05-0.50

-0.05-0.50

-0.51-0.07

+0.55+0.50-0.15

studies (Part V), petrologic and geochemical studies(Part VI), rock magnetic and physical properties studies(Part VII), and syntheses (Part VIII).

Site reports for the 18 holes at 11 sites drilled are intwo chapters, one each on the East Pacific Rise (Sites419 through 423 and 426 through 429) and Galapagosrift (Sites 424 and 425). These two chapters are detailedsummaries of the geological data obtained on Leg 54.The presentation is brief, and has been condensed intotwo chapters because the sites drilled in each area areclose together, and at each we recovered short, generallysimilar sediment and basalt sections which are best dis-cussed on a comparative basis. By doing so, we hope topresent a more comprehensive, intelligible, and conciseaccount of Leg 54 activities. The Site Reports areorganized as follows:

Site DataSummaryBackground and ObjectivesOperationsSediment LithologyBiostratigraphySediment Physical PropertiesInterstitial Water GeochemistryIgneous PetrographyIgneous Rock ChemistryIgneous Rock PaleomagneticsIgneous Rock Physical PropertiesConclusions

The Site Reports are co-authored by the entire scientificparty with additional paleontological contributions byDavid Bukry and John Barron. In general, Operationswere written by B. Rosendahl; sections on sediments byM. Hoffert and J. Natland (Lithology); R. Goll, D.Bukry, and J. Barron (Biostratigraphy); S. Humphris(Geochemistry); and N. Warren (Physical Properties).Sections on igneous rocks were written by R. Hekinian,E. Schrader, R. Fodor, S. Humphris, R. Srivastava, D.Mattey, Y. Dmitriev, and J. Natland (Petrography andChemistry); N. Warren (Physical Properties); and N.Petersen and W. Roggenthen (Paleomagnetics). Back-ground and Objectives and Conclusions were written byR. Hekinian and B. Rosendahl.

Numbering of Sites, Holes, Cores, Samples

Drill site numbers run consecutively from the firstsite drilled by Glomar Challenger in 1968; the site num-ber is thus unique. A site refers to the hole or holesdrilled from one acoustic positioning beacon. Severalholes may be drilled at a single locality by pulling thedrill string above the sea floor ("mudline") and offset-ting the ship some distance (usually 100 m or more)from the previous hole.

The first (or only) hole drilled at a site takes the sitenumber. Additional holes at the same site are furtherdistinguished by a letter suffix. The first hole has onlythe site number; the second has the site number with thesuffix A; the third has the site number with the suffix B;and so forth. It is important, for sampling purposes, todistinguish the holes drilled at a site, since recoveredsediments or rocks usually do not come from equivalentpositions in the stratigraphic column at different holes.

Cores are numbered sequentially from the top down.In the ideal case, they consist of 9.3 meters of sedimentor rock in a plastic liner of 6.6 cm diameter. In addition,a short sample is obtained from the core catcher (a mul-tifingered device at the bottom of the core barrel whichprevents cored materials from sliding out during core-barrel recovery). This usually amounts to about 0.2meter of sediment or rock. During Leg 54 the corecatcher sample was split, described, and stored alongwith the rest of the core, if at all possible, taking care tomaintain its proper vertical orientation. This samplerepresents the lowest stratum recovered in a particularcored interval.

The cored interval is the interval in meters below thesea floor measured from the point at which coring for aparticular core was started to the point at which it wasterminated. This interval is generally 9.5 meters (nomi-nal length of a core barrel) but may be shorter if condi-tions dictate. The interval can also be longer if the corebarrel was placed in the drill string during a long drillinginterval. On Leg 54 almost all core intervals were 9.5meters, because the drilling program called for nearlycontinuous coring.

When a core is brought aboard the Glomar Chal-lenger, it is labeled and the plastic liner and core are cutinto 1.5-meter sections. A full, 9.5-meter core wouldthus consist of six sections full and one 0.5-meter sec-tion numbered from the top down, 1 to 7. (Section 7would consist of 0.3 m of the lowest sediment from theplastic liner plus the 0.2 m of core-catcher material.)The procedure for labeling both full and partially fullcores is shown in Figure 6.

In the core laboratory on the Glomar Challenger,after routine processing, the 1.5-meter sections of sedi-ment core and liner are split in half lengthwise. One halfis designated the "archive" half, which is described bythe shipboard geologists, and photographed; and theother is the "working" half, which is sampled by theshipboard sedimentologists and paleontologists for fur-ther shipboard and shore-based analysis.

Samples taken from core sections are designated bythe interval in centimeters from the top of the core sec-

13

B. R. ROSENDAHL ET AL.

FULLRECOVERY

SECTIONNUMBER

PARTIALRECOVERY

PARTIALRECOVERYWITH VOID

1

2

3

4

5

6

7

Ml

I I

I I

I

CORE-CATCHERSAMPLE

SECTIONNUMBER

1

2

3

4

5

6

QO

-

SECTIONNUMBER

1

2

3

4

VO

ID

<-

QO>

CORE-CATCHERSAMPLE

CORE-CATCHERSAMPLE

Figure 6. Diagram showing procedure for cutting andlabeling core sections.

tion from which the sample was extracted; the samplesize, in cm3, is also given. Thus, a full sample designa-tion would consist of the following information:

Leg (Optional)Site (Hole, if other than first hole)Core NumberSection NumberInterval in centimeters from top of section

Sample 428A-4-3, 61-63 cm (10 cm3) designates a10-cm3 sample taken from Section 3 of Core 4 from thesecond hole drilled at Site 428. The depth below the seafloor for this sample would then be the depth to the topof the cored interval (3382.5 m in the example above)plus 4.5 meters for Sections 1,2, and 3, plus 0.61 meter(depth below the top of Section 3), or 3387.61 meters.Note, however, that subsequent sample requests shouldrefer to a specific interval within a core section (in cm)rather than depth in meters below the sea floor.

Sediment Description Conventions

Core Disturbance

Unconsolidated sediments are often severely dis-turbed by the rotary drilling/coring technique, and

there is a complete gradation of disturbance style withincreasing sediment induration. An assessment of de-gree and style of drilling deformation is made on boardship for all cored material, and shown graphically onthe core description sheets. The following symbols areused:

Slightly deformed; bedding contacts slightbend.

Highly deformed; bedding completelydisturbed, often showing symmetrical di-apir-like structures.

o o o o Soupy, or drilling breccia; water-saturatedintervals that have lost all aspects of origi-nal bedding and sediment cohesiveness.

o-o-OBiscuit structure; a drilling "breccia" inwhich the broken core material retainssome or all aspects of original bedding.

Consolidated sediments and rocks seldom show muchinternal deformation, but are usually broken by drillinginto cylindrical pieces of varying length. There is fre-quently no indication if adjacent pieces in the core linerare actually contiguous or if intervening sediment hasbeen lost during drilling.

Smear Slides

The lithologic classification of sediments is based onvisual estimates of texture and composition in smearslides made on board ship. These estimates are of arealabundances on the slide and may differ somewhat fromthe more accurate laboratory analyses of grain size, car-bonate content, and mineralogy. Experience has shownthat distinctive minor components can be accuratelyestimated (± 1 or 2%), but that an accuracy of ± 10 formajor constituents is more common. Carbonate contentis especially difficult to estimate in smear slides, as is theamount of clay present. Smear-slide analyses at selectedlevels as well as averaged analyses for intervals of uni-form lithology are given on the core description sheets.

Carbonate Data

Samples were taken for shore-based carbon-carbon-ate analysis using the LECO 70-second Analyzer. Theseand organic carbon values are also listed on the core de-scription sheets.

The LECO data were used to update the carbonatecontent (mostly shown as nannofossil foraminifer oozesor marls) depicted in the graphic lithology column. Noattempt was made to adjust smear-slide estimates orsediment names to reflect this correction.

Sediment Induration

The determination of induration is highly subjective,but field geologists have successfully made similar dis-

14

LEG 54 OBJECTIVES

tinctions for many years. The criteria of Moberly andHeath (1971) are used for calcareous deposits; subjec-tive estimate or behavior in core cutting is used forothers.

a) Calcareous sedimentsSoft: Ooozes have little strength and are readily

deformed under the finger or the broadplate of a spatula.

Firm: Chalks are partly indurated oozes; theyare friable limestones that are readily de-formed under the fingernail or the edge ofa spatula blade.

Hard: Cemented rocks are termed limestones.b) The following criteria are used for other sedi-

ments:If the material is soft enough for the core to besplit with a wire cutter, the sediment name onlyis used (e.g., silty clay, sand).If the core must be cut on the band saw or dia-mond saw, the suffix "stone" is used (e.g., siltyclaystone; sandstone).

Sediment Classification

The sediment classification scheme used on Leg 54 isbasically devised by the JOIDES Panel on SedimentaryPetrology and Physical Properties and adopted for useby the JOIDES Planning Committee in March 1974,with minor modifications. The classification is outlinedbelow.

I. General rules for class limits and order of com-ponents in a sediment name.A. Sediment assumes the names of those com-

ponents present only in quantities greaterthan 15 percent.

B. Where more than one component is present,the component in greatest abundance is list-ed farthest to the right, and other compo-nents are listed progressively to the left inorder of decreasing abundance.

C. The class limits are based on percentage in-tervals given below for various sedimenttypes.

II. Pelagic clay> 10% authigenic components<30% siliceous microfossils<30% CaCO3

< 30% terrigenous components

III. Pelagic siliceous biogenic sediments> 30% siliceous microfossils<30%CaCO3

< 30% terrigenous components (mud)Radiolarians dominant: radiolarian ooze (orradiolarite).Diatoms dominant: diatom ooze (or dia-tomite).Sponge spicules dominant: sponge spiculeooze (or spiculite).Where uncertain: siliceous (biogenic) ooze(or chert, porcelanite).

When containing 10-30% CaCO3: modifiedby nannofossil—, foraminiferal—, calcare-ous—, nannofossil-foraminiferal—, orforaminiferal-nannofossil—, depending up-on kind and quantity of CaCO3 component.

IV. Transitional biogenic siliceous sediments10-70% siliceous microfossils30-90% terrigenous components (mud)

<30% CaCO3

If diatoms < mud: diatomaceous mud (stone).If diatoms > mud: muddy diatom ooze (muddydiatomite).If CaCO3 10-30%: appropriate qualifier is used(see III).

V. Pelagic biogenic calcareous sediments>30% CaCO3

< 30% terrigenous components<30% siliceous microfossils

Principal components are nannofossils and fora-minifers; qualifiers are used as follows:Foraminifer % Name

<IO nannofossil ooze (chalk,limestone)

10-25 foraminiferal-nannofossilooze

25-50 nannofossil-foraminiferalooze

> 50 foraminiferal oozeCalcareous sediment containing 10-30 per centsiliceous fossils carry the qualifier radiolarian,diatomaceous or siliceous, depending upon theidentification.

VI. Transitional biogenic calcareous sediments>30% CaCO3

> 30% terrigenous components< 30% siliceous microfossils

If CaCO3 30-60%: marly is used as a qualifier:soft: marly calcareous (or nannofossil,

etc.) ooze,firm: marly chalk (or marly nannofossil

chalk, etc.).hard: marly limestone (or marly nan-

nofossil limestone).If CaCO3 > 60%:

soft: calcareous (or nannofossil, etc.)ooze.

firm: chalk (or nannofossil chalk, etc.).hard: limestone (or nannofossil limestone,

etc.).NOTE: Sediments containing 10-30% CaCO3

fall in other classes where they are de-noted with the adjective "calcareous,""nannofossil," etc.

VII. Terrigenous Sediments>30% terrigenous<30% CaCO3

< 10% siliceous microfossils< 10% authigenic components

Sediments in this category are subdivided intotextural groups on the basis of the relative pro-

15

B. R. ROSENDAHL ET AL.

portions of three grain-size components, i.e.,sand, silt and clay. Sediments coarser than sand-size are treated as "Special Rock Types." Thesize limits are those defined by Wentworth (1922)(Figure 7). The textural classification is accord-ing to the triangular diagram of Shepard (1954)(Figure 8). The suffix "-stone" is used to indi-cate hard or consolidated equivalents of the un-consolidated sediments.If CaCO3 is 10-30%: calcareous, nannofossil,etc. is used as a qualifier.Other qualifiers (e.g., feldspathic, glauconitic,etc.) are used for components >10%.

CLAY

SAND SILTSand-Silt Ratio

Figure 7. Terminology and class intervals of grade scales.

Millimeters

2.00

1.681.411.191.000.840.710.590.500.420.350.300.250.2100.1770.1490.1250.1050.0880.074

• 0.0625 -

0.0530.0440.0370.031 —0.0155 -0.0078 -

-0.0039 -0.00200.000980.000490.000240.000120.00006

1/2

1/4

1/8

1/16

1/32 -1/64 -1/1281/256

Phi (0)units

1.0 -

0.750.50.250.0 -0.250.50.75

• 1 . 0 •

1.251.51.752.0 -2.252.52.75

• 3 .0 •3.253.53.75

- 4.0 •

4.254.54.75

- 5.0- 6.0- 7.0- 8.0

9.010.011.012.013.014.0

Wentworth size class

— Granule

Very coarse sand

Coarse sand

Medium sand

Fine sand

Very fine sand

Coarse silt

Medium silt -Fine siltVery fine silt

Clay

Figure 8. Textural groups — terrigenous sediments.

VIII. Volcanic sedimentsa) Pyroclastic rocks are described according to

the textural and compositional scheme ofWentworth and Williams (1932). The tex-tural groups are:

Volcanic breccia 32 mmVolcanic lapilli 32 mmVolcanic ash (tuff, if indurated) 4

mmCompositionally, these pyroclastic rocks aredescribed as vitric (glass), crystal, or lithic.

b) Clastic sediments of volcanic provenance aredescribed in the same fashion as the terrige-nous sediments, noting the dominant com-position of the volcanic grains where possi-ble.At Site 424, we encountered a variety of Fe-Mn-rich sediments and green muds whichprobably are a product of near sea-floor hy-drothermal activity in the oceanic crust.These we call "Fe-Mn deposits" and "greenhydrothermal (?) muds," respectively.

Lithologic Symbols

Figure 9 shows the graphic symbols used to depict thelithologies encountered on Leg 54.

Core FormsThe core forms provide a variety of data and are

compiled at the back of each Site Report. Shipboardpaleontological determinations are provided in ap-propriate columns along the left hand margin. In thecolumn headed "Graphic Lithology," appropriate sym-bols are used to depict lithologies found in the cores.The columns titled "Drilling Disturbance" and "Sedi-mentary Structures" provide information on these as-pects of the cores according to the conventions previ-ously described. Drilling disturbance symbols wereshown in the section "Sediment Description Conven-tions" under the heading "Core Disturbance." Conven-tions relating to sedimentary structures are shown onFigure 10. All smear slides made aboard the ship are ap-propriately located in the column headed "LithologicSamples."

The broad column headed "Lithologic Description"provides a variety of data. Along the left margin arefound the color descriptions according to the Munsellcolor designations. All smear slides (abbreviated SS) areidentified by a centimeter designation corresponding tothat shown in the "Lithologic Sample" column. Thepercentage occurrence of each constituent is indicated,based on visual estimates. Estimates of the carbonateconstituents may vary by small or large amounts fromthose determined by the LECO.

BiostratigraphyRadiolarian studies on Leg 54 (R. M. Goll) use the

equatorial Pacific Quaternary zonation (Nigrini, 1971).

16

Pelagic

Non-biogenic

Pelagic Clay

Vertical bar percent(%) Designationfor Graphic Log.

Siliceous Biogenic

Pelagic Siliceous Biogenic - Soft

Diatom Ooze Radiolarian OozeDiatom-Rad orSiliceous Ooze

Pelagic Siliceous Biogenic - Hard

Diatomite Radiolariate Porcellanite Chert

Δ Δ Δ Δ ΔΔ Δ Δ Δ

Δ Δ Δ Δ ΔΔ Δ Δ

Δ Δ Δ ΔΔ Δ Δ

Λ _ A A AA A A A A

* A A A AA A A A

A A A A A

Transitional Biogenic Siliceous Sediments

Siliceous Component <50% Siliceous Component

Siliceous ModifierSymbol and According toHard or Soft.

Calcareous Biogenic

Pelagic Biogenic Calcareous - Soft

Nannofossil Ooze Foraminifer OozeNanno-Foram orForam-Nanno Ooze Calcareous Ooze

DDDODOO

CB4

Pelagic Biogenic Calcareous - Firm

Nannofossil Chalk Foraminifer Chalk

CB5

Pelagic Biogenic Calcareous - Hard

Limestone

1

1

1

1

1

1

1 1

1 I

I

Nanno-Foram orForam Nanno Chalk Calcareous Chalk

1 1 1 1 1

1 1

1

I I I 'I I I II ' I ' I ' II TTTlI ; i ; i

: i: iTf.

Transitional Biogenic Calcareous Sediments

1 ' 1 ' — 1 — " "1 1 1

1 1 1

1 1 1

1 ' 1 '

1 1

LEG 54 OBJECTIVES

Terrigenous Sediments Qualifiers Letter Overprint (as per examples)^— Zeolite Al Glauconite A3 Siderite A4 (other may be designated)

CJay/Claystone Mud/Mudstone Shale (Fissile) Sandy mud/Sandy mudstone Silt/Siltstone Sand/Sandstone

T4

Volcanic Lapilli Volcanic Breccia

Special Rock Types

BasicGravel Conglomerate Breccia Igneous

SR3

AcidIgneous

T6

Evaporites

Halite Anhydrite Gypsum

Concretions

Drawn Circle with Symbol (others may be designated)

Mn

= ManganeseP Pyrite Z - Zeoli te

m Fe-Mn deposits andGreen hydrothermal muds

Figure 9. Key to lithologic and biostratigraphic symbols.

17

B. R. ROSENDAHL ET AL.

Parallel

Contorted bedding(not artificial)

Graded bed A

•

Cross stratification

Gradational contract

(hand-drawn)

mem

¥//////////////,

Massive or homogeneous(no symbol necessary)

Load casts (hand-drawn)

(hand-drawn)

Sedimentary clasts O J M J*

Burrows *ΦSΦΦ$se§

TEXTURE

sed in graphic representation column

WEATHERING: ALTERATION

Used in alteration column

Figure 10. Sedimentary-structure symbols.

Coccolith and silicoflagellate studies (D. Bukry) employlow-latitude and eastern Pacific zonations (Bukry, 1975,1976; Bukry and Foster, 1973). Diatom studies (J. A.Barron) use the tropical Pacific zonation (Burckle,1972; Burckle and Updyke, 1977). Lettered diatom sub-zones appear in parentheses following the zone name.Preservation and abundance of diatoms and silicoflagel-lates are estimated from acid-cleaned, strewn-slide prep-arations.

Basement Description Conventions

Core Forms

Initial core description forms for igneous and meta-morphic rocks are not the same as those used for sedi-ments. The sediment barrel sheets are substantiallythose published in previous Initial Reports. Igneousrock representation on barrel sheets is too compressedto provide adequate information for potential sampling.Consequently, Visual Core Description forms, modifiedfrom those used onboard ship, were used for more com-plete graphic representation. All shipboard data per1.5-meter section of core are listed on the modifiedforms as well as summary hand-specimen and thin-sec-tion descriptions. The symbols and a number of formatconventions for igneous rocks used on Leg 54 are pre-sented on Figure 11.

All basalts on Leg 54 were split using a rock saw witha diamond blade into archive and working halves. Thelatter was described and sampled on board ship. On atypical basalt description form (compiled at the back ofeach Site Report), the left column is a visual representa-tion of the working half using the symbols of Figure 11.Two closely spaced horizontal lines in this column in-dicate the location of styrofoam spacers taped betweenbasalt pieces inside the liner. Each piece is numbered se-quentially from the top of each section, beginning withthe number 1. Pieces are labeled on the rounded, not thesawed surface. Pieces which were possible to fit togetherbefore splitting are given the same number, but are con-secutively lettered, as 1A, IB, 1C, etc. Spacers wereplaced between pieces with different numbers, but notbetween those with different letters and the same num-

Aphyric basalt

Variolitic basalt

Porphyritic basaltOlivine andplagioclasephenocrystsOlivine

plagioclase andclinopyroxenephenocrysts

Vein with alteredzone next to it

oGlass on edge(rounded piece)

Very fresh

•—C\ Weathered rind—' / on rounded piece

O 0

0 ° 0

m

Vesicles(approximate size)

Breccia(as graphicas possible)

\Moderatelyaltered

Dolerite(Diabase)

Serpentinite (shearorientation approximatelyas in core; Augen showntoward bottom)

Badlyaltered

Almost completelyaltered

Figure 11. List of symbols for igneous rock descriptionforms (some not applicable to Leg 54).

ber. In general, addition of spacers represents a drillinggap (no recovery). However, in cores where recoverywas high, it was impractical to use spacers. In thesecases, drilling gaps are indicated only by a change innumbers. All pieces have orientation arrows pointing tothe top of the section, both on archive and workinghalves, provided the original unsplit piece was cylindri-cal in the liner and of greater length than the diameter ofthe liner. Special procedures were adopted to ensurethat orientation was preserved through every step of thesawing and labeling process. All pieces suitable for sam-pling requiring knowledge of top from bottom are in-dicated by upward-pointing arrows to the left of thepiece numbers on the description forms. Since the pieceswere rotated during drilling, it is not possible to samplefor declination studies.

Samples were taken for various measurements on-board ship. The type of measurement and approximatelocation are indicated in the column headed "Sample"using the following notation:

X = X-ray fluorescence analysisM = magnetics measurementsS = sonic velocity measurementsT = thin sectionD = density measurementsP = porosity measurements

18

LEG 54 OBJECTIVES

Igneous Rock Classification

No igneous rocks other than basalts were recoveredon Leg 54. Classification was based mainly on mineral-ogy of minerals visible in hand specimens, and second-arily on texture and thin-section data (usually based on1000 point counts per thin section).

Basalts are termed aphyric, sparsely phyric, or mod-erately phyric depending on the proportion of pheno-crysts visible with the binocular microscope (~ ×12).Aphyric basalts were so called if phenocrysts were ab-sent. In a practical vein, this meant that if one piece ofbasalt was found with a phenocryst or two in a sectionwith all other pieces lacking phenocrysts, and no othercriteria such as grain size or texture distinguished thisbasalt from the others, then it too was described asaphyric. A note of the rare phenocrysts, however, wasincluded in the general description. This was done inorder to restrict the number of lithologic units to thosewith clearly distinctive and persistent visual differences.

Sparsely phyric basalts are those with 1 to 2 per centphenocrysts present in almost every piece of a given coreor section. Clearly contiguous pieces without pheno-crysts were included in this category, again with the lackof phenocrysts noted in the general description.

Moderately phyric basalts contain 2-10 per cent phe-nocrysts. Aphyric basalts within a group of moderatelyphyric basalts are separately termed aphyric basalts.

The basalts are further classified by phenocryst type,preceding the terms phyric, sparsely phyric, etc. Aplagioclase-olivine moderately phyric basalt contains2-10 per cent phenocrysts, most of them plagioclase, butwith some olivine.

REFERENCES

Bougault, H., 1977. Major elements: Analytical chemistry on-board and preliminary results. In Aumento, F., Melson,W. G., et al., Initial Reports of the Deep Sea Drilling Pro-ject, v. 37: Washington (U.S. Government Printing Office),p. 643.

Boyce, R. E., 1976. Definitions and laboratory techniques ofcompressional sound velocity parameters and wet-watercontent, wet-bulk density, and porosity parameters bygravimetric and gamma ray attenuation techniques. InSchlanger, S. O., Jackson, E. D., et al., Initial Reports ofthe Deep Sea Drilling Project, v. 33: Washington (U.S.Government Printing Office), p. 931-958.

Bukry, D., 1975. Coccolith and silicoflagellate stratigraphy,northwestern Pacific Ocean, Deep Sea Drilling Project Leg32. In Larson, R. L., Moberly, R., et al., Initial Reports ofthe Deep Sea Drilling Project, v. 32: Washington (U.S.Government Printing Office), p. 677-701.

, 1976. Silicoflagellate and coccolith stratigraphy,southeastern Pacific Ocean, Deep Sea Drilling Project Leg34. In Yeats, R. S., Hart, S. R., et al., Initial Reports of theDeep Sea Drilling Project, v. 34: Washington (U.S. Gov-ernment Printing Office), p. 715-735.

Bukry, D. and Foster, J. H., 1973. Silicoflagellate and diatomstratigraphy, Leg 16, Deep Sea Drilling Project. In vanAndel, T. J., Heath, G. R., et al., Initial Reports of theDeep Sea Drilling Project, v. 16: Washington (U.S. Gov-ernment Printing Office), p. 815-871.

Burckle, L. H., 1972. Late Cenozoic planktonic diatom zonesfrom the Eastern Equatorial Pacific, Nova HedwigiaBeihefte, v. 39, p. 217-246.

Burckle, L. H. and Updyke, N. D., 1977. Late Neogene dia-tom correlations in the circum-Pacific, Internat. Congr.Pacific Neogene Strat., First, Tokyo, Proc., p. 255-284.

Lonsdale, P., 1977. Deep-tow observations at the moundsabyssal hydrothermal field, Galapagos Rift, Earth Planet.Sci. Lett., v. 36, p. 92-110.

Melson, W. G., Rabinowitz, P. D., Natland, J. H., Bougault,H., and Johnson, H. P., 1978. Cruise objectives and majorresults, analytical procedures and explanatory notes. InMelson, W. G., Rabinowitz, P. D., et al., Initial Reports ofthe Deep Sea Drilling Project, v. 45: Washington (U.S.Government Printing Office), p. 5-20.

Moberly, R., Jr. and Heath, G. R., 1971. Carbonate sedimen-tary rocks from the western Pacific: Leg 7, Deep Sea Drill-ing Project. In Winterer, E. L., Riedel, W. R., et al., InitialReports of the Deep Sea Drilling Project, v. 7, Part 2:Washington (U. S. Government Printing Office), p. 977-985.

Nigrini, C , 1971. Radiolarian zones in the Quaternary of theequatorial Pacific Ocean. In Funnell, B. M. and Riedel, W.R. (Eds.), The Micropaleontology of Oceans: Cambridge(Cambridge University Press), p. 443-461.

Sclater, J. G. and Klitgord, K. D., 1973. A detailed heat flow,topographic, and magnetic survey across the Galapagosspreading center at 86°W, / . Geophys. Res., v. 78, p.6951-6975.

Shepard, F. P., 1954. Nomenclature based on sand-silt-clayratios, /. Sediment. Petrol., v. 24, p. 151-158.

Wentworth, C. K., 1922. A scale of grade and class terms ofclastic sediments, J. Geol., v. 30, p. 377.

Wentworth, C. K. and Williams, H., 1932. The classificationand terminology of the pyroclastic rocks, Rept. Comm.Sedimentation, Bull. Nat. Res. Counc, no. 80, p. 10-53.

19

B. R. ROSENDAHL ET AL.

APPENDIX

Scaling Wave Technique for Measuring Velocities on Shipboard

Figure / is a block diagram of the system. Instrument settings forthe frequency generator and the oscilloscope are given under "Instru-ment Settings;" the system's modus operandi is described under"Measurement Steps."

VELOCITY MEASUREMENT/equipment schematic

Hamilton Frame

Exact126 VCF/SweepGenerator output

(N)

0)

Exact 126 VCF/Sweep GeneratorTrig in: from B + Gate of Tektronix (rear panel)Range (Hz): 3 MHzOutput: to scope (Tektronix 485) Ch. 1Output: electrical "T" to frequency counterFunction: sineMain mode: gate

Measurement Steps

1. On 126 VCF: adjust the trigger level so the gated sine wavedisplays a flat initial base line b (Figure ii).

(U)

2. Adjust the amplitude to give an approximate 5-volt display on theTektronix oscilloscope.

3. Adjust the zero starting level so that the base line is aligned withthe top of sine waves (Figure in).

(Hi)

No sample adjustment4. Transducers in contact; i.e., no sample.5. Set the Horizontal Display on oscilloscope (485) to "INTEN."6. Adjust the Delay time dial on oscilloscope (485) until the display

appears as in Figure iv. This is the zero-time (no sample setting).

Parts belonging to the regular velocity measuring system are hatched.Two additional instruments for the "scaling wave" and the "pickpoint" methods are marked by the letter N.

Instrument Settings

Tektronix 485A triggering: external trigger from unit pulse generator

coupling: ACsource: EXTsweep mode: normal

B triggering:coupling: ACsource: "B runs after delay time"

A trigger hold off: "norm" positionHorizontal display: "INTEN"Time/div. and delay time: 2 µsCh. 2: from frame

coupling AC1MQ(volts/div. = 10 mV)

Ch. 1: from 126 VCF/Sweep Generator outputcoupling AClMß(volts/div. = 5 V)

Vertical mode: alt.Ch. 2 polarity: invertBW limit: in

(iv)

Measurement of Sample7. Place sample in the Hamilton Frame.8. Adjust Multiplier on 126 VCF until signal arrival is marked by a

scaling wave as shown in Figure v. There should be about 10 waves(N = 10) between start of the scale and the signal's first arrival.Record N.

(v)

9. On the 126 VCF, turn Main Mode switch to "RUN," record thefrequency f from the frequency counter

travel time (s) = N/f; for f in MHz

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