3. SITE 203
The Shipboard Scientific Party1

Location: Lau Basin
Position: 22°09.22'S, 177°32.77'W
Water Depth: 2720 meters (corrected)
Total Penetration: 409 meters

Contour interval 400 fathoms. (After Mammerickx, Chase,
Smith, and Taylor, 1971. Bathymetry of the South Pacific,
Charts 11 and 12: Scripps Institution of Oceanography,
California.)
Summary: Intermittently cored, the sediment is primarily a calcareous fossil ooze with high concentration of ash andvolcanic sands. The oldest dated sediment is early Pliocene, but extrapolation based on estimated accumulation ratio indicatesapproximate late Miocene age for acoustic basement.
BACKGROUND AND OBJECTIVESGeneralThe Lau Basin forms the interarc basin between the
Tonga and Lau ridges and has morphologic continuity
southward with the Havre Trough and the Taupo volcaniczone of New Zealand. Earlier work by Karig (1970)
summarized its general characteristics and suggested that
there was no observable systematic variation in depth or
structural style across the basin. The area is one ofridge-trough topography with axial trends generally
northeast-southwest. The acoustically opaque basement issimilarly lineated and has been interpreted as tilted fault
blocks. Sediment cover over most of the central portion of
the basin is very thin and patchy. It generally thickens near
Robert E. Burns, NOAA-Pacific Oceanographic Laboratories,
University of Washington, Seattle, Washington, Co-Chief Scientist;
James E. Andrews, University of Hawaii, Honolulu, Hawaii,
Co-Chief Scientist; Gerrit J. van der Lingen, New Zealand Geological
Survey, Christchurch, New Zealand; Michael Churkin, Jr., U. S.
Geological Survey, Menlo Park, California; Jon S. Gatehouse, San
Francisco State College, San Francisco, California; Gordon H.
Packham, Univeristy of Sydney, Sydney, New South Wales,
Australia; Thomas A. Davies, Scripps Institution of Oceanography,
La Jolla, California; James P. Kennett, University of Rhode Island,
Kingston, Rhode Island; Paulian Dumitrica, Geological Institute of
Romania, Bucharest, Romania; Anthony R. Edwards, New ZealandGeological Survey, Lower Hutt, New Zealand; Richard P. Von
Herzen, Woods Hole Oceanographic Institution, Woods Hole,
Massachusetts.

the margins of the basin and consists primarily of
calcareous pelagic sediments and volcanic detritus.
Site 203 was tentatively located on the basis of seismic
profile records from Argo, Conrad, Eltanin, Horizon, andKona Keoki. It was proposed with the objectives ofdetermining the age and composition of the interarc basin
sediments and dating the basement. As such, it is one of aseries of sites to be drilled on Leg 21 in several of themarginal basins in this region of the southwest Pacific.
Review by the JOIDES Panel on Pollution Prevention
and Safety indicated that the proposed site and drilling
program were acceptable with intermittent coring, moderate drilling precautions, and standard abandonment
procedures.

Site Survey

Site 203 was the only one on Leg 21 for which a
detailed site survey was not available prior to departurefrom Fiji. Although R/VKana Keoki had carried out a brief
survey in the northern part of the area, the actual site
selected for drilling was in the southern portion of the Lau
Basin. Here, available bathymetry indicated a narrower,smoother, and more clearly defined interarc basin than thesite which had been suggested originally. Because of thelack of specific survey data, the site approach was designed
to provide necessary site information prior to dropping the
beacon.
17

SITE 203
OPERATIONS
Site Approach

Six hours on the site approach were devoted to defining
local characteristics and making a final selection of adrilling site. A preliminary box pattern (Figure 1) showed
the area to be quite rough, with several small sedimentarybasins of apparently limited longitudinal extent (e.g.,
Figure 2). Just east of the area of the box survey, asomewhat larger basin was found, and the site was occupied
there after an initial pass to determine the east-west limitsof the basin. Although the length of this basin was notdetermined, it is presumed to follow the general
north-northeast trend of the Lau Basin. Sediment thickness
in the center of the pond reaches a maximum of 1.5 sec
two-way travel time, and the width of 6 nautical miles
makes this basin larger than others encountered within the
Lau Basin. Prominent seismic reflecting horizons occur at
0.2 and 0.4 sec subbottom across the width of the basin.
The approach profile crossing the basin shows no clear
evidence of slumping or mass movement of sediments fromeither the Lau or Tonga Ridges, suggesting generally pelagicand eolian sedimentation. Reflective horizons in the upper
three quarters of the section are roughly horizontal, while a
few of the deepest reflectors follow the basement slope
suggesting deformation during the early history of thebasin.
In order to obtain a representative section and basement
age with minimal drilling, the site was occupied at theeastern margin of the basin where sediment thickness was
0.55 sec.
Sonobuoys
Two successive sonobuoys malfunctioned during
attempts to record a vertical reference profile. Because of
the need to conserve equipment for measurements at latersites, no further trials were made and no vertical profile wasobtained at Site 203.
Drilling Program

The drilling program was planned to sample the principal
units indicated by the seismic reflection profile and to getcores at and in the basement.
Cores 1 and 2 sampled the uppermost 15 meters of thesection. The drill was then washed down to 108 meters, andCore 3 was obtained as a sample of the unit above the0.2-sec reflector. Core 4 was taken in the vicinity of the
0.2-sec reflector and Core 5 in the vicinity of the 0.4-sec
reflector.
Although drilling and coring had been routine, afterCore 5 was recovered and drilling operations were resumed,
the pipe was found to be jammed in the hole. Neither
rotation nor pumping could be accomplished, and several
hours were expended working the assembly loose.
In view of the constraint of having only two bottom
hole assemblies aboard, it was decided to abandon the site
short of the objective of reaching basement. Upon recoveryof the gear, it was concluded that loose sand which had
been drilled somewhere in the interval following Core 4 had
caved and frozen the pipe. During the working of theassembly, while trying to free it, several meters of the sand18

had been collected in the core barrel. These have beenretained as a sample, but are not considered to be a core.
Table 1 is a summary of the coring at Site 203.
LITHOLOGY
GeneralFive cores were taken at Site 203 before the drill string
became stuck and drilling operations were abandoned. The
principal lithologies are calcareous biogenic ooze andvolcanic ash. Data are insufficient for subdividing thesequence into lithologic units. Consequently, the following
discussion is on a core-by-core basis. Grain size and organiccarbon determinations and descriptions of each of the coresare given in Appendixes A, B, and F, respectively.
Core 1 (0 to 6 meters) in the soft surface sediment ismainly brown nanno ooze of Recent to late Pleistocene age.
The core is slightly to highly disturbed, with an increase inglass content downwards. Two layers in the core are richenough in ash to be called volcanic ash.
Core 2 (6 to 15 meters) which is extremely disturbed
and is composed of post-mid or late Pleistocene nannofossil
ooze with 5% to 10% volcanic glass. Most of the glass is silt
sized, colorless, and contains spherical to rod-like vesicles.
In a specimen from Sample 203-2-1, 99 cm, this glass has arefractive index of 1.506 to 1.510, suggesting a silica
content of about 68% according to the refractive
index—silica content curve of George (1924). A smaller
percentage of green glass is also present in the sample. This
has a refractive index of 1.580 to 1.596, indicating acomposition of 48% to 50% silica using the same method.
The other volcanic products are Plagioclase and clinopyroxene. The feldspar refractive index measured range
from 1.570 to 1.582, suggesting a calcic bytownite if only asingle composition is present. No quartz was detected in thesample by X-ray diffractometry.
The brown color of the samples is attributable togranules of iron oxide throughout the sediment. Theseoccur as radiating aggregates up to 25µ in diameter.
Apart from the abundant coccoliths, other organic
debris present includes foraminifera, Radiolaria, diatoms,
silicoflagellates, and holothurian remains. Small, circular,
brown organic bodies up to 5µ in diameter are also present.
Core 3 (108 to 117 meters) of early Pleistocene age
consists of an upper 6.9 meters of ash in sharp contact withan underlying 2.1 meters of nannofossil ooze. The ash issilty throughout most of its thickness but coarsens to sandyin its basal 20 cm. The ash is composed predominantly ofclear, colorless glass with a small proportion of pale brownglass together with minor clinopyroxene and Plagioclase
feldspar. Nannofossils are present in small proportions innearly all samples, but reach 30% in places. Foraminifera
are also present in some samples, but siliceous fossil remains
are absent. Bulk X-ray results from Sample 203-3-4,
120-122 cm, give 45% calcite, 5% quartz, 36% Plagioclase,
4% chlorite, and 11% montmorillonite in the crystalline
fraction. A specimen from the base of the ash (Sample
203-3-5, 86 cm) contains colorless glass with a refractive
index range of 1.514 to 1.54, pale brown glass with arefractive index of 1.54 to 1.57, and Plagioclase with arange of refractive indices from 1.55 to 1.57. These data

SITE 203

177°52'W

177°46'W

177°40'W

177°34'W- 21°54'S- 22°00'S-22°06 S

Figure 1. Glomar Challenger track 17November 1971. Survey for Site 203.

19

SITE 203

:;
1
1

co
Q
O
O

i3

*" a*

$r

£ -f "j*"^- - l f - 7 1 •S-. iji--T--.S.^KSW'

v.

^n

I

i •r

Figure 2. Reflection profile of sediment pond drilled at Site 203 and adjacent pond showing extensional deformation in the
Lau Basin.
TABLE 1
Coring Summary, Site 203

Core

Date

Time

Depth fromDrill Floor
(m)

1
2
3
4
5

11/18
11/18
11/18
11/18
11/18

0310
0402
0645
1028
1422

2730-2736
2736-2745
2838-2847
2959-2968
3130-3139

Depth Below
Sea Floor
(m)
0-6

6-15
108-117229-238
400-409

Total

Cored
(m)

Recovered(m)

Recovery
(%)

6
9
9
9
9

5.4
2.0
9.0
2.4
1.5

90
22
100
27
17

42

20.3

48

Note: Echo sounding depth (to drill floor) = 2727 meters;
drill pipe length to bottom = 2730 meters.

suggest a silica range of 56% to 66% for the colorless glass,
52% to 56% for the pale brown glass, and a broad possible
range of Plagioclase composition from andesine to
bytownite. The presence of quartz is in keeping with themore sodic Plagioclase than that found in samples fromCore 2.

20

The lithology of the nannofossil ooze in the basal part ofCore 3 is similar to that of Cores 1 and 2, except thatsiliceous fossil remains are absent. Volcanic glass is present
in quantities estimated in smear slides from 7% to 15%.
Cores 4 and 5 sampled more indurated parts of thesection and consist of separate pieces of rock up to 10 cm

SITE 203in length. Recovery was poor, amounting to 2.4 meters inCore 4 and 1.5 meters in Core 5. Both cores consist oflayers of gray ash alternating with layers of paler gray andyellow nanno ooze. Volcanic glass is present in all the oozes
except the basal 44 cm of Core 5. Both cores aremoderately to intensely mottled. Burrows include
Chondrites and Zoophycos types.
Core 4 (229 to 238 meters) straddles the PliocenePleistocene boundary. The percentage of nannoplankton
has been estimated from smear slides to range from about
5% to over 60%. Abundant foraminifera were noted in one
layer (Sample 203-4-1, 80 cm) where they were estimatedat 35%. Clay is present but difficult to estimate from smear
slides, but up to 30% is suggested for the ash-poor layers.
Iron oxide granules are present in these same layers in therange of 1% to 5%. Bulk X-ray data from a sample of one ofthese beds revealed a composition of calcite 25%, quartz
7%, chlorite 4%, Plagioclase 46%, augite 8%, montmorillonite 6%, and magnetite 4% for the crystalline phases. The
Plagioclase in this sample has a range of refractive index
from 1.56 to 1.57, suggesting a labradorite to bytownite
composition. Nearly all the glass in this sample is pale green
and altered. The volcanic ash horizons in the core show
some variety, in some the glass is a clear type with a low
refractive index, while in others green to greenish brownglass is the predominant type. The degree of alteration of
the darker glass is much greater than in the higher cores.
The refractive indices of the dark glasses are close to thatof the mounting medium (Caedex), i.e., about 1.56 andtherefore probably basaltic.
Core 5 (early to middle Pliocene), from 400 to 409
meters, shows the effects of volcanism most strongly; itconsists of volcanic ash overlying nanno ooze. The top of
the core consists of unconsolidated black sand, containing
glass with a refractive index of 1.58 and olivine, overlying asilty moderately indurated gray, glass-shard ash. The glass inthis latter sediment is mainly colorless with a low refractive
index. A specimen from Sample 203-5-1, 78 cm, shows thispale glass to have a range of refractive indices from 1.518
to 1.534 with most falling in the range of 1.526 to 1.530.
These values suggest a silica percentage of about 58% using
the curve of George (1924) in contact with 50% silica forthe glass in the overlying sand. The Plagioclase in the same
sample has a refractive index range from 1.564 to 1.578
with most grains between 1.568 and 1.574, indicating a
calcic labradorite to bytownite composition. No quartz was
detected by X-ray diffractometry, but minor quantities ofclinopyroxene are present. In other samples, up to
one-third of the glass is dark and usually altered.
Interbedded paler beds are richer in nannofossils (up to
40% of the sediment). Foraminifera are present in minor
quantities, but no siliceous organisms were noted.
Within the ash layer are two rounded cobbles of highly
vesicular olivine basalt. There are no marks on the basalt tosuggest that the rounding is the result of abrasion by the
drill bit so that the rounded cobbles and the black sandmight suggest that at the time of deposition volcanic
activity was taking place nearby and in shallow water.
However, the sand consists of freshly broken fragments ofgreen glass and olivine and is reasonably well sorted. The
basalt fragments are highly altered. It is possible that thesand and the basalt are of quite unrelated origins. The sandmay be material which has caved down the hole either froma sand layer somewhat above the level of Core 5 or,alternatively, is the result of the pulverizing of a thin layerof basalt by the drill bit.
The lower part of the core, beneath the ash layer,
consists of nannofossil ooze. The lower part of this ooze isbrown in color, whereas the upper part is yellow. The
boundary between the two parts is quite sharp and,
although it is inclined, the structure of the sediments does
not seem to be disturbed. This suggests that the boundary is
secondary in nature and may represent a front of ironenrichment associated with volcanism in a lower part of thesection beneath that part sampled (cf. Boström andPeterson, 1969). The suggestion of some kind of diagenetic
alteration is enhanced by the presence of about 40% ofmaterial identified as clay in the smear slides about 10% ofiron oxide in the lower (brown) part and the absence ofrecognizable glass shards.
Sample 203-5, CC contained a cobble of highly vesicularbasalt. Another basalt cobble was found jammed in the
opening of the drill bit after recovery of the entire string.
The vesicles comprise about half of the basalt from the corecatcher; the remainder consist mostly of highly altered glasswith thin needle-like feldspars, small crystals of pale green
clinopyroxene, and large fresh olivine phenocrysts.
A large quantity of black volcanic sand was foundjammed in the core barrel after recovery of the string. Thisis the same as the sand at the top of Core 5 and is probably
cavings from higher up in the hole, since the drill had notadvanced at all beyond the depth of Core 5 before
becoming stuck in the hole.
Discussion
Site 203 lies on the western side of the Lau Basin in a
depth of 2730 meters of water. The Lau Ridge to the west
is unexposed in the region except for a few shoals and reefs,
shows no sign of recent volcanic activity, and is thus notregarded as a source of the volcanic ash found at Site 203.
By contrast, the western side of the Tonga Ridge to the eastof the basin is characterized by an active series of exposed
volcanic islands and submarine volcanoes. The line of strikeof these volcanic features lies about 150 km east of Site
203, and they are the most likely source of the bulk of the
volcanic debris found in the cores.
A recent study of the chemistry and petrography of thelate Cenozoic volcanics of the western side of the Tonga
Ridge by Bryan, Stice, and Ewart (1972) reveals that the
volcanics there have similar features. They comprisebasaltic andesites, andesites, and dacites, and containbytownite to calcic labradorite as their feldspar. Basalts areabsent. The presence of small amounts of quartz in samples
from Cores 3 and 4 is also compatible with an origin on the
Tonga Ridge. Pigeonite and hypersthene occur in the
volcanics on the islands along with augite. Unfortunately,
the only pyroxene seen in the sediments at Site 203 is palegreen clinopyroxene, presumably diopsidic augite.
The basaltic debris which is present in larger quantities
in Core 4, and more especially in Core 5, may have a
different origin, since late Cenozoic basalts have not beenfound in the western Tonga Ridge volcanics. The basaltic

21

SITE 203

debris may be similar to the material which comprises thesea floor of the Lau Basin; Sclater et al. (1972) have foundthis to be tholeiitic basalt. The shallow water origin
suggested for the highly vesicular basalt and perhaps theglass-olivine sand in Core 5 is difficult to explain because it
appears that deposition of the whole sequence sampled at
Site 203 took place at about the present depth. This isindicated by the foraminifera which are typical of lower
bathyal assemblages throughout all the cores.
BIOSTRATIGRAPHY
GeneralThe five cores obtained from Site 203 represent asequence ranging in age from the middle Pliocene to
Recent.
Cores 1 and 2, consisting of nanno ooze, containabundant, well-preserved foraminifera and calcareous
nannofossils indicative of late Pleistocene to Recent. Alsopresent are a few Radiolaria having Pleistocene and Recent
affinities. The first upward appearance of the nannofossil
Emiliania huxleyi in Sample 203-1-1,60 cm, is indicative ofa latest Pleistocene age. The presence of the silicoflagellates
Dictyocha aculeata and D. messanensis without D. lingi or
Mesocena elliptica throughout Cores 1 and 2 indicates apost middle Pleistocene age, i.e., younger than the
Matuyama paleomagnetic epoch (top = 0.7 m.y. B.P.).
Abundant reworked older Pleistocene calcareous nannofossils were observed in the volcanic ash horizons of Core 1.
Core 3, essentially a nannofossil-rich ash, contains
abundant, moderately well preserved early Pleistocene
foraminifera and calcareous nannofossils. No Radiolaria
were found in this and subsequent cores.
Core 4, consisting essentially of an ash-rich nannofossil
ooze, contains few to common moderately well preserved
foraminifera and calcareous nannofossils. The PliocenePleistocene boundary occurs between Samples 203-4-1,
87-89 cm, and 203-4-2, 45-47 cm, based on the transition
between Globorotalia truncatulinoides and G. tosaensis.
The last appearance of discoasters in reasonable numbers
occurs between Samples 203-4-1, 75 cm, and 203-3, CC. In
Core 3 they are exceedingly rare, and hence, almost
certainly reworked. Even in Sample 203-4-1, 75 cm, thepresence of some battered Discoaster brouweri among
many undamaged specimens indicates at least somereworking.
Core 5, consisting mostly of nannofossil-rich ash andclay-rich nannofossil ooze, contains common to abundant
moderately well preserved calcareous nannofossils andforaminifera. The foraminifera are indicative of middle
Pliocene age (N20), whereas the nannofossils indicate abasal late Pliocene age (NN16). For the purposes of thisreport a middle Pliocene age is adopted.
Benthonic foraminifera indicate deposition in lower
bathyal depths throughout, and calcareous nannofossils of
neritic habitat are absent. The planktonic assemblages areof tropical affinity throughout.
An average sedimentation rate for the Pleistocene is 120
m/million years, although the thickness of nannofossil Zone
NN21 suggests a drastic decrease in deposition rates in theupper part of the section.

22

Foraminifera

Planktonic foraminifera are abundant and moderately
well preserved in all five cores obtained from Site 203. The
assemblages show that a sequence of high sedimentation
rate was drilled, ranging in age from the Recent to the
middle Pliocene (Zone N20).
Core 1 contains a well-preserved fauna of Recent orlatest Pleistocene age, including Globorotalia truncatulinoides, Globorotalia crassaformis, Globigerinoides ruber,
Globorotalia menardii, Globigerina digitata, and Globigerina dutertrei. The absence of Globorotalia menardii
flexuosa and yet the presence of G. menardii suggest a
postglacial or Recent age. Volcanic ash is important.
Core 2 contains a similar fauna except that the presenceof Globorotalia menardii flexuosa indicates greater age
within the late Pleistocene (Zone N22). Pumice fragments
are conspicuous in this core in addition to volcanic ash.
Core 3 contains a well-preserved fauna of earliest
Pleistocene age (lowest N22) as indicated by the common
occurrence of G. truncatulinoides and the rare touncommon occurrence of Sphaeroidinella dehiscens,
Globorotalia inflata, and Globigerinoides fistulosus.
Core 4 contains moderately well preserved, rare tocommon planktonic foraminifera. The Pliocene-Pleistocene
boundary occurs between Samples 203-4-1, 87-89 cm, and203-4-2, 45-47 cm, based on the first appearance ofGloborotalia truncatulinoides in moderate numbers in
Sample 203-4-1, 87-89 cm. A late Pliocene age (N21) for
specimens below Samples 203-4-2, 45-47 cm, is indicatedby an association of Globorotalia tosaensis, Globigerina
decoraperta, Globigerinoides quadrilobatus, Globorotalia
hirsuta, Sphaeroidinella dehiscens, and Globigerina
humerosa.
Core 5 contains a poor to moderately preserved,
common assemblage of planktonic foraminifera of middle
Pliocene age (N20) based on an association of Globorotalia
crassaformis, Sphaeroidinella subdehiscens, Sphaeroidinella
seminulina, Globigerinoides obliquus, Globoquadrina
altispira, Globigerina decoraperta, Globigerina humerosa,
Globorotalia cibaoensis, and Pulleniatina obliquiloculata
precursor.
Benthonic foraminifera are rare throughout and virtuallyabsent in Core 5. All forms noted were typical of the lower
bathyal environment.
Calcareous Nannofossils

The biostratigraphy of Site 203, as deduced from thecalcareous nannofossils, is summarized in Figure 3. For adetailed discussion of the floras, see the report by Edwards(Chapter 18).
Siliceous Microfossils

Radiolarians and silicoflagellates are rare to few and wellpreserved in Samples 203-1, 0-6 cm, and 203-2, 6-15 cm,
and absent in the underlying cores, except for Samples
203-3-6, 80-82 cm, and 203-3, CC, which contain very rarecorroded orosphaerid spines. The delicate skeletons of mostradiolarians and the abundance of collosphaerids in the firsttwo cores suggest a near-surface tropical water mass origin.

SITE 203
ADOPTED AGE

METERSZONE
NN21
t NN20PLEISTOCENE

Mesocena elliptica from this assemblage supports apost-middle Pleistocene age (D. aculeata Zone) or the
Brunhes Normal Paleomagnetic Epoch.

<

PHYSICAL PROPERTIES
108
117

229238

NN19

-

NN18

Introduction

At Site 203, bulk densities were determined by thestandard Gamma Ray Attenuation Porosity Evaluation(GRAPE) device. Calculations for porosity were made using
an assumed grain density of 2.65 gm/cc, but the results are
not discussed here since they have not been fully analyzed.
Sonic velocities were measured, using the Hamilton
frame device, and thermal conductivity (K) of the cores wasmeasured using the heated needle probe method.
Bulk Density

LATE PLIOCENE

<

400-^
409^

NN16

Figure 3. Bio stratigraphy of Site 203 as deduced from thecalcareous nannofossils.

The absence of the silicoflagellate Distephanus speculum inthe assemblages supports this conclusion.
The assemblages are rather uniform through the twocores. Among other taxa they contain: Ommatartus
tetrathalamus, Anthocyrtidium zanguebaricum, Theo~
corythium trachelium, Lamprocyclas maritalis, Lithopera
bacca, Lithocircus reticulata, Tholospyris acuminata,
Tholospyris(l) cupola, Acanthodesmia vinculata, etc.
Frequently found were well-preserved phaeodarians such as
Porospathis holostoma, CastanidiumC>) fenestratum, Protocystis xiphodon, P. thomsoni, P. harstoni, Lirella marina, L.
melo, L. inauris, Euphysetta elegans, E. lucanii plus
fragments of Aulographis taumorpha, Aulographonium
candelabrum, A. pulvinatum, dichotomous coelodendrid
spines, and many other remains. Phaeodarians are generally
only found in surface sediments, and hence, their presence
throughout the upper 15 meters is surprising. There is noevidence of dissolution of the hollow skeletons of thephaeodarians with depth in sediment. This might be mainly
due to the intense volcanic activity that saturated theseawater with silica and thus prevented dissolution of thesiliceous skeletons of phaeodarians as Riedel (1959) andStadum and Ling (1969) suppose.
There is no clear evidence among the radiolarians in
Cores 1 and 2 for a precise age determination, although
their Quaternary age is evident. In this respect thesilicoflagellates, which are infrequent, give much more
precise data. Two species occur throughout: Dictyocha
messanensis and D. aculeata. The absence of D. lingi and

GRAPE density measurement was made by linear
interpolation between the two calibration samples; distilledwater with a true density of 1.00 gm/cc and aluminum witha density of 2.60 gm/cc.
Bulk densities for Cores 3, 4, and 5 are shown on thegraph at the end of this chapter. Cores 1 and 2 were nottested because of the liner size, unfilled cores, and sloppy
material. The range of GRAPE densities for each core,
based on section averages and excluding obviously spurious
values, is given in Table 2.
Readings on the standards were run for each core barrel,
but very little drift was noticed. In Core 3 a gradualincrease from a density of 1.4 gm/cc atits top to 1.5 gm/cc
at the bottom of the core was observed. This increase indensity with depth is most likely due to the greatercompaction of sediment at the bottom of the core barrel
during coring and not an original density variation. In thelowermost core, Core 5, the most indurated sediment in thehole gave a wide range of density values (1.17 to 1.59
gm/cc). This is probably due to the short lengths of core
separated by empty spaces and to the space between coresample and liner wall which is common in cores of
indurated material.
TABLE 2Range of Bulk Density in Cores from Site 203

CoreBulk Density (gm/cc)

34
5

1.406-1.514
1.291-1.444
1.169-1.588

Sonic Velocity
Sonic velocity measurements made on the split half ofCore 3 ranged from 1.54 to 1.56 km/sec. On the more
consolidated sediments of Cores 4 and 5 sonic velocity wasmeasured on individual rock fragments and had values
ranging from 1.66 to 2.24 km/sec for the indurated ashes
and oozes and 4.20 km/sec for the basalt (assuming a basalt
density of 2.80 gm/cc). The basalt value is low, but this canprobably be accounted for by the vesicular character of thebasalt samples recovered.

23

SITE 203
Thermal Conductivity and Heat Flow

Thermal conductivity values were measured at 10 points
on Cores 1 through 4 at this site. Results are tabulated at
the end of this chapter. Values range from approximately
1.8 to 2.2 m cal/°C cm sec (TCU), uncorrected for in situ
sea-floor conditions. The highest value was measured inCore 4, which was sufficiently indurated to require drillinga small hole completely through this sample in order toinsert the needle probe. The limited data do not appear tovary systematically with either depth or appearance of thesediment.
No in situ temperature measurement was attempted at
this site, and hence no heat-flow data were obtained.
SUMMARY AND CONCLUSIONSThe Lau Basin site was drilled in an attempt to learn
more of the history and role of marginal basins in thepattern of sea-floor spreading and global tectonics. The site
occupies a somewhat anomalous, small sediment pond
within the Lau Basin in terms of structure and thickness ofthe sedimentary section encountered. The section is notappreciably disturbed except in the deeper layers.
Sediments encountered in the hole were volcanic-rich oozes
and clays and volcanic sands. Drilling was terminated at 409
meters when sands slumping into the hole jammed thebottom hole assembly. Two sonobuoys malfunctioned at
this site so that no vertical reflection data are available forstratigraphic correlation.
Sedimentation rates calculated on the basis of the
Pliocene/Pleistocene boundary and also Zone N21 (Bolli)
give rates of 120 m/million years and 80 to 120m/million
years, respectively. These high rates and the coarseness ofthe volcanic sands (ashes) suggest proximity to the source.
In the latter part of the Pleistocene, nannofossils suggest aslowing to about 50 m/million years.
The cored sand layers and also supplementary Sample 5(cored during attempts to free the drill string, andrepresenting slumped sands rather than in situ deposits)
contain volcanic glass with fresh surfaces and a high degreeof sorting which suggests transport from a nearby sourcewith little or no reworking, but which may be the result of
drilling activity. The bottom of Core 5 contained a 5-cm
fragment of highly vesicular olivine basalt with olivine
phenocrysts. The fragment is rounded, though not by
drilling activity.
Volcanic debris at the site is generally more acidic higher
in the section and may well be derived from the Tonga
Ridge, while the basalt at the base of the hole suggests
possible foramation of new sea floor in the extension of thebasin (e.g., Sclater et al., 1972).
The oldest material dated is middle Pliocene. At the
sedimentation rates indicated this would suggest sedimentation was initiated close to the Miocene-Pliocene boundary,based on 1.5 sec of sediment with a minimum velocity 1.5
km/sec, a rate supported by measurements on the cores.
Unfortunately, it is not possible to derive definitive
conclusions from the data available. Basement was notreached, so maximum age is an extrapolation, and the hole24

was not continuously cored so that the sedimentary record
recovered is very incomplete. The suggested age would
indicate that the Lau Basin is much younger than the Tonga
Ridge or the sea floor to the east of the Tonga Trench. The
lack of sediment disturbance throughout the upper threequarters of the section suggests that extension has not been
important in this local basin since early in its history.
Nannofossil data suggest that basin depths have remained
similar to those at present. On the other hand, seismicreflection profiles across an adjacent sediment pond
immediately to the east of the one drilled by Site 203 show
considerable folding and marginal faulting which would
indicate that the basin has been undergoing at least someextension to the present time. The rugged structure of the
Lau Basin floor and the different structural patterns ofadjacent sedimentary basins within it point to continuing
extension and opening of the Lau Basin, at least since the
Miocene, but also show that this has not been uniform orsymmetrical, occurring instead irregularly across its width
at various times and places.

REFERENCES
Boström, K. and Peterson, M. N. A., 1969. The origin ofaluminum-poor ferromanganoan sediments in areas ofhigh heat flow on the East Pacific Rise: Mar. Geol. v. 7,
p. 427.
Bryan, W. B., Stice, G. D., and Ewart, A., 1972. Geology,
petrography, and geochemistry of the volcanic islands ofTonga: J. Geophys. Res., v. 77, p. 1566.
George, W., 1924. The relations of the physical propertiesof natural glass to their chemical composition: J. Geol.,v. 32, p. 353.
Karig, D. E., 1970. Ridges and basins of the TongaKeruradec island arc system: J. Geophys. Res., v. 75,
p. 239.
Riedel, W. R., 1959. Siliceous organic remains in pelagic
sediments: In Ireland, H. A. (Ed.), Silica in Sediments.
Soc. Econ. Paleontol. Min., Spec. Publ. No. 7, p. 80.
Sclater, J. G., Hawkins, J. W., Mammerickx, J., and Chase,
C. G., 1972. Crustal extension between the Tonga and
Lau Ridges: petrologic and geophysical evidence: Geol.
Soc. Am. Bull., v. 83, p. 505.
Stadum, C. J., and Ling, H. Y., 1969. Tripylean Radiolaria
in deep-sea sediments of the Norwegian Sea: Micropaleontology, v. 15, p. 481.

NOTE CONCERNING THE APPENDICESThe appendices consist of tables of shore laboratory determinations of grain size, carbon content, and mineralogical composition, summary visual descriptions of the cores
recovered from the site, photographs of the cores and, finally, an overall summary of the results of drilling at the site.
The symbols used to represent lithology in the core summary forms are explained in Chapter 2 of this volume. The
lithologic description of each core contains typical resultsof shipboard examination of smear slides of each lithology.
In order to make the lithologic descriptions more complete
we have also included many of the shore laboratory results.
These are identified by being placed in square brackets.

SITE 203
APPENDIX A
Grain Size Determinations, Site 203

Core, Section,
Top of
Interval
Depth
(cm)
(cm)
1-4,113.0
3-3,40.0
3-5,56.0
3-5,88.0
5-1,10.0

Sand

Silt

Clay

(%)

(%)

(%)

Classification

5.6

13.8

111.4
114.6
114.9
400.1

0.0
2.0

41.6
78.3
79.9
30.7

44.6
21.7
18.0

Silty clay
Silt
Süt
Silty sand
Sand

62 A
92.7

6.9
2.6

4.7

APPENDIX B
Carbon-Carbonate Determinations, Site 203

Core, Section,
Top of
Interval(cm)
1-1,119.0
1-2,90.0
2-2,10.0
3-4,10.0
3-6,45.0
4-1,91.0
4-2,134.0

Depth
in Hole(m)

CarbonTotal

Organic
CarbonCaCO ,

(%)

(%)

(%)

1.2
2.4
7.6

7.6
7.6
7.7
0.5

0.0
0.0
0.0
0.0

63
63
64
4

7.7
5.7
0.5

0.0
0.0
0.0

64
47
4

112.6
115.9
229.9
231.8

APPENDIX C
X-ray Mineralogy Determinations, Site 203

Core

Cored
Interval
Below Sea
Floor (m)Sample Depth
Below Sea
Floor
(m)

Diff.

Amorp.

Calc.

Quar.

Plag.

Chlojr.

Mont.

Augi.

Magn.

Bulk Samples
3
108-1174
229-238

113.7
230.1

97.6
84.6

96.3
75.9

44.8
25.4

4.9
7.1

35.5
46.1

3.8
4.3

10.9
5.9

7.6

3.6

2-20µ Fraction
3
108-1174
229-238

113.7
230.1

98.9
80.7

98.3
69.8

-

13.3
11.5

86.7
59.5

4.1

-

21.3

3.6

<2µ Fraction
3
108-1174
229-238

113.7
230.1

92.3
81.5

87.9
71.0

3.9
1.8

27.9
21.3

14.4
8.7

53.9
56.6

8.6

1.2

—

Clin.

1.8

APPENDIX D

Thermal Conductivity Measurements, Site 203
Core,Section,Interval
Below
Top (cm)

ThermalConductivity(mcal/°C cm sec)

Standard
Deviation

Ambient
Core
Temperature(°C)

1-2,70
1-3,702-2,703-1,703-3,703-4,703-5,700.002157
0.001975
0.001915
0.001942
0.001824
0.001836
0.001970

0.005935
0.014463
0.005161
0.010625
0.009697
0.009060
0.007378

25.17
25.37
0.00
24.14
0.00
0.00
23.73

3-6,704-2,800.002228
0.002232

0.007888
0.013837

23.52
25.29

Remarks
Brown
Brown
Brown
Gray color
Gray color
Gray color
Lithologicalbreak 100 C
Brown

25

Site 203

Hole

Cored Interval.

Site 203

0-6 m

Hole

Core 2

Cored I n t e r v a l :6-15 mFOSSILFOSSILCHARACTER

CHARACTER

LITHOLOGIC DESCRIPTION

LITHOLOGIC DESCRIPTIONFORAM IRON OXIDE NANNO OOZE
dark brown, s l i g h t l y g r i t t y[63%

CaCO3]

2.5Y4/4

67% nannos
20% iron oxide
10% forams
2% glass

RAD GLASS SHARD BEARING IRONOXIDE FORAM RICH NANNO OOZE
brown, smooth and creamy
texture[64% CaCO 3 ]IRON OXIDE RICH NANNO OOZE
[63%

FORAM BEARING IRON OXIDE AND
GLASS SHARD RICH NANNO OOZE
olive brown, smooth withvisible forams, no layering
preserved

77% nannos
15% iron oxide

CaC03]" 9 glasslncreasi

10YR5/3

pyroxene
sil icoflag.

~znm/350" nannos
16% forams
15: iron oxide
I o•; glass
5% rads
2% other siliceous
fossils
2% minerals
73'' nannos
10 iron oxide
10% glass
5% forams
1! sil iceous
fossils
1" pyroxene" _l_0VR3/3
10YR4/3

GLASS SHARD RAD AND FORAM
BEARING IRON OXIDE RICH NANNO~2~5Y6/4

dark brown, creamy
IRON OXIDE BEARING NANNO GLASS

2.5Y4/4

yellow brown, slightly silty
Mixed zone.

10% iron oxide
2% glass
2% rads
72% glass
25% nannos
2% iron oxide
1% forams

T.5Y6/4

RAD FORAM IRON OXIDE BEARINGGLASS SHARD NANNO OOZE
medium brown, smooth withvisible forams

44% nannos
40% glass
10% iron oxide

FELDSPAR BEARING NANNO RICH
GLASS SHARD ASH
gray [14% sand, 42% silt, 45% clay]
SPONGE SPICULE GLASS SHARD
BEARING RAD FORAM RICH IRONOXIDE NANNO OOZE
medium brown, smooth and creamy
FORAM AND IRON OXIDE BEARINGGLASS RICH NANNO OOZE

70% nannos
15% glass
5% forams
5% iron oxide
2% radsCore
Catcher

FORAM, IRON OXIDE AND GLASSBEARING NANNO OOZE

82 nannos
6% glass
6% iron oxide
3%forams

2 03

Hole

Core 3

Cored I n t e r v a l ; 108-117 m-

Core 4

DEFORMAT

METERSLITHOLOGY'l** "** V*^#?> * ^LITHOLOGIC DESCRIPTIONft

1'*/ * XX **•*•»
1.0—

Cored Interval: 229-238 m

FOSSILCHARACTERoSECT I0

ABUND.

PRES.

FOSSILZONE

AGE

FOSSILCHARACTER

LITHO.SAM

Sit

5Y5/1

NANNO RICH GLASS SHARD ASH
gray, s i l t y , no l a v p r i n g
Part of the core was very
watery and l o s t i n c u t t i n q .
115 cm i n Section 1 disturbed
yellow (5Y6/6) laminae

LITHOLOGIC DESCRIPTION

80% g l a s s
17% nannos
1% forams
1% i r o n o x i d e
1% pyroxene

2.5Y7/4

3

F
N

C

M

2

M

J>Y6/3_
5Y4/1

3

S i t e 203

c

M

4

* II » * ^5Y4/2[2% sand, 80% s i l t , 18% c l a y ][63% sand, 31% s i l t , 7% c l a y ]FELDSPAR, FORAM AND NANNOBEARING GLASS SHARD ASH
dark gray, medium sandy

II

3

S

R7

—
- I —1- . -1_L__1—fi

2.5Y4/0— cycTJ ~2L
10YR5/4_ -r-_i_-T-_i_-ifi
M63

J-=T=-L=T=-J.

R

A

M
P

Core
Catcher

FORAM AND CHLORITE BEARING NANNOOOZECLAY AND FORAM BEARING NANNfl
OOZE[64% CaC03]

2.5Y6/4
TOYR87E
80% nannos
10% forams
8% c l a y
1% g l a s s
1% p h i l l i p s i t e

BEARING NANNO FORAM OOZE

CC

-

-

N

Cored I n t e r v a l : 400-409 m

XM

I
—%

A
A

Core 5DESCRIPTION

3

-

F
N

Hole

LITHOLOGIC- »*»_»?*»**<F

A l t e r n a t i n g layers o f
Ash: 45% glass
NANNO GLASS SHARD ASH and
40% nannos
GLASS SHARD NANNO OOZE
9% forams
The ash i s dark gray or o l i v e ,2% siliceous
the ooze i s generally a paler
fossilsgray and intensely mottled
2% other minerals
With pale y e l l o w .
„44% nannos[4% CaC0 3 ]35% glass
10% iron oxide
5% c l a y
5% forams

FOSSILCHARACTER[4% CaC03]

z.
ih

N

Cl

rrr

-

45% nannos
35% forams
16% clay
2% glass
2% other minerals

NANNO GLASS SHARD ASH
gray and brown

3

:
R

Core
Catcher[78« s i l t , 22% c l a y ]GZi i i i 1 1 1 1 1

C

j
:

OCENE

F
N
R

3

GLASS SHARD BEARING CLAY RICH
FORAM NANNO OOZE
pale y e l l o w , intensely mottled
i n p a r t s , moderately mottled i nothers[47% CaC03]
Burrows are generally gray.
CHONDRITES type burrows 74-86
cm i n Section 1.

~ Tθ7R3/3~

dark brown, slightly g r i t t y ,slightly mottled withmaterial from above

5% glass

FORAM AND CLAY BEARING. IRON
50% nannos
OXIDE AND GLASS SHARD RICH NANNO 20% αlass
15% iron oxide
9% clay
5% forams
1% Dyrite_ 10YJW/3.
Core
Catcher[93% sand, 5% s i l t , 3% c l a y ]OLIVINE GLASS SAND, green-brown
to black
NANNO AND CLAY BEARING GLASSSHARD ASH
vesicular BASALTNANNO GLASS SHARD ASH
gray passing down into paleyellow, intensely mottled
CLAY RICH NANNO OOZE
yellow overlying brown
CLAY RICH NANNO OOZE andhighly vesicular OLIVINEBASALT

80% glass
10% nannos
5% clay
4% feldspar
1% pyrite

SITE 203^mr\ f»m

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203-1-2

203-1-3

203-1-1
28

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203-1-4

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203-2-1

I

203-2-2

SITE 203

Ocm

1—25

I—50

1—75

100

125

150

203-3-1

203-3-2

203-3-3

203-3-4

203-3-5

203-3-6
29

SITE 203

0 cm

I—25

50

75

100

125

150

203-4-130

203-4-2

203-5-1

SITE 203
Velocity

Density (gm/cc)
LITHOLOGY

AGE

1 .00

ASHY NANNO OOZEPLEISTOCENE

-50

-100
GLASS SHARD ASH OVERLYINGCALCAREOUS OOZE-200

GLASS SHARD ASH AND NANNO OOZEPLEISTOCENE
PLIOCENE

1-250

1.50

2.00

2.50

3.00 1 .00

4.00(km/sec) and Impedence
7.00

10.00

/km
cc/
13.00

SITE 203 c o n t .
V e l o c i t y (km/sec) and Impedence

Density (gm/cc)
LITHOLOGY

AGE

1.00

-300

-350

GLASS SHARD ASH AND NANNO
oozi :. BΛSΛLI COBBLICS IN ΛSII.

PLIOCENE-400--(409 m Bottom of hole.^-

1.50

2.00

2.50

3.00 1.00

4.00

7.00

—1

—I

10.00

O~

. 3J
13.00