Multichannel seismic survey sonobuoy refraction survey and ...

CCOP/ SOPAC- TRIPARTITE
CRUISE REPORT
R/V S.P. LEE LEG I
MULTICHANNEL SEISMIC SURVEY
SONOBUOY REFRACTION SURVEY AND
DREDGING OF THE SOUTHERN PART OF THE
TONGA PLATFORM
by
Tun U Maung and David W Scholl
1 May 1982

INTRODUCTION
This survey was undertaken as part of the Joint Programme 01 Marine Geoscientific
Research and Mineral Resources Studies of the South Pacific Region sponsored by Australia,
New Zealand and the United States of America with the cooperation of CCOP/ SOPAC. The
USGS research vessel SAMUEL P.LEE was used for this survey.
Prior to this survey, fourteen E-W and one N-S single-channel seismic reflection
profiles were acquired by CCOP /SOPAC in 1979 totaling 2140km. Also, the southern part
of the Tonga Platform was traversed by EVA III, GEORSTOM and AUSTRADEC scientific
expeditions in 1977 and 1978 organized by ORSTOM and had acquired 12 single-channel
seismic and magnetic profiles. Based on these data and the existing oil company data
available at the Ministry of Lands, Survey and Natural Resources, Nuku'alofa, Tonga, an
"Assessment of the Petroleum Potential of the southern and northern parts of the Tonga
Platform'' was prepared by CCOP/ SOPAC. This survey is the outcome of the
recommendations made in that report.
CRUISE OBJECTIVES
The objective 01 this survey was, to gather multi-channel seismic, single channel
seismic, gravity, magnetic, and sonobuoy seismic: refraction data and to dredge for rock
samples over the southern part of the Tonga Platform south of Tongatapu and 'Eua up to
approximately Longitude 23° 3D', It is envisaged that the analysis of these data will provide a
better elucidation of the sub sea-bed geology (sedimentary rocks thicknesses and structures)
and tectonics than the existing single-channel seismic data in order to assess the petroleum
potential of this portion of the southern part of the Tonga Platform.
It was also decided to gather single-channel seismic, magnetic and gravity data from
Pago Pago, American Samoa enroute to Nuku'alofa, Tonga and from around 'Eua (at the end
of multi-channel work and dredging) enroute to Suva, Fiji, in order to provide additional data
to the studies of sub sea-bed geology and tectonics of the northern part of the Tonga Platform
and Lau basin and ridge respectively.

PERSONNEL PARTICIPATING
David Scholl Co-Chief Scientist, USGS Marine Geologist
Tun U Maung Co-Chief Scientist, CCOP/SOPAC Petroleum Geologist
Neville Exon Bureau of Mineral Resources, Australia; Marine
Geologist
Richard Herzer New Zealand Geological Survey, New Zealand;
Petroleum Geologist
Mark Sandstrom Australian National University, Australia; Organic
Geochemist
Sione Soakai Ministry of Lands, Survey and Natural Resources,
Kingdom of Tonga
Other participants from USGS were:
Robert Rowland Branch Chief, Pacific-Arctic Branch of Marine
Geology - multi channel
Tracy Vallier Chief of Watch
Andrew Stevenson Chief of Watch
Dennis Mann Multichannel
Jon Childs Sonobuoy seismic refraction
Graig McHendrie Navigator
Kay Kinoshita Navigator
Barbara Seekins Navigator
Chris Gutmacher Multichannel
Larry Kooker Electronic Technician
George Asuncion Electronic Technician
Jeff Rupert Marine Technician
Hal Williams Marine Technician
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EQUIPMENT AND FACIUTIES
The survey was conducted by the USGS research vessel SAMUEL P. LEE, a 208foot,
1300-ton vessel, equipped with a full complement of marine geophysical equipment
integrated in such a fashion so as to allow the simultaneous collection of multichannel
seismic reflection, single-channel seismic reflection, sonobuoy seismic refraction, gravity,
magnetic and bathymetric data. Also the vessel is capable of dredging and gravity coring. The
equipment used are as follows:

(1) Navigation Equipment:
Magnavox Integrated System MX-702A and MX-II05.
Edo Western doppler sonar
(2) Bathymetric Equipment:
Raytheon Line Scan Recorders with 3.5kHz and 12kHz transducers
(3) Gravity Equipment:
La Coste & Romberg S-53 sea gravity meter
La Coste & Romberg G-426 land gravity meter for land ties at Pago Pago,
Nuku'alofa and Suva
(4) Magnetic Equipment:
Geometrics proton magnetometer G801g
(5) Single-channel Seismic Equipment:
Raytheon Line Scan R"corder
100-metres long Teledyne streamer
95 or 148 cu.inch airgun
(6) Multichannel Equipment:
Globe Universal Sciences Model HDDR 4200 amplifer and HDDR 2000 Tape
recorder
Two Raytheon Line Scan Recorders and SIE dry write camera 2400 meters long
Seismic Engineering streamer
5 airguns with total capacity of 1313 cu.inch.
(7) Seismic Refraction Equipment:
Fairfield Select Inc. amplifiers and Hewlet-Packard 3968A tape recorder Two
Raytheon Line Scan Recorders
SQS 418 Navy sonobuoys (52 Nos deployed)
(8) Dredging and Coring:
Chain dredge and 3 metre long gravity corer consisting of plastic liner and
800lbs lead block as weight.
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PRELIMINARY RESULTS
During the survey 2357km of multichannel seismic data were recorded. Concurrently,
single-channel seismic, gravity and magnetic data were also recorded. In addition, 2176km of
single-channel seismic data together with gravity and magnetic data were recorded; 719km north
of Tongatapu between Pago Pago and Nuku’alofa; and 1457 south of Tongatapu while in transit
to various dredge-sites. The multichannel seismic track lines and the locations of sonobuoy
deployment from sonobuoy Nos. 5-49 are shown in Figure 1. The multichannel line Nos. 10 and
11 tie with the DSDP well site 203. Also, more than 750m of single-channel seismic, gravity and
magnetic data were recorded in transit from the last dredge-site D9 about 30km SW of 'Eua to
Suva with the objective of gathering more data in studying the Lau basin and ridge.
The three probable reefal buildups identified from the CCOP/SOPAC Line N-O were also
observed on the single-channel seismic record of E-W Line No. 11. One of the reefal buildups,
most likely the one in the centre, was also observed on the single-channel seismic record of N -5
Line No. 14. These establish the presence of probable reefal buildups in that area. No other
obvious reefal buildups were observed on any other single-channel seismic records.
In most of the lines, especially on Line Nos. 3-8, the sedimentary beds appear to thicken
from east to west from about 0.5 to 1.5 sec. to over 3.0 sec. (about 5600m). Angular
unconformities are observed at about 0.2-0.5 sees. and the sedimentary beds below the
unconformity apparently dip westwards; the dips are found to be very gentle. Many normal
faults, some of which are active up to recent times are observed on the single-channel seismic
sections. Magnetic anomalies are observed over the Pleistocene-recent volcanic trend and where
the probable shallow basement is believed to exists.
Some of the sonobuoy graphic records were analyzed on board using the digitizing table
and a desktop computer. Preliminary results of a few sonobuoy refraction profiles are included as
Appendix 8.
Locations for dredging and coring were chosen by the participating scientists in
consultations with the Co-Chief Scientists, by studying the Polaroid photographs (pasted together
to form a continuous strip for each line) of the single-channel seismic data. Though several
attempts to core were made on 6 or 7 sites chosen from the single-channel seismic data, none
successfully penetrated more than a few cm due to the hard seabed surface encountered.

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Also, 18 sites were chosen dredging from the single-channel seismic' data, but only 9
sites were actually dredged. Many of the remaining sites had to be abandoned due to the
alteration of arrival time in Suva by about 12 hours ahead of schedule. The latitudes and
longitudes and water depths of the dredge sites arc given in Appendix C and the locations are
shown in Figures 2(a) and 2(c). A short preliminary description of the dredge samples recovered
are given in Appendix I).
CONCLUSIONS AND RECOMMENDATIONS
Except for dredging, the programme was completed as planned. The area surveyed -
between Tongatapu and latitude 23° 30' on tile southern part of the Tonga Platform - appears to
have sufficient thicknesses and areal extent of sedimentary rocks below the seabed to constitute
an area of potential for accumulation of petroleum. The presence of possible reefal buildups is
confirmed by this survey. Also, it is likely that there are many fault and stratigraphic traps.
The multichannel seismic data after proper processing together with sonobuoy refraction
data may indicate the presence of more reefal buildups. It is recommended that a thorough
interpretation of all the data gathered during the present survey, i.e. multichannel seismic,
single-channel seismic, gravity, magnetic and sonobuoy refraction data be made in conjunction
with the results of the source rock investigation team of USGS which will visit Tonga in the
near future, be made to assess properly the petroleum potential of the surveyed area
WORK REMAINING
Data reduction and computer processing of all data gathered during the survey in Menlo
Park, California, by the Marine Geology Processing Centre of U.S. Geological Survey. The
processed multichannel and single-channel data are to be displayed in a 9-inch Mylar base
transparency. Processed gravity and magnetic data are also to be displayed on a 9-inch Mylar
base transparency at the same horizontal scale i.e. with the same shot-point spacing, so that the
available sets of data can be readily pasted together for interpretation.
REFERENCES
Dupont, J. in press: Morphologie et structures superficielles de l'arc insulaire des Tonga-
Kermadec, in Equipe de Geologie-Geophysique du Centre ORSTOM de Noumea.
Contribution a l'etude geodynamique du Sud-Ouest Pacifique. Travaux et Documents de
PORSTOM No. ___. 20pp.

Gauss, G.A., 1979: Tonga offshore survey 1-17 November 1979 Cruise TG-79-1.
CCOP/SOPAC Cruise Report No. 33, 3pp. 1 figure, 2.appendices.
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Maung, T.U., Anscombe, K., and longilava, S.L., 1981: Assessment of Petroleum Potential
of the southern and northern parts of the Tonga Platform. CCOP / SOPAC Technical
Report No. 18, 43pp. 5 appendices, 12 figures.

Appendix A: Narriltive
LIST OF APPENDICES
Appendix B: Pre1irninilry results of a few sonobuoy refraction surveys
Appendix C: Locations of Dredge Sites
Appendix D: A short preliminary description of the dredge samples recovered.
LIST OF FIGURES
Figure 1: Map showing multichannel seismic track lines and location; of
sonobuoy deployment.
Figure 2(a): Map showing dredge sites D-l to D-5
Figure 2(b): Map showing dredge sites D-6 to D-8
Figure 2(c): Map showing dredge site D-9

APPENDIX A
NARRATIVE
1800hrs GMT 26 March R/V S.P. LEE arrive Pago Pago, American Samoa
0000hrs GMT 28 March R/V S.P. LEE depart Pago Pago, American Samoa
0030hrs GMT 31 March R/V S.P. LEE arrive Nuku'alofa, Tonga
0500hrs GMT 2 April R/V S.P. LEE depart Nuku'alofa, Tonga
0830hrs GMT 2 April Start multichannel seismic survey on Line No.3
2000hrs GMT 13 April End multichannel seismic survey on Line No. 18.
1609hrs GMT 14 April Dredging on dredge-site D-1 on seismic Line No. 11.
The period between end of multichannel sun

Dredge Site 0-1
APPENDIX D
SHOR T PRELIMINARY DESCRIPTIONS
OF THE DREDGE SAMPLES RECOVERED
Amount recovered was 21 rocks samples weighing c1bout 301bs. It can be grouped into
four general categories.
Group 1: Volcanic siltstone-breccias. Fragments of siltstones in tan secondary cement -
slightly calcareous; with manganese crusts. 5 specimens.
Group 2: Volcanic siltstone with some interbeds of coarse sand, light brown.
One specimen with manganese crust. 11 specimens.
Group 3: Volcanic breccias brown und green, slightly rounded to angular c1asts of mafic
volcanic rocks. 4 specimens
Group 4: 1 piece pumice, approximately 12cm in longest dimension.
Dredge Site D-2
Amount recovered was one rock weighing about 2lbs. One cobble-sized block with one
fresh broken surface. Remaining surface of Ferro-manganese coated less than 1 mm thick.
Dredge Site 0-3
Amount recovered was half dredge bag of rocks, all sedimentary, many of which are
manganese encrusted. It can be grouped into 5 general categories.
Group 1: Sandstone, grey, coarse grained, poorly sorted, some calcareous matrix with
forams. Distinct bedding on mm and cm scale. Weathered angular lithic fragments of feldspar.
Some porosity. Clasts yellow, red and grey. Manganese crusts to lcm thick, some diffuse Mn in
matrix. Moderately weathered.
Group 2: Sandstone, buff to light brownish-grey, medium to coarse grained, very poorly
sorted, calcareous, foraminifera, angular to sub rounded, lithic fragments yellow and grey, some
quartz. Heavily weathered feldspar. Some pebble-sized pumice fragments. Manganese crusts to
lcm thick; some diffuse manganese in matrix.
Group 3: Limestone, forarn, cocolith, buff white, hored ½ cm diameter holes.
Minor manganese coatings in borings. Minor volcanic rock, fragments. Weathered.

Group 4: Limestone foraminifera. Extensively bored, interbedded with volcaniclastic
sandstones. Borings lined with manganese. Manganese also encrusting sample less than 3mm.
Buff-yellow weathered.
Group 5: Sandy mudstone, uniform light brown matrix speckled with sand-sized altered
volcanic lithic fragments; fairly rare forams. Rare crystals of feldspar, quartz and hornblende
granule to pebble-sized m ntmorillonite masses probably representing altered pumice. Pockets of
forams. Manganese coats to lcm thick.
Dredge Site D-4
Amount recovered 21 cobbles of pumice, 1 boulder of pumice and I cobble of soft
mudstone.
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Pumice: Dark to light grey (uniform and banded) unaltered with unfilled vesicles containing
delicate fibers of glass. Flour banding evident in colors and vesicles alignment. Blocks show no
signs of having been buried and only one (the boulder) has begun to acquire a Fe Mn stain.
Mudstone: Medium grey brown, soft, weathered, non-bedded, moderately burrowed,
tuffaceous, contains scattered granules of weathered pumice and pebble-sized clasts of light brown
and medium grey clay which may be altered lapilli. Sandy looking material is made up of clay
lithic clasts (altered volcanic sand or pellets?) and rare crystals of feldspar and ferrornagnesiuns.
Texture of rock is very poorly sorted (debris flow emplacement?) with pebble-sized clasts
apparently floating in the matrix.
Dredge Site D-5
Full dredge recovered. Rocks up to 45cm across. It can be grouped into 7 categories.
Group l: Calcareous siltstone; light grey-brown, moderately soft, slightly weathered (5%),
poorly sorted, thin to medium bedded with blocky fractures. Stringers of scattered forams. Very
homogeneous.
Group 2: Limestone; white, moderately soft, weathered (20%) poorly sorted (lime mud
tovery fine sand). Abundant forams, some boring with manganese veneer, some cross-bedding. No
volcanic detritus. Poorly to moderately bedded.
Group 3: Limestone; yellowish, moderately soft, more weathered (35%), extensively bored
with Mn02 coatings. Some cross-bedding on cm scale. Bedding on scale of mm to cm, volcanic
detritus, poorly sorted (lime mud to sand sized). Thin (less than 3mm) Mn02 crusts. Foram-rich,
glauconitic (?). The limestones are gradational to volcaniclastics.

Group 4: Calcareous mudstone with sand-sized volcaniclastic granules (2%) and coarse
fossil debris (mounlds of pteropods and heteropods, and small bivalves). Grades into volcanic
limestone and calcareous volcanic sandstones, with which it is interbedded. Forams present.
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Group 5: Calcareous volcaniclastic breccia; light grey weathering euhedral pyroxene
crystals. Thinly bedded with calcareous volcanic sandstone. Possibly graded. Clasts sand sized to
2cm; mainly less than lcm. Angular, occasional forams.
Group 6: Volcanogenic sandstome; light brown, weathering yellow (35%), brown, rich in
feldspar and lithic fragment, some fragments possibly quartz medium grained clasts with finer
matrix-supported sandy mudstone. Calcareous cement. Thin (less than 3mm). Manganese crusts
on upper surfaces. Clasts sub angular to rounded.
Group 7: Grey pumice cobbles QS in earlier stations. Abundant.
Dredge Site 0-6
Recovered full dredge, about 50 rocks and some pumice. It can be grouped into 5
categories.
Group 1: Limestone; fine grained pale yellowish brown, thin to medium, good bedding.
Minor boring. Silt to fine sand-sized carbonate grains. Some forams. Terrigenous materials
present in some specimens. Some thin managanese coatings. Possibly glauconitic (7) Outer shelf
facies (?)
Group 2: Calcareous siltstone and fine sandstone; buff to medium greenish-grey, medium
bedding (possibly cross-bedding). Bioturbation in siltstones but no borings. Sandstone medium
well sorted, texturally and mineralogically mature but grains seem to be labile and break down to
silt between fingers, and therefore probably feldspar rich. Probably shelf to upper slope facies.
Group 3: Sandstone and gritty sandstone. Fine sand to grit, brown, well bedded, thin to
medium bedded, some cross-bedding. Relatively hard. Grains are volcanic lithics, feldspars,
ferromagnesian minerals. Moderately weathered. Calcareous to non-calcareous. Lithic fragments
fresh to highly weathered (red). Some interbedded muddy sandstone.
Group 4: Volcanogenic pebbly grit. Varied orange to brown colour. Indistinct bedding.
Very poorly sorted, medium sand to pebble-sized, angular to sub rounded grams.
Group 5: Pumice as in other dredge hauls.

Dredge Site 0-7
Amount recovered was 5 pieces of manganese coated graywacke and 2 pieces of
pumice.
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Group 1: Volcanogenic graywacke, grey-green with white feldspar euhedral crystals.
Very poorly sorted, very fine sand, pebble-sized clasts. Grey, black and reddish volcainic
clasts. Hard silica-rich mud matrix. Euhedral black pyroxene. Feldspar varies from fresh to
heavily weathered. Sand beds - laminated fine volcanogenic gray green - both as clasts in
graywacke and as interbeds. Non-calcareous, nonfossiliferous. Manganese crust 2-3 mm thick.
Minor quartz. One large angular graywacke.
Group 2: Grey pumice as in other dredge hauls.
Dredge Site D-8
Full dredge recovered - 4 rock types and pumice.
Group 1: Calcareous sandstone, thin bedded, ferrornagnesian, cream colored.
Group 2: Very fine-grained, sandy, hard, dark reddish brown phosphatic mudstone (?);
matrix of fine platy mineral, thin bedded.
Group 3: Calcareous greywacke, thin bedded ferromagnesian, medium brownish
yellow, manganese coated less than 3mm to lcm.
Group 4: Massive laterite and graywacke, medium to coarse-grained, medium brownish
yeilow, manganese coated less than 3mm to 1 cm.
Group 5: Gray pumice.
Dredge Site 0-9
Amount recovered about half dredge bag full, consisting of 28 rocks mostly angular,
both igneous and sedimentary. It can be grouped into 6 categories. Croup description not
available. Individual rocks description available.
Group 1: Ultramafics - 8 specimens
Group 2: Layered Cabbros - 2 specimens
Group 3: Well lithified greywacke - 5 specimens
Group 4: Volcanic breccias - 10 specimens
Group 5: Rounded volcanic flow rock - I specimen
Group 6: Buff colored mudstones - 2 specimens