MARINE GEOLOGY AND SEDIMENTATION OF
MILNE BAY, NEW GUINEA.
by
D. Jongsma B.Sc.(Hons).
A thesis submitted in fulfillment of the requirements for the degree of Master of Science at the University of New South Wales.
Date: 10th January, 1970. MEMORANDUM
The following dissertation is the result of twelve months independent research in the School of Applied Geology at the University of New South Wales, and the Bureau of Mineral Resources Canberra, under the supervision of Dr. A.N. Carter.
Where the work of others, whether published, unpublished or personally communicated, has been referred to or made use of, the fullest acknowledgement has been given.
Date: 8 -5 - i<^ jo ACKNOWLEDGEMENTS
The author expresses his thanks to Dr. A.N Carter for his supervision in the preparation of this thesis. The assistance of Associate Professor F C. Loughnan, Dr. A.D. Albani, and Mr. G. Melville at the University of New South Wales is also gratefully acknowledged.
Special thanks goes to Dr. H.A. Jones and Dr. N.H. Fisher at the Bureau of Mineral Resources, for providing the opportunity to undertake this project. The helpful suggestions of Dr. P.J. Cook and the assistance of Mr. T. Nicholas, Mr. R.N. England and the laboratory staff at the B.M.R. is also gratefully acknowledged. Furthermore thanks go to the technical staff in the Marine Geological Section of the B.M.R, in particular Messrs D. Warren, R. Dulski and M. Tratt for their part in this project.
To Dr. C.V.G. Phipps and Professor W.G.H Maxwell of Sydney University thanks is expressed for making avialable the settling tube facilities.
Drafting and typing facilities kindly supplied by the Bureau of Mineral Resources are also gratefully acknowledged. SUMMARY
Milne Bay is a graben structure which originated during the formation of the Owen Stanley fault lineament on shore and the Pocklington Shear zone which runs east to Guadalcanal. The bay floor has been sinking in Quaternary times and a thick succession of marine sediments has collected within the bay. A (?)Pleistocene unconformity observed in the sparker records indicates rapid sub mergence in the central southern part of the bay. It is suggested that ultramafic basement material; derived from the upper mantle or lower oceanic crust due to collision of the simatic oceanic material with the sialic core of Papua, is at present sinking.
A trough running parallel to East Cape Peninsula shows a similar trend to structural features on the D'Entrecasteaux Islands to the north. This trend is postulated to have originated during the left lateral shear of the region, which caused the offset of the Owen Stanley Metamorphic Belt.
Bottom sediments are dominantly fine grained and poorly sorted. Deltaic progradation of terriginous material takes place in the western part of the bay, and calcareous sediments derived from marginal reefs accumulate on the slope and shoals to the east. Owing to a restricted bottom circulation a reducing environment occurs in the central region resulting in the deposition of calcareous sediments with a high organic content. LAY-OUT OF THESIS
This thesis is divided into three parts. Part I is introductory giving the physical, oceanographical, and geological setting of Milne Bay. Part II contains a discussion of sparker traverses taken in the bay, while Part III is concerned with the sedimentology of Milne Bay based on surface sediment samples.
Plates, figures and tables are distributed throughout the text except for Plate 1 which is found in the map pocket on the inside back cover. Appendices are found in the back of the thesis. LIST OF CONTENTS
SUMMARY
1. INTRODUCTION
(i) Locality of Area 1
(ii) Survey details 1 (iii) Purposes and scope of the investigation 2 (iv) Previous work 3 PART I GEOLOGY AND PHYSICAL SETTING 4 1. GEOLOGY 4
(i) Regional geology 4 (a) Owen Stanley Metamorphic Belt 5 (b) Papuan Ophiolite Province 6 (c) Cape Vogel Basin 8
(ii) Local geology around Milne Bay 8
(a) Dawa Dawa Beds 9 (b) Recent deposits 9 (c) Intrusive Rocks 10
(iii) Geological History and Structure 11 of the area
2. GEOPHYSICAL DATA 13
3. TOPOGRAPHY AND COASTAL MORPHOLOGY 13
4. CLIMATE 14 5. OCEANOGRAPHY 16 6. BATHYMETRY 17
(a) Regional Bathymetry 17 (b) Milne Bay Bathymetry 18
PART II SPARKER TRAVERSES 21
(i) Introduction 21 (ii) Traverse 1 22 (iii) Traverse 2 23 (iv) Traverse 6 24 (v) Traverse 7 25 (vi) Traverse 3 27 (vii) Traverse 4 27 (viii) Traverse 5 28 (xi) Structure and sedimentation 29
PART III SEDIMENTS OF MILNE BAY 34
1. INTRODUCTION 34 2. COLOUR OF THE SEDIMENT 35 3. TEXTURAL DISTRIBUTION 36 4. GRAIN SIZE ANALYSIS 38
(a) Introduction 38 (b) Sample statistics 39 (c) Discussion of the sample cumulative curves. 41 (i) Modality of the distributions 41 (ii) Gaps in the size distribution 42
(d) Sedimentary parameters of Milne Bay Samples 44 (i) Graphic Mean 44 (ii) Inclusive Graphic Standard Deviation 44 (iii) Inclusive Graphic Skewness 48 (iv) Graphic Kurtosis 49
(e) Sources of sediment 49 (f) Geological significance of the parameters 51
4. CALCIMETRY 53
(i) Analytical Method 53 (ii) Results 54 (iii) Distribution of Ca Co^ percentage 54
5. OXIDISABLE MATTER 55 6. MINERAL COMPOSITION 57
(a) X-Ray Mineral identification 57 (b) Sand fraction study 57
(i) Contribution of organisms 57 (ii) Heavy Mineral Analysis 58 (iii) Light mineral Analysis 60
(c) Clay mineral analysis 61
(i) Method of study 61 (ii) Results 63 (iii) Discussion of Clay Mineral Results 63
7. GEOCHEMICAL ANALYSIS 64 8. SUMMARY AND CONCLUSIONS REGARDING SEDIMENTS IN MILNE BAY 67 REFERENCES 68 7. Gravity Map 13a 8. Regional Bathymetry 17a 9. Sparker Traverses 21a 10. Structure Contours on Unconformity inMilne Bay 30a 11. A. Isopachs on Recent sediments in Milne Bay 30b 11. B Structure of Milne Bay 31a 12. Sediment Sample Stations 34a 13. Flow diagram of sample treatment 34b 14. Sediment of colour distribution 35 15. Textural classification diagram 36a 16. Textural distribution in Milne Bay 36b 17. Graphic calculation of parameters 39a 18. Frequency curve for sample 310 39b 19. Cumulative curves 41a 20. Cumulative curves 41b 21. Cumulative curves 41c 22. Graphic mean size distribution 44a 23. Mean size versus Sorting graph 45a 24. Inclusive Graphic Standard Deviation 45b 25. Inclusive Graphic Skewness distribution 48a 26. Graphic kurtosis distribution 49a 27. Nomograph used in calculation of Carbonate Content 54a 28. Distribution of Carbonate Content 54b 29. Distribution of Oxidisable material 55a 30. Clay mineral structures 63a TABLES
1. Rainfall at Samarai 15 2. Sedimentary Parameters 40 3. Gaps in Cumulative curves 43 4. Scales for sorting 46 5. Verbal Limits on Skewness 46 6. Verbal Limits on Kurtosis 47 7. Clay mineral Classification 62 3. Average sediment composition 66
PLATES
1. Milne Bay Bathymetry (pocket) 2. Traverse 1 22a 3. Traverse 2 23a 4. Traverse 6 24a 5. Traverse 7 25a 6. Traverse 3 27a 7. Traverse 4 and 5 23
FIGURES
1. Locality diagram la 2 Principal structural units 4a 3. Regional Geology of Papua 5a 4. Evolution of Papuan Ultramafic Belt 7a 5. Local geology of Milne Bay area 8a 8. Pocklington Fault 12a APPENDICES
1. Station Data and Sample attributes 2 X-Ray diffraction results 3. Clay mineral results 4. Direct reading optical spectrograph results INTRODUCTION 1. INTRODUCTION
(i) Locality of Area under study
Milne Bay is located between latitudes 10°15fS and 10°35'S and longitudes 150°20'E and 151°15'E (Fig. 1). The bay is bounded by two peninsulas which form the southeasternmost part of the mainland of New Guinea. It has an area of approximately 2000 sq. km and a maxi mum depth of just over 560m. In form it is a steep sided flat floored basin and connexion with the open sea to the east is impaired by a sill at 300m. depth.
(ii) Survey details
This report deals with sparker records and surface sediments taken during the beginning of 1968 by the Marine Geology Group of the Bureau of Mineral Resources. A total of 5 days was speent in the area collecting samples and running sparker traverses. Seven sparker traverses were run across the bay, see Fig. (9), and a total number of 30 bottom samples were recovered from various localities in the bay (Fig. 12).
The chartered survey vessel, the Kos II is an ex-whale chaser, a steel ship of 125 feet overall length. It was built in 1929 and is powered by a triple expansion steam engine driving a single screw. 14** I4«° ISO*
IOO 200 100 Km
SOLOMON
CONAL SC A
Fig. I - LOCALITY DIAGRAM
P/A/26 2 -2-
(iii) Purpose and Scope of the Investigation
Milne Bay is of particular interest from a Marine Geological point of view. It forms part of a region which was and still is subject to much tectonic activity. As a result of this tectonic activity, the relief on the mainland of Papua New Guinea is extremely high, while the adjacent ocean basins are deep with very steep sided slopes. The continental shelf around Papua New Guinea is either completely absent or in the very early stages of formation.
The extreme relief and high precipitation results in rapid denu dation and the supply of large amounts of sediment to the marine environment. The transportation and areal reach of these sediments is of much interest to the sedimentologist in reconstructing ancient environments. Furthermore at this latitude coral reef growth and organic life is at a peak also forming sources of sediment for Milne Bay.
Milne Bay is a restricted basin since circulation of bottom water with the open sea is impaired by a sill. The attributes of the sediments in Milne Bay are thus of interest from a geochemical point of view.
The purpose of this investigation is to evaluate the morphology and structural evolution of Milne Bay and to evaluate its relationship within the tectonic setting of the circum-Pacific Zone of island arcs and ocean trenches, by using the continuous seismic profiles. Further more, study of the sediments of Milne Bay may throw light on the -3- problems associated with evaluation of environmental conditions existing at earlier times when ancient formation were deposited.
(iv) Previous Work
Data on the marine geology of Milne Bay is scarce. The region to the south and east was the subject of reports by Krause (1965, 1967), which discussed the general tectonic framework of the northwestern Tasman Sea, the Coral Sea, and the South Solomon Sea. Previous regional geological studies are documented in the section on the geology of the region. Gravity data collected by Milsom (in press) is discussed in later sections of this thesis. The marine geology of the Huon Gulf region, 400km northwest of Milne Bay, has been described by von der Borch (1969) and Walraven (1968).
-4-
PART I GEOLOGY AND PHYSICAL SETTING
(1) Geology
(i) Regional geology
Stanley (1923) gave the earliest account of the geology of the Papua area, and Thompson and Fisher (1965) discussed the geology of New Guinea with reference to the mineral deposits. Thompson (1967) has described the geological history of the region. Reconnaissance mapping by the Bureau of Mineral Resources in the last decade is the main source of information on the geology of the Milne Bay region. (Davies 1965, 1967, Davies et al. 1968). The geology of the islands off the southeastern peninsula is the subject of a further report by Smith (1969).
Late Tertiary to Recent tectonic activity, associated with the circum-Pacific zone of island arcs and ocean trenches has profoundly affected the area (Weeks, 1959; Glaessner, 1950). A number of struct ural provinces (Fig. 2) have been recognized in Southeastern Papua - New Guinea (Thompson & Fisher, 1965) and these provinces are retained in the following summary of the regional geology.
In the eastern part of the Papua New Guinea mainland a belt of Cretaceous and possibly older metamorphic rocks form the sialic core called the Owen Stanley Metamorphic Belt. This sialic core is separated from younger submarine basic volcanics and pelagic sediments by a 4a
PAPUAN NEW BRl TA ! N OPHIOLITE
PROVINCE SOLOMON
SEA
CAPE
iVOGEL Port^. Moresby BASIN
PAPUAN OPHIOLITE PROVINCE Milne Bay 100 miles
Fig.2. Principal Structural Units in South Eastern New Guinea (after Thompson a Fisher, 1964)
P/A/263 -5- discontinuous band of ultramafic rocks called the Papuan Ultramafic Belt. This belt of ultramafic rocks together with the Tertiary volcanics to the north is termed the Papuan Ophiolite Province. South of the Owen Stanley Metamorphic Belt similar volcanic rocks of oceanic origin occur, and it is postulated that they belong to the same province (Thompson & Fisher, 1965). The Cape Vogel Basin is a structurally depressed and topographically low lying coastal zone, containing a thick succession of Miocene and Pliocene rocks (Fig. 2).
(a) Owen Stanley Metamorphic Belt
The Owen Stanley Metamorphic Belt extends from southwards almost to the Musa valley, and eastward to the D'Entrecasteaux Islands and \a Louisude Archipelago. Trans current faulting has caused a northward offset of the belt (Smith and Green 1961, Thompson and Fisher 1965).
The Owen Stanley Metamorphic Belt comprises greywackes and siltstones of Cretaceous or older age which have been regionally metamorphosed to schists and phyllites of the greenschist facies (fig. 3). These rocks form the sialic core of Eastern Papua New Guinea (Davies, 1969). Locally the metamorphics are intruded by granodiorites, granites and small lamprophyre dykes (Smith and Green, 1961). These Cretaceous metamorphic rocks form the Owen Stanley Mountain Range, which has a high relief. Since at least Middle Miocene times the Owen Stanley Metamorphic belt has been an emergent source of clastic sediments. (Thompson & Fisher, 1965) and now forms the Owen Stanley Range which rises over 4000 m above sea level. FIGURE 3
QUATERNARY RECENT 13 AHuvum PLEISTOCENE b RECENT 12 Raised coral IIB Volcomcs PLEISTOCENE IIA Alluvium, folded r Superficial Suite ITERTIARY SOLOMON PLIOCENE IOC Volcomcs IOB Sediments, clastic MID-MIOCFNE TO PLIOCENE IOA Sediments, mostly clastic
LOWER MIOCENE 8 D Sediments, volconogemc K Limestone 8B Basalt lavos UPPER OLIGOCENE 8 A Basalt lovas, some with c/ino-enstafite
5B Y////A Basalt lavas ond limestone 5 A Y////A Chert and calcilutite
MESOZOIC CRETACEOUS LI! 1.11 Bo salt lavas some of which may be L MIOCENE 1 Limestone 1 Basalt lavas ond minor andesite, i——— some limestone IA Metomorphics,^bosic ond calcic, greensch/st
Lough!on Is CRETACEOUS t OLOER etomorphics, s/ahc, green schist to ■nphibolite foaes ‘ X., _^Cape Vogti Goodenough IGNEOUS INTRUSIVES TERTIARY LOWER OR MID MIOCENE 9 D rnniiiiiii Gobbro 9C Quarti dionte *Eo^ Capo 9B Syenite 9 A GronodiOnte
OLIGOCENE ? 7 MM Gobbro ond doierite
EOCENE ? 6C Granite 6 B Gronod/or/te EASTERN PAPUA EOCENE 6 A Quorti d/onte (PUB)
GEOLOGY CORA L MESOZOIC Gobbro 1 CRETACEOUS ? oimnnD Papuan Ultra mafic Belt CRETACEOUS OR OLDER Ultromafics j
S* Mt Lam mg ton Active volcano Fault
P/A/264 -6-
A major strike fault lineament forms the northern margin of the Owen Stanley Metamorphics. This fault, the Owen Stanley Fault, can be traced as a distinct topographic break for more than 300km. Both vertical and lateral movement has occurred along this fault. -c Davies (1967) reports the fault to be a low angle thrust dipping east ward at an angle of 20°-30°.
(b) Papuan Ophiolite Province
The Papuan Ophiolite province crops out on either side of the Owen Stanley Metamorphic Belt in southeastern Papua New Guinea. The province is named, from its association of ultrabasic and basic plutonic rocks, and basic submarine lavas. It includes grey, red brown, and green siliceous claystones, inorganic calcilutite, and bedded chert. Thompson & Fisher (1965) recognized it as being a tectonic zone where there is no emergence and no emergent continental mass nearby. It is thus typified by an assemblage of oceanic igneous rocks and ocean floor deposits. No implication of an early orogenic stage is made here.
Two distinct units, the Papuan Ultramafic Belt, and an oceanic province can be recognized as making up the Ophiolite Province.
The Papuan Ultramafic Belt, described by Davies (1967), is composed of peridotites and gabbros. Starting in the northwest part of Eastern Papua - New Guinea it extends southeastwards for 900km, with widths of up to 40km. This ultramafic belt shows lithologic similarities to other such bodies occurring in orogenic zones on the Pacific margin, such as New Caledonia, Solomon Islands, Philippines, -7-
Celebes, Borneo, and Western United States. Thompson (1967) and Davies (1967) both suggest these ultramafic rocks to be part of the upper mantle which has moved westward since Cretaceous time. Due to collision with the sialic core of Papua the mantle has been forced upward along the Owen Stanley Fault (see Fig. 4), producing the Ultramafic Belt. It has been postulated (Davies 1969) that this exposed part of the mantle is slowly sinking at the present time.
The oceanic rocks of the Papuan Ophiolite Province are chiefly basic submarine lavas and associated limestones, marls, and cherts of Cretaceous to Lower Miocene age. No terrigenous sediments occur within the stratigraphic succession of these oceanic sediments and volcanics. These rocks are believed to be part of the mafic upper oceanic crust which has overridden the Papuan Ultramafic Belt and the sialic core of Papua (Davies 1969, Thompson 1967). See Fig. 4. Intrusions of leucocratic gabbro, diorite, trondjemite and rarely granodiorite occur in these oceanic rocks.
The present topography within the Ophiolite Province is rugged with high steep sided mountain chains. Earlier Pleistocene glaciation on the highest parts of the Ophiolite Province, such as Mount Wilhelm and Mount Albert Edward, demonstrates that the high elevations were also common in the Pleistocene.
Some parts of the coastline in Eastern Papua New Guinea show evidence of Recent submergence and these sections fall within the Ophiolite Province (Thompson & Fisher, 1965). Vertical displacements along the Owen Stanley Fault and erosional remnants of a mature 7a
LlI CD U U. < < tr 5 O h~ z z U) < < a> 5 => a. £ CE 2 LU is
U. s MV o o ll V cn 3 □ £ xx od *
\,X \N \ . X -X .XXJ I -8-
landscape on the crest of the Owen Stanley Range, indicate Pleistocene to Recent uplift of the Owen Stanley Metamorphic Belt relative to the Ophiolite Province (von der Borch, 1969). Thus while the Ophiolite Province is being submerged, the Owen Stanley Metamorphic Belt has been a positive structural element throughout Cainozoic time.
The Papuan Ophiolite Province probably extends under the sediments and volcanics of the Cape Vogel Basin.
(c) Cape Vogel Basin
This basin can be regarded as either a sedimentary basin or a section of a volcanic arc. It is structurally depressed and forms a topographically low lying coastal zone extending from Morobe in a southeasterly direction to Goodenough Bay.
A thick succession of Miocene and Pliocene sediments overlain by volcanics of Pleistocene to Recent age occur in the Cape Vogel Basin.
(ii) Local geology around Milne Bay
The geology of the Milne Bay area has been described by Davies (1967) and Davies et al., (1968). The following summary is based on these reports. A geological map of the area after Davies et al (1968) is shown in Fig. 5. 4 GEOLOGY OF MILNE BAY AREA FIG. 5 Low grade basic and calcic Alluvium E3B schists Prevost Vo/canics
Andesitic vo/canics ?Cretaceous \ ;K k Met a basalts Karada Metavo/canics
Raised coral limestone High grade schists and gneisses 15 Kilometres
Wamira Beds -unlithified sandstone, conglomerate, si It stone INTRUSIVES ?Pleisocene Fife Bay Beds-basic agglomerate, Tertiary granite tuff, intrusives
Tertiary- Mount Nelson Beds-basic agglomerate post-lower Ultra mafic bodies and conglomerate Miocene TTTTTT Mi la Gabbro -mainly gabbrofminor acid Tm L imestone, sandstone, si/tstone intrusives at Oura Oura mine Lower Miocene Suen Beds-limestone, sandstone, to East Cape Gabbro-gabbro si It stone, conglomerate upper Oligocene V' 4 P I Dawa Dawa Beds-marine basic vo/canics, Gabohusuhusu Syenite -syenite with minor gabbro 9°45— rT-l do/erite, limestone, detrital sediments + Touiwaira Beds-marine basic vo/canics, Eocene si limestone —------‘ Geological boundary ------Inferred geological boundary
I Strike and dip of strata
—Anticline
Cope Ventena/
Sekwia Kwioa Point I0°00' —
I0°I5' —
£ R R 0 U
I5I°I5‘ C56/A9/1 -9-
(a) Dawa Dawa Beds
On both sides of Milne Bay, and on the islands off the southern peninsula, basic volcanics, associated dolerite, basic detrital sediments, limestone agglomerate, and limey sediments crop out. These rocks termed the Dawa Dawa Beds (Davies, 1967) are of Upper Oligocene to Lower Miocene age.
Pillow structures are moderately common and some of the pillow basalt is well bedded. An extensive sequence of well bedded gently dipping flows and detrital sediments occur in the middle reaches of the Dawa Dawa River. Generally however, these basic rocks are not obviously bedded and form massive outcrops which show varying degrees of joint ing, shearing alteration and secondary veining. The total thickness of the Dawa Dawa Beds is estimated to exceed 3000 metres.
(b) Recent deposits
Recent raised coral reefs occur in the northwestern part of Milne Bay, the headwaters of the Maiwara River, and the northern margin of East Cape. Flat-lying deposits of Recent alluvium occur at the head of Milne Bay. The old raised coral reef limestone deposit situated at the westward margin of this deltaic unit indicates the old shoreline of Milne Bay. Recent alluvial deposits in the form of deltaic mangrove swamps also occur along the north western margin of Milne Bay. -10-
(c) Intrusive Rocks
The Dawa Dawa Beds are in places intruded by ultramafic rocks, gabbro, and syenite. Two small dunite bodies occur to the south of Milne Bay. One body crops out in the lower part of Gabahusuhusu Creek at latitude 10°12'S. longitude 150°21'E while the other one occurs in the Dawa Dawa River at latitude 1Q°28'S and longitude 150°26'E. The dunite consists of olivine and serpentine with accessory chromite. (Davies 1967). Dunite in Gabahusuhusu Creek is itself intruded by syenite.
Gabbroic rocks occur on East Cape and they crop out over an area of 13 square km. Nuakata Island, just east off East Cape, is composed of the same rocks.
The gabbro is dark green grey and granular on freshly broken surfaces. It consists of subhedral augite (20%) with elongate laths of labradorite (50-60%) and minor orthopyroxene (5-10%), opaque minerals (5%) and green secondary interstitial material (5-10%). Some micro- pegmatitic quartz diorite has also been reported to be present in the East Cape region (Baker, 1953).
The Gabahusuhusu Syenite (Davies et al, 1968) is a body occupying approximately 11 square km on the southwestern side of Milne Bay.
The syenite is younger than the Dawa Dawa Beds and intrudes into some minor gabbro. It is medium grained with a composition of perthitic potash feldspar (55-80%) albite (0-15%) biotite (5-10%), aegerine augite -11-
(10-15%), hornblende (0-15%) opaque minerals (2-5%), and zircon (1-2%). The gabbro into which it intrudes is composed of augite (10%) tremolite actinolite; after augite (30%), labradorite (40%), with minor orthopyroxene opaque minerals and fine grained alteration products.
Dyke swarms are present in the area to the southwest of Milne Bay. The dykes range in thickness from 1 to 7 meters and generally have a north easterly trend. The dyke rocks are porphyritic and contain phenocrysts of eagerine - augite and dendritic plagioclase.
(iii) Geological History and Structure of the Area.
The geological history of the area starts in the Upper Cretac eous with extrusion of basaltic pillow lavas, and the development of up to a thousand meters of probably deep water limestone. Compression from the east during Eocene times caused the oceanic crust and the upper mantle to be thrust over the sialic core of Papua (Davies, 1969) Subsequent removal of this thrust sheet by erosion and gravity sliding took place, together with the development of a pile of basalt lavas and limestone on the seafloor of the Milne Bay area.
A period of quiescence ensued during Oligocene times, with little sedimentation or volcanism taking place. The Upper Oligocene - Lower Miocene was a period of renewed seafloor volcanic activity over a wide area. In the Middle Miocene orogenic movements began which are still continuing today. Spectacular movements in a vertical sense and also strike-dip faulting in a left lateral sense occurred as a result -12- of this orogeny. The direction of faults in the Papua New Guinea is westerly to northwesterly. However, a markedly different trend in the structural pattern is found on the D’Entrecasteaux Islands to the north of Milne Bay. Not only is the structural pattern different but the geology of these islands also shows little similarity to that around Milne Bay . Low-grade Cretaceous schists, metasediments, graniteand ultramafics are overlain by Pleistocene to Recent volcanic rocks. The rocks on these islands are believed to form part of the Owen Stanley Metamorphic Belt because of their similar lithology (Thompson & Fisher, 1965).
The trend of many of the faults on the D’Entrecasteaux Islands is north-northeast. This direction is also maintained by an anticlinal fold axis on the southern part of Normanby Island (Fig. 5).
The structural geology in the region of Milne Bay is thus of vital interest since on the one hand it is the continuation of the Owen Stanley Fault lineament running northwest, while to the north, faulting and structural trends are at almost right angles to this direction. Krause (1967) has described a fault zone which is a regional shear probably coupled with folding and volcanism, called the Pocklington Fault. This fault zone can be traced on the bathymetric charts, it runs from as far west as Guadalcanal Island past Pocklington Reef and north of the Louisiade Archipelago to join up with the Owen Stanley Fault of some where in the region of Milne Bay (Fig 6). POSITION AS SHOWN BY KRAUSE,1967
Strike- slip fault with sense -jf- Normal Fault (U ~ up, D -dawn)
Postulated Rift Postulated Regional Stress
Fig.7 PRELIMINARY GRAVITY MAP OF MILNE BAY AREA (From a Gravity Survey of East Papua and New Guinea, after Milsom manuscript) Note : Gravity highs on northern and southern margin of Milne Bay with a low near Dawson Island in /me with trend of MNne Bay.
P/A/266 -13-
2. GEOPHYSICAL DATA
Results of a regional gravity survey of Eastern Papua by the Bureau of Mineral Resources show some features which are sign ificant in this study (Milsom manuscript). Figure 7 shows a preliminary gravity map of the area. South of Milne Bay around the Ulo Ulo area a gravitational high occurs, this high is probably due to some subsurface feature such as an ultramafic body Another gravity high occurs on the northern side of Milne Bay associated with the East Cape Gabbro. Directly eastward opposite the bay a gravitational low occurs over Dawson Island. It is likely that this low extends into Milne Bay itself (Milsom, manuscript).
The configuration of this gravity pattern suggests some movement of the bay relative to the land. The movement is probably a submergence of the bay floor in this region. A later discussion on the origin of Milne Bay deals with this theory in more detail.
3. TOPOGRAPHY AND COASTAL GEOMORPHOLOGY
The effective drainage area of the rivers draining into Milne Bay is part of the southern mountains and foothills of Papua. The mountains in the northwest are by far the highest, reaching elevations in excess of 1500m while the hills near Milne Bay are between 500m and 1000m. The drainage area covers about 30,000 sq. km. Three major rivers, the Maiwara, the Gumini, and the Dawa Dawa, carry most of the run-off of the area into Milne Bay. Small coastal rivers about 10km long occur on the East Cape Peninsula and the southern margin of the Bay. -14-
The southern coastline of Milne Bay is remarkably straight while the northern coastline is more indented. The western coastline shows convexities due to the building out of deltas at the river mouths. Swampy foreshores are found on the northwestern margin of the bay.
The islands off the southern peninsula also have indented irregular margins with coral reefs surrounding most of them. These islands reach elevations of 200m to 530m and have swamps on their foreshores.
Some small islands with coral reef surrounding them occur on the northeastern margin of the bay. Nuakata, the largest of these, reaches an elevation of 327m and shows an idented margin with fringing coral reefs.
4. CLIMATE
Milne Bay lies within the area affected by the southeast trade winds and the northwest Monsoons. The southeast trade winds blow between May and October, but may start and blow intermittently from March onwards. By July and September they are steady and reach a wind force of 5 to 6 for several days. The southeast trades blow between the latitudes of 5° North and 5° South. Heavy seas in Milne Bay are very rarely encountered because most of Milne Bay is protected from the high seas by outlying islands and reefs.
From October to April the northwest monsoons often bring squalls and heavy rain in the open seas but Milne Bay is protected from the worst of these. Wind speeds in the Milne Bay area are between 3 and 4 -15-
TABLE I
RAINFALL AT SAMARAI (Pacific Islands Pilot 1956)
Lat 10°37'S, long 150°40'E.
January 7.0 inches July 8.1 knots for most of the year. The climate in Papua - New Guinea is humid tropical Temperatures for most of the year range between 65° and 95° F. Although rainfall in the Milne Bay area is less than that for most parts of New Guinea, it is, very high compared with other parts of the world. The average annual rainfall is about 108 inches, as compared with up to 200 inches for some other parts of New Guinea. Because of its position, Milne Bay, which is surrounded by mountains in the northwest, receives most of its rainfall during the early part of the southeast trade winds season (see Table 1). 5. OCEANOGRAPHY There is little information available on the oceanographic conditions in Milne Bay and most of it is in the various coast pilot volumes. The Pacific Islands Pilot (1956) discusses the currents in the narrow straits leading into the bay. China Strait in the south of Milne Bay has a current of 6 knots flowing through its narrowest part. This current diminishes to 2 or 3 knots, in the wider parts of China Strait. Raven Channel, which connects Milne Bay with Goschen Strait and Goodenough Bay, has a current of about 5 knots flowing through it. A fairly weak current of about 2 knots is reported at the easternmost extremity of the bay. However, generally speaking, tidal effects are small since the difference between low and high tides in this region is only slight. The maximum difference in the height of tides is 2.7m, while the average is 1.5m (Admirality Tide Tables 1969). During heavy rainfalls large mountain torrents are reported to -17- flow into the bay. The Pacific Islands Pilot (1956) mentions turbid water for a considerable distance from shore during these heavy rainfall periods. Waves in Milne Bay have small amplitude and small periods due to their small fetch, having mostly been created within the bay itself. No sufficiently large opening to the ocean is present to cause long period swells. 6 BATHYMETRY (a) Regional Bathymetry The regional bathymetry of the South Solomon Sea is shown in Figure 8. Krause (1967) has described the bathymetry and structure of this area. Woodlark Island rests on Woodlark Ridge and has to the south of it a deep basin, the Woodlark Basin (Krause 1967). This basin has an extremely irregular floor which is cut into a chaotic arrangement of hills, ridges and irregular depressions about 3000m deep. These hills have a general east-west alignment with escarpments cutting through the region in various directions. To the south of the Woodlark Basin lies the Louisiade Archipelago which rests on the eastward extension of the Papua Peninsula. This extension of the Papua Peninsula becomes a region of parallel structural ridges, troughs, and closed basins of which Milne Bay is one. Tagula Island, Rossel Island, and Pocklington Reef rest on a series of en echelon ridges (Krause 1967). South of the Louisade Archipelago and the Pocklington ridge the seafloor slopes down to the deep water of the Pocklington Trough which TROBRIAND IS. 2000^ JOOO 4000 R Goodenough Bay WOODLARK BASIN IOOO r'd ge/ Pocklington /'^oO' Reef ( issel I. Tagula I. 75 Kilo metros J ______‘fUUO'^ 4000 POCKLINGTON TROUGH ) Fig.8. Regional Bathymetry of South Solomon Sea. Contours in Meters P/A/267 -18- forms an extension of the Coral sea basin. The Pocklington Ridge is fault bounded in the north and has a left lateral sense. The Pocklington Fault extends north of the Louisiade Archipelago up to the region of Milne Bay (Krause, 1967). North of Milne Bay another closed basin with depth in excess of 1000m occurs on the east by the D'Entrecasteaux Ridge. The D'Entrecasteaux Ridge joins in the north with the Trobriand Platform (von der Borch 1969), and southward with the southern extension of the Papuan Peninsula. On the northern margin of Goodenough Bay, Cape Vogel is connected to the D'Entreacasteaux Ridge by a sill between Goodenough Bay and Collingwood Bay. The southern margin of this ridge which slopes very steeply down to 1000m and is probably fault controlled. This fault may define the locus of dislocation which causes the offset of the continuation of the Owen Stanley Metamorphic Belt. (b) Bathymetry of Milne Bay Milne Bay is a restricted basin locked in on the west by the Papuan Peninsula and on the east coral reefs and islands. A sill at a depth of 300m forms the connexion with the deeper ocean to the north and south (PI. 1). Near land, on the west side, several rivers enter Milne Bay after passing through a marginal swampy delta. On the western edge of the bay a shallow gently sloping irregular shelf occurs. The edge of this shelf occurs at about 80m. Depth increases rapidly at the edge of this narrow shelf and at the bay margin in the north and south. Steep slopes with gradients as high as 9 in 10 occur between 80 and 250m depth. Another break in slope occurs at about 250m after -19- which the gradient decreases to about 1 in 10. This slope continues down to 500m at which level the almost flat bottom of the bay is encountered. In the north eastern part of the bay, south of Nuakata Island the situation is slightly different. Here the initial very steep slope between 80 and 250m is present after the edge of the rudimentary shelf is encountered. However, farther south of this steep slope a more gentle increase in depth takes place. This gentle gradient continues for a distance of about 18km until the floor of the bay is met at a depth of 500m. On the eastern side of Milne Bay there is a shoal which supports a few small islands. The southern end of this shoal is deeper and a channel with a maximum depth of 300m is the connexion with other restricted basins on the submarine ridge off the Papuan Peninsula. To the south a number of shallow (20m) channels such as China Strait and Fortescue Strait connect Milne Bay with the Coral Sea basin. Between East Cape and Nuakata Island a number of shallow connexions communicate with Goodenough Bay. In the northern part of the bay a narrow steep-sided trough extends from near the middle of the basin, northeastwards parallel to East Cape peninsula. The bathymetric contours indicate a feature resembling a submarine canyon, but although no seismic data are available, it seems unlikely that this trough has been formed by erosion and a structural origin is postulated. The trough runs at a right angle to other structural trends in the bay and it is probably connected with the structural features seen on Normanby Island to the north of East Cape where faults also trend northeast - southwest. -20- Milne Bay is the result of downfaulting of the bayfloor in the form of a graben. The southern margin of the bay is obviously fault controlled as evidenced by the extremely steep slope. In the north a similar situation is present although the margin is slightly indented due to erosion by short rivers subsequent to faulting. -21- PART II SPARKER TRAVERSES (i) Introduction Seven sparker traverses were run across Milne Bay (see Fig. 9). The sparker traverses were obtained by a continuous profiling system, comprising a 3 electrode spark array and a 1000 w/sec power source, combined with a 7 element hydrophone and an Ocean Sonics GDR-T recorder. The recorder uses 19-inch wet paper and during these traverses was programmed at one sweep per second; this sweep speed gives a horizontal scale line interval of 36.7m (20 fathoms) in water. Traverses were run at a speed 4.5 to 5 knots. The location of the traverses is as shown in fig. 9. Photographic reproductions of the traverses, accompanied by line drawn interpretations are shown in Plates 2 to 8. The vertical scale on the line drawings are in terms of two-way travel time quoted in seconds. Where sub-bottom thicknesses of strata or depths to reflectors are quoted in the descriptions of the profiles, a uniform velocity of 1700m/sec has been assumed. Unless otherwise stated, the attitudes of reflectors mentioned refer to the apparent attitude along the line of section. The term basement is used to indicate an irregular, strong reflector below which no obvious sedimentary bedding can be discerned. Note that due to bubble pulses all horizons are shown by a series of three or four lines on the original sparker records, (see Sargent, 1968). The sparker records are described in order from east to west. «)•«' — IUAKATA I. K5°J0'— FIG 9 Sparker Traverses in Milne Bay Direction shown by arrow SIOCIA I 10° 35' — 50* tO* i50»4B' C56/A9/I2 -22- (ii) Traverse 1 (Plate 2) The traverse 1 runs from south to north at the eastern end of the bay. It represents an almost straight section between Shortland Reef and Cocked Hat Island. The quality of this record is excellent showing many prominent subbottom features. The floor of the bay can be seen at 1.* The start of the traverse shows a shallow irregular bottom with a coral reef or basement outcrop at 2 in a depth of 40m. At 3 the bottom has an almost vertical slope which becomes less steep at 150m (4) and gradually flattens out into a deep channel at 340m (15). At 13 two acoustically impenetrable hummocks appear which represent basement rock forming the shoals around Nua Kata Island. Another high crops out at 17. Sub-horizontal bedding of the sedimentary fill between these basement highs can be seen at 10 and 11. An almost vertical slope at 18 marks the northern edge of the deeper basin, and at 14 coral reefs can be seen on the edge of shallow shelf which is underlain by basement rock. A strong reflector at 6 marks an unconformity which is well displayed in this and later profiles. Onlap of the overlying sediments is evident at 12. The unconformity probably represents a low sealevel stand during the Pleistocene. However since the maximum depth of the * Numbers refer to features indicated on the line drawn interpretation of the profile. . ^VrtifeHWntMvat* V*\" S5S5SJ5!^^SSC!riSW^S®sa *k** : fr;* ■'*•.;• vv V*..V ... **m^'*W'*m *mm*mM&i***±* . ' ' L- . . ' . ,4„. 'k-tup*-’{-\ NORTH PLATE TRAVERSE 1 2 C56/A9/I8 -23- unconformity is 425m some submergence of the bay must have taken place to account for this depth. Maximum eustatic sealevel lowering is in the order of 120 to 125 meters (Curray 1961). The amount of sub sidence in this section of the bay must thus be in the region of 300m. Conformity at 19 indicates the presence of a channel at the time when the unconformity originated. A very faint unconformity below the one described occurs at 8 and since no penetration (9) can be observed below this reflecting horizon it is suggested that this is basement rock. Multiple reflections are indicated at 16. (iii) Traverse 2. (Plate 3) This is a short traverse from Cocked Hat Island going southwest. The traverse begins in shallow water the seafloor being at 1. At the start the bottom is irregular (2) owing to growth of coral reef on this shallow shelf. Little penetration below this shelf indicates that it is underlain by basement rock (6). The edge of the shelf is marked by a hummock (3) which is probably a reef structure. Terraces occur around the indented margin of the shelf at 4. The shelf edge is deeply indented in this area, and the platform at A is in fact continuous with the rest of the shelf. Slopes at the edge of the shelf are steep (5) and may be fault controlled. Sediments can be seen to occupy the embayments (7) of the indented margin. The floor of the basin slopes gently southwards away from the edge of the shelf, and -24- subhorizontal stratification of the sediments underlying the bottom can be seen at 8 and 10. A prominent reflecting horizon at 12 has been interpreted as the continuation of the Pleistocene unconformity seen in traverse 1 just to the east of this traverse. Below this unconformity further penetration shows up more sediments. A notch in the seafloor at 11 and the bending of reflecting horizons below is due to some recent normal faulting. The possible throw of this fault is about 30 meters. A water-bottom multiple reflection can be seen at 13. (iv) Traverse 6. (Plate 4) The traverse runs from the south to north about 12km west of traverse 1. The seafloor is marked 1. The start of the traverse is in shallow water with a somewhat irregular seafloor. A coral reef on the edge of the shelf at 2, a small channel at 3, and a terrace at 4 are followed by a steep slope at 5 which is fault controlled. The slope of the floor of the bay decreases (6) and continues to do so smoothly until a fault scarp is encountered at 8 which changes to a gradual upward slope till the end of the traverse. In the deepest part of the traverse, apparently, conformable sediments are penetrated for 0.4 seconds (340m) at 7. As in Traverse 2, a normal fault down throwing to the south occurs near the axis of the basin. North of the fault an irregular reflector at 12 indicates the r~ 24 a PLATE 4 IP m n■ ya.mm —i m'■ > ior ^ JWSS8SS9 ...... m *m fa rkMTmY ‘ ' f A. v. iJSSkZA^m -T "-. .1. ■■>■--' • ”'-Fw?wjSw ■ fepgii liMgW aoslaSB 3S01HP .... r • t'-' ■ '• ■'.1 .•■ - p.khvP :P?3*I -».*.*/• • ..,v;. ------W(I1 SS v pte k/tyW. pStel' .^^dCiV-i. '-4; u-^-P-4- s e s ■TI ^II II Lfe2-2S5^|^ ° V1' ■,•',' / 'i'?J -T1-L..' , [vT \\v ’ -** ^ ¥mm. ,V<| "mV, f’’"M pi»« ‘VvT'PT TRAVERSE 6 -25- unconformity noted in Traverse 1 and 2. The presence of this unconformity at a shallow depth beneath the bottom at 12, and the fact that it cannot be detected to the limit of penetration at 7, indicate that the throw of the fault considerably exceeds its expression on the seafloor. The unconformity may be followed for the major part of the record, although it becomes less obvious in the latter part. However, a change in the reflecting behaviour of the horizons at 14 marks the presence of this unconformity in that part of the record. Multiple reflection are indicated at 15. (v) Traverse 7. (Plate 5) Traverse 7 extends from just south of the Obstruction Islands towards the southern peninsula of the mainland. Excellent penetration on this record shows very clearly the relations of the subbottom strata in the middle of Milne Bay. A 0.5 second delay occurs in the latter part of the record which is compensated in the line drawn interpretation. The bottom of the bay is marked 1 it shows a basin shaped depression. A marked unconformity is observed in this record at 2, and can be traced in the deepest part of the basin to a depth of 425m be neath the sea bottom in a water depth of 560m. This maximum depth of 985m is very much lower than the maximum low-level seastand, which is reported to be about 125 meters (Curray 1961, 1965, Van Andel 1968). Thus in this part of the bay, submergence of about 760m must have occurred This is much more than that postulated for the eastern part of Milne Bay and it is suggested that submergence here was at SECONDS TRAVERSE 7 SMBfif- PLATE ‘ -26- its highest due to a fault connected with the formation of the trough south of the East Cape Peninsula. Below the unconformity further penetration shows the presence of slightly distorted bedding (8) and some of these reflecting horizons are truncated near the unconformity surface (9). Since Pleistocene times sinking concommittent with sedimentation has gone on. Continuous horizontal reflecting horizons are present at (3), and a thickness of at least 425m is present in some of this section (13). Onlap of the sediments at the margins of the areas of active subsidence and maximum sedimentation is evident at 6, and small notches in the slope of the bottom (5) above these onlaps suggest downfaulting of the deeper parts of the basin as at 7. Uniform closely spaced reflecting horizons indicate a well bedded sequence of sediments at 4. At the end of the section the bottom rises again towards China Strait. Discontinuous, slightly wavy, reflecting horizons occur at 10; these may indicate slumping Further south at 11, undisturbed closely spaced reflectors are present. At 7 discontinuity and bending of the reflecting horizons has been interpreted as the result of faulting. The faults continue downwards into basement but do not extend to the top of the section having been covered by later sedimentation. At 12 a water-bottom multiple reflection occurs in this traverse. -27- (vi) Traverse 3 (Plate 6). This traverse runs from near Saraoni Island north eastwards to the middle of the bay and thence north-west to East Cape peninsula. The quality of the record is poor but gross features are still discernable. Near the start of the traverse the bottom (1) shows undulations on a shallow narrow shelf (2,4) probably due to presence of coral reefs. At 3 a very steep slope occurs between the two humps of 2 and 4. The floor of the bay at a depth of 525m is remarkably flat, over a distance of 13km until the slope on the northern side of the bay is encountered. Below the flat floor of the bay is a succession of horizontal reflectors to a depth below bottom of 125m. Basement rock occurs on the bottom of the steep slope at 6 and undulating reflectors in this area are possibly due to slumping. The upper slope at 7 is fairly uniform some slight penetration (9) seems to indicate some bedding below this slope. At 10 the edge of the shelf is reached again and the bottom shows uneven topography. A very indistinct horizon at 8, which subparallels the bottom slope at 7, occurs in the latter part of the record. This is possibly the unconformity related to the ones noted in the traverses to the east. (vii) Traverse 4 (Plate 7). This traverse starts in the northern part of the bay and runs south, covering the middle of the landlocked part of the bay. The bottom (1) descends steeply, with irregularities until it flattens out at a depth ***1 ‘T7 wt7.: '7 « ‘7r7v------v 77' ■ ' ’.-\7 ’*" -r*T.—;- r|4*v 7* ^r '.7. 3 fr-- f^\v *• *,~: 4-* - »tj m>[»i fT* '4*’ • l *- 7^’ '.' ",’ r£r ~7* £; 777------'' , >** - *• - • •** •'./ ■• r- *V ir- *• - s-Oi - ■ -- 7 ?* r;"r7' "7** 'i ^r’v :' .•*’- ~,Y- , —'rv .— -. •*• .**■.' t • '•“ ^ Va,; - • 14 'w: -, ; ft- - ■■ *■^------■ ■ * f f I! F7^,v-r-^4H-- ?*■ ■' -'•*—w w 2*«**$ > ^•7^Tv'V. '-77------77Vr ■’* ’’Ti ; r-»*T7 f-;■ ,rr-r' —•—■7.*' • • 7/' — ^4 ■* -'iT- ' ' 4 ’• '' '»-<•—X^:, x i &fcr*'^**5**s! r R -.-;7 ^ 7"' ":— V —n' -,•>-* >-**• -W - - - U*'- :v w ,^,— ~*v- ',rr''~"rz~' 'rr"'Zr t j— fc :J r^*77 '777 71 r > H m C56/A9/20 -28- of 480m. Irregular and wavy reflecting horizons indicate basement rock at 2. Slump structures occur at 3 and 4 on the steep slope of the bay's margin. The central part of the traverse shows many distinct continuous and horizontal reflecting horizons underlying the flat bottom (6). Some onlapping occurs at 5. The structure at 5 may also be due to a type of deltaic prograding seen in transverse section. At the end of the traverse near the southern margin of the bay a straight steep slope occurs which is obviously fault controlled (7). Some irregular bedding can be seen on the upper part of this slope and under the narrow shelf (8). Water-bottom multiple reflections are observed at (9). The maximum thickness of Recent sediments penetrated in this section is about 85 meters. (viii) Traverse 5 (Plate 7). This is the westernmost traverse in Milne Bay and covers the inner reaches in the shallow part of the bay. The traverse runs from south to north. An irregular bottom can be seen at 1 with below it fairly good penetration showing very irregular reflecting horizons (3). At 2 little PLATE 7 i, • lyyiryr ft? i .** r^rf*r\ 1 j*v; /'-^n’^r.,, yt: -«^y-Afc -*ii •"?-*[*: I V-lv «<-» • *v, “.V^" |gi*r’Tv>,^T*.*•;:;v^rWr ;~<*~--if 71^ PJjHfo yr ~,V^Tf*u •’ * —nM ’•*"'7? • ’f -V ,*Yy^ . . . ,—i vr-iWR*v-rr-, (Li, y*r*<'i\ -#r*^»- -^i *•- '•- '”S- -r'.^».-» ...,■ , ... t.-Tv? H’-*' • ' .* I\ * 1 1 • ^ ^ .' ,*f*- - »dW-( -1- ■,•■-■»,»'-«■, ' -H 1-*^- • f" rv'^rrr--. "*‘T i i‘r-..f41«rhv~*'~ “ 1 v:'#,^.^! l^fS^ i ••*>•*'# y^V'*"^’- „ :ii NORTH SOUTH 0000 0015 0030 0100 -1-O.8 TRAVERSE 4 V;; ■ ^ *:■• -• -y- jsy, ****“! v'C '•’ r$,X»*r ■ , . BP*'’f ? ‘ > • (C. s~M W‘. 2, k ? * /ivmm& F *v>:m %.'■; ■j '<&&■•** > XT- >«««-'SSmB • ro a «Mi!f SOUTH N ORTH 0230 0245 0300 0315 to Q 2 O o UJ to TRAVERSE 5 C56/A9/I6 -29- penetration is observed due to the presence of underlying basement rock or coral reef. Multiple reflections are indicated by 4. The traverse is on the edge of a prograding delta which is receiving sediments from the rivers to the west. The irregularity of the reflecting horizons is due to slumping of material down the foreset slope of this delta. Structure and Sedimentation Milne Bay is situated in a region which has been and still is tectonically very active. Evidence of recent uplift is found in numerous localities on shore where raised coral reefs occur. Recent raised coral is found west of Milne Bay and on East Cape Peninsula (Davis et al 1968). The uplift in these localities is about 30m. Further away to the northwest at Cape Frere, the raised coral is at an altitude of 500m, and westward on Misima Island, Recent coral reef occurs 460m above the present sealevel (De Keyser, 1961). The Milne Bay area is also subject to downward movements. Seismic profiles reveal and old landsurface which has been subject to erosion. The maximum depth, below sealevel, of this erosional surface is 900m in the sparker records. This is also the limit of penetration of the seismic profiles under discussion and hence the unconformity may be even deeper. However relative to the present sealevel the floor of Milne Bay has subsided at least 900m. The unconformity is postulated to have originated during the late Pleistocene, Wurm, glacial stage when sealevel was down to it lowest point of about 125m below its present level. -30- This drop in sealevel has been dated by Curray (1965) to have occurred about 18000 years before the present. It follows that an actual downward movement for the floor of Milne Bay of about 775m can be confidently assigned. This subsidence has been accompanied by rapid sedimentation. The profiles show a thickness of recent sediments of about 450 meters in the centre of Milne Bay (Fig. 11 A). Assuming the transgression to have occurred 18000 years ago, a sedimentation rate of 2 cm per year is obtained. The locus of sedimentation is in the middle of the basin, north of the outlet of China Strait. (Figs 10 and 11 A). This is either due to a predepositional configuration, where Milne Bay already formed a valley with its axis through the middle of the present bay, or a more rapid sinking of the middle part of the bay could have caused this locus of sedimentation to be situated here. Further transgressions are observed in the seismic profiles. Onlap of sediments has been noted in some traverses at different depths (see Traverse 7, Plate 5). The presence of these onlaps is yet another egression of the shifting coastline of Milne Bay. Both sinking of the bay floor and eustatic sealevel changes are involved in causing these onlaps. Sinking of the bay is probably the dominant factor, since as shown earlier, at least 775m of downward movement of the bay floor has taken place during Holocene times. In the western extremity of Milne Bay deltaic sedimentation is at present taking place. Large amounts of terrigenous material is carried down by rivers and accummulate in these parts. Slumping Contours, metres below sea level Inferred position of contours Fault Limit of unconformity \ Unconformity IO°25— FIG. 10 Structure contours on Pleistocene 10° 30 — unconformity Contour interval 50metres. Depth calculated on assumption that velocity of sound approximately 1-5km/sec in water and 1-7 km/sec in sediment. SIDEIA I 150*20' 150*50' 150*4 5' 151*05' C 5 6/A 9/21 Fault —?------— Fault Inferred Isopach contour Isopach contour position inferred iNUAKATA L I0°20 — I0°25 — 0.50------ I0°30'— FIG. 11A Isopachs of Recent sediments in seconds (2-way travel time) SIDEIA I. I50°20' I50°25' I50°30' 150°40' I50°45' l50o55' I5I°0( SARIBA I, C 56/A9/24 -31- down the foreset slope of this delta has been observed in the sparker traverse across it. Further slumping occurs on the steep slopes near the margins of the bay. The slumping on the marginal slopes is in many instances associated with faulting and is tectonically controlled. Faults are evident in the seismic profiles and can also be inferred from the bathymetry. The faulting in Milne Bay is invariably normal. Milne Bay itself is the result of a graben structure. Two large parallel faults trending almost eastwest control the margins of the bay (Fig. 11B). The Fault responsible for the extremely straight southern margin has been observed in traverse 4 (Plate 7). The northern more indented margin is postulated to be fault controlled on bathymetric evidence. Normal faulting of a lesser magnitude has been revealed to take place in between the two major faults controlling the graben structure. In some cases these faults are penecontemporaneous, onlap of sediment occurring near the fault scarp (Traverse 7, Plate 5). This stress release by way of normal faulting is typical of a graben structure. The main trend of faulting in Milne Bay parallels the major Owen Stanley Fault onshore and the Pocklington Fault offshore. Movements along these major faults has been noted by several authors to be vertical and in a left lateral sense (Davies 1968; Thompson & Fisher, 1965; Krause, 1967). The offset of the Owen Stanley Metamorphic Belt, the presence of splaying faults and a number of structural ridges and troughs in the Louisiade Archipelago, all point to a large amount of tectonic Fault, position approximate Fault inferred from bathymetry Fault (hachures show downthrow) 'east cape UAKATAI 10° 20 — FIG. 1^6 Structural Geology of Milne Bay SlDEIA I IO°35' — I50°20 I50°35' ^ ^I50°40' I50°50 /|50°55' SARI BA l. C 56/A9/22 -32- deformation in Eastern Papua. Rotational movement associated with this tectonic deformation is evident in the trend of faults and fold axes, in the D'Entrecasteaux Islands to the north, which is at almost right angles to the main east-west trend in Milne Bay. The submarine trough in Milne Bay which parallels East Cape maintains a similar direction to the structural trend on the islands to the North. Although no sparker traverse has been run across this trough it is possible to postulate a structural origin for this trough. The trough is postulated to be fault controlled since no abrasive sediment source is present at the head of the trough to cause such a feature. The Milne Bay graben structure is probably a result of the tensional stress associated with this rotational movement. Milne Bay provides an excellent example of a tectonically controlled sedimentary environment. Submergence of the basin together with deposition of sediments derived from uplifted country has gone on since at least the late Pleistocene. Stress releases of the crust during this period are evident in the faulting of the sedimentary strata. The tectonic setting of Milne Bay is that of a small sinking trough within a mobile zone. This mobile zone forms part of a large fracture system around the Pacific Ocean. Milne Bay is situated on the convex continental side of present day volcanic island arc. The volcanic island arc in question being the D'Entrecasteaux and the Solomon Islands. The probability arises that Milne Bay formed because of sinking of ultramafic material derived from the upper mantle. According to Davies (1969) and Thompson (1965), the oceanic crust has been forced against the sialic core of Papua, so bringing upper mantle material to -33- the surface. This ultrabasic material forms the Papuan Ultrabasic Belt, which is postulated to be sinking (Davies, 1969). The ultramafics also crop out in small bodies in the area surrounding Milne Bay. It is possible that Milne Bay is underlain by a similar body which is sinking due to its higher density to the surrounding country rock. The presence of a positive gravity anomaly on each side of Milne Bay, and a negative anomaly opposite the axis of the bay support this theory. PART III SEDIMENTOLOGY -34- PART III SEDIMENTS OF MILNE BAY (1) INTRODUCTION A total of 32 surface sediment samples were taken in Milne bay during this survey. Locality of the sample stations is shown in figure 12. The samples were taken along traverses approximately in the same position as the sparker traverses. These samples were studied over a period of nine months to determine various properties and relationships discussed in this section. A flow diagram of the sample analysis is shown in figure 13. Since the number of samples taken in Milne Bay is by no means enough to make many categorical statements about the environment it must be remembered that most of this work in analysing these samples is of a qualitative nature. Distribution patterns in Milne Bay obtained from the various parameters only hold true in the very general case, and on a smaller scale with many more sample stations most of these patterns would probably be profoundly modified. /EAST CAPE IUAKATA I o305 • 327 o 307 o303 o308 •328 • 333 o309 o 313 o 320 o 312 FIG 12. Milne Bay Sample Localities SIDEIA I /Vn I C 56/A9/25 Figure 12. ANALYSIS FLOW CHART 1. Disperse by soaking in distilled water 2. Wet sieved on 4 0 sieve if more than 10 gms Fraction> 4 0 Fraction<4 0 3. Dried and sieved at Vz 0 intervals 5. Split into 2 subsamples 4. Composition determined^ binocular microscope Subsamples (a) Subsample (b) (N B. Duplication of size 6. Grainsize analysis 10. Clay mineral analysis using sedimentatio by pipette X-Ray of tube). oriented untreated glycdated, and heated sample. if less than 10 gms Fraction>4$/ 7. Mounted on slide 8. Grain size distribution by using microscope and point counter. 9. Determine grainsize distribution. 11. Untreated sample, washed and dried 12. Split into 5 samples - a. b. c. d. and e. (a) Determine heavy and light minerals present. (b) Calcimetric determination. (c) Subsample powdered and used for X-ray diffraction study and D.R O.S study. (d) Treated with H to determined oxidisable content. (e) Retained for reference -35- (2) COLOUR OF THE SEDIMENT Colour determination of the samples was done by using the Rock Colour Chart (Geol. Soc. of America, 1959). The determination was done approximately 1Vz years after collection on a washed and dried sample. Strictly speaking colour determinations should be done as soon as possible after collection of the sample. The colour of the original sample however seemed to have been retained during the period elapsed. Figure 14 shows the distribution of the colours of the samples taken in Milne Bay. The colour varies from greyish green through olive grey yellowish grey to greyish olive. Comparison with figure 15 shows that the textural property of the sediments is related to its colour. An increase in coarser particles makes the samples lighter in colour, also an increase in carbonate fragments gives the sample a yellow appearance. Clay content determines the amount of darkness of the samples, thus the samples with a high clay content are olive grey. v//. I Greenish grey 5GY 6/1 1 1 l■■ A Light olive grey 5Y 6/1 IM Ii I Yellowish grey 5Y 7/2 1- I Olive grey 5Y 4/1 10° 15' — I - - 1 Greyish olive I0°20' — IO°25— 10° 30 — FIG 14. Surface Sediment Colour in Milne Bay SIDEIA I. IO°35' — I5b®20' IS0°2S' I50°30‘ I50°33' >I50°4S' 150°30 dI50°55' I3I°05' JY\0» rir^ __I___ /SARIBAI. Ho - I -36- (3) TEXTURAL DISTRIBUTION The percentage of sand silt and clay in the Milne Bay samples has been plotted on a triangular diagram using three end members. Shephard’s (1954) textural classification is used to describe the samples. The samples are classified purely on their grainsize, but it must be remembered that most samples have a high carbonate content and are thus calcarenites or calcilutites. Most of the samples (33%) are in the clayey-silt range of Shephard's classifications. The silty-sand and sandy-silt ranges both contain 20%, while respectively 2% lie in the sand, silt and silt-clay range (see Fig. 15). Figure 16 shows the textural distribution of the surface sediments in Milne Bay. The central region of the bay contains chiefly clayey silt. The clay content in the samples decreases near shore and toward the eastern part of the bay. South of Nuakata Island a shallow shelf is covered with sand which further south and with increasing depth grades into silty-sand and sandy-silt to silt. In the western part of the bay two samples are in the sand-silt- clay range. These samples occur on the edge of the prograding delta which is a product of the discharge of the rivers entering the bay in the west. The deposits of Milne Bay are similar to the silty clays found generally deeper and at further distances from shore in other parts of the world, e.g. Peru-Chile Trench (Trask, 1961), California off shore basins (Emery, 1960), Gulf of California (Van Andel, 1964), 36a 100 CLAY 0 — 4 mu (< 80) CLAY CALCILUTITE SANDY CLAY SILTY CLAY SAND CLAYEY SAND CLAYEY SILT SILT - CLAY SAND SILTY SAND • CALCISILTITE CALCARENITE SANDY SILT 100 SAND > 63mu ( >- 10) SILT > 63 mu (4-80) FIG 15 MILNE BAY SAMPLES Shepard (1954) TEXTURAL CLASSIFICATION CLAY EAST CAPE 10° 13' SAND UAKATA I 10*20 FIG 16 Surface Sediment Textural Distribution in Milne Bay SlDElA I 10*35' 130*20' 150*25' 130*30' 130*35' 150*30 SARI BAi C 56/A9/23 -37- Timor Sea (Van Andel and Veevers, 1967). This is probably due to the loss of coarser material in the sediment load of the contributing rivers soon after entering the bay. Furthermore since the energy of the environment of Milne Bay is low there is little reworking by currents to carry clastic material coarser than silt away from the near shore deltas. -38- (4) GRAIN SIZE ANALYSIS (a) Introduction A grain-size analysis of the Milne Bay samples was undertaken to determine the sedimentary parameters. The object of this study was to determine if these parameters could be used in any way to deleniate environmental conditions of sedimentation within the bay. Furthermore as a means of a more accurate description of the samples and for comparison with sediments from other areas this analysis is of importance. The term "size" has received much attention from many sedimentologists due to the fact that grain size depends to some extent on the particular technique adopted to measure this property. Methods of size analysis are described by Krumbein, (1932), Krumbein & Pettijohn (1938), Merdan, (1960), Irani and Callis (1963), Folk (1965). An excellent review of the different grain size measures obtained by different methods is given by Folk (1964). The methods used in this study were chiefly pipette for material finer than 4 phi and microscopic for material coarser than 4 phi. Some work was done using a sedimentation tube to determine the distribution of the fraction coarser than 4 phi. For elaboration on sediment size analysis by hydraulic methods see Buckley (1964) Emery (1938), Poole (1957), Schlee (1966) and Felix (1969). Sieving at Vz phi intervals was used for some samples with sufficient material coarser than 4 phi. However for most of the samples from Milne Bay -39- the sand fraction ( 40 ) was insufficient to use any other than the microscopic size analysis. For the samples with sufficient sand size material to do a sieve analysis and a sedimentation tube analysis the size distribution was found by these two methods, to determine the reproducibility of the microscopic method. It was found that the results using the three different methods i.e sieves, sediment tube, and microscope, on the same sample were reproducible. The methods used are standardised and need not receive description here. For further background see Folk (1965) Krumbein and Pettijohn (1938). (b) Sample Statistics Sample statistics represent the characteristics of a variable in a sample. To obtain sample statistics, a cumulative percentage was plotted against a phi size scale (1 phi * -log2 diameter in mm) using probability graph paper. From the curve obtained the different parameters were calculated by selecting certain percentiles. For further details on the methods of calculating parameters, see Folk (1964, 1965), Krumbein & Pettijohn (1938), Inmann (1952), Folk and Ward 1957; Krumbein (1932, 1934, 1935, 1936, 1964) and Tanner (1964). The parameters used in this study were those proposed by Folk and Ward (1957) (see Table 2). Figure 17 shows an actual example of how the various statistical parameters were obtained from the cumulative curve. A frequency curve is also shown in Fig. 18 for the same sample. The frequency curve shows a strongly bimodal distribution with minor peaks also present. The contribution of the various components in the sample to the shape of this frequency curve is indicated in fig. 18. The cumulative curves of some of the samples FREQUENCY % PERCENTAGE 90 50 2 -50 ------ — -40 GRAVEL -30 F ; g Mg 17 ------ alveoli 5 18 econdary N U M M U U T i D A E of P e r c e n t i l e s Sample Frequency table nellidae 310 Mode 2 obtained cumulative and Curve SAND / fragments parameters Shell for GRAIN from GRAIN curve Feacal Sample pel the Primary S'ZE lets are on graph SIZE p r o b a b i l i t y 310 in calculated T e r r e s t r i a l Mode are - 0 in coarse Secondary showing s u b s t i t u * e d Medium units 0 units graph. from silt Material broad silt Mode in this the c o m p o s i t i o n Clay formulae minerals CL AY -40- Sedimentary Parameters (after Folk and Ward 1957) Graphic mean Mz •= (06 + 050 + 084) 3 Inclusive Graphic Standard Deviation * 084 -016 + 095 - 05 4 6.6 Inclusive Graphic Skewness SKI = 016 + 084 - 2 050 + 05 + 095 - 2 050 2 (084 - 016 ) 2 (095 - 05) Graphic Kurtosis KG « 095 - 05 2.44 (075 - 025) -41- using a phi co-ordinate and a probability ordinate are shown in figures 19, 20 and 21. (c) Discussion of the sample cumulative curves. (1) Modality of the distributions. The mode of a sample is the most frequently occurring grain diameter. To find the mode one may either find the steepest slope (inflection point or points) on the cumulative curve drawn on an arithmetic ordinate or similarly find the grain size represented by the peak of the frequency curve (Folk, 1964). Two other methods of finding the mode are: (1) To mathematically compute the frequency curve by taking a succession of differences (Brotherhood and Griffiths, 1947) and finding the mode on this curve. (2) One can select an arbitrary grain size interval (say 1/4 0 or ) and by successively shifting this across the cumulative curve, find the grain-size interval which includes the greatest percentage of grains (Bush, 1951; Curry, 1960). Most samples in Milne Bay show more than one mode. The most abundant one is the primary mode while the others are secondary or subordinate. Modes are especially useful in studying mixed sources of material and they have genetic significance (Curray, 1960; Brezina, 1963a), however as a measure of average grain size they are of little grain size in phi units groin size in phi units Sample 302 Sample 303 to § to ft to" to 5 i £ fe *7 £ to to gram size in phi units gram size in phi units Sample 304 Sample 305 Sample 307 FIG 19 Cumulative Curves groin size in phi units groin size in phi units Sample 309 Sample 311 groin size in phi units grain size in phi units Sample 312 Sample 313 grain size in phi units groin size in phi units Sample 314 Sample 315 FIG. 20 Cumulative Curves 95 84 a*75 > 50 o I” 16 5 4 5 6 7 8 9 3 4 5 6 7 8 grain size in phi units grain size in phi units Sample 317 Sample 320 Sample 325 Sample 327 4 5 6 7 8 grain size in phi units grain size in phi units Sample 331 Sample 332 FIG. 21 Cumulative Curves -42- The samples in Milne Bay owe their bimodality and polymodality to the number of sources of the sediments. Tests from organisms such as foraminifera, pelecypods and radiolarians on the one hand, and clastic material derived from land on the other hand give rise to the different modes in the sediments of the bay. Those samples with an almost unimodal distribution (e.g. 311, 312, 317; figs 20 and 21) in general have been subjected to abrasion and reworking tidal currents causing a more normal distribution. (2) Gaps in the size Distribution Many of the cumulative curves of the Milne Bay samples show gaps between 4.50 and 60 , i.e. the curve flattens to become almost horizontal. This is either due to the absence of medium silt in the samples or may be a function of changes in analytical technique. (Griffiths 1957). As early as 1880 Sorby refers to the presence of gaps in the size distribution of sediments. Wentworth (1933), Udden (1914, Lough (1942) and Pettijohn (1949, 1957) noted gaps at -10 , 80, 3.50, 3-40, -1 to 1/^0, to 4/^0, O to 20 and 3 to 50 respectively Tanner (1958b 1959) Folk (1958a, b), Spencer (1963) and Rogers et al. 1963, also noted these gaps. In the tropics according to Bakker (1957) there is a deficiency of fine silt grains. This, is also the case in some of the Milne Bay samples. Since the gaps in the size distributions are not confined to the diameter at which the analytical technique (i.e. microscope or pipette analysis) has changed it seems unlikely that this is the only cause. An absence of certain grain diameters in the source material is a more plausible explanation. Table 6 shows the interval at which gaps occur in the Milne Bay samples. -43- TABLE 6 GAPS IN CUMULATIVE CURVES 302 between 6 0 and 7 0 303 between 5.5 0 and 9 0 304 Nil 305 between 4 0 and 5 0 306 between 3.50 and 4 00 307 between 5 0 and 5.5 0 309 between 4.5 0 and 5 0 310 Nil 311 Nil 312 Nil 313 between 4.5 0 and 5 0 slight one between 6 0 and 8 0 314 between 4.5 0 and 5 0 315 between 4.5 0 and 5 0 317 Nil 320 between 4.5 0 and 5 0 321 Nil 322 Nil 324 Nil 325 between 4.5 0 and 6 0 327 Nil 331 between 4.5 0 and 6 0 332 between 4.5 0 and 6 0 333 Nil -44- (d) Sedimentary Parameters of Milne Bay samples. (1) Graphic Mean Mz. This measure proposed by Folk and Ward (1957) is superior as a measure of average grainsize, to Trasks (1930) Median (diam corresponding to 50% mark on cumulative curve), since it is based on three points on the curve (McCammon 1962a). The graphic mean hence gives a better overall picture. The graphic mean size in the Milne Bay samples ranges between 2.470 and 8.320. The average of all the samples is 5.750 and is thus within the silt range. The graphic mean of the Milne Bay samples is similar to that of the sediments on the shelf south of Lae, New Guinea (Walraven 1968). The sediments of Milne Bay are however finer than those of Charlotte Harbour (Huang and Goodall 1967) M1* 2.01) they are coarser than those of the Mississipi Delta (van Andel 1960). The distribution of Graphic Mean size is shown in figure 22. There is a decrease in grainsize with increasing depth. This is partly due to a decrease in the grainsize of the terrestrially derived material and a decrease in reef debris in the deeper part of the bay. South of Nuakata Island the Graphic Mean is low due to a considerable amount of coral reef debris. Broadly speaking there is an increase in mean size with increasing carbonate content in the Milne Bay samples. (2) The Inclusive Graphic Standard Deviation Folk and Wards measure of standard deviation is an indication 10° 15' — I0°20 — IO°25 — 10° JO INS'— -45- of the sorting of sediments. A verbal scale of sorting proposed by these authors is shown in Table 4. The Inclusive Graphic standard deviation in the Milne Bay samples ranges from 1.10 to 3.32. They are thus poorly or very poorly sorted. Two thirds of the samples are very poorly sorted. A scatter diagram of the Graphic Mean versus Sorting shows that sorting decreases with a decrease in the Graphic Mean. This is similar to findings on the continental shelf south of Lae in N.G. (Walraven, 1968); and to those of Hough (1942), Inman (1949, 1953), Griffiths (1951a, 1951b), Folk and Ward (1957). The explanation of this dependence of sorting on mean size is probably due to a poly modal source (Folk 1964) of these sediments. In Milne Bay there is a slight decrease in the Graphic Standard Deviation (i.e. better sorting) in the samples taken from the eastern part of the bay south of Nuakata Island (see figure 25). This is probably due to the lesser influence of terrestrial material in this region of the bay and hence the source of the sediments is less polymodal. Poor sorting must be ascribed to the low energy environment, lack of reworking, and to the multisource origin of the sediment, particularly the presence of an important biogenic component of which the particle size may be unrelated to the conditions controlling the deposition of allogenic material. It is also relevant to note that the samples consist of a mixture of the top 8 to 10cm of the sediment, and although they are taken to be representative of a single horizon, in fact they may consist of two or more lithologically different laminations. 45a in phi units FIG. 23 Dependence of Inclusive Graphic Standard Deviation on the Graphic Mean. | Poorly sorted. < ^ • j Very poorly sorted EAST CAPE BENTLY BAY UAKATA I , ■O 2 67; o2 I2‘ o 2 83: o2 82, x 02 45 2 42 o 2 91- o 2 35 o | |7 ■'o 2 74. ol 50 10° 30 — o I-4 6— FIG 24 Inclusive Graphic Standard Deviation cr in phi units SIDEIA I IO°35' — I50°25' I50°30' I30°33' ^ ^50°40’ I50°30 I 51 °0S' SARlBA -46- TABLE 4 SCALES FOR SORTING (after Folk and Ward 1957) Sorting Term Value of Very well sorted well sorted - 0.35 0 moderately well sorted - 0.50 0 moderately well sorted - 0.71 0 poorly sorted - 1.00 0 very poorly sorted - 2.00 0 extremely poorly sorted - 4.00 0 TABLE 5 Verbal limits on Skewness (after Folk 1965) Term “i + 100 to + 0.30 strongly fine skewed + 0.30 to + 0.10 fine skewed + 0.10 to - 0.10 near symmetrical - 0.10 to - 0.30 coarse skewed - 0.30 to 1.00 strongly coarse skewed -47- TABLE 6 Verbal limits of Kurtosis (after Folk 1965) kg 0.67 very platykurtic 0.67 - 0.90 platykurtic 0.90 - 1.11 mesokurtic 1.11 - 1.50 leptokurtic 1.50 - 3.00 very leptokurtic 3.00 extremely leptokurtic (3) Inclusive Graphic Skewness Most sedimentologist agree that ideally grainsize distribution in a sample is log-normal This implies that the cumulative curve becomes a straight line when plotted with a probability ordinate and using a phi scale co-ordinate. In nature there is usually a departure from this ideal case. To measure the non-normality of a distribution one needs to compute both skewness (asymmetry) and Kurtosis (peakedness). The skewness measure adopted here is that proposed by Folk and Ward 1957, (see Table 2). This measure, the Inclusive Graphic Skewness, includes the "tails" of the curve as well as the central portion. Skewness is mathematically restricted to the range between -1 and +1. A skewness value of 0 means a symmetrical curve. Table 5 shows the verbal terms for different values of SKI. Curves with a tail to the left i.e. excess coarse material have a negative skewness and an excess of fines results in a positive skewness. The values of skewness in the Milne Bay samples (see fig. 25) range from 0.73 to -0.05. The main portion of the samples is strongly fine skewed. Only one sample is strongly coarse skewed, while almost equal proportions of fine skewed, coarse skewed and nearly symmetrical samples are encountered. Values as low as 0.01 show that some samples are almost symmetrical and show near ideal conditions. The distribut ion of Skewness of the samples in Milne Bay shows no obvious pattern and to evaluate its significance in terms of environment would require more sampling. -49- (4) Graphic Kurtosis K G This is a measure of the peakedness of the curve. Kurtosis is the quantitative measure of the departure from normality. It measures the ratio of the sorting of the central portion to that of the "tails" of the curve. If in the central portion sorting is better than in the "tails" then a curve is said to be excessively peaked or leptokurtic. Bimodal curves because of their lesser sorting in the central portion are characteristically platykurtic Table 6 gives the verbal limits of Kurtosis values. The distribution of the Graphic Kurtosis values in the samples are shown in fig. 26. As a consequence of the polymodality of the sample distribution, most of the curves are platykurtic with values between 0.58 and 1.77. Very leptokurtic curves result from near shore samples where the dominant central terrigenous component seems to be better sorted than the material in the extremities of the curve. (e) Sources of Sediment There are a number of sources for the sediments being deposited in Milne Bay at the present time. Near shore and especially in the Western extremity of the bay, rivers discharge their sediment load into a narrow shelf in the form of deltas. During periods of heavy rain much sediment is carried down by rivers, and the coarser material is dumped soon after the river enters the bay. The finer sediment is carried further, some of it in suspension and may in some extreme cases reach the middle of the bay. On the steep slopes near the margin of the bay, it is likely that slumping of the deposited sediments results T K^Very platykurtic FIG 26 Graphic Kurtosis K, n0 ^ I50°20‘ I50°25' I50°30‘ ^ ^50°40' I I JSARIBAI. -50- in turbidity currents which carry the sediment further into the bay. However, much sediment which would normally enter the bay is prevented from doing so by mangrove swamps at the rivermouths. These mangrove swamps are excellent mud traps (Keunen 1950) and hence sedimentation rates are slowed down considerably within the environment of the bay proper. Another source for the sediments is the profuse growth of marine organisms in these tropical waters. Both planktonic and benthonic foraminifera, together with radiolarians, molluscs, ostracods and other organisms thrive in the bay and contribute their tests, shells, and spicules to the sediment. In many cases the contribution of these organisms is more important than that of the land derived detrital material. Yet another source of sediment are the barrier coral reefs on the eastern margin and the fringing reefs around the landlocked part of the bay. Debris from these reefs in the form of calcium carbonate is in certain instances the chief component of the sediment at present accumulating in Milne Bay. Except for a few narrow channels the tidal currents in Milne Bay are not particularly strong, and hence reworking of sediment by these currents is likely to affect only small parts of Milne Bay. Re working and modification by organisms is widespread as is evidenced by many feacal pellets in the samples. -51- (f) Geological Significance of the Parameters The presence of so many sources of sediment the number of different transport mechanisms, together with the reworking by organisms necessitates a more qualitative rather than quantitative appraisal of the results of a grain size analysis. A further factor which must be taken into consideration is the lack of good control on the distribution of the various parameters due to the sparsity of the sampling stations. The following interpretations are thus limited by the abovementioned factors. The geological significance of the Graphic Mean is that it can be translated into terms of available kinetic energy (or velocity) of the depositioning agent (Sahu 1964). However average grains size is also dependent on the size distribution of the avialable source material From this study on Milne Bay it is evident (when one dis regards the biologic contribution) that the kinetic energy of the depositing agents in the bay is low, since mainly fine material is transported appreciable distances from the source. Standard Deviation ideally records the fluctuations in the velocity of the depositing agents about its average value. Again the size distribution of the source material controls the sorting of the sediments. Since the standard deviation of the Milne Bay sediments indicate very poor sorting and little is known of the size distributions of the source very little can be concluded about the environmental conditions. Skewness and Kurtosis of the samples are of qualitative interest only in this study. See Sahu (1964) for the significance of these two -52- grainsize measures. Summarising the properties of the Milne Bay sediments obtained from the size analysis we see that the sediments are in the silt range and tend to be poorly to very poorly sorted. They are on the whole finely skewed, except near shore, and their size distribution is typically platykurtic with a strong tendency to be polymodal. -53- (4) CALCIMETHY Calcium carbonate in sediments occurs in two forms, aragonite (rhombohedral) and calcite (hexagonal). The calcium carbonate in the Milne Bay sediments is the result of the dying off of organisms with a calcareous skeleton or test such as foraminifera, coral, and pelecypods. (i) Analytical method Calcium carbonate will react with hydrochloric acid to give off carbon dioxide according to the equation. Ca COs + 2HC1 C02 + H20 + Ca Cl2 Determination of the total amount of calcium carbonate in this study was carried out using apparatus similar to that described by Hulseman (1967) which measures manometrically the volume of CC>2 gas evolved from a known quantity of sample. The percentage of calcium carbonate in the sample was calculated using the following formula. % (at T°C) = (A/B) f (T°C) 100.091/22414 where A * volume of CC>2 gas (ml) B * mass of sample (g) f (T°C) - function dependent on temperature and being equal to 1.0 at 25°C. -54- A nomograph devised by Walraven (1968) was used to facilitate rapid calculation of the carbonate percentage in the sample. Figure 27 is a reproduction of this nomograph. The percentage of calcium carb onate may be read off directly, when the gas volume and the sample mass are entered. Throughout the analysis the temperature of the system was kept at 25° by emersion in a water filled tank. Appendix 1 shows the results of the calcimetry analyses. (ii) Results The carbonate content in the samples from Milne Bay varied from 5% to 100%. Both aragonite and calcite were present in the Milne Bay samples (see mineral identification by X-ray analyses). (iii) Distribution of percentage calcium carbonate The distribution of the carbonate content in the Milne Bay samples is shown in Fig. 28. There is a definite increase in carbonate content going from west to east in the bay. In the western part of the bay near the rivermouths the sediments contain little calcium carbonate due to a high influx of terrigenous non-calcareous material. Fringing reefs are present on the western margin of the bay but their contribution is not enough to drown the effects of sedimentation from the rivers. In the central and deeper part of the bay carbonate content increases due to a decrease in the influx of terrigenous sediments and an increase in the organic component. The eastern margin is enclosed by coral reefs and the sediments in this area contain up to 95% of NOMOGRAPH FOR THE CALCULATION OF PERCENTAGE CaC03 IN SEDIMENTS Gas Volume Percentage Calcite —- 2 grr, i- To occorrpany Record Fig. 27 'east cape UAKATAl 60 70 K>° 30- FIG. 28 Percentage Calcium Carbonate in Milne Bay Samples SiOEIA I 150*28' 151*08' C 5 6/A 9/17 -55- calcium carbonate which is derived from the reefs and the prolific animal life around these parts. Little or no terrigenous material enters the bay in the eastern side. The broad pattern in the bay is thus a terrigenous sedimentation in the western part of Milne Bay which grades into a backreef, limestone sedimentation in the east. (5) OXIDISABLE MATTER IN MILNE BAY SAMPLES To determine the amount of oxidisable material a small amount (2 grams) of sample were treated with hydrogen peroxide and allowed to stand for several days until all oxidisation of the sample had ceased. The distribut on in Milne Bay of oxidisable matter which includes mainly organic material and plant remains is shown in figure 29. The percentage of oxidisable material ranges from 0.8% to 12.7% by weight of the sample. From the distribution in Milne Bay it is evident that a fair percentage 7-12% of organic material is concentrated in the samples in the western part of the bay and 5%-10% in the deeper central portion. Near shore the percentage decreases and in the eastern section in shallower water, where water circulation is more effective the percentage decreases to between 0.3 and 3%. The preservation of oxidisable material in the samples is a function of the oxidation potential (Eh) of the environment (Krumbein and Garrels 1952). In the restricted humid environment of Milne Bay 5 - 10 % 'EAST CAPE 0 - 5 % BENTLY BAY UAKATA l.i I0°20'_ o 5-75 o 7.7 -O l’8 ^ 6-3- o5 *7 o 8-03 0 2-5 10° 30 — FIG. 29 Wt. Percentage of Oxidisable Matter In Milne Bay SIDEIA I IO°35 — I50°20’ I50°25' I50°30' 150°50 I5I°05' -56- at least partial stagnation is involved in the deeper parts with normally oxygenated waters at the surface. The presence of a high proportion of oxidisable material in the samples of the deeper and inner parts reflect a negative oxidation potential. On the eastern side of the bay where the shallower banks and slopes occur, a normal circulation of the water occurs and hence most organic remains are oxidised before being incorporated into the sediment and hence the lower values of this region. The samples in the western part of the bay owe their high oxidisable material content (up to 12%) to another factor besides a negative Eh. In this part of the bay the main influx of sediments takes place and it is suggested that rapid burial by fine-grained sediments prevents the organic material from being oxidised. -57- (6) MINERAL COMPOSITION (a) X-Ray mineral identification Semi-quantitative mineral determinations were made by X-Ray diffraction. The analyses were carried out using a P.W. 1051 X-Ray Diffractometer. The results in order of relative intensities of the minerals identified is shown in Appendix 2. Most samples contain calcite, albite chlorite, aragonite, quartz and halite. In addition near shore samples contain some muscovite. Albite is the most abundant mineral in three samples taken near shore. The rest of the samples have calcite or aragonite as the most abundant mineral in the sample. The halite in the samples results from the evaporation of the seawater in the samples. (b) Sand fraction study (i) Contribution of organisms The fraction coarser than 4 0 was analysed using a binocular biological microscope for the presence and abundance of remains of organisms. The most abundant organic remains in the samples are of foraminifera. Both planktonic and benthonic forms are present. Benthonic forms are most abundant in the samples taken at a depth of less than 200 meters. Samples taken from a greater depth than 200 meters chiefly contain planktonic forms. -58- Some samples contain an abundance of siliceous sponge spicules especially those taken in the vicinity of reefs. Shells of gasteropods and pelecypods occur in the samples near the outer eastern margin of the bay in the back reef environment, and in the forereef environment of the near shore fringing reefs. Coral fragments are abundant in the samples on the shoals south of Nuakata Island. Other remains of organisms are present in the form of chitenous material probably from crustaceans. Echinoid spines and fragments are sporadically encountered in some shallow water samples. In the central portion of the bay feacal pellets (0.1 to 0.2 mm in diam) are abundant. The feacal pellets are composed of reworked very fine-grained greenish sediment. It is notable that no benthonic foram tests are found where feacal pellets are ubiquitous. This may be due to the destruction of the foram remains by the very organism which produced the feacal pellets. (ii) Heavy mineral analysis The "heavy mineral" portion of a sample includes those which sink in a liquid with a specific gravity of about 2.9. The fraction which is buoyant is regarded as the light mineral fraction. A study of the heavy mineral fraction is useful in the concept of consanguinity and may hence delineate the source area (Pettijohn 1941, Krumbein & Sloss 1957, Milner 1950). Separation of the heavy mineral fraction in this study was achieved by using bromoform CHBr^ as the separating liquid. The sample was -59- first treated with concentrated hydrochloric acid to remove all carbonates and to concentrate the detrital minerals. After digestion the sample was sieved using a 44 micron sieve to remove the clay fraction and dried. The separation was achieved by introducing the sample into a test tube filled with bromoform and centrifuging for about twenty minutes. The lower portion of the test tube was frozen and the upper unsolidified bromoform and light mineral fraction poured out and collected on filter paper. The lower portion was allowed to melt and the bromoform containing the heavy minerals was likewise collected on filter paper. Both the light and heavy fraction were mounted. Optical determination of the minerals was done by use of a petrological microscope. The heavy minerals present in the samples consist of pyroxenes, (Augite and aegerine augite), hornblende, olivine, and opaques (hematite, magnetite, pyrite, and leucoxene). The pyroxenes vary in colour from bright green (aegerine augite), to brown, to almost colourless varieties (augite). They are the most abundant heavy mineral in these samples and some heavy fractions contain up to 80 percent pyroxene. Hornblende is also abundant, locally forming up to 50 percent of some samples, but is rare or absent in most cases. The olivine is typically bleached yellowish green in colour and occurs only in a few nearshore samples, notably in the southwestern extremity off the bay, where it constitutes up to 60% of the heavy mineral fraction. Opaque minerals in Milne Bay usually form about -60- 10% of the heavy mineral fraction. Hematite occurs in powdery aggregates and magnetite in grains. Pyrite has been observed in some samples where it fills foraminiferal tests and is obviously of authigenic origin. The presence of this authigenic pyrite supports the view that reducing conditions prevail in some parts of Milne Bay (Krumbein and Garrels 1952). The heavy mineral assemblage in Milne Bay is typical of a basic mafic igneous province. (Pettijohn 1941, Van Andel 1959, Krumbein and Sloss 1951). Milne Bay is surrounded by basalts with intrusions of soda rich gabbros and syenite (Davies et al. 1968) and these rocks are the only source for recent sediments accumulating in Milne Bay. (iii) Analysis of "light mineral" fraction This fraction of the sample includes the mineral constituents which do not gravitate in bromoform, i.e. specific gravity less than 2 87. Almost all the samples from Milne Bay contain felspar, mica, quartz volcanic rock fragments and some volcanic glass, together with some authigenic glauconite. The proportion of light minerals varies for different samples, there being an increase in content inshore especially near river mouths. Plagioclase (albite) is the dominant felspar while in some samples; notably in the southwestern margin of the bay; orthoclase is present. Quartz is only a very minor constituent in the Milne Bay samples. Mica is found in noticeable quantity in the near shore samples. -61- Together with the heavy mineral analysis, the light mineral fraction with its presence of much plagioclase and only traces of quartz and the presence of fine-grained basic volcanic rock fragments suggest a basic volcanic terrain. Albite in these samples indicates further that the basic volcanics are probably of marine origin. It is thus evident that the terrestrially derived detrital minerals result from the breakdown of the basic marine volcanics of the Dawa Dawa Beds. Furthermore the presence of orthoclase in the south western part of the bay is the result of weathering of the Gabahusuhusu syenite which outcrops to the south of Milne Bay (Davies et al., 1968). (c) Clay mineral analysis The clay mineral analysis is concerned with the composition of the size fraction finer than 2 microns (9 0). Clay minerals may be defined as "hydrated silicates with layer or chain lattices consisting of sheets of silica tetrahedra arranged in hexagonal form, condensed with octahedral sheets. They are usually of small particles size. (McKenzie, 1959). The clay minerals have been divided into different classes by Grim (1953). This classification is shown in Table 5. The structure of clay minerals are sensitive to environment and are there fore of importance in the study of Recent sediments. (i) Method of Study An oriented slide was made of the clay mineral fraction by pipetting a small aliquot after allowing the material coarser than 2 microns to settle, and allowing a centrifuged slurry of the clay to -62- TABLE 7 CLASSIFICATION OF CLAY MINERALS AFTER GRIM 1953 A Two layertype (1) Equidimensional-Koalinite group (2) Elongate Halloysite B Three layer types (1) Expanding lattice (a) Equidimensional Smectite group (b) Elongate Smectite group (2) Non expanding lattices Illite group C Regular - mixed layer types chlorite group D Chain structure types Attapulgite Sepiolite Palygorskite -63- dry on a glass slide. These orientated samples were analysed on an X-Ray Diffractometer by first running an untreated slide then a glycolated slide, and lastly the slide heated previously to 400°C. Results of the X-Ray clay mineral identification are shown in Appendix in. (ii) Results The dominant clay mineral in the samples from Milne Bay is of the mixed layer type. Chlorite - Smectite variety. The chlorite in the samples has partially lost the Brucite (Mg OH3) sheets (see fig. 30). This degraded chlorite forms the greatest portion of the mixed layered mineral chlorite - smectite. A little illite and kaolinite is present in sample 332, but for the greater part of the bay there is little or no illite or kaolinite in the samples. (iii) Discussion of Clay Mineral Results Marine environments are alkaline with a pH between 7 and 9, and it is therefore possible for cations to be added but not removed. Theoretically the expected clay minerals in a marine environment are illite, chlorite and smectite (Millot 1949). The absence of koalinite in the Milne Bay samples is thus as expected, however, the lack of illite in all but one sample needs an explanation. Almost every single author who has studied clays in a marine environment reports the presence of illite in his samples. (Powers, 1954; Millot, 1949; Grim, 1963; Milner 1962; Fafajee, 1951; Revelee, 1944; Bradley, 1940; Keunen, 1943; Correns, 1937). In fact in most marine sediments illite appears to be the dominant clay mineral. ^ A \ O. xP P \o vP 6 (OH) 14.2 A x XX 5Mk + A1 10 oa v_; p; 2k 'P' P 'O p\> 6 (OH) 6 0 6 0 3 Si + 1 A1 R-mA 3 Si + 1 A1 ✓ P \ Q ' / o / p\ qv ;:• 2(oh) + 40 Q Q p Q p 2 (OH) + 4 0 \ /\ /' \ A / XX X X 4A1 AX xx 6 Mg + A1 X V \ X V v vX'X '' x V ' P P P O 2 (OH)4-4 0 0 P P 0 0 O 2 (OH) + 40 3 Si + 1 A1 3 Ri + A1 60 6 0 Muscovite Chlorite KjAl^S.jAljJOjofOH), MgioAlj(Si*Alj) O^OH),, -'M 1 9.6-21 4 At «HjO -r/M\X«Pr >PQ^P^ai° a p p o >o 6(oh) 0 Q p P 0 p 2 (OH) + 40 / n v ✓ s y \ > x \ x, ✓ 7 2 A yy v X 4 A1 XX X X 4A1 V pX X" pX» 2 (OH) + 40 P 0 P 'p pX 2 (OH) + 40 b axis Knolinite Mon trnoril Ionite Al,Si ,O10(OHi, Al4(Si4O10 )2 (0H)4 • xH,0 Fig. 30 Structure of the Common Clay Minerals (after Grim. 1953) -64- It has long ago been noted that smectite occurs mainly in nearshore sediments and is particularly common in sediments derived from basic volcanic areas. (Dietz 1941, Grim 1943, Gorrens 1937). The region surrounding Milne Bay is largely composed of basic volcanic rocks (Davies et al., 1958). These basic volcanic rocks weather, producing mainly smectite and chlorite (Grim 1953) and it is these two clay minerals which are transported to Milne Bay. It would seem firstly that illite is not present in the source areas, and secondly that sedimentation is too rapid to permit diagenetic alteration of other clays to illite. 7. GEOCHEMICAL ANALYSIS A direct reading optical emission spectrograph was employed to determine the concentration of elements manganese, nickel, scandium strontium, titanium, vanadium, yttrium, zirconium, barium, calcium, cobalt, chromium, copper, iron, and magnesium in the Milne Bay samples. The method used is described by Ahrens and Taylor (1961; p. 189). The sample was powdered and mixed with 2 parts of graphite. This mixture was loaded in a preformed graphite electrode and arced as the anode with a constant current of 8 amperes (D. C.) for 130 sec. Both internal and rock standards were used in the determination. The results are shown in Appendix IV. The elements Mg, Fe, Ti, are high in the samples in the western part of the bay where terrigenous material is deposited. In comparison with the average sediment -65- composition of Poldervaart (1955) and Leith and Mead (1915) and Clarke (1924) these elements are also much high than average in the samples from the western part of the bay (see Table 8). This is due to the source rocks being of a basic composition. In the eastern parts the bay the average value of Ti and Fe is very much lower than average sediment but higher than Clarke's average limestone. Magnesium is only slightly higher than the average sediment but much lower than the average limestone. It is notable that the value for Fe are higher in the western part and lower in the eastern part of the bay than the average of Leith and Mead (1915) and Poldervaart (1955), but the overall average in the bay is close to their average. See Table 8. The elements Mn, Ni, Sc, V, Y, Zr, Cr, Co, Ba and Cu, also reflect the same type of distribution as that of Fe Ti and Mg. Thus the influence of terrestrial material is seen to be most marked in the western half of the bay. The values of Cu, Cr, Co, Ni, V, Zr and up to a point Sc suggest a basic source rock for these sediments. Calcium is most abundant in the eastern part of the bay. Strontium shows high values for the same samples as those that are high in calcium, a function of its easy admission into calcium carbonate (Mason 1952). This reflects the decrease in terrigenous material and the increasing influence of biogenic carbonate. eastern *The 324. to 311 samples includes part western The 333 to 326 and 310 to 302 samples. includes part sandstone shale values. limestone and a 0 G O CQ 0 0 G G 0 d 0 ctf o o •H 0 G ctf co o G a ctf +-> G d 0 t-Q CQ £ si G 0 TS bn T3 d 05 0 cti +-» rH G O CQ d > 0 CQ 5 0 0 0 G CQ G G CQ bn G a 0 CQ CQ 0 CQ 05 LO 5 CM rH G G CQ O cq G rt 0 xs CM G3 00 +■> T5 CM T3 LO £> 05 LO CM CO g O 00 0 P oo H •r-i o o ^ CO CO CO O CO G 0 cti G< G a G d G 05 G CM bn 0 05 0 d LO cj rH LO 05 LO < d G £ Jji 0} G 0 0 CQ g d G > O — 0 G > +■> -2 * * r I G 0 G O O a G G 0 . 0 S 0 G rH o> T3 LO Sj d P< * CVJ PQ rH m PQ iH g 0 > bn 0 d g o cq 0 0 bn G 0 0 G 0 -M < < •H T5 CO G g G o a g cti G g crj bn c G CQ 0 Ctf —l 0 o o a h o g 0 0 H 5S •f* t •H T5 "£ • T3 CO H W PQ < 99- -67- 8. SUMMARY AND CONCLUSIONS OF SEDIMENTS IN MILNE BAY The Milne Bay sediments can be roughly divided into two types, those which are mainly derived from terrigenous material and those that are mainly due to organic activity within the bay. The influence of terrigenous material carried into the bay decreases in the eastern half of the bay. Attributes of the sediments change gradually from one into the other going from west to east. From a predominantly clay- silt derived from basic volcanic rocks to calcareous sediments derived from foraminifera and coral growth. Heavy minerals and clay minerals in the sample reflect the source rocks around Milne Bay. The heavy minerals are typical of those derived from mafic or ultramafic rocks while the clay minerals are also those obtained from the weathering of basic volcanics. The geochemistry of the samples in Milne Bay further supports the influence of a basic source province in the Milne Bay samples. The amount and distribution of oxidisable material show a decrease in the oxidation potential in the deeper central part of the bay. Furthermore rapid sedimentation at the mouths of the rivers entering the bay causes a further increase in the amount of organic material in the sediments. Grain size distributions in the sample show poor sorting due to the contribution of a number of sources of the sediments. The average grain size of the sediments is partly controlled by the amount and size of foraminiferal tests and by the amount of fine grained material derived from the surrounding country rocks. BIBLIOGRAPHY -68- BIBLIOGRAPHY ADMIRALTY TIDE TABLES, 1969 -Vol 3. Hydrographers of the Navy. London. AHRENS and TAYLOR, 1961 - Spectrochemical Analysis. Addison Wesley, Reading Mass. p. 189. BAKER, D. J., 1953 - Ilvaite and prehnite in micropegmatite diorite south-east Papua. Amer. Miner. 38. pp. 840 - 849. BAKKER, J.P., und MULLER, J.J., 1957 - Zweiphasige Flussablagerungen und Zweiphasen verwitterung in den Tropen unter besonderer Berucksichtigung von Surinam. Hermann Lautensach - Festschr Stuttgarter Geograph Studien, 69. 365 - 397. BREZINA, J., 1963a - Classification and measures of grain-size distribution. Zvlastni Otisk Vestniku Ustredniho Ustavu, Geologickeho, 38; 409 - 412. BRITISH ADMIRALTY, 1956 - Pacific Islands Pilot Vol. 1. BROTHERHOOD, G.R., and GRIFFITHS, J.C., 1947 - Mathematical derivation of the unique frequency curve. J. Sediment. Petrol, 32: 211 - 217. BUCKLEY, D.E., 1964 - Mechanical analysis of macroscopic dispersal systems by means of a settling tube. Bedford Institute of Ocean ography report No. 10, 69-2, 43p. -69- CLARKE, F.W., 1924 - The data of geochemistry (fifth edition) U.S. Geol. Survey Bull 770. CORRENS, C.W., 1937 - Die Sedimente des Equatorial Atlantischen Ozeans, Duetsche Antlantischen Exped. Meteor 1925-27. Wiss. Eygeb. 3. CURRAY, J.R., 1960 - Tracing sediment masses by grain-size modes. Intern. Geol. Congr. 21st Copenhagen, Rept Session, Norden pp. 119-130. CURRAY, J.R., 1960 - Sediments and history of the Holocene transgression, Northwest Gulf of Mexico, in Shepard F.P., and others, eds. Recent Sediments, northwest Gulf of Mexico. Tulsa. Oklahoma. Am. Assoc. Petrol. Geol. p. 221-266. CURRAY, J.R., 1961 - Late Quaternary sea level; a discussion; Geol. Soc. Amer. Bull. V.72, p. 1707-1712. CURRAY, J.R., 1965 - Late Quaternary history, continental shelves of the United States in Wright Jr., H.E., and Frey, D.G., eds. The Quaternary of the United States Princeton, New Jersey, Princeton Univ. Press, P.723-735. CURRAY, J.R., and MOORE, D.G., 1969 - Pleistocene progradation of continental terrace, Costa de Nayarit, Mexico. Amer. Ass. Petrol. Geol. Mem. 193-215. -70- DAVIES, H.L., 1969 - The Papuan Ultrabasic Belt. Proc. 23rd Int Geol. Congr. Prague DAVIES, H.L., 1967 - Milne Bay, Papua - geological reconnaissance. Bur. Miner Resour. Aust. Rec. 1967/53. DAVIES, H.L., SMITH, I.E., CIFALI, G., and BELFORD, D.J., 1968 Eastern Papua Geological Reconnaissance. Bur. Miner. Resour. Aust. Rec. 1968/66. DIETZ, R.S., 1941 - Clay minerals in Recent Marine Sediments. Ph.D. thesis University of Illinois. DOEGLAS, D.J., 1946 - Interpretation of the results of mechanical analysis. J. Sediment Petrol 16: 19-40. EMERY, K.O., 1938 - Rapid method of mechanical analysis of sands. J. Sediment Petrol. V8. p.105-111. FAVEJEE, J. Ch.L., 1951 - The origin of the "Wadden" Mud. Meded. Landbouw. Wageningen 51. No. 5. p. 113. FELIX, D.W., 1969 - An inexpensive Recording settling tube for analysis of sands. J. Sediment, petrol. Vol. 39. 777-780. FOLK, R.L., 1959a - Interaction of source and environmen in controlling pellets of size versus sorting. Programme of Dallas Meeting - Sec. Econ. Palaeontologist - Mineralogists, pp. 67-68. -71- FOLK, R.L., 1962b - Sorting in some carbonate beaches of Mexico Trans. N.Y. Asad. Sci. Ser. 11, 25. 222-244. FOLK, R.L., 1962a - Of skewness and sands. J. Sediment. Petrol. 32 145 - 146. FOLK, R.L., 1965 - Petrology of sedimentary Rocks. Memphills Austin, Texas, 159. pp. FOLK, R.L., 1966 - A review of grain-size parameters. Sedimentology 6, 73-93. FOLK, R.L. and WARD, W.C., 1957 - Branzos River bar a study in the significance of grain-size parameters. J. Sediment. Petrol. 27. 3-27. FOLK, R.L., and ROBLES, R., 1969 - Carbonate sediments of Is la Perez Alacran Reef Complex, Yucatan J. Geol. 72. 255-292. FRIEDMAN, G.M., 1962b - On sorting, sorting coefficients and the lognormality of the grain-size distribution of sandstones. J. Geol., 70. 737-756. GLAESSNER, M.F., 1950 - Geotectonic position of New Guinea. Amer. Assoc. Petrol. Geol.Bull 34, 856-881. GRIFFITHS, J.C., 1957 - Some frequency distribution of detrital sediments based on sieving and pipette sedimentation. Bull. Geol. Sec. Am. 68, 1739. -72- GRIFFITHS J.C., 1967 - Scientific method in analysis of sediments. McGraw-Hill. New York. 508 pp. GRIM, R.E., 1953 - Clay mineralogy. McGraw-Hill, New York. GRIM, R.E., DIETZ, R.S., and BRADLEY, W.F., 1949 - Clay mineral composition. Of some sediments from the Pacific Ocean of the California Coast and Gulf of Mexico. Bull. Geol. Soc. Amer. 60. GRIM,R.E., and JOHNS, W.D , 1954 - Clay Mineral investigation in the Northern Gulf of Mexico. Clays and clay minerals. Proc. 2nd Nat. Conf. Clays and clay minerals 1954, p. 81 HERDAN, G., 1960 - Small particle statistics. Academic Press New York. N.Y. 418 pp. HOUGH, J.L., 1942 - Sediments of Cape Cod Bay, Massachusetts. J Sediment Petrol, 12. 10 and 30. HUANG, T.C., and GOODELL, H.G., 1967 - Sediments of Charlotte Harbour, Southwestern Florida. J. Sediment Petrol. V.37 449-475. HULSEMAN, J., 1967 - The continental margin off the Atlantic coast of the United States. Carbonate in sediments, Nova Scotia to Hudson Canyon. Sedimentology, 8, 2, 121-195. INMAN, D L., 1952 - Measures for describing the size distribution of sediments. J. Sediment Petrol 22, 125-145. -73- IRANI, R.R., and CALLIS, C.F., 1963 - Particle size, Measurement, interpretation and applications. Wiley, New York. N.Y. 165 pp KEYSER de, F., 1961 - Misima Island, geology and gold mineralisation. Bur. Miner. Resour. Aust. Rep. 57. KEUNEN, P.H., 1943 - The Snellius Expedition in the Eastern parts of the Netherlands, East Indies. Brill Leidin 5. KRAUSE, D.C., 1965 - Submarine geology north of New Guinea. Geol Soc. Amer. Bull. 76, 27-42. KRAUSE, D.C., 1967 - Bathymetry and geologic structure of the North western Tasman Sea - Coral Sea - South Solomon Sea area of the south-western Pacific Ocean. New Zealand Oceanographic Inst. Memoir 4, 46. pp. KRUMBEIN, W.C., 1932 - History of mechanical analysis. J Sediment Petrol. 2. 89-124. KRUMBEIN, W.C., 1934 - Size frequency distribution of sediments. J. Sediment. Petrol. 4, 65-77. KRUMBEIN, W.C., 1935 - Thin section mechanical analysis of indurated sediments. J. Geol., 43, 482-496. KRUMBEIN, W.C., 1936a - Application of logarithmic moments to size frequency distribution of sediments. J. Sediment. Petrol. 6, 35-47. -74- KRUMBEIN, W.C., 1936b - The use of quartile measures in describing and comparing sediments. Am. J. Sci. 32, 98-111. KRUMBEIN, W.C., 1938 - Size frequency distributions of sediments and the normal Phi curve. J. Sediment. Petrol 8, 84-90 KRUMBEIN, W C., 1964 - Some remarks on the Phi notation. J. Sediment. Petrol. 34, 195-197. KRUMBEIN, W.C., and PETTIJOHN, F.J., 1938 - Manual of sedimentary petrography Appleton-Century-Crofts. New York, 549 pp. KRUMBEIN, W.C., and GARRELS, R.M., 1952 - Origin and classification of chemical sediments in terms of pH and oxidation reduction potentials J. Geol 60, 1-33. KRUMBEIN, W.C., and SLOSS, L.L., 1951 - Stratigraphy and sedimentation. Freeman, San Francisco, 660 pp. KUENEN, Ph.M., 1950 - Marine geology 568 pp. John Wiley & Sons, New York. MASON, B , 1958 - Principles of geochemistry. 2nd Edition. John Wiley & Sons. Inc. New York. McCAMMON, R.B., 1962a - Efficiency percentile measures for describing the mean size and sorting of sedimentary particles. J. Geol. 70, 453-465. -75- MILNER, B.H., 1962 - Sedimentary Petrography. George Allen & Unwin, London. MILLOT, G., 1949 - Relations entre la constitution et la genese des roches sedimentaires argilluses. Geol. Appliq. Prosp. Min. 2. MILLOT, G., 1952 - Prospecting for useful clays in relations to their conditions of genesis. Sumposium - Problems of clay and laterite Genesis. Amer. Inst. Min. Eng. p. 107. PAGE, H.G., 1955 - Phi millimeter conversion table. J. Sediment. Petrol. 25. 285-292. PETTIJOHN, F.J., 1941 - Persistence of heavy minerals and geologic age. J. Geology. V.49, p.610-625. PETTIJOHN, F.J., 1957 - Sedimentary rocks (2nd Ed.) 718 pp. Harper & Brothers, New York. POLDERVAART, A. (Ed.) 1955 - Crust of the earth. Geol. Soc. Amer. Spec. Paper. 62, 132. POOLE, D.M., 1957 - Size analysis of sand by a sedimentation technique J. Sediment. Petrol. V.27, p.460-468. POWERS, M.C., 1954 - Clay diagenesis in Chesapeake Bay Area. Clays and Clay Minerals Proc. 2nd Nat. Conf. Clays and Clay Minerals, p.68. -76- RANKAMA, K., and Th. G. SAHAMA, 1950 - Geochemistry 912 pp. University of Chicago Press, Chicago. REVELLE, R., 1944 - Scientific results of Cruise VII of the Carnegie during 1928-1929. Carnegie Inst. Work. Pub. 556. ROGERS, J.J.W. DRUEGER, W.C., & KROG, M., 1963 Sizes of naturally abraded materials. J. Sediment Petrol. 33. 628-633. SAHU, B.K., 1964 - Depositional mechanism from the size analysis of clastic sediments. J. Sediment. Petrol. 34. 73-83. SARGEANT, C.E.G., 1969 - Further notes on the application of sonic techniques to submarine geological investigations, with special reference to continuous relfection seismic profiling. 9th C/wlth Mining and Metallurgical Congress Paper 28. SCHLEE, J., 1966 - A modified Woods Hole rapid sediment analyser. J. Sediment. Petrol. V.36, p.403 - 413 SHEPARD, F.P., 1954 Nomenclature based on sand-silt-clay ratio. J. Sediment Petrol. 24, 3, 151 - 158. SHEPARD, F.P., 1963 - Submarine Geology. Second Ed. Harper & Rew, 557 pp. SMITH, J.W., and GREEN, D.H., 1961 - The geology of the Musa Basin Area, Papua. Bur. Miner. Resour. Aust. Rep. 52. -77- SMITH, I.E , and PIETERS, P.E., 1969 - The geology of the Louisiade Archipelago, T.P.N.G. Excluding Misima Island. Bur Miner. Resour. Aust. Rec. 1969/93 SORBY, H.C., 1880 - On the structure and origin of non-calcareous stratified rocks. Anniversary address of President. Quart. J. Geol. Soc. London. 36. 46 - 84. SPENCER, D.W., 1963 - The interpretation of grain-size distribution curves of clastic sediments. J. Sediment Petrol. 33. 180 - 190. STANLEY, E.R., 1923 - The geology of Papua - Australian Government Printer, Melbourne. TANNER, W.F., 1958b - The zig-zag nature of type I and IV curves. J. Sediment. Petrol, 28, 372-375. TANNER, W.F., 1959 - Sample components obtained by the method of differences. J. Sediment. Petrol. 29. 408-411. TANNER, W.F., 1964 - Modification of sediment size distribution. J. Sediment Petrol. 39. 156-164. THOMPSON, J.E., 1962 - Nickel and associated mineralization in the Territory of Papua and New Guinea. Bur. Miner. Resour. Aust. Rec. 1962/157. THOMPSON, J.E., 1967 - A geological history of eastern New Guinea Aust. Petrol Expl. Ass. J. 83-93. -78- THOMPSON, J.E., and FISHER, N.H., 1965 - Mineral deposits of New Guinea and Papua, and their tectonic setting. Proc. 8th C/wlth. Mining and Metallurgic Congress, Australia and New Zealand Paper 129, 115-147. TRASK P.D., 1932 - Origin and environment of source sediments of Petroleum. Houston. Texas. 323 pp. TRASK, P.D., 1961 - Sedimentation in a modern geosyncline off the arid coast of Peru and Northern Chile. Int. Geol. Cong. 21st. Session Norden 23. 103-118. UDDEN, J.A., 1914 - Mechanical composition of clastic-sediment. Bull. Geol. Soc. Amer. 25. 655-744. Van ANDEL, Tj. H., 1960 - Sources and dispersion of holocene sediments, northern Gulf of Mexico in Recent Sediments, Northwest Gulf of Mexico, (ed. F.P. Separa et al.). Spec. Publ. Amer. Assoc. Petrol Geol. 34-35. Van ANDEL, Tj. H., and VEEVERS, J.J., 1967 - Morphology and sediments of the Timor Sea. Bull. Bur. Miner. Resour. Geol. Geophys. 83 173 pp. Van ANDEL, Tj. H., 1959 - Reflections on the interpretations of heavy mineral analysis. J. Sediment Petrol. V. 29. p.153-163. Van ANDEL, Tj. H., and POSTMA, H., 1954 - Recent sediments of the Gulf of Paria. Verh. Kon. Ned. Akad. Wetensch. 20, 5. -79- Von der BORCH, C.C., 1968 - Submarine canyons of southern Australia their distribution and ages. Marine geology 6. No. 4 267-279. Von der BORCH, C.C., 1969 - Marine geology of the Huon Gulf Region, New Guinea. Bur. Miner. Resour. Aust. Rec. 1969/30. 35 pp. WALRAVEN, F., 1968 - Recent marine sedimentation on the Continental Shelf south of Lae, New Guinea. Bur. Miner. Resour. Aust. Rec. 1968/99. WEEKS, L G., 1959 - Geologic architecture of circum - Pacific. Amer. Assoc. Petrol. Geol Bull. 43, 350-380. WENTWORTH, C.K., 1933 - Fundamental limits to the size of clastic grains. Science 77. 633-634. APPENDICES APPENDIX 1 SUMMARY OF SAMPLE STATION DATA, SAMPLE COLOUR, CARBONATE CONTENT, OXIDISABLE MATERIAL CONTENT, AND GRAINSIZE STATISTICS Sample Date Time Latitude Longitude Colour* Depth Carbonate Oxidisable Graphic Indl.Gr. incl. Gr. Kurtosis Sand silt Clay Number S E metres Percent kia t e r i al Mean Standard Skewness Bercent Percent Percent Percent Dev, T------302 19.1.68 0047 Z 10°24.5* 150°25.9* 5 GY 6/1 80 11 3.8 6.06 2.91 0,36 0 .75 31 46 23 • 303 0113 Z • 10°23.0• 150°25.71 5 GY 6/1 250 9 7.2 5.17 2,91 0,72 0 .99 60 24 16 a 304 0134 Z 10°21.5« 150°26 * 5 Y 6/1 225 8 12.4 7.90 2.12 -0.25 0 .88 15 47 38 ■ 305 0165 Z 10°20.2‘ 150°26.3• 5 GY 6/1 130 17 6.00 6.08 2.67 0.18 0 .59 28 50 22 a 306 0245 Z 10°19.5‘ 150°26.5* 10 Y 4/2 180 11 7.4 8.32 2.74 0-0.16 1 .36 6 51 43 a 307 0315 Z 10°21.9* 150°28.21 5 GY 6/1 400 5 7.7 8.13 2.82 -0.13 0,58 1 57 42 a 308 0404 Z 10°23.81 150°30.31 m 450 13 - m m - - m • a 309 - 10°26.7‘ 150°34.6‘ 5 Y 6/1 540 12 11 7.93 2,39 0.07 0 .91 8 59 33 a 310 - 10°29.0 * 150°39.4' 5 Y 4/1 60 54 1.8 3.60 2.35 -00.13 1 .77 57 39 4 a 311 2300 Z 10°31.31 150°52.7 * 5 GY 6/1 340 88 3.1 5.63 2.24 0.51 0 .80 21 69 10 a 312 2330 Z 10°29.6» 150°53.81 5 Y 7/2 520 70 2.5 6,48 2.42 0.06 0 .90 17 67 16 313 20.1.68 0015 Z 10°26.5 * 150°55.6« 5 GY 6/1 420 - m 5.57 1.45 0.44 1 .40 5 91 4 314 0102 Z 10°23.31 150°56.6 5 Y 7/2 310 72 0.3 5.20 2.35 0.56 0 ,68 44 45 11 a 315 0137 Z 10°21.7 * 150°56.81 5 Y 7/2 270 80 2.1 6.47 2.42 0.38 1 .10 13 70 17 a 316 0227 Z 10°27.71 151 °0.4« 5 GY 6/1 430 86 2.0 3.15 1.50 -0.31 1 .50 71 27 2 a 317 0310 Z 10 0 30 * 91 151°3.01 5 GY 6/1 320 84 3.3 4.97 1.46 0.55 1 .60 15 79 6 n 318 0410 Z 10°32.2' 151°3.5* 5 Y 6/1 200 97 - - - - «• a* m - a 319 0455 Z 10°29.8* 151°4.3 * 5 Y 7/2 400 92 2.1 m - - m - - - a 320 0532 Z 10°26.6« 151°4.7 * 5 GY 6/1 320 83 2.1 5.32 2.74 0.50 0 .93 45 41 14 a 321 0605 Z 10°25.3* 151°5.01 5 GY 6/1 100 92 0.8 2.47 1.10 0.29 1 .08 89 10 1 a 322 1100 Z 10°17.9 * 151°1.21 5 Y 6/1 30 84 0.8 3.56 1.42 0.14 0 .84 71 26 3 a 323 2222 Z 10°20.5* 151 °5.01 m 50 - - - - - m - - a 324 2301 Z 10°24.5* 151°5.01 5 GY 6/1 160 88 1.8 3.26 1.17 -0.06 1 .10 92 8.3 2.1 325 2VU68 0150 Z 10°26.5* 151 °52.5* 5 Y 6/1 520 50 m 5.28 2.32 0.12 0 .89 29 62 9 a 326 0404 Z 10°18.5* 151 °47 * 5 GY 6/1 40 98 1.4 - - - - m a 327 0435 Z 10°21.5* 151 °48 • 5 GY 6/1 530 54 5.7 7.10 2.83 0.01 0 .86 16 57 27 a 328 0460 Z 10°23.5' 151 °47 * 5 Y 7/2 540 44 12.7 - - - - m • a 329 0614 Z 10°25.5 * 151°46.5* 5 Y 7/2 530 50 5.7 - m - - - m a 330 m 10°25.5> 151°46.51 5 Y 7/2 530 50 5.7 - - - • - - m a 331 - 10°25 * 151°39.5» 5 Y 6/1 100 32 3.1 5.98 2.45 0.06 0 ,89 28 61 11 a 332 - 10°24.5« 151°361 5 GY 6/1 550 30 7.2 6.80 2.91 0,73 0 .74 1 75 24 333 a 0425 Z 10°25.5» 151°35.5» 5 GY 6/1 550 24 6.9 7.63 2.22 -0.05 0,.76 3 61 36 a 334 2130 Z 10°27.4* 151°45.4* 5 GY 6/1 530 48 8.0 7.67 1.99 0.21 0, 68 - - m * Symbols refer to Rock Color Chart, Geol, Soc, Am., 1959 , Comparison with the chart was made after the samples had been washed and dried. APPENDIX 2 X-RAY DIFFRACTION RESULTS The analyses were carried out using a Philips P.W. 1051 X-Ray Diffractometer, with the operating conditions as follows. kV 40 mA 24 Geiger Tube Cu.K. alpha R.M. 2 & 4 Mult 1. T.C. 4 Chart speed 1° - 20/min. Disc. Ch. 12 Slits \ & 1° div.J0 & 1° rec-filter Ni Chart range 5° - 80° The determinations were made by comparing the unknown patterns with standard A: S.T.M. index patterns and standard mineral patterns. The order of relative intensities of the minerals identified follows. Sample Number 1 2 3 4 5 6 302 Albite Halite Chlorite Quartz Calcite Muscovite 303 Albite Halite Calcite Quartz Muscovite 304 Halite Calcite Albite Quart z 305 Calcite Albite Halite Quartz Argonite(tr) 306 Halite Calcite Albite Quartz 307 Calcite Halite Albite Quart z Chlorite 309 Calcite Halite Albite Quartz Aragonite 310 Albite Aragonite Halite Quartz(tr) 311 Aragonite Calcite Halite Quart zIftr) Albite(tr) 312 Calcite Aragonite Quartz Albite(tr) Halite(tr. 313 Calcite Aragonite Halite Albite Quartz(tr, 314 Calcite Aragonite Halite Quartz Iftr) Albite(tr) 315 Calcite Aragonite Halite Albite! tr) 316 Calcite Aragonite Halite Albite!, tr) 318 Calcite Aragonite Quartz(tr) Halite!^tr) Chlorite(tr) 319 Calcite Aragonite 320 Calcite Aragonite Halite Quartz(tr) 321 Calcite Aragonite Halite 322 Aragonite Calcite Quartz Halite Albite(tr) 324 Calcite Aragonite Halite Albite(tr) 326 Aragonite Calcite Halite 327 Calcite Aragonite Halite Quart z Albite 328 Calcite Halite Albite Quartz Aragonite 329 Calcite Halite Aragonite Quartz Albite 331 Calcite Albite Quartz Aragonite Muscovite(tr) Chlorite(tr) 332 Halite Calcite Albite Quartz Aragonite Chlorite (tr) 333 Calcite Halite Quartz Aragonite Albite APPENDIX 3 CLAY CONTENT OP SAMPLES 302 Chlorite - degraded chlorite or smectite 303 Smectite 304 Chlorite - smectite 305 Chlorite - smectite 306 Chlorite - smectite - more chlorite than 304» 307 Mixed layer- chlorite-smectite, rich in chlorite. 309 Chlorite - smectite, mainly chlorite. 310 Chlorite - smectite. 311 Very little clay - minor amount of chlorite-smectite 312 Little diffraction i 313 Chlorite smectite 315 Chlorite - smectite 320 Chlorite - smectite 324 Chlorite - smectite; very lov? intensity 325 Chlorite - smectite 327 Chlorite - smectite 331 Similar to 307 - mixed layer - chlorite smectite, rich in chlorite. 332 Degraded chlorite or smectite; probably a little illite, also trace of kaolinite. APPENDIX^ DIRECT READING OPTICAL EMISSION SPECTROGRAPH RESULTS ' Sample 1° ppm ppm ppm 1o ppm ppm ppm P'pm 1° PPm ppm ppm 1o Number Mn Ni So Sr Ti V Y Zr Ba Ga Co Cr Cu Re % 302 0.08 235 36 300 0.56 130 43 140 225 4.5 45 320 88 6.8 2.3 303 0.11 140 40 180 O.58 150 48 180 120 4.0 50 200 110 8.2 2.1 304 0.10 200 54 290 0.60 170 100 220 110 5.8 100 230 115 9.7 2.0 305 0.10 100 44 320 0.55 180 250 160 60 7.6 55 •155 95 7.0 2.5 306 0.12 90 40 190 O.54 220 31 200 . 4.1 40 170 100 8.2 2.2 307 0.12 145 56 280 0.60 215 44 280 120 5.6 80 190 95 7.3 2.1 309 0.33 120 37 400 0.44 160 60 260 100 6.8 50 130 80 5.9 2.0 310 0.05 33 37 1150 O.42 96 50 130 160 >10 28 170 24 3.3 2.5 311 0.03 19 17 1300 0.14 46 31 -.100 <40 >10 15 56 14 1.1 2.2 312 0.07 33 16 1100 0.18 52 22 -100 <40 >10 12 62 21 1.6 1.9 313 0.07 33 19 1250 0.19 54 30 -100 80 >10 17 77 60 2.1 2.1 314 0.05 34 20 1300 0.19 52 33 -100 100 >10 13 &4 26 1.7 1.9 315 0.05 31 18 1200 0.17 52 31 -100 52 >10 16 6 2 16 1.5 1.7 316 0.05 30 17 1200 0.13 48 37 -100 150 >10 18 60 21 1.4 1.3 318 0.05 23 20 1650 0.07 42 48 -100 <40 >10 20 50 34 1.0 2.0 319 0.04 29 20 1500 0.12 46 43 -100 140 >10 25 54 30 1.0 2.1 320 0.03 34 21 1400 0.13 51 34 -100 110 310 27 50 16 0.8 1.9 321 0.05 26 18 1220 0.08 39 34 -100 <40 >10 19 55 15 1.7 1.7 322 0.03 25 21 1500 0.13 54 35 -100 <40 >10 13 100 12 1.0 2.3 324 0.05 27 20 1200 0.08 42 43 -100 100 >10 25 60 14 2.4 2.2 326 0.02 10 15 1500 0.05 29 25 -100 < 40 >10 11 35 8 0.3 2.3 327 0.27 70 23 900 0.37 120 25 100 120 >10 32 130 50 4.3 2.2 328 0.25 110 39 64O 0.43 160 84 210 180 9.0 58 165 90 7.1 2.2 329 0.12 56 23 800 0.32 85 28 100 120 >10 25 97 37 3.7 2.1 331 0.14 64 16 600 0.30 78 33 280 210 >10 16 86 40 3.5 1.9 332 0.20 100 35 540 O.46 160 40 130 110 9.0 43 150 75 5.3 1.9 333 0.22 120 41 520 0.43 160 120 220 240 9.0 57 170 73 3.0 1.8 Analyst: S.E, Smith, 'Bureau of Mineral Resources