Palaeogeography of the Rove-Bourewa Area, Southwest Viti Levu Island, Fiji Islands

PALAEOGEOGRAPHY OF THE ROVE-BOUREWA AREA, SOUTHWEST VITI LEVU ISLAND, FIJI ISLANDS

Kirti Kamna Lal

A thesis submitted in partial fulfilment of the requirements for the degree of Master of Science

School of Islands and Oceans Faculty of Science, Technology and Environment The University of the South Pacific

2010

First and foremost, I would like to express the deepest appreciation and gratitude to my principal supervisor, Professor Patrick D. Nunn (Pro-Vice Chancellor, the University of the South Pacific) for his faith in me and trusting me with this project. His consistent guidance and criticism helped me get through with the masters project and accomplish my goals. Many thanks to my co-supervisor Dr Suzanne Pohler (Lecturer in Marine Geology, Division of Marine Studies, School of Islands and Oceans, Faculty of Science, Technology and Environment, The University of the South Pacific) who assisted me in every way possible for this masters project. Their help and interest for this study is much appreciated. My thanks are further extended to Mr Johnson Seeto (Curator, Division of Marine Studies, School of Islands and Oceans, Faculty of Science, Technology and Environment, The University of the South Pacific) for providing help with shell identification and classification, and Dr Mark Stephens (Senior Lecturer, Division of Geography, School of Islands and Oceans, Faculty of Science, Technology and Environment, The University of the South Pacific) for his help and guidance during sample collection and laboratory analysis.

I would love to express my heartfelt gratitude to the people of Vusama for their kindness, love, and hospitality during the fieldwork at Bourewa (18th of January to 1st February 2009). Many thanks to Vusama villagers particularly to Mr Tikiko Tavagone (Dido, the Village Headman), Mr Ameniasi Cumu, Mr Vesito Rabua, and Mr Tomasi Vuniyayawa for their assistance in sample collection.

I am also thankful to Dr Fiona Petchey (Deputy Director) and her team at the Waikato Radiocarbon Dating Laboratory, University of Waikato, New Zealand for their help and assistance with sample radiocarbon dating.

Thanks are in order for the laboratory staff and technician at the Marine Science Laboratory (Lower Campus, The University of the South Pacific), Mr Jone Lima, and Mr Shiv Sharma for their assistance for the period of laboratory analysis. Sincere

ii thanks to the research assistants; Shalini Sanjana, William Young, Kacalini Rainima, and Sherika Singh for their help with sample analysis.

I would like to express my sincere gratitude to my friends and colleagues Mr Ravinesh Ram, Ms Prerna Chand, and Ms Rupantri Raju for their consistent criticism, help, and support throughout the course and compilation of the Masters project.

Special thanks is given to my family for their dependable encouragement and assistance. This journey would not have been possible without the succour and sacrifices that were made by them on my behalf. During this process I have gained a deeper appreciation of the gift of love, the joy of discovery, and the thirst of knowledge that my parents instilled in me. Thank you Ma and Papa, my sisters; Arti Gounder and Arti Sharma, my brothers-in-law; Arvind Gounder and Amitesh Sharma, and finally my delightful niece, Arishta Gounder whose presence was invigorating during bleak moments.

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Physical, chemical, and radiocarbon analyses of a 6-m sediment core from the Bourewa palaeolagoon, located adjacent to the Bourewa archaeological site, provide Holocene palaeosea-level data for southwest Viti Levu Island (Fiji Islands, southwest Pacific). The core dates as far back as 11,470 cal BP, marking the end of the Last Glacial Maximum and the beginning of the Holocene Interglacial. Sediment colour determination from Munsell Colour Charts, texture from particle-size analysis, and percent organic and carbonate content using the loss-on-ignition method was used to reconstruct sedimentary environments subsequent to the Last Glacial Maximum. Marine shells preserved in the sediment core show subsequent environmental conditions for the Rove-Bourewa area.

Five distinct environmental conditions associated with the Holocene succession are noted, initial terrestrial environment to a mudflat zone to a brackish lagoon system back to the mudflat zone and finally to the present dry land. The mudflat zones were the transition period from terrestrial to marine and then from marine to terrestrial environment. These conditions were associated with the rising sea level of the Holocene Interglacial. The palaeoenvironmental transformation from organic-rich terrestrial sedimentation to carbonate-rich marine sediments in the Rove-Bourewa palaeolagoon occurred around 6000 cal BP with the transformation to the brackish lagoon system.

The highest sea-level proxy data in the sediments recorded 4000 years ago when the climate conditions were optimum with the maximum diversity of marine organisms. Sea level was about 2 m above the present level during the Holocene Climate Optimum that lasted for about 300 years. Sea level gradually started to decline around 3400 cal BP, the end of the Holocene Climate Optimum as the brackish lagoon was exposed and it was slowly transformed into the present dry flat land. It was during the early stages of late-mid-Holocene sea-level fall when the southwest Pacific Islands were colonised by people, 3210 cal years BP.

Keywords: Bourewa, Holocene, Holocene Climate Optimum, Lapita, Palaeoclimatology, Palaeolagoon, Rove Peninsula, Sea level, Marine Shells.

DEDICATION ...... i ACKNOWLEDGEMENTS ...... ii ABSTRACT ...... iv TABLE OF CONTENTS ...... vi LIST OF FIGURES AND TABLES ...... ix LIST OF APPENDICES ...... xii

CHAPTER 1: INTRODUCTION ...... 1

CHAPTER 2: LITERATURE REVIEW ...... 4 2.1. CLIMATE AND SEA-LEVEL CHANGE: A GLOBAL PERSPECTIVE ..... 4 2.1.1. Analysis of Past Climates and Environments ...... 8 2.1.2. Holocene Climate Change – Past 12,000 years ...... 11 2.1.3. Climate and Sea-Level Change for Oceania ...... 14 2.2. RECONSTRUCTING PAST ENVIRONMENTAL CHANGES FROM SEDIMENTS: GLOBAL AND REGIONAL ...... 16 2.2.1. Sediments ...... 16 2.2.2. Sediment Analysis ...... 18 I. Colour ...... 18 II. Particle-size distribution and sediment texture ...... 18 III. Shell Taxonomy ...... 20 IV. Loss-On-Ignition ...... 20 V. Sediment stratigraphy...... 21 2.2.3. Radiocarbon Dating ...... 22

CHAPTER 3: STUDY AREA ...... 23 3.1. GEOGRAPHY OF THE FIJI ISLANDS ...... 23 3.2. MODERN ENVIRONMENTAL SETTING OF ROVE PENINSULA ...... 26 3.3. BOUREWA ARCHAEOLOGICAL SITE ...... 28 3.4. GEOGRAPHY OF THE BOUREWA PALAEOLAGOON ...... 31

CHAPTER 4: RESEARCH METHODS ...... 32 4.1. SELECTION OF STUDY SITE ...... 32 4.2. FIELD METHODS ...... 35 4.2.1. Corer ...... 35 4.2.2. Coring Technique ...... 38 4.2.3. Problems Encountered with Coring ...... 39 4.3. LABORATORY METHODS ...... 40 4.3.1. Physical Composition and Analysis ...... 41 I. Colour ...... 41 II. Sediment Texture Analysis ...... 43 III. Shell Taxonomy ...... 48 IV. Problems Encountered with Physical Sediment Analysis ...... 49 4.3.2. Chemical Composition and Analysis ...... 50 I. Loss-On-Ignition ...... 50 A. Organic Content ...... 51 B. Carbonate Content ...... 51 II. Radiocarbon Dating ...... 52 A. Sampling for Radiocarbon Dating ...... 53 B. Sample Pre-Treatment for AMS Dating at the Waikato Radiocarbon Dating Laboratory ...... 54 C. AMS Dating ...... 55 D. Radiocarbon Calibration ...... 56

CHAPTER 5: RESULTS AND INTERPRETATION ...... 59 5.1. PHYSICAL COMPOSITION ...... 59 5.1.1. Sediment Colour and Texture ...... 59 5.1.2. Particles >2 mm ...... 62 I. Material distribution in sediments >2 mm ...... 62 II. Shell Taxonomy ...... 64 5.2. CHEMICAL COMPOSITION ...... 72 5.2.1. Organic and Carbonate Content of the Sediment Core ...... 72 5.2.2. Radiocarbon Dating ...... 74 5.3. PALAEOLAGOON DEPOSITION PHASES ...... 76

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CHAPTER 6: DISCUSSION ...... 80 6.1. GEOCHRONOLOGICAL FRAMEWORK AND SEA LEVEL OVER THE PAST 10,000 YEARS FOR SOUTHWEST VITI LEVU ISLAND ...... 80 I. Phase 1 ...... 81 II. Phase 2 ...... 83 III. Phase 3 ...... 84 IV. Phase 4 ...... 85 6.2. HOLOCENE PALAEOGEOGRAPHICAL CHANGES IN THE ROVE- BOUREWA AREA ...... 86

CHAPTER 7: CONCLUSION AND DIRECTIONS FOR FURTHER RESEARCH ...... 88 7.1. CONCLUSION ...... 88 7.2. IMPLICATIONS FOR FURTHER RESEARCH ...... 90

REFERENCES ...... 92

APPENDICES ...... 101 APPENDIX 1 – SEDIMENT COLOUR AND TEXTURE ...... 101 APPENDIX 2 – SHELL TAXONOMY ...... 114 APPENDIX 3 – SHELL PICTURES ...... 125 APPENDIX 4 – LOSS-ON-IGNITION ...... 127 APPENDIX 5 – RADIOCARBON DATES ...... 132

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Figure 2.1. The three parameters of the Milankovitch Theory ...... 6 Figure 2.2. Average global temperature over the past 150,000 years ...... 7

Figure 2.3. Variations in CO2, temperature and dust from the Vostok ice core over the last 450 thousand years ...... 10 Figure 2.4. Climate change over the last millennium shown by air-temperature ... 13 Figure 2.5. Temperature and sea-level change in the Pacific Basin during the A.D. 1300 Event...... 15 Figure 2.6. The Udden-Wentworth grain size classification ...... 19

Figure 3.1. Map of the Pacific Islands showing the location of the Fiji Island Group...... 24 Figure 3.2. Map of the main Fiji Islands. Insert of Rove Peninsula with the major Lapita site ...... 24 Figure 3.3. The Pacific lithospheric plates ...... 25 Figure 3.4. Lapita pottery discovered during the excavations at the Bourewa Beach (2009) ...... 27 Figure 3.5. Stretch of the fringing reef from the modern Bourewa Beach high tide mark to the edge of the fringing reef ...... 28 Figure 3.6. Changes in the geography of the Rove Peninsula and the adjoining area ...... 29 Figure 3.7. Modern setting of the Rove Peninsula with the locations of the major features, excavation and study sites ...... 29 Figure 3.8. Sand ridges of the Bbourewa Beach ...... 30

Figure 4.1. Aerial photograph of the map of Rove Peninsula ...... 33 Figure 4.2. The Togolilo sinkhole ...... 34 Figure 4.3. Hand auger set ...... 36 Figure 4.4. 6 m corer held from the surface by the team that assisted in coring and sample collection ...... 37 Figure 4.5. Markings at every 10 cm on one of the extension rods sticking out of the ground ...... 38 ix

Figure 4.6. Using the corer in the field ...... 39 Figure 4.7. The Munsell Colour System ...... 42 Figure 4.8. Guide to texture by feel ...... 44 Figure 4.9. USA Test Sieves ...... 46 Figure 4.10. The soil texture triangle ...... 47 Figure 4.11. The equations used to calculate the percentage of organic and carbonate content for each sediment ...... 52 Figure 4.12. The sections of the 6 metre sediment core indicating the depths from which samples were selected for radiocarbon dating...... 53 Figure 4.13. The calibration graph of Sample No. 21 (depth of 210 cm) ...... 57

Figure 5.1. Core colour and texture profile ...... 60 Figure 5.2. Bar graph representing the average particle-size distribution for every 50 cm section of the core ...... 62 Figure 5.3. Bar graph showing the percent of average materials >2 mm in diameter for every 50 cm section of the core ...... 63 Figure 5.4. The number of shells and foraminifera found in every sediment sample ...... 65 Figure 5.5. Species cluster for the sediment core illustrating the relationship between the different shell species identified ...... 67 Figure 5.6. Average percentage of the two most abundant species throughout the sediment core in relation to the other species for every 50 cm sample 68 Table 5.1. Species habitat in order of abundance across the table throughout the core profile ...... 69 Table 5.2. All radiocarbon dates for the palaeolagoon sediment core ...... 74 Figure 5.7. Sample cluster illustrating the relationship between each 10 cm sediment sample ...... 71 Figure 5.8. Graph of organic content and carbonate content with depth ...... 73 Figure 5.9. The age of sediments for every 10 cm sediment sample in cal BP determined from the four ages obtained ...... 75 Figure 5.10. Results of coring ...... 77 Figure 5.11. Each row shows the percent sand and mud particles, and percent organic and carbonate content in each layer together with the rate of sedimentation ...... 78

Figure 6.1. Sediment stratigraphy of the 6 m sediment core...... 82

Figure 7.1. Maps showing the palaeogeography of the Rove-Bourewa area ...... 90

Appendix 1.1. Field and laboratory Munsell Colour readings for each sediment sample ...... 101 Appendix 1.2. Sediment texture by feel readings carried out in the field and in the laboratory ...... 104 Appendix 1.3. The particle-size distribution (percentage) of each material obtained after wet sieving of every 10 cm sample ...... 106 Appendix 1.4. Final sediment texture reading determined from the texture by feel method and particle-size distribution method ...... 109 Appendix 1.5. Colour versus texture for each sediment sample ...... 112

Appendix 2.1. The percentage of different materials present in the particle fraction >2 mm for every 10 cm sediment sample ...... 114 Appendix 2.2. Shell species identified in each sediment sample throughout the core profile is listed according to their habitat together with the number of foraminifera identified in each sediment sample...... 116 Appendix 2.3. Different species of shells identified and their niche ...... 122

Appendix 3.1. Pictures of shell species identified ...... 125

Appendix 4.1. Loss-on-ignition results table ...... 127 Appendix 4.2. Percentage organic matter versus carbonate content for every 10 cm sediment sample ...... 131

Appendix 5.1. Radiocarbon date determination graphs ...... 132 Appendix 5.2. Radiocarbon date for every 10cm sediment sample ...... 133

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The past holds the key to the future. This statement is very important for comprehending past and current climate change where the past provides analogues of what future climatic trends might be. Understanding and anticipating future climate and weather patterns is of extreme importance for human livelihood and survival strategies. Generally, palaeoclimatic reconstruction uses traditional and modern techniques (Chapter 2) to infer past conditions in relation to present day environments. Detection of palaeoenvironmental changes since the Last Glacial has proven useful for the interpretation of spatial relationships between the environment and climate pattern for the current Holocene Interglacial that is the major focus for this study (Ramirez-Herrera et al. 2007; Moriwaki et al. 2006; Monroe and Wicander 2005; Dickinson 2003, 2001; Kirch 2000; Pirazzoli 1991).

One of the best ways to study past climate variation and trends is from sediment analysis. Sediment analysis is able to provide information on Earth’s changing climate dating back tens of thousands of years. Many such studies have focused on sediment samples from lakes, ocean basins, marine/coastal margins, lagoons, and deltas and estuarine systems to identify long-term patterns of environmental as well as cultural development (Al-Zamel et al. 2007; Ramirez-Herrera et al. 2007; Vött et al. 2007; Drago et al. 2006; Moriwaki et al. 2006). This is for the reason that coastal and lagoonal areas are able to preserve a good record of sedimentological sea-level markers as they are sensitive to even a slight climate shift (Yum et al. 2003). For instance, the occurrence of blue grey (light coloured) sediments with a high carbonate content suggest an apparent coastal submergence and relative sea-level rise along the Mexican Pacific coast (Ramirez-Herrera et al. 2007).

The sedimentary process is principally controlled by the intensity of weathering, the nature and capacity of transporting media, and the kind of depositional environment.

Sedimentation starts with the alteration through chemical decay and/or mechanical fragmentation of parent materials. Deposition usually occurs when the transporting medium can no longer continue to entrain the material as a result of reduction in velocity or a change in the physical conditions of the medium (Hassan 1978). However, not all sediments have similar life histories. For example, ejecta from volcanic eruptions are transported by wind and settle either on land, ocean, or lakes to form pyroclastic sediments. A stratigraphic study of such sediment layers will show the fragmented volcanic particles in the sediment profile marking the period of volcanic activity in/around the area. Also plant remains may accumulate in marshland to form peat, and corals and marine organisms may develop into rock masses at the place of origin (Hassan 1978).

Similarly, a stratigraphic core study is able to provide data on climate and environmental change over time, hence the principal objectives of this Masters research are:

1. To study the chronological pattern of sediment deposition in the Bourewa palaeolagoon by analysing sediment colour and texture, organic and carbonate content, and radiocarbon dates from a 6 m sediment core. 2. To identify the palaeolagoon ecosystem from marine mollusc fossil record preserved in the sediment core profile. 3. To determine sea-level fluctuations and reconstruct past climate variability for southwest Viti Levu Island in Fiji (southwest Pacific).

Sedimentological data, combining stratigraphical, physical and macrofossil evidence, allow reconstruction of Holocene sea-level change for a former tidal inlet (palaeolagoon) located on the southwest of Viti Levu Island. An understanding of the Holocene history of the tidal inlet is of extreme importance as it is situated adjacent to the Bourewa archaeological site, the earliest-known human settlement for the Fiji Islands. Considerable research in and around the Rove Peninsula by Nunn over the past six years (2004-2009) allows it to be stated that Bourewa is the earliest human settlement site for the Fiji Islands.

The Holocene sea-level reconstruction along the coastal margins is able to indicate the gradual rise and fall of temperature marking the period of Deglaciation and the Early Holocene (Nunn and Peltier 2001; Pirazzoli 1991). The principal purpose of this study is to further add to the palaeosea-level data available through palaeogeographic reconstruction from a 6 m sediment core.

The thesis chapters are categorised as; Chapter 2 begins with background information on the topic, and palaeoclimatology and climate change studies, globally and in the Pacific. Chapter 2 also explains and evaluates the different methods of sediment analyses for the reconstruction of past climate change. Chapter 3 discusses the location of the study area and the choice of study site explained in terms of the geography and location of the palaeolagoon. Chapter 4 describes the methods used for sediment analysis. Chapter 5 focuses on discussing the key elements of the results and interpretation. Chapter 6 discusses sediment core stratigraphy that provides the geochronological framework and relative sea level of the Holocene period for the Rove-Bourewa area, and the Holocene palaeogeographical changes around the palaeolagoon. Chapter 7 is the conclusion and directions for further research.

Sediment analyses have provided information on Earth’s changing climate dating back thousands of years that have enabled the identification of long-term patterns of environmental and cultural development. In order to understand the nature of global environmental change, it is important to understand climate change and its significance.

This chapter briefly reviews the nature of global environmental change and summarizes the results of previously published work into sections as follows:

1. Background information on climate and sea-level change from a global perspective, the methods of analysis of past environmental and cultural development, climate change over the past 10,000 years, and the palaeoclimatology of the Pacific Islands and Ocean. 2. Reconstruction of past environmental changes from sediment analyses that are sediment colour and texture, organic and carbonate content, and sediment stratigraphy. 3. Reconstruction of past climate from marine and/or terrestrial gastropods and bivalves. 4. The importance of dating materials to know the approximate time of sediment deposition.

2.1. CLIMATE AND SEA-LEVEL CHANGE: A GLOBAL PERSPECTIVE

Earth’s climate is always changing. This change is caused by the periodic changes in wind, temperature, cloudiness, moisture, and atmospheric pressure collectively known as weather. These fluctuating global weather patterns, the hydrological

4 cycles, and the coverage of glaciers and ice sheets, and associated long-term sea- level change are thought to be best explained using the Milankovitch Theory. This theory states that the long term climate changes resulting in the glacial-interglacial intervals are due to fluctuations in the Earth’s orbit around the Sun. Three elements of the Earth-Sun geometry combine to produce variations in the amount of solar energy that reaches the Earth. These are known as the orbital eccentricity, Earth’s axial tilt, and precession.

Orbital eccentricity is a term used to describe the shape of Earth's orbit around the sun, the measure of the ellipse from circularity (Figure 2.1A and B). Eccentricity can mainly result from gravitational attractions among the planets. Currently, the Earth's orbit is nearly circular with the difference between closest approach to the Sun (perihelion) and furthest distance (aphelion) is only 3.4% (5.1 million kilometres). Figure 2.1A shows the perfect circle of the Earth’s movement around the Sun. Calculations indicate the shape of the Earth’s orbit changes from being elliptical (high eccentricity) to being nearly circular (low eccentricity) in a cycle that takes between 90,000 and 100,000 years. Figure 2.1B shows an eccentricity of 0.5 that is highly elliptical (Davis 2002; Thomas 2002). The amount of insolation received at perihelion is 20% to 30% greater than at aphelion, resulting in a climate that is similar to that of today, the interglacial periods.

Axial tilt or obliquity (Figure 2.1C) is the angle between Earth’s axis and a line perpendicular to the plane of its orbit around the Sun. This angle shifts about 1.5° (between 22.1° and 24.5°) from its current (average) value of 23.5° during a 41,000 year cycle. As the tilt changes, the seasons become more exaggerated. More tilt means more severe seasons, warmer summer and colder winters for the northern hemisphere and vice versa for the southern hemisphere (Kaufman 2002).

Sun

A C

Path of circular orbit of Earth around Variation in axial obliquity. the sun. No eccentricity.

perihelion Sun aphelion

Earth B D

Orbital eccentricity at 0.5. Precessional movement.

Figure 2.1. The three parameters of the Milankovitch Theory. (A) shows the circular orbital eccentricity of Earth’s rotation around the sun; (B) the orbital eccentricity has a value 0.5; (C) variation in the axial tilt of the planet with respect to the line perpendicular to the plane; (D) The rotation of the planet with reference to the axis. Adapted from online images at www.earthobservatory.nasa.gov/Library/Giants/Milankovitch/milankovitch

The final parameter is the precession of the equinoxes (Figure 2.1D), which causes the position of the equinoxes and solstices to shift slowly around Earth’s elliptical orbit in about a 19,000 to 23,000 year-cycle. Continuous changes in these three parameters cause the amount of solar heat received at any latitude to vary slightly over time thus explaining the overall heating and cooling of the planet (Monroe and Wicander 2005). The rise and fall of average global temperature over the past 150,000 years is illustrated in Figure 2.2.

Figure 2.2. Average global temperature over the past 150,000 years. Adapted from online image at www.ucar.edu/learn/1_4_1.htm.

The climatic cycling from warm to cold and back to warm periods since the Eocene epoch, about 50 million years ago was reconstructed from cave sediments showed that in high northern and southern latitudes and at high altitudes these cycles were accompanied by advances and retreats of glaciers. Sea level rose and fell as significant volumes of water were sequestered in continental ice sheets and later released as the ice melted. The climatic oscillations occur in regular cycles of about 41,000 years at the beginning of the period of oscillations and switching to a 100,000 year cycle about 800,000 years ago similar to the patterns presented by the Milankovitch Theory. The cycles are known in considerable detail because of data extracted from the long ice cores drilled in Greenland and Antarctica (McDermott 2004; Zhang et al. 2004). Much of the data on climatic events at the close of the last glaciation come from studies at northern latitudes.

As a general trend, rising global temperatures melt the ice caps, ice fields and mountain glaciers which causes sea level to rise. So too does the thermal expansion of ocean water, the net result begins a rise in global (eustatic) sea level. The last major shift in the global temperatures and sea level was at the end of the Last Glacial and the beginning of the Holocene Interglacial about 12,000 BP.

The following sections explain and review the methods used to reconstruct past climate variations that are vital for understanding the causes and effects of past climate change and assist in the prediction of future climate variation.

2.1.1. Analysis of Past Climates and Environments

Palaeoclimatology is the study of past climate change that helps portray and explain the long-term changes in the Earth’s average temperature, precipitation, and wind patterns. These changes may be recorded in plant pollen, glacial ice records, tree rings, and sea-level change. These can be determined respectively through the study of palynology, ice cores, dendrochronology, and marine sediments and/or tidal gauges.

Palynology allows the understanding of how vegetation changes over long timescales due to the distinctive shapes and surface textures of particular types of plant pollen. Pollen grains are resistant to decay and remain well preserved in sediment layers that are highly useful for interpreting past patterns of vegetation changes (Behling and Costa 2001; Roberts 1998). High pollen percentages correspond to warm conditions and lower pollen percentages are indicative of cooler climates. The basic assumption is that the amount of pollen of different species (type of vegetation) in a sample is related to the abundance of that species at the time of sediment deposition (Jones and Rowe 1999). For example, the occurrence of pine and spruce in lake sediments (over the past 7000 years) in the mid-Arctic region, Canada, is indicative of cooler temperatures that occurred around 4200, 3800-3400, and 2500 cal yr BP. While deciduous trees like oak plants species mark a period of warmer conditions around 5800-4500 and 3100 cal yr BP and the recent warming between 900 and 750 cal yr BP. It is concluded that temperatures for the region were cooler prior to 5700 cal yr BP, warmed during the mid-Holocene and cooled after 3800 cal year BP (Zabenskie and Gajewski 2007).

Pollen analysis also helps in understanding the links between climate and the environment through the food chain. Every biome is home to a special group of plants and animals that are interdependent. The climate determines a particular type

8 of vegetation in a region that usually ranges from each season. The type of plants would determine the type of soil (micro) organisms that are present and the plant eating animals (herbivores) living there (Jones and Rowe 1999).

Air bubbles trapped within fallen snow or ice contain different types of hydrogen and oxygen isotopes. These isotopes may date as far back as several hundred thousand years and represent the nature of the atmospheric environment when they were confined. The most successful site for reconstructing previous climate conditions from ice cores for the southern hemisphere is at Vostok (Bridgeman and Oliver 2006). Vostok is a Russian research station that was established in 1957, located 3490 m above sea level in East Antarctica. Ice-core data from Vostok (Figure 2.3) shows varying temperature, carbon dioxide (CO2) levels, and the concentration of dust particles in the atmosphere over the past 450 ka (thousand years ago). The variations of data in Figure 2.3 include the extreme increases and decreases in temperature preceding and following the interglacial phases (the five high temperature phases marked). The ratios of hydrogen and oxygen isotopes in the ice provide an index of former temperatures (blue), while the dust content (red) indicates wind strength and aridity. Carbon dioxide (green), on the other hand, provides a record of the changing concentrations of greenhouse gases in the atmosphere (Roberts 1998).

The study of dendrochronology helps retrieve climate information for the most recent centuries and occasionally as far back as a few millennia from tree rings. Outside the tropics, every year trees lay down one tree ring that becomes the wood and remains unchanged during the life of the tree. The age of a tree can be calculated by studying cut sections of tree trunks and counting the number of rings present. The rings also help determine how fast the tree grew and under what climatic conditions. Petrified tree rings (wood) provide climate information like rainfall and temperature during the epoch of its growth. For instance, wide and thick rings indicate a fertile, well- watered growing period for the plant whilst thin, narrow rings indicate a time of lower rainfall and often poor growing conditions (Roberts 1998). The technique of tree-ring dating is also used for the calibration of radiocarbon dates that will be later discussed in Chapter 4.

Figure 2.3. Variations in CO2, temperature and dust from the Vostok ice core over the last 450 thousand years. Adapted from online image at www.johanna.wandel.ca/babbles/archives/vostok.png.

Sea level changes determined from marine and/or coastal sediments (discussed in greater detail in Section 2.2) has proven to be one of the finest methods for reconstructing past climate and environmental change. The other principle sources of proxy data for palaeoclimatic reconstructions include terrestrial sediments such as lake sediments, bog sediments, sand dunes, and cave sediments. For instance, during times of wetter climates, lakes may develop and expand over large areas and during times of drier climates, lake levels drop and the aerial expanses recede that is suited for palaeoclimatic studies in arid or semi-arid areas. Cave sediments have a potential for providing detailed palaeoclimate archives with values comparable to ice cores and deep sea sediment cores. Cave sediments can be separated into two broad categories, clastic sediments and chemical sediments. Of these, stream-transported (moved mechanically) clastic sediments and calcite speleothems (formed in place, precipitated from solution in seeping, dripping, or flowing water) are both the most common and also the most useful for the time scale from the late Pleistocene to the present (Sasowsky and Mylroie 2007; White 2007; McDermott 2004.). The choice of proxy record (as with the choice of instrumental record) very much depends on what physical mechanism is to be reviewed.

One of the objectives of this study is the determination of sea-level fluctuations. Several studies show that sea-level fluctuations can be detected by means of sedimentological sea-level markers like sediment colour, texture, loss-on-ignition, shell classification, and radiocarbon dates of sediment organic content (Al-Zamel et al. 2007; Ramirez-Herrera et al. 2007; Moriwaki 2006; Gale and Hoare 1991). Since these methods of sediment analysis are also adapted for the purpose of this study, they are discussed in greater detail in Section 2.2.

2.1.2. Holocene Climate Change – Past 12,000 years

The Holocene Interglacial started at the end of the Last Glacial Period (Ice Age) 12,000 years ago. The Holocene Interglacial was a time of overall warming and sea- level rise globally as illustrated in Figure 2.4 in relation to the Last Glacial. Globally, three distinct periods of sea-level change are recognised during the Holocene. The early Holocene (12,000 – 6000 BP) was largely a time of sea-level rise, the middle Holocene (6000 – 3000 BP) was a time of comparative stability of sea level, and the late Holocene (3000 BP to present) marked a time of sea-level fall (Nunn 1999, 2007a).

The most significant interaction between humans and environments occurred within the past 3000 years, the late Holocene period mainly for the Pacific Islands and Oceans. This created conditions for the domestication of plants and animals by humans in a climate that was warm, moist, and mostly predictable compared to the Last Glacial (Nunn 2007a; Bridgeman and Oliver 2006; Smith and Reynolds 2005; Roberts 1998). Humans continued to increase their range of agriculture and complexity of civilization, benefiting from thousands of years of experience to satisfy their increasing needs.

During the last 2000 years, global climate has been relatively stable although two climate departures of relative importance occurred, the Little Climate Optimum (LCO), and the Little Ice Age (LIA). The LCO occurred about 900 to 750 BP (A.D. 1050 to A.D. 1200) with relatively warm temperatures, particularly in the Northern Hemisphere (Zabenskie and Gajewski 2007; Bertrand et al. 2005). The Little Ice Age

(LIA) followed with a slight decline in global temperatures and sea level. The records from cave sediments revealed the transition from the LCO also known as the Medieval Warm Period to the Little Ice Age at AD 1320 (Fleitmann et al. 2004). Speleothem records from South Africa indicate that the Little Ice Age, which extended from roughly AD 1300 to 1800, was about 1°C cooler than present while the Medieval Warm Period may have been 3°C warmer (Tyson et al. 2000). According to National Astronomical Space Administration (NASA) research, reduced solar activity from the A.D. 1400s to the A.D. 1700s was likely a key factor in the LIA, where average temperatures were possibly up to 2°C colder than today (Dole 2008). The period of the LCO and LIA for the Northern Hemisphere (mainly North America and Europe) was analogous to findings from the Pacific Basin and most parts of the Southern Hemisphere. In this region, the LCO was observed between 1200 to 700 BP (A.D. 750 to A.D. 1250) and the LIA occurred from 600 to 150 BP (A.D. 1350 to A.D. 1800) (Figure 2.4) (Nunn 2007a).

It is important to mention at this stage that the human-enhanced greenhouse effect through the combustion of fossil fuels may have played a significant role for the recent warming following the LIA. Much of this rise can probably be attributed to the global warming that occurred during the last century, coinciding with substantially increasing emissions of greenhouse gases (GHG), mainly carbon dioxide (CO2) in the atmosphere. Evidently a rise in temperatures leads to a rise in sea level.

The International Panel on Climate Change synthesis report (IPCC 2007) states that the recent rise in global temperatures followed and was a consequence of the Industrial Revolution. The IPCC was established by the United Nations in 1988 to look specifically at the nature and effects of future climate and sea-level changes. In the early 1900s, the average temperature of the planet was at 14°C. Then from the mid-1900s temperatures increased by 2.5°C, and from 1970 to 2005, it rose by 4°C. The IPCC report also projects a sea-level rise of between 9 cm to 88 cm by 2100, the main contributions coming from thermal expansion of sea water and the melting of polar ice and mountain glaciers.

Early Holocene Middle Holocene Late Holocene

Little Climate Optimum

Holocene Interglacial

Figure 2.4. Climate change over the last millennium shown by air-temperature. The Holocene Interglacial since the end of Last Glacial 12,000 years ago with the most recent climate shifts, the Little Climate Optimum (or Medieval Warm Period), and the Little Ice Age. The three stages of the Holocene Optimum are divided as Early Holocene, Middle Holocene and Late Holocene. Modified from Nunn (2007a).

The IPCC further projects the increasing impacts of climate change on the ecosystem, global activity sectors, and most particularly on regions of island countries during the twenty-first century with increasing temperature change. According to the report, sea-level rise is expected to exacerbate inundation, storm surges, shoreline erosion, and other coastal hazards, thus threatening vital infrastructure, settlements and facilities that support the livelihoods of island communities. Climate change is expected to reduce water resources on many small islands to the point where they become insufficient to meet demand during low- rainfall periods. Rising global temperatures and sea level will deteriorate coastal conditions, particularly through erosion of beaches while coral bleaching is expected to affect local subsistence resources.

2.1.3. Climate and Sea-Level Change for Oceania

The Pacific Islands and Ocean (Oceania) occupy more than one-third of the Earth’s surface. This vast region is the least-understood globally in terms of palaeoclimate mainly due to its remote location (Bridgeman and Oliver 2006). Climate change and more particularly sea-level rise is a major concern for the small island nations found in the Pacific Basin as mentioned in the previous section. Even a slight rise in sea level by a few centimetres will cause environmental change in the coastal areas, including coastal erosion that will constraint water resources due to increased salinisation of groundwater supplies and will result in human-induced pressures on coastal areas.

The patterns of glacial and interglacial stages discussed above have been observed globally. Particularly for the Pacific Island nations, the accompanying rise and fall in sea level with temperature has had significant effect on the coastline. The recent postglacial (Early Holocene, Figure 2.4) sea-level rise of 120 to 130 metres affected almost every part of the world’s coastline including the islands of the Pacific region (Nunn and Kumar 2006). Shorelines on these islands moved landward as sea level peaked during the mid-Holocene that has today shaped the modern coastal landscapes. The earliest human migration into the oceanic island groups from the Western Pacific Rim at the end of the mid-Holocene took advantage of newly formed coastal environments engendered by sea-level highstand (Dickinson 2001). The first people to enter the Pacific Islands came from the Bismarck Archipelago of Papua New Guinea approximately 1330 B.C. (3280 cal BP). Within a few hundred years, they had colonised most of the islands in Vanuatu, New Caledonia, Fiji, Tonga and the Samoa island group (Kirch 2000). The mapping, excavation and coring, and radiocarbon dating of coastal deposits have provided an effective means of reconstructing sea-level changes and mapping of shoreline development for oceanic islands (Ramirez-Herrera et al. 2007; Moriwaki et al. 2006; Gale and Hoare 1991). For the Pacific Islands, sea level reached a maximum during the mid-Holocene (6000 to 3000 years ago) as seen in Figure 2.4, perhaps 1 to 4 meters above its present level. The end of the mid-Holocene marks the time of human colonization of many islands. The Fiji Islands for instance, was

14 colonised near to the end of the mid-Holocene along the southwest of Viti Levu Island. This first human settlement for the Fiji Islands will be looked at more closely in Chapter 3.

The transition between the LCO and the LIA lasted about 100 years (marked on Figure 2.4 and shown more closely in Figure 2.5) and is also known as the A.D. 1300 Event (Nunn 2007c, 1999). It is thought to have caused rapid environmental changes and societal disruption throughout the Pacific Islands (Nunn 2007c). The A.D. 1300 Event notion was proposed by Nunn from climate and sea-level changes that appear to have had major and lasting effects on human societies. It is projected that most Pacific societies thrived during the warmer, drier, and more stable climates of the LCO in contrast to comparatively cooler climate of the LIA when many island societies collapsed. The effects of this A.D. 1300 Event led largely to the reduction in food resources available around the coast due to the about 70 to 80 cm sea-level fall between A.D. 1250 and A.D. 1350 (Nunn 2007c).

Transition Phase Temperature (°C) Temperature (°C) 1050 1150 1250 1350 1450 1550 1650 ~A.D. 750 Little Climate Little Ice Age Optimum A.D. 1300 Event Formersea-level elevation relativeto present (m)

Figure 2.5. Temperature and sea-level change in the Pacific Basin during the A.D. 1300 Event. Temperature rise and fall is closely followed by seal level. The transition period was when temperature rises and sea level drops. Modified from Nunn (2007c).

The sea-level fall exposed the fringing reefs and erosional benches that had developed below mean sea level during the LCO that was home to a vast variety of marine organisms. It is suggested that the ensuing food crisis resulted in conflicts between societies throughout the Islands in the Pacific Basin. A few examples come from the Fiji Islands, Hawaiian Islands, and Easter Island. The coastal areas were abandoned because of the loss of food resources that resulted in conflict and societal breakdown that caused people to occupy the interior parts of the islands. For example, the upland, inland fortified cave sites of the Sigatoka Valley, Fiji Islands, and the Waihina Valley in the Hawaiian archipelago (Nunn 2007a). 2.2. RECONSTRUCTING PAST ENVIRONMENTAL CHANGES FROM SEDIMENTS: GLOBAL AND REGIONAL

2.2.1. Sediments

Sediments are geological materials formed by Earth processes under ordinary surface conditions by the action of wind, water, ice, gravitational and biotic activity (roots, insects, worms, humans). The formation of sediments can be viewed in terms of three stages, weathering, transportation, and deposition. These three processes are sensitive to climate and vegetation conditions that control the type and intensity of weathering, and the nature and capacity of transportation. Hence geographers and palaeoclimatologists have argued that the analysis of sediments is a powerful means for reconstructing the environmental history of the planet (Huckleberry 2006; Gale and Hoare 1991; Hassan 1978).

Predominantly, the environmental interpretation of sediments is achieved by the use of proxy data such as sediment stratigraphy, sediment lithology, sediment mineralogical and chemical composition, and fossil content. Studies indicate that sediment profiles, mainly in coastal wetland areas, are likely to preserve a good record of sea-level change because of their sedimentological, vegetation, and faunal distribution (Al-Zamel et al. 2007; Ramirez-Herrera et al. 2007; Vött et al. 2007; Drago et al. 2006; Moriwaki et al. 2006).

Coastal plains comprising beach ridges and swamps have excellent potential for measuring sea-level and shoreline changes. A study done along the Mexican Pacific coast indicated that relative sea level change was a result of local land elevation. The occurrence of blue clayey silt/mud on top of a sand unit suggested a transgression marine flooding event (sand unit) followed by an apparent coastal submergence (marine blue clays) that was induced from repeated earthquakes and long-term tectonic deformation followed by a relative sea-level rise around 3400 BP (Ramirez- Herrera et al. 2007).

Sedimentary analysis of lagoon sediments from northwest Greece revealed that a freshwater lake system existed before the mid-Holocene sea-level rise that transformed into a barrier-lagoon system during the mid-Holocene sea level highstand. With the deceleration of sea-level rise at the end of the mid-Holocene and the beginning of the Early Holocene, the barrier-lagoon system migrated landward and transformed into a freshwater lake again due to Acheloos river water input during floods. Today the Etoliko Basin is a brackish water lagoon system induced by the continuous sea-level rise over the past century (Vött et al. 2007). This sea-level rise was associated with coastal erosion that resulted in the connection of Lake Etiliko to a lagoon system in the Etoliko Basin. Calcareous sand layers, marine and brackish environment species (shell fragments), and the absence of plant remains are all indicative of high sea level. Organic-rich clay particles, abundance of plant remains in coarse-grained sediments and an absence of marine species are markers of low sea-level intervals.

In addition, geochemical analysis of sediment is a good indicator of sea-level fluctuations. Studies show that high concentrations of metals like sodium and strontium in sediments indicate high sea level. The variability of these elements is controlled primarily by fluctuations in sea level rather than by climate or sediment source (Ramirez-Herrera et al. 2007; Chen et al. 1997).

The physical and chemical characteristics of sediments that are analysed as part of this study are sediment colour and texture, shell classification, sediment organic and carbonate content, and sediment core stratigraphy for the reconstruction of past

17 environmental changes. The use of these methods of sediment analysis is discussed in greater detail in the following sections.

2.2.2. Sediment Analysis

I. Colour

Weathering determines sediment colour development and distribution. The change in chemical composition of sediments during weathering also causes different coloured sediment particles over time. Sediment colour is influenced by the source rocks, the conditions of weathering, physical and chemical conditions at the site of sediment deposition, and post-depositional changes (Pity 1979). Soil colours are also well- known indicators of sediment character and composition. For instance, high content of organic matter produces dark coloured sediments like brown, black or grey. This usually occurs when sediments are exposed to the surface without additional deposition allowing vegetation to grow and as plants and leaves die, the sediments have a rich dark appearance.

The oxidation of iron minerals in organic matter produces dark coloured sediments like dark red where an increase in colour chroma is generally interpreted as increasing ferric oxide content (Scheinost and Schwertmann 1999). Reddish or yellowish coloured sediments also indicate good drainage system and well-aerated conditions, whereas mottled greyish, brownish, and yellowish colours indicate poor drainage in reduced (low oxygen) conditions (Hassan 1978). White or light-grey colours are produced mainly by sands that are composed of quartz or calcite and maybe of marine origin as they reflect visible light (Rapp and Hill 2006).

II. Particle-size distribution and sediment texture

The texture of sedimentary deposits refers to the combination of different particle sizes, such as gravel, sand, silt, and clay. The particle (grain) size range defines limits of classes that are given names in the Udden-Wentworth scale shown in Figure 2.6.

Particle-size analysis (granulometry) is performed to determine the texture and characterize the population of different grain sizes within a deposit (Huckleberry 2006). The methods of particle-size analysis are discussed in greater detail in Chapter 4. Sediment texture is readily determined by feel with fingers following the procedure in Figure 4.6.

Figure 2.6. The Udden-Wentworth grain size classification. Adapted from online image at www.rainmuse.com/chekjawa/images/uddenww.jpg.

The particle-size distribution of sediment grains and sorting that is to what degree are the grains of a similar size: well-sorted grains are all of similar size whereas the poorly sorted grains are of widely different sizes helps identifies sediment transport and depositional systems. They also give a good indicator of the velocity regime of the depositional environment. Coarse grains indicate the energy characteristics of the environment of deposition. For instance, medium to poorly sorted (medium to very fine sand and silt) are indicative of high water energy environments and may mark a period of high sea level in a coastal deposit. Fine particles like clay usually settle in lower velocity environments where there is minimum effect of wind, water, gravitational, and/or other organisms on the depositional environment. When combined with other chemical data like sediment colour, particle-size data can be

19 very useful for defining site formation processes. For instance, dark blue to blue-gray clayish silt is indicative of a possible marine-dominated setting (Ramirez-Herrera et al. 2007).

III. Shell Taxonomy

Fossil records from an area can be used to determine the environment, ecosystem and organism abundance. For the purpose of this study, marine/terrestrial shell organisms were identified and characterised that helped interpret the different environmental conditions at the time of sediment deposition in the Bourewa palaeolagoon. Studies of common and abundant foraminifera and ostracod species in a lagoon bordering Kuwait Bay showed that the sediment deposition in reef flats and mudflats consisted mainly of grey muddy sand with variable amounts of biogenic materials (whole shells and shell fragments of molluscs and foraminifera). The distribution and dominance of different benthic species (sea-floor dwellers) have relatively simple patterns that are governed by water depth; salinity, hydrodynamic conditions, and sediment size (Al-Zamel et al. 2007).

Therefore, the occurrence of different species from different parts of the ocean floor indicates the type of environmental deposition, either a shoreline or a backshore area. Shell organisms like mollusc and diatom assemblages are useful in interpreting brackish-water conditions in beach sediments. Beach sediments of fine to medium carbonate to biogenic sand usually have a high percentage of shell fragments.

IV. Loss-On-Ignition

Loss-On-Ignition (LOI) provides an effective means of estimating organic matter and carbonate content concentrations in sediment samples. In a first reaction, organic matter is oxidised at temperatures of about 500-550°C to carbon dioxide and ash. In a second reaction, carbon dioxide is evolved from carbonate at temperatures of 900- 1000°C (Dean 1974). The weight loss during the reactions is measured by weighing the samples before and after heating.

Higher concentrations of organic matter are indicative of inputs of organic-rich materials (topsoil, plant material) and/or conditions in which organic decomposition is inhibited for example, waterlogged or very acidic environments. Soil organic matter gives a hint of former surfaces of stability. In archaeological sites, organic matter accumulation is used to define vertical and horizontal variability of past human activity in an area. The irregular spatial patterning in some cases relates to intra-site features such as storage pits, hearths, and middens, or human activity areas such as animal processing sites (Huckleberry 2006). In coastal setting, carbonate content maybe an indication of marine incursion while high organic content is linked to terrestrial sediment inputs. Generally, organic and carbonate content have an inverse relationship (Zabenskie and Gajewski 2007).

The darker colour of sediments comes from the organic content in the sediment whereas sediment lightness (lighter colour) is related to increased carbonate content. This is due to the fact that sand primarily of a marine origin in coastal sediments is mainly composed of quartz crystals that reflect lower amount of light, while silt and clay particles reflect more light and hence is darker in colour and are primarily terrigenous (Ramirez-Herrera et al. 2007; Whittecar et al. 2007; Spielvogel et al. 2004).

V. Sediment stratigraphy

Sediment stratigraphy is the interpretation of horizontal layers that form the deposits at a site over time. The rates of sediment deposition may vary with time from different episodes of deposition. For example, in an area in which sand dunes accumulate, a period of strong winds will deposit a thick layer of sand on the dune, whereas a period of gentler wind will deposit only a thin layer of sand on the dune (Balme and Paterson 2006). Sediment stratigraphy is usually recorded in stratigraphical section scale drawings to build up a chronology of the order in which the layers and features were created.

2.2.3. Radiocarbon Dating

Radiocarbon dating of sediment samples is helpful for recognising the time of sediment deposition. This is related to the age determination of organic materials like wood, charcoal, marine and freshwater shells, bone, plant remains, and is possible for any material that was once part of a living carbon-based organism.

The following paragraph is paraphrased from the University of Waikato Radiocarbon Dating Laboratory website (www.radiocarbondating.com) that explains the radiocarbon dating principle. In general, the radiocarbon formed in the upper atmosphere is mostly in the form of carbon dioxide that is taken up by plants through photosynthesis. Along the food chain, plant eating animals transfer this carbon to all the living organisms. Hence, all living organisms have the same radiocarbon to stable carbon ratio as the atmosphere. The dating convention is that once an organism dies, the radioactive carbon will slowly decay. This decay of the radioactive carbon can be calculated using various dating options. Some dating options are the standard radiometric dating that can date large samples by direct counting using the Liquid Scintillation method. Another very common and the most abundantly used method of dating and used for this study is the Accelerator Mass Spectroscopy (AMS) dating that is able to date very small amounts of sample (<5g).

Radiocarbon measurements are always reported in terms of years “Before Present” (BP), “Present” being identified as A.D. (anno domini) 1950. The radiocarbon date obtained is calibrated on the assumption that the amount of radiocarbon in the atmosphere has always been the same as before A.D. 1950. The calibration of radiocarbon dates is discussed in greater detail in Research Method Chapter (Section 4.2.2II).

The Fiji archipelago is centred at 18°00' South and 175°00' East in the South Pacific Ocean (Figure 3.1). Previous research in and around the study area, southwest of Viti Levu (Figure 3.2), has been carried out mostly within the past six years predominantly focused on the prehistory of early human settlement. This research has been focused on a limestone promontory area called the Rove Peninsula, the most intensely studied part of which is a beachflat called Bourewa. Preliminary sediment analysis on various sediment cores around the study area was carried out by the author to understand the sediment type and to select the precise study site.

This chapter reviews the environmental change of the Fiji Islands group and summarizes the work previously done in the study area as follows:

1. The geography of the Fiji archipelago. The location, environment and climate, and sea-level change over the past 10,000 years. 2. Modern environmental setting of the Rove Peninsula. 3. A review of the Bourewa archaeological site. 4. The modern geography of the Bourewa palaeolagoon.

3.1. GEOGRAPHY OF THE FIJI ISLANDS

The Fiji archipelago is an oceanic island group of about 322 islands. Figure 3.1 shows the location of the Fiji Island group in the Oceania region, and Map A (Figure 3.2) is a closer view of the major islands. These islands are mainly mountainous covered with tropical rainforest and grassland savannas. The Fiji Islands is part of the Pacific Rim of Fire, the convergent plate boundary system between the Pacific and the Indo-Australian lithospheric plates. The tectonic activity of Fiji is very complex

Figure 3.1. Map of the Pacific Islands showing the location of the Fiji Island Group.

See insert B

Rove Peninsula Figure 3.2. (A) Map of the main Fiji Islands showing the location on the southwest coast of Viti Levu Island of the selected Lapita site with the evidence of Lapita-era occupation (approximately 3050-2500 BP) (Source: USP Media Centre). (B) Insert of Rove Peninsula with the major Lapita site, Bourewa with other sites where the evidence of early human occupation was discovered (Modified from Nunn et al. 2006).

(Map A of Figure 3.3) as it is located between two opposite facing subduction zones. Both the Indo-Australian plate and the Pacific plate subducts under the Fiji plate. The schematic cross-section of Figure 3.3B shows Fiji’s location between the two opposite-facing subduction zones.

Figure 3.3. (A) The Pacific lithospheric plates. (B) Schematic cross-section showing Fiji’s location between two opposite-facing subduction zones. Adapted from online image at www.mrd.gov.fj/gfiji/geology/educate/platect.html.

Since the Last Interglacial the shorelines around the northeast Fiji Islands emerged by around 5 m – 5.2 m responsible for the rapid emergence of the cliffs. Tectonic changes however, are difficult to isolate from contemporary eustatic changes for short periods of time such as the Holocene (postglacial). The presence of an emerged shoreline marking the culmination of Holocene sea-level rise is consistent with elsewhere in the region. For the Fiji Islands, comparative stability has been noted in the southeastern part of the group, uplift in the southern and northern, and variable

25 tectonics for the rest of the group including the southeastern part suggesting no net uplift occurred due to coseismic uplift (Nunn 2002, 1995). Within the Pacific Basin, global climate forcing during the Quaternary period (1.8 million years to present) was modified by various regional climate filters, particularly the effects of changing equator-pole temperature gradients. Generally, warmer temperatures would have reduced the thermal gradients between the equator and the poles. This would sequentially lower the rate of latitudinal heat exchange, shifting climate zones polewards. The opposite would have happened during cooler times. As heat transfer and wind speed increase, temperatures decrease and thus sea level drops (Nunn 2007a).

Recent climate change has had a similar impact on Fiji as for the rest of the South Pacific. Holocene sea-level changes reconstructed using radiometrically dated coral, geomorphological observations of relative sea-level change (Pirazzoli 1991), and the ICE-4G model (Nunn and Peltier 2001) shows a gradual rise in sea-level of 1 to 2 m above present between 6000 to 4000 years ago. This rise in sea-level was deduced as a result of melting polar ice. Middle to Late Holocene climate change is of considerable importance as it marks the era of earliest-known human occupation for the southwest Fiji islands around 3200 years BP. This was the time when climate was optimum for making long sea voyages possible for people to explore the vast Pacific Ocean and reside along the coastline as they were perhaps intimidated of living inland. The discovery and location of the first-known occupation are reviewed more closely in the following sections.

3.2. MODERN ENVIRONMENTAL SETTING OF ROVE PENINSULA

The Rove Peninsula has become a place of paramount importance in Fiji over the past six years due to the discovery of a large number of intricately-decorated dentate- stamped potsherds from Bourewa Beach (Nunn et al. 2004). These potsherds are indicative of the Lapita colonisers. Lapita pottery is the only pottery in the history of Pacific Island peoples to have been decorated with intricate patterns made using a technique known as dentate stamping (Figure 3.4). This unique pattern of pottery decoration dates from around 3450 cal year BP in the Bismarck Archipelago of

Papua New Guinea to as early as 2850 cal year BP in Tonga (Nunn 2005). Through numerous geoarchaeological investigations on Rove Peninsula, the earliest-known human settlement in the Fiji archipelago is generally regarded as being at Bourewa, established about 3050 cal BP.

Figure 3.4. Lapita pottery discovered during the excavations at the Bourewa Beach (2009). Note the dentate-stamped method of decoration on the pottery made by pressing small toothed (dentate) stamps into the leather-hard clay before firing (Kirch 2000). (Photos by Kirti Lal).

The Rove Peninsula (see Map A, Figure 3.2 for location) is a limestone promontory rising to about 35 m above mean sea level. The sediment composition of the northern Rove Peninsula is mainly or all alluvium as it is close to the mouth of Tuva River (shown more clearly in Figure 3.7) that brings in eroded loose, unconsolidated soil/sediments. The western side of the peninsula is fringed with broad coral reefs now exposed that extends 2.4 to 3 km from the shoreline (Figure 3.5). The southern part of the peninsula is mainly gravel from the massive sediment inflow from the adjoining Tuva River during times of flooding that has now developed into Natadola Harbour (Houtz 1959; Nunn 2007b). The northeast side is covered with mangroves forests adjacent to the Tuva River. Figure 3.6A shows the connection of the peninsula to the mainland at Natadola Harbour.

Reef edge

2.4 – 3 km Exposed fringing reef – Post Holocene Climate Optimum

High tide mark

Figure 3.5. Stretch of the now exposed fringing reef from the modern Bourewa Beach high tide mark to the edge of the fringing reef. (Photo by Kirti Lal).

3.3. BOUREWA ARCHAEOLOGICAL SITE

The human (Lapita) settlement in the Fiji archipelago appears to have been established as much as 3050 cal BP (1100 BCE) at Bourewa. Geomorphological work in this area shows that the Rove Peninsula did not exist 3000 years ago when sea level was 1.5 m higher than present day (Nunn 2007b). As seen in Figure 3.6B, the island was surrounded with fringing reef, separated by water gaps of 1 km or more from the mainland, Viti Levu Island. Since the time of Lapita occupation, the coast of the island on which Bourewa was located has extended seaward exposing more land. This was due to the drop in sea-level and alluvial sediment build-up associated with the spread of mangrove forest around the Rove Peninsula (Figure 3.6A).

The early Lapita people depended largely on marine foods so are thought to prefer the smaller offshore islands as they moved along the western tropical Pacific Islands because of the islands’ productive fringing reefs. Another Lapita settlement excavated along the side of the Rove Peninsula is at Rove Beach that was found to be a late to post-Lapita site (2700 to 2500 BP). Lapita-era occupation was also 28 discovered on Qoqo Island located in the mangrove swamp at the mouth of Tuva River (2950 to 2760 BP). Other Lapita sites around the Rove Peninsula were discovered at Waikereira, Jugendar’s Farm and the Tomato Patch (Nunn 2007b, 2005, et al. 2006, et al. 2004). The location of these sites is marked in Figure 3.7.

A B

VUSAMA ISLAND

Figure 3.6. Changes in the geography of the Rove Peninsula and the adjoining area. (A) Modern geography of the area. The Rove Peninsula is connected to the main island, Viti Levu at Natadola Harbour. (B) Geography of the area about 2950 BP around the time of first settlement, sea level was about 1.5 m higher than present, showing the locations on the Lapita settlements. Adapted from Nunn (2007b).

Figure 3.7. Modern setting of the Rove Peninsula with the locations of the major features, excavation and study sites. Adapted from Nunn (2009a).

The beginning of the Late Holocene was when climate was changing and environments and ecosystems were adjusting to the change, the earliest settlement at Bourewa was stretched along a barrier island. This barrier island later transformed into a sand spit (Figure 3.8) as sea level fell during the early part of the site’s occupation. There is evidence of post-holes within the spit deposits suggesting possible stilt-style houses, similar to those found elsewhere in the Lapita realm (Nunn 2007b) namely Papua New Guinea and Vanuatu. One of the reasons for people choosing to live in this area may have been to do with access to resources.

Figure 3.8. People built houses on stilt platforms on the sand ridges shown. These ridges were exposed during low tide and partially submerged during high tide. There was a fringing reef flat on the western side of the ridges and the tidal inlet on the southeast side. Adapted from Nunn (2009a). On one side of the sand barrier was the ocean with a broad fringing reef having an abundance of marine foods, while the leeward side was a partly enclosed sand- floored tidal inlet suitable for swamp cultivation of taro. The reconstructed sand barrier can be seen in Figure 3.8, with the fringing reef flat on the west and the tidal

30 inlet on the east. As sea level dropped, the surface fringing reefs were exposed (Figure 3.5), and the tidal inlet dried up. The resulting decline in food resources on both sides is the most likely explanation as to why the site was abandoned around 2450 cal BP (Nunn 2009a).

3.4. GEOGRAPHY OF THE BOUREWA PALAEOLAGOON

The core site is located on the west of the Rove Peninsula, 140 m inland from the Bourewa Beach and at an elevation of about 2 m above mean sea level. Figure 3.8 shows the location of the core site. The palaeolagoon was a tidal inlet during the time of Lapita settlement on the island (Figure 3.7) that was flooded with sea water during high tide and separated from the open marine conditions by a shallow/exposed sand bar. The Global Positioning System (GPS) site reference is at latitude 18°05.422 S and longitude 177°18.302 E.

The palaeolagoon area was highly overgrown with grass and shrubs since it had been uncleared for two years. Formerly the land was occupied by Indian farmers who used to practise sugar-cane and vegetable farming in the area. Taking this into consideration, the top 50 cm of the sediments was regarded as having been disturbed due to ploughing and farming practices.

The accumulation of sediments over time due to physical and chemical processes on the surface occurs in response to the different environmental conditions at the time of sediment deposition. For the purpose of this study, the palaeoclimatic reconstruction through sediments analysis of a 6 m long sediment core was used to determine the climate conditions for the southwest Viti Levu Island since the end of the Last Glacial.

This chapter describes the field and the laboratory methods used for sediment analysis as follows:

1. Selection of sediment extraction site for palaeogeographical framework. 2. The field methods used to extract the 6 m core from the Bourewa palaeolagoon. 3. The laboratory analysis of the sediments is divided as • physical composition which involved the identification of colour from the Munsell Colour Charts, texture by feel, sand to mud ratio from wet sieving, and shell taxonomy from stereomicroscopic observation. • determination of the organic and carbonate content percentage by loss-on- ignition (LOI) and radiocarbon dating of the sediment core at different core depths.

4.1.SELECTION OF STUDY SITE

Initially, the site of coring was intended to be a 120 m diameter sediment-filled sinkhole named Togolilo, located about 1.5 km from Bourewa Beach. The location of the sinkhole is given in Figure 3.8. A chronological sediment analysis from the sinkhole would help understand the palaeoclimatology of Rove Peninsula. This

32 sinkhole may have formed due to a surface collapse when the limestone below the land surface had been dissolved by ground water circulating through it and caverns may have developed underground. Eventually, the sinkhole became filled with sediments from around the area. However, preliminary coring in the sinkhole proved to be problematic due to the following reasons.

400m

Bourewa N Rove Beach Beach

Togolilo Mangrove Sinkhole Qoqo Island Major Core Site

Tuva River

Natadola Beach Vusama Village Viti Levu Island

Figure 4.1. Aerial photograph of the map of Rove Peninsula. The preliminary core sites are marked in blue stars. The red star shows the location of the 6 m core site in the middle of the palaeolagoon. Adapted from online Google Earth Image.

At the time of sampling, the Togolilo sinkhole had water in it that was approximately 1 m deep in its centre (Figure 4.2A) which made the extraction of samples almost impossible with the corer that was available (the corer and coring techniques are covered in Section 4.1.1). An initial attempt was made to core in the centre of the sinkhole and three sets of cores 30 cm to 40 cm long were obtained. The corer available however was unable to retain the samples and there were difficulties with the relocation of the core hole once a set of samples was removed due to the water level. It was also very difficult to core through the very dark (almost black, Figure 3.8B) clay sediments in 1 m deep muddy water.

The water level in the sinkhole fluctuates depending on the amount of rainfall in the area and only dries up during times of extreme drought for which the sample

33 extraction could not be put on hold for. Furthermore, the Togolilo sinkhole sediments could be interpreted as fairly recent with the change in weather conditions and activities around the sinkhole like animal grazing would determine the rate of erosion and sinkhole wall collapse that would add materials into the sinkhole. Hence if a chronological record of climate change was to be determined than sediment samples further deep would have to be attained, which was unworkable with the corer available. For these reasons, sediment analysis from the Togolilo sinkhole was not suitable for this palaeoclimatological study.

A B

Figure 4.2. The Togolilo sinkhole. (A) View of the sinkhole taken from the top of the sinkhole edge. (B) Clayey sediments retrieved from the middle of the sinkhole. (Photo by Kirti Lal).

The second site considered was Bourewa Beach. The beach sediments on the surface were of a sandy texture composed of shells, pottery, coral fragments, and limestone. Three test cores of 60 cm to 80 cm in length were extracted about five meters apart that were mainly composed of sandy beach material and soil. These sites were also not chosen for coring as the fringing reef and beach rocks hindered the extraction of samples deeper than 80 cm. As well as the difficulty in obtaining a long chronological picture of climate change the Beach is also unsuitable because the beach materials are continually moved and mixed around due to wave activity.

Another site considered was the palaeolagoon behind the Bourewa archaeological site that was a former tidal inlet (coastal lagoon) during the time of initial human settlement (Figure 3.6). The reason for selecting the palaeolagoon was that lagoonal systems can provide an understanding of sea-level changes because such 34 environments are sensitive to even a small variation in sea level. Several studies show that the sediment analysis of marine/coastal lagoon sediments provides much climate and sea-level information for the Holocene that lead to not only convincing interpretations of past and present environmental changes, but also for predicting future ones (Al-Zamel et al. 2007; Ramirez-Herrera et al. 2007; Vött et al. 2007; Drago et al. 2006; Moriwaki et al. 2006; Yum et al. 2003).

Three preliminary cores of 1.5 m to 3 m were extracted from different parts of the palaeolagoon, all of which showed sediment variation from sandy sediments to clayey sediments at a depth of 2 m (± 30 cm). A clear transition in sediment type was visible showing that there had been a major change in the sediment source in the tidal inlet at that time. It was therefore decided that the palaeoclimatological signature of Rove Peninsula would be best reconstructed from the palaeolagoon sediments. For the major sediment analysis, one 6 m sediment core was extracted at 10 cm intervals from the centre of the palaeolagoon. While more such cores would give a clear picture, one core was deemed appropriate for a 12-month Masters project.

4.2. FIELD METHODS

The site observation and sample collection was conducted from 19 to 31 January 2009. A pilot study of the Rove Peninsula was carried out a few months before the major sampling to determine the most suitable site for core extraction as discussed in the previous chapter and the Bourewa palaeolagoon was selected as the most suitable site for sampling. The following two sections describe the coring techniques used in the field.

4.2.1. Corer

The 6 m metal corer used is a hand auger set with bayonet connections which was available from the Department of Geography at the University of the South Pacific. Prior to coring, the hand auger was ensured to be in a good working condition. More sophisticated mechanical coring equipment was available at the Mineral Resources

Department (MRD) and the Westech Gold Mining Limited but due to prohibitively high operating charges they were not hired for sample collection. The corer used consists of eight parts; the auger head, three sets of solid aluminium extension rods and two sets of solid stainless steel extension rods, a cross handle connector, and the cross handle (Figure 4.3). The auger head is designed for augering in soils both above and below the groundwater level. The sharp extremities of the auger bits that angle downwards make the auger penetrate soil easily. The auger head features a closed bit with a restricted opening to prevent loss of sampled material when the auger is pulled out. It has two openings in the cylinder wall (Figure 4.3) to make it easy to empty the extracted materials.

4 2

Openings on either side of the cylinder 3

Figure 4.3. Hand auger set with bayonet connection. (1) The auger head. (2) Solid aluminium extension rods. (3) Solid stainless steel aluminium rods. (4) Cross handle connector. (5) The cross handle. (Photo by Kirti Lal).

The extension rods connect with a bayonet connection. The pins projecting from either side of the rods attach to each other, and then a hollow rod is slid on top to secure the rods in a bayonet socket. The advantage of the bayonet connection is that the rods connected together efficiently in very little time. The information on the corer was obtained online from Eijkelkamp Agrisearch Equipment (www.eijkelkamp.com). All the pieces of the corer connected together to form a 6 m

36 continuous corer that was used to extract sample up to a depth of six-metres from the surface (Figure 4.4). The handle connecter and handle were connected on top of the uppermost extension rod and rotated in a clockwise direction to drive it into the ground.

6 meter corer

Figure 4.4. 6 m corer held from the surface by the team that assisted in coring and sample collection. (Photo by Patrick Nunn).

An alternative to coring would be digging a pit at the site and doing a stratigraphical analysis of the horizontal layers that form the deposits over time. Yet coring was preferred over digging due to less labour intensity and increased safety in order to obtain samples of up to 6 m deep from the surface. Another reason the site was not dug was due to the depth of the water table, approximately 70 cm below the surface. Samples were collected at every 10 cm interval since a continuous 6 m long core could not be obtained in one go with this corer.

The following section covers the field and coring techniques that were used to obtain the samples for climate change study from the palaeolagoon.

4.2.2. Coring Technique

Prior to going out in the field, all the pieces of the corer were connected and laid horizontal on the floor. A ruler and an indelible marker were used to mark the corer at every 10 cm interval from the tip of the auger head to the topmost extension rod as shown in Figure 4.5. With the aid of these markings, samples were collected at 10 cm intervals.

10 cm interval markings on the extension rod

Figure 4.5. Markings at every 10 cm on one of the extension rods sticking out of the ground. (Photo by Kirti Lal).

The corer had to be rotated clockwise and pushed downward using the cross handle to drive it into the ground (Figure 4.6). Each 10 cm sample was removed and placed into clearly labelled air-tight polythene sampling bags. Samples were labelled as Sample Number 1, 0-10 cm depth, the next set of samples as Sample Number 2, 10- 20 cm and so forth. The corer was thoroughly cleaned with fresh well-water after each sample extraction to avoid contamination and mixing of sediments of different

38 depths. Samples were taken back to the Vusama Community Hall for immediate colour and texture determination.

Figure 4.6. The corer is rotated in a clockwise direction and pushed through the sediment profile to extract a sample every 10 cm (Photo by Kirti Lal).

The top 230 cm of the sediment core was mainly sandy. Since the sandy sediments at depths 130 cm, 150 cm and 220 cm were waterlogged, they were not collected in the corer. Therefore, 20 cm samples were collected and bagged for Sample Number 14 (120 cm-140 cm), Sample Number 16 (140 cm-160 cm), and Sample Number 23 (210 cm-230 cm). The samples at these depths were treated as one (10 cm interval) for the purpose of the laboratory analysis.

4.2.3. Problems Encountered with Coring

A number of minor problems were encountered while coring. The first problem was when the layer of clay soil was reached at a depth of 250 cm. Since clay particles

39 stick together, coring through the clay layer required a great deal of strength. It was also very difficult to remove the clay samples from inside the auger into the sampling bags. Difficulty was also faced while cleaning the auger to get rid of all the materials sticking inside the auger with limited amount of water. There was also the possibility of the core wall collapse, which fortunately did not happen.

Another issue was with the solid stainless steel extension rods, manufactured locally at a steel processing company (Mechanical Services Limited). The rods would expand with the rise in temperature at the hottest part of the day and would not connect with the corer head or the other solid aluminium extension rods. For this reason it was ensured that the extension rods were left connected to the auger. These problems were dealt with in the field to obtain the best quality samples from the Bourewa palaeolagoon.

To avoid sample contamination it was made certain that the sample bags were not torn or damaged in any way. The samples were taken back to the Vusama Community Hall for the first set of colour and texture readings and then brought back to the Marine Science Laboratory, the University of the South Pacific (USP) for further analysis as is discussed in the following sections.

4.3. LABORATORY METHODS

Closed shoes and a white coat were worn at all times while working in the laboratory. Gloves were used to handle samples for radiocarbon dating to avoid sample contamination that could affect the results.

In the laboratory at the Marine Science Laboratory (the University of the South Pacific), four sets of samples were selected for radiocarbon dating (discussed in section 4.3.2 IIA). The 10 cm interval sample was taken to be homogenous therefore; samples were sub-sampled using the coning and quartering method. The entire sample from the bag was emptied onto a large tray, mixed and flattened using gloved hands and divided into quarters with the index finger. The two quarters on the opposite side were removed and kept aside, while the other two quarters were

40 combined and mixed. The same process was continued until approximately 150 g of sample was left behind. This was air-dried for 5 days. The remaining samples kept aside were later used for colour and texture determination, particle size analysis, and loss-on-ignition (LOI) in the laboratory.

The coning and quartering method of sub-sampling was used for radiocarbon dating but not for any other sediment analysis. This method of sub-sampling had a few drawbacks. For instance, coning can lead to significant particle segregation. Also it is most unlikely that the sample can be divided exactly into quarters. Despite these drawbacks, this method of sub-sampling was adopted for radiocarbon dating because it appeared to be the best method after air-drying the sediments for radiocarbon dating.

Following the radiocarbon dating, samples were sub-sampled and removed, for the determination of sediment colour, texture and shell classification. For LOI the grab sample method of sub-sampling was used. The grab sample method involved simply grabbing a handful (picking out) of the required amount of sample direct from the sample bags. This method of sub-sampling was used as all the samples of the 6 m sediment core were not the same. The sediment composition varied and the coning and quartering method could not be used for the clay samples since clay particles did not disintegrate and mix easily (heterogeneous). Therefore grab sample method was used in order to have a consistent sub-sampling method for sediment analysis.

4.3.1. Physical Composition and Analysis

I. Colour

Soil colour is one of the attributes of sediments that can differentiate layers and horizontal disturbance of a deposition site. The Munsell colour notation has become the standard colour identification since the 1950s (Rapp and Hill 2006). The Munsell colour system was created by Professor Albert H. Munsell in the year 1912 that specifies colour based on three colour dimensions: hue, value (lightness) and chroma (colour purity or colourfulness). Hue is measured by the degrees around horizontal

41 circles (Figure 4.7) that are divided into five principal hues (Red, Yellow, Green, Blue, and Purple) along with five intermediate hues halfway between adjacent principal hues. Value is measured vertically from black (value 0) at the bottom to white (value 10) at the top with the natural gray lines that lie between black and white. Chroma is measured perpendicular from any point to the vertical axis from the centre of each slice. The Munsell Colour System is summarized in Figure 4.7 with all the colour schemes and along with an example.

Figure 4.7. The Munsell Colour System, showing the neutral values from 0 to 10 and the chromas of purple-blue (PB) at value 5. Notation 5PB 5/6. Online image adapted from www.wikimedia.org/wikipedia/commons/d/d5/Munsell-system.svg.

It is imperative that colour should be determined on the material before air-drying. Air-dried sediments tend to lose their natural colour and are usually about two units higher in value than the same sediment when moist. At random a pinch of the moist soil sample from each bag was put next to the standard Munsell colour chips to categorize the colour notation. Each colour notation is a combination of its specific hue, value, and chroma that supplements its own colour name. For instance the colour notation 10YR 4/6 was noted for mainly clay sediments. This means that the colour notation is of a hue at 10 yellow-red (YR), value/lightness of 4, and

42 chroma/strength of 6 thus, the colour name for this Munsell notation is light yellowish brown.

The sediment colour for each 10 cm interval sediment core was measured thrice by different individuals; once in the field and twice in the laboratory to ensure the consistency of the readings. The individuals were chosen according to their qualification and experience in research. Out of the three readings the most commonly occurring colour notation was selected as the final colour code. For the samples where all the three readings taken were different, a fourth reading was taken and cross checked with the previous three readings to ensure that the colour most closely related to the colour of the sample was chosen as the sediment colour.

II. Sediment Texture Analysis

The texture of sediments, determined from their particle-size distribution reflects the sediment origin and mode of deposition in an environment. Particle (grain) size range defines limits of classes that are given names in the Udden-Wentworth scale (Figure 2.6) that groups grains into mud, sand and gravel on the basis of their diameter. The boundary between mud and sand size grains is at 63 )m (0.063 mm), and the boundary between sand and gravel size grains is at 2 mm (Gale and Hoare 1991).

One of the most efficient methods of particle size distribution determination is from a laser particle size analyzer that utilizes the light-scattering principle to measure the particle size. Owing to the unavailability of a laser particle size analyzer at the University of the South Pacific, particle-size analysis was determined using the wet- sieving method to separate gravel, sand, and mud fractions in the sediment samples. The pipette method is a traditional method for the determination of percentage silt and clay in any given sample of the mud fraction separated after wet sieving. This method is still widely used, yet performing pipette analysis on preliminary samples proved to be very time-consuming and the results obtained were not very accurate. Consequently, the silt and clay particle proportions were not determined and only the relative sand and mud proportion of the grains were used to supplement the sediment texture. The texture determined following the procedure illustrated in Figure 4.6

43 together with the sand and mud fractions was compared to attain the final texture of the samples.

Figure 4.8. Guide to texture by feel. Modified from Thien (1979).

The texture of each sediment sample was determined by feeling the grains between the fingers. About a tablespoon of the moist sample was placed in hand, a small amount of water was added to moisten the sediments, and a visual inspection was done to see whether the particles adhered to each other to form a ball. Figure 4.8 summarises the process of sediment texture determination in a flow chart to 44 determine the sediment texture. Sand, silt, and clay are names that describe the size of individual particles in sediments. Generally, the largest particles are sand-sized that has a gritty feeling; silt is medium-sized with a very soft, silky or floury feel; the smallest-sized particles are clay-sized and felt sticky and very hard to squeeze. The remaining steps were followed to achieve the final texture description of each of the sediment sample.

Similar to colour determination, the texture of each sediment sample was done in replicates by three different individuals; once in the field and twice in the laboratory to ensure the reliability of the readings. Of the three readings the most commonly occurring texture of each sample was selected as the final texture. For the samples that had three different texture readings, a fourth reading was taken and cross checked with the previous three readings to ensure that the texture most closely related to the sample was the accurate sample texture.

Particle-size analysis by wet sieving was used to separate particles >2 mm, sand fraction (<2 mm, >63 μm), and mud fraction (silt and clay) (<63 μm). Wet sieving was more convenient and effective than dry sieving because once the sediment particles lost moisture they have the tendency to coagulate and adhere to one another (Gale and Hoare 1991). These integrated particles do not fully disintegrate when dry sieved thus all the particles do not fully separate. Wet sieving was carried out underwater using the United States of America (USA) Standard Test Sieves; metrics 2 mm and 63 μm as shown in Figure 4.9 as follows.

About 300 g of each sediment sample was taken out of the sample bag and soaked in tap water overnight to allow the particles to disintegrate. The following day a 2 mm sieve containing the wet 300 g sample was placed in a basin (Basin 1) containing about 2 inches of tap water. Tap water was used for sieving since no chemical analysis was involved on the separated materials. The sediments were sieved under water and constantly sifted with fingers to break the particles apart and enable particles <2 mm in diameter to pass through, while ensuring not to break any of the shells that might be present.

A B

Figure 4.9. USA Test Sieves. (A) Test Sieves of metrics 2 mm diameter. (B) Test Sieves of metrics 63 μm in diameter used for wet sieving (Photo by Kirti Lal).

The material that passed through the 2 mm sieve comprised of the sand and mud fraction while the material retained in the sieve were particles >2 mm that was later used for shell taxonomy. A 63 μm sieve was placed in another basin (Basin 2) and the material collected in Basin 1 was passed through the 63 μm sieve to separate the sand fraction from the mud fraction. Small amounts of the suspension in the basin were transferred into the 63 μm sieve to make certain the sand and mud fraction separated well. Hence the material retained in the 63 μm sieve was the sand fraction, and the material collected in Basin 2 was the silt and clay fraction.

The particles retained in the sieves were air-dried overnight then transferred to glass Pyrex beakers and oven-dried at 110°C for 24 hours, cooled and weighed. The mud fraction collected in Basin 2 was transferred to 1000 cm3 glass beakers and left undisturbed on the work bench overnight. The next day, all the clay and silt particles in the beaker had settled, the water remaining in the suspension was decanted and the still wet mud at the bottom of the beaker was transferred to a drying tray and oven- dried for 24 hours at 110°C, cooled, and weighed.

The final texture of the sediment samples was determined from both the texture by feel (with fingers) and sand and mud percentage. Texture by feel method specified the particle consistency with depth whereas the wet sieving of the sediment samples

46 determined the percentage of sand, and mud fraction in the samples. The soil texture triangle (Figure 4.10) was used to finally compare the percentage, sand, and mud to obtain the accurate texture of each sediment sample.

Figure 4.10. The soil texture triangle used to determine the percentage of sand, silt, and clay for a given sediment sample. Modified from Thien (1979).

The soil texture triangle gives the different proportions of sand, silt, and clay in sediments that have distinctive names. For instance, loam is defined as a soil with the combination of sand, silt, and clay in relatively equal proportions (The American Heritage Science Dictionary 2009). An illustration of this from the soil texture triangle (Figure 4.10) shows sandy loam sediments have a slightly higher proportion of sand in relation to silt and clay. They consist of up to 50 – 70% sand and 30 – 50% silt and clay. Sandy clay loam is a combination of 45 – 85% sand and the remaining 15 – 55% of the sediment is silt and clay. Sediments of a sandy clay texture comprises of 45 – 65% sand and 35 – 55% silt and clay. Silty clay is 40 – 60% silt and about 40 – 60% clay with a very small percentage (approximately 0 – 20% to none) sand. Clay sediments are about 40 – 100% clay and 0 – 45% sand. The sediment texture with a composition of 50% clay and 44% sand is sandy clay.

III. Shell Taxonomy

Similar to colour and texture, shell classification (taxonomy) can help interpret the past environment and more specifically ecosystem of the palaeolagoon. The accumulation of the sediments at the site of deposition is based on the assumption that the particle deposition or in this case the occurrence of shells and shell fragments was at the site of origin and not re-deposited from another site. Shell taxonomic analysis is based on the assumption that the dead shell organisms identified were originally from the study site and not brought in from elsewhere, keeping in mind the high incidence of waves bringing in materials from the nearby coral reef to the palaeolagoon during times of high sea level and storminess. Materials may also get transferred to and from the site by organisms living in the area at the time of sediment deposition that could influence the results. For instance, hermit crabs occupy abandoned gastropod shells and they could have carried the marine shells in and around the area. These assumptions are taken into consideration when interpreting the data.

Generally it was easier to work with whole shells than shell fragments where one whole shell represented one organism. Shell fragments were the broken pieces of shells that could belong to one or more organisms that could be a result of the organisms getting crushed or broken down by processes such as waves (during the time of high water energy) and sedimentation. The tides moving in and out of the palaeolagoon (tidal change) can break shells by shifting them along the intertidal flat. Thin shells are more vulnerable to fragment as the waves smash the shells against rocks, coral pieces, seafloor, and other organisms. As new sediments get deposited on top of the older ones, the weight of the sediments and weathering processes on the surface at the time of deposition crush the shells beneath it.

The materials >2 mm in diameter were easily distinguished and categorized as whole shells, shell fragments, coral fragments, limestone (bedrock), unidentified organic remains, and materials that could not be identified. Each category of particle was weighed to determine the percentage of different materials in each sediment sample. Stereomicroscopic (dissecting microscope) observation was carried on the whole shells to distinguish their features and identify them according to their taxonomic

48 levels. A stereomicroscope allows a three-dimensional visualization of the shells making it easier to study the finer surface markings on the shells. The shells were named according to the family and genus where possible.

The data collected was entered into a spreadsheet by core depth and number of species identified at each depth that was converted into a dendrogram using the Primer 5 software. The dendrogram was used to represent the shell taxonomy data as the branches are illustrated in a hierarchy of categories based on degree of similarity or number of shared characteristics of between the species (Figure 5.5) and samples (Figure 5.7) (Nonlinear Dynamics 2010). The dendrogram of the shells identified in the sediment core is plotted as a tree branch where each of the species is represented as nodes. The software transforms the data was by log n + 1 before multi dimensional scaling was used to detect the patterns in the results of the species present at different depths that is able to link the identified species either directly or indirectly, and either vertically or horizontally as is discussed in Section 5.1.2.

IV. Problems Encountered with Physical Sediment Analysis

Physical sediment analysis, particularly the determination of colour and measurement of sediment texture by feel, could be biased in terms of the procedure if carried out by just one individual. The determination of colour and texture by feel was therefore performed in replicates with the help of two colleagues to compare the results and determine the most commonly occurring colour notation/texture for each sample.

Wet sieving is a time-consuming procedure, especially for the clay sediments (Samples 25 to 60). Clay particles are very fine and flocculate when wet making it difficult for individual particles to pass through the 63 μm sieve. It was noted that wet sieving the sand fraction of Samples 1 to 23 was comparatively easy since samples were of a sandy texture. Particles were also lost due to spillage when transferring each separated particle fraction from one basin into another during wet sieving. While oven-drying, some of the mud particles stuck to the aluminium foil

49 they were dried on, thus lower amount of mud fraction for each sediment fraction was obtained.

Once sieved, the clay fraction for the top 1.9 m of samples did not settle even after leaving the suspension undisturbed for 2 days. This was due to the electrostatic repulsion of the clay particles that remained dispersed in the suspension. Clay particles have a negative electrical charge hence they tend to repel each other. The positively charged molecules (cations) such as sodium (Na), potassium (K), magnesium (Mg), and calcium (Ca) make clay particles stick together or flocculate. These cations occur naturally in soil therefore allowing for bonding between clay particles. To make the clay particles settle for these samples, approximately 10 grams of sodium chloride (NaCl) was added to the suspension and stirred. The NaCl initiated the electrostatic attraction of the clay particles thus allowing the particles to settle in the suspension.

Another problem was while wet sieving, some of the whole shells could have broken into pieces particularly when the particles were sifted with fingers and toothbrushe. Therefore, while wet sieving extra caution was taken, and where possible samples were just sieved under water and touched only occasionally.

4.3.2. Chemical Composition and Analysis

I. Loss-On-Ignition

The determination of the percentage organic matter and carbonate content in sediments by means of loss-on-ignition is based on sequential heating of the samples in a muffle furnace at 550°C and 950°C respectively. The LOI method was proposed initially by Dean (1974).

LOI was performed for every 10 cm sample. About 30 g of sediment was taken out of the sample bags and air-dried for two days. Particles tend to stick together as they lose moisture, therefore coagulated and hardened masses of sediments were disintegrated using a mortar and pestle to increase the surface area for maximum

50 combustion of the organic and carbonate matter. An empty clean dry ceramic crucible (M1) was weighed on an analytical balance, 5 g of the disintegrated sample was added to the crucible and the mass was recorded (M2). The sample and crucible were oven-dried for twenty-four hours at 100°C to remove excess moisture. The crucible and sample were removed after twenty-four hours, cooled in a dessicator, and re-weighed (M3). The weight difference (M4) before and after heating was the amount of excess moisture in the sediment sample. The sample and crucible were further heated in the Muffle Furnace to determine the organic and carbonate content in each sediment sample discussed individually below.

A. Organic Content

The crucibles containing the oven-dried samples were heated in a Muffle Furnace at 550°C for four hours. After four hours, the sample and crucible were allowed to cool for 10 minutes in the furnace, removed carefully and further cooled to room temperature in a dessicator, and re-weighed (M5). The weight difference between the oven-dried samples and furnace-ashed samples at 550°C was the amount of organic matter burnt (M6). The calculations are provided in Figure 4.11.

B. Carbonate Content

The crucible and samples were further heated for another two hours in the Muffle Furnace at 950 °C. After two hours the furnace was turned off and the crucible was allowed to cool for 10 minutes. The crucible was removed from the furnace, further cooled in a dessicator, and re-weighed (M7). The weight difference between furnace- ashed samples at 550°C and furnace-ashed samples at 950°C is the amount of carbonate content burnt (M8). The calculations are provided in Figure 4.11.

51 i. Mass of Excess Moisture

͇ͨ Ɣ͇͇ͧͦ ii. Mass of Organic Material(OM)

͇ͪ Ɣ͇͇ͧͩ iii. Percentage Organic Matter

͇ͩ $͉͇ Ɣ SRR$ Ɛ ͇͇ͦͥ iv. Mass of Carbonate Content (CC)

͇ͬ Ɣ͇͇ͩͫ v. Percentage Carbonate Content

͇ͬ $̽̽ Ɣ SRR$ Ɛ ͇ͦ ͇ͥ Figure 4.11. The equations used to calculate the percentage of organic and carbonate content for each sediment sample using loss-on-ignition.

II. Radiocarbon Dating

Radiocarbon dating uses the naturally occurring radioisotope carbon-14 (14C) to estimate the age of organic remains in a sample. 14C is an unstable isotope in the biosphere that is produced in the upper atmosphere by phenomena such as storms. It remains incorporated with atmospheric carbon dioxide (CO2) and enters plants and animals through photosynthesis and the food chain. As plants die or they are consumed by other organisms, the 14C fraction of this organic material declines at a fixed exponential rate due to the radioactive decay of 14C. Comparing the remaining 14C fraction of a sample to that expected from atmospheric 14C allows the age of the sample to be estimated (Balme and Paterson 2006).

The Accelerator Mass Spectroscopy (AMS) dating method was used to date the sediment samples since they were tested to contain low quantity of organic material in the samples. The AMS dating allows small amount of organics in samples (less than 5 g) to be dated. Radiocarbon measurements reported in terms of years Before Present (BP) is calibrated to give the dates as cal BP or cal BC (also known as B.C.E. or Before Common Era) discussed below.

The dating process involves a series of steps from sample selection and submission, to sample pre-treatment and dating, and radiocarbon calibration.

A. Sampling for Radiocarbon Dating

Four sets of samples from different depths were sent to the Radiocarbon Dating Laboratory at the University of Waikato, New Zealand. These four samples were selected according to their depths and composition, illustrated in Figure 4.12: one sample from the top of the core, one from the bottom, and two from the middle. Sediment deposition occurred from the oldest (bottom samples) to the most recent (the top samples). The middle samples were taken for the age of the deposits before and after the transition phase (sand to clay) to identify the approximate time of this major environmental change in the Bourewa palaeolagoon.

Surface

60 cm

210 cm

270 cm

600 cm Figure 4.12. The sections of the 6 metre sediment core indicating the depths from which samples were selected for radiocarbon dating.

The top 50 cm of the soil profile had been disturbed by previous human activities (particularly shallow ploughing) and is still being disturbed and mixed by the land crabs that burrow through it. Hence the top sample was from 60 cm depth. A sedimentary transition (sandy to clayey sediments) was noted at a depth of 2.3 m and 2.6 m, thus samples at depths 2.1 m and 2.7 m were chosen for dating to get the dates before and after the transition phase.

Approximately 120 g of the moist field samples 6, 21, 27, and 60 were spread out on a tray lined with aluminium foil and air-dried for five days. Each sample was shuffled periodically with gloved fingers to allow maximum drying of the particles. Upon drying, approximately 100 g of each of the sample was bagged in clearly labelled polythene sampling bags and mailed to the Waikato Radiocarbon Dating Laboratory.

B. Sample Pre-Treatment for AMS Dating at the Waikato Radiocarbon Dating Laboratory

The following information is paraphrased from the University of Waikato Radiocarbon Dating Laboratory website (www.radiocarbondating.com).

Radiocarbon dating was performed on the soil organics in each sample to obtain the approximate time of sediment deposition. Sample pre-treatment involved the removal of non-contemporaneous material (visible shells, root and wood fragments) from the soil sample in order to get a single date. One of the indiscernible non- contemporaneous materials was carbonate that was absorbed in small amounts in soil samples from percolating groundwater that easily affects the age of the samples therefore, carbonate was eliminated from the sediment before dating. This was done by heating the sample with dilute 10% hydrochloric acid (HCl) for approximately one hour. The suspension was vacuum-filtered to separate the acid-insoluble and acid-soluble fraction. The acid-soluble fraction was the carbonate contaminants that was not used for dating and discarded. The acid-insoluble fraction was the original, pristine sample, minus the carbonate contaminants.

The next step was the removal of humic acid contamination from the soils in the acid-insoluble fraction that was not removed by HCl. Humic acids are the decay products of biological materials deposited in the surrounding area of the sample matrix affects the age determination. The humic fraction is acid insoluble and is removed using a base extraction method with 1% hot sodium hydroxide (NaOH). After separation, the base soluble fraction was discarded, and the base insoluble fraction was further treated with dilute 10% HCl, rinsed with distilled water and dried in the oven. The final insoluble fraction obtained contained the sample minus the humic-acid contaminant that is the dateable component.

C. AMS Dating

The following information is paraphrased from online information at the Oxford Radiocarbon Accelerator Unit and the Waikato Radiocarbon Dating Laboratory.

AMS dating was performed by converting the atoms in the pre-treated sample (obtained in Part B) into a beam of fast moving ions (charged atoms). The mass of the charged atoms was measured by the application of magnetic and electric fields. After chemical pre-treatment, the samples were burnt to produce carbon dioxide

(CO2) and nitrogen gas. A small amount of these gases was passed into a mass spectrometer where the stable isotope ratios of carbon and nitrogen were measured. In most cases, these ratios provide useful information on the purity of the sample and clues about the diet and climatic conditions of the living organism; however, this was not relevant to the dates that were determined. The sample was then put into the ion source as CO2, ionised by bombarding it with caesium ions, and then focused into a fast-moving beam (energy typically at 25 keV).

Two magnets inside the spectrometer were used to separate the ions. The first magnet was used to select ions of mass 14 (this includes large numbers of 12CH2- and 13CH- ions and a very few 14C- ions). As they travel to the terminal (which is at about 2 MV), all of the molecular ions are broken up and most of the carbon ions have one of their four electrons removed making them C3+ ions. The second magnet selects

55 ions with the momentum expected of 14C ions and a Wien filter checks that their velocity is correct. Finally, the filtered 14C ions enter the detector where their velocity and energy are checked so that the number of 14C ions in the sample can be counted. This gives the conventional radiocarbon age.

D. Radiocarbon Calibration

The following information is reviewed from online information at the Oxford Radiocarbon Accelerator Unit. Radiocarbon calibration is needed on the conventional radiocarbon measurements since they are not true calendar ages. The true (correct) age involve the assumption that the atmospheric radiocarbon concentration has always been the same as it was in 1950. The reason for this is that 1950s was the decade when the testing of thermonuclear weapons injected large amounts of artificial radiocarbon into the atmosphere that affects the radiocarbon dates. For that reason, the age is calculated on the simplistic assumption that the amount of radiocarbon in the atmosphere has always been the same as before AD 1950.

Calibration is performed by comparing the conventional radiocarbon ages of the sample to those made on material (usually tree rings) of known calendar age. Many trees lay down one ring every year that remain the same/unchanged for the duration of the trees existence that have a valuable record of the radiocarbon concentration in the past. For instance, a tree that is 500 years old can be used to measure the radiocarbon in the 500 rings corresponding to each calendar year. Also tree ring widths vary from year to year with changing weather patterns from where it is possible to compare the tree rings in a dead tree to those in a tree that is still growing in the same region. This comparison allows one to determine the possible calendar age of the sample. There are two methods of calculating age ranges from the calibration curve. The first is the intercept method (not used here) that is done by drawing intercepts on a graph. These will be the years in which the radiocarbon concentration of tree rings is within two standard deviations of the measurement (for example between 2940 BP and 3060 BP for the measurement 3000 ± 30BP).

The second is the probability method that was used to calibrate the conventional radiocarbon age obtained for the palaeolagoon sediment samples. Due to the calculation complexity, the probability method requires the use of a computer software known as the OxCal program to calibrate the dates. This software gives a time range with a 95% certainty (McCormac et al. 2004; OxCal v3.10 Bronk Ramsey 2005). The probability method of calibration is explained using one of the sediment dates from the Waikato Radiocarbon Dating Laboratory as an example. The conventional date of the samples is expressed as a graph using the OxCal program. The graph in Figure 4.13 shows the probability curve for Sample Number 21 (depth of 210 cm). The results show the conventional radiocarbon age of 4148 ± 30 BP is calibrated.

Figure 4.13. The calibration graph of Sample No. 21 (depth of 210 cm) is shown as an example.

The left-hand axis shows radiocarbon concentration expressed in years `before present' and the bottom axis shows calendar years (derived from the tree ring data).

The pair of blue curves shows the radiocarbon measurements on the tree rings (plus and minus one standard deviation) and the red curve on the left indicates the radiocarbon concentration in the sample. The black histogram shows possible ages for the sample (the higher the histogram the more probable that age was). The results of calibration are given as an age range at a probability of 95.4% indicating that the sample came from between 4820 cal BP and 4440 cal BP (the highest and the lowest values for the 95.4% probability). In order to get dates in cal BC that is the true calendar age, the age in cal BP is subtracted with 1950. The answer gives the age range between 2870 cal BC and 2490 cal BC that is the calibrated date of the organics at sample depth of 210 cm. the calibration graph for the remaining three samples is given in Appendix 5.1.

The palaeoenvironmental reconstruction of the Bourewa palaeolagoon is based on the vertical changes observed in the sediment core stratigraphy. The physical and chemical laboratory investigation of the 6 m sediment core as discussed in the previous chapter helps refine a sediment core stratigraphy that is used to determine the extent of environmental changes over time for southwest Viti Levu.

The results and interpretation of the sediment core analysis are presented in this chapter as follows:

1. The results obtained from the physical analysis of sediments, the colour and texture readings of the sediment core profile, and the species diversity. 2. The results obtained from chemical sediment analysis. The sediment organic and carbonate content throughout the core profile and the time of sediment deposition from radiocarbon dates.

5.1. PHYSICAL COMPOSITION

5.1.1. Sediment Colour and Texture

The colour and texture readings reveal that the composition of sediments is not consistent throughout the 6 m sediment core. Sediment colour and texture varied along the core profile in alternating layers from the most recent (surface) to the oldest (6 m deep). This data was used to reconstruct the colour and texture stratigraphy of the sediment core as illustrated in Figure 5.1. The stratigraphy chart, from the surface to the bottom of the core shows that the top 40 cm samples are dark grey sandy loam sediments. In the following layer, 40 cm to 80 cm, sediments were

COLOUR TEXTURE Surface Surface

Very dark grey

Sandy Loam 40 cm

Very dark greyish 60 cm brown Sandy Clay 80 cm 80 cm Dark greyish 100 cm brown Very dark greyish 120 cm brown Sandy Loam

Dark grey 170 cm 170 cm

Sandy Clay Grey Loam 210 cm 210 cm

Light olive brown Sandy Clay to olive brown 260 cm 260 cm

Dark yellowish Clay to silty clay brown

600 cm 600 cm

Figure 5.1. Core colour and texture profile. The full colour versus texture data is tabulated in Appendix 1.5.

60 very dark greyish brown with a sandy loam to sandy clay texture (60 cm to 80 cm). At 80 cm the sediments were mainly sandy loam in texture until 170 cm with three colour variations, dark greyish brown (80 cm to 100 cm), very dark greyish brown (100 cm to 120 cm), and dark grey sediments (120 cm to 170 cm).

A change in both colour and texture was noted at a depth of 170 cm to grey sediments that was of a sandy clay loam texture. Following that there was a colour transition to light olive brown sandy clay sediments at depths of 210 cm to 260 cm. The final set of colour and texture of the core was of a consistent dark yellowish brown with clay to silty clay texture (260 cm to 600 cm). The replicate colour and texture reading of each sediment sample is presented in Appendix 1.1 and 1.2, respectively.

The particle-size distribution is the key factor for determining the final texture of each sample. The particle distribution separated the materials >2 mm, <2 mm >63 μm (sand fraction), and <63 μm (mud fraction) that was used to determine the final texture of each sediment sample. The percentage of materials >2 mm, sand fraction, and mud fraction is given in Appendix 1.3. The percentage of sand and mud fraction was applied to the soil texture triangle (Figure 4.8) to assess the descriptive texture. The result of the final texture readings are presented in Appendix 1.4. For simplistic understanding of the particle-size distribution data throughout the core profile, the average of every 50 cm sample is illustrated in a bar graph shown in Figure 5.2.

At the depth of 260 cm, the clay percent was >75% hence the texture was mainly clay. Colour and texture data reveal two transition phases within the sediment core. The first change occurred at 170 cm and the second at 210 cm. These two sediment depths showed a major shift in both the sediment colour and texture, most notably at 210 cm, discussed in greater detail later in Section 5.2.2.

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Figure 5.2. Bar graph representing the average particle-size distribution for every 50 cm section of the core.

5.1.2. Particles >2 mm

I. Material distribution in sediments >2 mm

The particles >2 mm separated by wet sieving were classified as whole shells, shell fragments, coral fragments, limestone, rocks, and unidentified materials. The percentage of each group of materials in each sample is represented in Appendix 2.1. Similar to particle-size distribution, the average percentage of materials is represented for every 50 cm sediment sample and illustrated as a bar graph in Figure 5.3.

Results show that the highest percentage of materials throughout the sediment core comprised of shell fragments (Picture A, Appendix 3) and the lowest percentage comprised of rocks and whole shells. The highest percentage of materials comprised

62 of limestone for the top 170 cm of the core profile, while shell fragments were more in abundance at depths 180 cm to 550 cm. The bottom 50 cm was more limestone (Picture D, Appendix 3) than any other material most probably due to limestone bedrock of the Rove Peninsula.

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Figure 5.3. Bar graph showing the percent of average materials >2 mm in diameter for every 50 cm section of the core.

The coral fragments (Picture B, Appendix 3) are typically highly eroded coral pieces and coralline algae. Almost 50% (Appendix 2.1) of the materials observed at depths 40 cm and 450 cm were coral fragments. The coral fragments identified were not named since the occurrence of corals is typical of marine origin and difficult to name due to it being highly weathered. Mainly cemented beachrock, lithified shell fragments, coral fragments and sand particles (Picture C, Appendix 3) was observed at depths 40 cm to 440 cm (Figure 5.3). The carbonate-rich materials of the beachrock reacted highly with hydrochloric acid proving that they were of a marine origin. Beachrocks are composed of calcite that precipitated in shallow seawater 63

(mainly the intertidal zone) through the action of marine organisms and rapid cementation of beach sediments (Allaby and Allaby 2003; Nunn 1994) was common in the top 30 cm and at core depths 450 cm to 590 cm.

The granule-sized (2 to 4 mm) and pebble-sized (4 to 64 mm) volcanic rocks in the sediments were highly eroded and difficult to identify. However, they were well- rounded which indicates they had been transported by running water from inland as they were incorporated with the sediments in the Bourewa palaeolagoon. Pieces of pumice, 2 mm to 5 mm in diameter, were found at sample depths 20 cm to 50 cm, 70 cm, 90 cm, 120 cm, and 380 cm. Shark teeth (Picture G, Appendix 3) were found at the depths 190 cm and 490 cm and were most likely carried to the palaeolagoon with the tides.

II. Shell Taxonomy

The depositional environment of sediments explains the type of organisms found in particular sediment layers. Conversely, shell taxonomy (classification) was used to interpret the environmental conditions of the palaeolagoon. Together with whole shells, another group of calcareous material abundant in the sediment core categorised was foraminifera (Picture I, Appendix 3). The total species count is presented in Appendix 2.2. Foraminifera (Picture H, Appendix 3) are single-celled protists that are made up of calcium carbonate shells. They are found at all sea depths and can tolerate a range of salinity, temperature and light conditions in the marine environment. They are primarily marine-dwelling organisms but can also survive in brackish water conditions (Korsun et al. 2001).

The total species count (shells and foraminifera) (Figure 5.4) shows that more foraminifera was present at those depths that had high shell organism numbers however, this was not the case throughout the core. At depths 400 and 500 cm, the shell count was high for this phase however, the foraminifera count remained low. This could have been small, short-lived marine incursions (times of storminess) when waves would have carried marine organisms into the palaeolagoon. The highest number of foraminifera was noted at the depth of 180 cm, which comprised

64 of 19 foraminifera organisms and 88 whole shells. However, the highest number of shells was found at the depth of 190 cm (133 species). The total species and foraminifera species count was halved for samples at depths 120 cm to 140 cm, 140 cm to 160 cm, and 210 cm since 20 cm samples were collected at these depths. For colour, texture, organic and carbonate content analysis, and radiocarbon dating, the 20 cm samples at these depths were treated as one sample.

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110

180

240

290

340 390

440

490

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Figure 5.4. The number of shells and foraminifera found in every sediment sample.

A total of 39 different shell species was identified throughout the core column. The species diversity was treated using the species cluster method. The result of the

65 application of the clustering technique is represented as a dendrogram (Figure 5.5). The species data was treated with a logarithmic transformation before plotting the dendrogram to see the relationship between each species clearly. Figure 5.5 shows one huge cluster of species, all linked/connected to each other. A closer look shows five sub-clusters within the major cluster. These five sub-clusters are of the species Nassarius sp., and Cerithium sp. both on their own and separate from the other species. The third sub-cluster is Atys sp., Tellina sp., Polinices sp. and Turbo sp., showing that these four species are closely related to each other. The fourth sub- cluster was of Neritina sp., Barbatia sp. and Strombus sp., and the fifth sub-cluster is collective of the remaining species.

Figure 5.5. Species cluster for the sediment core illustrating the relationship between the different shell species identified.

Total species count, Appendix 2.3 shows that the most common and abundant species throughout the core profile is Nassarius sp. followed by Cerithium sp. The high species count of these two species could be the reason why they are distinct and separate from the rest of the species. Another reason for their apparent abundance is that these species occur throughout the sediment profile (Figure 5.6).

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Figure 5.6. Average percentage of the two most abundant species throughout the sediment core in relation to the other species for every 50 cm sample.

The names of all shells identified and their place of habitat is provided in Appendix 2.3 and summarised in Table 5.1. Nassarius sp. (Picture E, Appendix 3) is a mud dwelling scavenger found mainly in the mudflat area and in the intertidal zone. Cerithium sp. (Picture F, Appendix 3) is a shallow water marine organism that lives in the intertidal zone. Organisms such as Cerithium sp., Peristernia sp., and Pyramidella sp. are shallow marine dwellers that are plentiful in the top 3 m of the sediment core. The most common moon snail species was Polinices sp. which resides on sandy seafloors of the intertidal zone. The layers with the highest percentage of shell fragments (57-60%) was from 180 cm to 210 cm core depth

(Figure 5.3) which also had the highest diversity of shallow water marine species, suggesting a marine incursion (seawater) into the palaeolagoon.

Table 5.1. Species habitat in order of abundance across the table throughout the core profile. Refer to Appendix 2.3 for specific numbers. Habitat Species Nassarius sp. Cerithium sp. Tellina sp. Polinices sp. Neverita sp. Natica sp. Atys sp. Fragum sp. Peristernia sp. Nerita sp. Patelloida sp. Ostreidae sp. Shallow water, sandy sea floor, Littorina sp. Strombus sp. Mitra sp. intertidal, sub tidal, dead coral or Pyramidella sp. Barbatia sp. Rissoina sp. rocks in shallow water Pupa sp. Periglypta sp. Epitonium sp. Tectus sp. Marginella sp. Fasciolaria sp. Anadara sp. Chama sp. Codakia sp. Dendropoma sp. Gafrarium sp. Murex sp. Oliva sp. Turbo sp. Barbatia sp. Arca sp. Reefs Pleuroploca sp. Conus sp. Angaria sp. Clavus sp. Mudflat Nassarius sp. Modiolus sp. Acteon sp. Mangroves Littorina sp. Cassidula sp. Freshwater Nerita sp. Patelloida sp. Neritina sp.

The initial study of the types of shallow water marine organisms around the Fiji was carried out by Morton and Raj (1980) to identify the different shell species present along Fiji’s coastline. Mudflat surveys conducted by Mr Johnson Seeto as part of a field survey for undergraduate students around the University of the South Pacific Marine Campus shoreline at Suva Point in Fiji revealed that Nassarius sp. and Cerithium sp. are the most common species in the mudflat zone. The shoreline and backshore area contain abundant surface-dwelling gastropods like moon shells, Nassarius sp. and Cerithium sp., and bivalves like Tellina sp. The occurrence of these species in the sediment samples indicate that the current mudflat shoreline around the University of the South Pacific’s Marine Campus could be similar to the

69 environmental condition of the Bourewa palaeolagoon at the time when these species existed.

Other common shells identified were Littorina sp. (periwinkles), Patelloida sp. (limpets), Nerita sp., and Gafrarium sp. Gastropods such as Turbo sp., Clavus sp., Angaria sp., Conus sp. and Pleuroploca sp., and bivalves Barbatia sp. and Arca sp. are reef organisms and also exist in areas adjacent to coral reefs. These organisms were dominant in the top 280 cm of the sediment profile, the first transition layer of the core profile. Two mangrove shell species were also identified, Littorina sp. and Cassidula sp.

Species such as Nerita sp., Patelloida sp., and Neritina sp. can be classified as both intertidal and freshwater organisms since they can survive in both environmental conditions. It is important to state that these organisms could have been introduced to the Bourewa palaeolagoon sediments from elsewhere even though there is currently no freshwater supply around the area. The only source of freshwater around the Rove Peninsula is the Tuva River, the mouth of which is presently about 1.5 km from Bourewa Beach. However, 3000 years ago (Figure 3.4B) the Tuva River estuary would have contributed freshwater and terrestrial sediments around the Bourewa area (Vusama Island) as sea level was 1.5 m higher that present day and much of the land was submerged under sea water.

The possibility of land snails in the surface to 1 m deep sediments could have colonized the area after it became terrestrial or they could have been washed into the palaeolagoon during times of flooding. A land snail identified at 170 cm core depth in the upper transition phase could have been washed into the area with heavy rainfall and sedimentation.

The sample cluster (not treated with logarithmic transformation) of the core profile reveals that sample depths are closely related to each other in terms of the species count and abundance. The sample dendrogram in Figure 5.7 shows five sub-clusters. PL1 is same as Sample Number 1 therefore; the first sub-cluster is of samples 19, 20 and 21 which are closely related to samples 17, 18, 23, and 24. The second sub- cluster is of samples 26 and 40 which are very close to samples 14, 16 and 25. The

Figure 5.7. Sample cluster illustrating the relationship between each 10 cm sediment sample. (PL – palaeolagoon)

71 third sub-cluster is of samples 11, 12, 27 and 50, and the fifth sub-cluster is the rest of the sample. The distinct sub-clusters are represented as the total number of species and the total number of Nassarius sp. at each depth because it is the most common species in the sediment core profile. Therefore the sample cluster relates to Nassarius sp. when creating the sample sub-clusters. The sub-clusters can be compared with the species count for every 10 cm sediment sample given in Appendix 2.2.

5.2. CHEMICAL COMPOSITION

5.2.1. Organic and Carbonate Content of the Sediment Core

The Earth’s surface accumulates sediments over time that is either of a terrestrial origin (land deposit) or of a marine origin (ocean deposit). Terrigenous deposits contain organic matter from decaying plants and animals as well as from the living organisms in an environment. Marine deposits, on the other hand, have high carbonate content. Results presented as a line graph in Figure 8.5 show that from the surface to a depth of 260 cm, the percentage of carbonate in the sediments is greater than that of organic matter. At the depth of 260 cm, there is a transition; the amount of organic matter becomes greater than the carbonate content till 580 cm.

The line graph (can be correlated to the percentage values of organic and carbonate content given in Appendix 4.2) show the inverse relationship between organic and carbonate content throughout the sediment profile. High percentage of organic content in sediments could be due to terrestrial deposition whereas high percentage of carbonate content probably reflects marine deposition associated with high sea- level or island subsidence. The current average elevation of the Bourewa palaeolagoon is about 1.5 m above mean sea level. It is covered with trees and shrubs that contribute to the soil organic matter. The occurrence of soil organic matter throughout the sediment core is interpreted as of terrestrial organic derivation. Carbonates in sediments come from dead marine organisms and coral reefs that are calcium carbonate (CaCO3). Therefore, the organic versus carbonate percentage can be a relative indicator of terrestrial versus marine inputs to the palaeolagoon. Palaeoenvironmental reconstruction of the study area does suggest an elongated sand

72 spit formerly partly enclosing a tidal inlet, the Bourewa palaeolagoon (Nunn 2007b). The tidal inlet existeed and the high carbonate content suggests a time of high sea level conceivable from the sharp increase in carbonate content at the depth of 260 cm.

Figure 5.8. Graph of organic content and carbonate content with depth.

At the core depth of 580 cm, another transition (change) between organic and carbonate content was noted. At 580 cm the carbonate content is greater than the organic. One possibility for this shift is that it is an experimental error because such a sharp change from high organic content to greater carbonate content is not plausible. Another possibility could be the influence of the carbonate-rich limestone bedrock (Picture G, Appendix 3) encountered at 6 m. The ancient carbonates in sedimentary rocks are dominantly calcite and dolomite that are CaCO3 minerals. Dissolved in the sediments at 580 cm and 590 cm, these minerals would give a high percent of carbonate content to organic.

5.2.2. Radiocarbon Dating

The radiocarbon dates obtained from the Waikato Radiocarbon Dating Laboratory showed that the core profile dates as far back as 11473 ± 37 BP (11550 – 11390 cal BP). This period marks the end of the Last Glacial and the beginning of the Holocene Interglacial. Table 5.2 gives the radiocarbon dates obtained for samples at core depths 60 cm, 210 cm, 270 cm, and 600 cm.

Table 5.2. All radiocarbon dates for the palaeolagoon sediment core. Dates from youngest to oldest (surface dates to the deepest). All dates were provided by the University of Waikato Dating Laboratory, calibrated using the Southern Hemispheric Atmospheric Dating Data from McCormac et al. (2004) and OxCal v3.10 Bronk Ramsey (2005). Conventional Calibrated Sample Depth Laboratory Sample 13 C Radiocarbon Radiocarbon Calendar Age Number (cm) Number Material Age (BP) Age (cal BP) Soil, 6 60 Wk-25329 -18.3 290 ± 30 450 – 150 AD 1500 – AD 1800 organics Soil, 21 210 Wk-25330 -26.9 4148 ± 30 4820 – 4440 2870 – 2490 BC organics Soil, 27 270 Wk-25332 -22.0 7892 ± 30 8770 – 8540 6820 – 6590 BC organics Soil, 60 600 Wk-25331 -22.6 11473 ± 37 11550 – 11390 9600 – 9440 BC organics

The organics at 270 cm deposited between 8770 – 8540 cal BP, at 210 cm the sediments dated from 4820 – 4440 cal BP, and the most recent sedimentation from 450 – 150 cal BP at the depth 60 cm. An average of the calibrated dates for each depth was used to calculate the dates for each 10 cm interval sample. These four radiocarbon dates were used to determine the median age of each 10 cm sediment sample (Appendix 5.2) and plotted into a line graph as represented in Figure 5.9.

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Figure 5.9. The age of sediments for every 10 cm sediment sample in cal BP determined from the four ages obtained. The four phases of sediment deposition are marked with regards to age and depth.

All of the results, the physical composition (colour, texture, and shell taxonomy), chemical (organic and carbonate) composition, and date of each sediment sample was plotted side-by-side, Figure 10. The trends in the physical and chemical data when correlated revealed four distinct environmental change in the palaeolagoon sedimentation since the Last Glacial.

5.3. PALAEOLAGOON DEPOSITION PHASES

Phase 1, dark yellowish brown silty clay/clay sediments (Figure 5.10A), 600 cm to 260 cm, contained relatively low numbers of (or no) organisms (Figure 5.10B and C), and more organic matter than carbonates except for the bottom 20 cm (580 cm and 590 cm) (Figure 5.10D and Figure 5.11). Sediments date from 11,470 cal BP to 7900 cal BP. This period marks the end of the Last Glacial and the Early Holocene over a period of approximately 3500 years when 340 cm thick sediment deposited at a rate of 97 cm/1000 year (Figure 5.11) with no discernible physical or chemical change however, sedimentation was comparatively rapid possibly due to wetter climatic conditions. The high precipitation rate could have caused erosion and the washing down of sediments from high altitudes to the site. The Bourewa palaeolagoon was dry land at this time.

Phase 2, 260 cm to 210 cm, is composed of olive brown sediments that have a sandy clay texture (Figure 5.10A), fewer shells compared to the overlying layer of sediments, and dates from approximately 7900 cal BP to 4600 cal BP. The 50 cm thick sample of Phase 2 deposition occurred over a period of 3300 years at a rate of 15 cm/1000 year that is much slower than Phase 1. This could possibly be due to climate stability at the time of Holocene Climate Optimum. During this time (approximately 7900 cal BP) is when sea water first entered the Bourewa palaeolagoon inferred from the introduction of sand to the deposit, the sharp rise in marine shell and foraminiferal inclusions, and the rapid rise in carbonates. The transition phase specifically noted at a depth of 260 cm (see Figure 5.8 and 5.11).

Phase 3, 210 cm to 170 cm, marks the only occurrence for the sediment core that is composed of grey sandy clay loam sediments that dates from 4600 cal BP to 3400 cal

C. Foraminifera D. Organic and Carbonate A. Stratigraphy B. Shell counts counts Percentages

Phase 4

Phase 4(i)

Phase 3

Phase 2

Phase 1

Figure 5.10. Results of coring. (A) Core stratigraphy showing depths, lithology and interpolated radiocarbon ages. (B) Counts of shells in every 10 cm sample. (C) Foraminifera count in every 10 cm sample. (D) Percentages of organic and carbonate in every 10 cm sample. 77

Terrestrial (P4)

49 cm/1000 years Transitional (P4i)

Marine (P3) 34 cm/1000 years

Transitional (P2) 15 cm/1000 years

Terrestrial (P1) 97 cm/1000 years

0 20 40 60 80 100 120 140 ,-

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Figure 5.11. Each row shows the percent sand and mud particles, and percent organic and carbonate content in each layer together with the rate of sedimentation.

BP. This layer is interpreted as a marine sediment from its distinct lithology, high numbers of shell and foraminifera, and high carbonate (low organic) content. The rate of sedimentation for Phase 3 is about 34 cm/1000 year, 40 cm in thickness that was deposited over a period 1200 years, is layer contains the greatest diversity of intertidal and mudflat species, and foraminifera. Phase 3 is probably when sea level was higher than the current level with a moderate sedimentation rate. The environment was not as stable as that of Phase 2 as it was a (open) coastal embayment. It is plausible to suppose that Phase 3 was deposited when sea level was at its maximum during the Holocene sea-level highstand and a shallow lagoon existed.

The final topmost layer, Phase 4 is from the depth of 170 cm to the surface that is largely similar except for the darker grey colouration and a high percent of sand of Phase 4(i) (shown more clearly in Figure 5.1). This phase lies in close proximity to the time of arrival of the Lapita people, 3050 cal BP (Nunn 2009a) when sea level has begun to fall from its maximum. A probable transition layer (4i), change from 78 marine to terrestrial environment that still has a higher occurrence of shell organisms (5 to 19 species) than the sediments lying above it (Figure 5.10). The rate of sedimentation for Phase 4(i) is around 34 cm/1000 year (same as that of Phase 3) plausible to occasional marine influence till 2000 cal BP (120 cm). The main part of Phase 4 is dated to Late Holocene and has low numbers of shells and foraminifera that suggests a significantly reduced influence from the ocean yet not its total exclusion from palaeolagoon sedimentation. It is likely that sea level at the start of Phase 4 deposition (2025 cal BP) was around 1 m higher than today indicating occasional marine incursions. This interpretation is supported by continuing high level of carbonate sediment and low level of organic sediment.

The results for each layer will be discussed in wider context in the next chapter.

The overall data analysis of the results obtained from the palaeolagoon sediment core allow five major environmental changes associated with the global rise of temperature and sea level since the Last Glacial Maximum to be identified. The environmental conditions noted are plausibly related to the sea-level rise during the Holocene transgression that not only explains the climate regime for the southwest Viti Levu, Fiji Islands but also for a greater part of the Pacific region.

The synopses of the research findings presented in Chapter 5 are reviewed in this chapter as follows:

1. The geochronological framework and relative sea-level change of the Rove- Bourewa area since the end of the Last Glacial. 2. The Holocene palaeogeographical changes around the tidal inlet (palaeolagoon) behind the Bourewa archaeological site that maybe applicable to much of the Pacific Islands and Ocean region.

6.1. GEOCHRONOLOGICAL FRAMEWORK AND SEA LEVEL OVER THE PAST 10,000 YEARS FOR SOUTHWEST VITI LEVU ISLAND

The Holocene Interglacial period began as the Last Glacial ended and ushered in changes in global climate in contrast to the colder temperatures and glacier advances of the earlier period. The warmer climate conditions of the Holocene Interglacial marked a time of optimal temperature, increased precipitation, and higher sea level that led to environmental change. Increased precipitation encouraged sediment accumulation along coastal margins which is evident for the southwest Fiji Islands as construed from the results obtained. The first layer of sediment (Phase 1) on top of

80 the Rove-Bourewa limestone bedrock (was hit at the depth of 600 cm) accumulated around 11,470 cal BP just as temperatures gradually rose after the Last Glacial period.

Sediment stratigraphy provides the chronological order of events for southwest Viti Levu Island. The stratified sediment core reveals a succession of phases which can be interpreted in terms of environmental changes in the Rove-Bourewa area. These four phases correlate with four distinctive environmental conditions, from the oldest (Phase 1) to the youngest (Phase 4) (Figure 6.1) that vary with time from different episodes of deposition. Each of these phases of environmental change is discussed in greater detail in the following sections starting from the oldest sediments to the youngest.

I. Phase 1

The foundation of the Rove-Bourewa area is the Pliocene Cuvu Limestone (Houtz 1959) which is covered with a 6-m sediment deposit. During the Last Glacial when sea level was approximately 130 m below the present level, the limestone bedrock along southwest Viti Levu was emerged. The first layer of yellowish brown sediments accumulated 11,470 cal BP as the Last Glacial ended and the consistent cooler and drier weather conditions started to change. Increasing temperatures and sea level were accompanied by an increased rate of precipitation allowed for rapid sedimentation around the area during the Early Holocene. Sedimentation during this time remained consistent and non-changing for about 3500 years. The events of this time may also have been associated with torrential rain, perhaps during tropical cyclones (Nunn 1999).

The organic-rich yellowish brown clay sediments in Phase 1 (Figure 5.10) has a very high percent of fine particles <63 μm (silt and clay) and therefore must have travelled a long distance from their places of origin to be deposited in the palaeolagoon. Very low shell species count in Phase 1 indicates a time of low sea level (see Figure 5.3) although this may have resulted from the fragmentation of the thinner whole shells as sedimentation increased. Species counts show the abundance

&!6 $ Sea level fall to present level Late Holocene - Mid-Holocene - Marine Terrestrial Lapita occupation at Bourewa ~ 3050 cal BP Sea level falling + 1.5 m

Marine Palaeolagoon Sea level + 2 m around 4000 cal BP

Terrestrial Marine Approaching mid-Holocene highstand -

Terrestrial environment Sea level rise Holocene Interglacial (Early) Precipitation - Temperature 9 -> - -: 8 --? - Last Glacial Figure 6.1. Sediment stratigraphy of the 6 m sediment core.

Species count 0-20 species 20-40 species 40- 60 species 60-80 species 80- >100 species (very low) (low) (moderate) (rich) (very rich)

82 of intertidal Nassarius sp. in this layer even though the land is inferred to have been exposed and not submerged under water as sea-level was low. Also a few reef shells, mangrove and freshwater species as Turbo sp., Littorina sp., Patelloida sp. and Nerita sp., respectively, were also identified in this layer. As species count or classification was based on the assumption that the organisms found in the area are from the site (location) they were found in, this seems invalid for this layer of sedimentation. The relatively low sea level had only began to rise hence the occurrence of these species in the inferred terrestrial sediments suggests they may have been introduced there from younger layers above by the influence of land hermit crabs and other burrowing organisms or could have been brought in during storm surges. The possibility is that hermit crabs could easily have moved these shells from the coast to the exposed dry land and later abandoning them there. The low carbonate content in Phase 1 is possibly due to the paucity of carbonate shell organisms incorporated within these sediments.

A piece of pumice (3 mm in diameter) at a depth of 380 cm was deposited approximately 9500 cal BP and could have originated from volcanic activity in or around the archipelago. Waves can carry these rocks to the shoreline and increased wind activity could have blown pumice rocks inland from the adjacent coastline.

II. Phase 2

A transitional layer of sediments lies between Phase 1 and Phase 3 that accumulated over a period of about 3300 years (Figure 6.1) with a relatively low sediment rate indicating climate stability about 7900 cal BP, the time of Early Holocene when environmental conditions reflected higher global temperatures and the deposition of slightly different types of sediments in relation to Phase 1 sediments. The sedimentation rate was relatively fast for Phase 1 with inferred increasing temperature and precipitation rates and sediment input in and around the coastal margins. The difference between Phase 1 and Phase 2 is quite distinctive in terms of sediment lithology as there is a higher percentage of sand particles and carbonate content in the latter both indicating an increasing marine influence.

The shell diversity in Phase 2 ranges from low to high of predominantly shallow- water marine species; Nassarius sp., Cerithium sp., Polinices sp., and bivalves, Tellina sp. and Fragum sp. and the most common reef species, Turbo sp. at sediment depth of 240 cm. Also common were the two freshwater species, Patelloida sp. and Neritina sp. that may have been introduced during times of flooding from the land. Sandy, carbonate rich sediments with mostly shallow-water marine-shell organisms indicate a time when marine conditions started to have a significant influence on palaeolagoon sedimentation in the Rove-Bourewa area. As Phase 1 sedimentation occurred, the climate and environment was progressing from the Last Glacial towards the Holocene Climate Optimum. This was the condition for most coastal margins around the Pacific as sea level decreased the land mass and the coastline moved further inland. However, during the transition period represented by Phase 2 the Rove-Bourewa area was not fully emergent until about 4600 cal BP when the marine sediments of Phase 3 were deposited.

It is around the Early to Middle Holocene, that coral reef establishment started around many Pacific Islands, hence the occurrence of reef organisms and coral fragments is greater in Phase 2 than Phase 1. Coral reefs bloomed in the company of the Early Holocene sea-level rise as the reef surfaces were able to ‘keep up’ with the rising sea-level till the HCO (around 4500 years ago). In other cases, the reef surface was able to ‘catch up’ only when sea level began falling in the Late Holocene, and in some places reefs had to ‘give up’ trying to grow upwards as sea level rose (Nunn 1994). The exposed reef surface as seen in Figure 3.4 along the Bourewa Beach is an example of ‘keep up’ coral reef that is now exposed as sea level has fallen by about 2 m from its maximum level (Figure 3.4). Therefore, as sea level was increasing for most of Phase 2 sediment deposition, the marine organisms and shell fragments that were deposited could have been introduced to the area during times of storminess and huge tidal activity from the nearby sea-level coral reef.

III. Phase 3

Phase 3 is represented by a 40-cm thick sediment section belonging to the end of Early Holocene to Mid-Holocene. Within the whole of the sediment core, Phase 3 is

84 the most distinct from the rest of the layers and easily identified from the sediment physical characteristics, and the colour. The grey sandy sediments with high carbonate content, high abundance of foraminifera and marine shell species indicate a time when sea level was greatest during the mid-Holocene and the area was a shallow water lagoon. The lagoon was an intertidal zone that was home to the intertidal organisms, most commonly Nassarius sp. and Cerithium sp. Storm surges and high wave activity carried reef Turbo sp. and other deeper sea water organisms into the lagoon.

The greatest abundance of intertidal shell species is concentrated in sediments found at the depth of 190 cm. The sediments from this depth date around 4000 cal BP making it the high point of the Holocene Interglacial. Former studies show that the maximum sea level for the tropical Pacific and most particularly for the Fiji Islands was observed around 4300 BP (Nunn 2007b; Dickinson 2003). This marks the mid- Holocene HCO when sea level was 2 m higher than its present level and the Rove- Bourewa area was fully submerged under sea water. This was the time when molluscs Nassarius sp. and Cerithium sp., and bivalves Tellina sp. flourished for almost 300 years. Shortly after this, sea level gradually declined (3700 cal BP) and the shell species count and diversity decreased.

IV. Phase 4

Post-mid-Holocene sea level began to decline by 3400 cal BP post HCO when sea level had reached 2 m above the present level and the Bourewa tidal inlet existed (Figure 3.7). Human settlement of Pacific Islands followed close on the heels of the mid-Holocene sea-level highstand, as attractive coastal environments evolved; the Lapita occupation of southwest Viti Levu Island occurred as sea level started to decline and was about 1.5 m higher than the present level 3050 years ago (Nunn 2009a, 2007b; Nunn et al. 2006, 2004).

In terms of sediment deposition, the period of Lapita colonisation occurs within the transitional Phase 4(i) (see Figure 6.1). A closer look at the 50-cm section Phase 4(i) (120 cm to 170 cm) shows that it is not very distinct from the rest of Phase 4

85 sediments in terms of sediment texture and chemical composition (organic and carbonate content). However in terms of colour and marine organism diversity, a very clear distinction is noted. This layer is more similar to Phase 3 sediments, suggesting that even as sea level decreased by 0.5 m, the tidal inlet was submerged during high tides and was exposed at low tides. The sediments in this layer accumulated 3400 cal BP to 2000 cal BP and it was around this time that the initial settlers occupied the sand spit along the Bourewa Beach.

For the rest of the sediments from 150 cm to the surface, this is interpreted as a period of gradual sea-level fall to its present level which can be related to the environmental changes of the Late Holocene. From about 3000 years ago to present was when there was net sea-level fall of 1.5 m.

6.2. HOLOCENE PALAEOGEOGRAPHICAL CHANGES IN THE ROVE- BOUREWA AREA

Phase 1 contained high terrestrial clay content as sediments must have travelled a long distance to get deposited in the Rove-Bourewa area, most probably from the surrounding hills. Increased sedimentation resulted from the optimal climatic conditions of the Holocene Interglacial but at this stage it was evident that the sea level had not reached its maximum level during sediment deposition in Phase 1. The change in environmental conditions in the Rove-Bourewa area occurred in the Early to Mid-Holocene when a marine influence was noted in the sediments as a result of rising temperatures and sea level as conditions approached the Early Holocene period.

Both temperature and sea-level optimum conditions are interpreted from increased sand particles, marine species and foraminifera. Lighter coloured sediments correspond to a marine environment that was at its maximum extent 4000 years ago and sea level was some 2 m higher than the present mean sea level. After the HCO, as sea level gradually declined, the Lapita people moved to the site and built their homes on stilt platforms along the sand spit (Figure 3.7).

During this time, west of the sand spit, there was a broad fringing reef while on the east, there was a tidal inlet. Both had a vast variety of food resources that must have appealed to the early settlers. The sea level did not remain consistent and continued to gradually decline till about 1000 cal BP when it reached its present level in the Late Holocene. The environmental conditions switched back to terrestrial conditions but still had marine influence during times of increased wave activity from storm surges and cyclones hence the incidence of sand particles and marine species in the Phase 4 sediments.

The chronology of environmental conditions of the Rove-Bourewa area reconstructed here is applicable to much of the coastal margins in the Pacific Islands and Ocean. This study is one of the first (if not the first of its kind) for a Pacific Island that is important for the development of such records. The slight sea level variation would not have had a major impact on the larger continents but for small island nations, even a small rise or fall in temperature would accompany sea level change and notable change along the coast would affect sedimentation and the livelihood of people living there. For most past of the Early Holocene, the Pacific Islands remained uninhabited until after the Mid-Holocene when sea-level fall occurred during which time they had colonised many of the islands, discussed in Chapters 2 and 3.

The physical and chemical sediment analysis carried out on a 6 m sediment profile from the Rove-Bourewa palaeolagoon proved satisfactory for a palaeogeographical study of the Fiji Islands. The data from this study are used to interpret similar environmental conditions for most part of the Pacific Islands and Ocean. The results correlate with the earlier studies of Holocene sea-level variations carried out elsewhere in the Pacific that provide a broad chronological framework for environmental change (Moriwaki et al. 2006; Nunn 2005; Dickinson 2003; Nunn and Peltier 2001; Pirazzoli 1991).

This chapter is organised as follows:

1. The general conclusion of past environmental study for southwest Viti Levu Island. 2. Suggestions for further palaeoclimatological research.

7.1. CONCLUSION

A 6 m layer of sedimentation occurred on top of the Cuvu Limestone outcrop in the Rove-Bourewa area since the Last Glacial. The organic material dated from the bottom of the core shows that sedimentation began at the end of the Last Glacial period around 11,470 cal BP, just prior to the Holocene Interglacial. Geological studies show that the Cuvu Limestone had formed in the Late Pliocene approximately 3.5 million years ago (Houtz 1959). The chronological order of sediments indicates a change from terrestrial environment in the early part of the

Holocene Interglacial (Early Holocene) to marine conditions (Mid-Holocene) and then back to terrestrial environment (Late Holocene). This order of sedimentation implies a gradual sea-level rise with increasing temperatures and precipitation of the Early Holocene creating a shallow lagoon followed by sea-level fall that dried up this lagoon.

The findings of this study corroborate with the studies done by Prof. Nunn in the area. The relatively high sea level of the HCO and the associated broad ‘keep-up’ fringing reef along the southwest coast of Viti Levu Island, together with the brackish shallow water lagoon system, resulted in the development of the sand barrier. As sea level continued to rise, tides moving in and out of the shallow water lagoon brought in sand and marine debris that built-up over time and formed the sand barrier (Figure 3.7). It is this sand barrier on which the early Lapita people that came into the Fiji Islands and resided in stilt platform houses. Thus the tidal inlet behind the sand barrier is now correctly termed as the brackish water lagoon system that existed when sea level was at its Holocene maximum.

The final major environment shift resulted from the declining sea level from its maximum (+2 m) to the present level at the end of the HCO evident from the exposed fringing reef along the coastline of Bourewa Beach. Sea level was at 1.5 m above present level when the earliest settlers came across the site, the abundance of marine food resources from the fringing reef and the shallow lagoon is thought to be the reason Bourewa Beach was favoured over the other sites in the Rove Peninsula.

During the 600-year occupation at Bourewa, sea level was falling that proposes that the changes in the nature principally lead to a reduction in marine foraging and a need to start horticulture around the area. Hence, the abrupt abandonment of the Bourewa settlement around 2500 cal PB occurred at a time when sea-level fall would have affected fringing-reef resources but also, as the study shows, would have caused coastal-lagoon to have become less extensive than earlier, rendering it unsuitable for either shellfish collection or aroid cultivation. The stages of Rove-Bourewa area relative to the sea level are shown in Figure 7.1. Today the Rove-Bourewa palaeolagoon that sits at an elevation of 2 m above mean sea level.

A B

Figure 7.1. Maps showing the palaeogeography of the Rove-Bourewa area. (A) Geography of the area at the time of first settlement about 2950 BP when sea level was +1.5 m. Adapted from Nunn (2007b). (B) The Bourewa sand ridges on which the Lapita people built stilt platform houses. Adapted from Nunn (2009a). (C) Current setting of the Rove Peninsula. The palaeolagoon is at an elevation of 2 m above mean sea level. Adapted from Nunn (et al. 2006).

7.2. IMPLICATIONS FOR FURTHER RESEARCH

This study reports the results of the first palaeogeographical study for the Fiji Islands that is supported by sediment core analysis. It was carried out in an area where appropriate equipment was not available, difficultly in access, and yet which clearly has great potential. It would be encouraging if more research were carried out in this and similar area. Borehole drilling would for deeper core extraction into the limestone bedrock of the palaeolagoon that could provide palaeoclimatic data prior to the Last Glacial period and even as far back as the beginning of the Quaternary

90 period. This would provide immense climate variation for much of the Pacific where such data is generally lacking. The use of more sophisticated instruments would save time of sediment analysis. For instance, using a particle-size analyser for sediment particle-size distribution.

Similar palaeosea-level research could be carried out at other Lapita sites on Rove Peninsula like Rove Beach, Qoqo Island, and Waikereira and other Lapita sites in Fiji as Yanuca (2825 BP), Ugaga (<2950 BP) and Kulu (>2350 BP), and the Sigatoka sand dunes (2600 BP) (Nunn 2009a). Sediment core analysis from these sites would provide very good palaeoclimatological data in relation to the initial Lapita settlement in Fiji and for most the south Pacific. These data would provide useful substantial data of the Rove-Bourewa area, and add to the palaeogeographic reconstruction of this location to early human settlement in the South Pacific.

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"#M " Appendix 1.1. Field and laboratory Munsell Colour readings for each sediment sample. Munsell Colour in Field Munsell Colour in Laboratory (I) Munsell Colour in Laboratory (II) Mean Munsell Colour Sample Sample Depth Munsell Munsell Munsell Munsell Colour Number (cm) Colour Munsell Colour Colour Munsell Colour Colour Munsell Colour Colour Munsell Colour Notation Notation Notation Notation 1 0-10 5Y 2.5/2 Black 5Y 3/1 Very dark grey 5Y 3/1 Very dark grey 5Y 3/1 very dark grey 2 10-20 2.5Y 5/2 greyish brown 5Y 3/1 Very dark grey 5Y 3/1 Very dark grey 5Y 3/1 very dark grey 3 20-30 2.5Y 3/2 very dark greyish brown 10YR 3/1 very dark grey 10YR 3/1 very dark grey 10YR 3/1 very dark grey 4 30-40 5Y 3/2 dark olive grey 10YR 3/1 very dark grey 10YR 3/1 very dark grey 10YR 3/1 very dark grey 5 40-50 2.5Y 3/2 very dark greyish brown 10YR 3/1 very dark grey 2.5Y 3/2 very dark greyish brown 2.5Y 3/2 very dark greyish brown 6 50-60 2.5Y 3/2 very dark greyish brown 2.5Y 3/2 very dark greyish brown 2.5Y 3/2 very dark greyish brown 2.5Y 3/2 very dark greyish brown 7 60-70 2.5Y 3/2 very dark greyish brown 2.5Y 3/2 very dark greyish brown 2.5Y 3/2 very dark greyish brown 2.5Y 3/2 very dark greyish brown 8 70-80 5Y 4/2 olive grey 10YR 3/2 very dark greyish brown 2.5Y 3/2 very dark greyish brown 2.5Y 3/2 very dark greyish brown 9 80-90 5Y 4/2 olive grey 10YR 4/2 dark greyish brown 2.5Y 4/2 dark greyish brown 2.5Y 4/2 dark greyish brown 10 90-100 5Y 4/2 olive grey 10YR 4/2 dark greyish brown 2.5Y 4/2 dark greyish brown 2.5Y 4/2 dark greyish brown 11 100-110 5Y 4/2 olive grey 2.5Y 4/1 dark grey 2.5Y 3/2 very dark greyish brown 2.5Y 3/2 very dark greyish brown

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12 110-120 5Y 4/2 olive grey 10YR 3/1 very dark grey 2.5Y 3/2 very dark greyish brown 2.5Y 3/2 very dark greyish brown 14 120-140 5Y 4/2 olive grey 10YR 3/2 very dark greyish brown 2.5Y 4/1 dark grey 2.5Y 4/1 dark grey 16 140-160 5Y 5/1 grey 2.5Y 4/1 dark grey 2.5Y 4/1 dark grey 2.5Y 4/1 dark grey 17 160-170 5Y 5/1 grey 2.5Y 4/1 dark grey 5Y 4/1 dark grey 5Y 4/1 dark grey 18 170-180 5Y 5/1 grey 2.5Y 5/1 grey 5Y 5/1 grey 5Y 5/1 grey 19 180-190 5Y 5/1 grey 2.5Y 4/1 dark grey 5Y 5/1 grey 5Y 5/1 grey 20 190-200 5Y 5/1 grey 5Y 5/1 grey 5Y 5/1 grey 5Y 5/1 grey 21 200-210 5Y 5/1 grey 2.5Y 4/1 dark grey 5Y 5/1 grey 5Y 5/1 grey 23 210-230 5Y 5/3 Olive 2.5Y 4/4 olive brown 2.5Y 5/4 light olive brown 2.5Y 5/4 light olive brown 24 230-240 5Y 4/3 Olive 10YR 5/6 yellowish brown 2.5Y 5/4 light olive brown 2.5Y 5/4 light olive brown 25 240-250 2.5Y 4/3 olive brown 2.5Y 4/4 olive brown 2.5Y 4/4 olive brown 2.5Y 4/4 olive brown 26 250-260 2.5Y 4/3 olive brown 2.5Y 5/4 light olive brown 2.5Y 5/4 light olive brown 2.5Y 5/4 light olive brown 27 260-270 2.5Y 4/3 olive brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 28 270-280 2.5Y 4/4 olive brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 29 280-290 2.5Y 4/4 olive brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 30 290-300 10YR 4/4 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 31 300-310 10YR 4/4 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 32 310-320 10YR 4/4 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 33 320-330 10YR 4/4 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 34 330-340 10YR 4/4 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 35 340-350 10YR 4/4 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 36 350-360 10YR 4/4 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 37 360-370 2.5Y 4/4 olive brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 38 370-380 2.5Y 4/4 olive brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown

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39 380-390 2.5Y 4/4 olive brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 40 390-400 10YR 4/4 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 41 400-410 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 42 410-420 10YR 4/4 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 43 420-430 10YR 4/4 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 44 430-440 10YR 4/4 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 45 440-450 10YR 4/4 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 46 450-460 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 47 460-470 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 48 470-480 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 49 480-490 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 50 490-500 10YR 4/4 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 51 500-510 10YR 4/4 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 52 510-520 10YR 4/4 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 53 520-530 10YR 4/3 brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 54 530-540 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 55 540-550 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 56 550-560 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 57 560-570 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 58 570-580 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 59 580-590 10YR 4/3 brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 60 590-600 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown 10YR 4/6 dark yellowish brown

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Appendix 1.2. Sediment texture by feel readings carried out in the field and in the laboratory. Sample Sample Depth Texture i Texture ii Texture iii Number (cm) (in Field) (in Laboratory) (in Laboratory) 1 0-10 sandy loam sandy loam sandy loam 2 10-20 sandy loam sandy loam sandy loam 3 20-30 sandy loam sandy loam sandy loam 4 30-40 sandy loam sandy loam sandy loam 5 40-50 sandy loam sandy clay loam sandy loam 6 50-60 sandy loam sandy loam sandy clay loam 7 60-70 sandy clay sandy clay sandy clay loam 8 70-80 sandy clay sandy clay sandy clay loam 9 80-90 sandy loam sandy clay sandy clay loam 10 90-100 loamy sand sandy clay sandy loam 11 100-110 loamy sand sandy loam sandy loam 12 110-120 sandy loam sandy clay loam sandy loam 14 120-140 loamy sand sandy clay loam sandy loam 16 140-160 loamy sand sandy clay loam sandy loam 17 160-170 loamy sand sandy clay loam sandy loam 18 170-180 loamy sand sandy clay loam sandy loam 19 180-190 sandy loam sandy clay sandy loam 20 190-200 loamy sand sandy clay sandy loam 21 200-210 loamy sand sandy loam sandy loam 23 210-230 sandy clay sandy clay sandy clay 24 230-240 sandy clay sandy clay sandy clay 25 240-250 sandy clay sandy clay silty clay 26 250-260 sandy clay sandy clay silty clay 27 260-270 silty clay clay clay 28 270-280 silty clay clay clay 29 280-290 silty clay clay silty clay 30 290-300 silty clay clay clay 31 300-310 silty clay clay silty clay 32 310-320 silty clay clay silty clay loam 33 320-330 silty clay clay silty clay 34 330-340 silty clay clay silty clay 35 340-350 silty clay sandy clay silty clay

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36 350-360 silty clay clay silty clay 37 360-370 silty clay clay silty clay 38 370-380 silty clay clay silty clay 39 380-390 silty clay clay clay 40 390-400 silty clay clay clay 41 400-410 silty clay silty clay clay 42 410-420 silty clay silty clay silty clay 43 420-430 silty clay silty clay silty clay loam 44 430-440 silty clay clay silty clay loam 45 440-450 silty clay clay silty clay loam 46 450-460 silty clay clay silty clay 47 460-470 silty clay silty clay silty clay 48 470-480 silty clay silty clay silty clay 49 480-490 silty clay clay silty clay 50 490-500 silty clay clay silty clay 51 500-510 silty clay clay silty clay 52 510-520 silty clay clay clay 53 520-530 silty clay clay clay 54 530-540 silty clay clay silty clay 55 540-550 silty clay silty clay clay loam 56 550-560 clay silty clay clay 57 560-570 clay silty clay silty clay 58 570-580 silty clay silty clay clay 59 580-590 sandy clay silty clay clay 60 590-600 clay silty clay clay

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Appendix 1.3. The particle-size distribution (percentage) of each material obtained after wet sieving of every 10 cm sample.

Gravel Grade Particles Sand Fraction Mud Fraction Sample Total Mass of Sample Sample (>2mm) (<2mm, >63μm) (<63μm) Depth After Wet Sieving and Number Mass after oven Percentage Mass after oven Percentage Mass after oven Percentage (cm) Oven drying (g) drying (g) (%) drying (g) (%) drying (g) (%) 1 0-10 9.42 5 131.66 67 55.62 28 196.70 2 10-20 16.74 8 127.92 64 56.78 28 201.44 3 20-30 16.08 7 153.03 68 56.03 25 225.14 4 30-40 19.88 9 158.25 68 53.77 23 231.90 5 40-50 12.85 6 161.32 72 51.35 23 225.52 6 50-60 17.20 8 160.22 70 50.05 22 227.47 7 60-70 32.22 14 149.77 65 48.76 21 230.75 8 70-80 24.67 11 155.19 68 49.95 22 229.81 9 80-90 16.66 7 171.63 73 46.31 20 234.60 10 90-100 18.76 8 170.94 74 42.42 18 232.12 11 100-110 18.56 8 158.56 72 44.40 20 221.52 12 110-120 15.83 7 161.83 73 43.33 20 220.99 14 120-140 22.15 8 220.01 76 47.67 16 289.83 16 140-160 30.75 13 163.80 70 38.32 16 232.87 17 160-170 22.80 10 176.16 74 38.36 16 237.32 18 170-180 17.00 7 159.75 69 54.08 23 230.83 19 180-190 17.98 8 159.87 69 53.02 23 230.87

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20 190-200 14.32 6 159.82 70 55.34 24 229.48 21 200-210 12.79 6 157.56 69 59.39 26 229.74 23 210-230 13.02 6 95.36 44 108.30 50 216.68 24 230-240 11.06 5 129.91 59 77.87 36 218.84 25 240-250 8.28 4 122.18 54 93.73 42 224.19 26 250-260 6.02 3 98.51 45 115.83 53 220.36 27 260-270 2.91 1 53.35 24 165.03 75 221.29 28 270-280 2.58 1 31.68 15 180.84 84 215.10 29 280-290 2.61 1 31.51 15 178.27 84 212.39 30 290-300 2.73 1 30.55 14 178.74 84 212.02 31 300-310 2.48 1 30.75 14 184.72 85 217.95 32 310-320 2.46 1 25.58 12 190.66 87 218.70 33 320-330 1.40 1 26.46 12 190.91 87 218.77 34 330-340 0.57 0 16.59 8 194.61 92 211.77 35 340-350 1.36 1 22.05 10 191.30 89 214.71 36 350-360 0.77 0 17.84 8 199.61 91 218.22 37 360-370 1.24 1 23.07 10 196.24 89 220.55 38 370-380 1.44 1 23.91 11 192.30 88 217.65 39 380-390 3.30 2 20.31 9 194.56 89 218.17 40 390-400 2.72 1 27.43 13 178.50 86 208.65 41 400-410 0.33 0 15.53 7 200.86 93 216.72

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42 410-420 0.55 0 18.18 8 206.72 92 225.45 43 420-430 0.89 0 19.79 9 206.46 91 227.14 44 430-440 0.59 0 17.45 8 208.64 92 226.68 45 440-450 0.68 0 17.21 8 205.90 92 223.79 46 450-460 1.26 1 2.60 1 199.24 98 203.10 47 460-470 0.23 0 20.98 9 202.13 91 223.34 48 470-480 11.28 5 22.07 10 194.38 85 227.73 49 480-490 1.16 1 24.53 11 197.42 88 223.11 50 490-500 3.01 1 23.58 10 198.59 88 225.18 51 500-510 1.49 1 22.35 10 197.65 89 221.49 52 510-520 1.54 1 25.76 11 198.42 88 225.72 53 520-530 1.88 1 31.97 14 191.44 85 225.29 54 530-540 2.16 1 27.10 12 192.76 87 222.02 55 540-550 0.58 0 18.46 9 197.24 91 216.28 56 550-560 0.61 0 14.45 6 215.62 93 230.68 57 560-570 1.67 1 15.60 7 207.92 92 225.19 58 570-580 31.29 14 14.86 7 180.15 80 226.30 59 580-590 31.93 15 29.95 14 154.24 71 216.12

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Appendix 1.4. Final sediment texture reading determined from the texture by feel method and particle-size distribution method. Particle Size Distribution Sample Sample Texture by feel Materials Material Material Sediment Texture Number Depth (cm) >2mm (%) >2mm, >63μm (%) <63μm (%) 1 0-10 sandy loam 5 67 28 sandy loam 2 10-20 sandy loam 8 64 28 sandy loam 3 20-30 sandy loam 7 68 25 sandy loam 4 30-40 sandy loam 9 68 23 sandy loam 5 40-50 sandy loam 6 72 23 sandy loam 6 50-60 sandy clay loam 8 70 22 sandy loam 7 60-70 sandy clay loam 14 65 21 sandy clay 8 70-80 sandy clay loam 11 68 22 sandy clay 9 80-90 sandy clay loam 7 73 20 sandy loam 10 90-100 sandy loam 8 74 18 sandy loam 11 100-110 sandy loam 8 72 20 sandy loam 12 110-120 sandy loam 7 73 20 sandy loam 14 120-140 sandy loam 8 76 16 sandy loam 16 140-160 sandy loam 13 70 16 sandy loam 17 160-170 sandy loam 10 74 16 sandy loam 18 170-180 sandy loam 7 69 23 sandy clay loam 19 180-190 sandy loam 8 69 23 sandy clay loam

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20 190-200 sandy loam 6 70 24 sandy clay loam 21 200-210 sandy loam 6 69 26 sandy clay loam 23 210-230 sandy clay 6 44 50 sandy clay 24 230-240 sandy clay 5 59 36 sandy clay 25 240-250 silty clay 4 54 42 sandy clay 26 250-260 silty clay 3 45 53 sandy clay 27 260-270 clay 1 24 75 clay 28 270-280 clay 1 15 84 clay 29 280-290 silty clay 1 15 84 clay 30 290-300 clay 1 14 84 clay 31 300-310 silty clay 1 14 85 clay 32 310-320 silty clay loam 1 12 87 clay 33 320-330 silty clay 1 12 87 clay 34 330-340 silty clay 0 8 92 silty clay 35 340-350 silty clay 1 10 89 silty clay 36 350-360 silty clay 0 8 91 silty clay 37 360-370 silty clay 1 10 89 silty clay 38 370-380 silty clay 1 11 88 clay 39 380-390 clay 2 9 89 silty clay 40 390-400 clay 1 13 86 clay 41 400-410 clay 0 7 93 silty clay

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42 410-420 silty clay 0 8 92 silty clay 43 420-430 silty clay loam 0 9 91 silty clay 44 430-440 silty clay loam 0 8 92 silty clay 45 440-450 silty clay loam 0 8 92 silty clay 46 450-460 silty clay 1 1 98 silty clay 47 460-470 silty clay 0 9 91 silty clay 48 470-480 silty clay 5 10 85 silty clay 49 480-490 silty clay 1 11 88 clay 50 490-500 silty clay 1 10 88 silty clay 51 500-510 silty clay 1 10 89 silty clay 52 510-520 clay 1 11 88 clay 53 520-530 clay 1 14 85 clay 54 530-540 silty clay 1 12 87 clay 55 540-550 clay loam 0 9 91 silty clay 56 550-560 clay 0 6 93 silty clay 57 560-570 silty clay 1 7 92 silty clay 58 570-580 clay 14 7 80 silty clay 59 580-590 clay 15 14 71 clay 60 590-600 clay * * * clay * Wet sieving for Sample Number 60 (depth 6 m) was not carried out. Only a small amount of sample was collected at this depth before reaching the limestone bedrock therefore, there was not enough sample to wet sieve.

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Appendix 1.5. Colour versus texture for each sediment sample Sample Sample Depth Sediment Texture Colour Number (cm) 1 0-10 sandy loam Very dark grey 2 10-20 sandy loam Very dark grey 3 20-30 sandy loam very dark grey 4 30-40 sandy loam very dark grey 5 40-50 sandy loam very dark greyish brown 6 50-60 sandy loam very dark greyish brown 7 60-70 sandy clay very dark greyish brown 8 70-80 sandy clay very dark greyish brown 9 80-90 sandy loam dark greyish brown 10 90-100 sandy loam dark greyish brown 11 100-110 sandy loam very dark greyish brown 12 110-120 sandy loam very dark greyish brown 14 120-140 sandy loam dark grey 16 140-160 sandy loam dark grey 17 160-170 sandy loam dark grey 18 170-180 sandy clay loam grey 19 180-190 Sandy clay loam grey 20 190-200 sandy clay loam grey 21 200-210 sandy clay loam grey 23 210-230 sandy clay light olive brown 24 230-240 sandy clay light olive brown 25 240-250 sandy clay olive brown 26 250-260 sandy clay light olive brown 27 260-270 clay dark yellowish brown 28 270-280 clay dark yellowish brown 29 280-290 clay dark yellowish brown 30 290-300 clay dark yellowish brown 31 300-310 clay dark yellowish brown 32 310-320 clay dark yellowish brown 33 320-330 clay dark yellowish brown 34 330-340 silty clay dark yellowish brown 35 340-350 silty clay dark yellowish brown 36 350-360 silty clay dark yellowish brown

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37 360-370 silty clay dark yellowish brown 38 370-380 clay dark yellowish brown 39 380-390 silty clay dark yellowish brown 40 390-400 clay dark yellowish brown 41 400-410 silty clay dark yellowish brown 42 410-420 silty clay dark yellowish brown 43 420-430 silty clay dark yellowish brown 44 430-440 silty clay dark yellowish brown 45 440-450 silty clay dark yellowish brown 46 450-460 silty clay dark yellowish brown 47 460-470 silty clay dark yellowish brown 48 470-480 silty clay dark yellowish brown 49 480-490 clay dark yellowish brown 50 490-500 silty clay dark yellowish brown 51 500-510 silty clay dark yellowish brown 52 510-520 clay dark yellowish brown 53 520-530 clay dark yellowish brown 54 530-540 clay dark yellowish brown 55 540-550 silty clay dark yellowish brown 56 550-560 silty clay dark yellowish brown 57 560-570 silty clay dark yellowish brown 58 570-580 silty clay dark yellowish brown 59 580-590 clay dark yellowish brown 60 590-600 clay dark yellowish brown

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"%M& " '

Appendix 2.1. The percentage of different materials present in the particle fraction >2 mm for every 10 cm sediment sample

Percent Materials Present in Each Sample > 2mm Sample Sample Limestone Depth Whole Shell Coral Unidentified Number and beach Rocks (cm) Shells Fragments Fragments materials rock 1 0-10 1 17 9 38 - 36 2 10-20 1 12 14 53 * 20 3 20-30 2 15 18 41 * 16 4 30-40 1 9 50 24 * 16 5 40-50 5 24 26 25 * 20 6 50-60 2 16 27 38 - 17 7 60-70 10 8 19 57 * 7 8 70-80 2 9 40 42 - 7 9 80-90 3 15 15 58 3* 6 10 90-100 3 14 22 51 2 8 11 100-110 3 14 25 46 2 10 12 110-120 6 32 14 47 * - 14 120-140 8 17 13 45 2 14 16 140-160 4 16 12 63 2 3 17 160-170 8 24 14 47 3 3 18 170-180 15 60 13 5 6 - 19 180-190 25 50 3 10 11 - 20 190-200 27 57 4 4 8 - 21 200-210 23 58 8 3 8 - 23 210-230 15 35 2 11 36 - 24 230-240 15 29 20 10 25 - 25 240-250 16 34 14 30 6 - 26 250-260 13 50 14 14 8 - 27 260-270 14 47 15 4 20 - 28 270-280 6 46 16 21 11 - 29 280-290 15 53 15 13 4 - 30 290-300 9 34 41 9 7 - 31 300-310 2 32 6 22 38 - 32 310-320 6 24 - 61 9 - 33 320-330 26 26 - 41 7 -

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34 330-340 - 86 14 - - - 35 340-350 - 42 14 - 9 35 36 350-360 - 61 - - 20 20 37 360-370 21 37 21 22 - - 38 370-380 7 37 23 21 12* - 39 380-390 13 41 9 25 13 - 40 390-400 23 21 17 21 17 - 41 400-410 - 100 - - - - 42 410-420 13 61 26 - - - 43 420-430 30 55 14 - - - 44 430-440 - 63 37 - - - 45 440-450 - 48 52 - - - 46 450-460 - 28 - 29 42 - 47 460-470 - 58 - 42 - - 48 470-480 - 42 - 58 - - 49 480-490 - 30 15 37 18 - 50 490-500 16 45 20 13 - - 51 500-510 11 45 20 25 - - 52 510-520 11 47 17 25 - - 53 520-530 - 13 7 7 73 - 54 530-540 - 24 6 9 61 - 55 540-550 - 100 - - - - 56 550-560 - 36 - 64 - - 57 560-570 - 43 28 29 - - 58 570-580 - 1 - 99 - - 59 580-590 - 1 - 99 - - 60 590-600 ------Materials not present n* – n = percentage rocks, * = pumice

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Appendix 2.2. Shell species identified in each sediment sample throughout the core profile is listed according to their habitat together with the number of foraminifera identified in each sediment sample. Species Habitat Sample Number Foraminifera Shallow water, sandy sea floor, intertidal, sub tidal, dead Terrestrial Number of shells Mudflat Reefs Mangroves Freshwater coral or rocks in shallow water Snails Gastropod: Littorina sp. – 1, Nassarius sp. – 1, Polinices sp. – 1, Nassarius sp. – 1 Turbo sp. – 1 Littorina sp. – 1 2 1 1 5 Strombus sp. – 1 Gastropod: Cerithium sp. – 2, Peristernia sp. – 2, Atys sp. – 1, Nassarius sp. – 1 2 4 6 Nassarius sp. – 1 Gastropod: Cerithium sp. – 2, Nassarius sp. – 2, Nerita sp. – 1, Nassarius sp. – 2 Turbo sp. – 1 2 3 4 8 Peristernia sp. – 1, Polinices sp. – 1 Gastropod: Peristernia sp. – 2, Littorina sp. – 1, Nassarius sp. – Nassarius sp. – 1 Clavus sp. – 1 Littorina sp. – 1 4 9 7 1, Rissoina sp. – 1 Bivalve: Fragum sp. – 1 Gastropod: Nassarius sp. – 5, Cerithium sp. – 2, Peristernia sp. Nassarius sp. – 5 Angaria sp. – 5 11 13 – 2, Polinices sp. – 1, Nerita sp. – 1 1 Bivalve: Tellina sp. – 1 Gastropod: Nassarius sp. – 5, Cerithium sp. – 2, Pyramidella sp. Nassarius sp. – 5 6 6 11 – 1, Rissoina sp. – 1 Bivalve: Fragum sp. – 1, Periglypta sp. – 1 Gastropod: Nassarius sp. – 3, Peristernia sp. – 3, Cerithium sp. Nassarius sp. – 3 Turbo sp. – 1 Nerita sp. – 1 – 2, Strombus sp. – 2, Nerita sp. – 1, Polinices sp. – 1 7 15 14 Bivalve: Barbatia sp. – 1 Barbatia sp. – 1 Gastropod: Nassarius sp. – 2, Polinices sp. – 1 Nassarius sp. – 2 Turbo sp. – 1 1 8 10 5 Bivalve: Anadara sp. – 1

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Gastropod: Cerithium sp. – 3, Nassarius sp. – 2, Patelloida sp. – Nassarius sp. – 2 Patelloida sp. – 1 1 9 13 8 1, Epitonium sp. – 1 Bivalve: Chama sp. – 1 Gastropod: Nassarius sp. – 5, Nerita sp. – 2, Cerithium sp. – 1, Nassarius sp. – 5 Turbo sp. – 2 Freshwater snail – 10 6 14 Mitra sp. – 1, Peristernia sp. – 1, Rissoina sp. – 1 1 Bivalve: Tellina sp. – 1 Gastropod: Nassarius sp. – 9, Cerithium sp. – 1, Littorina sp. – Nassarius sp. – 9 Turbo sp. – 2 Littorina sp. – 1 Neritina sp. – 1 1, Marginella sp. – 1, Murex sp. – 1, Neritina sp. – 1, 11 8 19 Dendropoma sp. – 1 Bivalve: Barbatia sp. – 1, Fragum sp. – 1, Barbatia sp. – 1 Gastropod: Nassarius sp. – 6, Atys sp. – 2, Cerithium sp. – 2, Nassarius sp. – 6 Neritina sp. – 1 Polinices – 1, Neritina sp. – 1, Oliva sp. – 1, Peristernia sp. – 1, Acteon sp. – 1 12 12 19 Tectus sp. – 1 Bivalve: Fragum sp. – 2, Periglypta sp. – 1 Gastropod: Nassarius sp. – 29, Cerithium sp. – 8, Nerita sp. – 1, Nassarius sp. – 29 Turbo sp. – 3 Littorina sp. – 2 Nerita sp. – 1 Littorina sp. – 2, Mitra sp. – 2, Polinices sp. – 2, Peristernia sp. – 14* 17 50 1, Strombus sp. – 1 Bivalve: Tellina sp. – 1 Gastropod: Nassarius sp. – 23, Cerithium sp. – 8, Peristernia sp. Nassarius sp. – 23 Turbo sp. – 1 Patelloida sp. – 1 – 2, Atys sp. – 1, Patelloida sp. – 1, Polinices sp. – 2, Neritina sp. Neritina sp. – 1 16* 11 44 – 1, Pupa sp. – 1, Strombus sp. – 1, Tectus sp. – 1 Bivalve: Tellina sp. – 1, Fragum sp. – 1 Gastropod: Nassarius sp. – 45, Cerithium sp. – 4, Atys sp. – 1, Nassarius sp. – 45 Conus sp. – 1 Patelloida sp. – 1 1 17 16 65 Patelloida sp. – 1, Marginella sp. – 1, Mitra sp. – 1, Polinices sp. Turbo sp. – 1 Neritina sp. – 1 – 2, Neritina sp.– 1, Peristernia sp.– 1, Pyramidella sp.– 1,

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Strombus sp.– 1 Bivalve: Fragum sp. – 4 Gastropod: Nassarius sp. – 56, Cerithium sp. – 8, Atys sp. – 5, Nassarius sp. – 56 Turbo sp. – 4 Patelloida sp. – 1 Strombus sp. – 2, Patelloida sp. – 1, Mitra sp. – 1, Neritina sp. – Neritina sp. – 2 18 19 88 2, Polinices sp. – 1 Bivalve: Ostreidae sp. – 1, Barbatia sp. – 2, Fragum sp. – 2, Barbatia sp. – Tellina sp. – 3 2 Gastropod: Nassarius sp. – 82, Atys sp. – 13, Cerithium sp. – 12, Nassarius sp. – 82 Turbo sp. – 2 Littorina sp. – 1 Patelloida sp. – 2 Polinices sp. – 3, Patelloida sp. – 2, Nerita sp. – 1, Littorina sp. Pleuroploca Nerita sp. – 1 19S 13 133 – 1, Peristernia sp. – 1, Pyramidella sp. – 1 sp. – 1 Bivalve: Tellina sp. – 8, Ostreidae sp. – 4, Fragum sp. – 2 Gastropod: Nassarius sp. – 76, Cerithium sp. – 13, Atys sp. – 5, Nassarius sp. – 76 Turbo sp. – 2 Cassidula sp. – Polinices sp. – 4 Arca sp. – 1 1 20 16 117 Bivalve: Tellina sp. – 12, Anadara sp. – 1, Fragum sp. – 1, Ostreidae sp. – 1 Gastropod: Nassarius sp. – 71, Cerithium sp. – 11, Fasciolaria Nassarius sp. – 71 Turbo sp. – 4 Patelloida sp. – 1 sp. – 2, Polinices sp. – 2, Atys sp. – 1, Epitonium sp. – 1, 21 11 104 Patelloida sp. – 1, Pupa sp. – 1 Bivalve: Tellina sp. – 4, Fragum sp. – 3, Ostreidae sp. – 2, Gafrarium sp. – 1 Gastropod: Nassarius sp. – 42, Cerithium sp. – 3, Patelloida sp. Nassarius sp. – 42 Turbo sp. – 2 Patelloida sp. – 3 – 3, Polinices sp. – 2, Atys sp. – 1, Mitra sp. – 1, Peristernia sp. – 23* 10 60 1 Bivalve: Fragum sp. – 3, Tellina sp. – 2 Gastropod: Nassarius sp. – 40, Cerithium sp. – 9, Polinices sp. – Nassarius sp. – 40 Turbo sp. – 2 Patelloida sp. – 1 24 15 62 3, Atys sp. – 2, Patelloida sp. – 1, Neritina sp. – 1 Neritina sp. – 1

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Bivalve: Tellina sp. – 3, Fragum sp. – 1 Gastropod: Nassarius sp. – 19, Cerithium sp. – 9, Atys sp. – 2, Nassarius sp. – 19 Turbo sp. – 3 Neritina sp.– 1 25 5 39 Neritina sp. – 1, Polinices sp. – 1 Bivalve: Tellina sp. – 3, Fragum sp. – 1 Gastropod: Nassarius sp. – 15, Cerithium sp. – 6, Polinices sp. – Nassarius sp. – 15 Turbo sp. – 2 26 10 30 1, Peristernia sp. – 1, Pupa sp. – 1 Bivalve: Tellina sp. – 3, Periglypta sp. – 1 Gastropod: Nassarius sp. – 6, Cerithium sp. – 3, Polinices sp. – Nassarius sp. – 6 Turbo sp. – 1 Patelloida sp. – 1 27 6 19 2, Atys sp. – 1, Patelloida sp. – 1, Mitra sp. – 1 Modiolus sp. – 1 Bivalve: Tellina sp. – 3 Gastropod: Nassarius sp. – 5, Polinices sp. – 1 Nassarius sp. – 5 28 2 7 Bivalve: Barbatia sp.– 1 Barbatia sp. – 1 Gastropod: Nassarius sp. – 4, Cerithium sp. – 1, Littorina sp. – 1 Nassarius sp. – 4 Littorina sp. – 1 29 1 8 Bivalve: Ostreidae sp. – 2 30 - 5 Gastropod: Nassarius sp. – 2, Atys sp. – 1, Polinices sp. – 2 Nassarius sp. – 2 31 2 2 Gastropod: Nassarius sp. – 1, Patelloida sp. – 1 Nassarius sp. – 1 Patelloida sp. – 1 Gastropod: Cerithium sp. – 2, Nassarius sp. – 2, Polinices sp. – Nassarius sp. – 2 32 - 6 1, Pyramidella sp. – 1 Gastropod: Nassarius sp. – 7, Epitonium sp. – 1, Polinices sp. – Nassarius sp. – 7 Turbo sp. – 1 33 2 10 1 34 1 Gastropod: Nassarius sp. – 1 Nassarius sp. – 1 35 1 1 Gastropod: Nassarius sp. – 1 Nassarius sp. – 1 36 - 2 Gastropod: Cerithium sp. – 1, Nassarius sp. – 1 Nassarius sp. – 1 37 1 5 Gastropod: Nassarius sp. – 3, Littorina sp. – 1 Nassarius sp.– 3 Littorina sp. – 1

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Bivalve: Fragum sp. – 1 38 1 4 Gastropod: Nassarius sp. – 4 Nassarius sp. – 4 39 1 7 Gastropod: Nassarius sp. – 5, Atys sp. – 1, Cerithium sp.– 1 Nassarius sp. – 5 40 1 17 Gastropod: Nassarius sp. – 14, Polinices sp. – 2, Nerita sp. – 1 Nassarius sp. – 14 Nerita sp. – 1 41 0 No Whole Shells Gastropod: Cerithium sp. – 1, Nassarius sp. – 1, Pyramidella sp. Nassarius sp. – 1 42 1 3 – 1 Gastropod: Nassarius sp. – 6 Nassarius sp.– 6 43 1 7 Bivalve: Tellina sp. – 1 44 1 1 Gastropod: Nassarius sp. – 1 Nassarius sp. – 1 45 - 2 Gastropod: Nassarius sp. – 1, Pyramidella sp. – 1 Nassarius sp. – 1 46 - 2 Gastropod: Cerithium sp. – 1, Nassarius sp. – 1 Nassarius sp. – 1 Gastropod: Nassarius sp. – 1 Nassarius sp. – 1 47 - 2 Bivalve: Fragum sp. – 1 48 - 1 Gastropod: Cerithium sp. – 1 49S - 2 Gastropod: Nassarius sp. – 2 Nassarius sp. – 2 Gastropod: Nassarius sp. – 9, Cerithium sp. – 2, Polinices sp. – Nassarius sp. – 9 Littorina sp. – 1 50 1 15 1, Littorina sp. – 1 Bivalve: Fragum sp. – 1, Codakia sp. – 1 Gastropod: Nassarius sp. – 3, Peristernia sp. – 2, Fragum sp. – Nassarius sp. – 3 51 - 8 1, Mitra sp. – 1 Bivalve: Tellina sp. – 1 52 1 4 Gastropod: Nassarius sp. – 3 Nassarius sp. – 3 Turbo sp. – 1 53 1 1 Gastropod: Nassarius sp. – 1 Nassarius sp. – 1 54 - 4 Gastropod: Nassarius sp. – 2, Cerithium sp. – 1, Polinices sp. – Nassarius sp. – 2

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1 55 - 0 No Whole Shells 56 - 1 Gastropod: Nassarius sp. – 1 Nassarius sp. – 1 Gastropod: Cerithium sp. – 1, Nassarius sp. – 1, Polinices sp. – Nassarius sp. – 1 57 - 3 1 58 - 1 Gastropod: Nassarius sp. – 1 Nassarius sp. – 1 59 - 1 Gastropod: Cerithium sp. – 1 - None * The species counted is divided by 2 since 20 cm sample were collected at these depths S Shark tooth found in the particles >2mm

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Appendix 2.3. Different species of shells identified and their niche. The shells are listed from the most abundant to the least abundant down the sediment core profile. Name of Shells Total Habitat Genus Species Family Count Carnivorous in nature, mud dwellers Nassarius sp. NASSARIIDAE scavengers and predators of other 630 (Nass_sp.) Nassa Mud Shells molluscs. Mainly found in shallow water, and sea-shore (intertidal) Shallow marine dwellers, most Cerithium sp. CERITHIIDAE 124 distributed in the tropics at the littoral (Ceri_sp.) The Ceriths zone Tellina sp. TELLINIDAE Shallow water in the intertidal zone 47 (Tell_sp.) Tellins Found on sandy seafloor bottoms in intertidal or deep waters 5-20 m. Also on Polinices sp. NATICIDAE 41 fine sandy shores intertidally to deeper (Poli_sp.) Moon Shells waters. Some species are also common on muddy bottom Atys sp. BULLIDAE Living underwater, mainly marine 37 (Atys_sp.) Bubble Shells tropical area Reef shells found under coral rocks or Turbo sp. TURBINIDAE 37 sometimes exposed in the intertidal reef (Turb_sp.) Turban Shells zone Fragum sp. CARDIIDAE Live in shallow water offshore to 50 m 27 (Frag_sp.) Cockle Shells deep Peristernia sp. FASCIOLARIIDAE Found mainly on dead coral in shallow 21 (Peri_sp.) Peristernias water of the intertidal zone They dwell in rocky and gravely bottoms Nerita sp. between tide marks or in brackish or (Neri_sp.) NERITIDAE 16 fresh water areas. The Neritidae are the Neritina sp. Nerites only archaegastropod family which has (Nena_sp.) spread to fresh water Shore-rock dwelling herbivores which Patelloida sp. PATELLIDAE 13 live primarily in the intertidal zone. Most (Pate_sp.) True Limpets are salt water but also freshwater

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Ostreidae sp. CRASSOSTREA Live under rocks, shallow reefs 10 (Ostr_sp.) True oysters Found in the littoral region. Some are Littorina sp. LITTORINIDAE found on rocky coasts at the high and 9 (Lito_sp.) The Periwinkles mid-tide level of the intertidal zone; others prefer mangroves Strombus sp. STROMBIDAE Live on sandy bottoms among beds of sea 8 (Stro_sp.) True Conchs grass in shallow tropical waters Mitra sp. MITRIDAE Mainly found in warm shallow water, 8 (Mitr_sp.) Miter Shells intertidal Pyramidella sp. PYRAMIDELLIDAE Shallow water, shallow water in sand 6 (Pyra_sp.) Pyrams Barbatia sp. ARCIDAE Found in coral reefs, under rocks. 5 (Barb_sp.) Arc Clams Shallow waters, subtidal zone Rissoina sp. RISSOIDEA Mainly shallow water in sand, intertidal 3 (Riss_sp.) Risso Snails Pupa sp. Shallow water, sandy substrates of 3 ACTEONIDAE (Pupa_sp.) marine waters. Periglypta sp. VENERIDAE Hard-shelled clams Live in shallow water 3 (Pegl_sp.) Venus clams Epitonium sp. EPITONIIDAE In tropical Pacific they live in weedy 3 (Epit_sp.) Wentle Traps coral-sand from shallow to deep water. Tectus sp. TROCHIDAE Common on rocks below low tide mark 2 (Tect_sp.) Top-shells Marginella sp. Live in sands in the tropics 2 MARGINELLIDAE (Marg_sp.) Fasciolaria sp. FASCIOLARIIDAE Found on sand in shallow water, 2 (Fasc_sp.) Tulip Shells intertidal Anadara sp. ARCIDAE Found in shallow waters 2 (Anad_sp.) Arc Clams Acteon sp. Generally found in shallow water, 1 ACTEONIDAE (Acte_sp.) mudflat area Angaria sp. Reef zone, on rocks between tide marks 1 ANGARIIDEA (Anga_sp.) Arca sp. Live under rocks, shallow reefs 1 ARCIDAE (Arca_sp.)

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Cassidula sp. MELAMPIDAE Seen on back mangroves, mangrove 1 (Cass_sp.) Land Snails trees, mud shores CHAMIDAE Found intertidal and sub-tidal areas. A Chama sp. 1 Rock-oysters or few species are found in shallow and (Cham_sp.) Jewel-boxes deep waters Tropical species live either in sand or on TURRIDAE Clavus sp. a hard reef substrate under coral rocks, 1 Turrid Shells (Clav_sp.) numerous species may be found at an

abyssal (4000-6000 m) depth Codakia sp. LUCINIDAE Shallow sands 1 (Coda_sp.) Lucina Clams Cone shells live in coral-sand or on a Conus sp. CONIDAE 1 hard reef substrate, under corals or in (Conu_sp.) Cone Shells crevices. Dendropoma sp. VERMETIDAE Found attached to rocks 1 (Dend_sp.) Worm-shells Gafrarium sp. Common on sandy shores. 1 VENERIDAE (Graf_sp.) Modiolus sp. MYTILIDAE Common on muddy bottoms in shallow 1 (Modi_sp.) Sea Mussels waters MURICIDAE Mostly intertidal or shallow subtidal zone Murex sp. 1 Rock shells or Murex among rocks and corals (Mure_sp.) shells Found all over the Pacific and warm Oliva sp. OLIVIDAE 1 waters, sandy substrates intertidally and (Oliv_sp.) Olive Shells subtidally. Pleuroploca sp. FASCIOLARIIDAE Common on rocks below tide marks, reef 1 (Pleu_sp.) Horse Conch

124

"(M&

A B

C D

E F

Appendix 3.1. Pictures of shell species identified. (A) Shell fragments; (B) Coral fragments; (C) Beach rock; (D) Bedrock limestone; (E) Nassarius sp.; (F) Cerithium sp.

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a b

G H

(G) Shark teeth; a – sediment depth 190 cm, b – sediment depth 490 cm; (H) Foraminifera.

c j e i

(I) The different species of shells present in the sediment core; a – Foraminifera, b – Nassarius sp., c – Cerithium sp., d – Atys sp., e – Tellina sp., f – Polinices sp., g – Pyramidella sp., h – Fragum sp., i – Patelloida sp., and j – Turbo sp.

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")M * *

Appendix 4.1. Loss-on-ignition results table. Mass of Mass of Mass of crucible Mass of Mass of Mass of Mass of crucible + Mass of crucible + Mass of Sample + sample after oven- Sample empty crucible + air-dried sample after 4 sample sample after 2 sample Depth 24 hrs oven- dried Number crucible sample sample hrs burning at remaining hrs burning at remaining (cm) drying at 110°C sample (g) (g) (g) 550°C (g) 950°C (g) (g) (g) (g) (g) 1 0-10 21.2613 26.2625 5.0012 26.1528 4.8915 25.6411 4.3798 24.2164 2.9551 2 10-20 24.1138 29.1131 4.9993 29.0003 4.8865 28.4693 4.3555 27.0747 2.9609 3 20-30 24.0016 29.0070 5.0054 28.9026 4.9010 28.3993 4.3977 26.9677 2.9661 4 30-40 24.5420 29.5473 5.0053 29.4538 4.9118 29.0216 4.4796 27.4823 2.9403 5 40-50 24.8794 29.8810 5.0016 29.8036 4.9242 29.3261 4.4467 27.8563 2.9769 6 50-60 24.1680 29.1686 5.0006 29.0928 4.9248 28.6356 4.4676 27.1600 2.9920 7 60-70 25.5025 30.5056 5.0031 30.4231 4.9206 29.9665 4.4640 28.4706 2.9681 8 70-80 24.1037 29.1056 5.0019 29.0247 4.9210 28.6539 4.5502 27.0626 2.9589 9 80-90 24.3987 29.3973 4.9986 29.3386 4.9399 28.9723 4.5736 27.3666 2.9679 10 90-100 20.2792 25.2777 4.9985 25.2247 4.9455 24.8983 4.6191 23.2572 2.9780 11 100-110 27.3270 32.3273 5.0003 32.2542 4.9272 32.0122 4.6852 30.2813 2.9543 12 110-120 24.1685 29.1694 5.0009 29.0788 4.9103 28.7723 4.6038 27.0899 2.9214

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14 120-140 21.4621 26.4644 5.0023 26.3985 4.9364 26.1391 4.6770 24.4551 2.9930 16 140-160 24.1142 29.1163 5.0021 29.0557 4.9415 28.8415 4.7273 27.1963 3.0821 17 160-170 22.0261 28.0273 6.0012 27.9409 5.9148 27.6983 5.6722 25.7192 3.6931 18 170-180 24.1048 29.1056 5.0008 29.0516 4.9468 28.8225 4.7177 27.2883 3.1835 19 180-190 22.9022 28.9023 6.0001 28.7953 5.8931 28.5206 5.6184 26.7048 3.8026 20 190-200 22.5851 28.5855 6.0004 28.5215 5.9364 28.2386 5.6535 26.4971 3.9120 21 200-210 22.9612 27.9621 5.0009 27.9058 4.9446 27.6725 4.7113 26.2843 3.3231 23 210-230 24.2013 29.4030 5.2017 29.2464 5.0451 28.8640 4.6627 28.0239 3.8226 24 230-240 23.0193 28.0201 5.0008 27.6389 4.6196 27.2938 4.2745 26.3413 3.3220 25 240-250 25.5059 30.5071 5.0012 30.1093 4.6034 29.8107 4.3048 28.7884 3.2825 26 250-260 24.5440 29.5443 5.0003 28.9139 4.3699 28.5964 4.0524 27.7965 3.2525 27 260-270 22.2314 27.2327 5.0013 26.8928 4.6614 26.4074 4.1760 26.0823 3.8509 28 270-280 21.2728 26.2734 5.0006 25.6004 4.3276 25.0951 3.8223 24.9102 3.6374 29 280-290 24.0034 29.0036 5.0002 28.6108 4.6074 28.0799 4.0765 27.8922 3.8888 30 290-300 20.6610 25.6620 5.0010 25.1516 4.4906 24.6409 3.9799 24.4135 3.7525 31 300-310 24.1052 29.1072 5.0020 28.8222 4.7170 28.2941 4.1889 28.1090 4.0038 32 310-320 27.3280 32.3290 5.0010 32.0506 4.7226 31.5064 4.1784 31.3227 3.9947 33 320-330 20.2794 25.2801 5.0007 24.9887 4.7093 24.4168 4.1374 24.3024 4.0230 34 330-340 21.4640 26.4666 5.0026 26.1800 4.7160 25.6168 4.1528 25.4899 4.0259 35 340-350 22.0286 27.0291 5.0005 26.7139 4.6853 26.1368 4.1082 26.0244 3.9958 36 350-360 22.5849 27.5849 5.0000 27.2925 4.7076 26.7384 4.1535 26.6155 4.0306

128

37 360-370 24.1706 29.1709 5.0003 28.8828 4.7122 28.3491 4.1785 28.1595 3.9889 38 370-380 24.1156 29.1158 5.0002 28.8253 4.7097 28.2754 4.1598 28.1214 4.0058 39 380-390 23.6298 28.6305 5.0007 28.3349 4.7051 27.7934 4.1636 27.6788 4.0490 40 390-400 24.8828 29.8839 5.0011 29.6059 4.7231 29.0761 4.1933 28.8417 3.9589 41 400-410 24.5427 29.5428 5.0001 29.2972 4.7545 28.7316 4.1889 28.5278 3.9851 42 410-420 22.9591 27.9598 5.0007 27.7060 4.7469 27.1125 4.1534 26.9755 4.0164 43 420-430 25.5052 30.5048 4.9996 30.2497 4.7445 29.6745 4.1693 29.5270 4.0218 44 430-440 21.4844 26.4852 5.0008 26.0087 4.5243 25.4173 3.9329 25.3076 3.8232 45 440-450 24.4006 29.4014 5.0008 29.1780 4.7774 28.6271 4.2265 28.3374 3.9368 46 450-460 24.0006 29.0009 5.0003 28.7325 4.7319 28.1563 4.1557 28.0807 4.0801 47 460-470 20.5796 25.5795 4.9999 25.3219 4.7423 24.7459 4.1663 24.6086 4.0290 48 470-480 19.8401 24.8408 5.0007 24.5663 4.7262 23.9901 4.1500 23.9117 4.0716 49 480-490 22.2288 27.2286 4.9998 26.9619 4.7331 26.3843 4.1555 26.3034 4.0746 50 490-500 23.0183 28.0182 4.9999 27.7403 4.7220 27.1454 4.1271 27.0911 4.0728 51 500-510 23.6251 28.6261 5.0010 28.3558 4.7307 27.7940 4.1689 27.6489 4.0238 52 510-520 22.5824 27.5826 5.0002 27.3232 4.7408 26.7584 4.1760 26.5425 3.9601 53 520-530 24.1140 29.1149 5.0009 28.8197 4.7057 28.2295 4.1155 28.1385 4.0245 54 530-540 22.0289 27.0295 5.0006 26.7184 4.6895 26.1479 4.1190 26.0455 4.0166 55 540-550 25.5053 30.5065 5.0012 30.1495 4.6442 29.5993 4.0940 29.4628 3.9575 56 550-560 21.4634 26.4636 5.0002 26.1335 4.6701 25.5770 4.1136 25.4165 3.9531 57 560-570 24.1055 29.1060 5.0005 28.7752 4.6697 28.1873 4.0818 28.1051 3.9996

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58 570-580 24.1696 29.1698 5.0002 28.8557 4.6861 28.2577 4.0881 28.0916 3.9220 59 580-590 22.2284 27.2294 5.0010 27.0018 4.7734 26.5335 4.3051 25.9110 3.6826 60 590-600 24.8800 29.8805 5.0005 29.7094 4.8294 29.2900 4.4100 28.3916 3.5116

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Appendix 4.2. Percentage organic matter versus carbonate content for every 10 cm sediment sample. Percent Percent Percent Percent Sample Depth Sample Depth Organic Carbonate Organic Carbonate Number (cm) Number (cm) Content (%) Content (%) Content (%) Content (%) 1 0-10 10 33 33 320-330 12 3 2 10-20 11 32 34 330-340 12 3 3 20-30 10 33 35 340-350 12 3 4 30-40 9 34 36 350-360 12 3 5 40-50 10 33 37 360-370 11 5 6 50-60 9 33 38 370-380 12 4 7 60-70 9 34 39 380-390 12 3 8 70-80 8 35 40 390-400 11 6 9 80-90 7 35 41 400-410 12 5 10 90-100 7 36 42 410-420 13 3 11 100-110 5 37 43 420-430 12 4 12 110-120 6 37 44 430-440 13 3 14 120-140 5 36 45 440-450 12 7 16 140-160 4 35 46 450-460 12 2 17 160-170 4 35 47 460-470 12 3 18 170-180 5 33 48 470-480 12 2 19 180-190 5 32 49 480-490 12 2 20 190-200 5 31 50 490-500 13 1 21 200-210 5 29 51 500-510 12 3 23 210-230 8 18 52 510-520 12 5 24 230-240 7 22 53 520-530 13 2 25 240-250 6 24 54 530-540 12 2 26 250-260 7 20 55 540-550 12 3 27 260-270 10 8 56 550-560 12 4 28 270-280 12 5 57 560-570 13 2 29 280-290 12 5 58 570-580 13 4 30 290-300 11 6 59 580-590 10 14 31 300-310 11 4 60 590-600 9 20 32 310-320 12 4

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"+M

A B

C D Appendix 5.1. Radiocarbon date determination graphs. (A) Sample 6, Wk-25329; (B) Sample 21, Wk-25330; (C) Sample 27, Wk-25332; (D) Sample 60, Wk-25331.

132

Appendix 5.2. Radiocarbon date for every 10cm sediment sample.

Sediment Radiocarbon Radiocarbon Sediment Radiocarbon Radiocarbon

Depth (cm) Dates (BP) Dates (cal BP) Depth (cm) Dates (BP) Dates (cal BP) 10 50 52 310 8326 8996 20 95 98 320 8438 9084 30 145 150 330 8542 9166 40 195 202 340 8647 9249 50 240 248 350 8759 9337 60 290 300 360 8871 9425 70 546 588 370 8976 9507 80 802 875 380 9081 9590 90 1074 1180 390 9193 9678 100 1315 1450 400 9305 9766 110 1586 1755 410 9410 9848 120 1827 2025 420 9515 9931 130 2098 2330 430 9627 10019 140 2340 2600 440 9738 10106 150 2611 2905 450 9850 10194 160 2852 3175 460 9955 10277 170 3123 3480 470 10060 10359 180 3364 3750 480 10172 10447 190 3636 4055 490 10284 10535 200 3892 4342 500 10389 10618 210 4148 4630 510 10494 10700 220 4792 5322 520 10606 10788 230 5377 5951 530 10718 10876 240 6020 6643 540 10823 10959 250 6664 7334 550 10927 11041 260 7249 7963 560 11039 11129 270 7892 8655 570 11151 11217 280 8004 8743 580 11256 11300 290 8109 8825 590 11361 11382 300 8214 8908 600 11473 11470

133