Late Pleistocene Raised Coral Reefs in the Eastern Red Sea – Rabigh, Saudi Arabia Ammar Manaa University of Wollongong

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2011 Late Pleistocene raised coral reefs in the eastern red sea – Rabigh, Saudi Arabia Ammar Manaa University of Wollongong

Recommended Citation Manaa, Ammar, Late Pleistocene raised coral reefs in the eastern red sea – Rabigh, Saudi Arabia, Master of Science - Research thesis, School of Earth and Environmental Sciences, University of Wollongong, 2011. http://ro.uow.edu.au/theses/3501

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Late Pleistocene raised coral reefs in the eastern Red Sea – Rabigh, Saudi Arabia

*A thesis submitted in partial fulfilment of the requirements of the award of the degree

MASTER OF SCIENCE

(RESEARCH)

From

University of Wollongong

Ammar Manaa

School of Earth and Environmental Sciences

2011

ABSTRACT

The Rabigh coast (Saudi Arabia) in the study area stretches for about 12 km between Al Kharrar Lagoon in the north and Sharm Rabigh in the south. Seven prominent Pleistocene coral reef sites were investigated with terrace heights ranging from 1 to 5 m above present sea level. In addition to field descriptions, 86 samples were collected from these seven sites to provide the data for this research. Of these seven sites, 4 of the sites were front reef, and 3 were back reef. In each of the front reef sites, there was a beach rock, upper and lower reef. The elevation of the upper and lower reef in the front reef sites ranges from 0.5 m to 3.20 m above present sea level. The two layers of beach rock and a back reef were identified in the study area. In the upper and lower reefs, corals were observed in almost all of the samples, with higher proportions for the upper than lower reef. Silicate minerals were rare in both lower and upper reef. The back-reef features much less coral compared to the lower and upper reef and algae was the dominant element in the beach rock. The upper reef can be part of the reef crest or the algal ridge in the reef system, such that erosion can occur at the front reef. The lower reef indicates an outer reef flat where this zone is a combination of the fore reef and lagoon environment with wave-breaking algal structures. The coral framework in the upper reef indicates a low energy environment during the formation of this reef. Within the back-reef calcareous mud was dominant, which indicates a low energy environment behind the reef crest, or a lagoon environment. Such an interpretation for the upper and lower reefs connects with transgression phases of the sea and represents slightly higher sea levels. The XRD results for the upper and lower reefs, and beach rock revealed variable percentages of aragonite followed by high-Mg calcite, and calcite, with a small increase in calcite and high-Mg calcite comparative to the lower reef. Calcite was the dominant mineral in the back reef area, with variable percentages of high-Mg calcite. The dominant diagenetic process in the Rabigh reefs was cementation. Fibrous calcite occurred in many upper and lower reef samples, and blocky calcite spar was the most common cement type in the back-reef area. Lower and upper reef were exposed to freshwater dissolution and cementation. There was also more cementation and diagenesis in the lower reef compared to the upper reef, and an equal distribution of calcite cement around most of the grains, with an average porosity of 14.8%, consistent with fresh water phreatic environment. The beach rock was suggestive of marine phreatic diagenesis. Amino Acid Racemisation (AAR) and 14C dating of bivalve shells from upper and lower reef were unsuccessful for deducing the age of these reefs. U/Th dating produced the most reliable results for the age of the reefs. The reefs were probably formed during the major highstand of isotope stage 5 where the age of the upper reef is more likely to be 122.8 ka (MIS 5e) whereas the lower reef could be MIS 7 with no evidence of major tectonics in Rabigh area during the last 125 ka. The contribution of this study is that it has produced a new coral reef model relevant to a low energy system in a dry and hot environment. i

ACKNOWLEDGEMENTS

I would like to thank the support of my supervisor Associate Professor Brian Jones for his continued guidance, expertise and knowledge in this area of research. His support has encouraged me throughout the process of research, especially at difficult moments. I would also like to acknowledge the ongoing professional support of

Professor Colin Woodroffe for his particular insights into the world of coral. Also, I would like to thank Professor Colin Murray-Wallace for his efforts in the area of quaternary dating methods. I would like to extend my thanks to Professor Amin

Ghaith for his guidance and expertise in the field work. Many thanks to my colleague

AbdulGhani who provided specific support and assistance at various steps of the research process. A final word of thanks goes to my family for their support and patience during this extended research period.

TABLE OF CONTENTS ABSTRACT ...... i ACKNOWLEDGEMENTS ...... ii TABLE OF CONTENTS ...... iii LIST OF FIGURES/PLATES ...... vi LIST OF TABLES ...... viii Chapter 1- Introduction ...... 1 1.1 Coral Reef ...... 1 1.2 The Red Sea ...... 2 1.3 Coral Reefs of the Red Sea ...... 5 1.4 Carbonate rocks...... 7 1.4.1 Classification of carbonates...... 8 1.4.2 Diagenesis of carbonate rock...... 9 1.4.3 Skeletal mineralogy of calcareous organisms and algae...... 11 1.5 Study area ...... 12 1.5.1 Overview ...... 12 1.5.2 Climate ...... 14 1.5.3 Wind ...... 15 1.5.4 Tidal currents ...... 18 1.5.5 Tidal range ...... 18 1.6 Regional geology ...... 19 1.6.1 Tectonic history...... 23 1.7 Sediments in Rabigh area ...... 23 1.8 Previous work ...... 25 1.9 Aims of the study ...... 28

Chapter 2- Review of the Quaternary history of reefs in the Red Sea with reference to past sea-level changes ...... 29 2.1 Introduction ...... 29 2.1.1 Reef growth and development ...... 29 2.1.2 Coral reef zones and structures ...... 30 2.1.2.1 Reef Front (fore-reef) ...... 30

iii

2.1.2.2 Reef crest (algal ridge) ...... 33 2.1.2.3 Back-Reef (reef flat) ...... 34 2.1.3 Reef platform...... 36 2.2 Quaternary Reef Terraces of the Red Sea Coast ...... 37 2.2.1 Eastern Coast of the Red Sea ...... 39 2.2.2 Western Coast of the Red Sea ...... 40 Chapter 3- Methodology ...... 44 3.1. Sampling ...... 44 3.2. Particle size analysis ...... 48 3.3. Petrographic Analyses ...... 48 3.4. X-ray diffraction (XRD) ...... 49 3.5. Dating ...... 50 3.5.1 Amino Acid Racemisation Dating (AAR) ...... 50 3.5.2 Radiocarbon Analysis………………………………………………... 52 3.5.3 Uranium-Thorium dating…………………………………………...... 54

Chapter 4- Stratigraphy of coral reefs in Rabigh area ...... 55 4.1 Field description ...... 55 4.1.1 Lower reef ...... 59 4.1.2 Upper reef ...... 65 4.1.3 Back-reef ...... 71 4.1.4 Beach Rock ...... 76 Chapter 5- Petrography, XRD and Diagenesis for Carbonate Rock ...... 79 5.1 Particle Size Result of the Modern Reef top Area ...... 79 5.2 Standard Petrography Result ...... 80 5.2.1. Lower reef ...... 80 5.2.2. Upper reef ...... 83 5.2.3. Back-reef ...... 85 5.2.4. Beach rock ...... 87 5.3. XRD results ...... 89 5.3.1. Lower reef ...... 89 5.3.2 Upper reef ...... 91 5.3.3 Back-reef ...... 94

5.3.4. Beach rock ...... 97 5.4 Classification and diagenesis of carbonate rocks in the Rabigh area...... 98 Chapter 6- Dating result and discussion...... 102 6.1 Amino Acid Racemisation (AAR) result and discussion ...... 102 6.2 14C results and discussion ...... 110 6.3 U/Th Dating ...... 114 Chapter 7- Discussions ...... 117 7.1 Beach Rock ...... 117 7.2 Lower reef ...... 119 7.3 Upper reef ...... 123 7.4 Back-reef ...... 127 7.5 Models and morphology of the coral reefs in Rabigh area………………. 131 CONCLUSIONS ...... 139 REFERENCES ...... 143 Appendix 1: Thin Section Results...... 164 Appendix 2: XRD Results ...... 168 Appendix 3: Pie charts show the XRD result in different locations ...... 172

LIST OF FIGURES/PLATES

Figure 1.1 Coral Reef Types ...... 2 Figure 1.2 Global Distribution of Coral Reefs ...... 3 Figure 1.3 Map of the Saudi Arabian Red Sea Coast ...... 4 Figure 1.4 Location map of Rabigh area ...... 13 Figure 1.5 Wind Regime in the Red Sea and Saudi Arabia ...... 17 Figure 1.6 Main geological division of Saudi Arabia ...... 19 Figure 1.7 Geological map of Saudi Arabia ...... 20 Figure 2.1 Six models of fringing reef development ...... 32 Figure 2.2 Cross-section of reef zones ...... 32 Figure 2.3 Types of carbonate platform...... 36 Figure 2.4 Coral terraces at Rabigh Coast ...... 39 Figure 2.5 Global sea-level change ……………………………………………… 40 Figure 3.1 Sample location map ...... 45 Figure 3.2 A graph showing the details of coral limestones in the front reef area.....46 Figure 3.3 A graph showing the details of coral limestones in the back-reef area.....47 Figure 4.1 Location map of study area showing sample sites...... 56 Figure 4.2 The near-shore zone along the Rabigh coast ...... 56 Figure 4.3 Coral reef with upper and lower sequences at location 3...... 56 Figure 4.4 The upper and lower reef along the Rabigh coast...... 57 Figure 4.5 Elevation profiles of upper and lower reefs ...... 58 Figure 4.6 Two carbonate deposit in the back-reef area at location 6 ...... 59 Figure 4.7 The lower reef in location 7 ...... 61 Figure 4.8 Different coral genera from the lower reef in location 1 ...... 62 Figure 4.9 Corraline algae and corals from the lower reef in location 1 ...... 63 Figure 4.10 Lower reef in location 4 ...... 64 Figure 4.11 Lower reef in location 3 ...... 65 Figure 4.12 Upper reef at location 1 ...... 67-69 Figure 4.13 Upper reef at location 4 ...... 70 Figure 4.14 Upper reef at location 3 ...... 71 Figure 4.15 Back-reef at location 2...... 74

Figure 4.16 Back-reef at location 5...... 75 Figure 4.17 The reef at location 6 ………………………………………………… 76 Figure 4.18 The Beach rock in the study area...... 78 Figure 5.1 Coral and poor with a few specks of carbonate in the lower reef...... 82 Figure 5.2 Thin section for the upper reef...... 84 Figure 5.3 Correlation of reef height with algae and echinoderms at location 3...... 85 Figure 5.4 Thin section beach rock ...... 88 Figure 5.5 Correlation of high-Mg calcite with height in the lower reef...... 91 Figure 5.6 Correlatoin of height with different minerals...... 93 Figure 5.7 Correlation of stratigraphic height ...... 96 Figure 5.8 Samples from the lower reef showing neomorphism...... 100 Figure 5.9 Samples from the lower reef showing different types of cements...... 100 Figure 5.10 Dissolution in some samples...... 101 Figure 6.1 D/L ratio for Asp, Glu, Val and Ala amino acids ...... 104 Figure 6.2 D/L ratio of the 4 bivalves shells ...... 105 Figure 6.3 Relation between Valine D/L ratio for middle and late Plestiocene molluscan fossils from A: Australia, B: Mexico and C: Saudi Arabia with mean annual temperature in these areas ...... 109 Figure 7.1 Extent of the Rabigh reef area between Sharm Al-Kharar in the north and Sharm Rabigh in the south, showing sample locations, coral terraces and morphology of the area...... ………………………... 122 Figure 7.2 Diagram of the back reef sequence showing present outcrops and the back reef rubble material. ……………………………………………………130

Figure 7.3 Morphologic profiles of carbonate platforms………………………. 132

Figure 7.4 Corals from the species (Fungia and Favites) in the lower reef...... 133

Figure 7.5 The upper terrace in the Rabigh area shows a well development branching reef system with an upward growth. c-d back reef area and the back reef rubble ...... 134

Figure 7.6 Model for the development of carbonate reefs in Rabigh area showing the different reef zones and characteristic features…………………...... 135

Figure 7.7 Modern coral reef in Jeddah area ………………………………….. 138

vii

LIST OF TABLES

Table 1.1 Petrographic properties of carbonate minerals...... 8 Table 1.2 Folk’s (1962) classification of carbonate texture...... 9 Table 2.1 Zonation and Coral Species within the Indian Ocean………………… 31 Table 2.2 Summary of the terraces in previous studies on the eastern and western coasts of the Red Sea...... 43 Table 3.1 Latitude and longitude and number of samples collected from each site 44 Table 3.2 Mass of each sample and the amount of HCl………………………….. 52 Table 4.1 Identification of the main coral genera in the lower reef……………. 63 Table 4.2 Identification of the main coral genera in the upper reef ...…………. 69 Table 4.3 Identification of the main coral genera in the back-reef ...... ……….. 73 Table 5.1 Percentage of the texture components in section 1…………………….. 79 Table 5.2 Percentage of the texture components in section 2…………………….. 80 Table 5.3 Quantitative composition in the lower reef at Rabigh area…………. 82 Table 5.4 Quantitative composition in the upper reef at Rabigh area…………. 85 Table 5.5 Quantitative composition in the back-reef at Rabigh area……………... 86 Table 5.6 Mineral percentages in the lower reef at Rabigh area……………….. 90 Table 5.7 Mineral percentages in the upper reef at Rabigh area……………….. 92 Table 5.8 Mineral percentages in the back-reef sequence at Rabigh area…………...95 Table 5.9 Mineral percentages in the beach rock units at Rabigh area………... 98 Table 6.1 Location of bivalve shell samples used in amino acid racemisation……..103 Table 6.2 Average amino acid racemisation………………………….……………..103 Table 6.3 Results of D/L ratio...... 103 Table 6.4Comparison between Keenan et al. (1987) and Rabigh area………...... 108 Table 6.5 Valine average D/L values in middle and late Pleistocene molluscan fossils from three different areas ...... 109 Table 6.6 Samples detail and results of radio carbon dating ...... 111 Table 6.7 Radiocarbon dates of coral limestones from the west coast of Saudi Arabia (Behairy, 1983)...... 112 Table 6.8 Results of age dating for coral samples using U/Th dating…...... 114

viii

Chapter 1- Introduction 1.1 Coral Reefs

Coral polyps are tiny sea creatures. They protect themselves by secreting calcium carbonate, which builds up to form hard skeletons around their soft, cylindrical bodies. Polyps stay all their lives in one place, fixed tightly to the skeletons of dead polyps. A reef builds up from the skeletons of millions of dead polyps. There are many types of coral reef and, according to Darwin's (1842) widely accepted theory of coral reef formation three types of reefs were recognised: fringing reefs, barrier reefs and atolls (Fig. 1.1).

Fringing reefs represent the most basic reef form and develop near the shoreline where favorable environmental conditions exist. They are considered as the main reef type in the Red Sea, dominating most of the shorelines in the north. Barrier reefs are long coral ridges separated from the coast by a deep lagoon (e.g. Great

Barrier Reef). Most barrier reefs rise from a platform or terrace. These barrier reefs may become a fringing reef if the lagoon between the barrier and the shore fills and narrows. Coral atolls are ring-shaped islands surrounding a shallow lagoon which may be almost enclosed or relatively open to the ocean (e.g. atolls of the Maldives).

Many factors control the growth of coral reefs including temperature, salinity, water turbulence, depth and light. Coral reefs mostly develop in shallow, warm water, usually near land, and mostly in the tropics; they prefer temperatures between

21-30°C, sufficient illumination and salinity levels between 34-36%. However, some corals grow in the deep, cold sea (called deep or cold-water corals) but only a few species of deep-water coral develop reefs (Watling, 2001).

Fig. 1.1 Coral Reef Types a) Fringing Reef. b) Barrier Reef. c) Atoll (Woodroffe,

2002).

Corals cover more than 250,000 km² of the Earth’s surface (Veron, 1995) and they appear off the eastern coast of Africa, southern coast of India, the Red Sea, northeast and northwest Australia, Polynesia, Micronesia, Florida, USA, Caribbean and Brazil (Shefer et al., 2004) (see Figure 1.2).

1.2 The Red Sea

The Red Sea is a marginal marine basin that began to develop at 20-30 Ma and is almost entirely enclosed by the African continent and the Arabian Peninsula

(Fig. 1.3).

Fig. 1.2 Global distribution of coral reefs (Barnes and Hughes, 1999).

Exchange of water masses with the Indian Ocean is restricted by the narrow and shallow sill (137 m maximum water depth) at the Strait of Bab el Mandab, which is currently 25 km wide in the south (Smeed, 2004). The Red Sea is a geologically recent opening and one of the youngest oceans on Earth. Its current extended form was developed through slow seafloor spreading over the last 4-5 Ma. The length of the Red Sea is about 1900 km and approximately 40 % of the Red Sea is quite shallow (less than 100 m) with about 25 % of the Red Sea being less than 50 m deep. No permanent river flows into the Red Sea but occasionally sediment is brought into the Red Sea via a number of wadis especially in the south. The Red Sea is regarded as one of the most saline seas in the world with salinity ranging between

36 and 40 ‰ (Fig. 1.3). The impact of evaporation and wind dynamics in the Red

Sea dictate water circulation patterns. Additionally, many biological species are endemic to the Red Sea, including coral reef and fish species, which have access to distinctive marine environments, such as sea-grass beds, salt-pans, mangroves, coral reefs and salt marshes.

Fig. 1.3 Map of the Saudi Arabian Red Sea Coast showing salinity profiles and indicating coral reef densities: shading represents areas of 500 m x 500 m quadrat reef coverage (modified from PERSGA/GEF, 2003, and Saifullah, 1996)

The Saudi Arabian Red Sea coast is divided into three regions that are somewhat diverse in types and distribution of coastal and marine reefs and environments. These are: northern region of the Gulf of Aqaba; the northern-central

region from south of the Gulf of Aqaba through to Jeddah; and the central-southern region from Jeddah south to the border with Yemen (which includes the Farasan

Bank and Islands; PERSGA, 2003).

1.3 Coral Reefs of the Red Sea

Since most hermatypic corals live in at temperatures higher than 18ºC, the average temperature in the waters of the Red Sea, which ranges between 21- 22ºC, is suitable for the growth of corals. The depth of many coastal waters being no more than 45 m deep is also conducive for coral growth. On the other hand, the coral reef system also protects a wide range of other marine life in the same environment. The salinity of the Red Sea waters ranges from about 36.5 ‰ at "Prem" island in the south up to 40.5 ‰ in the northern parts. It is clear from a study of marine charts of the Red Sea coral reefs that there are fewer reefs in the presence of rivers mouths and valleys. Being positioned close to a valley results in both a high proportion of clastic sediment deposits in the near-shore zone and decreased salinity levels, which in turn results in many gaps in the coral reefs. The researchers noted that the existence of living coral reefs that extend along the Red Sea coast were found to depths of more than 100 m. These coral communities might survive and not accrete as many mesophotic systems appear to do. However in most cases, these depths do not allow building of coral reefs, and this means that either the coral reefs developed when sea level was lower than at present or that the sea bed was higher than it is now.

The Red Sea is rich with coral reefs. Up to 200 coral species are found in the central Red Sea and the most efficient builder along reef margins is Stylophora, associated with Acropora hyacinthus, A. horrida and A. humilis. Some Indian and

Pacific Ocean fauna has moved into the Red Sea through the Bab-el-Mandeb Strait in the south. The Red Sea provides an appropriate environment for the development of a rich variety of fauna, of which coral reef growth is one. This is due to the favorable environmental conditions in the Red Sea in relation to temperature, shallow depths, water purity and high salinity. Coral reefs have developed an unusually high tolerance to the extreme temperatures and salinity that occur in the Red Sea. Such conditions that would be lethal or highly damaging to most hard corals found in other parts of the Indo-Pacific region or in the Caribbean.

Within the Red Sea the distribution of reefs is determined by region, so that the northern gulf area has much better developed reefs on the western Gulf of Suez than on the east coast (UNEP, 1992). Meanwhile, the Gulf of Aqaba contains primarily narrow fringing reefs or contour reefs. The mainland fringing reef is common throughout the Red Sea coastline, generally located near to entrances or sharms which are peculiar to the Red Sea (Ormond et al., 1984). Sharms are drowned valleys along the Red Sea coast that bear coral reefs and cut into the coastal plain of

Tihamah at the foot of the Precambrian granitic mountains of Higaz. The northern

Red Sea is the site of the most classical formations of fringing reefs, between 18-

20°N (UNEP, 1992). The fringing reefs in the southern part of this region can be found extending up to one kilometre seawards. The central Red Sea between Jeddah and Sudan is at its widest point, and accordingly is a source of a vast variety of reef types. On the Arabian side of the Red Sea the reef type is similar to that observed in the northern regions since barrier reefs are also clearly developed (UNEP, 1992). In the southern Red Sea area there is a noticeable lack of reef growth, and this is believed to be related to higher sedimentation rates and the large number of sandy beaches and shores in the southern area (UNEP, 1992). Therefore, it is observed that 6

along the entire length of the Saudi Arabian Red Sea coastline there are numerous coral reefs. Furthermore, with the notable exception of both the Jeddah and Yanbu areas, these coral reefs are maintained in an almost pristine condition (DeVantier and

Pilcher, 2000). There is no previous record of reef structures within the Rabigh area.

1.4 Carbonate rocks

Carbonate rocks are those deposits that consist of greater than 50% carbonate minerals, with up to half of the world’s ocean floors covered by carbonate sediments

(Lisitzin, 1971). Some areas are significant in their levels of carbonate sedimentation, such as shallow seas in tropical and subtropical areas located between

30° N and 30° S, such as the Bahamas, the Red Sea, the Arabian Gulf and along the

Queensland coast of Australia. There is also evidence of carbonate deposits in deep water marine environments, such as the Atlantic, Indian and Pacific Oceans (Flügel,

1982). The most important carbonate minerals are calcite, aragonite and dolomite

(Table 1.1).

The majority of carbonate deposits originally develop from marine sources including organic materials such as shells, or chemical processes seen when there is a high concentration of carbonate in the water. Limestone commonly develop from the concentration of bioclasts developed by calcareous organisms, therefore correlating with biological activity in areas such as shallow or warm seas that feature little or no siliciclastic input.

Table 1.1 Petrographic properties of carbonate minerals (from Milliman, 1974, and

Folk, 1974).

Low- Mg Calcite High-Mg Calcite Aragonite Dolomite

Formula (CaCO3) (CaCO3) (CaCO3) CaMg(CO3)2

Crystal system Trigonal Trigonal orthorhombic Trigonal

Mol% MgCO3 < 4 >4 to> 20 - 40-50

Environment Deep marine or Shallow marine Shallow marine Shallow marine fresh water

1.4.1 Classification of Carbonates

Folk (1962) and Dunham (1962) developed the carbonate classification systems most commonly used today. Both of these systems base their classification on rock texture which, in turn, is controlled essentially by depositional environment.

Dunham’s system centres on depositional texture, the level of matrix surrounding the grains at the time of deposition, and uses the terms mudstone, wackestone, packstone, grainstone and boundstone. This system is preferred because it is based on simple terminology that is environmentally significant, and is easily understood, thus leading to its significant use in industry and academic discussion. Dunham’s system is easily deployed for hand samples and thin section analyses, and is useful for facies description. However, there are limitations in its ability to assess diagenetic effects in detail, such as cement or dolomite. The Folk system has been used since the 1960s, and its popularity lies in the fact that it is useful for petrographic rock description. Moreover, it is both more flexible and comprehensive than the Dunham system, as it provides greater genetic understandings. However, the limitations of the

Folk system are that it is complicated, and requires a significant level of expertise to maximise the analysis. Within this research, it is more fruitful to apply the Folk classification system.

Table 1.2 Folk’s (1962) classification of carbonate texture

1.4.2 Diagenesis of carbonate rock

The chemical, physical and biological changes that occur within sediment after the time of deposition are known as diagenesis (Bates and Jackson, 1980). Such processes are realized through primarily six main mechanisms, including: cementation, microbial micritization, neomorphism, dissolution, compaction

(including pressure dissolution) and dolomitization. The transformation of sediments and growth frameworks of reefs to limestone starts during the process of deposition, although more significant transformations occur after burial and uplift of the limestone. The importance of diagenesis is that it influences reservoir quality, through the depositional environment, burial and diagenetic history. Within

9 carbonate rocks, diagenesis can commence early on, leading to either cementation or the preservation of permeability in the rocks. Factors that influence the diagenesis include composition and mineralogy of the sediment, pore-fluid chemistry and rates of flow, geological history of the sediment in relation to burial, uplift and sea level changes, the contextual climate, and the input of various pore-fluids (Bathurst, 1975).

Diagenesis can alter the porosity of carbonate sediments, although these reflect a general trend towards increasing depths of burial, with decreasing porosity. There are three major environments where carbonate diagenesis is observed, marine, near- surface meteoric and burial environments (Bathurst, 1971).

It is necessary for this research to understand in more detail the processes that create diagenesis: cementation, microbial micritization, neomorphism, dissolution and compaction. Cementation is simply the precipitation of cements in the carbonate sediments, occurring when the pore-fluids are supersaturated in the absence of kinetic factors. Additionally, the role of organic geochemical influences is significant, such that aragonite, calcite and dolomite are seen to be the most frequent carbonate cements in limestone. Limestone needs significant levels of CaCO3, with the source of this varying in different environments (Tucker and Wright, 1990). For marine environments, this is sourced from seawater, but in meteoric and burial environments it is related to the dissolution of sediment (Moore, 1989). Within reef rocks, peloids act as precipitates instead of grains or faecal pellets. Microbial micritization is the transformation of bioclasts to micrite on the seafloor, or below due to endolithic algae, fungi and bacteria. The boring of skeletal grains and fine- grained carbonate sediment creates micritic envelopes, such that micritized grains develop. These grains are often irregularly shaped, which makes them different to micritic faecal pellets. Neomorphism was a term first developed by Folk (1965) and 10

refers to replacement and recrystallization processes that are linked to changes in mineralogy. Due to the mixture of calcite and aragonite in carbonate sediments neomorphism is preferred instead of recrystallization. Neomorphic processes occur in water, and dry processes such as inversion or recrystallization are not usually seen in limestone as diagenetic environments are typically wet environments.

Additionally, the role of calcite replacing aragonitic grains and cements is known as calcitization, as it is another replacement process. Within this process original minerals slowly dissolve, with some remnants remaining in the original shells or neomorphic calcite. Dissolution occurs when carbonate sediments, cements and lithified limestone are immersed in undersaturated pore-fluids in relation to carbonate mineralogy. Grains are individually dissolved and this process is an essential factor in near-surface meteoric environments. In the equatorial Pacific seawater also causes dissolution of aragonite (Tucker and Wright, 1990). Finally, compaction is the process by which grain fractures occur due to the heightened burden on non-cemented carbonate sediments. Compaction can be either mechanical or chemical in nature, with mechanical compaction based on the fracturing of grains leading to sutured and concavo-convex contacts, while chemical compaction occurs in lithified limestone and creates stylolites and dissolution seams. Hundreds of metres of overburden are needed to create such structures (Bathurst, 1975).

1.4.3 Skeletal Mineralogy of Calcareous Organisms and Algae

The mineralogy of recent calcareous organisms and algae has been discussed by a range of authors, with the major characteristics outlined below (Lowenstam,

1963; Scholle, 1978; Montaggioni and Braithwaite, 2009). 11

Corals are predominantly composed of aragonite, although sometimes calcite has been observed (Houck, Buddemeier, and Chave, 1975). Calcareous algae are broken into two types – red algae and green algae. Red algae are typically located in reefs and secrete Mg-calcite crystals, creating a firm structure. Green algae secrete freely bound aragonite crystals in their cell walls. Bryozoans secrete calcite; however there is evidence of secondary aragonite. The foraminifera include encrusting species that secrete Mg-calcite skeletons. A vast range of molluscan assemblages are sourced in the reefs, and contain aragonite and calcite. Echinoderm skeletons are based on

Mg-calcite, so that echinoid spines are long yet only made of single crystals.

Arthropods are not well mineralized, and therefore, do not form sediment components. The minerals aragonite and high-Mg-calcite are metastable, and this means that over periods of time they are prone to changes.

1.5 Study area

1.5.1 Overview

The western coastline of the Kingdom of Saudi Arabia is about 1840 km long, accounting for 79% of the eastern seaboard of the Red Sea. The Rabigh coast

(N 22° 47′ 16.49″and E 38° 57′ 13.46″) is located about 130 km north of Jeddah

City, the main coastal city along the eastern side of the Red Sea (Figs 1.4, 1.5). The

Rabigh coast is about 30 km long and features lagoons, sand dunes and coral terraces. Al-Kharrar Lagoon is located in the northern part of the Rabigh area within the coastal plain and is connected to the adjacent Red Sea at its northwestern side by a narrow, shallow channel, while Rabigh Lagoon is located in the southern part of

the Rabigh area. Most of the Rabigh coast is characterized by raised coral reefs covered by terrigenous and marine sediments representing old shoreline deposits.

The Rabigh coast is characterized by these coral terraces in the area of the

"Marine Sciences College" where the coast is crescent shaped and the fossil reefs are up to 6 m above sea level. The backshore in this area is narrow (about 45 m) but the nearshore is broad ranging from 150 to 250 m wide, and consists of a hard flat coral reef platform covered by a thin layer of carbonate sediments (Gheith and Abou Ouf,

1994). The latter come from marine erosion of the submerged marine platform and the biological activities in this area where the water depth is less than 60 cm.

Fig.1.4. Location map of Rabigh area, The Marine Sciences College is situated at

location 1. The study aites are all numberd.

1.5.2 Climate

The climatic conditions in Saudi Arabia in relation to temperature are quite variable, with temperature rising to 50°C (122°F) in the June-August summer period, while during the winter period, the northern and central regions experience temperatures below freezing. The average temperature in Saudi Arabia is 25.3 °C (77

°F), with a highest monthly average temperature of 45 °C (113 °F) during July and

August, and the lowest monthly average temperature of 3 °C (37 °F) during January and December (Saudi Presidency of Meteorology and Environment, 2005).

Climatic conditions along the western coastline of Saudi Arabia include a belt of tropical humid climate, with humidity reaching up to 68% in some coastal areas.

However, in inland areas it is milder and drier across the entire year. The average annual relative humidity is thus 24.5%, with an average monthly relative humidity ranging from 10% in September at its lowest, and up to 46% in December at its highest. In contrast, the inland desert environment produces an extremely hot and arid climate combined with minimal levels of precipitation and significant evaporation (averages of 60 mm y-1 and 2050 mm y-1, respectively; Behairy et al.,

1991). The aridity of the area means that diagenesis of the last interglacial reef system was minimal.

The mean annual temperature in Saudi Arabia is 250C according to the Saudi presidency of meteorology and environment (PME) while the average annual temperature of the surface waters near the north of the Red Sea is 25°C, increasing to 26.6°C at 22° N and 28.8°C at 16° N, but the average annual surface water temperature decreases to 27.7°C at the Strait of Bab el-Mandeb. Finally, across the entire Red Sea basin there is significant seasonal variation in surface sea water temperature, ranging between 22 and 32°C. 14

The Saudi Arabian coast is characterised by localized and infrequent rainfall.

For example, the average rainfall is less than 70 mm/yr along the broader coastal plain at Tihamah, 16 mm/yr at Al Wejh, 63 mm/yr at Jeddah and 63 mm/yr at Jizan

(UNEP, 1997). The range of relative humidity is from a minimum of 50% during the winter season to a maximum of 68% during the summer season. The driest months are the late summer and autumn months of June-October when no rain falls. The wettest month is recorded as April, with an average rainfall of 21 mm. In some regions, such as the Rub Al-Khali, rainfall can be non-existent for up to 10 years.

During the spring season the northern region of the Red Sea can be affected by desert depressions, although this is not typical of the Rabigh area. Desert depressions produce heightened levels of atmospheric dust, and reduce visibility

(Morcos, 1970). Additionally, dust storms are a common occurrence and move out over the Red Sea creating low visibility conditions.

1.5.3 Wind

Two wind flows are important in the study area, firstly, from the

Mediterranean down the Red Sea axis in the central region, and secondly, from the

Indian Ocean following up the Red Sea axis. Both of the flows have the possibility of causing rain, and they meet at the mid-point in week variable winds. In summer these wind flows range the full length of the Red Sea, although they are in an anti- clockwise direction over Arabia and Iran and do not cause rain. Rain averages are insignificant at about 50 mm; however, this is generally achieved in just a few hours, and, therefore, can lead to flash floods and terrestrial run-off, again linked to the death of coral reefs. The development of reefs is more likely to be influenced by the

15 sea breezes as the alignment of reefs is influenced by the angle of the approaching waves. These winds are the most significant in the Red Sea area, and can create a median wave height of up to 0.6 m at the open and outer edges of the reef (Georeda,

1982).

The wind regime in the Rabigh region is characterized by such seasonal and regional variations in speed and direction with average speed generally increasing northward (UNEP, 1997; Patzert, 1974). The northern region of the Red Sea, generally understood as the region north of latitude 20° N (Fig.1.3), is subjected to north-northwest winds throughout the year, with speeds from 7 to 12 km h-1 (Rao and

Behairy, 1986). However, the occasional winds from this direction are slightly more frequent in summer than in winter. Southerly winds occasionally blow during winter months only, with this region being distinguished by low pressure calms (UNEP,

1997).

Fig. 1.5 Wind regime in the Red Sea and Saudi Arabia during winter and summer (Modified from Sheppard et al., 1992) (ITCZ: Inter tropical convergence zone).

1.5.4 Tidal currents

In the Rabigh region, tidal currents are typified by oscillatory and semidiurnal patterns, resulting in an average increase in sea level of 1 m during the winter period

(UNEP, 1997). The tidal velocity generated through the reef, sand bars and low island constrictions reaches 1-2 m/sec. Generally speaking, the tidal current speed operates anywhere between 50 and 60 cm/sec, reaching a maximum of 2 m/sec. This is considerably greater than that of the north-north-east current along the Saudi coast, which is 8-29 cm/sec (UNEP, 1997). Wind has limited impacts on the current speed.

1.5.5 Tidal range

The tidal range is between 60 cm in the north, at the Gulf of Suez, and up to

90 cm in the south at the Gulf of Aden. However, away from these nodal points the tidal range varies between 20 cm and 30 cm. The Red Sea near to Jeddah is almost without tide, and the north and north-eastern winds shape the water movement in such coastal areas. During winter sea level is 0.5 m higher than in summer periods.

Although the tidal range is low (20–30 cm), during high tide water inundates the adjacent sabkhas. The dominant north and northeastern winds during this time impact on the flow of lagoon water to the adjoining sabkhas, phenomena particularly marked during storms. Despite this, the low tidal range impacts the sabkhas through a thin sheet of water rather than inundating the sabkhas through a network of channels (Behairy et al., 1991).

Fig.1.6 Main geological division of Saudi Arabia

1.6 Regional geology

On a broad scale, Saudi Arabia can be geologically divided into four different terrains: the Arabian Shield, Arabian platform, Tertiary 'harrats' and the Red Sea coastal plain (Fig. 1.6). The study area is located in the middle of the narrow Red Sea coastal plain which is known as Tihamah. The coastal plain marks the eastern edge of the north-south Red Sea graben, which is bordered by older escarpments and

Oligocene-Recent sedimentary rocks (Vincent, 2008). This coastal plain extends along the eastern Red Sea for about 1800 km from the Gulf of Aqaba and the border with Jordan in the north, to the border with Yemen in the south (Sagga, 2004). The 19 breadth of the plain varies from place to place; it is very narrow in the north, as is the case north of Al Wajh, but it widens irregularly toward the south reaching 40 km wide in the region of Jizan (Chapman, 1978; Fig. 1.6). The coastal plain is bordered in the south by a group of small hills, followed by a series of mountains parallel to the western highlands (Al-Hejaz and Asir highlands). These highlands extend along the Red Sea from the border with Jordan in the north to the border with the Yemen to the south, with a length of almost 1550 kilometres, and they vary in width from a few kilometres to 140 kilometres (Sagga, 2004). Sharms are drowned valleys along the

Red Sea coast that bear coral reefs, and cut into the coastal plain of Tihamah at the foot of the Precambrian granitic mountains of Hejaz. The Tihamah is made of fluviatile alluvium in its inner part and in its outer part of Pleistocene coral reefs.

Fig. 1.7 Geological map of Saudi Arabia

There are a number of peaks that exceed a height of 2000 m above sea level, with the pinnacle of Al-Sawdah Mountain west of Abha (Fig.1.6) representing the highest peak at a height of 3015 metres above sea level. The highlands descend abruptly into the Red Sea, and gradually inward towards the east. The western highland formed as a result of geological movements that occurred during the

Triassic, which led to the separation of the Arabian plate from the African shield.

These movements have led to the formation of longitudinal valleys that permeate these highlands from north to south or vice versa and these lengthy valleys extend to the coastal plain, or to the interior regions where water is often lost in the sand (Al-

Shanti, 1993).

The western highlands are composed of granite, gneiss and schist, that are robust and resistant to erosion processes. These rocks are covered by flood basalt

(Al-Harrat) ranging in age from late Triassic to Quaternary (Al-Shanti, 1993). The coverage of the Al-Harrat is significant throughout the western Arabian plate, reaching up to 180,000 km2 from Yemen in the south through to Syria in the north.

Tertiary and Quaternary lava extends throughout Saudi Arabia associated with a fractured/faulted tectonic regime recognisable from the Oligocene or early Miocene at about 25 Ma at the start of rifting. The extension fissures along the axis of the Red

Sea have enabled the rise of basaltic magma, due to the stress created by the production of the magma at significant depths. Significant proportions of the magma have risen to the surface, and this has led to the creation of flows that formed the basaltic plateaus, or harrats, which extend throughout the Arabian Shield including the Red Sea coastal plain and escarpment.

In the Rabigh area the coastal plain is relatively narrow, about 20 km wide, and comprises thick sequences of sedimentary rocks, primarily Late Mesozoic and 21

Cenozoic (Vincent, 2008). It consists of continental and marine sediments and some volcanic cones with many salt marshes and sand dunes spread along the surface. In addition, no rivers occur in the area but many wadies descend from the western highlands to the Red Sea and the coastal plain is commonly cut through at the shelf edge by lagoons locally known as sharms (Brown et al., 1989). It is not clear whether the remains of Oligocene deposits in the coastal plain are left over from pre-rifting tectonic activity or were once more commonly distributed and now represent the last preserved remains of a later rift zone deposit.

Since the early Miocene, at about 25 Ma, and continuing until today, there is significant evidence of eruptions. Finally, the harrats of Saudi Arabia reveal consistent volcanologic, petrographic and structural features, and are predominantly positioned between 50 and 500 km east of the Red Sea coast. Such features include emissive axial zones that are organized around complex alignments of volcanic- emission centres and emission points lateral to such zones.

The marine beds formed during the opening of the Red Sea in the mid-

Miocene are overlain by clastic sedimentary and Pliocene reef rocks, which are now enclosed by Quaternary reefs (Vincent, 2008). The shoreline is generally a little jagged, and it contains many spikes, bays (sharms), uplifted coral reef terraces, clastic accumulation terraces and submarine coral reefs (Al-Shanti, 1993). Also scattered along the vicinity of the coast are about 1150 islands, differing in size and distance from the coast, and representing about 88% of the total islands in Saudi

Arabia, whereby Farasan Al-Kabir represents the biggest island with an area of 380 km2 (Al-Gazawe et al., 2007). The Tihamah is made of fluviatile deposits in its inner part and in its outer part of Pleistocene coral reefs.

1.6.1 Tectonic History

During the Mesozoic period there was a lack of evidence of tectonic activity, both in and around the Red Sea. Yet, the interlayering of basaltic rocks with

Cretaceous sedimentary rocks shows the start of volcanic activity, including the emplacement of thick trap rock sequences in Yemen (Guekens, 1966). The shorelines of early and middle Eocene age extend throughout the southern tip of the Red Sea, such that the horn of Africa was emergent by the end of the Eocene epoch (Mohr,

1962). During the Oligocene period the separate great uplifts on both sides of the

Red Sea developed, and these are accompanied by outpourings of alkaline basalts.

These alkaline basalts have now created thick trap series as high plateaus, located behind the Arabian and Ethiopian scarps. During the Pliocene and Pleistocene period, there was continued uplift and erosion along the southern borders of the Red

Sea (Ross et al., 1972). In the late Quaternary period, the tectonic history of the eastern Red Sea shows a major uplift in the northern part of the area, at the Gulf of

Aqaba, with the remaining sequence lacking any major uplift along the eastern Red

Sea coast, including the study area, which is at Rabigh.

1.7 Sediments in Rabigh area

The sediment in Rabigh area can be divided into the following types:

1 – Beach surface sediment: These sediments are found along the coast and around

Sharms Rabigh and Al-Kharrar. These sediments are limestone deposits rich in coral reef and shell material. They consist of calcareous sand and clay and extend to 10 m water depths. According to Basaham (2008), the coastal sediments of Sharms Rabigh and Al-Kharrar are siliciclastic-carbonate sediments that were deposited as a result of 23 a complex interplay of climatic and oceanographic processes. The oxic surface sediments in the mud fraction have developed as a result of the punctuated mixing of carbonate and siliciclastic (terrigenous) materials. Aeolian transport of terrestrial materials is dominant during dry periods, when the physical weathering is very active. On the other hand, wave and current sediment transport actions occurred in the shallow depths of the sharms. According to Gheith’s (2000) study, the surface features of most aeolian sand along the Rabigh coast have mechanical V-shaped pits, upturned plates and curved pitted grooves. These features proved that wind transported some of the beach and nearshore sand and its deposition was influenced by waves and tidal currents.

2- Deposits of calcareous sediments: These deposits cover a large area, extending from the coast in the west, through to the valleys in the east approximately 90 km away. Within the valley region the deposits generally consist of sandy limestone mixed with clay minerals from the floods originating in the adjacent western mountains. According to Al-Washmi (1999), calcareous sediments could have originated from erosion of the coastal reefal limestone terraces.

3- Flood deposits: these are alluvial mud deposits at the mouths of major valleys.

They consist of silt, clay and fine sand. Flood sediments may reach more than 20 m in thickness in this region (Al-Baroudi, 1990) and these areas are rich in plants, trees and palms. In addition, these sediments occupy the low ground in all the valleys and originated from water and wind erosion of igneous rocks in the adjacent mountains and the basalt rocks which contain a high proportion of iron oxides. Also, the

Arabian Shield rocks beneath the basalt consist of granite and when these rocks are weathered over long periods of time, they become fine sand and clay. According to

Al-Washmi (1999), the fine-grained detrital materials and fresh water were moved 24

by floods and wind to low subsidiary valleys, and then to the main valleys and taken away in a westerly direction depending on the topography of the area.

1.8 Previous work

Previously published work on the coral reefs of the Red Sea will be examined in chapter 2. Although the Rabigh area has not received much attention from researchers during the last century, more work has been done in surrounding areas, especially Sharm Al-Kharrar (El Abd and Awad, 1991; Abou Ouf and El-Shater,

1993; Abou Ouf, 1996; Al-Washmi, 1999; Basaham, 2008). The following section summarizes the conclusions of the work conducted on the Rabigh and Sharm Al-

Kharrar area.

A series of investigations about sedimentological and mineralogical aspects of the beach zone of the western coast of Saudi Arabia, to the north of Jeddah, have been conducted by Behairy (1980, 1983), Behairy et al. (1985, 1991), and

Durgaprasada Rao and Behairy (1984, 1986).

Behairy (1983) studied the age of three limestone coral terraces between

Jeddah and Yanbu, with one of them located at Rabigh. Based on radiocarbon ages from these reefs, Behairy (1983) indicated four marine transgressions between the mid-Pleistocene and present at about 31,000, 16,600-18,100, 9980 yr B.P. and mid-

Holocene, and he attributed the reason for the present elevations of the marine terraces above modern sea level to tectonic uplift on the west coast of Saudi Arabia.

Also, Behairy et al. (1991) studied the evaporitic supratidal and intertidal sediments around Sharm Al-Kharrar and illustrated two evaporative assemblages.

The first assemblage in the southern part of the sharm contains gypsum, high-Mg calcite, dolomite and aragonite in the subsurface sediments. Dolomite is absent in the

25 surface sediments, which indicates a replacement of aragonite by dolomite and active diagenetic processes. The persistence of aragonite in the subsurface sediments indicates a low Mg concentration that failed to reach the necessary level to initiate full diagenetic dolomitization of aragonite. The second assemblage in the central and northern part of the sharm includes gypsum and high-Mg calcite in the surface sediments and aragonite in the subsurface sediments with low concentrations of magnesium, in part due to processes of evaporation.

Moreover, numerous different textural, mineralogical and foraminiferal studies have been carried out on Sharm Al-Kharrar bottom sediments and the associated sabkha (El Abd and Awad, 1991; Abou Ouf and El-Shater, 1993; Abou

Ouf, 1996). Subsequent studies by Al-Washmi (1999) also investigated the textural composition and the gross mineralogy of the bottom sediments of Sharm Al-Kharrar and their conditions of sedimentation. The result shows that the southern part of

Sharm Al-Kharrar is connected with ancient valleys which are, during rainy periods, the source of the fine-grained detrital materials including quartz and feldspar. These materials are observed together with an increased deposit of suspended clay material that results from the mixing of saline water with fresh water through conditions of low energy. In contrast, in the northern part aragonite and high-Mg calcite are the dominant minerals with rare calcite and dolomite. Al-Washmi (1999) suggested that during the late Pleistocene, Sharm al-Kharrar was a site for fluvial deposition during the last glacial sea level lowstand. Subsequently it came under the influence of sea transgression during the Holocene.

Gheith and Abou Ouf (1994) studied and compared the textural characteristics, mineralogy and benthonic foraminifera along the shore-zone at

Rabigh and at the outlet of Sharm Al-Kharrar. The particle size results suggested that 26

the near-shore zone is characterized by coarse-grained sediments composed of carbonate grains with abundant benthic foraminifera while the backshore and foreshore are generally made up of finer grained sand. Amphiboles, pyroxenes and epidote are more common than stable heavy minerals, such as zircon and tourmaline, in the shore-zone sediments with only small amounts of quartz and feldspar. It has been determined that stable heavy minerals such as zircon and some tourmaline were derived from acidic igneous source rocks, due to their euhedral shape, and the large quantity of them found. Amphiboles, pyroxenes and epidotes are derived instead from metamorphic and acidic to basic source rocks. The heavy minerals in the shore zone sediments at Rabigh are concentrated by wind deflation of light grains.

Basaham (2008) studied the geochemistry of major and trace elements in the surface sediments of Sharm Al-Kharrar and provided data on the occurrence of some major and trace elements in the fine-grained mud fraction of these sediments. The results found that the sediments were predominantly silt sized particles, and that these featured low organic carbon and variable CaCO3. A number of elements revealed a wide range of concentrations in the sharm, including Al, Fe, Mn, Cu, Ni,

Cr, V and Ba. Additionally, this study explored the processes that determine the natural level of these elements, such as episodic freshwater flooding and mixing with seawater.

1.9 Aims of the study

The main aims of the current study are to:

1) describe the facies changes and deduce the diagenetic variations within the

different coral reef units, along the Rabigh coast;

2) define the reef system and interpret the palaeoclimate and palaeogeography

during the formation of old carbonate reef shorelines;

3) identify and analyse the relationships between old shorelines and sea level

changes during the late Quaternary; and

4) develop a coral reef model for a low energy system in a dry and hot

environment.

Chapter 2- Review of the Quaternary history of reefs in the Red Sea

with reference to past sea-level changes

2.1 Introduction

2.1.1 Reef growth and development

Coral reefs can be divided into Atlantic and Indo-Pacific coral assemblages, where the Atlantic assemblage is centred on the West Indies and the Indo-Pacific assemblage occurs through most of the tropical Indian and Pacific Oceans

(Woodroffe, 2002). Corals in each province have a different growth form. Also, as mentioned before, warm temperature, light and clean water appears to be essential for coral growth. For example, branching corals are more common in high turbidity areas due to its ability to cope with high sediment loads (Woodroffe, 2002). Scoffin

(1987) and Wood (1999) described reef growth involving five processes which include; primary framework, secondary framework, erosion processes, internal sedimentation and cementation. Many studies have been done on coral reef growth and different growth rates suggested by these studies variy from 2 mm/year as suggested by Smith and Kinsey (1976) to a maximum growth of 414 mm/year as originally reported in the Celebes by Verstelle (1932, cited in Hoeksema and Moka

1989). This variation in growth rate is subject to many factors, such as wave stress and sediment flux. In terms of reef development, six broad models of Holocene fringing reef development were identified by Kennedy and Woodroffe (2002) based on chronostratigraphic data (Fig. 2.1).

2.1.2 Coral reef zones and structures

Reef zones vary according to the geographic location and type of reef, with reef zonation best understood in relation to physiographic and biological distribution.

Reefs are organized into zone categories, as evidenced in the Indian Ocean, with

Madagascar, Seychelles and the Maldives Islands forming separate zone categories.

A number of physiographic and biological data are observed, generally about 7 or 8 categories (Table 2.1), such that the zonation categories at Madagascar and Mauritius both feature an outer slope, at 20 m for Madagascar and 5 m for Mauritius. Also, both focus on the sea-grass zone, which for Madagascar is about 700 m wide, and for

Mauritius it is about 100-200 m wide. Table 2.1 below illustrates that each zone features and exhibits different coral species.

However, some patterns found in reefs can be broadly grouped into three typical zones that generally characterize the reef - the reef-front, reef crest and back- reef (Fig. 2.2). The distinction between individual reef types, however, is not always certain (Davis, 1928), as reef zones are highly variable depending on depth, temperature, wave energy, current, light and sediment.

2.1.2.1 Reef Front (Fore-Reef)

The reef front is the outermost seaward slope of the reef. It slopes downward at steep angles, sometimes to great depths, and is divided into two parts, the deep fore-reef and the buttress zone. According to Orme (1977) the seaward slope is the outer reef surface that develops inclinations beyond depths of 18 m. The reef front is largely composed of crustose coralline algae (Orme, 1977). The deep fore-reef is the point at which the reef declines, reaching depths of between 5 and 20 m, and is 30

where the greatest number of coral species congregate because of the limited wave activity (Sheppard et al., 1992). Beyond that, as the light decreases with depth, reef- building corals become sparse and are steadily replaced by organisms like sponges, sea fans and solitary corals. Additionally, terraces are able to form in the reef front

Table 2.1 Zonation and coral species within the Indian Ocean (Stoddart, 1973).

Surface Inner Outer Slope Outer Reef Outer Flat Sea Grass Algal Ridge Flat Slope Upper

zone:

Acropora

Stylophora

Pocillopora

Middle Echinopora zone: Acropora gemmacea Thalassia Acropora Pachyseris cuneata Madagascar Acropora Cymodocea Favia Echinopora Goniastrea palifera Syringodium Porites Platygyra Palythoa Porites Lower

zone:

Diploastrea

heliopora

Porites somaliensis Stylocoeniella

armata Acropora Hydnophora Seychelles Porites microconos Favia Goniastrea pectinata Porolithon

Acropora Acropora Maldives Echinopora Pocillopora

Millepora

Fig. 2.1. Six models of fringing reef development. a) Accretion and progradation. b) Prograding reef. c) Reef over mud. d) Episodic progradation. e) Reef crest and lagoon. f) Storm built reef crest (Kennedy and Woodroffe, 2002).

Fig. 2.2. Cross-section showing the different reef zones and environments of different reef-building forms (James, 1984).

(Orme, 1977), although terraces effectively work as obstacles to the slope of the reef front (Guilcher, 1988). The Marshall Islands is of particular interest in respect to terraces, because at a depth of 15-21m the ‘20 m terrace’, has a width of up to 3.6 kilometres (Guilcher, 1988). Terraces are not a consistent feature of the reef front, and in the northern areas of the Red Sea there is no evidence of terraces (Guilcher,

1955). The Buttress zone is the shallow part of the outer reef and is a rugged zone composed of buttresses interspersed with deep channels that slope down the reef face funnelling sediment away into deeper water (Lalli and Parsons, 1995; Sumich, 1996).

On the upper reef slope, there exists a sheltered coral community dominated by

Porites species with an appearance of Acropora hemprichi, Pocillopora and Faviidae

(Head, 1987). In the Great Barrier Reef the most frequent types of corals observed in this zone are the branching Acropora (Wallace, 1975) while in the northern parts of the Great Barrier Reef the sediments in the reef fronts are made of coarse coral detritus, in particular broken Acropora fragments (Jell and Flood, 1978).

2.1.2.2 Reef crest (algal ridge)

The reef crest is a ridge between the back-reef and the fore-reef, often exposed at low tide. The reef crest experiences the highest wave action and for that reason only some corals can live in this zone like the typically short branching corals that are able to withstand moderate to high wave action. The growth of surge channels and reef front grooves can be seen with surge channels of up to 100 m, but generally 10-20 m, deep (Guilcher et al, 1956). The reef front can be connected at the subsurface level and, therefore, any operate as a blowhole at different points of the tidal cycle. The occurrence of sediments happens only when there is some level of protection provided against the impact of waves and, therefore, is observed in

33 smaller pools on the outer reef flat. Much of the sediment in this zone does not correlate with the morphological zones because of the impact of transport, mixing and distinctions between sediment zones (Guilcher, 1988). Sediments on the crest of the Great Barrier Reef are made up of coral and coralline algal fragments that are derived from the reef front, although they have had Halimeda and benthonic foraminifera added to them (Hopley, 1982).

2.1.2.3 Back-reef (Reef Flat)

The back-reef is the shallow areas extending from the shore to the reef crest.

This zone is the most sheltered side of the reef and the geomorphology varies in width and depth depending on location and reef type. It is generally the widest part of the coral reef (Coyne et al., 2003). It appears that an inverse relationship occurs between lagoon depth and width of the reef flat. Beyond the reef flat is the back-reef, which is replaced by a deep lagoon in barrier reefs and atolls, or a depression with fringing reefs (Darwin, 1842). Such a depression occurs north of Jeddah, Saudi

Arabia, and also at Madagascar (Guilcher, 1956). The shallow water in this zone experiences wide variations in salinity and temperature with an accumulation of sediments and occasional exposure during low tides. These depressions are the main sites of any loose sediment that does occur within the reef flat, and includes coralline algae, corals, Halimeda, foraminifers and molluscs (Orme, 1977). Around 15-40% of coral reef sediments are made up of coral fragments, and approximately 4-22% of reef flat sediments consist of molluscs fragments (Orme, 1977). Of particular importance on the Great Barrier Reef and Pacific Ocean reef flats are Halimeda sediments, with coralline algae playing an essential role in the flat reefs of the

Caribbean, and less so in the Indo-Pacific reef sediments (Orme, 1977). All these

factors tend to limit coral growth, diversity and live coral cover in this zone (Pilcher and Abou Zaid, 2003). However, most of the reef ecosystem species are supported by this zone, such as molluscs, worms, crabs and lobsters (Barnes, 1987). Also, soft corals, especially Tubipora and Xenia species abound in this environment, as is the case in Red Sea (Head, 1987), and there is evidence of green algae, including

Halimeda and Thalassia, on both the outer and inner reef flats of the Caribbean

(Orme, 1977). Inner reef flats provide some level of protection for algae to develop, and so are abundant for grazing (Orme, 1977). Often a considerable amount of the reef-top surface can be absorbed by lagoons, which can be shallow or deep in character. Shallow lagoons are understood to develop from the ‘central decay’ of platform reefs, while deeper lagoons develop from growth of the back-reef floor.

Lagoons create significant sediment sinks in the reef, with accumulation rates of up to 5.91 mm/yr (Hopley, 1982). Some lagoons reach up to 450 m in width with depths of up to 40 m in the Great Barrier Reef, and can occur at around 100 m from the reef front (Hopley, 1982).

It is rare for a lagoon to be absolutely free of reefs, with most featuring at especially least thickets of Acropora on the lagoon floor (Guilcher, 1988). However, in shallow lagoons, Stylophora pistillata covers most of the rocky outcrops around the Red Sea reefs, supporting the unusual presence of Favia, Platygyra, Cyphastre and Porites species (Head, 1987). Although the external surface of the reef flat appears and feels hard, similar to a pavement, it is interesting to note that internal aspects of the reef flat mass are often soft and very porous (Guilcher, 1988).

2.1.3 Reef platform

A carbonate platform is a carbonate body composed of calcareous deposits

(Wilson, 1975). Reefs on carbonate platforms are located between the internal lagoon and the slope where it can develop a rigid, wave- resistant structure and grow actively outward and upward, depending in the conditions of the area.

Platform growth is affected by many factors including light, water temperature, turbulence and pH. Also, carbonate platforms are constrained by climate, morphology, width, circulation and orientation of the margin and according to these factors they classified into many types (Fig. 2.3). The most recognized models of carbonate platform are ramps, rimmed shelves and drowned platforms.

Fig. 2.3 Types of carbonate platform according to Tucker (1990), Handford &

Loucks (1993) and Wright & Burchette (1996). From Pomar(2001). 36

Ramps are characterized with a gentle slope and, therefore, respond to sea- level changes with shifting of facies belts in contrast to rimmed shelves that undergo flooding and exposure of platform tops as the case in Persian Gulf and Shark Bay

(Read, 1985). An example of a modern ramp is the inner shelf of the Abu Dhabi complex in the Persian Gulf (Arabian Gulf), where about 1 m high of massive

Acropora corals appears with subsidiary Siderastrea and Porites (Bathurst, 1975). In the back reef area of the Abu Dhabi complex only scattered corals occur with an appearance of Echinometra with other echinoids and sponges.

Rimmed shelves are shallow platforms bounded at outer edges by high energy waves and marked by a pronounced increase in slope into deep water, as seen in Florida and Queensland (Read, 1985). For example, a 60 m wide terrace of large vertically growing Acropora was reported in southern Florida (Bathurst, 1975).

These corals are growing to the seaward of the reef-flat where they can find maximum protection from the incoming waves. While in the back-reef lagoon

Porites and Siderastred corals found with an absent of the Acropora.

This classification of carbonate platforms is essential for sequence stratigraphic interpretation, and to evaluate the carbonate sediment accumulations while the examples show some of the styles of growth in these reef platforms.

2.2 Quaternary Reef Terraces on the Red Sea Coast

The Quaternary has been defined as the time period covering the past 2.6–2.7 million years (Ma) of geological time (Gibbard et al., 2008). The Quaternary period is divided into two epochs: the Pleistocene and the Holocene. Constant alterations in

37 planetary climatic conditions influenced the Quaternary, such as progression and retreat of continental ice sheets, shift in atmospheric circulation and localized hydrological regimes. The altered conditions in climate are seen to impact on both the production and movement of fine detrital material to the ocean and, therefore, the chemical composition of the ocean.

Quaternary raised reef terraces contain successions of alternating reef environments, which represent transgressions or regressions caused by sea level fluctuations or reflect tectonic uplift. These raised reef terraces can be used as an indication of Quaternary climatic variations along the coasts and by interpreting the reef fabric, the sea level during the coral growth time can be inferred on the basis of species or growth form.

One method that is commonly applied to Quaternary reef investigations is called coral coring. By using a light handheld drill or drilling vessel, a reef can be vertically cored to shallow depths underwater. Studying these cores can help to understand the development and retreat in reef growth and gives accurate information about the sea level, salinity and temperature at different times in history.

The emergent Quaternary reef limestone along both coasts of the Red Sea occupy a vast area (Fig. 2.4) varying in width from 0.5 km to 10 km with different heights above sea level. Many studies have been done on the geology and geomorphology of the Red Sea coral reefs on both sides (western and eastern) and completely opposed views are taken by various researchers about reef terraces due to the complex relationship between eustatic sea level changes and local tectonics

(Gvirtzman and Buchbinder, 1978; Sneh and Friedman, 1980; Behairy, 1983; Jado and Zötl, 1984; Dullo, 1990; Sheppard et al., 1992). Some examples of these studies on both coasts of the Red Sea are provided below. 38

Terrace 2 About 5 m a.s.l

Terrace 1

About 2 m

a.s.l.

Mean Sea Level

Fig. 2.4 Coral terraces about 5 m above sea-level on the Rabigh coast (130 km north of Jeddah City).

2.2.1 Eastern Coast of the Red Sea

The coastline of Saudi Arabia is about 1,840 km long; accounting for 79% of the eastern seaboard of the Red Sea. The older coral reefs along this eastern coast were described by Nesteroff (1959) and 14C dating gave a date from a 30 m high terrace at "Abulat" Island, off the coast near Al Lith, as 35,000 years. This date may appear irregular because it approaches the limits of the time span that can be appropriately dated using radiocarbon dating techniques (up to 50,000 years). Sestine

(1965) reported a series of late Pleistocene reefs standing as wave-cut terraces at heights between 1- 12 m above modern sea level on the Red Sea coastal plain. Other raised reef terraces that stand at altitudes of 6, 19, 20 and 30 m above the mean sea level were observed by Skipwith (1973). On Tiran Island, situated at the mouth of

Gulf of Aqaba, there is a coral limestone terrace at a height of 520 m above sea level

(Behairy, 1983) and Vincent (2008) observed reefs more than 100 m a.s.l. to the 39 north of Haql. However, in the central and southwestern Saudi Arabian coast, the marine terraces are all at lower levels compared to their northern counterparts.

Behairy (1983) investigated three terraces, at 1, 3, 10 m a.s.l., and gave radiometric ages of 9980, 18,100, 16,600 and 31,000 years BP for coral limestone from the terraces. He used these dates to suggest four major marine transgressions between the mid-Pleistocene and present. However, eustatic sea levels at this time were low not high (Fig. 2.5).

Thousands of years before present

Fig. 2.5 Global sea-level change over the past 140,000 years according to the Red Sea isotope record (Baily et al., 2007 using data from Chappell and Shackleton 1986; Lambeck and Chappell, 2001).

2.2.2 Western Coast of the Red Sea

The Quaternary reef terraces on the Egyptian coast of the Red Sea are characterized by small-scale transgressive and regressive cycles (Ahmed, 1993). 40

These marine terraces exhibit different elevations above the present sea level (El-

Asmar and Attia, 1996). The Pleistocene reefs of the Red Sea have included some of the first references concerning raised reefs. A few Sudanese, Djibouti and Egyptian coral reefs were dated before 1980 (Veeh, 1968) while more published dates have appeared within the last three decades. Many of these dates led to extremely wide ranges of ages for the lower raised reefs previously referred to late Pleistocene times from 150 to 50 ka. A detailed study of Egyptian reefs conducted by El Moursi et al.

(1994) reported a direct correlation between the age and elevation of the Pleistocene coral reef terraces. By using U/Th dating method, ages between 87-131 ka have been shown for the four lower terraces, which indicate marine isotope (MIS5). They suggested that the higher terraces belong to MIS 7 and 9 by considering their stratigraphic relations and the field occurrence.

Moreover, during Quaternary times, the northern part of the Red Sea adjacent to the Egyptian coast (850 km long), never exceeded 200 km in width. This width is small compared to the 2250 km length from Suez to the Bab el Mandeb entrance from the Indian Ocean. This coast was rarely exposed to extreme hydrodynamic events and sedimentary conditions favoured the development of low-energy coral reef terraces during times of sea level highstand (Plaziat et al., 1995).

The Gulf of Aqaba is 180 km long and 25 km wide, narrow in the north and widening to the south with a maximum depth of 1850 m towards the east where the continental shelves and coastal plains disappear. The dominant reef type in the Gulf of Aqaba is the fringing reef, because the Red Sea here is devoid of a true continental shelf and the offshore profile is very steep (El-Asmar, 1997).

The coral reefs along the shores of the Gulf of Aqaba are excellent sea level indicators. Numerous uplifted fossil reefs are exposed near the shores of the gulf at the southern end of Sinai, and at the northeastern corner south of the town of Aqaba.

Dullo (1984) defined a reef terrace about 98 m above sea level. These are Pleistocene reefs that formed during sea level high stands and reached their present position as a result of sea level fluctuations combined with tectonic uplift (El-Asmar, 1997).

Uplifted Pleistocene reefs are not found on the northwestern shores of the gulf, but a fossil reef slightly above sea level near Elat was dated by Friedman (1965) at 4.7 ka.

Reefs of similar age are found at similar elevations along the southern coast of Sinai

(Gvirtzman et al., 1992) and the coast of Aqaba (Al-Rifaiy and Cherif, 1988).

The coastline along the Gulf of Eilat and the Red Sea is fringed by a narrow belt of modern coral reefs (Loya, 1972). Gvirtzman et al. (1977) reported a well preserved belt of three elevated fossil-reef terraces stretching along the coast of southern Sinai. He defined a sequence of progressive diagenesis, beginning with the initial fabrics of living corals and completed through the leaching of aragonite components and the precipitation of low-magnesium calcite from meteoric waters.

Also, in another study, Gvirtzman et al. (1973) suggested that these terraces were formed during periods of late Quaternary high-stand sea levels and the modern offshore fringing reef was dated as 10 ka and younger.

Table 2.2 Summary of the terraces in previous studies on the eastern and western coasts of the Red Sea.

Elevation(m) Terrace Above sea age Method reference interpretation location level Approaches "Abulat" 35,000 Nesteroff the limit of 30 14C Island years (1959) radiocarbon dating 1- 12 Sestine (1965) 6, 19, 20 and Skipwith (1973) 30 Tiran 520 Behairy, 1983 Island north of 100 Vincent (2008) Haql 1 9980 14C Behairy (1983)

Eastern Coast of the Red Red the of Coast Sea Eastern 3 18,100 14C Behairy (1983) 3 16,600 14C Behairy (1983) Approaches the limit of 10 31,000 14C Behairy (1983) radiocarbon dating

Lower 87 - El Moursi et al. U/Th MIS5 terrace 131 k (1994) Aqaba 98 Dullo (1984) Friedman near Elat 4.7 ka

(1965) of the Red Sea Red the of Western Coast Coast Western

Chapter 3- Methodology

3.1. Sampling

Seven prominent coral reef sites were investigated with reef heights ranging from 1 to 5 m above present sea level along the Rabigh coast (130 km north of

Jeddah City). In addition to field descriptions, 86 samples of carbonate rock were collected from these reefs to provide the data for this research (Table 3.1). Given the research aims, which included a focus on age dating methods, meant that only those parts of the reef that could be age-dated were chosen, which included coral and shells. Also, we collected carbonate rock samples in order to conduct the petrography and XRD analysis. Approximately 500 g samples of carbonate rock were collected from different elevations in each reef. Mollusc, echinoderm and some coral samples were collected also from each reef.

The collected samples were cut in the Saudi Geological Survey and a small amount of each sample was shipped to Australia to establish the laboratory analyses. Samples were categorised according to location, reef number and sample number. Therefore,

1.1.13 is the thirteenth sample from location 1, reef number 1.

Table 3.1 Latitude and longitude and number of carbonate rock samples collected

from each site.

Location Samples Latitude Longitude

1 29 N 22° 47´ 175˝ E 38° 57´ 335˝ 1N 5 N 22° 47´ 175˝ E 38° 57´ 335˝ 2 12 N 22° 46´ 164˝ E 39° 00´ 368˝ 2N 3 N 22° 46´ 241˝ E 39° 00´ 355˝ 3 10 N 22° 49´ 558˝ E 38° 55´ 743˝

4 11 N 22° 48´ 50˝ E 38° 56´ 903˝ 5 3 N 22° 45´ 778˝ E 39° 00´ 135˝ 6 4 N 22° 46´ 666˝ E 38° 59´ 758˝ 6S 2 N 22° 46´ 596˝ E 38° 59´ 877˝ 7 7 N 22° 46´ 475˝ E 38° 57´ 633˝ Total 86

Fig. 3.1 Sample location map

Fig 3.2 a graph showing the details of coral limestones in different locations in the front reef area. 46

Fig 3.3 a graph showing the details of coral limestones in different locations in the back-reef area.

3.2. Particle size analysis

Sediment samples were collected from the top of the modern reef sequence in the Rabigh area to determine the components of textural and physical properties of sediments in this area. Samples were collected from two sections perpendicular to the shore line at location 1 (Fig. 3.1) by shovel starting from the shoreline and going out to the near-shore zone. 12 samples were collected from first sector and 8 samples from second sector. The textural compositions of the sediments (gravel, sand and mud contents) were determined using the wet sieving analysis technique of Folk

(1968). For moisture content all the samples were air-dried. The results are provided in the form of Excel sheets and different comparison graphs shown in later sections.

3.3. Petrographic Analyses

Thin sections were prepared for petrographic analysis and the analyses were done in the University of Wollongong laboratories. Most of the samples (67) were thin sectioned except the coral and shell samples. The samples were cut for thin sections using a cut-off saw with embedded diamonds and ground flat before being mounted on glass slides using epoxy resin mixed with a blue dye to highlight cracks, pore spaces and voids in samples. The mounted samples were ground and polished using carbide grit until they were about 0.03 mm thick. The sections were covered with glass cover slips and were used for microscopic analysis to characterize the texture, identify the minerals, recognise diagenetic components, determine simple cement stratigraphies describe and classify the carbonates, and identify and quantify pore types in the samples.

The thin sections were examined under a petrographic research polarizing microscope using x10 eyepieces, giving 40x, 100x and 400x optical magnification.

The quantitative composition of the biota and non-skeleton grains was established by point counting (sampling target=300 and stage interval=5) and photomicrographs were taken for documentation.

The correlation of results between stratigraphic height and any component are limited in their ability to be generalized to other locations because of the small sample size, ranging between 2-10 samples per site. However, despite this methodological limitation, correlation analysis of these samples was still important because it revealed data about the relationship between environmental conditions during the formation of the reefs.

3.4. X-ray diffraction (XRD)

X-ray diffraction (XRD) analyses allow the identification of minerals based on their atomic structure. It provides information on the structure and phases as well as other structural parameters such as crystallinity, strain and crystal defects. X-ray beams reflect off matching atomic layers within a mineral over a range of diffraction angles. The reflected rays are detected only at specific angles because the X-ray beam has a specific wavelength. Every mineral has a unique diffraction pattern that can be used for identification.

To initiate the XRD analyses, samples were crushed by hand to a fine powder in an agate mortar and then back packed into the holder with no pressure. The packed powders consist of randomly orientated grains that ensure all crystallographic directions are sampled by the beam.

The correlation of results between the stratigraphic height and any mineral in the samples from any location was limited, due to the small sample size, ranging 49 between 3-14 samples per site. However, despite the small sample size, analysis of the relationship between environmental conditions during formation of the reefs was assisted by the use of XRD.

In this thesis, XRD analyses were used to determine the mineralogical composition of the samples. The percentages of minerals were calculated using

SiroquantTM software.

3.5. Dating

3.5.1 Amino Acid Racemisation Dating (AAR)

Amino acid racemisation (AAR) is used to estimate the age of various types of archaeological fossil materials such as bone, wood, fossils and shells. Amino acids are the building blocks of all proteins used by living organisms in the construction of their physical forms. AAR is based on the fact that all amino acids, except for one

(glycine), exist in two different forms, both of which otherwise have the same chemical structures. The L-amino acid molecular form has an extension to the left, while the D-amino acid form has an extension to the right. All living organisms produce the L-isomer. After the organism dies, the L-form reversibly converts to the

D-form through a process called racemisation. By determining the rate of their conversion, the D/L ratio can be used to indicate the age of the sample.

Many factors have been found to affect the speed of the reactions that causes amino acids to undergo racemisation, such as temperature, percentage of water and pH. However, diagenetic temperature is the main factor which plays the most significant role to affect this process since if the temperature goes up 1oC then the rate of racemisation increases by 15-20% (Murray-Wallace, 1993). 50

Amino acid dating is not able to obtain the age of the material purely from the

D/L data alone. Because of the rate problem, the amino acid dating technique must rely on alternative dating techniques, such as radiocarbon to calibrate the rate of racemisation result (Murray-Wallace, 1993; Wehmiller and Miller, 2000).

Amino acid racemisation is mostly used to date samples in the 5000-200,000 years range depending on diagenetic temperatures. However, it has been used to obtain dates as old as 1 Ma in South Australia (Murray-Wallace et al., 2001).

In this study, the extent of amino acid racemisation in bivalve shells has been analysed to estimate ages of the raised marine reef sites in the study area. The methods of preparing shell samples involve three steps; cleaning the surface of the sample, the removal of biomineral matrix and the hydrolysis of the protein into individual amino acids for analysis.

Two different subsamples from each sample were prepared to check for internal sample consistency. Shell samples were cut into small parts weighing about

100 mg and cleaned mechanically by using a dentist drill to remove any potential contaminants from the shell surfaces then covered with distilled water and sonicated

3 to 5 times until the specimen is clean. The samples were subsequently etched in 2

M HC1 and air dried, then dissolved in 8M HCl and hydrolysed, under nitrogen, for

22 hours at 110oC. Finally, the samples were evaporated to dryness, rehydrated using the rehydration solution and were ready for insertion into the RP-HPLC Autosampler

(Murray-Wallace, 1993).

Table 3.2 Mass of each sample and the amount of HCl.

Sample no Lab no Mass 2M Mass 8 M (g) HCL (g) HCL (mL) (mL) 2N.1.2 7900 A 0.0668 220 0.0515 1030 2N.1.2 7900 B 0.0841 278 0.0676 1352 1N.1.1 7902 A 0.1902 628 0.1528 3056 1N.1.1 7902 B 0.0630 208 0.0499 998 1.1.14 7903 A 0.0667 220 0.0532 1064 1.1.14 7903 B 0.0318 105 0.0258 516 2.2.4 7904 A 0.1470 485 0.1186 2372 2.2.4 7904 B 0.0923 305 0.0737 1474

3.5.2 Radiocarbon Analysis

Radiocarbon (14C) dating can be regarded as a dating method for establishing age estimates of organic and inorganic materials (Bowman, 1990), although it is applicable to only a relatively short span of Quaternary time (50 000 years), this method has been used most widely of all the radiometric techniques.

Radioactive carbon is generated when nitrogen-14 is bombarded by cosmic rays in the atmosphere (Currie, 2004). The radioactive carbon produced drifts down to the ground where it is assimilated by plants through photosynthesis (Currie, 2004).

It gets into animal bodies when they eat plants and consequently into human’s bodies when they eat plants and animals.

When a living organism dies, the absorption of 14C stops. Thereafter the radiocarbon (14C) that is already in the dead organism starts to decrease. 14C decays slowly and at a steady rate back to nitrogen-14 (Bowman, 1990). This fact is used to determine how much 14C has disintegrated, as well as how much is left in the sample

14 of fossil material. The rate at which C decays is known as the half-life and carbon-

14 has a half-life of 5730 years.

Radiocarbon dating can be undertaken on a range of biogenic materials, such as wood, charcoal, bone, soil and shell. Some of these materials cause technical and interpretational problems as samples can be contaminated by calcium carbonate from groundwater as well as humic acids from organic matter in the soil. However, in marine molluscs, it is usually possible to determine if contamination has occurred by comparing dates from different portions of the shell (Peacock and Harkness, 1990).

The level of radiocarbon in the biosphere is not constant and, therefore, it is essential to calibrate the radiocarbon date in order to generate accurate results (Currie, 2004).

In this study, five bivalve shell samples were sent for radiocarbon dating. The samples were prepared by taking about 20 g of each sample and the surfaces cleaned by using dentist drill then the samples were sent to the University of Waikato

Radiocarbon Dating Laboratory, New Zealand, where they were processed and analysed by using the following procedure. For radiocarbon dating the Waikato laboratory determined 14C activity through the measurement of beta particles.

Samples were converted to benzene through hydrolysis with lithium carbide and catalytic trimerisation of acetylene. Accelerator Mass Spectrometry (AMS) analysis was done for one sample. This technique allows small samples to be dated. Residual radiocarbon activity is measured using Perkin Elmer 1220 "Quantulus" Liquid

Scintillation (LS) spectrometers.

3.5.3 Uranium-Thorium dating

The uranium-thorium (U/Th) numeric dating method developed from detection by mass spectrometry of both the 234U and 230Th products of decay. This is conducted through the emission of an alpha particle, with the decay of 234U to 230Th forming part of the lengthier decay series beginning with 238U and ending with 206Pb.

U/Th dating is an absolute dating technique because it utilises the properties of the radio-active half-life of the two alpha emitters 238U and 230Th. The half-life of 238U is

T1/2=4,470,000,000 y, while the half-life of 230Th is much shorter, at T1/2=75,380 y.

When comparing uranium and thorium a precise approximation of the age of an object can be obtained, although this method is only suitable for those objects that initially have no 230Th content.

When using U/Th dating, the initial ratio of 230Th/234U from the time of sample formation must be identified, as over time, 230Th will build up in the sample due to radiometric decay. Therefore, the sample age is calculated based on the difference between the initial ratio of 230Th/234U and the ratio present in the sample being dated. The method works on the assumption that the environment is a closed system, that is the sample does not exchange 230Th or 234U. Also, the method is useful for those samples that retain uranium and thorium, for example teeth and carbonate sediments. The method has been used in samples aged between 1000 and

300,000 yr B.P.

Two Porites coral samples were sent to the University of Queensland for

Th/U dating. The results from these samples are discussed further in the dating results chapter.

Chapter 4- Stratigraphy of coral reefs in Rabigh area

4.1 Field description

The Rabigh coast in the study area stretches for about 12 km between Al

Kharrar Lagoon in the north and Sharm Rabigh in the south (Fig. 4.1). The Rabigh area is characterised by the presence of two lagoons, Al-Kharrar in the north, and

Rabigh lagoon to the south. The back-beach is narrow and the near-shore zone is occupied by a hard and flat pavement of coral reef where the depth of water is no more than 60 cm as far as the breaker line about 90 m from the shore (Fig. 4.2). The reef is covered with a thin layer of carbonate sediment caused by erosion of the submerged reef and biological activity in this region. Also, the area is characterized by long-shore coastal currents and tide, which can affect the sediment texture in this area.

Most of the Rabigh shoreline features marine coral limestone reefs which represent old near-shore reef deposits, covered with sediments deposited by wind that were derived from erosion of coral limestone and the adjacent mountains consisting of Triassic igneous and metamorphic rocks.

In general, the limestone reefs show a remarkable variation in width and height. Reefs are wider and more continuous in the back-reef and middle areas of the coast, seen at locations 1, 4 and 7 (Fig. 4.1), whereas in the north and south only individual eroded reef remnants appear. The reefs were separated into upper reef, lower reef and back-reef.

Fig. 4.1. Location map of study area showing sample sites

3 m

1 m

Fig. 4.2. The near-shore zone along Fig. 4.3. Coral reef with upper and the Rabigh coast. lower sequences at location 3.

3.5 m

1.5 m

a b

c d

e f

Fig. 4.4. a) The upper and lower reef along the Rabigh coast. b) Two layers of coral reefs at location 4. c) The infrastructures in the area where the reefs disappear. d) The coast taking a crescent shape in front of the marine sciences faculty cabin at location 1. e) Coral reefs and beach rock at location 1. f) Coral reef and beach rock at location 7.

Starting from the north, near the coast guard station (location 3), two layers of coral reefs appear with no record of beach rock (Fig. 4.3). For about 4 km southwards the coral reefs continue along the North Rabigh coast (location 4) and then the number and extent of the reefs decrease. In particular, the reefs disappear for a short distance because of infrastructures in the area and then appear again in front of the Marine Sciences Faculty cabin (location 1) where the shore is crescent shaped and two layers of beach rock also appear. A similar situation occurs at location 7

(Fig. 4.4). Figure 4.5 illustrates the elevation of the marine reefs along a vertical section parallel to the coast.About 4 km inland, east of location 1, a back-reef area appears (location 6) with a reef flat carbonate overlying a carbonate mudstone and a big flat area of carbonate toward the south (Fig. 4.6a). The same carbonate deposits and topography are present to the south at locations 2 and 5 (Fig. 4.6b, c, d).

4 3.5

2.5

(m)

2 1.5

Elevation 1 Upper reef 0.5 0 Lower reef Location 3 Location 4 Location 1 Location 7

Fig. 4.5 Elevation profiles of upper and lower reefs along a vertical section parallel to the coast.

Thus, two marine reefs that occur at elevations ranging from 0.5 m to 3.50 m above present sea level, two beach rock layers and an area of back-reef were identified in the study area.

1.6 m

a) b)

c) d) Fig. 4.6. a) Two carbonate deposit in the back-reef area at location 6. b) The flat carbonate area at location 5. c) The carbonates at location 2. d) The carbonates at location 5.

4.1.1 Lower Reef

Starting from the south at location 7, one coral reef emerges above sea level

(Fig. 4.7a-b). This reef with an elevation of about 1.2 m is well cemented and mostly dominated by Tubipora coral with an appearance of Acropora and Favites (Table

4.1). The reef is pale brown (5YR 5/2) in colour and is filled with sediment, shell and shell fragments. The shell and shell fragments fill approximately 50% of the reef area between corals (Fig. 4.7). At location 1, the lower reef was 1.2 m high and generally well cemented, with colours ranging between light gray (N7) to moderate, yellowish brown (10YR5/4). This reef is covered with thin sand and beach deposits and many coral genera were found in this reef where Fungia and Favites are the most prominent species in terms of cover and frequency with a minor occurrence of

Porites and Tubipora and a disappearance of Acropora (Table 4.1). Coralline algae dominate this reef and it also contains many gastropods and echinoid spines of the species Heterocentrotus mammilatus (Figs 4.8 and 4.9). Another reef with an elevation of 1 m appeared 30 m to the north of location 1, where it was covered with sand and beach sediments and appeared with the same colours and same fauna as the reef at location 1. Therefore, this reef was observed to be part of the reef at location

1. At location 4 the lower reef is about 1.4 m high and consists mostly of well cemented carbonate sand, showing a dusky blue colour (5PB3/2). Coral from the genus Fungia dominated, with an appearance of some Favites and some gastropods

(Fig. 4.10). At location 3 the lower reef has appeared with an elevation of about 1.1 m. This reef is quite similar to the lower reef in location 4, with a dusky blue colour

(5PB3/2) and well cemented carbonate as the main feature, but this reef shows a scarcity of corals (Fig. 4.11).

The lower reef in locations 4 and 3 must represent part of the back reef facies of the lower reef succession. The minor occurrence of reef corals and the dominance of coralline algae suggest that these sequences are not reef front deposit. That could propose that the reef front must be farther out and these sequence could represent rapid coral growth on the back reef platform. 60

Consequently, the lower reef in the study area occurs almost at the same elevations between sea level and 1.1 to 1.4 m (Fig. 4.5) and is well cemented with a darker colour toward the north. Bivalve shells and gastropods are found in all the locations. Location 1 included the area of highest coral coverage and diversity while northward the coral coverage and diversity decreased until location 3 where only few corals are found. The lower reef succession suggests that it is part of the back reef facies.

a) b)

c) d)

Fig. 4.7. The lower reef in location 7. a) The reef and adjacent beach rock. b) Tubipora musica coral dominated this reef. b) Tubipora musica coral. c) Acropora and Tubipora musica coral. 61 a) Favites b) Fungia

c) Fungia d) Favites

Fig. 4.8. Different coral genera from the lower reef in location 1, including Favites and Fungia.

a) Coralline algae b) Porites and echinoid spines

c) Favites and gastropods d) Favites

Fig. 4.9. Coralline algae, Porites and Favites corals, echinoid spines and gastropods from the lower reef in location (1).

Table 4.1 Identification of the main coral genera in the lower reef (based on Veron, 2000).

Location Main Coral genera in Order of Abundance 7 Acropora, Tubipora musica, Favites 1 Favites, Porites , Fungia, Tubipora musica, Stylophora 4 Favites, Fungia 3 No coral found

a) 3.5m

1.5 m

Fig. 4.10. The lower reef in location 4. a) and b) shows the difference in colour and content between the layers where the lower reef looks darker and more cemented than the upper reef. c) Bivalve shells, Tridacna gigas, were found at the base of the exposed lower reef. This was a more recent shell embedded into cemental beach rock adjacent to the reef.

Fig. 4.11. The lower reef in location 3. a) Overview of the lower reef, which consists mostly of cemented carbonate sand, overlain by the upper reef. b) Closer view of the reef showing a volcanic clast, which is an exotic clast from abroad, and not a natural component of the reef. The volcanic clast is much younger in age than the reef, and has simply been cemented into the reef.

4.1.2 Upper Reef

At location 1, although some parts of the upper reef are eroded, the original height of the reef ranges between 1.2 m and 2-3 m above sea level. The reef is poorly cemented, covered by sand and contains significant amounts of coral rubble. At the rear of the reef, coralline algae are dominant and a lot of gastropods are found.

Acropora is the dominant coral genus in this reef while Porites, Tubipora musica and

Favites are also found (Table 4.2). Also, many calcareous tube worms of about 10 cm length were found in this reef specifically in the top and upper parts (Fig. 4.12).

At location 4, large vertically-growing coral colonies are well expressed with a height of 2.4 m above the lower reef that is dominated by coralline algae. Most of the corals in this reef are from the genera Favites and Tubipora musica, with an appearance of some gastropods (Fig. 4.13). Finally, at location 3, the same reef appears up to height of 1.9 m above the lower reef representing a rapidly growing reef sequence (Fig. 4.13a). This reef is poorly cemented and contains common

65 coralline algae. Some Favites, Acropora and Porites coral are found (Table 4.2) with a lot of coral rubble and calcareous tube worms up to about 90 cm length (Fig. 4.14).

The upper reef is not a reef front sequence, as it shows poorly cementation. It could be either in the fore reef area or more probably in a back reef area that actually got these colonies growing up to this sea level.

Consequently the upper reef in the Rabigh area ranges in height between 1.9 and 2.4 m extending to an elevation of 3-3.5 m above present sea level. It is poorly cemented and dominated by coralline algae. The upper reef is highest in the middle,

2.4 m at location 4, while northwards at location 3 the reef decreases to 1.9 m, and southwards at location 1 the reef decreases to 1.8 m. No remnants of the upper reef were seen at location 7 (Fig. 4.5). The presence of clastic sediment is higher in the ancient valley areas, which include in Sharm Al-Kharrar in the northern area and

Sharm Rabigh in the southern area, and this has led to a decreased coral diversity and coverage, similar to the lower reef. Coral cover was generally low with an appearance of individual colonies, particularly Acropora as in southern Florida

(Bathurst, 1975). The upper reef succession probably accumulated in a back reef area.

a ) Coralline algae b ) Coralline algae

c ) Favites and Porites corals d ) Porites (showing etched annual bands)

e ) Calcareous worm tube f ) Favites

g) Acropora h) Acropora

i ) Porites j ) Acropora

k) Acropora l) Coralline algae

m) Tubipora musica n) echinoid spines

Fig. 4.12. The upper reef at location 1 occupied by: c-d-f-g-h-i-j-k-m) a variety of coral genera including Tubipora musica, Acropora, Porites and Favites. a-b-e-l-n) coralline algae, echinoid spines and calcareous tube worms.

Table 4.2 Identification of the main coral genera in the upper reef (based on Veron, 2000).

Location Main Coral Genera in Order of Abundance 1 Acropora , Porites, Tubipora musica, Favites, Stylophora 4 Favites, Tubipora musica, Stylophora 3 Favites, Acropora, Porites

3.5 m

1.5 m

a) b) c) d)

Fig. 4.13. The upper reef at location 4. a) Overview of the upper reef at location 4. b) Favites. c) Porites coral d) Coralline algae.

a) b)

c) d)

Fig. 4.14. The upper reef at location 3. a) Overview of the upper reef with calcareous worm tubes. b) Gastropods and Acropora coral. c) Sediment and coralline algae between corals. d) Porites coral.

4.1.3 Back-reef

At location 2, about 4 km to the east of location 1, a reef succession with a height of 3.20 m appears at the top of a flat area of carbonate which may represent the eroded middle of the lower reef succession (Fig. 4.15a). In the flat area, calcite shells were common with a disappearance of the aragonite shells. A few 30 cm

Tridacna gigas shells were found and taken for dating (Fig. 4.15b). The reef succession can be subdivided into two layers with the lowest reef unit rising about 2 m above the flat area and containing well cemented mud with occasional gastropods,

Clypeaster and regular echinoderms (Figs 4.15c-d). No corals were found in this layer except separate coral rubble.

The upper reef unit, with a moderate brown colour (5YR 4/4), is poorly cemented and contains coralline algae, gastropods and some calcareous worm tubes

(Figs 4.15e-f). Fungia, Tubipora musica and Favites corals appear in this layer in about 20% of the visible area (Table 4.3).

At location 5, a reef succession with an elevation of 0.75 m appears on top of an area of flat topography with an elevation from 0 to 0.2 m. the flat area is probably about the middle of the lower reef succession. In this area the lower part of the lower reef succession is different from the upper part where the lower part contains a few

Favites corals and a lot of gastropods, Clypeaster, regular echinoderms and coralline algae. In contrast, the upper part of the lower reef succession is mostly mud- dominated. The upper reef unit is poorly cemented with an appearance of Favites,

Fungia and Porites corals. Some corals are found in an upside-down position which indicates these coral may have come from another environment as coral rubble.

Many gastropods and regular echinoderms are present in this upper reef unit (Fig.

4.16).

At location 6, again a flat area appears with a raised reef succession about

1.60 m high where it can be divided into two layers, the lower unit up to an elevation of 0.8 – 1.10 m and the upper unit being about 0.5 – 0.8 m thick. In this area only a few Porites and Favites corals were found in the upper reef unit with lots of gastropods whereas the lower reef unit is characterised by coarse grains and more fossils with lot of gastropods, Clypeaster, regular echinoderms and coralline algae.

The upper reef unit is harder than the equivalent unit at location 2 with case- hardening at the top (Fig. 4.17). Also, another part of the upper reef unit, 0.55 m thick, appears to the south of the lower reef area and contains fewer fossils and more

Acropora and Favites corals.

Consequently, the flat areas in all the back-reef areas feature a high level of mud and contain calcite shells and gastropods which may represent the middle of the lower reef succession. The lower part of the sequence in the entire back-reef area also features a high level of mud material and is well cemented (Fig. 4.15c). The 72

most abundant species of bivalves is Trachycardium lacunosum (Reeve, 1845, cited in Hasan, 1994) and many gastropods and echinoid spines of the species

Heterocentrotus mammilatus (Linnaeus, 1758, cited in James and Pearse, 1969) were found. Only a few corals were found and some of them are upside-down (Fig. 4.16e) which indicates it is rubble that eroded out of the front reef. The similarity in content and form in location 5 and 6 suggests that both the reef and the flat area are part of the lower reef sequence. The upper part in location 2 and the reef south of location 6 are different with the appearance of coralline algae and the calcareous worm tubes and some Acropora and Favites corals which imply it is part of the upper reef.

Overall, the reef sequences in the Rabigh area could be a part of the back reef facies rather than fore reef. That will allow reefs to grown up in the quite back water area behind the reef front where big colonies coming up as the large vertically growing masses found in location 4 (Fig. 4.4b). The reef could represent a very broad platform where the back reef area signifies the inner part of it. This will be discussed more in later chapters.

Table 4.3 Identification of the main coral genera in the back-reef (based on Veron, 2000).

Location Lower Reef unit Upper Reef unit 2 No coral Tubipora musica, Favites, Fungia 5 Favites, Favites, Fungia, Porites Stylophora 6 Porites, Favites, Acropora, Favites Stylophora

a) b)

c) d) e)

Fig. 4.15. The back-reef at location 2. a) The two reef successions and the eroded flat area. b) Tridacna gigas shell found in the flat area. c) The lowest reef unit is mud-dominated and contains gastropods. d) Clypeaster in the lower reef. e) The upper reef contains some Porites coral fossils.

a) b)

c) d)

e) f)

Fig. 4.16. The back-reef at location 5. a) Overview of the two reefs successions and the flat area. b) The upper reef unit and the mud-dominated upper part of the lower reef sequence. c) Gastropods in the lower reef sequence. d) Fungia coral in the lower reef sequence. e) Porites coral in upside-down position and gastropods in the upper reef sequence. f) Porites coral at the top of the upper reef sequence.

a) b)

c) d)

Fig. 4.17. The reef at location 6. a) The flat area and the overlying upper reef unit. b) The upper reef unit contains coarse grains and is highly fossiliferous. c) The top of the upper reef unit is case hardened and has some Porites coral. d) Another reef succession to the south of location (6) has a different structure and has some corals.

4.1.4 Beach Rock

Changes in texture and colouration mark the beach rock in the study area. At location 1, where the entire beach dips toward the sea, the beach rock comprises two layers (Fig. 4.18). The first layer is cemented, black coloured, and is 20 to 40 cm thick. It contains massive coarse-grained carbonate sand; coral particles and common diagenetic carbonate cement. The second layer was light coloured with a thickness of

up to 20 cm. This layer is highly fossiliferous and is characterised by coral gravels and small shells in a fining upward sequence.

At location 7, the beach rock onlaps onto the coral reef and two beach rock layers appear with a thickness of 45 cm for the lower and 40 cm for the upper beach rock. The lower beach rock is black coloured and contains carbonate sand whereas the upper layer showed the same features as the lower beach rock layer in location 1 with a lot of coral gravel and small shells. Both of the beach rocks in locations 1 and

7 show the same features and the fining upward sequence of the coral gravels and small shells in the lower beach rock layers are mainly connected with transgressive phases of the sea and represent slightly higher sea levels (Friebe, 1993).

77 a) b)

c) d) Fig. 4.18. The beach rock in the study area. a) Two beach rock layers in location 1. b) The upper beach rock layer contains coarse grains, coral particles and shells. c –d) The beach rock in location 7 onlaps over the coral reef unit.

Chapter 5- Petrography, XRD and Diagenesis of Carbonate Rocks

5.1 Particle Size Result of the Modern Reef top Area

The whole series of samples were collected from the top of the modern reef sequence at location 1 in the Rabigh area (Fig. 4.1). The results of particle size analyses of the sediment in sections 1 and 2 (Tables 5.1 and 5.2) shows that sand is the dominant sized sediment in the area, followed by gravel. The percentages of sand range between 92.1 to 2.2% in section 1 and between 86.4 to 42.3% in section 2, while the gravel percentages range from 97.8 to 6.7% in section 1 and from 87.7 to

13.5% in section 2. The percentage of mud is low in both sections. Also, all the samples are poorly to very poorly sorted (sorting coefficient 1.12 to 2.4).

Table 5.1- Percentage of the texture components in section 1.

Sample No Environment Gravel Sand Mud S1 Shoreline 51.19% 44.75% 4.06% S2 Shoreline 28.22% 71.75% 0.02% S3 Intertidal 15.61% 84.35% 0.05% S4 Intertidal 31.22% 68.78% 0.05% S5 Near-shore(10m) 25.33% 73.66% 0.99% S6 Near-shore(22m) 6.66% 90.14% 3.20% S7 Near-shore(35m) 32.44% 66.34% 1.22% S8 Near-shore(40m) 21.78% 77.22% 0.99% S9 Near-shore(55m) 36.48% 63.26% 0.20% S10 Near-shore(60m) 6.83% 92.06% 1.11% S11 Near-shore(70m) 97.77% 2.19% 0.04% S12 Near-shore(90m) 34.69% 63.45% 0.33%

Table 5.2 - Percentage of the texture components in section 2

Sample No Environment Gravel Sand Mud N1 Shoreline 44.95% 55.03% 0.04% N2 Intertidal 21.35% 78.26% 0.37% N3 Near-shore(10m) 32.01% 67.76% 0.23% N4 Near-shore(15m) 14.60% 85.09% 0.29% N5 Near-shore(20m) 13.51% 86.44% 0.04% N6 Near-shore(30m) 29.40% 70.54% 0.03% N7 Near-shore(50m) 87.72% 42.25% 0.01% N8 Near-shore(60m) 40.77% 59.09% 0.11%

In general, the proportion of sand decreases in both direction towards the sea and close to the beach with an increase in the proportion of gravel in both direction that reflects the high wave and current activity closer to the open sea, which in turn leads to breaks in the modern solid offshore coral reef pier. These breaks lead to higher wave and current activity and creating currents across the reef platform and thereby increase the gravel percentages. Finally, the content of clay, in general, is low and this reflects the high energy removed of clay size detritus in suspension.

Clay size material would certainly be produced by bio-erosion across the reef platform.

5.2 Standard Petrography Result

5.2.1. Lower reef The exposed lower reef thickness in the Rabigh area ranges between 1.1 and

1.4 m (Appendix No 1). Corals were found in almost all the samples, except one sample, and ranged in abundance between 0 and 75%. Bivalves occur with a

maximum of 30.2% whereas algae reach a maximum of 33.2%. Echinoderms occur in some samples with no more than 7.3%. Foraminifera only appear in a few samples with a percentage always less than 4%. The matrix in the thin sections from the lower reef varies with micrite being dominant in the northern and southern parts of the study area while sparite is dominant in the middle. The average porosity is 14.2%

(Fig. 5.1). The lower terrace contains few gastropods and bryozoans which just appear in some samples with a maximum percentage of 5.1% for the gastropods and

38.1% for the bryozoans. Silicate minerals are uncommon in the lower terrace where quartz and plagioclase are the most common but show maximum values of 6.3% for quartz and 3.3% for plagioclase. The percentage of these two minerals increased in location 7 to 9.6% quartz, 3.4% plagioclase. Other silicate minerals include K- feldspar, tourmaline and hornblende with maximums of 1% and 1.6% for tourmaline and hornblende, respectively. There is no consistent correlation between stratigraphic height and any component except for a poor positive correlation between height and echinoderms at location 3 and a poor negative correlation between height and sparite in location 1. The correlation results are limited because of the small sample sizes of only 2-10 samples at each location; however the trends found indicate the importance of environmental conditions in affecting the formation of this reef sequence.

a) b)

Fig. 5.1 a) Coral and poor with a few specks of carbonate in the lower reef. b) The sample from the lower reef has been impregnated with blue-dye that fills open pores between and within cemented sandy matrix. The porosity is secondary caused by dissolution of primary biogenic framework (coral) or just by dissolution of the matrix.

Table 5.3 - Quantitative composition of the main component in the lower reef in the

Rabigh area (minimum, maximum and the average percentage for each component) in a transect from north to south.

Bivalves Location Number of Algae Echinoderms Porosity Sparite Micrite % Number samples % % % % %

3 5 0-13 2-33 0-7.2 6.3-19.3 0-4.3 5.3-32

Average 5.1 20.1 3.2 11.3 1.9 14.2

4 2 5-18 23-23.6 3.2-7.3 16.3-22.3 2.9-4 20.6-30.6

Average 11.7 23.3 5.3 19.3 3.5 25.6

1 10 0-30.2 0-33.2 0-6.8 3.7-26.7 0-33.1 0-27.2

Average 8.8 13.5 2.9 16.7 12.9 5.5

7 2 3.3-3.6 6.3-10.6 0.6-1 9.3-9.6 1.3-1.6 14.6-33.3

Average 3.5 8.5 0.8 9.5 1.5 24

5.2.2. Upper reef

The upper reef thickness in the Rabigh area ranges between 1.9 and 2.4 m.

Coral appears in all the samples (Fig.5.2a) in a higher proportion (average 30.4%) than in the lower reef (average 21.3%) and reaches a maximum of 84 % in location

1. Bivalves and algae appear in the north and decrease towards the south with maximum percentages of 10% for bivalves and 31% for algae. Only low percentages of echinoderms appear in some samples (Fig.5.2c) and they almost disappear in the south (location 1). Also, in the upper reef no foraminifera were seen. The matrix of the samples in the north (location 3) is mostly micrite and microsparite whereas in the middle area (location 4) it is almost all micrite (Fig.5.2). In the south (location 1) only a low percentage of matrix appears with an average of 2.5% for sparite and

13.9% for the micrite. The average porosity in the upper reef samples is 20.1%. The upper reef contains a few gastropods and bryozoans (Fig.5.2e) but they just occur in a few samples with minor percentages (average 1.65% for gastropods and 2.5% for bryozoans). Silicate minerals are less common than in the lower reef with an average proportion of 2.8% for quartz and 1.9% for plagioclase. In general, the only correlation with the height in the entire upper reef is with coral that shows a positive correlation with the height with an R2 of 0.5527. However, in location 3, algae and echinoderms (Fig. 5.3) show good negative correlation with height (R² = 0.9464 and

R² = 0.7346, respectively).

a) b)

c) d) e)

Fig. 5.2-a) Coral dominated this thin section in the upper reef. b) Coral with holes filled with miciritec dust in the upper reef. c) Echinoid spine shows radial pattern of pores in the upper reef. d) Echinoderm debris in the upper reef. e) Bryozoans in the upper reef.

Table 5.4- Quantitative composition of the main components in the upper reef in the Rabigh area (minimum, maximum and average percentage for each component) in a transect from north to south.

Location Number of Coral Algae Echinoderms Porosity Sparite Micrite Bivalves Number samples % % % % % % %

3 5 13-35.3 0-10 2.3-29.6 0-5.1 11.5-26 0.3-14.3 9-19.9

Average 22 4.5 15.6 1.9 19.6 3.6 14.5

4 7 1-40.9 0-10 0-18 0-61.6 7.6-38.6 0-2.6 17-46.3

Average 21.8 2.2 6.6 11.1 23 0.5 26.7

1 6 8.4-84 0-7.4 0-16.5 0-1 15.6-32.1 0-11.2 0-3.7

Average 47.4 1.2 2.8 0.2 20.8 3.5 1

250 250 y = -6.1606x + 207.35 y = -33.079x + 172.53 R² = 0.9464 R² = 0.7346 200 200

150 150

100

50 50 Height (cm) Height 0 (cm) Height 0 0 10 20 30 40 0 2 4 6 Algae % Echinoderms %

Fig. 5.3- Correlation of reef height (cm) with a) algae and b) echinoderms, at location 3.

5.2.3. Back-reef

Coral in the back-reef area is much less abundant compared with the upper and lower reefs. Only two samples have high coral proportions, with the highest percentage

85 being 13.6%. Also, the back-reef area is poorer in bivalves than the in the upper and lower reefs with a maximum of 4.5%. The proportion of algae in the back-reef varies and it ranges between 0 and 39.2%. Echinoderms are common in this area; however, they only appear in low percentage with an average of 2.4%. Micrite is the dominant matrix in the back-reef area indicating a quiet water depositional environment.

Quartz and plagioclase are the only silicate minerals seen in the back-reef with less than 2% as the highest proportion. In the lower part of the back-reef a moderate negative correlation appears between stratigraphic height and echinoderms. Also, a strong negative correlation appears between height and sparite. A high positive correlation occurs between bivalves and echinoderms, which can indicate the same environmental requirements for both of them.

Table 5.5- Quantitative composition of the main components in the back-reef area at Rabigh area (minimum, maximum and average percentage for each component) in a transect from north to south.

Location Number of Coral Bivalves Algae Porosity Sparite Micrite Echinoderms Number samples % % % % % % %

6 5 0-8.3 0.3-3 1.3-27 0.3-9 22.6-37.6 0-41.3 14.2-36.6

Average 1.9 2.1 18 3.2 30.8 10 26.1

2 11 0-54 0-4.5 0-39.2 0-6.2 5.1-46 0-51.5 0-45.4

Average 10.9 0.7 11.5 2.2 27.7 19.1 23.7

5 3 1.3-3.4 0-1.3 14.1-8.6 0.6-4 27.6-39.3 0-23 16.4-39.6

Average 2.1 0.8 16.9 1.9 33.2 9.4 25.5

5.2.4. Beach rock

The beach rock samples were taken from locations 1, 3, 4 and 7. In the beach rock calcareous algae are the dominant element with proportions ranging from 13.6% to

48.9%. The cellular structure of coralline algae is clearly visible in most of the studied samples (Fig. 5.4c). Except for one coral sample, recognisable coral fragments only appear in low percentages (less than 11.9%). Bivalves (Fig. 5.4e) occur in a range between 3.3% and 11.3%. The beach rock is poor in echinoderms and foraminifera with maximum percentages of 3.4%. The average of porosity is

8.4% and the matrix/cement is composed of micrite and sparite where the sparite content is higher in most samples. Many silicates occur but in low proportions including quartz (Fig. 5.41-b), K-feldspar, tourmaline and hornblende.

a) b)

c) d)

e) f)

Fig. 5.4 a-b) Thin section photomicrographs (plane and cross-polarised illumination) illustrating quartz grains in the upper beach rock. c) Thin section of algae in the upper beach rock. d) Thin section of fragments of Halimeda in the upper beach rock. e) Prominent fragments of bivalve shells in the upper beach rock. f) Gastropod section in micirite matrix in the lower beach rock. 88

5.3. XRD results

It is important to note that for the lower, upper and back-reef successions, the correlation results are limited because of a sample size of only 3-14 samples for each location. However, this analysis is still important because it suggests something of the relationship between environmental conditions and the formation of these units.

Also, the initial XRD analyses of the lower, upper and back-reef successions all showed the presence of sodium chloride which was produced by the evaporation of sea water. A second round of XRD analyses was conducted after removing the sodium chloride from the samples, which produced the following results.

5.3.1. Lower reef

The XRD result for the lower reef (Table 5.6) showed a highly variable percentage of aragonite followed by calcite and then high-Mg calcite. They range in amount 5.4-89.7%, 0.8-49.7% and 0-36.4% for aragonite, calcite and high-Mg calcite, respectively. Aragonite was the only phase detected within the shells in the lower reef. Dolomite is probably present in some samples with a maximum proportion of 1%. Ankerite and siderite occur throughout the lower reef in low percentages (maximum of 7% for ankerite and 1.3% for siderite) while evaporitic minerals appear in almost all the samples in a proportion of 0-10.9% for gypsum.

The clay minerals showed different occurrences whereby kaolinite is present in all the samples in a range between 0.4% and 4.2% while illite is present only in some samples in a range of 0-4.3%, except for one sample with 13.6%. Other silicate minerals occur in different proportions throughout the lower reef. These minerals are made up of quartz (0-7.4%), chlorite (0-4.3%), muscovite (0-10.3%), biotite (0-

6.7%), albite (0-21.3%) and orthoclase (0-31.2%). Only one good positive correlation (Fig. 5.4) appears in location 3 between stratigraphic height and the high-

Mg-calcite (R2=0.7).

Table 5.6 Mineral percentages at the lower reef from the Rabigh area (maximum, minimum and average percentages for each location) in a transect from north to south.

Number Aragonite Calcite H-Mg Calcite Gypsum Ankerite Orthoclase Muscovite Location of number samples %

3 6 5.4-82.7 1.2-49.7 2.3-21.9 0.8-10.1 0.4-4.6 2.3-9.6 0-5.5

Average 38.1 18.1 14.6 4.4 2.1 5.6 3.1

4 3 20.1-50.6 5.8-22.1 0-36.4 0.6-1.7 0.5-2.4 4-31.2 2.3-6.8

Average 30.5 12.6 18.1 1.2 1.8 13.8 5.2

1 14 12.2-89.7 0.8-37.7 0.5-33.4 0-10.9 0-7 0-6.8 0-10.3

Average 44.2 11.7 14.5 3.6 2.7 2.7 3.4

140

120

100

40 y = 2.4198x + 37.856 R² = 0.747

0 Height (cm) Height 0 5 10 15 20 25 30 35 40

High Mg Calcite %

Fig. 5.5- Correlation of high-Mg calcite with height in the lower reef at location 3.

5.3.2 Upper reef

The XRD result for the upper reef (Table 5.7) showed a highly variable percentage of aragonite followed by high-Mg calcite and then calcite. They range in amount from 0-81.8%, 0-62.8% and 0-47.5% for aragonite, high-Mg calcite and calcite respectively. These results show a slight increase in the amount of calcite and high-Mg calcite compared with the lower reef. Aragonite is still the only phase detected within the shells. Dolomite is recognized in some samples in the northern and middle parts of the Rabigh area, with a maximum proportion of 2.4%, but in the south no dolomite was recorded. Also, ankerite and siderite occur throughout the northern and middle areas of the upper reef in low percentages (maximum of 7.6% for ankerite and 1.9% for siderite) while they almost disappear in the south.

Evaporitic minerals occur in all samples in a proportion of 0-19.8% for gypsum. Clay

91 minerals showed an identical appearance with the lower reef where kaolinite is present in all samples in a range between 0% and 4.1% and illite is present only in some samples with a maximum of 7.6%. Other silicate minerals in the upper reef showed almost the same proportions as in the lower reef including quartz (0-3.2%), chlorite (0-12.4%), muscovite (0-9.1%), biotite (0-6.8%), albite (0-5.7%) and orthoclase (0-9.9%). In the north (location 3) albite and ankerite showed a positive correlation with height while ankerite showed a negative correlation with height toward the south and disappeared in location 1 (Fig. 5.6a, b and c). Also, a negative correlation occurs between quartz and height at location 3 (Fig. 5.6d).

Table 5.7 Mineral percentages in the upper reef in the Rabigh area (maximum, minimum and average percentages for each location) in a transect from north to south.

Location No of Aragonite Calcite High-Mg Gypsum Ankerite Orthoclase Muscovite no samples Calcite %

3 4 4.7-68.1 10.6-21 3.4-62.8 1-19.8 0-7.6 2.1-4 0-4.8

Average 34.1 15.6 25.9 5.9 3.6 3.9 2.8

4 8 3.6-81.7 1.8-47.5 2.4-53.6 0.4-10.5 0.3-2 0-9.9 0-9.1

Average 25.5 20.9 27.6 4.3 1 5.2 4.3

1 8 0-81.8 0-47.2 0-7.9 0-6.1 0-0.1 0-3.7 0-3.6

Average 47.4 10.1 2.8 2.2 0.1 2 1.3

A) B )

250 250 y = -85.11x + 211.23 y = 23.688x + 19.592 R² = 0.7088 200 R² = 0.9479 200

150 150

100 100

(cm) (cm)

50 50

0 Height Height 0 0 1 2 0 5 10 Ankerite % Ankerite %

C) D)

250 250 y = -123.38x + 167.27 200 200 R² = 0.7216

150 150

100 100

(cm) (cm)

50 y = 96.491x + 15.658 50

R² = 0.7468 Height Height 0 0 0 0.5 1 1.5 0 1 2 3 -50 Albite % Quartz %

Fig. 5.6- Correlation of height with a) ankerite in location 3 shows positive correlation, b) ankerite in location 4 shows negative correlation, c) albite in location 3 shows positive correlation, and d) quartz in location 3 shows negative correlation.

5.3.3. Back-reef

In the back-reef area, the XRD results (Table 5.8) showed a very low percentage of aragonite ranging between 0 and 9.2%, except for some big Tridacna shells. Calcite is the dominant mineral with a mean value of 56.7%, a minimum of

0% and a maximum of 99.3%. High-Mg calcite appears in the back-reef with a variable proportion, especially in location 2, where the mean value is 30.4%, ranging from a minimum of 0% and a maximum of 83.9%. In locations 5 and 6 high-Mg calcite only appears in some samples with a maximum of 13.2%. Dolomite is possibly presented in some samples with a maximum proportion of 0.3%. Siderite occurs throughout the lower back-reef unit in low percentages with a maximum of

3.7% while ankerite only appears in some samples with a maximum of 0.5%.

Evaporitic minerals occur in almost all the samples in low proportions ranging between 0-3.8% for gypsum. Silicate minerals also appear in low proportions throughout the back-reef. Kaolinite is present in all the samples in a range between

0% and 1.8% while the illite is present only in some samples in a range of 0-4.3%.

Chlorite and quartz only occur in some samples with a maximum of 1.4% and 1.1% for chlorite and quartz, respectively. Other silicates minerals appear in most samples with a maximum proportion of 4.3% for muscovite, 3.5% for biotite, 3.3% for albite and 7.9% for orthoclase. The lower part of the back-reef sequence at location 6 showed good negative correlations with stratigraphic height for aragonite, high-Mg calcite, albite and quartz while a good positive correlation occurred with calcite (Fig.

5.7a and b). Other correlations appear with height in location 2, with a negative one for high-Mg calcite and a positive correlation with quartz (Fig. 5.7c and d). The upper and lower units of the back-reef area showed no major different in the XRD

results except for a relatively higher percentages of aragonite in some samples of the upper unit.

Table 5.8 - Mineral percentages in the back-reef sequence in the Rabigh area (maximum, minimum and average percentages for each location) in a transect from north to south.

H-Mg Number Aragonite Calcite Gypsum Ankerite Orthoclase Muscovite Location Calcite of number samples %

6 6 0-1.7 76.7-99.3 0-13.2 0-1.3 0-0.3 0-1.4 0-1.5

Average 1 84.9 7.9 0.6 0.1 0.7 0.9

2 15 0-70.4 0-.86.9 0-83.9 0-2.4 0-0.5 0-7.9 0-4.3

Average 16.7 38.1 28.5 1 0.1 2.4 1.6

5 3 0-9.2 66.1-85.6 0-10 0.4-3.8 0-0.4 0.3-1.1 0-1.1

Average 3.2 78.6 6.1 2.4 0.3 0.7 0.5

b) y = 2.7938x - 158.33 140 140 R² = 0.8045 120 120 y = -36.273x + 114.58 R² = 0.9601 100 100 80

60 60 40 40

20 20

Height (cm) Height Height (cm) Height 0 0 0 50 100 150 0 1 2 3 Albite % a) Calcite % c) d) 160 y = 1.2561x + 10.623 160 140 y = -93.75x + 109.38 R² = 0.7652 140 120 R² = 0.7469 120 100 100

80 80 60 60 40 40 20 20 Height (cm) Height 0 Height (cm) Height 0 0 50 100 0 0.5 1 1.5 High-mg calcite % Quartz %

Fig. 5.7. Correlation of stratigraphic height with a) calcite in lower part of the terrace in location 6 shows a positive correlation, b) albite in location 6 shows a negative correlation, c) high-Mg calcite in location 2 shows a positive correlation and d) quartz in location 2 shows a negative correlation.

5.3.4. Beach rock

The lower beach rock unit results (Table 5.9) showed highly variable percentages of aragonite, ranging between 17.3% and 53.6%, followed in abundance by high-Mg calcite, ranging between 19.4% and 48.1%, while calcite only occurred in low percentages with a maximum of 12.4%. Dolomite is not recognized in the beach rock whilst ankerite and siderite occur in low percentages with maximum of

0.6% for ankerite and 1.2% for siderite. Evaporitic minerals also occur in low proportions with a maximum of 1.5% for gypsum, except for one sample with 22.4% gypsum. The clay minerals showed an identical appearance in the lower beach rock unit to that in the back-reef where the kaolinite is present in all the samples with maximum of 0.9% while illite is present only in some samples with a maximum of

5.8%. Other silicate minerals are highly variable with muscovite and orthoclase being most common with minimums of 1.1% and 6.4% and maximums of 9.3% and

8.9% for muscovite and orthoclase, respectively. Chlorite is not present in the beach rock while quartz, biotite and albite occur in low proportions throughout the lower beach rock.

On the other hand, the upper beach rock results (Table 5.9) showed a highly variable percentage of aragonite, ranging between 36% and 61.8%, followed by high-magnesium calcite, ranging between 14 and 29%, while calcite only appears in low percentages with a maximum of 9.4%. This is very similar to the lower beach rock but shows an increase in aragonite and a slight decrease for high-Mg calcite.

Dolomite is not recognized in the upper beach rock and ankerite and siderite are also not present. Evaporitic minerals occur in low proportions with maximum of 2.1% for

97 sodium chloride and 4.1% for gypsum. The clay minerals showed an identical appearance to the lower beach rock with kaolinite, present in all the samples, with a maximum of 3.5%, whereas illite is totally absent. Again, other silicate minerals have highly variable contents. Muscovite is dominant with a minimum of 8.2% and maximum of 16.5%, following by orthoclase with a minimum of 6.3% and maximum of 11.5% and then by biotite which appears in some samples with a maximum of

7.8%. Chlorite is not present in the upper beach rock while quartz and albite only occur in one sample with low proportions.

Table 5.9 - Mineral percentages in the lower and upper beach rock units in the Rabigh area (maximum, minimum and average percentages for each location).

Number Beach H-Mg of Aragonite Calcite Gypsum Ankerite Orthoclase Muscovite rock Calcite Samples

Lower 4 17.3-53.6 4.3-12.4 19.4-48.1 0.3-22.9 0-0.6 6.4-8.9 1.1-9.3

Average 34.2 7.7 30.8 6.5 0.2 7.7 5.7

6.3- 8.2- Upper 4 36-61.8 5-9.4 14-29 0-4.1 0 11.5 16.5

Average 44.7 7.1 19.7 2.1 * 8.4 11.5

5.4 Classification and diagenesis of carbonate rocks in the Rabigh area

The samples are classified using the Folk’s scheme (1962), shown in Table

1.2. The entire series of samples is classified as poorly washed biosparite, unsorted biosparite or packed biomicrite (Appendix 1).

The major diagenetic processes that are active in the study area are neomorphism and cementation with some compaction only appers in some lower reef

and beach rock samples. These diagenetic changes were controlled by the composition of the samples and have been studied using petrography and XRD.

Neomorphism occurs due to inversion where the calcite replaces aragonitic grains and cements. As the dissolution of the original minerals occurs there are some leftover remnants in the original shells and neomorphic calcite (Fig.5.8).

Cementation is identified as the main diagenetic process in the Rabigh reefs. The kind and distribution of cement in the reef around Rabigh vary, where calcite fills the granular voids in most samples. The carbonate cementation is predominantly crystalline calcite, although some of the samples contained dolomite which was only seen in the XRD and thin sections. Some samples show abundant calcite cementation which causes the replacement of framework grains by carbonate. Three major cement types are recognized in the thin sections: Fibrous, blocky and micritic cement while in some samples drusy and granular cement appears (Fig 5.9). Fibrous calcite occurs in many samples from the upper and lower reef (Fig. 5.9a) while blocky calcite spar is the most common cement type in the back-reef (Fig. 5.9b). Micritic cements are associated with algae, and comprise the third most common type of cement especially in the back-reef (Fig. 5.9c). The fabric of the cement showed some small crystals (10-20μm). The relationship between crystal size and rate of formation of nuclei compared to the collective growth rate shows that the presence of small crystals indicates rapid early marine cementation. Chemical compaction (dissolution) has occurred to varying degrees in some of the lower reef samples, but was not very extensive (Fig. 5.10). This compaction could be caused by dissolution that occurs during rainy periods.

Fig. 5.8 Samples from the lower reef showing neomorphism.

a b

c d

Fig. 5.9 a) sample from the lower reef showing Fibrous cement. b) blocky cement is the most common type in back reef . c) Micratic cement in the lower reef. d) drousy cement in the upper reef.

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Fig. 5.10 a) Dissolution of micrite matrix and granular cement takes place in a beach rock sample, b) dissolution of matrix in an upper reef sample.

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Chapter 6- Dating result and discussion

6.1 Amino Acid Racemisation (AAR) result and discussion

This is a technique that approximates the age of a sample by relating the changes in amino acid molecules to the time elapsed since their formation. All organic tissues have amino acids which have an asymmetric carbon atom, except glycerine, thus they have two different configurations, “D” or “L”. Existing organisms have their amino acids in “L” configuration and when the organism dies, the pattern management ceases and the ratio D/L shifts slowly near to equilibrium; this process is called racemisation. The degree of racemisation allows an estimation of the period of time since the specimen has died.

The four analysed bivalve shell sample locations and height are shown in

Table 6.1. Samples were collected from different altitudes but all collected from the surface without drilling. The measured quantities of amino acids (Table 6.2) from the analysed shell samples were converted to D/L ratios as shown in Table 6.3. The D/L ratio is based on the average of two different sub-samples from each of the bivalve shell samples. The results show low amino acid concentrations in all samples (Table

6.2). For example, sample UWGA7900A showed an aspartic acid D/L ratio of 0.55 and glutamic acid D/L ratio of 0.83. Histograms of D/L ratios (Figs 6.2-6.3) for aspartic, glutamine, valine and alanine summarize the data from the four samples.

From the analysis, the ontogenic trends in D/L Asp values are parallel to the trends of the shell amino acids. The high rate of racemisation in Asp is associated with lower concentrations of the total amino acids and higher comparative ratio concentrations of the amino acids (Fig. 6.2).

102

Table 6.1. Locations of bivalve shell samples used in amino acid racemisation Sample no Lab no Location Height

2N.1.2 7900 Back reef (Flat area) 50 cm

1N.1.1 7902 Lower reef 100 cm

1.1.14 7903 Lower reef 120 cm

2.2.4 7904 Back reef 320 cm

Table 6.2. Average amino acid racemisation results for three runs of bivalve shells from Rabigh, Saudi Arabia Aspx Aspx Ser Sample Glx D Glx L Ser L Val D Val L Ala D Ala L D L D 7900 140.14 252.65 338.73 409.22 0 97.42 217.36 279.05 425.61 569.44

7902 290.13 371.4 456.04 505.76 0 78.45 241.21 264.07 596.22 669.32

7903 516.74 713.55 530.11 858.94 0 89.68 236.01 451.3 449.67 754.21

7904 91.07 116.07 283.33 293.97 0 72.74 154.92 150.93 352.7 464.52

Table 6.3. Results of D/L ratios from bivalve shell samples

Sample D/L ratios

Aspx Glx Ser Val Ala

7900 0.55 0.83 0 0.78 0.75

7902 0.78 0.90 0 0.91 0.89

7903 0.72 0.62 0 0.52 0.60

7904 0.78 0.96 0 1.03 0.76

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Figure 6.1a: D/L ratio for Asp 1

0.5

0 1 2 3 4

Figure 6.1b: D/L ratio for Glu 2

0 1 2 3 4

Glx

Figure 6.1c: D/L ratio for Val 1.5

Vax 0.5

0 1 2 3 4

Figure 6.1d: D/L ratio for Ala 1

0.5 Ala 0 1 2 3 4

Fig. 6.1. The D/L ratios of aspartic (Asp), glutamine (Glu), valine (Val) and alanine

(Ala) amino acids from the four analysed shells

104

1.2

0.8 S7900 0.6 S7902 S7903 0.4 S7904 0.2

0 Aspx Glx Ser Vax Ala

Fig. 6.2. D/L ratios of the 4 bivalves shell samples

The results obtained are not conclusive, due to the limitations associated with racemisation. Racemisation depends on temperature, alkalinity, concentration of water and preservation conditions that may leave the accuracy of the amino acid dating questionable. Also, there was inadequate knowledge about the effective average racemisation rate in these fossils as a function of time, which allows the dependency on the D/L ratio for the determining age quantitatively (Brown, 1985).

From Figure 6.1 it is obvious that for any specific amino acid present, there is no typical racemisation constant that is applicable for all ordinary circumstances. It can be affirmed that the factors that determine the racemisation rate of amino acids

(Smith and Evans, 1980; Kriausakul and Mitterer, 1980a; Kriausakul and Mitterer,

1980b ) include size of macromolecule, ionic strength of the environment specific location in the molecule, bound state versus free state, contact with clay surfaces

(catalytic effect), presence of aldehydes, particularly when associated with metal

105 ions, concentration of buffer compounds, water concentration and pH in the environment, and temperature. In a fossil, the D/L ratio symbolizes the age and the environmental conditions under which it has been preserved.

Goodfriend and Weidman (2001) used HPLC analysis to determine evidence for changes in protein chemistry by ontogeny that may elucidate the ontogenetic trend in Asp racemisation rates. The geochemistry trends within the cells of the amino acids might be related to diagenetic amendments. The stability of amino acids varies (Vallentyne, 1969). Groenen et al. (1990) affirming that the rates of racemisation in proteins (amino acids) vary according to the position of the asymmetric atoms in the protein. The dissimilarity in the composition of the protein more often directs variation in the racemisation rate, which measures the amino acid ensemble. These yield patterns of orthogenetic variation in the observed Asp racemisation rate. The position of the amino acid peptide protein also contributes to the rate variation. The real time-age of the fossil can be derived from a D/L ratio and the equivalent racemisation rate constant is determined, as long as the environmental factors that are significant are specified.

The results in Table 6.4 are compared to the analysis reported by Keenan et al. (1987). They use the amino acid dating method to estimate the ages of molluscs from Quaternary marine terraces. The high mean annual temperature (about 210C) in the Mexico study area caused extensive racemisation of samples, with only two amino acids being dominant enough for resolving. According to the Saudi

Presidency of Meterology and Environment (PME), the mean annual temperature in the Rabigh area is about 250 C, which resulted in even more extensive racemisation in all the samples.

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To clarify this, Table 6.5 shows the relation between Valine acid D/L values and mean annual temperature in southern Australia, Mexico and Rabigh in Saudi

Arabia. The average D/L values of 4 samples from Rabigh area are taken and compared with average D/L values of equivalent age (MIS 7) bivalve mollusc samples in Mexico (Keenan, 1978) and southern Australia (Murray-Wallace, 1995) to illustrate the effect of contrasting diagenetic temperature on racemisation. A line chart was drawn (Fig. 6.3) to show the relation between these values and mean annual temperature. The rates of racemisation are known to approximately double for every 5°C increase in normal ambient temperature (0-25°C). This can be shown in points (a) and (b) where the difference in MAT=2°C, consistent with an increase in the racemisation = 0.213. While in Rabigh area (c) comparing with (a), the increase in MAT is 6°C which is accompanied by a doubling of the degree of racemisation

(0.81).

It can be concluded that the result of amino acid racemisation in the Rabigh area is likely to be the result of the high mean annual temperature (MAT) where heating accelerates the racemisation of shallow shells at an exponential rate, making them appear older. This dating technique is therefore considered to be unreliable for near-surface materials of this age from the Rabigh area. Therefore, the results from the amino acid racemisation cannot be considered consistent due to the lack of background data relating to samples from this area.

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Table 6.4 Comparisons between the results of Keenan et al. (1987) and results from

the Rabigh area

Keenan, E. M, Reference Rabigh result et al., (1978)

Fossil Molluscs Fossil Molluscs Material shells shells Bahia Rabigh, Saudi Locality Asuncion, Arabia Mexico

C.M.A.T 250C 210 C

Genera Tridacna gigas Tivela

ASP D/L 0.554 0.679

0.781 0.660

0.724 0.807 0.78

GLu D/L 0.827 0.626

0.907 0.751

0.617 0.991 0.97

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Table 6.5. Valine average D/L values in middle and late Pleistocene molluscan

fossils from three different areas

Valine average Reference Locality M.A.T Age D/L value

Lab result Rabigh, Saudi Arabia 250C -- 0.81 Keenan, E. M, et al. Bahia Asuncion, MIS 7 (200 210C 0.693 1978 Mexico ka) Murray-Wallace, C, Redcliff, SA, MIS 7 (220 190C 0.48 1995 Australia ka)

Valine

1 0.9

0.8 C = 0.81

0.7 B = 0.693 0.6 0.5 A = 0.48 0.4 0.3

0.2 D/L ratio Valine ratio D/L 0.1 0 10 15 20 25 30

CMAT (°C)

Fig. 6.3. Relation between valine D/L ratio for middle and late Pleistocene molluscan

fossils from A: Australia, B: Mexico and C: Saudi Arabia with mean annual

temperature in these areas

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6.2 14C results and discussion

The carbon-14 (14C) dating is a method that relies on the radioisotope carbon-

14 that occurs naturally, and is used to estimate the age of organic materials and remains up to the ages of about 40-50 ka from geological and archaeological sites.

Five bivalve shells samples were sent for radiocarbon dating. All the samples are composed of aragonite, except sample 4.2.1 which showed mixed calcite and aragonite where the calcite section was removed and aragonite was selected for dating. The results of 14C analysis of bivalve shells from the Rabigh area (Table 6.6) all showed numerical ages but most of them are near the 14C age limit of 40-50 ka while the 14C reservoir age is calculated at 440 ± 40 yr in the Red Sea (Siani et al.,

2000). Sample 1.1.13, with an elevation of 1.2 m above sea level, shows an Holocene age of 2360±40 year BP, but this date seems very unreasonable as this sample comes from the lower reef sequence, which is expected to be Pleistocene (see Fig. 4.10).

This fossil is observed to have grown embedded on the seaward margin of the lower reef but is obviously a Holocene addition that has been cemented into the lower reef.

The shell was in the base of the cliff and looks as it is a part of the cliff sequence but it must actually be part of a well cemented beach rock on the edge of the cliff exposed to wave action. Other possibility is that the lower Pleistocene reef is a palimpsest surface reoccupied during the early-mid Holocene following the culmination of the post glacial marine transgression.

For samples 1.2.7 and 2.2.4 the margins of error were ± 960 yr and ± 360 yr, respectively, which is large and could result from the small amount of the original sample or it might mean that the benzene samples had to be diluted with background benzene to get sufficient mass of benzene for liquid scintillation counting. Table 6.6

110

presents the results from radiocarbon dating, however, for samples beyond the range

of 14C dating, 1% contamination by modern 14C will yield an apparent age of 37,000

years. Since the results do not reflect the relative elevation of sea level at 40-50 ka it

is probable that the ages reflect slight contamination rather than the age of the

deposits.

Physical observations that are not dependent on the geochronological proof

usually give steady lower age boundaries for the coral reef successions and provide

more constraints for these ages. Examining the association between the location of

the reef succession and the position of major tectonic structures in the region

suggests the absence of recent activity on previously recognized faults.

Table 6.6. Samples detail and results of radiocarbon dating

δ13C ‰ Lab no Sample no Location Height (cm) VPDB Age (BP) ± 0.2

Wk-26593 1.1.13 Lower terrace 120 3.1 2360 ± 40 Wk-26594 1.2.7 Upper terrace 270 0.8 40,180 ± 960 Wk-26597 4.2.1 Upper terrace 230 2.2 43,570± 1500 Back reef Wk-26595 2.1.2 0 2.7 < 45,490 (Flat area) Back reef Wk-26596 2.2.4 320 3.0 53,020± 360 (terrace)

Behairy (1983) demonstrated four major marine transgressions using

radiometric ages of the corals in three terraces (Table 6.7). These terraces were

located in Saudi Arabia, north of Jeddah, with the first and second terraces being 1

and 3 m above sea level, and located near to the present shore line. The third terrace

is 10 m above sea level, and is located about 500 m inland. The first transgression

was attributed to an interstadial period occurring before 31,000 years B.P, and was a

111 time at which coral formation was favoured. The climatic conditions were said to be the same as the current times. Behairy (1983) considered that this transgression extended almost up to the foothills and resulted in the development of the third terrace. Behairy’s second transgression occurred between 16,000-18,000 years B.P. and resulted in the deposition of the second terrace (3 m above present sea level).

These findings are now considered to be inaccurate based on modern Quaternary sea- level variation models. The modern sea level curve is based on global examples and is correlated with the deep sea oxygen isotope data. The Late Pleistocene to

Holocene sea level curve (Fig. 2.4) shows that sea level dropped and it was about

121 ± 5 metres below present level during the last glacial maximum, around 25,000 years ago, and by 16,000 years was in fact increasing (Fairbanks, 1989). The existence of aragonite layers in Red Sea sediments deposited in the range of 20,000-

11,000 years B.P. are attributed to the lowering of sea level resulting in a hypersaline setting for the Red Sea (Milliman et al., 1969).

Table 6.7. Radiocarbon dates of coral limestones from the west coast of Saudi

Arabia (Behairy, 1983)

Terrace no. Height (m) Age (yrs B.P.)

1 1 9980 ± 140

2 3 18100 ± 370

2 3 16600 ± 210

3 10 31000 ± 1350

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Behairy’s (1983) third transgression responsible for terrace one was reported to have occurred at 9,980 years B.P but is of shorter duration. This should probably be combined with his fourth marine transgression also characterized by a terrace 1 m above present sea level. These terraces may represent the mid-Holocene highstand which is also responsible for the beach rock systems. Since the earlier interglacial fluctuations and associated terraces are found either below or close to the present sea level, Behairy (1983) suggested that tectonic movements were responsible for their current elevations. However, the dates obtained by Behairy (1983) are not consistent with known sea level positions unless significant uplift (of up to 130 m) has occurred in the last 15,000 years. Also, there is no geomorphic evidence for uplift and erosion in that period along the central Saudi coast. These dates suggest that the samples dated by Behairy could have some secondary carbonate which is younger. So the dates are a composite age which is actually considerably younger. Using the result of

Behairy’s (1983) 14C dating of Rabigh samples, sea level should have been more than 2 m above present mean sea level between 40,000 and 50,000 years ago whereas the global sea level during this time was 50-60 m lower than mean sea level in tectonically stable areas (Baily et al., 2007). Another interpretation is to suggest uplift of these terraces for which there is no evidence.

For this thesis, the poor resolution of data makes it impossible to ascribe a precise date to the maximum age of the reef succession. The exact ages of the reef succession are understood to be older than the 14C dates, and so the age of the upper reef is reasonably expected to be from stage 5e (125-110 ka), when the sea level was about 5 m above present mean sea level. This is consistent with a lack of uplift in the

Rabigh area. This means that the age of the lower reef is likely to be from stage 7.

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Another dating method with a wider age limit, such as U/Th dating, would be required to obtain the correct date for these reefs.

6.3 U/Th Dating

Two Porites coral samples were sent for U/Th dating, 1.1.7 from the lower reef succession and 1.2.5 from the upper reef. As the samples are slightly altered with elevated 234U/238U ratios above the typical seawater window of 1.146, Bill

Thompson's software was used to calculate the open-system model ages which are:

Table 6.8 Results of age dating for coral samples using U/Th dating

Sample U 232Th (230Th/ ±2s ±2s ±2s (230Th/238U) ±2s name (ppm) (ppb) 232Th)

1.1.7 3.6413 0.0024 2.49 0.003 2505.21 4.77 0.5651 0.0008

1.2.5 4.0801 0.0029 0.27 0.001 36696.19 169.36 0.8024 0.0013

uncorr. Thompson corr. Sample (234U/ 230Th Open- ±2s ±2s 230Th ±2s ±2s name 238U) Age system age Age (ka) (ka) (ka)

1.1.7 1.1264 0.0008 74.84 0.18 74.83 0.18 71.58 0.13

1.2.5 1.1187 0.0010 133.15 0.48 133.15 0.48 122.80 0.32

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These dates indicate MIS 5 corals for both the upper and lower reef succession but the only problem being an age reversal with the upper reef being a lot older than the lower reef. Sample 1.1.7 from the lower reef gave an age of 71.58 ka which indicate MIS 5a where the sea level was -15 m below present sea level while sample 1.2.5 gave an age of 122.80 ka indicating MIS 5e where the sea level was 3-6 m above present sea level.

The actual calculated values (Table 6.8) are within reasonable certainties where the errors in all the measurements are low and, therefore, the dates obtained are statistically valid but obviously they are not valid in terms of stratigraphy. The lower reef, which is more cemented, probably has younger aragonite cement associated with it. The younger dates in this terrace must reflect either replacement carbonate or secondary carbonate which has been incorporated into the dating. Both sequences could be stage 5. The upper reef is directly superposed on the lower reef where it is directly overlying it (Fig.3.2). That suggests either both of the layers could be stage 5e where the lower reef sequence could be an earlier 5e and then a second reef growing out over the top of it during later stage 5e, or the lower sequence could be stage 7.

Therefore, the U series ages indicate that the dates obtained from the AAR method and 14C methods should be considered unreliable. The primary inaccuracy with the AAR method is that the affect of surface heating accelerates the racemisation, and so results cannot be considered scientifically dependable. Suitable

AAR ages may be obtained if samples are collected from at least 1 m below the ground surface. Meanwhile the use of 14C methods consistently provides ages which are too recent and can only be used as minimum age constraints. Within this thesis the most appropriate date for the upper reef is 122.8 ka. Such a date is consistent 115 with the stage 5e sea level and lack of uplift, as well as being consistent with the stage 5e and terrace heights observed in that period. The lower reef could be either an earliest phase of 5e or stage 7 or earlier, which is consistent with its more cemented character.

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Chapter 7- Discussion

Based on the previous chapters and results obtained, this chapter will focus on environmental parameters and age control for the sequences. This approach will assist in determining the most likely succession of events and sequences for the

Rabigh area.

7.1 Beach rock

Along the Rabigh coast beach rock is exposed in the intertidal zone and it is composed of two layers of beach rock, where the lower unit ranges in thickness between 20-45 cm, and the upper unit is 20-40 cm. The exposures are parallel to the shore, with a seaward slope. The level of the prograding beach rock in this area reflects fluctuations in sea level, as they start at the high tide level and extend towards the sea for a few metres to low-tide level. The particle size results have shown that the intertidal zone is made of beach sands, unsorted skeletal fragments and lithoclasts. The current carbonate particles come from either the nearby eroding

Pleistocene terraces, or through the disintegration of marine skeletal materials. The particle size is between medium sand through to gravel size.

Petrography of beach rock in the Rabigh area reveals uncategorised carbonate grains that have been derived from the adjacent carbonate terraces and include both skeletal particles and intraclasts. Dominant skeletal particles are algae and molluscs, particularly bivalves. The rest of the skeletal particles include corals and echinoids in low numbers. The Rabigh beach rock is highly cemented, and this creates a low porosity of primary intergranular type. Limited dissolution of carbonate grains can lead to secondary porosity, and intragranular porosity. Within the beach rock in the

117

Rabigh area aragonite and high-Mg calcite are the most plentiful minerals found

(Appendix 2) and they represent the dominant cements in the beach rock. Dolomite is found in minimal amounts. Aragonite and high-Mg calcite precipitation and dolomite formation are the primary reactions in tropical intertidal settings, where the beach rock has formed (Morse and Mackenzie 1990). This is consistent with results from elsewhere in the Red Sea, Aqaba and Arabian Gulf coasts (Shinn, 1969;

Friedman and Gavish, 1971; Magaritz et al., 1979; Khalaf, 1988; Friedman, 2002).

The beach rock in the Rabigh area is typified by intergranular high-Mg calcite cement and aragonite needles, which are suggestive of marine phreatic diagenesis. Cementation of the beach sediments occurs in the marine waters within the intertidal and subtidal zones where the pore water is subject to evaporation. The particle size results have revealed that the coastal area at Rabigh is of moderate energy (wave heights ranges between 0.6-1.2 m and wind speed normally ranges between 5-25 knots) which is essential for the supply of seawater from which the

CaC03 cements precipitate. Along the intertidal zone the beach rock is well exposed throughout the Aqaba and Arabian Gulf coasts.

Within the Aqaba and Arabian Gulf marine phreatic zone, cementation has begun to form modern beach rock. The beach rock cements in the Rabigh area are based on prograding beach rock, which reflects sea level fluctuations, and thus the beach rock is similar to deposits in the Gulf of Aqaba, Red Sea and the northern coast of Puerto Rico and South America (Friedman, 2004). The beach rock is probably Holocene to Recent, and is not considered to be part of the reef structure. It is formed easily in such environments, in just a matter of years, and so is not an ancient feature. The higher beach rock deposition is reflective of the mid-Holocene high stand of sea level (up to 1 m high), and is regarded as a feature of the mid- 118

Holocene transgression rather than the Late Pleistocene reef structure. Material in the beach rock is probably a combination of Holocene reef top detritus and reworked coral reef terrace material.

7.2 Lower Reef

The lower reef of this study area is observed to have a darker colour in the north, at a similar elevation between 1.1 – 1.4 m (Fig. 4.5). Both the species

Coralliophila violacea, Latrius turritus, Cypraea turdus and other gastropod shells were observed in all locations in reasonable amounts. Location 1 revealed an area with the highest coral coverage and variety, while Location 3 revealed only a few corals (Table 4.1, Fig. 7.1). Such coverage is argued to be related to the ancient valleys in the north, as clastic sediment ran through these valleys during the rainy periods through to Sharm Al-Kharrar (Al-Washmi, 1999). This created a higher percentage of clastic sedimentary deposits and lower salinity levels and, therefore, led to decreased coral coverage. A consistent result is observed to the south where decreased coral diversity occurs, due to similar reasons, as Sharm Rabigh is approached.

As mentioned by Pandolfi and Jackson (2001; 2007), the abundance of a taxa in a fossil reef deposit reflects the abundance of this taxa during the reef growth. The occurrence of Tubipora corals in the lower reef indicate a shallow water environment as this coral is restricted to these environments and tends to be found in sheltered areas (Wood, 1983). Also, the appearance of Tubipora and the absence of Acropora along this terrace indicate it is part of a reef flat environment (Head, 1987; Orme,

1977), which is supported by the dominance of coralline algae, other corals and

119 molluscs. However, the appearance of coral species such as Fungi and Favites in locations 1 and 4 could indicate an outer reef flat – a zone with a combination of the fore reef and lagoon environments containing wave-breaking algal structures (Flügel,

1978).

Petrography and XRD results show the dominance of corals and other aragonite secreting organisms during the construction of the lower reef. The average

15.2% high-Mg-calcite content is due to the presence of bryozoans, foraminifera and bivalves (having a mixture of aragonite, and high-Mg- calcite skeletal structures).

Within the micritic matrix shell fragments, quartz grains and heavy minerals are embedded. The presence of detrital grains of quartz and heavy minerals in the lower reef indicates a supply of terrigenous materials. Such materials would have been sourced from the Tertiary mountains located to the east of the study area, and are common in the coastal plain due to surface water run-off and aeolian transportation.

The lower reef shows more cementation and diagenesis than the upper reef.

The thin sections from the lower reef show some leaching of aragonite accompanied by calcite replacement and low porosity (Table 5.3). Rapid cementation is characteristic of the lower reef, while is similar to that observed in a variety of other carbonate depositional environments including the Great Barrier Reef (Marshall and

Davies, 1981; Marshall, 1983), the Red Sea (Friedman et al., 1974) and Barbados

(Macintyre et al., 1968). Calcite cement is distributed equally around most of the grains leaving an average porosity of 14.8%. The calcite features are typical of a fresh water phreatic environment as mentioned by Meyers (1978). Cementation reduces the porosity in the lower reef but the carbonate cement does not fill all the pore spaces and sometimes it replaces the framework grains. Molluscan shell 120

fragments suggest limited recrystallization whereas the precipitation of equant blocky calcite crystals shows diagenesis under a meteoric vadose sub-environment.

The 14C dating results for the lower reef show the ages of 2362 ± 41 at sea level and 45488 at 1.2 m above sea level, while the U/Th dating method gave an age of 71.58 ka for the lower reef. This indicates a date of MIS 5a when the sea level was

-15 m below present sea level. As mentioned before in chapter 6, all of these dates are believed to be unreliable.

Both the occurrence of marine diagenesis and the strongly indurated nature of this sequence suggest that the lower reef is likely to have developed during early stage MIS 5 or stage MIS 7 or older, which is confirmed by the level of the reef.

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Fig. 7.1 Extent of the Rabigh reef area between Sharm Al-Kharar in the north and

Sharm Rabigh in the south, showing sample locations, coral terraces and morphology of the area (Google Maps, 2011).

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7.3 Upper Reef

The upper reef in the Rabigh area is characterised by coralline algae. It is not well cemented and occurs at a range of reef heights between 1.9-2.4 m with the top at an elevation of 3-3.5 m above present sea level. The upper terrace is thickest at the middle location 4, while the height and extent of the reef decrease through to the north and south. At location 7 (Fig. 4.5) there were no remnants of the upper reef, and as with the lower reef, the clastic sediment content was greater in the ancient valley areas, such as Sharm Al-Kharrar to the north and Sharm Rabigh to the south.

This has created a restricted variety and coverage of coral in these areas, consistent with the lower reef.

The coral framework in the upper reef indicates the environment during the formation of this reef. For example, the plates of Porites coral (Fig. 4.13c) are not filled by cementation. This is due to a lack of water moving through the system since deposition, both because of limited rain in the area and because the coral reef succession was emergent and above sea level. Also the coralline algae have grown to a height of 2 m in the upper reef (Fig. 4.12b) which indicates a low energy environment during the formation of this reef. That is different from reefs in other parts of the world which are subject to the effects of open-ocean circulation and more intense wave action. For example, in the Caribbean reef the seaward edge of the reef crest takes the brunt of the incoming wave energy where water is washed across the reef crest and into the lagoon, driving lagoonal circulation (Hubbard, et al., 1981) and restricting the size of the coralline algae.

Petrography and XRD results show that while the percentages of coral has increased in the upper reef (average 32%), the aragonite percentage has decreased.

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The corals are affected by fresh water diagenesis but they are not reduced in number because of neomorphism.

Decreased aragonite in the upper reef relates to the restricted dissolution by fresh water, and the precipitation of calcite lower in the reefs which is consistent with the findings by both Behairy (1980) and Dullo and Jado (1984).

Most of the samples show some meteoric digenesis. Within the meteoric environment, the aragonite elements, skeletal grains and cements are found to selectively dissolve, and then re-precipitate as sparry calcite mosaics. Such mosaics are made up of equant low-Mg-calcite crystals that line or fill the pores and, therefore, replace the aragonite skeleton grains (Tucker and Wright, 1990). The distribution of the sparry calcite mosaic is drusy in the thin sections; however, the precipitation could be sourced from the phreatic sub-environments in the meteoric vadose zone (Beier, 1985).

Less than 2% of silicate minerals are found in upper reef. These detrital minerals have been moved from the Tertiary outcrops in an arid climate to the depositional site as a response to mechanical weathering conditions, flash floods or wind action. In the field the upper reef is extremely friable (Fig. 3.21) and this is probably a reflection of its diagenetic history involving minimal marine cementation evidenced by acicular fringe carbonate cement.

The extensive presence of Acropora coral associated with other individual coral colonies, particularly Porites, Tubipora musica, Favites and Stylophora, the abundance of coralline algae and the high percentage of gastropods can all indicate this upper reef is a part of an ancient reef crest or an algal ridge in the reef system.

The fore-reef that would have been associated with this reef must have been eroded.

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Such an interpretation for the upper and lower reefs may connect with two transgressive phases of the sea and represent slightly higher sea levels.

The 14C dating results for the upper reef suggest an age between 40-53 ka at

3.2 m, but this age is nearly at the limits of 14C dating and is not a reliable result.

These dates possibly reflect minor contamination by modern carbon and would thus reflect minimum ages, since reefs of 40-53 ka would be below present sea level (Fig.

2.4), and it would be in fact challenging to locate such reefs above the present sea level in the absence of tectonic uplift. Tectonic uplift has not been evident since at least MIS 5e, and while at 40-53 ka sea level was lower than currently observed, this is not so for MIS 5e (Hearty, 1987).

The use of 14C dating has revealed an age of greater than 40 ka from the samples in this reef and the use of U/Th dating gave an age of 122.80 ka indicating

MIS 5e where the sea level was 3-6 m above present sea level. This suggests that the reef succession was formed during the 5e stage of the last interglacial, and, therefore, the formation of this reef is comparable to other reefs in the northern Red Sea. For example, the height of a reef terrace from the northern Red Sea, 3-6 m above sea level, was dated by U/Th and gave an age of 118-125 ka (El-Asmar, 1997). This is also consistent with the dating of a reef terrace 2 - 6 m above sea level on the

Sudanese coast, which gave ages of 125-142 ka (Hoang et al., 1996). Such dates suggest that the reef growth at stage 5e during the last interglacial are consistent with the results obtained from elsewhere along the Red Sea coast, including from northern

Egypt through to Ethiopia and Djibouti in the south (Hoang and Taviani, 1988;

Hoang and Taviani, 1991; Andres et al., 1988; Reyss et al., 1993). Moreover, the global sea level was believed to exist at approximately 2-6 m above present mean sea level during this period (Chappell and Shackleton, 1986; Woodroffe et al., 1995). 125

Tectonic uplift along the Red Sea coast of Saudi Arabia was first proposed by

Behairy (1983). Additionally, Gvirtzman et al. (1992) argued for a similar tectonic uplift of between 28-35 m during the last 300 ka. However, Hoang et al. (1996) has suggested that the major tectonic effects developed before the Last Interglacial and, therefore, there has been no major tectonic activity in the last 125 ka. Reyss et al.

(1993) suggested comparable stable conditions for the west coast of the Red Sea.

A number of similar last Interglacial reef terraces have been observed and analysed around the world. They include the Rendevous Hill ‘III’ terrace in

Barbados; the 'VIIIb' coral reef terrace in New Guinea; terraces 1-4 m high and 140-

81 ka age in A1 Aqaba, Jordan; Devonshire/Spencer's Point in Bermuda; terrace '112' on Sumba Island, Indonesia; and the Grotto Beach Formation in the Bahamas

(Fairbanks and Matthews, 1978; Aharon and Chappell, 1986; E1-Rifaiy and Cherif,

1988; Vacher and Hearty, 1989; Pirazzoli et al., 1991; Hearty and Kindler, 1993).

The definition of past sea level heights has been determined from around the world, especially in areas with tectonic consistency. The data about the relative sea level height during stage 5e along the coast in Western Australia reflect a sea level height of about +3 m minimum, while a sea level rise of about 5 m during stage 5e has been observed in the Bahamas, Bermuda Island and Florida (Stirling et al., 1998;

Chen et al., 1991; Muhs et al., 2002, 2004).

In locations such as Haiti and Barbados, the elevation of sea level at 2.7-5 m, and 6 m a.s.l. is dated to approximately 132 ka and 128 ka, respectively (Schellmann and Radtke, 2004; Dumas et al., 2006). However, in the eastern Atlantic Ocean, stratigraphic data from the Canary Islands reflect the highest MIS 5e points at between 0-2 m a.s.l (Zazo et al., 2002).

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The higher sea level is important for the evolution of the Rabigh reef, especially during the latter part of MIS 5 because the surface of the upper reef would have emerged from the water after the decline of the sea level. This can lead to reef top erosion. The features in the upper reef are observed to be similar to a number of other reefs, including the terrace V in Gulf of Aqaba, terrace 'I' in New Guinea, the recent reef terrace in Al-Aqaba, Jordan, terrace '0' on Sumba Island, Indonesia, and the Rice Bay Formation in the Bahamas (El-Asmar, 1997; Aharon and Chappell,

1986; El-Rifaiy and Cherif, 1988; Pirazzoli et al., 1991; Hearty and Kindler, 1993).

The low cementation and relatively open and friable nature of the upper reef at

Rabigh is similar to more recent coral terraces. This is probably a function of the very dry climate and lack of younger deposits along the Saudi Arabian coast. Hence very little diagenetic alteration has occurred in this terrace since its emergence probably near the end of MIS 5.

7.4 Back-reef

The expenditure of wave forces throughout the reef crest area means that the back-reef has become an environment of varied lower energy physical processes and sedimentary qualities. Sediment and rubble from the reef crest are deposited behind the crest, which widens the back-reef flat over time. The back-reef petrographic results demonstrate only a few corals, but fossils constitute the allochems and include algal grains, gastropods and echinoid spines that suggest deposition in a near-shore environment. A shallow lagoon typically sits behind the broad reef flat, and this creates the back-reef area which is primarily submerged at high tide, and contains depressions which retain water at low tide. As such, scattered coral colonies and patch reefs are observed in the back-reef area (Table 4.3). The deposition of 127 terrigenous sediment from the continent has led to poor coral development in the back-reef, and the upside-down corals suggests that they have been dumped from nearer the reef crest by wave action and do not originate from within this environment.

An increase of high-Mg-calcite to an average of 21.3% (Appendix 3) characterizes this reef. High-Mg-calcite could be derived from the skeletons of organisms such as echinoderms, which are common in this reef (Appendix 2), and by direct precipitation of marine cements.

Many of the abundant reefal high-Mg-calcite micrite cements probably resulted from biologically induced precipitation, thereby making automicrites important contributors to modern reef rigidity (Webb, 1996; Webb et al., 1998).

High-Mg-calcite formed blocky, palisade and scale-like crystals together with micrite. This blocky calcite spar can be an indicator of a meteoric phreatic environment (Given and Wilkinson, 1985).

The upper cemented part of the reef in some back reef areas (location 5 and

6) consist of rubble with a few upside-down corals, which indicate it is rubble that eroded out of the reef front. This reef in other back reef areas (location 2 and south of

6) is different with an appearance of coralline algae, calcareous worm tubes and some Acropora and Favites corals that probably represent low patch reefs.

The lower flat outcrops in all the back-reef area are mud-dominated and contain calcite shells and gastropods and probably represent the lagoonal facies. The most abundant species of bivalve in this facies is Trachycardium lacunosum (Reeve,

1845) and many gastropods and echinoid spines of the species Heterocentrotus mammilatus (Linnaeus, 1758) were found. The fact that calcareous mud dominates

128

the back-reef area gives an indication of a low energy lagoonal environment behind the reef crest. This lagoon environment is characterized by extensive shallow marine conditions, which would have been bordered by the mainland at the time of deposition (Flügel 1978).

The scattered coral growth with minor sediment accumulation reflects the presence of a back-reef lagoon or channel (Fig. 7.1), between the reef flat and the shoreline.

Guilcher (1988) has argued that such channels could be the outcome of runoff and sediment supply. Comparable channels occur at a depth of 1.5 m greater than the reef flat at Elat on the Red Sea coast, and at Mahe in the Seychelles (Kennedy and

Woodroffe, 2002).

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Fig. 7.2 Diagram of the back reef sequence showing present outcrops and the back reef rubble material. This diagram shows the back reef rubble coming over the top of the lagoonal fine muddier facies, as well as big Tridacna shells on the lagoon floor.

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7.5 Models and morphology of the coral reefs in Rabigh area

The morphology of a coral reef depends on many factors such as the climate, wave action, topography of the coast, the influence of geological inheritance, sea level change and the extent and pattern of reef growth. The characteristics of various parts of the carbonate platforms vary according to these factors.

The Red Sea reefs are a bit different from more open ocean reef systems.

Open ocean reef systems are characterised by a higher energy outer reef side where the reef drops into deep water and the wave effective portion is very well cemented.

Then the outer reef in a classic reef system is very well cemented but in the Red Sea reefs the wave energy is much less and, therefore, the outer part of reef may be not as well cemented. The other alternative is that the preserved reef sequence in the

Rabigh area is part of the back reef. It may have never been a part of the reef front but has grown up in the quiet back-water area behind the reef front. To sort out which part of reef system the Rabigh reefs belong to, some examples from other reef structures need to be discussed.

In the Bahamas, for example, the morphologic profile shows a rimmed flat- topped shelf with a wide platform (Handford & Loucks, 1993). This is similar to the

Red Sea morphology which consists of a rimmed shelf with a platform about 4 km wide in the Rabigh area (Fig. 7.1). The Rabigh sequence most closely reflects the rimmed shelve morphologic profile. The widths of these reef successions are strongly dependant on the wave and currents energies on the adjacent shallow shelves (Jonson, 1978). These waves and currents vary depending on the size and bathymetry of the ocean or the sea as mentioned by Elliott (1986). Referring to the previous examples, the coral platform in the Bahamas is widest where the currents

131 and wave amplitude have increased as shelf width decreases and the reef has a better connection to the open ocean. Similar conditions appear in Bermuda and South

Australia (Handford & Loucks, 1993). In the Rabigh area (Red Sea), although the shelf is narrow, the wave regime is restricted by a shorter fetch the mean currents and wave amplitude are lower resulting in a narrow reef platform.

Fig. 7.3 Morphologic profiles of carbonate platforms from Handford and Loucks (1993).

This also can be shown in the texture and the growth of the coral reef terraces. For example, porous and un-cemented coral reef occurs in the upper reef in the Rabigh area. The vertical growth of the corals at Rabigh indicate a low to moderate wave energy, while corals in Bahamas and Australia showed slow but compact growth as a result of high wave energy (Adey, 1978).

Also, sea level change plays a key role in the different morphologies of coral reefs around the world. In the Rabigh area, modern reefs contain a cap of mobile

132

conglomerate which could have formed during a higher sea level in the mid

Holocene and become exposed later by emergence when the sea level fell.

Differing increases in sea level can affect the growth potential of reefs in various parts of the world. In the Caribbean and Indo Pacific reefs, for example, studies showed some growth differences while the growth potential was probably the same in both areas. This difference is probably due to sea level rise in the Holocene

(Adey, 1978).

In the Rabigh area, the lower reef may have formed during stage MIS 5e or stage 7. The growth of delicate and thin plate-like corals in this reef (Fig. 7.4), indicate a low wave energy and low sedimentation environment.

Fig. 7.4 Corals from the species (Fungia and Favites) in the lower reef showed thin and plate-like skeletal form which indicates low wave energy and slow sedimentation during their time of formation.

Based on U series dating, the age of the upper reef is more likely to be 122 ka

(Stage 5a). This reflects the higher sea level at that stage. This reef shows a well developed branching coral reef system (Fig. 7.5), which contrasts with the lower reef. The upper reef particularly at location 3 (Fig. 7.5) shows an upward growth of

133 large skeletal corals. These large corals generally remain in place after death and are not eroded. The reef framework is only partly filled with fine-grained sediments.

Fig. 7.5a-b the upper reef in the Rabigh area shows a well development branching reef system with an upward growth. c-d back reef area and the back reef rubble.

In order to construct a better model for the Rabigh coral reef we would need to obtain cores from these coral reefs; this is recommended for further research.

However, from the dating, area description and other results of this study we can predict a model (Fig. 7.6), which can be compared to other models from the

Caribbean (Bahamas and Barbados) and Australia.

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Fig. 7.6 Model for the development of carbonate reefs in Rabigh area showing the different reef zones and characteristic features, including reef crest, low energy reef front, prograding seawards, rubble moving into the lagoon, a muddy back reef lagoon, and an arid landscape with low clastic sediment yields. 135

In the Rabigh coral reef model (Fig 7.6), the lower, upper and back reef area is a part of the platform. The outer part of the platform would have had more wave action (observing the modern wave action) whereas the inner part of the platform can just be growing vertically. The lower reef probably had an eroded top and extended seaward forming a shallow platform on which the upper reef grew. The upper reef grew on top of the lower reef, and extended farther seawards than the current eroded coastline. The height of the upper reef above the lower is about 2-3 m. The shallow lower terrace platform would have further reduced wave energy during the growth of the reef in MIS 5e. In the presence of a wide platform, wave energy will decrease even further, into the area where the reef system is growing.

Most present models are focused on high energy waves systems and normal reef growth systems. For example, along the reef front there is a protected coral community, mostly Porites species with an appearance of Acropora hemprichi,

Pocillopora and Faviidae (Head, 1987). The branching Acropora is the most frequent coral observed in the Great Barrier Reef (Wallace, 1975), and in the north of that reef the sediments along the reef front are made from coarse coral detritus, especially Acropora fragments (Jell and Flood, 1978). However, in Rabigh area, the reef front must have been farther offshore and the upper and lower sequences represents rapid coral growth on the back reef platform which shows large branching corals, encrusting corals and coralline materials (Fig. 7.5). The significance of this model is that it is developed from a relatively low energy system, showing coral reef growth that is typical in such a system.

The open framework of the reef and the extensive vertical growth of the corals indicate low incident wave energy. Also, the low energy system is suggested by the sparse presence of fragmented detritus in a relatively open framework, and the 136

scarce occurrence of encrusting coralline algae and massive corals. However, during storms there was still enough wave energy to move coral detritus from the reef crest landwards into the muddy back reef lagoon. Also, these storms allow the extension of the rubble crest and invented corals into the back-reef areas, as waves and currents go over the reef crest.

The lagoon continues to be carbonate dominated because of the dry coastal region, thus providing a limited supply of detrital clastic sediment. There are some clays present, but it is not dominantly a clastic back reef area. This is different to the

Great Barrier Reef, which has higher mountains behind the reef, with rivers bringing a large volume of mud and sand into the back-reef area (Hopley, 1982). In contrast, in the Rabigh area the climate is extremely dry with an absence of rivers coming into the area, and little rainfall, such that there is not much sand movement into the lagoon. Thus the area remained a carbonate-dominated system.

In the Rabigh area, corals grow vertically through the system, showing that it is an open framework and is not all cemented. Due to the drop in sea level since MIS

5e the exposed reef has been in a very dry environment with little sedimentation or meteoric diagenetic activity.

The lower coral reef succession would have been filled with rubble and become well cemented when it formed the shallow shelf on which the upper coral reef grew. The lower coral reef has been inundated, with some coastal erosion of the coral reef, and debris filling any holes that occurred. Lots of warm carbonate-rich water cemented the entire lower reef probably during MIS 5e, when the lower reef was submerged again.

Comparing this coral reef model with the modern reefs in the Rabigh-Jeddah areas, they both show open reef framework structure and are capped with a thin layer 137 of coralline algae (Fig 7.7). There is material being reworked landwards across the reef top forming the beach rock systems. Such features show that the model corresponds to the present reef growth in the Rabigh-Jeddah area, such that the modern reef has a similar reef structure and system to the MIS 5e reef. The contribution of this study is that it has produced a new coral reef model relevant to a low energy system in a dry and hot environment.

Fig. 7.7 Modern coral reef in Jeddah area showing an open reef structure and algae covering the branching hard coral (Rasul & Qutub, 2009).

138

CONCLUSION

In the Rabigh area, the upper and lower coral reefs, two beach rock and a back reef area were studied and dated in this thesis.

In the lower reef, corals were observed in almost all of the samples (average

21.3%), and silicate minerals were rare. The lower reef was cemented and featured a higher percentage of clastic sediment deposits and decreased coral coverage to the north and south near the sharms. The shallow water environment corals in this reef indicated that the reef was part of the outer reef flat of the reef system. The XRD results showed that the lower reef contained a high level of aragonite, calcite and high-Mg calcite, although aragonite was only found in the shells.

In the upper reef, coral appears in all of the samples with a higher proportion

(average 30.4%) compared to the lower reef. Silicate minerals are less common in the upper than in the lower reef, with an average proportion of 2.8% for quartz and

1.9% for plagioclase. The upper reef in the Rabigh area was characterised by the presences of poorly cemented, coralline algae. As in the lower reef the clastic sediment is observed to be greater in the ancient valley areas, for example Sharm Al-

Kharrar to the north, and Sharm Rabigh to the south. This created a locally restricted variety and coverage of coral, consistent with the lower reef. The outer part of the upper reef is part of the reef crest or the algal ridge in the reef system, but modern erosion has occurred at the reef front.

The framework of the coral in the upper reef indicates the environment during the formation of this reef. For example the plates of Porites coral were not filled by cementation, and this means that the reef was not inundated by sea water since MIS

5e. Also the coral and coralline algae grew to reach 2 m high in the upper reef

139 indicating a low energy environment during the formation of this reef. This is different to other reefs around the world, subject to the effects of open-ocean circulation and more vigorous wave action. The XRD results showed that the upper reef also revealed significantly variable percentages of aragonite, high-Mg calcite and calcite, with a small increase in calcite and high-Mg calcite comparative to the lower reef. The back-reef features associated with the upper reef show much less coral compared to the upper and lower reefs, with fewer bivalves (maximum of

4.5%) than in the reef crest. Echinoderms are common in the back-reef area, although with a low proportion averaging 2.4%. The XRD results showed that in the back-reef, calcite was the dominant mineral, with high-Mg calcite in the back-reef having variable percentages. In the back-reef succession, there was an increase in high-Mg calcite, with an average of 21.3%. High-Mg-calcite was derived from organism skeletons, such as echinoderms, which were common in the back-reef succession and was also linked to the direct precipitation of marine cements. The blocky calcite spar could be an indicator of a meteoric phreatic environment.

The lower flat outcrops in all the back-reef areas were mud-dominated and contained calcite shells and gastropods with only a few corals, some of which are upside-down which indicates it is rubble that eroded out of the front reef. Calcareous mud is dominant in the back-reef muds indicating a low energy lagoonal environment behind the reef crest. This environment was an extensive shallow marine environment, bordered by a hot arid mainland during the time of transgression.

Such an interpretation for the upper and lower reef may connect with transgression phases of the sea and represent slightly higher sea levels. The upper reef elevations are consistent with those of New Guinea, Indonesia and the Bahamas. 140

Algae were the dominant element in the beach rock. The beach rock results showed a variable percentage of aragonite, between 17.3 – 53.6%, and common high-Mg calcite, between 19.4 – 48.1 %. Calcite was observed in low percentages. In the upper beach rock calcite was still in low percentages (maximum 9.4%), which was comparable to the lower beach rock, but with increased aragonite (36-61.8%) and decreased high-Mg calcite (14-29%). Petrography and XRD results show the dominance of corals and other aragonite secreting organisms in contributing to the lower beach rock that was later subjected to marine phreatic diagenesis.

The dominant diagenetic process in the Rabigh reefs was cementation, and the distribution of cement in the Rabigh reefs varied so that calcite filled the intergranular voids in most samples. Within the thin sections there were three cement types. Fibrous calcite occurred in many upper and lower reef samples, and blocky calcite spar was the most common cement type in the back-reef. Micritic cements were associated with algae, and were the third most common cement, particular in the back-reef. The corals were affected by fresh water diagenesis but they were not reduced in number because of neomorphism, and the majority of samples showed the effects of meteoric diagenesis.

The AAR shows that samples had low amino acid concentrations because of oxidation and significant racemisation in the samples. The amino acid racemisation result in the Rabigh area was due to the high mean annual temperature (MAT) because this accelerates the racemisation process for shallow shells at an exponential rate. Five samples were sent for radiocarbon dating, and the results of the 14C analysis of the bivalve shells in the Rabigh area showed numerous ages but most of them were beyond the 14C age limit of 40-50 ka. One Holocene fossil was observed 141 to have grown embedded in beach rock adjacent to the lower reef. The results from radiocarbon dating, however, suggested some level of contamination of the samples with modern 14C and did not reflect sea level at this stage.

There were problems with poor resolution of data, so that accurate ages for the reefs were hard to define. The 14C dating results from the upper reef suggested an age between 40-53 ka at 3.2 m, but since this age is nearly at the limits of 14C, this age was not considered to be a sound result. Based on U/Th dating the age of the upper reef is more likely to be 123 ka (MIS 5e), whereas the lower reef could be earliest phase of 5e or stage 7 or earlier. There has been no evidence of major tectonics in Rabigh area during the last 125 ka and this is consistent with a number of other studies around the Red Sea such as Hoang et al. (1996) and Reyss et al. (1993).

This research has been able to develop a new model for coral reef development in low-energy systems and hot, arid environments. In this model the

Rabigh reef sequences is part of rapid coral growth on a back-reef platform in the quite back-water area behind the front reef. The front reef is characterised by an open framework of large branching corals on the reef, rather than the massive and encrusting corals and algae typical of higher energy reef systems. This model is consistent with both the samples in this study, and the modern coral reef system in the Rabigh-Jeddah area.

The study recommends the need for core samples by drilling to avoid the effect of contamination and heating in the different dating techniques. Also, the need for better dating, particularly the need to conduct more research using U/Th dating.

This is because of its greater reliability to provide age controls for the older coral reef sequences.

142

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163

Appendix 1: Thin Section Results

upper

Terrace sample Classification ALGA Echinoderm Microsparit Clasti Un- Gastropod Briyozo Feldspa Tourmalin Hornblen Plagioclas Loc no Height Coral Molluscs Foram Porosity Sparite Micrite Quartz Byrite no * E s e c Known s a r e d e

3 3.2.1 20 P.W.B 13.0 10.0 29.6 3.3 0 26.0 2.6 12.3 2.0 0 0 0 0.9 0.3 0 0 0 0 0

3.2.2 25 U.B 6.3 7.1 31.0 5.1 0 11.5 14.3 19.9 0 0 0 1.9 0 0 0 0 0 0 2.3

3.2.3 145 P.W.B 35.3 0 5.6 0 0 19.0 0.6 9.0 22.3 0 0 6.0 0 0 0 0 0 0.3 1.9

3.2.3 145 P.W.B 27.8 1.0 9.7 0.3 0 20.5 0.3 13.5 19.1 0 0 3.8 0 0 0 0 0 0 3.4

3.2.4 220 P.W.B 27.6 4.6 2.3 0.6 0 21.0 0.3 17.6 22.3 0 0 0 1.6 0 0 0 0 0.9 0.9

Average 22.0 4.5 15.6 1.9 0 19.6 3.6 14.5 13.1 0 0 2.3 0.5 0.1 0 0 0 0.2 1.7

4 4.2.2 185 P.W.B 11.0 10.0 15.6 14.6 0 7.6 0.3 24.6 7.3 2.6 0 0 2.0 0.7 0 0 0.3 0.7 2.6

4.2.3 160 P.W.B 40.9 0 2.3 0.6 0 23.5 0 21.5 2.0 0 0 0 0 8.5 0 0 0 0 0

4.2.4 90 P.W.B 40.0 0 0 0 0 37.0 0 23.0 0 0 0 0 0 0 0 0 0 0 0

4.2.5 55 P.W.B 1.0 0 3.3 61.6 0 15.3 0.6 17.3 0 0 0 0 0 0 0.7 0 0 0 0

4.2.6 40 P.W.B 1.3 1.0 18.0 0.6 0 38.6 2.6 37.3 0 0 0 0 0 0 0 0 0 0 0.3

4.2.7 140 P.W.B 25.0 2.6 7.3 0.3 0 22.6 0 17.0 24.0 0 0 0 0 0 0 0 0 0 1.0

4.2.8 160 P.W.B 33.3 1.6 0 0.3 0 16.3 0 46.3 0 0 0 1.0 0 0.6 0 0 0 0 0.6

Average 21.8 2.2 6.6 11.1 0 23.0 0.5 26.7 4.8 0.4 0 0.1 0.3 1.4 0.1 0 0 0.1 0.6

1 1.2.1 150 P.W.B 67.8 0 0 0 0 30.7 0 1.0 0 0 0 0 0 0 0 0 0 0 0

1.2.2 220 U.B 55.2 0 0.3 0 0 32.1 11.2 0.9 0 0 0 0 0 0 0 0 0 0 0

1.2.3 300 * 84.0 0 0 0 0 15.6 0 0 0 0.3 0 0 0 0 0 0 0 0 0

1.2.4 n U.B 8.4 7.4 16.5 1.0 0.3 16.8 9.7 3.7 0 22.9 1.5 0 2.1 0 3.7 1.2 0 0.6 3.9

1.2.5 n * * * * * * * * * * * * * * * * * * * *

1.2.8 n * 69.1 0 0 0 0 29.7 0 0 0 1.0 0 0 0 0 0 0 0 0 0

Average 56.9 1.5 3.4 0.2 0.3 25.0 4.2 1.1 0 4.8 0.3 0.0 0.4 0 0.7 0.2 0 0.1 0.8

 P.W.B (Poorly Washed Biosparite), U.B (Unsorted Biosparite) and P.B (Packed Biomicrite).

164

Lower

Terrace

Loc no sample no Height Classification* Coral Molluscs ALGAE Echinoderms Foram Porosity Sparite Micrite Microsparite Quartz Clastic Un Known Gastropods Briyozoa Feldspar Tourmaline Byrite Hornblend Plagioclase

3 3.1.1 110 P.W.B 29.2 4.2 33.0 4.2 0 10.7 1.1 5.3 8.8 0 0 0 0 0 0 0 0 1.6 1.6

3.1.2 95 U.B 14.0 13.3 26.0 2.6 0 19.3 4.3 9.3 9.6 0.3 0 0 0 0 0 0 0 0 1.0

3.1.4 50 P.W.B 75.6 0 2.0 0 0 10.3 0 10.6 0 0.3 0 0 0 0 0 0 0 0.3 0.7

3.1.5 100 P.B 29.3 3.3 9.3 7.2 0 10.0 4.3 32.0 0 1.6 0 0 0 0 0 0 0 0.9 1.9

3.1.6 40 P.W.B 38.0 4.8 30.3 1.9 0 6.3 0 13.9 3.4 0.0 0 0 0.9 0 0 0 0 0 0.4

Average 37.2 5.1 20.1 3.2 0 11.3 1.9 14.2 4.4 0.4 0 0 0.2 0 0 0 0 0.6 1.1

4 4.1.2 40 P.W.B 2.1 18.3 23.6 3.2 0.3 16.3 2.9 30.6 0 0 0 0 2.7 0 0 0 0 0 0.0

4.1.3 80 P.W.B 6.0 5.0 23.0 7.3 0 22.3 4.0 20.6 6.6 0.3 0 2.0 0 2.0 0 0 0 0 0.6

Average 60 4.1 11.7 23.3 5.3 0.2 19.3 3.5 25.6 3.3 0.2 0 1.0 1.4 1.0 0 0 0 0.3

1 1.1.1 60 U.B 5.4 0 9.4 0.5 0 17.3 14.3 8.9 0 3.4 1.9 0 0 38.1 0.4 0 0 0 0.4

1.1.2 80 U.B 47.3 0 0.7 0 0 21.2 3.4 27.2 0 0 0 0 0 0 0 0 0 0 0

1.1.3 65 U.B 67.4 0 0 0 0 23.5 8.9 0 0 0 0 0 0 0 0 0 0 0 0

1.1.4 60 U.B 4.5 23.8 12.8 5.3 2.4 3.7 33.1 0.4 0 0.9 6.1 0 3.7 1.1 0 0 0 1.1 1.1

1.1.5 90 U.B 0.3 8.9 24.3 13.1 0.3 12.1 18.4 8.1 0 4.5 3.0 0 3.8 0.3 0 0 0 0 2.8

1.1.6 50 U.B 0.7 18.6 28.3 6.8 1.0 16.2 21.8 0.3 0 1.0 0 0 5.1 0 0 0 0 0 0

1.1.7 105 * 73.2 0 0 0 0 26.7 0 0 0 0 0 0 0 0 0 0 0 0 0

1.1.9 55 P.W.B 0 30.2 26.1 3.3 0 10.4 10.8 4.4 0 6.3 0 0 3.3 0 0 0.8 0 0.8 3.3

1.1.10 70 U.B 63.5 0 0 0 0 19.3 17.1 0 0 0 0 0 0 0 0 0 0 0 0

1.1.12 120 P.W.B 28.4 6.1 33.2 0.3 0 16.2 1.2 6.1 0 4.4 0 0 0 0 1.2 0.6 0 0 2.1

Average 75.5 29.1 8.8 13.5 2.9 0.4 16.7 12.9 5.5 0 2.1 1.1 0 1.6 4.0 0.2 0.1 0 0.2 1.0

7 7.1.1 n P.B 24.6 3.3 10.6 1.0 1.3 9.6 1.3 33.3 1.3 6.6 0 0.3 1.3 0 1.0 1.0 0 1.0 2.0

7.1.3 n P.B 44.6 3.6 6.3 0.6 4.0 9.3 1.6 14.6 0 9.6 0 0 0.6 0 0.6 0.3 0 0.6 3.4

Average 34.6 3.5 8.5 0.8 2.7 9.5 1.5 24.0 0.7 8.1 0 0.2 1.0 0 0.8 0.7 0 0.8 2.7

 P.W.B (Poorly Washed Biosparite), U.B (Unsorted Biosparite) and P.B (Packed Biomicrite).

165

Back Reef

6 6.1.1 110 P.B 1.3 2.3 14.0 2.6 1.0 33.6 6.6 28.0 8.6 0 0 0 0 0 0 0 0 0 1.6

6.1.2 80 P.B 0.0 3.0 25.2 9.0 2.2 22.6 0.3 36.6 0 0.3 0 0 0.3 0 0 0 0 0 0.3

6.1.3 35 P.B 0.0 2.3 22.6 3.7 0 30.4 2.0 30.8 6.5 0 0 0.6 0 0 0 0 0 0 0.6

6.2.1 40 P.W.B 0.0 2.6 1.3 0.3 0 30.0 41.3 21.0 0.3 1.6 0 0 0 0 0 0 0 0 1.3

6.2t 50 P.W.B 8.3 0.3 27.0 0.3 0 37.6 0 14.2 0 0 0 10.8 0 0 0 0 0 0 1.1

Average 1.9 2.1 18.0 3.2 0.6 30.8 10.0 26.1 3.1 0.4 0 2.3 0.1 0 0 0 0 0 1.0

2 2.1.1 0 P.W.B 0.0 4.5 0.8 6.2 0 9.1 31.2 45.4 0 2.0 0 0 0 0 0 0 0 0 0.4

2.1.3 50 P.W.B 2.8 0.8 19.2 3.6 0 12.8 23.2 37.2 0 0.4 0 0 0 0 0 0 0 0 0

2.1.5 65 U.B 54.0 0 0.0 0 0 31.2 14.8 0 0 0 0 0 0 0 0 0 0 0 0

2.1.6 110 P.W.B 0.0 0.7 39.2 2.2 0 5.1 22.5 26.2 0 0.3 0.3 2.9 0 0 0 0 0 0 0.3

2.1.7 150 P.B 37.0 0 6.3 0 0 36.6 0 19.9 0 0 0 0 0 0 0 0 0 0 0

2.2.1 280 P.W.B 6.3 1.0 9.6 1.6 0 30.3 15.6 24.0 10.6 0 0 0 0 0 0 0 0 0 0.6

2.2.2 220 P.W.B 0.0 0.3 24.2 2.6 0.3 15.7 33.2 22.4 0 0.9 0 0 0 0 0 0 0 0 0

2.2.3 170 P.W.B 4.0 0 1.8 0.3 0 60.0 0 29.3 4.3 0 0 0 0 0 0 0 0 0 0

2.2.5 320 P.W.B 13.6 0.4 22.0 3.9 0.4 20.4 22.8 16.4 0 0 0 0 0 0 0 0 0 0 0

2N.1.3 100 P.W.B 2.1 0 3.2 3.6 0.3 46.0 3.9 30.0 5.4 0 0 3.2 0 0 0 0 0 0 1.9

2N.1.4 n U.B 0.0 0 0.0 0 0 37.7 51.5 10.3 0 0 0 0 0 0 0 0 0 0 0.3

Average 10.9 0.7 11.5 2.2 0.1 27.7 19.9 23.7 1.8 0.3 0 0.6 0 0 0 0 0 0 0.3

5 5.1.1 n P.B 1.3 0 18.0 1.0 0 39.3 0 39.6 0.6 0 0 0 0 0 0 0 0 0 0

5.2.1 75 P.W.B 1.6 1.0 18.6 4.0 0.3 27.6 23.0 20.6 0.3 0.6 0 1.3 0 0 0 0.6 0 0 0.3

5.2.2 70 P.W.B 3.4 1.3 14.0 0.6 0 32.6 5.1 16.4 26.1 0 0 0 0 0 0 0 0 0 0

Average 2.1 0.8 16.9 1.9 0.1 33.2 9.4 25.5 9.0 0.2 0 0.4 0 0 0 0.2 0 0 0.1

 P.W.B (Poorly Washed Biosparite), U.B (Unsorted Biosparite) and P.B (Packed Biomicrite).

166

Beach Rock

Loc no sample no Classification* Coral Molluscs ALGAE Echinoderms Foram Porosity Sparite Micrite Microsparite Quartz Clastic Un Known Gastropods Briyozoa Feldspar Tourmaline Byrite Hornblend Plagioclase

Lower 1S.BR1.1 U.B 1.3 21.3 37.9 0.3 1.0 3.3 27.6 4.3 0 1.3 0 0.0 1.6 0 0 0 0 0 0

1 1S.BR1.2 P.W.B 2.3 17.0 48.9 0.6 0.3 7.4 4.0 11.2 0 1.3 0 3.7 2.0 0 0.3 0.3 0 0 0.6

1.BR1.3 U.B 3.1 18.7 38.6 3.4 0 1.5 26.6 3.9 0 1.9 0 0.0 1.2 0 0.3 0 0 0 0.6

1.BR1.4 U.B 43.6 3.3 34.3 0.3 0 0 10.0 6.0 0 1.6 0 0.0 0.6 0 0 0 0 0 0

Average 12.6 15.1 39.9 1.2 0.3 3.1 17.1 6.4 0 1.5 0 0.9 1.4 0 0.2 0.1 0 0 0.3

Lower 7BRD2 P.W.B 9.9 6.8 13.6 0.3 2.2 28.8 1.8 9.2 0.3 6.2 0 2.3 0.3 16.4 0.3 0.3 0 0.3 0.6

7 7BRD3 P.W.B 0.0 8.8 29.8 1.1 0 12.2 18.7 9.5 0 6.1 0 5.7 0.0 0.0 0.3 0 0 0.3 7.3

Average 5.0 7.8 21.7 0.7 1.1 20.5 10.3 9.4 0.2 6.2 0 4.0 0.2 8.2 0.3 0.2 0 0.3 4.0

Upper 1.BR2.2 P.W.B 11.9 19.3 39.0 1.7 0 5.6 11.7 3.5 0 1.4 0 4.2 0.9 0 0 0 0 0 0.7

1 1.BR2.2 P.W.B 5.3 18.2 39.0 2.1 0.3 5.7 18.9 7.1 0 0 0 0.0 0.0 0 0 0.3 0 0 2.8

1.BR2.3 U.B 2.3 19.6 40.3 0.6 0 2.6 20.3 8.3 0 1.3 0 2.3 2.0 0 0 0 0 0 0

7BRU1 P.W.B 1.7 21.1 40.1 1.0 1.0 17.3 3.4 8.8 0 0.6 0 1.7 2.0 0.3 0 0 0 0 0.6

Average 5.3 19.6 39.6 1.4 0.3 7.8 13.6 6.9 0 0.8 0 2.1 1.2 0.1 0 0.1 0 0 1.0

 P.W.B (Poorly Washed Biosparite), U.B (Unsorted Biosparite) and P.B (Packed Biomicrite).

167

Appendix 2: XRD Results.

Lower Terrace Location Sample No Height (cm) Aragonite Calcite High Mg Calcite Dolomite Gypsum Chlorite Kaolin Quartz Albite Orthoclase Ankerite Siderite Illite Muscovite Biotite Mixed Layer 3 3.1.1 110 19.3 16.3 34.3 0.5 1.4 0 0.4 0 2.3 6.8 4.6 0.5 3.8 3.0 5.9 0.5 3.1.2 95 42.1 5.8 21.9 0 9.3 0 0.4 4.4 2.1 4.8 2.6 0 0 5.5 0.7 0.4 3.1.3 40 73.9 2.6 5.8 0 0.8 0.4 0.4 1.0 0.7 2.3 0.4 0.4 0 5.0 5.9 0.4 3.1.4 50 82.7 1.2 2.3 0.1 2.6 0 1.1 0.9 0.8 3.0 0.5 0.6 0.4 1.0 2.4 0.4 3.1.5 100 5.4 49.7 14.7 0 2.2 2.2 0.5 1.6 3.1 6.9 1.2 0.1 4.3 3.9 3.7 0.5 3.1.6 40 5.4 33.1 8.5 0 10.1 2.0 0.5 1.8 4.6 9.6 3.3 0.4 13.6 0 3.6 3.4 Average 38.1 18.1 14.6 0.1 4.4 0.8 0.6 1.6 2.3 5.6 2.1 0.3 3.7 3.1 3.7 0.9 4 4.1.1 90 20.1 5.8 0 0 1.7 0 4.1 7.4 21.3 31.2 0.5 0 0 6.6 0 1.2 4.1.2 40 20.8 22.1 36.4 0.2 1.3 0.8 1.2 0 1.8 4.0 2.4 0.4 2.6 2.3 3.3 0.4 4.1.3 80 50.6 9.8 18.0 0.6 0.6 0.4 0.7 0 0.8 6.2 2.4 0.5 0 6.8 2.1 0.4 Average 30.5 12.6 18.1 0.3 1.2 0.4 2.0 2.5 8.0 13.8 1.8 0.3 0.9 5.2 1.8 0.7 1 1.1.1 60 20.9 16.1 32.9 0 5.1 0 1.2 5.1 5.3 3.6 2.4 0 1.5 3.7 2.1 0 1.1.2 80 77.7 3.3 5.8 0.2 0 0 0.4 0.4 1.1 3.3 2.6 0 0 3.2 1.6 0.4 1.1.3 65 72.9 3.6 7.0 0.1 0.1 0 1.7 1.5 2.2 3.1 2.7 0.2 0.3 2.1 2.0 0.4 1.1.4 60 34.1 13.6 28.1 0 1.8 0.5 1.1 0 2.0 6.8 1.7 0 0 10.3 0 0 1.1.5 90 24.8 37.7 16.1 0 2.7 1.4 1.1 0.9 6.6 0 3.6 0 2.5 0 1.6 0.7 1.1.6 50 38.2 17.4 21.9 0.7 2.4 0 1.2 0 2.5 3.2 4.3 0 0 5.9 2.2 0 1.1.7 105 82.9 0.7 0.5 0 1.2 0 0.4 1.8 1.0 4.4 0 1.3 2.0 0 3.1 0.4 1.1.8 100 24.4 35.5 15.5 0 6.8 0.5 1.2 0.6 4.6 0.2 3.5 0 3.0 0 3.3 0.5 1.1.9 55 21.9 14.2 19.5 0.6 4.8 4.3 3.2 3.7 9.6 2.6 6.1 0 0 6.5 2.1 0 1.1.10 70 12.2 10.6 33.4 0.2 10.9 0 2.6 0.9 4.1 6.3 3.7 0 0 8.5 6.7 0 1.1.11 90 0 0 0 0 0.0 0 0 0 0 0 0 0 0 0 0 0 1.1.12 120 32.4 9.1 19.4 1.0 10.4 0 2.2 3.2 6.6 4.0 7.0 0 0 3.2 0 0.8 1.1.13 120 89.7 0.8 0.5 0.5 1.4 1.1 0.4 0.4 0.8 0 0 0.3 0 2.7 0.9 0.4 1.1.14 120 86.6 1.8 2.1 0 3.4 0.8 0.4 0.3 0.7 0.1 0 0 0 1.8 1.3 0.7 Average 44.2 11.7 14.5 0.2 3.6 0.6 1.2 1.4 3.4 2.7 2.7 0.1 0.7 3.4 1.9 0.3 7 7.1.1 n * * * * * * * * * * * * * * * * 7.1.2 n * * * * * * * * * * * * * * * * 7.1.3 n * * * * * * * * * * * * * * * *

168

Upper Terrace Loc Sample No Height (cm) Aragonite Calcite High Mg Calcite Dolomite Gypsum Chlorite Kaolin Quartz Albite Orthoclase Ankerite Siderite Illite Muscovite Biotite Mixed Layer 3 3.2.1 20 68.1 18.0 3.4 0 1.0 0 0.7 0.7 0.4 2.1 0.1 0.1 1.7 0 2.3 1.3 3.2.2 25 4.7 12.9 62.8 0.9 1.3 1.3 0.4 1.4 0.4 6.2 0 1.9 0.8 2.3 2.3 0.4 3.2.3 145 37.5 10.6 13.3 0 19.8 0 0.5 0 0.6 4.0 6.8 0 0 4.8 1.5 0.4 3.2.4 220 25.9 21.0 24.1 1.3 1.5 1.0 0.8 0 2.3 3.1 7.6 0.1 2.0 4.1 4.7 0.4 Average 34.0 15.6 25.9 0.6 5.9 0.6 0.6 0.5 0.9 3.8 3.6 0.5 1.1 2.8 2.7 0.6 4 4.2.1 230 81.7 1.8 2.4 0.3 0.4 0.9 0.5 1.1 1.1 2.8 0.4 1.3 0 1.1 3.6 0.5 4.2.2 185 16.1 20.9 36.0 0.2 2.9 0 1.7 0.1 0.7 7.6 0.3 0.8 3.7 3.3 4.5 1.4 4.2.3 160 38.3 14.9 20.7 0 3.5 0.4 1.5 0 0 0 0.3 0 0 9.1 3.2 0.4 4.2.4 90 21.9 22.8 27.4 0 3.5 0.5 1.6 0 0 7.6 0.8 0.1 0 8.0 5.4 0.4 4.2.5 55 3.6 13.2 53.6 2.4 10.5 6.5 0.3 0 0.3 5.0 1.7 1.6 0 0 0.7 0.3 4.2.6 40 7.7 34.0 32.4 0.2 3.5 0.3 1.8 0 0.5 4.4 2.0 0 2.2 7.0 3.9 0 4.2.7 140 4.6 47.5 21.4 0 4.8 0.9 0.6 0.2 3.2 4.5 1.4 0.3 7.6 0.2 2.3 0.5 4.2.8 160 30.3 12.3 27.1 0.3 5.3 0 1.7 0 0 9.9 0.6 0.6 1.3 5.6 4.5 0.7 Average 25.5 20.9 27.6 0.4 4.3 1.2 1.2 0.2 0.7 5.2 0.9 0.6 1.9 4.3 3.5 0.5 1 1.2.1 150 69.3 7.6 7.4 0 1.5 0.6 0.9 1.1 3.5 3.7 0.1 0 0 3.6 0 0.4 1.2.2 220 71.4 8.2 5.1 0 6.2 0 1.0 0.9 1.4 2.8 0 0 0 2.6 0.3 0 1.2.3 300 75.3 9.7 1.3 0 0.3 0.7 1.6 2.6 2.1 2.1 0 0.2 0.2 1.8 1.4 0.4 1.2.4 n 5.0 47.2 7.9 0 2.7 12.4 1.1 3.2 5.6 1.8 0 0 4.1 2.1 6.8 0 1.2.5 n 81.8 3.7 0.5 0 4.0 0 1.9 1.3 1.1 3.2 0 0 0 0 1.8 0.4 1.2.6 n 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1.2.7 n 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1.2.8 n 76.6 4.8 0.4 0 2.7 1.7 2.3 2.0 4.1 2.5 0 0.3 0 0.1 2.1 0.4 Average 47.4 10.1 2.8 0 2.2 1.9 1.1 1.4 2.2 2.0 0 0.1 0.5 1.3 1.5 0.2

169

Back-reef Loc Sample No Height (cm) Aragonite Calcite High Mg Calcite Dolomite Gypsum Chlorite Kaolin Quartz Albite Orthoclase Ankerite Siderite Illite Muscovite Biotite Mixed Layer 6 6.1.1 110 0 93.1 4.1 0.1 0 0 0.3 0 0.4 0.6 0 0.3 0 1.2 0 0 6.1.2 80 1.5 81.2 9.7 0 1.3 0 0.8 0 0.8 1.0 0.1 0.6 0 1.3 1.0 0.4 6.1.3 35 1.6 77.3 13.2 0 0.9 0 0.4 0.2 2.3 0.6 0.1 0.3 2.4 0 0.3 0.4 6.1.4 110 0.0 99.3 0 0 0 0 0.2 0 0 0 0 0.2 0 0 0 0.2 6.2.1 40 1.3 82.1 9.4 0.1 0.8 0 0.4 0 1.1 0.6 0 0.2 1.4 1.1 0.9 0.4 6.2.2 50 1.4 76.7 10.8 0.1 0.6 0 0.7 0.3 2.0 1.4 0.3 0.4 2.2 1.5 1.3 0.4 Average 1.0 84.9 7.9 0.1 0.6 0 0.5 0.1 1.1 0.7 0.1 0.3 1.0 0.9 0.6 0.3 2 2.1.1 0 1.6 79.8 4.7 0.1 0.6 0 1.8 1.1 3.3 1.1 0.4 0.2 2.3 1.2 0.6 0.4 2.1.2 0 70.4 20.2 0.4 0 0 0 0.4 1.0 0.4 2.1 0 0.5 0.4 0.3 3.5 0.3 2.1.3 50 1.5 82.9 5.1 0.2 0.3 0.7 1.0 0.9 2.7 1.0 0.3 0.2 1.6 1.1 0 0.4 2.1.4 50 0 0 0 0 0 0 0 0 0 0 0 0.0 0 0 0 0 2.1.5 65 0 5.1 74.5 0 2.2 0 0.9 0 0.2 7.9 0 3.7 0.9 3.2 0.6 0.6 2.1.6 110 0 3.5 80.5 0 2.2 0 1.6 0 0 5.8 0.3 0 0 4.3 1.4 0.3 2.1.7 150 0 4.1 83.4 0 1.3 0 0.7 0 0 5.8 0 0 0 3.3 1.1 0.3 2.2.1 280 1.2 86.9 3.8 0.3 0 0.1 1.2 0.3 1.3 1.2 0.2 0.5 0.6 1.1 1.0 0.3 2.2.2 220 2.4 82.2 5.6 0 1.7 0 0.8 0.3 1.2 0 0.5 0.6 3.3 0 0.9 0.4 2.2.3 170 0.8 84.4 4.6 0 2.6 0 0.5 1.0 1.2 1.1 0 0.2 0.5 1.9 0.7 0.4 2.2.4 320 43.1 55.5 0 0.2 0 0 0.3 0 0 0 0 0.4 0 0 0.1 0.4 2.2.5 320 0 4.3 83.9 0.3 1.5 0 0.3 0 0 4.3 0.2 0 1.7 1.6 1.3 0.4 2N.1 50 39.5 59.0 0 0.3 0 0 0.3 0 0 0 0 0.4 0 0.3 0 0.3 2N.2 100 90.6 0.6 0.2 0.3 0.5 0.4 0.4 0.7 0.4 0.2 0 0.3 0 2.3 2.7 0.5 2N.3 100 0 2.8 80.9 0 2.4 0 0.6 0 0.3 5.0 0 3.2 0 3.0 1.4 0.4 Average 16.7 38.1 28.5 0.1 1.0 0.1 0.7 0.4 0.7 2.4 0.1 0.7 0.8 1.6 1.0 0.4 5 5.1.1 25 0.4 85.6 0 0 3.8 1.4 1.7 0 0.9 0.7 0 0.2 0.9 0.5 0.9 2.7 5.2.1 75 0 84.1 8.4 0.3 0.4 0 0.4 0.7 1.7 1.1 0.4 0.2 0.6 1.1 0.3 0.3 5.2.2 70 9.2 66.1 10.0 0 3.1 0 1.0 0.3 1.7 0.3 0.4 0.4 4.3 0 1.1 1.8 Average 3.2 78.6 6.1 0.1 2.4 0.5 1.0 0.3 1.4 0.7 0.3 0.3 1.9 0.5 0.8 1.6

170

Beach Rock Loc Sample No Height (cm) Aragonite Calcite High Mg Calcite Dolomite Gypsum Chlorite Kaolin Quartz Albite Orthoclase Ankerite Siderite Illite Muscovite Biotite Mixed Layer Lower 1.1BR.1 36.2 4.3 21.3 0 22.9 0 0.3 0 0 6.4 0 0 0 6.4 2.0 0 1 1.1BR.2 29.7 12.4 34.3 0.1 1.5 0 0.9 0.1 0.4 8.0 0.6 0.4 0.4 6.0 4.6 0.4 1.1BR.3 53.6 6.5 19.4 0 0.3 0 0.4 0 2.0 7.3 0.1 0.2 0 9.3 0.5 0.4 1.1BR.4 17.3 7.5 48.1 0 1.2 0 0.8 0.5 0.4 8.9 0.1 1.2 5.8 1.1 6.6 0.4 Average 34.2 7.7 30.8 0 6.5 0 0.6 0.2 0.7 7.7 0.2 0.5 1.6 5.7 3.4 0.3 Lower 7.BRD.1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 7 7.BRD.2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 7.BRD.3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Average 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Upper 1.2BR.1 38.9 9.4 29.0 0 0.4 0 0.4 0 0 8.6 0 0 0 9.4 4.0 0 1 1.2BR.2 61.8 5.4 15.9 0 0 0 0.4 0 0 6.3 0 0 0 8.2 1.8 0 1.BR2.2 36.0 8.5 19.7 0 4.1 0 3.5 0 0 11.5 0 0 0 16.5 0 0 1.2BR.3 42.3 5.0 14.0 0 3.9 0 3.4 0.8 3.7 7.3 0 0 0 11.8 7.8 0 Upper 7.BRU.1 44.7 7.1 19.7 0 2.1 0 1.9 0.2 0.9 8.4 0 0 0 11.5 3.4 0 7 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Average 3.2 78.6 6.1 0.1 2.4 0.5 1.0 0.3 1.4 0.7 0.3 0.3 1.9 0.5 0.8 1.6

171

Appendix 3: Pie charts show the XRD result in different locations.

Lower Terrace- Lower Terrace- Lower Terrace- Locaation 1 Location 3 Location 4

172

Lower Terrace (Average) Aragonite

1.9 Calcite 5.2 7.4 0.8 11.7 High Mg Calcite Dolomite 6.6 Gypsum

22.1 Chlorite

112.8 Kaolin

13.6 Quartz Albite 5.4 3.8 Orthoclase 1.8 9.3 Ankerite

0.6 Siderite Illite

Muscovite 47.2 Biotite

42.4

173

Upper Terrace- Upper Terrace- Upper Terrace- Location 1 Location 3 Location 4

174

Upper Terrace (Average) Aragonite

Calcite 1.2 1.4 3.5 High Mg 7.8 4.6 8.4 Calcite Dolomite 3.9 11.1 Gypsum 2.1 2.9 Chlorite 3.7 Kaolin 107.0 12.4 Quartz 1.0 Albite

Orthoclase

Ankerite

56.3 Siderite

Illite

Muscovite

46.7 Biotite

Mixed Layer

175

Back Reef-Location 2 Back Reef-Location 5 Back Reef-Location 6

176

0.5 Back Reef (Average) Aragonite 0.8 1.3 3.0 Calcite 2.2 3.8 2.3 3.7 2.4 3.3 4.1 0.6 High Mg 20.9 0.3 Calcite Dolomite

Gypsum

Chlorite 42.5 Kaolin

Quartz

Albite

Orthoclase

Ankerite

Siderite

Illite

201.6 Muscovite

Biotite

Mixed Layer

177

178