Late Pleistocene raised coral reefs in the eastern red sea – Rabigh, Saudi Arabia

190 Pages·2012·10.59 MB·English

by  Christine Brown

University of Wollongong
Research Online
University of Wollongong Thesis Collection University of Wollongong Thesis Collections
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

By

Ammar Manaa

School of Earth and Environmental Sciences

2011
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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.
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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.

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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
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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
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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

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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
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