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1 This file is part of the following reference: Costen, Andrew Richard (1996) The sedimentary, hydrodynamic and turbidity regimes at inner shelf coral reefs, Halifax Bay, Central Great Barrier Reef, Australia. Honours thesis, James Cook University. Access to this file is available from: The author has certified to JCU that they have made a reasonable effort to gain permission and acknowledge the owner of any third party copyright material included in this document. If you believe that this is not the case, please contact ResearchOnline@jcu.edu.au and quote

2 THE SEDIMENTARY, HYDRODYNAMIC AND TURBIDITY REGIMES AT INNER-SHELF CORAL REEFS, HALIFAX BAY, CENTRAL GREAT BARRIER REEF, AUSTRALIA. Thesis submitted by ANDREW RICHARD COSTEN BSc (JCU) June 1996 in partialfulfilment of the requirements for the degree of Bachelor of Science with Honours in Geology in the Department of Earth Science James Cook University of North Queensland

3 STATEMENT OF ACCESS I, the undersigned, the author of this thesis, understand that James Cook University of North Queensland will make it available for use within the University Library and, by microftlm or other means, allow access to users in other approved libraries. All users consulting this thesis will have to sign the following statement: Tn consulting this thesis I agree not to copy or closely paraphrase it in whole or in part without the written consent of the author; and to make proper public written acknowledgement for any assistance which T have obtained from it. Beyond this, I do not wish to place any restriction on access to this thesis. ANDREW COSTEN

4 STATEMENT ON SOURCES DECLARATION I declare that this thesis is my own work and has not been submitted in any fonn for another degree or diploma at any university or other institution of tertiary education. Information derived from the published or unpublished work of others has been acknowledged in the text and a list of references is given. ANDREW COSTEN

5 ACKNOWLEDGEMENTS I would firstly like to thank my supervisors Ken Woolfe and Piers Larcombe for their patient reading and critical comments on all drafts. Thanks goes to Richard Purdon, Stu Watson Kevin Hooper, Paul Giveny and the crew of the James Kirby for invaluable assistance with the field work in sometimes difficult conditions. Thanks goes to Chris cuff who helped me with all things chemical, Peter Ridd for his assistance with the machines that went ping, Sonya and Chris for help with "Mal" and Charlotte Morgan for improving my artistic ability. The CRC Reef Research Centre is gratefully acknowledged for their financial assistance. I would like to thank all of my friends during this year of intellectual torment for the good times and the trips to the club which kept us all sane. I would especially like to thank Aaron Gorrie (Gordy) who also endured honours and my company for nearly five years while at JCU, thanks mate!. Last but by no means least my deepest thanks go to my parents Anne and Richard and my sisters Tracey and Cris who have always managed to be there for me during my university career. What I have achieved would not have been possible without them, thanks guys.

6 ABSTRACT Taxonomic, seismic, vibrocore stratigraphy, surficial sedimentology, turbidity and hydrodynamic data were collected from Paluma Shoals and Phillips Reef. Paluma Shoals are a series of five near-shore patch reefs located within the inner-shelf terrestrial sediment wedge of southern Halifax Bay. Phillips Reef is an isolated patch reef located approximately 15!an northeast of Paluma Shoals. These data sets were collected to compare and contrast the sedimentary, hydrodynamic and turbidity regimes at both Paluma Shoals and Phillips Reef. The taxonomic survey (Watson, 1996) ofpaluma Shoals indicated that total coral cover on the leeward reef flat (53.4±3%) was almost twice that of the windward reef flat (27.9±3.3%). The presence of juveniles was also detected at both the leeward and windward reef flats. The presence of juveniles «Scm) suggests that coral recruitment is occurring. The taxonomic survey suggests that the corals at Paluma Shoals are a healthy diverse population. From 79!an of high resolution seismic images, eight seismic facies were identified within the study area. These facies are consistent with those identified by previous investigations. Seven vibrocores were collected to ground truth the seismic profiles. Four postglacial facies were identified on the basis of grain size, stratigraphic relationship and mineralogy. A total of 135 surficial sediment samples were collected from the study area. Based upon field and laboratory observations and high-resolution laser diffraction grain size analysis, the study area has been divided into, two marine inner-shelf and four coastal facies assemblages. Entropy analysis of grain size distributions from 58 inner-shelf and coastal sediment samples resulted in statistical clusters which were visually discrete. Seven entropy groups were defmed and high resolution grain size maps compiled. High resolution grain size mapping of the inner-shelf of Halifax Bay was successful in producing a map which mirrored the distribution of the surficial sediment facies assemblage. A total of 1340 hours of continuous high resolution time-series hydrodynamic and turbidity data were recorded at Paluma Shoals (671 hours) and Phillips Reef (669 hours) between Julian days 248 and 276 (1995). Maximum turbidity values were an order of magnitude greater at Paluma Shoals (175 NTU) than Phillips Reef (15 NTU) and generally were higher. The hydrodynamic and turbidity data suggest that Paluma Shoals and Phillips Reef are influenced by the same regional hydrodynamic processes. The surficial sediment seaward of Paluma Shoals are predominantly muddy sand, sandy mud and gravelly muddy sand and on the reef top, muddy sand and sandy mud. Therefore, there is a large source of fine grained sediment available for resuspension. The surficial sediments surrounding Phillips Reef are mostly gravelly muddy sand. Therefore, there is less fine grained sediment available for mobilisation. The variations in near bed turbidity values at Paluma Shoals and Phillips Reef appear to be a function of local surficial sediment distribution, wind direction and hydrodynamics. At Paluma Shoals the complex interaction between these processes results in high turbidity values but limited sediment settling. At Phillips Reef the limited sediment resuspension and transport (low NTU values) may be attributed to the reefs depth and coarse grained nature of the surface sediments. Three main implications arose from the collection and collation of these data sets, these are: 1) The corals at Paluma Shoals exist in water conditions widely inferred within the literature as being detrimental to coral growth and distribution; 2) "turbid water reefs" such as Paluma Shoals are potentially common and are healthy diverse populations; 3) during coral reef initiation (c.a. 6.8 ky B.P.) sediment dynamic, hydrodynamic and therefore turbidity regimes may have been similar to those of today. Therefore, "turbid water reefs" may form modem analogues to coral reefs that underwent initiation 8.5-5ky B.P.

7 Contents Chapter 1: Introductiou and aims Introduction Aims Chapter 2: Regional setting The Great Barrier Reef Location of study site Bathymetry Climate Sediment sources Sediment partitioning Oceanography Chapter 3: Materials and methods II 3.1. Seismic survey I I 3.2. Vibrocore recovery and analysis Sediment sampling II 3.4. Grain size analysis CaC03 determination Optical mineralogy and textural examination of surface and vibrocore sediments XRD analysis Water turbidity Hydrodynamic data Meteorological data Coral Taxonomy Chapter 4: Reef morphology and coral taxonomy of Paluma Shoals and Phillips reef Introduction Reef morphology I. Paluma Shoals Reef morphology 2. Phillips Reef Coral taxonomy Chapter 5: Seismic and vibrocore stratigraphy Seismic stratigraphy

8 5.2. Description and interpretation of seismic facies Vibrocores Vibrocore facies description and interpretation Vibrocore descriptions Chapter 6: Surficial sedimentology Introduction Coastal facies Marine inner-shelf facies Coral reef sediments - Paluma Shoals Coral reef clay mineralogy Entropy groups Chapter 7: Turbidity and hydrodynamics Introduction Hydrodynamic processes Near-bed turbidity - Paluma Shoals and Phillips Reef Summary Sediment availability and transport Chapter 8: Discussion and Conclusions Introduction Implication Implication Implication Conclusions References Appendicies

9 List of Figures 2.1. Location map Bathymetric map and location ofpaluma Shoals and Phillips Reef Variation in sea temperature at Magnetic and Orpheous islands Typical tidal curve for a spring tide from the GBR shelf Positions of seismic lines, stations, vibrocores, current meters and... nephelometers Positions of surficial sediment samples KG954-GI to KG954-G Udden-Wentworth grin size classification chart Calibration curve between raw nephelometer output and SSC as determined by filtration of water samples Favidae coral colony Transect locations and schematic cross section - Paluma Shoals Stands of Goniastrea sp. emergent at low tide - Paluma Shoals Large Acropora colony - Paluma Shoals Figures 4.4. Large Favidae colony - Paluma Shoals Location of seismic stations, track lines and the distribution of seismic facies ChI, Ch2, Ch3 and PI Schematic cross section b. Structure contour map of reflector A c. Isopach map of seismic units TI and T Seismic profile Seismic profile Seismic profile... " Seismic profile Seismic profile Seismic profile Summary vibrocores from southern Halifax Bay Vibrocore KG954-VCI Data summary - VCI Vibrocore KG954-VC Data summary - VC Vibrocore KG954-VC3A

10 List of Figures Data summary - VC3A Vibrocore KG954-VC Data summary - VC Vibrocore KG954-VC Data summary _ VC Vibrocore KG954-VC Data summary - VC Vibrocore KG954-VC Data summary - VC Entropy grouped facies in vibrocores VCI-VC Aerial photograph and sample locations - Paluma Shoals Pleistocene gravel deposits Pleistocene gravels underlying mangrove deposits Relict gravel deposits Cross-section through Quaternary coastal Plain Grain size distribution - intertidal sandflat sand Grain size distribution - intertidal sand Grain size distribution - beach sand Coarse grained chennier sands overlying ancient mangrove mud Rhizophora sp. mangrove dominated tidal channel Grain size distribution - mangroved fringed tidal channel Grain size distribution - organic mangrove mud Surficial sediment distribution of the inner-shelf of southern Halifax Bay Carbonate distribution of the inner-shelf terrestrial sediment wedge Grain size distribution - muddy sand Distribution of the surficial sediment facies from the Townsville region Grain size distribution - gravelly muddy sand Grain size distribution - sandy mud Sample location and sediment types from two of the Paluma Shoals reefs Grain size distribution - sandy mud Grain size distribution - gravelly sandy mud

11 List of Figures Bay Grain size distribution - muddy sand - Paluma Shoals Grain size distribution - gravelly sand Entropy group of 135 inner-shelf and coastal samples from southern Halifax ~ Entropy group distributions Hydrodynamic, turbidity and wind data - Paluma Shoals hours 108 Hydrodynamic, turbidity and wind data - Paluma Shoals hours I~ 7.3. Hydrodynamic, turbidity and wind data - Paluma Shoals hours Hydrodynamic, turbidity and wind data - Paluma Shoals hours III 7.5. Hydrodynamic, turbidity and wind data - Phillips Reef hours.. I Hydrodynamic, turbidity and wind data - Phillips Reef hours Hydrodynamic, turbidity and wind data - Phillips Reef hours Hydrodynamic, turbidity and wind data - Phillips Reef hours Surficial sediment distribution of the inner-shelf of southern Halifax Bay and tidal current directions

12 List of Tables 3.1. Current meter and nephleometer deployment Percentage of coral cover at Paluma Shoals Percentage coral cover bt family at Paluma Shoals Abundance of juvenile corals encountered along 100m oftransect Characteristics of seismic facies from southern Halifax Bay Gradients of Reflector A reported by previous studies Vibrocore position, water depth and bed elevation data from leg 3 cruise KG Carbonate content and sediment type from Paluma Shoals XRD-peak area ratios for sediments collected from Paluma Shoals Summary of the main causes of turbidity, and difference in turbidity between Paluma Shoals and Phillips ReeL