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A THESIS Entitled PHOSPHATE DEPOSITS on the NORTHWEST AFRICAN CONTINENTAL SHELF and SLOPE Submitted for the Degree of DOCTOR OF

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A THESIS Entitled PHOSPHATE DEPOSITS on the NORTHWEST AFRICAN CONTINENTAL SHELF and SLOPE Submitted for the Degree of DOCTOR OF A THESIS entitled PHOSPHATE DEPOSITS ON THE NORTHWEST AFRICAN CONTINENTAL SHELF AND SLOPE submitted for the degree of DOCTOR OF PHILOSOPHY in the FACULTY CF SCIENCE OF THE UNIVERSITY OF LONDON by COLIN PETER SUNNERHAYES Royal School of fines Imperial College October 1970 ABSTRACT Phosphatic Limestones and Phosphorites outcrop extensively on the northwest African continental margin. Off Morocco these are Upper Cretaceous, Eocene and Miocene while off the Spanish Sahara they are Lower Pliocene. Cessation of Phosphorite formation after the Pliocene may reflect climatic and attendant sedimentological changes. The Oligocene appears to have been, over the entire region, a period of uplift and erosion which may relate to postulated cess- ation or slowing of Atlantic seafloor spreading. Phosphatic surficial sediments, always found in the vicinity of rock outcrops, are concentrated in a shelf edge belt and in patches on the shelf. Phosphate is concentrated in sand sized detrital grains of phosphorite and forms, in effect, placer..type concentrates. There is no relation between sediment phosphate and upweIling of nutrient-rich water. The sands are relict from low Pleistocene sealevel stands and are in part buried by a later silt blanket prominent at mid shelf depths off LAprocco but absent from the Sahara. Diff- ering phosphatic facies are defined using multi-element geochemical mapping techniques. The presence of a widespread Recent authigenic iron-manganese mineral phase among relict sands in regions of low organic productivity is disclosed mainly using geochemical techniques. Glauconite is locally forming within the sediments but much is undoubtedly detrital. Quartz is the only major detrital mineral phase. The uraniferous character of the phosphatic rocks and sediments permits their detection by submersible scintillation counter. The economic viability of these deposits is suspect owing to the low grade of both rocks (usually 20% P205) and sediments (usually < 57. P205) and their concentration mainly at water depths „:2.-300. ii ACKNOWLEDGEMENTS The research described in this thesis was carried out in the Applied Geochemistry Research Group, Geology Department, Imperial College, under the general direction of Professor J.S. Webb and the supervision of Dr. J.S. Tooms, Reader in Applied Geochemistry. The project, carried out with the aid of a H.E.R.C. research grant, would not have been possible without the cooperation and assistance of N.E.R.C. - R.V.U. staff and the Master and crew of R.R.S. John Murray. Thanks for supplying comparative sample material from different phosphate deposits go to Dr. R.V. Dingle, University of Capetown (Agulhas Bank); Dr. I. Kaplan, U.C.L.A. (California Borderland); Mr. J.W. Brodie, N.Z.O.I. (Chatham Rise and Campbell Plateau); Dr. H.W. Menard, S.I.O. (Tasman sea- mount); Dr. R.A. Gulbrandsen, U.S.G.S. (Phosphoria Formation samples); Dr. T. Pickering, Natural Resources Authority, Amman; Fisons Fertilizers Limited, Levington Research Station (Moroccan phosphorite). It is too difficult to acknowledge all those who have been, however remotely, concerned in some way with this project but, in particular thanks are due the following people and institutions for specific forms of assistance:- Dr. C.D. Nicholls, Geology Department, Manchester University, for permission to use the MS7 Mass Spectrometer, and to him and his staff for assistance in its operation; Dr. M. Dodson and Mr, D. Rex, Geology Department, Leech, University, for K.Ar. analyses; Dr. R. Chester, Oceanography Department, Liverpool University, for Infra-Red analysis of phosphate rock samples; Dr. M. Henderson, Geology Department, Manchester University and R. Curtis, Imperial College, Geology Department, for assistance with X.Ray Diffraction analysis of rock and sediment samples; Dr. G. Dorley and Dr. P. Suddaby, Geology Department, Imperial College, for assistance with electron micro- 111 probe analysis; Mr. D.B. Smith and Mr. T. Parsons, U.K.A.E.R.E., %antage, for assistance in scintillation analysis and prospecting; Mr. M. Humphries, U.M.E.L. Limited, Fleet, for assistance with equipment; Dr. E. Bossard and Dr. W. Li of the Geophysics Department, Imperial College, and Mr. S. Jones of N.E.R.C. R.V. Unit ran the sparker equipment at sea and Dr. Bossard gave much aid during the interpretation of profiles; Mr. D. Carter and S. Rye of the Micropalaeontology Section, Geology Department, Imperial Coll- ege, and Dr. H. Bleat of Soc. Nat. Petroles, Pau, France provided extremely valuable palaeontological analyses; Mr. R. Belderson of N.I.O. kindly provided sidescan sonar data and sediment subsamples from the Saharan shelf. All Applied Geochemi stry Research Group Technical Staff who participated in the sample preparation or analysis are warmly thanked as are Dr. R. Howarth and Ashlyn Armour Brown for assistance with data interpretation in which the late Jeffrey Khaleelee also provided indispensible instruction. Dr. B.R. Hazelhoff-Roelfzema assisted in scintillation counting experiments. Many people read bits and pieces of the finished and unfinished manuscript and provided useful discussion, more notably Dr. G.P. Glasby, Dr. H. Elderfield, Dr. P. Bush, and Dr. G. Evans of Imperial College Geology Dep- artment; Er. A. N c: holt and Dr. N.M. Pantin of the I.G.S.; Dr. D.S. Cronan of Ottowa University; Dr. A. Stride of N.I.O. and Dr. J.D. Millman of Woods Hole Oceanographic Institution. Great assistance in diagram reproduction, and photographic work was provided by Mr. J. Gee and Miss Helen O'Brien of the Geology Department, Photographic Section. Lastly the writer would like to thank Dr. John Tooms for his encouragement, comments and criticisms throughout the period of this work. Linda Davies is warmly thanked for typing and my wife, Lesley, for drafting. iv LIST OF CONTENTS Page Abstract Acknowledgements ii List of Contents iv List of Tables viii List of Figures INTRODUCTION 1 SECTION SEDIMENTS OF THE NORTHWEST AFRICAN CONTINENTAL SHELF & SLOPE 7 CHAPTER 1 SEDIMENT TEXTURE & MINERALOGY 3 (1.1) Introduction 8 (1,2) Analytical Methods 9 (1.3) Sediment Texture: Morocco 11 (1.3.a) Regional Pattern 11 (1.3.b) Cores 12 (1.3.c) Thickness 12 (1.3.d) Algal mats 13 (1.4) Mineralogy: Morocco 13 (1.4.a) Regional Carbonate Distribution 13 (1.4.b) Size Fraction Analysis 14 (1.4.c) Mineral Component Analysis 17 (1.4.d) Glauconite 20 (1.4.e) Organic Content, Colour and Redox Conditions 24 (1.5) Spanish Sahara 28 (1.5.1) Regional Sediment Characteristics 23 (1.5.2) Size Fraction Analysis 30 (1.5.3) Deep Sea Photographs 32 (1.5.4) Redox Conditions, Colour and Organic Content 33 (1.6) Sedimentation History 35 (1.6.1) Morocco 35 (1.6.2) Spanish Sahara 41 CHAPTER 2 THE DISTRIBUTION, MODE OF OCCURRENCE AND ORIGIN OF PHOSPHATE IN SEDIMENTS 44 (2.1) Introduction 44 (2.2) Morocco 45 (2.2.a) Regional Distribution of Phosphate (1) In Surface Sediments 45 (2) In Sediment Cores 47 (2.2.b) Intrasediment Phosphate Dispersion 49 (2.2.c) Intrasediment Phosphate Dispersion in Relation to Mineralogy 57 (2.2.d) Relation of Phosphatic Sediment to Phosphatic Bedrock Outcrops 61 (2.2.e) Moroccan Shelf Phosphatic Sediments: Summary and Conclusions 63 Page (2.3) Spanish Sahara 65 (2.3,a) Distribution of Phosphate in Surface Sediment 65 (2.3.b) Distribution of Phosphate in Cores 67 (2.3.c) Discussion of Saharan Data 68 (2.4) General Conclusions 69 CHAPTER 3 REGIONAL SEDIMENTARY GEOCHEMISTRY 71 (3.1) Introduction 71 (3.2) Analytical Methods 72 (3.3) Single Element Dispersion in Relation to Mineralogy 73 (3.3.1) Size Fraction Analysis 73 (3.3.2) Histogram Analysis of Population Subset 1 75 (3.3.3) Single Element Distribution in Relation to Sediment Type off Morocco 77 (3.3.4) Summary 80 (3.4) Correlation Coefficient Analysis 80 (3.4.1) Population Subset 3 81 (3.4.2) 17 2 82 (3.4.3) II 4 83 (3.4.4) V9 1 83 (3.4.5) Summary 85 (3.5) Factor Analysis 86 (3.5.1) Introduction 86 (3.5.2) Description of Method 86 (3.5.3) Factor Analysis Results 88 (3.5.4) R-Scores 91 (3.5.5) Summary 98 CHAPTER 4 SUMMARY OF MAIN CONCLUSIONS AND RECOMMENDATIONS FOR FUTURE RESEARCH: SEDIMENTS 100 (4.1) Summary of Main Conclusions 100 (4.2) Recommendations for Future Research 102 SECTION II PHOSPHATIC ROCKS OF THE NORTHWEST AFRICAN CONTINENTAL SHELF AND SLOPE 104 CHAPTER 5 GEOLOGY AND STRUCTURE OF THE NORTHWEST AFRICAN CONTINENTAL MARGIN 105 (5.1) Introduction 105 (5.2) Profiling Operations and Record Interpretation 106 (5.3) Continental Margin Geology and Structure 107 (5.3.1) Spanish Sahara 107 (5.3.2) Morocco 110 (5.3.2.a) Surface Characteristics 110 (5.3.2.b) Subsurface Characteristics 112 (5.3.2.c) Geology 114 (5.4) Discussion: Continental Margin Development 116 (5.4.1) Morphology 116 (5.4.2) Spanish Sahara 118 (5.4.3) Morocco 119 (5.4.4) Summary of Conclusions 121 vi Page CHAPTER 6 PETROGRAPHY OF OFFSHORE MOROCCAN PHOSPHATIC ROCKS 123 (6.1) Introduction 123 (6.2) Glauconitic and Pelletal Phosphatic Rocks 124 (6.2.a) Glauconite 125 (6.2.b) Pellets 127 (6.2.c) Quartz and Foraminifera 129 (6.2.d) Matrix 130 (6.2.e) Pebbles 132 (6.3) Non-glauconitic, Non-pelletal Phosphatic Rocks 136 (6.4) Dating 138 (6.4.1) Cretaceous Samples 139 (6.4.2) Tertiary Samples 139 (6.5) Interpretation 140 (6.5.1) Depositional Environments 140 (6.5.2) Phosphate Mineralisation 145 (6.5.3) Comparison with Onshore Moroccan Phosphorite 149 CHAPTER 7 GEOCHEMISTRY OF PHOSPHATE-ROCKS 152 (7.1) Introduction 152 (7.2) Analytical Methods 154 (7.3) Moroccan. Offshore Phosphatic Rocks 154 (7.3.1) Electron Microprobe Investigation 154 (7,3.2) Results of
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