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The Hydrogeological Structure of Fault Zones in Poorly Lithified Sediment, Gulf of Corinth Rift

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The Hydrogeological Structure of Fault Zones in Poorly Lithified Sediment, Gulf of Corinth Rift The hydrogeological structure of fault zones in poorly lithified sediment, Gulf of Corinth rift. Sian Eleri Loveless A thesis submitted for the requirements for the degree of Doctor of Philosophy University of East Anglia School of Environmental Sciences April 2013 This copy of the thesis has been supplied on condition that anyone who consults it is understood to recognise that its copyright rests with the author and that use of any information derived there from must be in accordance with current UK Copyright Law. In addition, any quotation or extract must include full attribution. Abstract Often, the structure of fault zones cutting poorly lithified sediment examined in outcrop indicate such fault zones should behave as hydraulic barriers, but hydrological observations indicate they behave as conduit-barriers. This thesis investigates the hydrogeological structure of fault zones cutting poorly lithified sediment to better understand the observed conduit-barrier behaviour. The macro- and micro-structure of fault zones was investigated at outcrops of five fault arrays cutting syn-rift sediment of the rapidly extending Gulf of Corinth rift, Central Greece. Fault zone evolution was interpreted from these observations and changes to sediment hydraulic characteristics in fault zones estimated. Based upon the field data, characteristic fault zone hydrogeological structure was represented in two-dimensional numerical fluid-flow models in order to assess likely hydraulic impacts. Fault zone structure is found to be dominated by a mixed zone and differs to those previously reported. Two models of fault zone evolution are proposed for faults cutting: 1. Only poorly lithified sediment, in which beds are rotated and smeared in the mixed zone, where these can mix at the grain-scale through distributed, controlled particulate flow. 2. Sediment of contrasting competency, with mixed zones comprising blocks and lenses, and fine-grained smears in which strain localisation and fault-tip bifurcation are central to their evolution. Both models apply to fault zones that juxtapose fine and coarse-grained sediment. Numerical models show that the majority of these fault zones will behave as barriers to fluid-flow due to a reduction in hydraulic conductivity. Fault zones of all sizes influence fluid-flow, but hydraulic impact increases with fault throw. Conduit-barrier behaviour can be explained by anisotropies, particularly from slip-surface cataclasites, in fault zones cutting poorly lithified sediment only. Fault hydraulic behaviour is strongly dependent on structural hetereogeneities and their geometry in the fault zone. The cumulative effects of these faults will be significant for sub- surface fluid-flow. ii Table of Contents Page Abstract ii List of Figures ix List of Tables xiv Acknowledgements xv Chapter 1: Introduction 1 1.1 Rationale 1 1.1.1 Faults and fluid flow 1 1.1.2 Faults and groundwater 2 1.2 Aim 5 1.3 Hydrogeological structure of fault zones 8 1.4 Thesis structure 16 Chapter 2: Geological and hydrogeological setting of the Gulf of Corinth rift 19 2.1 The Gulf of Corinth rift 19 2.1.1 The Gulf of Corinth rift evolution 19 2.1.2 Hydrogeology of the Gulf of Corinth rift 23 2.2 Geological settings of outcrops 26 2.2.1 Outcrop mapping methods 27 in poorly lithified gravels (PLG) Appendix 4 2.2.2 Outcrop 1 – Loutraki 28 2.2.3 Outcrop 2 – Akrata 31 2.2.4 Outcrop 3 – Voutsimos 34 .4 Head 2.2.5 Outcrop 4 – Mentourgianika 37 2.2.6 Outcrop 5 – Pirgos 40 contour contour types for models of faults 2.3 Summary 42 Chapter 3: Fault zone structure and evolution – Loutraki case study 44 3.1 Introduction 44 3.2 Fault zone structure data collection 45 iii 3.2.1 Fault zone structure characterisation 45 3.2.2 Measurement of clast orientation 45 3.2.3 Hand sample collection and thin section preparation 46 3.2.4 Production of grain-size distributions 46 3.3 Analysis of fault zone structure 47 3.3.1 Fault 1A 47 3.3.2 Fault 1B 52 3.3.3 Fault 1C 52 3.3.4 Fault 3 55 3.3.5 Fault 4 57 3.3.6 Fault 5 58 3.3.7 Mixed zone thickness with fault throw 60 3.4 Fault zone structure and evolution 61 3.4.1 Fault zones in poorly lithified sediment 62 3.4.1.1 Fault zone structure in poorly lithified sediment 62 3.4.1.2 Clast rotation in mixed zones 62 3.4.1.3 Grain-scale mixing in mixed zones 63 3.4.1.4 Cataclasis in mixed zones 64 3.4.1.5 Fault zone evolution in poorly lithified sediment 66 3.4.2 Fault zones in sediment of contrasting competency 68 3.4.2.1 Fault zone structure in sediment of contrasting competency 68 3.4.2.2 Fault zone evolution in sediment of contrasting competency 68 3.4.3 Damage zones in the Loutraki outcrop 69 3.5 Summary 70 Chapter 4: Constraints on fault zone structure and evolution 72 4.1 Introduction 72 4.2 Fault data collection and analysis methods 74 4.2.1 Data collection and analysis of fault zone structure 74 iv 4.2.2 Data collection and analysis of fault zone 76 micro-structure 4.2.3 Analysis of fault population characteristics 76 4.3 Fault zone structure 77 4.3.1 Fault zones in poorly lithified sediment 77 4.3.2 Fault zones in sediment of contrasting competency 83 4.3.3 Fault zones juxtaposing fine and coarse-grained sediment 89 4.3.4 Mixed zone thickness and fault throw 92 4.4 Fault population attributes 94 4.5 Fault zone structure and evolution 96 4.5.1 Fault zone structure and evolution in poorly lithified sediment 96 4.5.2 Fault zone structure and evolution in sediment of contrasting competency 99 4.5.3 Fault zone structure and evolution in faults juxtaposing fine and coarse-grained sediment 102 4.5.4 Damage zone structure 103 4.6 Fault population characteristics 104 4.7 Summary 106 Chapter 5: The hydraulic properties of fault zones 108 5.1 Introduction 108 5.2 Estimating sediment hydraulic properties 111 5.2.1 Estimating porosity and grain-size from thin section image analysis 111 5.2.2 Estimating hydraulic conductivity from empirical equations 113 5.2.3 Estimating hydraulic anisotropy 114 5.3 Porosity and hydraulic conductivity of sediment samples 115 5.3.1 Porosity and hydraulic conductivity from image Analysis 115 5.3.1.1 Zones of mixed sediment 116 v 5.3.1.2 Slip-surface cataclasite 119 5.3.1.3 Disaggregation bands in sands 119 5.3.1.4 Sediment smears 120 5.3.1.5 Trends in porosity and hydraulic conductivity with fault throw 120 5.3.2 Spatial patterns of hydraulic conductivity across fault zones 123 5.3.2.1 Fault 1A, Loutraki 123 5.3.2.2 Fault 1C, Loutraki 125 5.3.2.3 Fault 5, Loutraki 127 5.3.2.4 Fault 2, Akrata 129 5.3.3 Hydraulic anisotropy from flow path tortuosity 131 5.4 Hydraulic properties of fault zones 132 5.4.1 Hydraulic properties of zones of mixed sediment 133 5.4.2 Fault zone heterogeneity 135 5.4.2.1 Sediment smears 136 5.4.2.2 Lenses and blocks 137 5.4.2.3 Slip-surface cataclasite 137 5.4.2.4 Disaggregation bands 138 5.4.3 Fault zone anisotropy 138 5.5 Summary 139 Chapter 6: Numerical fluid-flow models representing fault zones in poorly lithified sediment 141 6.1 Introduction 141 6.2 Fluid-flow analysis of fault zones 143 6.2.1 Developing numerical fluid-flow models 143 6.2.2 Model result analysis 151 6.2.3 Analysis of outcrop evidence of fluid-flow 152 6.3 Numerical fluid-flow model results 152 6.3.1 Faults in poorly lithified gravels (PLG) 153 6.3.1.1 Small faults in poorly lithified gravel (PLG Sm 1 and 2) 154 6.3.1.2 Large faults in poorly lithified vi gravel (PLG Lg 1 and 2) 156 6.3.2 Faults in sediment of contrasting competency (CC) 158 6.3.3 Faults juxtaposing fine and coarse-grained sediment (J) 162 6.4 Fluid-flow evidence from outcrops 165 6.5 Implications of numerical fluid-flow model results 169 6.5.1 Fault zones in poorly lithified gravel (PLG) 169 6.5.2 Fault zones in sediment of contrasting competency (CC) 171 6.5.3 Fault zones juxtaposing fine and coarse-grained sediment (J) 173 6.5.4 Hydraulic boundary conditions 174 6.6 Fluid flow at outcrops 175 6.7 Summary 177 Chapter 7: Summary and conclusions 179 7.1 Summary of results 179 7.1.1 Objectives 179 7.1.2 Hypothesis 188 7.2 Context 186 7.2.1 Hydrogeological structure of fault zones in poorly lithified sediment 188 7.2.2 Hydrological implications 190 7.2.3 Limitations of the research 193 7.3 Further research 194 7.4 Concluding statement 196 Appendix 1 Fault data 197 Appendix 2 Image analysis procedure using ImageJ 199 Appendix 3 Porosity and hydraulic conductivity of thin section samples 200 Appendix 4 PLG model results 202 4.1 Model results and parameters for small faults in poorly lithified gravels (PLG Sm 1 and 2) 200 4.2 Model results and parameters for large faults in poorly vii lithified gravels (PLG Lg 1) 203 4.3 Model results and parameters for large faults in poorly lithified gravels (PLG Lg 2) 204 4.4 Head contour types for models of faults in poorly lithified gravels (PLG) 205 4.5 Vector types for models of faults in poorly lithified gravels (PLG) 206 4.6 Streamtrace types for models of faults in poorly lithified gravels (PLG) 207 Appendix 5 CC model results 208 5.1 Model results and parameters for faults in sediment of contrasting competency (CC) 208 5.2 Head contour types for models of faults in sediment of contrasting competency (CC) 211 5.3 Vector types for models of faults of faults in sediment of contrasting competency (CC) 212 5.4 Streamtrace types for models of faults in in sediment of contrasting competency (CC) 213 Appendix 6 J model results 214 6.1 Model results and parameters for faults juxtaposing fine and coarse-grained sediment (J) 214 6.2 Vector types for faults juxtaposing fine and coarse-grained sediment (J) 215 6.3 Streamtrace types for faults juxtaposing fine and coarse-grained sediment (J) 216 Definitions 217 References 218 viii List of Figures Page Figure 1.1 Conceptual diagram of possible impacts of faults on 3 groundwater.
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