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04 University of Plymouth Research Theses 01 Research Theses Main Collection
2007 Controls on long-term drainage development of the Carboneras Basin, SE Spain
Blum, Astrid Juliette http://hdl.handle.net/10026.1/2220
University of Plymouth
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by
Astrid Juliette Blum
A thesis submitted to the University of Plymouth in partial fulfilment for the degree of
DOCTOR OF PHILOSOPHY
School of Geography Faculty of Social Science & Business
February 2007
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Controls on long term drainage development of the Carboneras Basin, SE Spain Abstract The impact of external and internal controls on long-term drainage evolution can play an important role in the research on global changes. For longer term controls such as tectonics and climate this necessitates the use of a long time-scale such as the Plio/Pleistocene, and the integration of both geological and geomorphological data. This thesis uses data from Plio/Pleistocene alluvial deposits (deltaic and fluvial) of the Carboneras Basin in southeast Spain to address these issues. The Carboneras Basin, an intermontane basin of the Belie Cordillera, was one of the last of a series of sedimentary basins which underwent transition from marine to continental conditions during the Plio/Pleistocene in this region. The basin is still tectonically active, controlled by surface uplift of the basin, differential uplift of the Sierra Alharnilla/Cabrera mountain range and activity along the 40 km long strike-slip Carboneras Fault. This study follows the evolution of a basin-scale drainage network using a multidisciplinary approach to determine the long-term influences of extrinsic and intrinsic controls on the drainage system of the Carboneras basin. Geological and geomorphological data is evaluated to trace the depositional and erosional record of the drainage systems. Palaeogeographic reconstruction of the marine and deltaic Pliocene deposits revealed large fan delta sediments in the northern part of the Carboneras Basin. Detailed field investigations discovered a 'Gilbert' type delta, suggesting the occurrence of a steep palaeocliff created by vertical movements along the Carboneras Fault Zone. Palaeocurrent measurements suggest three fluvial inputs from N-NW directions into the Carboneras Basin: the Rambla de Lucainena, Rambla de Ios Feos and Rio Gafares. The Rio Gafares, responsible for the Gilbert type fan delta, was the biggest and probably most important drainage system in terms of sediment supply to the basin during the Upper Pliocene. After a fall in sea level the transverse, antecedent Rio Gafares evolved developing a staircase of straths and terraces. Four terrace levels have been assigned for the Rio Gafares. Detailed investigations of river terrace deposits established an ongoing connection between the adjacent Sorbas Basin and the Carboneras drainage until the Late Pleistocene. A probable river capture of the Rio Gafares finally limited the catchment size of the river and decreased the sediment supply to the Carboneras Basin. This can be seen in the provenance distribution and the lack of Amphibole-mica-schist, which was used as a marker clast for Nevado Filabride component, derived from the Sorbas Basin. The terraces of the Gafares system are mainly controlled by tectonically driven uplift ofthe Sierra Cabrera. Additional to the north-south draining Gafares River a strike parallel river, the Rio Alias, developed south of the mountain front by the confluence of the Rambla de Lucainena and Rambla de Ios Feos. Four Quaternary terrace levels have been determined for the Rio Alias and have been age correlated to terrace levels of the Sorbas Basin, using pedogenic calcrete stages. A combined examination of the palaeoterrace distribution and modern river network has identified post sedimentary displacement of the river channel across the Carboneras Fault Zone. Three fault strands have been recognized and lateral and vertical displacement along the strike-slip fault has been demonstrated. Mapping fan delta conglomerates revealed vertical movement since the Late Pliocene. The lateral component, calculated from offset terrace conglomerates, has an estimated strike-slip movement of 14 mm I a· 1 since the Upper Pleistocene. This study has established the drainage history of the Carboneras Basin indicating the significance of river capture and river re-routing in sediment supply to the basin. The occurrence of four aggradational periods associated with the terrace levels appear to be climate controlled. However the overall incision is a response to uplift. As this uplift was differential, leading to enhanced regional gradients between sedimentary basins, the uplift was indirectly key to re-routing major sediment transport routes (the main rivers) both within and between sedimentary basins, through river capture.
3 Table; of Contents
Copyright:statetnent
Title page 2
AbstraCt 3
List of Contents 4
List:of Figure 11
:List ofl'able IJ
Acknowledgmenfs 15
Author's Declaratio!l 16
Main:text 17
References 278
4 1 CHAPTER: INTRODUCTION TO THE GEOLOGICAL AND
GEOMORPBOLOGICAL SETTING OF THE CARBONERAS BASIN 17
1.1 INTRODUCTION 17 1.1.1 SE Spain 18 i Carboneras Basin 19
1.2 AIM OF THE STUDY 22 1.2.1 Objectives 22
1.3 BETIC CORDILLERA EVOLUTION 23 1.3.1 introduction 24 1.3.2 The Internal and External Zones 25 i The External Zone 25 ii The Internal Zone 25
1.4 ALPINE BASEMENT GEOLOGY 26 1.4.1 Nevado-Fiilibride Complex 27 1.4.2 Alpujamde Complex 28 1.4.3 Malaguide Complex 28 1.5 REGIONAL NEOGENE SEDIMENTATION 29
1.6 THE CARBON ERAS BASIN 31 1.6.1 Introduction 31 i Definition of the study area 31 ii Location ofthe study area 32 1.6.2 Tectonics 33 1.6.3 Neogene Basin Fill 34 i Serraval/ian-Tortonian deposits 34 ii Messinian sequence 35 iii Pliocene marine sequence 38
1.7 THE TERRACE SEQUENCE 38 1.7.1 Introduction 38 i strath and river terrace definition 39 1.7.2 The main river systems of the Carboneras Basin 40
2 CHAPTER: GEOMORPHOLOGICAL AND SEDIMENTOLOGICAL
FIELD TECHNIQUES 41
2.1 INTRODUCTION 41
2.2 APPROACH 41
2.3 FIELD SEASONS AND CARTOGRAPHIC MATERIALS 42
2.4 SEDIMENTARY LOGGING OF GEOLOGICAL SECTIONS 43
5 2.5 RIVER TERRACES ANALYSIS 46 2.5.1 Mapping of the terrace deposits 46 i Maximum clast size 47 ii Palaeojlow direction 47 iii Clast Provenance 48 iv Statistical analysis 50 2.5.2 Dating of the river terraces 52 i Soil profiles I Pedogenic classification 52 ii Calcrete stage I Pedogenic classification 52 2.5.3 Terrace height diagram 54 2.5.4 River channel cross profiles 54
3 CHAPTER: FINAL MARINE BASIN INFILL 55
3.1 INTRODUCTION 55
3.2 THE ADJACENT BASINS 56
3.3 STRATIGRAPHY OF THE CARBONERAS BASIN 59
3.4 CUEVAS FORMATION 64 3.4.1 Lower Unit 65 i Facies description 65 ii Reconstruction ofthe palaeoenvironment 65 3.4.2 Upper Unit 66 i Facies description 66 ii Reconstruction of the palaeoenvironment 70 3 .4.3 Shoreface deposits 71 i (i) Facies description 71 ii Reconstruction ofthe palaeoenvironment 72 3.4.4 Summary 74
3.5 POLOPOS FORMATION 75 3.5.1 Beach deposits 75 i Facies description 75 ii Reconstruction ofthe palaeoenvironment 76 3.5.2 Fan delta sequence 79 i fan delta definition/terminology 80 ii Fan deltas in SE Spain 81 3.5.3 Fan delta deposits of the Lucainena and Feos system 82 i Outcrop near confluence of the Lucainena and Feos system (GR. 863953) and (GR. 857955) 83 ii Reconstruction ofthe palaeoenvironment 86 3.5.4 Fan delta deposits of a third river system 86 i Outcrop near El Argamason (GR. 920944) 86 ii (ii) Reconstruction of the palaeoenvironment 91 3.5.5 Summary 92 i Identification ofthe fan delta feeder channel 94 3.5.6 Coastal plain deposits 98
6 i Facies description ofunit a) 98 ii Facies description of unit b) 98 iii Reconstruction ofthe palaeoenvironment 101 3.5.7 Summary 102
4 CHAPTER: EVOLUTION OF THE PRIMARY DRAINAGE
SYSTEM 105
4.1 INTRODUCTION 105 4.1.1 Dividing river terraces into different levels 105 4.2 DRAINAGE RECONSTRUCTION 107 4.3 THE PLIOCENE TOPOGRAPHY 109 4.4 TERRACE SEQUENCE OF THE RIO GAFARES 110 4.4.1 The modern Rio Gafares 110 4.4.2 Introduction to the terrace sequence 113 4.4.3 Terrace highest above the modern river- (terrace level 1) 119 i Description: terrace level 1 119 ii Strath terrace Sierra Cabrera (GR. 892009 and 897998) 119 iii Reconstruction of the palaeoenvironment: terrace level] 123 4.4.4 Terrace second highest above the modem river (terrace level2) 123 i Description: terrace level 2 12 3 ii (ii) Reconstruction of the palaeoenvironment: terrace level 2 135 4.4.5 Terrace lowest above the modem river (terrace level3) 138 i Description: terrace level 3 138 ii Reconstruction of the palaeoenvironment: terrace level 3 143 4.4.6 River incision 144 4.4. 7 Provenance development 146 4.4.8 Discussion of the Gafares evolution 147 i Alpujarride Units - Provenance change as an indicator ofdrainage evolution 147 ii Neogene component - Provenance change as an indicator for river incision 147 iii Amphibole-mica-schist - Provenance change as an indicator for river incision 148 iv Provenance change as indication for drainage rearrangement 149 4.4.9 Summary of the evolution of the Rio Gafares 150 4.5 THE MODERN RIO ALIAS 153 4.6 THE TERRACE SEQUENCE OF THE RIO ALIAS 158 4.6.1 Previous work on terrace remnants within the study area 158
7 4.6.2 Conglomeratic deposits highest above the modem river 162 i Description: highest conglomeratic deposits 162 ii Reconstruction of the palaeoenvironment: highest conglomeratic unit 165 4.6.3 Terrace highest above the modem river- (terrace level I) 165 i Description: terrace level 1 166 ii Reconstruction of the palaeoenvironment: terrace level 1 175 4.6.4 Terrace second highest above the modem river- (terrace level 2) 179 i Description: terrace level 2 179 ii Reconstruction of the palaeoenvironment: terrace level 2 189 4.6.5 Terraces level 3 192 i Description: terrace level 3 192 ii Reconstruction of the palaeoenvironment: terrace level 3 202 4.6.6 Terrace level 4 205 i Description: terrace level 4 205 ii Reconstruction of the palaeoenvironment: terrace level 4 210 4.6. 7 Terrace age 211 4.6.8 Provenance development 213 4.6.9 Incision 216 4.6.1 0 Discussion of the fluvial evolution of the Rio Alias 216 i incision 216 ii Tectonic implications 219 4.6.11 Summary of the evolution of the Rio Alias 219
5 CHAPTER: TECTONIC CONTROLS ON FLUVIAL LANDFORM
DEVELOPMENT 221
5.1 INTRODUCTION 221 5.l.l Vertical movements 221 5.1.2 Lateral movements 222 5.2 REGIONAL STRUCTURAL SETTING 223 5.3 REGIONAL UPLIFT HISTORY OF THE BETIC CORDILLERA 225 5.3.1 The Carboneras Basin 226 i This study: Calculated uplift rates using Pliocenefan delta deposits 226 ii Discussion 227 5.4 TECTONICALL Y DRIVEN UPLIFT OF TOPOGRAPHIC HEIGHTS 229 5.4.1 The Carboneras Basin 230 i This study: Calculated uplift of the Sierra Cabrera using Quaternary terrace deposits 231
8 ii Discussion 232 5.5 THE CARBONERAS FAULT ZONE {CFZ) 232 5.5.1 Introduction 232 i Location 233 ii Subdivision 233 iii Activity 234 iv Tectonic-drainage 235 5.5.2 Displacement 235 i Activity 235 ii Vertical displacement along the CFZ 236 iii This study: Vertical uplift along the middle fault strand ofthe CFZ 238 iv Discussion 240 5.5.3 Lateral displacement 241 i Carboneras Fault Zone 241 ii modern river 243 iii river terrace dislocation 243 iv lateral displacement of the fan delta deposits 246 5.5.4 Discussion 249 i vertical offset along the CFZ 249 ii lateral offset along the CFZ 250 5.6SUMMARY 252
6 CHAPTER: CONTROLS ON THE LONG-TERM DRAINAGE
EVOLUTION OF THE CARBONERAS BASIN 254
6.1 INTRODUCTION 254 6.2 INTRINSIC CONTROLS ON DRAINAGE EVOLUTION 255 6.2.1 Topography 255 6.2.2 Geology I Geomorphology 255 6.3 EXTRINSIC FACTORS INFLUENCING THE DRAINAGE EVOLUTION 257 6.3.1 Sea level 257 6.3.2 Climate 259 i Mediterranean 261 ii Carboneras Basin 263 6.3.3 Regional uplift 266 i Incision 267 ii Carboneras Basin 268 6.3.4 Differential tectonics 269 i Tectonic uplift 269 ii Carboneras Basin 270
2.
9 7 CHAPTER: CONCLUSION 272
7.1 PALAEOGEOGRAPHIC RECONSTRUCTION 272 7 .1.1 Pliocene 272 7.1.2 Quaternary 273 i Rio Gafares 274 ii Rambla de Ios Feos/Lucainena 274 iii Rio Alias 276 iv Rio Saltador 277
7.2 SUMMARY 277
10 List of Figures
Figure 1.1 Maps showing the location of the study area. 20 Figure 1.2 Outline of the main structural patterns. 21 Figure 1.3 Map of the Belie Cordillera region showing the seismicity distribution. 24 Figure 1.4 Schematic geological map of the study area. 27 Figure 1.5 Schematic map illustrating various basins and sub-basins. 33 Figure 1 .6 Drainage systems of the Carboneras Basin. 40 Figure 2.1 Udden-Wentworth scale used for grain-size determination. 43 Figure 2.2 Sedimentary features. 45 Figure 3.1 Stratigraphic framework for the Nijar- Carboneras area. 58 Figure 3.2 Pliocene stratlgraphy of the Campo de Nijar I Carboneras Basin. 63 Figure 3.3 Lower and Upper Cuevas Viejas deposits. 67 Figure 3.4 Sequence of the upper part of the Cuevas Fm. 68 Figure 3.5 Overview of the lower and upper Cuevas Formation. 69 Figure 3.6 Shoreface deposits along the northern margin of the Carboneras Basin. 73 Figure 3. 7 Beach deposits north of the Rio Alias. 77 Figure 3.8 Photo and sedimentary log. 78 Figure 3.9 Sketch map of the Lucainena and Feos fan delta outcrops. 83 Figure 3.10 Feos fan delta deposits. 84 Figure 3.11 Lucainena fan delta deposits near Polopos. 85 Figure 3.12 Simplified maps of the fan delta distribution. 88 Figure 3.13 El Argamason fan delta. 89 Figure 3.14 El Argamason fan delta quarry. 90 Figure 3.15 A: Map illustrating the average dip direction of the fan delta foresets. 90 Figure 3.16 Shaded relief map. 97 Figure 3.17 Coastal plain deposits within the fan delta area. 99 Figure 3.18 Overview of the coastal plain deposits north of La Palmerosa. I oo Fig. 4.1.1 Extract of a 1:10,000 and a 1:25,000 map. 107 Figure 4.2.1 Main types of drainage developed in the study area and the adjacent basins. I 08 Figure 4.4.1 Aerial photograph showing the modern Rio Alias draining from North-5outh. Ill Figure 4.4.2 Modern drainage network of the Gafares River system and its tributaries. 112 Figure 4.4.3 Map of the terraces of the Rio Gafares. 116 Figure 4.4.4 North-South longitudinal profile of the Rio Gafares and height range diagram. 117 Figure 4.4.5 Map of the Gafares headwaters showing cross profile locations. 118 Figure 4.4.6 Strath terraces of the Rio Gafares. 121 Figure 4.4.7 Terrace hill at an altitude of 226 m. 122 Figure 4.4.8 Terrace hill. 126 Figure 4.4.9 Terrace al330m within the Sierra Cabrera at terrace level2. 127 Figure 4.4.1 0 Geological sketch map of the area of the main terrace finding. 129 Figure 4.4.11 Terrace deposits of terrace level 2 of the Gafares River. 130 Figure 4.4.12 Terrace deposits of hilltop 208 m. 133 Figure 4.4.13 Terrace deposits near Los Ranchos 134 Figure 4.4.14 Gafares terraces remnants of terrace level2. 137 Figure 4.4.15 Terrace level 3- west of the modern Gafares within the Sierra Cabrera. 140 Figure 4.4.16 Gafares terraces remnants of terrace level3. 141 Figure 4.4.17 Staircase diagram for the Rio Gafares. 145 Figure 4.4.18 Provenance development of the Rio Gafares. 146 Figure 4.4.19 The modern incised Rio Gafares. 149 Figure 4.5.1 Modern drainage network of the Rio Alias. 155 Figure 4.5.2 Modern Rio Alias. 156 Figure 4.5.3 Sketch map of the modern drainage systems within the Carboneras Basin. 157 Figure 4.6.1 Sketch map of the Rio Alias. 160 Figure 4.6.2 West-East longitudinal profile of the Rio Alias and height range diagram. 161 Figure 4.6.3 Upper conglomeratic deposits of the Rio Alias. 163 Figure 4.6.4 Terrace deposits on top of large cliff. 168 Figure 4.6.5 Terrace conglomerates of level1 near Cortijo de Norias. 169 Figure 4.6.6 River conglomerates of terrace level 1. 172 Figure 4.6. 7 Geological sketch map of the surrounding area of terrace hill 169. 173
11 Figure 4.6.8 Well preserved terrace deposits of hill 169 of terrace level 1. 174 Figure 4.6.9 Sketch map of the Rio Alias showing the location of the terrace level. 178 Figure 4.6.10 Terrace remnants at the top of a steep cliff along the Rio Alias. 181 Figure 4.6.11 Terrace deposits on the eastern side of the meander loop. 182 Figure 4.6.12 Terrace deposits south of the gorge of the modern Rio Alias. 184 Figure 4.6.13 Well preserved river terrace NE of El Llano de don Antonio. 186 Figure 4.6.14 Sketch map of the Rio Alias showing the location of terrace level 2. 191 Figure 4.6.15 Photograph of the road outcrop SE of the village of El Argamason. 193 Figure 4.6.16 Terrace deposits on top of the Carboneras Fault. 196 Figure 4.6.17 Photo and sketch of the lower terrace remnants on top of the CFZ. 197 Figure 4.6.18 Terrace deposits along the Carboneras Fault Zone. 198 Figure 4.6.19 Eastern part of the Rio Alias. 200 Figure 4.6.20 Sketch map of the Rio Alias showing the location of terrace level 3. 204 Figure 4.6.21 Examples of terrace deposits of terrace level. 208 Figure 4.6.22 Location map of terrace level 4. 209 Figure 4.6.23 Staircase diagram showing the individual terrace levels of the Rio Alias. 217 Figure 4.6.24: Contour map of the study area showing the main drainage systems. 218 Figure 5.1: Betic Cordillera and fault zones. 224 Figure 5.2 Map of fan delta deposits across the Carboneras Fault Zone. 228 Figure 5.3 Gilbert fan delta deposits along the Carboneras Fault Zone. 239 Figure 5.4 Generalized aggradational and degradational response of a stream. 240 Figure 5.5 Modified satellite image showing the abandoned meander loop. 242 Figure 5.6 Rio Alias showing a rectilinear pattern across the Carboneras Fault Zone. 244 Figure 5.7 Channel migration caused by strike-slip faulting. 248 Figure 5.8 Examples of different fracture types across the Carboneras Fault Zone. 248 Figure 7.1: Sketch map of the consequent drainage evolution of the Carboneras Basin. 275
12 List of Tables
Table 2.1 Lithofacies scheme, textural characteristics and sedimentary characteristics. 44 Table 2.2 Provenance description compared with Rondeels mapped units. 51 Table 3.1 Table presents the mean and Standard deviation of the largest clasts within the conglomerates at the two locations south of El Castillico. 72 Table 3.2 The table presents the mean and Standard deviation of the largest clasts within the conglomerates at three locations at Cortijada La Arboleda del Area. 76 Table 3.3 The table presents the mean and Standard deviation of the largest clast within the conglomerates. 87 Table 3.4 Summary of key geological and geomorphological attributes. 104 Table 4.4.1 The table presents the provenance distribution data of the modern terrace deposits of the Rio Gafares. 113 Table 4.4.2 The table presents the provenance distribution data of the terrace deposits of terrace hilltop 226 of the Rio Gafares. 120 Table 4.4.: Table summarising the described and analysed terrace deposits of terrace level 1 and their location in the field. 120 Table 4.4.4 The table presents the provenance distribution data of the terrace deposits of terrace level 2 within the Sierra Cabrera. 125 Table 4.4.5 The table presents the provenance distribution data of the terrace deposits of terrace level 2. 132 Table 4.4.6 Table summarising the described and analysed terrace deposits of terrace level 2 and their location in the field. 135 Table 4.4.7 The table presents the provenance distribution data of the terrace deposits of terrace level 3. 142 Table 4.4.8 Table summarising the described and analysed terrace deposits of terrace level 3 and their location in the field. 142 Table 4.4.9 Summary of key geological and morphological attributes for each of the Pleistocene- modern terraces/strath levels. 152 Table 4.5.1 The table presents the provenance distribution data of the modern terrace deposits. 154 Table 4.6.1 The table presents the provenance distribution data of the highest conglomeratic deposits. 164 Table 4.6.2 Table summarising the described and analysed conglomeratic deposits of and their location in the field. 164 Table 4.6.3 The table presents the mean and Standard deviation of the largest clasts within the conglomerates at the two locations wesUsouthwest of Los Cortijillos. 165 Table 4.6.4 The table presents the provenance distribution data of the terrace deposits of terrace level 1 . 171 Table 4.6.5 Table summarising the described and analysed fluvial conglomerates of terrace level1 and their location in the field. 171 Table 4.6.6 The table presents the mean and Standard deviation of the largest clasts within the conglomerates at three outcrops of terrace level 1. 175 Table 4.6.7 The table presents the provenance distribution data of the terrace deposits of terrace level 2. 187 Table 4.6.8 Table summarising the described and analysed fluvial conglomerates of terrace level 2. 188 Table 4.6.9 The table presents the mean and Standard deviation of the largest clasts within the conglomerates at the five terrace remnants of terrace level 2. 188 Table 4.6.10 The table presents the mean and standard deviation of the ten largest clasts within the conglomerates of the subunits. 195 Table 4.6.11 The table presents the provenance distribution data of the terrace deposits of terrace level 3. 20 I Table 4.6.12 Table summarising the described and analysed fluvial conglomerates of terrace level3. 201 Table 4.6.13 The table presents the provenance distribution data of the terrace deposits of terrace level 4. 207 Table 4.6.14 Table summarising the described and analysed fluvial conglomerates of terrace level 4. 210
13 Table 4.6.15 Table summarizing the terrace correlations of terraces of the Sorbas Basin with terraces of this study. 212 Table 4.6.16 Table showing the average distribution of Nevada Filabride clasts within each individual terrace level from T1-T modern. 213 Table 4.6.17 Summary of key geological and morphological attributes for each of the Pleistocene- modern terraces levels. 215 Table 5.1: Uplift rates of major European basins. 229 Table 5.2: Uplift rates of the major topographic highs within the Carboneras/Aimeria Basin.230 Table 5.3: Table showing the different estimated times of activity of the Carboneras Fault Zone. 237
14 Acknowledgments
There is a long list of people who helped and supported me during the last few years.
First of all I would like to thank Anne and Martin for their great supervision and support in Spain and back at Plymouth. I would like to thank them for all their patience answering my thousand questions. Great thanks to Anne for cheering me up during the last few weeks I months of writing up.
Many, many thanks to Jim Griffiths for his tremendous support, without him the final version of this dissertation wouldn't have been possible.
My sincerest thanks to David Bridgland, my external examiner, for the interesting discussions and all the critical comments. His ideas had a major influence on the final product of this thesis.
There are a number of people from Plymouth, who I would like to acknowledge for their fast and efficient help when necessary, thanks to Ruth, Roland, Ian, Pauline, David and Naomi.
The field season in Spain where fantastic and therefore many thanks to Lindy and Petra from Urra, who always provided me with one of the most beautiful campsite spaces.
Great thanks to Toni for many hours of great (awesome!) discussion about my fan delta.
And, of course, a special thanks to Dave, who with his never ending enthusiasm really supported me in the field (stucked van) and later back in England.
There are other people from or working in Spain, who I actually haven' t met in the field, but who where unbelievable important due to their knowledge of the area. I wish to thanks Liz for clearifying some terraces and special thanks to Julio Aguirre for sharing his immense knowledge of the Carboneras Basin with me.
Back home I would thank the people who provided me with time (Saskia for looking after the 'pests') and those ones, who actually had to live with me during the last months (and before as well, but then it can't have been that hard) of this thesis - thanks to Axe!, Maurice and Lucien for all their patience.
Vielen tausend Dank!!!!
15 Author's declaration
At no time during the registration for the degree of doctor of Philosophy has the author been registered for any other University award without prior agreement to the Graduate Committee.
This study was financed with the aid of a studentship from the School of Geography.
Relevant scientific field trips and conferences were regularly attended at which work was often presented in form of posters or oral presentations. /(J. 3.0'6
Presentation and Conference Attended:
December 2002: BSRG Norwich, UK.- The Gafares River, SE Spain -a transverse drainage system.
August 2002: Dryland Rivers Aberdeen, UK - A river runs through it -long tenn external control onfluvia/landfonn development.
December 2001: BSRG Plymouth, UK. - River rearrangement in a tectonical/y active mountain front: a case study from the Plio I Pleistocene ofSE Spain.
August 200 I: ICFS Lincoln, Nebraska, USA - Using long-term drainage records to quantify tectonic deformation in an active strike-slip setting.
March 2000: FLAG Mainz, Germany - Long term drainage evolution of the Gafares river system, SE Spain.
September 1999: Field Conference Urra, Spain - The influence of tectonics on fluvial /andform development in the Carboneras Basin, SE Spain
Word count of main body of thesis: 39.897
16 1 CHAPTER: INTRODUCTION TO THE GEOLOGICAL AND
GEOMORPHOLOGICAL SETTING OF THE
CARBONERAS BASIN
1.1 Introduction
The nature of long-term changes in river systems as a response to external controls can provide valuable data for understanding both local and global changes in climate and sea-level change (Blum and Tornqvist, 2000). Sea-level, climatic and tectonic changes all influence the geomorphology of a drainage system. How extrinsic (e.g. sea-level change, climate and tectonic) and intrinsic factors (e.g. underlying geology) impact on river systems, is complex and has been the subject of considerable debates e.g. (Mather and Harvey, 1995;Jones et al., 1999b ). For much of the 1990s research focused on base-level changes controlling river behaviour, e.g. (Schumm, 1993). In more recent research climatic and tectonic changes gained more and more attention
(Lewin, 1995; Antoine, 1997; Aguirre, 1998b; Holbrook and Schumm, 1999;;
Antoine et al., 2000; Maddy et al., 2000; Bridgland and Maddy, 2002; Antoine et al.,
2003 b; Stokes and Mather, 2003; Bridgland et al., 2004; Jones, 2004; Westaway et al., 2004; Cunha et al., 2005 and Maddy et al., 2005).
River terrace sedirnents and their geomorphology provide the essential field evidence to examine long-term fluvial system behaviour of northwest European rivers (Maddy et al., 2001). River deposits are highly sensitive indicators of tectonic or climatic changes, e.g. is the increase in sediment supply a factor of source area rejuvenation
(Mather and Harvey, 1995). It has to be further investigated, however if the change in
17 sediment supply is driven by tectonics or climatic changes. Measuring the amount of incision of the river channel, for example, gives the researcher an idea about the total uplift which has been affected the study area. If the uplift was generated by regional uplift or by differential tectonics should to be considered in detail. Thus an investigation of river deposits over a longer time-periods (hundred thousand to million years) will give a considerable amount of information about the factors influencing drainage evolution.
1.1.1 SE Spain
The Mediterranean basins have been subjected to fluctuations in sea-level over the last 3 Ma. Over this time period, the Mediterranean has been a zone of persistent
Cenozoic tectonic activity, and crusta! deformation in places has involved hundreds of rrieters of Quaternary elevation (Lewin, 1995). With the onset of continental conditions in the sedimentary basins of SE Spain during the Pliocene, fluvial systems became established.
The basins in SE Spain (Fig. 1.1, C: Map of the Betic Cordillera) provide an especially significant area in which the relationships between tectonics, sedimentation and river development can be explored by analysis of well preserved sedimentary exposures. Moreover the dryland climate and hence the lack of vegetation facilitates the use of remote sensing data. As a result of these features numerous studies have focused on the Plio/Pleistocene river systems of the Betic Cordillera in SE Spain; namely the rivers of the Sorbas e.g. (Mather, 1991; Harvey et al., 1995; Mather and
Harvey, 1995), the Vera (Stokes, 1997; Stokes and Mather, 2003; Wenzens, 1992b)
18 and the Guadix Basin (Viseras and Fernandez, 1992). These studies have shown that tectonics and structural controls have exerted a strong influence over fluvial systems.
The Carboneras Basin (see Fig. 1.1, map C), situated south of the Sorbas and Vera
Basins in the Betic Cordillera in SE Spain, shows all the above mentioned characteristics of a well preserved sedimentary basin, but its drainage evolution has been very much neglected by researchers in the past and is therefore the focus of this thesis. Previous work in adjacent basins (e.g. drainage records of the Sorbas and Vera
Basin) enables this research to be placed into a wider regional context of the drainage evolution within the Mediterranean.
i Carbo11eras Basi11
The Carboneras Basin has a drainage record which spans some 2 Ma. A long history such as this is crucial to investigating tectonic, climatic and sea-level changes which operate on such time-scales. Although climatic and tectonic perturbations can occur within a relatively short time frame of a few thousand years, to obtain significant information about longer term trends (for example in regional tectonics), longer time scales (e.g. million year) are required.
19 A
Fig. 1.1 Maps showing the location of the study area. A: Sketch map of Spain and adjacent countries. Box indicates the area of the Betic Cordillera. B: Regional map demonstrating the subdivision of the Be tic Zone, modified after Weijermars ( 1991) . Box indicates the study area. C: The Carboneras Basin and the surrounding basins. Shadings represent the topography, map derived from Espaiia (1992).
20 In addition to the influences of sea-level and climate, the Carboneras Basin is also strongly controlled by tectonics expressed as epirogenic uplift and strike-slip motion.
The strike-slip Carboneras Fault Zone, which cuts across the Carboneras Basin (Fig.
1.2: Structural map of the study area), is by far the longest continuous fault mapped in the southern Betic Cord ilia, with 40-50 km onshore and more than 100 km offshore
(Gracia et al., 2006).
These unique basin characteristics make the Carboneras Basin an excellent study area for investigating the influence of sea level, climate change, and the importance of tectonic control on the drainage record.
Fig. 1.2 Outline of the main structural patterns in the southeastern Internal Betic Cordilleras; E-W striking dextral Gafarillos Fault (GFZ); N010E-trending trending Palomares Fault and N040E trending Carboneras Fault (CFZ), also referred to as the 'Serrata' Fault. A-N = Almeria-Nijar Basin, C= Carboneras Basin, S= Sorbas Basin, T= Tabernas Basin and V= Vera Basin. Shaded relief map derived from Espafia, (1992).
21 1.2 Aim of the study
The aim of this thesis is to reconstruct the drainage evolution of the Carboneras Basin and to evaluate the impact of long-term external controls on the fluvial development.
This study will determine the relative significance of tectonic movements, climate and sea-level changes for the early stages of the drainage system (fan delta development) and for the succeeding river development.
1.2.1 Objectives
The Carboneras Basin is used as a case study to reconstruct a drainage system over the last three million years using evidence from the sedimentology of the basin fill and ensuing geomorphological development of the landscape through erosion. This study will trace the evolution of the fluvial drainage system from its net depositional record during the marine phases to the net erosional record of the fluvial systems during the incision and river terrace development. The palaeotopography after the withdrawal of the Pliocene Sea will be established by mapping and studying the final marine record. The consequent and subsequent river systems will be examined using evidence from river terraces. These data will provide detailed information about the drainage evolution within the Carboneras Basin.
This study objectives are to:
l) reconstruct the former marine palaeogeography and relief which provides
the topography on which the consequent drainage system develops
22 2) describe the consequent fluvial systems and trace their evolution; document
the environment of deposition, provenance distribution and palaeocurrent
pattern
3) describe and analyse the style of defonnation affecting the developing river
systems
4) address the relative importance of sea-level, climate and tectonics on the
fluvial landfonn development using existing published literature and new
data obtained from this thesis
The purpose of this study is not only to describe the factors influencing drainage evolution, but also vice versa, which means to use the drainage record to gain infonnation about variations in external and internal controls during the last 2 Ma within the Carboneras Basin.
1.3 Evolution of the Betic Cordillera
Section 1.3 provides an introduction to the geological setting of the area. The first part describes the evolution of the Betic Cordillera in relation to plate movements in the western Mediterranean. The second part will describe the palaeoenvironment of the intennontane sedimentary basins developed during the Neogene focusing on local tectonic and relative sea-level controls. The third part concentrates on the Carboneras
Basin and its Neogene stratigraphy.
23 The metamorphic rocks of the Betic Zone are important for the drainage system analysis since by identifying the clasts within the fluvial conglomerates it is possible to relate the clast assemblages to source areas, which facilitates the reconstruction of the drainage network (chapter 2, section 2.4.6).
1.3.1 Introduction
The Betic Cordillera (Fig. 1.1 B) is the major feature of Alpine-age structure in southern Spain (Dabrio and Polo, 1981) and continues across the Strait of Gibraltar and into the Rif Mountain of Morocco, surrounding the western end of the
Mediterranean (Albonin Sea). The mountain range originated from relative movements between the African and the Iberian plates during the Early Mesozoic
(Smith and Woodcock, 1982). The subsequent collision of the two plate boundaries caused nappe emplacement during the Oligocene (Weijermars et al., 1985). It is, however, difficult to locate a plate boundary between these two continents and the present-day seismicity is scattered across the whole region (see Fig. 1.3).
Fig. 1.3 Map of the Betic Cordillera region showing the seismicity distribution for the period 1973-2005, modified after Martinez-Martinez et al. (2006). Study area shown in Fig. 1.2 in square.
24 1.3.2 The Internal and External Zones
The Alpine belt is divided into an External Zone in the north and an Internal zone in the south (Egeler and Simon, 1969).This division is based on lithological, tectonic and paleogeographic criteria (Sanz de Galdeano, 1990).
i The External Zone The External zone comprises non-metamorphic sedimentary rocks of essentially
Mesozoic and Tertiary age (Weijermars, 1991) and was strongly shortened during the
Miocene by thin-skinned thrusting and folding. It is further divided into Prebetic and
Subbetic zones. The Prebetic Zone represents the former shelf environment where shallow marine deposition prevailed, whereas the deposits of the Subbetic Zone are characterized by a pelagic facies reflecting deeper marine environments.
ii The Internal Zone
The Internal Zone (Betic Zone) of the orogenic belt is largely formed by a pre-
Neogene basement of metamorphic nappes, which are commonly arranged into three thrust sheet complexes, based on differences in tectono-metamorphic evolution
(Huibregtse et al., 1998).
The topography of the Internal Zone consists predominantly of E-W trending mountain ranges and intramontane depressions defined by Neogene strike-slip deformation along the major fault zones (Bousquet, 1979; Huibregtse et al., 1998) creating a basin-and-range style topography. Ongoing faulting has helped to define the Neogene sedimentary basins, generating localised areas of compression and extension (Hall, 1983; Huibregtse et al., 1998). Several Neogene basins in the Internal
25 part of the Betic Cordillera (Sorbas, Vera, and Carboneras Basins) have been interpreted as having originated in association with strike-slip faults (Huibregtse et al.,
1998). Neogene deposition took place simultaneously with rapid subsidence of the basins and subsequent uplift of the pre-Neogene basement (Cloetingh et al., 1992).
The origin of the basins is also demonstrated by the character of the Neogene basin fill, since the proximal provenance of high energy deposits indicates areas of local basement uplift and erosion closely associated with areas of rapid subsidence and deposition, characteristic of a strike-slip setting. The Neogene sedimentation is strongly controlled by coeval tectonism (Weijermars et al., 1985; Sanz de Galdeano and Alfaro, 2004). This tectonic activity has continued into the Quaternary with movement along many of the faults with associated large-scale differential uplift between the basins (Harvey and Wells, 1987).
1.4 Alpine Basement Geology
The basement rocks have been grouped into three tectonic complexes, within which there are several tectonic units (Egeler and Simon, 1969). From the highest-grade complex these are:
(3) the Malaguide Complex
(2) the Alpujamde Complex
(I) the Nevado-Filabride Complex
The Nevado- Filabride is the lowermost tectonic complex of the Internal Zone of the
Betic Cordillera. This complex underlies the Alpujlirride Complex, which in turn is
26 overlain by the Malaguide Complex. The first two complexes consist of Precambrian,
Palaeozoic and especially Triassic rocks, affected by Alpine metamorphism (see Fig.
1.4: Schematic geological map of SE Spain), whilst the Malaguide complex is unrnetamorphosed and comprises Palaeozoic, Mesozoic and Cenozoic sediments
(Sanz de Galdeano and Vera, 1992). There are no strict boundaries to the different complexes and in the field the different complexes are distinguished by lithological and metamorphic characteristics.
Vera Basin
Sorbas Sorbas Basin •
Carboneras Basin
1881 Nevado Filabride Complex Mediterranean Alpujarride Complex ~ Malaguide Complex Neogene basin fill Almerla D
Fig. 1.4 Schematic geological map of the study area and its adjacent basins showing the nappe units of the Betic Cordillera. Note that the third metamorphic basement complex (Malaguide complex) does not crop out in this area. Map modified after Platt et al. (2005).
1.4.1 Nevado-Fihibride Complex
The Nevado-Filabride Complex is the dominant Betic complex. Egeler (1963), introduced the term Nevado-Filabride Complex. The main exposure is 125 km long and up to 35 km wide, and makes up the bulk of the Sierra de Ios Filabres and Sierra
27 Nevada (Egeler, 1964). The highly deformed complex can also be found in the cores of the Sierra Alhamilla and Sierra Cabrera. The rocks consist of monotonous graphitic-bearing quartzite and mica-schists. A Precambrian-to-Palaeozoic age has been attributed to the lower black series (Gomez-Pugnaire et al., 2000). This series is locally overlain by a Perrno-Triassic sequence of metamorphosed feldspathic sandstones and carbonates, and an association ofmetabasic rocks (oflate Jurassic age) and serpentinite slivers, marble and calcareous mica schist (of Cretaceous age)
(Hodgson, 2002).
1.4.2 Alpujarride Complex
The Alpujamde Complex is partly composed of Palaeozoic rocks identical to those of the Nevado-Fihibride Complex, Permo-Triassic phyllite and quartzite (Gomez
Pugnaire et al., 2000) and a thick sequence of Middle to Late Triassic dolomitized platform carbonates (Hodgson, 2002). No post-Triassic rocks have been found. The majority of the Alpujamde Complex shows only lower greenschist facies metamorphism.
1.4.3 Malaguide Complex
The Malaguide Complex is most extensively exposed in the western Betic north of
Malaga. It is also exposed in a thin strip along the Internal/External zone boundary and only occurs as small outcrops at the base of Middle Miocene sedimentary successions in the Almeria area. The complex comprises a well differentiated sequence of Palaeozoic clastic and carbonate rocks, Perrno-Triassic red-beds and
28 dolostones, Middle to Late Triassic carbonate rocks and evaporites, Jurassic to
Cretaceous carbonate rocks and lower Tertiary shallow-marine limestones (Hodgson,
2002).
1.5 Regional Neogene Sedimentation
Section 1.5 describes the palaeoenvironment of the intermontane basins of the Internal part of the Belie Cordillera. These basins changed from marine to continental deposition typically during the Plio/Pieistocene (Sanz de Galdano and Vera, 1992).
The basin characters were influenced by sea-level variations during the Neogene with three major trangressive cycles of the following age (1) Serravallian - Tortonian, (2)
Messinian, and (3) Pliocene, with decreasing importance in this order (Weijermars et al., 1985).
The oldest sediments of the basins were deposited after a period of open marine deposition during the Burdigalian. Hemipelagic marls and turbidites, which indicate deep-water conditions, were deposited in an east-west trending seaway. This connection, which existed during the Middle and early to late Miocene (Huibregtse et al., 1998), was an open communication between the Mediterranean and the Atlantic
Ocean. With surface uplift oflarge parts of the Betic Cordilleras during the Tortonian, the relative sea level was progressively lowered and the strait became more restricted.
In the northern basins a transition from a marine to continental environment occurred towards the latest Tortonian-early Messinian (Sanz de Galdano and Vera, 1992) whereas the more eastern basins kept their marine character during most of the
29 Messinian. Earliest Messinian sedimentation started as a transgressive sequence of onlapping coastal and shallow marine sandstones and conglomerates, which lie unconformably on the Tortonian turbidites. With further deepening of the basins open marine pelagic marls were deposited in the centre of the basins. The maximum margins of the Messinian Sea were marked by large fringing reef complexes. With the closure of the Arc of Gibraltar, which has been attributed to tectonic uplift and eustatic sea-level fall (Weijermars, 1988), the Mediterranean Sea became more and more isolated. Hypersaline conditions were reached and are represented by the extensive gypsum deposits of the Messinian Salinity Crisis. In some areas the gypsum deposits are over I 00 m thick and intercalated with laminates of mud, mar! and limestone. During the desiccation of the Mediterranean Sea intra-Messinian erosion occurred in some parts of the basins, indicated by erosion surfaces and unconformities
(Riding et al., 1999). The Mediterranean Salinity Crisis was abruptly terminated by the subsequent Pliocene transgression. Saline water of the Atlantic Ocean entered into the Mediterranean, when local graben tectonics reopened the Strait of Gibraltar at 5
Ma BP (Weijermars, 1988b). By the end of the Messinian continued uplift had weakened the marine connection in the more continental basins. During the Middle
Pliocene an unconformity appeared in these basins corresponding to a new stage of tectonic deformation. The sediments of the continental basins are formed by marls and limestone in the centre of the basins, changing to alluvial deposits towards the borders
(Sanz de Galdano and Vera, 1992). In some areas white carbonate marker beds indicate the development of lacustrine conditions due to fluctuation of relative sea level during that period (Calvo et al., 1998). This stage is called the 'Lago Mare' complex and can be found within the majority of the sedimentary basins, e.g. Sorbas
Basin (Mather, 1991; Mather et al., 2001; Fortuin and Dabrio, 2005) and Carboneras
30 Basin (Aguirre and Sanchez-Almazo, 2004). The Pliocene sediments of the more peripheral basins are bioclastic calcarenites, marls, grayish limestone and fan delta deposits (Sanz de Galdano and Vera, 1992). In the Early Pleistocene a new tectonic event is recognized, implying the differentiation of areas with important subsidence or uplift (Sanz de Galdano and Vera, 1992). Continued uplift of the basins resulted in the definitive withdrawal of the sea. In the Late Pleistocene all basins had become continental. Differential uplift and deformation during that time stimulated a switch from net aggradation to net erosion.
1.6 The Carboneras Basin
1.6.1 Introduction
Section 1.6 gives a detailed description of the Carboneras Basin, its margins, the lithostratigraphic units and the tectonic implications of the basin fill. It will outline the geographic definition of the basin as used throughout this thesis.
i Deji11ition of the study area
Various names have been used to define the area between the Sierra A1hamilla and the
Mediterranean coastline south of the Sierra Cabrera mountain front (see Fig. 1.5: Map of the Carboneras-Nijar-Aimeria Basin). These are:
o Campo de Nijar I (Rondeel, 1965; Addicott et al., 1978)
o Nijar Basin (Dabrio, 1986-1987; van de Poel, 1994; Lu et al., 2002; Fortuin
and Krijgsman, 2003; Bassetti et al., 2006);
31 o Almeria-Nijar Basin (Aguirre and Sanchez-Almazo, 2004)
o Nijar-Carboneras Basin (Chapelle, 1988)
o Carboneras-Nijar Basin (van de Poel, 1992)
o Almeria-Carboneras Basin (Harvey et al., 1995)
o Carboneras Basin by (Mather, 1993b; Aguirre and Sanchez-Almazo, 1998;
Dillett et al., 2003; Braga et al., 2003a) whereas Braga et al. (2003a) only
defined the area around the village ofCarboneras as the Carboneras Basin.
As this thesis focuses on the fluvial evolution of the area the author will use the modem hydrologic basin (i.e. drainage basin) to delimit the margins of the
'Carboneras basin' rather than use the limits of the sedimentary infill (i.e. the
sedirtJentary basin). The name 'Carboneras Basin' will thus refer to the catchment
areas of the four major river systems. It has to be taken into account that the drainage area might change over time (e.g. due to river capture), as the basin becomes more tectonised.
ii Location of the study area
The Carboneras Basin (Fig.l.S) is one of a series of east-west orientated basins developed in the internal zone of the Betic Cordillera. The Carboneras Basin is bounded to the north and west by intensely tectonised, and mostly metamorphic, pre
Neogene rocks of the Sierra Cabrera and Alhamilla. These latter sierras separate the
Carboneras basin from the Sorbas Basin to the west and north. The southern margin is a poorly defined topographic high which separates the Carboneras Basin from the
Agua Amarga Basin in the South. Towards the East the basin is limited by the
Mediterranean Sea.
32 Vera Basin
Sorbas Sorbas Basin •
Mediterranean
Cerro Blanco-EI Barranquete Sub-Basin
Fig. 1.5 Schematic map illustrating the various basins and sub-basins around the study area. Throughout this study the Carboneras Basin is referred to as the area most clearly related to the modern Carboneras drainage.
1.6.2 Tectonics
The Carboneras Basin is characterized by two major fault systems: the Gafarillos- and
Carboneras Fault Systems (see Fig. 1.2: structural map of the region) . The E-W-
striking dextral Gafarillos Fault Zone (Stapel et al. , 1996) cross-cuts the basement of
the Sierra Cabrera and is finally cut off by the Carboneras Fault Zone towards the
east. The Carboneras Fault System (CFZ) is located on the SE side of the Carboneras
Basin and is formed by a network of individual faults up to several kilometres long.
The exposed portion of the CFZ has a total length of 40 km. The width varies between
I A and 2.5 km since the zone is divided into several individual strands. These strands run parallel to each other, sometimes two, sometime three or more. Towards the south of the Carbon eras Basin, in the Almeria Basin, the southern end of the fault system
(here called La Serrata Fault) exhibits a NE-SW (050°) trend. To the north of the town
33 of Carboneras the zone changes to a NNE-SSW (020°) trend. Further north it merges with the N-S- trending Palomares Fault which extends to the north into the Vera Basin
(Keller et al., 1995). This change in trend forms a restraining bend that has thrown up the Sierra Cabrera basement blocks (Keller et al., 1995). The Neogene sedimentation in the Carboneras Basin was strongly controlled by contemporaneous displacement along the Carboneras Fault System (Keller et al., 1995; Bell et al., 1997; Huibregtse et al., 1998).
1.6.3 Neogene Basin Fill
The stratigraphy of the Carboneras Basin is characterized by three major transgressive cycles (Weijermars et al., 1985): (i) Serravallian-Tortonian, (ii) Messinian and (iii)
Pliocene. i Serravallian-Tortonian deposits
The oldest sediments of the Carboneras Basin, south of the Sierra Cabrera, are late
Burdigalian to Tortonian in age, and crop out near the Serrata Fault Zone (van de
Poel, 1994). The succession unconformably overlies the metamorphic Alpujarride basement of the Sierra Cabrera. It comprises a conglomerate at the base and thin bedded marls and graded silt-sandstone turbidites with occasional interlayered conglomerates (Huibregtse et al., 1998). The well-bedded turbidites and deep marine marls containing detritus from the Sierra de Ios Filabres record the fact that the Sierra
Cabrera was not yet present as an uplifted area and that the coastline during this period was situated along the Sierra de Ios Filabres (Huibregtse et al., 1998).
Contemporaneous reef debris and Alpujarride detritus derived from the Sierra
Alhamilla show that the Sierra Alhamilla mountain range must have existed in the
34 fonn of an elevated land mass during that time (Weijennars et al., 1985). Turbiditic sandstones and conglomerates, supplied by a huge submarine fan system from the
Sierra de Ios Filabres (Weijennars, 1991), filled local depressions along the southern margin of the Sierra Alhamilla. The submarine fan indicates that the modem mountain range of the Sierra Alhamilla was only a shallow regional basement during the
Tortonian transgression (Huibregtse et al., 1998). Addicott et al. (1978) first identified deposits of Middle Miocene age in this area, adjacent to the Nijar-Lucainena road.
Although initially he assigned the sequence to the early Tortonian, using planktonic foraminifera, the following year Addicott et al. (1979) revised the age to Middle
Miocene. During the Tortonian period, the volcanic belt of the Cabo de Gata was fonned (Bousquet, 1979). Deep, subtropical, open oceanic conditions were predominant in the Carboneras and its adjacent basins at this time (van de Poel, 1994).
ii Messinian sequence
The Messinian rocks were deposited in one major sedimentary cycle. They have been subdivided into a lower Turre Fonnation, a middle Yesares Fonnation and an upper
Feos Fonnation, based on richness in marine fossils, bio-chemical precipitates and terrigenous debris (van de Poel, 1991; Fortuin and Krijgsman, 2003). The lower part of the Messinian sedimentation (Turre Fonnation) is a transgressive sequence of onlapping coastal and shallow marine sandstones and conglomerates (Azagador
Member) that unconfonnably overlies the Tortonian turbidites or directly overlies the metamorphic basement. With ongoing transgression a deepening of the basin occurred and open marine pelagic marls (Abad Member) were deposited. Messinian palaeogeography of the Almeria area was characterised by an archipelago whose islands correspond approximately to present day mountains. Many of these islands
35 were fringed by coral reefs in atoll-like patterns (Dabrio et al., 1981). Along the basin margin (Sierra Alhamilla) large barrier reefs (Cantera Member) developed, indicating the largest extent of the basin. The Late Miocene platform carbonates from Nijar
(Sierra Alhamilla) have also been extensively dolomitised, indicating that dolomitising fluids derived from the Carboneras Basin were involved in the dolomitisation, even if the Nijar platform carbonates do not contain evaporite facies
(Lu and Meyers, 1998). The lack of reef limestone deposits along the present day margin of the Sierra Cabrera establishes the absence of an uplifted basement block here (Huibregtse et al., 1998). On top of the reef deposits a mixed clastic-evaporitic series with oolitic limestone (Oolite Member of the Yesares Formation) is developed along the western basin margin (van de Poel, 1991 ).
With an increase in salinity and the closure of the Strait of Gibraltar, hypersaline conditions were reached and recorded by large gypsum deposits in the basin. These gypsum deposits form the middle and largest part of the Yesares Formation. The
Manco Limestone deposits, beds of unfossilferous, vuggy limestone or limestone breccia ('gypsum-ghost limestone' after van de Poel, 1991), are most common at the base or top of the Yesares Formation.
Van de Poel (1994) divided the last depositional sequence within the Messinian, the
Feos Formation, into a lower and an upper Sorbas Member, characterised by laminated pelite with calcarenitic intervals and limestone beds comparable to the
Sorbas Member of the Sorbas Basin and an overlying Zorreras Member indicating early continental and brackish conditions. The late Messinian brackish lacustrine
36 deposition was probably protected from the direct erosive influence of the
Mediterranean dessication due to the uplift of the Agua Amarga Basin and the
adjacent Castillico Ridge (van de Poel, 1994). Towards the SW of the basin there is no evidence of major barriers, but the wide shelf formed by the southern Nijar
Almeria Basin and the Gulf of Almeria may have inhibited erosive processes coming
from this direction. The overlying Zorreras Member, with its fluvial fan deposits,
green conglomerate and marls, shows influence of fresh-water supply to the most
central part of the basin, reflecting increasingly humid climatic conditions. The uplift
of the Sierra Cabrera basement indicates a tectonically active phase during the late
Messinian.
Fortuin and Krijgsman (2003) studied the evaporitic deposits of the northern part of the Carboneras Basin (which they call the Nijar Basin) in 2003 and their stratigraphic correlation was generally in line with that of van de Poel (1991). Fortuin and
Krijgsman (2003) only correlated the Upper Manco Limestone of the Gafares area
(northern part of the Carboneras Basin) with the Sorbas Member of the Sorbas Basin and the Feos Formation with the Zorreras Member of the Sorbas Basin.
Aguirre and Sanchez-Almazo (2004), on the other hand, presented a reinterpretation of the previously established stratigraphic framework of van de Poel (1992) and the palaeoenvironrnent condition for the post-evaporitic deposits of the Gafares area.
Aguirre and Sanchez-Almazo (2004) argued that the brackish conditions were also established at the basin margin. They characterized the continental post evaporitic sediments as fluvial channel filled conglomerates and alluvial plain sand.
37 The marine deposits were represented by silty marls and river-dominated fan delta conglomerates.
iii Pliocene marine sequence
The Neogene marine sedimentary filling of most of the littoral basins of the Betic
Cordillera is usually topped by a very characteristic Pliocene depositional marine unit.
This third and final lower to mid Pliocene marine transgression consists of yellow bioclastic calcarenites or greyish marls and siltstone, depending on the location within the basin (Sanz de Galdano and Vera, 1992; Bardaji et al., 1995). It is locally overlain by fan delta sediments, beach and shoreline deposits and then by terrestrial sediments
(alluvial fan deposits and river terraces). The subdivision of the Pliocene basin fill within the Carboneras basin is still controversial and will be described in detail in chapter 3.
1.7 The Terrace Sequence
1.7.1 Introduction
Evidence for consequent developed drainage systems, after the Pliocene marine stage, is represented by series of palaeo river terraces and strath terraces. They can be found all over the northern part of the Carboneras Basin, generally unconfoimably overlying shallow marine sediments or metamorphic basement rocks.
38 i strath a11d river terrace deji11itio11 In the lower reaches of the rivers evidence is predominantly from depositional records of river terrace fragments. Strath terraces and river terraces can be identified in the field by their flat surfaces, but strath terraces can be easily mistaken for bedding planes. The possibility that the surface is a bedding surface can be excluded if the surface cuts erosionally across geological structures and cannot be traced into an underlying surface within the geological record. Erosional widening of valley floors in bedrock occurs leaving a surface called strath (Bull, 1991 ). A strath is defined as the base of the former aggradational river terrace which has already been eroded away or (b) the base of a former floodplain where there has never been any deposition.
Strath formation is a continuous process of response to long-term uplift, and its occurrence varies spatially along a river depending on stream power, and hence position, upstream (Merritts et al., 1994). River terraces described in this study are defined as 'fill terraces', after Bull (1991), which means a terrace which was formed by valley aggradation and subsequent channel incision into the alluvium. River terrace deposits are generally unconsolidated in nature and therefore highly susceptible to erosion. Usually as rivers incised further into the valley bottom, terraces along their sides were gradually eroded away by hillslope processes (Burbank et al., 1996). The exact palaeo-height of the terrace top can hence be inaccurate due to previous erosion.
Terrace bases of the same heights can have a similarity of age over relatively large areas. Sudden changes in base level or climatic conditions reflect in the formation of paired terraces on both sides of the valley. Where the river has sufficient time to adjust to changes meandering often occurs and unpaired terraces are the result.
Terrace sequences, therefore, reflect both lateral migrations of the river channel and
39 also vertical displacements through a sequence of downcutting and aggradational phases.
1.7.2 The main river systems of the Carboneras Basin
The investigation of the terrace record reveals important information about the evolution of the consequent drainage systems in the Carboneras basin. The study of their fossil evidence has revealed three main drainage systems, located in the northern region of the Carboneras Basin: the Rio Gafares; the Rambla de los Feos and Rambla de Lucainena (Fig. 1.6). Parts of the consequent drainage systems originated in the adjacent Sorbas Basin, before becoming established within the Carboneras Basin itself (Mather, 1991 ). Their reconstruction is the main focus of this study and the terrace sequence is described and discussed in detail in Chapter 4.
Fig. 1.6 Drainage systems of the Carboneras Basin overlain onto a shaded relief map, derived from Espaiia ( 1992).
40 2 CHAPTER: GEOMORPHOLOGICALAND
SEDIMENTOLOGICAL FIELD TECHNIQUES
2.1 Introduction
In basin analysis studies, crucial infonnation can be attained from a combination of various types of field investigations. A large database of sedimentological and geomorphological results fonns the basis for this study. The approach used in this thesis is clarified and explained below.
2.2 Approach
The study adopts a mainly abductive approach, whereby initial investigative field work was undertaken without any prior theories in order to develop research hypotheses for later testing (Holt-Jensen, 1999). This was done using a critical rationalist approach during the main field work in an attempt to disprove the null hypotheses in accordance with the Popperian approach (Williams and May, 1996).
This style of research was adopted because it enabled hypotheses to be derived on the basis of empirical evidence, as opposed to potentially misleading, entirely abstracted theorising.
41 2.3 Field seasons and cartographic materials
Field investigations were carried out during seven field seasons between December
1998 and January 2003. Before each field season the area was studied in detail with respect to the ancient drainage system by using a range of topographic and geological maps (summarised below) as well as black and white stereo aerial photographs (scale
I :30,000) and satellite images. The grid references within the text and diagrams refer to the grid of the I :25,000 maps if not stated otherwise.
Topographic Maps a) Cartognifia Militar de Espafia I :25,000:
• Sheet: El Agua del Medio
• Sheet: Carboneras
• Sheet: Polopos
• Sheet: Campohermosa b )Cartognifia Militar de Espafia I :50,000:
• Sheet: Sorbas c) Ministerio de Fomento- Instito Geognifico National I :50,000:
• Sheet: Parque Natural Cabo de Gata-Nijar
Geological Maps
IGME- Instituto Geologico Minero de Espafia I :50,000:
• Sheet: Carboneras; Sorbas; Mojacar; Almeria
~2 Digital Maps
Mapa Militare Digital de Espaiia: 1:800,000; I :250,000; 1:50,000
Satellite images
Google Earth (Earth, 2005)
2.4 Sedimentary logging of geological sections
Detailed logging of sedimentary units was carried out on all well exposed outcrops.
Collected data from the vertical profiles were drawn up as graphic sedimentary logs
(Jones et al., 1999a). Photographs and field sketches were taken. Samples of marine and fluvial deposits were analysed using comparative procedures after Keller.hals and
Bray (1971). The Udden-Wentworth scale (after McManus, 1988) was applied (Fig.
2.1). Udden-Wentworth-Scale Inch mm Boulders
Cobbles
Gravel
Sand
Silt
Clay
Fig. 2.1 Udden-Wentworth scale used for grain-size determination of the obtained samples.
43 Facies classification and lithofacies codes refer to Miall (1996) and Graham (1988)
(Table 2.2). A standard key (Fig. 2.2) for lithological composition, sedimentary structures, bed thickness, textural characteristics and fossil content after (Nichols,
1999) was applied to the obtained data.
Code Lithofacies Sedimentary Structure
Gms matrix supported generally none, sometimes a gravel-boulder conglomerate weak clast imbrication and poorly sorted vertical orientation of clasts Gm clast supported weakly bedded I massive gravel-cobble conglomerate weak clast imbrication moderately-well sorted Gb clast supported horizontal bedding gravel-pebble conglomerate well imbricated well sorted Gl clast supported low angle cross-beds gravel-pebble conglomerate imbricated well sorted Gt clast supported trough cross-beds gravel conglomerate well sorted Gp clast supported planar cross-beds gravel conglomerate well sorted Sm sand massive fine-coarse moderate-well sorted Sh sand horizontal lamination fine-coarse moderate-well sorted Fm silt-mud massive
Table 2.1 Lithofacies scheme, textural characteristics and main sedimentary characteristics referred to within the text and figures, adapted from (Miall, 1978; Mather, 1991 ).
44 Symbols used on graphic sedimentary logs Uthologlcsl Composition Sedimentary StrucUu
Claystone Through cross ~ bedding Slltstone Planar cross 1~ I bedding
• Sandstone fine Horizontal ~ lamination • Sandstone medium water escape 00 structure Sandstone coarse [i§J Bloturbatlon
Sandstone pebbly [EJ Plant material Conglomerate clast supported ' ~ Vertebrlies Conglomerate Roots matrix supported I ~ • Limestone []!] Colonial corals Gypsum [[] Solitary coral
VolcSllc rock Bed boundaries: sharp gradational C.-bonate nod~es ~ - - -- (pedogenlc) ""- ...... --- erosional Palaeocurrent Strong carbonate direction cement
Fig. 2.2 Sedimentary features noted in the field and used in graphic sedimentary logs within this thesis, modified from Nichols ( 1999).
45 2.5 Analysis of River Terraces
The palaeochannel evolution was deduced from the distribution of different river terraces. Sedimentological and geomorphological analysis of river terrace deposits were carried out and the technique is outlined below.
2.5.1 Mapping of the terrace deposits
Within the study area all river terraces were mapped and classified as far as possible on the basis of visual continuity. Heights were surveyed from the base of the modem stream to the base of the terraces (in order to minimise the error caused by erosion of the terrace top). Where possible the constituents terrace sediments were examined and described and samples were taken, using standard procedures,e.g. (Jones et al.,
1999a). Based on their lithological differences and the heights of their bases each individual terrace was grouped into a terrace level. For each terrace level one type section was identified sensu the North American Stratigraphic Code (1983). Regional validity is demonstrated by the presentation of numerous additional sections along the river, in order to rule out a single localised event, e.g. landslide. The characteristics of each terrace level was then used to describe the sedimentary processes and the palaeoenvironment during each phase of aggradation. Combining these data on each terrace level enabled the development of the individual river to be reconstructed.
The latter approach, adopted principally by geologists for geologic sections is here used to create more scientific rigour in the definition and useage of geomorphologic criteria (river terraces). The main characteristics of each terrace level was then
46 analysed and the sedimentary processes and the palaeoenvironment during the time of deposition was defined.
i Maximum clast size River bed particle size may vary along the direction of stream flow (longitudinally), between the stream banks (cross sectionally) and vertically within the beds. The 10 largest particles within one section of a terrace were measured along their long axis
(a-axis), in order to get an idea about the flow competence during clast deposition.
The range between the smallest and largest sample was recorded and mean and standard deviation were calculated. Unfortunately the distance between the individual terrace remnants was usually quite large (a few hundred metres - up to a kilometre), so the clasts size measurements were used to support general statements (such as whether the analyzed terrace deposits belong to the same terrace level, etc.). The investigation of downstream trends in the clast size distribution was therefore rather limited. A direct comparison of clast-size distribution between terraces of this study and other previously published work on terraces of other researches has not been undertaken, because of the subjectivity of the researcher during sampling (i.e. operator-induced variability, (see Wohl et al., 1996)).
ii Palaeojlow direction The palaeoflow of the Pleistocene rivers was defined by analysing the bedding structures of the fluvial deposits (e.g. cross bedding) and by measuring the alignment of imbricated clasts. Palaeocurrent measurements were taken from the imbricated bedload fraction (>4cm). In order to determine the palaeoflow direction clasts exceeding 4 cm in size were chosen since they provide a more accurate picture of
47 channel direction, developing at higher flow stages when the whole channel is utilized
by the flow. At each sampling site an average of25 imbricated clasts were chosen and
their orientation was measured in order to provide statistically significant data (Miall,
1990). The obtained palaeocurrent data were plotted onto a Rose diagram or presented
onto individual maps, where the palaeoflow direction was indicated by arrows. The
author notes here that for most of the outcrops the palaeocurrent measurements
methodology was not sufficiently accurate. The measuring procedures were tested in
the field and showed clearly that only on large and very well preserved outcrops
where the clast imbrication was obvious could exact palaeocurrent directions be
obtained. The author only obtained palaeoflow data from sections where the flow
direction was clear.
iii C/ast Provenance
The analysis of clast provenance is a very useful tool for identification towards
sediments sources, transfer and storage (Collins et al., 1998) and the reconstruction of
the drainage history of the basin. Provenance analysis of sediments is aimed at
identifying the parent-rock assemblage of sediments (Weltje and H., 2004). The
sediments can reveal important information about change in source area, deformation
of the hinterland, river incision and basin subsidence. Provenance analysis is most
effective in basins with variable basement/hinterland lithologies where the source area
can be effectively identified. The basement lithology within the northern part of the
Carboneras basement consists mainly of the Alpujarride Complex (Metacarbonates)
and varies from the Sorbas Basin, whose northern margin is characterised by the
Nevado-Filabride Complex (amphibole-mica-schist as the main characteristic provenance). A change in provenance is therefore a very effective evidence for
48 expanding or contracting source areas. During this study the author: (I) identified the
types of sedimentary material and their provenance and (2) assigned the population of clasts to specific assemblages of source rock.
Clast assemblages were obtained from the conglomeratic units of the terrace remnants. The assemblages were derived by identifying the lithology of the clasts.
Bridgland, (1986) recommended to select 250 clasts for each outcrop. Hovewer the
strongly cemented nature of terrace conglomerates of this study only allowed a total of 100 clasts, following the recommendations of Mather, (1991) and Stokes, (1997).
Clasts longer than 2 cm in long axis length were selected and determined from a I m2
section (Mather, 1991; Harvey et al., 1995; Stokes and Mather, 2000). Clasts less than
2 cm were not readily identifiable in the field (Mather, 1991 ). Data are displayed in pie charts. Pie charts have been used previously to compare lithological variations e.g., (Mather, 1991; Stokes, 1997; Jones, 2000) and were similarly used in this study.
The provenance of the source rock was compared to the metamorphic Betic nappe units of the Sierra Cabrera and the surrounding area (Rondeel, 1965). The correlation is shown (Table 2.2).
Problems occur when the analyzed clasts are not freshly eroded from the basement, but are reworked from older, underlying sediments. During this study the amphibole mica-schist is the main indicator that the provenance source of these clasts, the
Nevado-Filabride Complex, was derived from the Sorbas Basin. However, amphibole-mica-schist is also a common clast within the Neogene Azagador conglomerate, which is abundant in the Sierra Cabrera. Hence the amphibole-mica schist could have easily been reworked from the Neogene sediments. Detailed
49 investigations have shown that this is not the case (this will be fully explained in
Chapter 4).
iv Statistical analysis
Statistical tests used are described by (Sokal and Rohlf, 1981; Zar, 1996). Statistical analysis has been used to analyse significant variations in the provenance distribution:
The frequency of counts for a marker provenance type (Nevado Filabride component) was compared with the equal distribution expectation by means of the Chi-square test.
The following formula was applied:
2 2 k (fi- fl) X =L A i=l fi
after Zar (1996).
Here, fi is number clasts counted in class i (i.e. provenance type), ]i is the frequency expected in class i if the null hypothesis of equal distribution and the summation is performed over all k categories of data (k = 5). Comparing the results with an expected ratio, the data were analysed to determine whether the magnitude of an overall observed deviation is of statistical significance. Each terrace level was analysed separately. The null hypothesis of equal distribution was applied. The 95% confidence level was employed in determining whether or not a deviation was significant.
Analysis of variance (ANOV A) was used to test for variations in maximum clast size of fan delta sediments between different sample locations of the same depositional unit. Differences at P < 0.05 were considered significant throughout these experiments.
50 Nappe Units (source area) (Rondeel) Lithology found in the terrace deposits (this study) I. ALPUJARRIDE
a) Mica schist sequences • dark grey-brownish colour Schist • garnet bearing in graphitiferous rocks Garnet-Mica-Schist
b) Phyllite - Quartzite sequence • multicoloured phyllits white, red Metacarbonate • yellow, white, violet, pink quartzites
c) Limestone -Dolomite sequences • grey-blue dolomites grey Metacarbonate • yellow-brown dolomites • grey-black limestones black Metacarbonate • yellow marly limestone
II. MALAGUIDE
a) Schists b) Phyllites c) Pe/ites d) Greywackes e) Sandstone f) Conglomerates g) Carbonates
Ill. NEVADO-FILABRIDE
a) Amphibole-Mica-Schist Amphibole-Mica-Schist b) Me/a-Carbonate c) Chlorite Mica-Schist d) Amphibolite e) Tourmaline gneisses f) Garnet-Mica-Schist Garnet-Mica-Schist g) Quartzite Quartz h) Graphite-Schist Schist
IV. NEOGENE INFILL
a) Azagador (Tortonian) Conglomerate/Sandstone b) Reef (Messinian) Reef debris c) Marts (Messinian) Marls, Sandstone
Table 2.2 Provenance descnpt1on compared w1th Rondeels (1965) mapped umts.
51 2.5.2 Dating of the river terraces
Dating of river terraces is often difficult due to a lack of datable material or the
landforms being beyond the maximum age limit of most suitable dating techniques
(Stokes and Mather, 2003). Terraces are therefore correlated and assigned to a relative
stratigraphic framework on the basis of heights, provenance assemblage, calcrete
stage and the degree of soil development. Previous work by Harvey and Wells,
(1987); Mather, ( 1993b ); Harvey et al. ( 1995) and Stokes (1997) has shown that that
soil and calcrete development can be used to correlate fluvial terraces. The analyzed terrace levels of this study have been compared to previous work and dated terraces in
the adjacent Sorbas Basin (Harvey and Wells, 1987; Mather, 1993b; Harvey et al.,
1995; Kelly et al., 2000, Candy et al., 2005 and Maher, 2006b ).
i Soil profiles I Pedogenic classification
Particularly when the parent material is gravel, soil development generally starts at the time of deposition without much inheritance from previous soils. Soils on river terraces have a high potential as relative age indicators (Harvey et al., 1995). Where soils occur, the terrace soil profiles were described by their colours using the nomenclature from Munsell Soil Colour Chart (Hue/Co1our/Chroma).
ii Calcrete stage I Pedogenic classification
The majority of terraces within the study area are capped by a pedogenic calcrete crust. At each site, calcrete profiles were recorded and analyzed. The calcrete classification after Machette (1985), modified by Gile et al. (I 966), was used to identify the stage of the calcrete horizon and to predict a relative age for the river
52 terrace since abandonment. Although pedogenic development varies locally and with source area geology and may not be sensitive indicator of surface age, some age differentiation is possible (Harvey, 1984). Three degrees of crust development can be recognized and ascribed to approximate age ranges (Harvey, I990):
I. The youngest indurated crusts show only intergranular cementation,
incomplete development and very limited, discontinuous, laminar calcrete layers
(Harvey, I990). .These are described as weak crust and assigned by Dumas
(I969) to a Wiirmian age (70 ka for laminar calcrete in the Sorbas Basin (Candy
et al., 2005). In the Mediterranean region, rates of calcrete development appear
to be very rapid, indicating that" immature stage II calcrete could form within
I 000 years (Candy et al., 2005).
2. Mature crusts show complete cementation of a massive petrocalcic horizon of
up to about 50 cm thickness, secondary brecciation and recementation, and
discontinuous, laminar calcrete several millimetres in thickness (Harvey, I990).
Mature crusts suggest formation over a considerable period of surface stability,
under climate with sufficient moisture to allow mobility of CaC03 but with at
least a seasonal soil moisture deficit to allow surface or near surface carbonate
precipitation (Harvey, I984). They have been assigned by (Dumas, 1969) to Mid
Pleistocene ages; stage III-IV.
3. Ancient crust with massive petrocalcic horizons of I m or more in thickness
and laminar calcretes several centimentres thick are confined to Early Quaternary
surfaces (Harvey, 1990); stage IV and greater.
53 2.5.3 Terrace height diagram
The terraces were mapped onto a I :25.000 topography map. Where there was a modem river nearby, the heights of the terrace base above the modem stream bed were plotted onto a longitudinal profile of the river channel. In areas where the modem river bed is situated away from the ancient river terraces (e.g. at the Gafares
River) the best fit line (mid-section line) was drawn through the terraces.
If time since abandonment can be estimated and the heights of the terrace above the valley bottom are known, a minimum mean rate of river incision can be calculated
(Jones et al., 1999b) using long river profiles.
2.5.4 River channel cross profiles
Valley cross profiles were recorded mainly in areas where strath terraces (erosional record) were found, in order to identify the morphological surfaces precisely and to semi-quantify the general incision of the river. To obtain a greater accuracy I: I 0,000 topographic maps were used.
54 3 CHAPTER: FINAL MARINE BASIN INFILL
3.1 Introduction
The final marine stage of the Carboneras Basin corresponds in age with the Pliocene.
Chapter 3 aims to trace the transition from marine to continental sedimentation within the Carboneras Basin. The final marine phases are examined in order to allow a reconstruction of the palaeo processes and further to establish the palaeorelief of the basin onto which the fluvial systems (discussed in chapter 4) were developed.
Section 3.2 outlines the characters of adjacent sedimentary basins during the Pliocene with special attention drawn to the Sorbas and Vera Basins. Section 3.3 focuses on the
Pliocene deposits of the Carboneras Basin. Sedimentary successions are considered in ascending stratigraphical order. Lithostratigraphy is used to define the sedimentary successions. The base and top of each Iithostratigraphic unit is defined and the contact with the underlying and overlying deposits is described. By means of key locations and following the stratigrapgic guidance of the North American Stratigraphic Code
(1983), the characteristics and variations within the various stratigraphic units are illustrated. Interpretation of the facies units is used to reconstruct the processes operative at the time of deposition, and collectively these data will facilitate reconstruction of the palaeoenvironments. In the context of their spatial distribution these findings are then used to reconstruct the palaeogeography of the Carboneras basin.
55 3.2 The adjacent basins
As mentioned in Chapter I, (Section 1.5 Regional Neogene Sedimentation) the eastern-most basins of the Betic Cordillera were desiccated during the End of the
Messinian, due to a restriction of the Mediterranean-Atlantic gateway. The Sorbas and Nijar basins formed isolated or semi-enclosed basins (Fortuin and Krijgsman,
2003). After the Messinian salinity crisis marine conditions were re-established by the last marine transgression within the basins situated marginal to the modem
Mediterranean, such as the Carboneras, Vera, Agua Amarga and the Almeria-Nijar
Basins (Fortuin et al., 1995). Pierre et al. (2006) confirms that the inflow of marine waters occurred contemporaneously within the whole Mediterranean at the base of the
Pliocene. The Pliocene sediments of these basins are usually separated by an unconformity from the underlying Messinian sediments. The deposits generally form very characteristic strata in the marginal basins. Bioclastic calcarenites, marls and greyish limestones form the lower part of the Pliocene sediments (Bardaji et al.,
1995). These are topped by beach and large fan delta deposits (Sanz de Galdeano and
Vera, 1992). In the Vera Basin the lower Pliocene stratigraphic unit (Cuevas
Formation) is characterized by pelites and (marginally) fossil-rich conglomerates of marine origin, characteristic of shallow marine conditions (YOlk and Rondeel, 1964).
To date the most detailed sedimentary work on the Cuevas Fm was carried out by
Stokes (1997), who divided the shallow marine deposits into basinal and marginal units for the Vera Basin. Strontium isotope dating of foraminifera suggests an age of
5.1 ± 0.4 Ma for the lower Pliocene marls of the Vera Basin (Fortuin et al., 1995).
The subsequent sea-level regression is documented by coastal plain deposits (Espiritu
Santo Formation) in many basins during the Upper Pliocene (Wenzens and Wenzens,
1997). In the Vera Basin the Espiritu Santo Formation is described as a fan delta
56 sequence represented by conglomerates with foreset bedding, grading laterally basinwards into sandstone and pelite (deltaic deposits) (Volk, 1967). Electron Spin
Resonance dating (ESR) of the underlying deposits at the bottom of the fan delta in the Vera Basin suggests an age of over 2.358 Ma (Wenzens, 1992b).
Sedimentary basins situated further inland, such as the Sorbas Basin, did not re establish marine character. They switched from marine to continental conditions during the Late Messinian I Early Pliocene (Mather, 1991 ). The Pliocene deposits in these basins are characterized by marls, limestone and !ignites in the lacustrine areas of the centre of these basins, changing to alluvial deposits towards the borders (Sanz de Galdeano and Vera, 1992).
Precise stratigraphic correlations between individual basins are very difficult to establish. Spatially rapidly varying sedimentology and lithostratigraphy together with a lack of exact dates only allows for a very general correlation. Comparing the literature, Neogene deposits are named differently within and between individual basins. Most ofthe nomenclature is based on work done by Volk and Rondeel (1964).
A summary of the Neogene stratigraphic framework for the Nijar-Carboneras region is shown in Fig. 3.1.
57 A 8 c Nijar Basin Gafares area Age Carboneras-Nijar Basin (m. years) Haq et al. 1987 margin centre Basin centre 1.65 Molata Form. 0 :J Cuevas Form. Pliocene D. Cuevas Form. 5.2 g e... Zorreras 0 0 Member Zorreras Member "- Post-evaporitic unit u.. ..0 en "-• 0 Sorbas Q) u.. Member e (Sorbas- (Zorreras- z ... Like sed.) like sed) ...E u..0 < 0 Agua Cl) Ul u.. Amarga Q) 00 z Oolite ... Ul Breccia Gypsum ea Evaporitic unit (IJ f Member Cl) ea Member Q) tiJ Ul > (Yesares Member) w ~ -c: Ma-neo -est------::i e... upper 0 LL Abad Mart Cantera A bad E CS) ...... Member 0 Pre-evaporitic unit .. lower Member LL 6.3 upper ~ CS) upper A bad ...,: ... AzagadorSandSone ... Member Q: lower ::::J lower Azagador 0 Azagador ...... Member Member 3.3 Stratigraphy of the Carboneras Basin
The area between the towns of Almeria and Carboneras has been subject to numerous studies. Many researchers concentrated on the deposits of the Messinian salinity crisis (Dabrio et al., 1981; Franseen and Mankiewicz, 1991; van de Poel, 1991, Martin and Braga, 1993; Lu and Meyers, 1998) and the post-evaporitic deposits (Aguirre and
Sanchez-Almazo, 2004). Only a few workers focused on Pliocene processes
(Boorsma, 1992; Aguirre, 1998a, 1998b; Braga et al., 2001; Martin et al., 2004).
Most of this research has been carried out towards the South of the basin in the
Almeria, Serrata or Agua Amarga area (Martin et al., 2003) (Fig. 1.5). The Pliocene deposits and their topography have an important influence on any consequent fluvial drainage. This chapter therefore describes and analyses the Pliocene marine deposits of the northern margin of the Carbon eras Basin, which had been previously described by Dabrio ( 1986-1987); Mather, (1993b ); Aguirre et al. (1996) and Martin et al.
(2004)
Within the Carboneras Basin the deposits of the globally recognised third and final marine transgression during the lower to mid Pliocene (Haq et al., 1987) unconformably overlieMessinian sediments (Aguirre, 1998b). Those Pliocene shallow marine deposits consist of either yellow bioclastic calcarenites or greyish marts and siltstone, depending on the location within the basin. They are locally covered by fan delta sediments or beach and shoreline deposits which are themselves overlain by terrestrial sediments or fluvial river terraces. The nomenclature of the final subdivision of the Plio I Pleistocene basin fill within the Carboneras Basin is not standardised (see Fig. 3.2). In order to enable the reader to correlate the findings of
59 thls PhD with other literature, a brief summary of the previous work on Pliocene deposits withln the study area is given below:
In Addicott et al. (1978) Pliocene deposits of the Campo de Nijar (Fig.1.5) were divided into two units: an underlying Cuevas Viejas Formation and the Morales
Formation. The Cuevas Viejas Fm consists of yellow-grey, very fine micaceous, calcareous sandstones or siltstones with few interbeds of coarse-grained sandstones.
The younger Morales Fm, which is partly intercalated with the Cuevas Viejas Fm, but generally overlies the Cuevas Viejas Fm deposits, consists of coarse grained sandstone and pebble to cobble conglomerates. In the southern part of the basin the
Morales Fm consists of cobble and pebble conglomerate composed of well-rounded quartz and interbedded well-sorted coarse grained quartzose sandstones with thlck (up to 2 m thick) beds of giant oysters (Addicott et al., 1978).
Van de Poel et al., (1984) divided the Pliocene deposits of the Campo de Nijar into an underlying Molata Fm, consisting of three depositional units: a) yellow-white calcarenites; b) limestone with remains of pecten and ostrea; and c) conglomerates
(Fig. 3.2). The Molata Fm is overlain by the Campo de Nijar Fm, a unit of silt deposits with a red coloration.
Dabrio (1986-1987) described the shallow marine Pliocene deposits for the Alias area as laid down by prograding shallow shelf-talus and fan delta systems. He focused on the lower calcarenites which show large scale sets of cross-bedding and intense burrowing of some of the foresets, indicating wind-driven currents induced by storms
60 between two emerged islands. He did not assign the deposits to individual members or formations.
Mather (1991) described the Pliocene sequence within the northern part of the
Carboneras Basin as Polopos Formation, a conglomeratic unit overlying the Cuevas
Viejas Formation (Fig.3.2). The Cuevas Viejas Fm is described as thoroughly bioturbated, yellow to green sands, silts and muds. The Polopos Formation is subdivided into three units: a lower conglomeratic unit, a dividing sandstone horizon
(lbaiiez sandstone unit) and an upper conglomeratic unit (Mather and Westhead,
1993a), the latter one being deposited during the Pleistocene.
Boorsma (1992) defined three stratigraphic subdivisions in the Cerro Blanco I El
Barranquete subbasin in the La Serrata area (Fig. 1.2) (Almeria-Nijar Basin of this study - see chapter 1 for detailed description). Unit 1 represents Early and Middle
Pliocene calcareous marine sediments. On top of the yellow calcarenites Middle
Pliocene to Pleistocene fan delta and gravely beach deposits can be found. Unit 3 is made up of fluviatile sediments which were deposited during the Quaternary (Fig.
3.2).
Keller et al. (1995) divided the Pliocene deposits in the upper Carboneras Basin near
El Llano de Don Antonio into four different units: (1) A lower Pliocene debris flow
(thickness 13-32 m) which consist of clasts of limestone and grey marls within a cream matrix of fme- to medium-grained calcareous sandstone. This is overlain by (2) an upper Pliocene sandy limestone (- 88m) with coarse-granule-grade quartz clasts and meter-scale cross bedding. The top of the Pliocene sequence (3) is composed of
61 calcareous sandstone (> 58m) with large scale cross stratification. The overlying (4)
Plio/Pleistocene conglomerates (> lOOm) are matrix supported conglomerates with granule-pebble grade quartz, schist and grey limestone clasts in a calcareous sandstone matrix.
Aguirre ( 1998b ), in contrast, used a taphonomical approach to divide the Pliocene infill of the northern part of the Carboneras Basin. His results distinguish between
Pliocene I (early Pliocene to lowermost late Pliocene) and Pliocene II (late Pliocene) units. The Pliocene I (marine bioclastic sandstone) and Pliocene II (conglomerates and sandstone) deposits are described as two unconformable overlying units. The lower unit (Pliocene I) shows a shallowing upwards trend from outer platform facies
(Early Pliocene in age) deposited below the storm base to inner shelf facies affected by waves (lowermost part of the Late Pliocene). Pliocene 11 is a deepening-shallowing upwards sequence deposited in a fan delta and Late Pliocene in age (Aguirre and
Sanchez-Almazo, 1998).
62 Mather, 1991 This study, 2004 Van de Poel, 1984 Boorsma, 1992 Carboneras Basin Carboneras Basin Campo de Nijar Almeria-Nijar Basin centre marain . E Unit ill Continental deposits 1.1.. fluvial conglomerates .... fluvlatile sediments ~ ? z . ------······· Cll .. "C . conglomerates and red silts .. E c.0 .. LL lbanez sandstone unit .. E . Unitll IV . (/) . 0 red sandstone (,) .. a. ------fan delta and 0 ? calcareous fossil rich gravely beach deposits 0 Lower conglomerate unit c conglomerates and sands 0.. 0 ------fan delta deposits conglomerates :;::; ·. CO coarse grained bioclastic ··· .... E limestones with ..... algal remains and shells of E E 0 LL LL LL Pectinidae and Ostrea (/) CO ...... CO ------"Q) CO Unit I bioturbated, 0 > yellow to green sands, calcareous marine sediments (/) silts and muds ~ CO yellow-white bioclastic > calcarenites Q) ::J () marts . During this study detailed field investigations of the northern part of the Carboneras
Basin have established a clear division into two major sequences which are described and discussed in the following section (Fig. 3.2).
The marine deposits of the study area have been divided into two formations which are separated by an unconformity. They are called the Cuevas Fm and the Polopos
Fm, after Mather ( 1991 ). These general units were divided, based on their lithofacies, into subunits. The Cuevas Fm was subdivided into a lower and upper Cuevas Fm. The
Polopos Fm consists of four subunits: a) shore face deposits; b) fan delta sediments; c) beach material and d) coastal plain deposits. These sediments have been mapped, described and analysed in the field. These data will be discussed in the following section.
3.4 Cuevas Formation
With the ongoing Pliocene transgression after the Messinian salinity crisis, marine conditions were re-established within the Carboneras basin. Harvey and Wells (1987) established a marine continuity across the modem mountain range (Sierra Cabrera,
Sierra Alhamilla) at the northern basin margin into the adjacent Sorbas Basin. Deep marine sediments were deposited along the northern basin margin, when the sea level reached its Pliocene maximum. Three marine units have been mapped and described in the following sections. Regarding their stratigraphical location and their lithological composition they have been identified as units of the Cuevas Fm.
64 3.4.1 Lower Unit i Facies description The lower part of the marine deposits forms a very distinct unit within the field due to its light colouration and very fine texture. The sediment is composed of very fine grained, calcareous siltstone and marls. The colouration is light yellow to greyish (Fig
3.3). The deposits show a massive homogeneous structure, with no sedimentary features. The fossil content of these deposits consists of very small shell fragments, which due to their poor preservation and strong cementation within the marls could not be analysed any further.
The marly deposits of the lower part of the Cuevas Fm can be found mainly along the modem drainage of the Rio Alias. Where the river incised deeply enough into the underlying sediments, while-yellow marls can be observed in the cliff adjacent to the river valley. A good location to study the marine deposits is north of the Alias channel
(Fig. 3.3) at GR. 928954. At this cliff section the Neogene deposits are slightly tilted towards the east and the lower Cuevas deposits therefore form heights of up to 20m.
The marls show a more silty lithology and are therefore part of a transition between the lower marls and the overlying calcarenites of the upper Cuevas Fm.
ii Reconstruction of the palaeoenvironment
The fine, massive marls were probably deposited in relatively deep water, interpreted here as an inner basin environment. The fine grain size suggests a low energy of deposition and the homogenous structure suggests burrowing of the mud-siltstone deposits. These data therefore suggest a basinal part of the Pliocene marine sequence.
65 The described deposits seem to be coeval with the basinal facies part of the Cuevas
Vijas Fm of the Vera Basin described by Stokes (1997).
3.4.2 Upper Unit i Facies description The deposits of the lower marine unit are generally overlain by yellow coarse sand
(bioclastic calcarenites) (Fig. 3.4). In contrast to the underlying sediments, sedimentological structures are very common within these deposits. The calcarenites show planar cross bedding with beds of up to I m thickness. The deposits contain large fragments of oyster shells, scallops, echinoid spines and coralline algae. Fig. 3.5 shows the Cuevas Fm and its overlying sediments.
The calcarenites of the Cuevas Fm are the volumetrically most abundant facies in the
Neogene complex within the study area. The best exposures can be found all along the northern margin of the Carboneras Basin south of the mountain front. Numerous caves (cuevas) have been eroded into these deposits. Two key localities along the
River Alias (close to Cortijo el Molino de Abajo GR. 946 899 and north of Cortijada
La Arboleda del Arco, GR. 955 935) show the cross-bedded sandstone (Fig. 3.4).
These deposits form steep cliffs along the minor and major drainage lines of the river.
66 ...... ·...... ··. ······.. ..auiiise;;; .. .
.-z
Fig. 3.3 Lower and Upper Cuevas Viejas deposits. A: Location map of a well preserved outcrop of the lower and upper Cuevas Formation. The x indicates the outcrop location. 8: Cuevas Fm. Note the white marls (lower unit) and the overlying calcarenite (upper unit) deposits. C: Silty mudstone with fragment of marine fauna of the lower Cuevas Fm. The camera lens cap is 6 cm in diameter. The arrows indicate shell fragments.
67 ···:. <( au, ·1;s··* e~····
Fig. 3.4 Sequence of the upper part of the Cuevas Fm. A: Simplified map showing the outcrop locations. 8: Cuevas calcarenites with low angle planar cross-bedding structures (GR. 933954). Note the underlying white marls of the Cuevas Formation and the overlying beach conglomerates. C: River cut section incised deep into the shallow marine deposits of the upper Cuevas Fm (GR. 904946). Note the cross stratification of the calcarenites. The couple of metres deep gorge starts at a knickpoint and runs up to the bridge across to the village of El Argamason.
68 B beach deposits
marls
Fig. 3.5 Overview of the lower and upper Cuevas Formation and the overlying sediments (GR.927954). The location is the same as the one described for the lower Cuevas Fm. - please refer to map in Fig. 3.3. A and 8: Cuevas Fm with overlying Polopos Fm. beach deposits and Quaternary river terrace remnants on top. Deposits dip towards the ESE (except for the fluvial terrace).
69 ii Reconstruction of the palaeoenvironment Sedimentological characteristics and the palaeontology of these deposits are typical of shallow marine deposits. No beach indicators are found, which excludes their possible interpretation as shoreline prisms. Large cross beds indicate turbulence and a high energy environment. According to Dabrio (1986 - 1987) the cross beds near Cortijo el
Molino de Abajo (GR. 946 899) were formed by wind-driven currents, induced by storms through a narrow, shallow passage between two emerging islands. The shallow marine deposits point towards a sea-level regression during the lower Pliocene with a transition from an open marine to a shallow marine environment. The area was probably broken up by islands composed of uplifted metamorphic basement material and volcanic ridges. The shallow marine conditions were first established at the northern margin of the Carboneras · Basin and moved south with the ongoing withdrawal of the Mediterranean Sea. Roveri and Taviani (2003) used the palaeobiological content of similar calcarenites in the Apennine basin to suggest deposition on the middle to outer continental shelf at water depths not deeper than lOOm.
A shallow marine environment can therefore be assumed for the calcarenites. These deposits seem to be coeval with the outer shelf deposits of the Cuevas Fm of the Vera
Basin described by Stokes (1997). They also correspond to van de Poel 's (1984) unit a of the Molata Fm; Boorsma's unit 1 (1992) and Aguirre's unit I (1998b) The palaeontological composition has been described and analysed in detail by Aguirre,
(1998a, 1998b ).
70 3.4.3 Shoreface deposits i Facies description
The conglomeratic lithofacies (Fig. 3.6) crops out at three locations within the basin:
(a) northeast of the village of El Argamason (GR. 916955); (b) south of El Castillico
(938923) and (c) north ofCortijo del Medico (GR. 935923).
A 2 to 3 m thick, clast-supported pebble conglomeratic section with moderately to well sorted clasts is preserved near the village of El Argamason. The clasts measure an average size of 3.5 cm for the largest clasts (along the long-axis). The provenance typically consists of 85% rounded to well rounded quartz with fragmented to whole shells dominated by oysters (Ostrea sp.) and scallops (Pecten sp.). The number of identifiable species is low. A distinct feature is the abundance of macrofossils. North ofCortijo del Medico (GR. 935923) large numbers ofbarnacles (Balanus sp.) up to 5 cm in length, are often attached to the clasts and preserved in an upright position.
They occur as dense clusters of individuals growing on top of each other. The oysters are accumulated in horizontal beds and the shells are oriented parallel to the bedding.
The ostrea-balanid beds vary in thickness with beds up to 50 cm. Occasionally whole shells of oysters, pecten, and barnacles occur within the conglomerates. Here the oyster shells are less disarticulated. The maximum clast size is larger at the two latter locations, south of the El Castillico ridge (shown in the table 3.1 below).
71 Length (a-axis) L (cm) location n=IO
mean +- SD range
N of Cortijo del Medico (938923) 4.5 ± 1.27 3-7
S of El Cast!Uico (GR. 935923). 5.63 ± 1.63 4-9
Table 3.1 The mean and standard deviation of the largest clasts within the conglomerates at the two locations south of El Castillico (GR. 938923) and (GR. 935923). ii Reconstruction ofthe palaeoenvironment The well rounded, well sorted pebble conglomerates are interpreted as shallow marine shoreface and swash zone deposits. The larger clast size within locations (b and c) point towards a high energy environment of deposition. The ostrea-balanid beds at section (GR. 935923) clearly show taphonomic signatures indicating rapid burial events with low reworking and transport (Aguirre and Jimenez, 1997). The rapid burial is indicative of a high sedimentation rate. This is related, in turn, to the rapid progradation of the El Argamason fan-delta system from the north. The occurrence of whole shells of oysters also supports the theory of a short distance of transport and low reworking. The presence of thick-shelled shallow marine fossils including Ostrea and Balanus indicates an upper shoreface environment (Bourgeois and Leithold,
1984). The occurrence of Balanus in life position further supports this idea (Le Roux et al., 2006). The sediments equivalent to the one described above crop out north of
Carboneras at Algarrobico beach (Aguirre, 1995). The age attribution of the sediments is based on regional correlations done by Aguirre (pers. Comm., 2002). The presence of Globorotalia margaritae together with G. puncticulata allow these deposits to be assigned to the lower Pliocene (Pliocene I).
72 IJee c ·········· u~. <( ·········...... ~Pe, ·· ......
c::IOO.-OONOOONIOIO,..._' +-z Fig. 3.6 Shoreface deposits along the northern margin of the Carboneras Basin (GR. 916955). A: Location map of the shoreface deposits. X indicates the location of the outcrop. B: Photo of the shoreface conglomerates with oyster beds in the lower part. Picture taken towards the north. C: Detailed picture of the well sorted conglomerates. D: Provenance distribution of the shoreface deposits and the clast determination data, n shows the number of samples. 73 3.4.4 Summary After a regional exposure event during the Early Pliocene, sea-level rise inundated the Carboneras Basin and thick sequences of marine carbonates filled in the basin's relief (Goldstein, 2000). Pliocene carbonate deposition was dominated by clinoforms prograding from several areas of gently sloping substrate (Dillett et al., 2003). These last carbonates of the basins sedimentary succession are calcarenites-calcirudites made up ofbryozoan, bivalve and coralline algal bioclasts (Martin et al., 2004). These deposits are divided here into three facies associations: a lower, an upper part and a shoreface unit. All three units belong to the Cuevas Formation. The first two units are most widely represented within the Vera Basin. The Cuevas Fm consists of bioturbated, calcareous silts, sandstones and conglomerates with common pectinids. The deposits are further characterized by abundant and diverse remains of other marine organisms (van de Poel, 1994). · The Pliocene age of the Cuevas Fm is indicated by the presence of the Mediterranean Globorotalia margaritae and G. puncticulata planktonic foraminifer zones in the Vera and Nijar basins (Chapelle, 1988). The same assemblages, including also Globigerinoides rubber, G. oblique and G. trilobus are referred to the Zanclean stage of the Mediterranean Pliocene by (Addicott et al., 1978). The above described sediments correspond with Addicott's Morales Fm which consists of cobble and pebble conglomerate composed of well-rounded quartz and interbedded well-sorted coarse grained quartzose sandstones with thick (up to 2 m) beds of giant oysters (Addicott et al., 1978). 74 The author did not adopt van de Poel's division (van de Poel, 1991), since his Molata Fm is widely accepted as 'Cuevas or Cuevas Viejas Fm' in the literature (Addicott et al. 1978; Mather, 1993b and Fortuin and Krijgsman, 2003). 3.5 Polopos Formation The marine - fluvial clastic sediments described below were deposited in different depositional environments within the basin. They are in part equivalent in age but of varied lithofacies. 3.5.1 Beach deposits i Facies description The conglomerates of this unit are matrix supported. The clasts are well rounded and moderately sorted. The average clast size is gravel grade with the largest clasts varying between 2.3 cm and 9.7 cm (see Table 3.2). The clasts are orientated in parallel beds of a few centimetres thickness within a sandy matrix of medium sand. Shell fragments can rarely be found. The material weathers in rounded blocks up to 3 to 5 m in diameter (Fig. 3.7) and has a black appearance. The conglomerate consists mainly of well rounded quartz pebbles with a sandy matrix. The black colouration is due to small schist fragments. The provenance distribution, shown in Figure 3.7, has to be interpreted with care, as the clast count ignored the schists fragments, due to their size being smaller than 2 cm (see chapter 2). 75 Length (a-axis) L (cm) location n=lO mean +-SD range Cortijada La Arboleda del Arco: (933955) 2.3 ± 0.48 2-3 (934954) 4 ± 1.05 3-6 (938953) 9.7 ± 1.97 8-13.5 Table 3.2 The mean and standard deviation of the largest clasts within the conglomerates at three locations at Cortijada La Arboleda del Area. The above described conglomerates are preserved along the Rio Alias, north of Cortijada La Arboleda del Arco (GR. 934954), (Fig. 3.7) and further west between the Rio Gafares and the village of El Argamason (GR. 904958), (Fig. 3.8). ii Reconstruction of the palaeoenvironment Moderately sorted, small clasts of gravel size, orientated in parallel individual beds, but showing no sign of imbrication, point towards a beach environment (Massari and Parea, 1988). The well sorted clasts are very common in beach environments and the roundness of the clasts is a result of substantial abrasion along the shore (Collinson et al., 2006). However, the median grain size and the well sorted nature of the beach gravels, displayed in Fig. 3.7. and Table 3.2, tells us very little about the processes of sorting, since what is important here is relative, and not absolute, size, since in nature a continuum of sediment size always exists (Buscombe and Masselink, 2006). 76 c:~N(<)IOO~oooo~::oo c Fig. 3. 7 Beach deposits north of the Rio Alias. A: Simplified map showing the spatial distribution of the beach deposits. Grid references refer to the 1:50.000 map Parque Natural Cabo de Gata-Nijar. 8: Photo of the beach conglomerates. Picture taken towards the North. C: Detailed picture showing the conglomerates. The weathered rounded blocks are a common feature of the beach deposits in the study area. D: Provenance distribution of the shoreface deposits and the clast determination data, shows the number of samples. 77 (m) en :!: above logged base en 8 ------~ }fL... E · ~ LL ..... quartz E +--- -gravel lenses LL Cl) !m Alpujarride Complex +--- calcarenites rn > I§ Nevado Filabride Complex ~ I:=:::O:::O:::O::j Neogene infill () D Quartz - Schist Fig. 3.8 Photo and sedimentary log of the upper Cuevas Fm , beach deposits of the Polopos Fm and Quaternary terrace deposits (GR. 934956). 78 Coarse-grained (gravel to boulder size) conglomerate beaches are common in the temperate, present-day coast of SE Spain as well as in the Pliocene and Pleistocene deposits of the area (Martin et al., 1994). Beach progradation is usually recognized in a seaward gently-dipping layer comprising conglomerates on top and sand at the bottom. In most cases beaches are part of wave-dominanted coarse-grained delta or fan delta systems which can supply an abundance of coarse-grained sediments to the coastline (Massari and Parea, 1988). These workers also stated that wave-worked conglomerates are typically associated with tectonically active coastlines. On the two studied sections the beach deposits always overly the calcarenites of the Upper Cuevas Formation and are capped by well preserved fluvial deposits (Fig. 3.8). 3.5.2 Fan delta sequence Earlier studies (Harvey and Wells, 1987; Mather, 1991; Mather, 1993b and Harvey et al., 1995) have shown that a drainage system within the Sorbas Basin was already partly established at the time when the Carboneras Basin was still marine. The existence of the proto drainage is verified by the deposition of fan delta sediment within the northern part of the Carboneras Basin. The Pliocene Feos and Lucainena river systems were draining from the North (Sorbas Basin) towards the South (Carboneras Basin) depositing large amounts of fan delta material at the basin margins. 79 i fan delta definitiotllterminology Fan deltas have been studied in detail all around the world. The size and location of deltas provide a record of base level, and water and sediment supply as a proxy to past climate conditions (Kleinhans, 2005). Terminology and architecture of fan deltas play the most important role in their classification (Dabrio et al., 1991). The term 'delta' in geomorphology and sedimentary geology has traditionally been associated with rivers, to denote the coastal prism of land-derived sediment built by a river into a lake or sea (Holmes, 1965; Miall, 1984). A delta can be defined as a deposit built by a terrestrial feeder system, typically alluvial, into or against a body of standing water (Nemec and Steel, 1988, Nemec, 1990a). A delta is usually divided into a delta top or delta plain; a delta front and a pro delta. The term 'fan delta' originally referred to an alluvial fan prograding into a body of water. The term is also often loosely used for deltas with a very steep hinterland and coarse grained delta (Nichols, 1999). The use of terminology around the fan delta concept is far from clear. Too many uncertainties between fan delta, braidplain delta and river delta appear in the literature. Alluvial deltas have been classified by their a) feeder system (Holmes, 1965); b) thickness distribution (Coleman and Wright, 1975); c) tectono-physiographic setting (Ethridge and Wescott, 1984); d) delta front regime (Galloway, 1975) and delta front regime and grain size (Orton, 1988). Nemec and Steel (1988) discussed the above mentioned terminologies and proposed a new classification based on grain size and delta-face slope and the main physiographic attributes. This is the framework which is the most appropriate for the study area and will be used for the current work. For the latter differentiation Nemec and Steel (1988) refers to Postrna's (1990) concept of the three main criteria: a) physiography of delta-front shoreline; b) delta-face slope gradient. and c) depth of the delta toe (Postma, 1990). Additional to the delta architecture, 80 Postma (1990) also distinguished between different types of feeder channels according to their gradient. He divided the systems into (a) alluvial systems dominated by gravel with a very steep gradient; (b) steep gradient, often gravel alluvial systems; (c) moderate-gradient, gravely-sandy alluvial systems and (d) low gradient alluvial systems. In general fan delta morphology is dependent on the offshore slope characteristics and the depth of the standing body of water into which the delta progrades. These two features are decisive for the formation of different fan delta facies. Two different fan delta types can be distinguished. They can be defined as Gilbert type fan delta and 'non' Gilbert type fan delta. Mass-flow-dominated, gravely fan deltas are, strictly speaking, 'Gilbert type fan deltas' (Postma and Roep, 1985). A Gilbert type sequence is tripartite, defined by topset, foreset (delta face) and bottomset, and conforms to fan morphology in plan view (Nemec, 1990a). The sediments on the subaqueous delta slope are mainly transported by mass movement. ii Fan deltas in SE Spain Research on Spanish fan delta systems entering the Mediterranean has a long history. Many recent studies focused on the large Montserrat and Sant Llorenc del Munt system of the Ebro Basin (Burns et al., 1997; Lopez-Blanco et al., 2000; Steel et al., 2000 and Rasmussen, 2000). Fan delta sediments are very common in the sedimentary basins of the Betic Cordillera in SE Spain (Femandez et al., 1990; Santisteban Navarro and Martin-Serrano Garcia, 1990). Dabrio and Polo (1988, 1990) studied in detail the fan delta associations in the Murcia province and also summarised the most 81 important fan delta systems in SE Spain in his field guide (Dabrio et al., 1991). Fan deltas have also been described in the adjacent Vera Basin (Yolk, 1967; Weijermars et al., 1985; Stokes, 1997; Stokes and Mather, 2003). 3.5.3 Fan delta deposits of tbe Lucainena and Feos system Detailed data on the fan delta deposits of the proto Rambla de Feos and Lucainena were published by Mather ( 1991, 1993b ). In her studies Mather defined the conglomerates overlying the Cuevas Viejas Formation as the Polopos Formation after the type locality near the village of Polopos. The Polopos Fm can be divided into three principal stratigraphic units: a Lower and Upper Conglomerate Unit, separated by a persistent red sandstone, the Ibafiez Sandstone Member (Mather, 1991 ). Provenance was used to further sub-divide the conglomeratic units into 2 drainage systems. Each system is characterized by: (a) a dark coloured low grade metamorphic mica-schist and phyllitic material of the Lucainena System derived from the Sierra Alhamilla and (b) a unit with abundant amphibole-mica-schists of the Feos System derived from the Sierra de Ios Filabres (Mather, 1991). The lower conglomeratic unit of the Feos system represents mass flow conditions in a subaqueous, marine environment with wave reworked gravels on top, representing probably a fan-delta front. This unit was terminated by the deposition of the Ibafiez Sandstone Member (Mather, 1993b ). The red colouration and the carbonate nodular development is typical of pedogenesis (Wright and Alien, 1989). Mather (1991) suggests a coastal plain palaeoenvironment for this unit. The Ibafiez Sandstone Member exists at several places within the Carboneras Basin and is described and is discussed in detail in 82 section 3.5.2. The reddish sediments are topped by a second conglomeratic unit of the Polopos Fm. i Outcrop near confluence of the Lucainena and Feos system (GR. 863953) and (GR. 857955) Well preserved outcrops of conglomeratic deposits are situated near the confluence of the Rambla de Lucainena and Feos (Fig. 3.9; 3.10 and 3.11). The conglomerates consist of matrix supported, sub-rounded clasts in a coarse sandy, well cemented matrix. The deposits are moderately to well sorted. The clast assemblage consists mainly of 55% Alpujamde, 19% Nevado Filabride, 10% Neogene deposits and 16% Schist. At GR. 857955 the clasts show weak bedding with fining upwards and intercalated sandy beds. In some places a weak flow alignment is recognizable, but usually the conglomerates have little internal structure, apart from a very weak fining upwards. The conglomerates intercalate at some locations (GR.871958) with the calcarenites and oyster beds of the shallow marine facies of the Cuevas Formation. •N • .$ Polop::lopo~~ "iii 0 fan delta deposits 0. Q) "0 ~ .5 1/)Q) o"O Q) c I.L~ main drainage net outcrop location 1 km • settlement Fig. 3.9 Sketch map showing the location of the Lucainena and Feos fan delta outcrops investigated during this study. 83 Carboneras Basin 3km Provenance n Quartz 0 Conglomerate 0 Marls 10 Shist 15 Triassic Iron 6 a Alpujarride Complex Amphiboi-Mica-Shist 20 § Nevado Filabride Complex Garnet-Mica-Shist 2 IEffi] Neogene infill Sandstone 0 16% Reef debris 0 CJ Quartz Others 0 -Schist Metacarbonate (white) 35 1 Metacarbonate (red) 5 Metacarbonate (black) 5 55% Metacarbonate (grey) 6 D Fig. 3.10 Feos fan delta deposits. A: Sketch map of the area. X indicates the location. 8: View from the Alias I Fees river bed towards the N showing the Feos fan delta deposits (GR.863953). C: Detailed look at conglomerates showing the large clasts size and the moderate sorting. D: Provenance distribution and the clast determination data, n shows the number of samples of the Feos fan delta unit. 84 Q) Ol ro +-' c: c: m ·- Ql .!::? ~ ~ E c: a:i "0 ·~ ro o ro E c::Cl) li ~ .O>-~~~·~ ~._ i:::H 1 1-1 ~ .5 Cl) Cb Ql Cl) Cb ~~ 41 01 c<11 ~~ '0 c '(ij <( E \ Fig. 3.11 Lucainena fan delta deposits near Polopos. A: Map showing fan delta distribution within the northern part of the Carboneras Basin. B: Detailed view of the fan delta conglomerates. Note the rounded blocks of fan delta conglomerate and the absent of Gilbert type foresets. Picture is taken looking North. 85 ii Reconstruction ofthe palaeoenvironment The above described sediments show evidence for sub-aqueous deposition. The intercalation with the underlying shallow marine sediments of the Cuevas Formation, the nature of the mass flow deposits which require a water-rich environment and the fining upwards sequence of the beds (increase in matrix) are all evidence for a typical sub-aqueous flow. The weak grading indicates a turbulent flow, where the clasts are free to move. However no dewatering structures have been observed. The deposits resemble those described by Mather ( 1991, 1993b ), who interpreted them as fan delta~ front sediments. The fan delta conglomerates in the area around the confluence of the Lucainena and Feos systems do not show typical 'Gilbert type' features', they are referred to as 'non Gilbert type' fan deltas. It is very difficult to establish the precise age of the deposits. In the field it can be seen that they overlie and therefore post-date the Cuevas Formation. Stratigraphic relations of the conglomeratic unit suggest that these deposits are Gochar age equivalent (Mather, 1991, 1993b ). 3.5.4 Fan delta deposits of a third river system i Outcrop near El Argamason (GR. 920944) The El Argamason fan delta unit is situated SE of the village of El Argamson 2 (GR.911952). The delta deposits cover an area of nearly 7.3 km • To the North they are approximately limited by the Rio Alias, to the West by 'Cerro Gordo' (GR. 905938) (just west of the Carboneras Fault Zone) and towards the South by the Carboneras road (Fig. 3.12). 86 Sediments of the El Argamason area are of conglomeratic origin and unconformably overly the shallow marine calcarenites. The conglomerates are matrix supported with clasts embedded in a sand-gravel matrix. The largest clasts have a size of 2.7-5.1 cm along the long-axis. The texture can be described as well sorted. At the quarry 'Las Quebradas' southeast of El Argamason (Fig. 3.13 and Fig. 3.14) the deposits are very well preserved and show large planar foresets. The individual foreset beds are non- graded and generally around 40-50 cm thick. Measurements of the dip direction of the I beds revealed that the mean flow was moving towards 152° (Fig. 3.15) with an average dip of the delta slope of 15°. The provenance distribution is clearly dominated by well rounded quartz pebbles (72%). Dewatering structures are common. Marine fauna is very rare. Deposits around the Cerro Gordo are topped by a massive calcrete and do not show any bedding structures. The Standard Deviation (Table 3.3) demonstrates that the largest clasts are well sorted with a small range between the samples. Lengtb (a-axis) L (cm) location n=lO mean +- SD range E of Cerro Gordo (905936) 9.1±1.10 7-10 Fan delta quarry (9219435) 2.7 ± 0.8 2-4 Fan delta quarry (932938) 5.1 ±0.7 4-6 Table 3.3 The mean and standard deviation of the largest clast within the conglomerates at the three locations. 87 Vera Basin t N Sorbas Basin main drainage Lucainena fan delt•a Sierra Alhamilla basement volcanics fan delta main drainage Fig. 3.12 Simplified maps of the fan delta distribution. A: Sketch maps showing the fan delta distribution within the northern part of the Carboneras Basin. 8: Detailed map showing the spatial distribution of the El Argamason fan delta deposits. Grid references refer to the 1:50.000 map Parque Natura l Cabo de Gata-Nijar. One grid measures 5 km . 88 Fig. 3.13 El Argamason fan delta. A: Photo showing an overview of the fan delta deposits within a gravel quarry . Picture is taken towards the NW (GR. 921957). Band C: Fan delta foresets. Photos are taken from different angle and therefore not represent the original dip direction (B: GR.919938) and (C: GR.921938). Arrows indicates the fan delta foresets. 89 A B 2m colluvium • (? tl' .. . -. ' ·) .~t. ··, Fig. 3.14 El Argamason fan delta quarry (GR.921939). A: Photo showing fan delta conglomerate beds dipping in a SE direction. Photograph taken towards the ESE. 8: Simplified sketch of fan delta slope deposits. Note the planar cross bedding and the well developed fan delta foresets. 88 N A t 97 n number et readings /' dip direction 95 93 Fig. 3.15 A: Map illustrating the average dip direction of the fan delta foresets of the El Argamason Fm. Grid references refer to the 1:50.000 map Parque Natural Cabo de Gata-Nijar. 8 : Compass rose demonstrating the overall palaeocurrent direction. N indicates the number of compass readings. 90 To test if the variety of maximum clasts length was by chance or if the distribution was assigned to different part of the fan delta system a 'One-way analysis of variance' (ANOV A) was carried out. The results revealed a significant difference in the mean maximum length (a-axis) of clasts between samples from the three different location within the fan delta system (905936); (9219435) and (932938) (ANOVA; F = 147.23; p < 0.001). ii (ii) Reconstruction ofthe palaeoenvironment The well sorted nature of the clasts, their roundness and the existence of abundant dewatering structures at the El Argamason location conglomeratic unit points towards a subaqueous environment of deposition. The occurrence of large planar foresets and the angle of dip (15°) indicates a fan delta environment (Nemec, 1990a; Kleinhans, 2005). The fan delta deposits show typical characteristics of a Gilbert type fan delta. These deltas are characterized by their large foresets. The topsets might have been eroded by subsequent fluvial motion. The bottomsets are not visible in places such as the Agua Amarga Basin, where they would have been expected. Here they have probably been eroded and reworked by Iongshore drift and wave action during the marine regression. The fan delta foresets reach a maximum height of 178 m (at the eastern side of the Carboneras Fault Zone). At this location, the fault scarp reveals conglomeratic deposits down to an elevation of 100 m, which give a minimum thickness of 78 m for the fan delta deposits. This is measured on the NW side of the delta with foresets dipping towards the SE. Considering that the fan delta foresets were deposited in a 91 sub-aqueous environment, below the wave base, leads to the assumption that during the time of deposition relative sea level was at least 80 m higher than today. The deposits at the location near the topographic high of the Cerro Gordo (GR. 905936) do not show any foresets, nor any dewatering structures. The size of the largest clasts and the occurrence of a pedogenic calcrete top support the idea that this area might represent the fluvial part of the fan delta system. The significant difference in maximum clast size demonstrates that the conglomerates on top of this topographic high very likely belong to a different part of the fan delta system than the ones described above on the eastern side of the fault zone. 3.5.5 Summary Both types of fan deltas, 'Gilbert type' and 'non Gilbert type', have been found in the study area. Gilbert type fan deltas are primarily found in strike-slip basins characterised by high fault slip-rates (Colella, 1988). Steep subaqueous coastlines and basin shapes are favoured settings for Gilbert type deltas, since they are confined and protected from longshore drift, tidal current and wave action. The Carboneras Basin provided an ideal environment for fan delta development. During the Pliocene, when the northern part of the Carboneras basin was still occupied by the Plio-Mediterranean Sea (Addicott et al., 1978; van de Poel et al., 1984), the adjacent Sorbas basin was already subaerial in origin (Mather, 1993a) and an initial drainage system was established. Rapid uplift of the Sierra Alhamilla followed by the uplift of the Sierra Cabrera mountain ranges during the Pliocene generated a steep shoreline in the Carboneras Basin. The simultaneous uplift of the Sorbas Basin and expansion of its 92 drainage system provided a large amount of coarse fluvial sediment for fan delta evolution. The two smaller deltas, the Lucanaina and Feos fan delta, were partly supplied by detritus from the Sierra de Ios Filabres transported from the Sorbas Basin (Mather, 1991 ). The lack of any Gilbert type features can be explained by shallower water depth in this area. In contrast, the El Argamason fan delta shows typical Gilbert type characteristics. The close proximity to the Carboneras fault zone might be one reason for the Gilbert type features observed within the El Argamason fan delta deposits. The increased topography around the fault, caused by vertical displacement, provided a steeper shoreline during the Pliocene favouring Gilbert type fan delta development. The sea level during the time of the deposition of the fan delta must have reached the present day mountain range of the Sierra Cabrera indicated by the spatial extent of the underlying shallow marine deposits (described above). The occurrence of Gilbert type features and the present topography suggest a protected marine embayment with a steep subaqueous coastline, without strong longshore drift and a lack of tidal currents. The Sierra Cabrera mountain range to the north and a volcanic ridge to the southeast delimited the bay (Colella, 1988) suggest that the favourable conditions for a steep coastline are generated by the rapid uplift of the drainage area (in this case the Sorbas Basin), providing a large amount of coarse sediment. Alternatively they might have been fault controlled, where high rates of vertical motion causing the development of a steep coastline (here the Carboneras Fault Zone). 93 i Identification ofthe fan delta feeder channel A fan delta always requires some sort of alluvial feeder channel. The main question which still remains unanswered in terms of the El Argamason fan delta is: Which feeder channel transported all the conglomeratic material to the delta? An important fact is hidden within the fan delta architecture. The delta, which usually consists of topset, foreset and bottomset, gives data about the direction in which the material has been transported. Within the El Argamason delta the bottomsets and topsets are mostly eroded; the foresets dip mainly towards 152°. The dip direction of the foresets implies that the fan delta material must have been transported from the north-west (the opposite direction to the regional dip). The well rounded quartz and metacarbonate pebbles are very similar to the material of the pre Neogene metamorphic basement. Roundness is clearly related to abrasion during transport, increasing with higher energy and longer distance (Fisher and Bridgland, 1986). The roundness of the quartz pebbles within the fan delta deposits indicates that they have been transported for a long way or must have been reworked from underlying deposits. The metamorphic basement rocks of the Sierra Cabrera consists mainly of vein quartz. They are therefore too close to the area of deposition and are unlikely to be the source of the clasts as the roundness of the clasts point towards a long distance of transportation. The idea that the clasts have been reworked from older deposits within the Sierra Cabrera is unlikely as the only unit which consists of quartz conglomerates is the Azagador Member of the Turre Fm, which crops out northwest of the fan delta. The Azagador conglomerate, however, contains clasts of a lot of different lithologies, whereas the fan delta conglomerate is mainly composed of quartz pebbles. The short distance between the Azagador deposits and the fan delta 94 would not be sufficient to break down or erode the other clasts and select only the quartz. Therefore the Sierra Cabrera basement rocks and the Neogene sediments within the mountain range cannot have been responsible for the source of the fan delta sediments. If we are definitely dealing with reworked conglomerates, they can only have been derived from the adjacent basins (i.e. Sorbas Basin). Quaternary marine terraces towards the east of the fan delta, near Carboneras, e.g. Bell et al. (1997) demonstrated that this area was still marine during the deposition of the fan delta deposits and therefore cannot be responsible for the fluvial input. Furthermore the volcanic ridge southeast of the fan delta excludes the possibility of a feeder channel coming from this direction, since no volcanic clasts have been found within the fan delta sediments. Towards the south of the fan delta the Agua Amarga sub-basin is a lower lying area. The highest fan delta deposits can be found at an elevation of around 190 m. The highest hill in the Agua Amarga basin is 140 m. There is no sign of a later subsidence of the area in the south. In the southwest (Almeria area) fan deltas were deposited during the Upper Pliocene (Aguirre and Jimenez, 1998) indicating a longer marine character for this area. That no river remnants can be found in this area supports the latter hypothesis. For those reasons, the southwest cannot be the source area for fan delta sediments. The only river remnants can be found in the west (Rio Alias), north-west (Rio Gafares) and north (Rambla de Ios Ranch os). The Rio Alias can be excluded from the list of possible feeder channels for the El Argamason fan delta because it post dates the fan delta deposits. Running parallel to the uplifting mountain front, the Rio Alias must have evolved after the Carboneras Basin was already continental and the mountain front was already uplifted (Chapter 4). The Rambla de Ios Ranchos is a very small stream that shows no sign 95 that its channel was once bigger and could be responsible for the large volume of fan delta deposits. The extent of the Plio/Pleistocene fan delta sediments suggests that significant drainage must have entered the Carboneras Basin from the north at this geographic point during the Plio/Pleistocene. The fan delta deposits cover an area of roughly 7.3 2 3 km and have a volume of approximately 0.8 km • The nearest candidate for the supply of this material is the Rio Gafares. The Gafares has a modem catchment area 2 of 19.4 km , largely composed of weak lithologies (graphite-mica-schist) which rapidly breaks down to suspended sediment grade material on transport and subordinate quantities of more robust vein quartz, which is the main component of the fan delta clastics. This would appear to imply that the volume of the fan delta may underestimate the size of the catchment area required to supply it. In addition the catchment is transverse to the mountain front which suggests that the river system has had sufficient water discharge and stream power to sustain incision at a rate sufficient to keep pace with the regional uplift, as there is little evidence to suggest transverse drainage by headcutting along a structural weakness. The modem stream has insufficient stream power to be andecedent and to have created the scale of transverse valley within which it flows. This would imply a larger catchment area than that observed today and would suggest the Rio Gafares is the most likely candidate for the feeder channel of the El Argamason fan delta (Fig. 3.16). 96 UJ Cl) 0) ea c ·-l! "C c ea "':;, 0) c( 0 ·-a:: Fig. 3.16 Shaded relief map, derived from Esparia (1992) showing the reconstruction of the palaeodrainage of the northern Carboneras Basin. The Pliocene Gafares catchment area may have extended further West towards the Sorbas Basin, indicated by the low relief. 97 3.5.6 Coastal plain deposits i Facies description of unit a) The last unit of the Polopos Fm consists of light brownish to light reddish massive silty-clay deposits (Fig. 3 .17). These deposits do not show any evidence of sedimentary structures. Macrofossil are very rare. The deposits contain white marker horizons of small size, rounded quartz pebbles and white carbonate nodules of approximately 1 cm diameter. The carbonate nodules form beds of I 0 to 20 cm thickness and occur every 1 to 2 m (Fig. 3.17). The sediment is very susceptible to gullying. The sediments occur mainly between the fan delta lobes within the quarry. They are restricted to individual patches (GR.923943 and GR.921938). ii Facies description of unit b) The area around La Palmerosa (Fig. 3.18) is characterized by dark red coloured silty sediments. The silt deposits reach thicknesses of 6-10 m and show onl"y very rare weak bedding structures. They contain fragments of pecten and oysters shells, which are accumulated in 50 cm thick beds, gently dipping towards the SE. In the upper part of the depositional unit a massive pedogenic calcrete development is common. This layer reaches a thickness of up to I m and contains small, well rounded quartz pebbles. Unit b appears to fill the depression southwest of the fan delta deposits. They are best visible in the area around La Palmerosa, along the Rambla de Yeseras (GR.892923 - 910935). 98 o transverse antecedent drainage: Streams which are transverse to the axis of a mountain front and drain perpendicular to strike. They have maintained their courses across axes of uplift and are thus antecedent o aggressive subsequent drainage: Stream which stimulate aggressive behaviour in their headwaters o beheaded original consequent drainage: Streams which have been beheaded by aggressive subsequents. The above described types are illustrated on Fig. 4.2.1 . Sierra de Ios Filabres ~op.«a~·~~ ---····················· · · ···· ····················-········~~ (flo&• Metamorphic Basement ,.-- Original consequents ~ Transverve antecedents ·---- Beheaded original consequents Aggressive subsequent ~ Former consequents Fig. 4.2.1 Main types of drainage developed in the study area and the adjacent basins, modified after Mather and Harvey ( 1995 ). 108 4.3 The Pliocene topography The Carboneras and Agua Amarga Pliocene sub-basins were the last two marine basins to exist prior to the final emergence of the south-eastern region of the Betic Cordillera (Martin et al., 2003). The end of Cuevas Formation deposition was marked by the complete withdrawal of the Pliocene Sea. The mainly flat topography of the shallow marine calcarenites of the Cuevas Formation built the base for the subsequent drainage systems. The final marine phase was examined in Chapter 3 in order to establish the palaeorelief of the basin. This section summarizes the key findings of Chapter 3. At the beginning of the Pliocene the northern border of the Carboneras Basin was formed by the Sierra Cabrera, an elevated land mass consisting of Palaeozoic Mesozoic age metamorphic rocks of the Betic nappe units. The mountain range is composed of metacarbonate, quartzite, micaschist and phyllites from the Alpujamde complex and metacarbonates and breccias from the Malaguide complex (IGME, 1978). The basin floor was gently sloping towards the southeast and the basin centre. The Carboneras Basin was filled by Neogene marine sediments of the Turre Formation overlain by shallow marine marls and calcarenites of the Cuevas Formation towards the basin margins. Vertical displacement along the Carboneras Fault Zone (CFZ), generated a steep, deep offshore topography SE of the fault and favoured the development of a Gilbert type delta during the early Pliocene (Chapter 3). Fan delta sediments were deposited across the fault zone and filled the low lying eastern part of the CFZ with up to 80m thick delta gravel. During the same time two smaller fan deltas were deposited towards the west (Mather, 1993b), not showing any 109 . Gilbert type features and therefore presumably deposited in shallower, less sheltered water. The existence of fan delta sediments indicates the location of river mouths on the northern fringes of the basin. The three fan deltas of the Carboneras Basin were fed by individual feeder channels, which formed parts of the proto drainage system, the Lucainena, Feos and Gafares system. 4.4 Terrace sequence of the Rio Gafares 4.4.1 The modern Rio Gafares The modem Rio Gafares (Fig. 4.4.1) runs from north to south with a length of 13 km 2 and a catchment area of 19.4 km . Figure 4.4.2 shows the drainage network of the Rio Gafares. The headwaters and associated tributaries lie within the uplifted basement highs of the Sierra Cabrera at the northern basin margin. The mountain range is bounded by E-W compressional faults to the north and south, and cross-cut by NW SE and NE-SW faults (Huibregtse et al., 1998). The mountain range has been rising 80 m Ma- 1 since the Pliocene, whereas the bordering southern part of the Sorbas Basin, has been uplifted in excess of 160 m Ma- 1 since the Pliocene (Mather, 1993a). Draining through the rising mountain range, the river has incised deep into the bedrock, creating a V-form valley. The mountainous catchment area of the Rio Gafares is largely composed of graphite-mica-schist and metacarbonate. Further towards the south, the river runs across a lowland area (150 m as!) for approximately 3 km with underlying Neogene deposits. The Rio Gafares then joins the Rio Alias west of the hamlet of El Argamason. 110 Fig. 4.4.1 Aerial photograph showing the modern Rio Alias draining from North South. Note the deep incised river valley within the Sierra Cabrera mountain range. Most of the terraces south of the mountain front can be find within the 'Los Ranches' area. The confluence of the Rio Gafares with the Rio Alias is just of the photo. 111 N ~ ) river 2km ...... catchment boundary Fig. 4.4.2 Modem drainage network of the Gafares River system and its tributaries, drawn from 1:25,000 map, sheet El Agua del Medica, Polopos. 112 The modern Gafares is an ephemeral river. The gravels within the river channel are moderately to poorly sorted and clast supported (GR. 895965). The clasts are sub- · rounded and imbricated. The composition (Table 4.1) consists mainly of 69% mica- schist fragments and a large proportion of Neogene deposits (23%). The measurements from imbricated clasts indicate a N-S flow direction. Provenance Rio Gafares Modern terrace deposiiS (couniS) quartz 0 conglomerale (Tortonian) 10 marls 5 schlsl 70 iron rich metacartxmate (Trlassic) 0 amphibole-rnica·schist 0 gamel·mica·schist 2 sandstone 0 reef debris 0 others 0 metacartlonate (white) 15 metacartlonate (red) 10 metacarbonate (black) 0 metacartlonate (grey) 0 gypsum 0 volcanics 0 Table 4.4.1 The table presents the provenance distribution data of the modern terrace deposits of the Rio Gafares {lowland), n=100. 4.4.2 Introduction to the terrace sequence The spatial extent of 7.3 km2 of the Plio/Pleistocene fan delta sediments (Chapter 3), suggests that a significant drainage must have entered the Carboneras Basin from the north (in the vicinity of the hamlet of El Argamason) during the Plio/Pleistocene. The nearest candidate to supply this material is the Rio Gafares. The Pleistocene drainage record of the Rio Gafares is documented by a series of inset river terrace and erosional strath landforms that are cut into the metamorphic basement and Neogene deposits. 113 --~------No terrace remnants have been found within the catchment area, north of the Sierra Cabrera. Further downstream, within the mountain area the main river channel of the Gafares system is incised deeply into the underlying bedrock creating a 3.5 km long valley. Here the fluvial remnants are located in close proximity to the modem Rio Gafares (Fig. 4.4.3). The landforms can be traced across the mountain range onto the lowland area south of the Sierra Cabrera, where the river is incised into weakly lithified Late Miocene-Pliocene shallow marine marls and calcarenites. Numerous terrace deposits are presented east of the modern river in this region. The conglomerates of the terrace deposits consist of various sedimentary facies, which are defined on the basis of grain size, lithology, provenance distribution and sedimentary structures. The maturity and stage of the pedogenic calcrete refer to (Gile et al., 1966 and Machette, 1985). A description and interpretation of each terrace remnant follows. The terrace remnants are presented in levels according to their base heights above the modem river bed, starting with the highest. A height range diagram in Figure 4.4.4 presents the studied terrace deposits and strath terraces. The description is followed by an analysis of the individual terrace deposits and a general reconstruction of the palaeoenvironment during the terrace deposition. At some location cross profiles have been taken from a 10:000 map (Fig. 4.4.5). As a result of previous work in the Sorbas and V era Basin (Harvey and Wells, 1987; Mather, 1991; Stokes, 1997) four terrace levels have been pre-assigned to the Rio Gafares. Terrace level 2 has been subdivieded into a and b unit due to differences in height and provenance distribution between the individual terrace remnants of this level. However the author has tried to avoid adding another level, since the Carboneras Basin was one of the last basins during the Plio/Pleistocene to stay 114 marine. The drainage systems of the Carboneras Basins must therefore be younger than the one in the Sorbas Basin which makes it very unlikely that the rivers in the Carboneras Basin created more terrace levels in less time (see discussion in Chapter 6). Due to a lack of preserved material of the youngest one (e.g only very few conglomeratic deposits close to the modem river), only three have been described and analysed. 115 .. ·~. .. <( 2.! "Cii CD 0 0 m Q. CD c: "0 ~ Q) 1! In 0 .c ea ~ i! m 1! 1ii In ~ Cl} Q) c: I 0 .c... ea 0 .-z z .. Fig. 4.4.3 Terrace remnants of the Rio Gafares. A: Map showing an overview of the Carboneras Basin. Box marks the dimensions of the detailed sketch map. 8: Sketch map showing the distribution of all the Gafares terrace remnants. Grid references refer to the 1:25.000 map (IGN, 1985), (Grid=1km) . 116 0 • • • • • • • • • N • .. • ~ 0~'\. • ~., .. • I 4><{,. ~« ~ 4) • iLC> C> E .... . / Fig. 4.4.4 North-South longitudinal profile of the Rio Gafares and height range diagram from the headwaters in the Sierra Cabrera to the confluence with the Rio Alias south of the mountain front. The heights of the terraces were measured at the base of the deposit. 117 89 90 I I B h oo- e cross profile -• terrace • 1 km .·. . t N Carboneras Basin A Fig. 4.4.5 Rio Gafares. A: Overview map of the study area. Box indicates the location of map B. B: Map of the Gafares headwaters showing cross profile locations used in diagrams of Chapter 4. 118 4.4.3 Terrace highest above the modern river- (terrace levell) i Description: terrace level] ii Strath terrace Sierra Cabrera (GR. 892009 and 897998) The highest fluvial remnants of the Rio Gafares are presented as strath terraces within the northern region of the Sierra Cabrera. The strath terraces are situated ea. 54m above the modern river bed and show a flat surface top. They are clearly visible on the cross profile diagram (Fig. 4.4.6). Due to the lack of sediments no further analysis could be carried out. Terrace remnant of hilltop 226 m (GR. 912960) The depositional terrace, south of the Sierra Cabrera mountain front, is situated approximately 1.5 km east of the modern river. Located north of the village of El Argamason, on hilltop 226m (GR. 912960), terrace deposits overly shallow marine sediments of the Cuevas Formation (Fig. 4.4.7). The conglomerates reach a thickness of approximately 3 m and thin out towards the northern end of the terrace. The clasts are subangular, poorly sorted and clast supported. The provenance distribution of the class shows a high percentage of both quartz (13%) and Neogene components (13%). The Nevado Filabrides content is relatively small ( 1%). The top of the terrace is capped by a 0.5 m thick mature calcrete; stage III-IV (Gile et al., 1966 and Machette, 1985). 119 Provenance Rio Gafares Terrace h/1/lop 226 (counts) ~ .. "'o"'"~- ~ .. "'E'0 ~le quartz 13 conglomerate (Tortonian) 6 ma~s 2 schist 35 Iron rich metacarbonate (Triasslc) 0 amphibole-mlca-schist garnet-mica-schist 0 sandstone 5 reef debris 0 o~em 0 metacarbonate (white) 11 metacarbonate (red) 3 metacarbonate (black) 10 metacarbonate (grey) 14 gypsum 0 volcanlcs 0 Table 4.4.2 The table presents the provenance distribution data of the terrace deposits of terrace hilltop 226 of the Rio Gafares, (lowland), n=1 00. Terrace level1 Terrace location Terrace left hand Terrace right hand Average m (Sierra Cabrera) river side river side above the (looking upstream) (looking upstream) modern river bed base of terrace base of terrace Strath terrace E 370 (Gr. 892009) 55 of La Rondena Strath terrace N 340 (GR. 897998) 52 of Cortijo Matlas Muiioz Average m 54 above modern river for level 1 Terrace location jlowlandl Terraces Los 222 (GR. 912960) 59 (anomalous) Ranch os (anomalous) Average m - above modern river for level1 .. Table 4.4.3 Table summansmg the descnbed and analysed terrace depostts of terrace level 1 and their location in the field. 120 <( ·, : I I I ....I _ I I t ! :! I • •• I ~ \· r ~ 1:0 / ill I 0 1f""W ~ ·I i 0 0 I I 0 ~ ~ ~ ::; ~ ..~ ) ...-....;; ~ ~ I J!" ~ eQ. I! i ! :1 17[" i 0 Jl 0 I • 11--+ ~ is / I I() 0 ~ ~ ~ ~ ~ (W)Sli!B!IIII Fig. 4.4.6 Strath terraces of the Rio Gafares. A: Long river profile of the Rio Gafares. B: Detail of the terrace heights diagram within the Sierra Cabrera. Note the triangles are the strath terraces. C: Cross profile of the Gafares valley within the Sierra Cabrera, indicating the flat surface of the strath terrace 54 m above the modem river bed. Longitudinal data were drawn from the 1:25.00 maps, cross profile data derived from the 1:10.000 maps for greater accuracy. 121 Fig. 4.4.7 Terrace hill at an altitude of 226 m (GR. 912960); south of the mountain front. Hill is approximately 64 m high. A: Photograph of the terrace conglomerates of level 1 or level 2. 8: Detailed view of the clasts. Notebook measures 21 cm. Conglomerates contain large amount of boulder size clasts. C: Map of the terrace location. Pie chart presents the provenance distribution of the conglomerates. 122 iii Reconstruction of the palaeoenvironment: terrace levell Level 1 is mainly fonned by two strath terrace deposits within the Sierra Cabrera. The height range diagram (Fig. 4.4) shows that the heights of terrace hilltop 226 m is in line with the strath terraces within the Sierra Cabrera. However since the strath terrace only provides an erosional record of the palaeoriver no comparison can be made between the terrace remnants within the mountain and the aggradational evidence in the lowland (hilltop 226 m). The author will therefore not group the 226 m hilltop into terrace level 1. A reconstruction of the palaeoenvironment cannot be archieved from the strath terraces, due to the lack of sedimentological infonnation. 4.4.4 Terrace second highest above the modern river (terrace level2) The upper reaches of the Rio Gafares provided a number of good exposures of terrace remnants. i Description: terrace level 2a and 2b Within the Sierra Cabrera terrace remnants are well preserved as small track side exposures. The area south of the mountain front provides numerous outcrops of excellently preserved fluvial deposits. Terrace level two has been subdivided into level a and b, as explained above. Terrace and strath terrace SE of La Rodena (GR. 889009, 888011) -level 2a South east of the hamlet La Rondena a well developed terrace (GR. 889009) and one strath terrace (Gr. 888011) have been preserved (Fig. 4.4.8). They are situated 123 approximately 42 m above the modem river bed. The sediments of the terrace deposits are characterised by conglomerates of lithofacies Gm (see Chapter 2, table 2.3. for lithofacies code). They are clast supported polymodal and poorly sorted. The conglomerates do not show any form of stratification, nor could any imbrication be observed. The provenance distribution is mainly dominated by grey and white metacarbonates and schist fragments. They comprise neither Nevado Filabrides components nor any Neogene clasts The terrace shows signs of pedogenic soil development with a weak red soil colouration (SYRS/6 after Munsell). The 3.5 m thick deposits are topped by a mature calcrete of stage III-IV of 50 cm thickness. · Terrace SE of Granadino (GR. 893005)500m further downstream a second terrace crops out along a dirt track near the hamlet of Granadino. Little is preserved, but the flat surface of the terrace is well recognizable in the field. Terraces near Cortijo Matias Mufloz (GR. 894997 and 896999) -level 2b Another lSOOm down the modem river, two terrace remnants, and show very well preserved conglomerates. The paired terraces (outcrops are located 15 m apart along the river) near Cortijo Matias Mufioz are situated 19 and 20 m respectively above the modem stream bed (GR. 894997 and 896999) (Fig. 4.4.9). The conglomerates are 2- 3m thick and of a light beige colouration. They are clast supported and poorly sorted (lithofacies Gm), but without any sedimentary structure. The clasts are sub-angular to angular. The deposits are still mainly dominated by Alpujamde clasts, but include, in contrast to the above-described terrace, Nevado Filabride (4%) and Neogene (2%) components. The terrace remnants only crop out as an indurated horizon along the cliff, a calcrete surface therefore could not be identified. 124 Terrace E ofLos Loberos (GR. 896994) - level 2b Further downstream a fifth terrace at the same height above the- river (40m) IS preserved. The terrace north of Los Loberos (GR. 896994) is 2 m thick and overlies metacarbonate and mica-schist of the Alpujarride Complex. The clast supported and poorly sorted conglomerates are composed of angular graphite-mica schist fragments within a silty matrix. The black colouration of the conglomenites is mainly derived from the underlying mica-schists. The provenance distribution pf the conglomerates is very similar to the terrace described above, with 63% Alpujarride clasts, 2% Nevado Filabride components, 2 % Neogene sediments, 0% Quartz and 33% Schist material. No calcrete top has been observed. Provenance Rio Gafares Terraces level 2a,b Sierra Cabrera (counts) ... Cl> ...Cl> Cl> 0 Cl> 0 ~ Cl> Cl> Cl> CD "'CD =ri ri ri C) C) C) quartz 0 0 0 conglomerate (Tortonian) 0 0 mans 0 0 0 schist 6 20 20 Iron rich metacarbonate (Triasslc) 0 0 amphibole-mlca-schist 0 2 1 garnet-m lea-schist 0 0 0 sandstone 0 0 0 reel debris 0 0 others 0 0 0 metacarbonate (white) 11 10 20 metacarbonate (red) 0 2 1 metacarbonate (black) 3 7 6 metacarbonate (grey) 4 12 1 gypsum 0 0 0 volcanics 0 0 0 Table 4.4.4 The table presents the provenance distribution data of the terrace deposits of terrace level2 within the Sierra Cabrera (Rio Gafares), n=100. 125 0 N -E -Ql i L() u 1: ..... c E :1 .!! .:i•e "0 3 ~ 0 ~.8 ...... Sew L() 0 0 0 0 0 0 0 0) ,..._ L() (") ..- 0) ("') ("') ("') M ("') N (w) st46184 IIl OI (.) Fig. 4.4.8 Terrace hill (GR. 889009). A: Terrace creating a flat surface at 363m. 8: Detail on the river conglomerates. C: Provenance distribution of the terrace deposits. 0 : Cross profile of the Gafares River valley within the Sierra Cabrera, indicating the flat surface of the river terrace at 363 m heights; (drawn from the 1:10,000 maps). 126 ______.. ·------·------------·------·------·------·------ ------·------··------------~~=~==~==~=====~=~~~~~~~_ .. ______------·_ .,. ___ _ 0 c ., .. ! I 0 'el Fig. 4.4.9 Terrace at 330m within the Sierra Cabrera at terrace level2 (GR. 895998). A: View up the river - arrows indicating a paired terrace on both sides along the valley slope. 8: Detailed view on the conglomerates. C: Provenance of terrace deposits. D: Cross profile across the river valley showing a flat surface 330m heights. 127 Terraces between Gafares and El Argamason: 'Los Ranchos-level2b Within an area of 2 km2 more than 10 terrace fragments are located SE of the small village of Gafares, called 'Los Ranchos'. Figure 4.4.1 0 shows a geological sketch map of the area with the terrace locations. The best preserved ones are described below. They are located {proximal- distal) on hilltop 219 m (GR. 899968), hilltop 212 m (GR. 904968), hilltop 208 m (GR. 906964), hilltop 204 m (GR. 908963), hilltop 198 m (GR. 905959) and hilltop 189 m (GR. 902956). The terrace deposits mainly overly shallow marine sediments of the Cuevas Formation. On some locations an up to 6 m thickness of conglomerates overlies black, sandy beach material (Chapter 3) and locally has a black appearance. The black colouration is derived from small mica schist fragments within the fluvial deposits. The terraces are all located in close proximity (fewer than 1 km apart) and show a very similar lithology. The fluvial deposits of hilltop 219 m (GR. 899968) have been chosen as the type section for terrace level 2. Type locality- Los Ranchos -terrace hilltop 219 m (GR. 899968) -level 2b The terrace remnants of hilltop 219, SE of the village ofGafares, are 2-3 m thick (Fig. 4.4.11 ). The conglomerates are matrix supported and can be characterised as lithofacies Gms. They are poorly sorted and sub-rounded. The maximum length along their long-axis is 30 cm. They contain large boulders of grey or black metacarbonate. Signs of imbrication are visible and yield an overall palaeodirection of 105° ESE. Despite the good preservation, no stratification has been observed. The clast assemblage is quite similar to the terrace deposits within the mountain area (described above), with Nevado Filabride component of 1% and Alpujfmide components of 43%. 128 N t 97 96 1 km Q) c ~ .9 -en - Plio/Pieistocene conglomerate (T3) 0 · ·- Q) a:: a: - Plio/Pieistocene conglomerate (T2) Calcareous conglomerate (beach) Q) c: Calcarenites (sandy Cuevas Fm) ~ .Q - Gypsum (Yesares Fm) a.. Dnotmapped Fig. 4.4.10 Geological sketch map of the area of the main terrace finding. The map focuses on the Rio Gafares terrace level 2, south of the mountain front in the El Argamason I Los Ranchos area. 129 ------· ·------·------·------------· ·· ·------·------·------· ______------~ ------ ... ·£::~::::f.t"~~~:t:t::::y~-:.------ ·------------~ 0 Fig. 4.4.11 Terrace deposits of terrace level 2 of the Gafares River, south of the mountain front. A: Well preserved fluvial terrace of hill 219, which was defined as type location. B: Soil fonnation towards the top of the terrace. Note the red colouration. Munsel colour chart for scale. C: Provenance distribution of the conglomerates. 130 The proportions ofNeogene clasts has increased from 2% in the Sierra to 14% within these terrace conglomerates in the lowland area (the significance of this will be discussed at the end of the 4.4 section). The upper part of the deposits of hilltop 219 shows a clear red colouration to the conglomerates. The top is capped by a well developed mature carbonate crust (stage III-IV). The terraces mainly overly calcarenites of the Cuevas Fm. Los Ranchos- hilltop 208 m (GR. 906964) - level 2b The conglomerates of this terrace form a ea. 3 m thick fluvial deposit. They are poorly-moderately sorted and sub-angular. The clasts are matrix supported and have an overall black appearance. The conglomerates overly yellow calcarenites of the Cuevas Fm, but the base of the conglomerates is not visible and the type of contact could not be identified. The provenance distribution of the conglomerates is shown in Fig. 4.4.12. A few hundred metres to the SE another terrace (hilltop 204 m - GR. 906964), with a very distinctive flat surface is found. Unfortunately this terrace does only show rounded pebbles on top of a well developed calcrete surface, but does not reveal any good, well preserved conglomerates. Los Ranchos- hilltop 198 m (GR. 905959) - level 2b The fluvial deposits at location (GR. 905959) are maybe the largest, most obvious terrace remnant of this area. The conglomerates reach a thickness of 5 m. The fluvial sediments overly black, sandy, fine to medium grained beach deposits (Chapter 3). There is a sharp contact between the two units (see Fig. 4.4.13). The terrace itself 131 consists of matrix supported (lithofacies Gms), poorly sorted, medium rounded clasts. The large boulder size conglomerates are mainly white and grey metacarbonate. The palaeocurrent direction which was obtained from imbricated clasts is 120· SE. Los Ranchos- hilltop 189 (GR. 902956) -level2b A well preserved terrace remnant can be found SW of the above described deposits. The conglomerates are poorly sorted and subrounded. The clasts measure a maximum size of 31.7 cm (along the a-axis). The provenance distribution (Table 4.4.5) shows with 1% an only small amount of Nevado Filabride components. The clasts show a strong imbrication and a palaeocurrent of 129· was measured, demonstrating a flow of the palaeoriver towards the SE. The fluvial conglomerates of this terrace remnant are capped by a mature, well developed calcrete top of stage Ill. Provenance Rio Gafares Terracesleve/2 lowland (counts) :g ...... "'~ "' 0"' 0 "'CO "' Ill! Ill!"' Ill!"' C) C) C) quartz 1 0 0 conglomerate (Tortonian) 14 0 3 marls 0 6 4 schist 45 30 33 iron rich metacarbonate (Triassic) 0 0 0 amphibole-mica-schist 1 3 gamet-mica-schist 0 0 1 sandstone 0 0 3 reef debris 0 0 others 5 2 0 metacarbonate (white) 15 27 18 metacarbonate (red) 4 25 3 metacarbonate (black) 5 7 13 metacarbonate (grey) 25 10 17 gypsum 0 0 0 volcanlcs 0 0 0 Table 4.4.5 The table presents the provenance distribution data of the terrace deposits of terrace level2, lowland (Rio Gafares), n=100. 132 ·------------ ------,,:;.:::-:-:-:-:-:::-:~ ------_.. ______·------·------·------_,. ____ _ ------·------·------· 0 Fig. 4.4.12 Terrace deposits of hilltop 208 m (GR. 906964) of the Rio Gafares, south of the mountain front. A: Fluvial terrace remnants weathered in round blocks. Block is approximately 1.5 m high. 8: Detailed photo of the terrace deposits overtapping the undertying sequence. Note the black colouration is due to small schist fragments. C: Provenance distribution of the conglomerates and the clast determination data, with n showing the number of samples. 133 beach deposits Fig. 4.4.13 Terrace deposits near Los Ranches (GR. 905959). A: Terrace conglomerates overlying black beach sediments, weathered in rounded block (for detailed description of the beach deposits see chapter 3). 8: Conglomerates of the fluvial terrace deposited on top of beach sediments. C: Terrace remnants overlying beach sediments. Conglomerate bed filling in the wavy topography on top of the beach deposits. Note the irregular margin of the basal conglomerates. l34 Terrace level 2 Terrace location Terrace left hand Terrace right hand Average m (Sierra Cabrera) river side river side above the (looking (looking upstream) modern river bed upstream) base of terrace as/ base of terrace SE La Rondena 363 (GR.889009) 365 (GR.888011) 42 Granadino 350 (GR. 893007) 37 N of Cortijo 320 (GR. 894997) 322 (GR. 896999) 35 Matlas Muiioz 34 E of Los Loberos 315(GR. 896994) 31 Average m 37 above modern river for level 2 Terrace location Jlowlandl Terraces Los 215(GR. 899968) 30 Ranches 208 (GR. 903968) 25 206 (GR. 906964) 25 202 (GR. 910963) 28 193 (GR. 905959) 30 184 (GR. 902956) 37 Average m 29 above modern river for level 2 .. Table 4.4.6 Table summans1ng the descnbed and analysed terrace depos1ts of terrace level 2 and their location in the field. ii (ii) Reconstruction of the palaeoenvironment: terrace level la, b The analysis of the field description, together with the terrace height diagram and the river cross profiles have shown that within the mountain area the above described terrace deposits (T2) might belong to the same terrace level, deposited approximately around the same time. The terrace and strath terrace SE of Rondena are situated higher than the other terraces, also the clast distribution does not show any Nevado Filbrides components as do the other terrace conglomerates of this level. It has therefore been assigned to level 2a. South of the mountain front the described terrace 2 are all located within 1.5 krn . The lithology and the provenance distribution, the palaeocurrent and the clast size allow them to be grouped into one level. Hilltop 219 shows a slightly different provenance distribution, however lithology, height and 135 calcrete stage are very similar to the other terrace deposits of level 2b. The similarity of the provenance distribution (Fig.4.4.14) also allows the terraces to be traced up from the headwaters downstream to the ones south of the mountain front. Lithofacies Gms is the dominant lithofacies in the conglomerates. This facies consists of clast supported, massive conglomerates. The large gravel to boulder size conglomerates (maximum clast size range from 20-30 cm along the long axis) point towards deposition within a high energy fluvial environment. The large clast size and poor-moderate sorting of these sediments suggests transport as bedload (Costa, 1984). The lack of a preferred orientation of the clasts suggests a transport in which the clasts were not completely free to move, indicating a higher flow viscosity. A high sediment to water ratio is also suggested by the poor sorting and could be evidence for a hyperconcentrated flow (Costa, 1984;Mather, 1999). The red colouration is due to pedogenic modification, suggesting a subaerial exposure of these sediments. The mature calcrete (stage IV) on top of some terraces suggests an Early to Mid Pleistocene age (Harvey, 1984; Wells, 1987; Bell et al., 1997). 136 t:: ······· nl .... "5 . Ql ... ·a. Fig. 4.4.14 Gafares terraces. A: Map showing an overview of the Carboneras Basin. Box marks the dimensions of the detailed sketch map. B: Sketch map showing the distribution of the Gafares terrace remnants. Terrace remnants of terrace level 2 are darker coloured and their provenance distribution is presented within pie charts. Grid references refer to the 1:25.000 map (IGN, 1985), (Grid=1 km). 137 within the clast assemblage (Fig. 4.4.15). The deposits comprise large clasts of mica schist and metacarbonate. No pedogenic modification or calcrete is evident. Terraces between the hamlets ofGafares and El Argamason: 'Los Ra11chos' South of the mountain front three terrace remnants are situated approximately 9 m above the modern river channel (Fig. 4.4.16) overlying shallow marine marls and calcarenites of the Cuevas Formation (GR. 903967); (GR. 906967); and (GR. 906959). Only the terrace deposits of hilltop 177 have been well enough preserved for detailed analysis. Terrace hilltop 177 (GR. 906959). The fluvial deposits of this terrace remnant (GR. 906959) consist of a 2 m thickness of conglomerates. The conglomerates are clast supported and moderately to poorly sorted (Gms). The clasts are subrounded and vary in size from gravel to pebble size. The mean long axis is 18.5 cm. The sediments show no internal structure and consist mainly of black and grey metacarbonates and graphite-mica-schists. The provenance distribution is similar to the terrace deposits in the Sierra Cabrera comprising 63% of Alpujarride components. A weakly developed calcrete crust (stage II-III) was found on top of the terrace deposits. Figure 4.4.18 shows the provenance distribution of the location for the terrace of level 3 south of the mountain front. (GR. 903967); (GR. 906967); and (GR. 906959). 139 4.4.5 Terrace lowest above the modern river (terrace level 3) With the ongoing incision, the Rio Gafares cut down further into the underlying bedrock of the Sierra Cabrera leaving two terrace remnants close to the modem river behind. The fluvial deposits situated around 10 m above the modem river bed reach 2 m in thickness and overly metamorphic basement rocks of the Alpujarride complex. i Descriptiotr: terrace level 3 Terrace SE ofGranadino (Gr.895004) This terrace deposits are preserved ea. 6-8m above the RiQ Gafares bed, next to the junction of the Barranco de Aguillas along the slope. · The pebble-boulder size conglomerates are poorly sorted subrounded and clast supported. They mainly comprise schist material (54%) and a relative high component of Neogene deposits (13%). Palaeocurrent measurements have been carried out and the palaeo-flow direction indicates a mean flQw to the SW. -""- . Terrace opposite Cortijo Matias Mufloz (GR. 895996) The conglomerates of the terrace deposits opposite Cortijo Matias Mufioz (GR. 895996) are situated 5-l 0 m above the modem river bed and have been chosen as the type locality as a function of their good terrace preservation (Fig. 4.4.15). The 2 m thick conglomerates are poorly sorted and characterized by lithofacies Gms. They are clast supported within a poorly sorted, grey, silty matrix. The clast size varies between 2 cm and 80 cm along the long axis. The larger clasts show weak signs of imbrication. The clasts are aligned parallel to the modem river channel with a palaeocurrent direction of 180°. No Nevado Filabride components can be found 138 within the clast assemblage (Fig. 4.4.1 5). The deposits comprise large clasts of mica schist and metacarbonate. No pedogenic modification or calcrete is evident. Terraces between the hamlets ofGafares and El Argamason: 'Los Ranchos' South of the mountain front three terrace remnants are situated approximately 9 m above the modem river channel (Fig. 4.4.16) overlying shallow marine marls and calcarenites of the Cuevas Formation (GR. 903967); (GR. 906967); and (GR. 906959). Only the terrace deposits of hilltop 177 have been well enough preserved for detailed analysis. Terrace hilltop 177 (GR. 906959). The fluvial deposits of this terrace remnant (GR. 906959) consist of a 2 m thickness of conglomerates. The conglomerates are clast supported and moderately to poorly sorted (Gms). The clasts are subrounded and vary in size from gravel to pebble size. The mean long axis is 18.5 cm. The sediments show no internal structure and consist mainly of black and grey metacarbonates and graphite-mica-schists. The provenance distribution is similar to the terrace deposits in the Sierra Cabrera comprising 63% of Alpujarride components. A weakly developed calcrete crust (stage II-III} was found on top of the terrace deposits. Figure 4.4.18 shows the provenance distribution of the location for the terrace of level 3 south of the mountain front. (GR. 903967); (GR. 906967); and (GR. 906959). 139 ~ Alpujarride Complex ~ Nevado Filabride Complex [ffiJ Neogene infill [:=J Quartz -Schist c Fig. 4.4.15 Terrace level 3- west of the modern Gafares within the Sierra Cabrera (GR. 895997). A: Terrace deposits 11 m above the modern stream. 8: Detailed view on the large clasts - here the graphite-mica-schist clasts are strongly deformed. C: Provenance distribution of the river conglomerates. 140 t:: IQ ~ ·Q)a. ...~. .. .l!l "StJ) ·;;; (") 0 :0 0. ~ )( 8 .i! c ~ ..!!! c: Q. ·;; c:<11 8 8 Q) > ~ ~ ~ i Q) ~ ~ ~ £ :g tiJ ~ 8 .ll nsu .!!! ~ l! .c~ u:: Q) Q) U 'E 0 "0 5i t! 1il c Q) -~ ~ 0 Q. Q) "'::> -e ii: < z I 0 ~ 0"' 11101 Fig. 4.4.16 Large and small scale location map of the Rio Gafares. A: Map showing an overview of the Carboneras Basin. Box indicates the location of the detailed sketch map. B: Sketch map showing the distribution of the Gafares terraces (Grid=1km). Terrace remnants of level3 are darker coloured and their provenance distribution is presented within pie charts. Grid references refer to the 1:25,000 map (IGN, 1985). 141 Provenance Rio Gafares Te"aces level 3 (counts) Sierra 'lowland Cabrera ..."' g Ill .,8i 0 ., ...... ,0 m"' li ..: Cl li Cl Cl quartz 0 0 0 conglomerate (Tortonlan) 3 0 3 ma~s 2 0 schist 45 15 23 iron rich metacarbonate (Triassic) 2 0 0 amphibole-mica-schlst 0 0 1 gamet-mlca-schlst 2 0 sandstone 6 0 3 reef debris 0 0 0 others 8 0 4 metacarbonate (white) 13 5 18 metacarbonate (red) 6 0 2 metacarbonate (black) 4 1 5 metacarbonate (grey) 4 20 30 gypsum 0 0 0 volcanics 0 0 0 Table 4.4. 7 The table presents the provenance distribution data of the terrace deposits of terrace level3 (Rio Gafares), n=100. Terrace /eve/3 Terrace location Terrace left hand Terrace right hand Average m (mountain) riverside river side above the (looking upstream) (looking upstream) modern river bed base of terrace as/ base of terrace as/ SE of Granadino 315 (Gr.895004) 13 anomalous E of Cortijo 295 (GR. 895996) 8 Matias Murioz Average m 8 above modern river for level 3 Terrace location .(lowland) 195 (GR. 903967) 11 186 (GR. 906967) 8 175 (GR. 906959i 15 Average m 11 above modern river for level 3 .. Table 4.4.8 Table summans1ng the descnbed and analysed terrace depos1ts of terrace level 3 and their location in the field. 142 ii Reconstruction of the palaeoenvironment: terrace leve/3 Terrace level 3 comprises two remnants within the mountain, and three remnants in the lowland area. Except for the terrace SE of Grenadino, they can all be grouped into terrace level 3, using field description, provenance distribution and mainly terrace heights. The terrace SE of Grenadino (Gr.895004) does not seem to belong to this level. The provenance distribution of this small terrace near the modern river bed is mainly dominated by schist fragments and only 33% of Alpujamde components. In contrast to it, the other terraces of this level consists of 63% Alpujamde clasts. This shows that the terrace remnant south of Grenadino is the equivalent terrace of the tributary stream (Barranco de Agiiillas) which enters the Rio Gafares just 10 m north of it. The terrace deposits near Cortijo Matias Munoz differ in their lithology from the ones south of the mountain front. The angularity of the clasts and the lack of sorting point towards a short distance of transport and a rapid deposition. The large clast size suggest a high-energy flow, maybe a gravity flow, where large masses of loose sediment are mobilised on a sloping surface, which is typically after heavy rainfall (Miall, 1984). This seems to be a localised feature since these characteristics cannot be found in any of the other terrace remnants, suggesting a slope failure in this area. This is a feasible explanation since the terrace deposits are situated at the outside of a sharp, high angle meander loop of the modern river, favouring bank side erosion and slope instability. The deposits south of the mountain front measure a much smaller clast stze (maximum clast size 18.5 cm long axis). The lack of sorting indicates a rapid 143 deposition. The poor sorting and the lack of any sedimentary structures point towards a transport as bedload in a turbulent flow (Miall, 1978; Costa, 1984). The existence a stage II calcrete development suggests a Late Pleistocene age for the terraces. 4.4.6 River incision The incision of the Rio Gafares was measured from the modern river channel up to the base of the terrace remnants. The heights between the various terrace levels and the modern channel differs between the mountain area and the lowland part (see Table 4.4.9). The incision between terrace levels Tl - T2 lies around 21 m within the mountain area. Between T2-T3 the river incised approximately 25 m within the Sierra Cabrera and only 14 m in the low lying area. Incision after the aggradational period of terrace level 3 is very similar with 8 m in the mountain area and 9 m in the lowland south of the mountain front. The staircase diagram demonstrates the incision of the Rio Gafares for the mountain area and for the area south of the mountain front (Fig. 4.4.17). 144 Rio Gafares terrace levels Rio Gafares terrace levels A mountain area B lowland 360 height (m) 340 240 +54 m 320 220 +33m 300 200 Terrace 4? modern modern 280 180 Fig. 4.4.19: Staircase diagram for the Rio Gafares. The different terrace level are 260 conglomerates 160 shown with there total amount of incision. A: Profile through the mountain terraces. Please :::r a- (::::::::::::::::::::::::::1 Neogene sediments note that there are no data for terrace level 4. c B: Terrace levels and incision shown in the cc :::r 240 ~ metamorphic basement 140 lowland area. :T ro 3 0 c ::Im ::I 4.4.7 Provenance development The provenance of the terrace conglomerates is divided into 5 groups. Each group gives an indication of the source area of the clasts (see chapter 2, section 2.4.6). The Nevado Filabride complex which mainly comprises Amphibole-Mica -Schist is used as a marker lithology for the localized source area of the Sierra de los Filabres (Sorbas Basin). provenance development % 80 60 •level1 !>'! level2 40 ll.ll level3 IJ modern 20 c s s.., ~.. i a" f Fig. 4.4.18 Provenance development of the Rio Gafares showing the variation in provenance between T2, T3 and the modern river (terrace level T1 only exists in the form of strath terraces, so no provenance analysis has been carried out) In general the amount of Upper Alpujarride (metacarbonate), quartz and Nevado Filabride components decreases with the increasing age of the river system. The amphibole-mica-schist (main trace component of the Nevado Filabride) has been traced in decreasing proportions of the total clast assemblage from terrace 2-modem. In contrast, the amount of Neogene components and schist fragments (Lower Alpujarride components) increases from the oldest to the younger terraces (Fig. 4.4.18 and Table 4.4.9). 146 4.4.8 Discussion of the Gafares evolution i Alpujtirride Units- Provenance change as an indicator of drainage evolution The idealised basement stratigraphy for the western Sierra Cabrera is described by Rondeel (1965) as Lower Alpujamde composed of an underlying mica-schist sequence, followed by a phyllites-quartzite unit, topped by an Upper Alpujamde limestone-dolomite unit. This stratigraphic order is represented within the terrace levels Tl-T modem of the Rio Gafares within the Sierra Cabrera through the erosional unroofing of the basement. With the Early Rio Gafares gradually eroding into the Upper Alpujamde Unit, the provenance of this unit (dolomite and metacarbonate) can be found in large amounts in terrace level 2 and in decreasing proportion within the terrace levels as they get younger. The opposite is true for the Lower Alpujamde Unit (schist). With the river incising further into the metamorphic bedrock and finally reaching the Lower Alpujarride mica-schist unit, the proportion of mica-schist clasts increases as the terraces get younger. ii Neogene component -Provenance change as an indicator for river incision It is very difficult to measure a significant increase in Neogene components from T2- T3, since the sediments of the Younger Neogene (e.g. marls of the Abad Member and calcarenites of the Cuevas Formation) only occur within the basin, but not within the mountain area. The only exception is the sandstones of the Azagador Member which is preserved at the southern border of the Sierra Cabrera (Fig. 4.4.19). Therefore more Neogene components were found in the terraces south of the mountain front (e.g. Los Ranchos, hilltop 219 m) compared to the terraces within the Sierra Cabrera (e.g. terraces near La Rondena). The increase in Neogene components from the headwaters of the river to further downstream is due to the increase in availability of 147 the underlying Neogene sediments south of the mountain front and the subsequent eroston. iii Amphibole-mica-schist- Provenance change as an indicator for river incision Arnphibole-mica-schist mainly belongs to the lowermost complex of the structural units in the Betic zone, the Nevado Filabride complex. This unit is mainly found in situ within the Sierra de Ios Filabres at the northern margin of the Sorbas Basin, whereas the Sierra Cabrera is principally composed of rocks of the Alpujarride complex (Rondeel, 1965). Arnphibole mica-schist within the terrace conglomerates could therefore only have been derived from the bedrock of the Sierra de Ios Filabres or as reworked clasts from an older conglomeratic sedimentary unit (e.g. Tortonian Azagador Mbr conglomerate that may have originally been sourced from the Sierra de Ios Filabres). The Azagador Member can be found all across the Carboneras Basin and even at the southern margin of the Sierra Cabrera. However the amphibole mica schist within the Azagador Mbr conglomerates occur only as small fragments (approx. 1 cm) and never as larger rounded clasts (several cm along the long axis within the river conglomerates). Furthermore a detailed study (Hodgson, 2002) described the Azagador Mbr overlying the pink-reddish well cemented sandstone beds of the Chozas Formation. The red beds consist of sandstone and sandstone conglomerates. The terrace deposits of the upper terrace levels of the Gafares do not contain large or equal amounts of red sandstone. It seems therefore to be unlikely that only the amphibole-mica-schist should have been derived from the Azagador Mbr, but no underlying red sandstones. The possibility of reworked amphibole-mica-schist material from the Azagador Member within the Plio/Pleistocene terrace remnants is therefore unlikely. 148 Fig. 4.4.19 The modem incised Rio Gafares draining from the mountain front into the lowland area. View is 0.5 km across. iv Provenance change as indication for drainage rearrangement The existence of amphibole-mica-schist in terrace level 2 and 3 (1%) identifies, as discussed above, the Sierra de Ios Filabres (Sorbas Basin) as a potential source area for the terrace deposits. This shows that there must have been a connection between the Sorbas Basin and the Carboneras Basin through the Rio Gafares during the deposition of terrace level 2 and 3 and probably level 1 as well. The decrease in Nevada Filabride components from terrace level 2 to the modern river deposits suggests a restriction of the $ediment supply from the Sierra de Ios Filabres and therefore an exhaustion of the Sorbas-Carboneras connection after terrace level 3. This decrease in amphibole-mica-schist clasts derived from the Sierra de Ios Filabres and the related disconnection might have been the result of river capture or river re- 149 routing of the Rio Gafares. Mather and Harvey (1995) proposed a drainage rearrangement for the. Rio Gafares similar to the one they discovered for the Rambla de Ios Feos (Harvey and Wells, 1987; Mather, 1993; Harvey et al., 1995). The Rambla de Ios Feos capture is a classic example for drainage re-routing and will be described in the later part of this chapter. In the case of the Rio Gafares it is not exactly clear what caused the disconnection to the Sorbas Basin. From the provenance record of this study and the knowledge about the mountain uplift we have from previous work (Harvey and Wells, 1987; Mather and Blum, 2000) we can assume that the main drainage of the Rio Gafares was re-routed due to a direct or indirect consequence of the ongoing uplift of the Sierra Cabrera. There is no topographic or sedimentological evidence for a possible capture from the Rio Aguas. Since no terrace remnants have been found at the northern margin of the Sierra Cabrera, due to erosion it is very difficult to reconstruct the exact processes. 4.4.9 Summary of the evolution of the Rio Gafares The consequent drainage system of the Carboneras Basin is a transverse drainage through the Sierra Cabrera. Oherlander ( 1985) defined transverse drainage as rivers that cut across tectonically controlled geological structures such as faults, folds and orogenic mountain belts. The primary drainage represented by the Gafares and Rambla de Ios Feos was probably antecedent, which means that the river existed prior to tectonic activity and incised into an uplifting surface. This can be assumed due to the fact that during the Messinian the lack of reef deposits along the margin of the Sierra Cabrera points towards an uplift of this mountain range post dating the Messinian. This signifies that the Sierra Cabrera was not elevated above sea level 150 prior the Pliocene, favouring a consequent drainage from the Sorbas Basin towards the deeper Carboneras Basin towards the South. Harvey and Wells (1987) also support the theory of a Pliocene marine continuity across the Alhamilla-Cabrera axis. With the withdrawal of the Pliocene Sea the drainage across the Sierra Cabrera developed and fan deltas and river terraces were deposited within the Carboneras Basin. Nevado Filabride components were preserved within the terrace levels of the Rio Gafares, a lithology with no mapped local source in the Sierra Cabrera. The only major source area is in the higher grade metamorphics of the Sierra de Ios Filabres at the northern margin of the Sorbas Basin. We can therefore assume that the Nevado Filabride clasts were most likely supplied by detritus originally derived from the northern margin of the Sorbas Basin. With the ongoing uplift of the Sierra Alhamilla Cabrera range the Gafares drainage was re-routed, possibly by river capture. The re routing of the Gafares headwaters resulted in a change of clast assemblages within the terrace deposits. However with the loss in catchment size the Gafares system suffered a reduction in water and sediment supply to the systems and could not keep pace with the mountain uplift, which meant a complete disconnection from the Sorbas Basin and a restriction of the headwaters to the Sierra Cabrera. 151 --u-. ~ CD Q) CD -· C" Terrace! Height Incision Sedimentology Provenance Soils (/) - m-sa> Strath ran e -CDxo~ • Level 1 Strath 370-340 m Description N/A N/A -:::J~ QcnC.O Early (mountain) N/A Pleistocene Interpretation a. I (/) CD c Q) 3 3 a;· 8. 3 Level2 Terrace 365-315 m incised by 21 m Description mature (GR. 899968) Q.CDQ) (mountain) (mountain) -3m thick calcrete Q)3-< :::J-o 215-184 m and by? m -gravel-boulder size o.t..... ft.ld l lf Q)(l)- (lowland) (lowland) conglomerates '<....,;;x:--...., ~ . ~CD below level 1 -clast supported ~m'< -poorly sorted -.mC/)(0 Mid -sub-rounded ....,~0 Pleistocene -mature calcrete (50 cm Q) 0- -eo thick) =r - · -red colouration I!IEBII Alpujarride CD_-£ -palaeocurrent 118 IDDDJl Nevado Filabride d5 Q) Interpretation Vl -:::J GEJ. Neogene infill N ~a. -high energy >3 hyperconcentrated flow 0 Quartz coo -pedogenic modification CD ...., - Schist C/)=:J"- · "0 a.O Level 3 Terrace 295 m incised by 25 m Description a...... tn weak (GR. 906959) CD 0 (mountain) -eo (mountain) -clast supp. calcrete CD - · Late 195-175 m and by 14 m -lack of sed. structure 3_...., £ Pleistocene (lowland) (lowland) -moderately sorted s · Q) below level 2 Interpretation CD;::: a.::::!. traction current ....,- cC'" .,.. __ o- modem Terrace incised by 8 m Description no calcrete, (GR. 895965) 3 CD (/) (mountain) -poorly sorted • no soil o-Q) 0 and by 9 m -clast supp. _...., Ho/ocene Q CD (lowland) -imbrication CD Q) below level 3 Interpretation -o CD=r traction current ~0 Q)- CO CD =r CJ) CD 4.5 The modern Rio Alias The subsequent Alias system developed as a strike orientated drainage south of the Sierra Cabrera mountain front, axially draining the Carboneras Basin from W to E. The modem Alias is formed by the confluence of the Rambla de Lucainena and Rambla de Ios Feos. The transverse Feos system, draining from N-S via a wind gap within the Sierra Alhamilla I Cabrera, joins the Rambla de Lucainena 4 km south of the mountain front (Fig. 4.5.3). The Lucainena system runs along the north-western margin of the Carboneras Basin axially draining the basin from west-to-east. The originally consequent Lucainena system incised into and headcut across the Sierra Alhamilla. Being able to headcut through weaker lithologies the river successively captured the south to north flowing drainage of the Sorbas Basin (Mather, 1991, 1993a; Mather and Harvey, 1995). The Lucainena system is still headcutting back and future river captures are imminent (Mather and Harvey, 1995). The most recent work done on the evolution of the Lucainena drainage is by Maher, (2006) . Approximately 3 km after the confluence of the Feos- and Lucainena system, the modem Rio Alias is· joined by a third river, the Rio Gafares. The Rio Alias channel meanders further east, crossing the Carboneras Fault Zone after 2.5 km. Another 4 km eastwards (see Fig. 4.5.2) the Rio Alias is joined by a fourth river, the Rio Saltador, before entering the Mediterranean Sea, 4 km further east, at the river mouth, north of the village of Carboneras. Most streams in the northern part of the Carboneras Basin drain from North to South or NE - SE. Only a few very small tributaries (ramblas) join the Alias from the south, e.g. Rambla de la Palmerosa. 153 The four large rivers which join (or form) the Alias all have very different catchment area to each other, in terms of size and underlying geology. The most western river, the Rambla de Lucainena is draining the western part of the Sorbas Basin, the modem Rambla de Feos is restricted to the gap between the two mountain ranges, Sierra Alhamilla and Cabrera, the Rio Gafares is restricted to the Sierra Cabrera and the Rio Saltador is draining the eastern part of the Sierra Cabrera. Since those rivers, in flood events, transport significant amounts of sediment down their channels into the Rio Alias, we can expect a whole variety of clasts assemblages within the Alias system. This diversity makes it very difficult to allocate a single terrace remnant to one of the various terrace levels on the basis of provenance, since the provenance distribution within any one terrace level can change dramatically (see Fig. 4.5.3 and Table 4.5.1 for provenance distribution data of the modem Rio Alias). Provenance Rio Alias Modem re"aces (counts} ... .., ~ ~ "' ...... :;:"' lli ~ ~ Cl quartz 0 0 0 conglomerate (Tortonian) 0 8 3 mans 7 11 2 schist 45 25 33 iron rich metacarbonate (Triassic) 4 3 0 amphibole-mica-schist 0 3 garnet-mica-schist 0 0 sandstone 0 0 1 reef debris 0 20 0 others 0 0 metacarbonate (white) 21 12 31 metacarbonate (red) 12 6 10 metacarbonate (black) 0 10 15 metacarbonate (grey) 5 13 2 gypsum 0 0 3 volcanics 0 0 5 Table 4.5.1 The table presents the provenance distribution data of the modern terrace deposits, n=100. !54 b b N b + 0 2 b I km I Mediterranean .J Abandoned meander loops ...... Deep canyons ~+ Nick points i.li Gypsum escarpment ••• Azagador escarpment Major faults ~ Main drainage net ~~l b Basement rocks 0 Fig. 4.5.2 Modern Rio Alias. A: View of the river bed of the modem Alias near El Uano de don Antonio (GR.935953) showing the modern terrace on the left hand side of the picture. Person is 86 cm for scale. Note the width of the modem valley. B: Detail of the modem river bank conglomerates (measuring tape= 1 m). Note the light imbrication of the clasts in the lower third of the picture. C: Provenance distribution of the conglomerates of the modern river. 156 +Z ...ns .ce c: ·-m ·:::::::::· nJ il~ m 1/) C'O m ~· nJ... Q) c: 0 .c... nJ (.) N E .)I! ~ Ci E ~ 8 0 Ci Q) 0 .0 ~ ..!!! ~~ .!: tJ - "0 u. Q) ·- ns ·- ·E o ij N Ci) ~ ._E "'""a>t: ._u G>ns._ .e.~~ow>"3'!J!o~-5o 111111111111111111111111 E - u; ~ 1 iE~ID~ I D Fig. 4.5.3 Sketch map of the major modern drainage systems within the Carboneras Basin and their provenance distribution. The sample location is indicated by a star. Note the large variety of the provenance distribution between the different sample locations. 157 4.6 The terrace sequence of the Rio Alias Numerous terrace fragments can be found along the valley sides of the Rio Alias. They have been grouped according to their heights above the modem river bed, mapped, described and analysed (see chapter 2 and section 4.2 for detailed methodology). Mapping the land form sequence reveals a spatial clustering of terrace fragments within the individual terrace levels. Figure 4.6.1 shows the location of the terrace remnants of the Rio Alias within the study area and Fig. 4.6.2 presents a terrace height diagram. 4.6.1 Previous work on terrace remnants within the study area Harvey (1995) investigated river terraces of the Feos system in line with his work carried out on the Sorbas drainage. Terrace remnants are preserved all the way from the Sorbas Basin into the Carboneras Basin, via the gap in the Alhamilla/Cabrera mountain range. This connection was the main link between the Sorbas and the Carboneras Basin until the Late Pleistocene as shown by Harvey and Wells, (1987); Mather, (1991). Harvey and Wells, (1987) suggested that the main drainage of the Sorbas Basin, draining into the Carboneras Basin via the Feos system was cut off by river capture. During this period, due to ongoing regional uplift of the Sorbas Basin, the Rio Aguas of the Vera Basin was aggressively headcutting back towards the west capturing the main Sorbas drainage. (Harvey and Wells, 1987; Harvey et al. 1995). Harvey et al. (1995) mapped four main terrace levels downstream of the Aguas/Feos capture site (terrace A-D, with A being the oldest). Candy et al. (2005) dated the calcrete of the terraces associated with the river capture (C terrace) at 69.8±2.2 ka. 158 Levels A-C are very similar to the ones upstream of the capture and all three terrace levels can be traced across the Sorbas/Carboneras Basin margin within the mountain area. South of the mountain front terrace A is impossible to follow due to overlying younger deposits (Harvey et al., 1995). However Mather (1991) found fluvial conglomeratic sediments overlying the Feos fan delta deposits, which may be equivalent of terrace A. Terrace B has been deformed by faulting (Harvey and Wells, 1987) and since the formation of terrace C there has been almost no dissection in the Feos system (south of the mountain front, i.e. in the Carboneras Basin); with deposits of terraceD overlying C gravels (Harvey et al., 1995). In order not to confuse the terrace levels of this study with those of Harvey et al., (1995) and Harvey and Wells (1987), this study will use a different nomenclature (terrace 1-3 or 4 depending on the river staircase). The number I terrace level was assumed to be the oldest, as it was the highest. Although it can be very difficult to use the heights of the terraces in a tectonic active area on its own, together with lithology, provenance distribution and the large scale tectonic movements a general agreement between heights and age can be obtained. Possible correlation of the terrace levels in this study with those of Harvey and Wells (1987) and Harvey et al. (1995) will be discussed after careful field investigations and examinations of the river remnants. 159 ~ Cl) c ~ Cl) ~ 0 .. Q. 0 Q) "'0 0 ~ :;::; !.! e! · - Q) a> Cl) 0>0 E 1'0c:G>- Q. 0 ·n; "0 g> -o-L. 1'0 8 .... G> L. i .2_ "0 Q) ill Q. (fJ 1'0 c: a...- Net>...,. 0 E~ :H- f- f- I- iX ( 0 0 ~ 0 0 1 ~~ ~ .. .si :98E..., +z ~-8 Fig. 4.6.1 Sketch map of the Rio Alias, its tributaries and conglomeratic deposits, e.g. fan delta sediments, upper conglomeratic unit and terrace deposits. The terrace remnants are grouped into level from 1-4, with 1 (T1) being the oldest fluvial terrace remnant. The ones which are described in detail in the text are numbered. 160 0 N .·.. ... , .... • •• I .., .... • ('t) •: • • I ...... NI / t-1 ... CD I :· I :: ~ ...... 00 0 ~ N ~ .., ~ CD ~ 00 ~ 0 0 8 ~ 8 I() N ~ ~ Fig. 4.6.2 West-East longitudinal profile of the Rio Alias and height range diagram of the terrace remnants. Beginning at the Lucainea-, Feos-, Alias confluence downstream to the river mouth entering the Mediterranean. The heights of the terraces was measured at the base of the deposit. The terrace were grouped into different levels (see text for details). 161 4.6.2 Conglomeratic deposits highest above the modern river Two conglomeratic deposits (40 m above the modern river bed) have been studied in detail and described below. They are grouped into this paragraph in order to separate them from the river terrace conglomerates described in 4.6.3. i Description: highest conglomeratic deposits Section west of Los Cortijillos (GR. 877951) At hilltop 219 a conglomeratic unit crops out north of the modem Rio Alias. The outcrop is no.l (upper conglomeratic deposits) in Figure 4.6.1. The conglomerates are matrix supported (Gms), with a medium sandy matrix. They are sub-rounded and weakly cemented. Most of the conglomerates lack internal structure. Where bedding occurs it is typically sub-horizontal. Some of the beds show scours, which are infilled with sandy deposits (Sm-Sh). The provenance data is shown in Table 4.6.1 and Figure 4.6.3, the maximum clast size in Table 4.6.3. Section south-west of Los Cortijillos (GR.875943) The outcrop (Fig. 4.6.3) south of the modern Rio Alias shows at least three different facies: (a) medium grained sand, weakly horizontal laminated (Sh) overlying and intercalated with (b) clast-supported polymodial conglomerates (Gm) and (c) matrix (sandy matrix) supported conglomerates (Gms). The clasts in both lithofacies units are well to moderately sorted. Their provenance distribution is presented in Fig. 4.6.3 and Table 4.6.2. The measured palaeocurrent direction is 323. NE, but imbrication is not very abundant. Towards the top, these deposits show a slightly red colouration. The base of the deposits is situated 40 m above the modem Rio Alias. The terrace heights above the modem river channel are illustrated in Fig. 4.6.2 and Fig. 4.6.1 (no.2- upper conglomeratic deposits) shows the location in relation to other outcrops. 162 w .. ______.. ------______·------·------.. __"- _ ·------·------·------f:::E:::E~::::jF:g:-:·~ '1~. N 0 c Fig. 4.6.3 Upper conglomeratic deposits of the Rio Alias. A: Detailed picture of the conglomerates north of the modem river channel (GR. 877951 ). A large amount of reef debris has been found within the conglomerates. B: Terrace deposits of the upper conglomeratic unit south of modem Alias (GR.876943). C: Sketch map showing the location of the two outcrops. D and E: Provenance distribution pie charts. Note the relatively large amount of Nevado-Filabride components. 163 Rio Atlas Provenance Highest conglometatJc unit (counts) quartz 0 0 conglomerate (Tortonian) 2 0 ma~s 10 7 schist 20 35 iron rich metacarbonate (Triassic) 7 6 amphibole-mlca-schist 25 22 garnet-mica-schist 0 sandstone 0 0 reef debris 0 others 0 0 metacarbonate (IMlite) 35 33 metacarbonate (red) 6 3 metacarbonate (black) 5 3 metacarbonate (grey) 2 1 gypsum 0 0 volcanics 0 0 Table 4.6.1 The table presents the provenance distribution data of the highest conglomeratic deposits, n=100. Terrace location Terrace location Average m above the (lowland) base of terrace modern river bed as I hilltop 219, west of 200(GR. 877951) 40 Los Cortijillos (no.1) upper congl.) section south-west of 200 (GR.875943) 40 Los Cortijillos (no.2 upper congl.) Average m above 40 modern river .. Table 4.6.2 Table summanstng the descnbed and analysed conglomeratic deposits of and their location in the field. The mean maximum length of the clasts is very similar between the two outcrops, as is the height above the modem river bed (40 m). At both locations the maximum clasts show a large range in size along their a-axis (Table 4.6.3). 164 Length (a-axis) L (cm) location n=IO mean +- SD range upper conglomerate unit (877951) 18.6 ± 2.41 15-22 upper conglomeratic unit (876943) 19.5 ± 5.2 13-30 Table 4.6.3 The mean and Standard deviation of the largest clasts within the conglomerates at the two locations wesUsouthwest of Los Cortijillos (GR. 877951) and (GR.875943). ii Reconstruction of the palaeoenvironment: highest conglomeratic unit The overall palaeoenvironmental setting represented by the described facies association is difficult to interpret. The multiple lithofacies units suggest successive depositional events. The variety in grain size between the units points towards rapidly varying flow conditions. The red colouration is associated with pedogeneses, which indicates a sub-aerial environment. These conglomerates seem to correspond with the Upper conglomeratic Unit of the Po1opos Formation of Mather (I 993b). Mather (1991) suggested a braidp1ain environment for the upper conglomeratic unit of her Polopos Formation. 4.6.3 Terrace highest above the modern river- (terrace levell) A large number of terrace remnants have been found at heights of approximately 57 m above the modern river channel. They are mostly situated within the western part of the Rio Alias, before the confluence of the Rio Gafares. The majority of the terrace remnants show a very distinct flat top surface, readily recognizable in the field and on the topographic map. Only the best preserved ones have been described below. A few terraces show a distinctive flat surface, capped with a calcrete crust and loose 165 pebbles on top, but do not expose any conglomerates below the calcrete top. They therefore have been mapped onto Figure 4.6.1, but they have not been numbered and have not been plotted onto the terrace height diagram (Fig. 4.6.2). A detailed descriptive analysis of these deposits is not possible. i Description: terrace level] Section south of Feos, Lucainena, Alias junction (GR. 866946) The terrace outcrop south of the Lucainena-Alias junction (GR. 866946) is one of the most impressive ones along the Rio Alias (Tl no.1 on Fig. 4.6.1 ). The 10-15 m thick fluvial conglomerates form the top of a 45 m high cliff at the southern end of a meander bend (Fig. 4.6.4). The cliff is situated south of the triple junction of the Lucainena, Feos, and Rio Alias. Although the conglomerates are not well cemented, they are matrix supported (Gms), have subrounded clasts and moderately to poorly sorted and capped by a massive stage IV calcrete. The largest clasts measure a maximum of21 cm along their a-axis. Unfortunately the access to the conglomerates is only possible from the top of the cliff and with a height of at least 45 m access is thus very limited. Therefore no further intensive analysis of the river deposits has been carried out. Section west of Cortijada de Ios Alamillos (GR. 878953) The outcrop west of Cortijada de Ios Alamillos (hilltop 209) reveals 2 m of thick well cemented, matrix supported conglomerates (Gms), moderately sorted with no calcrete top. The unit does not show any signs of stratification. The largest clasts measure on average 11 cm along the a-axis and the provenance distribution shows a relatively large amount of Nevado Filabride (30%) and Alpujamde (61 %) material and only 166 very small Neogene (9%) and schist (ll %) components (Fig. 4.6.9). The mean pa\aeocurrent direction was 51 o, which indicates a palaeoflow towards the NE. The terrace is no.2 ofTl at Figure 4.6.1. Type locality- Section east ofCortijo de las Norias (GR. 886947) The region between Cortijo de \as Norias and Cortijo e1 Molino de Abajo has the best terrace outcrops (Fig. 4.6.5). The area lies in the inside of a meander loop of the modem Rio Alias (see map on Fig. 4.6.1) and provides well preserved examples of terrace deposits. The section east of Cortijo de \as Norias was chosen as the type locality for the terraces of level 1 (number 3a and b on Fig. 4.6.1.), since it provides a very well preserved terrace conglomerate. The deposits are matrix supported and moderately to poorly sorted (Gms). No bedding or any stratification is visible. A massive calcrete caps the conglomerate and occurs towards the top. The carbonate crust contains small, well rounded pebbles, mostly quartz, and has a reddish appearance; it can be defined as massive stage IV calcrete. The c\ast assemblages taken from the non-calcrete section contains 26% Nevado Filabride material, less than 2% quartz and only 9% schist. The clasts show a clear imbrication. The mean palaeocurrent direction shows a palaeoflow of 116° SE. The terrace deposits extend further towards the west and were exposed beautifully during building work of a pipeline (January 2003) along the dirt track (Fig. 4.6.5), (GR. 884948). The conglomeratic deposits show the same lithological features as the ones described above. The provenance distribution is, with 23% Nevado Filabride material, 0% quartz and only 7% schist, also very similar to the adjacent outcrop of Cortijo de las Norias described above. Red soils development is only very localised and not laterally extensive. 167 A (d) Jc~~~ '--. conglomerates ~ erosion surface eroded blocks (b) gypsum l::J " (a) Cj marls m Alpujarride Complex § Nevada Filabride Complex [:fff~ Neogene infill c=J Quartz 52% -Schist c 0% Fig. 4.6.4 Terrace deposits on top of large cliff. Photograph taken facing South. Cliff is 45 m high. A and B: Thick river terrace (d), overlying marls (a), gypsum (b) and shallow marine (c) deposits. C: Provenance distribution of the terrace conglomerates. 168 Fig. 4.6.5 Terrace conglomerates of level 1 near Cortijo de Norias. A: Outcrop laid open during building work for pipeline (GR. 887947). Fluvial deposits overlying fine grained marine sediments. 8: Detailed picture of the upper part of the terrace deposits. This is one of the rare locations of terrace level 1, where soil is developed. Only a thin veneer of calcrete is preserved. C: Provenance distribution of (GR. 887947). 0: East of Cortijo de Norias (GR. 885945). The tape measure is 1 m high. The palaeocurrent direction is 116°. The clasts are well cemented. E: Provenance pie charts for these conglomerates. 169 Section easternpartofthe meander (E ofmodern river- GR. 891957) A well preserved terrace remnant (Fig. 4.6.1 number 4) on the eastern side of the modem Alias meander bend has been investigated (Fig. 4.6.6). The fluvial deposits can be found 50 m above the modem channel. The conglomeratic deposits reach 6 m in thickness. The conglomerates consist of matrix supported (Gms), well rounded clasts. The clasts are moderately sorted. No obvious sedimentary structure has been observed. Towards the top there is a weak red colouration to the sandy matrix. The unit is topped by a massive pedogenic calcrete in some places (stage N). Section NW ofEl Llano de don Antonio (GR. 934954) Exposures west of El Llano de don Antonio show a group of individual terraces remnants, situated south of the mountain front; overlying elevated Neogene deposits (see Fig. 4.6.7 for a geological sketch map). The terrace deposits are located close (between 100 and 500 m) to the modem Rio Alias. They are located less than one kilometre apart from each other. Only one of the terrace remnants (number Sa and b on Fig. 4.6.1) is well enough preserved to warrant further investigation, however. These deposits are described and analysed below. The terrace deposits of hilltop 169 (GR. 934954), are composed of l - 2.3 m thick conglomerates erosively overlying shallow marine calcarenites of the Cuevas Fm or small grained beach conglomerates of the Polopos Fm (Fig. 4.6.8). The conglomerates are matrix supported and comprise poorly sorted, sub-rounded clasts within a sandy matrix (Gms). The conglomerates lack any internal structure. The clasts show an average maximum of 17 cm along their a-axis and do not show imbrication. Palaeocurrent measurements were therefore not possible. The 170 conglomerates contain a large amount of amphibole-mica-schist (16%), and quartz (9%). The pedogenic calcrete development on top of the terrace is massive with a thickness ofO.S- l m (stage IV). Provenance quartz 0 0 2 0 0 10 conglomerate (Tortonian) 0 0 5 0 0 2 mans 0 2 6 0 3 schist 32 10 9 7 18 8 iron rich metacarbonate (Triassic) 3 2 2 2 11 7 amphibole-mica·schist 20 30 26 22 13 17 gamet-mlca·schlst 0 2 0 0 0 0 sandstone 0 0 0 0 0 2 reef debris 7 10 0 0 others 0 0 0 0 0 0 metacarbonate (white) 45 35 28 35 35 21 metacarbonate (red) 4 7 6 12 15 12 metacarbonate (black) 3 12 8 5 1 20 metacarbonate (grey) 3 5 8 2 12 5 gypsum 0 0 0 0 0 0 volcanics 0 0 0 0 0 0 Table 4.6.4 The table presents the provenance distribution data of the terrace deposits of terrace level 1, n=1 00. Terrace location Terrace location Average m above the (lowland) base of terrace modern river bed asi hilltop 215, south of 210 (GR. 866946) 38 Luc./Feos/Aiias confluence (number 1) hilltop 209 (number 2) 207 (GR. 878953) 47 near Cortijo de Ias Norias 202 (GR. 886947) 47 (number 3) 198 (GR. 884948) 45 Section eastern part of the 195 (GR. 891957) 50 meander (number 4) Terraces NW of El Llano de don 158 (GR. 932954) 80 Antonio (number 5) 167 (GR. 934954) 94 Average m above modern river 57 for level 1 .. Table 4.6.5 Table summans1ng the descnbed and analysed fluvtal conglomerates of terrace level 1 and their location in the field. 171 c Fig. 4.6.6 River conglomerates of terrace level 1 (GR. 892956) within the eastern meander bend of the modern river Alias. A and C: Photographs showing conglomeratic deposits of the same terrace. B and D: Provenance distribution charts. Data where taken from the same terrace, but at different heights. 172 r"T1 ii) c5' ::J · 93 94 0 .,.,. a.· (I)~ 0....., N oG) ::J (I) )>0 ::J 0 t -eo 0 - · Q) 2. £ ...... c: o- i ...··· en ; I A' ! I ~ (I) 96 :I 0 0 I\ , en D Plio-Pieistocene conglomerate (T3) ~ 0 ·- =~ 3 J ! ~ a.. a.. Plio-Pieistocene conglomerate (T1) Q) I ;< '"0 i / : D Calcareous conglomerate (fan delta) 0 it ~ I I Q) -:;: // c: D Calcareous conglomerate (beach) (I) ...... ;:/ ~ en ...... 2 D Calcarenites (sandy Cuevas Fm) -.....-...l c a.. a D Limestone (marty Cuevas Fm) c 95 ::Jc. Gypsum (Yesares Fm) s· D CO D Tortonian andesites ...,Q) (I) Q) - Triassic sediments 0 0Notmapped -ar 1 km ~ Q) -- Faultline £ ~ ~ Q) CO ::J (I) Q)..., m 0 Fig. 4.6.8 Well preserved terrace deposits of hill 169 of terrace level 1 of the Rio Alias (GR. 934954 ) - please see text for further explanations. A: Overview of the river terrace, demonstrating the flat surface on top of the conglomerates. The terrace is situated nearly 94m above the modern channel of the Rio Alias, where the photographer is standing. 8: Well cemented, poorly sorted conglomerates (b), overlying beach deposits (a), described in detail in section 4.6.3. Note the large clast size. The measuring tape is 1m long. C: Provenance distribution of the terrace conglomerates. The conglomerates contain a relatively large amount of quartz components. 174 Length (a-axis) L (cm) location n=IO mean +- SD range terrace level I (GR. 866946) 21 ± 2.4 18-25 terrace level I (GR. 878953) 11.7 ± 2.98 8-16 terrace level I (GR. 932954) 14±2.26 12-18 Table 4.6.6 The table presents the mean and Standard deviation of the largest clasts within the conglomerates at three outcrops of terrace level 1 (one in the upper reaches, one in the upper-middle reaches and one in the lower reaches of the Rio Alias). ii Reconstruction ofthe palaeoenvironment: terrace level I The above described terraces have been difficult to allocate to one level - Tl. Though the terrace surface (number I) of the huge cliff south of the triple junction (GR. 866946) is situated only 38 m above the modem river bed, compared to 58 m for the other terrace bases of this level it is not clear to which terrace level this terrace belongs. According to the terrace height diagram the terrace deposit should belong to terrace level 2. Findings in the field (e.g. provenance distribution and lithology of the conglomerates) do not support this idea. The lower heights above the modem river in comparison with the other terrace remnants of level I, might be due to movements triggered by small faults or tension cracks at the bottom of the cliff (Fig. 4.6.4), since the terrace remnant is situated just a few hundred metres south of the Feos-Lucainena confluence. The terrace deposit of hilltop 209 (GR. 878953), (number 2) do not show a calcrete surface. However the lithology of the clasts and the similarity of the provenances places this terrace into terrace level I. 175 There are slight difficulties in assigning the terrace remnants (number 4) of the eastern part of the meander (E of modern river- OR. 891957) to one specific terrace level or even to one specific river, because of the spatial. positioning (see Fig.4.6.1 for location and Fig. 4.6.6 for conglomerate details). The deposits reach the same height above the modern river channel as the other Alias terrace deposits of level 1, however the Rio Gafares enters the Rio Alias just 500 m east of this outcrop. Using the provenance distribution in order to distinguish between the two different rivers, the conglomerates of the above described terrace are more likely to have been deposited by the Rio Alias. The terrace remnants near El Llano de Don Antonio (no.S) are located 80-94 metres above the modem Rio Alias. This is nearly double the heights than the terraces near Cortijo de !as Norias (levell). The fact that they are overlying beach sediments of the Polopos Formation shows how far north of the basin they are located (see Chapter 3 for beach sediment distribution). The only terraces, so far, overlying beach sediments are the terraces of the Rio Gafares in the Los Ranchos area, which show also a similar terrace top heights. The large amount of quartz components within the conglomerates near El Llano de Don Antonio is not comparable to any of the other terraces of the Alias, or Gafares system. However they could easily been a result of the river incising into and eroding fan delta material. The Gafares Gilbert type fan delta, which contains mainly quartz pebbles (see Chapter 3 for details), is located just SSW of the discussed terrace deposits. Doubts appear if these terrace remnants might be related to the Rio Gafares and they have been left laterally displaced by the Carboneras Fault Zone, or due to their close proximity to the mountain front and they have simply been uplifted by the Sierra Cabrera and are therefore showing different heights than the other 176 terraces of the Rio Alias Tl. If they belong to another terrace level, higher than T1, that would question the previous work carried out on the Aguas/Feos drainage by Harvey and Well (1987) and Harvey et al. (1995). Further investigations into these terrace remnants are needed. The terrace deposits of terrace level 1 show a very similar provenance distribution (Fig. 4.6.9). The conglomerates are entirely characterized by lithofacies Gms. The large clast size and the orientation and imbrication of the coarse clasts at some localities suggest bedload transport. The sandy matrix of most of the deposits and the lack of obvious architectural elements with unsorted sediment is typical for conglomerates deposited rapidly within a non cohesive debris flow (Costa, 1984; Miall, 1984). The red colouration of the matrix towards the top suggests pedogenic modification - only possible after a long period of sub-aerial exposure. The massive calcrete crust of stage IV (Machette, 1985) on top of some terrace remnants points towards an Early Pleistocene age during the time of deposition (Bell et al., 1997; Harvey, 1984, 1990; Harvey et al. 1987). The terrace of terrace level 1 corresponds with Harvey's A terraces (Harvey, 1984; Harvey et al. 1987). The recent study of (Maher, 2006b) assigns the aforesaid fluvial conglomerates to terrace A. Kelly et al. (2000) studied the terrace deposits in the adjacent Sorbas Basin and dated the calcretes associated with the terraces with U/Th. For Terrace A of the Sorbas Basin the age is close to the upper age limit with a finite age estimate of 224 ± 160 ka (508/T). 177 Q.CJ)-n - · :r -· ~occ :::::'!. :E • C" - · ~ 581 5941 c :::J. Alpujarride Complex ~CO~ B 0 ..... Cortijo de !as Norias (GR. 882947) and Cortijo de la Olla (GR. 909959). They are located on average 43 m above the modem river channel. There are numerous clear flat top terrace remnants along the modem Rio Alias. The best preserved ones will be described below. Section between Cortijo de /as Norias (GR. 882947) and Cortijo el Molino de Abajo (895946)- type locality hilltop 182 (GR.891950) The conglomerates of the three terrace remnants (GR. 891950, 891943, 895946) are situated south of the meander bend of the modem Rio Alias (Fig. 4.6.1 ). They all show very similar features. Hilltop 182 m (GR.895946) is the type locality for this terrace level (outcrop is no. 6c on Figure 4.6.1). The terrace deposits consist of a 2 m thick conglomerates. They are mainly clast supported, moderately sorted and of lithofacies Gm. The clasts are sub-rounded to sub-angular and well cemented. Large boulders are often included within the conglomerates (maximum average clast size along the a-axis 12.6-19.5 cm). Pa1aeocurrent measurements have derived a flow of 30°-34° indicated a flow towards the NW. The conglomerates are topped by a mature, stage lii calcrete. A large amount of angular quartz pebbles within the calcrete has been found. 179 Cliff top along modern Alias (GR. 885950) The exposure (GR. 885950) on top of the cliff (Fig.4.6.1 no. 7) along the modern Alias channel (Fig. 4.6.10) is composed of interbedded 10-20 cm thick, clast supported gravel beds (Gm) and siltstone (Sm). Individual beds of conglomerates are either massive (Gm) or show weak internal bedding (Gh) with fining upwards. The beds vary from cobble-grade clast-supported conglomerates to fine-grained sand/siltstone. Clast shape is commonly sub-angular to sub-rounded. No clear clast imbrication was noted. The siltstone displays very weak horizontal lamination. Stratigraphically these sediments erosively overlie marine marls of the Cuevas Formation. The conglomerates are capped by a carbonate crust of stage III-IV. Section SW ofCortijo del Higueral (GR. 892961) The terrace deposits of GR. 892961 are situated exactly in between the two rivers Alias and Gafares (see Fig. 4.6.1 - terrace no. 8). Using the heights above the modern river they could belong to either fluvial systems, the Alias or Rio Gafares. Detailed investigation into the lithofacies and provenance provided some clues to their origin. The conglomerate unit is 6.4 m thick, clast supported and poorly sorted (Gms), with a large amount of bigger clasts (largest clast 9.6 cm in average along the a-axis). The clasts are weakly imbricated and show an average palaeoflow direction of 176°. The palaeocurrent direction does not provide any further information about which river deposited the conglomerates, since both rivers flow N-S in this section. The clast assemblage contains a large amount ofNevado Filabride material (12% compared to 1% in the equivalent terrace deposit of the Rio Gafares), 24% Quartz (compare to 0% Gafares equivalent) and 13% Schist (35% Gafares conglomerate). Using these data it is most likely that the above described terrace conglomerates have been deposited by the Rio Alias instead of the Rio Gafares. 180 m wf/ I I \ I I I 0 I~\ ---- 0 0 0 0 0 \ ~ \ \ \ /1 ~ \ 0(; ~ I -....E 3: - <( Fig. 4.6.10 Terrace remnants at the top of a steep cliff along the Rio Alias. A: Photograph showing terrace deposits on top of large cliff along the modem River Alias (GR. 885950). 8: Sketch of terrace sediments with (GM) being conglomeratic beds intercalated in siltstone (Fm), showing a sharp contact between the two facies. 181 Section eastern part ofthe meander (E ofmodern river- GR. 8944957) The very eastern part of the outcrop (GR. 8944957) is topped by a 2 m thick conglomeratic deposit (terrace number 9 on Fig. 4.6.1 ). Two lithofacies units can be distinguished (Fig.4.6.11). The underlying deposit (unit a) is 1.7 m thick and comprises matrix-supported conglomerates with a medium sand matrix and small gravel clasts (Gms). The deposit is moderately sorted and the clasts are rounded. Weak, small scale (30 cm in height) cross beds can be seen. The overlying unit (b) is dominated by clast-supported conglomerate, with well rounded, well - moderate sorting (Gm). The largest clasts measure an average of 18 cm along their long-axis. The clasts are not well imbricated and from examining the provenance distribution, they do not differ obviously in their content from unit (a). The upper unit is capped with a mature calcrete top, stage IV. m Alfl'4anlde Complex 1551 Nevado Fllabride Complex 1::::::::::::1 Neogene lnftll D Quattz - Sdllst c Fig. 4.6.11 Terrace deposits located on the eastern side of the meander loop of the modem Rio Alias. A: Photograph showing terrace deposits divided into (a) upper facias and (b) underlying facies. Please note that there is no calcrete layer on top of the underlying facies (b). 8: and C: Provenance distribution of facias (a) and (b). 182 Section south ofCerro de la Presa (N of modern river channel-GR.904949) The stretch, north of the modem river channel, contains two (GR.904949 and 902949) well exposed river terraces remnants. The terrace at GR.904949 (no 1Ob on Fig.4.6.1) consists of a conglomeratic unit (Gm) overlying silty- muddy fine layered sediments of lithofacies Fm. The conglomerates are clast supported, sub-rounded and the clasts are moderately sorted. No imbrication or stratification was visible. The provenance of the clasts consists mainly of Alpujarride components (60%). The terrace shows a distinct flat top with no major calcrete development. Section south ofCerro de la Presa (S of modern river channel, GR.905947) The conglomerates of the terrace hill (no.l1, Fig. 4.6.1) south of the deeply incised gorge of the Rio Alias (OR. 905947) differ from the above described sediments. These terrace deposits are clast supported, but moderately to poorly sorted (Gm). They contain a large amount of large boulders and have a black appearance. Individual clasts are partly iron coated (Fig. 4.6.12). The conglomerates show no sedimentary structures or imbrication. The conglomerates contain a relatively large proportion of Nevado Filabride components (see Table 4.6.7 for provenance distribution details). The clasts are well cemented. No finer grained facies have been found at this location. The largest clasts measure an average size of 17 cm along their a-axis (Table 4.6.9). A stage III-IV calcrete caps the conglomerates. 183 c ~ .,. ;;; ! ~ 8 Q. ~ E ·c 8 ..0 ;= ~ ~ ~ s : ~~ il ~ Cl: j :! 0 ~ 11 1 01 ~ 0 Fig. 4.6.12 Terrace deposits south of the gorge of the Rio Alias (GR. 905947) and (GR. 906946). A and 8: Photographs showing a detailed view of the conglomerates (GR. 905947). Note the bigger clast (20-30 cm) for scale on the left hand side in picture A. C and D: Provenance distribution chart of the conglomerates. E: Overview of the terrace remnant (GR. 906946). Note the bedding of the conglomerates and the dipping of the beds towards the SE. F: Detailed view of the conglomeratic deposits which differ in terms of lithology from the others of terrace level 2. 184 Section south ofCerro de la Presa (S of modern river, GR. 906946) The conglomerates of the hilltop of height 165 m (GR. 906946), south of Cerro de la Presa (Fig. 4.6.12), differ from the other terraces of level 2, which are situated, in close proximity and at a similar heights, south and north of the modem river channel (see no. 12 Fig. 4.6.1 ). The moderate to well sorted, clast supported (Gl) conglomerates show low angle cross-bedding structures, with a dip towards the SE. At 21% they contain a large aproportion of well rounded clasts. Section SE ofLos Larcones (GR. 962966) The outcrop SE of Los Larcones provides an excellent example of river sediments The terrace location is shown on Fig.4.6.1, outcrop no. 13 ). The picture in Figure 4.6.13 shows a 4 m high fluvial succession overlying volcanic strata. The lower part comprises fine layered silty-mudstone (Fm) conformably overlain by conglomeratic beds. The conglomeratic beds are clast supported (Gh), moderately sorted and intercalated within finer matrix-supported, poorly sorted conglomerates (Gms). Many of large cobble size clasts are included within both lithofacies types. Metre-scale channelised beds, filled with clast-supported cobble-grade conglomerates (Gm), are preserved in the north-western section of this outcrop. 2 m of conglomerates are overlain by coarse sand beds dipping and increasing in thickness towards the south. Small scale cross beds can be identified (Sh). This 1.5 m thick sand bed is topped by a moderately sorted conglomeratic unit (Gms). The whole sequence is capped by a pedogenic calcrete crust stage III-IV (Gile et al., 1966; Machette, 1985). 185 Q) ~:::s ....If) !0r) ~ r ~ \ E =" I I .I u ~ : I 0 ·~ ~ ~ ll J 0 E cao ~ i) '() 0~ o~00 l ~~ 0 ~ ~ = Gl ~ ~ '0 u. il Jj I i ! 11101 Fig. 4.6.13 Well preserved river terrace NE of El Llano de don Antonio, SE of Los Larcones (GR. 9622966), 3-4 thick. A and 8: Overview and sketch of the terrace deposits. Note the massive flood deposit (d) overlying the channel conglomerates (c). C: Provenance distribution pie chart of unit c. D: The conglomerates (c) are overlying a 30 cm thick greyish silty mud deposit (b), which lies on top of yellowish volcanics. 186 Rio Alias Provenance Tenacesleve/2(counm) ,.._ ,.._ 0 0 ~ quartz 30 20 25 25 0 15 23 11 8 20 conglomerate (Tortonian) 2 1 5 0 0 5 4 2 5 10 mar1s 7 10 4 1 5 5 2 2 schist 12 15 25 13 18 4 12 21 26 37 Iron rich metacarbonate (Triasslc) 2 1 3 5 11 6 5 5 0 0 amphibol~ica-schlst 25 26 21 12 13 30 2 0 12 3 garnet-mica-schist 0 0 0 0 0 0 0 0 0 sandstone 0 0 0 0 1 0 3 0 reef debris 0 0 2 0 0 0 0 0 0 others 0 0 0 0 0 7 0 0 1 3 metacarbonate (white) 5 5 7 3 35 30 27 27 35 12 metacarbonate (red) 9 3 16 15 22 15 15 8 13 Cl) metacarbonate (black) Cl)cu 11 20 3 6 1 3 14 14 7 9 0 metacarbonate (grey) 0 6 6 3 20 12 2 0 0 0 0 t.s gypsum 0 0 0 0 0 0 0 0 0 0 c0 volcanlcs 0 0 0 0 0 0 0 0 0 0 Table 4.6.7 The table presents the provenance distribution data of the terrace deposits of terrace level 2, n=1 00. Terrace location Terrace location Average m above the (lowland) base of terrace as I modern river bed cliff top along 195 (GR. 885950) 42 modern Alias no. 7 Section between 182 (GR. 891950) 43 Cortijo de las Norias and Cortijo el Molino de Abajo no.6a Section between 185 (GR. 891943) 49 Cortijo de las Norias and Cortijo el Molino de Abajo no.6b Section between 180 (GR. 895946) 52 Cortijo de las Norias and Cortijo el Molino de Abajo no.6c Section SW of 185 (GR. 892961) 37 Cortijo del Higueral no.8 187 Terrace location Terrace location Average m above the (lowland) base of terrace asi modern river bed Section eastern 190 (GR. 8944957) 48 part of the meander (E of modern river) no.9 Section south of 158 (GR. 905947) 48 Cerro de la Presa (S of modern river channel) no.11 Section south of 163 (GR. 906946) 54 Cerro de la Presa (S of modern river channel, hilltop 165) no.12 anomalous Section south of 164 (GR. 902949) 45 Cerro de la Presa (N of modern river channel) no.1 Oa Section south of 158 (GR. 904949) 46 Cerro de la Presa (N of modern river channel) no.1 Ob Section SE of Los 94 (GR.962966) 55 larcones no.13 Average m above 47 modern river for level1 .. Table 4.6.8: Table summansmg the descnbed and analysed fluv1al conglomerates of terrace level 2 and their location in the field. Length (a-axis) L (cm) location n=10 mean+- SD range terrace level 2 (GR. 891943) 19.5 ± 3.75 14-27 terrace level 2 (GR. 891950) 12.6 ± 2.37 11-19 terrace level 2 (GR. 892961) 10.8 ± 1.55 8-21 terrace level 2 (GR. 8944957) 18.3 ± 2 15-21 terrace level 2 (GR. 905947) 16.8 ± 1.62 14-20 Table 4.6.9 The mean and Standard deviation of the largest Clasts within the conglomerates at the five terrace remnants of terrace level 2. 188 ii Reconstruction ofthe palaeoenvironment: terrace level 2 After careful field investigation all of the above described terrace remnants, except one, can be allocated to the same aggradational river period, terrace level 2. The provenance distribution of the terrace of level 2 is mainly characterized by a large amount ofNevado Filabride component (Fig.4.6.14). Terrace deposits of terrace level 2 show a large variety of lithofacies. The main facies are clast supported conglomerates (Gm) intercalated with horizontally bedded silt- sand units (Fm, Sm). The multiple alternating beds of sand and conglomerates are the products of successive depositional events. The moderate sorting and the accumulation of the siltstones in bedforms suggest cohesionless sediment as dispersed grains (Miall, 1984). The small scale of the sedimentary structures point towards a shallow water depth. On some units the angularity of the clasts (especially the quartz clasts) points towards a short transport history. Maximum clasts size varies between 9.6-19.5 cm. The abrupt changes in grain size within the sandstone units (e.g. conglomeratic intervals) indicates fluctuation in flow conditions during food. The abundance of coarse grained sediment, the complexly interbedded conglomerates, und the fining and coarsening upwards sequences all provide evidences suggesting a braided stream environment for terrace level 2. The clasts are less well cemented than the conglomerates of terrace level 1 which might be a result of less leaching of free carbonate, indicating a more arid environment. The mature carbonate crust (stage Ill calcrete) indicates a Mid-Pleistocene age for the time of deposition (Bell et al., 1997). The deposits oflevel 2 can be correlated with Harvey's B terraces {Harvey and Wells, 1987). Kelly et al. (2000) dated the terrace remnants of the B terraces in the Sorbas Basin with a minimum age of 147 ± 25 ka. 189 Anomalies The conglomerates of the hilltop 165 (GR. 906946), south ofCerro de la Presa (no.12 on Fig.4.6.1 ), does not seem to be similar to the other terrace conglomerates of level 2. According to its height above the modern river it would fit best into terrace level 2. However its clast distribution and the cast lithology do differ from the rest of the terrace deposits of terrace level 2. The large amount of well rounded quartz pebbles, the good sorting and the bedding of the clasts points more towards a fan delta deposit, than a terrace conglomerate. The El Argarnason fan delta is situated just I km towards the SE and is separated from the 'terrace' hill by a feature which appears to be an abandoned meander loop. It is therefore very likely that the conglomerates on hilltop 165 belong to the Pliocene fan delta (Chapter 3). 190 0 t:: ~u .m E Q. m ~ 1ii c: IU E c: Q) Q) '8 e> E Q. ) 0 e 0 ~ ~8 i 0 ~ ~.. I= -~ ~ IL i l! ~iS'~ .!~ Fig. 4.6.14 Sketch map of the Rio Alias. A: Small scale map of the study area. B: Map showing the location of the river deposits of terrace level 2 and their provenance distribution. Please note that the terrace remnants (Section SE of Los Larcones, GR. 962966, located 2 km further towards the East) is off the map and is inserted as extra map in C. 191 4.6.5 Terrace level3 i Description: terrace level 3 Fluvial deposits of terrace level3 can be found mainly within the more eastern part of the river, east of the village of El Argamason. This terrace level consists of 7 terrace remnants, with their base situated 17 m above the modem channel of the Rio Alias. Type locality - Section across new bridge - SE of El Argamason (GR. 914952) The section (Fig.4.6.1 no. 14) to the left and right of the new bridge to El Argamason across the Rio Alias presents an excellent road side outcrop (Fig. 4.6.1 5). Shallow marine calcarenites of the Cuevas Fm form the base of this section. There is a sharp contact with the overlying fluvial sediments. The fluvial deposits mainly comprise massive, poorly sorted conglomeratic beds intercalated within a massive siltstone and matrix- supported conglomerates. Facies of Gm and Gh form the dominant lithologies within the sequence and represent well developed channel deposits. The conglomerates are defined by an irregular top contact with the massive overlying siltstone and show a general fining upwards sequence. The clast assemblage contains 5% Nevado Filabride material. The palaeocurrent measurements show a palaeo-flow direction of 134°. The top of the conglomerates is capped by a laminar, stage 11 calcrete development. 192 N s dirt track I Sh- shallow marine calcarenltes Sm 1m road ~ Alpujarride Complex ~ Nevado Filabride Complex m:ttH Neogene infill 57% CJ Quartz .. Schist Fig. 4.6.15 Photograph of the road outcrop SE of the village of El Argamason (GR. 914952 ). A and 8: Well preserved terrace deposits representing terrace level 2 and complementary sketch illustrating the channel fill and bar forms. C: Provenance distribution of the conglomerates. 193 Section in deformed terrace deposit across the Carboneras Fault Zone (CFZ), S ofMolino de /as Cruces (GR. 914948) and (GR. 916947) Fluvial deposits of the section across the Carboneras Fault Zone (Fig. 4.6.1 no. IS) have been subdivided into 4 units (Fig.4.6.16). Unit (a) is laterally the most extensive unit. The conglomeratic deposits overly a white marly unit. The contact between the two units is in some places amalgamated. The conglomerates are clast-supported and well sorted (Gh - Gl). They show horizontal bedding and planar cross-bedding structures (Fig.4.6.17). Imbrication is difficult to identify. Some of the conglomerate beds are weakly folded. Unit (b) overlies unit (a) is well to moderately sorted and contains sub-angular to sub rounded clasts, The clasts are matrix supported (Gms) and sub-angular, The ten largest clasts measure an average length along their a-axis of 8.8 cm. The deposits have got an overall reddish appearance. The provenance distribution shown in Fig. 4.6.16 illustrates a large amount (24%) ofNevado-Filabrides components. Unit (c) can be found near the top of the terrace remnants and is broken into large blocks of conglomerate deposits. The clast supported conglomerates (Gm) are moderately to poorly sort, and sub-angular to angular. The schists are broken up into very small fragments giving the deposit a black appearance. The clasts are very small with an average maximum length of 5.8 cm (along the a-axis). No sedimentary structures have been found. Unit (d) only crops out at a few places and forms the top of the terrace remnant. Only individual blocks can be found. The conglomerates are poorly sorted. The average 194 maximum size of the clasts (along a-axis) is 21 cm, but there is a wide range in clast size (see Table 4.6.10). The conglomerates are capped by a well developed, thick calcrete of stage III-IV. Terrace remnants further along the Carboneras Fault (GR. 926954) Ca. I km further downstream, along the Carboneras Fault Zone (Fig. 4.6.18), a strong fractured terrace deposit can be found at the same heights (no. 16 on Fig.4.6.1 ). This terrace is situated on the most recent line of tectonic activity and is therefore only partly preserved. The conglomerates are clast supported (Gm), moderately sorted with sub-angular to sub-rounded clasts. An average maximum clast size of 14 cm (a- axis) has been measured (Table 4.6.1 0). No stratification was visible. Pedogenic calcrete development is not preserved. Length (a-axis) L (cm) location n=10 mean±SD range terrace levei3(GR. 916947) unit (h) 8.8 ± 0.63 8-10 terrace level3 (GR. 916947) unit (c) 5.8 ± 1.93 4-10 terrace level 3 (GR. 916947) unit (d) 21 ± 4.43 15-30 terrace level3 (GR. 926954) along fault 14 ±2.5 12-17 Table 4.6.10 The mean and standard deviation of the ten largest clasts within the conglomerates of the subunits at locations (GR. 916947). 195 ~ .() \J , '(j I ()I '(j'()" ,, " : '() E ' m 0 ,._E .... . :i1~~:t::;. i _; 8 ~ ~ = U Ql ..: C) ir .k ~ C) '3'-§l~Jj Q.~~::lfi ;;ID< :Z z 0 I(/) E ID Fig. 4.6.16 Terrace deposits on top of the Carboneras Fault (GR. 923948). A : Photograph of terrace remnants on the western side of the fault, marking the subunits and their location in relation to each other. 8: Log, detailed pictures and provenance distribution of the conglomerates. lt is not always clear if the units overly each other. The only contact, which has been found in the field, between two units, is between (b) and {c). 196 -.&::. C) J n\} \\~t I ~~ / " .. ~.. ' I 0 • \. 1 ~- . ~ \ \ (.!) ~-- " \~\\~ ,' ~'J O' rsN )J; 't \". ad!Jf \(· u (I) ~ E ) ~ '? s[-- \ ~ ~ ~ ~ Fig. 4.6.17 Photo and sketch of the lower terrace remnants on top of the Carboneras Fault Zone (GR. 916946). The conglomeratic deposits are situated approximately 8 m above the modem river bed. Sedimentary structures occur at the base of the deposits. they show clear planar cross-beds. 197 w 1ii Q. E )( 0 e' j! (.) 0. 11) 8 :g 18 " .0 - '-' Ill "" 11) = .!: :2 lL Cll 1:: 0 c m u GJ ~ 1ii § ~ ~ § £ c( z z 0 (/) 11101 c ; r; ~ Fig. 4.6.18 Terrace deposits along the Carboneras Fault Zone (CFZ). A: View from the top of a terrace remnant across the CFZ. B : Detailed view on the underlying conglomerates (GR. 916947). C : Terrace deposits on the opposite of the fault (GR. 926953). D and E: Provenance distribution of the two conglomeratic deposits. 198 Section west ofEl Albarico, along the road (GR. 965965) The fluvial deposit at this outcrop can be found along the road from Carboneras towards El Llano de Don Antonio (no. 17, see Fig.4.6.1 for its location). The deposits are approximately 2 m thick, clast supported, moderately sorted and of lithofacies Gms. This terrace remnant is one of only a few to contain locally derived volcanic clasts. It also contains a large amount (19%) of Amphibole-mica-schist (Nevado Filabrides component). A laminar calcrete (stage II) has been observed on top of the conglomerates. Section along the Rio Carboneras (GR. 974973) Figure 4.6.19 shows a well preserved outcrop of a terrace remnant (no. 18, Fig.4.6.1) along the Rio Carboneras (Rio Alias renamed after the confluence with the Rio Saltador). All other fluvial sediments found along this part of the river have been identified as level 4 or younger. The terrace remnants are well preserved, at least I 0 m thick and situated approximately 5 m above the modem river channel. The conglomerates are matrix supported (Gms), well rounded and well cemented. There are beds of coarse sand (Sh), with a thickness of 20 cm, or lenses intercalated within the conglomeratic deposits. The clasts are relatively large, with the largest clast of 19.2 cm (along the a-axis). There is only a small amount 2% Nevado Filabride material, but 13% volcanic clasts. Imbrication of clasts can be measured and indicates a palaeoflow direction of 50° towards the NE. This direction is evidence for the author's earlier assumption that this terrace remnant belongs, together with the two terrace deposits near El Albarico, to an old abandoned meander loop of the Rio Alias. 199 ···:...... , ,_ tro .c 0 E Q) ro ·a Q) Q) ...... 0 (/) c ro E c Q) "0 ~ 0 .....0 E Q. ..,_I ) 0 0 i2 .-- ii-- ~ Q. E )( ~ ~ ! u U~ ~ = t) =.. -.5 :2 u. "' t 0 c l1 ~., & ~ - ·;: ~ ~ ~ al §. ! 2 0 <( z z a bl ~ ~ lliJIDID! f f ~ Fig. 4.6.19 Eastern part of the Rio Alias. A: Overview map of the area. B: Sketch map showing the location of individual the terrace deposits of level 2 and 3 and their provenance distribution. The dark blue line is indicating the abandoned meander loop of the Rio Alias. C: View on the very well preserved terrace conglomerates (GR972973). Note the thickness of the deposits is up to 3-6m. 200 Rio Alias Terraces level 3 (counts Provenance ...... I() I() (t.o .a (t-o ..I() CO "'.... "'C> etCOil> C> C> C> eo"' eo"'~~ CO ..a; .. ""'CDci end CDci mo S!co .... *"'.z .z .z .z ~ ~CO a:ci a:~ a:~ a:~ a:~ n:ci n:ci (!)Z (!)~ Terrace location Terrace location Average m above (lowland) base of terrace as/ the modern river bed Type locality - Section 115 (GR. 914952) 13 across new bridge - SE of El Argamason no.14 ' Section deformed 105 (GR. 914948) 6 terrace deposit -CFZ (unit a) no.15a Section Alias across 115 (GR. 916947) 17 the CFZ (unit, b,c and d)no.15b Terrace remnants 111 (GR. 926954) 26 further along the CFZ no.16 Section west of El 70 (GR. 965965) 28 Albarico, along the road no.17 Section along the Rio 35 (GR. 974973) 8 Carboneras no.18 Average m above 16 modern river for /eve/1 .. Table·4.6.12 Table summanstng the descnbed and analysed fluvtal conglomerates of terrace level 3 and their location in the field. 201 ii Reconstruction of the palaeoenvironment: terrace leve/3 The individual terrace remnants described above differ significantly in their lithology, clast assemblage (Fig. 4.6.20) and general appearance, so that is it difficult to assign them all to one level. The weak folding of the conglomerates of the terrace remnants across the CFZ (GR. 914948) indicates deformation before lithification. The weak deformation might have reduced the heights above the modem river channel by a few metres. The terrace remnants are located on top of the CFZ, which may be a source for the deformation. The reconstruction of the palaeo processes and environment is very difficult for · terrace level 3. The fluvial sediments of the type location show a wide range of lithofacies units and architectural structures. The sharp contact between the underlying calcarenites and the fluvial sediments with the basal conglomerates commonly marks the onset of deposition after a time interval dominated by tectonic uplift or erosion. The small-scale architectural development towards the northern end of the outcrop and the fining upwards sequence of the channel deposits point towards a lateral accretion surface deposited by a point bar in a meandering river. Similar sedimentary features have been described by (Stokes and Mather, 2003). The coarse pebble to cobble size clasts of the channel and the deep basal scour at the channel base, together with the overlying fine overbank deposits support this theory. The palaeocurrent direction for the Gm elements was trending towards 7 4', suggesting a flow towards the E, perpendicular to the bar element. These features support the theory that the terrace remnants of location (GR. 914952-no.l4), (GR. 914948- no.lSa) and (GR. 916947-no.lSb) are situated in the inside of an abandoned meander loop, which is now mainly filled with continental sediments post-abandonment 202 (Harvey, 200 l ). However the size of the meander loop probably does not extend as far as the fault scarp along the fan delta deposits. This will be discussed in detail in Chapter 5 and Figure 5.5. The majority of the terrace remnants show a laminar pedogenic calcrete development and can be correlated with the C terrace remnants of (Harvey and Wells, 1987; Harvey et al., 1995). Kelly (2000) dated the C terrace of the Sorbas Basin at 88 ± 11 ka. This date corresponds with a major aggradational event across the Mediterranean (OIS 5b/a boundary) (Macklin et al., 2002). However more recent work, carried out by (Candy et al., 2005) suggests an age of 69.8±2.2 ka for the calcretes of the C terraces. 203 f t ro I .c (.) E Q) ro ·a. CJl ~ Q) ~ ..... (.) Q) CJl c: c: c: ro ea 0 ..... c: Q) Q) \;l > \;l ~ _I 0 ro CO () ,' e 0 ~- , E 0...... , ...... " I I I ' \ ' ) 0 I ' \ ' 'I I I I / 8 __/ / / ' / __, -._ I I , __ \ V) I \ I £5! I~IDID \ ' T·•• ~ ' ' <( ' ' ..- E ~ cl 0 m Vl u m I m E Fig. 4.6.20 Sketch map of the Rio Alias. A: Small scale overview map. B: Map showing the location of the river deposits of terrace level 3 and their provenance distribution. Note the large variety of the provenance distribution. 204 Abandoned meander loop along Section SE ofLos Larcones (GR. 962966) The above-described outcrop along the Rio Carboneras (T3-no. 18) and the two outcrops SE of Los Larcones (T2 no. 13 and T3 no. 17) form an abandoned meander loop (Fig. 4.6.19). The topographic map shows a distinct low where the road was constructed. The area shows three terrace deposits at different levels. During the deposition of terrace level 2 and 3 the Pleistocene Rio Alias drained along an abandoned meander loop, which can only be recognized by the examination of the palaeo river deposits. After the deposition of terraces of level 3 the Rio Alias was redirected into its modem bed. This is shown by the existence of a not very well preserved terrace level 4 remnant (Fig.4.6.19, T4) just above the modern river bed (north of Los Blemontes, GR. 961969). 4.6.6 Terrace level 4 i Description: terrace level 4 Terrace remnants of terrace level 4 are located approximately 5 m above the modern river bed. They are developed along the entire Rio Alias. The conglomerates are characterised by beds of cobbles (Gm) intercalated with beds of silt and mud (Sh - Fm). The clast assemblage is very similar throughout all the terrace remnants along the river. Only 2% - 5% Nevado Filabride components have been found within the conglomerates, compared to 13%- 24% in terrace level 3. Section Rambla de Lucainena (GR.845958) The fluvial deposits of the outcrop (no. 19 - Fig.4.6.l) along the Rambla de Lucainena (GR. 845958) can be seen best in the diagram in Figure 4.6.21. The terrace 205 deposits reach a maximum thickness of 10 m. The clasts are well sorted and sub rounded. The terrace remnants contain matrix-supported .conglomeratic beds intercalated with finer sandy beds. ln some places the conglomeratic beds are very, very thin ( The silt- fine sand beds show cross-bedding structures toward the upper part of the terrace section. The clast assemblage comprises 3% Nevado Filabride components. The top of the terrace is made of a laminar, weakly developed pedogenic calcrete crust of stage Il. Section Rio Alias (GR. 876946) The terrace deposit (GR. 876946) is located just east of the dirt road (no. 20, see Figure 4.6.1) which crosses the Rio Alias. The conglomerates of this terrace remnant are found ea. 3 m above the modem river bed and reach a thickness of 2 m. The clast provenance is illustrated in Figure 4.6.22 in relation to the terrace location along the nver. Section NW ofCortijo el Molino de Abajo (GR. 899949) Two terrace outcrops are located NW of Cortijo el Molino de Abajo. They mark the start of a gorge occupied by the modern Rio Alias, which is deeply incised into the underlying Cuevas Fm sandstone (no. 21 a,b - Fig. 4.6.1 ). The upper deposit is located ea. 5 m (no.21 a) above the modern river channel, whereas the lower one (no.21 b) creates the bottom of the modern river bed. The clast assemblage of these deposits is very similar to the ones described above (see Fig. 4.6.22 for map with provenance pie charts). 206 Type locality- Section SW ofCortijada La Arboledil del Arco (GR. 933952) The section SW of Cortijada La Arboleda del Arco (GR. 933952) is well preserved (Fig 4.6.21 ). The deposits (no. 22 on Fig.4.6.1) can be found 2-3 m above the modem river bed, by the dirt road. They show a sequence of 4 m thick conglomeratic channel deposits (Gms) intercalated with fine grained, silty mud beds (Fm). The clast assemblage consists of only 2% Nevado Filabride material, no quartz and mainly Alpujarride components. The largest clasts show an average length of 11.6 cm along their a-axis (with a standard deviation of 4.6 and a clast range between 7-22 cm). Although the outcrop is well preserved it was not possible to measure any palaeocurrent direction of the clasts. Only a very weakly developed pedogenic calcrete top (stage 11 calcrete) has been identified. Provenance Rio Alias Terraces leve/4 (counts) CO CO O>ro O'l..O N lOO> v~ lON • O'l ~ • O'l N """~ 0:: ll) • -~~CO • O'l • . 8l N .~N 0:: 0:: O::O'lci O::C')ci (!)~~ 1:0~ (!)gj~ Z quartz 3 0 0 0 0 conglomerate (Tortonian) 0 5 7 2 7 marts 10 5 4 2 7 schist 30 20 25 16 28 Iron rich metacarbonate (Triassic) 10 1 2 3 0 amphibole-rnica-schist 3 4 2 8 2 garnet-mica-schist 0 1 0 0 0 sandstone 0 0 3 1 0 reef debris 3 10 5 5 11 others 0 0 0 0 0 metacarbonate (white) 30 35 23 27 35 metacarbonate (red) 8 15 6 9 7 metacarbonate (black) 10 2 7 16 13 metacarbonate (grey) 7 17 23 8 3 gypsum 0 0 0 0 0 volcanics 0 0 0 0 7 Table 4.6.13 The table presents the provenance distribution data of the terrace deposits of terrace level 4, n=1 00. 207 Qc=J c-oo o 0 l?'o 0 0 0 channel oD Gms o ~c:::J~ ,_ ( Sm - __ ___.. ~-- Gh C Gm shallow marine dirt track Fig. 4.6.21 Examples of terrace deposits of terrace level 4 (Lucaineana/Aiias River). Their provenance distribution is shown in Fig. 4.6.22. A and 8: Photo and sketch of the terrace remnants details of terrace level 4 along the Lucainena River (Gr. 845957) C and 0 : Photo and sketch of river deposits along the Alias River (GR. 933952). 208 - · ...... :J ::r .,-· 9;CDCQ < . I --r ~ I a. c • 585 sgo Js coc:n Q) Q) • --· N t (D~N ...,:Jr Sierra Q) Q) 0 Rios N (") -- (") ~ attaa ro>-s. -41QQ or ..., o>" a· "Qj Cabrera CD en :J ~ ~ en 3 -{!; Q) '< Q) etas :J ~-o cn(l)o p. ca{'oOt' . 3- ~ ~\0 ~-::r -oCD ~"' eo· o- (!) ~ o en ::r- lllBBBJ Alpujarride Complex Q)Q. r3 ~(I) - Nevado Filabride Complex en < -~ N 0 -o(l) a: k:::::;:::::J Neogene infill \0 ...... 0 CD-o en CD 0 Quartz (I)Q. . '?>~ :J,...... (!) ~ -Schist ::r...,..., (!) Q) ~0 [:·:·:·::1 Volcanics (") -oCD ...., 0 <0 ...... c (!) (") ~ major drainage :J ...., Rambla Q) 0 :J"O o en de Lucainena 0 provenance pie chart (!) 0 a.- 0 km 3 ...... u;· (D..., I I -...... · ...,cu 5:£ 585 sgo sgs sgg a· - :J (!) < I I I I 0 (!) ---~ ro--=ro Terrace location Terrace location Average m above {lowland) base of terrace a si the modern river bed Section Rambla de 205 (GR. 845958) 4 Lucainena 2 km before the confluence with the Rambla de Ios Fees no.19 Section Rio Alias no.20 170 (GR. 876946) 3 Section NW of Cortijo el 128 (GR. 899949) 3 Molino de Abajo no.21a Section NW of Cortijo el 125 (GR. 899949) 0 Molino de Abajo no.21 b exception Type locality - Section SW 80 (GR. 933952) 3 of Cortijada La Arboleda del Arco no.22 Average m above modern 3 river for level 1 .. Table 4.6.14 Table summans1ng the descnbed and analysed fluv1al conglomerates of terrace level 4 and their location in the field. ii Reconstruction ofthe palaeoenvironment: terrace leve/4 The conglomerates of terrace level 4 all show very similar characteristics. The most · dominant feature is the alternation between sandy facies (Sh), with low angle cross- bedding and conglomeratic beds (Gms and Gh). Very obvious is the appearance of finer grain size facies, like (Fm). Compared to the older terrace levels, described before in this chapter, terrace deposits oflevel 4 show a significant lack of larger clast sizes. This could signify a change in sediment supply (e.g. lack of larger clasts, due to the absence of tectonic activity, bank side stability) or for a decrease in flow velocity. The horizontal, gentle bedding of the finer grain sizes supports the latter suggestion. The thickness of the terraces (e.g. a terrace of the Rambla de Lucainena (GR. 845958- no.l9) measures a thickness of at least 10 m) does not support the theory of a shortage in sediment supply. The provenance distribution is extremely constant along the 210 river, despite the input of the Feos and Rio Gafares. It is also very similar to that of the modem river. The spatial distribution of the terrace remnants identifies a sinuous river, close to the course of the modem stream. The palaeoenvironment during the deposition ofterrace level 4 suggests traction currents with frequent flood event~, very similar to recent conditions. 4.6. 7 Terrace age The terraces of the Feos, Lucainena, and Rio Alias are difficult to date. No precise timescale can be given, although it is possible to constrain the timescale involved by using published data. Correlation between the terrace sequence of the adjacent Sorbas Basin is provi~ed by comparison of number, altitudinal spacing and longitudinal profile. The Sorbas Basin terraces postdates deposition of the Gochar Formation (Mather, 1991; Harvey and Wells, 1987) and are dated by using U/Th series (K.elly et al., 2000) and (Candy et al., 2005). Using the correlation and the calcrete development as a relative age indicator for the terrace deposits this study shows an estimated age for the terraces as follows: Massive calcrete (stage IV and greater)- Early Pleistocene = (Tl of this study) Mature calcrete (stage III-IV)- Mid Pleistocene = (T2 of this study) Laminar, incompl.ete calcrete (stage Il)- Late Pleistocene = (T3 of this study) No calcrete- Holocene age= (T4 of this study) This is based on previous published work by Dumas (1969), Harvey and Wells (1987) and Bell et al. (1997). Further correlations with dated terraces of the Sorbas Basin is summarized in Table 4.6.15. 211 al-l D) Ill Ul 0' :;·iD Harvey (1987 and 1995) Kel/y (2000) Macklin (2002) Candy (2005) This study !:fi" Sorbas Basin Sorbas Basin Mediterranean Rivers Sorbas Basin Carboneras Basin ::T~_.... Pedogenic ca/crete unhseries aggradation events . U-series Pedogenic ca/crete ~UI iil .... A terrace A terrace A terrace T1 D) massive calcrete 224± 160 ka 304±26 ka massive calcrete @ 0" Ul ::T C terrace C terrace 88 ka C terrace T3 - The sediment input of four different river systems into the Rio Alias, and their different hinterland geology, is responsible for the varying provenance distribution within the individual terrace levels (see Table 4.6.17 for summary of the terrace levels). The clear decrease in Nevado Filabride component between the terrace (Tl- T3) and (T4-T modem) suggests a change in source area, i.e. a disconnection with the Sorbas Basin, as already identified by (Harvey and Wells, 1987; Mather, 1991) and recently (Maher, 2006b). In order to prove a significant change in Nevado Filabride clasts within the terrace before the river capture (Tl-T3) and in the ones after the capture event (T4-Tmodem) a Chi-square test was carried out. provenance Tl T2 T3 T4 T modern Nevado Filabride 19.1 14.4 12.5 3.8 1.3 clasts count (mean) Table 4.6.16 Table showing the average distribution of Nevado Filabride clasts within each individual terrace level from T1-T modern. •Overall Tl-T4: Chi squared equals 20.648 with 4 degrees of freedom. The two- tailed P value equals 0.0004. By conventional criteria, this difference is considered to be extremely statistically significant. •Tl-T3: Chi squared equals 1.379 with 2 degrees of freedom. The two-tailed P value equals 0.5018. By conventional criteria, this difference is considered to be not statistically significant. 213 •T4-Tmodem: Chi squared equals 1.800 with l degrees of freedom. The two tailed P value equals 0.1797. By conventional criteria, this difference is considered to be not statistically significant. •mean of (Tl-T3) - mean ( T4-Tmodem): Chi squared equals 8.000 with I degrees of freedom. The two-tailed P value equals 0.0047. By conventional criteria, this difference is considered to be very statistically significant.. Since the catchment area of the Rambla de Ios Feos and Rio Gafares got restricted due to river captures (Rambla de Ios Feos) and mountain uplift (Rio Gafares) the change in source area can be cleary seen in the decrease of Nevado-Filabride component. Figure 4.6.23 shows the modern drainage systems of the Carboneras Basin and their possible connection to the Sorbas Basin. Aside from the Nevado Filabride clasts and in contrast to the Rio Gafares, the Alias terrace levels do not show a clear tendency towards a specific decrease or increase in any of the other provenance groups. This might be due to the fact that the Rio Alias is formed by two first order streams (Lucainena and Rambla de Ios Feos) and is joined by two more large first order streams (Gafares and Rio Saltador). Each river or tributary has an individual catchment area with a very distinct source area. The Rio Saltador is aggressively headcutting back and therefore changing its source area constantly, but this will only affect the provenance distribution of the Rio Alias further downstream near the entrance into the Mediterranean Sea. 214 "'U-4 ~ - ~ Height Height above Incision Sedimentology Provenance Soils Type locality ~CD" asl(m) mod. river (m) (Mapa Militar) g:. Level 1 158-210 38-94 ? Description massive (GR. 886947) (!)' ------(average 57) matrix supported calcrete, (GR. 886948) ::Jl'l (!), ...... , lack of sed. structures red colouration Early red colouration of the upper 3(f) Pleistocene Interpretation conglomerates 0 c o..3 cohesive debris flow (!) (GR. 891950) ...., 3Q) Level2 158-195 37-55 incised by 10 Description mature calcrete (average 47) below level 1 mod. sorted • :.-< clast supported ~ 0 ...., ...... Mid horizontal bedding Q)"A C1 (!) P/eistocene ~'< Interpretation - CO (!) (!) braided river < 0 Level3 70-115 6-28 incised by 31 Description laminar calcrete (GR. 914952) (!) 0 • ~CO (average 16) below level 2 Interpretation ~r Bar development in a Q) Late ::J braided river 0.. Pleistocene environment a 3 tectonic deformation ....,0 Level4 80-205 0-4 incised by 13 Description no calcrete, (GR. 933952) -o ::::r below level 3 no soil 0 0 Interpretation ~ CO ~::::::::: ::::U ~====· ·::u c=;· traction current in a '1;2· Q) :::11- sinuous river ~ Q) Holocene • :::::: environment with ...., frequent flood events . co= Pie cham modern incised by 3 Description no calcrete, no (GR. 935952) ar lli!I liJ Alpujarrlde below level 4 soil (/) IIIIIl ~ Nevado Filabride 0...., Interpretation CD ~. Neogene infill traction current Q) C1 Quartz meandering river ::::r 0...... - Schist • ::::r -(!) 4.6.9 Incision The staircase diagram in Figure 4.6.23 displays the amount of incision for the individual terrace levels of the Rio Alias (Table 4.6.17). There has been an overall incision of 57 m for the Alias valley, with a 10 m downcutting after the deposition of terrace 1 and a deep incision after terrace T2 (31 m). Valley incision was less between T3 and T4 (13 m). Only limited incision has occurred after T4 (3 m) for the younger terraces (T4-modern). 4.6.10 Discussion of the fluvial evolution of the Rio Alias i Incision Examining the incision between the individual terraces levels of the Rio Alias, there is one distinct phase of incision: the 31 m incision between terrace level 2 and 3 (T2- T3). This downcutting of the river channel is accompanied by a great variety in the provenance assemblage between the individual terraces of this level (T3). This large amount of incision might be a result of relative base-level change due to the differential uplift of the Sierra Alhamilla/Cabrera axis. This would also explain the great variety of clasts assemblage within the conglomerates ofT3 of the Rio Alias due to progressive downcutting into the bedrock units. The large incision event is also recognizeble in the terrace staircase of the Rio Gafares (Chapter 4, section 4.4 and Fig.4.4.19). The low valley incision of 13 m between T3 and T4 of the Rio Alias might be a result of a drop in discharge and a resulting reduction of stream power due to the river capture of the Rambla de Ios Feos. This is in line with Harvey and Wells (1987); Harvey et al. (1995) and (Mather and Harvey, 1995), who measured a high 216 incision for the Rambla de los Feos before the capture event and nearly none after the Aguas/Feos capture after the formation of terrace C (= T3 of this thesis). Harvey et al. (1995) stated that the incision of terrace A-C in the Feos valley was mainly progressive, but punctuated by episodic aggradation and dissection. This seems to be similar for the Rio Alias, whereas here following the Feos capture event the Alias was still supplied by water from the Rambla de Lucainena. Rio Alias terrace levels +57 m 200 Terrace 2 +47m 180 160 140 Fig. 4.6.23 Staircase diagram showing the individual terrace levels of the Rio Alias. The total incision is shown to the right of the terrace deposits. Note the large incision event between T2 and T3. 2 17 -...... E Q) Q) 0> "0 c '- Q) 0 :E Q) (1J c ·- '- > eo ::I ·c ·s: "0 Q) 0 c c cc c ·n; ·n; (1J c -0 .0 0 0 E E (1J 0 .. gs ( D .. Fig. 4.6.24 Contour map of the study area showing the main drainage systems. Note the speculated connection between the Aguas-Feos and the Aguas-Gafares system. The contour map already suggests a possible drainages route for the Rio Gafares, connecting the SorbasBasin with the Carboneras. Map modified after (Mapa Militar Digital de Esparia, 1992). 218 ii Tectonic implications The terraces of the Rio Alias have mainly been affected by tectonic movements along the Carboneras Fault Zone. Terrace remnants along the CFZ show evidence of deformation and lateral displacement. The terrace deposits are folded, fractured and displaced. Field investigations (section 4.6.5) have shown that the terrace deposits along the CFZ (GR. 926954) belong to the same terrace level as the remnant a few hundred metres further downstream along the CFZ (S of Molino de las Cruces, GR. 916947). The provenance distribution of the terrace deposits across the fault are very similar to the ones S of Molino de las Cruces (unit b), which we would expect from two terrace deposits at the same level (see Fig. 4.6.18). However the terrace height diagram (Fig. 4.6.2) shows that the section further along the CFZ is situated higher than the outcrop S of Molino de las Cruces. Assuming that a) the river gradient during the aggradational phase of terrace level 3 was similar to the one today and b) the above-described terrace deposits belong to the same terrace level, it can be suggested that after the deposition of those fluvial sediments the terrace remnant has been displaced laterally or vertically. Evidence for the lateral displacement can be found by examining the modern Rio Alias channel, which shows three smaller, very parallel offsets across the CFZ. The vertical and lateral displacement along the CFZ will be described and discussed in detail in the following Chapter 5. 4.6.11 Summary of the evolution of the Rio Alias A total of four terrace levels have been assigned to the Rio Alias (see staircase diagram Fig. 4.6.23). The sediment characteristics for terrace level 1 suggest a high stream power, with a sufficient supply of pebble to boulder size clasts. The relatively 219 thin terrace accumulation (2-4 m) implies a short aggradational period. Levels 2-4 record the progressive incision of the Rio Alias into the Neogene basin fill. The 10 m incision between Tl and T2 is relatively small compared to the 31 m of incision between T2 and T3. The large incision after the aggradation of T2 suggests an increase in stream power, possibly as a result of a) an increase in gradient or fall in relative base level, due to an uplift event of the Sierra Alhamilla!Cabrera axis or b) a climatically induced increase in discharge. After the deposition of T3 gravels , the Rio Alias was disconnected from the Sorbas drainage, due to river capture of the upper Rio Aguas by the lower Rio Aguas (Harvey et al., 1995) and the catchment of the Feos system was reduced in size. Together with the disconnection comes a decrease in the overall grain size of the conglomerates. Tl and T2 show an average maximum clast size of 16 cm (along the a-axis), T3 13 cm and within the T4 conglomerates the size is reduced to 5 cm (as it is for the modern river conglomerates as well). The controlling factors behind the changes in the drainage characteristics will be difficult to unravel, due to the length of the river and the direct and indirect influence of tectonics on the system. These issues are discussed in chapter 6. Terrace remnants deposited during the aggradational phase of T3 show a large variety in clast size, provenance distribution, height above modern stream and sedimentary structures. The overall reconstruction for this level is very difficult, due to the amount of influencing factors (e.g. river capture of the Feos system and displacement and deformation of the terrace deposits). The terrace deposits of T4 show a large similarity with the ones of the modern river and indicate a sinuous river. The influence of tectonics on the terrace conglomerates seems to be very significant and will therefore be discussed in more detail in Chapter 5. 220 5 CHAPTER: TECTONIC CONTROLS ON FLUVIAL LANDFORM DEVELOPMENT 5.1 Introduction Tectonic and structural controls have exerted a strong influence over fluvial systems in the Mediterranean basin in terms both of large-scale drainage basin morphology (size and shape) and river development (Macklin et al., 1995). River development is strongly influenced by vertical and lateral tectonic movements. 5.1.1 Vertical movements River behaviour is very susceptible to any kind of gradient change, so where rivers encounter zones of active subsidence or uplift their normal longitudinal profile will be altered (Holbrook and Schumm, 1999). Alteration of the slope will automatically cause changes in stream power (since stream power may be defined as yQS, where y is specific weight of water =1, Q is stream discharge, and S is slope (Bull, 1979). Changes in stream power will affect the stream discharge and thus the sediment supply transported by the stream. Additionally, changes in topography influence not only the stream power, but also the flow direction. Rivers might respond to deformation of the longitudinal profile in various forms. The river may be either antecedent to the mountain range or deflected around it, e.g. (Holbrook and Schumm, 1999). Examining palaeo and recent fluvial drainage systems, especially on a large scale and over a long term period, can. therefore provide considerable tectonic information. 221 This study examines the influence of uplift on the drainage evolution: Various forms of uplift might have affected the river systems: (a) regional uplift due to external factors, such as erosional isostasy, glacio- and hydro-isostasy, crusta] thickening, etc (b) orogenic uplift due to nappe displacement; and (c) vertical uplift along the fault strands of the fault zones. Most types of uplift result in gradient change of the river profile. Although it is possible to calculate general uplift rates, these uplift mechanisms might be superimposed onto each other and thus impossible to isolate. It is not only the uplift created by tectonic movements which changes the course of the streams. Lateral displacement of the Pliocene fan delta deposits and Quaternary river terrace deposits along the strike-slip fault strands provides essential information about the recent activity of the faults. 5.1.2 Lateral movements River channel changes affected by strike-slip movements have been used as geomorphic evidence to determine displacement rates along fault lines in recent literature (Ouchi, 2005). Strike-slip movement can displace the main channel and the amount of lateral offsets can be surveyed and measured (Zhang et al., 2004). There are various theories of how a river will behave if being affected by strike slip motion, but as Zhang et al. (2004) stated even along the same segment of the fault the amount of offset is not always similar. The importance of demonstrating the affects of river changes is clear in inhabited regions. An awareness of active strike-slip faults in recent time is essential for the 222 evaluation of earthquake and tsunami hazards, depending on the location (Garcia et al., 2006). This study will use the Neogene fan delta deposits and the river terraces to demonstrate the ongoing tectonic activity within the Carboneras Basin and to evaluate the amount of tectonic movement. 5.2 Regional Structural Setting Neogene convergence in southeastern Spain is controlled by strike-slip deformation along major fault zones. Deformation was accompanied by relatively rapid subsidence of the Neogene basins and uplift of the pre-Neogene basements (Cloetingh et al., 1992). This resulted in mountain belts with altitudes of up to more than 3000 m in the Sierra Nevada (Huibregtse et al., 1998). Many of the boundaries within the Betic Cordillera between the Neogene sedimentary basins and basement uplifts are formed by major strike-slip fault zones (see Fig. 5.1 ). The Neogene evolution of southeast Spain shows a complicated history of activity and inactivity of the major faults zones. Movement along the fault zones in turn controls basement uplift, basin subsidence and local deformation and the sedimentation pattern (Huibregtse et al., 1998). Tectonic movements within SE Spain are still ongoing during the Quaternary. Reichert et al. (200 I) stated that the Betic Cordilleras have experienced a number of moderate to strong seismic events during the last 2000 years. 223 N • External Zone A t D Olistostrome Unit CJ Flysch Unit D Neogene-Quaternary Basins • Metamorphic Basement 0 200kn • Nevado Filabride Complex D Alpujarride Complex /" Strike-slip fault + Neogene Antiform B c Fig. 5.1 Betic Cordillera and fault zones. A: Schematic geological map of the Betic Cordillera. 8 : Tectonic schematic map of the eastern Betics. C: Shaded-relief image showing the offshore segment of the Carboneras Fault Zone, after Canals et al. (2004). 224 Tectonic activity in sedimentary basins within the Internal Zone of the Betic Cordillera has been the subject of numerous studies, e.g. (Egeler, 1964; Bousquet, 1979; Santanach et al., 1980; Megias et al., 1983; Hall, 1983; Konert and van den Eeckhout, 1983; Goy and Zazo, 1986; Weijermars et al., 1985, Weijermars, 1988b, 1991; Sanz de Galdeano, 1990, Sanz de Galdeano and Lopez-Garrido, 1999; Sanz de Galdeano and Alfaro, 2004; Wenzens, 1992a; Mather and Harvey, 1995; Wenzens and Wenzens, 1995, 1997; Mather, 2000; Lopez-Garrido and Sanz de Galdeano, 1999; Montenat and Ott d'Estevou, 1999; Poisson et al., 1999; Andeweg and Cloetingh, 2001; Jonk and Bierrnann, 2002; Stokes and Mather, 2003 and Marin Lechado et al., 2005). In terms of the Carboneras Basin, work has mainly been focused on the topographic highs of the Sierra Alhamilla and Sierra Cabrera, as well as on the strike-slip movements of the Carboneras Fault Zone. 5.3 Regional uplift history of the Betic CordiUera The uplift history of the Betic Cord illera occupies a time frame of the last 8 Ma (Sanz de Galdeano and Alfaro, 2004). There was little uplift prior to Tortonian times, so that the Tortonian transgression covered the entire area of the Betic Cordillera, except for topographic highs within the Sierra Nevada and Sierra Filabres (Sanz de Galdeano and Alfaro, 2004). The latter study concluded that the regional uplift of the Betic Cordillera is most marked in its central sector (Sierra Nevada) and less pronounced in the eastern Betics. Maximum uplift rates reported for SE Spain show values of around 150 m I Ma (Silva et al., 2003). Present-day uplift rates in the eastern Betics have been recently estimated from levelling data (Gimenez et al., 2000), obtaining results 225 sensibly higher than the ones obtained from geological data (e.g. uplift of marine marker deposits) and. periods of several millions of years (Booth-Rea et al., 2004) 5.3.1 The Carboneras Basin Within the Cabo de Gata, a Miocene volcanic province in the southeastern part of the Carboneras/Almeria Basin, the distribution of coastal deposits overlying the last volcanic episode has been used to study the uplift history of the area. Martin et al., (2003) estimated uplift rates of the Cabo de Gata area by using well-dated shoreline markers. They calculated upper Neogene uplift rates similar to the eastern Betic basins of 50 m I Ma as a consequence of regional uplift in connection with the rest of the Betic Cordillera. i This study: Calculated uplift rates using Pliocene fan delta deposits This study has estimated relative uplift rates (U) of the Carboneras Basin and compared the altitude above present sea level of reference surfaces (R), (equivalent to former sea-level), with known age (A), such as the top of the Pliocene fan delta sediments. ( U) is simply obtained as (R-SL)IA, whereas the eustatic sea-level changes (SL) have to be taken into consideration for the equation. The Pliocene fan delta deposits (described in detail in Chapter 3) are located east of the village of El Argamason, on both sides of the fault (see Fig.5.2). On the eastern side of the Carboneras Fault Zone the top of the fan delta foresets are preserved at a maximum heights (R) of 178 m as! (GR. 916942). These sediments show clear features of subaquaous deposition, e.g. steep foresets and dewatering structures (see 226 Chapter 3 for details). Located on the eastern side of the strike-slip CFZ these deposits should not have undergone a large amount of vertical uplift due to the fault slip activity (Bell et al., 1997). With the highest Pliocene sea level (SL) 90 m above the present-day level (Haq et al., 1987) and the fan delta material Pliocene in age (Aguirre, 1998b) we can demonstrate that the Carboneras Basin underwent relative uplift of at least of 88 m since the End of the Late Pliocene: (178 m)- (90 m)= 88 m This gives us a relative uplift rate of U=(R-SL)IA of at least -44 m I Ma, with (A) being 2 Ma marking the end of the Late Pliocene. The uncertainty on the age of these deposits together with the palaeobathymetry error has to be taken into consideration when comparing them with other uplift data. The main error in the uplift rates is usually always associated with the absolute age value attributed to the sedimentary reference surfaces. ii Discussion These results are supported by Brachert et al. (2002) who studied the area around the town of Carboneras and stated that after the withdrawal of the Pliocene Sea, the Carboneras Basin was already uplifted too far to be inundated by the sea again. The rate of -44 m I Ma is in line with regional uplift rates of 50--60 m I Ma for the Somme (Antoine et al., 2000) and 40 to 100 m I Ma for the Thames Basin (Maddy et al., 2000) and (Westaway et al., 2002). It is also comparable to the 80 m I Ma calculated by (Mather, 1991) for the Sorbas Basin, keeping in mind that this rate was calculated for the southern margin of the Sorbas Basin, as compared to basin centre for the Carboneras Basin. 227 I l ID \. m 'tJ ~ - 1)11'~ ~ \:~ c ' lil~~ ~IS).... Ic I'U .e E - I'U ~ ml m.... - Fig. 5.2 Fan delta deposits across the Carboneras Fault Zone (CFZ). A: Overview map of the fan delta location within the Carboneras Basin. 8: Sketch map illustrating the difference in altitude between the fan delta deposits on the western side and eastern side of the CFZ. Grid references refer to the 1:25.000 Mapa Topografico Nacional de Esparia, Carboneras sheet. 228 study Mather Maddy Antoine Stokes this study (1991) (2000) (2000) (2003) (2006) uplift - 80 m I Ma 40- 100 m I Ma - 50 - 60 m I Ma > 20 m I Ma -44m1Ma (Sorbas Basin) (Thames Basin) (Somme River) (Vera Basin) (Carboneras Basin) Table 5.1 Uplift rates of major European basins. Comparing these uplift rates it has to be taken into account, that rates which are calculated over a longer time period typically tend to be lower as pulses of more rapid tectonic activity become time-averaged. However they show an interesting comparability between SE Spain and NW Europe. 5.4 Tectonically driven uplift of topographic heights The major topographic highs within the Internal Zone of the Betic Cordillera decrease in altitude from west to east. The recorded uplift ofNeogene rocks was highest at the margins of the western Sierra Nevada (Braga et al., 2003b). Towards the eastern sierras the Sierra Cabrera is the less uplifted mountain range (it emerged during the late Messianian, Braga et al. (2003b), suggesting a progressive uplift from west to east of the sierras). The altitude of the sierras reflects the time at which they became emergent, the highest mountains being the first to rise above sea level. Vertical movements induced by an approximate N-S to NNW-SSE regional compression were also accompanied by reactivation of ancient strike-slip and normal faults located to the south of the Sierra Nevada (Alpujarran Corridor) and to the north of the Filabres (Almanzora Corridor) (Sanz de Galdeano and Alfaro, 2004). These active 229 faults were responsible, from the late Miocene onwards, for a cumulative tectonic displacement of 1000 m or more (Sanz de Galdeano and AI faro, 2004). A great part of the deformation within the eastern Betic Basins was controlled by the displacements of the Lorca, Palomares and Carboneras sinistral strike-slip faults. Despite their great importance, they did not create very important reliefs, if compared with the central sector of the Betic Cordillera (Sanz de Galdeano and Alfaro, 2004). 5.4.1 The Carboneras Basin Within the Carboneras Basin a pronounced regional topographic gradient is present from north to south and from west to east. The formation of the gradient can be explained by the uplift of the Sierra Alhamilla and Sierra Cabrera mountains. Structural, stratigraphical and sedimentological studies suggest that the Sierra Alhamilla was elevated towards the end of the Tortonian. Neogene uplift rates were calculated at between 700 to 500 m I Ma for the Miocene (Weijermars et al., 1985). (Mather, 1991) estimated an uplift rate of more than 160 m I Ma for the Sierra Cabrera since the Pliocene. study Weijermars et al. Mather Faulkner et al. Martin et al. Silva et al. (1985) (1991) (2003) (2003) 2003 uplift - 500 m I Ma > 160 m I Ma -300 m I Ma -50m1Ma 80-100m1Ma (Sierra Alhamilla) (Sierra (Sierra (Cabo de (La Serrata) Cabrera) Cabrera) Gata) Table 5.2 Uplift rates of the major topographic highs within the Carboneras/Aimerla Basin. 230 i This study: Calculated uplift of the Sierra Cabrera using Quaternary terrace deposits During the work of this PhD the total amount of uplift of the Sierra Cabrera mountain range have been determined by the analysis of Pleistocene river terrace deposits. It is thought that incision is a direct response to crusta! uplift and therefore provides an approximate measure of the amount of uplift (Maddy, 1997 and Maddy et al., 2000). Particularly in arid environments we cannot assume that the river incision keeps up with the uplift, so the calculated rate will only be a minimum uplift rate. In a mountain area, kilometres away from the coast, river incision can be set equal to the amount of uplift of the mountain range: The total uplift (TU) of the Sierra Cabrera has been calculated by the altitude above present sea level of reference surfaces (R) (here base of the oldest terrace level) - the altitude of the modem river bed (M): (TU) = (R) - (M) 370m-315m =55 m This means that the minimum uplift of the Sierra Cabrera is >55 m since the development of the highest terrace I strath terrace during the Early/Middle Pleistocene (Chapter 4, section 4.4) for a detailed description of the terrace deposits of the Gafares River and Fig. 4.6.23. staircase diagram of the Rio Alias. If we correlate the highest strath terrace of the Rio Gafares with the highest terrace of the Sorbas Basin (A terrace}, which has been dated by Candy et al. (2005) of- 304 ka, we can calculate a minimum uplift of the Sierra Cabrera of0.18 mm I a. 231 ii Discussion The amount of 0.18 mm I a of calculated uplift rate of the Sierra Cabrera since the Early Pleistocene is very similar to the estimated uplift rates of > 160 m I Ma of (Mather, 1991) and 170 m I Ma of Braga et al (2003b). Silva et al (2003) estimated (0.15-0.8 m/ka) as a general uplift rate for SE Spain. These rates are much less than the 300 m I Ma Faulkner et al. (2003) calculated for the Sierra Cabrera. The variation of uplift rates can be explained a) by the location of the studied river terrace deposits (e.g. not located at the highest uplifted area); b) the age of the terrace (e.g. the observed highest terrace is much younger (e.g. the strath terrace is maybe late Lower Pleistocene or even younger) or c) that the largest amount of uplift occurred prior to the formation of the first terrace. Thus the overall similarity of uplift rates in SE Spain is very interesting and warrants further investigation. 5.5 The Carboneras Fault Zone (CFZ) 5.5.1 Introduction The Carboneras Fault Zone (CFZ) is part of the Trans-Alboran shear zone (Larouziere et al., 1988) which constitutes part of the diffuse plate boundary between Africa and Iberia (see map Fig. 5.1 ). The shear zone is several hundreds of kilometres long and extends from SE Spain to the eastern Rif in Morocco. The CFZ represents a major sinistral strike-slip fault in the Betic Cordillera, accompanied by pressure ridges and pull-apart basins (Boorsma, 1992). The CFZ belongs to a set of three NE-SW faults (Carboneras, Palomares and Lorca faults) which were possibly activated during the Middle Miocene, and became extremely important throughout the Quaternary (Sanz 232 de Galdeano, 1990). The CFZ separates the Cabo de Gata Block (Neogene volcanics) from Neogene basinal sediments and the metamorphic basement of the Alpujamde Complex (Reichert and Reiss, 2001). i Location The Carboneras Fault Zone (CFZ) is located on the SE side of the Carboneras Basin and is formed by a network of individual fault strands up to several kilometres long (Fig. 5.1 and 5.2). The exposed portion of the Carboneras Fault System has a total length of 40 km with a width that varies between 1.4 and 2.5 km (Keller et al., 1995). In the southern end of the Carboneras Basin the fault system (Serrata Fault) exhibits a NE-SW (050°) trend. To the north of the town of Carboneras the fault changes to a NNE-SSW (020°) trend and further north it merges with the N-S- trending Palomares Fault which extends to the north into the Vera Basin. This change in trend forms a restraining bend which originally has upthrown the Sierra Cabrera basement block (Keller et al., 1995). Faulkner et al. (2003) indicated that movements on the Carboneras and Palomares Faults are not contemporaneous, although some overlap might have occurred. Presently the Palomares Fault clearly cuts the Carboneras Fault (CFZ) which means that later movements on it post-date displacement on the CFZ. ii Subdivision The Carboneras Fault Zone has been sub-divided into several minor faults. These are the Almeria Fault or Serrata Fault, along the La Serrata ridge. Keller et al. (1995) further sub-divided the area north of the town of Carboneras into the Polopos, Sopalmo, and Colorados Faults. These fault zones are in close proximity to each other and are generally steeply dipping towards both the NNW and the SSE (Keller et al., 233 1995). Huibregtse et al. (1998) described the CFZ in the area of study as only two subvertical N040E-striking boundary faults. The south-western continuation of the CFZ continues offshore into the Gulf of Almeria, forming the Spanish on-shore segment of the Trans-Alboran shear zone (see Fig. 5.1, C). The submarine part of the fault is 100 km long and 5-10 km wide (Gracia et al., 2006) and suggests a strike-slip motion (see Fig. 5.1, C) combined with vertical component~. The onshore segment of the major sinistral transcurrent shear zone strikes approx. NE-SW and anastomoses in E-W striking minor faults of about 50 km length (Reichert and Reiss, 2001 ). ;;; Activity The hypothesis that the CFZ is still active during the Quaternary is supported by many researchers. Keller et al. (1995) stated that deformation along the fault zone continued throughout the Quaternary, and is represented by minor reverse faults sub-parallel to the Serrata fault, various 040° trending folds to the NW of El Saltador Alto and uplift and subsidence of marine terrace north and south of Carboneras respectively (Bousquet, 1979). During a Meteor cruise 51 parasound investigations have found several fault strands in the Gulf of Almeria, with missing recent sedimentary cover (Reichert et al., 2001). The sediment loss occurred in an area with relatively high sedimentation rates, leading to the conclusion that faulting along the CFZ must be very recent (Reichert et al., 2001 ). Furthermore several earthquakes between 1990- 2000 have provided evidence for recent strike-slip motion along the CFZ (Geofisica, 2006). The most recent earthquake in the study area was in June 2005 along the Carboneras coast with a magnitude of 4.0 on the Richter scale (Geofisica, 2006). 234 iv Tectonic-drainage Many researchers have studied the Carboneras Fault Zone from a tectonic point of view (Keller et al., 1995; Huibregtse et al., 1998; Scotney et al., 2000; Reichert et al., 2001). Only a few have focused on the tectono-stratigraphic importance during the Neogene (Boorsma, 1992; Bell et al., 1997). However nobody has published the relationship of tectonic movements along the CFZ to drainage development, which is one of the main objects of this study. The CFZ is an ideal study site because of its importance, large size, tectonic history and well preserved deposits due to the arid climate. 5.5.2 Displacement Neogene sedimentation m the Carboneras Basin was strongly controlled by contemporaneous displacement along the Carboneras Fault System. Estimates of the amount and time of displacement along the CFZ show huge variations. These are discussed below: i Activity Keller et al. (1995) suggests seven episodes of movement, with the main phase of activity prior to the Langhian, minor activity during the Tortonian and episodic faulting throughout the late Messinian (see Table 5.3). Huibregtse et al. (1998) agreed with the idea of progressive development of the fault zone during multiple displacement phases, but did not agree that most of the displacement occurred prior to the Langhian. (Hall, 1983), on the other hand, argued that the Carboneras and Palomares faults form a coherent system active since Burdigalian times. Jonk and 235 Biennann (2002) suggested that most of the displacement along the CFZ took place in the Early Tortonian. Scotney et al. (2000) divided the CFZ in the Sierra Cabrera region into two individual strands each SO m wide. They conclude that the 10.8 ± 1.9 Ma Serravallian - Tortonian boundary constrains the end of movements on the southern end of the CFZ, which may have been predominantly dip-slip. The main phase of left-lateral strike-slip movements on the northern strand of the fault zone may have occurred after this time (whereas geological constraints do not preclude earlier strike-slip movements) (Scotney et al., 2000). Keller et al. (1995) pointed out that tilted Pliocene sands which cover the CFZ are unconfonnably overlain by upper Pliocene sands, indicating tectonic activity during that time. This is in line with the results in this thesis, which suggest strong vertical uplift along the fault zone prior to the Pliocene, creating a steep coastline for the subsequent Gilbert type fan delta deposits of at least 80 m (min. thickness of the fan delta sequence on the eastern side of the fault) and strike slip movements ongoing into the Holocene. ii Vertical displacement along the CFZ The Carboneras Fault Zone is a complex system of faults which clearly affects the Upper Pleistocene deposits. Strike-slip faulting, as well as certain vertical movements, have been recorded (Goy and Zazo, 1986). With an offset of around 40 km, the fault must cut through the entire crust and lithosphere (Faulkner et al., 2003). Bell et al., (1997) estimated the vertical uplift along the CFZ using Quaternary fluvial and marine terraces. This resulted in an average vertical slip rate of 0. S - 1 mm/ year over that time frame. 236 CFZ activity c: 7fi cu ...... ; Cll cu g -: .... ~ cu .!11 c:v ...... /9 Ojeo CIIQ' ClJO -s tR Qiii)' O(Sf? .a CD' ..... <;{fa> ,_ ~8 ...... ~-....;. AGE ~~ ,0 '-- .Scv "'8 Epoch Stage .:::::- .:::::' ..... 8-....;. c: .!!} CV (MA) ...... r::::-....;. ;f :: l Cl.) ~ ~ Holocene Pleisto cene 1.81 cCD CDu ·-0 ? ? ? 5- -D. 5.3:: Messinian -7.25 "E L ~ ~ ? 10- Tortonian .Q. - -11.61 Ul a. Cl) '6 c Serravallian "Cc: Cl) -13.6!:: ~ u M E 0 Q) 15- ·-:2 Langhian ~?5l • - -15.97 Burdigallian E 20- I- 20.43 Table 5.3 Table showing the different estimated times of activity of the Carboneras Fault Zone (CFZ) by various researchers. 237 iii This study: Vertical uplift along the middle fault strand of the CFZ During this study there have been 3 individual fault strands of the CFZ recorded (see map Fig. 5.2). Previous studies, e.g. (Keller et al., 1995; Scotney et al., 2000) have shown (Table 5.3) that these fault strands have been active at least since Tortonian times. Bell et al. (I 997) on the other hand proved Quaternary activity along fault strands approximately 3 km further towards the east. This leads to the assumption that the activity along the Carboneras fault strands has been decreasing in age from west to east. The middle fault strand (Fig. 5.2) runs through the fan delta deposits. The fan delta sediments on the western side of the fault strand reach altitudes of up to 253 m (Fig. 5.2 and 5.3). The conglomeratic quartz deposits on top of Cerro Gordo are not very thick and show no sedimentary structure or dewatering features and are regarded as the fluvial part of the fan delta sequence. The highest altitude fan delta deposits to occur on the eastern side are 178 m. This gives us a difference of 75 m in altitude between the western and eastern side of the fault zone. It could mean that the western side of the fault zone has been vertically displaced by up to 75 m since the deposition of the fan delta during the Late Pliocene, i.e. 0.038 mm I a with 2 Ma marking the End of the Upper Pliocene. However, this is a very inaccurate rate, since we do not know how much of the surface of the fan delta foresets has already been eroded. 238 Fig. 5.3 Gilbert fan delta deposits along the Carboneras Fault Zone. Photo taken from the Cerro Gordo. A: View of the fan delta quarry, approximately 3 km across. Photo has been taken from Cerro Gordo on the western side of the CFZ towards the NE. B: Fan delta conglomerates on the eastern side of the fault zone topped by a massive calcrete crust. Note the channel development in the middle of the photo. C: Small dewatering structure within the conglomerates on the lower part of the fan delta sediments of the western side of the CFZ. Note the calcite infilling on the left hand side. 239 iv Discussion Silva et al. (2003) calculated the uplift of the strike-slip La Serrata ridge by using the mountain front sinuosity and valley width/height ratio. They measured differential uplift rates of 80-100 m I Ma for La Serrata (Silva et al., 2003). Their data corresponds with the amount of vertical uplift of 75 m since the Late Pliocene of this study, provided that the fan delta deposits on the eastern side are equivalent in age to the one across the fault zone. The idea of vertical uplift along this strand of the CFZ mainly during the Pleistocene is further supported by the stream profile of the modem Alias. No anomalies can be found within the modem long river profile across the fault, including any vertical movements during the Holocene (see longitudinal profile of the Rio Alias in Fig. 4.6.2). Furthermore the modem river does not show any difference in degradation on the western side of the fault in comparison to the eastern side, where more aggradation should take place as Holbrook and Schumm (1999) suggested (Fig. 5.4). Degradation Aggradation ------..... Fault Fig. 5.4 Generalized aggradational and degradational response of stream as it crosses a fault after Holbrook and Schumm ( 1999). The occurrence of abundant meander loops along the fault might suggest an increase in stream power (e.g. empirical work by Ouchi ( 1985), due to an increased gradient as 240 a result of vertical movements, however the meander loop is situated on the western side of the fault (the uplifted side). Furthermore it might be influenced more by the lateral movements of the fault, since the Pleistocene river channel seemed to pick out the weaker material along the line of displacement (see Fig. 5.5). 5.5.3 Lateral displacement Drainage offset along a strike-slip fault can provide valuable evidence on the magnitude of the strike-slip movement (Summerfield, 1991; Ouchi, 2005). The most obvious lateral impact on a river is the result of active strike-slip faulting (Wallace, 1968). The lateral (horizontal) offset of a stream can be seen in plan view and is generally not considered to deform the longitudinal profile of the channel. The lateral displacement of a strike-slip fault elongates the longitudinal profile of a channel by adding a new section (Ouchi, 2005). i Carboneras Fault Zone Bousquet (1979) admits that the northeastern part of the fault (the study area of this thesis) is the most complicated one. He found several approximately parallel faults with high-angle dips. He also concluded that the Quaternary terrace (corresponding to Alias terrace level 3 of this study), between the two main faults (this study western and middle strand) is strongly folded and faulted. The folding (terrace GR. 914948) has been noticed during this study and is described in Chapter 4). 241 Fig. 5.5 Modified satellite image (derived from (Google Earth, 2007) showing the channel bed of the modem Rio Alias (light blue) and the possible extend abandoned meander loop (dark blue). The middle strand of the Carboneras Fault Zone is presented in white. Please note the Pleistocene meander loop is situated on the western side of the fault line, which rules out the idea that the meander loop might be a result of vertical movements across the fault, due to the associated increase in slope and stream power. 242 In the study area the offset of the (ii) modern river, (iii) terrace remnants and (iv) fan delta deposits show that there has been an obvious strike-slip movement along the fault, which is still active during the Holocene. The well preserved data even allow quantification of the displacement rate. ii modern river The Alias River has developed parallel to the mountain front with a flow direction from west to east. In its middle part the Alias channel is deflected three times in a 90° angle (exactly across the CFZ). Three times it has been displaced towards the NE along the three individual fault strands and shows a rectilinear pattern across the fault zone (Fig. 5.6). The three displaced channel parts are all exactly deflected in the same direction, despite different underlying geology. iii river terrace dislocation A second indication for lateral displacement along the CFZ is provided within the terrace history of the Rio Alias. Examining two terrace deposits of level 3 on either side of the fault there is a very significant similarity between both remnants. Terrace conglomerates of the terrace 113 m (GR. 91694 7) situated on the western side of the CFZ (middle strand) show the same clast lithology and provenance distribution as the remnants across the fault strand of Ill m (GR. 926954) (see Chapter 4, Fig. 4.6.18 of terrace deposits along the fault). The two terrace deposits are very likely to belong to the same terrace level. This would suggest a lateral strike-slip offset of I km. 243 ~ • E ~ ~ c: 'iii m cCl) "' ,j\01 - Cll E I!! v~ CO c:Ql ~ 0 ~ ~ ..c ~ ... 0 01 ,... -u :§ u"' ·~ 4 c( 4 , -r-('l(f)"V Fig. 5.6 Schematic map of the Alias channel and its terrace deposits, with small overview map inserted. A: Modem Rio Alias showing a rectilinear pattern across the Carboneras Fault Zone. The NE flowing parts of the channel are referred to as offset channel segments. Note that the terrace deposits located in the offset reach are always younger than the fluvial remnants upstream of the offset segment. 8: A schematic diagram illustrating geometrical properties of an offset stream, modified after Ouchi (2005). 244 Discussion The two terraces are situated 1 km apart and it could be argued that they could have been deposited within a meander loop. With the distance of 1 km and a thickness of 2- 3 m, the terrace remnants should have a significant difference in heights of app. I 0 m in order to fit onto the long river profile. To explain the same heights by vertical movements along the fault is out of the question, since we would expect an uplift of the deposit on the western side of the fault, increasing the difference in altitude even more. It is therefore very convincing that the fluvial deposits used to belong to the same terrace remnants, but have been moved by 1 km along the strike-slip fault in a NE direction. The post-sedimentary displacement must have occurred during the Late Quaternary since the terraces belong to terrace level 3. We do not have any absolutely dated river deposits of this level, but the carbonate stages suggest a Late Pleistocene age for these conglomerates (chapter 4). Correlating the terrace deposits to (Candy et al., 2005)'s C terrace of the Sorbas Basin with an relative age of -70 ka, we can calculate a lateral displacement of 14 mm I year since the Mid Late Pleistocene. terrace along the old and new sectio11 oftire offset river channel One important fact supporting the theory of offset channel segments across the CFZ, is the observation that only younger terraces are found in the proposed offset reaches of the channel, compared to older terrace deposits along the upstream and downstream channel part (see Chapter 4 and Fig. 5.6 for details). Valley response to channel offset When a river channel is transected by a dextral strike-slip fault, the right bank downstream of the fault will be eroded, whereas the left bank will undergo deposition 245 (Zhang et al., 2004). This can be found in the field at the middle and right hand fault strand, where no terrace deposits can be found on the right hand river bank (see Fig. 5.7). This further supports the theory that the Rio Alias channel has been offset across the CFZ. fault deposition downstream upstream erosion deposition deposition • • erosion ...... anomalous erosion Fig. 5.7Channel migration caused by strike-slip faulting. Erosion on the right bank and deposition on the left river bank, modified after Zhang et al. (2004) for the Rio Alias. iv lateral displacement of the fan delta deposits Boorsma (1992) observed a lateral displacement of 2 km of the Middle Pliocene fan delta deposits of the La Serrata area. Very similar distances have been recorded in this current study. The Pliocene fan delta near El Argamason, deposited by the Early Rio Gafares (see Fig. 5.2), shows a very strange geometry. By looking at the geological and topographic map it is obvious that the north-western part of the delta deposits are left with a steep NW facing wall (Fig. 5.3). This wall is situated exactly on the middle strand of the CFZ. To the SE the entire former depression (during Pliocene time) was filled by a minimum of 80 m thickness of fan delta deposits. Towards the SW red 246 coastal plain sediments overly the delta deposits in many areas. Towards the SW across the fault a second steep cliff appears. This seems to be the uplifted Pliocene palaeoshoreline during the deposition of the fan delta. This SE facing ridge has well rounded quartz pebbles on top, which adjoin the reddish soil of the coastal plain deposits (see Fig.5.6). It is impossible to sensibly recreate the palaeo-geography without moving the steep palaeo-cliff line back towards the NW facing wall of the fan delta deposits: Detailed mapping of the delta and coastal plain deposits location provide an estimated displacement of2 km since the end of the Late Pliocene. 247 Fig. 5.8 Examples of different fracture types in the Carboneras Basin. A: Recent fault scarp displacing Pliocene fan delta deposits (GR. 92495). B: Synsedimentary faulting in Pliocene sediments (GR. 929947). Each of the coloured bands represents different types of fault gouge that have been juxtaposed due to movements on the fault. C: Synsedimentary fault in fan delta conglomerates (GR. 91 0940). D: Tensional joints with symmetrical calcite filling the joint opening (GR. 908939). 248 5.5.4 Discussion During this study movements of the CFZ, lateral and vertical, have been recorded and analysed. Ongoing tectonic activity during the Quaternary has been observed. The results are in line with some previous work, such as Boorsma ( 1992), who pointed out that present-day movement along the main fault is illustrated by 100-115 m left-lateral offset of stream courses in the La Serrata area. The similarity between the two studies is mainly because both authors worked on relatively young sediments (both Pliocene fan delta conglomerates and modem stream channels) within the basin itself (an area where there is enough displacement space), compared to other studies on basement rocks within the Sierra Cabrera (Huibregtse et al., 1998; Scotney et al., 2000; Jonk and Biermann, 2002). i vertical offset along the CFZ This study measured the vertical uplift along the CFZ using displaced Pliocene fan delta deposits and estimated an amount of 76 m of vertical uplift since the End of the . Pliocene. Compared to other literature this rate is below the one of Bell et al. (1997), who estimated the uplift along the CFZ with an average vertical slip rate of 50- 100 m I Ma. The reason for the variation between Bell et al. ( 1997) and this work could be the fact that this study calculated the uplift rate on the second most western strand of the CFZ and (Bell et al. (1997) obtained their data 4 km further east and different fault strands might move at different rates and at different times. A progressive increase in vertical activity towards the more eastern strands could be one explanation for the dissimilar uplift rates. 249 ii lateral offset along the CFZ The rectilinear pattern along the fault zone of the modern Alias channel is already very obvious by studying the topographic map (Fig. 5.6), but it could be argued that the rectilinear pattern could simply be meander bends of the modern river. However further investigations have shown that the three 'meander bends' are all exactly deflected in the same direction, despite different underlying geology. Using the additional results from the Pleistocene terrace remnants the idea of the offset of the stream channel along the CFZ becomes more convincing. Along the Alias River a 1 km lateral offset since the deposition ofT3 (14 mm I a) has been calculated by measuring the distance between two terrace remnants of terrace level 3. This strike-slip movement is mainly measured from the middle of the CFZ strands in this area. (Scotney et al., 2000) also divided the CFZ into different strands. He observed two strands, both located within the mountain area of the Sierra Cabrera and stated nearly pure left-lateral strike-slip for the southern strand, which is close to the middle strand of this study area. The obtained lateral offset data from this project does not fit in with the slip rates of Bell et al. ( 1997) calculated for the northern part of the Carboneras Basin. By using marine and fluvial Quaternary terraces Bell et al. ( 1997) stated a sinistral slip rate of 0.2 mm/year during the Quaternary. One reason for this could be the location of his study area. His data were mainly obtained from fluvial deposits within the lower reaches of the Rio Alias. This is east of the three fault strands of the CFZ, which were the subject of this present research, and could mean that his terrace deposits were not affected by the majority of movements along the fault. Also as described above, if the fault activity is moving from W to E with time, his palaeo-terraces in the far eastern part are the last to be active. These findings 250 are in accordance with Keller et al. (1995), who observed that the fault activity within the CFZ fault system moved from one fault strand to another with time. The calculated offset rate of 14 mm/a from this study fits into the range of offset data of various fault zones around the world, e.g. Pucci et al (2007) calculated 15.7 mm/a of stream deflection for the Diizce segment of the North Anatolian Fault Zone. The San Andreas Fault shows even stronger displacement rates as Grove and Niemi (2005) calculated. They estimated a long term slip rate between 17-35 mm/a for the San Andreas Fault, with 25 mm/a for gravel quarry deposits and 21-25 mm/a for Holocene sediments. This is in line with work done by Becker et al. (2005) who stated a 23 mm/ a displacement rate for the Indio segment of the San Andreas Fault. The strong displacement of the Alias stream channel along the CFZ suggests that other rivers crossing the fault zone should have also been offset. Compared to the consequent drainage of the Alias the other rivers and tributaries in the fault zone are relatively small. Wallace (1968) observed that large rivers are often offset more than small ones. Additionally Gaudemer et al. (1989) working on the San Andreas Fault demonstrated that only one third of the rivers along the San Andreas fault were deflected in the direction of the fault. Alien (1962) noted that flow direction nearly perpendicular to the strike of the strike-slip fault is an important condition for the preservation of stream offset; otherwise the stream will follow the zone of fault slip. So lateral displacement seems to be a phenomenon which does not affect all rivers in the same way . 251 5.6 Summary Comparing previous studies it is evident that (a) there has been an extensive strike slip motion along the Carboneras Fault System; (b) major vertical tectonic activity started prior to Pliocene times and (c) that there was a definite vertical and lateral movement along the fault ongoing through the Quaternary. This study has indicated that: o basin uplift must have be in excess of- 44 m I Ma (calculated from Pliocene fan delta deposits) o uplift rates of the Sierra Cabrera are in the region of 0.18 mm I a o vertical uplift along the CFZ must have taken place prior to the Pliocene in order to create a steep enough gradient for the Gilbert type fan delta to occur and to provide the necessary accommodation space to exceed the stacking pattern fan delta sedimentation o Pliocene fan delta deposits have been vertically offset o three individual fault strands of the CFZ between the village of El Argamason and Cortijada El Llano de Don Antonio exist, with fault activity increasing with time towards the east o a rectilinear pattern of the modem nver across the fault zone has been observed o left lateral displacement of a minimum of 2 km took place along the CFZ since the Late Pliocene o lateral offset of Upper Pleistocene river sediments of 1 km (14 mm I a) occurred 252 o vertical fault movements along the middle strand of the CFZ must have stopped during the Pleistocene, since there is no sign of post-sedimentary vertical displacement of the Pleistocene fluvial terrace deposits, nor of the Holocene modem channel o tectonic activity of the CFZ is still ongoing through the Quaternary It is important to see how reliable the fluvial pattern is for the identification of a specific structural pattern. The analysis of one single drainage pattern is generally not enough to give evidence of fault movements and to quantify it, but consideration of various individual drainage features can provide accurate information on the fault activity. For this study the author has investigated a combination of fan delta deposits, terrace remnants and the modem stream channel. By gaining knowledge about the tectonic activity in the study area relative information about other controlling factors on the drainage evolution can be made. For example as Boorsma (1992) already stated relative sea-level fluctuations as interpreted from the sedimentary record do not always have a eustatic origin and thus have to be interpreted in terms of relative subsidence and uplift of the area. This is especially important for the Carboneras Basin and for the Plio/Pleistocene sediments. The above summarized results lead us back to one of the main questions in the beginning of this project: how important are external controls on the drainage development and which is the most influencing factor? This will be explored in Chapter 6. 253 6 CHAPTER: CONTROLS ON THE LONG-TERM DRAINAGE EVOLUTION OF THE CARBONERAS BASIN 6.1 Introduction Spatial and temporal changes in sedimentation of a drainage system can be clearly identified from the sedimentary record of a river system. Typically river development during the Cenozoic has led to the formation of staircases of terrace deposits (Bridgland and Maddy, 2002). The consequent rivers within the Carboneras Basin display a typical evolving drainage system. The main controlling factors responsible for changes in drainage evolution can be divided into those intrinsic to. the basin and those extrinsic. Intrinsic controls include the geology and geomorphology of the basin and of the catchment area. Extrinsic controls include relative sea level, regional uplift, differential tectonics and climate. Intrinsic: Topography Geology I Geomorphology Extrinsic: Relative sea level I Climate Tectonics The complex interplay of these controlling factors is usually difficult to unravel, due to the rare possibility to study each of them in isolation (Amorosi et al., 1996); (Birkeland, 1990). However within the following section the author tries to evaluate 254 and discuss the controlling factors on the Rio Carboneras system individually. The Betic Cordillera provides an excellent area in which interactions between tectonics, sedimentations and river development can be explored (Lewin, 1995). 6.2 Intrinsic controls on drainage evolution 6.2.1 Topography The topography of the Pliocene marine shelf deposits and fan delta sediments is very important in establishing the initial Plio/Pleistocene drainage patterns within the Carboneras Basin. The first drainage channels were developed onto the low gradient topography of the shallow marine shelf and between low lying areas within the fan delta. Therefore the topography appears to be important in controlling where the initial drainage systems develop, it cannot account for the overall dissection of the basin by the Plio/Pleistocene drainage network (Stokes, 1997). 6.2.2 Geology I Geomorphology The geology and geomorphology of the drainage basin play an important role in the river development. Geomorphic control plays a central role in river evolution. Climatic, tectonic and base-level changes are all reflected in the geomorphology of river systems (Jones et al., l999b). The geomorphic components of basin stratigraphy are still poorly understood and their significance underestimated. Bishop (1995) highlighted the importance of geomorphic processes such as river capture, beheading and diversion for drainage evolution and river rearrangement. Offset fluvial valleys, 255 including rivers beheaded and deflected by strike-slip faults, have been used to estimate tectonic activity, e.g. horizontal displacements on strike-slip faults (Zhang et al., 2004). The geomorphic component is usually coupled with the overall geology of the drainage basin. Underlying geology is crucial for sediment erosion rates and processes of the catchment area and valley incision of the river channel. Interactions between the mountain uplift and the valley incision are all related to the bedrock geology. Differences in the longitudinal river profile can be interpreted in terms of the balance between mountain uplift and stream incision. This gives essential clues about the different states of profile development. When stream incision exceeds rock uplift, incision propagates upstream giving rise to a concave profile. The inability of stream incision to counter rock uplift leads to a progressive steepening of the stream gradient, resulting in a convex profile (Hovius, 2000). Mather (1991, 1993a) has indicated how important geomorpholological and geological changes are in the evolution of the drainage system. River capture is an important feature for the Rambla de Ios Feos, since after the rambla was captured by the aggressively headcutting Rio Aguas, not only did the rambla experience a reduction in erosion rate (Mather et al., 2001), but also 73% of the main Sorbas Basin drainage was re-routed (Mather and Blum, 2000). One important factor is the geological characteristic of the catchment area (e.g. bedding parallel to the strike direction) which influences the development of aggressive subsequent streams in the Sorbas Basin (Harvey and Wells, 1987; Mather, 2000). This phenomenon can be seen within the Carboneras Basin as well. The development of the Rio Saltador is strongly controlled by the local geological structure. With the uplift of the Sierra Cabrera the Neogene deposits along the basin margin have been tilted by uplift and are now strike 256 parallel to the mountain range. This structural arrangement favours the headcutting back of several streams along the weak lithologies of the Neogene infill, e.g. the Rio Saltador and Rambla de Lucainena. The longitudinal profile of the Rio Gafares shows a convex shape within the mountain area and a concave shape south of the mountain front, implying that a) the modern river has insufficient stream power to keep up with the mountain uplift of the Sierra Cabrera or/and b) the underlying bedrock geology is more resistant in the mountain area than in the lowland and does not allow the channel to cut down. The convex river profile could also be a result of an earlier river capture of the Rio Gafares. This is very likely, since, as discussed in Chapter 3, the catchment area of the Rio Gafares must have extended much further, draining a larger area than it drains today, due to the large sediment volume of the fan delta. 6.3 Extrinsic factors influencing the drainage evolution 6.3.1 Sea level Sea level acts as the lowest base-level below which rivers cannot erode. The lowering of sea-level means a lowering in base level. When the lowering of the base-level is not balanced by lengthening the river course, incision will result in changes in profile upstream (Summerfield, 1985), while higher sea-levels would produce periods of aggradation, particularly in the lower reaches of river valleys. Longitudinal profile adjustment forced by a fall in sea level will start at the coastline and progresses landward by headward erosion resulting in knickpoint migration (Leeder, 1996). 257 However,it is not clear how far upstream a river is affected by sea-level changes. (Schumm, 1993) suggested that the effects of base-level change will tend not to be propagated far upstream, particularly in large rivers which tend to accommodate small base-level variations through modification of the internal variables such as sinuosity or charinel morphology. Experimental approaches on fluvial response to sea-level changes have been carried out, where other influencing factors have been kept constant (van Heijst and Postma, 2001). European field studies have shown that mainly only lower parts of the river have been influenced by sea-level changes: e.g. La Seine (Antoine et al., 2000). This is supported by observations of Quaternary river valleys in NW Europe, where Bridgland and Allen (1996) demonstrated that large scale fluctuation of sea level has had little effect on fluvial activity except in the lower reaches of valleys. This seems to be true for the fluvial deposits of the Carboneras Basin, where the majority of terraces are preserved upstream, away from the coast and the resulting influence of sea-level. Maher (2006) stated that the influence of sea-level on terrace development of the Rio Alias has been limited to no more than 7 km upstream. This corresponds to the findings of this thesis, where no significant correlation between sea-level fall and incision or sea level highstand and aggradation has been found. The only evidence which could be a result of sea level lowering is the development of the meander loop in the lower reaches of the Rio Alias (Rio Carboneras) during the aggradational stage of T2 (see Chapter 4 for details). This might be a result of an increase in river length, due to a fall in sea-level. However, the upstream part of the Rio Alias, Rambla de los Feos and Lucainena and the Rio Gafares would not have been affected so strongly and local knickpoints and vertical drops across mountain 258 fronts and fault strands would eliminate the influence of the sea-level lowering by creating local base levels. This can be seen within the long river profile of the Rio Gafares, where local knickpoints along the mountain front create a discontinuity of the channel gradient. These findings correspond with work carried out by Maher (2006), who pointed out that terrace aggradation and incision of only the most eastern part of the Rio Alias (the El Saltador sub-reach) was influenced by Quaternary sea-level changes. They are furthermore supported by further river studies, such as Macklin et al. (1995), who already stated that away from the coast the steep valley floor gradients of most Mediterranean rivers ensured that base-level changes, associated with fluctuations in sea-level, had very little impact on channel development inland. As Schumrn et al. (1987) summarized it is not possible to relate terrace remnants throughout the entire lengths of the valley to one specific stimuli such as climatic variations or base-level change. 6.3.2 Climate In recent years it has become evident that factors other than base level are significant in triggering incision and aggradation (Miall, 1996;.Tucker and Slingerland, 1997; Jones et al., 1999b; Blum and Tomqvist, 2000; Bridgland, 2000; Maddy et al., 2000). Rivers have been forming terraces in synchrony with the oscillation between glacials and interglacials, probably in response to Milankovitch scale climatic fluctuation (Bridgland, 2000). At present it is still not clear how long the minimum duration of a climatic change required to influence river behaviour is and how big the amplitudes of these climatic shifts have to be in order to cross the thresholds for a change in the 259 fluvial system (Vandenberghe and Maddy, 2001). The fact that incision is probably a relatively short-lived event (Maddy et al., 2000) compared to the duration of a single glacial-interglacial cycle is an important problem for the discussion of climatic control on drainage evolution (Antoine et al., 2000). Climatic controls will affect the rates of sediment production and transportation and the amount of discharge within the drainage systems. Incision, for example, occurs when the sediment supply is limited and the discharge high, e.g. at the beginning of warm events when hillslope stabilization reduce sediment supply (Maddy et al., 2001). In semi-arid regions, this might occur during warm, wet intervals when discharge is more constant and sediment supply is reduced by an increase in vegetation cover within the drainage basin catchments (i.e. higher water I sediment ratio). Phases of aggradation on the other hand, may reflect more cold, dry periods, when discharge was erratic due to seasonal flooding and sediment yields increased due to reduced vegetation cover (Amor and Florschutz, 1964). Limited studies on arid-zone rivers suggest that a minor change in climate can lead to significant changes in flow regime, sediment transport, and associated channel style (Nanson and Tooth, 1999). In areas with no uplift the climatic influence is still shown by the aggradational and erosional record (Vandenberghe, 1995). In areas with uplifting mountains, like SE Spain (study area) the climatic influence on drainage development could be less important. 260 i Mediterranean In non- glacial areas such as the Mediterranean, river valley evolution has long been regarded as the result of climatic fluctuation. Semi-arid and arid systems are very sensitive to small changes in regional rainfall (Frostick and Reid, 1989) and sediment transport rates. The climate of the Mediterranean basin over the Quaternary period has 3 2 been controlled by slow (10 - 10 years) insolation changes driven by orbital cycles 1 2 and also by abrupt (10 - 10 years) shift in atmospheric-oceanic circulation. The affects of climate are typically felt via the impact on vegetation and thus the generation of effective runoff. Preserved evidence for the impact of climate in the Mediterranean region is poor and the response of the system complex is often very difficult to unravel (Macklin et al., 1995). Since climate change is relatively synchronous globally (within the resolution of age data on most fluvial deposits) it can be expected that the phases of changes in fluvial behaviour should be broadly correlatable. There is evidence for a high degree of synchrony in major river aggradation events across the Mediterranean in catchments with very different sizes, tectonic regimes and histories (Macklin et al., 2002). Climate-related changes in catchment hydrology and vegetation cover over the last 200 ka would appear to be the primary control of large-scale (catchment wide) sedimentation over time periods of between 103 and 104 years (Macklin et al., 2002). Pleistocene climate ofSE Spain Pleistocene climates in SE Spain are thought to have been dry (Amor and Florschutz, 1964) with intense seasonal storms (Sabelberg, 1977). However the discussion about 261 whether the SE of Spain was glaciated or not is still ongoing and mainly focused on data from high altitude regions, such as the Sierra Nevada. (Schulte, 2002) discovered four end-moraines located between 1600 and 2980 m a.s.l. in the Sierra Nevada as a result of late Pleistocene glaciation. (Mather, in press) supported the theory of glaciation in higher altitudes and stated that during OIS 2 only mountain headwaters above ~1000 m were glaciated in the Mediterranean area. Results of high-altitude palynological surveys demonstrate that Upper Pleistocene climates in SE Spain appear to have been dry during the cold phases, with insufficient moisture to support extensive tree cover (Pons and Reille, 1988). No substantial vegetation changes have been recorded in the last 250,000 years (Munuera and Carri6n, 1991 ). Marine record Th/U dating of Strombus bubonius-bearing marine terraces in the Almeria region by (Hillaire-Marcel et al., 1986) has demonstrated the presence of the warm water S. bubonius fauna in the Mediterranean basin at the end of the Mindel-Riss interglacial (OIS 7) and during each high sea-level episode of the Riss-Wiirm interglacial (OIS 5). Recent work by Zazo et al. (2003) supports these findings and has shown that during OIS 5, 7, 9, 11 and older, warm fauna occurred within marine terrace deposits of the Almeria region. They proposed similar climatic conditions as today during the last interglacial and at least two interglacials of the Middle Pleistocene. At the end of OIS Se, the disappearance of a major proportion of the warm 'Senegalese' fauna indicated a sudden change in surface conditions and climate, switching from oolitic to non-oolotic deposits. 262 ii Carboneras Basin Today the climate of the Carboneras Basin and its surrounding basins is arid with precipitation of approximately 210 mm I a (recorded over historic period 1880-1992), (Esteban-Parra et al., 1998). Temperature ranges from -3 to 52'C (records from Cortijo Urra Field Study Centre, in Sorbas), (Mather et al., 2002). Most precipitation concentrated in short-episodic stormy events in autumn and spring, the so called 'Cold-Drop Events' (L6pez G6mez and L6pez G6mez, 1987). The precipitation shows large values of inter-annual variability and large disparities between wet and dry years (Trigo et al., 2004 ). Pleistocene climate Evidence for palaeoclimate conditions can be derived from palaeosols. All the calcretes described in Chapter 4, (located on top of the conglomerates) have been interpreted as pedogenic calcrete (in contrast to groundwater calcretes, (Nash and Smith, 1998)). The development of carbonate within soils is often attributed to arid and semi-arid conditions. Most Pleistocene terraces (Tl-T3) in the Carboneras Basin are capped by a laminar-massive calcrete (stage II-IV). This is typical of aridsols, which suggest that the Carboneras Basin was affected by relatively arid conditions through the Pleistocene. Harvey et al. (1995) pointed out that the red colouration of the Quaternary soils of the Feos and Rio Aguas is indicative for arid climate. This is in line with results from the adjacent Sorbas (Mather, 1991) and Vera Basin (Stokes, 1997). Mather (1991) stated that the uppermost deposits of the Gochar Fm of the Sorbas Basin (Late Gochar times) show well developed calcretes and therefore suggest arid conditions, whereas the lowest parts of the Pliocene Gochar Fm within the Sorbas Basin, are lacking in carbonate (despite a prolific supply) indicating that 263 leaching was operative at this time and that more humid conditions affected the basins during the Pliocene (Mather, 1991 ). Climatic control It has previously been established that the regional patterns of Quaternary aggradation/incision are related to northern European glacial/inter-glacial cycles (e.g. (Harvey, 1990; Candy et al., 2005; Maher, 2006). Climatically generated signals within the fluvial terrace deposits are complex to interpret. The overall clast size within the conglomerates of the Rio Alias decrease in size as the terraces get younger (see summary of the Rio Alias in Chapter 4). This terrace characteristic is possibly due to a reduction in peak discharge and thus stream power. However, the loss in stream power is more likely to be a result of the river capture of the Aguas river in the Sorbas Basin and the disconnection of the Sorbas drainage, rather than a climatic induced discharge variation. The occurrence of sedimentary features, which are characteristic for a meandering river environment (e.g. lateral accretion surface, abandoned meander loops within the deposits of T3), do not necessarily prove a change from cold to warmer climate, as it was considered by (Mol, 1997; Van Huissteden and Vandenberghe, 1988). Vandenberghe (2001) suggested that meandering rivers co-exist with braided rivers in the same region without any climatic control. Thus, cold environments were not always characterised by braided river patterns and fluvial aggradation, while warm conditions do not necessarily initiate meandering and incising rivers (Vandenberghe, 2003). The assessment of the impact of climate control on the river development of 264 the Carboneras drainage seems to be a very complex one and additional data (e.g. vegetation cover) would be necessary to conclude the climatic control more accurately. However, by correlating the terraces of the study area to the fluvial deposits in the Sorbas Basin further conclusions can be made about the palaeoclimatic conditions during the aggradational phases. This work shows the Carboneras and Sorbas Basin were still connected during the aggradational phases of Tl-T3. We can therefore correlate the terrace levels of the Carboneras Basin (at least for Tl-T3) to the terraces of the Sorbas Basin. T1 ofthe Rio Alias can be correlated to the A terrace in the Sorbas Basin, which was dated as 304 ka (Candy et al., 200S) and approximately corresponds to the marine oxygen isotope stage (OIS) 9. Terrace level 2 of the Rio Alias can be correlated to Harvey et al.'s (199S) B terrace of the Sorbas Basin. The terrace was previously dated by Kelly et al. (2000) at 147±2S ka which would correspond to the OIS Se sea-level highstand within the Mediterranean (Zazo et al., 2003). However, the most recent date by Candy et al. (200S) suggests an age of 207 ± 11 ka and the terrace would therefore be correlated to OIS 7c. The same problem occurs for the terrace level 3. Here, Kelly et al. (2000) dated the C-terrace in the Sorbas Basin at 88 ± 28 ka and the aggradational event which resulted in the deposition of the fluvial sediments ofT3 therefore seemed to match with the high sea level, interstadial period at around 88 ka. Zazo et al.,'s (2003) results show a highstand of sea level at 87 ka, which are supported by Macklin's et al. (2002) 88 ka event in the Mediterranean (OIS Sa). New dates by Candy et al. (200S) suggests an age of77 ± 4.4 ka. The aggradational phase for T3 for the Carboneras Basin would have taken place during OIS Sa. In any case, the terrace levels Tl-T3 still correspond with Zazo et al. (2003) findings of marine fauna in the 265 Almeria region during OIS 5, 7, 9 and 11. The T4 terraces of the Rio Alias might correspond to the Sorbas D terraces which are dated by Kelly et al. (2000) with 30.3 ± 4.4 ka and therefore again match up with Macklin et al. (2002)'s Upper Pleistocene interstadial during OIS 3. It should be noted that the calcrete dates show the end of the aggradational phase of the river and, therefore, the main depositional event might be even older. However, this is only the case if the top of the terrace (the youngest part) has not been eroded before the calcrete development. We can therefore use the terrace ages as a general time for the aggradational period and at least distinguish between the different major glacial and interglacial events. Results from this study have shown that the pedogenic carbonate development indicates an arid climate during the Pleistocene (Tl-3) and that the aggradational phases of the river systems correlate to the main interstadial periods. However, as far as the Pleistocene terrace levels are concerned climate might have provide the trigger for erosion and aggradation phases, nevertheless the staircase development within the Carboneras Basin might be due to an additional factor controlling the incision processes, e.g. relative uplift. 6.3.3 Regional uplift Structural controls on drainage development have been widely documented. In recent years more and more studies have demonstrated that the rivers response to climate 266 forcing is often superimposed upon a background of progressive uplift (Bull, 1991; Bridgland, 1994; Bridgland, 2000; Maddy, 1997; Antoine et al., 2000). Looking at the Milankovitch cycles and the change of the climatic cyclicity during the Mid Pleistocene Revolution from 41 kyr obliquity driven to a 100 kyr eccentricity driven, there is a good correlation between worldwide river terrace cycles, coupled with a worldwide increase in uplift (Bridgland and Westaway,in press). There are many theories on the causes for such uplift ranging from direct erosional isostasy to glacio and hydro-isostasy. The concept of valley incision caused by crusta! uplift has been examined by Bull, ( 1991 ). The formation and preservation of river terraces without significant uplift has even been considered unlikely (Veldkamp and Vermeulen, 1989). There is also a relation between the uplift rate and the terrace preservation. In settings with slow uplift rates, terraces are formed but are mostly subsequently eroded, while a rapid uplift might prevent the formation of terraces (Veldkamp and van Dijke, 2000). i Incision River incision caused by regional uplift has been discussed in recent literature for NW European rivers (Bridgland, 1994; Antoine et al., 2000; Maddy et al., 2000). Observations have shown that uplift rates during the Middle Pleistocene have increased with an increase in climate oscillations. This is demonstrated by well developed staircases registering each I 00 ka climate cycle as a separate terrace in NW Europe (Maddy, 1997) and (Antoine et al., 2000) Uplift rates over the Quaternary period range between 50-60 m Ma- 1 for the Somme (Antoine et al., 2000, Antoine et al., 2003 a), 40 to 100 m Ma-I within the Thames Basin (Maddy et al., 2000; 267 Westaway et al., 2002); 96 m Ma-1 for the Rio Guadalhorce in southern Spain (Schoorl and Veldkamp, 2003) and 200 m Ma- 1 for the Gediz River in western Turkey (Westaway et al., 2004). The Sorbas Basin has experienced uplift rates of 80 m Ma -I at the basin centre (Mather, 1991 ), whereas uplift rates for the V era Basin are calculated at less than 20 m Ma-1(Stokes and Mather, 2003). ii Carboneras Basin Within the study area the terrace staircase of the Rio Alias shows an average incision of 32 m Ma-1 (basin centre). It has to be considered that this rate is a maximum incision rate. Therefore, it is in line with the above mentioned uplift rates for other river basins across Europe. However it must be emphasised that the age of the terraces within the study area has only been determined on visual field examination of the calcrete profile and correlated to dated terraces in the adjacent basins (Harvey and Wells, 1987; Harvey et al., 1995; Kelly et al., 2000; Candy et al., 2004a; Candy et al., 2005). Unfortunately no dating has been carried out on the calcretes within the Carboneras Basin itself as yet. Terrace level deposits have therefore only estimated ages attributed to them. Correlations between uplift periods and incision periods are limited to large scale temporal variations. That regional uplift occurred within the Carboneras Basin has been demonstrated above, whether this is a result (a) of changes in the lower crusta! flow, as Westaway et al. (2003) and Bridgland and Westaway (in press) stated for NW European rivers and rivers in Turkey or (b) if the regional uplift is a result of isostatic compensation, due to the fluvial incision and the resulting erosional removal of sediments Molnar and England (1990) and Fielding (1994), is not clear.. 268 6.3.4 Differential tectonics Other external controls on fluvial systems, e.g. tectonic movements has been widely neglected in fluvial geomorphology (Vandenberghe and Maddy, 2000). Burbank et al. (1996) and Goldsworthy and Jackson (2000) have studied the influence of tectonic deformation on river geomorphology. Only in recent years has more research been undertaken to determine the tectonic influence on river behaviour (Holbrook and Schumm, 1999; Krzyszkowski et al., 2000; Maddy et al., 2001; Westaway et al., 2002; Ouchi, 2005 and Dumont et al., 2006). Increase in fluvial-landscape relief emanates from rising geological structures through the process of tectonically induced downcutting by streams (Bull, 1990). A river could keep up with the mountain rise as long as the rate of stream incision is greater than the uplift rates (Holbrook and Schumm, 1999). i Tectonic uplift Uplift as a principal controlling mechanism for fluvial incision is a debated subject in the geological and geomorphological literature. Uplift rates calculated by longitunal profiles are subject to widespread discussion (Kiden and Tomqvist, 1998). Schumm (1993) demonstrated that alluvial rivers are usually able to accommodate changes in valley slope by changes in channel plan form. For instance, fluvial response to differential tectonic uplift and resulting increased valley slope may be an increase in sinuosity in order to maintain channel gradient. Work done by Burbank et al. (1996) identified that in rapidly deforming regions, an equilibrium is maintained between 269 bedrock uplift and river incision, with landsliding allowing hill slopes to adjust to rapid river down cutting. ii Carbo11eras Basi11 The Rio Gafares is another example of the importance of tectonics in mountain belt area. For the Rio Gafares the incision was probably episodic, reflecting both tectonic and climatic control as suggested for the Rambla de los Feos by Harvey and Wells (1987). The minimum incision for the Rio Gafares since the deposition of the terrace level l has been estimated at 54 m within the Sierra Cabrera. This amount is in line with the incision caused by the Rio Alias (basin centre), which shows an overall maximum incision of 57 m for the last 304 ka. The amount of incision of the Gafares within the lowland cannot be estimated, since no terrace 1 has been recorded in the basin centre. The same amount of incision for the mountain area and the basin centre can have various reasons: (a) the mountain area can have been affected by mountain building processes resulting in a steeper channel gradient and an increase in stream power for the Rio Gafares and (b) the basin centre (Rio Alias) has been more sensitive for sea-level lowering, due to the close proximity to the Mediterranean Sea and (c) an increase in incision due to the weaker lithology within the basin centre (e.g. mainly marls and calcarenites). The most likely scenario might have been that during T1 and T2 uplift of the Sierra Cabrera was augmented, increasing the channel gradient and favouring incision of the Rio Gafares. During the Late Pleistocene the river was not able to keep up with the uplift and was disconnected from the Sorbas drainage after the deposition of terrace 3 sediments. The loss of the Sorbas drainage (i.e. loss in stream power) and the resulting decrease in catchment size is shown by the decline of incision after T3 and the loss ofNevado Filabrides components. 270 This study has demonstrated that the river staircase evolution of the Carboneras Basin is strongly controlled by regional uplift as well as tectonically driven mountain building processes. The Gafares and Rambla de Ios Feos were mostly affected by the uplift of the Sierra Cabrera mountain range, whereas the terrace development of the Rio Alias was mainly regional uplift driven. Due to the strike parallel alignment of the Rio Alias the direct influence of mountain uplift on the river development was reduced. However, the development of the Rio Alias has been strongly influenced by tectonic activity- direct and indirect: (a) Indirect by river capture and river re-routing of the Feos and Rio Gafares respectively, which further downstream (Rio Alias) influenced the discharge, sediment distribution and clast assemblage of the Rio Alias; (b) directly by lateral and some vertical displacement of the river channel across the Carboneras Fault Zone. It is very difficult to separate between mountain uplift, due to crusta! thickening and vertical stress field movements (Sanz de Galdeano and Alfaro, 2004), crusta! uplift, due to flow in the lower continental crust (Westaway et al., 2003) and isostatic compensation, due to erosion (Molnar and England, 1990). Since the field (in contrast to laboratory experiments) does not offer the possibility to eliminate variables, there can be no clear statement drawn on the importance of the geomorphologic and tectonic components of the drainage evolution. However the investigated terrace deposits have been one of the major keys for understanding the drainage evolution. They have been mapped, studied and correlated with other research (Table 6.1) and show a very good wider picture of the drainage evolution of the Carboneras Basin over the long term. 271 7 CHAPTER: CONCLUSION 7.1 Palaeogeographic reconstruction The topic of this Ph. D. thesis is the long term drainage evolution of the Carboneras Basin over the last 3 Ma. The tectono-stratigraphic evolution of the consequent and subsequent river systems has been the focus of this study in order to place the basin evolution into a temporal and spatial framework. The reconstruction of the drainage was the basis for the evaluation of the influences and controls on the drainage systems and their relative importance. This section will summarize the drainage evolution in a temporal framework. 7.1.1 Pliocene The onset of the Pliocene was marked by a marine transgression in the Carboneras Basin. Fine grained marts of the Cuevas Formation were deposited within the deeper part of the basin and were later locally overlain by coarse-grained calcarenites. Shallow marine shelf conditions prevailed at the basin margins south of the Sierra Cabrera and east of the Sierra Alhamilla during the creation of Cuevas Formation. The shallow marine calcarenites and grey marts of the Cuevas Fm created the underlying topography for the subsequent deposits of the Polopos Fm. At three locations the calcarenites of the Cuevas Fm are overlain by lenses of oyster beds, pectens and mega barnacles, interpreted as shoreface deposits belonging to the lower part of the Polopos Fm. With the ongoing differential uplift of the Sorbas Basin 272 continental conditions were established within the adjacent basin, establishing a west to south-east flowing drainage system. Additionally there was a marine regression in the Upper Pliocene as is shown to the west of Almeria by deltaic facies, to the east of Almeria by lagoon facies (Goy and Zazo, 1986) and in the northern part of the Carboneras Basin by fan delta sequences (this study). With the increased gradient difference between the Sorbas and Carboneras Basin, the main drainage of the Sorbas Basin was directed towards the south, depositing large fan delta systems into the still marine Carboneras Basin (Gafares, Feos and Lucainena fan delta). At the littoral margins of the fan deltas the conglomerates were reworked and deposited as beach material along the shore (fan delta and beach deposits belonging to the Polopos Fm). In sheltered depressions along the fan delta lobes coastal plain deposits accumulated, consisting of silty muds with a strong red colouration. The reddish appearance points towards pedogenic modification of the deposits. 7.1.2 Quaternary The withdrawal of the Pliocene sea and change from marine to continental character led to the development of the drainage system within the Carboneras Basin itself. The already established Feos systems in the northern part and the Lucainena in the western part of the basin joined together, forming the west-east flowing Rio Alias. From both sedimentary and structural records it is clear that the primary drainage system of the Carboneras Basin evolved by the interplay of different tectonic movements. Regional uplift of the adjacent Sorbas Basin and the mountain uplift of the Sierra Alhamilla and Sierra Cabrera created the necessary gradient towards the Carboneras Basin. 273 i Rio Gafares The transverse drainage of the Rio Gafares and Feos cut across the uplifting Sierra Cabrera, creating deep v-shaped valleys. The ongoing uplift of the Sierra Cabrera was responsible for the development of a river staircase including four terrace levels (Tl T3) for the Rio Gafares. Due to its more mountainous location, the Gafares River was probably the first one to be disconnected from the Sorbas main drainage. The disconnection to the Sorbas Basin resulted in re-routing of the drainage of the Sorbas Basin and a decrease in the Gafares catchment area. The large Gafares river system, responsible for up to 80m thick Pliocene fan delta deposits, that cover an area of 7.3 2 3 km and have an approximate volume of0.8 km , was restricted to a small catchment 2 size of 19.4 km , due to a possible -river capture of the Rio Aguas. Evidence for the drainage re-routing can be found in the change in the provenance of the terrace conglomerates within the Gafares terrace levels Tl-T3. The change in source area and catchment restriction can be clearly seen in the decrease of Nevado Filabrides components (here mainly amphibole-mica-schist), sourced from the Sierra de Ios Filabres. Three major aggradational events (Tl-T3), with a total incision of 54 m have been recorded from the examination of the Gafares river terraces. ii Rambla de Ios Feos/Lucainena The transverse Feos system, located in a low between the Sierra Alhamilla and the Cabrera range, draining the Sorbas Basin towards the Carboneras Basin, was another river to be disconnected from the Sorbas drainage system. Here river capture, due to extensive headward erosion by the Rio Aguas (Harvey and Wells, 1987) originally limited to the drainage of the Vera Basin, was responsible for a major change in sediment supply to the Carboneras Basin (see Fig. 7.1 ). 274 Upper Pliocene •differential uplift of the Sorbas Basin and development of a southward flowing drainage network •development of three fan deltas in the marine Carboneras Basin •retreat of the Pliocene sea Carbon eras Basin ~~~~~W~~--r.-=----=~-~ Early Pleistocene •evolution of the consequent drainage in the Carboneras Basin •uplift of the Sierra Alhamilla Cabrera axis •evolution of the strike- (/ ~~~~lel drainage of the Rio •development of the Carboneras transverse antecedent river Basin ...... system of the Feos, ~~~--===.:..:..:..______....::______j Lucainena and Gafares late Pleistocene •ongoing uplift of the Sierra Cabrera •headward erosion of the strike-oriented Rio Aguas and capture of the Feos and possibly Gafares drainages •change in catchment for the Rio Gafares and Rambla de Ios Feos Carboneras Basin Fig. 7.1 Sketch map of the consequent drainage evolution of the Carboneras Basin. 275 With the disconnection to the Sorbas Basin, the Carboneras Basin suddenly lost its two most important sediment suppliers. The third river, the Rambla de Lucainena is still eroding headwards trough weak lithologies and has captured drainage from the southern part of the Sorbas drainage (Mather, 2000). iii Rio Alias Additional to the north-south flowing rivers a fourth river, the Rio Alias developed parallel to the mountain front to drain the Carboneras Basin from west-east. Investigations of the river deposits revealed four terrace levels with a total incision of 57 m. Detailed analysis of the terrace conglomerates and the correlation with the Rambla de Ios Feos terraces have shown that the terrace levels of the Alias are comparable with the ones of the Feos system. The main evolutionary difference between these two rivers is due to tectonic influence. The Feos was mainly controlled by the differential uplift of the Sorbas Basin, which created the gradient towards the southern Carboneras Basin and was responsible for the headward ersosion by the Rio Aguas. The Rio Alias on the other hand was only indirectly influenced by the differential uplift of the Sorbas Basin and the river capture. As a strike orientated river the Alias owes its origin to the orogenic uplift of the Sierra Cabrera. Additionally the Alias is also strongly influenced by the strike-slip movements of the Carboneras Fault Zone (CFZ). In the area where the Alias crosses the CFZ, the fault zone is 3 km wide and divided into three individual fault strands. Examination of the river terrace remnants and the modern river have shown that the river channel was laterally displaced by each of the strands at different times. A progressive movement of the fault activity from west to east has been recorded. 276 iv Rio Saltador Headwards erosion through weak lithologies is very common in the sedimentary basins of the Betic Cordillera. The Saltador River is another example of how orogenic uplift controls drainage directions. The river runs parallel to the mountain front of the Sierra Cabrera. The Neogene basin fill has been uplifted into a nearly vertical position along the basin margin. The soft Messinian marls and the brittle calcarenites provide an ideal west-east running structure for the drainage to erode and to incise. 7.2 Summary 1. Through the integration of geological and geomorphologic data, the long-term drainage evolution of the Carboneras Basin over the last 3 Ma years has been established. 2. The evidence of three fan deltas in the northern part of the basin demonstrates that there was a connection between the differentially uplifted Sorbas Basin to the north and the still marine Carboneras Basin during the Pliocene. 3. Nevado Filabrides component within the conglomeratic deposits of the older terrace levels of the Rambla de Ios Feos and Rio Gafares present evidence for an ongoing Pleistocene connection to the Sorbas Basin during the uplift of the Sierra Cabrera, creating transverse drainage. 4. Evidence for a re-routing of the river and a possible river capture was found within the terrace record of the Rio Gafares. 5. Analysis of fan delta deposits confirmed basin uplift. 6. The existence of three fault strands of the Carboneras Fault Zone (CFZ) has been suggested. 277 7. Vertical uplift of the western side of the middle fault strand of the CFZ was confirmed by the existence of a steep Pliocene coastline and by the displacement offan delta deposits across the fault. 8. Strike-slip movement along the Carboneras Fault Zone during the Quaternary was suggested by the lateral displacement of fan delta and terrace conglomerates. External controls, such as climatic changes and tectonic activity have strongly influenced the long-term drainage evolution of the Carboneras Basin during the last 3 Ma. The fact that the main river systems of the Carboneras Basin developed four terrace levels, which correspond to interstadial phases of the Pleistocene and which can be correlated to river systems in drainage basin all across Spain and Europe, demonstrates the climatic origin and states the importance of climatic control on drainage evolution. For the river systems of the Carboneras Basin, climate may have triggered the major aggradation and incision phases, however regional uplift might have been the over-riding control on the progressive incision of the river systems onto which the impact of tectonic control was superimposed. 278 List of References Addicott, W.O., Suavely Jr., P.D., Poore, R.Z. and Bukry, D. 1979. 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