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Geology of the Arid Zone of Almeria, South East Spain - An Educational Field Guide

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An educational field guide
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An educational field guide
South East Spain
This guide has been produced and financed with the support of the hydrological management project between the
Carboneras Desalinisation Plant and Almanzora-Western Almería Council. In the Natural Park of Cabo de Gata and its
area of influence, a grant given by the Southern State Water Company (ACUSUR) and the Regional Ministry of
Environment (la Consejería de la Junta de Andalucía), is gratefully acknowledged
Editor, Technical Director and Co-ordinator: Miguel Villalobos Megía
Scientific Supervisor: Juan C. Braga Alarcón
Authors: Juan C. Braga Alarcón José Baena Pérez
José Mª. Calaforra Chordi José V. Coves Martínez
Cristino Dabrio González Carlos Feixas Rodríguez
Juan M. Fernández Soler José A. Gómez Navarro
José L. Goy Goy Adrian M. Harvey
José M. Martín Martín Antonio Martín Penela
Anne E. Mather Martin Stokes
Miguel Villalobos Megía Caridad Zazo Cardeña
Word Processing: Juan González Lastra
Infographics: Félix Reyes Morales
Design: Teresa del Arco Rodríguez, Juan Sánchez Rodríguez, Juan González Cué
Photography: The photographs are the property of the authors whose names are inserted in the section headings,
except for where specified at the foot of the photograph (in brackets)
Translation: Jason Wood
© of the edition: State Water Company for the Southern Basin SA (ACUSUR), 2003
© of the edition: Regional Ministry of Environment, 2003
© of the 2
nd
edition: Fundación Gypaetus, 2007
© of the data, text, photos and illustrations: Authors, 2003
Technical Assistance: Tecnología de la Naturaleza, SL (TECNA)
Printing: Bouncopy
ISBN: 978-84-935194-7-6
Legal Deposit: xxxxxx
D
uring recent decades, the Province of Almería has developed as one of the more
economically dynamic regions of Andalucía and Spain. Its exceptional environmental
conditions due to a favourable geographical situation, and the enterprising character of
its people, have made the blossoming prosperity and rapid consolidation of one of the
most vigorous and technologically advanced horticultural zones in Europe possible. However,
through time, this shining development has come to have a negative bearing on a historical problem
in Almería: the scarcity of hydrological resources. In reality the hydrological demands for agricultural
use considerably exceed the natural resources that are available, so that as a consequence, it has
motivated a growing social sensitivity and demands for solutions to this problem.
This situation has required, on the basis of their competency, the intervention of the Medio Ambiente
(Environmental Agency), which through the public company Aguas de la Cuenca Sur S.A. (ACUSUR),
has put an ambitious plan of action into practise: the Global Plan of Priority Hydrological Action in
Almería Province, known as Almería Plan, whose work, is declared to be of general state interest.This
plan has meeting the demands for water of the agricultural organisations in the Almerían coastal
zone as the main objective.
Part of this work, on the other hand, has been the need to achieve protection of a region with
exceptional ecological and environmental value, at times not fully recognised amongst its own
population. Indeed, through strict application of the criteria developed by the European Union in its
Strategy for the Preservation of Biodiversity, the Province of Almería, and especially its semi-arid
zones, are declared to be one of the regions of greatest environmental and ecological importance in
Europe.The presence of unique habitats, the biological diversity that provides a wealth of species,
turns the east coast of Almería into a veritable “Natural Wonder” in the context of continental Europe.
To all this can be added the exceptional geological value placed on these arid landscapes. All of these
conditions mean that Protected Natural Spaces have already been declared and proposed as places
of community interest, and these occupy a considerable area of Almería. By European law, the Spanish
government must guarantee their conservation.
In order for the partly unavoidable work of the Almería Plan to go through in these precious spaces,
both the Junta de Andalucía (provincial government) and the Medio Ambiente (environmental
agency), given their respective environmental concerns, decided to maximise the methods of
environmental protection. All joint work has been subjected to rigorous controls and has employed
a significant use of correctional means, whose aim is to reduce the extent of the possible
environmental impact that work generates in the construction phase.
In a complementary fashion, several administrations had agreed to fulfill the European Habitat
Directive, putting into place a broad program of compensatory measures. In this case the ultimate
aim is contributing to an improvement in the global quality of the natural environment of these
regions that were affected by the management of new hydrological resources, but also with the
purpose of spreading an awareness amongst the inhabitants of these regions that everyone must
keep a vigil and act in a responsible manner in order to conserve the environment.
The volume that is presented is framed in this context. A publication that we hope will contribute to
drawing the Almerían population closer to the exceptional qualities of the natural environment which
surrounds them. A recognition essential for establishing the basis of respectful relationship, that will
make both the conservation and sustainable use of this noble region a possibility.
Teófilo García Buendía Fuensanta Coves Botella
Manging Director of ACUSUR Director of the Medio Ambiente
PROLOGUE
Prologue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
How to use this guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
INTRODUCTION
The Geological Timescale and some basic geological principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Largescale Geological Units in Andalucia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Largescale Geological Units in the arid region of SE Almeria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Geological History and Geographical Evolution of SE Almeria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
NEOGENE BASINS OR DEPRESSIONS OF ALMERIA
The Almeria-Nijar Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
· Geological Features and Evolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
· Volcanic Periods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
- Origin of magmatic processes and volcanic features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25
- The Cabo de Gata volcanic complex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
- Hydrothermal Alteration and mineralisation in the volcanic complex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
- The gold of Rodalquilar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
· Sedimentary periods in the volcanic archipelago . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
- Sedimetary episodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
- Deposits of the earliest marine basins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
- Re-initiation of sedimentation since the last volcanic period . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
- Messinian reefs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
- Evaporites and carbonates since reflooding of the Mediterranean . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
· The last period: recent evolution and continentalisation of the Bay of Almería . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
· DIDACTIC ITINERARY: THE ALMERIA-NIJAR BASIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
1. Alluvial dynamics of the ramblas: Las Amoladeras . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
2. Fossil beaches of the Rambla de las Amoladeras . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
3.The dune system at the outlet mouth of Rambla Morales . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Index
4.The lagoon of Rambla Morales . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
5.The Salinas (Saltpans) of Cabo de Gata . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
6. Volcanic Domes of Punta Baja, El Faro and Vela Blanca . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
7.The volcanoes of Mónsul . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
8.The Barronal dunefield . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
9.The Los Frailes volcano . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
10.The fossil dunefield of los Escullos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
11. Infilling Alluvial Fans of la Isleta-Los Esculllos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
12. Volcanic calderas of Rodalquilar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
13. Mining and mineralogical processes in Rodalquilar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
14.Post-volcanic sediments at la Molata de Las Negras . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
15.The bentonites of Cabo de Gata . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
16. Marine sediments of Cañada Méndez . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
17.The quay at Agua Amarga . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
18.The Mesa Roldán reef . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
19. El Hoyazo de Níjar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
The Sorbas Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
· Main Geological Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
· The Sorbas Karst . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
- Origin of the Sorbas gypsum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
- Karst : slow dissolution of rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
- Genesis and evolution of the gypsum karst of Sorbas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
- Surficial karst landscape of Sorbas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
- Subterranean scenery: dissolution features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
- Subterranean scenery: crystallisation features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
· DIDACTIC ITINERARY: THE SORBAS BASIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
1.The southern margin of the Sorbas Basin and panorama at Peñas Negras . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
2.Turbidites of the peñas negras fan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
Index
3. Infilling of the basin through until deposition of the gypsum: the Los Molinos del Río Aguas series . . . . . . . . . . . . . . . . . . . . . . . . 117
4.The karst plain, the cornice (escarpment) and block falls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
5.The resurgence (springs) of Los Molinos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
6. Infilling of the basin after gypsum deposition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
7.Fluvial-karst barrancos: the Barranco del Infierno . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
8.Fossil Beaches of Sorbas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
9. Dolinas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
10. Lapiés . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
11.Túmulus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
12.The Cariatiz Reef . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
The Tabernas Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
· Rasgos geológicos y evolución . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
· Erosional Landscape . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140
· Evolution of the drainage networ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
· The ramblas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143
· Mechanisms of erosion in the desert: currents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144
· Mechanisms of erosion in the desert: evolution of slopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146
· DIDACTIC ITINERARY: THE TABERNAS BASIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149
1.The turbidite succession of the Tabernas submarine fan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
2.The Las Salinas travertines of the Tabernas Desert . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154
3.Escarpment landforms in the vicinity of Cerro Alfaro . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
4.Tunnel erosion (piping) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
5. Quaternary alluvial fan-lake system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
Index
10
PROLOGUE
T
he arid landscapes of Almería are
well known amongst professors of
geology, and other taught subjects
related to the teaching of earth
sciences, of an astonishingly high number
of European universities, who appreciate it and
use it as a huge natural laboratory to carry out
practical field investigation.This has been due
to two special features, an extraordinary
geological record within its sedimentary basins
and the high quality of outcrop exposure.
The geology of this region has, in fact, inspired
an enormous scientific literature produced at
the highest level. However, up until now
publications of a more informative tone that
seek to focus their efforts on the general
educational potential of this exceptional
geological landscape, have not existed.
This has been the objective of this work, to deal
with this singularly important geological region
with a broad vision in a manner that is more
widely informative. Within this volume, three
itineraries are put forward, each one of which
connects a series of field stops where it is
possible to observe or interpret several of the
most outstanding geological features in Almería
Province.These features are of great importance
for understanding the origin and evolution of
the geological landscape in Almería; a history
peppered with events so extraordinary as the
formation of the volcanic archipelago of Cabo
de Gata, the desiccation of the Mediterranean
Sea or the colonisation of the coastline by
tropical coral reefs.
The guide aims to be a product that is simple to
use. On one hand it is intended for
self-interpretation, or interpretation without the
assistance of a guide or teaching professional, at
the higher end of secondary education, the
university level, for different disciplines related
to the teaching of earth and environmental
sciences. On the other hand, it is a didactic
guide to support the teaching professional, that
clearly “translates” information, so that it can be
adapted to the most suitable pedagogical level
each time.
It has been structured into four large chapters,
an initial one of introductory character, and
three more corresponding to each of the three
sedimentary basins that might be visited.
These three chapters each consist of a general
part, in which basic concepts required in order
to understand the phenomena that are
interpreted in the field locations of the itinerary
area explained, folowed by a detailed
description of the proposed itinerary.
The itineraries are can be completed within the
three most emblematic Natural Protected
Spaces in eastern Almería and the immediate
surrounding area: the Cabo de Gata-Níjar
Natural Park, the Gypsum Karst Natural Park of
Sorbas and the Tabernas Desert Natural Park.
These are places where the didactic use of the
guide for environmental purposes will arise, as
well as it being the first, basic line of evidence in
management material used by the public. It is
hoped that in this sense the guide can be easily
used and will increase the environmental
understanding of the population visiting these
emblematic Natural Spaces.
Miguel Villalobos Megía
Guide Co-ordinator
11
Introduction
The Almería-Níjar Basin
Didactic Itinerary of the Almería-Níjar Basin
The Sorbas Basin
Didactic Itinerary of the Sorbas Basin
The Tabernas Basin
Didactic Itinerary of the Tabernas Basin
THE COLOURS IN THE GUIDE
This guide is structured in various sections that can be identified
by a colour code in the lower and upper right corners of each
page.
The colours correspond as follows:
SYMBOLS AND COLOURS OF LOCATION MAPS FOR POINT OF INTEREST
Location maps for points of interest are found in the didactic itinerary
sections.These are located in a box in the upper right corner of the page.
The full page maps that appear at the beginning of each chapter have an
additional explicative legend.
The symbols and colours correspond as follows:
How to use this guide
Juan C. Braga - José M. Martín
13
There is a series of basic principles that one
needs to understand prior to setting out on any
explanation about the geology of a region:
The geography and landscape of a region are
always changing.The mountains and valleys
that surround us or the position of the
coastline today have not always been as we
know them now, now, neither have these
features always been there.The land that we
walk on, in the majority of cases, has risen up
from the depths of an ancient sea, and the
distribution of land and sea will change
through time.
These changes result from complex geological
processes: sediments that are transformed into
new rocks and erosion of rocks that already
exist into sediments; uplift or emergence of
land areas, with the consequent retreat of the
sea, and flooding of other areas, that are
invaded by seas and oceans, where
accumulation of sediment starts again that will
later be transformed into other rocks, followed
by renewed emergence and further
destruction, etc.
By studying the internal structure and
composition of rocks, their age (that should be
measured in millions of years) and the way
that they are distributed in a region, geologists
can reconstruct the way in which the
landscape and geography of the region has
changed, where the coastline was situated at
different times, where there was a volcano,
when the mountains were uplifted that are
emerged now, etc.This reconstruction is not
simple and requires the accumulation of much
knowledge from very distinctive specialist
fields within geology. However, once
recognised, even with provisional status, such
that our understanding will improve with time,
it is converted into a story that can be
entertained.
All of these geological processes, without
exception, are extraordinarily slow from a
human perspective.The duration, the pace,
of geological processes is counted in millions of
years.The pre-history and history of humans
has been instantaneous in comparison with the
long history of our planet that began at least
4,600 million years ago.
INTRODUCTION. The Geological Timescale and some basic geological principles
THE GEOLOGICAL YEAR
If we compressed all of the known geological time of our
planet, some 4,600 million years, into a natural year of only
365 days, we would observe:
That through the Precambrian, about which we know
virtually nothing, save that it gave shelter to practically
no life, only extremely primitive forms lived through
until the 16th of November, almost a complete year.
That the Palaeozoic era, in which distinct forms of life
developed and diversified, reached up to the 13th of
December.
That the Mesozoic era, that of the large reptiles, lived
through to the 26th of December, the time at which, for
example, the great dinosaurs became extinct.
That the Tertiary era, with the development of the
majority of mammals, reached up to the 30th of
December. The first primates did not appear until the
29th of December.
That the Quaternary era, with the appearance of our
more immediate relatives, occupied only part of the
31st of December. In fact, only towards the last minute
of the year did Homo sapiens sapiens, ourselves,
appear.
Precambrian Palaeozoic era Mesozoic era Tertiary era Quaternary era
Sudden extinction of large reptiles (65 m.a.)
Appearance of the first primates (40 m.a.)
Appearance of Homo erectus (3 m.a.)
Appearance of Homo habilis (1.5 m.a.)
Appearance of Homo sapiens neanderthalensis (70,000 a.)
Appearance of Homo sapiens sapiens (35,000 a.)
Start of the Christian era (2,000 a.)
Fall of the Roman Empire (1,600 a.)
Discovery of America (500 a.)
French Revolution (200 a.)
Start of the industrial revolution (100 a.)
Average duration of human life (70 a.)
20 : 19 : 00.00
19 : 99 : 33.91
18 : 17 : 19.19
21 : 08 : 58.52
23 : 52 : 00.11
23 : 58 : 00.09
23 : 59 : 48.28
23 : 59 : 49.02
23 : 59 : 58.57
23 : 59 : 58.89
29 : 59 : 59.30
00 : 00 : 00.48
JANUARY
MAY JUNE JULY AUGUST
FEBRUARY MARCH APRIL
SEPTEMBER OCTOBER NOVEMBER
DECEMBER
15
PERMIAN
PALAEOGENE NEOGENE
MILLIONS OF YEARS
TRIASSIC JURASSIC CRETACEOUS
Holocene
Pleistocene
Pliocene
Miocene
Oligocene
Eocene
Palaeocene
Upper
Lower
Upper
MALM
Middle
DOGGER
Lower
LÍAS
Upper
Middle
Lower
CARBONIFEROUS
DEVONIANSILURIANORDOVICIANCAMBRIAN
Upper
Lower
Upper
Lower
Upper
Middle
Lower
Upper
Lower
Upper
Middle
Lower
Proterozoic
Archean
Upper
Lower
Middle
CENOZOIC/TERTIARY
MESOZOIC
PALAEOZOIC
0.01
11.8
5.3
23.5
34
53
65
96
135
154
180
205
230
245
250
250
272
300
325
360
375
385
410
425
435
455
470
500
540
2.500
4.600
QUATERNARY
PRECAMBRIAN
TABLE OF
GEOLOGICAL TIME
Juan C. Braga - José M. Martín
16
3. The Neogene Basins or depressions overall
comprise the third largescale unit in
Andalucía. During the emergence of the Betic
Cordillera there were times in which the sea
extensively covered depressed regions that
are emerged today, such as the Guadalquivir
Basin and other intermontane basins like
Guadix-Baza,Tabernas, Sorbas or Almería-
Níjar.They are young sediments, less than 25
million years old, characterised by having a
very limited degree of deformation, such that
they hold a great value for studying the
recent geological history in this western
sector of the Mediterranean.
In Andalucía three largescale geological units may be differentiated:
1. The Iberian Massif or Hercynian Massif
of the Meseta outcrops to the north of
Guadalquivir and forms the mountainous
lineament of Sierra Morena. It consists
mainly of strongly folded and deformed,
metamorphic (schists, quartzites and
limestone marbles) and igneous (granites
and similar) rocks, of very ancient age
formed between more than 550 and 250
million years ago (Precambrian and
Palaeozoic). They form part of the old Iberian
continent whose coasts were covered by
the sea that occupied the greater part of the
modern Andalucían territory.
2.The Betic Cordillera constitutes the second
largescale unit, and the first formed from
extension. This much younger, large alpine
mountain chain, had already started uplifting
approximately 25 million years ago (in the
Lower Miocene) and continues uplifting
today. It runs from Cádiz in the west to
Almería in the east, extending to Murcia,
Valencia and the Balearics. At the latitude of
the Rock of Gibraltar it is inflexed producing
a more or less symmetrical structure along
the north of Africa. Internally, a complex
structure is present as a consequence of the
Largescale Geological Units in Andalucia
GEOLOGICAL UNITS
piling up of rocks through thrusting during
the slow collision of the Alboran Plate up and
onto the Iberian Plate, and later uplifting.
The primary internal structure is divided into
a younger External Zone, nearer to the
Iberian Massif, and an older Internal Zone,
closer to the modern littoral zone.Within
the latter, several stacked tectonic units can
be recognised, in turn, essentially from
the bottom towards the top they include the
Nevado Filábride Complex, Alpujárride
Complex and Maláguide Complex.
Hercynian Massif of the Meseta
BETIC CORDILLERA
Neogene Depressions
Campo de Gibraltar Complex
External Zone
Internal Zone
17
Almería is located, from a geological point of
view, at the southeastern extreme of the Betic
Cordillera. The old Betic relieves (Sierra de
Gádor, Filabres, Alhamilla, Cabrera, etc.)
constitute the margin and the basement of a
series of much younger intermontane marine
basins (Tabernas, Sorbas, Almería), that were
filled with sediments simultaneously with the
emergence of the Betic Cordillera structure.
Meanwhile, in the vicinity of Cabo de Gata,
numerous similarly recent volcanoe rumbled in
full activity.These three geological terrains are
clearly distinguishable today in the surrounding
Almerían desert landscape.
THE BETIC SIERRAS
The core of the mountains in this region
consists of very old rocks, some even around
550 million years old. They are grouped under
the generic name of the Nevado-Filábride
Complex (alluding to the fact that they make
up a good part of the Sierra Nevada, and its
eastern extension, the Sierra de los Filabres).
They are mainly graphitic micaschists: display
dark, yellowish and orange colours with a slaty
appearance and a flaggy characteristic, that is
to say, they are divided into well-defined,
more or less irregular laminations. Quartzites
which form rough crests and sharp cliffs, due
to their better resistance to erosion, are also
common.
Quartzites display dark, yellowish and orange
colours, and also have a flaggy appearance,
although poorly defined. Metamorphosed
limestones and marbles are also found but
to a lesser extent, such as those quarried in
the Sierra de Macael. Locally rocks related to
granite appear, known as gneiss. All of these
arose from the transformation
(metamorphism) of existing rocks that
suffered elevated temperatures and pressures
at great depth in the interior of the earth.
Largescale Geological Units in the arid region of SE Almeria
Skirting the core of the previously mentioned
mountains another band appears, also
consisting of very old rocks although somewhat
younger than the former, that are grouped
under the name of Alpujárride Complex
(alluding to the fact that it extends from
Alpujarra, where for one part it constitutes the
southern flank of the Sierra Nevada, and for
the other, the coastal chain: sierras de Lújar,
Contraviesa, Gádor, etc.).
Characteristic flaggy appearance (schistosity) of dark
micaschists in the core of the Nevado- Filábride Complex.
Quartzite crests in the Nevado- Filábride core of the Sierra
Alhamilla (photo M.Villalobos).
Juan C. Braga - José M. Martín
This strip mainly comprises two very distinct
types of rock, easily recognisable in the field.
One of these are schists, known in the region as
'Launa', which are slightly transformed clays, of
vivid blue, red and glossy grey colours.
Traditionally they have been used to make
impermeable roof slates in the construction
industry.The other rocks are limestones and
dolomites, composed of calcium and
magnesium carbonates, which produce white,
grey or black escarpment relieves, for example,
the north flank of the Sierra Cabrera, Sierra
Alhamilla, the escarpments of Lucainena or
Turillas, close to Níjar, or the many cliffs of the
Sierra de Gador. All of these limestones and
dolomites were formed at the bottom
of a tropical sea more than 200 million years
ago. Afterwards, in the same manner as the rest
of the material from the Alpujarride complex,
they suffered transformation (metamorphism) at
elevated temperatures and pressures, which
came about at great depth in the earth's
interior.
Material from the old Betic mountains has
suffered an intense deformation expressed as
folds of distinct scales and fractures, in addition
to their slaty characteristics (schistosity). In some
places the rocks are literally destroyed, mashed
up by fractures.They are also mineralised, and
have historically been the object of exploitation
to yield iron (Sierra Alhamilla), lead and silver
(Sierra de Gador and Sierra Almagrera), and
other minerals.
Largescale Geological Units in the arid region of SE Almeria
18
THE SIERRA DE CABO DE GATA
The Sierra de Cabo de Gata is an individual
mountain range, different to the others, formed
from volcanic rocks during two stages of
volcanicity, one from approximately 14 to 10
million years ago and the other from 9 to 7.5
million years ago. In reality, they represent only
a small percentage of rocks of this nature,
constituting the bottom of the Alboran
seafloor and extending to Melilla, outcropping
discretely in the Isla de Alboran.
Alpujarride limestone relief of the Sierra de Gador (Photo,M.
Villalobos).
Typical purple colour of phyllites or 'Launas' in the material of
the Alpujarride Complex (Photo,M. Villalobos).
19
Major Geological Units of arid SW Almeria
Detail of stratification in Alpujarride limestone rocks (Photo,
M.Villalobos).
Volcanic rocks from this area formed a
landscape of volcanoes, submarine or emergent,
individual or grouped, to form small islands.
These volcanic structures are recognisable in the
terrain of Cabo de Gata, in many cases, where
they are seen to form steep, more or less conical
hills in the area: Los Frailes, Mesa de Roldan,
Cerro de los Lobos, La Tortola, etc. Brecciated
volcanic rocks (formed from fragments
of different composition or aspect) are very
abundant, resulting from diverse volcanic
processes: differential cooling of distinct parts of
lava flows, eruptions, nuee ardentes, avalanches
down the sides of volcanoes, etc.
DEPRESSIONS OR LOW-LYING AREAS
The rocks that occupy the low-lying areas of
the Almerían landscape, modern depressions
such as the Almanzora Valley, Andarax Valley,
Tabernas, Sorbas Basin, Campo de Níjar plain
or El Poniente or El Poniente, consists of
geologically young material, accumulated in
the last 15 million years,while the Mediterranean
Sea surrounded the mountains and the
volcanoes of Cabo de Gata forming a small
archipelago.The Betic mountains, and in general
all of the Iberian Peninsula, were uplifted from
the depths of the Mediterranean Sea.
In these marine inlets the products of
sedimentary erosion of the emerged land
accumulated: boulders, pebbles, gravel, sand
and mud. Limestone rocks also formed from
the accumulation of the remains of marine
creatures. In a changing global climate, the
region passed through cold and much warmer
periods.
In the warm periods, the seawater temperature
(in the western Mediterranean) was similar to
those of the tropics today, in the order of 20º C,
and coral reefs developed along the margins of
islands and emerged lands.Theses coral reefs,
like those of Purchena, Cariatiz, Nijar, Mesa
Roldan, etc., are amongst the best fossil
examples that exist in the world.
In colder periods, the western Mediterranean
had a temperature similar to today, and
limestones were formed from the remains of red
algae, bryozoans, molluscs etc., like those
occurring on the actual seafloor of the platform
that encircles Cabo de Gata.These conditions, or
yet colder ones, prevailed in the region from
5 million years ago.
Juan C. Braga - José M. Martín
The Betic mountains (Nevado-Filabride and
Alpujarride complexes) originated from
collision of the African continent with Europe.
The Betic rocks are formed from sediments
deposited at the bottom of the sea hundreds of
millions of years ago. These rocks were buried
at many kilometres of depth (beneath other
rocks), under such pressure and temperature
that they were transformed, changing the
appearance of the minerals that make them up
(this process is known as metamorphism). Later,
they slowly emerged. The structure of the Betic
Cordillera was yet to be uplifted at different
speeds according to the arrangement of blocks
compartmentalised by large regional fractures.
The Sierra Nevada-Sierra de los Filabres block,
for example, was the first to emerge from the
sea, around 15 million years ago, and has
stayed up since this time, as the most elevated
relief in Andalucía and one of the most
elevated in Spain and Europe.The bottom of
the Alborán Sea is subsiding and extending,
thanks to fractures through which volcanic
material of Cabo de Gata was once extruded.
Since emergence of the Sierra Nevada-Sierra
de los Filabres, that still continue to be
uplifted, the Sierra de la Estancias emerged
from the sea around 9 million years ago.
Later, around 7 million years ago, the Sierra de
Gádor and Sierra Alhamilla emerged. Although
today they seem like high mountains to us,
they are believed to be quite young in
geological terms, and their rate of uplift on
a human scale is very low, For example, the
average velocity of uplift for the Sierra
Alhamilla since emergence from the sea is less
than 2 cm each year.
The last relief to emerge, which is for certain
the youngest mountain range of the peninsula,
is Sierra Cabrera that came out of the sea
5.5 million years ago.
During the past 2 million years, Almería, like
the rest of the planet, has suffered from strong
Quaternary climatic variations. In the glacial
stages, the sea fell more than 100 metres from
its present level and the climate was much
colder. In the interglacial stages, as now, the
sea was in a position similar to that of today,
and the climatic conditions would also have
been similar in character.
The process of marine retreat from these
basins can also be seen in relation to the
present-day geography, in that the interior
depressions, those most removed from the
modern Mediterranean, were the first to
Geological history and geographical evolution of SE Almeria
20
emerge, whilst those closest to the coast have
been abandoned by the sea only recently from
a geological point of view. For example, the
high valley of Almanzora, above Albox, was
vacated by the sea around 7 million years ago,
however, the sea extended over land
surrounding the Bay of Almería until just
100,000 years ago.
With the final retreat of the sea to its current
position, for the moment, the impressive
geological record for this area, accumulated
over a period of 15 million years, is exhibited in
Almería under exceptional conditions of
preservation. It is an area of maximum
educational and scientific value for studying
and understanding the evolution of the
Mediterranean and the formation of the Betic
Cordillera over the past 15 million years.
The Almeria-Nijar Basin
Geological Features
Juan C. Braga - José M. Martín
23
The Almería-Níjar Basin has been a small
marine sedimentary trough since 15 million
years ago, the time at which emergence of
the relieves occurred, that today constitute the
Sierra Nevada and the Sierra de los Filabres
massifs, whose foothills were located at the
coastline.
In this period, however, the Almería Basin was
not individualised from the Sorbas and
Tabernas basins. In this marine basin,
sediments started to arrive from the
dismantling of the emergent relieves through
the fluvial network. Extensive submarine fans
were generated on top of the marine platform,
while the fully active volcanoes of Cabo de
Gata were rumbling, probably fashioning
a tropical volcanic archipelago.
It was much later, about 7 million years ago,
when uplift of the Sierra de Gádor and Sierra
Alhamilla caused the individualisation of the
Almería-Níjar Basin, to the south of these same
hills and between the emerged volcanic relieves
of Cabo de Gata.
Sierra Cabrera emerged 5 million years ago, and
it definitively separated the Sorbas and Vera
basins.
Geological Features and Evolution
GEOLOGICAL LOCATION OF THE ALMERIA-NIJAR BASIN
Neogene-Quaternary sediments
SIERRAS
1. Sierra Nevada
2. Filabres
3. Sierra de Gádor
4. Alhamilla
5. Cabrera
6. Sierra de Cabo de Gata
Neogene volcanic rocks
Betic substratum
The Almería-Níjar Basin therefore included all
of the current, low-lying land present between
Sierra de Gádor, Sierra Alhamilla, Sierra Cabrera
and the coastline, including the volcanic
relieves of the Sierra de Cabo de Gata.
A region that had constituted a marine seafloor
during the last 15 million years in which
a sedimentary record has remained,with
unsurpassed observable characteristics,
exceptional for the understanding of evolution in
the Mediterranean Basin at this time,and its
geography, climate and ecology.
1
2
3
4
5
6
El Ejido
Almería
Sorbas
Níjar
Vera
Vera Basin
Sorbas Basin
Almería-Níjar Basin
Tabernas Basin
Campo de Dalias Basin
Carboneras
Tabernas
Geological Features and Evolution
24
SIMPLIFIED GEOLOGICAL MAP OF THE ALMERIA BASIN
Sierra de Gádor
Sierra de Alhamilla
Sie
rra d
e
Ca
b
o
d
e
Gata
Níjar
Almería
Sª Alhamilla
Old Quaternary terrain
(Pleistocene: 1.8 Ma to 10,000 yrs)
Recent Quaternary (Holocene) formations, from 10,000 years ago
to present
Pliocene terrain (5.2 to 1.8 Ma)
Fluvial deposits
Alluvial fans
Littoral barries and/or fringes
Albuferas
(saltpans)
Travertines
Dunefields
Deltas
Miocene terrain (23.7 to 5.2 Ma)
Miocene volcanic
formations (15.7 to 7.9 Ma)
Ancient basement
Sª Alhamilla
Níjar
Pozo de Los Frailes
Alquián
Sea level
Sea level
Cabo
de Gata
Roquetas de mar
According to Zazo and J.L. Goy
MAGMAS AND MAGMATIC ROCKS
Magmas are formed through the partial melting
and emplacement of rocks at high temperature
in the interior of the Earth. They consist of a
mixture of liquid, dissolved gases (water vapour
and carbon dioxide) and minerals.
Magmas that come directly from the partial
melting of rocks at depth are called primary
magmas. Sometimes they reach the surface
straight away, however, it is more common that
they remain static at different levels within
the mantle and the continental crust, forming
magmatic chambers. In such a situation the
magmas may partly crystallize, assimilate
the country rock and suffer other modifications,
the final result of which is a series of derived
magmas of different compositions. This process
is known as magmatic differentiation.
Magmas are generally less dense than the
material within which they are forming, and,
therefore, they tend to climb up through the
mantle and continental crust, until they cool and
crystallize, giving place to intrusive rocks.
Magmas that solidify slowly underneath the
terrestrial surface form bodies of intrusive
rocks. Cooling happens very slowly, so that the
minerals may crystallise in an ideal manner,
creating rocks with large-sized crystals such as
granites.
When the magma reaches the surface, it gives
way to volcanic or eruptive activity. The results
are volcanic rocks and so-called volcanic
features. Cooling is very rapid, so that the rocks
do not crystallise well, forming a vitreous
matrix or a very fine crystal size.Within this
VOLCANIC EPISODES
Origin of magmatic processes and volcanic features
MELTING OF PRIMARY
MAGMAS
matrix a proportion of small minerals of larger
size (phenocrysts) may be present, which had
crystallised previously in the magma chamber.
At times, during its ascent, the magma is
injected into fissures, forming dykes.These are
also known as hypabyssal rocks.
Parasitic cone
Main cone
Lava flow
Plutonic rocks
Dykes
Derived
magma
Partial melting
of the crust
CRUST
MANTLE
Magma
chamber
25
Juan M. Fernández
MAGMAS AND PLATE TECTONICS
Although there are a great variety of types
and compositions of magmas, the three most
important generic types are the basaltic group
(or basic, 50% of silica), the siliceous group
(or acid, 65 to 70% of silica), and the andesitic
group (or intermediate) such as those of Cabo
de Gata.
The origin of magma is related to the dynamics
of the lithospheric plate margins:The majority of
basaltic magmas originate through partial
melting of the mantle in divergent plate
boundaries (mid-oceanic ridges). Andesitic and
siliceous magmas are generated in subduction
zones by partial melting of both the oceanic plate
and the continental crust.
The origin of Cabo de Gata volcanism is
complex, and under discussion at present.
In whatever case, it is related with the orogenic
process of crustal thickening in this area,
the Alborán domain, due to the collision of the
African and European plates; and afterwards
their thinning through phenomena of
extensional or transtensional character.
Island arc
Trench Trench Rift valley
CONTINENTAL CRUST OCEANIC CRUST
Plateau
basalts
Lithospheric
mantle
Continental
crust
Oceanic
crust
Upper mantle
(asthenosphere)
Mid-oceanic ridge
26
Origin of magmatic processes and volcanic features
27
ACTIVITY AND VOLCANIC FEATURES
The type of eruption and the products resulting
from volcanic activity depend, above all, on two
important aspects: the viscosity of the lava,
which determines fluidity, and the gas content
of the lava.
Basaltic magmas, poor in silica, are fluid. At the
surface they flow rapidly, forming lava flows
that at times travel great distances (this type of
volcanism is known as effusive). If the basaltic
lava is rich in gas, it is released with ease by
means of intermittent explosions, creating
pyroclastic types of cone (also known as cinder
cones).The alternation of lava flows and
pyroclastic episodes fashions another type of
volcanic edifice known as the Stratocone
volcano.
Acidic magmas, on the other hand, rich in
silica, are much more viscous. Upon exiting
onto the surface, they cannot flow easily, and
form accumulations around the eruptive
mouth (domes), or flow very slowly forming
lava flows over short distances (this type of
volcanism is called extrusive).
BASALTIC MAGMAS
ACIDIC MAGMAS
PYROCLASTIC CONE OR CINDER CONE STRATOCONE
Lava flows
Pyroclastic
levels
Pelean Dome Cumulate Dome Crypto-dome
DOMES OF SILICEOUS MAGMA
SOME TYPES OF DOME
Origin of magmatic processes and volcanic features
Origin of magmatic processes and volcanic structures
EXPLOSIVE VOLCANISM
PYROCLASTIC FLOWS
The high viscosity of lavas from acidic magmas
means that on occasions gases cannot be
easily liberated, accumulating as bubbles, and
increasing their internal pressure until they are
unleashed in enormous explosive phenomena
that violently erupt huge volumes of
semi-molten rock into the atmosphere.
The so-called pyroclastic flows are generated
by this means, their solidification then
produces rocks known as pyroclastics.
They can be of different types:
Ignimbrites
A mixture of very hot gas, ash and rock
fragments is launched from the volcano in an
eruptive column.The density of the mixture,
greater than that of air, means that it falls
rapidly, smothering the underlying hillside in
the form of a covering flow comprising a
glowing cloud of gas.They create rocks rich
in ash and pumice.
Lithic Breccias or Agglomerates
The flow forms from the rupture, explosive or
otherwise, of the summit of the volcano.
Rock fragments that made up the actual dome
dominate in this case.
CALDERAS
The largest and most explosive volcanic eruptions
throw out tens and hundreds of cubic kilometres
of magma onto the earth's surface.When too
high a volume of magma is extruded from a
magmatic chamber, the earth subsides or
collapses into the vacated space,forming an
enormous depression called a caldera. Some
calderas can be more than 25 kilometres in
diameter and several kilometres deep.When, after
the formation of a caldera, the magmatic chamber
receives new supplies from deeper zones, the
interior of the caldera can return to a state of
uplift, a phenomenon known as resurgence.
The calderas are one of the most dynamically
active volcanic features and are frequently
associated with earthquakes, thermal activity,
geysers, hydrothermal waters etc.
28
IGNIMBRITES
BRECCIAS AND AGGLOMERATES FORMATION OF A VOLCANIC CALDERA
Ash
cloud
Nuee Ardente
Pyroclastic flow
Pyroclastic flow
Nuee
Ardente
Dome
Eruptive Column
Volcanic
ash fall
1
2
3
Juan M. Fernández
29
GEOLOGICAL CONTEXT AND AGE
The Cabo de Gata volcanic complex is the
largest-sized element of all the volcanic
manifestations in SE Spain. It continues to
expand beneath the Alboran Sea, and has been
brought into its present position by the
operation of the Carboneras-Serrata Fault.The
greater part of volcanism in the Alboran basin is
actually submerged.The volcanic structures of
Cabo de Gata also indicate signs of having been
generated, by and large, beneath the sea. Some
of the oldest volcanic structures could have
grown out of the sea sufficiently enough to
reach the surface, forming islands of volcanic
origin fringed by marine sedimentary platforms.
The age of the Cabo de Gata volcanic complex is
known through the study of fossils present in
sedimentary rocks associated with the volcanic
elements and from dating with isotopes (mostly
Potassium/Argon) in the volcanic rocks.Volcanic
activity developed in a broad period that extends
from around 14-15 to around 7.5 million years
ago (that is to say, Middle and Upper Miocene).
During this interval the volcanic activity occurred
The Cabo de Gata Volcanic Complex
in various cycles.The better-known and
conserved volcanic features are the most recent,
produced between 9 and 7.5 million years ago.
The base of the volcanic complex outcrops at
various points (Serrata de Níjar and Carboneras)
and is formed of Betic basement rocks
(carbonate rocks and phyllites of the Malaguide
and Alpujarride complexes) and some marines
sediments (marls) from the Lower-Middle
Miocene.Towards the top, the volcanic activity is
fossilised by marine sedimentary deposits of the
terminal Miocene (Messinian reefs).
Betic Basement
Alboran Basin
Adra
Sorbas
Basin
Almería
Basin
Pollux
Bank
Chella
Bank
Cabo de
Gata
Las Negras
S. Jose Islet
Polarca
Ridge
SUBMARINE VOLCANISMTHE CABO DE GATA VOLCANIC COMPLEX WITHIN THE CONTEXT OF THE ALBORAN SEA
Calderas
Sedimentary
levels
Volcaniclastic
deposits
Sea level
Magmatic Chambers
Hydrothermal
Systems
Platform
Mediterranean
Sea
(Alboran Sea)
Genoveses
Ridge
Sabinal Bank
Almería
Sorbas
Níjar
Serrata de Níjar
Carboneras Fault
Almería Canyon
Sª Alhamilla
Sª Nevada
Sª de Los Filabres
Sª de Gádor
Neogene Basins
Volcanic Rocks
Emerged
Submerged
30
La Serrata de Nijar is a zone of volcanic origin, associated with the Carboneras
Fault. The rocks, concealed beneath the sedimentary filling of the Campo de
Níjar, have been uplifted and project outwards at the surface of La Serrata
because they are caught up between different fractures in the fault zone.
El Cerro de Garbanzal is a unique volcanic structure,almost circular in plan,
formed by the extrusion of a massive dome-flow.The geometry of this type of
structure is known in some places as fortified domes or 'tortas'. Quite eroded,
it is preserved as a ceiling above marine sedimentary remains.
RELIEF FEATURES OF THE CABO DE GATA VOLCANIC COMPLEX
PlioQuaternary
Miocene
Basement
Volcanic Complex
Nijar-Almeria
Basin
Serrata de
Nijar
Carboneras Fault
Miocene sediments
Cabo de Gata
Barronal
San José
LA ISLETA
Las Negras
Agua Amarga
Car
b
o
n
e
ra
s
Fa
u
lt
Se
rrat
a de
N
íjar
Mesa Roldán
Carboneras
Los lobos
Rodalquilar
Rodalquilar
Caldera
Los Frailes
Caldera
White ignimbrites Ancient massive rocks
Del Garbanzal Dome-Flow
Sierra de
Cabo de Gata
A
C
E
D
A
B
B
The Cabo de Gata Volcanic Complex
31
Mesa Roldan (and Los Lobos) are excellent examples of volcanic structures
fossilised by marine sedimentary rocks and crowned by terminal Miocene
coral reefs. It may be characterised by an andesitic lava dome, enclosed by
fragmented rocks (dome breccias), produced by submarine eruptions with
little or no explosiveness. Linked with the Los Frailes volcano, they are the
most recent volcanic emissions in Cabo de Gata.
The Rodalquilar Caldera, one of the most notable volcanic features, was generated
because of the collapse of the caldera floor into the underlying magma chamber in
a series of highly explosive volcanic processes, producing the deposition of various
pyroclastic rock units (ignimbrites).The later hydrothermal alteration of these rocks
gave place to the characteristic mineral deposits of this area, especially gold.
The Los Frailes Volcano formed around 8 million years ago above older rocks (more than 10-12 ma)
that extended towards the southern limit of the Sierra de Cabo de Gata. In this case, the volcanic
activity did not give place to typical central volcanoes, but to an extensive landscape of more or less
dispersed volcanic domes. Levels of fossiliferous marine sediments were deposited between the phases
of eruption of the different domes that serve as guide levels. Additionally, they produced some highly
explosive eruptive processes (ignimbrites), related to the collapse of calderas.
Volcanic Ashes Massive Nucleus
Caldera
Los Frailes Caldera
Rodalquilar
Complex
FrailesPyroxene Andesites
Lighthouse
White Rhyolites Amphibole Andesites
Pre-Caldera
Rocks
MAGMATIC CHAMBER
Rodalquilar Complex
Sediments (Messinian and Pliocene)
Dome Breccias
Messinian
Carbonates
Conglomerates
(reworked breccias)
D
E
C
The Cabo de Gata Volcanic Complex
RECENT SEDIMENTS
MESSINIAN CARBONATES
MIOCENE SEDIMENTS
LA SERRATA SEQUENCES
PYROXENE ANDESITES
LAS NEGRAS AND CARBONERAS SEQUENCE
ESTRADA DOME, PANIZA DOME, ETC.
GARBANZAL DOME
RODALQUILAR DOME
SEDIMENTS AND ALLUVIUM
ANDESITES
WHITE RHYOLITES
BETIC BASEMENT
Post-Volcanic
Sediments
Volcanic
Sequences
Substratum
Juan M. Fernández
32
HYDROTHERMAL SYSTEMS
The hydrothermal systems associated with the
volcanic complex of Cabo de Gata has
generated important mineralization of
economic interest whose profits have left a
marked impression in the history and upon
the countryside of this district.Without doubt,
the most acclaimed deposits are gold from
Rodalquilar, exploited until very recent times.
Exploitation of other lesser metals has existed,
however, such as lead and zinc, copper and
manganese.
Other non-metallic mineralization of
commercial interest has also been generated in
association with this system. Bentonites are
actually the most important. Long ago the area
had benefited from alunite, a mineral
(aluminium sulphate and sodium or potassium)
that was concentrated in yellow-coloured virgin
seams cutting the white-coloured and
pulverised looking, altered volcanic rock. It has
numerous industrial applications, amongst
others it is used as a source for the production
of alum, for the tanning of leather, etc.
Hydrothermal processes are a frequent
phenomenon in volcanic areas.They are
produced when a magmatic body cannot reach
the surface, cooling slowly at hundreds of
metres or a few kilometres of depth. In these
conditions, the sub-volcanic body supplies heat
to the surrounding area, that can reach
temperatures of around 400-500 C, and emits
gases and acid-rich fluids, such as hydrochloric
or sulphurous (between 200 and 350 C).
These hydrothermal fluids rise up through the
intruded rocks, transforming them
(hydrothermal alteration) and cleaning many
chemical components out of them (lixiviation),
such as gold and many other metals that were
originally very dispersed in the rocks. Upon
arriving in more surficial zones the fluids cool
and mix with water of subterranean or marine
origin, which provokes the metals and other
Hydrothermal Alteration and Mineralization of the Volcanic Complex
disassociated components to precipitate in
fissures and fractures, forming hydrothermal
deposits, such as the famous Rodalquilar gold.
In Cabo de Gata, the main hydrothermal gold
deposits are located in the Rodalquilar complex
of calderas, associated with an intense zone of
hydrothermal alteration.This alteration zone is
produced by intrusion and cooling, beneath the
calderas, of a magmatic body. The hydrothermal
fluids carried by this body wash out the gold at
depth and utilised the various fractures existing
in the caldera to circulate and deposit the gold
in more superficial zones.The formation age of
the deposits is estimated at around 10.4 million
years.
A. GEOLOGICAL SKETCH B. HYDROTHERMAL SYSTEM
Rodalquilar Caldera
Magma
Degassing from Magma
Simplified from Arribas et al., 1995
Magmatic
Vapours
(SO2, HCl, etc.)
Meteoric
Waters
Fumeroles
Cinto Los Tolles
33
Hydrothermal Alteration and Mineralization of the Volcanic Complex
LOCATION OF MINERALIZATION THROUGHOUT
CABO DE GATA
Hydrothermal breccia of white
chalcedony with native gold
(Photo Arribas).
Smelting works of Los Alemanes Nuevos, to
the west of San José, for the recovery of lead
and zinc (photo J. M. Alonso).
Exploitation of alunite from
galleries in the proximity of
Rodalquilar.The
mineralization corresponds
to yellow-coloured veins
(lodes).
Bluish and greenish colouration
corresponding to superficial alteration
minerals of copper and lead sulphides.
Overview of typical scenery
in bentonite clays: white-
coloured powdered masses,
greasy to the touch and very
plastic.
Exploitation of Manganese
from Cerro del Garbanzal.
Mineralization corresponds to
the dark zone.
MINERALIZATION
El Cabo
de Gata
El Barranquete
Fernán Pérez
Las Hortichuelas
Rodalquilar
Los Escullos
San José
Bentonites
Alunite
Gold
Galena and Blende
Copper
Manganese
El Pozo de
los Frailes
Las Negras
Agua Amarga
La Islica
El Llano de D.Antonio
Carboneras
INDUSTRIAL MINERALS
METALLIC MINERALS
Carlos Feixas
THE DISCOVERY
(End of the 19
th
century - 1939)
The existence of gold in the Almerian district of
Rodalquilar was casually discovered at the end
of the 19th century. Gold was detected in lead
smelting works of Cartegena and Mazarron, that
utilised quartz coming from the lead mines
of Cabo de Gata as a flux.The Mazarron smelters
sought out the gold-bearing quartz, and with its
scarce gold content they financed the cost of
transport.
In an authentic state of gold fever many
concessions were registered in this era
that gave way to a multitude of litigation that
delayed the mine consolidation throughout the
whole of the 20th century.
This first stage of discovery of gold from
Rodalquilar, and the development of the first
mines, coincided with the great Almerian
economic crisis. This involved emigration
of workers to Algeria, and subsequently to
America, a decline in lead mining and later in
iron mining, and a crisis in the grape market.
The Rodalquilar Gold
34
Old lodes economic for lead at the end of the 19th century in
quartz dykes, from some of which the existence of gold was
detected in Rodalquilar (Photo, Col. Evaristo Gil Picón).
Extraction workers in the Los Ingleses Mine (around 1930)
(Photo, Col. Evaristo Gil Picón).
Ruins from the first treatment plant installed around 1915 in
the Ma Josefa mine, in El Madronal (Rodalquilar) (Photo, Col.
Evaristo Gil Picon).
The English company Minas de Rodalquilar
handled a total of 107,000 tons of mineralized
rocks until 1939, obtaining 1,125.5 kg of gold.
Of these only 39 tons corresponded to the
period 1936-1939.
The Rodalquilar Gold
THE DREAM (1940-1966)
In 1940, the state decreed the seizure of the
mines, entrusting the task of investigation to
the Spanish Institute for Geology and Mining
(IGME), that looked at the old lodes that had
been exploited without favourable results. Until
1942, the date at which this seizure ended, a
total of 37 kg of gold was recovered.
At the end of 1942 the National Institute of
Industry (INI), through the Adaro National
Enterprise for Mineral Investigation (ENADIMSA),
amplified and intensified investigations,
abandoning the lodes and concentrating in the
'El Ruso, first transport lorry for the Rodalquilar mines
(around 1940) (Photo, Col. Evaristo Gil Picon).
May 1956.The head of state at that time attends the production
of one of the gold ingots,with all of the propaganda exhibited
by the regime (Photo,Col. Evaristo Gil Picón).
Drilling workers in the open cast mines opened during the
ENADIMSA period of exploitation (Photo, Col. Evaristo Gil
Picon).
Cerro del Cinto area, where mineralisation
appeared in a disseminated form in the acidic
volcanic rock body, determining a 4000 ton
mass of mineralised rock with 4.5 grams of gold
per ton.
Until 1966 Rodalquilar lived its golden dream.
Its population came to reach 1400 inhabitants.
It was furnished with infrequent services for this
time in rural populations, cinema, social club,
administration buildings, school, etc.
In the first years of activity from this period
in the order of 700 manual labourers worked in
Rodalquilar, the greater part of them dedicated
to the construction of infrastructure and
workings. At the end of this, between 200 and
300 workers were permanently involved in the
exploitation. ENADIMSA continued, in principle,
with the subterranean system of extraction
that had been emplaced by the English.
In1961, however, the first open cast workings
were undertaken in the Cerro del Cinto.
During this period the bulk of gold production
in Spain shifted to Rodalquilar, with more than
90% of the total production. However this
dream only lasted a while. Investment exerted
pressure to make new workings, and salary
rises in the 70's decade considerably increased
the production costs in a deposit already so
difficult because of the irregular distribution of
economic reserves. All of this forced the
closure of the workings in 1966.
The Rodalquilar Gold
36
REALITY (1967-1990)
The closure of the mines in 1966 put an end to
the period of splendour. A little afterwards the
population declined very abruptly to 75
inhabitants, in summary nearly identical to that
of today.
After exploitation was carried out by ENADIMSA
in the previous period, the concessions and
licences returned to their owners. Even though
investigation had been forgotten in this period,
so often realised by national mineral concerns,
including, to a greater degree, foreign ones.
This period is characterised by intensive
investigation of the Rodalquilar mining district,
but having emphasis on genetic models of gold
mineralisation.
In spite of all this reality prevailed, although it is
estimated that that around 3 tons of gold
reserves are awaiting recovery, their exploitation
is not possible because of the complexity of the
deposit.
Mining town of Rodalquilar (photo Evaristo Gil Picón).
Juan C. Braga - José M. Martín
37
SEDIMENTARY BASINS IN THE VOLCANIC ARCHIPELAGO
Sedimentary Episodes
From the first volcanic episodes and
subsequent to the last, the sea invaded the
volcanic relieves generating an extensive
archipelago. In the marine basins between
volcanic relieves marine sedimentary
deposits were produced. Five sedimentary
episodes can be recognised:
1. In an early episode sediments were
deposited upon the first volcanic rocks.
Their age is Lower Tortonian (between
9 and 8.7 million years).They are mainly
bioclastic carbonates.
2. In a second phase sediments formed above
rocks of the last volcanic event.Their age is
Upper Tortonian to Messinian (between
5.5 and 6.5 million years ago).They are also
bioclastic carbonates, and marls, that
accumulated in deeper zones.
3. Above the previous episode, a series of
related units characterised by the presence
of reef bodies were deposited. Their age is
Messinian (around 6 million years old).
Neogene Sediments
Sierra de Filabres
Sierra de Gádor
Alhamilla
Almería
Níjar
Sorbas
Vera
Cabrera
Betic Substratum
TERTIARY BASINS IN THE SOUTHEASTERN PENINSULA
GEOLOGICAL MAP OF THE CABO DE GATA AREA
Neogene Volcanic Rocks
Carboneras
Fernán Pérez
Cabo de Gata
San José
Rodalquilar
Las Negras
Carboneras
Serrata
Almería Basin
Cabo de Gata
Key in the following page
>>>
4. After the deposition of the reefs a
phenomenon known as the Mediterranean
Messinian Salinity Crisis took place.The
Mediterranean dried out 5.5 million years ago
as a consequence of its disconnection with the
Atlantic. During this period material around
the borders underwent partial erosion and in
the central area of the large Mediterranean
Basin, and in its marginal basins, important
38
thicknesses of gypsum and other salts were
deposited.Above these,or above the eroded
surface, carbonate sediments typical of warm
seas were deposited: oolites and stromatolites.
5. A last marine episode that passes into
continental deposition half way through
(in the Pliocene, between 5 and 2 million
years ago).
SEDIMENTARY EPISODES
STRATIGRAPHY OF THE CABO DE GATA AREA
Undifferentiated Recent detritus
Conglomerates
Bioclastic Sands
Marl, Mud and Sand
Calcareous Breccia
Carbonates with oolites and stromatolites
Gypsum
Sierra Cabrera Cabo de Gata
PLIOCENEMESSINIANTORTONIAN
Millions of years
Coastal reefs
Bioherms, patch reefs
Reef Blocks, slumps
Marls, at times with intercalated diatomites or calci-turbidites
Bioclastic carbonates, locally volcaniclastic conglomerates
Volcanic rocks of around 8 million years old
Bioclastic carbonates, locally volcaniclastic conglomerates
Volcaniclastic rocks more than 9 million years old or undifferentiated
Betic Substratum: Micaschists, Quartzites, Dolomites, Amphibolites, etc
QUATERNARY
Sedimentary Episodes
Juan C. Braga - José M. Martín
39
Deposits of the First Marine Basins
Since the formation of the earliest volcanic
relieves of Cabo de Gata the sea invaded the
area generating small marine basins, extensions
of the self-same Mediterranean Sea. In these
small marine basins, and above the volcanic
relieves, the first marine sediments known in the
Cabo de Gata area were deposited, some 9 to
8.7 million years ago (Lower Tortonian).
The majority of the rocks are carbonates coming
from sediments formed by skeletons (fossils) of
bryozoans, bivalves, calcareous red algae,
echinoderms (sea urchins), barnacles, and
foraminferans (these types of rock are denoted
as bioclastic carbonates).These fossil remains
(shells, winkles etc.) are quite similar to those
organisms that are actually living in the
Mediterranean waters just off of Cabo de Gata
today. Together with carbonates generated by
living marine beings, sediments also
accumulated through the denudation of the
volcanic relieves emerged there (these are
called volcaniclastic deposits).
The Agua Amarga Basin, towards the west of the
town, is one of the areas where these sediments
are better represented.
The sea, in the Lower Tortonian, surrounded
the volcanic relieves.The coastline had
characteristics similar to those of today.
Details of the present-day sea bottom at La
Polarca.The organisms (bryozoans and red
algae) are similar to those that were living
and producing sediment in this period.
Sediments (bioclastic carbonates) from
the Lower Tortonian comprising the
remains of fossils of bryozoans, red
algae and bivalves.
The Agua Amarga Basin, for example, was
a small prolongation of the
Mediterranean during this period that
extended between recently emerged
volcanic relieves in the Cabo de Gata area.
Sedimentary structures indicate that the
bioclastic carbonates from the Lower
Tortonian in the Agua Amarga Basin
formed in littoral and shallow
marine environments.
Furthermore, one can
understand a succession in this
material, in which each phase
had a distinctive geography,
characterised by different
sedimentary processes.
Cross stratification stemming from the
accumulation of sand-sized carbonate grains
of the skeletons of marine organisms
(bryozoans, bivalves,red algae, etc.) in
submarine dunes at little depth.
Taken from Betzler et al. 1997
Emerged
Land
Agua
Amarga
Present
Coastline
PalaeoCoast
line
Sedimentation within
marine basin
PALAEOGEOGRAPHY OF THE AGUA AMARGA AREA 9 MILLION YEARS
AGO (LOWER TORTONIAN)
Juan C. Braga - José M. Martín
40
The Re-initiation of Sedimentation After the Last Volcanic Episode
The last volcanoes in the Cabo de Gata area
were active between 8.7 and 7.5 million years
ago. In this period the domes of some of the
most characteristic relieves of the Natural Park
were formed, like those of the upper part of
Los Frailles, the Cerise de Lobos and Mesa de
Roldan.The extrusion of volcanic material
broke through the older sedimentary rocks in
some places, enclosing blocks within some of
the lavas.
On top of these new volcanoes, and on
occasions on top of older rocks, towards the
end of the Tortonian geological stage, around
7 million years ago, a shallow marine platform
was initiated that marked a renewed incursion
of the Mediterranean around the archipelago
of small islands generated by the volcanic
activity. In this shallow marine environment
mostly carbonate sediments formed from the
remains of marine fossils that were deposited,
for which reason they are called bioclastic
carbonates.
Volcanic eruptions fragmented the sedimentary rocks from the lower episode (Lower Tortonian), light pink
material in the photo, and enveloped them in lavas, dark material in the photo.
Present-day marine bottom in Cabo de Gata.The
organisms present (bryozoans, bivalves and red algae),
are the carbonate producers, that accumulate on the
bottom generating carbonate sediment.
Upper Tortonian bioclastic carbonates comprising the
fossil remains of bryozoans, bivalves and red algae.
41
The Re-initiation of Sedimentation After the Last Volcanic Episode
Stratification and cross-lamination typical
of beach depsoits.
Sheeted fans in the Rambla de los Viruegas.Trough stratification typical of submarine
dunes in shoals.
Accumulations of the remains of organisms
that produce carbonates.
Inside these shallow marine basins the organisms
produced from carbonate,that is to say those that
have shells, chambers etc., lived in a preferred style
immediately beneath the zone pounded by the
surf, associated to a great extent by plant meadows
with a marine flora.The carbonate particles
produced in this factory were distributed by storms
towards the coast,where they accumulated
in beaches and bars,and out towards the sea, in
successive sheets.Towards zones of even greater
depth the carbonate particles became finer each
time and,finally, gave way to marls formed from
a mixture of clays,transported into the sea by
suspension, and microskeletons of planktonic
organisms.
Beaches
Shoals
Factory
Nivel del mar
Fan Sheets
SEDIMENTARY MODEL FOR THE UPPER TORTONIAN
Juan C. Braga - José M. Martín
42
Messinian Reefs
CORAL REEFS
Some 6 million years ago, in the Messinian
geological stage, and after deposition of the
temperate carbonates and marls described
previously, an increase in the water
temperature allowed the formation of coral
reefs in the SE Peninsula and, particularly, in
the Cabo de Gata region. At the present day,
coral reefs live in waters of little depth in
intertropical latitudes, where the average
winter water temperature does not fall under
20º C. In these sites huge volumes of rock and
sediment are constructed by means of their
calcareous skeletons.The presence of reefs in
our region indicates that, in the period of their
formation, the water was warmer than in the
modern Mediterranean.
In Cabo de Gata the coral reefs formed on top
of or around the volcanic relieves.
Some of the most characteristic places within
the Natural Park are found to be the reefs of
Cerro de Los Lobos, la Molata de Las Negras,
La Higueruela and Mesa de Roldan. These
relieves were islands or high sea bottoms that
were colonised by coral reefs and could be
completely covered or surrounded by reefs.
Reefs constructed from coral (light tones in the photo), fringing islands of volcanic origin in modern seas, as
would have happened 6 million years ago in Cabo de Gata.
Calcareous corals that presently live in the tropics are
the constructors of reefs.
In Mesa Roldán, 6 million years ago, a coral reef fringed
and covered a volcanic dome (dark tone).
Coral reef
Volcanic Dome
Juan C. Braga - José M. Martín
43
Evaporites and Carbonates After the Recovery of the Mediterranean
In certain sectors of Cabo de Gata such as
La Molata de las Negras, Mesa Roldan and
others, above the last reefal episode an
erosion surface is observed that affects
the reef and removes the greater part of its
deposits.This erosion surface is the
expression of Messinian desiccation in
this part of the Mediterranean, known as the
Salinity Crisis.
Its age is approximately 5.5 million years
(Terminal Messinian). In effect, around this
time the Mediterranean dried-up, by closing
the communication between the Atlantic
and the Mediterranean, therefore removing
the entry of water from the former. During
this period, the reefs around the border
remained exposed to erosion, and in
the central sectors, as much in
the main marine basin, the
Mediterranean, as in the small
marginal basins that
communicated with it, like
that of Sorbas or Almería,
important massive deposits of
gypsum were formed.
Situation prior to deposition of the evaporites,
with formation of reefs in the margins and
muddy-marly sediments in the basin.
Deposition of evaporites in the centre of the
Mediterranean while it is disconnected from the
Atlantic and dries out.
Deposition of evaporites in the interior of
marginal basins as they are being invaded by
the first pools of water in the process of
Mediterranean reflooding.
SEDIMENTARY INTERPRETATION FOR THE GYPSUM IN A MEDITERRANEAN CONTEXT
Coastal reef
Normal Salinity
Desiccation
Erosion Sill Marginal Basin
Gypsum
Precipitation
Gypsum and
other evaporites
5.9 Ma bp (5.5 Ma bp)
Field view of
gypsum banks.
Following deposition of the gypsum, both above this level and on top of the erosion surface
that reached the reefs, a sedimentary deposit formed fundamentally by carbonates with
stromatolites and oolites can be identified.
The oolites are particularly spherical, with an internal structure of concentric calcium carbonate
layers.
Field view of
stromatolites
features, with
their typical
laminar
structure.
J. Baena - C. Zazo - J. L. Goy - C. J. Dabrio
44
RECENT EVOLUTION AND EMERGENCE OF THE BAY OF ALMERÍA
The Bay of Almería and Andarax Valley, Campo
de Níjar and area of Roquetas del Mar
surrounding it, made up a large sedimentary
basin during the Pliocene and Quaternary (since
5.2 million years ago), with material mostly
deposited in a marine environment.
At the start of the Pliocene the sea occupied all
of the present low-lying areas: in the west up
to the slope of the Sierra de Gádor, through
the Andarax Valley reaching up to the location
of Rioja and bordering the Sierra Alhamilla,
penetrating across all of the Campo de Níjar
where only the Sierra de Cabo de Gata and
parts of the Serrata de Níjar were emerged.
The Andarax River, that presently discharges
into the sea close to Almería and in a north-
south direction, was located further to the
northeast, between Rioja and Viator, during
the Pliocene.
The high relieves that bordered the
sedimentary basin were traversed by ramblas
which, as at present, provided detrital material
(blocks, pebbles, sand) to the marine basin.
During the Plio-Quaternary uplift in the region
was initiated, leading to the displacement of the
coastline in a southerly direction.
During the Quaternary, as a consequence of
repeated climatic changes, alternating cold
glacial periods and warm interglacials, the sea
level suffered strong variations that could have
been in the order of 130 metres.These
variations were responsible for continuous
changes in the position of the coastline, and for
the distribution and abundance of the different
marine and continental deposits.
In the Bay of Almería a magnificent record of
these distinctive sedimentary environments can
be observed, ranging from continental (alluvial
fans, dune systems, etc.) to littoral and
transitional (submarine deltas in ramblas,
beaches, lagoons and littoral features, etc.).
Detail of a cemented sand beach. Remains
of a typical tropical marine fauna
(Strombus bubonius) indicated by the
pencil. Rambla de Amoladeras.
Marine deposits of a pebble beach covered
by continental deposits with a calcareous
crust above it.Retamar.
Deep marine
deposits in the Bay
of Almería.Yellow
muddy
limestones,locally
called Marls with
Leprosy.
Shallow
marine
carbonate
deposits.
Whitish
calcarenites
with fauna.
Detail of a cemented pebble
beach. Retamar.
45
RECENT EVOLUTION AND EMERGENCE OF THE BAY OF ALMERÍA
EVOLUTION OF THE COASTLINE IN THE BAY OF ALMERÍA FROM THE PLIOCENE (5 MILLION YEARS AGO) UNTIL THE PRESENT
Continental Interior
CONTINENTAL AREAS MARINE AREAS
Littoral Fringe
Shallow Water Ancient Delta
Ancient Coastline
Deep Water Modern Delta
Modern Coastline
Airport
Airport
Almería
Almería
Modern position
of the Rio Andarax
Modern position
of the Rio Andarax
Ancient position
of the Rio Andarax
Ancient position of
the Rio Andarax
Ancient
Coastline
Ancient
Coastline
Modern
Coastline
Modern
Coastline
SIERRA DE GÁDOR
5,000,000 YEARS AGO 1,800,000 YEARS AGO 900,000 YEARS AGO
SIERRA ALHAMILLA
SIERRA DE GÁDOR
SIERRA ALHAMILLA
Airport
Almería
Modern position
of the Rio Andarax
Ancient position of
the Rio Andarax
Ancient
Coastline
Modern
Coastline
SIERRA DE GÁDOR
SIERRA ALHAMILLA
46
ILLUSTRATIVE GEOLOGICAL PROFILES OF THE STRUCTURE OF THE SEDIMENTARY FILL IN THE BAY OF ALMERÍA
Quaternary Deposits
(from 1.8 million years ago to Present)
Upper Pliocene Deposits
(from 3 to 1.8 million years ago)
Lower Pliocene Deposits
(from 5.2 to 3 million years ago)
Miocene Deposits
(from 23.7 to 5.2 million years ago)
Volcanic Terrain
(from 15,7 to 6,5 million years ago)
Ancient Basement
Sea Level
Sea Level
Sea Level
Pozo de los Frailes
Alquián
Níjar
Sª de Gádor Almería Basin Extension of
La Serrata
Cabo de Gata Basin
Pollux Bank
Sierra de Gádor
Sierra Alhamilla
Mediterranean Sea
Cabo de Gata
Punta del Sabinar
Aguadulce
ALMERÍA
Níjar
El Alquián
SSierra de Gata
Campo de Níjar
Roquetas de Mar
Bay of Almería
El Pozo de
los Frailes
Almería
Sª Alhamilla
Sª Alhamilla
Pre-Neogene
Substratum
Neogene
Volcanic Rocks
Neogene and
Quaternary Basins
RECENT EVOLUTION AND EMERGENCE OF THE BAY OF ALMERÍA
The Almeria-Nijar Basin
Didactic Itinerary
CABO DE GATA-NIJAR
NATURAL PARK
1
A. Martín Penela
49
1. Alluvial Dynamics of Ramblas: Las Amoladeras
A broad valley floor is exhibited, usually with a low sinuosity.
Its river bed is occupied by numerous interweaved channels
and the bottom covered by sediments organised into bars
and channel deposits.Their sediments are mostly made up of
gravel-sized particles.
The channels are very mobile, and develop as furrows
that interweave amongst themselves, adjacent to the
bars, that appear as small mounds, upon which
vegetation is frequently established.The bars, of
different form and size, change their arrangement
and morphology after each flood.
The floodplain represents a portion of the river bed
that is only inundated during important floods. In it a
great part of the fine materials that were transported
in suspension can be deposited, giving rise to deposits
that favour the development of fertile soils.
THE RAMBLAS
The Rambla de las Amoladeras is a superb
example of alluvial systems in arid zones.These
river courses, usually dry, represent channels in
which currents of short duration can flow as a
direct result of precipitation, scarcely receiving
water from other sources.
The dynamics of this alluvial system are
fundamentally controlled by the climate and the
shortage of vegetation. Seasonal rains,
frequently stormy and of short duration, create
an important surface torrent, with great erosive
power, that supplies water and sediment to
theses river beds.
Channels
10/100 m
0
Bars
Floodplain occupied by
water only during the
largest flood events
Channels Bars
50
FLOODS
As a result of intense storms, the dry
riverbeds in the ramblas can be
transformed, in a short time, into violent
torrents of water loaded with sludge and
detritus.These very intensive floods, sudden
and powerful, can be unduly catastrophic
and cause great destruction in agricultural
zones and to built structures, in the river
beds of the ramblas or within the same
floodplain. The large floods take place
sporadically, tied to seasonal changes or
times of rain.
1. DRY PERIOD 2. PERIOD OF STRONG FLOODS
3. PERIOD OF DIMINISHING FLOW 4. PERIOD OF SCARCE ACTIVITY
PHASES IN A FLOOD
1. Alluvial Dynamics of Ramblas: Las Amoladeras
Damage caused by a flood .
51
ALLUVIAL TERRACES
Alluvial terraces are deposits positioned
sporadically along the side of a valley that
correspond to non-eroded segments of
earlier alluvial sediments. When a
rejuvenation of the alluvial system is
produced by climatic, tectonic or other
changes, water currents deeply erode the
sediments within their channel, giving
rise to a new river course in a lower
topographic position with respect to the
older channel.
Flood-susceptible river bed
Older Terraces
2
nd
Terrace
1
st
Terrace
1
st
Terrace
BarsChannel
Substratum
Stage of alluvial infilling.The
current deposits most of the
sediments that it transports
and produces a river fill.
If the conditions repeat
themselves, they will be
succeeded by new phases of
filling and erosion from which
various terrace levels will
originate.
A change in base level
means that the rambla
evolves in order to reach
a state of equilibrium.
On top of the previously
formed deposits a new
channel is emplaced
which erodes the pre-
existing alluvium that
had come to construct
the older terrace level.
1
2
3
STAGES IN THE FORMATION OF A SYSTEM OF TERRACES
1. Alluvial Dynamics of Ramblas: Las Amoladeras
Alluvial Terrace in the Rambla de Amoladeras.
C. Zazo - J. L. Goy - C. J. Dabrio - J. Baena
52
2. Fossil Beaches of the Rambla de Las Almoladeras
The surrounding area of the Rambla de las
Amoladeras are characterised by the presence
of one of the most complete geological records
of fossil Quaternary beaches, and with the best
conditions for observation, in the Spanish
coastal zone.These marine beaches, that
fundamentally developed between the last
200,000 years and the present day, were
partially covered on the surface by a dune
system that started to form around 2500 years
ago. In the talus of the right hand margin of the
river mouth of the rambla, a mixture of deposits
consisting of well-cemented sands and pebbles
with a marine fauna can be seen, that represent
ancient beaches, and consequently, the position
of the coast at that time. Average absolute
dating (Uranium-Thorium), has obtained ages
of 180,000 years, 128-130,000 years and
95-100,000 years for the three differentiated
beach levels. All of the beaches contain fossils of
Strombus bubonius.They dominate Tyrrhenian
beaches, a name that is derived from the
Tyrrhenian Sea, for it was there that beaches
with this characteristic fauna were described for
the first time.
An interpretation of the geometry of the
outcrop allows differentiation of, from left to
right: in the first place some conglomeratic
sediments (A) corresponding to the oldest
beach, of unknown age, which contains the
remains of a fossil fauna like that which actually
lives in our coasts.
This beach is separated from those which follow
it by a deposit of cemented sand that
corresponds to a fossil dune field, that formed
when the sea descended, leaving the beach
deposits emerged and dried out, such that it
allowed the wind to accumulate sand.
The following deposits (B, C and D) consist of
cemented conglomerates rich in Strombus
bubonius.The separation between the distinct
beaches consists of erosive surfaces, generated
during falling sea level in the coldest periods.
53
2. Fossil Beaches of the Rambla de Las Almoladeras
Each position of the coastline has left behind an associated fossil beach level.In the river mouth outcrop of the Rambla de las Almoladeras, four superimposed fossil beach levels can be observed
with ages of more than 250000, 180000, 128000 and 95000 years, respectively.The latter three levels contain the remains of a marine mollusc (Strombus bubonius), that still persists in modern
tropical coasts,so that a warm, almost tropical, climatic character existed in the coast during these stages.
Fault planes
Modern Beach
Sea Level
Modern Beach
Sea Level
Modern Dunes
Well
Dunes
NE
SO
Rambla Amoladeras
95.000 years 128.000 years 180.000 years >250.000 years
ACTUAL SECTION
INTERPRETED SECTION
Surge
Channels/Grooves
Beach Level Fault Plane
or Wall
Fosil dune
D
C
B
A
54
The fossil beaches of the littoral zone in
Almería contain abundant fossils of marine
species that do not inhabit theses coasts at
Present times, although they had populated
the littoral zone between 180,000 and 70,000
years ago. Strombus bubonius is, amongst
others, a fossil of special importance. This has
become used as an excellent palaeoecological
indicator, in that it reveals variations in salinity
and water temperature of the sea with great
sensitivity. Its presence in these fossil beaches
tells us that the sea which bathed the Almería
coastline was at other times warmer,
possessing subtropical conditions.
Strombus bubonius is a marine mollusc
Gastropod, typical of warm seas, originating
from the African equatorial Atlantic, entering
into the Mediterranean through the Straits of
Gibraltar when the atmospheric and surface
water temperature of the sea are a few degrees
higher than they are at present. During the last
glaciation, between 65000 and 10000 years
ago, oceanic waters cooled, so that they
prompted a new migration of this species
towards the African equator, in whose
coastline they are found living today, actually
forming part of the diet of townsfolk in this
littoral zone.
MODERN AND ANCIENT GEOGRAPHIC
DISTRIBUTION OF STROMBUS BUBONIUS
Details of the shape of Strombus bubonius from fossil beach
levels,above which the modern littoral boundary is positioned.
Dorsal and Ventral views of an example of Strombus bubonius.
Mediterranean Sea
Tropic of Cancer
0 1000km
Gulf of Guinea
Equator
S. bubonius, (modern) S. bubonius, (fóssil) Cold Canary Current
Lake Chad
Canary
Islands
ÁFRICA
IBERIA
Atlantic Ocean
River Nile
River Niger
2. Fossil Beaches of the Rambla de Las Almoladeras
C. Dabrio - J. L. Goy - J. Baena - C. Zazo
55
3. The Dune System in the River Mouth of Rambla Morales
FORMATION AND DEGRADATION OF THE DUNE SYSTEMS OF CABO DE GATA
Sea level
Active beach
Strombus bubonius
Fossil
Pleistocene beaches
Strombus bubonius
Westerly Winds
Sea level
Primary dune system
Holocene active beach
2
nd
active beach episode
Modern active beach
Second dune system
11
1
1
1
1
1
11
2
2
2
2
2
1
23
1
1
On top of the fossil beaches and dunes,the first active beach
of Holocene (less than 10,000 years old) is deposited (1).
A slight fall of sea level leaves the beach, slightly more
extended, under the effects of erosion by westerly winds, that
carry along the finest elements (sand) in the form of a train of
dunes (primary system).
A new rise in sea level deposits another beach episode (2)
above the previous erosional surface. Dunes continue
advancing.
Another rapid fall in sea level causes a repetition of the same
phenomenon which forms a new train of dunes (2
nd
system), that
advances mixing with the previous one.
Finally the last rapid rise in sea level
emplaces the modern beach (3).The dunes
advance, but they have been disappearing
due to intensive quarrying of sand in order
to cover pastural land with sand.
Exploitation of these dune systems is
actually completely prohibited.
The dune systems that are observed in the
surroundings of the river mouth of the Rambla
Morales are produced by the action of westerly
winds, that lift up sand from the beaches and
transport it towards the river bed, accumulating
it around small bushes or topographic
irregularities in the surface. In this way dune
construction is initiated.
Fossil Pleistocene dunes
A
B
C
E
D
The variation in sea level occurring in this coast
throughout the Pleistocene-Holocene has given
rise to various phases of dune formation.
The oldest dunes are cemented, the most recent
may be: semi-mobile, covered over by
vegetation, or mobile, which are those that
finally bury the earlier ones, in their advance
towards the land.
C. Dabrio - J. L. Goy - J. Baena - C. Zazo
View of the lagoon from the river mouth of the Rambla
Morales.It can be observed how the present,
topographically higher, littoral barrier causes a closing
of the rambla, such that it impedes its normal drainage
into the sea.This situation persists up until when, in
a state of high energy, the rambla breaks through the
littoral barrier nourishing the sea with sediments.
Aspect of the modern beach that forms part of the
littoral fringe which closes off the inlet of the rambla.
4. The Lagoon of Rambla Morales
56
In the river mouth of Rambla Molares a small
lagoon, with an almost permanent character,
has been created. Its origin stems from
interaction between the rambla system itself
with the beach. During two times of the year
(end of spring - start of autumn) the
phenomenon called gota fría is registered in
the Mediterranean coast, that comprises intense
and torrential rains concentrated in periods of
very short time (several days). During these
periods the ramblas transport a great quantity
of water and sediment, that is finally to be
deposited in the sea, eroded from the beaches
that previously closed off the river mouth,
showing a great capacity for cleaning out the
rambla (high energy stage).
These sediments are redistributed along the
length of the coastline,during periods of good
weather (low energy stage),by means of littoral
currents or drift currents,that in the case of the
Rambla Morales circulate in a southeasterly
direction, regenerating beaches and barriers once
more.As these beaches are topographically higher
than the bottom of the rambla, towards the land
they leave a small depression that fills up with
water from scarce rainfall that accumulates during
inter-storm periods.This water, not having the
strength of movement, remains stagnant creating
a lagoon in the river mouth of the rambla.
Aerial view of the river mouth of Rambla Morales.
Lagoon
RRiver Mouth of
the Rambla de
Morales
Closing barrier of
the river mouth
57
4. The Lagoon of Rambla Morales
1. HIGH ENERGY STAGE
2. LOW ENERGY STAGE
3. NEW STAGE OF HIGH ENERGY
Littoral Barrier
(Beach-Dunes)
Bars
Littoral
drift
Rambla Morales
Sediments Sediments Sediments
Rambla
Ancient littoral barrier
Temporary lagoon
New littoral barrier
Littoral
drift
Littoral
drift
Lagoon
Lagoon
deposits
Rambla
SIMPLIFIED SCHEME OF LAGOON FORMATION PROCESSES IN THE RIVER MOUTH OF THE RAMBLA MORALES
J. L. Goy - C. J. Dabrio - J. Baena - C. Zazo
Sierra
Lagoon Border
Bahada
River
Floodplain
Ram
bla
Wind
Beach
Laguna
Littoral Drift
Waves
Oleaje
Cabo de Gata
Barrier Beach
Lagoon
Alluvial
Fan
58
THE NATURAL ALBUFERA
The modern salt pans (salinas) of Cabo de Gata
constitute a magnificent example of an
'albufera' or backshore lagoon system set up as
a Mediterranean salt pan by man.This type of
system is natural, and is generated thanks to a
depressed area at the back of the coastline,
where freshwater accumulates. It is
permanently separated from the sea by a
beach-barrier, forming mainly from sandy
sediments carried by the ramblas and
displaced along the length of the coastline by
littoral drift.
The lagoons receive hydrological supplies from
rainwater, from rivers that discharge into
them and, on occasions, from
subterranean aquifers and from
the sea itself.
The lagoon tends to fill with
sediments from diverse
sources.The most
important are provided by
the alluvial apparatus
that drain the
surrounding relieves of
the sierras. Sandy
sediments from the
beaches that wash over the barrier beach and
mud carried by the wind have less importance.
Evaporation, controlled primarily by direct
sunshine and by the wind, plays a very notable
part in the dynamics of these lagoons,
contributing effectively to their desiccation,
which is why they can be a suitable mechanism
for the manufacture of salt.
Aerial view of the active alluvial fan systems that
originate from the Sierra de Cabo de Gata relief. In
many cases they behave as coalescing fans, in that
they are laterally connected and superimposed one
upon another.
Evaporation
5. The Salt Pans (Salinas) of Cabo de Gata
Lagoon
Active alluvial fans
Sierra de Gata
IDEALIZED GEOMORPHOLOGICAL SKETCH OF THE SALINAS
59
Alluvial Fans origina-
ting from the
surrounding Relieves
Rain
Currents
Evaporation
Atmospheric Dust
Fine Sediments and
Some Precipitates
Transfer of Water and Sediment
Infiltration
Sea
Depressed Area
Groundwater
Older Lithified and
Cemented Barrier
Present Barrier
Reworked Littoral Fringe
Erosion Surface formed
during periods of Low Sea Level
A
B
C
E
D
A schematic section of the lagoon
showing the diverse dynamic and
morphological elements.
The deposits of the lagoon (E) connect
with those of the alluvial fans (A) and
with those of the backshore part of the
beach (B) that obtains sediments
carried during large storms when
swells can spill over the barrier beach.
The model is only active, as at present,
during the periods which high sea level
is maintained that coincide with
interglacials. On the other hand, during
glaciation the sea level had remained
lower, placing the beach towards the
south. In these periods the zone could
remain subjected to the erosive action
of external agents (wind, currents, etc.),
forming an erosive surface (C).
When the lagoon and the littoral fringe
(strandplain) are active, during
interglacial periods, the beach grows
(progrades) towards the sea (D) and
a thick covering of sediments
accumulates in the lagoon (E).
View of the salinas from the south.
5. The Salt Pans (Salinas) of Cabo de Gata
Beach
Littoral Fringe
Salt Pans
Albufera
Fan Cones
Sierra de Cabo de
Gata
Lagoon
Alluvial Fan
System
IDEALIZED GEOMORPHOLOGICAL SKETCH OF THE SALINAS
60
WORKINGS OF A MARITIME SALT PAN
The natural lagoon systems like that of Cabo de
Gata have historically been utilised by man in
the extraction of salt: these are the
characteristic maritime Mediterranean salt pans.
Basically this consists of taking water from the
sea in a controlled process of evaporation, by
which means a progressive increase in salinity
is produced, until a stage of saturation and
precipitation of common salts (halite, NaCl) is
reached.
In each a circuit that consists of several
concentration pools (A, B, C) of broad extent and
little depth is established, fed directly by water
from the sea with a salinity of 36 grams per litre.
The seawater is introduced by a channel to
the first concentration pools (A), in which the
marine macrofauna is retained (fish,
gastropods,…) and a settling of (terrigenous)
material from suspension is produced.
Precipitation of calcium-magnesium carbonates
(upon increasing salinity from 36 to 140 grams
per litre) and the elimination of micro-
organisms (algae, bacteria,…) occurs in the
marine water upon achieving an intermediate
concentration (B). After this initial phase,
the water follows its path through different
concentrations (C), favouring the precipitation
of calcium sulphate (upon reaching a salinity
of 140 to 325 grams per litre). Once these
undesirable products have been taken out of
solution, the brine goes through crystallisation
Evaporation
Concentrates
Precipitates
Pump
or
basin
36 g/l
80 g/l
140 g/l
350 g/l
325 g/l
370 g/l
Sea
(Salinity in grams per litre)
Brine
Mg Cl2
A
B
C
D
SALINISATION PROCESS
Floating salt
(halite) layers
formed in the
absence of
wind.
Aerial view of the salt pans from the east.The letters correspond
to the identification of different areas of the salt pans referred
to in the text.
(D) where the precipitation of common salt
(at 325-370 grams per litre) occurs, extracted for
storage, purification and finally sale.
A
B
C
D
5. The Salt Pans (Salinas) of Cabo de Gata
Juan M. Fernández
61
6. Volcanic domes of Punta Baja, El Faro and Vela Blanca
TTHE VOLCANIC SERIES
The coast in the vicinity of the Cabo de Gata
lighthouse shows an excellent outcrop of massive
volcanic rocks that form the structure of a
volcanic feature known as domes.Their age
of formation is greater than 12 million years.
They are surrounded by a complex sequence of
pyroclastic rocks and lava flows, of varying
composition, that have been affected by
hydrothermal alteration.
Climbing up the vela Blanca hill gives an overview
of the volcanic rock succession that exists in the
southern end of the Sierra de Cabo de Gata.:
Surrounding the Punta Baja-Cabo de Gata
domes, white-coloured rocks known as tuffs
can be recognised.They have a pyroclastic
origin (ignimbrites), that is to say, they are
produced by highly explosive eruptions.
These are the oldest rocks in the area.
Above them, other levels of greyish-coloured
tuffs are developed, also pyroclastic in character.
On top of this andesitic lava flows (rock of
intermediaate character) can be recognised.
They form a well-defined promontory, that is
repeated on the slope through the influence
of various faults. At a distance, columnar
jointing can be recognised.
The Vela Blanca dome cuts across the tuffs and
might have formed simultaneously with the
previously mentioned lava flows. It is highly
altered and impregnated with manganese
oxides, which give it a very dark coloration
(Punta Negra).
Above the flows, another level of pyroclastic
rocks appears that extends several kilometres
towards the north.
The highest peak (Bujo, 374 m) corresponds to an
andesitic dome that cuts through the previous
sequence.Similar domes are recognised at
different points in the southern massif of Cabo de
Gata.
White tuffs (pyroclastic rocks, ignimbites)
Grey tuffs (pyroclastic rocks, ignimbites)
Massive amphibolitic andesites (domes)
Massive amphibolitic andesites (flows, dykes and domes)
Pyroclastic rocks (pyroxene andesites)
Recent alluvial deposits
White tuffs
Bujo (373 m)
Dykes
Andesitic pyroclastic levels
Lava flows
Faults
Cerro de vela blanca (213 m)
Punta negra
Cala Rajá
Punta Baja Dome
Alluvium
Grey tuffs
Vela
Blanca Dome
Finger reef
62
VOLCANIC STRUCTURES
The dome complex of Punta Baja-El Faro-Vela
Blanca comprises several massive lava bodies
aligned in an east-west direction, probably
exploiting a fracture in this orientation as they
are extruded.
Domes are volcanic features that originated
when viscous lava, rich in silica, flowed slowly
onto the surface, and accumulated around,
solidified and plugged its own exit point.
At times the lava does not manage to exit onto
the surface, and forms an accumulation beneath
the intruded rocks, that is called a 'cryptodome'.
The complex in this area contains two principal
domes, one beneath the lighthouse and the
other at Punta Baja, in both of which a
spectacular series of characteristic volcanic
structures may be recognised:
The most pronounced is columnar jointing,
typical of massive rocks. It is produced through
the slow cooling of lava after its emplacement.
Upon cooling the volume of lava diminishes
slightly, and this contraction is accommodated
by the formation of regularly-spaced joints, in a
perpendicular arrangement with respect to the
cooling surface of the lava.The peculiar shape
of these hexagonal columns of rock, means that
they have been utilised, in this and many other
place in the Sierra de Cabo de Gata, for
obtaining paving slabs.
Other structures observed in these rocks are
lamination and flow banding.This is mostly
generated towards the margins of the domes,
and includes folds that can be formed during
the extrusion. The colour bands indicate slight
differences in the composition of the lava during
extrusion, whilst the flow lamination is produced
by resistance to flow of viscous lava around the
margins of the dome.
Country rock (white tuffs)
Nucleus
Marginal lamination
Breccia (Mónsul type)
Partial emergence
Columnar jointing
Colour bands
CRYPTODOME AND ASSOCIATED STRUCTURES
6. Volcanic domes of Punta Baja, El Faro and Vela Blanca
63
White tuff at Cala Rajá, pyroclastic material (ignimbrite) in which the domes of Punta
Baja, El Faro and Vela Blanca are enclosed.
Columnar jointing in the Punta Baja dome.
Fanning of Columnar joints in Punta Baja, traditionally used for the extraction of
decorative paving blocks.
Flow lamination on the margin of the El Faro dome in Cabo de Gata.
6. Volcanic domes of Punta Baja, El Faro and Vela Blanca
Juan M. Fernández
7. The Mónsul volcanoes
64
Mónsul inlet
Dunefield
Beach
Parking
La Media
Luna inlet
Agglomerates or volcanic
breccias
Andesitic lavas with
columnar jointing
Beaches and Dunes
Debris
Feeding zone of the volcano
Sea level during the eruption
In the panorama in front, the feeder zone of
the volcano can be distinguished. It consists
of darker, andesitic lavas, and exhibits a very
characteristic structure known as columnar
jointing.These structures are produced due to
the contraction of lava upon cooling.
INTERPRETATION OF THE OBSERVED PANORAMA
RECONSTRUCTION OF GENETIC PROCESSES
TTHE MONSUL SUBMARINE VOLCANOES
The steep volcanic cliffs surrounding the area
of Mónsul consist of volcanic agglomerates
(or breccias).They are a type of rock formed from
angular blocks of (andesitic) volcanic rock, with
a diameter that ranges from millimetres to
metres,enclosed within a fine, sand-sized matrix,
also of volcanic origin.
This material takes its origin from submarine
eruptions produced around 10 to 12 million
years ago, from submerged volcanoes.The
volcanoes were located next to one another, in
a manner in which, once an explosion had
occurred, the erupted material was deposited
in stacked layers on the marine seafloor.
C. Dabrio - J. Baena - J. L. Goy - C. Zazo
65
8. The ‘barchan’ dunefield of Barronal or Mónsul
Wind carries out two fundamental processes,
erosion and accumulation, which create certain
morphological features; dunes are amongst these.
The term 'dune' is used in a broad sense to
designate the majority of accumulation features,of
sand deposits.
In the dunefields of the Almería littoral zone the
dominant types, according to their morphology in
TYPES OF DUNES IN CABO DE GATA
B
ARCHAN DUNES
LINEAR (SEIF) DUNES
PARABOLIC DUNES
DUNES ACCUMULATING DUE TO VEGETATION
Mónsul barchan dunefield.
Movement of sand in favour of the wind
direction in the Mónsul dunefield.
Vegetation
Crest
Corner (horn)
Wind
Wind
Wind
Depression
Lunite
Wind
Dune
Volcanic substratum
Leeward face
Windward face
2. Migration of the Barchan and
increase in size
1. Accumulation of sand
due to vegetation
Wind
plan view, are: barchans, or half-moon dunes, with
their corners or points facing in the same
direction as the wind; parabolic dunes, with the
corners (horns) facing in the opposite direction
to the wind; linear (seif) dunes, produced when
a flat zone,with sandy material covering its floor,
exists close to a relief orientated almost
perpendicular to the dominant wind direction.
Wind
Wind
Juan M. Fernández
9. The Los Frailes Volcano
66
LOWER UNIT:
AMPHIBOLITIC ANDESITES
The lower unit of Los Frailes constitutes the
collapsed floor of a magma chamber that was
vacated during an individual or several very
intense eruptions. In these eruptions a great
volume of magmatic material left the surface
through rapid and very explosive phenomena,
and the roof of the magma chamber collapsed
giving rise to a chaotic mixture of rock
fragments, associated with dome remains and
lava flows, that constitute the most common
material in this lower unit.The explosive intervals
are marked by intervals of pyroclastic rock (tuffs)
of different types, that are found intercalated
GEOLOGICAL PANORAMA OF THE LOS FRAILES VOLCANO FROM THE LA ISLETA VIEW POINT
Morrón de Mateo
SW NE
Bentonite quarries
Cerro de
Santa Cruz
Sacristán
caves Sedimentary levels
El Fraile (493 m)El Fraile Chico
San Felipe
castle
Rambla
SEDIMENTARY UNIT
LA ISLETA DOMES
ALLUVIAL FANS
DACITES
BASALTIC ANDESITES
AMPHIBOLITIC ANDESITES
Summit domes
Fossil beach of Los Escullos
The Los Frailes hill (473 m), is one of the most
distinctive elements of the volcanic Complex.
It consists of two readily distinguishable units
a lower unit of amphibolitic andesites and an
upper unit of dark basaltic andesites, that
correspond to the two main summits (El Fraile
and the more recent El Fraile Chico). Both of the
Los Frailes rest upon andesites, strongly altered
by hydrothermal processes, that make up the
southern volcanic massif of Cabo de Gata.
between the units of chaotic breccias. In
numerous places layers of sedimentary rocks are
found in addition, pertaining to beach and
shallow marine environments, rich in fossils;
67
9. The Los Frailes Volcano
these are intercalated within the volcanic rocks
of the lower unit, and are very abundant
between the lower and upper units.The age of
the lower unit is believed to be between 10.8
and 12.4 million years by some authors, and
around 14.4 million years by others.
UPPER UNIT:
BASALTIC ANDESITES
The summit of Los Frailes is composed of a unit
of basaltic andesites.These rocks are the most
basic (poor in silica) in Cabo de Gata, although
with properties that did not reach the point of
being basalts.
INTERPRETED GEOLOGICAL PANORAMA OF THE LOS FRAILES VOLCANO FROM THE LA ISLETA VIEW POINT
San
José
Cerro de
Enmedio
El Fraile
RELLLANA de
Rodalquilar
OLD AGGLOMERATES
(ANDESITES)
AMPHIBOLITIC ANDESITES
(12-10 M.A.)
MASSIVE ANDESITES
IGNIMBRITES OF THE
RODALQUILAR CALDERA
VOLCANO-SEDIMENTARY UNIT
SEDIMENTARY LEVELS
SUMMIT DOMES
BASALTIC ANDESITES (8 M.A.)
LAVA FLOWS
SW NE
They are relatively well preserved rocks, without
alteration, whose age is estimated at 8.5-8.6
million years.They are also situated above
sediments rich in fossils from the Tortonian,
belonging to shallow marine environments, and
beach sediments.This data indicates that this
upper unit of Los Frailes constituted a volcanic
island during its formation 8 million years ago.
The unit is built from two main emission centres,
that discharged several massive lava flows
(at around 1000º C temperature), whose
characteristic columnar jointing has been utilised
for the quarrying of paving stones (several hills
can be seen in the middle of the slope).
Other eruption phases gave rise to abundant
agglomerates or pyroclastic breccias, in
eruptions somewhat more explosive.The end of
magmatic activity is marked by the extrusion
of the domes that constitute the two
previously-mentioned pinnacles (summit
domes), that sealed the eruption vents. Erosion
has been intense up until now, although the
greater relative resistance of the massive lava
domes has configured a roughly conical erosive
morphology for this unit.
C. Zazo - J. L. Goy - J. Baena - C. Dabrio
68
10. The fossil dunefield of Los Escullos
In the Almerían littoral zone there have been
three important phases dune system
development during the Quaternary: greyish
cemented dunes,formed of the fragments of
schists, volcanic rocks, and quartz grains, such as
those that are observed in Rambla Amoladeras,
and which formed at a time known to be
between 250,000 and 180,000 years ago; white-
coloured oolitic dunes,consisting of rounded
grains known as oolites, around 128,000 to
100,000 years old (last interglacial period); and
finally, greyish, uncemented dunes , that illustrate
the same coloration and composition as the first,
although in this case they were not cemented,
formed from around 6,000 years ago to the
Present.
In the Los Escullos cove, beneath the San Felipe
castle, we can observe, without doubt, the best
exposure corresponding to white, oolitic dunes
in the Natural Park. However, other exposures
exist in the Rodalquilar and Los Genoveses
beaches.
These ancient dune systems are excellent
indicators, not only of the position of the
coastline at the time of its formation, but of the
ecological and environmental conditions.
In effect, the oolitic dunes were generated due
to the movement of old oolitic beach sediments
by the wind, formed in a warmer environment
than at present.This is knowwn through the
existence of an associated fauna (Strombus
bubonius)that belongs to warm seas, and by the
ooliths themselves.Through the microscope it
can be observed that the ooliths are composed
of a nucleus of quartz grains or rock fragments
or faecal pellets and a coretex that shows
concentric layers of aragonite. Oolites actually
form in the infralittoral zone, at a few metres
depth, on the seafloor of warm waters that are
saturated in carbonate and highly agitated by
waves.
The San Felipe castle of Los Escullos sits on top of a
spectacular fossil oolitic dunefield.Without doubt the best
record of this type of deposit in the area of the Natural Park.
In the Cabo de Gata Natural Park area, fossil oolitic
dunefields exist in other places: here the exposures of Los
Genoveses may be observed.
San Felipe castle of los Escullos
Oolitic
dunefield
Isleta del Moro
69
10. The fossil dunefield of Los Escullos
Microscopic view (thin section) of the components of dune
oolites from Los Escullos (Photo A). Upon increasing the
resolution (Photo B) the ooliths can be identified perfectly as
the spherical structures that stand out within the sandy matrix.
OOLITIC DUNES OF LOS ESCULLOS
DET
AIL OF THE OUTCROP
INTERNAL STRUCTURE OF THE DUNES
Oolitic dunes
Los Escullos
Los Frailes
Dirección de paleovientos
Sea
O
Ooliths
BA
J. L. Goy - C. Zazo - C. Dabrio - J. Baena
70
11. Alluvial fans of the La Isleta-Los Escullos coastal plain
The Sierra de Cabo de Gata exhibits an abrupt
relief, with strong slopes, that contrasts with the
gentle morphology of the littoral depressions
(coastal plains).The abrupt change of slope that
is produced in the courses of small barrancos as
they exit from the mountain relieves,and enter
the depression, provokes a fall in their capacity to
transport and the consequent accumulation
(deposition) of the sediments (blocks, pebbles,
silts, etc.) which they moved towards the most
low-lying areas.An open alluvial fan in thus
formed.
SIMPLIFIED GEOLOGICAL SCHEME OF THE QUATERNARY DEPOSITS IN THE LA ISLETA-LOS ESCULLOS AREA
Phase 6 (c)
Alluvial fan
deposits
HolocenePleistocene
Quaternary
Channel deposits of
terraces and rivers
Gravity deposits Marine deposits Aeolian
deposits
Present river Beach
Aeolian dunes
Colluvium and
undifferenciated
slope deposits
Fluvial deposits Slope deposits Littoral deposits
2
nd
Terrace
1
st
Terrace
Abandoned
river
Phase 6 (b)
Littoral barrier
Phase 6 (a)
Phase 5
Phase 4
Phase 3
Phase 2
Phase 1
Volcanic rocks
Miocene
71
A fall in sea level, linked to the slow uplift of
the relief, caused incision of the initial
barranco (primary river course) in the
deposits of the older open fan, upon whose
surface soils were already able to develop.
The formation of subsequent fans, during the
initiation of a new rise in sea level, gives way
to incised fans at a lower altitude to the
previous one.
In the area of La Isleta-los Escullos, several
incised surfaces (roofs of fans), inclined
gently towards the sea are observed, that
represent distinct phases of fan formation
throughout the Quaternary. Theses are due
to changes in the climatic conditions,
tectonics and eustacy (oscillations of sea
level), and their study provides very
interesting information about such
conditions.:
11. Alluvial fans of the La Isleta-Los Escullos coastal plain
PROCESSES OF DEPOSITION AND INCISION IN ALLUVIAL FANS
OPEN FAN
Sierra de Cabo de Gata
Sea level
Fan formation phase 1
Paleosuelo
Slow uplift
Fan formation phase 2
Aerial view of La Isleta-Los Escullos in which phase 2 alluvial fans may be observed,with a schematic overlay.
Sea level
Sierra de Cabo de Gata
INCISION
La Isleta
Los Escullos
72
PANORAMA FROM THE LA ISLETA VIEWING POINT AND INTERPRETATION OF THE ALLUVIAL FAN SYSTEM
Cerro de Los Filabres
Los Escullos
Beaches
Oolitic dunes
Undifferentiated slope deposits Beaches
Fossil oolitic dunes
Phase 3 alluvial fans
Phase 2 alluvial fans
Phase 1 alluvial fans
Volcanic rocks
Phase 3
alluvial fan
Phase 1
alluvial fan
Phase 2
alluvial fan
Alluvial fan
entrenchment
LA ISLETA VIEWING POINT
11. Alluvial fans of the La Isleta-Los Escullos coastal plain
Juan M. Fernández
73
12. Rodalquilar volcanic calderas
One of the most significant volcanic structures
of the Cabo de Gata Volcanic Complex are the
Rodalquilar calderas, from the centre of which
known gold deposits are located. Rodalquilar
shows the superposition or nesting of two
successive calderas; the larger is the
Rodalquilar caldera, and inside it the La Lomilla
caldera is located (thus named after La Lomilla
de Las Palas).Theses calderas are collapse
structures produced by highly explosive
eruptions, that gave place to tow large units of
pyroclastic rock, known as the Cinto
ignimbrites and the Lázaras Ignimbrites,
respectively. Calderas are collapse features that
are produced when, during an explosion of
great magnitude, the magma chamber is very
INTERPRETED GEOLOGICAL SKETCH OF THE RODALQUILAR VOLCANIC CALDERA
rapidly vacated and its roof collapses, leaving
behind a roughly circular depression.
Detail of the Cinto collapse breccias. Concentration
of (dark) blocks within a pumice flow (light-
coloured).
Detail of the Cinto
pumice flows.The dark
stippled area
corresponds to large
quartz crystals.
Collapse breccias
Domes of the
caldera margin
Pre-caldera
rocks
Caldera de Rodalquilar
SE
NW
600
400
200
Sea level
-200
-400
-600
-800 m
Caldera de la Lomilla
Lázaras ignimbrite
Cerro del Cinto
Mines
La Rellana
La Isleta
Cinto ignimbrite Unaltered andesitic intrusions
Altered andesitic
intrusions
74
GEOLOGICAL HISTORY
The Rodalqular Caldera and the Cinto
Ignimbrite
The Rodalquilar Caldera is the larger, with a 4km
by 8km width and an oval shape. Its origin is
related to the thick pyroclastic unit of the Cinto
Ignimbrite, which formed 11 million years ago,
on top of a mass of older mass of andesitic
flows (A), due to collapse of the magmatic
chamber.
Since the collapse of the Rodalquilar Caldera
and formation of the Cinto Ignimbrite (B), the
magmatic chamber refilled itself, and the
ignimbrites filling the caldera bulged outwards,
making way for the present Cerro del Cinto
(a resurgent dome). This phenomenon is very
common during caldera formation processes,
and is called resurgence (C).
La Lomilla Caldera and the Lázaras
Ignimbrite
A new episode of intense eruptive activity gives
way to the formation of the Lázaras Ignimbrite,
simultaneously with the collapse of the La
Lomilla Caldera 9D). this caldera is 2 km in
diameter and is nestled in the Rodalquilar
Caldera.
FORMATION OF THE MAGMATIC CHAMBER
B. FORMATION OF THE RODALQUILAR CALDERA
C. RESURGENCE
The system of fractures generated during
the collapse were later infilled through the
development of a hydrothermal system and by
mineral deposits.
Thin layers of sedimentary and volcanic rocks
were deposited on top of the planar surface of
the Lázaras Ignimbrite.
Rodalquilar Caldera
Filling of the caldera
Cinto Ignimbrite
Collapse
breccias
Ring
dome
Resurgent dome
Resurgence
Pre-caldera volcano
Pre-caldera andesites
Magma chamber
12. Rodalquilar volcanic calderas
75
Resurgence and hydrothermal systems
The end of magmatic activity in
Rodalquilar is marked by the emission
of a series of flows and the extrusion of
andesite on the surface, and the formation
of an intrusion just underneath the
Rodalquilar calderas.This new phase
of resurgence of the magmatic system is
accompanied by a doming of the pile of
volcanic material, the opening of fractures
and the development of the hydrothermal
system, which produced alteration of the
rocks and the formation of mineral
deposits.The age is younger than 9 million
years. In this phase a series of very
extensive fractures formed with a north-
south orientation, that were partly infilled
through mineralization.
Finally, all of the associated volcanic
deposits were covered by marine
carbonate sediments at the end of the
Miocene (latest Tortonian and Messinian),
forming the features of La Molata, Romeral,
Molatilla, etc.
Domes formed on the ring-like margin of the caldera.
The Lázaras Ignimbrite corresponds to a tuff formed
from pumice fragments (dark colours) in a matrix of
fine ash (light colours).
La Molata carbonates on top of the ignimbrites of
the Rodalquilar caldera.
RESURGENCE AND FORMATION OF THE HYDROTHERMAL SYSTEM
D.FORMATION OF THE LA LOMILLA CALDERA
La Lomilla Caldera
Intrusion
Resurgence
Andesites
Hydrothermal system
Sediments
Lázaras Ignimbrite
Reef complex
Contact
12. Rodalquilar volcanic calderas
Carlos Feixas
13. Mining and metallurgical processes in Rodalquilar
76
MINING IN RODALQUILAR
Exploitation of gold in Rodalquilar has been
carried out by means of two very different
methods, such that it relates to extraction as
much as to the retrieval of precious metal.
Mining in the 19
th
century and at the start of
the 20th century, was carried out by internal
exploitation of high-grade quartz veins through
means of shafts and galleries. On the other
hand, mining took a new path from 1956
through the National Company ADARO,
characterised by combined exploitation; interior
workings with high grade material (over 5
g/ton), and cutting or quarries on the outside,
with lower grade material (1 to 1.5 g/ton)> the
mixture of these products allowed intermediate
grades of 3 g/ton to be obtained, optimal for
the type of extraction plant that was working it.
In the last decades of the 19th century and the
start of the 20th century, the recovery of gold
was carried out through means of smelting
furnaces obtaining a lead blende rich in
gold and silver. In the second half of the 20th
century, recovery was carried out through the
operation of electric furnaces, after
concentrating by means of washing with
cyanide solutions.
Mine entrance of 'Lode 340' during the period of maximum
activity in the mining district of Rodalquilar.The
photograph is taken roughly in the 50's decade (Photo,
Evaristo Gil Picón).
Opening of the track that connected the Cerro del Cinto
mine workings with the grading and concentration plant.
This infrastructure already meant an enormous advance
that opened up the possibility of mechanising the quarrying
system (Photo, Evaristo Gil Picón).
77
13. Mining and metallurgical processes in Rodalquilar
QUARRYING METHODS
The extraction workings in the
interior are achieved by following
the auriferous lodes and exploiting
raised chambers (A); the materials
was removed by shafts and
galleries (B).The outside workings
were carried out on small, terraced,
quarry benches (C). The minerals
obtained in this way were mixed
and piled up ready for transport to
the treatment plant (D).
Cerro del Cinto quarry cuttings
completed by ADARO in order to
supply the treatment plant.
The darker structures
correspond to the richest lodes
(Photo, Juan M. Fernández).
Spoil rock
Mineralization
D
B
A
C
78
METALLURGICAL METHODS
The quarried mineral was mixed in a storage
shed (1), and afterwards subjected to initial
crushing in a grinding machine (2), and secondly
in a mill (3). Later it was classified in vibrating
sieves (4 and 5).This product was submitted to
electromagnetic separation (6), in order to
eliminate metals other than gold.Afterwards it
was milled in ball mills (7).The remains were
classified in pressure washers (8) in order to
separate the fines, without gold, and return the
pieces with gold to the mills for grinding. The
minerals concentrated in this way were mixed in
two heavy tanks (9) with a solution of cyanide
(10) in order to subject it to the following
chemical reaction in a medium with pH 9 to 11:
4 Au + 8 CNNa + O
2
+ 2 H
2
O --->
4 Na(CN
2
Au) + 4 NaOH.
In 4 cleaning tanks (11) the mixture of mineral
and cyanide is removed and ventilated in order
to obtain the solution rich in gold, that is
reclaimed in the tank (12).The cyanide solution
is rinsed in tanks (13) and afterwards put
through a filter. Immediately following the
ventilation continues under a partial vacuum by
means of pumps in tanks (14) and, straight
afterwards, is added to zinc dust in a tank (15,
16) in order to activate gold precipitation in the
following reaction:
2 NaAu(CN)
2
+ Zn ---> Na
2
Zn(CN)
4
+ 2Au.
This process is known as “Merril Crowe”.
The precipitate in the tanks comes from a
process of retrieval through precipitation by
means of zinc dust, with zinc content of
between 10 and 40%; it is put through an
electric heater for drying, where the last traces
of humidity are removed. The dry product is
precipitated by acid washing and the precipitate
is removed through filtration.The gold is
obtained by fusion in an electric furnace.
OPERATIONAL RECONSTRUCTION ACCORDING TO THE
METALLURGICAL PROCESSES IN THE ACTUAL
INSTALLATIONS OF RODALQUILAR
Photograph from an era when the mining
installations of Rodalquilar were working.The
photo dates from the 50's decade (Photo,Evaristo
Gil Picón).
System of cleaning tanks in operation (Photo,
Evaristo Gil Picón).
1
2
3
4
5
6
7
8
10
9
9
11
11
11
11
12
13
14
15
16
17
13. Mining and metallurgical processes in Rodalquilar
Juan C. Braga - José M. Martín
79
Field view of
bryozoans and
fossil bivalves
that formed the
limestone
of Unit A.
The remains of calcareous algae and bryozoans
that presently live on the seafloor of the Cabo de
Gata platform produce a sediment similar to that
which formed the limestone of Unit A.
14. The Post-volcanic sediments of La Molata de las Negras
In La Molata de Las Negras sedimentary rocks
are present that record the geological history of
the Cabo de Gata region since the volcanic
activity. Above the volcanic basement a series
of sedimentary units may be observed that
correspond to deposits formed in a small basin
(an inlet or bay), connected with the
Mediterranean, and presently emerged, uplifted
UNIT A
Consists of bioclastic limestones; rocks composed
of the remains of bryozoan skeletons,bivalves, red
algae,starfish, sea urchins and foraminiferans.
These organisms lived in the small marine basin of
Las Negras,joined to the Mediterranean in the
Upper Tortonian-Lower Messinian,around 7
million years ago.The organisms whose remains
form these rocks are similar to those that today
live,and produce sediment,in the marine platform
surrounding Cabo de Gata.The climate in the
region during this period would have been similar
to present or slightly warmer. A small proportion of
above the present sea level. The presence of
coral reefs and oolitic limestones indicates that
during the formation period of units B, C and D
(Messinian), the climate of the western
Mediterranean was warmer than at the present
day and similar to that of tropical latitudes at
present.
theses rocks comprises clasts and grains coming
from the erosion of the volcanic relieves.
A
B
C
BiohermLa Joya
La Molata
Volcánics
D
80
UNIT B. CORAL REEFS
TAfter deposition of the bioclastic limestones
there was a stage of uplift and deformation of the
basin seafloor, in such way that before
the following unit (unit B) was deposited, the
bioclastic limestones were inclines and
underwent erosion (observed in the panorama
and view point from the central part of the
hillside).
In Unit B, formed during the Messinian around
6 million years ago, coral reefs stand proud in
the form of isolated pinnacles (bioherms), such
Tarbellastrea coral colony, one of the components of the Unit
B bioherms.
Slumped blocks of bioherms intercalated between fine-grained sediments in the basin
B.Scattered distribution of
bioherms in the platform
A. Diagram of a reef mound
(bioherm)
Breccias and calcarenites
Hemispherical colonies
Sticks
10 m
100 m
Basin Slope Platform
Laminar colonies
as that which stand out in the panorama, easily
appreciable from this perspective.These reefs
are mainly formed through the in situ
accumulation of the calcareous skeletons of
corals belonging to several genera (Porites,
Tarbellastrea and Siderastrea). Between the coral
colonies and around the pinnacles, algae and
invertebrates lived, whose skeletons also
contributed to the formation of carbonate
sediment. Blocks derived from these reefs, such
as that observed to the left of the large pinnacle,
fell down slope and became mixed with the
marls and mud that were being deposited in the
sea offshore, in deeper regions, situated towards
our left. Marls formed through the settling of silt
from suspension in seawater, and through the
accumulation of the skeletons of planktonic
micro-organisms such as foraminifers, unicellular
algae, and at times diatoms.
DISTRIBUTION AND STRUCTURE OF BIOHERMS IN THE REEF STRUCTURE
14. The Post-volcanic sediments of La Molata de las Negras
81
Microscopic view of ooliths that
formed the carbonates of Unit D.
Field view of stromatolites, with their
typical laminated structure.
UNIT C
Corresponds to a fringing reef that was
advancing from our right towards our left.
Here the corals are almost exclusively Porites
and the coral colonies are surrounded by
foraminifers and encrusting red algae;that in
turn are covered by stromatolites, that is to say,
carbonates that are precipitated (or bound)
by the action of micro-organisms, mainly
UNIT D
Rests on an erosion surface that had an effect on
the reef (Unit C) and removed a large part of its
deposits.This erosion surface is the expression of
the Messinian desiccation of the Mediterranean at
this locality, known as the salinity crisis. Its age is
end Messinian (around 5.5 million years ago).
Unit D is fundamentally formed from stromatolites
and oolitic carbonates.The latter are made up of
microscopic, spherical particles, called ooliths, with
an internal structure of concentric layers of calcium
carbonate. Oolites are presently forming in the
shallow, agitated waters of tropical seas.
Stromatolites are domes or irregular constructions
formed by miilimetre-thick (or less) layers of
carbonate.
DIAGRAM SHOWING ONE PHASE OF REEF GROWTH
cyanobacteria.Towards the sea (towards the
left), the reef gave way to a slope where debris
coming from its destruction accumulated.
The grain size of this debris is segregated
downslope,in a way that it continually
becomes finer. Between the reef debris,other
organisms grew, such as calcareous green
algae (Halimeda) and bivalves.
N-S
Distal slope
Lagoon
Bioclastic breccias
10 m
0
10 m
Calcirudites
Calcarenites
Calcilutites
Coral blocks
and breccias
Reef crest
Coral thicket
Coral pinnacles
Proximal slope
Talus
slope
Reef
framework
laguna
14. The Post-volcanic sediments of La Molata de las Negras
Carlos Feixas
15. Bentonites of cabo de Gata
82
GENESIS AND NATURE
OF BENTONITES
Bentonite is a rock composed of minerals
from the clay group. Their internal structure
of superimposed layers of different chemical
composition defines their key characteristic:
their capacity to absorb a quantity of water
several times greater than their own volume.
This is produced through storage of fluid
in the spaces that exist between the different
layers.
Bentonites originate from the alteration
of volcanic rocks, also through processes of
hydrothermal alteration (rise of hot solutions
through fractures) or also through weathering
alteration (due to the action of meteoric
water).
The special composition of the Cabo de Gata
volcanic complex means that within it the
greatest concentration of bentonite deposits in
Spain formed. In fact, they constitute the only
exploited industrial minerals that exist within
the Natural Park.
The Cabo de Gata bentonites are by nature
around 75% to 95% Calcium-Sodium-
Magnesium types, and the rest of the rock
consists of other types of clays and small
quantities of other minerals originating from
volcanic rocks.They display various colours,
from reds, greens, yellows and blacks, to whites.
The deposits have an irregular and stratified
morphology.
200 m
200 m
Volcanic rock
Descent of cold meteoric water
Increased heat
Ascent of hot hydrothermal solutions
Bentonite
Alteration of volcanic
rocks to bentonite
Increased heat
SIMPLIFIED DIAGRAM OF BENTONITE FORMATION
83
15. Bentonites of cabo de Gata
Bentonite quarry exploited in an intermittent fashion in the
Serrata de Níjar. The bentonite masses that display some
colouration hold less commercial interest than those that are
white.
Quarrying of white bentonite in the area of Morrón de Mateo.
The main areas of quarrying within Cabo de
Gata are found in:
Cantera de Los Trancos (A)
Cortijo de Archidona (B)
El Morrón de Mateo (C)
Undifferentiated Recent detritus
Pliocene sand and conglomerate
Marls, clay, sand and carbonate
Gypsum
Carboneras
Las Negras
Rodalquilar
Fernán Pérez
B
C
A
San José
Cabo de Gata
5 Km
Serrata
Fringing reef, marl and bioclastic carbonate
Bioclastic carbonate
Volcanic rocks
Betic substratum
DISTRIBUTION OF QUARRYING. GEOLOGICAL MAP OF THE CABO DE GATA AREA
84
Bentonite mining is carried out through an
open cast quarry method. In a modern quarry
the following activities are undertaken:
Conditioning and preparation
The discovery of productive layers takes place
with the help of excavating machines or
mechanized tractors.
Extraction
Once the surface is cleaned off, quarrying is
carried out by cutting down benches
lengthwise along the face, with a height of
about 10 metres and a length close to 50
metres.
Drying and classification
The material quarried in this way is spread out
across large areas or “heaps”, cleaned of
impurities and classified by qulaity according
to the use for which it is destined.
Storage
The dried and classified material is stored in
large uncovered piles ready for transport to
treatment plants or for direct sale.
The mineralized body might be covered by non-mineralized
rocks that need to be removed for quarrying.
Los Trancos quarry is the principal bentonite mining concern
in the park.The extent of the quarry benches can be observed,
taking the lorries as a scale.
Volcanic rock
Bentonite
Extraction Pile
Drying Classification
Conditioning
and preparation
15. Bentonites of Cabo de Gata
85
USES AND APPLICATIONS
Bentonite clays, due to their physical properties,
are utilised in many industrial fields.
In the smelting industry they are used, along
with siliceous sand, to prepare the mould of
manufacture parts, in that they are capable
of fusing together the sand, without altering
the composition of the cast.
Addition to cements allows mortars to remain
fluid for a longer period of time, for which its
use is essential in special cements.
As an integral part of drilling mud. Due to its
addition, the viscosity of the drilling mud
increases and is capable of pulling out broken
components more easily. Additionally, it is
capable of covering and keeping the walls of
the borehole intact when drilling of the
borehole finishes.
Its addition to powdered irons minerals means
that they can be recovered in a profitable way
from smelting.
Their capacity for absorbing water and ionic
exchange means that they can serve as
cleansing aids and fertilizers, also as
discolourants and clarifiers of wines and oils.
Properly compacted it is an excellent
impermeable material, used to this end for
holding back and securing residues in storage
containers and potentially contaminant
substances.
Characteristic field view
of bentonite clays: white-
coloured powdered
masses, greasy to the
touch and very plastic.
15. Bentonites of Cabo de Gata
Juan C. Braga - José M. Martín
86
In the outcrops of Cañada Méndez,
exceptionally exposed carbonate sediments
generated in temperate and shallow marine
platforms, with temperatures and salinities
identical to the modern Mediterranean, are
exposed. They are located directly on top of
volcanic rocks 9.6 million years in age. At the
very base of the sediment succession, just
above the volcanics and immediately beneath
the carbonates, sand of volcaniclastic character
appear (that is to say, supplied by erosion of the
same volcanic rocks) with a few marine fossils
(essentially the remains of shells).
Two different carbonate units are represented.
The lower stands out here as the most
important, known informally as the red unit
due to its characteristic colour. It is Lower
Tortonian in age, roughly 9 million years old.
These carbonates are bioclastic in nature.
They consist of the abundant, highly
fragmented remains of calcareous marine