The Tabernas Basin
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The Tabernas Basin Geological Features GEOLOGICAL FEATURES AND EVOLUTION J. C. Braga - José M. Martín SIMPLIFIED GEOLOGICAL MAP AND STRATIGRAPHICAL SUCCESSION FOR THE TABERNAS BASIN Taken from Weijermars et al, 1985 AGE LITHOLOGY DEPOSITIONAL SETTING ALLUVIAL FANS. Conglomerates and sands FILABRES PLIO-PLEISTOCENE PLIO-PLEISTOCENE FAN DELTA and DELTA. Conglomerates and sandstones PLIOCENE Gypsum RESTRICTED BASIN NO Tabernas Geological Section MARINE BASIN Seismite Marls Rambla de Tabernas MESSINIAN Filabres Desierto de Tabernas Alhamilla Seismite Rambla de Tabernas Cerro Geological Section Alfaro Yesón alto CN-340 Alfaro (742 m) Reefs ALHAMILLA Seismite Geological Section (Gordo SE Megabed) Baños SUBMARINE FANS. Marls, sandstones and turbidites Río Andarax SERREVALIAN-TORTONIAN SERREVALIAN-TORTONIAN Pechina COASTAL PLATFORM. Conglomerates GÁDOR BETIC BASEMENT Schists, quartzites, phyllites and marbles 137 GEOLOGICAL FEATURES AND EVOLUTION About eight million years ago (in the Miocene) extensive sedimentary package that the rivers intermontane basin between this new relief, to the configuration of emerged and submerged eroded from the emerging relief.This material, the south, and los Filabres, to the north. land around the littoral margin of Almería was comprising alternations of marl and sand, are similar to that of today, but not identical: the sea amongst those which have, to a great part, In this depositional environment, marine at times, extended through the territory of the Tabernas fashioned the eroded landscape of the Tabernas lagoonal for others, the deposition of limestones, Desert up to the foot of the Sierra de los Filabres Desert. marls, muds and sands, and enclosed gypsum, in whose borders fossil coral reefs of this age continued up until around 2 million years ago (in formed, reliably marking the position of the Later, some 7 million years ago (in the Upper the Pliocene, almost at the start of the Quaternary), ancient coastline. In the slopes of this ancient Miocene), the Sierra Alhamilla was uplifted, when the sea ultimately retreated, leaving the sea, submarine fans deposited a thick and closing a narrow and elongated, marine sediments exposed to the action of erosive agents. DISTRIBUTION OF EMERGED LAND 8 MILLION DISTRIBUTION OF EMERGED LAND 7 MILLION DISTRIBUTION OF EMERGED LAND 4 MILLION YEARS AGO YEARS AGO YEARS AGO 1 2 3 Vélez-Rubio Guadix Huercal-Overa Vera Guadix Alcalá la Real Baza Almanzora Vera Corridor Huercal Sorbas Tabernas Sorbas -Overa Tabernas Guadix Carboneras Granada Vera Carboneras Berja Alhama Sorbas Berja Almería Tabernas Carboneras Adra Adra Almería La Tórtola Berja Motril Almería Adra Andarax Corridor Nerja Present Day Coastline Present Day Coastline Mediterranean Sea Present Day Coastline Western Basin Reefs Braga, Martín and Quesada 138 GEOLOGICAL FEATURES AND EVOLUTION The Tabernas Basin has been configured since then as a long and narrow depression Graphic Scalebar (approximately 20 km in length and 10 km in maximum width) VERA between the Sierra de los SIERRA DE LOS FILABRES Filabres and the Sierra Alhamilla, situated to the west of the SORBAS CABRERA Sorbas Basin and in continuation TABERNAS with it. ALHAMILLA CARBONERAS NÍJAR SIERRA DE GÁDOR ALMERÍA CABO DE GATA Neogene Sediment Neogene Volcanic Rocks Betic Substratum 139 THE ERODED LANDSCAPE The soft nature of the sediments that have filled storms.Within them the riverbeds are very the Tabernas Basin from 10 to 8 million years broad and well-fitting, with steep and vertical ago, the slow and continual uplift of the sierras sides, although they generally appear dry. that border it, and the arid yet stormy climate that has characterised this territory for a good In the soft and readily eroded foothills, the part of the more recent Quaternary, have stream produces grooves, which grow towards conditioned the model for one of the most rills and runnels, and terminate in furrows spectacular erosive landscapes in continental separated by sharp crests.This landscape Europe. is given the name ‘Badlands’,alluding to its difficulty for being worked or put into A geological landscape reminiscent of Africa agricultural production. that has captured the attention of geologists, naturalists, geomorphologists, photographers Turbidite sequences in the Tabernas Desert . and film producers for generations: the Tabernas Corridor, the most southerly desert in Europe. This spectacular erosive landscape is not, therefore, attributable to human action, but to the concurrence of a series of geological factors and its own natural evolution, upon which the peculiarity of being one of the most important scientific and educational places for the study and comprehension of the natural phenomena of erosion and desertification in the Mediterranean Basin has been conferred. The temporary and torrential character of precipitation generates a rambla type of fluvial system, normally dry, but which discharges a great amount of sediment and water in an Eroded landscape of the almost instantaneous manner during strong Tabernas Desert. 140 Evolution of the Drainage Network Antonio Martín Penela 4 MILLION YEARS AGO 2 MILLION YEARS AGO FILABRES The eroded landscape of the Tabernas desert is During the latter stages of the Pliocene, around a consequence of the geological evolution of Tabernas 2 million years ago, the elevation of the the region over the length of the last 4 million mountainous relives and the fall in sea level years, and more specifically, of its tectonic and Pliocene continued, since then practically all of the Coastline climatic evolution in the past 150,000 years. ALHAMILLA Province of Almería has become emerged. In the Lower Pliocene, about 4 In this period, areas subjected to erosion and Mediterranean Sea million years ago, a fall in sea level areas of sedimentation were differentiated. took place simultaneously with a The latter were represented by small lakes strong uplift of the adjacent relieves, installed in the most low-lying zones, and GÁDOR Sierra Alhamilla, Sierra Gador and alluvial fans in those that material coming from ent Day Co Almería res ast Sierra de los Filabres, already emerged P lin the recently-formed mountainous massifs was e and with some elevation. As a consequence, deposited. broad surfaces of the region became emergent FILABRES and important fan deltas developed that The main drainage during this period collected water coming from the Sierra de los were made up of a fluvial system Filabres. One of these is the precursor of the of close appearance to the modern River Andarax, that already occupied Tabernas modern River Andarax, which was a similar position, although its river mouth forming an important delta in its (outlet) is somewhat displaced to the north, outlet to the Mediterranean. ALHAMILLA towards the position of La Rioja. Palaeocoastline GÁDOR Present Day Coastline Almería 141 Evolution of the Drainage Network THE PRESENT DAY FILABRES The establishment of more arid climatic conditions in the Upper Pliocene, led to the total desiccation of lacustrine areas and almost Tabernas total inactivity in the alluvial fans. It is since this period when erosive processes clearly became dominant in the region, initiating the sculpture of the modern landscape and the ALHAMILLA Distribution of streams in a section of the development of the fluvial network, which Rambla de Tabernas.The high drainage deeply excavated the Neogene and Quaternary density (increased number of streams per unit of surface area) is typical of gullied areas. sediments in the Tabernas Basin.The Andarax River continued as the principal river, in which all the water from the basin is drained, even if in reality the water and sediment carried by GÁDOR it to the sea is quite scarce. Since the late Pleistocene, at a time when the modern configuration of the fluvial network Almería was initiated, the factors that have allowed its strong incision, the development of badlands, and its general evolution have been: tectonics, the nature of the material, weak and easily- eroded lithologies, and the climatic conditions. Characteristic features of the present-day erosive sculpture in the Tabernas Desert. 142 Ramblas Antonio Martín Penela Ramblas constitute the main arteries of majority of cases, circulating only water from of factors such as progressive uplifting of the the drainage network in the Tabernas Basin. surface currents originating as a result of region, the arid and stormy climate, the soft and Through these the transport, and also the storms.The erosive processes in the ramblas erosive nature of the material. deposition, of particles coming from the erosion take place during floods, excavating laterally of the basin and the surrounding sierras is along the length of its margins. The rivers of the Tabernas Basin are continually achieved. down-cutting, trying to reach their equilibrium During the last 100,000 years the ramblas have with the base level of the sea.The occasional They comprise braided fluvial systems, evolved, deepening and widening their river torrential precipitation and sparse vegetation characterised by the development of numerous beds, starting to form valleys almost 100 metres cover allows an intense water-bourne erosion sandy bars between which multiple channels deep and river courses whose width exceeds a that unleashes an intense processes of incision, are initiated during flood periods.The flow of hundred metres.This important development of with a dense drainage network of dendritic water in the riverbed is ephemeral, in the rambla valleys is a consequence of a combination type, and abrupt and unstable hillsides. 1 2 3 BASE LEVEL BASE LEVEL BASE LEVEL At the end of the Pleistocene incision of the fluvial network was In the Holocene the rivers excavated deeply in order to reach their equilibrium with base level. initiated.The ramblas adopt a meandering morphological pattern. It produced a generalised incision of the river courses. 143 Mechanisms of erosion in the desert: currents Antonio Martín Penela RAINDROP IMPACTS SHEET EROSION Raindrops tear away Hardened ground particles of the ground that favours the initiation are transported down slope of sheeted flows, by saltation.This process helped by the slope, hardens the surface.