Geological and Lithological Diversity of Spain
Geological Evolution of Spain
1. Geological Evolution. Lithological Variety.
Geological Evolution
Archean or Cryptozoic (Precambrian)
At the end of the Precambrian time, there was hardly any land in the area of what we know today as Spain. This area was located between two continental plates, an African one (Gondwana) and another Paleoeuropean one (Laurasia). Between them was located the ancient sea of Tethys. In the Precambrian Archean era, orogenic movements succeeded, which had little impact on the Peninsula. Cores have been found from this era in Galicia, in the area of Cangas de Narcea (Asturias), in the northern part of the Montes de Toledo, and the western Central System.
Primary or Paleozoic
After the Precambrian, a process of sedimentation began, and the Caledonian Orogeny produced little resonance on the peninsular sun and only affected some areas of the Galician region. In the Carboniferous period, a great orogenic capture began, known by the name of Hercynian. Strong lateral pressures emerged from the seafloor, forming mountain ranges belonging to the European Hercynian system. In the space now occupied by the peninsula, this system had a NW-SE direction, from Galicia to the current Guadalquivir Valley. During the Paleozoic, a range of folding stood, which had already been razed in the late Paleozoic, becoming emerged land in a base whose surface erosion is called a peneplain; this Hercynian block was slightly tilting toward the Mediterranean, i.e., opposite to the actual western plateau. Granitic rocks outcrop that determine an area of predominantly siliceous land. Coinciding with the end of the Hercynian cycle, there was intense magmatic activity: volcanic and plutonic intrusions.
Secondary or Mesozoic
The Secondary or Mesozoic Era is a period of tectonic calm. This calm promotes the erosive action raging on the ridges in the Paleozoic land, making them irrelevant or a peneplain. What there was in the Mesozoic were movements, i.e., sinking or submergence of some land and elevation or rise of others. These movements, in turn, cause the rise or fall in the level of seawater. We talk about marine transgression when water moves over land and regression when it retreats. In the space where the Pyrenees now stand and where the Béticas were then placed, two deep ocean trenches or geosynclines continuously piled sedimentary materials and organic matter. The salty ocean water and the release of carbon from accumulated organic matter resulted in a chemical process forming carbonate rocks such as calcium carbonate. The land surface surrounding the cited geosynclines were: the base of the plateau and some ancient massifs, remnants of Hercynian folding.
Tertiary or Cenozoic
From the Tertiary develops the Alpine orogenic cycle or Alpine orogeny, having maximum activity in the Miocene and Pliocene periods of the Alpine-Himalayan paroxysm. The Tertiary compressed and lifted the sediments deposited in the Pyrenees and Bética, while sinking the northeast of the old Paleozoic massif in the Ebro. This isostatic process contributed to the surfacing of the Pyrenees, the Béticas, and the relief of the Balearic Islands. The plateau began to swing toward the Atlantic Ocean and is structured around her mountain ridges. The formation of the Catalan Cordilleras was also completed. The valleys of the Ebro and Guadalquivir were marine arms that slowly filled in with base materials and sediments. The Paleozoic base of the Plateau failed, folded, fractured, and broke, resulting in a relief rife with flaws. The Galaico-Leonese massif corresponds to a fracture system that was subsequently attacked by erosion. Other areas were plunged into the resulting block interior depressions or sedimentary basins that form the North and South Submeseta. In contrast, the Montes de Toledo owes its current appearance to differential erosion and rejuvenation of the underlying relief. In the relief units outside the plateau and ridges, some other types of tectonic structures appear: the Alps and Saxon-type structure in alternating folds and faults.
Quaternary or Anthropozoic
The post-Alpine tectonic is developed, which “ends” with the geological evolution of the peninsula and that is the current highlight. It is the final slope of the plateau to the west, determining the orientation of most peninsular rivers to dominate this stage. In this stage, epirogenic movements that cause progress or setbacks in ocean waters and shoreline correcting wide gulfs are produced. Permanent settlement of the rivers and the erosive force of those transported and deposited amounts of coarse debris that filled the depressions and coastlines. As a result of alternating glaciation, Quaternary climates are affected. The peninsular ridges are less important than those of central Europe. An impact of Spanish glaciation is their impact on the shaping of relief due to river erosion. In cold periods, the river flow decreases by ice; with rising temperatures, increased river flow and its erosive force.
Lithologic Variety of Spain
The crag can be divided into four basic soil types: siliceous, limestone, clay, and volcanic, the latter affecting only the Canary Islands. In contrast, the Balearic Islands are similar lithologically to the type of materials on the peninsula. The type of material is of great importance in shaping the relief.
Siliceous Land
Located in the oldest areas in the Precambrian and Paleozoic, Spain consists mainly of granites, gneisses, slates, and consistent quartzites. The siliceous rock was covered with sediments that were washed away by erosion after the action of water, which facilitated the outcrop of these materials, which are the oldest in the peninsula, also partly decomposed, emerging modeling of rounded shapes, domes or bowls, and caballeros stones, and a scrum in the cold areas. In cold areas, water percolates through the cracks and, on freezing and becoming ice, acts as a wedge, cracking and fragmenting the solid rock. The result is a landscape of vertical walls and edges of crests and needles; fragments of stones rolling down the hill are uprooted and are accumulated at the foot of the mountain. The siliceous land of Spain is mostly located in the west of the peninsula, from Galicia and the western part of Asturias to the Sierra Morena, with discontinuous small patches in the Pyrenees, Catalan Cordilleras, Sistema Ibérico, and Cordillera Penibética.
Limestone Soils
Dated mainly in the Mesozoic. Abundant sedimentary formations of marine origin. In addition to the limestone crag, there are conglomerates, sandstones, and marls. The most characteristic modeling of the limestone soils is karst, a very complex relief that comes from the calcium carbonate rock composed mostly of this. We are facing an erosion of the water twice: on the one hand, the dissolution of the limestone in the interior, and, second, mechanical wear on the surface. It can be summarized as:
- Lapiaz (or Lenar): Surface with deep grooves and sharp edges where the water penetrates into the interior.
- Gorges, canyons, or ravines: Depressions that have been shaped where the karstification process affects the entire thickness of the limestone crag.
- Dolina: Surface cavity caused by the sinking of the limestone strata.
- Caves or chasms: Subterranean formations.
- Poljes: Large flat-bottomed and elliptical depressions with reddish ground.
The available limestone land on the map of the peninsula follows the shape of the letter Z reversed: the upper tracing starts from the Catalan coast and continues through the Pyrenees and the Cantabrian Mountains to Asturias, then down the Iberian, reaching the Béticas, and ends in the Gibraltar Strait.
Clay Soil
Spain’s clay soil is formed by late Tertiary and Quaternary sediments. They are modern rock, and sometimes impervious as clay, that have been affected by orogenic movements; therefore, they are essentially flat land, horizontal, easy, and rapid erosion due to the softness of the areas where they alternate. In areas with long dry periods between rains and sparse vegetation, it is a landscape of erosion where the creek has become the initial surface in a maze of narrow slits, the cárcavas. They are located in the southeast peninsula and in the Ebro Valley, also appearing frequently in various parts of the mainland.
Volcanic Terrain
They correspond to the volcanic island of the Canary Islands in Spain. Volcanic activity from the Miocene to the present is the origin of the Canary archipelago. On the peninsula, there are small and isolated patches of volcanic terrain in southern Almeria and the Submeseta.
Differential Erosion
Separate erosive agents act, giving rise to a variety of relief in line with the provision of strata or the hardness of them. For example, the alternating rugged crag above the horizon with less resistance on the flanks below leads to a hill or a mountain witness. More important are the reliefs on coasts.