Geological Eras and Landforms of the Iberian Peninsula
Geological Eras of the Iberian Peninsula
Paleozoic Era: Began 570 million years ago and lasted until 230 million years ago. During this era, two plates, or continents, were separated by the Sea of Tethys. Two orogenies occurred: the older Caledonian, which barely affected peninsular space, and the Hercynian, which developed during the Carboniferous period. As a consequence, a great mountain range arose in a NW-SE direction, becoming a massif called the Hesperian Massif, which occupies much of central and western Iberia. Additionally, the Ebro Massif emerged to the northeast, along with the Aquitaine Massif to the north, and the Betic-Rif Massif to the southeast.
Mesozoic Era: Spanned from 230 to 65 million years ago. This was a phase of erosion and sedimentation. Epirogenic movements, slow vertical shifts of the Earth’s crust, caused fluctuations in sea level, resulting in stages of marine transgression and regression. Erosion destroyed the older layers of sediment, depositing solid limestone. Typical rocks from this era include limestone, marl, and sandstone.
Cenozoic Era: During the first half of this era, the Alpine Orogeny folded Tertiary sediments deposited during the Mesozoic, forming the Cantabrian Mountains, the Pyrenees, and the Betic Mountains. Material eroded from these mountain systems filled the Ebro Basin and the Betic valley, uniting the Pyrenees and the Betic system with the peninsula. At the end of the Tertiary period, the Alpine Orogeny caused the Iberian Massif to tilt. Orogenic stress fractured the massif, resulting in the Central System and the Montes de Toledo. The Balearic Islands separated from the mainland, and the Strait of Gibraltar formed.
Quaternary Era: The Quaternary covers the last million years of the 65 million years of the Cenozoic Era. During this period, ice ages occurred, alternating with warmer interglacial periods. These formed cirque glaciers and valley glaciers. The current form of the mountains developed, and low areas were filled with sediments eroded from the mountains.
Structural Landforms
Folded Structures
When compressive forces act on plastic materials, undulations of the strata, known as folds, occur. There are two types of folds based on the age of the core materials:
- Anticline: The fold is formed by inclined strata from a central axis. It is convex, and its core contains the oldest materials.
- Syncline: The strata are inclined toward the central axis. It has a concave shape, and the materials in its core are the youngest.
These folds can create a Jurassic relief if anticlines form the raised structures and synclines the depressed ones. Conversely, a relief is formed if synclines are high and anticlines form the valleys.
Faulted Structures
Faulted relief occurs when rigid materials undergo tectonic pressure and, unable to bend, they break. A fault is a tectonic break in a rock mass, accompanied by displacement. This differs from a fracture, which does not necessarily involve movement. When faults border a sunken area, they define a graben, whereas if they border a raised area, they define a horst. If the uplifted blocks correspond to mountains and the valleys to the depressed areas, the resulting relief is referred to as Germanic.
Types of Landforms
Karst: Formed by the dissolution of limestone, mainly due to the action of water. For karst relief to develop, a large expanse of massive limestone is necessary. Some features appear on the surface, such as lapiaces, dolines, and poljes. Others are underground, including galleries, chasms, stalactites, and stalagmites.
Granite: Develops on fractured granite where water erodes, leaving behind softer and harder areas. This creates landforms such as tors.
Fluvial (Inland): Rivers erode the surface, breaking up and dissolving rock. Most erosion occurs in the upper reaches of a river as it flows through mountains, creating valleys, canyons, and waterfalls. As it flows through areas of low slope, it usually forms undulating curves called meanders and abandoned meander bends called oxbow lakes. In its lower course, the river deposits the transported material, forming features such as deltas.