Geology

Geological highlights

Structural Geological. The Orígens Geopark is located along the ECORS Pyrenees seismic profile. A geophysical profile made through the Pyrenean mountain range that runs parallel to the Valley of the Noguera Pallaresa river. At the time, this profile was a very significant milestone at international level for modern geology.

Sedimentology and stratigraphy. It is worth noting the carbonate platforms of Vilanoveta and Les Collades, located between Sant Corneli and the Serra de Carreu, recognized as sites of international relevance; the Ilerdian stratotype, an international-level type section of a part of the Paleogene, located east of Tremp; the deltaic deposits of the Tremp and Ager basins showing exceptional outcrops; and  the  synorogenic conglomerates recording the Pyrenees uplift recorded on the mountains of  Collegats, Gurp, Pessonada or Comiols.

Hydrogeology. The territory has numerous groundwater springs associated with its particular geological structure. Highlights include the Basturs lakes, west of Isona, showing a characteristic dome-like morphology alike landforms identified on Mars. It is also worth mentioning the Montcortes lake, associated with sackung type vertical fractures related with dissolution of Triassic evaporites or the salt spring in Gerri de la Sal, also linked to the dissolution of evaporitic rocks.

Edaphology. Soils, often underrepresented in Geopark’s heritage, have an essential role on the management of ecology linked to human activities. The Orígens Geopark pays special attention to soil heritage as a non-renewable natural resource, as it plays a key role in the dynamics of ecosystems and landscape, as well as it supports of socio-economic activities and cultural heritage. The Pyrenees Soil Interpretation Centre in Tremp has a permanent exhibition of soil monoliths taken from soils of the Pyrenees.

In 2000, the Catalan Government listed the main geosites and geozones throughout the Inventory of Areas of Geological of Catalonia.

Geological history

Geopark Orígens is located on the southern flank of the Pyrenees.

The Pyrenees consist of an alpine folding mountain range resulting from the continental drift of the Iberian plate during the Mesozoic and its final collision with the European plate during the Cenozoic.

This territory presents a relief shaped by a series east-west trending mountain ranges and basins which orientation is determined by the arrangement of several thrust sheets. At the same time, it presents the geological record of more than 500 million years (Ma) of geological history.

The Axial Pyrenees, in the northern part of the Geopark, shows the oldest rocks of this mountain range. The structural configuration of this area is characterized by antiformal stacking of the thurst sheets associated with the alpine orogeny, namely, Orri, Rialp and Nogueres. The rocks that make them up, mostly of Paleozoic age, outcrop in the Vall Fosca area. These were previously intensively deformed by the hercinian orogeny and some are also affected by the intrusion of batholites and the associated metamorphism of the contact rocks.

The pre-Pyrenees, south of the Axial Zone, is characterized by tectonic structures known as the south-Pyrenees upper thrust sheets formed mainly by Mesozoic and Paleogene bedrock. These tectonic structures consist of three main thrust sheets that from north to south are called Bóixols, Montsec and Serres Marginals, shaping mountain ranges with an east-west orientation. Simultaneously at the misé-in-place of these thrust sheets, the Tremp, Àger and Oliana basins were formed. These record the sediments, structures and paleoenvironments preceding, contemporary and subsequent to the different tectonic episodes reflecting the formation of the Pyrenees. In parallel with the Pyrenees uplift during the Eocene and Oligocene, the changing relief generated large alluvial systems that were installed along the mountain range foothills, resulting in the deposition of the conglomerates that shape the mountains of Collegats, Pessonada, Gurp or Comiols.  Its spatial distribution and characteristics are conditioned by the Pyrenees tectonic evolution and have allowed to establish and reconstruct the regional sedimentary and structural context.

The subsequent climatic instability during the Quaternary, characterized by several glaciations, conditioned the expansion of glaciers in the topographically higher areas, modelling their topography and accentuating the incision of the drainage network dominated by the rivers Noguera Pallaresa, Noguera Ribagorzana, Segre and Flamisell. These processes generated the spectacular gorges of Mont-Rebei, Terradets or Collegats. The Quaternary sediments in the Pyrenees consist of glacial, torrential, alluvial or slope deposits. Other significant Quaternary sediments are the tufa deposits recorded in the Basturs lakes and El Mont de Conques area.

Geological Map

Geological map of the Orígens Geopark (Lleida Province, Catalonia). Made by Cartographic Institute of Catalonia (2015).

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