Geoparque Unesco

Stratigraphy and the study of sedimentary rocks

Turbidic Channel in Arro

Sedimentary rocks of deep marine origin.
Municipality: Aínsa-Sobrarbe

To access the PIG (Point of Geographical Interest), take the N-260 road from Aínsa towards Campo, and after reaching Arró village (Km 426), turn and take the road leading up to Los Molinos. After approximately 4Km, we reach the outcrop, past the Los Dolores Hermitage, on the right hand side of the road. On the left hand side, opposite the outcrop, there is a car park

Characteristic Turbidites in the “Turbidic Channel in Arro”.

Geological Context

Rocks in the surroundings are sediments of deep marine environments (turbidites) of the south-central Pyrenean Eocene Basin (stretching from the Lutetian to the Bartonian stage). More specifically, it belongs to the turbidic system of Arro, which is framed by the Fosado System on its base, and the Gerbe System on its top. These systems, among others, form the system known as Hecho Group (Mutti et al., 1972). The Arro System was developed during the Upper Ypresian and it is the first stage of sedimentation rich in sand of the Eocene turbidic Basin.

Along the eastern sub-basin of Aínsa and in this area of Geological interest, this turbidic system is formed by facies of turbidic channels and its characteristic filling of deposits..

Geological Significance

The turbidic systems located in different sedimentary basins all around the World currently have a high economical value. For instance, more than 80% of major productive crude oil fields are developed within this type of sedimentary system. For this very reason, understanding the formation of turbidic systems and their features as reservoirs is highly important in order to develop exploration strategies. Thus, turbidic channels and other associated features are currently the target of a lot of crude oil research. Channel systems are frequently observed in this kind of study, and examples such as this provided by these geotopes are useful to suggest new hypothesis for crude oil geologists and other scientists, in order to better understand unexplored counterparts in their studies.

At this spot, we can also observe the physical expression and the facies, on a large scale, of the filling and the sandy growth of a canyon, in this case, the canyon known as Charo-2, within its structural frame. Deposits formed from unstable deposits, such as debris flows, hyper-concentrated flows and dunes stand out.

Atiart Canyon

Cut of a submarine canyon.
Municipality: La Fueva

In order to access the point of geological interest, first you must reach the houses 700m before Fosado. Once there, park your car and walk 500m heading west across the fields until you reach the gorge, where you will find an outcrop cut by a submarine canyon.

Outcrop cut by a submarine canyon.

Geological Context

At the south of the Ferrera Mountain range, we find a system of dipping faults (known as the Cabezonada-Arro by some authors) from the Ypresian-Lutetian stage. The Atiart dipping fault belongs to this system. It is an overlapping dipping fault system cutting the topographic surface from NNW-SSE to NW-SE.

These structures strongly determine sedimentation in this area of the basin during the Ypresian stage, since each of them give way to a ramp where a series of erosions are marked, overlapping the turbidic system in Torla-Fosado. Some of these marks, which are very large, can be observed at this point of interest.

Geological Significance

The fact that the sedimentation process and the tectonic activity overlapped during the same period of time, which can be easily observed in the terrain, allows us to study the complex dynamic evolution of this area.

The dipping fault in Atiart has an upper block formed by platform facies with fauna in situ, which belongs to the Castigaleu group and to the Castisent 1 base. The lower block is formed by proximal turbidites.

The Atiart dipping fault is important because it has been traditionally used as a reference for dating the Cotiella mantle formation (Ypresian stage).

Thanks to the study of this canyon, we can answer some questions about its large scale submarine erosion features and about the details of their faults, erosion, and the value of its contribution to related turbidic systems.

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