The Cardener valley that is wide in the alluvial plain of Les Hortes and Reguant suddenly narrows in El Fusteret. This apparently capricious relief results from the complex geological structure of Súria that Cardener river crosses
In Súria, in a sequence from northwest to southeast although not exactly in line, the following, enchained geological structures can be identified:
– Northern or Ribera de Coaner anticline
– Mig-Món fault – Balsareny anticline
– Tordell fault – Súria-Castelltallat anticline
– Súria diapir or diapiric anticline
These tectonic structures have a common origin in the plasticity of the Cardona saline formation in the underground and, partially, in the compression of the Pyrenean orogeny.
Súria salt diapir is comparable to the better-known Cardona diapir, but the top of te Súria diapir is fully covered by Quaternary sediments brought by Cardener river. The top of the Súria diapir spans at least on Pla de Reguant where from time-to-time sinkholes appear and, on the left bank of the Cardener, on the area of El Salí well where, in 1912, potash was discovered among the sodium salt of the Cardona geological formation; soundings would be needed for a more accurate boundary. The rise of the salt tilts the strata of other rocks surrounding the diapir that, as a whole, arrange as anticlinal fold.
The small stream of Camprubí or Fusteret shows the tilt by the rise of the salt in Súria diapir strata. The stream of Camprubí is a tributary on the left bank of Cardener river. It cuts a deep valley perpendicular to that of the river, from the southern end of the Súria salt mining waste dump field to the Fusteret neighbourhood. The stream of Camprubí outcrops mudstone and limestone strata of the Sanaüja lacustrine complex (Priabonian, Upper Eocene) which are here called Súria geological formation, and which are deeply tilt towards the southeast by the diapiric uplift. These rocks of the Súria formation are older than the red mudstones and sandstones of Artés geological formation. Therefore, stratigraphically they are placed below, but the diapir pushes them to outcrop. If moving from the stream of Camprubí to the southeast in the direction of the tilt of the strata, rocks become more modern.
The images that are picked looking east -so with north on left side and south in right- and arranged in a sequence going Camprubí stream up from El Fusteret neighbourhood display the tilt strata on the southeastern side of the Súria diapiric anticline. The light-coloured, squared and consistent rocks are lacustrine limestones. The 1st image is in the Súria-Manresa FGC railway next to the Súria waste disposal site, the 2nd and 3rd between the railway and the spring of La Serra, and the 4th between the spring of La Serra and the salt mining waste dump field.
In addition to the rock layers, the 4th image displays the stream of Camprubí. In rainy seasons, brine coming from the salt mining waste dump field flows by the stream of Camprubí. The overall tilt of the strata towards the southeast drives most of the brine that is sourced in the huge salt waste dump field and filtered through the ground towards this direction to reappear in the stream of Camprubí, rather than towards the northwest, thus to the stream of Tordell.
[photos Jordi Badia]