The folds of the strata –anticlines and synclines with all variations and combinations you may think- change enormously in scale, from folds of kilometric length whose interpretation is often difficult in the overgrown or overly artificialized landscape, to microfolds of metric or centimetric size that can be seen closely in full. Sometimes, not always, the microfolds reproduce at small scale the large folds of the same territory.
The long banks of roads and railways often reveal microfolds that would otherwise remain hidden. On the other hand, the increasing difficulty to stop one car on a roadside and the trend to cover slopes with metal nets to prevent from falling stones on the road or on the railway hinder the observation of the microfolds.
The slope of the C-16 motorway in the Serrat del Maneló, in the southeastern part of the Manresa municipal area, opens one beautiful microfolds area. Here, one pack of roughly one meter thick of alternating narrow layers of sandstone and mudstone twist on a sinusoidal shape, while the strata above and below, apparently similar in composition and age of sedimentation, remain straight.
Tectonic compression is the main cause of fold formation, at any scale; although, the interpretation of the origin of the microfolds in the Serrat del Maneló that are packed into a flat stratigraphic sequence remains as a mystery. There is speculation whether an earthquake or a tsunami that would have shaken the superficial and unconsolidated sediments is in the origin of the microfolds outcropping in Serrat del Maneló.
In any case, microfolds like those that are discovered by the road C-16 in the Serrat del Maneló contributes to the understanding of the geology at a larger scale that geological maps try to capture.
[photo Jordi Badia]