The main interest of this location is the ability to observe
important aspects of the structure and sedimentation south of the Pyrenees.
Queralt combines three tectonic units: the Ebro basin, Cadí thrust
sheet and lower Pedraforca thrust sheet. Foraminifera
fossils are found in the Queralt conglomerates.
The ease of access, the outstanding panoramic views and the
availability of a range of different teaching levels (elementary to university)
makes Queralt an ideal location for geology field studies.
View from the Sanctuary of Queralt showing the
anticlinal folds of the lower Pedraforca thrust sheet.
Relief
The Serra de Queralt mountains rise abruptly above the subdued
lowlands of the Ebro basin to the south. The highest peak is Cap de la
Tartanera, 1426 metres. The monastery of Santa Maria de Queralt, 1150 metres, is
located above the town of Berga. The River Demetge has cut a gorge through the
mountain range.
Land Use
The predominant land use is forestry. The Serra de Queralt has PEIN
designation making it a protected space of natural interest.
Geological Situation
The Queralt relief corresponds to the front of the Pyrenees
thrust sheets with the mountains rising above the Ebro basin lowlands. The Cadí
and lower Pedraforca thrust sheets overlap with outcrops of the Cadí revealing
layers of marl with middle Eocene sandstones and conglomerates. The Pedraforca
lower thrust sheet is composed of Cretaceous limestone, Garumnià and some Early
Eocene materials.
Geological information
The sanctuary of Queralt is very well known to the general
public, geologists and schools. The ease of access by coach and the magnificent
panoramic views have made it one of the most popular places for geology field
excursions. Teaching concepts can be applied at many different levels, from
elementary to university.
An itinerary from the junction of the Sant Llorenç de Morunys
road allows the three tectonic units to be recognised: the Ebro basin, Cadí
thrust sheet and lower Pedraforca thrust sheet. The overlapping Vallfogona
structure can be seen on the same road. The conglomerate unconformities are also
very visible, containing fossil nummulites.
Geological description
The Serra de Queralt is the first of the Pyrenees mountain
ranges that stands out above the Ebro basin. This corresponds to the front of
the overlapping units in the south Pyrenees.
The highest tectonic unit to the north is the lower Pedraforca
thrust belt. Its Keuper base acts as a level of separation. Above is a series of
Jurassic and carbonated Late Cretaceous (Maastrichtian). Above the marine
material is a Garumnià continental series with red clay, sandstone and lake
limestones accompanied by a reduced number of fossilized remains and
conglomerates. There is a progressive unconformity associated with the last
tectonic movements of the lower Pedraforca thrust belt.
The next unit, lower and further south, is the Cadí thrust
sheet. This consists of a series of deep lower Eocene beds with a narrow band of
marl alternating with sandstones, above which are Queralt conglomerates.
The southernmost unit, the Ebro basin, is formed of a series of
Eocene and Oligocene deposits. The contact between the Ebro basin and
allochthonous units is through the Vallfogona overlap, an EW structure which
stretches from Solsona to Garrotxa containing the fossilized remains of
Oligocene conglomerates.
The Queralt series is low (400 m) and begins on the Garumnià
red clays. The base is limestone with nummulites and detrital limestones. Then
begins a series of carbonated sediments with detrital alveolines that gradually
change to a more coarse level of conglomerates created from the dismantling of
the nearby relief. These conglomerates have nummulites and other fossils present
in the matrix.
Importance as a geological record
The main geological processes in Queralt are the sedimentation
of material from the Early Eocene, while undergoing active tectonic compression.
The result is a sedimentary 'Growth Strata', which forms a progressive
unconformity related with the growth of the anticlinal upper block that forms
the front of the Pedraforca lower thrust sheet.
Comparative analysis
There are other even more spectacular examples in Catalonia
where progressive unconformity is observed, (for example Sant Llorenç de
Morunys), but not where several geological aspects combine in such a small area
as is the case in Queralt.
Other heritage sites in the area
The Sanctuary of Queralt dates from the 18th century and is
built in a Renaissance style.
Definitions
Fold and Thrust Belt
A Fold and thrust belt is a series of mountainous foothills,
adjacent to an orogenic belt, that form due to compression. Fold-thrust belts
commonly form in the forelands adjacent to major orogens as deformation
propagates outwards. Fold and thrust belts usually comprise both folds and
thrust faults, commonly interrelated.
A thrust fault is a type of fault, or break in the Earth's
crust across which there has been relative movement, in which rocks of lower
stratigraphic position are pushed up and over higher strata. They are often
recognized because they place older rocks above younger. Thrust faults are the
result of compressional forces.
Nummulites
Dying planktonic foraminifera (marine microorganisms)
continuously rain down on the sea floor in vast numbers, their mineralized
shells preserved as fossils in the accumulating sediment. A nummulite is a type
of foraminifera characterized by its numerous coils, subdivided by septa into
chambers.
