Géology
Generalities
The vineyards of Condrieu stretch along the eastern edge of the Massif Central.
In this area, the right bank of the Rhône Valley is characterised by extreme topographic variation.
The vines have made their home on very steep slopes that provide a transition between the valley floor and Pelussin Plateau.
The vines cling to the mother rock thanks to numerous terraces (called chayées locally), which are narrow and require sustained care.
PEDOGENESIS AND ALTERATION
Description
Since the primary era, the rocks have been subject on several occasions to the effects of chemical and
biochemical alteration; in the tropical climates that existed at those times, this alteration destroyed
considerable amounts of rock. No traces of these major alterations can today be recognised in the
environs of Condrieu. Nowadays the climate is not aggressive, although the vegetation-hosting soils
that clad the mother rock cause a very moderate form of alteration. As a result, there is "active
pedogenesis" (or soil evolution/formation) relative to the soils and to the waters that circulate through them.
Granites and metamorphic rocks are in some cases highly sensitive to alteration and to current pedogenesis:
•Quartz, ahighly resistant mineral, has not been affected by pedogenesis in our climate;
•Feldspathshave an architecture that is very prone to water-influenced alteration.
These are both silicates, which decompose into two categories of product:
-Elements that dissolve into, and are carried away by, water running through the soil (potassium,
sodium, calcium);
-Aluminium silicates (clays), which form where the feldspaths were previously located;
•Micas,which are also silicates but are less easily altered than feldspaths; when they do, they yield
soluble potassium, iron and magnesium.
In conclusion, we can say that the various attacks to which these rocks are subject result in elimination
of their initial structure, the acquisition of a new permeability, and partial transformation into clay.
Since the primary era, the rocks have been subject on several occasions to the effects of chemical and
biochemical alteration; in the tropical climates that existed at those times, this alteration destroyed
considerable amounts of rock. No traces of these major alterations can today be recognised in the
environs of Condrieu. Nowadays the climate is not aggressive, although the vegetation-hosting soils
that clad the mother rock cause a very moderate form of alteration. As a result, there is "active
pedogenesis" (or soil evolution/formation) relative to the soils and to the waters that circulate through them.
Granites and metamorphic rocks are in some cases highly sensitive to alteration and to current pedogenesis:
•Quartz, ahighly resistant mineral, has not been affected by pedogenesis in our climate;
•Feldspathshave an architecture that is very prone to water-influenced alteration.
These are both silicates, which decompose into two categories of product:
-Elements that dissolve into, and are carried away by, water running through the soil (potassium,
sodium, calcium);
-Aluminium silicates (clays), which form where the feldspaths were previously located;
•Micas,which are also silicates but are less easily altered than feldspaths; when they do, they yield
soluble potassium, iron and magnesium.
In conclusion, we can say that the various attacks to which these rocks are subject result in elimination
of their initial structure, the acquisition of a new permeability, and partial transformation into clay.
These form the sharp slopes between the low-lying alluvial terraces on the banks of the Rhône and
Pelussin Plateau, as well as the plateau itself.These are magmatic rocks, among which the dominant
types are granites (Condrieu, Vérin, Saint-Michel, Chavanay), metamorphic rocks, leptinites and
anatexites (in northern Condrieu, western Verlieu in the communeof Chavanay, southern Chavanay,
and Saint-Pierre-de-Boeuf).
These rocks have fairly similar compositions, characterised by the following minerals: quartz, black
and white mica, and feldspaths.
All of these rocks are fairly resistant to mechanical erosion, which partly explains the presence of the
steep slopes that support the vines.
Quaternary Terrains
Loess: during the last glaciations, about 15,000 years ago, the glaciers of the Alps were just a few
kilometres from the valley, which had an icy, steppe-like climate. Violent winds carried large
quantities of mineral, limestone, quartz and clay particles, and this matter was deposited at the head
of the glaciers, forming l?ss sheets.
Today a few rare examples remain, and can be viewed mainly at Saint-Pierre-de-Boeuf and Chavanay.
In conclusion, the terrains of the Condrieu AOC area are almost entirely granites and metamorphic
rocks dating from the primary era, with small quantities of lœss sheets.
These rocks from the primary era have a great capacity to store heat, and therefore help the Viognier
grapes in Condrieu to ripen well.
STRUCTURAL DETAILS
Certain events have decisively influenced these rocks. Over geological time, they have been
affected by intense tectonic forces which have caused a number of crack-inducing deformations
-afundamental factor in the behaviour of the rocks.
Major tectonic phases, faults and fractures
The first tectonic phase of major importance belongs to the Hercynian orogenesis at the end of
the primary era. This resulted in cracks, faults and fractures that appeared following horizontal
compressions. These shifts are systematically oriented NE-SW.
The second phase, which registered with only low intensity on the eastern edge of the Massif Central,
corresponds to the much more recent Alpine orogenesis. This reactivated older faults.
Outcrop fracturing
Coincident with the major tectonic phases was minor fracturing that affects the eruptive and
metamorphic rock on the metre and decimeter scales. These fractures are fully visible in all the
outcrops in the area. The fractures permit infiltration of surface water, and are therefore of
fundamental importance: they promote penetration of water into the rocks, and thus development of
alteration phenomena related to earth activity. For these reasons, terracing is required where the
vines thrive.
affected by intense tectonic forces which have caused a number of crack-inducing deformations
-afundamental factor in the behaviour of the rocks.
Major tectonic phases, faults and fractures
The first tectonic phase of major importance belongs to the Hercynian orogenesis at the end of
the primary era. This resulted in cracks, faults and fractures that appeared following horizontal
compressions. These shifts are systematically oriented NE-SW.
The second phase, which registered with only low intensity on the eastern edge of the Massif Central,
corresponds to the much more recent Alpine orogenesis. This reactivated older faults.
Outcrop fracturing
Coincident with the major tectonic phases was minor fracturing that affects the eruptive and
metamorphic rock on the metre and decimeter scales. These fractures are fully visible in all the
outcrops in the area. The fractures permit infiltration of surface water, and are therefore of
fundamental importance: they promote penetration of water into the rocks, and thus development of
alteration phenomena related to earth activity. For these reasons, terracing is required where the
vines thrive.
