The Soils of Alta Langa

Sedimentary rocks are defined as those generated by the accumulation of sediment of various origin. In this case, the sedimentary deposits were all formed on the sea bed (or lagoon bottoms) of the so-called Piedmont Tertiary Basin, whose waters covered all of southwestern Piedmont for 30 million years.

In ancient times, the sea extended over all of today’s Piedmont flatlands, and rose to cover some of the lower hills as well, so that where the Langhe is today, there was a deep basin that extended as far as the Ligurian Apennines and reached the Alps around Cuneo, and to the north skirted the Turin hills. This vast depression was formed by powerful shifts in the Earth’s crust, which resulted in the formation of the Alps. While on one hand the collision of the plates raised up the mountain range, on the other it sank downward, making the sea as deep as almost one kilometer at some points.
Within this basin, for a very long time – over thirty million years – huge amounts of sediment accumulated, forming layers of uninterrupted deposits several kilometers in depth.

These changes all influenced the sedimentary deposits, which vary in composition according to some conditions: during the more turbulent phases, larger components were transported and accumulated, such as pebbles, gravel (over 2 mm) and sand (between 2 and 1/16 mm), while during calmer periods there was an accumulation of finer particles, like silt (between 1/16 and 1/250 mm) and clay (smaller than 1/250 mm). Depending on the origin of the currents, minerals rich in magnesium or potassium were deposited, and the fossil record shows that the organisms living in the Basin varied according to its depth and the climatic conditions of the period.

The history of the Basin is written in the rocks. The sediments were gradually buried by other strata and then transformed into rocks by compression over time. Thus, the layers composed primarily of silt and clay turned into the soft, bluish gray rocks called marl. On th other hand, those composed of sand have kept their name if they have not bonded together, but when instead they have undergone lithification, they have become arenites, also known as sandstone, the famous “Pietra di Langa”, highly regarded as a building material, today as in the past.

All the sedimentary rocks in the area are rich in limestone, or calcium carbonate (CaCO3), consisting of the fossilized shells of microorganisms and the direct precipitation from seawater onto the sea bed, making the resulting rocks alkaline, i.e. with a high pH.

The pH of the soil has a great impact on the life of plants, because it influences their capacity to absorb nutrients through their roots. In general, grapevines can prosper in either type of soil, but as we shall see, on the Alta Langa hills, the most coveted locations for vineyards are often those with a high calcium carbonate content, which modulates the absorption of nutrients and contributes to the overall health of the vines, as well as having considerable impact on the aromatic profile.
The long history of the Basin ends about 2.5 million years ago, when the sea drained away from Piedmont. In fact, the thrusts deep within the Earth’s crust changed direction about 10 million years ago, because after the downward push, the plates began to rise up again, lifting up the entire area and causing the layers of sediment to emerge gradually, tilted in a northwesterly direction. Progressively, the rocks that had been hundreds of meters underground were lifted to the surface, where they were immediately exposed to weathering, which began to modify them, a process that is still under way today. Being made up of finer particles, the marls were less prone to erosion, and formed soft, rolling hills with long, gentle slopes. The sands, being more easily eroded, formed steep slopes and hills with sharper, harsher summits. This led to the formation of impressive systems of ravines.