Chenin Blanc: Geology of the Three Major Geologic Regions

In the last blog, Chenin Blanc: Geology of the Loire, I ended by writing that next blog would be a closer look at the three geologic regions of the Massif Central, the Paris Basin and the Massif Armoricain. This dive into the soils of the region is to answer the question of why Chenin Blanc found a home in the Loire valley.

It was very interesting to read that the Massif Central, where the source of the Loire river is located is made up of 450 extinct volcanoes some of which were still raging only 10,000 years ago. The lava which was the result of volcanic activity in the region metamorphosed into deposits of granite, gneiss, and schist (slate).
Following the northerly journey of the Loire river, the geological region changes from the Massif Central to the Paris Basin. (For a very abbreviated explanation of the formation of the Paris Basin, please check out this blogpost: Champagne Part 2: Geology).
About 300 million years ago, the Massif Armoricain and the Massif Central were already formed and were part of an extremely high chain of mountains. The foot of these mountains was a warm and humid jungle and over the course of tens of millions of years, these mountains were slowly eroded. The sediment rolling down the hillsides and over the jungle formed a giant arid desert of sediment. This desert area began slowly tilting, allowing an ocean to creep over the basin eventually forming the basement of the Paris basin. Through geologic time, the oceans receded, then came back again, receded, came back and receded once more. The massive amounts of planktonic algae that grew formed the current day chalk in these regions.
The Loire river is now taking a left turn and making it's way through the Massif Armoricain. The Massif Armoricain like the Massif Central is made up of cooled lava from ancient volcanoes, with the oldest rocks thought to be 650 million years old. Granite, gneiss, schist, and other metamorphic rocks can be found here.
We have now entered the region where Chenin Blanc found it's home.

Next blog will be about the regions in the Loire valley where Chenin Blanc is grown and how the soils impacts the type of Chenin Blanc that is made.

References:
1. Jon-David Headrick Selections, Geologgy and Geography of the Loire.