Central Vineyard Geology
After leaving behind the largely volcanic rocks of the Massif Central, the waters of the Loire flow northwards, heading for one of its most famous wine towns, Sancerre, before the river arcs slowly around past Orléans, now en route for Vouvray and the vineyards of the Touraine. Before reaching Sancerre and the Central Vineyards, however, it first crosses onto a plain of much younger rocks, the multifaceted limestones and marls of the Bassin Parisien. These many limestones and marls, and their associated soils, will define the river’s wines as far downstream as Anjou, when these superficial rocks attenuate, gradually giving way to the ancient bedrock of the Massif Armoricain.
More detail on the river and its rocks than I provide in this very brief introduction can be found in my introduction to the geology of the Loire Valley. For the purpose of this instalment of my guide to this region, however, there is one key message I should like to get across, and that is this; for all the joy that awaits us in the Nantais, in parts of Anjou, in the Côte Roannaise, Côtes du Forez and the other vineyards of the Upper Loire, the Loire Valley is, for the most part, a valley of limestone and limestone-derived soils. It is only natural that many of the wines that are made along its banks reflect this fact; Sancerre and Pouilly-Fumé, not to mention (looking further downstream, as I hinted in the previous paragraph) Vouvray, Chinon and Saumur, all give us wines which speak quite clearly of their calcareous origins.
While the physiography of these limestone regions is perhaps not quite as complex as the geological jigsaw we find in the Nantais, it is nevertheless not quite as straightforward as it might at first appear. Limestone has a surprising diversity, in terms of its age, its composition, its structure and its physical properties. And, of course, it also has some influence on the vines that grow on it, as they send their roots deep into soils and even into the fissures of the very rock itself. Some types of limestone are, as you would perhaps expect, more favoured than others. And nowhere has this been explored more thoroughly than in the Central Vineyards, especially in Sancerre. Here in this part of my guide to the wines of the Loire Valley, I explore the geology of this corner of France.