The region of Chablis lies on the eastern edge of the Paris Basin. The region's oldest soil dates back to the Upper Jurassic age, over 180 million years ago and includes a vineyard soil type that is calcareous, and known as Kimmeridge Clay. All of the Chablis Grand Cru and Premier Cru vineyards are planted on this primarily Kimmeridgean soil, which imparts a distinctively mineral, flinty note to the wines. Other areas, particularly most of the Petit Chablis vineyards, are planted on slightly younger Portlandian soil, still of similar structure. The chalk landscape resembles some areas of Champagne and Sancerre.