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The oldest rocks in Touraine date back to the Upper Jurassic, around 160 million years ago. The Turonian stage was defined in Touraine and geologists agree it spans between 93 and 88 million years ago.
Mid-Turonian white tuffeau is the main building material used in Touraine, namely for the Loire châteaux. It formed around 90 million years ago on the sea bed that then covered Touraine. Sandy limestone deposited during the Upper Turonian, around 88 million years ago, is called yellow tuffeau. In the Le Grand-Pressigny region, it produced large flint slabs that were used by prehistoric man then used to make Merovingian tombs discovered in the château courtyard then, later still, to build the château itself.
There must have been giant reptiles e.g. dinosaurs in Touraine in the Mesozoic Era but there is no trace of their remains. Around 15 million years ago, during the Mid-Miocene, a marine gulf flooded the Touraine lowlands. The sediment deposited at the bottom is called shelly sand. Fossils produced by shelly sand are wide-ranging: sea creatures, particularly molluscs, fish and mammals from the sea and river. There are also plants and land animals. But erosion washed away most shelly sand deposits. The sea didn’t return to Touraine. That makes fossils far rarer for recent periods as the land-based setting didn’t protect them.
Fossils are the remains, natural moulds or imprints of plants and animals preserved in rocks. When these organisms die, their skeletons, shells or, rarer still, soft tissue mineralise and bury into sediment. The museum’s abundant collection, mainly from the Lecointre collection, primarily dates from the Mesozoic Era, the Late Cretaceous to be precise, between 100 and 70 million years ago, represented by tuffeau and flint clay, and the Tertiary Era, the Miocene to be precise, between 15 and 5 million years ago, represented by shelly sand and its rich fauna. It is displayed in the Renaissance château cellars.