A HISTORY OF TOURAINE THROUGH ITS ROCKS
3 - FROM OXFORDIAN TO LOWER CRETACEOUS

Simplified stratigraphical scale (the millions of years (MY) correspond to the period's beginning) :

4500 MY 540 MY 250 MY 65 MY
Eras Precambrian Paleozoic (primary era) Mesozoic (secondary era) Cenozoic (tertiary + quaternary eras)
Periods Triassic Jurassic Cretaceous
Epochs Liassic Dogger Malm lower Cretaceous upper Cretaceous
154 MY 146 MY 141 MY 135 MY 96 MY
Stages Oxfordian Kimmeridgian Portlandian

At the beginning of upper Jurassic, the sea deposits the most ancient sediments rising to the surface in Touraine...
In Malm (= upper Jurassic), and more exactly in Oxfordian stage, approximately 150 million years ago, the sea deposited limestones which constitute the most ancient rocks rising to the surface in Touraine. These limestones appear thanks to anticlinal structures (anticlinal = fold of geological strata in rounded peak, giving after erosion, a structure where the most ancient rocks are situated in the middle). These anticlinal structures are situated in the north of Touraine, between Souvigné and Sonzay and in the southwest, around Richelieu. Limestones have a fine (sublithographical) granulometry, characteristic of a rather deep sea. The important thickness of these limestones (200 - 400 m) indicates that the basin sank during the deposit of sediments. Fossils are mainly represented by ammonites.


Sublithographical limestone from Oxfordian stage with ammonite (Oppelia) - origin: Pouant ("Département de la Vienne"), on the west of Richelieu


Sublithographical limestone from Oxfordian stage with burrow's track - origin: Pouant ("Département de la Vienne")

At the end of Jurassic, the sea is always present but its sediments are known only in drillings...
After marine Oxfordian, two other stages end Jurassic: Kimmeridgian and Portlandian. These two stages are not known by rising to the surface but Kimmeridgian was recognized in several oil drillings with marine limestones.

During the greatest part of lower Cretaceous, Touraine is emerged...
At the beginning of lower Cretaceous, the sea withdrew and sediments left by the seas of upper Jurassic largely disappeared because of continental erosion which, under a warm climate, was probably intense. At the end of lower Cretaceous, more exactly in Albian stage, an east coming sea reached a part of Touraine. Like the last sediments of Jurassic, those of Albian stage are known only in drillings where they are represented by tens of metres of sands.

The stages of lower Cretaceous :

135 MY 131 MY 123 MY 117 MY 113 MY 108 MY ==> 96 MY
Berriasian Valanginian Hauterivian Barremian Aptian Albian

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The natural context   Touraine's Depths   From Oxfordian to lower Cretaceous   In Cenomanian   In Turonian   In Senonian   In Paleogene   In Neogene   In Quaternary   Map of Indre-et-Loire   Simplified geological map (north)   Simplified geological map (south)

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