A HISTORY OF TOURAINE THROUGH ITS ROCKS
7 - IN PALEOGENE

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 Paleogene Neogene Quaternary
65 MY 53 MY 33,7 MY 23,5 MY 5,3 MY 1,75 MY
Epochs Paleocene Eocene Oligocene Miocene Pliocene

At the beginning of the tertiary era, Touraine is emerged, in the tropics...
Whereas the center of the Paris Basin was subject to several marine incursions from the English Channel, Touraine, in the southwest, stayed emerged from Paleocene to the end of Eocene. In a tropical, warm and wet climate, the surface's alteration of the secondary fields was intense and had consequences for the evacuation of the most soluble elements (limestone's particles) and the enrichment in silica, iron oxides and kaolinite. The result was the formation of lateritic red grounds, similar to those we know in Amazonia today. Besides, phenomena of erosion on weak distances, but also the presence of ancient rivers, resulted in the deposit of colorful clays, sands, gravel and conglomerates (these conglomerates, named "perrons" in Touraine, are very hard and sometimes voluminous blocks, with elements of flint reworked from secondary fields and cemented in an also siliceous matrix).
All these deposits of Paleogene are not fossiliferous and their precise age is difficult to establish.

      
Conglomerate from Paleogene - origin: Pont-Boutard      Sight in section of a conglomerate from Paleogene showing fragments of sponges reworked from Senonian - origin: la Chapelle-Blanche-Saint-Martin

See a conglomerate's block with a metric size.

Then several lakes cover a big part of Touraine...
Between upper Eocene and Oligocene, lakes settle down and deposit limestone muds which appear today, after compaction, in the form of very resistant limestones. The rare fossils which they contain are lake gastropods, mainly pond snails.


Lake limestones with moulds of gastropods (pond snails) - origin: Artannes

A bit later, a strait cut Touraine in two parts along an east-west axis...
In lower Oligocene (Stampian stage), a strait along the axis of the current Loire links the Atlantic Ocean with the sea of Étampes which covered then a big part of the center of the Paris Basin. For this strait, the only remains known in Touraine are situated near Fondettes and are constituted by limestones with moulds of potamids (gastropodous molluscs), indicating a more lagoonal than marine environment.


Lagoonal limestone from Stampian with moulds of Potamides lamarcki - origin: Fondettes

See the map of the extension of the Stampian in the Paris basin.

<<< IN SENONIAN IN NEOGENE >>>

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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