FALUNS

IN SOME WORDS...

    - Definition : the faluns are ancient marine deposits, constituted by sandstone-like limestones, calcareous muds and sands more or less shelly.

   - History : after a long emersion during the beginning of the tertiary era, a gulf, opened on the Atlantic Ocean, settled down in middle Miocene, about fifteen million years ago, on a vast territory along the current axis of la Loire.

After the withdrawal of this faluns' sea, most of the sediments which it left were cleared by the erosion, but the rare fragments which remain display a rich and varied biological activity, under a subtropical climate.

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

4600 MY 540 MY 250 MY 65 MY
Precambrian Paleozoic (primary era) Mesozoic (secondary era) Cenozoic (tertiary era... ... + quaternary era)
65 MY 53 MY 33,7 MY 23,5 MY 5,3 MY 1,75 MY 0,01 MY
Paleocene Eocene Oligocene Miocene Pliocene Pleistocene Holocene


   - Fossils : they are locally very numerous, mainly in the form of fragment. They constitute then an important proportion of the sediment.
The whole fossils are often worn by the ancient marine currents. We find especially shells, bryozoans, corals, sea urchins and remains of vertebrates (bones and teeth of fishes, reptiles and mammals).

   - Deposits : the map below shows the supposed extension of the faluns' sea and the various deposits where the fossils represented on this site were found :

         - for Touraine : Savigné-sur-Lathan, Channay-sur-Lathan and Pont-Boutard on the west of Tours, Paulmy, Ferrière-Larçon and le Louroux on the south of Tours

         - for Blésois : Thenay

         - for Anjou : Doué-la-Fontaine.



A LITTLE MORE FOR THE CURIOUS...                  Or return previous page

   - The different facies : we are in the habit of distinguishing two facies :

         - the "savignéen" facies (from Savigné-sur-Lathan, in Indre-et-Loire). These are sandstone-like limestones or calcareous muds, rich in bryozoans, corresponding to a sedimentation in the open sea, in a rather deep water (around 50 m).

         - the "pontilévien" facies (from Pontlevoy, in Loir-et-Cher). These are sands, rich in fragments of shells, with grains of quartz and pebbles. The sedimentation was made in littoral zone, between 0 and 40 metres of depth.

Intermediate facies exist between both previous facies. Besides, on the same vertical line, several facies generally follow one another, testifying to a complex history.

   - The age of the faluns : Cenozoic (tertiary era) - medium Miocene

To be completely precise, a first marine transgression, characterized by the deposit of clays, took place in lower Miocene (Aquitanian stage), around 23 million years ago.

From the study of mammals, among others things, we realized that after this first marine episode and its withdrawal, there had been no one sea of the faluns, but three seas of the faluns, separated by periods of emersion. The most ancient of these seas is the one which reached the biggest extension (corresponding to the map above). Faluns of Touraine and Blésois belong to this first transgression of the sea which has been spread between approximately 16,5 and 15 million years ago (Langhian stage, corresponding about to the ancient Helvetian stage).

After a period of emersion, the second sea of the faluns reached only Anjou, between approximately 12,5 and 11 million years ago (upper Serravallian stage). The deposit of Doué-la-Fontaine belongs to this period.

After a new period of marine withdrawal, the third and last sea of the faluns stretched, as the previous one, as far as Anjou, between approximately 6 and 5 million years ago (upper Messinian stage).

stratigraphical scale of Miocene :

23,5 MY 20,3 MY 15,8 MY 14,7 MY 11 MY 7,1 MY ==> 5,3 MY
Aquitanian Burdigalian Langhian Serravallian Tortonian Messinian

   - Paleontology : the faluns' fossils presented on this site belong almost all (unless otherwise specified) to the first transgression of the sea of Langhian and thus date about fifteen million years.

Fossils of the faluns are plentiful and varied. In the savignéen facies, corresponding to the open sea, we find a big number of bryozoans, sea urchins, as well as mollusks (oysters and pectinids) with shell in calcite (one of the forms of limestone's crystallization). Shells in aragonite (other form of limestone's crystallization) or in calcite/aragonite of the other mollusks were dissolved. But we find sometimes their internal or external moulds.

It is in the pontilévien facies, corresponding to a more littoral sea, that fossils are most varied. Bryozoans are almost absent but, on the other hand, all the mollusks were preserved. Here, we also find corals, characteristic of a shallow and warm environment.

Remains of vertebrates can be found in all the facies. Their dark colour is due to the impregnation by dioxide of manganese.

The teeth of sharks, rays and osseous fishes were found in large numbers in the region of Savigné-sur-Lathan.

The remains of ground vertebrates (reptiles and mammals) were brought by the rivers which flowed into the sea, during the floods. But some ground vertebrates are previous to the faluns. Their origin is in the erosion of sands from continental origin (lower Miocene, Burdigalian stage), erosion by the sea itself or by the rivers which flowed into it. In the same way, we find sometimes reworked fossils into the faluns, dating from the secondary era, such as sponges of Senonian.

   - Use of faluns : formerly, faluns were exploited for the amendment of farmlands. Today, they are used as aggregate and were intensely exploited in the basin of Savigné-sur-Lathan. We may regret the quasi-disappearance of such a heritage, even if the mutiplication of coalfaces and the innumerable discoveries of fossils allowed an important headway into the knowledge of the faluns' history.

Ecologically, we may also regret that a part of the basin of Savigné has been "moth-eaten" by numerous quarries exploited below the water table of the faluns, with all the problems which can be created when we put in the open air such a water table (greater risks of pollution of the water table, dangerousness of the steep coalfaces in lakes so created, ...).

   - Suggestions of tours : for returning to the disappearance of the heritage evoked previously, the most optimists will console little by noting that a particularly educational quarry was transformed into quarry-museum. This quarry (called "la décharge de Channay") allows, among other things, the school groups to get acquainted on the field with geology. Besides, the tour of the remarkable museum of Savignéen, at Savigné-sur-Lathan, is unavoidable for the passionate persons, but also for the general public which wishes to discover the region by deviating a little from traditional tours of the castles of la Loire.

For the visitors of Sud-Lochois, the museum of Le Grand-Pressigny also allows to discover a remarkable collection of fossils, not only from the faluns, but also from the other geological formations of Touraine, without forgetting naturally all the part concerning the regional prehistory for which this museum was created.

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