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OFFICE DE TOURISME DU PAYS DE LALBENQUE | |
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OFFICE DE TOURISME DU PAYS DE LALBENQUE | |
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Situated in the departements or Lot, Aveyron and Tarn et Garonne, the Causse de Limogne contains underground erosion and surface features characteristic of the "Karst" landscapes which typically arise from the action of phosphate pits, natural caverns infilled with the phosphate deposits which were fertilisers. The rapid development and short duration of the industry brought great changes to local life, but few memories of this "golden age" remain. Indeed, thanks to the work of the palaeontologists, who have established an uninterrupted fossil record of 32 million years, the events of the Tertiary era are better documented than those of the late 19th century. |
A gallery
preserved from erosion.
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A long story… Our history begins 160 million years ago, in the Mid-Jurassic system of the Secondary era. At that time Quercy was part of a littoral sea zone in which extensive beds of calcareous muds were deposited. Over time these beds have consolidated into the massive hard limestones which form the underlying structure of the causses and which gives them their particular character. |
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the close of the Jurassic system, 35 million years ago, the sea level fell. As a result of
the associated earth movements, and the processes of erosion and deposition, new rock
formations came into being. Subsequent rises in sea level at the time of the Upper
Cretaceous system (about 100 million years ago) covered these and again caused the
formation of a littoral sea upon the bed on which were deposited layers of oolitic
limestone. At the turning point between the Tertiary and Secondary eras (62 million years ago), at about the time of the extinction of the dinosaurs, the sea finally retreated. The fall in the level of the oceans together with local upthrusts of the land created changes of level which favoured the circulation of water percolating through fissures in the limestone. |
 Phosphatière du Cloup d'Aural (Bach)
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 Puits de descente du Mas de Pauffié (Oligocène supérieur, moins vingt sept millions d'années).
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This in turn facilitated the solution of the limestone through the transformation of insoluble carbonates into soluble bicarbonates. Thus at the dawn of the Tertiary era there developed throughout Quercy a series of vast caverns several hundred metres below the then existing ground surface level. Simustaneously the surface Cretaceous oolitic limestone was eroded ; affressive ground waters caused the solution and transportation of the carbonates, leaving behind the accumulation of the insoluble residues. Of these the fine sands were easily transported through the limestone fissures and eventually filled the sub-adjacent cavities. The coarser argillaceous minerals, not easily transportable in suspension, remained at the surface. They formed a thick and complex layer which due to the effects of a tropical climate underwent leaching (laterisation), the process by which the least soluble minerals were eventually concentrated, to form mainly phosphatic nodules and peastones (pisolites) of iron exides.
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lowering of the ground surface by erosion eventually removed the capping of the former
cavities. Under favourable conditions the sand was transported further into the rock mass
causing the cavities to become open. Subsequently under gravity they became filed with
argillaceous phosphate-rich materials and the remains of living organisms which provided a
secondary source or phosphates. The processes of emptying and filling may not have been immediately consecutive.Thus one phosphate mine may have an infilling which represents a short interval of time while adjacent ones may have infillings separated by many millions of years. It all depends on the moment when the sand started to be transported. The oldest infilling dates from fifty million years ago while the most recent dates from 18 million years ago. All possibilities exist between these two extremes. |
 A curious walnut
tree going to meet the sun. |
 Il y a plus d'un siècle sur le causse de Limogne |
The working of the phosphate mines of Quercy 1865 discovery of the first deposits of phosphorite by
Jean André Poumarède. 1870/1886 Period of intense exploitation, principally by
English companies. One hundred and sixty-one quarries and 2000 workmen enumerated. Thirty
thousand tonnes of mineral ore extracted every year, representing a commercial value of 1m
gold francs of the time. |
| 1888/1920 Sporadic and seasonal exploitation of the spoil
to recuperate any ore with with a 40% phosphate content which had been abandoned by the
earlier operators. Attempts to convert to lime and cement. 1932/1938 Inventory and studies of the cavities by Bernard Gèze. 1942 Unsuccessful attempt to restart operations linked to the blockade of North African phosphates and the desire of young men to escape STO ( forced labour in Germany ) Depuis 1965 onwards. Inventory and paleontological investigations. |
 Dragons' teeth |
Phosphorite nodule |
As from summer 1999 " Les Escaliers du Temps " at Cloup d'Aural are open by special arrangement with the Offices de Tourisme at Limogne or at Lalbenque.
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Phosphorite nodule |
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Phosphorite nodule |
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Tourisme |
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