Paris basin

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The Paris Basin, or Anglo-Paris Basin, is a fossil sedimentary basin found in northeast France , western Belgium, and southeast England . It began to sink into the Permian after the Variscan Orogonese , but did not become individualized until the Upper Triassic . Until resolution of subsidence in the Oligocene accumulated in the Paris basin over 3000 meters of sediment.

etymology

The Paris basin, French Bassin de Paris or bassin parisien , was named after the French capital Paris , but the actual basin center is a little further east in the Brie .

geography

The geological provinces of France with the Paris Basin in the north

The Paris basin is elliptical in plan. Its longest stretch of about 600 kilometers runs in a north-east- south-west direction between Metz and Poitiers , while in a south-east-north-west direction it is just under 400 kilometers. It is framed by the following Variscan basement eruptions :

It was connected to the Aquitaine Basin via the Seuil du Poitou in the southwest , to the northwest it opened to the English Channel ( Hampshire-Dieppe Basin ), to the north it communicated with the Belgian Basin via the Seuil de l'Artois , to the east a connection to the Rhine Graben and southeast over the Seuil de Bourgogne to the Bresse Graben . It was also in exchange with the trenches in the northern massif central ( Limagne trench , Roanne trench ).

The basin is also constructed asymmetrically in the profile section, with a thinner and shallower inclined west wing and a somewhat steeper, more powerful east wing. The basin center is, as already mentioned, east of Paris on the eastern edge of the Brie (east of Château-Thierry ). The bore of Courgivaux pelvic center hit the Variscan basement rocks at a depth of 3186 meters, while below Paris Center, the basement about 2,000 feet deep is.

geomorphology

Geological map of France

Geomorphologically , the Paris basin is a layered landscape comparable to a stack of plates . Due to the higher angle of incidence (in a westerly direction), the strata in the eastern part of the basin are much more clearly formed than in the west. Starting from the eastern edge of the basin (Vosges), the following layers can be found:

In the west (with only a slight inclination to the east) the layers of the Doggers, the Upper Cretaceous, the Eocene and the Oligocene (in some cases only the Oligocene) can be recognized.

geology

Basement

Outline map of the Paris Basin. The surrounding basement massifs in red, yellow-dashed the connections to other basins

The Variscan basement of the Paris Basin is now quite well known due to numerous deep boreholes, seismological , gravimetric and geomagnetic investigations. Similar to the surrounding basement massifs, it consists primarily of crystalline rocks ( gneiss and granite ) with little to weakly metamorphosed sedimentary terranas from the Neoproterozoic and the Paleozoic Era .

The basement is traversed by several important lineaments . The most important is undoubtedly the Bray disorder , as it represents a Variscan Terrang boundary. Its northern course from Dieppe to Gouvieux , which has been traced to the surface, is marked by the Bray anticline . Underground, the southeast trending fault separates the Cadomian Block to the west from the Rheno Hercynian Zone to the east. In the center of the pelvis it can no longer be seen on the surface, but here it should slowly turn in eastward via Bouchy and Juvanzé and then continue in the Vittel fault (northern edge of the Vosges). In its hidden part, the fault separates the Central Armorican Zone in the southwest from the Saxothuringian Zone in the northeast. The Vittel Fault separates the Saxothuringian Zone in the north from the Moldanubian Zone and the Morvan-Vosges Zone in the south.

Another clear fault zone of the basement is indicated by a positive magnetic anomaly with a simultaneous negative gravity anomaly . This fault zone, up to 25 kilometers wide in its northern part, follows staggered fracture zones starting from Fécamp at Rouen , Rambouillet , Montivilliers , Gien , Sancerre , to touch the northern edge of the Massif Central at Cérilly . Vertical displacement amounts of up to 500 meters occurred on it, with the eastern part sagging. The fault also acted as a sinistral lateral shift with offset amounts of up to 70 kilometers, recognizable by a laterally shifted band of leukogranites in the northern Massif Central, which is continued in the northern Morvan. The multi-phase development history of this fault zone should go back to the Neoproterozoic.

Also worth mentioning is the northeast-trending Metz Fault , which follows the Terrang boundary between the Rheno-Hercynian and Saxothuringian zones.

Stratigraphy of the sediment sequence

West-east section from the Pays d'Auge to the Upper Rhine Plain

The sedimentation in the area of ​​the Paris Basin began after the Variscan orogeny subsided towards the end of the Pennsylvania :

Perm

In the lower perm, the post-orogenic collapse of the variscus occurred with the crust stretched. Widespread rift systems filled with continental debris, the sediments of the Rotliegend (predominantly red-colored arkoses ) were formed. The 350 meters thick sediments underlie the eastern part of the Paris Basin, especially the area around the Vosges (they can, however, reach a thickness of up to 600 meters in the Saint-Dié Basin ). On the surface, for example, they are at Villé and Saint-Dié ( Saint-Dié formation ). The following formations can be separated in the Rotliegend of the Vosges (from young to old):

Towards the end of the Rotliegend the variscid chain was already largely leveled, so the Central Massif-Morvan-Vosges-Black Forest were only an insignificant mountain range (the so-called Burgundian spur ).

Triad

Conglomeratic red sandstone cliffs near Saint-Dié

The following red sandstone (to be seen at Épinal and Sarrebourg ) from the Lower Triassic was of continental origin (predominantly fluvial sediments in Zopfstrom- and Delta facies ) and was also restricted to the eastern edge of the basin (Vosges, Lorraine ). The direction of sedimentation was generally to the northeast to the Germanic basin that was forming . The red sandstone reaches a maximum thickness of 490 meters. Like the previous Rotliegend, it was also deposited under arid to semi-arid climatic conditions. It can be broken down as follows (from hanging to lying):

The differences in relief were largely straightened after the red sandstone sedimentation was completed (the red sandstone even already contains isolated marine horizons), so that during the Central Triassic the Muschelkalkmeer , a tropical shallow lake in an arid environment, was able to advance from southwest Germany into the eastern area of ​​the Paris Basin (up to to Champagne ). The deposits of shell limestone can be broken down as follows:

At the beginning of the Middle Muschelkalk, the connection over the Seuil de Bourgogne broke off, so that evaporites ( gypsum , rock salt ) were deposited in the basin . During the Upper Muschelkalks, the sea then reached its (preliminary) peak ( Calcaire à cératites ).

The subsequent transgression of the evaporitic Keupermeer finally reached the western part of the Paris basin. The Keuper is structured as follows:

From the Mittelkeuper onwards, subsidence movements occurred in the Brie area for the first time, and thus the beginning of an independent sedimentary development in the Paris Basin. Towards the end of the Triassic ( Rhaetian ), the sandstones of the Grès rhétiens and above the marls of the Marnes de Levallois sedimented in the basin center .

law

In the Lias there was another transgression, also coming from the east, which gradually spread across the entire basin. During the Hettangian , Sinemurian and lower Pliensbachian period it left behind clastic deposits on the edge of the basin (sands and sandy marls - Grès d'Hettange or Grès de Luxembourg , Grès de Virton and Marnes sableuses de Hondelange ), but inside the basin the layered limestone of the Calcaire à gryphées . The subsequent sedimentation was dominated by marl limestone and clay slate until the end of the Toarcian . At the end of the lias, detritic sediments were again deposited at the basin edges ( Minette - iron-containing sediments of the Aalenium in Lorraine). The Liastransgression brought about a connection between the North Boreal Sea (via the English Channel and Central England) and the Germanic Sea in the Paris Basin from the Sinemur onwards. At the same time, the Seuil du Poitou opened and a connection was established to the Aquitaine Basin and thus to the Atlantic .

The sequence of layers of the Lias in detail (from young to old):

At the beginning of the Great Dane , detritic sediments were again deposited in the Aalenium at the basin edges ( Minette in Lorraine), which contained iron . It now opened the Seuil de Bourgogne and allowed access to the Tethys range , which was to remain until the end of the Lower Cretaceous. The Doggermeer was a warm, flat lake in which mainly limes were deposited ( oolite limestone of the Bajocium ). It reached its maximum extent in the Bathonium . During Calloviums and the Lower Oxfordian ( Terrain à Chailles ) prevailed marl deposits.

The dogger consists of the following formations (from hanging to lying):

After the start of the Malm , the marls in the Upper Oxfordian were replaced by reef limestone (strata of the Côte de Meuse ). The reef limestone slowly retreated to the south-east into the Jura region during the Kimmeridgian and were replaced by fine-Detritic marls. The very hard, sublithographic limestone of the tithonium was laid over it .

The Oxfordium is made up of the following formations (from young to old):

The marl-emphasized kimmeridgium consists of:

The tithonium closing off the Jura contains the formations:

chalk

At the beginning of the Chalk, the Paris Basin fell dry due to the Purbeck regression and the Upper Jura was eroded. The angular discordance of the Lower Cretaceous can reach down to the Upper Oxfordium (Oolithe de Saucourt). From now on, continental sediments were deposited up to the Aptium , mainly clays and delta sands in Wealden facies . At the same time took place but already from the Berriasian from Jura in the southeast starting a slow marine incursion that in Barremian should reach the Beck Center again. In the course of the Albium / Aptium, a connection with the Boreal North Sea was finally established again. Glauconite green sands and clays from Gault were sedimented at this time .

The following formations characterize the Lower Cretaceous (from young to old):

With the beginning of the Upper Cretaceous in the Cenomanian , the influence of the North Sea on the sedimentation in the Paris Basin set the tone - this was to persist until the Lower Eocene. In the Cenomaniac, access to the Aquitaine Basin opened up via the Seuil du Poitou, whereas the connection via the Seuil de Bourgogne was broken. The cenomaniac formed a myriad of different facies in the Paris Basin. It was not until the Turonian that the conditions with the chalk deposits began to re-standardize - with the exception of the Touraine , which received more detritic sediments from the Massif Central. The chalk sedimentation lasted in the Paris basin until the end of the campanium .

Paleogene

After a long-lasting emersion during the entire Maastrichtium , a new transgression occurred in the course of the Danium . The sea advanced into the Paris Basin from both the north (boreal area) and west (Atlantic Ocean). During the Danian and the Selandian , the two influences were still in balance - biogenic algae limestone and marl were sedimented - but the influence of the North Sea already became decisive in the Thanetium , as can be seen on the sands of the Sables de Bracheux near Beauvais . In the Ypresium , a connection to the Atlantic opened over the English Channel and enabled the immigration of the large foraminifera Nummulites planulatus ( Sables de Cuise ). After a coarse glauconite phase, the Lower Lutetium developed an extensive lime sedimentation with the Pierre à liards (Nummulite limestone with Nummulites laevigatus ) and the Banc royal ( Milliolite limestone with Orbitolites complanatus ).

In the middle lutetium, the Artois anticline emerged as part of the large bulge London-Brabant-Ardennes and definitely prevented the Paris basin from accessing the North Sea. From the Upper Lutetium the Paris Basin was therefore only an offshoot of the Western English Channel with restrictive sedimentation, which after deposition of sands of Auversien and sands and limestones ( Calcaire de Saint-Ouen of) Marinésien in the plaster of the Ludien culminated.

One final transgression to the center of the Paris Basin took place in the Oligocene . It formed lagoonal sediments (green tone) followed by the brackish Marnes à Huîtres . Limes were deposited in the Brie further east at the same time. At the height of the Oligocene Transgression, the sea reached the Orléanais via the Seine valley and left behind the Sables de Fontainebleau . Then the retreat took place over the Loire valley . What remained in the Beauce was a huge inland lake with freshwater limestone sedimentation.

Neogene

In the course of the Neogene there were no further marine incursions in the central Paris Basin. Transgression pulses were limited to the periphery - the Loire furrow (in the Middle Miocene and again in the Pliocene ( Redonia )) and the English Channel (as far as Upper Normandy in the Pliocene).

From the Pliocene onwards, the Paris basin was epirogenetically raised by 100 to 200 meters. This brought about an accentuation of the strata, a carving out of island mountains and an increased incision of the river courses.

The last geomorphological changes took place under periglacial conditions in the cold ages of the Pleistocene ("Ice Age") . At the same time, from Picardy to Beauce, fertile loess was deposited on the chalky stratified panels.

Stratotypes

The Paris Basin is of great importance for the history of geology , as it contains numerous stratotypes of the levels defined here (arranged from young to old):

Important fossil sites

Reconstruction of galloping palaeotheria

Significant fossil- bearing formations in the Paris Basin include:

Natural resources

The Paris Basin has the following natural resources:

See also

literature

  • Chantraine, J. et al .: Carte géologique de la France au millionième . Ed .: BRGM. 1996, ISBN 2-7159-2128-4 .
  • Gradstein, F., Ogg, J. & Smith, A .: A Geologic Time Scale . Ed .: Cambridge University Press. 2004, ISBN 0-521-78673-8 .
  • Pomerol, C .: France geologique . In: Guides géologiques régionaux . Masson, 1980, ISBN 2-225-65494-8 .

Individual evidence

  1. ^ Marchal paper, F .: Les insectes du Buntsandstein des Vosges (NE de la France). Biodiversité et contribution aux modalités de la crise biologique du Permo-Trias . In: Thèse ULP Strasbourg 1998, p. 160p., 30 pl .