Grès d'Hettange

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The Grès d'Hettange is a sedimentary formation of the eastern Paris basin . It was deposited in the Lower Jurassic and represents the original stratotype of the hettangium .

Type locality

The Grès d'Hettange, from the French. grès for sandstone , was named after its type of locality , the now disused Gries (Carrière Gries) quarry near Hettange-Grande .

history

In 1864 the Swiss geologist Eugène Renevier suggested using the outcrop in the Gries quarry as a stratotype for a new geological stage. By separating from the original Sinemurium, which was previously the lowest level of the Jurassic, the Hettangium was created . Since 1985, the Gries quarry has been transformed into a 6 hectare educational reserve naturelle géologique (geological nature park).

geography

The Grès d'Hettange , here as Grès de Luxembourg north of Luxembourg (city)

The Grès d'Hettange, known in Luxembourg as Grès de Luxembourg , in Belgium as Formation de Luxembourg and in German-speaking countries as Luxembourg sandstone , occurs in the eastern Paris basin . The formation follows a 1 to 5 kilometer wide band from Charleville-Mézières via Sedan , Virton , Arlon ( Belgium ) in the west across Luxembourg to Echternach in the east. From here it continues south to Thionville in France . The further course of the formation at the surface to the east is prevented by the southwest-striking Hettange-Rodemack fault . The formation can be traced underground to around 20 kilometers south of Longwy . Somewhat separated from the main occurrence, the sandstone also occurs in the Mullerthal in Luxembourgish Switzerland and reaches German territory southwest of Bitburg .

stratigraphy

The Grès d'Hettange is embedded in the calcaire à gryphées as a body of sand in a wedge shape . So it is underlain by the lower layer member of the Calcaire à gryphées, which still belongs to the lower Hettangium (layers with Arietites bisulcatus , Arietites rotiformis and Psiloceras planorbis ). Below are the Marnes rouges de Levallois of the upper Rhaetian . The Grès d'Hettange is overlaid by the upper limb of the Calcaire à gryphées with Psiloceras johnstoni , an alternation of silty marls and sandy limestone that was deposited in the deeper water. The sandstone ends with an emersion horizon and is then replaced by a 20 meter thick marly-sandy transition layer (with arietites) to the actual Calcaire à gryphées.

In Luxembourg, the formation is compliantly underlain by the Marnes d'Elvange and covered by the Marnes et calcaires de Strassen .

The Grès d'Hettange is diachronous and becomes noticeably younger towards Belgium. If he is still of Upper Hettang age at the type locality near Hettange-Grande, he must already be placed in the Sinemurium in Belgium . Its thickness is also subject to strong fluctuations. For example, at the type locality it has a total thickness of around 50 meters (of which 25 meters open), in Luxembourg around 80 meters and at Arlon an impressive 110 meters. South of Hettange-Grande, it quickly loses its thickness and then interlocks with the Calcaire à gryphées.

The southern Belgian Formation de Luxembourg lies concordantly on the marls of the Jamoigne Formation . Its hanging wall is concordantly overlaid by the clay-silty Ethe formation . The formation can be divided into five members (from hanging to lying):

  • Stockern member
  • Virton member
  • Orval member
  • Florenville member
  • Metzert member

To the east, the Formation de Luxembourg interlocks above the Florenville member with three members of the fine-grained Arlon Formation . The basic Metzert member, only present in the east, starts in Oberhettang. The Florenville member following with a discontinuity begins in the east at the turn of the Sinemurium, but is stratigraphically much higher in the west. The Orval member follows a clear connection with the Strassen member of the Arlon formation. Under the Virton member is the involvement of the posterity member and, above that, the final interlocking of the Hondelange member .

Lithology

The Bockfelsen built up from the Grès de Luxembourg and the upper town of Luxembourg

The Grès d'Hettange was deposited near the beach in the shallow, warm epicontinental sea of ​​the lower Lias.

The type locality is a relatively coarse-grained sandstone with few fossils in the lower section, which then has very fossil-rich shill layers (storm deposits) with 130 different taxa of bivalves and gastropods in the hanging wall . For this reason Renevier had proposed the Gries quarry as a stratotype of the hettangium. The lower section contains signs of channel facies and is formed as a very massive and hard sandstone. The upper, yellow-colored section is softer and has a flat appearance. It belongs to the Schlotheimia angulata ammonite zone and thus to the upper hettangium.

The Grès de Luxembourg , located further north and closer to the edge of the Ardennes, consists essentially of an alternation of yellow sandstone layers with light-colored sand-lime brick layers. The sometimes obliquely layered and often highly rugged sandstone layers are made of quartz grains up, but the calcareous sandstone layers contain Kalkbruchstücke and additionally cemented by lime cement. The area of ​​origin of the detritus are the Ardennes , the Eifel and the Hunsrück , which were then subject to intensive weathering. It was supplied via the Eifelgraben , facing southwest , which connected the Paris Basin in the Hettangium with the Germanic Basin .

The Metzert member of the Formation de Luxembourg in southern Belgium is a progressive sand body. The angle discordance that closes the member is an important sequence boundary that can be found in the entire Paris Basin and where reprocessing took place. The remaining members have, similar to the Grès de Luxembourg, a characteristic sandstone-sand-lime brick alternation. They are (as subtidal sand body English. Sand waves ) to interpret which of tidal currents were moving. The analysis of existing sloping structures reveals a predominantly west-south-west direction of transport.

geomorphology

Compared to the Calcaire à gryphées that surrounds it, the Grès d'Hettange is much more resistant to erosion and therefore forms morphological ridges in the terrain, for example between Hettange-Grand and Mondorff-les-Bains and between Roussy-le-Bourg and Preiche .

Structural geology

The sandstone formation generally shows a very shallow dip to the southwest. In the area of ​​the Eifelgraben it is folded into a flat syncline dipping to the southwest ( Weilerbach syncline ). In addition, the formation is traversed by numerous southwest trending faults that can offset up to 100 meters (for example at the Audun-le-Tiche fault ). At the already mentioned Hettange-Rodemack fault it is cut off towards the Thionville Graben . The sequence of layers was raised in connection with the Variscan basement in the course of the alpine orogenesis after the end of the Oligocene and was slightly deformed into southwest-striking undulations. After falling below the plasticity limit, the association broke rigidly due to disturbances. The alpine uplift movements continue to this day, for example the center of the Ardennes is still rising by 1 millimeter per year.

Fossil content

As fossils in the Grès d'Hettange can be cited:

Economical meaning

The Grès d'Hettange and the Grès de Luxembourg are excellent aquifers . The sandstones were dismantled as building blocks and were used in road construction as paving stones and border stones.

Age

Absolute age requirements for the Grès d'Hettange (or Grès de Luxembourg) are not known. Precise biostratigraphic age assignments are also difficult due to the poverty of key fossils and the pronounced diachronicity. The formation is thought to cover the Upper Hettangian to Lower Sinemurian period and is between 194 and 197 million years old BP . In Belgium, the Formation de Luxembourg barely extends into the Pliensbachian , where it has a minimum age of 189 million years BP.

literature

  • Feuille Thionville-Waldwisse XXXIV-II and XXXV-II . In: BRGM (ed.): Carte géologique de la France à 1/50000 . N ° 114.

Web links

Individual evidence

  1. ↑ Hanzo, M .: Réserve naturelle géologique d'Hettange-Grande (Moselle) . In: Bull. Inf. Géol. Bass. Paris . tape 31 , no. 3 , 1994, p. 31-33 .
  2. ^ Laugier, R .: Le Lias inférieur et moyen du Nord-Est de la France . In: Mém. Sci. Terre . tape 21 , 1971, p. 300 f .
  3. ↑ Terquem, O. & Piette, E .: Le Lias inférieur de l'Est de la France comprenant la Meurthe, Moselle, le Grand Duchy of Luxembourg, la Belgique et la Meuse . In: Mém. Soc. géol. Fr. (2), VIII, (1), 1865, pp. 176 p., 18 pl .