The Ieper Group (; ) is a group of rock strata in the subsurface of northwest Belgium. The group is subdivided into three marine formations, all formed during the Ypresian, a single age of the geologic timescale (55.8 to 48.6 million years ago, the oldest age of the Eocene epoch). Both age and group are named after the West Flemish town of Ypres, for which the Dutch name is "Ieper".
History of definition Ypresian
In the original description of his newly introduced Ypresian stage Dumont (1850) did mention neither stratotype nor type locality. He simply referred to the "collines d'Ypres" or Ieper Hills, as the area where the unit is best developed. However, it remains unclear what is meant by this term. The town of Ieper is situated in western Belgium, at the southern end of a small, NW-SE oriented depression ( above mean sea level), surrounded from north to south by a series of low hills (between ). Dumont probably envisaged the elevated zones a few km north and east of Ieper (St.-Jan, Zillebeke, etc.), where clay beds have been quarried for brick and tile making for quite a long time.Steurbaut, 2006, p.74
A new stratotype for the Lutetian was proposed by Blondeau (1981) about north of Paris. The neostratotype is located on the right bank of the river Oise at St. Leu d'Esserent and the large quarry at St. Vaast-les-Mello (Oise).Molina et al., 2006, p.15
Since 2003, the Global Stratotype Section and Point (GSSP) defined by the International Commission on Stratigraphy (ICS) for the Ypresian is set in the Dababiya section close to Luxor, Egypt,Ypresian Stage at Encyclopedia Britannica where the uppermost Tarawan Limestone, the Esna Formation and the lowermost Thebes Limestone define the Ypresian sequence.Dupuis et al., 2003, p.44 Several other proposals for the lithostratigraphic redefinition of the top of the Ypresian exist; among others the Punta Torcida Formation of the Austral or Magallanes Basin in Tierra del Fuego, the Azkorri Sandstone in the Gorrondatxe section of the North Pyrenean Foreland or Basque–Cantabrian Basin,Bernaola et al., 2006, p.75Larrasoaña et al., 2008, p.396 the Agost section close to Alicante in the Agost Basin in the Betic Cordillera,Larrasoaña et al., 2008, p.411 and the Fortuna section north of Murcia in the Prebetic realm of the Betic Cordillera,Molina et al., 2006, p.8Guerrera et al., 2014, p.172 all in Spain. Other proposed type sections for the Ypresian-Lutetian boundary are located in France, Italy, Israel, Tunisia, Morocco, Cuba and Mexico.Ypresian/Lutetian boundary stratotype - University of ZaragozaMolina et al., 2006, p.2
Stratigraphy The Ieper Group was redefined by Steurbaut in 2006,Steurbaut, 2006, p.76 and is since 2017 subdivided into five formations by the National Commission for the Stratigraphy of Belgium, from youngest to oldest:Ieper Group - National Commission for the Stratigraphy of Belgium
Age Chron Group Formation Member Lithologies Maximum thickness Notes Ypresian C22n Zenne Aalter Oedelem Sand Sandstone Aalter Formation at Fossilworks.org C22r Beernem Sand Sandstone Ieper Gentbrugge Aalterbrugge Lignite Lignite Gentbrugge Formation Vierzele Sand Sandstone Pittem Clay Claystone Merelbeke Clay Claystone Kwatrecht Complex Mons-en-Pévèle Micaceous sandstone A few meters Mons-en-Pévèle Formation C23n Hyon Mont-Panisel Sandstone Hyon Formation - National Commission on the Stratigraphy of Belgium Bois-la-Haut Sand Sandstone Egem Claystone Tielt Egemkapel Sandstone Tielt Formation - National Commission on the Stratigraphy of Belgium Kortemark Siltstone C23r Kortrijk Aalbeke Claystone Kortrijk Formation - National Commission on the Stratigraphy of Belgium C24n Roubaix Claystone C24r Orchies Mt. Héribou Claystone Het Zoute Siltstone Landen Tienen Oosthoek Sand Sandstone Tienen Formation at Fossilworks.org Knokke Clay Claystone Dormaal Sand Sandstone
Outcrops The Kortrijk Formation predominantly consists of marine clay. It occurs in the west and north of Belgium, the Tielt Formation, consisting of fine sand, is found in the subsurface of western and central Belgium and the Gentbrugge Formation, which comprises an alternation of clay, silt and fine sand, crops out in East and West Flanders.
The Ieper Group lies stratigraphically on top of the Landen Group (upper Paleocene) and below the Zenne Group (like the Ieper Group early Eocene in age). Unlike the Zenne Group, the Ieper Group can also occur in more southern parts of Belgium, for example in the Mons Basin.
Paleontology The Tielt Formation has provided fossils of mammals, birds and reptiles.Smith & Smith, 2003
See also List of fossiliferous stratigraphic units in Belgium Ypresian formations Fur Formation of Denmark London Clay Formation of England Silveirinha Formation of Portugal Wasatchian formations Nanjemoy Formation of the eastern United States Wasatch Formation of the western United States Itaboraian formations Itaboraí Formation of Brazil Laguna del Hunco Formation of Argentina
References
Bibliography
Other Ypresian