Ieper Group

The Ieper Group (Dutch: Ieper Groep; French: Groupe d'Ypres) 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".

Ieper Group
Groupe d'Ypres
Stratigraphic range: Ypresian
~54–50 Ma
↓
TypeGeologic group
Sub-unitsKortrijk, Mons-en-Pévèle, Tielt, Hyon & Gentbrugge Formations
UnderliesZenne Group
 Aalter Formation
OverliesLanden Group
 Tienen Formation
Thickness>225 m (738 ft)
Lithology
PrimarySandstone, claystone
OtherSiltstone
Location
Coordinates51.3°N 4.3°E / 51.3; 4.3
Approximate paleocoordinates46.7°N 1.5°E / 46.7; 1.5
RegionEast & West-Flanders, Antwerp, Hainaut, Flemish & Walloon Brabant
Country Belgium
ExtentCampine Basin
Type section
Named forIeper
Ieper Group (Belgium)

History of definition

Ypresian
Main article: 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 (15 to 20 metres (49 to 66 ft) above mean sea level), surrounded from north to south by a series of low hills (between 25 and 45 metres (82 and 148 ft)). 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.[1]

A new stratotype for the Lutetian was proposed by Blondeau (1981) about 50 kilometres (31 mi) 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).[2]

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,[3] where the uppermost Tarawan Limestone, the Esna Formation and the lowermost Thebes Limestone define the Ypresian sequence.[4] Several other proposals for the lithostratigraphic redefinition of the top of the Ypresian exist;[5] 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,[6][7] the Agost section close to Alicante in the Agost Basin in the Betic Cordillera,[8] and the Fortuna section north of Murcia in the Prebetic realm of the Betic Cordillera,[9][10] all in Spain. Other proposed type sections for the Ypresian-Lutetian boundary are located in France, Italy, Israel, Tunisia, Morocco, Cuba and Mexico.[5][11]

Stratigraphy

The Ieper Group was redefined by Steurbaut in 2006,[12] and is since 2017 subdivided into five formations by the National Commission for the Stratigraphy of Belgium, from youngest to oldest:[13]

AgeChronGroupFormationMemberLithologiesMaximum thicknessNotes
YpresianC22nZenneAalterOedelem SandSandstone[14]
C22rBeernem SandSandstone
IeperGentbruggeAalterbrugge LigniteLignite50 m (160 ft)[15]
Vierzele SandSandstone
Pittem ClayClaystone
Merelbeke ClayClaystone
Kwatrecht Complex
Mons-en-PévèleMicaceous sandstoneA few meters[16]
C23nHyonMont-PaniselSandstone25 m (82 ft)[17]
Bois-la-Haut SandSandstone
EgemClaystone
TieltEgemkapelSandstone25 m (82 ft)[18]
KortemarkSiltstone
C23rKortrijkAalbekeClaystone125 m (410 ft)[19]
C24nRoubaixClaystone
C24rOrchies
Mt. HéribouClaystone
Het ZouteSiltstone
LandenTienenOosthoek SandSandstone[20]
Knokke ClayClaystone
Dormaal SandSandstone

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.[21]

See also

References
  1. Steurbaut, 2006, p.74
  2. Molina et al., 2006, p.15
  3. Ypresian Stage at Encyclopedia Britannica
  4. Dupuis et al., 2003, p.44
  5. Ypresian/Lutetian boundary stratotype - University of Zaragoza
  6. Bernaola et al., 2006, p.75
  7. Larrasoaña et al., 2008, p.396
  8. Larrasoaña et al., 2008, p.411
  9. Molina et al., 2006, p.8
  10. Guerrera et al., 2014, p.172
  11. Molina et al., 2006, p.2
  12. Steurbaut, 2006, p.76
  13. Ieper Group - National Commission for the Stratigraphy of Belgium
  14. Aalter Formation at Fossilworks.org
  15. Gentbrugge Formation
  16. Mons-en-Pévèle Formation
  17. Hyon Formation - National Commission on the Stratigraphy of Belgium
  18. Tielt Formation - National Commission on the Stratigraphy of Belgium
  19. Kortrijk Formation - National Commission on the Stratigraphy of Belgium
  20. Tienen Formation at Fossilworks.org
  21. Smith & Smith, 2003

Bibliography
Other Ypresian
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