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2.3.1. Lonzée Member - LON

Authors:   Dumont  (1878) and herein.

Description: From bottom to top:

-basal grey to green clay-silt, overlying Silurian bedrock, with many moulds of bivalves and gastropods;

-grey-green glauconitic clay-silt, with planar bedding; no macrofossils;

-blue clay with numerous bivalves, belemnites, shark teeth,  teleosts, mosasaurs (thickness: up to 60 cm);

-fine grey sand with large blocks of glauconitic sandstone with many bivalves, belemnites, microfauna etc.(thickness: 145 cm);

-glauconitic, dark green-blue clays, with many bivalves, belemnites, shark teeth, fish vertebrae (thickness: 20 cm);

-indurated calcarenite and sand  (thickness 15 cm);

-yellowish green or brown, glauconitic, very sandy clay, with numerous silicified shell fragments (thickness: 30 cm).

Stratotype: No stratotype fixed; at present there are no outcrops in the succession.  

Area:  Known occurrence of this member is restricted to the area around Lonzée near Gembloux (Namur)

Thickness: About 3 m (unpublished section drawn by M. Glibert in 1936).

Age: ? Coniacian – Santonian - ? basal Campanian:

Cephalopods:  Actinocamax verus, Gonioteuthis westfalica westfalica, G. westfalicagranulata,  G. granulata, ? G. granulataquadrata. Inoceramids:  Inoceramus (Heroceramus) cf.hercules, I. (Volviceramus) cf.koeneni

Remarks: -Formerly considered as belonging to the Mons Basin: Marlière (1954, 1957), following data in Leriche (1929), considered the Glauconie de Lonzée as being the littoral extension of the Craie the Saint-Vaast  (Saint –Vaast Chalk Formation, see above, p.  ooo).

In their study of the bivalves Malchus et al. (1994, 1996) demonstrated that the Lonzée fauna is strongly related to the Vaals-Aachen fauna  (Liège-Limburg Basin) and not at all to the faunas from the Mons –Paris Basin. Thus, Malchuset al. confirmed the view originally expressed by Rutot (1894). The belemnites at Lonzée indicate a Santonian age (Christensen, 1994), but the inoceramids are partially of Coniacian age (Malchus et al., 1994).

- References:  Christensen (1994), Dumont  (1878), Leriche (1929), Malchus  et al. (1994, 1996), Marlière  (1954, 1957),  Rutot (1894).