2.8.1. Aalter Formation - Aa

Authors: Dewalque (1868).

Description: marine unit, consisting of a grey green, glauconiferous, clayey sand with fine sandy clay layers and many thin sandstone layers. It is followed upwards by grey, fine sand, very fossiliferous at the top. The whole is covered by brown green to dark green glauconiferous, very fine, locally silty sand, with many fossil fragments.

Stratotype: a composite stratotype was designated by Steurbaut & Nolf (1989) be-tween Aalter, Molenstraat ("Oude Molen" area), sheet 21/3-4 (Aalter - Nevele), co-ordinates: x = 85.90, y = 197.82, z = +26 m, and Aalter, Weibroekdreef bridge, sheet 21/3-4, co-ordinates: x = 86.15, y = 198.20, z = +19 m. The first mentioned area is considered as a lectostratostype.

Area: the formation occurs in the northeastern part of West-Flanders and the north-western part of East-Flanders Flanders. It outcrops in the region of Aalter, at the base of the hillrow in the northern part of West- and East-Flanders and in a few outliers (Gent, the hills in the south of West-Flanders).

Thickness: 30 m, decreasing to the east.

Members: the formation is subdivided into the Beernem Mbr and the Oedelem Mbr.

Age: Late Ypresian to Early Lutetian.

Remarks: the formation is also discussed by Depret & Willems (1983), Dewalque (1868), Dumont (1839), Geets & Jacobs (1988), Gulinck (1967), Gulinck & Hac-quaert (1954), Hacquaert (1939), Jacobs (1975), Jacobs & Geets (1977), Maréchal (1993), Mourlon (1873), Nolf (1970, 1972) and Steurbaut & Nolf (1989).