5.22 Martinrive Formation - MRT

Authors: Groessens, 1975; Paproth et al., 1983.

Description: Most of the formation consists of dark limestones (packstones to wackestones) with crinoidal concentrations and numerous chert nodules. The lowermost part contains abundant calcite nodules with chicken-wire structure (pseudomorphs after anhydrite). The uppermost part of the formation is thick-bedded, with fine-grained, peloidal grainstones and lime mudstones, locally dolomitized and devoid of chert. In the Ourthe valley, chicken-wire nodules are also present at this level.

Stratotype: Left bank of the River Amblève, along the Aywaille road immediately downstream from the Martinrive bridge.

Area: The formation is restricted to the western part of the CSA. It passes laterally into the Leffe Formation.

Thickness: About 50 m

Age: Upper Ivorian. The formation straddles the Polygnathus communis carina (Dollymae bouckaerti Subzone) and Scaliognathus anchoralis europensis Conodont Zones; Protognathodus cordiformis is present in its uppermost part in the Ourthe valley. The upper part of the formation has yielded E. michoti, C. modavensis, Eoforschia sp., and Tournayella sp., an association which is assigned to the Cf3aForaminifer Subzone. The formation lies in the RC3gRugose Coral Zone. The formation corresponds to the TST of the third-order sequence 4 of Hance et al. (2001).