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2.5.13 Fumal Formation - FUM

Authors: Verniers, 1976 ms, 1983a; Verniers & Van Grootel, 1991.

Description: Grey mudslate, mudstone, siltstone and fine sandstone with quartzic pelite in the e-divisions. Sedimentology: three types of sequential patterns occur: (a) thick Tde sequences (average between 24 and 28 cm) with absent or very rare T(b)cde sequences; (b): medium thick to thick Tde sequences (average between 17 and 25 cm) with rarely present to very frequent T(b)cde sequences (6 to 30% of all sequences) of about the same thickness as the Tde sequences; the c-divisions are either thicker or thinner than 10 cm but there is a higher frequency (80%) of c-divisions thinner than 10 cm. (c): medium thick to thick Tde sequences (average between 14 and 18 cm) and no T(b)cde sequences. Lower and upper boundaries are not observed: the upper boundary is situated in an observation gap of ± 20 m between this formation and the Vichenet Fm.

Stratotype: the area around the village of Fumal; stratotype sections in the three gullies in the steep slope in the Bois aux Guisses, 700 to 1000 m south-east of the church of Fumal (sections JD-1, to 3 in Verniers, 1983); parastratotype in the outcrops just south to south-west of the church of Fumal.

Area: Mehaigne area and Orneau valley.

Thickness: Mehaigne area: thickness of recorded sections: 242 m; estimated thickness of formation: 330 m (Verniers, 1983a).

Age: The chitinozoans, the only fossils found in this formation in the Mehaigne area, belong to the Cingulochitina cingulata global biozone and possibly the Conochitina pachycephala global biozone of Verniers et al. (1995), middle Sheinwoodian to lower Homerian (middle to upper Wenlock). More accurately, most of the upper two thirds of the formation can be assigned to the Welsh Conochitina subcyatha biozone, lower Homerian (upper Wenlock), and the uppermost part of the formation to the subzone D3 (Verniers, 1982), corresponding to the Sphaerochitina lycoperdoides global biozone of Verniers et al. (1995), lower to middle part of the Homerian (upper Wenlock) (Verniers, 1999). This implies a mid Wenlock age for the lower third, and an early Homerian for the upper two thirds of the formation (Verniers, 1999).

Remarks: Synonym: MB7 Fm (Verniers, 1981, 1983a).