Author:

Keywords:

biostratigraphy, Chitinozoans

Abstract:

The biostratigraphy with chitinozoans of the Upper Ordovician rocks of the Fauquez area is studied in detail. The Chitinozoans of four recently defined formations, the Bornival, the Huet, the Fauquez and Madot Formations (Van Grootel et al., 1997) are studied from 53 samples. Except for the Fauquez Formation, in which the clingani or linearis Graptolite Biozone was recognised (Maletz & Servais, 1998), the rocks are devoid of any graptolites or conodonts. The chitinozoans are poorly to moderately preserved but nevertheless several Baltoscandianbiozones (Nõlvak & Grahn, 1993; Nõlvak, 1999) could be recognised. Also correlations with the Type Ashgill area (Vandenbroucke, in prep.) and the Belgian Condroz Inlier (Vanmeirhaeghe, in prep.) on Avalonia can be made. The Bornival Formation, which is subdivided into three members, contains Belonechitina robusta and Conochitina minnesotensis, whereas Lagenochitina baltica was recovered from the second member. The presence of a few specimens of Belonechitina hirsuta is probaly due to reworking. The co-occurence of B. robusta and L. baltica indicates a Cheneyan or younger age. The Huet Formation contains L. baltica, L . prussica,‚ and B. robusta. These three species co occur in Baltica in the late Caradoc and the early Ashgill. In the Fauquez Formation, these three species co-occur together with Tanuchitina bergstroemi?, indicating a late Caradoc to early Ashgill age, corroborated by the graptolite data. The Madot Formation contains the same chitinozoan assemblage. Trilobites, probably found in the Madot Formation (Richter & Richter, 1951) indicate an early Ashgill age. Martin & Rickards (1979) studied acritarchs in four samples in the Fauquez area and obtained a broad Caradoc to Llandovery age for the Madot Formation, not contradictory to our results. References: MALETZ, J. & SERVAIS, T., 1998, Upper Ordovician graptolites from the Brabant Massif, Belgium. Geobios 31(1): 21-37. MARTIN, F. & RICKARDS, B., 1979. Acritarches, chitinozoaires et graptolithes ordoviciens et siluriens de la vallée de la Sennette (Massif du Brabant, Belgique). Annales de la Société géologique de Belgique, 102: 181-197. NÕLVAK, J., 1999. Ordovician Chitinozoan biozonation of Baltoscandia. Acta Univ. Carol. Geol. 43 (1/2): 287- 290. NÕLVAK, J. & GRAHN, Y., 1993. Ordovician chitinozoan zones from Baltoscandia. Review of Palaeobotany and Palynology 79: 245-269. RICHTER, E. & RICHTER, R., 1951. Trilobiten von Ashgill-Alter aus dem Massif du Brabant (Grand-Manil). Bulletin de l’Institut Royal des Sciences naturelles de Belgique, 27 (16): 1-6.