Chitinozoans of the Lower Llanvirn Huy and the Middle Caradoc Sart-Bernard Formations (Middle to Upper Ordovician): Implications for the Stratigraphy of the Condroz Inlier (Belgium)

This paper reports on chitinozoans from the early Llanvirn (mid Darriwilian) Huy Formation found at three localities in the central Condroz Inlier: the Huy and Sart-Bernard railway sections and the Wépion borehole. In addition, it presents data on chitinozoans from the middle Caradoc (upper Sandbian to lower Katian) Sart-Bernard Formation, known from the eastern Sart-Bernard railway section and historically confused with the Huy Formation. We confirm the distinct palaeontological and lithological differences between the two formations, already noted by some authors. Our data, however, suggest that the Huy Formation is probably absent in the eastern Sart-Bernard section and demonstrate that the supposed stratigraphic hiatus between the Huy and Sart-Bernard formations is at least partly occupied by the soon-to-be-defined Chevreuils Formation. The chitinozoans indicate an early Aberedidien (early Llanvirn, mid Darriwilian) age for the Huy Formation and a Burrellian-Cheneyan age (middle Caradoc, late Sandbian to early Katian) for the Sart-Bernard Formation, thus narrowing the known stratigraphic range of these units. The chitinozoans of the Huy Formation have a northern Gondwana signature, whereas those of the Sart-Bernard Formation show clear Baltoscandian affinities.