Late Frasnian phillipsastreid biostromes in Belgium

Abstract

In the Belgian Namur-Dinant Basin the boundary between the Lustin Formation and the Aisemont Formation (in the Lower rhenana conodont Biozone) corresponds to a fall followed by a rise in sea level, leading to the first recorded late Frasnian coral crisis. The Aisemont Formation records a transgressive-regressive cycle. Prior to the crisis most of the colonial rugose corals were members of the Family Disphyllidae, but these were largely replaced by corals belonging to the Phillipsastraeidae. Among these Frechastraea colonized all environments of the basin and was the main constructor of a biostromal reef in its northernmost proximal area, in the fair-weather wave zone. Corals did not encrust each other and therefore were not firmly attached, but they hug tightly the substrate (a dead coral colony) and rest closely on it to resist to the turbulence of waves. During the Silurian and Devonian, up until the late Frasnian crisis, shallow-water reefs in turbulent water were usually built by encrusting stromatoporoids, whereas rugose corals were restricted to waters of lower energy. Indeed, they were unable to encrust substrates, unlike stromatoporoids and post-Palaeozoic scleractinians, and to live in turbulent habitats. In Belgium argillaceous sedimentation prevented the development of stromatoporoids and provided an opportunity for the corals to colonize empty niches and to construct biostromes in relatively high-energy environments.At the same time Alveolites and stromatoporoids were dominant in a mid-proximal environment below the fair-weather wave base, but within the storm wave zone, where they also constructed biostromes.

Biochemostratigraphy of the Upper Frasnian in the Namur–Dinant Basin, Belgium: Implications for a global Frasnian–Famennian pre-event

“…Neuville Formation δ O and δ C profiles seem to correlate with a transgression cycle which started around the Lower rhenana Zone after a regression during the immediately underlying jamieae Zone (Joachimski et al, 2004;Poty and Chevalier, 2007;da Silva and Boulvain, 2008). This is also consistent with a drop in the brachiopod diversity at the top of the Neuville Formation in the Neuville railway section where Bed 21 (Fig.…”

“…2 and 3c-d) comprises limestones and argillaceous limestones in its lower and upper parts (lower and upper members); the middle part (middle member) consists of shales and nodular shales (Lacroix, 1999). Both limestone horizons are known in the Belgian literature as the first and second 'biostromes with Phillipsastrea' of Coen-Aubert and Lacroix (1979) devoid of biostromal units (Poty and Chevalier, 2007;Denayer and Poty, 2010). The shales of the middle member are correlated with the Lower Kellwasser Horizon (Bultynck et al, 1998).…”

“…3c) is located along the north-western side of the road from Engis to Amay in Engis (Fig. 1, Coen-Aubert and Lacroix, 1979;Mottequin, 2005;Poty and Chevalier, 2007;Denayer and Poty, 2010) and exposes the top of the Lustin Formation and almost the entire Aisemont Formation.…”

“…3d) is located along the road from Nandrin to Esneux (Fig. 1, northern flank of the Dinant Synclinorium), north-west of the Tavier stream (Mottequin, 2005;Poty and Chevalier, 2007;Denayer and Poty, 2010) and offers a good opportunity to study the upper part of the Lustin Formation, the Aisemont Formation and the lower part of the Famenne Formation, but only the brachiopods from the lower carbonate member of the Aisemont Formation were investigated herein.…”

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“…Poty and Chevalier (2007) described phillipsastreid biostromes from the Frasnian of Belgium. Numerous platy Frechastrea-Alveolites associations occur in the Aisemont Formation, and these were formed below the fair-weather wave base.…”