Suchergebnisse

As a result of the "new geological map of Wallonia" program undertaken by the Walloon Government since 1990, all the maps at 1/25 000 scale covering the outcrop areas of the Brabant Massif have been finalised. During the long period of mapping (1993-2017) our understanding of the stratigraphy and tectonics of the Brabant Massif has evolved significantly and this led to several inconsistencies between different maps. We present here an overarching geological map of the outcrop areas of the Brabant Massif, resulting from the merging of these 21 maps, updated according to the most recent findings and insights. The resulting map, at a scale of ~1/200 000, shows a coherent image of the outcrop areas of the Brabant Massif. This map better illustrates the geological history and structural architecture of the Brabant Massif compared to previous maps (e.g. Fourmarier, 1921; Legrand, 1968) and allows for a better understanding of the geology of the Brabant Massif. Also, it fully complements the subcrop map of the Brabant Massif of Piessens et al. (2005, in prep.).

We have undertaken an exhaustive review of the literature to check if the ichnogenus Oldhamia could be used as a biostratigraphical tool in the Cambrian. On the 19 occurrences observed worldwide and positioned in the recent global chronostratigraphy of the Cambrian, only 16 have a time range sufficiently precise to constrain the stratigraphic interval during which the organisms producing Oldhamia lived in the Cambrian. They are clearly distributed in two age groups: a "younger" group of 14 occurrences shows a very well constrained time range from the base of Stage 3 to the three quarter of Stage 5 and an "older" group of 2 occurrences shows a poorly constrained time range which seems restricted to the Fortunian. With this contrasting situation we propose two alternative interpretations: in the first we accept all the results and in the second, more restrictive, we reject the age of the "older" group as scientifically insufficiently substantiated. Oldhamia can only be used as a stratigraphic tool in the second interpretation: it appears in the upper part of Stage 2, shows an acme in Stage 3 and 4 and rapidly disappears during Stage 5. This rapid disappearance could be interpreted as the arrival of the Cambrian agronomic revolution in the deep marine setting. The overview also shows that this ichnogenus has a cosmopolitan distribution.