Lower Carboniferous Zoophycosfrom the Tournai area (Belgium): Environmental and ethologic significance

The aim of this work is to describe and interpret well preserved Lower Carboniferous Zoophycos from Belgium. They are compared to other similar Zoophycos studied by the same authors from Jurassic and Lower Cretaceous from France. Finally, some general conclusions are proposed which are also supported by data from the literature. Lower Carboniferous deposits in the Tournai area (Belgium) are characterized by the abundance of well preserved Zoophycos previously described as Spirophyton. The upper unit of the Tournai Limestones, the Antoing Formation (Ivorian), was studied here. It is usually made of fine-grained carbonate mudstones or wackestones, occasionally passing to packstones. The paleoenvironmental setting is typical of the deep part of a carbonate ramp, with occasional storm deposition. he general organization of Tournaisian Zoophycos is the same as that seen in Jurassic and Lower Cretaceous specimens of southeastern France: a single open tube and a lamina with an upward helicoidal growth. This similar organization suggests a similar ethology for the corresponding tracemaker considered as a deep sediment feeder with an efficient mining program. The more simple morphology of the Tournaisian burrow system suggests that this program is less complex than for the Mesozoic equivalents. Zoophycos is best developed in fine-grained sediments. In opposition to the Jurassic examples of southeastern France, this sediment must have still been soft, never slightly firm, when colonized. In addition, the abundance of Zoophycos at the top of locally frequent storm deposits could indicate a fairly opportunistic behavior. Considering the above mentioned assumption, the increasing complexity of the morphology and the modification of the related ethology, a possible evolution from an r-strategy to a K-strategy is suggested for the Zoophycos-creating organism during geologic time.