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

The aim of this work is to describe and interpret well preserved Lower Carb oniferous Zoophycos from Belgium. They are compared to other similar Zoophy cos studied by the same authors from Jurassic and Lower Cretaceous from Fra nce. Finally, some general conclusions are proposed which are also supporte d by data from the literature. Lower Carboniferous deposits in the Tournai area (Belgium) are characterized by the abundance of well preserved Zoophyc os previously described as Spirophyton. The upper unit of the Tournai Limes tones, the Antoing Formation (Ivorian), was studied here. It is usually mad e of fine-grained carbonate mudstones or wackestones, occasionally passing to packstones. The paleoenvironmental setting is typical of the deep part o f a carbonate ramp, with occasional storm deposition. The general organizat ion of Tournaisian Zoophycos is the same as that seen in Jurassic and Lower Cretaceous specimens of southeastern France: a single open tube and a lami na with an upward helicoidal growth. This similar organization suggests a s imilar ethology for the corresponding tracemaker considered as a deep sedim ent feeder with an efficient mining program. The more simple morphology of the Tournaisian burrow system suggests that this program is less complex th an for the Mesozoic equivalents. Zoophycos is best developed in fine-graine d sediments. In opposition to the Jurassic examples of southeastern France, this sediment must have still been soft, never slightly firm, when coloniz ed. 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 organis m during geologic time.