Zoophycos distribution and sequence stratigraphy. Examples from the Jurassic and Cretaceous deposits of southeastern France

Abstract

The trace fossil Zoophycos is characteristic in certain Jurassic and Cretaceous basinal deposits of southeastern France. These deposits are cyclic marl/limestone alternations, in which depositional sequences can easily be recognized. Two kinds of sequence have been studied: the marl/limestone couplet and the third-order sequence. Detailed observations show that Zoophycos has a particular position in the sequences. In the marl/limestone couplet, the trace is concentrated towards the upper part of the calcareous beds. The burrow is also present in the lower part of the beds and at the top of the underlying marls, but is less abundant. The same kind of burrow distribution occurs in the third-order sequences: Zoophycos is concentrated in the upper part of the calcareous bundles, which are interpreted as lowstand systems tracts, while it is totally lacking in the superimposed more marly sequence, which probably corresponds to the lower part of the transgressive systems tracts. The burrow may be present throughout the highstand systems tracts, which overlie the maximum flooding surfaces, but is less abundant. The particular distribution of Zoophycos is related to the fluctuations of certain environmental factors, the most important of which are the carbonate productivity, the sedimentation rate and the substrate consistency. Zoophycos can be proposed as a useful marker of sequence boundaries and of the transgressive surfaces in distal deposits where other signals for sequence analysis are often lacking.