Zoophycos in storm-affected environments: a case study from lower Maastrichtian deposits of the Mateur-Beja area (Northern Tunisia)

摘要

The lower Maastrichtian deposits of the Mateur-Beja area in northern Tunisia are mainly composed of fine-grained marl and limestone alternations occasionally interbedded by coarse-grained calcarenites and gravel deposits. In the coarse-grained intervals sedimentary structures are indicative of storm-induced high-energy currents in an outer ramp to slope setting and of local reworking by bottom currents in the basin. In deeper environments, fine-grained sediments accumulated mainly while settling from storm-induced suspensions. The lower Maastrichtian deposits contain abundant Zoophycos exhibiting two main morphotypes, skirt-shaped Zoophycos in deposits around storm-wave base and tongue-shaped Zoophycos in somewhat deeper sediments. The types differ in burrow architecture, morphology of lobes, and size of structural elements. These differences are attributed to different behavioral programs modulated by the availability of benthic food that decreased seaward. Storm-affected environments seem to be a prerequisite for these Zoophycos-producers to choose their habitat.