The onset of the early Toarcian flooding of the Pliensbachian carbonate platform of Central Tunisia (North-South Axis) as inferred from trace fossils and geochemistry

Posted on 13.07.2021 - 15:03
The flooding of the Lower Jurassic shelf in the North Gondwana Palaeomargin during early Toarcian occurred on a fragmented and irregular topography affected by differential subsidence. The onset of Toarcian sedimentation, in two adjacent sections was characterised by the deposition of limestones under high-energy conditions. The Châabet El Attaris section was located in a depressed sub-basin, and recorded restricted environmental conditions owing to water stagnation and an oxygen-depleted sea-bottom. The sedimentation of limestones bearing gutter cast structures is related to gravity flows probably linked to storm activities. These processes favoured the remobilization of sediment at the sea floor, as well as oxygen input to deep waters, as shown by the record of trace fossils including Zoophycos, Ophiomorpha, Chondrites and Diplocraterion . The Kef El Hassine section is located in the upper part of a tilted, less subsident block, as evidenced by its reduced thickness compared with Châabet El Attaris section; the absence of dark mudstones implies oxic conditions. The Polymorphum Zone consists of limestones showing evidence of sedimentation under high-energy conditions, along with hardgrounds. The occurrence of Zoophycos (deeptiers) in the upper part of some limestone beds of the Polymorphum Zone is linked to minor erosive processes.

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Reolid, Matias; Soussi, Mohamed; Reolid, Jesús; Ruebsam, Wolfgang; Taher, Ilef Belhaj; Mattioli, Emanuela; et al. (2021): The onset of the early Toarcian flooding of the Pliensbachian carbonate platform of Central Tunisia (North-South Axis) as inferred from trace fossils and geochemistry. Geological Society of London. Collection. https://doi.org/10.6084/m9.figshare.c.5510162.v1
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