New filamentous bivalve rich event beds in the Eocene deposits from Gafsa Basin: sedimentology, sequential analysis and
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ORIGINAL ARTICLE
New filamentous bivalve rich event beds in the Eocene deposits from Gafsa Basin: sedimentology, sequential analysis and environmental significance in Tethyan platform Abdel Majid Messadi1 Accepted: 6 November 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Detailed analysis of Middle Eocene deposits in the Tamerza region, located in western part of Gafsa Basin, shows the presence of several metric corrugated levels. A sedimentological study was applied to these levels showing their geodynamic characteristics, significance in energy, residence time on the sea-floor, and sequential analysis. To study these levels, detailed field work was combined with stratigraphic and sedimentological analyses, as well as systematic sampling of these levels. This facies represents shallow subtidal deposits of a moderate-energy environment. Detailed analysis of undulated facies, under petrographic microscope, reveals the stacking of micrometric sequences (400–500 μm thick) marked by an abrupt change from packstone and, sometimes, grainstone to mudstone textures. Filamentous bivalves occur in massively bedded limestones, which consist of wackestones-packstones containing planktonic foraminiferas. The filaments are smaller (200 μm in average length), isolated, and show varied orientations. In the upper part, the lamination of filament, evolution of facies texture has been a key feature in interpreting them as turbidities. The differences between the three subfacies (F1, F2 and F3) are related to the higher energy. Slope deposits include a wide variety of processes requiring detailed study to set up mechanisms involved and their geological significance. Gravitational flows seem for most, resulting from the differences in density between the fluid/sediment and the ambient fluid. Shell beds have been interpreted as hiatal shell concentrations, as transgressive system track deposits associated to special currents, or as primary biogenic concentrations, among other origins. These bio-events are the expression of communications between different local basins and can be used to establish correlations in North Africa and in other continents during the Middle Eocene interval. Keywords Lutetian-bartonian · Filament events · Bivalves · Calciturbidites · Gasfa basin · Tethyan margin
Introduction Shell beds are a source of ecological information; in addition, the biofabric and taphonomic signatures of individual components provide information about environmental parameters, such as energy levels, residence time on the seafloor, and sedimentation rates (Fürsich and Pandey 1999, 2003). Shell concentration has been increasingly recognized as an important tool for palaeoenvironmental reconstructions (Kidwell 1991; Fürsich et al. 1991; Fürsich and Oschmann * Abdel Majid Messadi [email protected] 1
Laboratory Water Energy and Environment (L3E ENIS), Faculty of Sciences of Sfax, Route de la Soukra km 4, Sfax, Tunisia
1993; Aberhan 1992, 1994; Abbott and Carter 1994; Fürsich 1995; Rivas et al.
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