Harlet, Déborah Caroline Stella (2024). Sedimentology and stratigraphy of the Ktawa Group: the record of a shallow marine siliciclastic platform of Late Ordovician age in the Anti-Atlas, Morocco. (Thesis). Universität Bern, Bern
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Abstract
Detailed facies association observations are crucial for interpretations and calibrations of depositional environments of shallow marine deposits, which in turn, are fundamental for reconstruction of a relative sea level curve. An important aspect of basin evolution is flexural isostasy, which affects the accommodation space available in the basin, which therefore can have feedback on the relative sea level curve reconstructed. To investigate these processes, the Ktawa Group of Late Ordovician age in the Central Anti-Atlas (South Morocco) was studied. The group is composed of shallow marine siliciclastic sediments dominated by storm-wave action. Detailed sedimentology, stratigraphy and subsidence analysis were conducted through this field-based study. Two possible depositional models were reconstructed for the Lower Ktawa Formation (older formation in the Ktawa Group) based on two different hypotheses on facies associations. These hypotheses are either a ramp-like setting deposited during a regression, or a bimodal setting composed of a ramp deposited during a forced regression followed by a barrier-lagoon system formed during the transgression. Furthermore, the Lower Ktawa lowstands could be deposited as megalobe geometries prograding toward the North (+/- 45°). Each megalobe may have been emplaced in the depression and accommodation space created by the deposition and isostatic adjustment of the previous megalobe. This emplacement progressively shifted toward the East, until the deposition of the Rouïd-Aïssa Formation (overlying the Lower Ktawa Formation). The Rouïd-Aïssa Formation deposits would show a proximal-to-distal trend from the West to the East relatively. A ca. 90° shift in the proximal-to-distal trend between the Lower Ktawa and Rouïd-Aïssa Formations is observed. This shift might be induced by tectonic influence. Finally, the Ktawa Group (Sandbian-Katian) was deposited prior to the Late Ordovician glaciation maximum (Hirnantian). Lowstands observed in the field of the Ktawa Group were interpreted as likely driven by allocylic glacio-eustasy with autocyclicity in the emplacement of megalobes. This thesis combines the above data to gain a new understanding of the sedimentology and stratigraphy of the Ktawa Group in the Central Anti-Atlas.
| Item Type: | Thesis |
|---|---|
| Dissertation Type: | Cumulative |
| Date of Defense: | 12 July 2024 |
| Subjects: | 500 Science > 550 Earth sciences & geology |
| Institute / Center: | 08 Faculty of Science > Institute of Geological Sciences |
| Depositing User: | Hammer Igor |
| Date Deposited: | 23 Jan 2025 09:51 |
| Last Modified: | 23 Jan 2025 09:51 |
| URI: | https://boristheses.unibe.ch/id/eprint/5756 |
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