This study presents the first provenance analysis of Jurassic and Lower Cretaceous siliciclastic intervals of the Essaouira-Agadir Basin (EAB). A common practice in provenance studies relies on correlations between clastic sediment preserved in a basin (sink) with a potential source in the hinterland; but such approach relies on the tacit assumption that the modern geology must be largely similar to the one exposed during the active period of the studied source-to-sink system. The source of a siliciclastic sediment is by definition eroded, and therefore absent from the modern geology and correlations may be further complicated by the fact that multiple candidate sources may share similar detrital fingerprints. To address these issues and untangle the complex evolution of the Moroccan margin, this study presents a method to reconstruct the surface âpalaeogeologyâ using low-temperature thermochronology and isopach mapping. The surface geology exposure at critical time intervals shows significant changes compared to the modern geology, with implications for candidate source areas. Ephemeral yet important (km-scale) sedimentary basins are recorded and covered large parts of the hinterland. These areas behaved initially as sinks and later as sources of sediment, having a major influence on source-to-sink systems while leaving close to no trace in the modern geology. Constraining their location is necessary to develop accurate provenance models. The study examines the Jurassic and Lower Cretaceous (Toarcian, Middle Jurassic, Kimmeridgian and Hauterivian) with a focus on the Barremian-Aptian regression in the EAB. Fluvial sandstones were sampled and analysed; thin section petrography and scanning electron microscope (SEM), heavy minerals analysis, and detrital zircon geochronology were conducted and integrated with a large dataset of published low-temperature thermochronology. Integrating the palaeogeology reconstructions with detrital datasets allows shifts of sources to be tracked through time. Lower to Middle Jurassic strata in the EAB were sourced from the erosion of Palaeozoic sediments within the Western and Central Anti Atlas. Upper Jurassic and Lower Cretaceous sediments were mostly sourced from the erosion of a Triassic-Jurassic overburden that covered the West Moroccan Arch at the time but not preserved in the modern geology. Detrital zircon geochronology showed a strong affinity with the expected fingerprint of the region. Significant regressions associated with falling relative sea level are interpreted to have allowed basinward shift of fluvio-deltaic systems to the shelf edge, allowing sediment supply to the slope/offshore domain during the Lower Cretaceous. Seismic imaging suggests the presence of Lower Cretaceous high reflectivity deepwater channels located in structural lows controlled by syn-sedimentary diapiric salt movement. An overall NNW drainage direction is observed offshore the northern part of the EAB. The Mesetian domain was likely undergoing denudation and shedding a clastic-rich sediment supply to the north of the studied region. Due to the NNW deflection, mixing between MAM and Meseta sands is probable, and is likely to have happened 18 offshore Essaouira creating good quality deep water reservoir sands deposited during the discrete periods of regression.
|Date of Award||1 Aug 2022|
- The University of Manchester
|Supervisor||Jonathan Redfern (Supervisor) & Stefan Schroeder (Supervisor)|
- Source to sink
- Essaouira-Agadir Basin