During the Early Cretaceous a regionally extensive cover of dominantly siliciclastic sediments was deposited across the North African continental margin. Historically, these siliciclastic sediments have been considered to be a relatively homogeneous lithofacies known as the ‘Nubian sandstone’. This lithofacies is generally described as coarse grained, cross-bedded sandstone and is ascribed to a braided fluvial depositional environment. However, there have been few detailed sedimentological studies carried out on these sediments. Furthermore, the stratigraphic relationships between regional Early Cretaceous continental strata in different North African countries has only briefly been described and has only locally been related to equivalent marine deposits. In order to address these problems, this study focuses upon two main approaches. Firstly, outcrop analysis of the Messak Fm (SW Libya) and the Sidi Aïch Fm (C Tunisia) details and contrasts the lithofacies variability of Early Cretaceous siliciclastic sediments in North Africa. Secondly, a unified stratigraphic framework is erected for the Early Cretaceous of Algeria, Tunisia, Libya and Egypt and the palaeogeographic evolution is reconstructed. Detailed sedimentological investigation of the Messak Fm has identified greater variation in lithofacies and depositional processes than was previously recognised. By lithostratigraphic correlation with outcrops in northwest Libya, we show a fluvial system transported sediment northward into a wide fluvio-paralic basin covering western Libya. Several episodes of marine influence culminating in a distinct and regionally correlatable transgressive episode are identified. This is the first time that marine influence has been identified in the Murzuq Basin and increases the maximum known extent of marine transgression in the Early Cretaceous of Libya by 600km. The sedimentology of the Messak Fm is contrasted with the sandstone dominated Sidi Aïch Fm which, although showing similar lithofacies, was deposited in a marginal-shallow marine environment.Building upon previous reviews and new insights from the Messak Fm and Sidi Aïch Fm, a synthesis and reinterpretation of the spatial and temporal heterogeneity of sediments and depositional environments in this region throughout the Early Cretaceous is presented. During the Berriasian-Barremian, the North African platform coastline was dominated by a dry subtropical climate with moderate vegetation. The interior of the platform experienced a Savannah-like semi-arid climate with limited vegetation and palaeosol development but was crossed by extensive fluvial networks draining the equatorial tropics. During the Late Barremian-Early Aptian, simultaneous aridification and marine transgression led to a decreased detrital flux to the marginal basins and widespread deposition of marine carbonates and mudstones. During the Late Aptian-Albian the platform returned to a humid tropical climate. Widespread coarse grained fluvial sediments mark the base of this sequence and palaeosols occur locally. The results of this work have implications for the development and controls of large-scale fluvio-paralic systems and illustrate the fact that, in a limited accommodation epicontinental setting, relative sea-level may be the key control on sedimentation and depositional processes for many hundreds of kilometres inland of the lowstand coastline.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:568649 |
| Date | January 2013 |
| Creators | Wood, Jonathan Derek |
| Contributors | Redfern, Jonathan |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://www.research.manchester.ac.uk/portal/en/theses/sedimentological-characterization-and-regional-palaeoenvironmental-implications-of-the-messak-fm-sw-libya(e5da88e0-fa5a-463a-a16d-be60247de5dd).html |
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