The Medjerda Zone of Northern Tunisia: basin analysis and structural evolution of the Teboursouk area

Fordham, David (1996) The Medjerda Zone of Northern Tunisia: basin analysis and structural evolution of the Teboursouk area. (MPhil thesis), Kingston University, .


Recent analysis of the Medjerda Zone of northern Tunisia has demonstrated that the Tunisian Atlas thrust belt extends considerably further south-eastwards than previously recognised, terminating in the North-South axis which forms the mountain front of the thrust system. Therefore, areas hitherto considered to be foreland and autochthonous are now thought to form an allochthonous part of the Atlassie thrust belt. One such area is the Medjerda Zone of northern Tunisia where the traditionally accepted, autochthonous and diapiric structural model has recently been challenged by an allochthonous, thin skinned thrust-tectonics model. Fieldwork undertaken during the course of this studentship in the Fedj el Hadoum and Djebel Goraa areas of the Medjerda Zone has led to the rejection of both models coupled with the proposal of a revised evolutionary model which recognises the area as forming an allochthonous component of the Atlassie thrust belt. This new model is therefore proposed in which a Triassic template was subject to NW-SE orientated extension which led to the development of a suite of submarine en-echelon half grabens whose basin-bounding extensional faults faced south-east. Subsequent filling of the basins with varying thicknesses of marine Cretaceous-Eocene rocks was followed by the deposition of mostly continental Oligocene-Miocene clastic rocks. The Cretaceous-Eocene succession contains two notable source rocks which were sufficiently buried during the Late Cretaceous in the deeper I parts of the basin to enable the generation of hydrocarbons. Expulsion of hydrocarbon and metal-bearing basinal brines subsequently occurred which utilised permeable fault rocks along the south-easterly facing, extensional faults to escape. In the process the basinal brines came into contact with Triassic gypsum in the footwall block which led to the precipitation of lead/zinc mineralisation within the fault zones where, in addition, present day oil seeps are also located. Subsequent deformation during the Atlassie orogeny resulted in the emplacement of thrusts through the half graben structures with the accompanying development of folds within the sedimentary successions.

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