The University of Manchester Research Stratigraphic trapping potential in the Carboniferous of North Africa: developing new play concepts based on integrated outcrop sedimentology and regional sequence stratigraphy (Morocco, Algeria, Libya) Link to publication record in Manchester Research Explorer Citation for published version (APA): Redfern, J., Vining, B. A. (Ed.), & Pickering, S. C. (Ed.) (2010). Stratigraphic trapping potential in the Carboniferous of North Africa: developing new play concepts based on integrated outcrop sedimentology and regional sequence stratigraphy (Morocco, Algeria, Libya). In B. A. Vining, & S. C. Pickering (Eds.), Petroleum Geology: From Mature Basins to New Frontiers—Proceedings of the 7th Petroleum Geology Conference (Vol. 7, pp. 725-734). Geological Society . 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Oct. 2021 Petroleum Geology Conference series Stratigraphic trapping potential in the Carboniferous of North Africa: developing new play concepts based on integrated outcrop sedimentology and regional sequence stratigraphy (Morocco, Algeria, Libya) S. Lubeseder, J. Redfern, L. Petitpierre, et al. Petroleum Geology Conference series 2010; v. 7; p. 725-734 doi: 10.1144/0070725 Email alerting click here to receive free e-mail alerts when new articles cite this article service Permission click here to seek permission to re-use all or part of this article request Subscribe click here to subscribe to Geological Society, London, Petroleum Geology Conference series or the Lyell Collection Notes Downloaded by Jonathan Redfern on January 26, 2011 © Petroleum Geology Conferences Ltd. Published by the Geological Society, London Stratigraphic trapping potential in the Carboniferous of North Africa: developing new play concepts based on integrated outcrop sedimentology and regional sequence stratigraphy (Morocco, Algeria, Libya) S. LUBESEDER, J. REDFERN, L. PETITPIERRE and S. FRO¨ HLICH School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Oxford Rd, Manchester M13 9PL, UK (e-mail: [email protected]) Abstract: The lower Carboniferous (Tournaisian to Visean) of North Africa is characterized by cycle-stacks of predominantly shelfal to marginal marine sandstones and limestones, thick shelfal mudstones and less common but important interbedded fluvio-deltaic sandstones. The cyclic sedimentation pattern continues into the Mid Carboniferous (Serpukhovian to Bashkirian), when mixed siliciclastic–carbonate sequences give way to tropical carbonates, before an abrupt return to continental deposits in the upper Carboniferous (Bashkirian to Gzhelian). The alternation of widespread shallow marine and more discrete fluvial reservoirs with interbedded offshore mud- stone seals is interpreted to result from high-frequency, high-amplitude Carboniferous glacio-eustatic sea-level changes. The large base-level changes during that time, combined with climatic conditions that produced high amounts of terrigenous mud, provided favourable conditions for the development of stratigraphic traps in the clastic-prone lower Carboniferous, while the advent of tropical carbonates produced reefal buildups in the Mid Carboniferous. Four stratigraphic trapping types are recognized: (1) truncation traps in which reservoir units were eroded on subaerially exposed proximal palaeohighs and thick underlying transgressive and highstand systems tract (TST and HST) mudstones form the bottom-seal and the rapid transgression of the offshore facies forms the top-seal; (2) pinchout traps of lowstand wedges on the flanks of distal palaeohighs, which were only affected by subaqueous reworking of previous TST–HST mudstones and were buried during the sub- sequent transgression; (3) incised valleys of the lowstand systems tract (LST), filled with thick fluvial and tidal sandstones, cutting either into TST–HST mudstones in the lower Carboniferous, or into exposed carbonate plat- forms in the Mid Carboniferous; (4) Waulsortian-type reefal buildups of the Mid Carboniferous. The four trapping types are discussed using selected outcrop examples, and are placed into regional sequence stratigraphic context of the Carboniferous depositional systems and sequence development of North Africa. These concepts can be readily applied to the subsurface and offer significant potential for new plays across North Africa. Keywords: stratigraphic traps, sequence stratigraphy, Carboniferous, Morocco, Algeria, Libya A tentative sequence stratigraphic scheme for the Carboniferous of fossiliferous Carboniferous sediments. The sequence strati- of North Africa has been developed to guide reservoir prediction graphic scheme and correlation presented here must be considered in poorly explored areas and to provide a framework for further a preliminary working document due to the vast area covered and analysis of potential stratigraphic traps. Seven important outcrop the relatively widely spaced dataset currently available. In certain sections across North Africa were reviewed and correlated. Of data-poor areas the scheme remains very conjectural at present. these, five sections have been interpreted based on published In addition to the limited dataset, different fossil groups used for sources and two sections (SW Anti-Atlas, Morocco; NW Murzuk biostratigraphic dating sometimes suggest very different ages Basin, Libya) were logged for this study (Figs 1 & 2). All sections (Wendt et al. 2009), exemplifying the need to continue and are located along the southern Palaeozoic outcrop belt, comprising update the research on the extensive outcrops. exposures in the Anti-Atlas, the Bechar Basin, the Reggane, Ahnet The regional correlation shows the general facies patterns and and Mouydir Basins, the southern Illizi Basin, and the northern palaeogeography of the Carboniferous from Morocco to western Murzuk to southern Ghadames Basins. The presented chronostrati- Libya. This correlation allows assessment of the broad trends, graphic chart has been compiled based on a comprehensive review although it should be emphasized that in detail, on a basin scale, of a large amount of published literature, of which only selected the stratigraphy and sedimentology are undoubtedly more compli- key publications are referred to in this summary paper. cated than can be shown on the generalized correlation panel. The following sections describe each phase of Late Devonian to Late Carboniferous deposition, ending with a comparison of these North African Carboniferous sequence framework phases with global sea-level cycles. Over many decades of studies in North Africa there have been a Late Devonian (‘Strunian’) regression number of publications on the stratigraphy and sedimentology of the Carboniferous; an excellent regional summary is provided by A latest Devonian (‘Strunian’) regression is recognized across all Diaz et al. (1985). However, of these studies, only a few attempt of NW Africa, with the deposition of shelf sandstones in the Anti- any sequence-type interpretation. In this paper we present the first Atlas (e.g. Kaiser et al. 2004), Bechar Basin, Ougarta Arch, north- regional sequence stratigraphic scheme, based on a large amount ern Hoggar region and the Illizi and Ghadames Basins (Conrad of available published biostratigraphic and sedimentological data, et al. 1986; Lubeseder 2005; Fig. 3). A regionally extensive uncon- integrated with new field work. formity developed in the Murzuq Basin of Libya and across Good quality sedimentological and biostratigraphic published surrounding palaeohighs (the Gargaf Arch and Tihemboka Arch) work on a regional scale is very limited, despite the vast outcrops and presumably reached far into the Ghadames Basin. The VINING,B.A.&PICKERING, S. C. (eds) Petroleum Geology: From Mature Basins to New Frontiers – Proceedings of the 7th Petroleum Geology Conference, 725–734. DOI: 10.1144/0070725 # Petroleum Geology Conferences Ltd. Published by the Geological Society, London. 726 Lubeseder, 2006 12°W 6° 0° 6° 12°E 18° Outcrops Carboniferous Upper Devonian / 36°N Lower Carboniferous Pre-Cambrian basement Rif Tunisia Sections (Fig. 2) Morocco Meseta s Atla Middle J. Antar Ben Zireg Algeria 32° Atlas Tafilalt B. High Meharez High S. LUBESEDER Bechar Basin Berkine B. SW Anti-Atlas Maider B. Zousfana Valley Jebel Tazout & Ghadames Basin Anti-Atlas O Jebel Ouarkziz ugart southern outcrops Foum Zguid a Arch TimimounB. Libya Plain Dra Illizi Basin ET AL Tindouf Basin Ahnet Basin Gargaf Arch 28° Jebel Berga Mouydir B. Reggane B. Idri Tassili Murzuk Basin Dor el Gussa Al Awaynat Reggane Basin Ghat Reguibat Bled