Palaeohighs: their influence on the North African Palaeozoic petroleum systems

Abstract

We present new insights for the characterization of the petroleum system evolution in North Africa based on a review of the stratigraphic architecture description of some selected North African Palaeozoic basins. During Palaeozoic time, the Gondwana platform was divided into sub-basins bounded by structural highs. Most of the highs were inherited from north-south and SW-NE Pan-African crustal faults which were reactivated during the Palaeozoic and later, in the Austrian and Alpine tectonic phases. We studied the stratigraphic architecture of the Palaeozoic succession around four main highs showing a clear tectonic activity during the Palaeozoic sedimentation. The Gargaff Arch, in Libya, is a major SW-NE broad anticline which slowly grew up during the Cambrian and Ordovician and stopped rising during the Silurian. The activity resumed during Late Silurian and early Devonian and during the Late Devonian. The Tihemboka High is a north-south anticline in between Libya and Algeria. The uplift started during the Cambro-Ordovician then stopped during most of the Silurian. The activity resumed during the Late Silurian and continued until the Lower Carboniferous. The Ahara High, separating the Illizi and Berkine basins in Algeria, has continuously grown during the Cambro-Ordovician, stopped rising during the Silurian, and grew again continuously during the Devonian. The Bled El-Mass High is a part of the Azzel-Matti Ridge separating the Ahnet and Reggane basins in Algeria. The high mostly rose during the Cambro-Ordovician then subsided relatively less quickly than the surrounding basins during the Silurian and Devonian. The uplift timing and chronology of each palaeohigh partly controlled the petroleum systems of the surrounding basins. Topographic lows favoured the occurrence of anoxic conditions and the preservation of Lower Silurian and Frasnian source rocks. Complex progressive unconformities developed around the palaeohighs form potential complex tectonostratigraphic traps. Finally, hydrocarbons could have been trapped around the highs during pre-Hercynian times, preserving reservoir porosity from early silicification. Mixed stratigraphic-structural plays could then be present today around the highs.

Sedimentary imprints of former ice-sheet margins: Insights from an end-Ordovician archive (SW Libya)

“…The Murzuq Basin developed on the northwestern part of the Gondwana super-continent. This is one of the subsiding north African intracratonic basins preserving an extensive Lower Palaeozoic record formed subsequently to the Panafrican orogeny (Beuf et al, 1971;Black et al, 1994;Boote et al, 1998;Coward and Ries, 2003;Guiraud et al, 2005;Eschard et al, 2010;Ghienne et al, 2013). From the Cambrian to the Devonian, the broader North Gondwana platform had an off-shelf gradient towards the NNW (Coward and Ries, 2003;Eschard et al, 2010;Ghienne et al, 2013).…”

“…This is one of the subsiding north African intracratonic basins preserving an extensive Lower Palaeozoic record formed subsequently to the Panafrican orogeny (Beuf et al, 1971;Black et al, 1994;Boote et al, 1998;Coward and Ries, 2003;Guiraud et al, 2005;Eschard et al, 2010;Ghienne et al, 2013). From the Cambrian to the Devonian, the broader North Gondwana platform had an off-shelf gradient towards the NNW (Coward and Ries, 2003;Eschard et al, 2010;Ghienne et al, 2013). Thereafter, until the Cenozoic, intracratonic basins were affected by multistage tectonics, re-activating inherited Panafrican structures (Bellini and Massa, 1980;Davidson et al, 2000;Galeazzi et al, 2010), responsible for their present configurations.…”

Ordovician shallow-marine tidal sandwaves in Algeria – the application of coeval outcrops to constrain the geometry and facies of a discontinuous, high-quality gas reservoir

“…This landmass consisted of several terranes that accreted during the late Proterozoic Pan-African Orogeny (Craig et al 2010;Eschard et al 2010;Galeazzi et al 2010). Major north-south faults resulting from this accretion were reactivated several times during geological history, although, away from these faults, the landmass was relatively rigid and stable.…”

“…A consequence of this periodic tectonic activity was the development of structural highs above several of these Pan-African lineaments; these include the Amguid-el Biod High and the Tihemboka Arch along the west and east sides, respectively, of the Palaeozoic depocentre that forms the Illizi Basin ( Fig. 1) (Boote et al 1998;Eschard et al 2010;Galeazzi et al 2010). By latest Ordovician times, when the glacial -post-glacial sediments were deposited, there was little or no tectonic activity affecting the sediment thicknesses across the Tassili N'Ajjer outcrops.…”

“…1a); hydrocarbons have been produced from the Lower Palaeozoic succession since 2006. A simplified chronostratigraphy over the main culmination, the Tiguentourine field, is presented in Figure 2 Beuf et al 1971;Whiteman 1971;Eschard et al 2005;Le Heron & Craig 2008;Eschard et al 2010). The primary reservoir interval comprises the complex Late Ordovician glacial deposits of the Tamadjert Formation.…”