Architecture stratigraphique des séries sédimentaires du Dévonien de l ouest de la Libye

Wide, shallow marine cratonic platforms were the place of the early colonization of land areas by plants and animals in Devonian times. These events are well recorded in western Libya along the Gargaf arch which separates the Ghadamis and Murzuk basins. This study describes lithologies, diagenesis, key-surfaces, and stacking patterns of depositional sequences at the outcrop and in the subsurface of the Ghadamis basin. The overall regional sediment distribution is modeled and compared to the neighboring basins and the worldwide record to discuss the role of local vs. large scale tectonics and sea level controls on the paleolandscape evolution. These results provide clues for a better understanding of this period and the functioning of the broad cratonic platforms with consequences on location and origin of hydrocarbon source rocks and reservoirs.Les plate-formes cratoniques, larges et peu profondes, furent le lieu, au Dévonien, de la première colonisation des aires continentales par les faunes et les flores. Ces événements sont bien enregistrés à l ouest de la Libye dans les sédiments déposés le long de l arche cratonique de Gargaf qui sépare les bassins de Ghadames et de Murzuk. Cette étude décrit les lithologies, la diagenèse, les surfaces-clés, l empilement des séquences de dépôts de ces sédiments à l affleurement et en subsurface dans le bassin de Ghadames. La distribution régionale des sédiments est comparée aux bassins environnants et à l enregistrement mondial pour discuter le rôle des contrôles tectoniques locaux et régionaux sur l évolution des paléopaysages et des paléosurfaces continentales. Ces résultats fournissent des indications clés et sur le fonctionnement des larges plate-formes cratoniques et leurs conséquences sur la localisation et l origine des roches mères et des réservoirs pétroliers.RENNES1-BU Sciences Philo (352382102) / SudocSudocFranceF

Stratigraphic architecture of the Devonian succession in Awaynat wanin area, Ghadamis Basin, Western Libya

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Unraveling tectonic and climatic controls on sedimentation: cratonwide correlation of depositional events across the swales and arches of the Devonian North African platform

International audienc

Stratigraphic architecture of the Devonian succession in the Ghadamis basin of western Libya – correlation with the Illizi basin in Algeria

1 p.During Palaeozoic times, the structuring of North Gondwana induced the formation large epicratonic platforms in North Africa. These platforms are comprised of extensive, shallow sub-basins or swales separated by smooth tectonic arches. The sub-basins were slowly subsiding whereas the arches were periodically eroded by tectonic uplift or eustatic sea-level drops. The resulting architecture of sedimentary rocks into these basins is characterized by thin, laterally extensive, mixed marine and non marine sediment wedges truncated by large unconformities representing long time gaps. The aims are here (1) to illustrate this typical architecture from the example of the Devonian rocks preserved in the Ghadamis basin and the Illizi basins (2) to discuss the observed geometries of the sediment bodies wedging out along the local tectonic arches of Gargaf and Tihemboka, and (3) to examine the origin and the influence of the parameters that control both the sequence architecture and the reservoir distribution on such large cratonic areas. The Devonian formations are among the largest oil reservoirs in Northern Africa. The Devonian rocks are characterized by the intercalation of sandstones, claystones and shales interbedded with few carbonate beds. They represent a broad range of depositional environments from fluvial to offshore marine shelf organized into a complex stack of tens of m-thick, unconformity-bounded, transgressive-regressive sequences. The architecture of the sedimentary units, reconstructed from the correlation of field observations and subsurface data (wells and seismic data), shows that fluvial and shoreface sandstones units are well-developed close to the arches and thin out laterally in the shale unit that thicken and deepen towards basins depocenters. Offshore marine, organic-rich shale units (secondary source rocks and seals) are prominent marker beds followed along hundreds of km from Libya to Algeria, and possibly further, when they correlate to the Kaçak and Kellwasser events

Nature and stratigraphic architecture of the Devonian succession in the Ghadamis basin of western Libya

1 p.During Palaeozoic times, the structuring of North Gondwana induced the formation large epicratonic platforms in North Africa. These platforms are comprised of extensive, shallow sub-basins or swales separated by smooth tectonic arches. The sub-basins were slowly subsiding whereas the arches were periodically eroded by tectonic uplift or eustatic sea-level drops. The resulting architecture of sedimentary rocks into these basins is characterized by thin, laterally extensive, sediment wedges truncated by large unconformities representing long time gaps. The aim is here to illustrate this architecture from the example of the Devonian rocks preserved in the Ghadamis basin and along the Gargaf Arch in NW Libya, and to discuss the origin and the influence of the parameters that control both the sequence architecture and the reservoir distribution on such large cratonic areas. The Devonian rocks exposed along the Gargaf arch in Awaynat Wanin area are characterized by the intercalation of sandstones, claystones and shales interbedded with few carbonate beds. They represent a broad range of depositional environments from proximal fluvial to offshore marine shelf organized into a complex stack of six 30 to 80m-thick, unconformity-bounded, transgressive-regressive sequences. The overall architecture of the sedimentary units and depositional environments in the Ghadames basin is reconstructed from the correlation of field observations and subsurface data (wells and seismic data). They show an overall thinning out of the sandstone units in the shale units, northwestward, in a dip direction along hundreds of kilometres, but a better consistency across strike (except for the Frasnian-Famennian sandstones). Offshore marine, organic-rich shale units are prominent marker beds into the whole basin. The most important are the Eifelian Emgayet shales and the Frasnian radioactive shales and limestones. These units are both seal and secondary source rocks units

Land-sea interactions during Devonian times on the cratonic platform of western Libya

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Carriage by the housefly ( Musca domestica ) of multiple-antibiotic-resistant bacteria that are potentially pathogenic to humans, in hospital and other urban environments in Misurata, Libya

International audienceUsing standard microbiological procedures, bacteria that are potentially pathogenic to humans were isolated from 150 houseflies collected in the Libyan city of Misurata (50 flies each from the Central Hospital, streets and abattoir). Salmonella spp., Yersinia enterocolitica and Edwardsiella tarda were isolated from flies collected on the streets and in the abattoir but not from those collected in the hospital. Shigella sonnei was detected in just one fly, which was collected in the abattoir. Of the flies collected in the hospital, streets and abattor, 42%, 42% and 32% were positive for Escherichia coli, 70%, 50% and 62% for Klebsiella spp., 2%, 20% and 10% for Aeromonas spp., 96%, 36% and 34% for Pseudomonas spp., 20%, 12% and 16% for Staphylococcus spp., and 24%, 22% and 18% for Streptococcus spp., respectively. When the antibiotic susceptibilities of the fly isolates were investigated, the Enterobacteria isolated from the houseflies collected in the hospital were found to be resistant to significantly more of the commonly used antibiotics that were tested than the Enterobacteria isolated from the flies caught in the streets or abattoir. Whatever the source of the flies from which they were collected, the Pseudomonas isolates frequently showed resistance to multiple antibiotics, with >50% each being resistant to at least 10 antimicrobial agents. Two isolates of Sta. aureus (both from flies collected in the hospital) were resistant to methicillin. The present study supports the belief that the housefly is a potential vector of multiple-antibiotic-resistant, pathogenic bacteria, including methicillin-resistant Sta. aureus, in the hospital environment. Given their mobility, it seems likely that houseflies carry such pathogens from hospitals to surrounding communities, and vice versa

Palaeohighs: their influence on the North African Palaeozoic petroleum systems

International audienceWe 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 Panafrican 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 Lybia, 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 tectono-stratigraphic 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