Papers by Nezha EL KAMALI
Le Cretace moyen (Albien superieur a Turonien) de la region d'imi N'Tanout est classiquem... more Le Cretace moyen (Albien superieur a Turonien) de la region d'imi N'Tanout est classiquement subdivise en trois formations. Leur analyse tant strati graphique que sedimentologique permet de proposer un premier essai d'interpretation en terme de stratigraphie sequentielle. Il parait possible de reconnaitre dans l'intervalle de temps considere. sept sequences de depot. La premiere (SD1) se confondrait avec la formation vraconienne du Kechoula ; les six autres (SD2 a SD7) s'etagent dans le Cenomano-Turonien. Si, aux imprecisions stratigraphiques pres, ces sept sequences sont correlables en nombre aux cycles de 3eme ordre du supercycle UZA-2 du diagramme de HAQ et al., (1987), l'interpretation des corteges sedimentaires, surtout dans l'intervalle Vraconien-Cenomanien reste particulierement delicate.
T here's a building boom at the Hanford Site, a once-secret complex on the windswept plains of so... more T here's a building boom at the Hanford Site, a once-secret complex on the windswept plains of southeastern Washington state. Construction crews are working to finish a 27-metre-tall concrete structure there by June. If all goes well, the facility will finally enable the US Department of Energy (DOE) to begin treating the toxic, radioactive waste that accumulated at the site for more than 40 years, starting during the Second World War. Decades after the site stopped producing plutonium for nuclear weapons, the legacy of Hanford's activities is still causing trouble. Just this year, a tunnel holding railway carriages full of radioactive material collapsed. Separately, at least a dozen employees who were tearing down a contaminated building reportedly tested positive for plutonium inhalation. But the site's biggest challenge lies underground, in 177 carbon-steel tanks. Together, these buried containers hold more than 200 million litres of highly hazardous liquids and peanut-buttery sludge-enough to fill 80 Olympic-size swimming pools. More than one-third of the tanks have leaked, contaminating groundwater with radioactive and chemical waste. In a 1989 legal agreement with the state of Washington and the US Environmental Protection Agency, the DOE committed to immobilizing the most dangerous waste in sturdy glass logs through a process called vitrification. Several years later, the agency agreed to vitrify other tank waste as well. All told, the process is expected to generate tens of thousands of logs, each weighing multiple tonnes. Those containing high-level waste would be shipped to a permanent storage facility; the rest could be stored on site. But the effort has been plagued by cost overruns, delays and safety concerns. Although the DOE has spent roughly US$20 billion on the tank problem since 1997, no waste has been vitrified. Four years ago, the agency hit reset. Rather than making a single vitrification plant, it split the project in two. One plant-the building now under construction-would begin vitrifying the less-hazardous, 'low-activity' liquid in the tanks. A bigger, more-complex plant to process the high-level sludge would follow once researchers resolved some thorny safety questions. On both fronts, there have been signs of progress. This year, the DOE reported that it had resolved crucial questions related to treating the high-level waste. And a laboratory needed for real-time analysis of the low-level waste is nearing completion. If work continues as planned, the site could crank out its first glass logs as early as 2022. Hanford's critics, accustomed to missed deadlines and
The rock engravings, the subject of this article, are artistic representations made by people fro... more The rock engravings, the subject of this article, are artistic representations made by people from cultural communities who no longer exist. The rock art was a way of expressing their thoughts, culture and beliefs, before the invention of writing. The engravings represent an archive of an ancient civilization which developed over thousands of years throughout North Africa, from the Atlantic to Egypt and from the Atlas Mountains to the Sahel. Morocco has more than 300 listed rock art sites, scattered throughout the country. Foum Chenna is a major site in the Anti-Atlas Mountains of southern Morocco. The engravings were predominantly made by pecking out images of human figures, animals and patterns, and the area today is the center of interest for the recently-formed Association of Rock Art Heritage of Southern Morocco, based in Zagora. Foum Chenna is a place of primary importance with more than 800 schematic engravings made using the pecked technique, a characteristic of this period....
Journal of Iberian Geology, 2018
Microfacies, fossil macroinvertebrates and microfossil assemblages (foraminifera and ostracods) a... more Microfacies, fossil macroinvertebrates and microfossil assemblages (foraminifera and ostracods) and δ 13 C from the Rhoundjaïa Formation (Ksour Mountains, Western Saharan Atlas, Algeria) were studied. During the Late Cenomanian-Early Turonian, the Ksour Basin was an isolated platform at mid to outer shelf depths. The neritic conditions were interrupted by pelagic conditions in transgressive intervals. This deepening of the palaeoenvironment is reflected by changes in the foraminiferal assemblages. The composition of benthic and planktic foraminiferal assemblages, characterized by low diversity and abundance of low oxygen tolerant species, reflects a carbonate platform with biotic stress conditions (oxygen and nutrient fluctuations and sea-level changes). Planktic foraminiferal assemblages are dominated by opportunists such as Muricohedbergella and Planoheterohelix, which colonized new ecospace on the shelf during the transgression. The Oceanic Anoxic Event 2 (OAE2) is not represented by organic rich facies but does coincide with the successive proliferation of different opportunist organisms such as microgastropods and small echinoid (hemiasterids) and the heterohelicid shift. The continuous presence of trace fossils (Thalassinoides and Planolites-like) and benthic macroinvertebrates allows us to exclude anoxic conditions during the Whiteinella archaeocretacea Zone. The proliferation of Planoheterohelix indicates the record of eutrophic conditions and the transition from oxygenated to poorly oxygenated waters during stratified open marine settings at the time of maximum flooding. The subsequent increase in thin-shelled bivalves and cytherellid ostracods would confirm the stress conditions at the time of the δ 13 C isotopic excursion in the upper part of the W. archaeocretacea Zone. The Lower Turonian is represented by a shallowing upward trend in the Ksour Basin. Comparison of the taxonomic composition of the planktic foraminiferal assemblages (phenogram and class diagram) indicates the high degree of relationship of the Ksour Basin with the Northeast Sicily Basin, Central Tunisia Basin and Egypt. This work sheds light on the impact of the OAE2-related environmental perturbation in environments where anoxic conditions were not reached, as well as the response of the fossil assemblages to the biotic crisis. Keywords Microfacies • Foraminifera • Ostracods • Opportunist • Biotic crisis • North Gondwana Palaeomargin Resumen Se han estudiado las microfacies, las asociaciones de macroinvertebrados fósiles y microfósiles (foraminíferos y ostrácodos) y el 13 C en la Formación Rhoundjaïa (Montes Ksour, Atlas Sahariano Occidental, Argelia). Durante el Cenomaniense superior-Turoniense temprano, la Cuenca de Ksour fue una plataforma relativamente aislada con unas características entre plataforma media y externa. Las condiciones neríticas cambiaron a condiciones pelágicas durante los intervalos transgresivos. La profundización de los paleoambientes queda registrada por cambios en las asociaciones de foraminíferos. La composición de las asociaciones de foraminíferos bentónicos y planctónicos caracterizada por baja diversidad y por la abundancia de species tolerantes de baja oxigenación, refleja una plataforma cabonatada con condiciones de estrés biológico (variaciones en el grado de oxigenación, contenido en nutrientes y nivel del mar). Las asociaciones de foraminíferos planctónicos están dominadas por oportunistas tales como Muricohedbergella y Planoheterohelix, que colonizaron el incremento de ecoespacio creado en la plataforma durante la transgresión. El evento anóxico oceánico 2 (Oceanic Anoxic Event 2, OAE2) no está representado por facies ricas en materia orgánica sino que coincide con la sucesivas etapas de proliferación de diferentes grupos de oportunistas como microgasterópodos y pequeños equinoideos (hemiastéridos) y la proliferación de heterohelícidos. El registro
L'histoire de notre planète se lit dans les dépôts sédimentaires qui se sont superposés sous la f... more L'histoire de notre planète se lit dans les dépôts sédimentaires qui se sont superposés sous la forme de couches ou strates successives. L'étude de ces strates est la stratigraphie. Autrefois, la stratigraphie se contentait d'étudier les strates fossilifères. Puis après, on s'est aperçu que la plupart des événements géologiques (orogenèse, volcanisme, …) survenus dans une région avaient également laissé des traces. Stratigraphie = la discipline de la géologie qui étudie l'agencement dans le temps et dans l'espace, des formations géologiques et des événements qu'elles matérialisent afin de reconstituer l'histoire de la Terre et son évolution.
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Papers by Nezha EL KAMALI