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The current knowledge of the stratigraphy of Niger benefited greatly from the mining, hydrocarbon, hydrogeological, and paleontological sciences. Exploration by early explorers and studies of the aquifers initially sparked our understanding of the surface and shallow formations. Then, the discoveries in 1957 of important Uranium reserves and soon a...
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... African Rift System (WCARS). It covers an area of approximately 2×10 4 km 2 in the northwestern part of the Eastern Niger Basin (Fig. 5-25) and extends for about 300 km north-south and 50 -80 km west-east. The basin is developed on a Precambrian basement and consists of a graben and two halfgrabens controlled by NW-SE-trending border faults (Fig. 5-31, Fig. 5-32). The basin is divided into three structural units: the western depression, the eastern depression I and the eastern depression II (Fig. ...
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... for about 300 km north-south and 50 -80 km west-east. The basin is developed on a Precambrian basement and consists of a graben and two halfgrabens controlled by NW-SE-trending border faults (Fig. 5-31, Fig. 5-32). The basin is divided into three structural units: the western depression, the eastern depression I and the eastern depression II (Fig. ...
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... Glacial, periglacial, Glacio-marine, fluvial channel infill ( Fig. 7-31) Thickness: ~80 m ( Fig. 7-35). Overlying Unit: Tanzuft Fm, unconformable Underlying Unit: Legrand (1993) and Denis et al. (2007) mention the Tigillites sandstone, which is in Niger the equivalent of the Hawaz Formation. Contact between the Hawaz Fm and the Chirfa Fm is erosive because of glacial ...
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... volcanic ash having undergone a diagenetic evolution (silicification, Cu, U mineralization) (Fabre et al., 1983). The sedimentary rocks of the Tchirezrine 2 Member consist of a succession of fine-to very coarse-grained sandstones (arkoses) that were deposited in a complex fluviatile system that can be described as a braided and meandering system (Fig. 7-131). Analcimolite beds deposited in river floodplains associated with this fluviatile system occur intercalated between sandstones. The Member comprises very various and complex mineralogical assemblages, with the distinctive feature of presenting both tetravalent (U IV ) and hexavalent (U VI ) uranium mineralization, the second one being ...
Citations
The two historic fortresses of St. Jeronimo and Santiago de la Gloria, and the Royal Customs House in Portobelo are all made of corals because it was more abundant and easier to cut than the igneous rock found inland. Therefore, the Spaniards used corals for most of the construction. Known as “reef rock,” coral is easily shaped, tough as granite yet light as pumice. Some walls in Santiago de la Gloria Fort and St. Jeronimo Fort were as much as 3 metres thick, made entirely of cut coral. Coral stone is also naturally porous, which helps it withstand the humid and salty coastal environment. Its light weight compared to other stones made it easier to transport and work with during construction. This article will identify the two primary genera of corals that were used to build these historic buildings.
The two closest volcanic centres to Nueva Gorgona are the Cerro Chame Dome, situated east of the Chame River (the easternmost point of this study; see Fig. 2-01), and El Valle Volcano, located 28 km to the northwest. These volcanic centres are the reasons for the presence of black sands on the beach at Nueva Gorgona (and other beaches to the west). Representative beach sand samples were collected and analyzed for magnetic mineral content (%) and radioactivity levels along a 4.74 km stretch of beach. Samples were taken every 150-200 metres from areas dominated by low and high tides. The average percentage of magnetic material (mainly magnetite) on the beach ranges from 67% (at low beach level) to 90% (at high beach level); however, rich concentrations of heavy minerals occur locally. Black sand is present along most parts of the beach, either on the surface or in shallow layers. However, it tends to disappear at low beach levels in the east, near the Chame River, due to the narrowness of the beach in this area. The black sand originates primarily from the erosion of crystalline basalt and fine-grained andesitic to rhyolitic tuff. The basalt is exposed in the western portion of the beach and on Cerro Chame. The older, well-bedded fine-grained tuff also occurs on the beach and is reminiscent of the El Hato ignimbrite from the El Valle volcano. The tuff’s age is estimated to be from the Late Pleistocene (~32ka) while the basalt is younger.
