Specific sediment yield in Tigray-Northern Ethiopia: Assessment and semi-quantitative modelling   总被引：2，自引：0，他引：2  

Nigussie Haregeweyn  Jean Poesen  Jan Nyssen  Gert Verstraeten  Joris de Vente  Gerard Govers  Seppe Deckers  Jan Moeyersons 《Geomorphology》2005,69(1-4):315-331

  相似文献   

A geochemical method for removing the effect of tephra on lake diatom oxygen isotope records     

Angela L. Lamb  Tim S. Brewer  Melanie J. Leng  Hilary J. Sloane  Henry F. Lamb 《Journal of Paleolimnology》2007,37(4):499-516

The analysis of oxygen isotope ratios (δ¹⁸O) in biogenic silica (e.g. diatoms, sponge spicules, phytoliths) is an increasingly utilised palaeoclimatic proxy for lakes and oceans, providing an alternative to carbonate δ¹⁸O. Currently, the problems associated with the cleaning and extraction of pure diatom silica, especially from lake sediments, may compromise the precision associated with δ¹⁸O_diatom records. This is because, despite improvements in cleaning techniques, it is still difficult to remove silica-containing contaminants (e.g. tephra, silts and clays) from biogenic silica. Where it has proved difficult to remove all the silica bearing contaminants from a sample, mass balance calculations involving point counting have been used, but these are inherently inaccurate as they only consider the surface area of the contaminant, rather than volume. The new method described here assesses the volume of contamination in each sample of biogenic silica by using major and trace element geochemistry, allowing the δ¹⁸O of the contamination to be removed from the biogenic silica δ¹⁸O value by linear mass balance. In this case, diatom silica was contaminated with tephra, however the method should also be applicable to other contaminants such as silts and clays.  相似文献   

Fossil fuel energy resources of Ethiopia: Coal deposits     

Ahmed Wolela   《International Journal of Coal Geology》2007,72(3-4):293-314

The gravity of Ethiopian energy problem has initiated studies to explore various energy resources in Ethiopia, one among this is the exploration for coal resources. Studies confirmed the presence of coal deposits in the country. The coal-bearing sediments are distributed in the Inter-Trappean and Pre-Trap volcanic geological settings, and deposited in fluvio-lacustrine and paludal environments in grabens and half-grabens formed by a NNE–SSW and NNW–SSE fault systems. Most significant coal deposits are found in the Inter-Trappean geological setting. The coal and coal-bearing sediments reach a maximum thickness of 4 m and 300 m, respectively. The best coal deposits were hosted in sandstone–coal–shale and mudstone–coal–shale facies. The coal formations of Ethiopia are quite unique in that they are neither comparable to the coal measures of the Permo-Carboniferous Karroo Formation nor to the Late Devonian–Carboniferous of North America or Northwestern Europe. Proximate analysis and calorific value data indicated that the Ethiopian coals fall under lignite to high volatile bituminous coal, and genetically are classified under humic, sapropelic and mixed coal. Vitrinite reflectance studies confirmed 0.3–0.64% Ro values for the studied coals. Palynology studies confirmed that the Ethiopian coal-bearing sediments range in age from Eocene to Miocene. A total of about 297 Mt of coal reserve registered in the country. The coal reserve of the country can be considered as an important alternative source of energy.  相似文献   

Palynological evidence for a latest Carboniferous-Early Permian glaciation in Northern Ethiopia     

Robert Bussert  Eckart Schrank 《Journal of African Earth Sciences》2007,49(4-5):201-210

Palynomorphs extracted from glacigenic sediments in Northern Ethiopia are latest Carboniferous-Early Permian in age. These sediments were hitherto thought to be either of Upper Ordovician or of Late Carboniferous-Early Permian age. The predominantly glaciolacustrine and glaciofluviatile sediments were deposited in glacial troughs and valleys that were eroded into Precambrian basement rocks and into Early Palaeozoic deposits, possibly equivalents of Upper Ordovician sediments in Eritrea. In the latest Carboniferous-Early Permian, glaciated uplands to the north of Ethiopia must have existed in Eritrea and/or in southern or central Saudi Arabia.  相似文献   

Crustal velocity structure across the Main Ethiopian Rift: results from two-dimensional wide-angle seismic modelling   总被引：1，自引：0，他引：1  

G. D. Mackenzie  H. Thybo  P. K. H. Maguire 《Geophysical Journal International》2005,162(3):994-1006

  相似文献   

Flood and Shield Basalts from Ethiopia: Magmas from the African Superswell   总被引：24，自引：1，他引：24  

KIEFFER  BRUNO; ARNDT  NICHOLAS; LAPIERRE  HENRIETTE; BASTIEN  FLORENCE; BOSCH  DELPHINE; PECHER  ARNAUD; YIRGU  GEZAHEGN; AYALEW  DEREJE; WEIS  DOMINIQUE; JERRAM  DOUGAL A.; KELLER  FRANCINE; MEUGNIOT  CLAUDINE 《Journal of Petrology》2004,45(4):793-834

The Ethiopian plateau is made up of several distinct volcaniccentres of different ages and magmatic affinities. In the NE,a thick sequence of 30 Ma flood basalts is overlain by the 30Ma Simien shield volcano. The flood basalts and most of thisshield volcano, except for a thin veneer of alkali basalt, aretholeiitic. In the centre of the province, a far thinner sequenceof flood basalt is overlain by the 22 Ma Choke and Guguftu shieldvolcanoes. Like the underlying flood basalts, these shieldsare composed of alkaline lavas. A third type of magma, whichalso erupted at 30 Ma, is more magnesian, alkaline and stronglyenriched in incompatible trace elements. Eruption of this magmawas confined to the NE of the province, a region where the lavaflows are steeply tilted as a result of deformation contemporaneouswith their emplacement. Younger shields (e.g. Mt Guna, 10·7Ma) are composed of Si-undersaturated lavas. The three maintypes of magma have very different major and trace element characteristicsranging from compositions low in incompatible elements in thetholeiites [e.g. 10 ppm La at 7 wt % MgO (=La₇), La/Yb = 4·2],moderate in the alkali basalts (La₇ = 24, La/Yb = 9·2),and very high in the magnesian alkaline magmas (La₇ = 43, La/Yb= 17). Although their Nd and Sr isotope compositions are similar,Pb isotopic compositions vary considerably; ²⁰⁶Pb/²⁰⁴Pb variesin the range of  相似文献   

Petrology and Isotope Geochemistry of the Pan-African Negash Pluton, Northern Ethiopia: Mafic-Felsic Magma Interactions During the Construction of Shallow-level Calc-alkaline Plutons   总被引：2，自引：0，他引：2  

ASRAT  A.; BARBEY  P.; LUDDEN  J. N.; REISBERG  L.; GLEIZES  G.; AYALEW  D. 《Journal of Petrology》2004,45(6):1147-1179

The Negash pluton consists of monzogranites, granodiorites,hybrid quartz monzodiorites, quartz monzodiorites and pyroxenemonzodiorites, emplaced at 608 ± 7 Ma (zircon U–Pb)in low-grade volcaniclastic sediments. Field relationships betweenmafic and felsic rocks result from mingling and hybridizationat the lower interface of a mafic sheet injected into partiallycrystallized, phenocryst-laden, granodiorite magma (back-veining),and hybridization during simultaneous ascent of mafic and felsicmagmas in the feeder zone located to the NW of the pluton. Therock suite displays low ⁸⁷Sr/⁸⁶Sr₍₆₀₈₎ (0·70260–0·70350)and positive  相似文献   

Groundwater origin and flow along selected transects in Ethiopian rift volcanic aquifers   总被引：1，自引：1，他引：0  

Seifu Kebede  Yves Travi  Asfawossen Asrat  Tamiru Alemayehu  Tenalem Ayenew  Zenaw Tessema 《Hydrogeology Journal》2008,16(1):55-73

The disruption of lithologies by cross-cutting faults and the variability in volcanic structures make the hydrogeology of the rifted volcanic terrain in Ethiopia very complex. Along two transects, selected due to their hydrogeologic characteristics, groundwater flow, depth of circulation and geochemical evolution have been conceptualized. The groundwater flow continuity between the high rainfall plateau bounding the rift and the rift valley aquifers depends principally on the nature of the bounding faults. Up to 50% of recharge to the rift aquifers comes from the plateau as groundwater inflow where the rift is cross cut by transverse fault zones. Recharge from the mountains is found to be insignificant where the rift is bounded by marginal grabens; channel loss and local precipitation are the principal sources of recharge to the rift aquifers in such cases. At a regional scale, there is a clear zonation in the geochemical compositions of groundwaters, the result of aquifer matrix composition differences. The environmental isotope results show that the majority of the aquifers contain modern groundwaters. In a few localities, particularly in thermal groundwaters representing deeper circulation, palaeo-groundwaters have been identified. Deeper groundwaters in the rift floor have a uniform ¹⁴C age ranging between 2,300 and 3,000 years.  相似文献   

More than a safety net: Ethiopia’s flagship public works program increases tree cover     

《Global Environmental Change》2022

More than one billion people worldwide receive cash or in-kind transfers from social protection programs. In low-income countries, these transfers are often conditioned on participation in labor-intensive public works to rehabilitate local infrastructure or natural resources. Despite their popularity, the environmental impacts of public works programs remain largely undocumented. We quantify the impact on tree cover of Ethiopia’s Productive Safety Net Program (PSNP), one of the world’s largest and longest-running public works programs, using satellite-based data of tree cover combined with difference-in-differences and inverse probability treatment weighting methodologies. We find that the PSNP increased tree cover by 3.8% between 2005 and 2019, with larger increases in less densely populated areas and on steep-sloped terrain. As increasing tree cover is considered an important strategy to mitigate global warming, our results suggest a win–win potential for social safety net programs with an environmental component.  相似文献   

The Mai Maikden sedimentary sequence: a reference point for the environmental evolution of the Highlands of Northern Ethiopia     

Ogbaghebriel Berakhi  L. Brancaccio  G. Calderoni  M. Coltorti  F. Dramis  Mohammed M. Umer 《Geomorphology》1998,23(2-4)

This paper presents a geomorphologic–stratigraphic analysis of a travertine dammed lacustrine–swampy sedimentary sequence, composed of clay, peaty layers and phytoclastic travertine sands, deeply incised by the Mai Maikden river, on the Highlands of Tigray (Northern Ethiopia). Radiocarbon datings of peaty deposits allow us to establish that the travertine dams have developed at least between 7310±90 yr B.P. and 5160±80 yr B.P. In the upper part of the sequence, palaeochannels filled with travertine and limestone coarse gravels and blocks, indicate the activation of concentrated erosion on the surrounding slopes. Later, both the travertine dam and the lacustrine–swampy deposits were buried by alluvial and colluvial sediments, still mixed with large amounts of organic matter, testifying to generalized slope erosion processes. The end of travertine deposition may be connected with a progressive reduction of vegetation cover and the subsequent decrease of CO₂ in groundwater. The occurrence of the latter phenomena may be related to the onset of drier climatic conditions even though the finding of a large prehistoric settlement in the area, also indicates some influence of human impact.  相似文献