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Williams M.A.J.,University of Adelaide | Williams F.M.,University of Adelaide | Duller G.A.T.,Aberystwyth University | Munro R.N.,Old Abbey Associates | And 7 more authors.
Quaternary Science Reviews | Year: 2010

Our results show that the late Pleistocene Nile in northern Sudan was shifting position and actively aggrading at 145 ± 20 kyr, 83 ± 24 kyr, 32 ± 8 kyr and 20.7 ± 0.2 kyr and indicate, for the first time, a phase of high-energy flow in the White Nile at 27.8 ± 3.2 kyr, with still high but somewhat reduced flow in that river at 13.3 kyr, 10 kyr and 4.8-4.0 kyr. Beach ridges associated with a 386 m strandline of the White Nile have OSL ages of 27.5 ± 2.7 kyr and 14.5 ± 1.6 kyr. The Holocene terraces and former channels of the main Nile have ages of 11 kyr, 6.5-5.0 kyr and 4.8-4.0 kyr, after which there was a general decline in flood discharge. The now arid main Nile valley in northern Sudan was significantly wetter during the early to middle Holocene, with a lake up to 450 km2 in area, fed by an overflow channel from the early Holocene Nile between 9.5 kyr and 7.5 kyr. Previously stable late Pleistocene dunes were reactivated at intervals during the Holocene, with five samples from the White Nile valley indicating brief phases of Holocene dune activity at 9.9 ± 2.0 kyr, 9.0 ± 2.8 kyr, 6.6 ± 0.9 kyr, 4.8 ± 0.9 kyr and 2.9 ± 0.5 kyr, the earliest of which occurred within periods of generally wetter climate and higher Nile flow. The youngest freshwater shells on the Khor Abu Habl alluvial fan west of the White Nile correspond to a time of regionally wetter climate between 1.7 and 1.0 kyr. Our results suggest that millennial scale climatic instability may have been characteristic of Holocene climates in this region. © 2010 Elsevier Ltd. All rights reserved.

Williams M.A.J.,University of Adelaide | Duller G.A.T.,Aberystwyth University | Williams F.M.,University of Adelaide | Woodward J.C.,University of Manchester | And 5 more authors.
Quaternary Science Reviews | Year: 2015

It has long been hypothesised that beds of highly organic mud or sapropels seen in marine sediment cores retrieved from the floor of the eastern Mediterranean accumulated during times of high Nile fluvial discharge. Our recent fieldwork in the valleys of the Blue Nile, the White Nile and the main Nile has for the first time revealed a sequence of extreme flood episodes synchronous with sapropel units S5 (124kyr), S4 (102kyr), S3 (81kyr), S2 (55kyr) and S1 (13.5-6.5kyr). There are more weakly defined links with Nile floods and sapropel units S9 (240kyr), S8 (217kyr), S7 (195kyr), S6 (172kyr), but the dating error terms are too large to allow us to be too definite. During times of extreme floods over the past 125kyr, wide distributary channels of the Blue Nile flowed across the Gezira alluvial fan in central Sudan and transported a bed load of sand and gravel into the lower White Nile valley. The sands were reworked by wind to form source-bordering dunes, all of which contain heavy minerals of Ethiopian provenance. These source-bordering dunes were active at 115-105kyr, 60kyr and 12-7kyr, all times of extreme Blue Nile floods. The flood and dune sediments were dated using a combination of optically stimulated luminescence (OSL) and radiocarbon analyses. The Quaternary record of Nile floods discussed here shows a precessional signal and reflects episodes of stronger summer monsoon and more northerly seasonal movement of the ITCZ, linked to times of higher insolation in northern tropical latitudes. Progressive aggradation of Holocene Nile channels in northern Sudan has had a profound influence upon human settlement in the last 8kyr. © 2015 Elsevier Ltd.

Taha M.E.M.,University of Gezira | El-Zorgani G.A.,Agricultural Research and Technology Corporation | El-Hassan A.M.,University of Gezira | Salghi R.,University Ibn Zohr
Journal of Materials and Environmental Science | Year: 2013

This study was conducted to assess the prevalent effect of organochlorines insecticide residues on randomized population sample from El-Hosh Town community, South Gezira. 36 human urine samples such as 12 from male, 12 from female and 12 from children were collected from randomized population samples. Residues of organochlorine pesticides were extracted by hexane and analyzed by gas chromatography (GC). The results revealed that, only DDE was detected. DDE was detected in four out of 12 (33%) female and 3 out of 12 (25%) male urines in concentrations ranging between 4.64 -5.31 ppm. No detectable residues of DDE were found in children. DDE concentrations in females (5.17 ppm) were higher than those in male urines (4.18 ppm). The results indicated that the DDE residues level were not associated with age or weight. Although the use of most of these compounds has been severely restricted more than thirty year ago, the presence of their residues indicate their characteristic of long term persistence.

Taha M.E.M.,University of Gezira | El-zorgani G.A.,Agricultural Research and Technology Corporation | El-Hassan A.M.,University of Gezira | Salghi R.,University Ibn Zohr
Journal of Materials and Environmental Science | Year: 2013

This study was conducted to assess the presence of organochlorines insecticide residues in some common foods from el-hosh town community, south gezira. 48 samples (16 tomatoes, 16 meats and 16 eggs) were randomly collected during the period december 2007 to august 2008. pesticide residues were determined by gas chromatograph with electron-capture detector (gc-ecd) after dichloromethane extraction and cleanup on silica gel phase cartridges. the results revealed that, only dde was detected. all food samples were free of organochlorine pesticides in the four seasons of the years except for two meat samples in spring season. concentrations of these samples were 1.102 to 0.811 ppm. these findings suggest that, a restricted and controlled use of such persistent pesticides may be useful for decreasing their contamination levels in different food items, therefore, the monitored varieties of food are safe to people's health. this study recommended continuous monitoring of persistent organochlorine pesticides in food in order to safeguard human health and mark their decline with time after the restriction of their usage.

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