Southwestern Chad Research Articles

Demographic and Clinical Features of Visceral Leishmaniasis in Chad: A Prospective Cross-Sectional Survey.

Visceral leishmaniasis (VL), caused by the protozoan Leishmania donovani complex, is endemic in many parts of the world. Little known in Chad, VL has been recently documented from previously nonendemic areas. We report an epidemiological investigation of VL in the Léré district hospital in southwestern Chad. After informed consent, 40 VL patients were enrolled in the study. Diagnosis made using the formalin serological test was confirmed by polymerase chain reaction on blood samples. Clinical parameters were obtained from the physician or nurse caregiver, and from patients. Of a total of 40 serology positive patients, L. donovani DNA was found in 33 (82.5%), with 55% being male patients. The most affected age groups were 15-29 (47.5%) and 0-14 (32.5%) years. Fever, weight loss, and pallor were frequent symptoms. Notably, splenomegaly and hepatomegaly were uncommon clinical signs. Common comorbidities included malaria (25%) and hepatitis B (15%), followed by gastric ulcer (10%) and tuberculosis (7.5%). These comorbidities were concurrent with VL and were diagnosed microscopically in blood and serum for malaria and tuberculosis, respectively, and by the rapid diagnostic test using serum for hepatitis B and gastric ulcer. Thirty-five percent of cases were treated with meglumine antimoniate, and three patients (7.5%), all with comorbidities, died. Sixty percent of patients lived close to the main town. Our data demonstrate that VL is endemic in the health district of Léré. Improving health education regarding L. donovani infection in endemic areas of Chad and providing training of health workers on early detection and management of VL are needed to help save lives.

Prevalence and risk factors of geohelminths in primary schools children aged 5 to 15 years in the city of Moundou, southwestern Chad

Geohelminthiases are endemic in Chad and constitute a serious public health problem. This study aimed at determing the prevalence and risk factors of intestinal geohelminthiasis in children aged 5–15 years in the city of Moundou, Chad. This was a cross-sectional and descriptive study carried out in the city of Moundou. A total of 333 pupils participated in this study and it included children aged from 5 to 15 years attending three public primary schools in Moundou. A questionnaire was administered to each student after obtaining Informed Consent from either parent. Stool samples were collected in a sterile container and, the formalin-ethyl ether concentration technique was used to identify parasite. Parasitic load was assessed using the Mc Master cell method. The collected data were analyzed using Excel; Word 2016 and SPSS 20 software. An overall prevalence of 16.52% was obtained, 9.3% for Trichuris trichiura, 6.9% for Ascaris lumbricoides, and 1.2% for Hookworms. Male participants were more infected (67.24%) than females (32.76%). The age group]9–13] was the most infected (53.44%), followed by the age group [5–9](44.83%) and finally the age group]13–15] (1.73%). The Ouhoud school was the most infected (55.17%) followed by the Adoum Dallah school (39.66%) and finally the Centre school (5.17%). However, no statistically significant difference between gender and geohelminthiasis infection was recorded (p > 0.05). Regarding risk factors, statistical analysis showed that age group]9–13] (OR = 1.997 at 95% CI at [1.085–3.677]), Central Public School (OR = 1.55 at 95% CI at [0.63–2.46]), tap water (OR = 29 at 95% CI at [20.89–38.70]), not maintaining latrines (OR = 2.37 at 95% CI at [0.62–3.78]), and maintenance of latrines by pupils (OR = 1.5 at 95% CI at [0.63–2.46]) were risk factors. This study shows a high prevalence of geohelmenthiasis among children of three primary schools in Moundou, Chad. Although males were more infected than female there was no significant difference between gender and geohelminth infections (p = 0.114). was no gender difference. Identified risk factors of geohelmenthiasis infections among the study population were: age between 9 and 13 years, school water consumption, the use of unmaintained latrines and latrines maintained by students. Surveillance of geohelminthiases and hygiene should be intensified to reduce the pathological risk related to these parasites in Chad.

Major, trace elements and Sr–Nd–Pb isotopes systematics of mafic dykes from the Figuil (northern Cameroon) and Léré (southwestern Chad) areas

In this study, field descriptions of the dolerite dykes cross‐cutting the Pan‐African basement (DPB) and the dolerite and gabbroic dykes cross‐cutting the Cretaceous sedimentary basin (DGCSB) are used together with petrographic, bulk‐rock geochemistry, as well as Sr–Nd–Pb isotopic data to constrain the geodynamic setting and origin of these mafic (basanite, basalt and basaltic andesite in composition) rocks that outcrop in the Figuil–Léré area. The DPB dykes are alkaline with SiO2 of 46.63–49.03 wt% and MgO of 3.93–7.11 wt%. In contrast, the DGCSB dykes are subalkaline with SiO2 ranging between 50.24 and 53.16 wt% and MgO fluctuating between 5.22 and 7.90 wt%, comparable to dykes described in other regions of the Cameroon Line (CL). The rocks studied belong to the tholeiitic series and were emplaced in within‐plate basalts (WPB) and mid‐ocean ridge basalts (MORBs) setting. The variations in major and trace elements from the basanite to basaltic andesite compositions are dependable with fractional crystallization (FC) of different mineral phases such as opaque minerals, olivine, clinopyroxene, amphibole and alkali feldspar. Most samples exhibit negative Nb–Ta and positive Sr anomalies, which together with the negative correlation between MgO and 87Sr/86Sr, and isotopic ratio of 206Pb/204Pb <19.5 (18.27–19.49) suggests interactions of crustal components. Nevertheless, this contamination seems limited because there is a positive correlation between SiO2 and 143Nd/144Nd plot and low Ba contents (72–210 ppm) of the samples compared to the mid‐continental crust (259–628 ppm). Trace element modelling proposes a derivation of the Figuil–Léré dykes from parental melts generated by 4%–15% partial melting of a source containing garnet peridotite in the mixed lithospheric–asthenospheric mantle. The isotopic data of the dykes studied with hybrid magma composition are characterized by more radiogenic 87Sr/86Sr, 143Nd/144Nd and 206Pb/204Pb isotopic ratios with a dominant mixing of depleted MORB mantle (DMM)–enriched mantle 1 (EM1)–enriched mantle 2 (EM2), like those of other mafic dykes of the CL.

Study of the physico-chemical and bacteriological quality of water intended for consumption in the town of Gagal, southwestern Chad

The city of Gagal suffers from insufficient drinking water, and the population turns to surface water, wells and drillings without guarantee of quality. In order to characterize the hydrogeochemical and bacteriological properties of the waters of the aquifer system in the city of Gagal, to contribute to improving its knowledge, field campaigns were undertaken to sample the groundwater.The present study focuses on the hydrogeochemical and bacteriological characterization of drinking water in Gagal, southwestern Chad. The methodology consisted of acquiring existing data, a field campaign, and a chemical and bacteriological analysis of the water in the laboratory. The results of the physicochemical analyses revealed that the values of the parameters such as conductivity, pH (5.23), Ca²⁺ (26.11 mg/L), Mg²⁺(5.14 mg/L), Na⁺(3.54 mg/L), K⁺(1.34 mg/L), HCO3-(81.74 mg/L), Cl-(11.77 mg/L), SO4-(1.94 mg/L), and NO3- (8.70 mg/L) conformed to the WHO potability standards. Piper's diagram showed calcic and magnesian bicarbonate facies represented by 75%; and calcic and magnesian sulfate chloride facies in 25% of the analyzed waters. The bacteriological (Total coliforms (0 to more than 135,200 CFU/100 ml), Escherichia coli (0 and 14,400 CFU/100 ml), faecal enterococci (0 and 4600 CFU/100 ml)) study confirmed that the water from the wells and boreholes showed pollution of bacterial origin. Using these waters may endanger the populations with the risks of hydric diseases.

Paleostress Reconstruction from 3D Seismic Data and Slip Tendency in the Northern Slope Area of the Bongor Basin, Southwestern Chad

Paleostress Reconstruction from 3D Seismic Data and Slip Tendency in the Northern Slope Area of the Bongor Basin, Southwestern Chad

Soil Characteristics and Pedoclimatic Evaluation of Rainfed Sorghum (Sorghum bicolor (L.) Moench) in the Mayo-Lemié Division, South-Western Chad

In recent decades, many regions in the Chad Republic in Central Africa have experienced a continuous decline in agricultural yields. In order to determine the main factors leading to this decline in yields and mainly Sorghum yields, this study was conducted in South-Western Chad, in the Sudano-Sahelian environment. Three soil profiles of variable depths, namely, M1, M2, and M3, were dug along a toposequence, respectively, in the footslope, mid-slope, and the upslope. Soil samples collected from each horizon in the three soil profiles were labelled and sent to laboratories for mineralogical, geochemical, and physicochemical analyses. For land evaluation, climatic characteristics are divided into rating groups with respect to the crop and its climatic requirements. Parametric values were attributed to each soil characteristic for soil evaluation and the land index calculated. The main minerals identified in the studied soils are quartz, K-feldspars, plagioclase, kaolinite, smectite, illite, associated to traces of anatase, sepiolite, calcite, and interstratified minerals. In all the analyzed samples, silicon content is very high. It is closely followed by aluminum, iron, and potassium. The presence of kaolinite and smectite suggests that monosiallitisation is a crystallochemical processes acting at the bottom of profile towards bisiallitisation. All samples collected from the three soil profile horizons are mainly sandy and globally poor in nutrients. The pedoclimatic assessment of Sorghum cultivation reveals that the studied soils are marginally to moderately suitable for the production of Sorghum due to soil texture, wetness, and soil fertility. The decline in yields is related to low base saturation, in line with low exchange base content in the studied soils. These limitations could be solved by restoration of the cation balance through fertilization and liming, combining organic inputs with mineral fertilizer, and the realization of channels for the drainage of water at the base of the soil sequence.

Geodynamic framework of the magmatic activity of Cretaceous Léré basin (Southwestern Chad, Central Africa)

Numerous 5 to 20 m-wide dolerite dykes crosscut vertically to sub-vertically basement granitoids around and within the Cretaceous Léré basin, SW Chad (Central Africa). They extend along strike on several hundred meters length. Léré dolerites exhibit various textures, from classical doleritic texture to sub-ophitic via ophitic and intersertal textures. They are composed of euhedral and subhedral crystals of andesine and labradorite, anorthoclase, augite, olivine, ilmenite and Ti-magnetite. Calcite and amphibole are present. Estimated crystallization temperatures are between 1050 and 1105 ± 50 °C. Occurrence of dyke swarms in Léré basin is controlled by Pan-African strike-slip faults created during an extensional tectonic phase during Paleozoic to Early Mesozoic. These lavas, analyzed with ICP-MS and ICP-AES, are basalt, trachybasalt and basaltic trachyandesite with some continental tholeiite affinity. Dolerites of Léré basin have evolved by limited fractional crystallization differentiation, accompanying by minor assimilation process. Three groups of rocks are identified (according to Y/Nb ratios), linked to different mantle sources which have intermediate compositions between E-MORB and OIB.

Geochronology and correlations in the Central African Fold Belt along the northern edge of the Congo Craton: New insights from U-Pb dating of zircons from Cameroon, Central African Republic, and south-western Chad

The Central African Fold Belt (CAFB) is the least well-known of all major Pan African belts. Here, we present new geochronologic work carried out in several critical areas of western Central African Republic, the region standing between northern Cameroon and southwestern Chad, and southern Cameroon. Our results allow us to: (1) clarify the regional extension of the Congo Craton in SE Cameroon and in the SW Central African Republic; (2) demonstrate that the units thrust along the northern edge of the Congo Craton from Cameroon to the Central African Republic are comparable in nature and in age; (3) better constrain the limits and described better the role of the Adamawa-Yadé crustal block during the Pan-African pre-collisional and collisional events in relation to the Congo Craton and the Yaoundé-Yangana nappe units to the South, and to the Poli-Leré magmatic arc to the North and; (4) clarify some of the elements of correlation with NE Brazil. Overall, a model involving two subduction zones is proposed to explain the evolution of the Pan-African belt north of the Congo Craton. The main steps include; (1) break-up and basin development from the early Tonian to at least 620 Ma on the northern edge of the Congo Craton, and on both the southern and the northern edges of the Adamawa-Yadé Block, concomitantly with the development of the Poli-Leré arc in northern Cameroon and Chad; (2) pre-tectonic plutonism in all domains since c. 800 Ma with culmination between 650 and 620 Ma; (3) collisional events starting around 620 Ma with metamorphism reaching the granulite facies at c. 600 Ma in all the domains; (4) nappe tectonics with thrusting of the Yaoundé-Yangana units onto the Congo Craton, accretion of the Poli-Leré arc to Adamawa-Yadé Block, and widespread syntectonic magmatism (600–580 Ma) with emplacement partly controlled by transcurrent regional shear zones, and emplacement of post-tectonic granitoids (c. 550 Ma) in both Adamawa-Yadé block and Poli-Leré magmatic arc. Collisional and post-collisional (620–550 Ma) events were synchronous along the entire belt from Central Africa to Brazil.

Mapping hydrothermal alteration mineral deposits from Landsat 8 satellite data in Pala, Mayo Kebbi Region, Southwestern Chad

The different image attribute extracting techniques, spectral enhancement ability, pixel classification methods have been applied on the Landsat 8 OLI satellite image data to map geological features and spatial distribution of hydrothermal alteration zones, which have been recorded to be associated with gold mineralization in the Pala, Mayo Kebbi region of southwestern Chad. Radiometric calibrated, noise filtered and image enhanced Landsat 8 OLI data were subjected to colour composite, band rationing and crosta analyses in order to enhance spectral reflectance and compositional information, create colourful multispectral images which enable the mapping of desired spectral bands into principal component images for the purpose of accentuating salient information needful to delineate hydrothermal alteration zones within the study area.Composite ratios 4/2-6/7-6/5 indicate relative spatial distribution of iron-oxide in the southeast while clays and hydroxyl minerals occur in the west and northwestern part of the study area. The eigenvectors and eigenvalues for hydroxyl minerals from the crosta analysis indicate highest loadings of opposite signs (-0.721498 & 0.649465; bands 6 & 7) in PC3, representing ‘’H’’ image. The eigenvectors and eigenvalues for iron-oxides on the other hand present highest loading of opposite signs (0.895721 & -0.443283; bands 2 & 4) in PC4, representing the “F” image. The white coloured pixels within the bright reflections generated from Crosta composite image of H, H+F & F in RGB delineate hydrothermal alteration zones. The plot of delineated zones of hydrothermal alteration on the Landsat 8 true colour indicate spatial distribution of the alteration areas within the host greenstone belt belonging to the Precambrian Goueygoudoum series and they plot mainly along major structural features, suggesting structural control. Field control revealed that some areas delineated by band rationing as hydrothermal alteration zones appear to be the result of intense weathering. Accordingly, we recommend that remote sensing delineation of hydrothermal alteration zones should be checked by a relevant ground-observation based control procedure.

Fractional Crystallization and Crustal Contamination of Doleritic and Trachytic Dykes Crosscutting the Cretaceous Sedimentary Basins from Figuil (North Cameroon) and Léré (South-Western Chad): Geodynamic Implications

Fractional Crystallization and Crustal Contamination of Doleritic and Trachytic Dykes Crosscutting the Cretaceous Sedimentary Basins from Figuil (North Cameroon) and Léré (South-Western Chad): Geodynamic Implications

After the flood and with the people – Late Holocene changes of the woody vegetation in the southwestern Chad Basin, Nigeria

The development of cultivated landscapes under the influence of food production has decisively shaped the composition and appearance of West African savannas as present today. With trees and shrubs forming an important constituent of such landscapes, and its composition characterizing different types of land-use, anthracology is a tool particularly well suited to trace developments and changes through human exploitation of the landscape. Within the West African savanna belts, regions shaped by prolonged annual floods, such as the Middle Senegal Valley, the Inland Niger Delta and the Chad Basin, offer particular ecological preconditions for land-use. We present here a charcoal study for the Chad Basin of northeast Nigeria, demonstrating the special development of a cultivated landscape in an alluvial context. Charcoal samples from stratified Late Stone Age and Iron Age sites within the southwestern Chad Basin, Nigeria were analyzed. Main focus is on the site Mege, spanning more than 2500 years of occupation history. The results are supplemented with and compared to data from other, earlier as well as contemporary sites, in similar or slightly different environments and representing different settlement types, in order to discern general trends. The results illustrate the exploitation of woody vegetation mainly from the clay soils. This is in stark contrast to the results from other regions within the savanna belt, where the vegetation on sandy soils was preferentially exploited for fuel wood. The vegetation changes evidenced through the charcoal assemblages are attributed to reduced flooding as a consequence of falling lake levels during the Late Holocene. Parklands, typical cultivated landscapes of West African savannas, are invisible in the charcoal spectra, and fallow species and useful trees are rarely present. We postulate that the ecological conditions of the floodplain environment have decisively paved a different, less obvious trajectory of cultivated landscape development between 2000 BC and AD 1500 and that the cultivated landscapes present in the region today largely result from the increasing human impact of the last 500 years.

Petrography and Geochemical Characterization of Dolerites from Figuil (Northern Cameroon) and Léré (Southwestern Chad)

This work presents the petrographic and geochemical data of the dolerite dykes crosscutting the Pan-African basement of Figuil (North-Cameroon) and Lere (South-West Chad) in order to approach their petrogenesis and their emplacement context. Two groups of dolerites have been highlighted by petrographic and geochemical studies. These groups were discriminated by their TiO2, Fe2O3, REE, Ba, Nb, Zr, La and Hf contents which are relatively higher in group I; group II, on the other hand, has higher MgO, Mg#, Sc, Ni and Cr contents. The mineralogical assemblage of these dolerites is made up by plagioclases, pyroxenes, olivine, oxides, amphibole, biotite and sometimes pyrite, calcite, apatite, epidote and chlorite. The behaviour of the major and trace elements suggest that studied dolerites have an evolution dominated by fractional crystallization. Most dolerite samples show higher REE concentrations and (La/Yb)N > 8.7, (Tb/Yb)N > 1.9 and Dy/Yb > 2 ratios characterizing a garnet-bearing mantle. The difference in incompatible elements between the two groups is explained by the degree of partial melting of the same source which becomes more important over time. Low (Ce/Yb)N values (3.3 - 11.58) also suggest relatively low partial melting degree of the source. Fractional crystallization process was possibly combined with minor crustal contamination as shown by enrichment of Th/Yb from group II to Group I that might be due to turbulent magma emplacement. The chemical compositions of these dolerites are similar to that of continental tholeiites with slightly moderate negative Nb-Ta anomalies which are attributed to crustal contamination of magmas. As other dolerites of Cameroon, continental tholeiitic signature of the studied dolerites is evidenced in geotectonic discrimination diagrams with Group II dolerite compositions falling within the field of tholeiitic basalts and group I within the field of alkali basalts.

Adorning the Body, Asserting Status: Prestige-Goods and Social Distinction at Ancient Chadic Chiefdom of Houlouf (Northern Cameroon)

Copper and alloyed copper artefacts, carnelian and glass beads have been recovered in archaeological excavations since the middle of the 20th century in the Chadian plain in northern Cameroon, northeastern Nigeria and southwestern Chad Republic. The initial research projects conducted by Marcel Griaule and Jean-Paul Lebeuf resulted in the “creation” of the Sao Civilization, characterized by a relatively high level of art craftmanship. They made impressive large pottery vessels, terracotta figurines, iron objects, and copper and alloyed copper artefacts, called “Sao Bronzes”. These artefacts were generally analysed from their supposed artistic characteristics; production techniques – the lost wax technique – were addressed but no metal production features were ever recorded in the first decades of research on northernmost Cameroon mounds. The Houlouf archaeological project conducted from 1981 to 1991 allowed for a better understanding of the production and use of the copper/alloyed copper artefacts and other prestige goods recovered from archaeological contexts. They range widely in nature, forms, and shape. There are ordinary personal adornment items – finger-rings, arm-rings, and ankle rings, necklaces, waist-beads – to very specialized cavalry – leg-guards – and archery – arm-bands -, including exceptional figurines. This contribution brings to light the context of use and socio-political implications of these prestige artefacts and outlines their meaning in the developing Central Sudan long-distance trade networks.

Women who change into men: a gendered history of precarity in ‘useful’ Chad

AbstractThis article is about two generations of women in south-western Chad – the baou déné and the mosso. It addresses the puzzle of how these groups of women are present in the everyday life of the region known as ‘useful’ Chad, while women as economic agents are absent from stories about the region and about successive schemes to make it profitable. The baou déné are wealthy farmers, but the last generation of these ‘women who have a lot of things’ is disappearing. Younger women are referred to as mosso, meaning ‘to fall down’. They are more likely to make a living from small trade than from farming and their lives are defined by precarity. Drawing on a range of historical and contemporary sources, I show how the erasure of women happened in different ways over time. In the colonial era, administrators and travel writers were unable to imagine that women transformed forests into cotton fields. In this century, the idea that women farm just like men was disseminated by oil companies, facilitating land expropriation while drowning out stories of women's marginalization. The baou déné and the mosso are the products of specific historical processes and profit-making schemes, and the silences about women's places in them helped make profits, empire and ‘useful’ Chad possible.

Numerical Dust Storm Simulation Using Modified Geographical Domain and Data Assimilation: 3DVAR and 4DVAR (WRF-Chem/WRFDA)

Dust storms have severe environmental, economic, health, weather, and climate change impacts. A severe dust storm that hit Egypt on 22 January 2004 was selected as a case study to establish an accurate numerical model to simulate dust storms over Egypt using the Weather Research Forecast with a chemistry module (WRF-Chem). Two simulation setups using WRF-Chem were conducted using two geographic domains: the first exclusively included dust sources within Egypt, while the second included an external dust source, the Bodele Depression in southwestern Chad. The first simulation was only able to capture the core of the dust plume from the internal dust source Egyptian Qattara Depression, but the second was able to capture the spatial dust distribution from both the Qattara Depression and the Bodele Depression. Moreover, the results from our second simulation model had less errors than comparable results using moderate resolution imaging spectroradiometer (MODIS). We then investigated the impact of meteorological data assimilation methods using both three-dimensional and four-dimensional variational assimilation algorithms to simulate the aerosol optical depth of the dust storm using weather research forecast data assimilation (WRFDA) framework.

Annual GPS tracking reveals unexpected wintering area in a long-distance migratory songbird

Recent technological development has made it possible to pinpoint precise locations of small migratory songbirds throughout their annual cycle, providing the opportunity for improving our understanding of year-round habitat use. Here, we use GPS loggers to map the exact location and habitat use at stationary sites throughout the annual cycle of a long-distance migratory songbird, the Red-backed Shrike Lanius collurio. Although the main staging sites confirmed previous findings from light-level geolocation studies, one individual wintered in south-western Chad, an area with only a few historical records of this species. This study highlights opportunities for answering new questions and gaining more knowledge using fine-scale tracking of migratory songbirds.

Pedo-sedimentary constituents as paleoenvironmental proxies in the Sudano-Sahelian belt during the Late Quaternary (southwestern Chad Basin)

Climate and environmental changes since the Last Glacial Maximum in the tropical zone of West Africa are usually inferred from marine and continental records. In this study, the potential of carbonate pedo-sedimentary geosystems, i.e. Vertisol relics, to record paleoenvironmental changes in the southwestern part of Chad Basin are investigated. A multi-dating approach was applied on different pedogenic organo-mineral constituents. Optically stimulated luminescence (OSL) dating was performed on the soil K-rich feldspars and was combined with radiocarbon dating on both the inorganic (14Cinorg) and organic carbon (14Corg) soil fractions. Three main pedo-sedimentary processes were assessed over the last 20 ka BP: 1) the soil parent material deposition, from 18 ka to 12 ka BP (OSL), 2) the soil organic matter integration, from 11 cal ka to 8 cal ka BP (14Corg), and 3) the pedogenic carbonate nodule precipitation, from 7 cal ka to 5 cal ka BP (14Cinorg). These processes correlate well with the Chad Basin stratigraphy and West African records and are shown to be related to significant changes in the soil water balance responding to the evolution of continental hydrology during the Late Quaternary. The last phase affecting the Vertisol relics is the increase of erosion, which is hypothesized to be due to a decrease of the vegetation cover triggered by (i) the onset of drier conditions, possibly strengthened by (ii) anthropogenic pressure. Archaeological data from Far North Cameroon and northern Nigeria, as well as sedimentation times in Lake Tilla (northeastern Nigeria), were used to test these relationships. The increase of erosion is suggested to possibly occur between c. 3 cal ka and 1 cal ka BP. Finally, satellite images revealed similar geosystems all along the Sudano-Sahelian belt, and initial 14Cinorg ages of the samples collected in four sites gave similar ages to those reported in this study. Consequently, the carbonate pedo-sedimentary geosystems are valuable continental paleoenvironmental archives and soil water balance proxies of the semiarid tropics of West Africa.

Influence of biodegradation on carbazole and benzocarbazole distributions in oils from the Bongor Basin, Chad

A suite of oils from the Bongor Basin, South Western Chad was characterized geochemically to investigate the behavior of carbazoles and benzocarbazoles during biodegradation. The oils show similar maturity levels and organic facies type with biodegradation as the primary control on molecular compositions. According to compositional variation, the biodegradation levels of oils fell within PM level 0–8 [PM biodegradation scale (Peters, K.E., Moldowan, J.M., 1993)]. Absolute concentrations of carbazole, methylcarbazoles, C2-carbazoles, and benzocarbazoles in the oils show an increase from PM level 1–3, fluctuation at PM level 4–7, and sharp decrease above PM level 7. Relative abundances of the carbazole series indicate that C0–C2-carbazoles are more susceptible to biodegradation than benzocarbazoles, 2- and 3-methylcarbazoles are more susceptible than 1- and 4-methylcarbazoles, partially shielded dimethylcarbazoles are more susceptible than the exposed ones and both of these are more susceptible than shielded dimethylcarbazoles. Benzo[c]carbazole seems to show a higher ability to resist biodegradation than benzo[a]carbazole in heavily biodegraded oils. Therefore, ratios of 1-/(2-+3-) methylcarbazole, 4-/(2-+3-) methylcarbazole, 1,8-dimethylcarbazole/total dimethylcarbazoles, 1,8-/1,3-dimethylcarbazole, and 1,8-/2,4-dimethylcarbazole may be used to assess the degree of biodegradation in this area.

Hydrochemical Studies of the Groundwater Resources of the Middle Zone Aquifer in the Southwestern Chad Basin.

Hydrochemical Studies of the Groundwater Resources of the Middle Zone Aquifer in the Southwestern Chad Basin.

The Declining Middle Zone Aquifer of the Southwestern Chad Basin in the last Millenium.

The Middle zone aquifer is the most extensive and most widely exploited of the three well known aquifers of the Chad Formation. This aquifer is confined by variable thickness of argillaceous deposits of 100 - 150 m thick. This led to the variable heads in boreholes drilled to this zone. Boreholes drilled from 1960 to 2010 shows a drastic decline in piezometric heads. The piezometric heads of over 20 m above ground level ( agl) observed in 1960 to 1.2 m agl in 2010 have declined over the last half century. In the present work the heads at 0.2 m/ year giving the present piezometric head at an average of 0.5 m agl. The lower heads in old boreholes are attributed due to siltation, encrustation and ageing of borehole. Furthermore, lack of present day recharge and poor borehole construction methods play a vital role in determining the piezometric head.