From the Libyan border to the Nile – Neoproterozoic magmatism and basement evolution of southern Egypt

ABSTRACT

In southern Egypt, Neoproterozoic granitoids intrude the crust from Libya in the west to the Nile River in the east. Best exposed at Gebel Uweinat, Gebel Kamil, Bir Safsaf, Gebel El Asr and Gebel Umm Shaghir, these rocks represent the transition between the rejuvenated Archean to Paleoproterozoic crust of the east Saharan craton and the juvenile Neoproterozoic crust of the Arabian–Nubian Shield to the east. We present U-Pb zircon geochronology and whole rock geochemistry from 16 Neoproterozoic (c. 628–580 Ma) granitoids across southern Egypt which document the synchronous production of diverse compositions indicative of an intraplate or intracontinental tectonic setting. Our data better constrain the age relationships, petrogenesis, and Pan-African crustal growth associated with the amalgamation of Gondwana and contribute to understanding the crust-modifying processes that led to the development of the Saharan metacraton in the Ediacaran.     

Proterozoic deformation of the East Saharan Craton in Southeast Libya, South Egypt and North Sudan

The basement areas in Southeast Libya, South Egypt and North Sudan, west of the Nile, between Gebel Uweinat and the Bayuda Desert, are part of an approximately 1000-km-wide, complexly folded, polymetamorphic zone with a regional N-NNE-NE-ENE trend of foliation and fold axis. Since this belt extends southwestward into the area of Zalingei in the southern Darfur block (West Sudan), it is named the Northern Zalingei fold zone. Sr and Nd isotopic studies suggest that this zone is older than Pan-African and further indicate that, apart from Archean rocks in the Gebel Uweinat area, this belt is of Early-Middle Proterozoic age. An Early-Middle Proterozoic three-stage deformational and anatectic event established the present-day fold and fault geometry in the western parts of this zone in the Gebel Uweinat—Gebel Kamil area. The Pan-African tectono-thermal episode was most effective in the eastern part of the belt, near the boundary with the Nubian Shield volcano-sedimentary-ophiolite-granitoid assemblages. It caused migmatization, granite emplacement, mylonitization and large-scale wrench faulting which was related to Late Proterozoic accretionary and collisional events of the Arabian-Nubian Shield with the margin of the East Saharan Craton.     

Stratigraphy and facies development of the pre-Cenozoic sediments in southern Egypt: a geodynamic approach

The study of the geology of southern Egypt, in-between the Red Sea and the Libyan borders, south of latitude 24°30′N reveals a succession of the Precambrian Arabo–Nubian Shield along the Red Sea coast overlain by Paleozoic–Mesozoic sediments. The Paleozoic section in the study area is well developed in three sub-basins, namely, Uweinat–Gilf, South Nile, and Etbai. Paleozoic sediments are well developed in the three sub-basins mostly sandstones of Cambrian overlain by glaciogene sediment conglomerates at base namely Gabgaba Formation and by the Naqus Sandstone at top. The tectonic events during the Early Paleozoic Caledonian Orogeny are marked by several unconformities and tectonic uplift and down faulting expressed in the many faults in the Uweinat–Gilf and South Nile sub-basins. The Carboniferous is well-developed sandstones in the three studied sub-basins. The glaciation at the Permian is reflected in sea-level fall, hence continental sediments are well developed in many parts of Egypt—a phase of the Hercynian Orogeny. Volcanics are very well common in the study areas ranging in age from 48 to 34 Ma at Uweinat and Gebel El-Asr. Vulcanicity continued during the Paleozoic and Mesozoic at the Triassic of Nasab El-Balgum and in the south Western Desert, the south Eastern Desert, and Etbai area. The highly seismic conditions in southern Egypt continued up to very recent times where tremors were noticed in the 80s and 90s of the last century pointing to very unstable area.     

Fluoride in Quaternary groundwater aquifer,Nile Valley,Luxor, Egypt

The occurrence of fluoride in ground water is the focus of the public and has attracted the attention of many scientists all over the world due to its importance in public health. Deficiency or increase of fluoride uptake is considered a public health problem due to the narrow permissible limit which should not exceed 1.5 mg/l according to the World Health Organization (WHO). The range of fluoride tolerance and toxicity is narrow. Deviation from the optimal levels therefore results in dental health effects such as caries and fluorosis. Many studies have found fluorosis to be invariably associated with high concentrations of fluoride in drinking water. Fluorosis is a considerable health problem in many areas of the world including Brazil, China, East Africa, Ghana, India, Kenya, Korea, Malawi, Mexico, Pakistan, South Africa, southeastern Korea, Spain, Sri Lanka, Sudan, Taiwan, Tanzania, and Turkey. Fluoride in groundwater of Quaternary aquifer of the Nile Valley, Egypt, does not gain the attention of the authors in the Nile Valley which makes the public health status of fluoride is not certain. The present work aims at investigating the fluoride concentration of Quaternary groundwater aquifer at Luxor as a representative area of the Nile Valley to be a base line for subsequent studies and criteria for public health. Ground water samples were collected from Quaternary groundwater aquifer at Luxor area, Egypt and analyzed for the purpose of investigating fluoride content. The results showed that fluoride concentration in the study area ranges between 0.113 and 0.452 with an average of 0.242 mg/l. Sources of fluoride in the study area can result from the natural dissolution from fluoride-rich minerals, fertilizers and from groundwater recharge. It is worth mentioning that low fluoride content in the study area is considered a public health threat specially limited growth, fertility, and dental caries. Corrective measures should be taken to avoid the public health impacts of fluoride deficiency at Luxor area as well as similar areas in the Nile Valley. A public health program should be initiated to account for the deficiency of fluoride in groundwater and deal with the other supplementary fluoride sources in food or fluoridation of drinking water supplies.     

Geology and geochemistry of Kurkur bentonites,southern Egypt: provenance,depositional environment,and compositional implication of Paleocene–Eocene thermal maximum

A large lower Eocene bentonite deposit at the top of Sinn El-Kaddab plateau, southern Egypt, is investigated. It forms isolated anticlinal hills as mesa and cuesta geomorphic units. The Sinn El-Kaddab plateau (497 m above sea level) with Gebel Abyad in northern Sudan represent the most southern margin of Tethys realm in East Africa. Clay and silt fractions constitute up to 95 % of the bentonite and calcium montmorillonite is the predominant phase (70–87 %). These sediments were deposited during the Paleocene–Eocene Thermal Maximum (PETM) event. Grain-size distribution in conjunction with their geologic setting argues in favor of a low energy deep hemipelagic, restricted basin within the outer shelf zone. They suggest sporadic deposition in a basin characterized by relief oscillation, in response to continuous tectonic uplifting. The sediments of the peripheral parts of the basin are more calcareous and were deposited in an arid climatic condition. Calcium montmorillonite was deposited in subtropical warm climate, with alternating wet and dry seasons. Compositionally, the bentonite shales are basic to intermediate and exhibit a rather limited range of K₂O/Na₂O and SiO₂/Al₂O₃ ratios. They suggest mature polycyclic siliciclastics as the main provenance and within-plate alkali basalts as a main igneous precursor. They are the product of intensive physical weathering process in response to combined effects of both tectonic disturbance and prevailed climatic conditions during the PETM event. Geochemically, they are interpreted in terms of mixing of two end-members: pure clastic terrigenous component (inherited from the source area) and carbonate-rich matrix.     

Mode of formation of the Nile Gorge in northern Egypt: a study by DEM‐SRTM data and GIS analysis

This is an overview of the mode of formation of the Nile Gorge in northern Egypt. It is based on the interpretation of the Shuttle Radar Topography Mission (SRTM) data along with detailed analysis of landsat image, geological map and seismic data. The results show that the current course of the Nile was caused by a differential uplift of two plateaus: Ma'aza, to the east, and Western Desert plateau, to the west of the river. This uplift is caused by dynamic forces resulting from subsurface convection processes. It also contributed to the formation of several drainage systems, basins and structural features. Abundant faults and fractures that are parallel to the Nile Valley on both flanks that are associated with uplift are proven to be contemporaneous with formation of the river. We conclude that understanding of the uplift is crucial to visualizing the Nile course and its geodynamic formation. The information derived from the SRTM data reveals invaluable knowledge in support of the presented remotely sensed geological features. The paper clearly explains the stages of formation of the Nile segments in space and time and structural controls on the path of the Nile River in Egypt. Copyright © 2015 John Wiley & Sons, Ltd.     

The geometric configuration of the newly discovered Abu Deleig sedimentary sub-basin,Central Sudan,using remote sensing,structural analysis,and geophysical survey

Abu Deleig area is a transitional area between the Butana basement terrain to the east; and the Khartoum and Shendi sedimentary basins to the west and northwest directions, respectively. The existence of sedimentary basins within this region of Sudan was previously unknown. Landsat images have been used for delineation of lineaments and drainage system, followed by a structural analysis and geophysical investigations including gravity and resistivity methods. The interpretation of the remotely sensed data revealed that the drainage pattern is structurally controlled. The structural analysis defined the trends of the shear and tensional fractures. The structural analysis revealed that Wadi Al Hawad is the southern continuation of the Keraf Shear Zone. The related minor fractures in a NE–SW direction exhibit normal faults governing the geometry of the Abu Deleig sub-basin. The geophysical investigations confirmed the findings of structural analysis and portrayed the subsurface geometry of the sub-basin. The newly discovered sub-basin has a prism-like shape with its apex occurring at Abu Deleig town and extends to 40 km in NW direction. The depth to the basement increases from 20 m at Abu Deleig in step form to more than 300 m, where it is linked with the Shendi Basin in the northwestern part. The results of this study, however, did not confirm any link of Abu Deleig sub-basin with Atbara Basin to the NE or Khartoum Basin to the west as have been previously suggested.     

Lithostratigraphic and sedimentary evolution of the Kom Ombo (Garara) sub-basin,southern Egypt

Southern Egypt is mostly covered by clastic sediments belonging to the Paleozoic and the Mesozoic. The Precambrian basement rocks bound the Etbai area to the east and Gabgaba area to the west. The basement extends further west forming dissected small and major exposures in southern Egypt, south of latitude 23° 30′ N but are covered by Cretaceous-Lower Tertiary sediments further north, the Western Limestone Plateau. The clastic sediments in southeast Egypt, on the western side of the basement rocks in-between latitudes 22° N and 24° 35′ N, built two sub-basins, Kom Ombo (Garara) sub-basin in the north and south Nile Valley sub-basin in the south. These are separated by a dissected basement wall. The two sub-basins have different lithostratigraphic successions, Paleozoic (Early to Late) in the south Nile Valley sub-basin whereas Late Paleozoic-Mesozoic-Tertairy in the Kom Ombo sub-basin. The platform clastic sediments within both sub-basins were possibly supplied from an easterly located Paleotethys extending to North Gondwana. The Oxfordian opening of the Indian Ocean associated with rise in sea level supplied more waters to the north and sediments by passed the filled southern Nile Valley sub-basin and reached the adjacent Kom Ombo sub-basin defining a depositional shift. On the other hand, during the Jurassic, Northern Egypt received Neotethys waters that filled deeper sub-basins (e.g., the Maghara sub-basin), hence the difference in lithology between Jurassic northern and southern sediments. Since the Jurassic, most of Egypt received Tethys waters. In the drilled wells studied, the younger top sediments surrounding the well sites are related to the Tethys geostratigraphy. The sub-basins in southern Egypt are controlled by N-S faults defining constant subsiding basins. The E-W Guinea–Nubia Lineament bounds the northern side of the Kom Ombo sub-basin, where it is closed by a northern basement arch.     

Cisuralian coals of the Mullaley Sub-basin,northern New South Wales

The Mullaley Sub-basin of the Gunnedah Basin extends from Quirindi in the southeast, to north of Narrabri, to west of Dunedoo in northern New South Wales. There have been more than 100 boreholes sunk to basement investigating the (lower Permian) Cisuralian coal and coal seam gas resources of the Mullaley Sub-basin since the early 1990s. A desktop review of this open file information has allowed the formal correlation and naming of six Cisuralian coal members attaining a maximum 35 m of cumulative thickness within an upward coarsening sedimentary package totalling no more than 150 m. In ascending order, the coal members are: Bibblewindi (0–10 m), Bohena (3–18 m), Collygra (0.5–3 m), Coxs (1.5–4 m), Tullamullen (0.5–4 m) and Mooki (0.5–3 m).

Cisuralian coal seams in the Maules Creek Formation of the southern Mullaley Sub-basin are here correlated with those of the Greta Coal Measures at Werris Creek and Muswellbrook. It is apparent that basement paleotopography played a significant role in the Cisuralian coal development as coals are best developed where the sedimentary sequence is greater than 60 m thick, as there the thick seams (Bohena and Bibblewindi coal members) occur towards the base of the sequence. The maximum western limit of the Cisuralian coals (Rocky Glen Ridge) is further east than previously inferred with new drilling information showing the Porcupine Formation directly overlying the barren pelletoidal claystones of the Leard Formation or the underlying volcanics (Boggabri Volcanics/Werrie Basalt). Early marine transgressions at the top of the Maules Creek Formation have stopped development of the Mooki, Tullamullen and Coxs coal members in the northern and eastern Mullaley Sub-basin and allowed the development of localised paraconglomerate (diamictite) intervals up to 10 m thick. Thick (>20 m cumulative) coal occurrences are localised to the Jacks Creek and Pilliga East State Forest areas southwest of Narrabri. The coal resource potential of the Mullaley Sub-basin is estimated at 13–28 billion tonnes.     

Mineral chemistry and geochemical aspects of Gebel Filat granites, South Eastern Desert, Egypt

Gebel Filat granites form one of Egyptian younger granite intrusions in Wadi Allaqi region, South Eastern Desert of Egypt. They are perthitic monzogranites composed mainly of K-feldspars, plagioclase, and quartz with minor biotite. Plagioclase feldspars are Na-rich and have low anorthite content (An_2–3). Potash feldspars are mainly perthitic microcline and have chemical formula as (Or_96–96.6 Ab_3.4–4 An₀). Biotite is Mg-rich and seems to be derived from calc-alkaline magma. Chlorite is pycnochlorite with high Mg content, revealing its secondary derivation from biotite. The estimated formation temperatures of biotite and chlorite are (689–711°C) and (602–622°C), respectively. Gebel Filat monzogranites are metaluminous, high-K calc-alkaline, I-type granites. They are late orogenic granites related to subduction-related volcanic arc magmatism. They are enriched in LILE and depleted in HSFE indicating highly differentiation character. The REE patterns display an enrichment in LREE due to presence of zircon and allanite as accessories and depletion in HREE with slight negative Eu anomaly $ \left( {{\text{Eu}}/{\text{Eu}} * = 0.51 - 0.97} \right) $ . The parent magma of Gebel Filat monzogranites were emplaced at moderate depths (20–30 km) under moderate conditions of water-vapor pressure (1–5 kbar) and crystallization temperature [700–750°C]. The source magma of these granites seems to be derived from partial melting of lower crust material rather than upper mantle. The geochemical characteristics of pegmatites revealed that they are related to post orogenic within plate magmatism and not genetically related to the parent magma of Gebel Filat monzogranites. Distribution of radioactive elements (U and Th) in the studied rocks indicates normal U–Th contents for Filat monzogranites and U–Th bearing pegmatites. The positive correlations of each of Zr and Y versus U and Th are attributed to presence of zircon and allanite as accessories which incorporate U and Th in their crystal lattice.     

Groundwater flow dynamics in the complex aquifer system of Gidabo River Basin (Ethiopian Rift): a multi-proxy approach

Hydrochemical and isotope data in conjunction with hydraulic head and spring discharge observations were used to characterize the regional groundwater flow dynamics and the role of the tectonic setting in the Gidabo River Basin, Ethiopian Rift. Both groundwater levels and hydrochemical and isotopic data indicate groundwater flow from the major recharge area in the highland and escarpment into deep rift floor aquifers, suggesting a deep regional flow system can be distinguished from the shallow local aquifers. The δ¹⁸O and δ²H values of deep thermal (≥30 °C) groundwater are depleted relative to the shallow (<60 m below ground level) groundwater in the rift floor. Based on the δ¹⁸O values, the thermal groundwater is found to be recharged in the highland around 2,600 m a.s.l. and on average mixed with a proportion of 30 % shallow groundwater. While most groundwater samples display diluted solutions, δ¹³C data of dissolved inorganic carbon reveal that locally the thermal groundwater near fault zones is loaded with mantle CO₂, which enhances silicate weathering and leads to anomalously high total dissolved solids (2,000–2,320 mg/l) and fluoride concentrations (6–15 mg/l) exceeding the recommended guideline value. The faults are generally found to act as complex conduit leaky barrier systems favoring vertical mixing processes. Normal faults dipping to the west appear to facilitate movement of groundwater into deeper aquifers and towards the rift floor, whereas those dipping to the east tend to act as leaky barriers perpendicular to the fault but enable preferential flow parallel to the fault plane.     

An example of post-collisional appinitic magmatism with an arc-like signature: the Wadi Nasb mafic intrusion,north Arabian–Nubian Shield,south Sinai,Egypt

We present new data for the Neoproterozoic mafic intrusion exposed in Wadi Nasb, south Sinai, Egypt (northernmost Arabian–Nubian Shield; ANS). The Nasb mafic intrusion (NMI) intrudes metasediments, Rutig volcanics, and diorite/granodiorite, and is intruded in turn by younger monzogranite and quartz-monzonite. Available geochronological data for the country rocks of the NMI provide a tight constraint on its age, between 619 and 610 Ma, during the hiatus between the lower and upper Rutig volcanics. The NMI is neither deformed nor metamorphosed, indicating post-collisional emplacement, and uralitization by late-magmatic and sub-solidus alteration is restricted to the margins of the intrusion. A quantitative fractionation model indicates a fractionating assemblage of 61% primary amphibole, 10% clinopyroxene, 28% plagioclase, 1% biotite, 0.4% apatite, and 0.15% Fe-Ti oxide. Contrary to the recent studies, we find that the nearby diorite of Gebel Sheikh El-Arab is not co-genetic with the appinitic gabbro of the NMI. Although there are volcanic xenoliths in the NMI, we find no chemical evidence requiring contamination by continental crust. A subduction-related signature in a post-orogenic intrusion requires the inheritance of geochemical tendencies from a previous subduction phase. Given that the fine-grained gabbro of the NMI is consistent with a near-primary mantle melt, we attribute this inheritance to persistence and later melting of the slab-modified mantle domains, as opposed to partial melting and assimilation of the juvenile continental crust. The fine-grained gabbro composition indicates derivation at temperature and pressure conditions similar to the sources of mid-ocean ridge basalts: mantle potential temperature near 1350°C and extent of melting about 7%. Such temperatures, neither so high as to require a plume nor so low as to be consistent with small degrees of melting of a volatile-rich source, are most consistent with a lithospheric delamination scenario, allowing the upwelling of fertile, subduction-modified asthenosphere to depths ≤50 km.     

GIS based analysis of doline density on Taurus Mountains,Turkey

The Taurus Mountain is one of the most important karstic region of the world and dolines are characteristics landforms of this area. However, the number and distribution of doline are unknown in the study area. The aims of this study are to explain the total number of dolines, distribution of doline density, effects of slope conditions and the change of doline orientation in the Taurus Mountains. According to the 1/25000 scale topographic maps utilized in this study, a total of 140,070 dolines were determined in a 13,189 km² area on eleven high karstic plateaus bordered by steep slopes and deep gorges. These plateaus are substantially affected by highly-faulted and jointed systems and about 80% of each plateau is covered with neritic limestone. The dolines are located at an elevation between 10 and 2870 m. Average elevation of all dolines is 1842 m. 90% of dolines are located between 1300 and 2270 m and only 5% of dolines found under 1330 m. According to this results, the densest doline zone corresponds to the alpine and periglacial zone above the treeline. Doline density reaches?>?100 doline/km² on Mt. Anamas and the Seyran, Geyik and Akda? ranges as well as the Ta?eli plateau. Maximum density (187 doline/km²) is found on the Akda? Mountains. However, 66% of the study area is characterized by low density, 29.9% with moderate density, 3.4% with high density and 0.7% with very high density. The highest doline densities are seen on gentle slopes (15°–25°/km²) and steep slopes (>?35°/km²) are limited doline distribution. According to the rose diagram formed by the azimuths of the long axis of the dolines at the Central Taurus, two direction are dominant in doline orientations (NW–SE and NE–SW). However, dominant directions are NE-SW at eastern, NE–SW and NW–SE at central and NW-SE at western part of the Central Taurus. According to this elongations, doline orientations are formed an arc which is formed by tectonic evolution of the Central Taurus.     

The Darfur Dome,western Sudan: the product of a subcontinental mantle plume

Field investigations, K-Ar age determinations and chemical data were used to describe the development of an intraplate volcanic province, the Darfur Dome, Sudan. Magmatism started 36 Ma ago at a small subvolcanic complex (Jebel Kussa) in the center of the dome and was active in the same area between 26 and 23 Ma. Two major volcanic fields (Marra Mountains and Tagabo Hills) developed between 16 and 10 Ma. Volcanism started again at 6.8 Ma with a third volcanic field (Meidob Hills) and at 4.3 Ma in the Marra Mountains and with the reactivation of the center. Activity then continued until the late Quaternary. Having started in the center of the Darfur Dome, volcanism moved in 36 Ma 200 km towards the NNE and 100 km SSW No essential difference in the alkaline magma types (basanitic to phonolitic-trachytic, with different amounts of assimilation of crustal material) in the different fields, was observed. Magmatism is thought to have been produced by a rising mantle plume and volcanism was triggered by stress resolution along the Central African Fault Zone.     

Assessing the spatiotemporal dynamics of vegetation cover as an indicator of desertification in Egypt using multi-temporal MODIS satellite images

Desertification is the major environmental threat in the arid and semiarid regions. The soil-adjusted vegetation index (SAVI) was used as an indicator to monitor the desertification change in Egypt. A multi-temporal satellite data of moderate-resolution imaging spectroradiometer were used to estimate SAVI and land surface temperature. Also, Global Multi-resolution Terrain Elevation Data 2010 and climatic data were used for the analysis. This research focuses on assessing the trend of the vegetation cover change in the seasons of January, March, June, September, and December for the years 2002, 2005, 2008, and 2011. The magnitude of the vegetation cover change in periods 2002–2005, 2005–2008, and 2008–2011 at ≤100 and >100 m elevation was analyzed. A major increase in the vegetation cover that occurred in the period 2002–2005 was about 3,400 km², as a result of two national megaprojects (Toshka Project and El-Salam Canal). In contrast, vegetation cover decreased by 5,500 km² in March during the period 2005–2008, coinciding with the period when the management of the megaprojects failed. Vegetation cover changed again by 1,500 km² in the period of 2008–2011, and the vegetated areas in the Nile Delta were affected by the sea level rising which was responsible for the soil salinization. Three sites were chosen in this investigation (Kom Ombo, El-Oweinat, and Nile Delta) in order to observe the difference of desertification dynamics and to understand the relationship between the vegetation cover distribution and other environmental variables. Anti-desertification policies and advanced agricultural management are highly required in Egypt to decrease any environmental crises and food shortage.     

U-Pb (zircon) ages for the gneissic terrane west of the Nile,southern Egypt

The first U-Pb zircon ages are reported for the gneissic bedrock inliers previously interpreted as part of the Nile Craton. The inliers crop out in the Egyptian Western Desert, east of the Uweinat area and west of the Eastern Desert. Multi- and single-grain zircon analyses of granitoid gneiss and migmatite from Gebel Um Shagir, Aswan, and another locality approximately 160 km south-west of Aswan, yield simple discordia with near modern day Pb loss trajectories, and the following Neoproterozoic crystallization ages: 626+4/–3, 634 ± 4 and 741 ± 3 Ma. In contrast, multi- and single-grain U-Pb analyses (zircon and sphene) from an anorthositic gabbro at Gebel Kamil (22°46N 26°21E) and an anorthosite at Gebel El Asr (22°46N 31°10E) yield Archean and Paleoproterozoic emplacement ages. The former yield a crystallization age of > 2.67 Ga and a metamorphic age of 2.0 Ga; the latter a metamorphic age of 0.69 Ga and an inheritance age of 1.9–2.1 Ga. Because high grade gneiss and migmatite of Neoproterozoic, Paleoproterozoic and Archean age crop out west of the Nile, pre-Neoproterozoic crust should no longer be identified by its metamorphic grade. By contrast, mapping the anorthosite and related rocks might provide first-order estimates for the extension of pre-Neoproterozoic crust in north-east Africa. It is suggested that Archean and Paleoproterozoic crust of the Uweinat and Congo Craton are contiguous because these U-Pb (zircon) data show no evidence for a Neoproterozoic thermal overprint in the Gebel Kamil area and there is no pronounced Neoproterozoic magmatic activity south of the Uweinat inlier and north of the Congo Craton.     

Use of water balance calculation and tritium to examine the dropdown of groundwater table in the piedmont of the North China Plain (NCP)

The groundwater table in the piedmont plain was only about 1–2 m in depth in the 1950s and 1960s, but it lowered dramatically afterwards to about 25–27 m in depth (currently 21–23 m above sea level) due to overpumping of groundwater and drought in the region. This change has adversely affected the sustainable development and food supply of this important agricultural area. The groundwater table at Luancheng Experimental Station of the Chinese Academy of Sciences, located in the piedmont, dropped from 39.36 m in 1975 to 21.47 m above sea level in 1999, at an average rate of 0.72 m/year. Water balance components, such as daily rainfall, pan-evaporation, and evapotranspiration (by lysimeter after 1995) have been recorded since the 1970s, and they were used as variants to simulate monthly water table change based on a physically based statistical model. Groundwater samples were collected during the period 1998–2001, and tritium was measured in the laboratory to trace the groundwater flow from the Taihang Mountains to the piedmont. A reasonable exploitation rate of 150 mm/year was obtained from the model by assuming the annual water table is constant. The recharge and groundwater flow from the Taihang Mountains plays an important role in the water balance of the piedmont area, and it was estimated to be about 112.5 mm/year by using the variation of tritium with the depth, which followed a good exponential function. The simple water balance calculation indicated that the water table could recede at a rate of 0.8 m/year, which is close to the actual situation.     

Detrital zircon provenance evidence for an early Permian longitudinal river flowing into the Midland Basin of west Texas

ABSTRACT

Collision of Gondwana and Laurentia in the late Palaeozoic created new topography, drainages, and foreland basin systems that controlled sediment dispersal patterns on southern Laurentia. We utilize sedimentological and detrital zircon data from early Permian (Cisuralian/Leonardian) submarine-fan deposits in the Midland Basin of west Texas to reconstruct sediment dispersal pathways and palaeogeography. New sedimentological data and wire-line log correlation suggest a portion of the early Permian deposits have a southern entry point. A total of 3259 detrital zircon U-Pb and 357 εHf data from 12 samples show prominent groups of zircon grains derived from the Appalachian (500–270 Ma) and Grenville (1250–950 Ma) provinces in eastern Laurentia and the peri-Gondwana terranes (800–500 Ma) incorporated in the Alleghanian-Ouachita-Marathon orogen. Other common zircon groups of Mesoproterozoic-Archaean age are also present in the samples. The detrital zircon data suggest throughout the early Permian, Appalachia and Gondwana detritus was delivered by a longitudinal river system that flowed along the Appalachian-Ouachita-Marathon foreland into the Midland Basin. Tributary channels draining the uplifted Ouachita-Marathon hinterland brought Gondwana detritus into the longitudinal river with headwaters in the Appalachians or farther northeast. This drainage extended downstream westward and delivered sediments into the Permian Basin near the west terminus of the Laurentia-Gondwana suture. Estimated rates of deposition and proportions of zircons from more local (Grenville) versus more distal (Pan-African) sources indicate that river strength decreased throughout early Permian time. Primary sediment delivery pathway was augmented by minor input from the Ancestral Rocky Mountains and wind deflation of fluvial sediments north and east of the basin. Slope failure associated with early Permian deposition in the southeastern margin of the Midland Basin triggered gravity flows leading to submarine fan deposition.     

Volume estimation and stage division of the Mahu landslide in Sichuan Province,China

The Mahu lake, the third deepest lake in China, is located on the west bank of the Jinsha River in Leibo county, Sichuan Province. It is a dammed lake created by an old landslide on the ancient Huanglang river, a tributary on the west bank of the Jinsha River. Previous studies (Wang and Lu in J Mt Res S1:44–47, 2000) suggested that this landslide was caused by an earthquake approximately 372 ka (Middle Pleistocene), during which a few hundreds of million cubic meters of debris were deposited between 1177 and 900 m a.s.l. (above sea level), covering an area of around 15 km². Our further investigations, including geodetic survey, borehole drilling, and field reconnaissance, combining with five chronological data, have made some new discoveries at this site. First, the toe of the landslide extends from 900 m a.s.l. down to 320 m a.s.l., i.e., the local bed elevation of the contemporary Jinsha River. Second, the area of the landslide deposits is 17.3 km² with a volume of 2.38 km³, much larger than the previous estimation. Thus, it should be one of the largest known landslides in China. And the lower elevation of the landslide’s toe also rules out the possibility that it is a hanging valley on the ancient Huanglang river. Our work suggests that this landslide was created by five events according to the overlapping characteristics of the deposits and five chronological data, which are old than 52,600 years, old than 16,000 years, old than 15,500 years, 5800 years, and old than 4200 years, respectively.     

Assessment of the Hydrogeochemical Characteristics of Groundwater Resources at some Wadis in the East of El Minia Governorate, Eastern Desert, Egypt

The El Minia governorate lies within the Nile Valley, surrounded by calcareous plateaus to the east and west. The present study focuses on the hydrogeochemistry of the Eocene limestone aquifer at some wadis in the east El Minia governorate, Eastern Desert, Egypt. Hydrogeologically, two main aquifers are encountered in the study area, namely the Maghagha marly limestone and the Samalut chalky limestone aquifers. The Maghagha aquifer is composed of alternating layers of marly limestone and shale with thicknesses ranging from 3.49 m to 177.05 m and a groundwater depth ranging from 8.5 m to 59.27 m which reflects low groundwater potentiality. The groundwater salinity representing this aquifer ranges from 603.5 mg/L to 978.5 mg/L, reflecting fresh water type. Samalut aquifer is made up of chalky, cavernous and fractured limestone with thickness ranging from 30 m to 205 m and groundwater depth ranging from 9 m to 86.77 m, which indicates good groundwater potential. The groundwater salinity of the concerned aquifer ranges from 349.7 mg/L to 2043.9 mg/L, reflecting fresh to possibly brackish water types. Groundwater in the study area is of meteoric water origin; recent recharge is mainly controlled through the presence of fractures and their densities. The majority of groundwater samples in the study area are suitable for drinking and irrigation purposes.