A new record and a new ichnospecies of Arachnostega from the Middle Miocene of Egypt     

Olev Vinn  Ahmed M. El-Sabbagh  Magdy M. El-Hedeny  Mohamed A. Rashwan  Saleh A. Al Farraj 《Proceedings of the Geologists' Association. Geologists' Association》2018,129(6):790-796

The ichnogenus Arachnostega Bertling, 1992 is recorded for the first time from a bioeroded, coral-rich, Middle Miocene limestone bed in the middle Siwa Escarpment Member (Marmarica Formation) at Siwa Oasis, northern Western Desert of Egypt. These burrowing traces are preserved on the surface of a few internal moulds of bivalves and gastropods. Until now, the ichnogenus Arachnostega included a single ichnospecies, A. gastrochaenae Bertling, 1992. In the material studied herein, two ichnospecies are identified, described, illustrated and compared with other, similar traces. One of these is a new ichnospecies of Arachnostega; this is here named A. siwaensis ichnosp. nov. It is distinguished from A. gastrochaenae in the possession of tunnels that usually branch in a V-pattern; intervals of ramification are longest in the main branch and decrease in second- and third-order branches. Arachnostega traces were produced in a warm, low-energy, shallow-marine (<10?m water depth) environment. Polychaetes are the most likely producers of marine Arachnostega, which are commonly occurred in the same studied bed. This new occurrence is significant in extending the known stratigraphical and geographical ranges of Arachnostega into the Middle Miocene of Egypt.  相似文献   

An analysis of climatic and human induced determinants of agricultural land use changes in Shupiyan area of Jammu and Kashmir state,India     

Rehana Rasool  Mifta ul Shafiq  Pervez Ahmed  Parvaiz Ahmad 《GeoJournal》2018,83(1):49-60

The economy of the Jammu and Kashmir state depends mostly on traditional forms of occupation. Unaffected and unaltered by modern day industrial developments and changing times, the indigenous traditional occupations of farming, animal husbandry and horticulture forms the backbone of the state economy. But in the last few decades, Agriculture in the state as well as the study area is receiving a set back and Horticulture is flourishing leaps and bounds. The present study aims to analyze various determinants responsible for this change. Climatic as well as field data was thoroughly analyzed to comprehend the situation. A Mann–Kendall test was done on the climatic data to support the hypotheses. It was observed that initially changing climatic trends proved to be the triggering factor supporting this change, but in due course of time, the determinants took an economic and psychological turn. The perusal of Indian Meteorological Data reveals an increasing trend of annual mean maximum temperature from 16.78 °C in 1985 to 17.58 °C in 1995 and an increase from 5.30 °C to 7.00 °C in the annual mean minimum temperature, and as such acting as a triggering factor for the land use conversion. Further, the mean annual rainfall shows a decrease from 100.75 mm in 1981 to 79.43 mm in 1991. The greater economic returns from horticulture as well as the changing behavioral patterns of people over the time further cemented its growth. The farmers have since persisted with the horticulture activity as it has proven to be an economically a much better lucrative enterprise.  相似文献   

Laboratory Investigation of the Influence of Geotextile on the Stress–Strain and Volumetric Change Behavior of Sand     

Brahim Abdelkader  Ahmed Arab  Marwan Sadek  Isam Shahrour 《Geotechnical and Geological Engineering》2018,36(4):2077-2085

This paper presents the results of triaxial tests conducted for the investigation of the influence of geotextile on both the stress–strain and volumetric change behavior of reinforced sands. Tests were carried out on loose sand. The experimental program includes drained compression tests on samples reinforced with different values of both geotextile layers (1 ≤ Ng ≤ 3) and confining pressure (\(\upsigma_{\text{c}}^{\prime }\)) varying from 50 to 200 kPa. Tests show that the contribution of geotextile is negligible until an axial strain threshold that range between 2.5% for a confining pressure of 50 kPa to lower than 1% for 100 and 200 kPa confining pressure. At higher values of ε_a, geotextile induces a quasi-linear increase in the stress deviator (q) and volume contraction in the reinforced sand. Tests show a negligible influence of the number of geotextile layers (Ng) on the contribution of geotextile to both stress–strain and volumetric change, when normalized with Ng. Tests also show that the contribution of geotextile to the stress–strain mobilization augments with the increase in the confining pressure, while its contribution to the volume contraction decreases with the increase in the confining pressure. The reinforced soil becomes contracting in the case of 2 and 3 geotextile layers.  相似文献   

Adsorption of Congo red and crystal violet dyes onto cellulose extracted from Egyptian water hyacinth     

Salahuddin  Nehal  Abdelwahab  Mohamed A.  Akelah  Ahmed  Elnagar  Marlen 《Natural Hazards》2021,105(2):1375-1394

Natural Hazards - The present investigation has highlighted the utility of floating aquatic Egyptian hyacinth, which is considered as a significant reason for environmental problems in Nile River,...  相似文献   

Biotic response to the latest Cenomanian drowning and OAE2: A case study from the Eastern Desert of Egypt     

Emad Nagm  Sreepat Jain  Kamel Mahfouz  Ahmed El-Sabbagh  Aziz Abu Shama 《Proceedings of the Geologists' Association. Geologists' Association》2021,132(1):70-92

The changes in macrofauna and microfauna, before, during and after the latest Cenomanian global Oceanic Anoxic Event (OAE2), from the Eastern Desert of Egypt are documented, along with an inferred paleoenvironment. The age of the studied OAE2 interval is constrained by the last occurrence of the marker calcareous nannofossils species Axopodorhabdus albianus along with the previously identified positive δ¹³C excursion from the coeval ammonite Vascoceras cauvini Zone (= Neocardioceras juddii Zone), enabling correlation with the peak ‘b’ of the OAE2. Based on the studied microfaunal assemblages, a warm shallow restricted lagoonal environment with mesotrophic conditions and strong seasonality is inferred. The presence of a rare ammonite (and ostracods) attest to the intermittent introduction of marine waters within this inner ramp setting. In terms of sequence stratigraphy, two 3rd order depositional sequences are recorded. The top surface of the first depositional sequence, at the sequence boundary, SB Ce 5 (the start of the OAE2), is marked by an abrupt faunal change with reduced abundances of the macrofaunal elements. This is in tune with other Egyptian records of relatively smaller loss (10 %) at the Cenomanian-Turonian boundary, as compared to much higher numbers (53–79% of species), globally. This faunal (biotic bottleneck) and lithological change (from siliciclastic-dominated deposits to a largely carbonate-dominated one) at the SB Ce 5 is attributed as a response to the latest Cenomanian drowning (the highest sea-level during the Phanerozoic), that also resulted in the formation of carbonate platform.  相似文献   

Red Sea faulting and salt diapirism as a potential geotechnical hazard in Jazan,southwest Saudi Arabia: inferences from gravity data     

Ibrahim  Elkhedr  Mogren  Saad  Qaysi  Saleh  Abdelrahman  Kamal  Ghrefat  Habes  Zaidi  Faisal  Hakami  Ahmed 《Natural Hazards》2021,108(3):2613-2628

Natural Hazards - The main objective of this study is to detect the subsurface extension of salt diapirs and structural deformations in the city of Jazan and its suburbs using gravity data. Salt...  相似文献   

Mineralogy and geochemistry of fine-grained Dahab stream sediments,Southeastern Sinai,Egypt: emphasis on the intergrowths of Fe–Ti oxides     

Surour  Adel A.  El-Kammar  Ahmed. M. A.  Arafa  Ebtisam H.  Korany  Hala M. 《中国地球化学学报》2021,40(6):871-894

Acta Geochimica - Mineralogical and geochemical characteristics of stream sediments collected from 30 stations in the Dahab-Wadi Kid area (southeastern Sinai, Egypt) are presented. The studied...  相似文献   

Geology and Mineral Chemistry of Uranium- and Thorium-bearing Minerals in Rare-Metal (NYF) Pegmatites of Um Solimate,South Eastern Desert,Egypt     

Mohamed A. ALI  Ahmed E. ABDEL GAWAD  Mohamed M. GHONEIM 《《地质学报》英文版》2021,95(5):1568-1582

The garnet muscovite granitic pegmatite of Um Solimate, in southern Egypt, represents a promising asset for strategic and economic metals, especially Bi–Ni–Ag–Nb–Ta as well as U and Th. The ore bodies occur as large masses, pockets and/or veins of very coarse-grained pegmatites, which consist mainly of K-feldspar, quartz and albite with subordinate muscovite, garnet, and biotite. Radiometric data revealed that eU- and eTh-contents of the pegmatites reach up to 39 ppm and 82 ppm, respectively. The studied pegmatites are enriched in primary U and Th minerals (uraninite, coffinite, thorianite and uranothorite) as well as Hf-rich zircon and monazite, which give rise to anomalous radioactive zones. Niobium-tantalium-bearing minerals (i.e. ferrocolumbite, microlite and uranopyrochlore), xenotime, barite, galena, fluorite, and apatite are ubiquitous, and, consequently, the studied pegmatites belong tothe Niobium–Yttrium–Fluorine-type (NYF) family. The noble metal mineralization includes argentite (Ag2S), native Ni and Bi as well as bismite and bismoclite. In addition, beryl and tourmaline are observed in pegmatites near the contact with metasediments and ultramafic bodies. The observed compositional variations of Ta/(Ta+Nb) and Mn/(Mn+Fe) ratios in columbite (0.08–0.45 and 0.11–0.57, respectively) and Hf contents in zircon (3.54–6.46 wt%) may reflectan extreme degree of magmatic fractionation leading to formation of the pegmatite orebody.  相似文献   

Gravity map of Kalabsha area, northwest of Aswan Lake, and its structural significance     

E.M. Abdelrahman  A. Tealeb  H.A. Ahmed 《Journal of Geodynamics》1991,14(1-4)

A detailed gravity survey was carried out in one of the seismo-active areas at the northwestern region of the High Dam Lake (Kalabsha area) to study its subsurface structure. In order to understand the seismicity of the area, the establishment of a geodynamic model from geological and geodetic data is of great importance. After a series of adjustments and corrections of the measured gravity data, free-air and Bouguer anomaly maps were constructed for the Kalabsha area, and several interpretation techniques were applied to analyse these anomalies. The results of the analysis indicate that the Kalabsha area is affected by several faults trending mainly E-W and N-S. The active area located west of Gebel Marawa is bounded by a set of faults striking NE-SW, N-S and E-W. The throws of these faults range from 160 to 370 m.The minimum depth to the basement complex is about 200 m and its maximum depth is around 600 m. The thickness of the sedimentary column (Nubia sandstone) in the Kalabsha area decreases due west and increases toward the southern and eastern parts of the area. The results explain the tectonic framework of the area well.  相似文献   

Drought and human adjustment in Saudi Arabia   总被引：1，自引：0，他引：1  

Abdulla Ahmed Al-Taher 《GeoJournal》1994,33(4):411-422

Drought is one of the natural hazards which causes death and damage for property particularly in drylands of the world. Drought as a natural hazard tends to limit and disrupt human activities. On the other hand, man has tried to adjust his living conditions to this hazard. The adjustment to drought is different from one country to another. Adjustment to drought is affected by culture, income, and by the political system in the country. In the case of Saudi Arabia adjustment to drought hazard is usually the work of both individuals, and government. The Saudi Arabian government has spent large sums of money to reduce impact of drought hazard.  相似文献