Sedimentological characteristics and geochemical evolution of Nabq sabkha, Gulf of Aqaba, Sinai, Egypt (original) (raw)
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Sedimentological characteristics of continental sabkha, south Western Desert, Egypt
Continental sabkha is recorded in the extreme middle part of the southWestern Desert of Egypt representing one of the most promising areas for sustainable development, especially for agriculture. The geomorphologic units of the area are formed under the influence of structural, lithological, and/ or climatic controls. These units include pediplain, depressions, mass-wasted blocks, residual hills, drainage lines, and aeolian landforms. The effective deflation process is reinforced by the lack of protective vegetation cover and the susceptibility of weakly consolidated rocks to wind removal. Different rock units covering the area range in age from Early Cretaceous to Quaternary. Quaternary deposits include playa/ sabkha deposits where the continental sabkha is divided into four zones A, B, C, and D. Underground waters coming from the north and east were progressively enriched in solute by interaction with the surrounding sedimentary and igneous rocks. Most of the evaporite minerals grow displacively as a result of evaporative pumping. Mineralogically, the continental sabkha salt complex includes gypsum, natroalunite, tamarugite, bloedite, eugsterite, nitratine, halite, and D’ansite. Some of the major and trace elements (SiO2, Al2O3, Fe2O3, MgO, CaO, Na2O, K2O, as well as Rb, Ba, Zr, Sr, Y, V, and Zn) were measured. The correlation and enrichment of these major and trace elements indicate the origin of the salt complex in the sabkha.
A combination of field work, mineralogical and geochemical analyses have been used to study the characteristics of the supratidal flat sabkhas developed on the southern Corniche of Jeddah. Mineral significances of sabkha deposits are considered a guide for understanding the mode of formation while, study of the chemistry of sabkha reflects the diagenetic history and pollution. Gypsum, halite, aragonite, Mg-calcite, quartz and feldspar are the dominant minerals present while, calcite, dolomite, amphibole and pyrite occur in small amounts. Significant vertical alteration of both carbonate and evaporite minerals with depth are noticed in the studied sabkha sequence. Distribution of elements (iron, manganese, copper, zinc and lead) in the sabkha sediments from four holes indicates characteristic differences. The downward increase of Fe concentration in sabkha sequences can be related to diagenetic processes, while enrichment of Cu, Zn and Pb are related to a pollution of the area due to dumping untreated municipal sewage and industrial waste in the sea.
Holocene evolution of Dahab coastline e Gulf of Aqaba, Sinai Peninsula, Egypt
Dahab is a little Bedouin-village in Sinai Peninsula on the east coast of the Gulf of Aqaba and it lies approximately 90 km north of Sharm-el-Sheikh City. Dahab means " gold " in the Arabic language; over the past 20 years it has become one of the most visited tourist sites in Egypt. The basement complex is composed mostly of biotite aplite-granite, mica-aplite granite, granodiorite, quartz diorite, alaskite, and diorite. This composition correlates to similar igneous rocks in the most southern areas of Sinai and the Red Sea. Wadi Dahab is composed of igneous and metamorphic rocks and the coastline is formed of fragments of its rocks mixed with fragments of coral reef. The morphology of Dahab's coastline is characterized by a hooked marine spit composed of fluvial sediments carried by marine currents from the mouth of Wadi Dahab. This spit encloses a shallow lagoon, but the active deposition on the lagoon bottom will turn it into saline marsh. This paper investigates the evolution of the Dahab spit and lagoon during the Holocene and over the last 100 years, as well as the potential impacts of future management of the coastal area. The coastline mapping during the study was dependent on GIS techniques and data were collected by using total station, aerial photographs and satellite image interpretation as well as soil sample dating.