provenance of recent sediments, along the red sea coast, egypt

INTERNATIONAL JOURNAL of ACADEMIC RESEARCH

Vol.5.No. 2.March,2013

F.S. Ramadan, S.M. Zaid. Provenance of recent sediments, along the Red Sea coast, Egypt. International Journal of Academic Research Part A; 2013; 5(2), 38-49. DOI: 10.7813/2075-4124.2013/5-2/A.5

PROVENANCE OF RECENT SEDIMENTS, ALONG THE RED SEA COAST, EGYPT F.S. Ramadan, S.M. Zaid Geology Department, Faculty of Science, Zagazig University, 44511 Zagazig (EGYPT) DOI: 10.7813/2075-4124.2013/5-2/A.5

ABSTRACT Fifteen samples were collected from the recent sediments of 15 Wadi- floors, from depth of 30cm along the Egyptian Red Sea coast. The samples were analyzed for grain size, mineral and chemical compositions in order to interpret their differences and nature of provenance. Heavy mineral analyses and trace element concentrations of studied wadis have revealed the relative abundance of both heavy minerals (opaques and non- opaques) and trace elements in different areas along the coast. Application of cluster analyses, on both heavy minerals and trace elements variations give good evidence for the tectonic setting leading to the definition of four main clusters (mineral associations): amphibole association, opaque-amphibole-trace association, trace -amphibole-epidote association and opaque- trace element association. These clusters could be related to four different provinces. Heavy minerals and trace elements distribution shows regional variability induced by provenance and local variability reflecting genetic differences in the coastal sediments. The analysis and results of heavy mineral and trace element assemblages of the Red Sea are clearly reflecting diverging plate boundaries in most cases. Key words: Provenance, Red Sea, Heavy minerals, Trace elements, Egypt 1. INTRODUCTION The study area locates along the Red Sea coast; it extends from Marsa Um Gheig southwards to Ras Banas. it lies between latitudes 24° 00´ to 26° 00´ N and longitudes 34° 10´ to 34° 10´ E (Fig. 1), and covers about 2 28.000km . Generally, the Eastern Desert comprises crystalline igneous and metamorphic rocks with relative vast belt of Phanerozoic sedimentary rocks, covered with continental regolith. They are dissected by different drainage system that drains ultimately to the Red Sea. The area comprises fifteen wadis. These drainage systems are Wadi Malek El Oud, El Gemal, Sharm El Faqiri, Ghadir, Um Tundoba, Samadai, Igla, Abu Kalb, Abu Dabbab, Waseat, Mubarak, Um Areik, Um Gerifat, Um Lasifa, and Wadi Muhammad Maktal. Red Sea coastal sediments are composed mainly of mixed carbonates and non-carbonates minerals. Carbonates are derived from the disintegration of recent and fossiliferous coral reefs and the associated biological communities. Terrigneous sediments are derived from the neighboring Red Sea Mountains, especially at the valley mouths. Thus, the carbonate and non-carbonate minerals have distinctly different origins and both types are potentially dilutes each other (Mansour, 1995). The floor of these wadis is filled with Quaternary and recent transported valley filling sediments. Near the heads of these wadis the wash consists almost entirely of granitic blocks and boulders. At the mouths the blocks and boulders give place to gravels and sands. Silt and clay mostly cover the flat floor of the studied wadis. Wadi deposits in the study area are formed of sediments mainly precipitated by surface water and forming medium, fine and very fine grain size sediments. These sediments have different mineralogical and chemical composition depending on the country source rock type. The linkage between plate tectonic setting and sediment composition has been long recognized (Pettijohn, 1984). These criteria have been used successfully to indicate ancient plate tectonic settings in many regions of the world. Nevertheless, certain problems were apparent when these methods were used, such as the following (1) sediment positions are controlled not only by tectonics but also by the weathering history, transport mechanisms, depositional conditions and postpositional processes, (2) some suites of sands and sandstones of the different tectonic settings overlap significantly and (3) the relationships between plate tectonic setting and sediment compositions are identified and in some cases poorly understood (Nechaev and lsphording, 1993). Heavy minerals are of great value in solving many problems related to depositional environment as; lithology of source rocks, transportation history, climates and re1ief, correlation, paleogeography, tectonism and provenance studies (Folk, 1980). Several investigations on the recent sediments were carried out on the Egyptian Red Sea coast by many authors such as Philobbos et al., (1983); Mansour (1991, 1992, 1999 and 2000); Mansour and Sadiek (1994); Mansour et al. (1997); Ali et al, (2001) and others. However, investigations including chemical weathering, climate, provenance and tectonic setting of these alluvial sediments along the Red Sea coast are rare. The present work aims to reconstruct the parent rock assemblages of the recent alluvial sediments, their

38 | PART A. NATURAL AND APPLIED SCIENCES

Vol. 5. No. 2. March, 2013


tectonic provenance, and the physiographic conditions under which these sediments deposited, using an integrated provenance approach involving heavy minerals analysis and trace elements data from fifteen wadis (Fig. 1)

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2. SAMPLES AND METHODS Fifteen samples were collected from the recent sediments of fifteen Wadi-floors with a grab sampler from depth of 30 cm along the Egyptian Red Sea Coast from Marsa Um Gheig in the north to Ras Banas in the south, throughout the period between September 2010 and October 2011 (Fig. 1). Each sample weighing about 5 kg represented the alluvial sediments of each Wadi. The textural composition of the sediments (carbonate, sand and mud contents) has been determined using wet sieving analysis technique of Folk (l968). Carbonate content was determined by leaching the samples with cold diluted l0% hydrochloric acid. The weight of acid soluble material (CaCO3) is expressed as a percentage of the total weight of sample. The heavy minerals in the fine and the very fine grained sand fraction (Ø3 and Ø4) have been separated using bromoform (sp. gr. 2.85). Identification was made with the polarizing microscope and about 500 mineral grains of each fraction were counted in order to determine the relative frequency percentages. The samples were chemically analyzed for trace elements using an X-ray fluorescence (XRF) spectrometer (energy dispersive, Philip EXAM- 6 systems) on pressed powder pellets. In order to check the accuracy of the data, international standards SDO-1, SCO-1, GSD-9 and SO-1 were analyzed along with the samples. In order to delineate the mineral provenances and environmental setting of the different localities; SPSS program was used to classify and cluster the degree of similarity and dissimilarity between the different samples as cases and variables 3. RESULTS The coastal Red Sea sediments at the southern part of the Eastern Desert are the result of interplay of aeolian fluvial and marine influx of sedimentary materials (Mansour, 2000). The influence of these sources is more or less localized resulting in a particular textural and compositional distribution, especially in the near shore area. The predominant sediment type is the coarse fractions (Table 1). The distribution of coarser sediments reflects the abundance of terrigneous sediments in the nearshore zone away from the beach. Table 1. Grain size, percentage of light fraction and chemical analysis of trace elements (in ppm) of studied sediments

Carb = carbonate; Qm = monocrystalline quartz; Qp = polycrystalline quartz; Qt = total quartz; F= feldspars; L.F= lithic fragment The heavy minerals suites were separated from fine and very fine sand fractions of 15 wadis alluvium sands. They were identified microscopically. About 500 grains were counted in each mount. Generally, Alluvium sands consist of quartz, feldspar and rock fragments as well as minor quantity of heavy mineral grains (sp.gr. >2.9). Heavy minerals are generally studied in terms of opaques and non- opaques. However, the opaques represented nearly the whole bulk of the heavy mineral suite, the samples contain high amount of non- opaques in both fine and very fine fractions (Table 2). 3.1. T h e light fraction The W adi alluvium sands consist essentially of quartz and feldspars and some rock fragments. Quartz is the main mineral constituent in different samples. It ranges from about 60- 70% of the total light minerals (Table 1). It forms either monocrystalline or polycrystalline types. Among quartz grains, monocrystalline quartz (95.2 vol %) is dominant over polycrystalline quartz. The most of monocrystalline quartz grains show straight to slightly undulatory extinction (GM and GMGM and GM