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Abstract
The present work tries to understand the physical and biological factors of the intertidal environment through studying the intertidal area between Quseir and Marsa Alam along the Red Sea coast.
Thirteen transects are carefully selected to reflect the various subenvironments and sediment fades identified along the studied area. The intertidal area in this study is divided into upper, middle and lower intertidal zones to provide consistency for sample collection. Generally the studied intertidal area is composed of rocky submerged hard ground covered by thin film of sediments and is characterized by the presence of shallow depressions filled with sediments. The topographic profiles and schematic block diagrams which describe the nature of’the supratidal area and the width of the intertidal area presents data base help in locating the most adequate places for tourist and construction sites.
Fifty beachrock samples are collected and examined by thin section petrography and scanning electron microscope. They are ’dominantly composed of igneous and metamorphic rock fragments and mineral fragments with variable percentages of bioclastic grains. Three types of cements are described, which are fibrous aragonite, micrite and pseudo-peloidal cements. Different microfilaments and microorganisms are dominantly observed, so the proposed mechanism for the studied beachrock cementation includes both biological and physiochemical. Microorganisms promote the nucleation of carbonate minerals by-providing substrate or by changing the water chemistry, then the cementation process is developed due supersaturation resulting from evaporation and CO? degassing owing to wave agitation and increasing temperature.
Thirty seven sediment samples are also collected and subjected to grain size analysis indicating that the area is covered dominantly bymedium to coarse sand, moderately to poorly sorted and nearly symmetrical to coarse skewed. The foraminiferal investigation of these sediment samples led to identification of 98 foraminiferal species and subspecies. The overall composition of the studied fauna shows that the percentages of porcelaneous, hyaline and arenaceous fo’raminifera are 71%, 26% and 3%, respectively and the planktonic/benthonic .ratio is approximately equal to zero. Such ratios can be used as an indicator of the intertidal zone in the geologic history taking into consideration the climatic conditions.
The foraminiferal density and diversity coincide’with each others having higher values at fine grained sediment samples and lower values at coarse grained sediment samples demonstrating that the type of substrate may be the main ecological factor controlling the foraminiferal distribution in such littoral environment. Generally the study area is subjected to low rate of pollution and this is confirmed by the complete absence-of Ammonia tepida, which is suggested by several authors as a better monitor to high’ concentrations of selected toxic elements and/or organic compounds, but it is obvious that transects which are nearby human impacts having faunal density more lower than the average and this demonstrates the sensitivity of the foraminifera to the environmental changes and confirms that foraminiferal density can be used as an early warning indicator of possible, anthropic contamination.