Document Type : Original Article
Abstract
THE AIM of the current work is to identify the mineralogical …… composition of sand and clay fractions in order to evaluate the genesis and degree of homogeneity of soils in the study area.
Landsat ETM (Path 174/Row 43) image (2012) and digital elevation model (DEM) were used in ERDAS Imagine 9.2 software to produce the physiographic map of the study area. From the physiographic point of view, the landscapes include five units, i.e. sedimentary plain, low wadi plain, dissected erosion plain, terraces and wadi bottom. Ten soil profiles were selected to represent the main physiographic units. The morphological description was done and soil samples have been collected for physical and mineralogical analysis.
The data reveal that the sorting index (So) of all soil profiles in the study area is poorly and very poorly sorted indicating aqueous media of transportation. The obtained data of skewness (Sk) reveal the symmetry of distribution towards coarse skewed throughout the majority of soil profile layers.
With regard to the mineralogical composition of these soils, the sand fraction consists of light and heavy minerals. The light minerals are the main constituents of sand fraction and consist mainly of quartz (> 90%) followed by feldspars (plagioclase and orthoclase) in addition to muscovite and calcite minerals. On the other hand, the heavy minerals composed of opaques and non-opaques. Opaque minerals are generally the major heavy fraction constituents in all the examined soils. These minerals composed essentially of iron oxide minerals (e.g., magnetite, ilmenite and hematite). The complementary non-opaque minerals are recalculated to be 100%. These minerals consist of: (a) igneous origin minerals or unstable minerals (amphiboles, pyroxenes and epidotes); these minerals are mainly dominating the non-opaque minerals in the study area. (b) sedimentary origin minerals which are also named ultrastable or index minerals include zircon, rutile and tourmaline, these minerals are the second abundant minerals in the study area and, (c) metamorphic origin minerals or metastable minerals (garnet, kyanite, staurolite, sillimanite and andalusite) are detected in considerable portions in the studied soils.
The source rocks of the sand fraction in the study area are the mixture of igneous, sedimentary and metamorphic rocks. The igneous rocks are the first source of sands in sediments of the study area. The vertical distribution of the uniformity ratios and weathering values are changed irregularly depthwise. This indicates that these sediments were inherited from multi-sources and/or may be subjected to different sedimentation cycles.
The abundance and distribution of amphiboles and pyroxenes minerals indicate that the studied soils are recent, poorly developed and immature from the pedogenic point of view. The soils units are mostly not affected by Nile sediments. The soils are weathered from the Red Sea igneous rocks and the sedimentary rocks of the surrounding area and transported by the action of water during the wet period throughout the streams in the study area.
The data reveal that clay minerals suite is dominated by smectite, followed by kaolinite, while illite mineral is detected in few amounts. Furthermore, some nonclay minerals, e.g., quartz, feldspars, calcite and dolomite are, however, detected in considerable amounts in some clay fractions.
It is well known that the clay minerals could be present as a result of inheritance from parent material by alteration, degradation of primary minerals, synthesizing and addition. Chemical decay is somewhat limited due to the prevalence of aridity, while the mechanical weathering contributes to a great extent. The variation in the relative content of the present clay minerals may be attributed mainly to sedimentation regime varieties and /or to the nature of the source rocks.
Keywords
)
View on SCiNiTO