Formation and Taxa of some Wadi Dahab Tributaries Soils, South Sinai, Egypt

Abstract

Geological parent material is a soil forming factor which controls the particle size distribution (PSD), geochemical characterization, and mineralogical properties. In Wadi Dahab Basin at southeastern Sinai of Egypt, four main tributaries (Al-Ghaib, Zoghra, Abu-Khashab and Um-Ism) and their subtributaries, having different geological parent materials, were selected and mapped. Sixteen pedons containing 51 sediment samples across the slope gradient (1335-9 m) of Wadi Dahab Basin representing all its tributaries and subtributaries were exhaustively analysed for the purposes of: (1) detecting the lithologic discontinuities (LDs) through soil morphology and uniformity indices; (2) recognizing the weathering intensity using the geochemical data; (3) identifying the sediments provenance via heavy mineral distribution; and (4) classifying the soils up to family level. LDs in most pedons revealed sequences of deposition and erosion processes and the heterogeneity of the parent material. The vertical distribution of coarse fragments within a pedon is proposed as a morphologic indicator (as with other clay-free basis indices) to detect LDs in soils. The Fe2O3 and Al2O3 were relatively enriched at downslope positions while SiO2, MgO, K2O, and Na2O were strongly lost during sediment weathering and soil formation, with the exception of CaO that was highly affected by CaCO3 content. The heavy minerals characteristics suggest their mixed sources from sandstone, limestone, granites, and metamorphic rocks. The heavy minerals concentration and geochemical oxides in most studied pedons followed the LD set, indicating further approaches for detecting LDs. Pedons from upslope positions were immature sediments and classified as Entisols while pedons from the downslopes of Wadi Al-Ghaib, Wadi Zoghra, and Wadi Dahab's delta were submature sediments and classified as Aridisols. Furthermore, six families were identified across the study area. Indices based on PSD, geochemical, and mineralogical data were evaluated and further implications of the results were discussed in the text.