Petrography and geochemistry of the Lower Carboniferous Abu Durba sandstones, West Central Sinai, Egypt

Abstract

Petrographically, the Lower Carboniferous Abu Durba sandstones are classified as quartz arenites reflecting their high maturity and have an average framework composition of Q96F2L2. The sandstones are rich in SiO2, Zr, Sr, and Ba and depleted in most other major and trace elements, compared with the average upper continental crust. The positive correlation between Al2O3 and most trace elements signifies that trace elements are associated with clay minerals rather than with source rocks. Provenance discrimination diagrams, major elemental ratios (Al2O3/TiO2 and K2O/Na2O), and SiO2, Cr, Ni, V, and Zr contents in sandstones reveal that the sandstones are mainly derived from quartzose recycled sedimentary rocks with subordinate felsic plutonic sources. The chemical index of alteration (avg. 88.21) and Rb/Sr ratio (> 0.8) values for the Abu Durba Sandstone indicate an intensive degree of weathering either of the original source or during transport before deposition, and may reflect intense recycling in the source area. Also, low index of compositional variability values and high SiO2/Al2O3 ratios indicate high mineralogical maturity of Abu Durba Sandstone. The discriminant function-based multidimensional diagrams reveal that the Abu Durba Sandstone was deposited in a rift basin, which is consistent with the general geology of West Central Sinai during the Lower Carboniferous. The older sandstones of Naqus (Lower Cambrian) and Abu Thora (Lower Carboniferous) formations in addition to the Precambrian basement rocks are probably the sources of the Abu Durba Sandstone.