干旱区生态环境知识资源中心

The purpose of the present paper is to identify the source of iron oxides as well as the paleo-oxygenation conditions by using major oxide and trace element geochemistry of the Quseir and Sabaya formations exposed at the Dakhla-Kharga basin, Western Desert, Egypt. The iron-rich paleosol occurs chiefly overlying different Upper Cretaceous rocks, particularly the red clay of the Campanian Quseir Formation at the Dakhla Oasis or the Cenomanian Sabaya Formation at the Kharga Oasis. The iron-rich paleosols consist mainly of massive yellow goethite-rich beds with high concentrations of Fe( OH). The presence of high Fe/Mn ratio with a wide range of variation indicates that the sources of the iron-rich paleosols are from the discharge of iron-rich Nubian Aquifer water controlled largely by localized fractures which formed spring mounds deposited of Pleistocene age. These mounds were exposed to subaerial weathering that resulted in the formation of lateritic goethite ore during tropical climatic periods. There is evidence of hydrothermal vents ( hot spring) such as found native Au, magnetite. and high concentrations of zirconium, cobalt. and vanadium. In the depositional history of Mut and Zayat ironstones, four main processes will be clarified as follows: ( 1) the syn-depositional, ( 2) diagenetic, ( 3) hot spring processes, and ( 4) post-diagenetic ( soil formation). At the end, the high Fe2O3 concentrations and replacement of lithic fragments by microcrystalline goethite indicate that the Dakhla-Kharga sedimentary rocks were subjected to ferrugination. These alterations thought to be result of either post-depositional hydrothermal alteration or syn-depositional interaction with seawater at low temperatures or some combination of the two processes.