抄録
Kaolin deposits initially formed as a lateritic crust on a nearby basement complex, then were transported to the central Wadi Kalabsha and deposited as flood plain and river bar deposits. Repeated fluvial influx and drying out of the kaolin resulted in the following facies: a) Intraformational disorganized conglomerate over the flood plain and/or on the flat bar-tops; b) Intraformational partially organized and organized conglomerates on the slip faces of bars and river banks, and/or as lateral point bars in sinuous streams; and c) Pisolites of kaolinite, kaolinite-hematite, hematite-kaolinite and hematite composition, either in erosion hollows and/or on the slip faces at the downstream end of lognitudinal and diagonal bars in braided rivers.
The surface of the fluvial kaolin deposits was subjected to a second phase of in situ lateritization which resulted in a partial or complete dissolution of quartz and the formation of pisolitic laterites containing traces of gibbsite, geothite, hematite and anatase. Isotopic analyses of δ18O and δD of separated kaolinites showed that the pisolitic kaolin deposits are sedimentary and weathering in origin. The original reworked sedimentary-lateritic pisolites may be deposited during the late Mesozoic while the pisolitic laterites may be formed later as a crust in the Tertiary.
