Petrography and geochemistry of Pharaonic sandstone monuments in Tall San Al Hagr, Al Sharqiya Governorate, Egypt: implications for provenance and tectonic setting

Authors: SAMIR MAHMOUD ZAID, OUSSAMA EL BADRY, FATMA RAMADAN, MAHMOUD MOHAMED

Abstract: Petrographic and major and trace element compositions of Tanis sandstones from Tall San Al Hagr, Al Sharqiya Governorate, Egypt, have been investigated to determine their source, provenance, intensity of paleoweathering of the source rocks, and tectonic setting. Tanis sandstones are yellowish brown in color, siliceous, partly calcareous, and originated from sands deposited in fluvial channels. Texturally, Tanis sandstones are medium- to very coarse-grained, mature, and moderately sorted. Scarcity of feldspars indicates that the sandstone is extensively recycled from a distant source. Their average modal composition (Q_99.75F_0.03L_0.22) classifies them as quartz arenites (quartzite), which is consistent with the geochemical study. Chemical analyses revealed that sandstones have high SiO₂ and Fe₂O₃^t and low Al₂O₃ and TiO₂ values, which are consistent with the modal data. Sandstone samples are enriched in most trace elements such as Zr and Ba, and they are depleted in V, Pb, Sc, Rb, U, and Th. The petrography and geochemistry results suggest that Tanis sandstones were deposited in an intracratonic basin or a passive continental margin of a synrift basin. They were mainly derived from deeply weathered granitic-gneissic sources, supplemented by recycled sands from an associated platform. The CIA and CIW values (60.2 and 87.74, respectively) of the Tanis sandstones indicate moderate to intensive weathering either of the original source or during transport before deposition, and may reflect low-relief and warm humid climatic conditions in the source area. The heavy-mineral and trace element results reveal that the Gebel Ahmar quarry is the probable source for the Tanis sandstones.

Keywords: Provenance, Pharaonic sandstone, Tanis, Egypt

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