Mineralogy, geochemistry, petrography, and depositional environment of Gebel El-Qurn, Early Eocene, West Luxor, South Egypt

Esmat A Abou El-Anwar,S H Abd El Rahim,H S Mekky

doi:10.1186/s42269-018-0008-3

Esmat A Abou El-Anwar, S H Abd El Rahim + Show 1 more

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https://doi.org/10.1186/s42269-018-0008-3

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Abstract

BackgroundLuxor represented the modern Egyptian city that occupies the site of ancient Thebes. Thebes Mountain on the West Bank of the Nile, opposite the town of Luxor, is among the most famous historical sites of the world. Carbonate rocks exposed at Gebel El-Qurn, west Luxor, south Egypt has been investigated for mineralogical, petrographical, and geochemical studies to illustrate its depositional environments.ResultsWe revealed that the carbonate rocks in the Gebel El-Qurn, west Luxor, are mainly of Lower Eocene age. The carbonate rocks that belong to the Thebes Formation were deposited under shallow, warm, oxidizing, open marine environment. Petrographically, they are differentiated into five microfacies: (1) nummulitic bioclastic wackestone/mudstone, (2) nummulitic biosparite grainstone, (3) nummulitic rudstone microfacies, (4) pelecypod biomicrite wacke/packstone, and (5) biomicrite dolomitic lime-mudstone. Diagenetically, carbonate rocks were subjected to cementation, compaction, neomorphism, dissolution, and dolomitization processes. Mineralogically, XRD revealed that the studied carbonate samples consist mainly of calcite as well as dolomite, quartz, halite, pyrite, and clay minerals. EDX data indicated that the dolomite of the Gebel El-Qurn is non-stoichiometric in composition, and the size of crystals is up to 80 μm.Geochemically, the carbonate rocks of the Gebel El-Qurn are impoverished in Sr and Na content. This may be attributed to the diagenetic processes, which took place under less saline environment than seawater. Dolomite crystals were formed by re-crystallization under mixed marine-meteoric environment. The positive correlation between Sr and Fe2O3 indicates that the studied carbonates were deposited under control of bacterial activity. The studied carbonate rocks are characterized by light REE (LREE) enrichment with respect to heavy REE (HREE). The total radioactivity measurements are ranging from 4 to 5.9 ppm for U and from 5.5 to 6.6 ppm for Th. The radioactivity measurements are less than the background level of carbonates, and they are in the permissible limits for carbonates used in cement industries and as building stones.ConclusionsThe petrographical and geochemical observations, as well as mineralogical investigation, indicate that the carbonate rocks in the Gebel El-Qurn were deposited in a shallow, warm open marine environment.

Highlights

Luxor represented the modern Egyptian city that occupies the site of ancient Thebes
The Thebes Mountains are sedimentary rocks that are composed mainly of shales, marls, chalk, and limestones. They consist of three important formations, from base to top, the Paleocene Tarawan Chalk, the Paleocene/Eocene Esna Shale, and the Lower Eocene Thebes Formation which were unconformably overlain by the Plio-Pleistocene conglomerate (Said 1962)
Mineralogically, the studied carbonate rocks consist of six minerals, mainly of calcite as well as dolomite, quartz, halite, pyrite, and clay minerals

Summary

Introduction

Luxor represented the modern Egyptian city that occupies the site of ancient Thebes. The modern Egyptian city that occupies the site of ancient Thebes, is famed for its magnificent ancient monuments. The Thebes Mountains are sedimentary rocks that are composed mainly of shales, marls, chalk, and limestones They consist of three important formations, from base to top, the Paleocene Tarawan Chalk, the Paleocene/Eocene Esna Shale, and the Lower Eocene Thebes Formation which were unconformably overlain by the Plio-Pleistocene conglomerate (Said 1962). They were mainly deposited through the Paleocene–Lower Eocene age in a pelagic and shallow environment under and above the phototropic zone (Said 1990). Thebes Mountains in Luxor were studied by many authors: biostratigraphy (Perch-Nielsen et al 1978; Strougo and Hassaan 1984), sedimentology, and structural geology (Yehia 1986; El-Kammar et al 1991; Elwaseif et al 2012), in addition, recently, the environmental studies (El-Bayomi 2007; Leisen et al 2008)

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