Nile River evolution in Upper Egypt during the Holocene: palaeoenvironmental implications for the Pharaonic sites of Karnak and Coptos

Here we present the results of a geoarchaeological study, undertaken in Upper Egypt, in the western part of the Karnak Temple and in Coptos. The geoarchaeological approach helps to better understand the fluvial dynamics of the Nile River in the close vicinity of these two Pharaonic sites, 35 km apart. Our investigation focused on i) a jetty discovered by the archaeologists of the Supreme Council of Antiquities (SCA) in front of the first pylon at Karnak and ii) the remains of Ancient Coptos, an important site from Predynastic to Roman times. We studied several stratigraphic profiles, manual boreholes (maximum depth of 5.5 m) and percussion drillings (maximum depth of 25 m). Sedimentological and magnetic susceptibility analyses help to characterise Nile River deposits and to identify the presence of aeolian deposits (associated with wadi fan deposits) in the lower part of the boreholes at both Karnak and Coptos. The data clearly indicate the continuous occupation of the Nile River around the sites during a part of the Dynastic period. Fluvial dynamics characterised by flood events, sandy accretions and thick Nile silty-clayed deposits are presented and discussed here for subsequent palaeoenvironmental reconstruction. Accurate levelling of the different profiles and boreholes, together with a topographic survey allow us to recover long sedimentological sequences and to correlate the different sedimentary units. Finally, in order to obtain a chronostratigraphic sequence, radiocarbon dates were obtained from wood, charcoal and ash samples (analyses undertaken at the laboratory of radiocarbon dating of IFAO, Cairo, Egypt). For Karnak, the presence of the Nile River in front of the first pylon in Karnak is attested from ca. 1450 BC until ca. AD 350 (from the beginning of the 18th dynasty until the end of Roman times), with a probable early flowing activity during the second part of the Middle Kingdom (1994-1650 BC) and the Second Intermediate Period (1650-1550 BC). The construction of a Geographic Information System (GIS) including the borehole results and the integration of Shuttle Radar Topography Mission data (SRTM), with the superimposition of False Colour Composition of a LANDSAT ETM+ image, helped to obtain a spatial interpretation of the results.