Source of Nile sediments in the floodplain at Saqqara inferred from mineralogical, geochemical, and pollen data, and their palaeoclimatic and geoarchaeological significance

摘要

We present results of mineralogical (light, heavy and clay minerals), geochemical and palynological investigations of floodplain sediments at Saqqara. Our investigations provide new insights into our understanding of the source of the Holocene Nile sediments, local palaeoclimate and palaeoenvironment of the floodplain at Saqqara as well as the Holocene palaeoclimatic variations at the Nile headwaters. We also investigate the relationship between Nile floods and global climate changes and the impact of changing flood conditions on episodes of societal and central governmental collapse at the end of the Egyptian Old Kingdom. The Holocene sequences recorded in two shallow drill cores (SAQA 21 and 22) were investigated and subdivided into six sedimentary units, from underlying Late Pleistocene sand and gravels (unit I) to overlying modern soil (unit VIII). Early Holocene sediments were essentially missing in the studied cores, probably due to intensive erosion during the well-known 8.2 kyr cal BP arid event. Middle Holocene sediments are represented by unit II, which reflect high Nile floods of Equatorial African origin with less contribution from Ethiopian sources. The Old Kingdom sediments (unit III), seems to be mainly of White Nile sources with frequent contributions from the Blue Nile. Late Holocene sediments (unit IV-VII) show an increased contribution from Blue Nile River sources. Low Nile flow episodes were recorded at 5.2 (between units II and III), 4.2 (between units III and IV), 3.5 (within unit IV) and 2.7 kyr cal BP (between units V and VI). The second event corresponds to the First Intermediate Period (FIP) and the third probably coincides with the Second Intermediate Period (2nd IP), periods of disorder in Egypt. (C) 2018 Elsevier Ltd and INQUA. All rights reserved.