The Holocene history of the Faiyum Lake (Egypt) based on sediment characteristics, diatoms and ostracods contents

Abstract

There are relatively few Holocene lake sediment core sequences available for north-east Africa. This study examines the developmental history of Faiyum Lake (Egypt) by detailed lithostratigraphic description together with microfossils and geochemistry, of two adjacent lake sediment cores. The recovered sedimentary sequence consists of predominantly lacustrine facies divisible into five sedimentary units. Early Holocene sediments (Unit II; c. 9.9–8 ka cal BP), overlying late Pleistocene aeolian sands (Unit I), comprise sub-mm laminations (non-glacial varves) of white diatomite and calcite inter-bedded with yellowish-green mineralogenic layers indicating a deep freshwater lake phase. Early middle Holocene sediments (Unit III, c. 8 to 6 ka cal BP) consists by pockets of non-glacial varved laminae intercalated with turbidites and increasing thick silty clay layers, indicating a shallow freshwater lake phase with increasing nutrients. The late middle Holocene lake phase, Unit IV (c. 6 to 4 ka cal BP) is grey massive mud with occasional thick (>1 cm) diatomite-carbonate layers and thin gypsum and iron-hydroxides layers indicative of a lake shrinking phase but with a large level fluctuation sand evaporation phases when freshwater inflow diminished. The late Holocene lake phase (unit V, c. 4 ka cal BP-present) reveals bioturbation and increasing fine sand with artifacts corresponding to further lake level declines and fluctuations as water management intensifies during and after Middle Kingdom and Ptolemaic times. Together with geochemical and microfossil evidence, sedimentology of the studied cores indicate a series of major environment changes affecting the whole lake system throughout the Holocene.