全球变化知识资源中心

Compositional and textural attributes of dated fluvial and coastal to offshore deposits of the Nile delta in northern Egypt provide a means to determine whether, when, and to what extent climate change modified sedimentation of the Nile about 4000 years ago. This mid-Holocene period has been interpreted by climatologists and earth scientists as one of increased aridity, evaporation, and salinization, along with diminished rainfall and decreased Nile flood levels. Egyptologists also consider this as a time of major historic change from the end of the pharaonic Old Kingdom to the First Intermediate Period. Attention here is paid to diverse assemblages of mineralogical, geochemical, palynological, and faunal components, as well as to grain size, in numerous sediment core samples that became significantly altered within a 200- to 300-year period between 4300 and 4000 years before present (BP). This is the approximate time of the well-recognized climatic event of ca. 4200 years BP recorded in Eastern Mediterranean and Levant regions. In some core sections, such compositional changes are also identified but over a somewhat longer period that overlaps timewise with those of the shorter 200- to 300-year phase; these are attributed to the same major climatic event around 4300 to 4000 years ago. Some seemingly older dates and highly variable sediment textural types likely result from a stop-and-go downslope fluvial transport process involving repeated sequences of alternating sediment storage and subsequent erosional events that occurred during seaward flow along this extensive fluvial system. Findings summarized herein pertaining to the Nile's response to marked changes in climate and environmental conditions about 4000 years BP are needed to better decipher Egypt's evolving societal history at that time.