Diatoms in ancient building materials: application of diatom analysis to Egyptian mud bricks

Mud bricks where commonly used in ancient Egypt by the time of the First Dynasty (Old Kingdom) c. 3000 years BCE. Ancient mud bricks were fabricated by mixing mud, sand, water and plant material followed by sun drying. Algae, and in particular diatoms, are commonly associated with mud and water and consequently diatom analysis of mud bricks offers the possibility of revealing more about the provenance and uses of these building products. Small samples of displaced mud brick fragments were collected from near two ancient Egyptian monuments, the XIIth Dynasty Pyramid of Amenemhat III at Hawara and the Ptolemaic temple complex at Dimai. Initial analysis showed that the Pyramid mud brick sample contained more organic matter than either the light or dark grey mud brick samples from Dimai. Of the latter, the, light grey sample possessed the highest proportion of carbonate. Diatoms were scarce and poorly preserved in the Pyramid mud brick sample but were sufficient to show that most were planktonic species (e.g. Aulacoseira granulata, Cyclostephanos dubius). The Dimai mud bricks contained abundant, generally well-preserved diatom remains, both of planktonic and benthic taxa. Cocconeis and Punctastriata predominated in the light grey mud brick and Cyclostephanos and Punctastriata in the dark grey mud brick. For Dimai material, the diatom `mud' component was most probably extracted from near-by (now terrestrial) diatomite deposits laid down in a former large shallow lake. For the Pyramid mud brick, the few predominantly planktonic diatoms are thought to have been introduced from Nile water used during manufacture. Results are based on only a few preliminary samples and diatom assemblages are influenced by taphonomic processes but it is shown that diatoms in ancient Egyptian mud bricks provide important clues to manufacturing processes, selection of extracted materials and to past environmental characteristics associated with the raw materials. Diatom analysis of archaeological building materials is potentially a useful biogeoarchaeological tool, not only for mud brick typification but also for making spacetime cross-correlations between mud brick facies, within and between monuments. Whether Ancient Egyptian builders exercised any preference for diatom rich resources for mud brick manufacture is unclear but the well known insulating properties of diatomites suggest that in a warm climate such material would confer some benefit to the occupants of buildings thus constructed.