Pollen analysis of Iron Age cow dung in southern Africa

Thick accumulations of consolidated cow dung occur in ancient kraals (byres or corrals) in the bushveld and highveld areas of Zimbabwe, Botswana, and South Africa dating from the last 2000 years. They originated from long-ter m cattle herding by Iron Age people. The "vitrified" or baked dung deposits are thought to be a product of the burning of cow dung as fuel, either for domestic purposes or for iron smelting. In order to establish the palaeoec ological potential of this material. 36 samples of cow dung from archaeolog ical sites within the present-day savanna and grassland biomes were analyze d for pollen and other microfossils. Of the samples, 29 contained pollen to gether with other microfossils that support a faecal origin of the material such as sordariaceous ascospores, Thecaphora, Gelasinospora, and Chaetomiu m, and eggs of the intestinal parasite Trichuris. Similar microfossils were also found in recent fresh cow dung from the same study areas. The presenc e of pollen grains and spores in most of the Iron Age samples lead to the a ssumption that they survived the burning because fire temperatures were not high enough to destroy them. Pollen in these cow dung pieces is apparently sealed and can be preserved under open-air conditions at sites under which pollen in other deposits like soils, will decay away. Good pollen preserva tion and palynomorph diversity were found with mainly Poaceae, and secondly Chenopodiaceae acid Cyperaceae as the most important pollen types, while t rees and shrubs indicating savanna are rare. In the case of the samples tha t came from the subtropical savanna biome the latter result is unexpected a nd suggests that the cattle were kept in more open vegetation than the wood y environments of today. Recent cow dung samples reflect the composition of present-day vegetation by showing considerably higher proportions of tree pollen than the fossil assemblages.