The production and preservation of faecal spherulites: Animals, environment and taphonomy

Previous papers have detailed the nature and optics of the microscopic faecal spherulites found at various archaeological sites in the last 15 years. Early indications gained about the spherulite-producing species, the quantities produced and the environmental controls have subsequently been analysed in more detail, mostly under U.K. conditions. This paper presents the results of those experiments as well as a limited study of taphonomic factors leading to the spherulites' preservation or destruction in the stratigraphic record. Spherulites are initially deposited in the small intestine of many animals, probably as a by-product of the neutralization of acid chyme from the stomach or abomasum. Numbers are highest in ruminant herbivores, low in omnivores and low-to-absent in carnivores. No spherulites have been found in the caecal digesting herbivores. They reach maximum abundance in dung from animals grazing or rooting on alkaline soils (pH>7) and are very low-to-absent when the soil is below pH 6. Spherulite preservation is due to a complex of factors, but dissolution occurs rapidly under conditions of high throughflow where the host stratigraphy is below pH 7.7.