Role of tephra in the preservation of fossils in Cenozoic deposits of East Africa

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Abstract
Summary: Volcanism has been particularly important in preservation of fossils at some East African sites. It has supplied sediment for burial, and carbonatite ash which has chemically aided fossilization. Moreover, subaerial tuffs have preserved the remains of faunas unlike those of riverine and lacustrine environments. Examples include faunal sites at Napak, Uganda; Songhor and Koru, Kenya; and Laetoli, Tanzania. Some, and perhaps most, of the carbonatite ash erupted from East African volcanoes was natrocarbonatite, alkali-rich and broadly similar to the modern natrocarbonatite. The pre-modern natrocarbonatites have been leached of their alkalies by meteoric water. In some examples the original natrocarbonatite composition can be reliably inferred from textural and chemical evidence; in other examples only the possibility or probability of former natrocarbonatite ash can be demonstrated. Fossiliferous tuffs at Napak, Koru, Songhor, and the Footprint Tuff at Laetoli contain good evidence of natrocarbonatite ash; evidence is suggestive for Rusinga, and for the fossiliferous aeolian tuffs of the Laetolil Beds at Laetoli.