Late Quaternary primary tephras in Sacred Lake sediments, northeast Mount Kenya, Kenya

In this paper, a sequence of five Late Quaternary tephras occurring as disc rete, well-preserved horizons in lake sediments on the northeastern flank o f Mount Kenya are characterised and their ages determined by a combination of high-resolution indirect radiocarbon dating and direct U/Th dating. The grain size characteristics suggest that the tephras are of fairly local ori gin. These Na-K-rich alkali pyroclasts with a trachytic chemical compositio n have a highly correlated chemistry and mineralogy, suggesting that they w ere probably derived from the same genetic series and possibly erupted from a single source vent. Morphological differences are attributed to the pecu liar characteristics of each eruption episode. The magma source was probabl y a small, highly differentiated magma chamber following the olivine basalt -trachyandesite-trachyte-phonolite series, which broadly reflects the Quate rnary rock suite of Mount Kenya. (C) 2000 Elsevier Science Limited. All rig hts reserved.