Diagenetical changes in Pleistocene small mammal bones from Olduvai Bed I

Fossil bones of small mammals from two levels at Olduvai Bed I (Tanzania) were analysed for a range of elements using electron microprobe techniques. Comparison of the fossil samples is made with those of recent samples collected from close to the Natron alkaline lake (Tanzania). Values for the elements Na, Sr, Ba are significantly higher, and S lower in the fossil samples relative to the recent samples. In addition, concentrations of the rare earth elements reach exceptionally high concentration levels (i.e. > 6 wt.%) in one of the sites, whereas these elements are not detected in the recent samples. The high concentrations of these elements in the fossil samples are clearly a result of diagenetic alteration, although the effects of digestion are likely to have had some influence on the processes involved in the incorporation of elements during fossilisation. Statistical analyses show there are significant differences in the chemical compositions of fossil bones from two levels in Bed I. Observed changes in the rare earth element patterns, in particular the Ce anomaly, suggest that relative differences in the redox potentials of the burial and depositional environments existed at the two levels. Fluctuations in the size and extent of the palaeolake are considered to be the likely cause of these differences.