Palaeoanthropological research on the late Middle Pleistocene to the early Holocene occupation in the Nakuru-Naivasha Basin
The Central Rift Valley of Kenya occupies a key geographical position in the Pleistocene landscape of East Africa. It also occupies a special position in the study of African, and particularly East African prehistory, as it was the place where Louise Leakey developed his earliest work. The area has a rich human and environmental history, involving changing lake levels, tectonics and shifting population boundaries. Its palaeoanthropological record is patchy and most of the information in need of revision and updating. Most importantly, its caves, sediments and palaeolake shores contain large unmapped prehistoric sites. In Africa aims to bridge the temporal gap between the famous Acheulean sites in and around the area and the numerous Holocene ones by examining the known Middle Stone Age localities in the area and searching for new ones, as well as extending the Later Stone Age record of the valley deeper into the Pleistocene.
Since the pioneer studies of Louis Leakey1, this outstanding archaeological area in the Rift Valley has remained central to discussions of the Later Stone Age (LSA) and Acheulean traditions of eastern Africa. The basin contains the key ‘type’ localities of the East Africa LSA – Gamble’s Cave, Nakuru, Prolonged Drift, Elmenteita, Nderit Drift and early Neolithic traditions in Hyrax Hill and Njoro cave by Louise and Mary Leakey2-3. In the 1970s and early 1980s, several of these sites were excavated and the industries described in detail. The first radiocarbon chronology for the Holocene occupation of the area was established at this time, together with models for the relationships amongst the different LSA industries, and between these and the Pastoral Neolithic traditions4-15. More recently, Alex Wilshaw has carried out a comprehensive revision of the LSA lithic material from the basin, stressing the need for greater contextualisation, quantitative comparisons and temporal span of analyses in order to test models of affinities and functionality of the Holocene material record16. The area is also home to one of the earliest LSA sites in Africa – Enkapune Ya Muto17.
The Central Rift Valley is also the home of two of the most important Acheulean sites of eastern Africa – Kilombe and Kariandusi, the subject of excavations in the 1970s by John Gowlett and many subsequent analyses18-24. The morphology of the numerous bifaces from these sites has strongly influenced and continues to inform our understanding of Acheulean adaptations and cognition25. Excavations at Kilombe by Gowlett, Curnoe and their team have been re-initiated in the last two years.
The Middle Stone Age (MSA) in the Central Rift Valley is much less well-known. MSA sites have been located at the margins of the basin, such as at Cartwright’s site26-27, while MSA lithics were recently found near Kilombe28. The confirmation, and if possible extension of the presence of early modern human occupation in the Nakuru-Naivasha basin is thus of great importance as the spatial bridge between the northern (from Baringo to Turkana to the Ethiopian Rift to the Middle Awash) and southern (from Olorgesailie to Olduvai and beyond) parts of the Rift Valley. The Nakuru-Naivasha basin is relatively small, but with high relief, so that periods of humidity result in exaggerated rises in lake levels. The geology and geomorphological history of the basin have been the subject of a number studies29-36, including the late Quaternary changes in the level of lake Naivasha and their relationship with palaeoclimates shifts and lake-level fluctuations elsewhere in eastern Africa37-38.
The work of In Africa in the Central Rift focuses on two areas. First, on a series of exposures identified near the Gamble’s Caves rockshelter, as well as on the site itself. A preliminary reconnaissance of the area south of Lake Nakuru, around the known sites of Nderit, Elmenteita and the Gamble’s Caves, revealed several exposures containing archaeological artefacts and faunal remains, as well as sedimentary sequences of palaeolake high stands that could yield detailed palaeoenvironmental data to associate to the known archaeological record of the area and to data from the Ol Njorowa Gorge, South Naivasha20. Thus the work plans to carry out a landscape survey of the area, to contextualise the findings from the Gamble’s Caves. The main objective of re-opening the latter is to check and date the lower end of the stratigraphic sequence originally excavated by Louis Leakey in the 1920s. Since bedrock was not reached by earlier excavations, work will open the front of Gamble’s II, and extend the excavations down from the small exposed area at the south bottom corner, and obtain new samples for dating, lithic and isotopic analyses. The second area to be investigated by the project is along the Malewa Gorge. This was surveyed many years ago by R Foley, who still has both the photographs and description of the strate where Middle Stone Age artefacts were found at the time. The objective of the work is to attempt to re-locate these, and obtain stratigraphic and technological information that would allow integrating the data into a broader picture of prehistoric occupation of the basin.