KYULE MWANZIA DAVID

This paper outlines both the archaeological and later prehistoric research that has so far been undertaken on the Kenyan side of the Lake Victoria basin. We introduce the regions current demographic distribution and geophysical setting to provide a background for the various prominent paleoanthropological findings and discoveries in the region. Significant aspects that require further research have also been highlighted.

Lemudong’o is located on the western margin of the southern Rift Valley approximately 100 km west of Nairobi (Fig. 1), an area deeply incised by three major permanent river systems. Stratified lavas, air-fall and water-laid tuffs, alluvial, and fluviolacustrine sediments, and paleosols of Late Miocene to Late Pleistocene age crop out over a w25 50 km area. Wright (1967) reconstructed three paleolakes and shoreline facies, assumed to be Plio-Pleistocene in age, in the vicinity of an isolated Basement Complex inselberg. Radio- metric dating demonstrates the paleolake deposits exposed at Lemudong’o are Late Miocene in age. During archaeological surveys and excavations in this region in 1995-96 (Kyule et al., 1997) and 1999–2002 (Ambrose et al., 2000; 2002; Hlusko et al., 2002), 55 new archaeological sites (Acheulean, Middle Stone Age, Later Stone Age, Neolithic and Iron Age), and several paleontological occurrences were discovered. Here we describe the preliminary results from research at the Late Miocene fossil site of Lemudong’o. The most productive Late Miocene paleontological site in the area is exposed in Lemudong’o Gorge, GvJh15, GvJh32 (Figs. 2 and 3). Lithologic units include paludal (marsh) and lake margin claystones, lacustrine diatoma- ceous silts and claystones, and coarser alluvial deposits with interstratified tuffs. Similar ex-posures occur within tens of kilometers, though their correlation to the Lemudong’o strata is not yet confirmed, and fossils are scarce and taxonomically non-diagnostic. Lemudong’o Gorge is a fault-controlled, deeply incised gully system bounded on the east by the Enkoria fault (Wright, 1967). Fossiliferous sedi- ments are exposed at two localities approximately 500 m apart. Locality 1 (Lemudong’o 1, GvJh15, coordinates: 1(18.19S, 35(58.74E, approximate elevation 1600–1620 m) was discovered in 1994, and is located in the upper reaches of the main gully. It contains the higher levels of the depo- sitional sequence, and the main fossiliferous horizons. Locality 2 (Lemudong’o 2, GvJh32, coordinates: 1(17.98S, 35(59.04E) was discovered in 1999 and includes lower strata and a poorly- exposed horizon with sparse, generally non- diagnostic fossil material. No significant unconformities occur in the main sedimentary sequence.

Archaeological evidence suggests modern human behavior patterns emerged during the late Middle Stone Age (MSA) and early Later Stone Age (LSA) in Africa between 50 and 100 ka. Sites of this age are scarce and their chronologies are ambiguous. We report on excavations at new archaeological sites in the central and southern Kenya Rift Valley that contain late MSA and early LSA occurrences with stratified volcanic ashes (tephra) that are being dated by the 40Ar/39Ar technique and chemically fingerprinted for regional tephrostratigraphic correlation. Obsidian artifacts are being sourced to study mobility and interaction patterns.Marmonet Drift (GtJi15) is located in the Naivasha-Nakuru basin close to the main obsidian sources. Four main MSA horizons and twelve tephra are stratified in a 21 m paleosol sequence. Assemblages from the three earliest horizons contain radial cores and faceted platform flakes. The youngest horizon contains retouched points and has the most distant obsidian sources.Sites on the western margin of the southern Rift are 60-90 km from the major central Rift obsidian sources. Ntuka River 4 (Norikiushin, GvJh12) contains a 2.5 m sequence with large obsidian backed ‘‘microliths’’, blades with faceted platforms and points from radial cores, stratified above and between two tephra. Ntuka River 3 (Ntumot, GvJh11) contains a 9 m sequence with two stratified tephra. Obsidian bifacial points and narrow backed microliths are stratified 1-3 m below the lowest tephra. Three major LSA horizons lie 3-5 m above this tephra. The youngest LSA is dated 29,975 bp. In the central and southern Rift the highest frequencies of non-local lithic raw materials occur in the youngest MSA and in MSA/LSA occurrences. Lithic source distance data indicate increased range size and/or intensification of regional exchange networks. Dramatic changes in socio-territorial organization may have accompanied the MSA/LSA transition. Supported by grants from the National Science Foundation (BCS-0113565) and the L.S. B. Leakey Foundation.

Survey in southwest Kenya above the western margin of the Gregory Rift Valley since 1994 has led to the discovery of LSA, MSA, Acheulean and possible Oldowan occurrences, as well as fossil-bearing sites representative of the early Pliocene. A long sedimentary sequence of airfall and waterlain tuVs, fluvial and lacustrine sediments and paleosols is exposed in the region of the confluence of the Ewaso Ngiro, Narok, Seyabei, Ntuka and Olonganaiyo rivers. At Lemudongo, a total of 278 well-preserved fossil bones and teeth of a variety of species including carnivores, primates, suids, bovids, hippopotamids, crocodilians, hyracoids and rodents, were collected in one day along a 70 m area of sediment outcrop. Three potentially datable tuVs are stratified within this 6 m-thick fossil-bearing paleosol. The presence of Nyanzochoerus kanamensis suggests this locality is older than 2•5 m.y.a. Four Acheulean sites have low densities of handaxes and cleavers, mainly made on phonolite, basalt and quartz. None are clearly in primary context. Excavations at Ntuka River 3 have yielded a long sequence of new Early LSA microblade industries in discrete horizons that have high densities of well-preserved bones and teeth of equids, bovids, micromammals and humans. Paleosol stable carbon and oxygen isotope analysis at this site demonstrate substantial environmental changes through time in the 7•5 m sedimentary section. In the Ntuka area, Late Quaternary sediments contain numerous in-situ early and late MSA and early LSA sites with well-preserved faunas, a penecontemporary fossil carnivore den site and other fossil-bearing sites with minimally fragmented faunas associated with low artefact densities. This provides a rare opportunity to compare faunal and lithic resource exploitation patterns through time during the Middle and Early Later Stone Age, and to compare faunal exploitation patterns of humans and carnivores on the same landscape.