Wetland Diagenesis and Traces of Early Hominids, Olduvai Gorge, Tanzania

Abstract

Lateral variations in whole-rock and clay geochemistry of basal Bed II claystones in Olduvai Gorge, Tanzania, reflect water quality differences across the Eastern Lacustrine Plain ∼1.75 myr ago. Bulk Ba/Sr and (Na2O+K2O+MgO)/Al2O3 range from 1.4 to 4.2 and from 0.7 to 1.4, respectively, and indicate leaching of lacustrine claystones beneath freshwater wetlands at times following lake retreat. Bulk MgO/Al2O3 (0.3–1.0) and molar Mg/Al (0.5–3.9) ratios of <0.2-μm clays reflect alteration of Mg-rich lacustrine clays. These indicators point to freshest conditions near Locality 43 of Hay (1976; HWK-East; Leakey, 1971), moderate conditions to the east (Locality 40-MCK), and high salinity and alkalinity to the west (Localities 85-VEK, 45-FLK).Clay geochemistry and artifact abundances are well correlated (r=−0.67, p<0.005), suggesting a relationship between paleo-water quality and hominid paleoecology. This pattern is consistent with predictions of greatest artifact discard/loss around freshwater sources where scavanging opportunities were greatest for hominids. This quantifies a relationship between artifact density distribution and a paleoecological proxy over landscape scales for the first time in Early Stone Age archaeology. In contrast, fossil bone abundance is uncorrelated (r=0.14, p=0.6), reflecting more complex taphonomic processes. Quantitative tests of landscape-scale land-use models are important for understanding early hominid behavior and its evolution.

Hominins, sedges, and termites: new carbon isotope data from the Sterkfontein valley and Kruger National Park

“…On the whole, while it is certainly possible that sedges contributed to the C 4 signal of South African australopiths, we find it highly improbable that sedge consumption alone was responsible. It is worth noting, however, that early hominin habitats such as the wetlands of the Eastern Lacustrine Plain at Olduvai Gorge (Hay, 1976;Deocampo et al, 2002) might have been better sources of C 4 sedges. Puech et al (1986) have also suggested that the dental microwear of early East African hominins is consistent with the consumption of such foods.…”

Palaeoenvironmental significance of the clay mineral composition of Olduvai basin deposits, northern Tanzania

“…The development of Mg-rich smectite in the study area is most pronounced in the upper part of Bed I, the interval for which this process is most extensively documented (Hover and Ashley, 2003;Deocampo et al, 2002;Deocampo, 2004). In higher strata, lower Mg values are compatible with lower salinities and alkalinities recorded by an interval with largely zeolite-free freshwater deposits (Mees et al, 2005).…”

“…During the Bed IV stage, illite-rich detrital material was derived from the north and west, where the pre-Quaternary substrate is composed of Precambrian metamorphic rocks, dominated by gneiss and quartzite (Hay, 1970(Hay, , 1976. The detrital origin of illite in Bed IV and the upper part of Bed III is confirmed by its chemical composition, which is different from that of Mg-rich illite and celadonitic clays recognised for Beds I and II (Deocampo et al, 2002;Deocampo, 2004).…”

“…In the source area, smectite was formed by weathering of volcanic material (Hay, 1976;Hover and Ashley, 2003). This mineral can be transformed to Mg-rich smectite in a saline alkaline lake margin environment, which is recognised for Olduvai Basin deposits by TEM analysis (Hover and Ashley, 2003) and by studies of the fine clay fraction (Deocampo et al, 2002). The presence of Mg-rich smectite is confirmed by chemical analysis of the total clay fraction.…”

“…All other studies concentrate on a narrow stratigraphical interval that is most relevant for palaeoanthropological research, i.e. the top of Bed I and the base of Bed II (Hay and Kyser, 2001;Deocampo et al, 2002;Hover and Ashley, 2003;Deocampo, 2004). In this paper, we report clay mineral data for all main units, sampled in the southeastern part of the basin (Fig.…”