Omo-Turkana Basin Research Articles

By the lakeshore: Multi-scalar geoarchaeology in the Turkana Basin at GaJj17, Koobi Fora (Kenya)

The Late Pleistocene archaeological record in the Turkana Basin is important for studying Homo sapiens evolution, but the record in this region is poorly documented, despite a long history of significant paleoanthropological discoveries. Ambiguity around ages and site formation processes are paramount problems. We investigated the chronometric, geological, archaeological, and paleoenvironmental context of GaJj17, a locality with an artifact-bearing deposit in the Koobi Fora region. Sedimentological facies analysis coupled with micromorphological evidence indicate the depositional environment at the site changed over time from a fluvial system to an aeolian one, forming the remnant lunate feature seen today. Caliche caps the site and likely mitigated erosion of the site during high lake stands; similar deposits (∼25 m2) are found within a 2 km radius and are archaeologically sterile. Optically stimulated luminescence dating indicates the deposit and associated artifacts and fossils were emplaced circa 52–43 thousand years ago. Small (average length ∼ 3.5 cm) flakes dominate the stone artifact assemblage and include unretouched triangular flakes on diverse raw materials indicating shared affinity with Middle and Late Pleistocene lithic toolkits elsewhere in eastern Africa. Hippopotamus, crocodiles, and fish are well-represented in the faunal assemblage, along with a small sample of terrestrial ungulate specimens. More taphonomic research to understand the accumulating agent(s) of the faunal assemblages is needed. These results contribute to our understanding of Late Pleistocene archaeological site formation processes in lacustrine contexts of the Omo-Turkana Basin.

Participatory design of robust and sustainable development pathways in the Omo-Turkana river basin

Study regionOmo-Turkana Basin, trans-boundary basin between Ethiopia and Kenya (North eastern Africa). Study focusSignificant investments in large dams have been mobilized in the Omo-Turkana basin to expand hydropower and support extensive irrigation projects. Assessing the impacts of these infrastructures, particularly on local stakeholders, constitutes a crucial foundation for socially inclusive as well as environmentally and economically sustainable development. This study showcases the potential of a participatory decision-analytic framework in investigating the impacts of alternative development pathways on competing stakeholders’ interests in the Omo-Turkana basin to support strategic planning under both current and projected hydroclimatic and socio-economic conditions. The optimal operation of the planned system expansion, including the current and future dam cascade and the irrigation projects, is investigated to provide insights into multisectoral trade-offs. Five main sectors with competing interests are considered: hydropower production, environmental protection, indigenous recession agriculture, fish yield in Lake Turkana, and large-scale commercial irrigated agriculture. New hydrological insights for the regionResults show that the planned infrastructure can negatively impact local stakeholders, particularly in terms of fish yields in Lake Turkana. Still, a potential exists for negotiating operational compromises that are both efficient and socially inclusive. Moreover, even though the performance of the planned infrastructure is expected to decline in the future under changing climate and irrigation demands, this can be mitigated by timely implementing robust solutions triggered by the alterations of streamflows in the northern part of the basin.

When timing matters\u2014misdesigned dam filling impacts hydropower sustainability

Decades of sustainable dam planning efforts have focused on containing dam impacts in regime conditions, when the dam is fully filled and operational, overlooking potential disputes raised by the filling phase. Here, we argue that filling timing and operations can catalyze most of the conflicts associated with a dam’s lifetime, which can be mitigated by adaptive solutions that respond to medium-to-long term hydroclimatic fluctuations. Our retrospective analysis of the contested recent filling of Gibe III in the Omo-Turkana basin provides quantitative evidence of the benefits generated by adaptive filling strategies, attaining levels of hydropower production comparable with the historical ones while curtailing the negative impacts to downstream users. Our results can inform a more sustainable filling of the new megadam currently under construction downstream of Gibe III, and are generalizable to the almost 500 planned dams worldwide in regions influenced by climate feedbacks, thus representing a significant scope to reduce the societal and environmental impacts of a large number of new hydropower reservoirs.

Introduction to special issue Kanapoi: Paleobiology of a Pliocene site in Kenya

This paper introduces this Special Issue of the Journal of Human Evolution entitled “Kanapoi: Paleobiology of a Pliocene site in Kenya.” Kanapoi, West Turkana, Kenya, is part of the Omo-Turkana Basin and is the type site of the earliest known genus of Australopithecus, A. anamensis. Kanapoi preserves among the earliest earliest evidence of Australopithecus in deposits dated between 4.195 to 4.108 million years old. Explored by several teams since the 1960s, the Kanapoi sediments have yielded a rich and abundant fauna, providing important information about the paleoenvironments and the context surrounding the earliest evolution of the genus Australopithecus, as well as about the evolution and biogeography of African Pliocene vertebrate faunas.

Isotopic equifinality and rethinking the diet of Australopithecus anamensis.

Australopithecus anamensis has comparable δ13 Cenamel values to Ardipithecus ramidus, and both have been characterized as C3 feeders in open woodland habitats similar to "savanna" chimps. Unlike Ar. ramidus and "savanna" chimps, A. anamensis shows a derived dentognathic morphology for tough foods and a dental microwear pattern similar to the C3 -C4 -mixed-feeding A. afarensis. Here I test the hypothesis that changing the variables (ε*enamel-diet , δ13 CC3, δ13 CC4 values) used to calculate the percentage of dietary C4 foods (%C4 diet) by 1-2‰ does not make a substantial difference for hominin diet reconstructions [van der Merwe, Masao, & Bamford, 2008, South African Journal of Science 104:153-155]. I estimate vegetation structures for A. anamensis with pedogenic carbonate and faunal enamel δ13 C values from the Pliocene Omo-Turkana Basin (4.2-3.9 Ma). I recalculate A. anamensis' %C4 diet based on new body size-dependent estimates of the ε*enamel-diet value and alternative δ13 CC3 and δ13 CC4 values. The Pliocene Omo-Turkana Basin shows evidence for dietary resources with a wide range of δ13 C values including canopy-driven 13 C depleted ground C3 foods. Alternative equation variables changed by 1-2‰ yield higher C4 estimates for A. anamensis (15-31%) than previously thought (0-10%). The choice of δ13 CC3 and δ13 CC4 values for estimating %C4 is not a perfunctory task and potentially explains the δ13 C isotopic equifinality of A. anamensis and "savanna" chimps. My integrative diet model reconciles the carbon isotopic data with the dentognathic and microwear evidence of A. anamensis' diet and suggests that "savanna" chimps are not proper dietary analogs of A. anamensis. A foraging strategy across heterogeneous habitats of the Pliocene Omo-Turkana Basin incorporating an array of 13 C-depleted and 13 C-enriched C3 foods and a portion of C4 resources may have served as one of the selective pressures for A. anamensis, the earliest habitual biped [van der Merwe et al., 2008, South African Journal of Science 104:153-155].

Hominin diversity and high environmental variability in the Okote Member, Koobi Fora Formation, Kenya

The newly described partial skeleton of Paranthropus boisei KNM-ER 47000 as well as the FwJj14E Ileret footprints provide new evidence on the paleobiology and diversity of hominins from the Okote Member of the Koobi Fora Formation at East Turkana about 1.5 Ma. To better understand the ecological context of the Okote hominins, it is necessary to broaden the geographical focus of the analysis to include the entire Omo-Turkana ecosystem, and the temporal focus to encompass the early Pleistocene. Previous work has shown that important changes in the regional vegetation occurred after 2 Ma, and that there was a peak in mammalian turnover and diversity close to 1.8 Ma. This peak in diversity included the Hominini, with the species P. boisei, Homo habilis, Homo rudolfensis, and Homo erectus co-occurring at around 1.8 Ma. There is considerable debate about whether H. habilis and H. rudolfensis indeed constitute separate species, but even if we consider them both as H. habilis sensu lato, the co-occurrence of three hominin species at any one time and place is rather unusually high diversity for hominin standards (even if not so for other mammalian groups such as suids, bovids, or cercopithecids). Here we use mammalian faunal abundance data to place confidence intervals on first and last appearances of hominin species in the early Pleistocene of the Omo-Turkana Basin, and use these estimates to discuss hominin diversity in the Okote Member. We suggest that in the early Pleistocene a wide range of depositional environments and vegetation types, along with a high frequency of volcanism, likely maintained high levels of environmental variability both in time and space across the Omo-Turkana region, and provided ecological opportunities for the coexistence of at least three hominin species alongside a diverse mammalian fauna.

Diversity analysis of Plio-Pleistocene large mammal communities in the Omo-Turkana Basin, eastern Africa

Knowing how the diversity of large mammal communities changes across space and time provides an important ecological framework for studying hominin evolution. However, diversity studies that apply methods currently used by neoecologists are rare in paleoanthropology and are also challenging due to diversity's unusual statistical properties. Here, we apply up-to-date analytical methods for understanding how species- and genus-level large mammalian diversity in the Omo-Turkana Basin changed through time and across space at multiple spatiotemporal scales (within each formation:102−3 km2 and 104−5 years; and within the basin as a whole: 103 km2 and 105 years). We found that, on average, Koobi Fora's large mammal community was more diverse than Nachukui's, which in turn was more diverse than Shungura's. Diversity was stable through time within each of these formations (alpha diversity), as was diversity in the basin as a whole (gamma diversity). Compositional dissimilarity between these three formations (beta diversity) was relatively low through time, with a 0.6 average proportion of shared species, suggesting dispersal acted to homogenize the region. Though alpha and gamma diversity were fairly stable through time, we do observe several notable peaks: during the KBS Member in Koobi Fora (30% increase), the Lokalalei Member in Nachukui (120% increase), and at 1.7 Ma in the entire basin (100% increase). We conclude by (1) demonstrating that habitat heterogeneity was an important factor influencing alpha diversity within each of the three formations, and (2) hypothesizing that diversity stability may have been driven by equilibrial dynamics in which overall diversity was constrained by resource availability, implying biotic interactions were an important factor in structuring the communities that included hominins as members. Our findings demonstrate the need to quantify how large mammal diversity changes across time and space in order to further our understanding of hominin ecology and evolution.

Paleoecological insights from fossil freshwater mollusks of the Kanapoi Formation (Omo-Turkana Basin, Kenya)

The Early Pliocene Kanapoi Formation of the Omo-Turkana Basin consists of two fluvial/deltaic sedimentary sequences with an intermediate lacustrine sequence that was deposited in Paleolake Lonyumun, the earliest large lake in the basin. Overall, the geology and vertebrate paleontology of the Kanapoi Formation are well studied, but its freshwater mollusks, despite being a major component of the benthic ecosystem, have not been subjected to in-depth study. Here I present the first treatment of these mollusks, which have been retrieved mainly from the lacustrine but also from the upper fluvial sediments, with a focus on paleoecological implications. Overall, the freshwater mollusk fauna is reasonably diverse and contains the gastropods Bellamya (Viviparidae), Melanoides (Thiaridae), Cleopatra (Paludomidae) and Gabbiella (Bithyniidae), as well as the unionoid bivalves Coelatura, Pseudobovaria (Unionidae), Aspatharia, Iridina (Iridinidae) and Etheria (Etheriidae). Material is typically recrystallized and lithified and its taphonomy suggests deposition in a system with intermediate energy, such as a beach, with post-depositional deformation and abrasion. The mollusk assemblage is indicative of perennial, fresh and well-oxygenated waters in the Kanapoi region. It suggests that Paleolake Lonyumun had largely open shores with limited vegetation and that swampy or ephemeral backwaters were rare. Overall, these findings support earlier paleoecological interpretations based on the fish assemblage of Paleolake Lonyumun at Kanapoi. Moreover, mollusk assemblages from this lake are very similar across the Omo-Turkana Basin (Nachukui, Usno, Mursi and Koobi Fora Formations) suggesting that the lacustrine paleoecological conditions found in the Kanapoi Formation existed throughout the basin.

Aridity and hominin environments

Aridification is often considered a major driver of long-term ecological change and hominin evolution in eastern Africa during the Plio-Pleistocene; however, this hypothesis remains inadequately tested owing to difficulties in reconstructing terrestrial paleoclimate. We present a revised aridity index for quantifying water deficit (WD) in terrestrial environments using tooth enamel δ18O values, and use this approach to address paleoaridity over the past 4.4 million years in eastern Africa. We find no long-term trend in WD, consistent with other terrestrial climate indicators in the Omo-Turkana Basin, and no relationship between paleoaridity and herbivore paleodiet structure among fossil collections meeting the criteria for WD estimation. Thus, we suggest that changes in the abundance of C4 grass and grazing herbivores in eastern Africa during the Pliocene and Pleistocene may have been decoupled from aridity. As in modern African ecosystems, other factors, such as rainfall seasonality or ecological interactions among plants and mammals, may be important for understanding the evolution of C4 grass- and grazer-dominated biomes.

Ichthyofaunal diversity of the Omo-Turkana basin, East Africa, <span lang="EN-US">with specific reference to fish diversity within the limits of Ethiopian waters</span>

The freshwaters of the East African nation of Ethiopia are divided into nine main drainage basins. One of these, the Omo-Turkana basin, spans a large part of southwestern Ethiopian highlands and northern Kenya, and consists of the Omo-Gibe (or simply, Omo) River and a northern portion of Lake Turkana. Despite some development activities, including proposed dam construction with potential impacts on ichthyofaunal diversity, the Ethiopian part of the basin generally lacks comprehensive study or full scientific documentation. During the current surveys 31 species were identified from the lower Omo River and Ethiopian part of Lake Turkana, with some new records for the basin. The Omo River system was found to be richer in species while Lake Turkana has a higher abundance. Ichthyofaunal diversity within Ethiopian waters is specifically addressed, and an annotated checklist for native species of the basin is provided.

Tephrostratigraphy of the Waki-Mille area of the Woranso-Mille paleoanthropological research project, Afar, Ethiopia

Tephra geochemistry and 40Ar/39Ar geochronology are reported for the Waki-Mille area in the northwestern part of the Woranso-Mille paleoanthropological project area in the west central Afar region of Ethiopia. Previous studies documented dentognathic fossils that are morphologically intermediate between Australopithecus anamensis and Australopithecus afarensis and some that are attributed to Australopithecus afarensis. Additional dentognathic remains from the study area were assigned to the newly identified species Australopithecus deyiremeda. These fossil hominin taxa were recovered from volcanic and sedimentary strata containing tuffs ranging in age from more than 3.77 million years ago (Ma) to less than 3.469 Ma. One of the tuffs was correlated based on geochemistry, feldspar mineralogy, and age to the Lokochot Tuff of the Omo-Turkana Basin of southern Ethiopia and Kenya. Variations in major and minor element abundances in volcanic glass demarcate ten geochemically distinct tuffs and tuff sequences, including three that are geochemically similar to widespread regional tuffs, specifically the Lomogol, Lokochot, and β− Tulu Bor/Sidi Hakoma tuffs. A new 40Ar/39Ar age for the Waki Tuff, which is geochemically similar to the Lomogol Tuff, is 3.664 ± 0.016 Ma. Other tuffs in the Waki-Mille area are geochemically dissimilar to regional tuffs documented to date. Identification of tuffs based on character, stratigraphic position, and geochemistry refines local stratigraphic correlations and delineates the geographic distributions of precisely dated fossiliferous levels within the Waki-Mille area.

Paleoenvironments of the Shungura Formation (Plio-Pleistocene: Ethiopia) based on ecomorphology of the bovid astragalus

The Shungura Formation in southwestern Ethiopia preserves a long and relatively continuous record of eastern African mammalian and hominin evolution. This study reconstructs habitat preferences of the Shungura Formation bovids from ca. 3.4–1.9 Ma (million years ago), based on the ecomorphology of fossil bovid astragali. Habitat predictions are made using a Discriminant Function Analysis informed by functional analysis of the astragalus that controls for body size and phylogenetic signal. The high abundance of astragali in the Shungura record allows for habitat reconstructions on sub-unit timescales, rather than aggregating samples at the level of geological member.During much of the time period examined, the lower Omo Valley was dominated by relatively mesic habitats in close proximity to the ancestral Omo River. Previous research has suggested that environmental change at ∼2.85 Ma caused significant habitat change at Shungura, but the astragalar data do not support major habitat change at this time. However, there are significant fluctuations in inferred habitats, with more open habitats indicated in sub-units C-08 and C-09 (∼2.56 Ma), and in unit F-01 (just after 2.36 Ma). The cause of sub-unit fluctuations in habitat signal is difficult to determine, but local factors, including spatial habitat heterogeneity around the river channel and in its floodplain, may play a contributing role. In the light of faunal evidence from elsewhere in the greater Omo-Turkana Basin, hominins in the area likely had access to a variety of heterogeneous habitats.

New single crystal 40 Ar/ 39 Ar ages improve time scale for deposition of the Omo Group, Omo–Turkana Basin, East Africa

Six tuffaceous beds within the Omo Group of the Omo–Turkana Basin have been dated using the 40 Ar/ 39 Ar single crystal total fusion method on anorthoclase, yielding eruption ages. The Omo Group constitutes up to 800 m of subaerially exposed sediments surrounding Lake Turkana within the East African Rift system in northern Kenya and southern Ethiopia. Rhyolitic explosive eruptions produced tuffs and pumice clasts that are considered to have been deposited shortly after eruption. The new age data on feldspars from the pumice clasts range from 4.02 ± 0.04 Ma for the Naibar Tuff of the Koobi Fora Formation to 1.53 ± 0.02 Ma for Tuff K of the Shungura Formation. The Orange Tuff in the KBS Member of the Koobi Fora Formation was dated at 1.76 ± 0.03 Ma, providing good control in this part of the sequence where formerly there was a >200 ka gap. Data are consistent with earlier measurements and significantly improve age resolution within the Omo Group, which has yielded many vertebrate fossils, including hominin fossils comprising a number of species. We suggest new age estimates for a limited number of hominin specimens. Supplementary material: Eleven tables and nine figures are available at www.geolsoc.org.uk/SUP18506 .

The Early Oldowan Stone-Tool Assemblage from Fejej FJ-1A, Ethiopia

Located in the Omo-Turkana basin at the northern limit of the Koobi Fora sedimentary Formation, the Fejej region has recently proven to be a rich study area for understanding early hominin behaviour and paleoenvironmental conditions. Among the rich fossiliferous and stone artefact localities discovered so far at Fejej, the FJ-1a archeological site has yielded a faunal and lithic assemblage in primary context. The archeological level is situated within a 15 meter fluvial sequence beneath a volcanic tuff. Geochronological data from the FJ-1 sequence indicate an age of nearly 1,9 Ma for the FJ-1a artefact level. The stone industry was knapped from locally available raw materials (mainly quartz and basalt) and rocks had been carefully selected according to specific petrographical and formal criterion. Hominins mastered several distinct stone knapping methods and used more or less exhaustive reduction sequences in order to produce small flakes. The different techniques used for stone reduction are defined in this paper thanks to a series of refits of flakes onto cores. Along with the refits, an in-depth analysis of the flakes, cores and worked pebbles provides an overview of the technological capacities of hominins present at the site nearly 2 million years ago. After the Fejej FJ-1a site was abandoned the archeological materials were rapidly buried, leaving an almost undisturbed archeological level. This site appears to represent a short episode of hominin occupation.

Palaeobiology and evolution of the late Cenozoic freshwater molluscs of the Turkana Basin: Unionidae Rafinesque, 1820, partim Coelatura (Bivalvia: Unionoidea)

The Plio-Pleistocene freshwater molluscs of the Omo-Turkana Basin were long considered to be a prima facie example of punctuated equilibrium evolution. However, the absence of a study on their taxonomy has significantly hampered the debate on assumed evolutionary patterns. This paper addresses the systematics and palaeobiology of the bivalve genus Coelatura Conrad, 1853 in the basin. It reveals that a Coelatura species was assigned to the extinct genus Pseudobovaria Adam, 1957 in earlier studies, while another species formerly assigned to Coelatura is not discussed here because it belongs to the extinct Pseudodiplon Adam, 1957. Six Coelatura species are recognized in the Plio-Pleistocene Omo-Turkana Basin, two of which are new to science: C. rhomboidalis sp. nov. and C. magna sp. nov. These two species are considered lacustrine adapted species, both with a strongly dorsally protruded umbo. This adaptation apparently evolved twice independently in the basin within a ∼1 Ma period, but it is not observed in any other fossil or extant Coelatura species. Three of the other Coelatura forms can be identified as belonging to the extant C. aegyptiaca, C. bakeri and C. alluaudi. Disentangling the genealogical relationships of these extant species with neontological techniques will provide a test of the palaeontological systematics here proposed. General evaluation of the Turkana Basin coelaturids, and particularly their apparent absence from the first so-called punctuative Suregei Isolate period, corroborates the hypothesis of biological invasions in the basin, but indicates that in situ evolutionary events occurred occasionally.

The Omo‐Turkana Basin Fossil Hominins and Their Contribution to Our Understanding of Human Evolution in Africa

The Omo-Turkana Basin, including the hominin fossil sites around Lake Turkana and the sites along the lower reaches of the Omo River, has made and continues to make an important contribution to improving our murky understanding of human evolution. This review highlights the various ways the Omo-Turkana Basin fossil record has contributed to, and continues to challenge, interpretations of human evolution. Despite many diagrams that look suspiciously like comprehensive hypotheses about human evolutionary history, any sensible paleoanthropologist knows that the early hominin fossil record is too meager to do anything other than offer very provisional statements about hominin taxonomy and phylogeny. If history tells us anything, it is that we still have much to learn about the hominin clade. Thus, we summarize the current state of knowledge of the hominin species represented at the Omo-Turkana Basin sites. We then focus on three specific topics for which the fossil evidence is especially relevant: the origin and nature of Paranthropus; the origin and nature of early Homo; and the ongoing debate about whether the pattern of human evolution is more consistent with speciation by cladogenesis, with greater taxonomic diversity or with speciation by anagenetic transformation, resulting in less taxonomic diversity and a more linear interpretation of human evolutionary history.

Stable Isotope Ecology in the Omo‐Turkana Basin

Stable isotopes provide an independent assessment of paleoenvironments in the Omo-Turkana Basin. Stable isotopes track the flow of oxygen and carbon through ecosystems and accordingly are not directly related to changes in mammalian faunal composition or sedimentology. Therefore, isotope studies give insight into the paleoenvironmental conditions in which human evolutionary trends have been recorded. The development of stable isotopes as indicators of continental environmental conditions has proceeded in parallel with questions about the conditions of human environment. What was the vegetation? How hot was it? How dry? What were the diets of animals living among early humans? And most persistently, how important were "savannas" to early hominids? In this review, we take the opportunity to provide extensive background on the use of isotopes in anthropological sites. The application of stable isotope ecology to anthropological sites in the Turkana Basin has a long history, but in many ways the Omo-Turkana Basin has been a proving ground for the development of new proxy methods for understanding tropical terrestrial environments in the Neogene and Quaternary. For that reason, we also describe some of the fundamental aspects of isotope ecology that developed outside the field of paleoanthropology.

Fossil Mammals and Paleoenvironments in the Omo‐Turkana Basin

Although best known for its fossil hominins, the Omo-Turkana Basin of Kenya and Ethiopia is the source of one of the best records of vertebrate evolution from the Late Cenozoic of Africa. Located near the heart of the East African Rift Valley, the basin serves as an important frame of reference for the continent. The fossil record from this region plays a key role in our efforts to understand the environmental and ecological context of human evolution in Africa. The Omo-Turkana faunal data shed light on key questions of human evolution: What kinds of environments did early humans inhabit? How did these environments change over time? What is the relationship between faunal change in East Africa and broader patterns of climatic change?

Paleosol carbonates from the Omo Group: Isotopic records of local and regional environmental change in East Africa

Pliocene and Pleistocene sedimentary rocks from the Omo–Turkana Basin in East Africa are well known for fossil and archeological evidence of human evolution and provide a unique opportunity to study four million years of environmental change in a rift basin. This study uses carbon and oxygen isotope ratios of pedogenic carbonates to examine environmental variability across ~ 5000 km 2 within the Omo–Turkana Basin. An expanded isotopic dataset, including the first isotopic data on pedogenic carbonates from the Shungura Formation and new data from the Nachukui and Koobi Fora formations, is compared to published isotopic records from both the Omo–Turkana Basin and the lower Awash Basin, Ethiopia. Regionally, the carbon isotope record indicates a steady increase of C 4 vegetation in floodplain environments for the past 4 million years. The oxygen isotopic record indicates that the isotopic composition of rainfall was depleted in 18O relative to today's waters and that both basins likely received more rainfall in the Pliocene than today. A shift to higher δ 18O values in paleosol carbonate after 2 Ma in the Omo–Turkana Basin but not in the lower Awash Basin suggests that the ecology and hydrology in these two rift basins were influenced by different climatic regimes. In addition to regional trends, pedogenic carbonates sampled from different parts of the basin show that the distribution of C 4 vegetation and soil water δ 18O values varied with proximity to the axial river system, and specifically that C 3 vegetation was more dominant in soils of the Shungura Formation compared with coeval sediments downstream in the Nachukui and Koobi Fora formations. This large isotopic dataset from pedogenic carbonates provides the opportunity to examine how terrestrial systems responded to global climate change during the last 4 million years, from both local and regional perspectives. The isotopic data indicate that local basin and climate dynamics strongly influenced the impact of large-scale environmental change in East African rift basins.

Geochemistry of the Fejej Tuffs (South Omo, Ethiopia), their Tephrostratigraphical Correlation with Plio-Pleistocene Formations in the Omo-Turkana Basin

The FJ-1 Tuff and three additional isolated outcrops of volcanic tuffs listed in the Fejej area (South Omo, Ethiopia) are associated with a single volcanic event and correspond to the same ash deposit subsequently truncated by erosion. Data from new chemical analyses given by X-ray fluorescence allow correlation of these tuffs with the Borana Tuff of the Koobi Fora Formation, which is itself correlated with a tuff in the Upper G member or with the H-1 tuff of the Shungura formation. The geochronological assessment of this tephra is in agreement with previous magnetostratigraphical and biostratigraphical studies, attributing the Fejej FJ-1 Tuff to between 1.95 to 1.90 Ma.