14C and Th/U Dating of Pleistocene and Holocene Stromatolites from East African Paleolakes

1986 ◽  
Vol 25 (3) ◽  
pp. 312-239 ◽  
Author(s):  
Claude Hillaire-Marcel ◽  
Odette Carro ◽  
Joel Casanova
Keyword(s):  
Water Level ◽  
Residence Time ◽  
Rift Valley ◽  
Eastern Africa ◽  
East African ◽  
Isotopic Equilibrium ◽  
Dissolved Carbon ◽  
Three Generations ◽  
Detrital Component

During recent humid episodes, stromatolites were built along paleolake margins, some 60 m above the modern water level of Lakes Natron and Magadi (southern Gregory Rift Valley). Three generations of stromatolites are observed, the more recent ones frequently covering pebbles and boulders eroded from the older ones. The youngest one yielded 14C ages ranging from approximately 12,000 to 10,000 yr B.P. Their δ13C values (≥2.6%) suggest isotopic equilibrium between the paleolake total inorganic dissolved carbon and the atmospheric CO2, thereby lending credence to the reliability of the 14C. An initial 230Th/232Th ratio in the detrital component was determined by Th/U measurements on the 14C dated stromatolites. Using this value a 230Th/234U chronology for the older stromatolites was calculated. Ages of ≥240,000 and 135,000 ± 10,000 yr were obtained for the first and second generations, respectively. A humid episode apparently characterized eastern Africa during each glacial-interglacial transition. 18O and 13C measurements on stromatolites, when compared to values on modern waters and carbonates, provide paleohydrological information. Long residence time of the paleolake waters and less seasonally contrasted regimes are inferred.

Pastoralism in Eastern Africa

2021 ◽  
Author(s):  
John Galaty
Keyword(s):  
East Africa ◽  
Rift Valley ◽  
Religious Conversion ◽  
Social Systems ◽  
Rural Poverty ◽  
Small Towns ◽  
Eastern Africa ◽  
Rainfall Regime ◽  
East African ◽  
History Of

The Rift Valley is a stage on which the history of Eastern Africa has unfolded over the last 10,000 years. It served as a corridor for the southward migration from the Upper Nile and the Ethiopian highlands of Nilo-Saharan and Afro-Asiatic speakers and cultures, with their domestic animals, which over time defined and restructured the social and cultural fabric of East Africa. Genetic evidence suggests that, contrary to other regions in Africa where geography overrides language, the clustering of East African populations primarily reflects linguistic affiliation. Eastern Sudanic Nilotic speakers are dedicated livestock keepers whose identification with cattle over thousands of years is manifested in elaborate symbolism, networks created by cattle exchange, and the practice of sacrifice. The geographical attributes of rich grasslands in a semi-arid environment, close proximity of lowland and highland grazing, and a bimodal rainfall regime, made the Rift Valley an ideal setting for increasingly specialized pastoralism. However, specialized animal husbandry characteristic of East Africa was possible only within a wider socioeconomic configuration that included hunters and bee-keeping foragers and cultivators occupying escarpments and highland areas. Some pastoral groups, like Maasai, Turkana, Borana, and Somali, spread widely across grazing areas, creating more culturally homogeneous regions, while others settled near one another in geographically variegated regions, as in the Omo Valley, the Lake Baringo basin, or the Tanzanian western highlands, creating social knots that signal historical interlaying and long-term mutual coexistence. At the advent of the colonial period, Oromo and Maasai speakers successfully exploited the ecological potential of the Rift environment by combining the art of raising animals with social systems built out of principles of clanship, age and generation organizations, and territorial sections. Faced with displacement by colonial settlers and then privatization of rangelands, some Maasai pastoralists sold lands that they had been allocated, leading to landlessness amid rangeland bounty. Pastoral futures involve a combination of education, religious conversion, and diversified rangeland livelihoods, which combine animal production with cultivation, business, wage labor, or conservation enterprises. Pastoralists provide urban markets with meat, but, with human population increasing, per capita livestock holdings have diminished, leading to rural poverty, as small towns absorbing young people departing pastoralism have become critical. The Great East African Rift Valley has had a 10,000-year history of developing pastoralism as one of the world’s great forms of food production, which spread throughout Eastern Africa. The dynamics of pastoral mobility and dedication to livestock have been challenged by modernity, which has undermined pastoral territoriality and culture while providing opportunities that pastoralists now seek as citizens of their nations and the world.

scholarly journals Specific limits and emerging diversity patterns in East African populations of laminate-toothed rats, genus Otomys (Muridae: Murinae: Otomyini): Revision of the Otomys typus complex

Zootaxa ◽  
2011 ◽  
Vol 3024 (1) ◽  
pp. 1 ◽  
Author(s):  
PETER J. TAYLOR ◽  
LEONID A. LAVRENCHENKO ◽  
MICHAEL D. CARLETON ◽  
ERIK VERHEYEN ◽  
NIGEL C. BENNETT ◽  
...  
Keyword(s):  
Cytochrome B ◽  
Dna Sequences ◽  
Rift Valley ◽  
High Elevation ◽  
Eastern Africa ◽  
12S Rrna ◽  
East African ◽  
Test Species ◽  
The North ◽  
Great Rift Valley

We combined evidence from biogeography, craniodental traits, linear and geometric morphometrics (233 skulls), cytogenetics (karyotypes of 18 individuals) and mitochondrial DNA sequences (44 cytochrome b and 21 12S rRNA sequences) to test species limits within Otomys typus s.l. (Muridae: Murinae: Otomyini), a complex that is patchily distributed across alpine zones of Ethiopia and East Africa. Our results confirm the specific validity of O. dartmouthi, O. jacksoni, O. orestes, and O. uzungwensis, forms recently removed from synonymy under typus s.l.; support elevation of four other alpine forms to species (O. fortior, O. helleri, O. thomasi, and O. zinki); identify three additional new species (O. cheesmani sp. nov., O. simiensis sp. nov., O. yaldeni sp. nov.); and enable redefinition of O. typus s.s. as a species restricted to certain mountains west of the Great Rift Valley in Ethiopia (Simien and Guna Mountains in the north, extending to the highlands of the western rim of the Rift Valley). Phylogenetic interpretation of the cytochrome b data clearly demonstrates that the alpine morphotype once united under O. typus s.l. has originated independently at high elevations on several mountain ranges in eastern and northeastern Africa; although generally adapted to high-elevation vegetation, such alpine species are ecologically segregated from one another. Patterns of morphometric, genetic, and ecological differentiation among populations once misassigned to nominal O. tropicalis and O. typus more parsimoniously reflect regional cladogenesis along elevational gradients, rather than multiple, successive colonization by different ancestral forms from southern Africa as earlier supposed. Although incomplete and preliminary, information gathered for O. tropicalis indicates that it too is a species composite; several lines of research are discussed to redress its polyphyletic content. Our results, together with other recent taxonomic studies of Otomys, appreciably elevate the level of endemism within eastern Africa and underscore the significance of Africa's eastern highlands to the continental diversification of Otomyini.

scholarly journals The geological history of the Lake Rudolf Basin, Kenya colony

1939 ◽  
Vol 229 (560) ◽  
pp. 219-274 ◽  
Keyword(s):  
Rift Valley ◽  
Public Works ◽  
General Description ◽  
Geological History ◽  
East African ◽  
The Public ◽  
Geographical Society ◽  
History Of ◽  
African Rift ◽  
At Home

The Lake Rudolf Rift Valley Expedition was designed to carry out many different lines of investigation in the Lake Rudolf Basin. One of the chief of these was a study of the geological history of that part of the East African Rift Valley. The expedition was assisted financially by The Royal Society, The Geological Society of London, The Royal Geographical Society, The Percy Sladen Trustees and the Geographical and Geological Sections of the British Association. A general description of the activities of the Expedition was given in a paper read before the Royal Geographical Society (Fuchs 1935). Owing to the tragic loss of two members of the expedition, Dr W. S. Dyson and Mr W. R. H. Martin, two fruitless months were spent searching for them. Consequently a great amount of the work planned for the east side of the lake had to be abandoned. Nevertheless, the considerable distance travelled within the 50,000 sq. miles of the Rudolf Basin has enabled me to make out the chief events of its geological history. I am very much indebted to all those who assisted us in the field and at home, in particular to the Kenya Government, the Officers of the King’s African Rifles, and Mr H. L. Sikes of the Public Works Department; I would also like to thank Mr A. M. Champion, Provincial Commissioner of Turkana, who wholeheartedly assisted us in every way possible both in the field and at home, for he has placed at my disposal his own excellent topographical maps and his extensive observations on the geology of the area. I am also deeply indebted to Professor O. T. Jones, Mr Henry Woods and Mr W. Campbell Smith for their criticisms. Mr Campbell Smith has also given me provisional identifications of the rocks.

The Recent History and Pleistocene Deposits of the Plateau North of Lake Eyasi, Tanganyika

1941 ◽  
Vol 78 (3) ◽  
pp. 173-184 ◽  
Author(s):  
P. E. Kent
Keyword(s):  
Rift Valley ◽  
Recent History ◽  
Middle Pleistocene ◽  
East African ◽  
The Difference ◽  
Lake Beds

ONE of the objectives of the East African Archaeological Expedition of 1934–5 was the examination of the plateau north of Lake Eyasi—the Vogel River area—where, it was hoped, a continuation of the richly fossiliferous Oldowaya Middle Pleistocene lake beds would be found. This hope was essentially realized ; deposits with an interesting Middle Pleistocene fauna a little earlier than that of Oldoway were found, with the difference that they were entirely terrestrial. The development of precisely datable beds resting upon a main Rift Valley Scarp made possible a study of physiographical changes associated with the faulting.

scholarly journals Mitochondrial phylogeography of baboons (Papiospp.) – Indication for introgressive hybridization?

2009 ◽  
Vol 9 (1) ◽  
Author(s):  
Dietmar Zinner ◽  
Linn F Groeneveld ◽  
Christina Keller ◽  
Christian Roos
Keyword(s):  
Phylogenetic Relationships ◽  
Evolutionary History ◽  
Introgressive Hybridization ◽  
Distinct Species ◽  
Eastern Africa ◽  
East African ◽  
Hamadryas Baboons ◽  
Olive Baboons ◽  
Initial Separation ◽  
Molecular Studies

Abstract Background Baboons of the genus Papio are distributed over wide ranges of Africa and even colonized parts of the Arabian Peninsula. Traditionally, five phenotypically distinct species are recognized, but recent molecular studies were not able to resolve their phylogenetic relationships. Moreover, these studies revealed para- and polyphyletic (hereafter paraphyletic) mitochondrial clades for baboons from eastern Africa, and it was hypothesized that introgressive hybridization might have contributed substantially to their evolutionary history. To further elucidate the phylogenetic relationships among baboons, we extended earlier studies by analysing the complete mitochondrial cytochrome b gene and the 'Brown region' from 67 specimens collected at 53 sites, which represent all species and which cover most of the baboons' range. Results Based on phylogenetic tree reconstructions seven well supported major haplogroups were detected, which reflect geographic populations and discordance between mitochondrial phylogeny and baboon morphology. Our divergence age estimates indicate an initial separation into southern and northern baboon clades 2.09 (1.54–2.71) million years ago (mya). We found deep divergences between haplogroups within several species (~2 mya, northern and southern yellow baboons, western and eastern olive baboons and northern and southern chacma baboons), but also recent divergence ages among species (< 0.7 mya, yellow, olive and hamadryas baboons in eastern Africa). Conclusion Our study confirms earlier findings for eastern Africa, but shows that baboon species from other parts of the continent are also mitochondrially paraphyletic. The phylogenetic patterns suggest a complex evolutionary history with multiple phases of isolation and reconnection of populations. Most likely all these biogeographic events were triggered by multiple cycles of expansion and retreat of savannah biomes during Pleistocene glacial and inter-glacial periods. During contact phases of populations reticulate events (i.e. introgressive hybridization) were highly likely, similar to ongoing hybridization, which is observed between East African baboon populations. Defining the extent of the introgressive hybridization will require further molecular studies that incorporate additional sampling sites and nuclear loci.

Drinking water quality in the Ethiopian section of the East African Rift Valley I—data and health aspects

2003 ◽  
Vol 311 (1-3) ◽  
pp. 65-80 ◽  
Author(s):  
Clemens Reimann ◽  
Kjell Bjorvatn ◽  
Bjørn Frengstad ◽  
Zenebe Melaku ◽  
Redda Tekle-Haimanot ◽  
...  
Keyword(s):  
Water Quality ◽  
Drinking Water ◽  
Rift Valley ◽  
East African Rift ◽  
Drinking Water Quality ◽  
East African ◽  
African Rift

Reconstructing vegetation changes in the Ethiopian Highlands: 18000 years of Afromontane vegetation dynamics recorded in high altitude wetlands.

2021 ◽  
Author(s):  
Femke Augustijns ◽  
Nils Broothaerts ◽  
Gert Verstraeten
Keyword(s):  
Rift Valley ◽  
Altitudinal Gradient ◽  
Fungal Spores ◽  
Climatic Changes ◽  
Eastern Africa ◽  
Plant Domestication ◽  
Ethiopian Rift ◽  
Vegetation Changes ◽  
Afromontane Forest ◽  
Spatial Coverage

&lt;p&gt;Within eastern Africa, Ethiopia stands out for its steep topography, resulting in an altitudinal zonation of climate and vegetation. To understand future vegetation changes, we need information on past vegetation covers and vegetation responses to environmental and climatic changes. Pollen studies are available for low and high elevations in Ethiopia, but they are low in number and limited in spatial coverage. In addition, explicit research to altitudinal patterns of environmental changes are missing. However, archaeological evidence from SW Ethiopia suggests vertical migration of humans in response to humidity fluctuations, highlighting the need for research to spatial dynamics of human activities and vegetation in Ethiopia. On the other hand, sedimentological evidence suggests a millennia long agricultural history in Ethiopia&amp;#8217;s highlands and several authors identify this region as a center of plant domestication.&amp;#160;&lt;/p&gt;&lt;p&gt;It is clear that a thorough understanding of the past vegetation cover and its alteration by humans and climate is missing for Ethiopia. These research gaps impede identification of the timing and location of the onset of agriculture in the ancient Ethiopian landscape, resulting in poor understanding of e.g. contemporary degraded landforms. In our study, we aim to reconstruct and quantify the vegetation history along an altitudinal gradient in the Southern Ethiopian Rift Valley and to identify the role of man and climate on this evolution. Therefore, several lakes and swamps are selected as study sites along an altitudinal gradient (1100-3000 m a.s.l.) in the Gamo Highlands near the city of Arba Minch, along the Southern Ethiopian Rift Valley. Here, we will present the results of pollen, charcoal and NPP analyses from two wetland sites situated at 2300 and 3000 m a.s.l. The records show an increase of Afromontane forest taxa around 13 ka BP, at the expense of Montane ericaceous taxa. At 8 ka BP, a shift in the composition of the Afromontane forest is observed, together with a change in the fungal assemblage and decrease of grasses. Around 6 ka BP, Wooded grassland taxa increase simultaneously with &lt;em&gt;Delitschia&lt;/em&gt; fungal spores. Montane forest taxa increase again at 2.5 ka BP, together with a shift in fungal spores, followed by an increase in charcoal accumulation during the last millennium. Most of the observed transitions can be linked to other vegetation records from Ethiopia, and reflect responses to climatic changes such as the African Humid Period. However, the exact timing and&amp;#160; nature of the vegetation changes differs substantially between records, and asks for a denser sampling of palaeoecological records across Ethiopia. In this study, we will link the reconstructed vegetation changes with anthropogenic and natural driving forces, and come up with a reconstruction of the long-term landscape development in the study area in SW Ethiopia. &amp;#160;&amp;#160;&lt;/p&gt;

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