Search

In the semiarid Bulal transboundary catchment of southern Ethiopia, groundwater is the only reliable drought-resilient water source. The central and southern parts of the catchment are dominantly overlain by the transboundary aquifers of the Bulal basalts, while the basement rocks outcrop in the eastern part. This study uses an integrated geographic information system (GIS), remote sensing (RS), and analytical hierarchal process (AHP) to identify and delineate the groundwater potential zones of the semiarid Bulal catchment within the Ethiopian territory. Based on their relative importance to groundwater occurrence and movement, ten input parameters were chosen. According to Saaty's AHP approach, the input themes and each of their distinct features were given normalized weights. A composite groundwater potential zone index (GWPZI) map was generated by integrating all the input layers employing the GIS-overlay analysis technique. The map was validated using the yield of wells from the catchment. The GWPZI map depicts four groundwater potential zones: high (representing 27% of the total area), moderate (20%), low (28%), and very low (25%). The geological feature has the greatest influence on the distribution of groundwater potential. Areas with high potential are mainly overlain by the Bulal basaltic flow, while low groundwater potential zones are in the regolith over the basement rocks. Unlike conventional methods, our novel approach is effective in identifying relatively shallow GWPZs throughout the catchment, and it can be applied in similar semiarid regions. The GWPZI map serves as a quick guide for effectively planning, managing, and developing the catchment's groundwater resources. [ABSTRACT FROM AUTHOR]

Two new rock art sites in Irob district of eastern Tigrai, northern Ethiopia, are presented. One of the sites, Ra Bolo, contains images of domestic cattle and human figures while the other, Adhay Bolo, appears to contain only images of caprines, the only example of such a scene not just in the region but in all of Ethiopia. The sites fit well with the already established northern Ethiopian assemblage of paintings and engravings. The paintings belong to the earliest phase of Ethio-Arabian "Surre-Hanakiya" style, an attribution which is supported by other types of archaeological data. These new rock art sites are also compared with other rock art sites in Ethiopia. Archaeological faunal data from northern Ethiopia and elsewhere in Ethiopia is discussed and questions are raised about the validity of the hypothesized ages of the rock art in south-central Ethiopia. [ABSTRACT FROM AUTHOR]

Quantifying and characterizing the spatial distribution of freshwater availability and water scarcity plays an indispensable role in managing water resources in a basin. This study aimed at quantifying green and blue water resource availability using an eco-hydrological model under different land use land cover conditions between 2000–2010 and 2020 in the upper Awash basin, central Ethiopia. Further, the agricultural water scarcity is assessed for dominantly cultivated crops in the basin. The freshwater components such as the green water (GW) flow (∼1041–1240 mm/yr), blue water (BW) flow (277–304 mm/yr), and GW storage (809-872 mm/yr) were observed to be high in the western highlands compared to the central and eastern parts of the basin. The results of GW scarcity indices show low to moderate scarcity for rainfed crops, and moderate to significant BW scarcity for irrigated sugarcane. Integrating GW potential to reduce BW scarcity in the basin is thus crucial. [ABSTRACT FROM AUTHOR]

A multiproxy oxygen and carbon isotope (δ13C and δ18O), growth rate, and trace element stalagmite paleoenvironmental record is presented for the Early Holocene from Ethiopia. The annually laminated stalagmite grew from 10.6 to 10.4 ka and from 9.7 to 9.0 ka with a short hiatus at ~9.25 ka. Statistically significant and coherent spectral frequencies in δ13C and δ18O are observed at 15-25 and 19-23 years, respectively. The observed ~1‰amplitude variability in stalagmite δ18O is likely forced by nonequilibrium deposition, due to kinetic effects during the progressive degassing of CO2 from the water film during stalagmite formation. These frequencies are similar to the periodicity reported for other Holocene stalagmite records from Ethiopia, suggesting that multidecadal variability in stalagmite δ18O is typical. Several processes can lead to this multidecadal variability and operate in different directions. A hydroclimate forcing is likely the primary control on the extent of the partial evaporation of soil and shallow epikarst water and associated isotopic fractionation. The resulting oxygen isotope composition of percolation water is subsequently modulated by karst hydrology. Further isotopic fractionation is possible in-cave during nonequilibrium stalagmite deposition. Combined with possible recharge biases in drip-water δ18O, these processes can generate multidecadal δ18O variability. [ABSTRACT FROM AUTHOR]

We introduce a new method to compute plant distribution in Ethiopia under paleoclimatic conditions using fuzzy logic. Using a published map of the potential vegetation for Ethiopia we decipher the boundary conditions for the main vegetation units shown, reflecting modern climatic conditions for temperature and precipitation in this region. Fuzzy logic using these climatic values on a GIS platform then derived the computational map of the potential vegetation. Comparing it with the original map shows a general correspondence of about 90%. By changing the underlying climate parameters, we then used this model for hypothetical paleoclimatic conditions to simulate the vegetational response on these changed climate settings. Finally, vegetational response maps for Ethiopia are presented for two scenarios: (i) a colder and drier condition (such as the Last Glacial Maximum) and (ii) a warmer and wetter condition (such as the last interglacial) than today. [ABSTRACT FROM AUTHOR]

The acid ponds of the Danakil Depression in northern Ethiopia are polyextreme environments that exceed the normal physicochemical limits of pH, salinity, ion content, and temperature. We tested for the occurrence of DNA-based life in this environment using Metagenomic Shotgun DNA sequencing approaches. The obtained sequences were examined by the bioinformatic tools MetaSpades, DIAMOND and MEGAN 6-CE, and we were able to bin more than 90% of the metagenomics contigs of Dallol and Black Water to the Bacteria domain, and to the Proteobacteria phylum. Predictions of gene function based on SEED disclosed the presence of different nutrient cycles in the acid ponds. For this study, we focused on partial or completely sequenced genes involved in nitrogen metabolism. The KEGG nitrogen metabolism pathway mapping results for both acid ponds showed that all the predicted genes are involved directly or indirectly in the assimilation of ammonia and no dissimilation or nitrification process was identified. Furthermore, the deduced nitrogen fixation in the two acid ponds based on SEED classification indicated the presence of different sets of nitrogen fixing (nif) genes for biosynthesis and maturation of nitrogenase. Based on the in silico analysis, the predicted proteins involved in nitrogen fixation, especially the cysteine desulfurase and [4Fe-4S] ferredoxin, from both acid ponds are unique with less than 80% sequence similarity to the next closest protein sequence. Considering the extremity of the environmental conditions of the two acid ponds in the Danakil depression, this metagenomics dataset can add to the study of unique gene functions in nitrogen metabolism that enable thriving biocommunities in hypersaline and highly acidic conditions. [ABSTRACT FROM AUTHOR]

Obsidian is abundant in the Main Ethiopian Rift (MER). Petrological and geochemical features of obsidian from four volcanic centers in the MER, namely Birenti, Dofen, Fentale and Kone, are presented. Compositional and petrological variability is noted among the Dofen and Fentale obsidian, but not in those from Kone and Birenti where each have separate but uniform elemental composition. The Fentale and Kone obsidian were source materials for the artifacts of a number of Middle Stone Age and Later Stone Age/Neolithic sites in the region. We have yet to determine whether Dofen and Birenti were sources for archeological artifacts. The study also shows that volcanic episodes from a single center do not necessarily result in compositional variability. [ABSTRACT FROM AUTHOR]

The Chew Bahir Drilling Project (CBDP) aims to test possible linkages between climate and evolution in Africa through the analysis of sediment cores that have recorded environmental changes in the Chew Bahir basin. In this statistical project we consider the Chew Bahir palaeolake to be a dynamical system consisting of interactions between its different components, such as the waterbody, the sediment beneath lake, and the organisms living within and around the lake. Recurrence is a common feature of such dynamical systems, with recurring patterns in the state of the system reflecting typical influences. Identifying and defining these influences contributes significantly to our understanding of the dynamics of the system. Different recurring changes in precipitation, evaporation, and wind speed in the Chew Bahir basin could result in similar (but not identical) conditions in the lake (e.g., depth and area of the lake, alkalinity and salinity of the lake water, species assemblages in the water body, and diagenesis in the sediments). Recurrence plots (RPs) are graphic displays of such recurring states within a system. Measures of complexity were subsequently introduced to complement the visual inspection of recurrence plots, and provide quantitative descriptions for use in recurrence quantification analysis (RQA). We present and discuss herein results from an RQA on the environmental record from six short (< 17 m) sediment cores collected during the CBDP, spanning the last 45 kyrs. The different types of variability and transitions in these records were classified to improve our understanding of the response of the biosphere to climate change, and especially the response of humans in the area. [ABSTRACT FROM AUTHOR]

Abstract Oxygen and carbon (δ18Ο/δ13C) isotope, growth rate and trace element data are reported for a U-Th dated, annually-laminated stalagmite, GM1 from Goda Mea Cave, Ethiopia. The stalagmite grew intermittently around the last interglacial. The proxy records are used to develop a conceptual growth model of the stalagmite and to assess its potential for revealing a climate signal in this climatically sensitive northeastern African region during an important period in the evolution of Homo sapiens and dispersal of Anatomically Modern Humans out of Africa. Speleothem deposition is of short-duration occurring at ∼129 ka, ∼120 ka, in an undated growth phase, and at ∼108 ka; probably due to tectonic activity. δ18Ο composition is very stable within growth phases (1σ variability < 0.76‰), as are Mg/Ca, Sr/Ca and Ba/Ca, all indicative of well-mixed source-waters. A shift to positive δ18Ο values and increased variability in Mg/Ca, Sr/Ca and Ba/Ca prior to growth hiatuses is observed, indicating a loss of the well-mixed water source prior to growth cessation. Mean δ18Ο composition (−3.82 to −7.77‰) is lower than published modern and Holocene stalagmites from the region. Geochemical data, statistical analyses, and a conceptual model of stalagmite growth, demonstrate that climatic conditions recorded by GM1 were wetter than the Holocene. The ∼129 ka growth phase particularly presents an annual record of the relative Intertropical Convergence Zone (ITCZ) position. The GM1 record, the oldest high-resolution continental climate record from Ethiopia so far published, presents evidence that any early human migrations which occurred during MIS 5 are likely to have occurred during a wet event in northeast Africa. Highlights • Stalagmite GM1 discontinuously deposited at ∼129 ka, 120 ka, an undated growth phase, and ∼108 ka. • Multi-proxy analysis necessary to identify climatic from karstic signal. • Low δ18O at ∼129 ka and ∼108 ka attributed to wetter climatic conditions. • The first annually-resolved stalagmite record of the last interglacial from Ethiopia. • The earliest Modern Human dispersal out of Africa occurred during humid climate conditions. [ABSTRACT FROM AUTHOR]

The Sof Omar Cave System, a spectacular and extensive cave system in Southeastern Ethiopia represents a maze of dry cave passages, which subsequently were crossed by a subterranean watercourse formed by the Weib River, forming combined underground passages of a total length of 15.1 km, the longest and most extensive in Ethiopia. The Sof Omar cave and subterranean river system developed on Jurassic limestone beds particularly on the Gebredarie Series (massive, crystalline limestone beds intercalated with thin marl and mudstone beds). The cave system and the subterranean River developed along a generally horizontal outline within a 20 m thick layer. The Sof Omar gorge is a wide but shallow doline, whose central section is incised by the ancient surface route of the Weib River. Prominent half dolines opening toward the sink and resurgence areas, as well as consistently inward dipping limestone beds at these localities imply collapse phenomenon. Karstification triggered by rift-related uplifting and extension during the mid-Miocene East African rifting, accompanied by extensive collapse along bedding planes likely initiated the caving process. The rifted and collapsed chambers were later widened by slow but persistent dissolution. The dry cave passages were formed earlier than the subterranean river course, though the latter might have partly followed the pre-existing cave passages and enlarged them to form the current subterranean river course. The Sof Omar caves are still at the heart of the cultural and religious life of the local population, where the dry cave passages, domes, and chambers are considered as important religious and cultural locales. With its subterranean river, large chambers connected by narrow and long rift passages, a unique and prominent sinkhole above the caves, wooded gorge teeming with numerous and unique tropical plant and bird species, the Sof Omar Cave System and adjoining gorge has outstanding scenic values. Apart from these naturally outstanding values, what makes the Sof Omar Cave System unique and unsurpassed in the world is its cultural significance. The caves form part of the cultural and religious life of the local population leading to the unique harmony between nature and culture. The cave system and its adjoining forested gorge is a natural–cultural heritage site that requires an active geoconservation. [ABSTRACT FROM AUTHOR]

Abstract: Lalibela is a medieval settlement in Northern Ethiopia famous for its 11 beautifully carved rock hewn churches, registered as World Heritage Site in 1978. The rock hewn churches are grouped into three based on their proximity: the Bete Medhane Alem (Church of the Holy Saviour), Bete Gabriel–Rufael (Church of St. Gabriel–Rafael) and Bete Giorgis (Church of St. George) groups. The churches are carved out of a single, massive scoriaceous basalt hill which was deposited along an East–West extending palaeovalley in the Oligo-Miocene Trap basalt of the northwestern Ethiopian plateau. The Rock Mass Rating (RMR) classification scheme was used to classify the rock mass (assuming each church as a separate rock mass) based on their uniaxial compressive strength and the spacing and conditions of discontinuities. Though most of the churches are hewn from medium to high strength rock mass, discontinuities make them vulnerable to other deteriorating agents mainly weathering, and water infiltration. Most of the rock hewn churches are affected by pre-carving cooling joints and bedding plane discontinuities, and by mostly but not necessarily post-carving tectonic and seismic induced cracks and fractures. Material loss due to deep weathering triggered by rain water infiltration and uncontrolled groundwater seepage affects most of the churches, particularly the Bete Merqorios (Church of St. Mark) and Bete Aba Libanos (Church of Father Libanos) churches. The scoriaceous basalt which is porous and permeable allows easy passage of water while the underlying basalt is impermeable, increasing the residence time of water in the porous material, causing deep weathering and subsequent loss of material in some of the churches and adjoining courtyards. [ABSTRACT FROM AUTHOR]

An annually laminated, uranium-series dated, Holocene stalagmite from southeast Ethiopia has been analysed for growth rate and δ13C and δ18O variations at annual to biennial resolution, in order to provide the first long duration proxy record of decadal-scale rainfall variability in this climatically sensitive region. Our study site (10°N) is climatically influenced by both summer (June-August) and spring (March-May) rainfall caused by the annual movement of the Inter- Tropical Convergence Zone (ITCZ) and modulated by large-scale anomalies in the atmospheric circulation and in ocean temperatures. Here we show that stalagmite growth, episodic throughout the last 7800 years, demonstrates decadal-scale (8-25 yr) variability in both growth rate and δ18O. A hydrological model was employed and indicates that this decadal variability is due to variations in the relative amounts of rainfall in the two rain seasons. Our record, unique in its combination of length (a total of ∼1000 years), annual chronology and high resolution δ18O, shows for the first time that such decadal-scale variability in rainfall in this region has occurred through the Holocene, which implies persistent decadal-scale variability for the large-scale atmospheric and oceanic driving factors. [ABSTRACT FROM AUTHOR]

The geomorphological map described below covers an area of about 100 km2, located on the southeastern slope of Mt. Amba Aradam (northern Ethiopia). It has been produced within the Ethio-Italian Cooperation Programme, in order to understand the recent evolution and present-day trends of the area as a basic tool for land reclamation/rehabilitation projects. The survey was carried out in three successive work campaigns (February 1995, February-March 1996 and December 2002) following the Italian Environmental Agency guidelines. The main geomorphological processes responsible for present-day landscape modelling in the investigation area, are gravity-driven mass movements and slope erosion due to running water. They strongly affect human activities, especially in terms of agriculture and infrastructure management. This map may therefore represent a useful document for land management as well as the initial step for the assessment of geomorphological hazard and risk. [ABSTRACT FROM AUTHOR]

Gaet'ale (GAL) and Mud'ara (MUP) are two hypersaline ponds located in the Danakil Depression recharged by underground water from the surrounding highlands. These two ponds have different pH, salinity, and show variation in the concentration of many ionic components. Metagenomic analysis concludes that GAL is dominated by bacteria as in the case of the other hypersaline and acidic ponds in the Danakil Depression. However, Archaea dominated the ponds of MUP. In the current study, the application of SEED and KEGG helped to map the ordered steps of specific enzyme catalyzed reaction in converting CO2 into cell products. We predict that highly efficient and light-independent carbon fixation involving phosphoenolpyruvate carboxylase takes place in MUP. On the contrary, genes encoding enzymes involved in hydrogenotrophic and acetoclastic methanogenesis appeared solely in ponds of GAL, implying the biological source of the hazardous methane gas in that environment. Based on the investigation of the sources of the genes of interest, it is clear that cooperative interactions between members of the two communities and syntrophic metabolism is the main strategy adapted to utilize inorganic carbon as a carbon source in both MUP and GAL. This insight can be used to design biotechnological applications of microbial communities in production of methane biogas or to minimize CO2 emissions. [ABSTRACT FROM AUTHOR]

During the past 25 ka, southern Ethiopia has undergone tremendous climatic changes, from dry and relatively cold during the Last Glacial Maximum (LGM, 25–18 ka) to the African Humid Period (AHP, 15–5 ka), and back to present-day dry conditions. As a contribution to better understand the effects of climate change on vegetation and lakes, we here present a new Predictive Vegetation Model that is linked with a Lake Balance Model and available vegetation-proxy records from southern Ethiopia including a new phytolith record from the Chew Bahir basin. We constructed a detailed paleo-landcover map of southern Ethiopia during the LGM, AHP (with and without influence of the Congo Air Boundary) and the modern-day potential natural landcover. Compared to today, we observe a 15–20% reduction in moisture availability during the LGM with widespread open landscapes and only few remaining forest refugia. We identify 25–40% increased moisture availability during the AHP with prevailing forests in the mid-altitudes and indications that modern anthropogenic landcover change has affected the water balance. In comparison with existing archaeological records, we find that human occupations tend to correspond with open landscapes during the late Pleistocene and Holocene in southern Ethiopia. [ABSTRACT FROM AUTHOR]

The Chew Bahir Drilling Project (CBDP) aims to test possible linkages between climate and hominin evolution in Africa through the analysis of sediment cores that have recorded environmental changes in the Chew Bahir basin (CHB). In this statistical project we used recurrence plots (RPs) together with a recurrence quantification analysis (RQA) to distinguish two types of variability and transitions in the Chew Bahir aridity record and compare them with the ODP Site 967 wetness index from the eastern Mediterranean. The first type of variability is one of slow variations with cycles of ∼20 kyr, reminiscent of the Earth's precession cycle, and subharmonics of this orbital cycle. In addition to these cyclical wet-dry fluctuations in the area, extreme events often occur, i.e. short wet or dry episodes, lasting for several centuries or even millennia, and rapid transitions between these wet and dry episodes. The second type of variability is characterized by relatively low variation on orbital time scales, but significant century-millennium-scale variations with progressively increasing frequencies. Within this type of variability there are extremely fast transitions between dry and wet within a few decades or years, in contrast to those within Type 1 with transitions over several hundreds of years. Type 1 variability probably reflects the influence of precessional forcing in the lower latitudes at times with maximum values of the long (400 kyr) eccentricity cycle of the Earth's orbit around the sun, with the tendency towards extreme events. Type 2 variability seems to be linked with minimum values of this cycle. There does not seem to be a systematic correlation between Type 1 or Type 2 variability with atmospheric CO 2 concentration. The different types of variability and the transitions between those types had important effects on the availability of water, and could have transformed eastern Africa's environment considerably, which would have had important implications for the shaping of the habitat of H. sapiens and the direct ancestors of this species. [ABSTRACT FROM AUTHOR]

The Tulu Kapi syenite-hosted gold mineralization in the Western Ethiopian Shield has been under exploration during the last few decades. The geochemical and petrological characterization of the intrusive rocks and their alterations including the gold hosting syenites are crucial in appraising the economic potential of the mineralized belt on a larger scale. The present study concerns with the geochemical and petrogenetic behaviour of the gold-hosting syenites and other associated intrusions using an integrated field, geochemical and petrological investigation. The Tulu Kapi area is situated within a strongly sheared and NE-SW foliated, low-grade (lower greenschist to lower amphibolite facies) volcano-sedimentary belt (the "Birbir belt") that is intruded by mafic-ultramafic and granitic intrusives (chlorite-serpintine-talc schist, birbirite, metagabbro, metadiorite, metagranite and metasyenite). Major and trace element geochemistry revealed that the gold mineralization hosting syenites, associated diorites and granites are ferroan, calc-alkaline, metaluminous to slightly peraluminous bodies formed in a volcanic arc subduction to syn-collisional tectonic setting by the fractionation of underplated, LREE-enriched basaltic magma with substantial crustal input to possible crustal melting. The underplated basaltic magma was sourced from a LREE-enriched mantle by reworking of sediment laden crustal slabs at depth in a subduction zone. Fractional crystallization resulted in the formation of Ca-rich plagioclase, which continually reacted with hydrothermal fluids to more fractionated Na-rich plagioclase, forming the gold mineralization hosting altered syenites viz. albitization. • Geochemically the Tulu Kapi gold-hosting intrusives are ferroan, calc-alkaline, and metaluminous to slightly peraluminous. • The intrusives formed in a volcanic arc subduction/syn-collisional setting in the southern part of the African Nubian Shield. • The intrusives formed by fractionation of underplated, LREE-enriched basaltic magma with substantial crustal input. • The gold-hosting Tulu Kapi Syenites show strong hydrothermal alteration (albitization). • Continuous interaction of Ca-plagioclase with the hydrothermal fluids resulted in albitized domains. [ABSTRACT FROM AUTHOR]

The Adwa – Yeha felsic plugs and domes are chain of towering inverted cone-shaped isolated plugs and circular domes with wide basal diameters and steep-sided, narrow tops. They form contrasting prominent topography from the Trap basalt ridges of the Adwa – Axum - Tekeze volcanic ridge, located just west of the Northern Afar Depression. The felsic plugs and domes are concentrated in the Adwa – Yeha area, in a zone of about 20 km wide and 30 km long and generally aligned along NNE-SSW direction, parallel to the regional structural grain of the Precambrian basement and the Miocene - Pliocene rift margin faults. In this study, we investigated these felsic plugs and domes using petrological and major and trace element geochemical methods in order to constrain their petrogenetic evolution. Their possible tectonic link to the Western Afar Margin has also been investigated combining our geochemical data, with assessment of regional tectonic setting and geochronological data from previous studies. The results ascertain that the felsic plugs and domes are peralkaline trachytes and peralkaline to sub-alkaline rhyolites, formed by Assimilation Fractional Crystallization (AFC) of basaltic magma which involved removal of olivine, pyroxene, plagioclase, and Fe–Ti oxides, and moderate amount of crustal input. The eruption of the felsic plugs and domes occurred along reactivated Precambrian weakness zones during the formation of the western Afar boundary faults. • The Adwa – Yeha felsic plugs are concentrated along a NNE-SSW aligned zone west of the Western Afar Margin. • The felsic plugs and domes erupted during the Miocene along reactivated Precambrian weakness zones along terrane boundaries. • The eruption of the felsic plugs and domes possibly occurred following the formation of the western Afar boundary faults. • The plugs and domes are peralkaline rhyolites and trachytes. • The felsic plugs and domes are formed by Assimilation Fractional Crystallization of basaltic magma. [ABSTRACT FROM AUTHOR]

An integrated field, petrological, as well as major and trace element geochemical study of a suite of basaltic and associated rhyolitic rocks of the Alaje Formation from the continental flood basalts of the Aiba area of northern Ethiopia has been conducted. The study constrained the geochemical and petrogenetic association of the basaltic and rhyolitic rocks. The results show that the Alaje Formation is constituted by three layers of transitional to tholeiitic basaltic suites intercalated with three layers of alkaline, pantelleritic trachytes/trachy dacites and comenditic rhyolites. The dominant phenocrysts in the porphyritic basalts are plagioclase, with some clinopyroxene, Fe–Ti oxide and olivine. The basalts: (i) have high-Ti concentrations, (ii) show uniform LREE enriched and slightly HREE depleted pattern, and (iii) have low Y/Nb and Zr/Nb ratios, all implying their co-genesis and evolution from homogeneous source parental magma, and their derivation by shallow level fractional crystallization of magma sourced from an enriched component of the mantle. The associated rhyolitic rocks: (i) contain some plagioclase phenocrysts, (ii) plot along the differentiation lines of the associated basalts, (iii) show strong negative anomalies in P, Ti, and Sr, (iv) show general LREE enrichment and HREE depletion, and (v) have very low La/Nb, Rb/Nb, Ta/Nb and Th/Nb ratios. All these suggest their derivation by low-pressure fractionation of mantle derived basaltic magma, with little or no crustal contamination. The rhyolitic rocks of the Alaje Formation from the Aiba area have nearly the same geochemical signatures as other well-constrained rhyolitic rocks of similar stratigraphic context and age in other parts of the Northwestern Ethiopian plateau. • The Alaje Formation is a cyclic intercalation of tholeiitic to transitional basalts and pantelleritic trachytes and rhyolites. • All the basalt layers show uniform geochemical signature implying their co-genesis from homogeneous source parental magma. • The basalts are derived by shallow level fractional crystallization of magma sourced from an enriched mantle component. • The rhyolitic rocks are derived by low-pressure fractionation of mantle derived basaltic magma. [ABSTRACT FROM AUTHOR]

How do we convert variabilities and trends in hundreds of potential parameters that are typically analyzed in the framework of a scientific drilling project to actual climate proxies? Using the case study from the Chew Bahir core from the southern Ethiopian Rift, we will show that deciphering climate information from lake sediments is challenging, because of the complex relationship between climate parameters and sediment composition. Establishing a reliable climate proxy for a new terrestrial archive requires the stepwise development of a profound understanding of both climate-controlled and non-climate controlled processes in the catchment. As a contribution towards an enhanced understanding of human-climate interactions the Chew Bahir Drilling Project, as part of HSPDP (Hominin Sites and Paleolakes Drilling Project) recovered 280 m-long sediment records from a deep, tectonically-bound basin in the southern Ethiopian rift in late 2014. The Chew Bahir record covers the past ~600 ka of environmental history, a critical time period that includes the transition to the Middle Stone Age, and the origin and dispersal of modern Homo sapiens. By deconvolving the relationship between sedimentological processes and geochemical parameters and strongly climate-controlled processes in the Chew Bahir basin, such as weathering (incongruent dissolution), transportation and authigenic mineral alteration, site-specific indicators for climate shifts on different magnitudes are being developed to eventually provide a detailed and reliable climate record. This study uses a multi indicator approach including whole rock and clay mineral analyses (XRD), XRF geochemistry and sedimentology such as grain size analysis. We will illustrate how sensitively the degree of authigenic transformation in especially clay minerals and zeolites has recorded even subtle shifts in the hydrochemistry of paleolake and porewaters, thereby representing a robust tool for differentiating contrasting chemical environments controlled by climatic change. The precise time resolution, largely continuous record and (eventually) a detailed understanding of site specific proxy formation, will give us a continuous record of environmental history on decadal to orbital timescales. Our data enable us to test current hypotheses of the impact of a variety of climate shifts on human evolution and dispersal. [ABSTRACT FROM AUTHOR]

The Chew Bahir Drilling Project (CBDP) aims to test hypothesized linkages between climate and human evolution, dispersal and technological innovation by the acquisition and analysis of long (~280 m) sediment cores that have recorded environmental change in the Chew Bahir basin, southern Ethiopia. In this time-series analysis project, we consider the Chew Bahir palaeolake to be a dynamical system consisting of interactions between its different components, such as the waterbody, the sediment beneath lake, and the organisms living within and around the lake, and humans within the lake catchment. Recurrence is a common feature of such dynamical systems, with recurring patterns in the state of the system reflecting typical influences. Identifying and defining these influences contributes significantly to our understanding of the dynamics of the system.We use methods of linear and nonlinear time series analysis, such as change point detection, semblance analysis and recurrence plots, to identify and classify recurring types of variability and transitions on the time scales of human life spans. For example, we investigate the rapidness of transitions, possible precursor events, and tipping points in our palaeoenvironmental data and discuss their possible impact on the living conditions of humans in the region. First results of the analysis show that we indeed find, as an example, recurring threshold-type transitions, when the Chew Bahir system switched from one stable mode to another, such as from stable wet to dry conditions. Such a rapid change of climate in response to a relatively modest change in forcing appears to be typical of tipping points in complex systems such as the Chew Bahir. If this is the case then the 14 dry events idenfified at the end of the African Humid Period (15–5 kyr BP) could represent precursors of an imminent tipping point that, if properly interpreted, would allow predictions to be made of future climate change in the Chew Bahir basin. [ABSTRACT FROM AUTHOR]

The sediments of the Chew Bahir playa lake in southern Ethiopia were cored down to 280 m depth in the context of HSPDP (Hominin Sites and Paleolakes Drilling Project) and CRC (Collaborative Research Center) 806 "Our way to Europe" projects. The main aim is to reconstruct the paleoenvironmental conditions during the development of anatomically modern humans (AMH) and to test hypotheses about human evolution, dispersal and technological innovation. Based on several dating methods (14C, Ar/Ar, optical stimulated luminescence, chemical fingerprints of tephras) the composite core is shown to cover the last ~600 ka and therefore brackets the time period of important steps in cultural evolution, from Late Acheulean to Middle/Late Stone Age technologies, the origin of AMH, as well as the most recent "Out of Africa" human dispersal events. The multiproxy record of the composite core (e.g., chemical and physical sediment properties, stable C, O and Sr isotope ratios of carbonates, microfossil assemblages and biomarkers) indicates long- and short-time hydroclimatic changes mainly driven by orbital controlled insolation (mostly the Earth's precession ~15-25 ka, but also eccentricity ~90-120 ka). We compare our Chew Bahir data with results from other long marine and terrestrial paleoclimatic records. Here we focus on particularly strong wet and dry fluctuations at Chew Bahir during the last 200 ka to test established hypotheses for human dispersal and technological innovation. The record indicates that at least some of the human dispersal waves have taken place during wetter environmental conditions offering green corridors in East Africa, one of the source regions of our ancestors. [ABSTRACT FROM AUTHOR]

The evaluation of groundwater geochemistry of transboundary aquifers has an important role in the management and sustainable use of groundwater resources in arid and semi-arid regions. This study presents the results of an integrated hydrogeochemical study of the Bulal transboundary aquifers located in the Borena zone, along the Ethiopia-Kenya border. The main aquifers are basic volcanic rocks, subordinate felsic pyroclastic deposits, and metamorphic basement rocks. These aquifers are overlain by alluvio-lacustrine sediments, eluvial soil and regolith. The groundwaters are dominated by Na+ and HCO 3 − and mixed water types. Silicate weathering and evaporation are the dominant hydrogeochemical processes controlling the chemistry of the groundwaters in most parts of the catchment. However, dissolution of evaporitic minerals might have also played a significant role in adding major ions into the groundwater system. Groundwater in the volcanic aquifers are Na–HCO 3 , Ca–Mg–HCO 3 , Na–Ca–HCO 3 and Na–Cl–SO 4 water types while Ca–Mg–HCO 3 , Na–Ca–Cl–SO 4 and Ca–Mg–SO 4 water types are dominant in the metamorphic basement aquifers. The groundwater in the catchment mainly evolved from Na–HCO 3 in the west, Ca–Mg–HCO 3 in the north, and Na–Ca–Cl–SO 4 in the central east and southeast to Na–Ca–HCO 3 type in the southern low-lying areas along the groundwater flow direction. The study has significant implications for the management of groundwater quality in the region. • Groundwater chemistry is investigated using an integrated approach. • Ca–Mg–HCO 3 , Na–Ca–Cl–SO 4 and Na–Ca–HCO 3 are the dominant hydrochemical facies. • Groundwater chemistry is governed by silicate weathering and evaporation. • The study has significant implications for managing groundwater quality. [ABSTRACT FROM AUTHOR]

• Water footprints (WF) for rainfed and irrigated crops in the basin were examined. • The more intensively cultivated western part has higher WFs than the eastern part. • Teff and sorghum have higher green water consumption than maize. • Our novel approach can be used to characterize WFs in other data scarce regions. • Green water resources potential should be accounted in policymaking of the basin. The water resources in the upper Awash basin in central Ethiopia are intensively utilized by the densely populated urban centers and extensive agricultural activities in the wide rift plains surrounding the major cities. The green, blue, grey and total water footprints of major crops dominantly cultivated in the sub-basin (teff , maize, sorghum and sugar cane) are characterized. The water footprints were analyzed for the period 2000 to 2010 using climatic as well as soil and crop yield data from the Debrezeit, Wonji, Melkassa and Metehara stations. The temporal and spatial variations of total water footprints (TWFs) in the basin were analyzed and mapped. The temporal trends of the Water Footprints (WFs) are interpreted using Mann-Kendall and Sen's slope tests. The crop production in the sub-basin mainly depends on green water consumption. Teff and sorghum crops in the climatically similar Debrezeit and Melkassa areas had relatively higher TWFs (4205 m3/ton and 2539 m3/ton, respectively) compared to maize. Blue water requirement to supplement rainfed agriculture decreases from Metehara, Melkassa, Wonji to Debrezeit in that order. The TWF of irrigated sugarcane (117–212 m3/ton) is less than those of rainfed crops such as maize which has a minimum TWF of 1752 m3/ton. The spatial and temporal variations in WFs in the sub-basin are determined by both climatic (effective rainfall, evapotranspiration, length of wet spell and length of growing period) and non-climatic parameters (such as fertilizer consumption, soil types, crop yields and agricultural management practices). Our results suggest cultivating less water-intensive, high-yield crops can significantly decrease the TWFs in the sub-basin. The results could be used to develop well-informed regional and national freshwater resource management policies. More broadly, our novel approach of characterizing WFs at the sub-basin scale using limited amount of locally measured data sets could be a useful tool in other parts of the world where locally measured data sets are scarce. [ABSTRACT FROM AUTHOR]

The Gohatsion Formation consists of a cyclic intercalation of fine siliciclastic and evaporite/carbonate beds and has been subdivided into three informal members, namely the Lower Mudrock Member, the Gypsum Member and the Upper Mudrock Member. Four lithostratigraphic sections were constructed at the Gohatsion, Dejen, Mugher and Jemma localities. Lithofacies analysis of the succession at outcrop and petrographic scales indicate a broad tidal belt influenced by seasonal and regional climate and sea level changes. Integrated lithofacies depositional models for the corresponding informal members have been proposed in order to demonstrate the lithological response to local and global climate change and sea level fluctuations that occurred during the initial phase of the Tethyan Sea transgression during the early to middle Jurassic. Lithofacies of the Lower Mudrock Member show deposition within a siliciclast-dominated back barrier tidal flat system. Deposition of the Gypsum Member occurred in a marine coastal sabkha belt, whereas the Upper Mudrock Member was deposited in a broad coastal shelf prone to seasonal marine flooding. The models show that all the members of the Gohatsion Formation were formed within a broad coastal tidal belt with continental influence and sediment delivery from the northwest, and a slowly encroaching transgressive marine influence from the southeast. • The Gohatsion formation has been reclassified into 3 informal members. • Depositional environment for the Lower Mudrock Member is mixed tidal flat. • Depositional environment of the Gypsum member is marine coastal sabkha. • Depositional environment of the Upper Mudrock Member is a broad coastal shelf. [ABSTRACT FROM AUTHOR]

Six sites in Ethiopia and Kenya, all adjacent to key paleoanthropological sites have been investigated as part of the Hominin Sites and Paleolakes Drilling Project (HSPDP), aiming at an enhanced understanding of climatic influences on human physical and cultural evolution. The recovered sediment cores from the six sites all together span the last ~3.5 Ma. The sediment core records archive environmental change during diverse milestones in human evolution, and times of dispersal and technological and cultural innovation. The 280 m-long Chew Bahir lacustrine record, recovered from a tectonically-bound basin in the southern Ethiopian rift in late 2014, covers the past ~600 ka of environmental history, a time period that includes the transition to the Middle Stone Age, and the origin and dispersal of modern Homo sapiens. Developing a continuous climate history based on sediment core composition is not straightforward because on one hand some indicators might only be preserved intermittently and on the other hand the physical and chemical properties of the sedimentary deposits do not have a linear relationship to climate. Here we present the first outcome of our ongoing work on deciphering direct paleoenvironmental information from authigenic mineral transformations in the long (~280 m) Chew Bahir sediment cores. First results suggest mineralogical and geochemical indicators record wet, dry and hyper-arid climate intervals. Preliminary work suggests that the most extreme evaporative phases are represented by authigenic mineral assemblages including Mg-enriched clays, low-temperature authigenic illite and euhedral analcime. SEM and Energy Dispersive Spectrometer (EDS) analyses confirm that the variations in the analcime abundance that are evident in the XRD dataset seem to be distinctly formed deltoidal icositetrahedrons. These are known to form in highly saline and alkaline brines (pH 9 and higher) and can be associated with pronounced arid phases. Understanding and determining the degree of authigenic mineral alteration in the Chew Bahir records will enable interpretation of µXRF-derived indicators (e.g. K correlated with aridity), and provide direct paleohydrologic data. Together with a well-constrained age-model, our growing understanding of site-specific proxy formation and the establishment of climate proxies for Chew Bahir will provide a robust environmental history on decadal to orbital timescales. [ABSTRACT FROM AUTHOR]

Investigations on short (≤18.8 m) sediment cores retrieved along a NW-SE transect across the Chew Bahir (CB) basin, Southern Ethiopian Rift, have shown that they can provide valuable climate information (Förster et al., 2012). The relationship between mineralogical and geochemical properties of the core samples is closely linked to the hydroclimate history of the region. During dry climate episodes both the illitization of the smectites and the octahedral Al-to-Mg substitution in the phyllosilicate materials has been documented. An enhanced potassium fixation during dry intervals is also linked to the increase in layer charge caused by the authigenic changes in octahedral composition (Förster et al., 2018). The ongoing work, a non-destructive spectral analysis of reflectance in a wide spectral range from 0.3 to 17 µm on selected core samples from both wet and dry intervals from the long (~280 m) cores from Chew Bahir basin supports this interpretation. The spectral range from 0.3 to 6 µm is suitable for investigating the absorption bands of OH, H2O, M-OH lattice vibrations as well as the crystal field transitions of transition metal ions. This allows a detailed examination and differentiation of various clay minerals as well as indications of single primary minerals (olivine and pyroxene). The wavelength range longward 7 µm provides further mineralogical data such as on the presence of feldspars and the results of the short-wave channel to be substantiated. First results show that the main mineralogical structure is characterized by montmorillonite (rare illite and kaolinite are also present). Strongly variable parts of calcite are also spectrally detectable. Characteristic reflectance minima (Christiansen features) close to 8 µm indicate the presence of Ca-rich plagioclase. The high variability of a band close to 1 µm is used together with the spectral information above 7 µm to identify the diverse individual minerals within the olivine, pyroxene and feldspar group minerals. The results are compared with µXRF scan data and will be further verified by petrographic data of the rocks in the catchment. Overall, the presented spectral study (0.3 to 17 µm) is a suitable and non-destructive method to examine the main mineralogical components of the samples. The results can be directly compared with hyperspectral remote sensing data that are available for the Chew Bahir basin.Förster, V., Junginger, A., Langkamp, O., Gebru, T., Asrat, A., Umer, M., Lamb, H., Wennrich, V., Rethemeyer, J., Nowaczyk, N., Trauth, M.H., Schäbitz, F. (2012) Climatic change recorded in the sediments of the Chew Bahir basin, southern Ethiopia, during the last 45,000 years, Quaternary International, 274, 25-37.Förster, V., Deocampo, D., Asrat, A., Günter, C., Junginger, A., Krämer, H., Stroncik, N., Trauth, M.H. (2018) Towards an understanding of climate proxy formation in the Chew Bahir basin, southern Ethiopian Rift. Palaeogeography, Palaeoclimatology, Palaeoecology, 501, 111-123. [ABSTRACT FROM AUTHOR]

Cores from terrestrial archives, such as the lacustrine sediments from the Chew Bahir basin in southern Ethiopia, which cover the last ~600 ka, often reflect both local, regional and global climate influences. In our analysis we were able to identify several time windows in which the Chew Bahir climate is in resonance with regional and global climate change.As a contribution to understanding and differentiating these connections recorded in the Chew Bahir sediments, we have correlated the 2nd principal component of the MSCL based color reflectance values representing wet conditions in the Chew Bahir basin, with the wetness index from ocean core ODP 967 from the eastern Mediterranean Sea. The correlation between these two time series was calculated using the Spearman correlation coefficient in a sliding window. Episodes with high correlation between the two records of wetness could indicate a strong link between both regions, possibly through an increased outflow of the river Nile into the eastern Mediterranean Sea due to higher precipitation values on the Ethiopian plateau.Our preliminary results show that when correlating the two records, two distinct temporal units can be distinguished. Between ~570 ka and ~350 ka the correlation is dominated by cycles that correspond with orbital precession whereas the second unit (after 350 ka) reveals a strong influence of atmospheric CO2. This observation suggests that both orbital precession and atmospheric CO2. may cause a synchronization of different regions in the African climate system, possibly depending on boundary conditions which are still to be identified.As a next step we'll investigate the nonlinear relationships between the two records by focusing on the transition between the two main observed phases. The transition around ~350 kyrs however, is not only highly interesting from a climatic perspective, but it is also a noteworthy period for human cultural evolution as a transition from Acheulean to Middle Stone Age (MSA) technologies takes place at this time. So far our results outline that during this climatically and evolutionary relevant episode a relatively stable, long-lasting, pan-African wet phase may have existed, with possible green corridors connecting the habitats of hominins, and ample resources supporting large population sizes. [ABSTRACT FROM AUTHOR]

Abstract Archaeological findings, numerical human dispersal models and genome analyses suggest several time windows in the past 200 kyr (thousands of years ago) when anatomically modern humans (AMH) dispersed out of Africa into the Levant and/or Arabia. From close to the key hominin site of Omo-Kibish, we provide near continuous proxy evidence for environmental changes in lake sediment cores from the Chew Bahir basin, south Ethiopia. The data show highly variable hydroclimate conditions from 116 to 66 kyr BP with rapid shifts from very wet to extreme aridity. The wet phases coincide with the timing of the North African Humid Periods during MIS5, as defined by Nile discharge records from the eastern Mediterranean. The subsequent record at Chew Bahir suggests stable regional hydrological setting between 58 and 32 kyr (MIS4 and 3), which facilitated the development of more habitable ecosystems, albeit in generally dry climatic conditions. This shift, from more to less variable hydroclimate, may help account for the timing of later dispersal events of AMH out of Africa. Highlights • Multiproxy record from S Ethiopia extends knowledge about environment and climate of past 116,000 yrs during human expansion. • Hydroclimate during Marine Isotope Stage (MIS) 5 was much more variable (frequency and amplitude) than during MIS 3 and 4. • Earth system models and model simulations of intermediate complexity emulate corresponding amplitude shifts in hydroclimate. • Environment was arid during MIS 3 and 4, but permanent lake water bodies existed as inferred from our biological proxies. [ABSTRACT FROM AUTHOR]

Given its proximity to the Strait of Bab el Mandeb and the Red Sea, the Horn of Africa is particularly important for understanding human and faunal migration events to and from Africa. Towards the end of the Pleistocene, the Middle/Later Stone Age (MSA/LSA) transition represents a critical step in human cultural evolution. However, in the Horn of Africa, the environmental conditions associated with this transition remain poorly understood. The Goda Buticha (Buticha cave) sequence, located in southeastern Ethiopia, and dated from ca. 63 ka cal BP to ca. 1 ka cal BP, provides a rare opportunity to examine the environmental contexts associated with major cultural sequences documented in the region during this time period. A preliminary analysis of the rich microvertebrate (and especially rodent) remains recovered from the levels dated between 43 and 4 ka BP identified fourteen different rodent genera, including two species that are locally extinct in southeastern Ethiopia today. While the taphonomic signature is similar throughout the sequence, indicating an in situ accumulation by an owl without major perturbation, the palaeoecological analysis showed environmental change through time, characterized by open-dry setting during the Late Pleistocene, shifting to wetter and more wooded conditions heading to the Holocene. These results are generally consistent with other diverse records which include the large mammals, speleothems and lake basins records, and allow a better understanding of the dynamics of environmental contexts associated with observed cultural change and continuity in eastern Africa from the Late Pleistocene to Late Holocene. [ABSTRACT FROM AUTHOR]

The Main Ethiopian Rift (MER) is renowned as a focus of investigations into human origins. It is also the site of many large volcanic calderas, whose eruptions have spanned the timeframe of speciation, cultural innovation, and dispersal of our species. Yet, despite their significance for dating human fossils and cultural materials, the timing and geochemical signatures of some of the largest eruptions have remained poorly constrained at best. Here, through a programme of field surveys, geochemical analysis and 40Ar/39Ar dating, we report the ages of MER ignimbrites and link them to widespread tephra layers found in sequences of archaeological and paleoenvironmental significance. We date major eruptions of Fentale (76 ± 18 ka), Shala (ca. 145–155 ka), Kone (184 ± 42 ka and ca. 200 ± 12 ka) and Gedemsa (251 ± 47 ka) volcanoes, and correlate a suite of regionally important tephra horizons. Geochemical analysis highlights the predominantly peralkaline rhyolitic melt compositions (7.5–12 wt% Na 2 O + K 2 O, 70–76 wt% SiO 2) across the central MER and remarkable similarity in incompatible trace element ratios, limiting the correlation of deposits via glass composition alone. However, by integrating stratigraphic and geochronological evidence from proximal deposits, lake sediment cores and distal outcrops at archaeological sites, we have traced ash layers associated with the ca. 177 ka Corbetti, ca. 145–155 ka Shala and ca. 108 ka Bora-Baricha-Tullu-Moye eruptions across southern Ethiopia. In addition to strengthening the tephrochronological framework that supports paleoenvironmental and archaeological work in the region, our findings have wider implications for evaluating the hypothesis of a middle Pleistocene 'ignimbrite flare-up' in the MER, and for evaluating the impacts of these great eruptions on landscapes, hydrology, and human ecology. • Quaternary explosive eruptions in the Main Ethiopian Rift linked to palaeoanthropological and archaeological archives. • Review of the Pleistocene calderas of Main Ethiopian Rift. • An improved middle to late Pleistocene tephrostratigraphy for the Ethiopian Rift. [ABSTRACT FROM AUTHOR]

Goda Buticha is a newly discovered cave site in southeastern Ethiopia, containing MSA and LSA cultural material, faunal remains, beads, and human skeletal remains. A 2.3 m-deep sedimentary sequence records two occupational phases separated by a sharp chronological hiatus, in the Upper Pleistocene (∼ 43–31.5 ka cal BP) and in the mid- Holocene (7.8–4.7 ka cal BP). Faunal remains suggest changes in paleoecological conditions that are in agreement with patterns documented in regional speleothem-based reconstructions. The lithic assemblage at the base of the sequence is clearly MSA, with Levallois production, unifacial and bifacial points, relatively large debitage and use of local raw materials, associated with a microlithic component. The overlaying LSA assemblage contains diagnostic artifacts (backed microliths and bladelet production), with ubiquitous use of obsidian and MSA elements that appear in the Holocene. In the absence of indications for post-depositional mixture, the apparent cultural continuity of MSA elements from the Upper Pleistocene into the Middle Holocene at Goda Buticha may represent yet another variation of the elusive MSA/LSA transition. Goda Buticha is a key site for reevaluating the dynamics and tempo of this transition in eastern Africa. [ABSTRACT FROM AUTHOR]

The horn of Africa provides the setting for the evolution of early modern humans and their dispersal out of Africa as well as for the entry, many thousands of years later, of pastoralists who brought Near Eastern and, later, South Asian livestock into Africa. However, significant gaps remain in our understanding of the late Upper Pleistocene archaeological record of the horn of Africa, mainly due to the paucity of well-stratified sites from the period. The discovery in southeastern Ethiopia of a number of caves with rich Upper Pleistocene and Holocene archaeological deposits, many of which also had rock art depicting domestic animals, offers an unprecedented opportunity for exploring the later prehistory of the region. In 2007, 2008 our survey documented twenty-one cave sites and shelters with evidence of cultural deposits, including Middle Stone Age (MSA) and Later Stone Age (LSA) stone artifacts, faunal remains, and rock art. Active and fossil speleothems, important for paleoclimatic reconstructions and chronology, were found from two other caves in eastern and western Harerghe. Test excavations were conducted at three sites, with abundant archaeological material documented from stratified deposits at two of these sites – Gilbo Tate and Goda Buticha. The latter is a subject of another paper in this volume. Rock art was recorded at eighteen sites, three of which (in western Harerghe) had not previously been documented. At many of the sites, much of the art is faded and in a vulnerable state, and continued efforts to document and conserve this art are urgently needed. [ABSTRACT FROM AUTHOR]

Abstract: East African paleoenvironments are highly variable, marked by extreme fluctuations in moisture availability, which has far-reaching implications for the origin, evolution and dispersal of Homo sapiens in and beyond the region. This paper presents results from a pilot core from the Chew Bahir basin in southern Ethiopia that records the climatic history of the past 45 ka, with emphasis on the African Humid Period (AHP, ∼15–5 ka calBP). Geochemical, physical and biological indicators show that Chew Bahir responded to climatic fluctuations on millennial to centennial timescales, and to the precessional cycle, since the Last Glacial Maximum. Potassium content of the sediment appears to be a reliable proxy for aridity, showing that Chew Bahir reacted to the insolation-controlled humidity increase of the AHP with a remarkably abrupt onset and a gradual termination, framing a sharply defined arid phase (∼12.8–11.6 ka calBP) corresponding to the Younger Dryas chronozone. The Chew Bahir record correlates well with low- and high-latitude paleoclimate records, demonstrating that the site responded to regional and global climate changes. [Copyright &y& Elsevier]

Abstract: Landslide hazard is one of the crucial environmental constraints for the development of Ethiopia, representing a limiting factor for urbanization and infrastructures. The high relief and the rugged topography induced by a strong Plio-Quaternary uplift, the occurrence of clayey horizons within the sedimentary sequences, the dense network of tectonic fractures and faults, the thick eluvial mantles on volcanic outcrops, and the thick colluvial–alluvial deposits at the foot of steep slopes are the predisposing factors for a large variety of mass movements. Heavy summer rainfall is the main triggering factor of most landslides, some of which undergo a step-like evolution with long-lasting quiescence intervals. First generation movements are commonly restricted to shallow phenomena, such as soil slips or mud flows in eluvial–colluvial material. Fast moving slope failures, such as rock slides, topplings and falls, are also triggered by earthquakes. To mitigate the landslide risk, any first priority measure should include adequate drainage of slopes in order to reduce water infiltration. On the other hand, appropriate site selection for buildings, transferring risky settlements, accurate geological control of works, and education campaigns are all strongly recommended. [Copyright &y& Elsevier]

Despite eastern Africa being a key location in the emergence of Homo sapiens and their subsequent dispersal out of Africa, there is a paucity of long, well-dated climate records in the region to contextualize this history. To address this issue, we dated a ∼293 m long composite sediment core from Chew Bahir, south Ethiopia, using three independent chronometers (radiocarbon, 40Ar/39Ar, and optically stimulated luminescence) combined with geochemical correlation to a known-age tephra. The site is located in a climatically sensitive region, and is close to Omo Kibish, the earliest documented Homo sapiens fossil site in eastern Africa, and to the proposed dispersal routes for H. sapiens out of Africa. The 30 ages generated by the various techniques are internally consistent, stratigraphically coherent, and span the full range of the core depth. A Bayesian age-depth model developed using these ages results in a chronology that forms one of the longest independently dated, high-resolution lacustrine sediment records from eastern Africa. The chronology illustrates that any record of environmental change preserved in the composite sediment core from Chew Bahir would span the entire timescale of modern human evolution and dispersal, encompassing the time period of the transition from Acheulean to Middle Stone Age (MSA), and subsequently to Later Stone Age (LSA) technology, making the core well-placed to address questions regarding environmental change and hominin evolutionary adaptation. The benefits to such studies of direct dating and the use of multiple independent chronometers are discussed. • Four independent dating methods applied to ∼293 m lake core from southern Ethiopia. • Reveals 620 ka high-resolution sedimentary record near key fossil hominin sites. • Mean accumulation rate of 0.47 mm/a comparable to other African lacustrine sediments. • Accumulation rate fell to 0.1 mm/a during MIS 2, likely due to reduced sediment supply. • Use of multiple independent chronometers is a powerful approach in lake settings. [ABSTRACT FROM AUTHOR]

Many Plio-Pleistocene lake basins in eastern Africa associated with early hominins contained waters that were alkaline, enriched in silica due to weathering of volcaniclastics and hydrothermal activity, and evaporatively concentrated. Such conditions are favorable for the formation of silicate minerals precipitated from solution, or neoformed through alteration of detrital parent material. The most common authigenic silicates thus produced include the zeolite family of minerals and a number of clay minerals, particularly 2:1 clays of the illite and smectite families. Particularly in the absence of well-preserved paleoecological records, these minerals may provide important evidence of paleoenvironmental conditions. Stratigraphic variations in lacustrine authigenic silicates can give an indication of changes in cation proportions in paleolake waters over time. For example, in Pliocene deposits of the Baringo Basin, Kenya, fluctuations between phillipsite (K-rich) and analcime (Na-rich) facies suggest changing salinity levels because more saline waters have greater Na/K ratios. In one interval in the Chemeron Formation, analcimic muds are interbedded with freshwater diatomites, suggesting a link between high amplitude of environmental variability and peak orbital eccentricity ~2.6 Ma. In the Lake Magadi basin in southern Kenya, marked increases in zeolite abundance and greater dominance of Na-rich phases indicate hydrological closure and enhanced evaporative concentration suggesting a long-term increase in aridity accelerating ~380 ka. In short cores of the Chew Bahir basin of southern Ethiopia, greater analcime abundances and incipient low-temperature illitization of smectite (indicating greater K uptake in more saline waters) are associated with Late Pleistocene arid episodes such as the Younger Dryas. In the Olduvai Basin of northern Tanzania, fluctuations in the Al/Mg ratio of authigenic clay minerals record changes in salinity, as greater Mg is incorporated into clays during saline episodes. These clay mineral changes are accompanied by shifts in the oxygen isotope composition of structural oxygen, indicating equilibrium with variably saline waters. Both elemental and isotopic changes fluctuate over precessional timescales, suggesting orbital control of hydrologic balance ~1.8 Ma.Authigenic silicates can be an important source of paleolimnological data, particularly over the range of salinities between the relatively freshwater conditions under which biological proxies readily accumulate, and the extreme salinities associated with evaporites such as halite and trona (Na-carbonate). [ABSTRACT FROM AUTHOR]

The Kenyan and Ethiopian rifts in eastern Africa are known for their diverse landscape, ranging from arid and semi-arid savannahs to high and lush mountainous regions, where anatomically modern humans were present since ~195 ka BP. Lacustrine sediments and paleo-shorelines indicate water availability fluctuated dramatically during this period from deep fresh water lakes, to shallow highly alkaline lakes, to completely desiccated lakes. To investigate the role lakes have played through time as readily available water sources to humans, an enhanced knowledge of the pace as well as the magnitude of these changes near key paleo-anthropological sites in eastern Africa is essential. Hydro-balance models are used to calculate paleo-precipitation rates and the potential pace of lake level changes. Such models, which were successfully applied to numerous lake basins in Kenya, could prove similarly useful for investigating paleo-lake basins in Ethiopia. However, these models did not consider changes in hydrological connectivity during humid periods, which may have led to an overestimation of paleo-precipitation rates. Here we present a comprehensive hydro-balance modelling approach that simulates multiple rift lakes from the southern Ethiopian Rift (Abaya, Chamo, Chew Bahir) simultaneously, considering their temporal hydrological connectivity. During the high stand at the peak of the African Humid Period (AHP, 15-5- ka), the lakes were hydrologically linked and display cascade-like behavior, flowing southwards from Abaya to Chamo to Chew Bahir and finally spilling over into Lake Turkana. We further used the Surface Energy Balance Algorithm for Land (SEBAL) to calculate the evaporation of Lake Chew Bashir's catchments and used the energy balance to determine possible paleo-evaporation conditions due to shifts in precipitation patterns. The results suggest an increase in the long-term precipitation trend of 20.6% to 28.6% throughout the whole Southern Ethiopian Rift is necessary to fill Lake Chew Bahir to its overflow level. Furthermore, it was demonstrated that Lake Chew Bahir was highly dependent on the water supply from the upper lakes Abaya and Chamo and dries out within ~30 years if the hydrological connection is cut off and the precipitation amount decreases to present day conditions. Several of such rapid lake level fluctuations, from a freshwater to a saline lake, might have occurred during the termination of the AHP, when humid conditions were less stable due to a change in precessional cycle. Fast changes in fresh water availability requires high adaptability for humans living in the area and might have caused strong migration pressure towards more favorable regions such as the Ethiopian Highlands within single generations or even less. [ABSTRACT FROM AUTHOR]

Eastern African hydroclimate in the early Holocene created a lush landscape in what iscommonly referred to as the African Humid Period (AHP: ∼15 to 5 ka). The termination ofthe AHP was characterised by a climatic shift towards drier conditions. This resulted in thedesiccation of many lakes and may have pressured hunter-gather societies to move towardsconcentrated pastoralist settlements at the shores of the few remaining lake areas or rivervalleys. During the AHP, Lake Chew Bahir, in the East African Rift System, was presumablyexpansive with a paleo-shoreline ∼30 m higher than present day, and likely served as animportant freshwater source and refugia. Today it is a predominantly dry playamudflat with ephemeral swamps in the deltaic areas. Strontium (Sr) isotope ratios(87Sr/86Sr) preserved in carbonate-rich lacustrine strata provide regionally-specificrecords of past variability in weathering and regional drainage patterns. Duringhumid episodes, the Chew Bahir catchment expands northwards to include theChamo and Abaya catchments. As these catchments are dominated by volcaniclithology, with low Sr isotopic ratios, additional water inflow from here can potentiallychange the overall Sr isotope ratio of the lake water in Chew Bahir in a measurableway. This study aims to reconstruct the hydrobalance of paleolake Chew Bahir using athree-step approach. We first establish the Sr isotope ratio of the input end members bysampling modern waters from the Chew Bahir and adjacent catchments, includinggroundwater, lakes, springs and rivers. We then analyse the Sr isotope ratios of microfossilsfrom the time period of the most recent AHP lake level high-stand from three shortcores (CB05, CB06 and CB03) along a transect from the centre to the westernmargin of the Chew Bahir basin. Finally, we use the paleo Sr isotope record over thelast 15 ka to develop an isotopically-enabled hydrobalance model to quantify pastlake levels. Over the last ∼15 ka 87Sr/86Sr ranges from 0.7059 to 0.7066, withhigher values during the start of the AHP, decreasing towards the termination. Thissuggests a larger input of water entering paleolake Chew Bahir from the northerlycatchments and paleo-connectivity of these lake systems during humid periods.This study provides valuable data for reconstructing millennial-scale change inhydrobalance and freshwater availability, in a highly-sensitive climate region, overa key time period for the transition from hunter-gather societies to pastoralism. [ABSTRACT FROM AUTHOR]

Efforts to date the oldest modern human fossils in eastern Africa, from Omo-Kibish 1-3 and Herto 4,5 in Ethiopia, have drawn on a variety of chronometric evidence, including 40 Ar/ 39 Ar ages of stratigraphically associated tuffs. The ages that are generally reported for these fossils are around 197 thousand years (kyr) for the Kibish Omo I 3,6,7 , and around 160-155 kyr for the Herto hominins 5,8 . However, the stratigraphic relationships and tephra correlations that underpin these estimates have been challenged 6,8 . Here we report geochemical analyses that link the Kamoya's Hominid Site (KHS) Tuff 9 , which conclusively overlies the member of the Omo-Kibish Formation that contains Omo I, with a major explosive eruption of Shala volcano in the Main Ethiopian Rift. By dating the proximal deposits of this eruption, we obtain a new minimum age for the Omo fossils of 233 ± 22 kyr. Contrary to previous arguments 6,8 , we also show that the KHS Tuff does not correlate with another widespread tephra layer, the Waidedo Vitric Tuff, and therefore cannot anchor a minimum age for the Herto fossils. Shifting the age of the oldest known Homo sapiens fossils in eastern Africa to before around 200 thousand years ago is consistent with independent evidence for greater antiquity of the modern human lineage 10 ., (© 2022. The Author(s).)