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International audience; Pleistocene archaeology records the changing behaviour and capacities of early hominins. These behavioural changes, for example, to stone tools, are commonly linked to environmental constraints. It has been argued that, in earlier times, multiple activities of everyday life were all uniformly conducted at the same spot. The separation of focused activities across different localities, which indicates a degree of planning, according to this mindset characterizes later hominins since only 500,000 years ago. Simbiro III level C, in the upper Awash valley of Ethiopia, allows us to test this assumption in its assemblage of stone tools made only with obsidian, dated to more than 1.2 million years (Myr) old. Here we first reconstruct the palaeoenvironment, showing that the landscape was seasonally flooded. Following the deposition of an accumulation of obsidian cobbles by a meandering river, hominins began to exploit these in new ways, producing large tools with sharp cutting edges. We show through statistical analysis that this was a focused activity, that very standardized handaxes were produced and that this was a stone-tool workshop. We argue that at Simbiro III, hominins were doing much more than simply reacting to environmental changes; they were taking advantage of new opportunities, and developing new techniques and new skills according to them.

National audience; Silicon (Si) is the most abundant element on the earth’s surface after oxygen. Si can be found in minerals, electronic chips, cosmetic products, and plants for instance. Here we review the Earth's terrestrial Si cycle, focussing on ecosystem services. We show that silicon can participate in the inherent and manageable properties involved in all ecosystem services. As records of the past, phytoliths can be useful parameters in cultural services. Si is involved in provisioning services because Si may influence the production of food and fibers. Si is also involved in regulating services because of Si involvement in carbon sequestration. Regulating and provisioning services may be improved through Si management, e.g. by application of Si to fertilize soils and plants.

During the Neogene, major tectonics events occurred: uplift of mountain ranges (including the Tibetan Plateau and surrounding regions), opening and closing of seaways, and large variations of atmospheric CO2 and sea level. What were the consequences of such changes on the dispersal of hominoid populations? We focus on the Miocene to Pliocene time interval (23 Ma-2.6 Ma). First, we analyze the spread of hominoids from their original geographic range, the tropical forests of Africa during the Early Miocene to the first expansion to Eurasia during the mid-Miocene Climate Optimum. Niche modelling combined with paleoclimatic simulations, provides means to circumvent the fragmentary nature of this record. We identify how the large climatic changes during Miocene Transition impact the potential habitats of hominoids and compare our findings to both the related fossil records and paleoenvironmental proxies.Second, we analyze human distribution during the Mid to Late Pliocene (4-3 Ma), i.e. before the triggering of the large perennial Greenland ice sheet, and of huge amplitude northern hemisphere glacial interglacial cycles, while CO2 evolved between 400 and 300 ppm. In Africa, tropical areas experienced drastic hydrological changes, mainly driven by precession cycles, which deeply modulated monsoon intensity and precipitation patterns, as illustrated by the paleoshore level record of Mega Lake Chad. To explore how orbital parameters strongly modify hydrological cycles over tropical Africa and, the associated dispersion of the genus Australopithecus, we simulated the response of climate, vegetation, and hydrological cycles of the mid to Late Pliocene conditions.For both geological contexts, we provide and analyze a series of Earth System models (IPSL-CM5A2 LR-low resolution-) coupled simulations. Moreover, we associate these fully-coupled simulations with high resolution atmosphere-only model simulations, and a dynamic vegetation model (ORCHIDEE). Both models were used to estimate ecological niches with a spatial resolution of 50 km.We describe the imprint of slow climate changes during the Miocene Climate Transition (MCT) as well as more rapid climate evolution during mid to Late Pliocene, associated with higher frequency oscillation of orbital parameters.This study demonstrates how, for these periods, climate and especially hydrological variations were pivotal to the understanding of hominoid migrations. We compare our findings to fossil records and paleoenvironmental proxy reconstructions.To conclude, we discuss the strengths and limitations of such approaches, which were made possible through a large trans-disciplinary effort between paleontologists, paleoanthropologists, paleoenvironmentalists, paleoclimatologists, and niche modelers.

International audience; Dissolution is one among several taphonomical processes that may bias paleoenvironmental, paleoclimatic or taxonomic interpretation of phytolith assemblages. To improve our understanding of dissolution on grass phy-toliths, we studied systematic changes of surface features, morphotype assemblages, and dissolution rates of phytoliths extracted from two grass species Hyparrhenia involucrata (Panicoideae), Nastus borbonicus (Bambu-soideae), one soil from La Re ' union Island (approximate mean age < 800 yr), and three paleosols from Ethiopia (approximate age of 4.4 million years). We used heavy-liquid to extract phytoliths, and 1% Na2CO3 to perform partial dissolution experiments. Physicochemical surface properties, morphotypes, and assemblages were analyzed using optical and scanning electron microscopy, laser diffraction, and X-ray diffractometry. Our results show that 1) phytoliths from different grass species may have different dissolution rates: phytoliths from the leaves of Hyparrhenia involucrata (Panicoideae) are more prone to dissolution than those from Nastus borbonicus (Bambusoideae). 2) Silicon (Si) released by phytolith assemblages (i.e., phytolith dissolution rate) decreases as follows: plant > soil > paleosol. 3) Dissolution leads to cavity formation on phytolith surfaces and disappearance of fragile silica particles. 4) Partial dissolution does not significantly change percentages of common grass phytolith morphotypes in a given assemblage. These results provide a benchmark for assessing the reliability of paleoenvironmental reconstructions using grass phytolith assemblages from buried soils and sediments.

GDR Rift colloquium 2022Collection of abstracts. This conference was an opportunity to review current research in the Rift or on the Rift,and share and discuss during targeted workshops. These workshops were the place to initiate new projects, launch new collaborations, enrich our sometimes too disciplinary visions, and exchange. The colloquium was also a moment dedicated to a joint reflection on target areas, federating observatories allowing the acquisition, sharing, and distribution of interdisciplinary data over the long term. Specific workshops were proposed to identify and build these target areas with our Rift partners. We gathered 70 students and researchers, and 36 abstracts were presented either during oral presentation or with posters.

International audience; While in tropical soils recycling of plant phytoliths has been shown to represent a major pool of Si available for plants, the main Si pools available for plants in temperate soils are still poorly constrained. We characterised the various Si pools of temperate forested and cultivated soils in France by selecting seven paired sites (adjacent wheat and forest plots) for four soil groups: Luvisols, Albeluvisols, calcaric and hypereutric Cambisols. We showed that CaCl2-extracted Si (bioavailable) is mostly controlled by pH and allophanes (short-range ordered aluminosilicates) but not by phytoliths. Cultivation, by decreasing the soil organic carbon content increases the allophane content and the SiCaCl2 concentration. Our work highlights the importance of allophanes as the missing link between the soil solution and the clay minerals that could explain the reported correlation between the clay mineral content and bioavailable Si.

International audience; Abstract: In order to understand mammalian evolution and compute a wide range of biodiversity indices, we commonly use the ‘bioregion’, a spatial division adapted to ecological and evolutionary constraints. While commonly conducted byneontologists, the establishment of bioregions in palaeontology is generally a secondary analysis, shaped on subjective time scales and areas specific to the investigated questions and groups. This heterogeneity, coupled with the scale dependency of biodiversity indices, prevents the clear identification of macroecological and macroevolutionary trends for large taxonomic groups like extinct mammals. Here we tackle this issue by providing a coherent framework for Neogene and Pleistocene mammals of the Old World following two steps: (1) a temporal scale adapted to mammalian evolutionary history (i.e. evolutionary fauna) is defined by poly-cohort analysis; (2) bioregions are then computed for each evolutionary fauna by clustering, ordination and intermediate approaches at multiples spatial scales (i.e. continental to regional) for Eurasia and Africa. Additionally, providing a coherent framework for a wide range of mammalian datasets, our results show: (1) the synchronous emergence and fall of five mammalian evolutionary faunas identified at chronological scales varying from the epoch to the geological stage; (2) a transition from a longitudinal to a latitudinal biogeographical structuring between the Miocene and Pliocene, especially in Europe; (3) the long-term affinity of southern Asian with African faunas, in sharp contrast with the modern Palaearctic bioregion extension; and (4) the establishment of a vast Mediterranean bioregion from fragmented areas in the Late Miocene to its full extent in the Pleistocene.

13 pages; International audience; Kisima Ngeda (KN), a spring on the northern margin of saline Lake Eyasi, Tanzania, sustains an Acacia-Hyphaene palm woodland and Typha swamps, while the surrounding vegetation is semi-desert. To study the vegetation changes associated with this spring, which represents a plausible modern analog for the fossil springs documented in the nearby paleoanthropological and archaeological sites of Olduvai Gorge, we analyzed the pollen content of a 43 cm-long sediment core that documents vegetation changes since the last ~1200 years (from cal yrs. C.E. 841 to 2011). Our results show that (1) Hyphaene palms, which require meso-halophytic soil conditions were most abundant in the area of the coring site until cal yrs. C.E. ~1150 when the groundwater supplying the KN spring was likely lower than at present, allowing intrusions of saline lake waters. (2) From cal yrs. C.E. ~1200, a peat began to develop, the palm woodland was replaced by a Mimosaceae woodland, and the increased presence of Typha pollen indicates the presence of more wetlands. (3) From cal yrs. C.E. 1600, the groundwater level of the KN spring increased and reached its highest level in the last 1200 years. (4) Peaks of wetland expansion, which reflect increased groundwater flow and level in response to amplified rainfall in the recharge area (Mt Oldeani, Ngorongoro Highlands), occurred at cal yrs. C.E. ~1200–1400 and ~1650–2011. These outflows of groundwater at Kisima Ngeda were linked to the intensity and frequency of positive Indian Ocean Dipole (IOD) events, which trigger heavy rains in eastern Africa. We conclude that the Kisima Ngeda hydrological system, which has been active for more than 1200 years, responds rapidly to regional climate change driven by changes in the sea surface temperatures (SSTs) of the Indian Ocean. Yet, it is also capable of remaining active during dry intervals as inferred from the Kisima Ngeda record prior to cal yrs. C.E. 1200. Our results support the hypothesis that this type of system helped to maintain Plio-Pleistocene hominin populations and activities in the arid lowlands of the rift on a multi-decennial scale.

International audience; Pliocene and Pleistocene sediments from West Turkana (Kenya, East African Rift System) form emblematic syn-rift successions for understanding the evolution of extensional basin and continental rifting. They also constitute world-renowned fossil-bearing strata from which >500 hominin fossils were discovered over the past decades, with >100 inventoried archeological sites. However, associated sedimentary dynamics and architectures as well as paleoenvironments are only partially reconstructed and the relative contribution of climate and tectonism to paleoenvironmental change over time remains unclear. Here, through the interpretation of sedimentary facies, the delineation of sequences and the analysis of δ13C in soil carbonates, we provide the first exhaustive reconstruction from ~4 to ~0.75 Ma of (i) fluctuations of the paleolake that occupied the Turkana Depression, (ii) the successive sedimentary dynamics and related paleolandscapes that characterized the West Turkana area and (iii) respective roles of climate and tectonism in the sedimentation. We show evidence for seven major transgression-regression (T-R) cycles between ~4 and ~ 0.75 Ma superimposed locally by lower amplitude T-R cycles., Comparing the sedimentological interpretations and the δ13C values in soil carbonates (literature data), we reveal that fluctuations of rainfall over the Ethiopian Dome, which hosts the drainage basin of the Omo River — the main tributary of Lake Turkana — controlled high-amplitude lake level fluctuations during the Plio-Pleistocene period. We also demonstrate that vegetation and tree cover evolved differently in the Omo Valley and West Turkana. Furthermore we outline that two different sedimentary systems reflecting two distinct modes of sedimentation alternated through times in the West Turkana area as a response to the variations in sediment supply coming from the western rift shoulder (i.e. Lapurr Range) that alternatively generated wave- or river-dominated sedimentary systems. In conclusion, we reveal that climate regulated water input, paleolake water-level fluctuations and vegetation. Tectonism determined sediment supply to the basin controlled in West Turkana by pulses of increased activity of the main border fault (i.e., the Murua Rith Lapurr Fault).

International audience; Understanding Plio-Pleistocene paleoenvironments in the East African Rift and how they have changed over time is fundamental across geosciences, the most emblematic being perhaps their role in hominin evolution. In the northern Turkana Depression, among the three main Formations of the Omo Group, the Nachukui Formation is exposed on the western shore of present-day Lake Turkana. It consists of a > 700 m succession of fluvial-deltaic-paralic-lacustrine sediments deposited between ca. 4.00 and ca. 0.75 Ma, which have been extensively investigated using depositional environments and sequence analyses during the RiLakS project. Additionally, we use δ13C isotopic ratios in soil carbonates as a proxy of paleovegetation.Facies and sequence analyses reveal that proto-lake Turkana experienced 7 high-amplitude Transgression-Regression (T-R) cycles between ca. 4.00 and 1.25 Ma, which are locally superimposed by lower amplitude, secondary T-R cycles. Paralic or offshore depositional environments are observed quasi-continuously, at least in basinward sections, which suggest a more prolonged persistence of lacustrine conditions than hitherto accepted. Remarkable match between reconstructed evolution of palaeolake level and evolution of woody cover in the Lower Omo Valley suggests that rainfall in the drainage basin of the Omo river, i.e. rainfall over the Ethiopian dome, controlled high-amplitude paleolake fluctuations during the Plio-Pleistocene whereas rainfall in West Turkana had only limited influence. Additionally, we reveal that variation in sediment supply from the rift shoulder caused two different sedimentary dynamics, i.e. accommodation-dominated and supply-dominated systems, to alternate during the deposition of the Nachukui Formation, likely due to successive pulses of activity of the border fault.Finally, a reconstruction of paleolake fluctuation in the Turkana Depression is proposed and successive sedimentary paleolandscapes are presented. Respective influences of climate (local to regional) and tectonic (i.e. border fault activity) on paleoenvironments are deconvoluted. Our work highlights that the continuous reconstruction of depositional environments at various localities in a well-constrained chronological context is essential to reliably reconstruct paleoenvironments. However, until now, such powerful approach remains rarely associated with traditional site by site investigations.

The late Pliocene corresponds to a large cooling over Northern Hemisphere associated with sporadic occurrences of glaciations. The most important event occurred during the marine isotope stage M2 (MIS M2, 3.312–3.264 Ma) when a large glaciation took place with a sea level drop from 20 to 60 m, but its duration is short and the summer insolation forcing change at 65°N is weak. De Schepper et al (2013) invoked to explain the onset and termination of this glaciation with the opening and closing of the Central American Seaway (shallow CAS). Based on their hypothesis, we have intensively studied the onset mechanism of MIS M2 through a series of sensitivity experiments using the IPSL AOGCM and the asynchronous coupling with an Ice sheet model (GRISLI). Our results demonstrate that the shallow CAS helps to precondition the low-latitude oceanic circulation and affects the related northward energy transport, but cannot alone explain the onset of the M2 glaciation, the most important contribution on MIS M2 are from the large change of pCO2 as well as the internal feedbacks of vegetation and ice sheet. Moreover, we have also investigated the period from the late Pliocene to the early Pleistocene (3-2.5 Ma) through a transient-like simulation using the same AOGCM and ISM. This enables to simulate the Greenland Ice Sheet (GRIS) onset and development using the pCO2 reconstructions from different proxies. All these simulations were analyzed with emphasis on cryosphere and focused on the Northern Hemisphere (mid-to-high latitudes). Here we used the same modeling simulations but with a focus over the tropical Africa. We first depict the large changes of temperatures and hydrological cycle produced over this area during these two periods and compare our data to reconstructions. Moreover, by prescribing our climate results as inputs for the vegetation model (Biome4), we compare more directly the simulated plant functional types (PFTs) with that constructed by the pollen data. In addition, we further quantify the respective impact of various driving factors on these PFTs variations.

The Turkana Depression consists of several Oligocene to Pliocene North-South oriented half-grabens that connect the Ethiopian and Kenyan rift valleys within the eastern branch of the Cenozoic East African Rift System. In the northern portion of the Turkana Depression, exposed on the west side of modern Lake Turkana, is the Nachukui Formation that consists of a > 700 m pile of fluvial-deltaic-lacustrine sediments deposited between 4.2 and 0.7 Ma. The Nachukui Fm is a world-class fossil-bearing succession into which more than 500 hominin fossils were discovered, including major discoveries for the understanding of Human evolution and more than 100 archaeological sites. Most significant discoveries include Australopithecus anamensis, Kenyanthropus platyops, Paranthropus aethiopicus, Paranthropus boisei and specimens of Homo (i.e., H. rudolfensis and H. erectus) and early members of H. sapiens, as well as the earliest evidence of Acheulean stone tool technology and, more recently, the most primitive Lomekwian stone tool technology. Palaeoenvironmental changes may have had a strong influence on evolution, including that of the human lineage. However, in the Turkana Depression, palaeoenvironments are still very partially reconstructed and the respective role of climate and tectonism is still debated. Here, we used the interpretation of depositional environments, the delineation of depositional sequences and a record of d13C in pedogenic carbonates (i.e. paleovegetation proxy) to reconstruct 1) palaeolake Turkana fluctuations between ca. 4 and ca. 1.2 Ma and 2) the successive sedimentary palaeoenvironments and resulting landscapes that characterized the West Turkana area during the same time interval. Facies and sequence analyses reveal that palaeolake Turkana experienced eight low-frequency transgression-regression (T-R) cycles between ca. 4 and ca. 1.2 Ma; superimposed lower amplitude and shorter duration T-R cycles are also locally identified revealing subordinate-order fluctuations. In the same time, two different palaeolandscapes (labelled type-1 and type-2) alternated through times revealing variations in sediment supply coming from the western rift shoulder. A statistical treatment of the d13C record using a modified k-mean clustering allows us to confront a paleovegetation proxy and the sedimentological record. This combined approach reveals that the evolution of rainfall over the Ethiopian dome (i.e., drainage basin of the Omo river) controlled long-term palaeolake Turkana fluctuations during the Plio-Quaternary period while tectonism likely controlled the occurrence of different palaeolandscapes in West Turkana forced by changes in the rate of sediment supply. Finally, our study shows that traditional methods of basin geology (i.e., facies and sequence analysis) are key tools to provide large-scale paleolandscape reconstructions and palaeolake fluctuations needed for investigating the interactions between hominins and palaeoenvironments. Such a powerful procedure, however, is rare for hominins sites and has yet to be integrated in the workflow utilized by the paleontology and archeology communities.This is a contribution of the Rift Lake Sedimentology project (RiLakS).

International audience; During the mid-to-late Pliocene (ca. 4–3 Ma), several hominin species were present in central Sahel, eastern andsouthern Africa. The potential for the discovery of hominin remains from this interval is limited by the availabilityof exposed Pliocene deposits and the ability to investigate them. As a result, most discoveries have beenmade in the Afar region of Ethiopia and in the Lake Turkana basin, thus unveiling only a portion of Pliocenehominins' probable geographical presence. In this study we provide a continental view of geographic areaspotentially accessible to these hominins. To do so, we estimate the climatic envelope suitable for mid-to-latePliocene hominin presence, using the earth system model IPSL-CM5A and the Maxent habitat suitability algorithm.Our analysis reveals high habitat suitability for these hominin species in semi-arid regions where annualthermal amplitude and mean annual precipitation are moderate, mostly corresponding to tropical xerophyticshrublands. Our habitat model estimates geographically continuous, suitable climatic conditions for homininsbetween central Sahel and northeastern Africa, but not between eastern and southern Africa. This discontinuitysuggests that southern African and eastern African hominins were separated by an environmental barrier thatcould only be crossed during particularly favourable periods or by undertaking long-range dispersal overclimatically hostile habitats. Under climate conditions of northern hemisphere summer at perihelion this climaticbarrier is not present. In contrast, the Turkana basin, the Laetoli region, and a large part of southern Africaremain suitable for all precession angles, suggesting that these areas may have functioned as refugia. The constantpresence of these stable areas combined with the periodic establishment of corridors for dispersion canpotentially explain hominin diversity in eastern Africa.

International audience; Pollen grains are valuable paleoclimate and paleovegetation proxies which require extensive knowledge of morphotypes and long acquisition time under the microscope. The abundance of damaged, folded, and broken pollen grains in the fossil register and sometimes also in modern soil and sediment samples, has so far prevented automation of pollen identification. Recent improvements in machine learning, however, have allowed reconsidering this approach. Here we present an automated approach which is capable of assisting palynologists with poorly preserved pollen samples. Called multi-CNNs, this approach is based on multiple convolutional neural networks (CNNs) integrated in a decision tree system. To test it, we built a system designed for three botanical families very common in the modern and fossil pollen assemblages of Eastern Africa, namely Amaranthaceae, Poaceae, and Cyperaceae. Our system was tested on stacked optical images of 8 pollen types (6 Amaranthaceae, 1 Poaceae, 1 Cyperaceae) using a training dataset of 1102 intact pollen grains and three validation datasets of intact (276 grains), damaged (223 grains), and fossil pollen (97 grains). We show that our system successfully recognizes intact, damaged, and fossil pollen grains with very low misclassification rates of 0%, 2.8%, and 3.7%, respectively. The use of augmentation on stacked optical images during the training increases classification accuracy. Following a palynologist's approach, our system allows grains without obvious characters to be classified into a class of high taxonomic level or as indeterminable pollen. This is the first software able to process grains with a wide range of taphonomical stages, which makes it the first truly applicable to automated pollen identification of fossil material.

Si is one of the most abundant element on earth and an abundant literature shows its beneficial effects on plant growth and resistance. We here question the influence of termites, as key soil bioturbators, on the distribution of Si in a tropical soil. The abundance and forms of Si in termite mounds build by Odontotermes obelus (TM) or in the soil eroded from TM but redistributed on the ground surface (EROD) were compared to those measured in the 0-5 (Ctrl(0-5)) and 70-120 cm soil layers (Ctrl(70-120)). Although termites use the soil from Ctrl(70)-(1)(20) for building their mounds, we found that TM and EROD had intermediate soil physical, chemical and mineralogical properties between Ctrl(0-5) and Ctrl(70)(-1)(20). Clay content was not significantly different between soil materials. However, the lower variability measured in TM than in the soil suggested that termites used soil layers with higher amounts of clay fraction and with a preference especially for layers enriched in 2:1 clay minerals (smectite) most likely because they provide better physical properties in terms of plasticity and water retention than kaolinite. Finally, phytoliths and bioavailable Si (Si-CC) contents were increased in TM in comparison with Ctrl(70)(-1)(20), suggesting an incorporation of phytoliths in termite construction through their saliva and/or an increasing availability of Si-CC from the minerals. In conclusion, this study highlights how termites, through their feeding and building activities, impact Si distribution in tropical soils.

International audience; A fossil hominin cranium was discovered in mid-Pliocene deltaic strata in the Godaya Valley of the northwestern Woranso-Mille study area in Ethiopia. Here we show that analyses of chemically correlated volcanic layers and the palaeomagnetic stratigraphy, combined with Bayesian modelling of dated tuffs, yield an age range of 3.804 ± 0.013 to 3.777 ± 0.014 million years old (mean ± 1σ) for the deltaic strata and the fossils that they contain. We also document deposits of a perennial lake beneath the deltaic sequence. Mammalian fossils associated with the cranium represent taxa that were widespread at the time and data from botanical remains indicate that the vegetation in the lake and delta catchment was predominantly dry shrubland with varying proportions of grassland, wetland and riparian forest. In addition, we report high rates of sediment accumulation and depositional features that are typical of a steep topographic relief and differ from younger Woranso-Mille fossil localities, reflecting the influence of active rift processes on the palaeolandscape. Q1 Until recently, field work in the Woranso-Mille area (Afar, Ethiopia) has concentrated on exposures along the Mille River that include more than 120 m of fossiliferous sedimentary and volcanic strata that are between 3.8 and 3.2 million years (Myr) old. East of Korsi Dora (Fig. 1a), sedimentary sequences that are younger than the extra-regional approximately 3.57-Myr-old Kilaytoli tuff 1 have yielded specimens of at least two hominin species, Australopithecus afarensis and Australopithecus deyiremeda 2-5

International audience; Hominins evolved in Africa during a period of overall regional cooling, drying, and increasingly variable climate. Despite prevailing regional aridity since the mid-Miocene, data show that early hominins Sahelanthropus tchadensis, Orrorin tugenensis, and Ardipithecus ramidus lived in environments made of mosaics of grasslands, mixed grasslands, woodlands, and forests, where wooded habitats were maintained by edaphic rather than regional (climatic) humidity. Groundwater systems (springs, seeps, shallow aquifers) and surface water (rivers, lakes), locally create wetter and more wooded environments in addition to that supported by precipitation alone. However, edaphically sustained woodlands are rare to missing in most published paleoeclogical interpretations of hominin archeological sites. To explore the importance of groundwater to the record of hominins in Africa, we provide newly acquired field data from spring sites in the Awash Valley, Ethiopia, and Lake Eyasi-Lake Manyara region, Tanzania, and re-evaluate published data from the Ardipithecus-bearing Aramis Member, Ethiopia. Results show that (1) in arid Eastern Africa, a wide variety of microhabitats such as groundwater-fed wetlands, Hyphaene palm woodlands, Phoenix reclinata palm woodlands, and structurally complex and species-rich forest patches exist due to local variability of geologic, topographic, and hydrologic conditions. (2) These microhabitats carry some characteristic pollen and phytolith signals, that may be easily masked by the signal of surrounding grass-dominated shrublands and grasslands. (3) The Aramis Member (Awash Valley, Ethiopia), which is to date, the best documented paleo-groundwater ecosystem, is not a riparian habitat. It is one of N 50 examples (within 22 geographically distinct areas) in Africa and the Middle East where evidence of groundwater systems co-exist with hominin and/or archeological remains. Springs are commonly localized features of limited area within a landscape, but provide ecological continuity through time and diverse microhabitats, some of which may be densely forested. At the local scale, springs create microclimates, distinctive vegetation, and increase soil nutrients, species richness, structural complexity, and provide habitat for animals. At the landscape scale, they represent hydro-refugia favoring increased connectivity among animals and allowing migrations during dry periods. We conclude that in the East African Rift where low, highly seasonal rainfall and high evaporative demand limit vegetation growth in many areas, groundwater-fed zones create diverse microhabitats and play a major role in ecosystem functioning. It is likely that, within a context of increasing aridity and expansion of grass-dominated open habitats during the Mio-Pliocene, early hominins and many other animals viewed edaph-ically sustained woodlands as attractive habitats.

A fossil hominin cranium was discovered in mid-Pliocene deltaic strata in the Godaya Valley of the northwestern Woranso-Mille study area in Ethiopia. Here we show that analyses of chemically correlated volcanic layers and the palaeomagnetic stratigraphy, combined with Bayesian modelling of dated tuffs, yield an age range of 3.804 ± 0.013 to 3.777 ± 0.014 million years old (mean ± 1σ) for the deltaic strata and the fossils that they contain. We also document deposits of a perennial lake beneath the deltaic sequence. Mammalian fossils associated with the cranium represent taxa that were widespread at the time and data from botanical remains indicate that the vegetation in the lake and delta catchment was predominantly dry shrubland with varying proportions of grassland, wetland and riparian forest. In addition, we report high rates of sediment accumulation and depositional features that are typical of a steep topographic relief and differ from younger Woranso-Mille fossil localities, reflecting the influence of active rift processes on the palaeolandscape.

International audience

Assessing the dynamics of the silica cycle in the critical zone remains challenging, particularly within the soil, where multiple processes are involved. To improve our understanding of this cycle in the Tropics, and more specifically the role played by vegetation, we combined elemental Si mass balance with the delta Si-30 signatures of the compartments involved in the waterplant-rock interactions of a tropical forested watershed, Mule Hole (Southern India). To accomplish this, we analysed (1) the d30Si values of present-day litter phytoliths from tree leaves and grass, as well as soil amorphous silica (ASi); (2) the Si isotope fractionation induced by phytolith dissolution; (3) the silicon mass balance inferred from isotopes at the soil-plant scale; and (4) the consistency between water sources and the delta Si-30 signatures in the ephemeral stream. The delta Si-30 values of present-day litter phytoliths and soil ASi vary within a narrow range of 1.10-1.40 parts per thousand for all samples, but two deep vertisol samples which likely trapped phytoliths from different vegetation growing under more humid conditions, as indicated by pollen analysis. A homogeneous signature of litter is a minimum condition for using delta Si-30 as a proxy for the litter/phytolith source of Si. However, litter-ash dissolution experiments demonstrate that the incipient dissolution of phytoliths fractionates Si isotopes, with the preferential dissolution of 28 Si over 30 Si yielding delta Si-30 values as low as -1.41 parts per thousand. Values close to the whole-sample signatures, i.e., above 1 parts per thousand, were recovered in the solution after a few hours of water-ash interaction. At the soil-plant scale, the average delta Si-30 value of soil-infiltrating solutions is slightly lighter than the average phytolith signature, which suggests phytoliths as the source of soil dissolved Si. The isotopic budget of dissolved Si within the soil layer, which was obtained based on previous elemental fluxes, is imbalanced. Equilibrating the isotopic budget would imply that up to 4100 mol ha(-1) yr(-1) of silica is taken up by vegetation, which is almost twice as large as that initially estimated from the elemental budget. The additional Si flux taken up, and likely stored in woody stems, was estimated assuming that Si isotopes followed a steady-state model for the whole Si plant uptake and then followed a Rayleigh model once in the plants. The delta Si-30 value of the additional Si flux taken up should be close to 0 parts per thousand, i.e., enriched in light Si isotopes compared to the litter. If steady-state conditions apply, the source could correspond to soil ASi dissolution or deep (saprolite) root uptake. At the outlet of the watershed, the stream exhibits low delta Si-30 values (0.28-0.71 parts per thousand) during peak flows and high delta Si-30 values (1.29-1.61 parts per thousand) during the recessions at the end of the rainy season. Heavy delta Si-30 signatures are consistent with the expected domination of seepage at the end of floods. The light delta Si-30 values during peak flow are slightly lower than the overland flow signature and reflect either a sampling bias of overland flow or a minor but significant contribution of another Si source within the stream, possibly the partial dissolution of phytoliths from the suspended load, with slight isotopic fractionation. This study confirms that vegetation controls the silicon cycle in this dry tropical forest. It also shows that silicon isotopes yield a better grasp of the mass balance and sources and potential mechanisms involved than the consideration of only silicon concentrations. However, this proxy still relies on working hypotheses, notably steady-state and/or Rayleigh fractionation models, which need to be confirmed in further studies. (C) 2018 Elsevier Ltd. All rights reserved.

International audience; At present, Lake Chad (∼ 13 • N, ∼ 14 • E) is a shallow freshwater lake located in the Sahel/Sahara region of central northern Africa. The lake is primarily fed by the Chari-Logone river system draining a ∼ 600 000 km 2 watershed in tropical Africa. Discharge is strongly controlled by the annual passage of the in-tertropical convergence zone (ITCZ) and monsoon circulation leading to a peak in rainfall during boreal summer. During recent decades, a large number of studies have been carried out in the Lake Chad Basin (LCB). They have mostly focused on a patchwork of exposed lake sediments and outcrops once inhabited by early hominids. A dataset generated from a 673 m long geotechnical borehole drilled in 1973, along with outcrop and seismic reflection studies, reveal several hundred metres of Miocene-Pleistocene lacustrine deposits. CHADRILL aims to recover a sedimentary core spanning the Miocene-Pleistocene sediment succession of Lake Chad through deep drilling. This record will provide significant insights into the modulation of orbitally forced changes in northern African hydroclimate under different climate boundary conditions such as high CO 2 and absence of Northern Hemisphere ice sheets. These investigations will also help unravel both the age and the origin of the lake and its current desert surrounding. The LCB is very rich in early hominid fossils (Australop-ithecus bahrelghazali; Sahelanthropus tchadensis) of Late Miocene age. Thus, retrieving a sediment core from this basin will provide the most continuous climatic and environmental record with which to compare hominid migrations across northern Africa and has major implications for understanding human evolution. Furthermore, due to its dramatic and episodically changing water levels and associated depositional modes, Lake Chad's sediments resemble maybe an analogue for lake systems that were once present on Mars. Consequently, the study of the subsurface biosphere contained in these sediments has the potential to shed light on microbial biodiversity present in this type of depositional environment. We propose to drill a total of ∼ 1800 m of poorly to semi-consolidated lacustrine, fluvial, and eolian sediments down to bedrock at a single onshore site close to the shoreline of present-day Lake Chad. We propose to locate Published by Copernicus Publications on behalf of the IODP and the ICDP. 72 F. Sylvestre et al.: The Lake CHAd Deep DRILLing Project (CHADRILL) our drilling operations onshore close to the site where the geotechnical Bol borehole (13 • 28 N, 14 • 44 E) was drilled in 1973. This is for two main reasons: (1) nowhere else in the Chad Basin do we have such detailed information about the lithologies to be drilled; and (2) the Bol site is close to the depocentre of the Chad Basin and therefore likely to provide the stratigraphically most continuous sequence.

More than 40 years of scientific investigations of the hominin bearing Plio-Pleistocene sediments of northern Tanzania have provided a number of paleobotanical data, which, taken as a whole, provide today a way to investigate vegetation changes between 4 and 1 Ma, at a time when our early ancestors emerged. Here, I have integrated the data from all vegetation proxies obtained for the paleontological sites of Laetoli, Olduvai, and Peninj (i.e. macroscopic plant remains, pollen and phytolith assemblages, carbon and oxygen isotopic ratios measured on carbonates, and organic biomarkers). This important, yet discontinuous botanical record suggests some similarities between past and present-day vegetation at the regional scale: Afromontane forests with Olea , Podocarpus , Juniperus , Hagenia abyssinica in the highlands, and wooded grasslands with grasses and drought-adapted Acacia , Commiphora , Capparidaceae, and Chenopodiaceae and/or Amaranthaceae in the lowlands were present in the southern Serengeti–Crater Highlands region since 4 Ma. Grasses of the C 4 photosynthetic type made their first appearance in the record at ∼3.7 Ma, i.e. during the mid-Pliocene, ∼700 ky before major p CO 2 and temperature decline. C 4 grasses became dominant in the vegetation soon after (∼3.66 Ma), probably in response to reduced precipitation. At ∼2.6 Ma, phytolith and isotope indicate grassland with abundant C 4 xerophytic grasses that document strong aridity during the Intensification of Northern Hemisphere Glaciation period (∼2.7–2.5 Ma). After 2 Ma, the detailed and diverse record at Olduvai indicates complex vegetation patterns linked to oscillating precipitation, varying lake levels, and the presence of geological faults. Hence, despite low (basin-averaged) reconstructed paleo-precipitation amounts of ∼250–700 mm/y, C 4 -grasslands, closed woodlands, wetlands, and palm-groves co-occurred on short spatial scales near saline Lake Olduvai. Freshwater wetlands and palm-rich woodlands occurred in highly localized areas on the lake margins, where aquifer barriers and/or outcrops caused by geologic faults allowed groundwater discharge. Botanical evidence of paleo-springs at Laetoli, Olduvai, and Peninj includes the marked presence of Typha (cattail) and Hyphaene (palm tree) in association with Acacia pollen grains, and (at Olduvai) abundant forest indicator phytoliths and organic and isotopic biomarkers. At Olduvai, freshwater wetlands were most developed when lake level and fluvial competence where low, i.e. during dry periods. When wet–dry climate variability was extreme in East Africa (∼1.9–1.7 Ma), freshwater springs may therefore have offered a sustainable habitat (i.e. refuge) for several species, including hominins, and favored hominin and artifact concentration at these specific places, particularly during environmentally stressful times.

We have analyzed the phytolith content of 37 samples from the paleosol capped by Tuff IC dated 1.84 Ma within Middle Bed I at Olduvai Gorge, Tanzania. Samples were obtained from different trenches sampling an area of about 25 ha to document the paleovegetation associated with the abundant faunal remains and hominin artifacts in FLK, AMK, PTK and DS sites. The analysis reveals the abundance of globular granulate and forest indicator phytoliths (from 3% to 86% relative to the total number of phytoliths in the assemblages) attributed to woody plants, and of short cell grass phytoliths (up to 22%). The presence of palm phytoliths (up to 57%) attests for meso-haline soils in the area in agreement with the presence of the saline/alkaline Olduvai paleolake and one (or more) groundwater discharge areas (freshwater springs and/or wetland). Phytoliths provide botanical evidence for a mixed paleovegetation dominated by forest and woodland with patches of open-spaces occupied by grasses, prior to the deposition of Tuff IC. The presence of fern phytoliths in some assemblages suggest shaded and humid habitat, which supports the presence of freshwater (watercourses or springs) that might have attracted hominins and other animals. Yet, we have found that our phytolith extractions (residues) also include micrometric zeolites (chabazite, clinoptilolite, phillipsite), which attest that the phytolith signal in the Zinj paleosols is certainly affected by dissolution. This study completes the spatial analysis of the area and reveals that the wooded area extends north, south, and west of FLK Zinj, with palm trees preferentially located in the periphery, like the Zinj, AMK, and DS sites. The phytolith-inferred distribution of plants does not support the hypothesis that topography was influential in the location of these sites, particularly given that trees and/or shrubs were dominant all over. Rather, it is the presence of freshwater ponds that seem to have been the attractive factor for hominins at this particular place and time.

International audience; The role of silicon (Si) in alleviating biotic and abiotic stresses in crops is well evidenced by empirical studies; however, the mechanisms by which it works are still poorly known. The aim of this study is to determine whether or not phytolith composition and distribution in wheat are affected by drought and, if so, why. Durum wheat was grown using hydroponics in the presence of polyethylene glycol (PEG)-6000 to perform a water-stress simulation. We developed an original method for in situ analysis of phytoliths in leaves via X-ray imaging. PEG was efficient in inhibiting water uptake by roots and creating stress, and prevented a small fraction of Si from being accumulated in the shoots. The application of Si with PEG maintained shoot and root fresh weights (FW) and relative water content at higher values than for plants without Si, especially at PEG 12%. Our data show that, under water stress in the presence of Si, accumulation of phytoliths over the veins provides better support to the leaf, thus allowing for a better development of the whole plant than in the absence of Si. The development of silicified trichomes in durum wheat depends primarily on the availability of Si in soil and is not an adaptation to water stress.

AMK (Amin Mturi Korongo) is a newly discovered site situated under Tuff IC (Bed I, 1.84 Ma). It contains several fossiliferous levels and the top one is situated on the same paleosurface as FLK-Zinj. For the first time this allows sampling the “Zinj” paleoenvironment well into the Secondary Gorge and expands the known area of this paleolandscape. Fossils found at this site show exceptional preservation. Several articulated units have been discovered, indicating minimal postdepositional disturbance and rapid sedimentation. This assemblage allows a general estimation of time span (the most elusive variable in archaeological analyses) for the formation of AMK. Phytolith analyses have discovered a dense palm forest at the site, expanding the forested area known on the slightly elevated platform that contains the FLK-Zinj – FLK-NN – PTK sites. Although a few artifacts have been discovered in the vicinity of AMK, the site was mostly naturally (i.e., non-anthropogenically) formed. This is of major relevance to determine that factors other than forested habitats must have influenced the formation of anthropogenic sites on the same platform as AMK in the Olduvai lacustrine basin.

Paleovegetation studies are essential to ecologically frame hominin evolution. The analysis of the phytolith content of 22 paleosol samples collected along the vertical sequence of the channel containing the BK (Bell's Korongo) archaeological levels, provided evidence of the paleovegetation that accompanied the evolution of the riverine system that formed this site 1.353 million years ago, when climate was particularly arid. The analysis reveals the abundance of forest indicator phytoliths (46% to 92% of the assemblages), rare grass silica short cells and sedges phytoliths (up to 15% of assemblages), and palms (up to 10% of the phytolith assemblages). The vegetation of the BK fluvial system was therefore characterized by abundant woody plants. It did not vary significantly diachronically in the period of time under scrutiny. The alluvial paleovegetation corresponds well to the fluvial dynamic that formed BK, including the presence of sterile samples recovered in areas where the water traction changed the soils frequently. This spot of dense paleovegetation together with the fluvial watercourse (in a paleolandscape likely dominated by sparse/open vegetation) could have been attractive, seasonally, for animals and hominins.

We analyzed phytolith and diatom remains preserved at 45 Miocene and Pliocene localities dated between 8 and 1 Ma in northern Chad (16-17 degrees N). Some of these localities yielded cranial remains, lower jaws, and teeth of the hominin species Australopithecus bahrelghazali (similar to 3.6 Ma) and Sahelanthropus tchadensis (similar to 7 Ma). Of the 111 sediment samples analyzed, 41 yielded phytoliths, 20 yielded diatoms, and seven yielded both phytoliths and diatoms. Freshwater planktonic and tychoplanktonic diatom species, indicative of lacustrine conditions, are dominant (>91%) in the samples. The phytolith assemblages indicate an opening of the vegetation and a general trend toward an expansion of grass-dominated environments during the time spanning the two hominin occurrences in Chad. The phytoliths suggest the presence of a mosaic environment, including closed forest patches, palm groves, and mixed/grassland formations, between 7.5 and 7 Ma, the replacement by palm grove-like vegetation at approximately 6.5-5 Ma, and the presence of exclusive grass-dominated formations after 4.5 Ma. The type-locality of S. tchadensis (TM266) was likely similar to modern palm grove formations with an arboreal cover percentage >= 40%. The type locality of A. bahrelghazali (KT12) was a grass-dominated ecosystem (likely savanna) with an unrated percentage of arboreal cover. Furthermore, the grass phytolith data support the existence of a (recurrent) Sahelian-like dry climate in northern Chad since at least 8 Ma. Therefore the local closed vegetation formations in the Djurab region at 7.5-7 Ma were sustained by aquatic systems (such as lakes or related rivers, marshes) rather than by extensive annual precipitation.

The cycles of C and Si are closely related to the weathering of silicates. In both cycles, terrestrial plants make significant contributions to the weathering budget and soil formation. The perturbation of the terrestrial Si cycle by human occupation has become a challenging issue because of possible impact on the equilibrium of aquatic ecosystems and agriculture sustainability. The recycling of Si stored in plants as phytoliths may control the Si cycle in the short-term. A review of the recent literature shows that the biogeochemical cycling of Si that is generally not impacted by atmospheric input or fertilisation, is significantly altered by agriculture through the depletion of the phytoliths pool. We present here new evidence that the exportation of straw can lead to the depletion of the soil phytoliths pool in ∼10 years. In order to maintain the current levels of Si in crops, the contribution of other soil silicates such as clay minerals to the phytoavailable silica pool may become a key parameter, when straw is exported.

This study presents mineralogical and geochemical data from a borehole drilled near the locality of Bol (13 degrees 27'N, 14 degrees 44'E), in the eastern archipelago of the modern Lake Chad (Chad). Samples were taken from a similar to 200 m long core section forming a unique sub-continuous record for Central Africa. Among these samples, 25 are dated between 6.4 and 2.4 Ma. Dominant minerals are clays (66% average) mixed with varying amounts of silt and diatomite. The clay fraction consists of Fe-beidellite (87% average), kaolinite, and traces of illite. Clay minerals originate from the erosion of the vertisols that surrounded the paleolake Chad. Sedimentological data indicate that a permanent lake (or recurrent lakes) existed from 6.7 until 2.4 Ma in the vicinity of Bol. By comparison with modern latitudinal distribution of vertisols in Africa the climate was Sudanian-like. Changes in the sedimentation rate suggest a succession of wetter and dryer periods during at least six million years in the region during the critical time period covering the Miocene-Pliocene transition.

Starch granules have been found to be preserved in association with archaeological remains and their identification may provide direct botanical evidences of the plants used by ancient humans. However, subtle morphological differences between starch granules make their taxonomic identifications difficult. In order to improve the identification of these plant remains, we used an image analysis program that measures up to 123 different optical and morphological characters. With Random Forest tests we analyzed ~ 5000 starch granules extracted from underground storage organs (USO), seeds, and fruits of 20 different East African edible plant species. Our results show that correct identification rates are up to 74% for some species ( Echinochloa colona, Cyperus rodundus) , ~ 80% for some suprageneric taxa (Poaceae, Fabaceae), and 80% for underground storage organs. However, on average, success rates are just ~ 53% for species (up to 70% with a dataset reduced to herbaceous species), 60% for families, and 72% for plant parts. Yet, this automated system is not perfect, but it is still more powerful than the human eye, for which the average success rate is just of 25% for species level identifications. We evaluated the performance of our system and found that accuracy rates of identifications of starch granules are highly sensitive to the number of groups (species) to identify (r 2 = 0.83) and, to a lesser extent to the number of characters used by the identification system (r 2 = 0.87). It is therefore crucial to narrow down as much as possible the number of target species, by analyzing additional proxies. We conclude that better results can be achieved if the candidate field is narrowed. If not, the automated identification of starch granules will remain unsatisfactory to provide acceptable interpretations in archaeological contexts.

Few proxies exist to identify aridity in the depositional record, although drylands cover ca 30% of the modern continental surface. New exposures in a siliciclastic and carbonate sequence in an arid to hyperarid basin at Olduvai Gorge, Tanzania provide a unique multi‐proxy record of a 1·85 Ma landscape that was exploited by early humans. The 2 m thick sequence of clastics and carbonates that are exposed along a 450 m outcrop records climate change over a single precession (dry‐wet‐dry) cycle. Siliciclastic data (sedimentary structures, grain size, mineralogy) and biological data are combined with data for a 10 to 35 cm thick limestone (stable isotopes, elemental geochemistry, petrography) to generate a depositional facies model for a site DK (Douglass Korongo) on this dry rift basin landscape. This site was situated on a low gradient, distal portion of a volcaniclastic alluvial fan. The clastics are intercalated distal alluvial fan sandy silts and lake clays that accumulated in a low energy environment. Groundwater discharge and the alkaline springs and seeps during wet‐to‐dry change in climate made a freshwater carbonate‐rich environment. Bedded lithofacies (a lime mudstone with fossils) were deposited in shallow standing (spring‐fed) pools, while nodular lithofacies with calcite spherulites indicate permanently saturated ground (seeps). Both environments experienced similar diagenesis, that is, the precipitation of authigenic barite from supersaturated groundwater, desiccation and pedogenesis, and late‐stage calcite precipitation. Compositional and isotopic data suggest that a fresh groundwater‐fed system was available to early humans even during dry intervals of the precession cycle. ISSN:2055-4877

International audience; Climate influences terrestrial Si and C cycles. To evaluate how drought influences Si dynamics in African savannahs we studied 12 sites along a climatic gradient of precipitation and drought-stress in South Niger. We analysed plant traits and Si (phytolith) content in 12 specimens of a drought adapted grass species (Pennisetum pedicellatum Trin.), and in surface soils. Phytolith/amorphous silica (ASi) was quantified by the 1%Na2CO3 (nc) digestion method, and the acid plus heavy-liquid extraction method (bz). Phytolith morphotypes were also analysed under the microscope. Our results show that with increasing drought-stress (decreasing AET/PET and precipitation, and increasing temperature), ASi in P. pedicellatum (ApSinc and ApSibz) increases, while ASi in soils (AsSibz) decreases. ApSinc shows higher correlation with precipitation of the wettest month (Pwet, r = −0.84, p < 0.001), AET/PET (r = −0.73, p < 0.01) and length of dry season (r = 0.83, p < 0.001) than with AsSibz (r = −0.59, p < 0.05). Plant height increases with increasing precipitation (r = 0.61, p < 0.05). Leaf area is positively correlated with AsSibz (r = 0.81, p < 0.01). Bulliform phytoliths in P. pedicellatum growing under driest climate represent up to 12% of the leaf phytolith assemblage and just 2% in specimens sampled south of ∼13°N at more humid sites. Thus, the abundance of silicified bulliform cells is strongly negatively correlated with Pwet (r = −0.92, p < 0.001) and AET/PET (r = −0.93, p < 0.001). Other intra-specific variations, e.g. the length of bilobate phytoliths, are not observed along the climatic gradients documented here. We conclude that drought and evapotranspiration rates influence plant height and leaf size, increase Si uptake by the C4 grass P. pedicellatum, and favour silicification of the bulliform (motor) cells triggering leaf movements. In surface soils, greater phytolith accumulation is likely due to higher plant productivity and weaker soil erosion at humid sites.

International audience; Dendritic phytoliths that precipitate in grass inflorescences are often used in archaeology to trace the use of cereals (i.e. grasses harvested for their edible grain) and their domestication by early human societies. High amounts of these morphotypes are sometimes interpreted in terms of cereal accumulation in archaeological contexts. In sub-Saharan Africa, few cereals were domesticated during the mid-Holocene, but many wild grasses are still largely harvested by modern societies for food. The harvesting of wild cereals is also considered as one of the first stages toward early grass domestication. To evaluate how well dendritic phytoliths and/or other phytoliths produced in the grass inflorescences could help trace the use of wild cereal grains in sub-Saharan Africa, we analyzed the phytolith content of 67 African species (including 20 wild cereals), and 56 modern soils. We used test-value analysis and ANOVA to evaluate how well grass inflorescences could be distinguished from leaf/culm parts based on their phytolith content. We also measured the abundances of these phytoliths in natural soils from sub-Saharan Africa to provide a benchmark percentage abundance above which anthropogenic accumulation may be suspected in archaeological deposits. Our results confirm that, although rondel type phy-toliths are abundant, only the dendritic phytolith morphotype is exclusive to the grass inflorescences. Yet, dendritic phytoliths do not occur in all species. They happen to be most frequent and found in greatest abundance (>34% relative to total phytolith count) in Panicoideae grasses (Sehima ischaemoides, Sorghastrum stipoides, and Sorghum purpureo-sericeum), and in one Eragrostideae species (Eragrostis squamata), which are not considered cereals. Inflorescences of the wild African cereals studied here do not happen to be particularly rich in dendritics (>3% relative to sum of grass silica short cell phytoliths plus dendritics are likely to indicate anthropogenic accumulation of grass inflorescences. Yet, the absence or low abundance of dendritic phytoliths in archaeological deposits may not always indicate the absence of anthropogenic accumulation of grass inflorescence material.

There is an increasing body of evidence showing that land use may affect the concentration and flux of dissolved silica (DSi) and amorphous, biogenic Si particles (ASi/BSi) in surface waters. Here, we present a study of riverine waters collected within the Kaveri River Basin, which has a long history of land occupation with + 43% population increase in the watershed during the last 30 years associated with agricultural practices including canal irrigation from reservoirs and, more recently, bore well pumping. We report total dissolved solids (TDS) and suspended material (TSM) for 15 river stations and 5 reservoirs along the Kaveri itself and its main tributaries sampled during pre-monsoon, monsoon and post-monsoon periods in 2006 and 2007. The TDS in the Kaveri River globally increases from the upper reaches (humid to sub-humid climate) to the lower reaches (semi-arid climate), and at a given station from monsoon (M) to hot season (HS). The DSi concentrations range from 129 μmol L − 1 (M) to 390 μmol L − 1 (HS) in the main Kaveri stream and reaches up to 686 μmol L − 1 in the Shimsha River (HS). Our results indicate that DSi and the main solutes of the Kaveri River have not drastically changed since the last 30 years despite the population increase. The pollution index of Van der Weijden and Pacheco (2006) ranges from 13% to 54% but DSi does not seem to be affected by domestic wastewater. ASi is mostly composed of diatoms and phytoliths that both play roles in controlling DSi. We suggest that DSi and ASi delivered to the cultivated areas through irrigation from reservoir may have two important consequences: increasing Si bioavailability for crops and limiting Si flux to the ocean.

A geomorphological, sedimentological, stratigraphic, and geometric study of 30 trenches excavated around FLK Zinj (Bed I, Olduvai Gorge) has enabled the partial reconstruction of the paleolandscape surrounding this site for a radius of similar to 1000 m. This is the largest sample of geological and archaeological information yet available to reconstruct the topography, ecology, and geomorphology of the Zinj paleosurface and the hominin activities preserved within it. Contrary to previous interpretations, which place FLK Zinj on an isolated and narrow peninsula, it appears that the site was located on the edge of an elevated platform traceable for hundreds of meters. Hominins created FLK Zinj (and other sites, such as the recently discovered PTK and AMK) within the wooded habitats of this platform rather than the more open and grassy environments situated on lower portions of the lacustrine floodplain. Input areas, probably in the form of alluvial fans, existed to the south, following a North-South direction. These input areas are partially responsible for changes in the type sequence. Restricted erosion documented on the wooded platform was mostly caused by runoff processes. An archaeological study of the excavated trenches reveals a sharp contrast in fossil and stone tool density between FLK Zinj and the surrounding landscape, further supporting the contention that the site may have acted as a "central place" where repeated carcass transport, butchery, and consumption took place. Taphonomic studies indicate that at this stage of human evolution, hominins had primary access to carcasses and were not dependent on other carnivores for obtaining meat.

International audience; The multi component FLK North archaeological site was discovered over 50 years ago, and its interpretation has been highly controversial since. Explanations of the dense bone and stone tool accumulation range from a site on a featureless lake margin that is dominantly anthropogenic in origin to a site near a freshwater wetland that is dominated by carnivore activity (e.g. felids and hyenas). FLK North occurs stratigraphically between the Ng'eju Tuff (1.818 AE 0.006 Ma) and Tuff IF (1.803 AE 0.002 Ma), and is composed of 9 distinct levels. Analysis of newly recovered fossil bones and artifacts has shown that the bones of large animals are largely the product of felid hunting and feeding behavior, followed by hyena gnawing and breakage of some bones. The expanded sample of felid prey remains is significant for understanding the contrasts between the mortality profiles of fossil assemblages produced by carnivores and those produced by hominins. Geologic mapping in the environs of the site has revealed rich sedi-mentological and paleoecological records and a thin, but persistent tuff (here named Kidogo Tuff) that is w1.5 m below Tuff IF. Electron microprobe analyses of the tuff mineralogy revealed a unique geochemical fingerprint that permits its use for correlation of widely separated outcrops and facilitates the high resolution reconstruction of the landscape at the time of site formation. The 9 archaeological levels comprise a relatively continuous record through a Milankovitch precession cycle (dry-wet-dry). As the lake receded into the central basin during the dry part of the cycle, surface water supplies dwindled and groundwater-fed springs and wetlands became the dominant freshwater supply. The FLK North archaeological record essentially ended when level 1 was covered with 0.4 m of Tuff IF in a violent volcanic eruption of nearby Mt. Olmoti. However, the overlying Bed II sediments contain scattered archaeological material and a freshwater carbonate deposit that is similar to those found associated with other Bed II archaeological sites, e.g. VEK, HWK and HWKE. The recognition of the ecological association of springs, wetlands and archaeological remains is a powerful predictive tool for locating new archaeological sites in this region that is known for hominin remains.

Davis, B.A.S. et al., Modern pollen samples provide an invaluable research tool for helping to interpret the quaternary fossil pollen record, allowing investigation of the relationship between pollen as the proxy and the environmental parameters such as vegetation, land-use, and climate that the pollen proxy represents. The European Modern Pollen Database (EMPD) is a new initiative within the European Pollen Database (EPD) to establish a publicly accessible repository of modern (surface sample) pollen data. This new database will complement the EPD, which at present holds only fossil sedimentary pollen data. The EMPD is freely available online to the scientific community and currently has information on almost 5,000 pollen samples from throughout the Euro-Siberian and Mediterranean regions, contributed by over 40 individuals and research groups. Here we describe how the EMPD was constructed, the various tables and their fields, problems and errors, quality controls, and continuing efforts to improve the available data.

International audience; Recent excavations at FLK North (Olduvai Gorge, Tanzania) have produced new information on the orientation of archaeological materials at various levels of the site. This information includes the uniform distribution of material azimuths, which contrasts with previous inferences of highly patterned orientations of materials in the Bed I archaeological sites. Those previous inferences of patterned material orientations are based on Mary Leakey's 50-year-old drawings of artifact and fossil bone distribution, but are not verified by our precise measurements of archaeological objects made in situ. Nor do those previous results agree with the general lack of geological, geomorphological, and/or taphonomic data that would indicate significant post-depositional movement of archaeological materials in the sites. We argue here that Leakey's drawings are incomplete (only portions of each assemblage were drawn) and inaccurate in their representation of the original locations, shapes and orientations of most archaeological specimens. This argument is supported by several important mismatches in object representations between a photograph taken of a small portion of the FLK 22 Zinjanthropus site floor before the removal of the archaeological items, and the sketch of the same area drawn by Leakey. Thus, we conclude that primary orientation data of excavations (i.e., direct measurements taken from items) generated prior to object removal are the only valid indicators of the relative isotropy or anisotropy of these important paleoanthropological assemblages.

To identify the phytolith signal of lacustrine environments, which are prone to preserving faunal remains including hominins, we analyzed the phytolith content of 46 grass and sedge species, and of 26 soil and mud samples. The samples were collected in Chad (Central Africa), in the Sudanian and Sahelian phytogeographical zones, near temporary and permanent water-bodies (including Lake Chad) and in grass-dominated biomes on well-drained soils. Altogether, we observed and counted separately 80 different phytolith types, including 38 grass silica short cells (GSSCs). Phytolith type diversity and relative abundances were analyzed in the botanical specimens to improve the phytolith taxonomic resolution. For the Poaceae, we used a valuetest analysis to identify significant cohorts of phytoliths to characterize aquatic, mesophytic, and xerophytic species. Our results show that the abundance of Cyperaceae in swampy areas may be deduced from the combined abundance of blocky and elongate phytolith types, but not by the typical silicified Papillae phytoliths, which were barely found preserved in the soil/mud. The abundance of aquatic Poaceae near water-bodies is inferred from the presence and abundance of a cohort of eight GSSC types (including notably several trapeziform GSSCs within the bilobate, cross, and saddle categories), which averages 42% in the mud samples, but only 23% and 14% in the samples from the Sudanian and Sahelian zones, respectively. The characterization is unclear for mesophytic grasses, but obvious for xerophytic grasses whose abundance in the Sahelian grasslands is inferred from the presence and abundance of a cohort of five GSSC types (mainly tabular saddles), which averages 50% in the soil samples from the arid Sahelian zone, and b19% in the more humid Sudanian and swamp samples. In conclusion, considering the full morphological diversity of grass silica short cell phytoliths (rather than just the broad morphological categories) allows greater discrimination of the aquatic environments. Such approach is therefore required for analyzing vegetation distribution at a local scale.

International audience; Meat-eating was an important factor affecting early hominin brain expansion, social organization and geographic movement. Stone tool butchery marks on ungulate fossils in several African archaeological assemblages demonstrate a significant level of carnivory by Pleistocene hominins, but the discovery at Olduvai Gorge of a child's pathological cranial fragments indicates that some hominins probably experienced scarcity of animal foods during various stages of their life histories. The child's parietal fragments, excavated from 1.5-million-year-old sediments, show porotic hyperostosis, a pathology associated with anemia. Nutritional deficiencies, including anemia, are most common at weaning, when children lose passive immunity received through their mothers' milk. Our results suggest, alternatively, that (1) the developmentally disruptive potential of weaning reached far beyond sedentary Holocene food-producing societies and into the early Pleistocene, or that (2) a hominin mother's meat-deficient diet negatively altered the nutritional content of her breast milk to the extent that her nursing child ultimately died from malnourishment. Either way, this discovery highlights that by at least 1.5 million years ago early human physiology was already adapted to a diet that included the regular consumption of meat.