Papers by raymonde Bonnefille
Geographie Physique Et Quaternaire, Nov 30, 2007
Nouvelle séquence pollinique d'une tourbière de la crête Zaïre-Nil (Burundi)
Review of Palaeobotany and Palynology, Mar 1, 1991
ABSTRACT This paper presents the pollen analysis of a core, 11.5 m long, from a valley peatbog in... more ABSTRACT This paper presents the pollen analysis of a core, 11.5 m long, from a valley peatbog in the Burundi highlands, east of Lake Tanganyika. Nine radiocarbon dates provide a chronological frame of ca. > 32,500 to 3200 yr. B.P. At the bottom of the fossil sequence, pollen spectra indicate that open grassland occurred at 2000 m altitude during the last Glacial period. The pollen diagram mostly documents the composition and history of the humid montane forest during the Holocene time. The forest starts at ca. 9500 B.P. extrapolated date, with maximum development maintained until 6000 yr. B.P. Several forest decreases are documented since 4000 yr B.P., without any clear pollen indicator of anthropogenic activity. The most important one at ca. 3200 yr B.P., appears synchronous with an early date for the Iron Age in Burundi.
Implications of pollen assemblage from the Koobi Fora Formation, East Rudolf, Kenya
Nature, Dec 1, 1976
ABSTRACT
Palynology, stratigraphy and palaeoenvironment of a pliocene hominid site (2.9-3.3 M.Y.) at Hadar, Ethiopia
Palaeogeography, Palaeoclimatology, Palaeoecology, 1987
... 120 km south of Hadar where the Awash River flows along a swampy plain that is the remnant of... more ... 120 km south of Hadar where the Awash River flows along a swampy plain that is the remnant of a large Holocene lake. ... In fluviatile samples, such as those of the Awash or the Omo river fromsouthwest Ethiopia (Buchet, 1982), Typha pollen percentages are virtually always ...
30,000-Year-Old Fossil Restionaceae Pollen from Central Equatorial Africa and Its Biogeographical Significance
Journal of Biogeography, May 1, 1990
The Restionaceae are taxonomically close to the Poaceae, and are herbaceous plants mostly distrib... more The Restionaceae are taxonomically close to the Poaceae, and are herbaceous plants mostly distributed in the Southern Hemisphere. We report here the identification of fossil pollen attributed to the genus Restio, and resem- bling Restio mahonii (N.E.Br.) Pillans. The pollen was found in two highland peat bogs from Rwanda and Burun- di, and dates from 30,000 yr BP. The fossil pollen grains are abundant, and are associated with other swamp compo- nents, such as Sphagnum. These results show that there was
Intertropical last glacial and Holocene climatic change
Review of Palaeobotany and Palynology, 1998
Numerical interpretation of a high resolution Holocene pollen record from Burundi
Palaeogeography, Palaeoclimatology, Palaeoecology, Jun 1, 1994
ABSTRACT The Holocene history of the tropical montane forest is reconstructed using a high resolu... more ABSTRACT The Holocene history of the tropical montane forest is reconstructed using a high resolution pollen record from a valley swamp (3°35′S, 29°41′E), at 2000 m elevation. The post-glacial establishment of the montane rain forest is evidenced at ca. 10,600 yr B.P. Numerical analysis combines the Correspondence Analysis with the Cluster Analysis of both 38 modern and 101 fossil pollen spectra including 125 identified pollen taxa. Four distinct successionnal stages of forest development have been identified. The past vegetation recorded during the early Holocene period (10,600–3800 yr B.P.) was more closely related to modern pollen spectra from secondary forest rather than to primary forest samples from Burundi. At 3800 yr B.P., a sharp decrease of arboreal pollen percentages and a noticeable increase of Celtis, a semi-decidous tree indicate the opening of montane forest due to a drier climatic event. The beginning of the anthropogenic impact evidenced after at 3500 yr B.P., contemporaneously with the Early Iron Age in Burundi, follows the late Holocene climatic shift.
Memories of Frank Brown in the Lower Omo Valley
Evolutionary Anthropology, Nov 1, 2017
Late Pleistocene and Holocene vegetation history of the Bale Mountains, Ethiopia
Quaternary Science Reviews, Sep 1, 2007
A sediment core recovered from Garba Guracha, a glacial lake at 3950m altitude in the Bale Mounta... more A sediment core recovered from Garba Guracha, a glacial lake at 3950m altitude in the Bale Mountains of Ethiopia, at the boundary of the Ericaceous and Afroalpine vegetation belts, provides a 16,700-year pollen record of vegetation response to climatic change. The earliest vegetation recorded was sparse and composed mainly of grasses, Amaranthaceae–Chenopodiaceae and Artemisia, indicating an arid climate. At 13,400cal
Mid-Holocene land-surface conditions in northern Africa and the Arabian Peninsula: A data set for the analysis of biogeophysical feedbacks in the climate system
Global Biogeochemical Cycles, Mar 1, 1998
Large changes in the extent of northern subtropical arid regions during the Holocene are attribut... more Large changes in the extent of northern subtropical arid regions during the Holocene are attributed to orbitally forced variations in monsoon strength and have been implicated in the regulation of atmospheric trace gas concentrations on millenial timescales. Models that omit biogeophysical feedback, however, are unable to account for the full magnitude of African monsoon amplification and extension during the early to middle Holocene (˜9500–5000 years B.P.). A data set describing land‐surface conditions 6000 years B.P. on a 1° × 1° grid across northern Africa and the Arabian Peninsula has been prepared from published maps and other sources of palaeoenvironmental data, with the primary aim of providing a realistic lower boundary condition for atmospheric general circulation model experiments similar to those performed in the Palaeoclimate Modelling Intercomparison Project. The data set includes information on the percentage of each grid cell occupied by specific vegetation types (steppe, savanna, xerophytic woods/scrub, tropical deciduous forest, and tropical montane evergreen forest), open water (lakes), and wetlands, plus information on the flow direction of major drainage channels for use in large‐scale palaeohydrological modeling. The data set is available in digital form by anonymous ftp.
Plant Wax Biomarkers in Fluvial-Lacustrine Sediments from the Omo-Turkana and Awash Basins in Eastern Africa
AGU Fall Meeting Abstracts, Dec 1, 2013
Climate of The Past, Mar 30, 2010
Pollen data collected in Africa at high (Kuruyange, valley swamp, Burundi) and low altitude (Vict... more Pollen data collected in Africa at high (Kuruyange, valley swamp, Burundi) and low altitude (Victoria, lake, Uganda; Ngamakala, pond, Congo) showed that after 6 ky before present (BP), pollen of deciduous trees increase their relative percentage, suggesting thus the reduction of the annual amount of precipitation and/or an increase of in the length of the dry season. Until now, pollen-climate transfer functions only investigated mean annual precipitation, due to the absence of modern pollen-assemblage analogs under diversified precipitation regimes. Hence these functions omit the potential effect of a change in precipitation seasonality modifying thus the length of the dry season. In the present study, we use an equilibrium biosphere model (i.e. BIOME3.5) to estimate the sensitivity of equatorial African vegetation, at specific sites, to such changes. Climatic scenarios, differing only in the monthly distribution of the current annual amount of precipitation, are examined at the above three locations in equatorial Africa. Soil characteristics, monthly temperatures and cloudiness are kept constant at their present-day values. Good agreement is shown between model simulations and current biomes assemblages, as inferred from pollen data. To date, the increase of the deciduous forest component in the palaeodata around 6 ky BP has been interpreted as the beginning of a drier climate period. However, our results demonstrate that a change in the seasonal distribution of precipitation could also induce the observed changes in vegetation types. This study confirms the importance of taking into account seasonal changes in the hydrological balance. Palaeoecologists can greatly benefit from the use of dynamic process based vegetation mod-
Cenozoic vegetation, climate changes and hominid evolution in tropical Africa
Global and Planetary Change, Jul 1, 2010
... dates from the earliest palaeoanthropological research during the first half of the twentieth... more ... dates from the earliest palaeoanthropological research during the first half of the twentieth century ([Howell and Bourlière, 1963], [Isaac and McCown ... In contrast, fossil wood and plant remains had documented more humid forests for the Miocene ([Jacobs and Kabuye, 1987] and ...
CLAM age model and biomes of sediment core Bear_Lake
CLAM age model and pollen profile of sediment core Lake_Tanganyika
Températures et précipitations des derniers 40 000 ans en Afrique équatoriale
Quaternary Science Reviews, 1998
New compilations of African pollen and lake data are compared with climate (CCM1, NCAR, Boulder) ... more New compilations of African pollen and lake data are compared with climate (CCM1, NCAR, Boulder) and vegetation (BIOME 1.2, GSG, Lund) simulations for the last glacial maximum (LGM) and early to mid-Holocene (EMH). The simulated LGM climate was ca 4°C colder and drier than present, with maximum reduction in precipitation in semi-arid regions. Biome simulations show lowering of montane vegetation belts and expansion of southern xerophytic associations, but no change in the distribution of deserts and tropical rain forests. The lakes show LGM conditions similar or drier than present throughout northern and tropical Africa. Pollen data indicate lowering of montane vegetation belts, the stability of the Sahara, and a reduction of rain forest. The paleoenvironmental data are consistent with the simulated changes in temperature and moisture budgets, although they suggest the climate model underestimates equatorial aridity. EMH simulations show temperatures slightly less than present and increased monsoonal precipitation in the eastern Sahara and East Africa. Biome simulations show an upward shift of montane vegetation belts, fragmentation of xerophytic vegetation in southern Africa, and a major northward shift of the southern margin of the eastern Sahara. The lakes indicate conditions wetter than present across northern Africa. Pollen data show an upward shift of the montane forests, the northward shift of the southern margin of the Sahara, and a major extension of tropical rain forest. The lake and pollen data confirm monsoon expansion in eastern Africa, but the climate model fails to simulate the wet conditions in western Africa.
Temperature and rainfall estimates for the past 40,000 years in equatorial Africa
Nature, 1990
... be resolved 7 . Here we present new quantitative estimates of temperature and precipitation u... more ... be resolved 7 . Here we present new quantitative estimates of temperature and precipitation using a multivariate analysis 8 of pollen time-series data from peat ... We also estimate that the mean annual rainfall decreased by 30% during the last glacial period, in agreement with ...
Palaeoenvironment of Lake Abijata, Ethiopia, during the past 2000 years
Geological Society, London, Special Publications, 1986
Summary Multidisciplinary studies, including the examination of sedimentology, palynology, diatom... more Summary Multidisciplinary studies, including the examination of sedimentology, palynology, diatoms and organic matter have been undertaken on a 6 m core from Lake Abijata, Ethiopia. The bottom of this core has been dated at 1720 ± BP. Analyses have shown four distinct stages in lake evolution. Two transgressive phases that have been recognized can be correlated with other lake level evidence. The transgressions result from changing inputs from lowland and highland regions within the catchment. They are most probably related to changes in seasonal rainfall patterns.
A surge in obsidian exploitation more than 1.2 million years ago at Simbiro III (Melka Kunture, Upper Awash, Ethiopia)
Nature Ecology and Evolution, Jan 19, 2023
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Papers by raymonde Bonnefille