Discovered in 1988 by R. Oslisly and B. Peyrot, Elarmékora is a high terrace that, today, is situated 175 m above the Ogooué River in the historical complex of Elarmékora, attached to the Lopé ...National Park in Gabon, a World Heritage site since 2007. The site yielded a small lithic assemblage, including mainly cobble artefacts embedded within the 1 m thick alluvial material. Based on geomorphological and palaeoclimatological criteria, the preliminary dating suggested an age of 400 ka. However, Elarmékora could be a key site for Atlantic Central Africa if this lithic industry can be dated absolutely. In 2018 and 2019, two field trips were organized to collect surface samples as well as samples in vertical depth profiles with the aim of measuring their
-produced cosmogenic nuclide (
Be and
Al) content. Results suggest a surface abandonment between 730 and 620 ka ago representing a minimum age for the cobble artefacts. Concurrently, technological reappraisal of the artefacts suggests an atypical lithic industry that should, for the moment, be considered as 'undiagnostic' Earlier Stone Age. This age bracketing may be compared with a similar age range obtained for prehistoric occupations in Angola using the same approach. This age will place Elarmékora among the oldest evidence for the presence of hominins in western Central Africa and raises the question of a 'West Side Story' to early human dispersals in Africa. This article is part of the theme issue 'Tropical forests in the deep human past'.
Discovered in 1988 by R. Oslisly and B. Peyrot, Elarmékora is a high terrace that, today, is situated 175 m above the Ogooué River in the historical complex of Elarmékora, attached to the Lopé ...National Park in Gabon, a World Heritage site since 2007. The site yielded a small lithic assemblage, including mainly cobble artefacts embedded within the 1 m thick alluvial material. Based on geomorphological and palaeoclimatological criteria, the preliminary dating suggested an age of 400 ka. However, Elarmékora could be a key site for Atlantic Central Africa if this lithic industry can be dated absolutely. In 2018 and 2019, two field trips were organized to collect surface samples as well as samples in vertical depth profiles with the aim of measuring their
in situ
-produced cosmogenic nuclide (
10
Be and
26
Al) content. Results suggest a surface abandonment between 730 and 620 ka ago representing a minimum age for the cobble artefacts. Concurrently, technological reappraisal of the artefacts suggests an atypical lithic industry that should, for the moment, be considered as ‘undiagnostic’ Earlier Stone Age. This age bracketing may be compared with a similar age range obtained for prehistoric occupations in Angola using the same approach. This age will place Elarmékora among the oldest evidence for the presence of hominins in western Central Africa and raises the question of a ‘West Side Story’ to early human dispersals in Africa.
This article is part of the theme issue ‘Tropical forests in the deep human past’.
Bayon et al. (Reports, 9 March 2012, p. 1219) interpreted unusually high aluminum-potassium ratio values in an Atlantic sediment core as indicating anthropogenic deforestation around 2500 years ...before the present (B.P.). We argue that there is no terrestrial evidence for forest destruction by humans and that the third millennium B.P. rainforest crisis can be clearly attributed mostly to climatic change.
Lacustrine records hold considerable archives providing access to valuable information. However, to decode this information it is necessary to know how the lake in question and its catchment area ...function. In this study we propose to highlight the different factors that govern sedimentation by studying different core samples covering the Holocene taken from lake Ossa, Cameroon. To do this we chose to use organic matter as a tracer of changes in sedimentation by coupling two complementary methods: spectrophotometry for color measurement and Rock Eval pyrolysis for bulk geochemical analysis. Spectrophotometry is used classically to quantify color and obtain data very rapidly, at very high resolution and non-destructively. Rock Eval data give geochemical indication on organic matter composition. Thus, it was possible to highlight different types of organic matter at different stages of transformation, including different sources that can be responsible of this transformation (distal, proximal, autochtonous). The synthesis of this information led to the formulation of a scenario of how Lake Ossa was filled. Although this lake had already been used for paleoclimatic/environmental purposes, we show here that most of the forcing responsible for the sedimentation in the lake was due to the paleotopography and the rise in the lake level during the Holocene.
•We test the usefulness of spectrophotometry to track organic matter in lake sediment.•Coupled with Rock Eval analyses, it allows identifying organic matter origin.•Lake Ossa study proposes a methodology that can be transposed to other environments.
Until now, sedimentary DNA (sedDNA) studies have only focused on cold and temperate regions were DNA is relatively well preserved. Consequently, the tropics, where vegetation is hyperdiverse and ...natural archives are rare, have been neglected and deserve attention. In this study, we used next-generation sequencing to barcode sedDNA from Lake Sele, localized in the tropical lowlands of Benin (Africa), and compared the taxonomic diversity detected by DNA analyses with pollen assemblages. Plant sedDNA was successfully amplified from 33 of the 34 successfully extracted samples. In total, 43 taxa were identified along the 5000 years spanned by the sediment: 22 taxa were identified at the family level and 21 at the genus level. The plant diversity recovered through sedDNA from Lake Sele showed a specific local signal and limited overlapping with pollen. Introduced plants, grown and cultivated close to the water, such as sweet potato, were also well recorded by sedDNA. It appears, therefore, to be a promising approach to studying past diversity in tropical regions, and could help in tracking the introduction and history of agriculture. This is the first time this method has been used in the field of domestication and dissemination of several specific crops, and the results are very encouraging.
•Next-generation sequencing is used to barcode sedDNA from a lake in the tropics.•Plant sedDNA is successfully amplified over 5000 years and 43 taxa are identified.•Plants cultivated close to the water are well recorded by sedDNA.
In recent years, Nguène Lake and Kamalété Lake (Gabon, West Central Africa) have been studied repeatedly, providing comprehensive reconstructions of environmental changes over the last millennia. ...Both lakes are in different geomorphological and environmental settings. They are therefore excellent sites to test new methodological approaches. Indeed, the sedimentary cores provide various facies, and the previous studies provide references for calibrating the results of new methods. In this methodological issue, the present study aims to evaluate the potential of spectrophotometric and Rock-Eval coupled analysis to describe the Holocene lake and marsh deposits from tropical moist forests. This assessment is carried out on samples taken from two well-documented reference cores. The spectrophotometric analysis provides reproducible colour measurements, which inform about the nature of the main colour-bearing constituents. Coupled with Rock-Eval pyrolysis, this technique can be used to describe lithological changes and identify the probable source of sedimentary organic matter. In the studied cases, this approach identified the facies dominated by detrital terrigenous inputs ('iron bearing' signature and high OI values) and those associated with a more abundant primary production ('chlorophyll' signature, low OI and high HI), providing a distinction between palustrine and lacustrine dynamics. However, although the facies are comparable, sedimentary dynamics and sediment sources may vary depending on geomorphological and climatic contexts
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, OILJ, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Vegetation changes during the past 1300 years are reconstructed in western equatorial Africa using a high-resolution pollen record from Lake Kamalété. This small marshy basin (c. 5-7 ha) is located ...in forest-savanna mosaic in Lopé Reserve (0°43'S, 11°46'E), central Gabon. The Kamalété pollen data show the persistence over the past 1300 years of a relatively stable forest-savanna mosaic, associated with significant changes of the forest component. Three successive stages of forest dynamics occurred. First, at 1325 cal. BP, moist semi-evergreen rainforest existed around the catchment of Lake Kamalété. However, it appears from the consistent presence of >70% Gramineae pollen that the site was always primarily in savanna. Secondly, from c. 1240 to 550 cal BP, a noticeable increase in shade-intolerant plant species indicate openings in the rainforest canopy. The persistence of gap-colonizer species, such as Macaranga, Tetrorchidium and Musanga for several centuries in the rainforest, is explained by recurring canopy disturbance associated with shifts in available moisture. These hydrological changes may be related to a succession of longer and more severe dry seasons than observed today. Thirdly, at 550 cal BP, mature forest was re-established, corresponding to progressive savanna colonization by forest pioneer species such as Aucoumea klaineana, Lophira alata and Fagara macrophylla. This new phase of forest expansion coincided with a marked lithological change, indicating an increase in lake-level. It is concluded that the major vegetation changes observed are due to climatic variability, and anthropogenic action had limited influence.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, OILJ, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Caves with stromatolites of South Gabon ; exceptional paleontological sites (Ngounie Province)
Although the presence of stromatolitic constructions was mentioned in the schisto-limestone series of ...the Neoproterozoic syncline of Niari-Nyanga by old geological investigations, it is very difficult to observe them in nature. However, in some caves of the Ngounie province, dug in the dolomitic formations, there exist splendid outcrops of giant stromatolite colonies of the Conophyton kind. This is the case in the caves of Ntsona, Diengui and Ndoungou, where the outcrops appear in walls and also form the ceilings of the passages. In the cave of Ntsona, the superposition of two layers, separated by a dolomitic bed, brings precise data for a paleoenvironmental approach. The exceptional importance of these stromatolithe constructions militates for their conservation and the inscription into the sites on the indicative list of the World Heritage.
Si la présence de constructions stromatolithiques dans les séries schisto-calcaires du synclinal néoprotérozoïque du Niari-Nyanga a été mentionnée dans des recherches géologiques anciennes, leur observation dans la nature est très difficile. Toutefois, dans quelques grottes de la province de la Ngounié, il existe de beaux affleurements de colonies de stromatolithes géants du genre «Conophyton». C'est le cas des grottes de Ntsona, Diengui et Ndoungou où les bancs apparaissent dans les galeries et en constituent aussi les plafonds. Dans la grotte de Ntsona, la superposition de deux bancs, séparés par un banc compact de dolomies, offre des données pour une approche paléoenvironnementale. L'exceptionnelle importance de ces formations stromatolithiques justifie leur conservation, comme le projet de leur inscription sur la liste indicative du Patrimoine Mondial.
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