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Relative impact of sea level change and sediment supply on shallow offshore Niger delta margins from palynodebris and lithofacies data
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Abstracts / Quaternary International 404 (2016) 174e213
How dynamically do river systems react to climatic fluctuations? Or are they mainly characterized by an internal fluvial variability? With a multimethodological approach the behavior of two river systems during the LGM was analyzed in southern Cameroon. The search for climatic signals in late Quaternary alluvial sequences remains a challenge in southern Cameroon. Significant grain-size changes in the stratigraphies and sedimentological data indicate major modifications of fluvial dynamics. However, the main triggers for these modifications remain to be specified. Since vegetation cover has a strong influence on hydrology, fluvial dynamics and floodplain, the climatic signal can be better interpreted with additional information on the palaeovegetation. Pollen and macro-remains are good indicators of the former plant cover, but their presence is restricted to specific preservation conditions in waterlogged (clayey) sediments. Most palaeochannel sequences, especially those dating around the LGM, comprise sandy sediments with very low potential for pollen preservation. On the other hand, these sediments often contain abundant phytoliths and freshwater sponge spicules. Phytoliths offer a diagnostic tool for palaeovegetation research. They are used to reconstruct ancient vegetation from terrestrial and lake sediments, palaeosoils, and deep-sea cores, with a time-depth of up to 20 Ma. Sponge spicules are siliceous support structures of freshwater sponges that are conserved after the death of the sponge. For Africa, 58 species have been described. Although sponge spicules always originate from wet environments, they can be eventually deposited in secondary locations through eolian or fluvial transport. Spicules transported from distant places usually exhibit a higher degree of deterioration in the form of broken or pitted spicules, while complete and well-preserved spicules point to in situ deposition. Meandering and anabranching to anastomosing river sections were investigated with remote sensing of LANDSAT-ETM+ and ASTER data to identify suitable stillwater locations, like oxbows, abandoned and seasonal branches and backswamps for sediment sampling. Sediments were sampled every 20 cm with an Eijkelkamp Edelman corer and at some locations a thin percussion probe (3 cm diameter, 50 cm length) enabled the sampling of waterlogged sediment and stratigraphy studies of laminated clayey sediments. Phytolith and freshwater sponge spicule samples were taken from six Late Pleistocene alluvial sequences with chronostratigraphic data. From each sample, 15e20 g of dried sediment was processed. Keywords: LGM, fluvial dynamics, remote sensing, Alluvial alluvial sequences, sSponge spicules RELATIVE IMPACT OF SEA LEVEL CHANGE AND SEDIMENT SUPPLY ON SHALLOW OFFSHORE NIGER DELTA MARGINS FROM PALYNODEBRIS AND LITHOFACIES DATA O. Adojoh 1, *, M. Fabienne 1, D. Robert 1, O. Peter 2. 1 School of Environmental Sciences, University of Liverpool, UK; 2 Shell UK Limited, Aberdeen, UK. E-mail address: [email protected].
The concept of using palynodebris (palynomacerals) associated with pollen data offers additional information in the interpretation of climate, eustasy and palaeoenvironmental analysis during the last deglaciation period across the Niger Delta margin. Non-palynologists usually utilise the term “junk” owing to their lack of awareness of the usefulness in reconstructing palaeoenvironmental change in areas where non-biostratigraphic tools (fauna, seismic, wireline logs) are biased. This research involves a multi-proxy study based upon three gravity cores of just under 3 metres length each. These materials (late Pleistocene to mid-Holocene in age) have been collected from the sea bed (approx. 40 mbsf) from offshore locations of the Niger Delta, and have been sampled at every 2 cm implying a high-resolution study. The palynological and lithofacies component results suggest that assemblages of palynodebris (translucent phytoclasts, opaque phytoclasts and amorphous organic matter) associated with the 5e15 micron sieved fraction, were deposited under different environmental conditions. The littoral vegetation and associated palynodebris distributions dominate
* Corresponding author.
over the hinterland vegetation as a result of turbidity flow, oxidation and mangrove sediment trapping mechanism restricted to the proximal settings of Niger Delta. Evaluation of palynodebris integrated with palaeovegetation, lithofacies and trace elements components have led to the recognition of palaeoenvironmental change from deltaic marginal marine through to continental shelf settings. Mudstones with dominant mangrove pollen were deposited in the anoxic palaeoenvironments during a humid climate period suggested to be associated with an abundance of translucent phytoclasts characteristic of estuary / tidal flats settings. Conversely, hinterland pollen and very fine sand and siltstones have been deposited during dry climate periods, in association with an abundance of opaque phytoclasts and Amorphous Organic Matter (AOM) indicating delta plain and lagoonal palaeoenvironmental settings. Palynodebris, integrated with the aforementioned proxies allowed the interpretation of depositional settings especially in this case of limited deltaic floral diversity. Keywords: Niger Delta, palynodebris, phyoclasts, eustasy, palaeoenvironments, climate, mangroves
TOWARDS AN UNDERSTANDING OF THE MILLENNIAL VARIABILITY OF THE WEST AFRICAN MONSOON SYSTEM: A COMBINED PALYNOLOGICAL AND GEOCHEMICAL APPROACH R. Lem*, F. Marret, J. Marshall. School of Environmental Sciences, University of Liverpool, UK. E-mail address: [email protected].
The last decades have seen catastrophic droughts in the Sahel, strongly affecting millions of people. It has been discovered that the reduction in precipitation was linked to changes in the adjacent oceanic temperatures, but what remains unclear is whether this pattern of recent weak precipitation is part of a natural cycle or is linked to climatic warming. In order to understand the natural variability of the African monsoon it is necessary to look back in time. The long-term history of the West African Monsoon variability has mainly been deduced from a few sites from Western Africa, but these often contain gaps. Coupled ocean-eatmosphere general circulation models have been developed to simulate past environmental conditions and help to better understand forcing mechanisms (lower seaesurface temperatures for example), but palaeodata from climate proxies remain essential to validate and calibrate the models. Inspection of a 34 m marine sediment record collected off the Ogooue River mouth, Gabon, allows for the identification and timing of terrestrial and marine environmental changes across western equatorial Africa over the past 140 000 years. Palynological analysis documents vegetation change throughout the core sequence and through the combination of elemental geochemistry, magnetic susceptibility, and foraminiferal identification, a thorough and innovative multiproxy record is established. It is envisaged that the study will play a pioneering role in the advancement of palaeoclimatic change research, and more specifically enhanced understanding of the movement of the West African Monsoon system across western equatorial Africa, during the mid to late Quaternary period. Keywords: palynology, West African Monsoon, multi-proxy approach
CENTES ET PERSPECMUTATIONS SOCIO-ENVIRONNEMENTALES Re VELOPPEMENT DURABLE DANS LE BASSIN DU FLEUVE TIVES DE De NIN NIGER AU Be I. Yabi 1, 2, 3, *, I.T. Imorou 4, S. Zakari 4. 1 Laboratoire Pierre Pagney ‘Climat, Eau, Ecosyst emes et D eveloppement’ (LACEEDE), Benin; 2 D epartement de e G eographie et Am enagement du Territoire (DGAT), Benin; 3 Universit d'Abomey-Calavi (UAC-B enin), Benin; 4 Laboratoire de Cartographie (LaCarto), Universit e d'Abomey-Calavi (UAC-B enin), Benin. E-mail address: yafi[email protected].
tendue d'environ 48 000 km2 (presque 42 % de la superficie Avec une e ninois du fleuve Niger est un des quatre grands nationale), le bassin be
Abstracts / Quaternary International 404 (2016) 174e213
How dynamically do river systems react to climatic fluctuations? Or are they mainly characterized by an internal fluvial variability? With a multimethodological approach the behavior of two river systems during the LGM was analyzed in southern Cameroon. The search for climatic signals in late Quaternary alluvial sequences remains a challenge in southern Cameroon. Significant grain-size changes in the stratigraphies and sedimentological data indicate major modifications of fluvial dynamics. However, the main triggers for these modifications remain to be specified. Since vegetation cover has a strong influence on hydrology, fluvial dynamics and floodplain, the climatic signal can be better interpreted with additional information on the palaeovegetation. Pollen and macro-remains are good indicators of the former plant cover, but their presence is restricted to specific preservation conditions in waterlogged (clayey) sediments. Most palaeochannel sequences, especially those dating around the LGM, comprise sandy sediments with very low potential for pollen preservation. On the other hand, these sediments often contain abundant phytoliths and freshwater sponge spicules. Phytoliths offer a diagnostic tool for palaeovegetation research. They are used to reconstruct ancient vegetation from terrestrial and lake sediments, palaeosoils, and deep-sea cores, with a time-depth of up to 20 Ma. Sponge spicules are siliceous support structures of freshwater sponges that are conserved after the death of the sponge. For Africa, 58 species have been described. Although sponge spicules always originate from wet environments, they can be eventually deposited in secondary locations through eolian or fluvial transport. Spicules transported from distant places usually exhibit a higher degree of deterioration in the form of broken or pitted spicules, while complete and well-preserved spicules point to in situ deposition. Meandering and anabranching to anastomosing river sections were investigated with remote sensing of LANDSAT-ETM+ and ASTER data to identify suitable stillwater locations, like oxbows, abandoned and seasonal branches and backswamps for sediment sampling. Sediments were sampled every 20 cm with an Eijkelkamp Edelman corer and at some locations a thin percussion probe (3 cm diameter, 50 cm length) enabled the sampling of waterlogged sediment and stratigraphy studies of laminated clayey sediments. Phytolith and freshwater sponge spicule samples were taken from six Late Pleistocene alluvial sequences with chronostratigraphic data. From each sample, 15e20 g of dried sediment was processed. Keywords: LGM, fluvial dynamics, remote sensing, Alluvial alluvial sequences, sSponge spicules RELATIVE IMPACT OF SEA LEVEL CHANGE AND SEDIMENT SUPPLY ON SHALLOW OFFSHORE NIGER DELTA MARGINS FROM PALYNODEBRIS AND LITHOFACIES DATA O. Adojoh 1, *, M. Fabienne 1, D. Robert 1, O. Peter 2. 1 School of Environmental Sciences, University of Liverpool, UK; 2 Shell UK Limited, Aberdeen, UK. E-mail address: [email protected].
The concept of using palynodebris (palynomacerals) associated with pollen data offers additional information in the interpretation of climate, eustasy and palaeoenvironmental analysis during the last deglaciation period across the Niger Delta margin. Non-palynologists usually utilise the term “junk” owing to their lack of awareness of the usefulness in reconstructing palaeoenvironmental change in areas where non-biostratigraphic tools (fauna, seismic, wireline logs) are biased. This research involves a multi-proxy study based upon three gravity cores of just under 3 metres length each. These materials (late Pleistocene to mid-Holocene in age) have been collected from the sea bed (approx. 40 mbsf) from offshore locations of the Niger Delta, and have been sampled at every 2 cm implying a high-resolution study. The palynological and lithofacies component results suggest that assemblages of palynodebris (translucent phytoclasts, opaque phytoclasts and amorphous organic matter) associated with the 5e15 micron sieved fraction, were deposited under different environmental conditions. The littoral vegetation and associated palynodebris distributions dominate
* Corresponding author.
over the hinterland vegetation as a result of turbidity flow, oxidation and mangrove sediment trapping mechanism restricted to the proximal settings of Niger Delta. Evaluation of palynodebris integrated with palaeovegetation, lithofacies and trace elements components have led to the recognition of palaeoenvironmental change from deltaic marginal marine through to continental shelf settings. Mudstones with dominant mangrove pollen were deposited in the anoxic palaeoenvironments during a humid climate period suggested to be associated with an abundance of translucent phytoclasts characteristic of estuary / tidal flats settings. Conversely, hinterland pollen and very fine sand and siltstones have been deposited during dry climate periods, in association with an abundance of opaque phytoclasts and Amorphous Organic Matter (AOM) indicating delta plain and lagoonal palaeoenvironmental settings. Palynodebris, integrated with the aforementioned proxies allowed the interpretation of depositional settings especially in this case of limited deltaic floral diversity. Keywords: Niger Delta, palynodebris, phyoclasts, eustasy, palaeoenvironments, climate, mangroves
TOWARDS AN UNDERSTANDING OF THE MILLENNIAL VARIABILITY OF THE WEST AFRICAN MONSOON SYSTEM: A COMBINED PALYNOLOGICAL AND GEOCHEMICAL APPROACH R. Lem*, F. Marret, J. Marshall. School of Environmental Sciences, University of Liverpool, UK. E-mail address: [email protected].
The last decades have seen catastrophic droughts in the Sahel, strongly affecting millions of people. It has been discovered that the reduction in precipitation was linked to changes in the adjacent oceanic temperatures, but what remains unclear is whether this pattern of recent weak precipitation is part of a natural cycle or is linked to climatic warming. In order to understand the natural variability of the African monsoon it is necessary to look back in time. The long-term history of the West African Monsoon variability has mainly been deduced from a few sites from Western Africa, but these often contain gaps. Coupled ocean-eatmosphere general circulation models have been developed to simulate past environmental conditions and help to better understand forcing mechanisms (lower seaesurface temperatures for example), but palaeodata from climate proxies remain essential to validate and calibrate the models. Inspection of a 34 m marine sediment record collected off the Ogooue River mouth, Gabon, allows for the identification and timing of terrestrial and marine environmental changes across western equatorial Africa over the past 140 000 years. Palynological analysis documents vegetation change throughout the core sequence and through the combination of elemental geochemistry, magnetic susceptibility, and foraminiferal identification, a thorough and innovative multiproxy record is established. It is envisaged that the study will play a pioneering role in the advancement of palaeoclimatic change research, and more specifically enhanced understanding of the movement of the West African Monsoon system across western equatorial Africa, during the mid to late Quaternary period. Keywords: palynology, West African Monsoon, multi-proxy approach
CENTES ET PERSPECMUTATIONS SOCIO-ENVIRONNEMENTALES Re VELOPPEMENT DURABLE DANS LE BASSIN DU FLEUVE TIVES DE De NIN NIGER AU Be I. Yabi 1, 2, 3, *, I.T. Imorou 4, S. Zakari 4. 1 Laboratoire Pierre Pagney ‘Climat, Eau, Ecosyst emes et D eveloppement’ (LACEEDE), Benin; 2 D epartement de e G eographie et Am enagement du Territoire (DGAT), Benin; 3 Universit d'Abomey-Calavi (UAC-B enin), Benin; 4 Laboratoire de Cartographie (LaCarto), Universit e d'Abomey-Calavi (UAC-B enin), Benin. E-mail address: yafi[email protected].
tendue d'environ 48 000 km2 (presque 42 % de la superficie Avec une e ninois du fleuve Niger est un des quatre grands nationale), le bassin be