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Stratigraphy and pollen analysis of recent sediments in the Douala Estuary, Cameroon

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Ellison, JC and Strickland, P (2010) Stratigraphy and pollen analysis of recent sediments in the Douala Estuary, Cameroon. Project Report. World Wildlife Fund.

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Abstract

Stratigraphy of the Doula Mangrove estuary, Cameroon was investigated by sampling two cores, one at the seaward edge of mangroves, and a second in the centre of the landward mangrove basin. These cores were investigated using percent organic, radiocarbon dating, and pollen analysis techniques, to reconstruct relative sea-level history of the last few hundred years. Results showed lower levels of inorganic sand at 2.0 - 3.5 m below the mangrove surface, fining upwards to silty clay to 1.5 - 0.8 cm below the mangrove surface, with evidence of rapid deposition and mixing. This fining upwards sequence demonstrated decreasing wave and/ or current energy, and pollen results confirmed recent colonization by mangroves with near surface mangrove facies of organic silty clay dominated by mangrove pollen. Inorganic stratigraphy indicated consistent mineral allochthonous sedimentation in association with river flood events, at rates of around 2.6 mm a-1 under the present mangroves. Results show that the Douala estuary mangrove area is a prograding sedimentary sequence with stable sea-levels over the last few hundred years, having no evidence of mangrove stratigraphy lower than present tidal levels. While sea-level has been stable, there is accumulation of sand and silt in the bay, which over time reaches tidal levels that can be colonized by mangroves. Hence despite sedimentary accumulation, there is no evident subsidence that is the case for other delta areas in the world, likely because of the bedrock confinement of the Douala estuary area with higher landforms on most sides, and proximity to the volcanically active Mount Cameroon

Item Type: Report (Project Report)
Publisher: World Wildlife Fund
Additional Information: Report submitted to WWF Central Africa Regional Programme Office May 24, 2010
Date Deposited: 14 Jul 2011 06:22
Last Modified: 18 Nov 2014 04:15
URI: http://eprints.utas.edu.au/id/eprint/10542
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