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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.

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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

Item Type: Report (Project Report)
Authors/Creators:Ellison, JC and Strickland, P
Publisher: World Wildlife Fund
Additional Information:

Report submitted to WWF Central Africa Regional Programme Office
May 24, 2010

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