Document Type

Journal Article

Department/Unit

Department of Geography

Title

Impacts of flamingos on saline lake margin and shallow lacustrine sediments in the Kenya Rift Valley

Language

English

Abstract

Studies of modern, Holocene, and Pleistocene sediments around saline to hypersaline, alkaline Lake Bogoria and Lake Magadi show that evidence of flamingo activity in marginal areas of these lakes is nearly ubiquitous. Flamingos produce discrete structures such as webbed footprints (~ 9 cm long, ~ 11 cm wide) and nest mounds (~ 30. cm wide, ~ 20. cm high), and they also extensively rework sediments in delta front, delta plain, and shoreline areas. Large (~ 0.5-2. cm in diameter), pinched, 'bubble pores' and ped-like mud clumps are formed by the trampling and churning of wet clay-rich sediments in these settings. Flamingo nest mounds, although superficially similar to some thrombolite mounds, are typically internally structureless, unless formed on pre-existing sediments that preserve internal structures. The flamingo mounds consist of a dense, packed oval-shaped core, a surrounding 'body' of packed sediment, and an external layer with a ped-like texture of clumped mud. The nests may contain open holes from roots or feather shafts incorporated into the nest, and (or) burrows produced once the nests are abandoned. In areas with high densities of flamingos, lake margin sediments may be preferentially compacted, particularly at breeding sites, and become resistant to subaerial erosion and the effects of transgressive ravinement on time scales ranging from seasons to tens of thousands of years. The relatively well-compacted nest mounds and associated sediments also contribute to the stability of delta distributary channels during regressive-transgressive cycles, and can lead to the minor channelization of unconfined flows where currents are diverted around nest mounds. Pleistocene exhumed surfaces of relatively well-indurated lake margin sediments at Lake Bogoria and Lake Magadi that are interpreted as combined regressive and transgressive surfaces (flooding surface/sequence boundary) preserve evidence of flamingo activities, and are overlain by younger, porous lacustrine silts that preserve large bubble pores produced by flamingos. © 2012 Elsevier B.V..

Keywords

Biogenic structures, Bioturbation, East African lakes, Flamingo, Mud mounds, Thrombolite

Publication Date

2012

Source Publication Title

Sedimentary Geology

Volume

277-278

Start Page

32

End Page

51

Publisher

Elsevier

DOI

10.1016/j.sedgeo.2012.07.007

ISSN (print)

00370738

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