Abstract
Abstract. We describe the Chipalamawamba Beds, early to middle Holocene deposits at the southern margin of long-lived Lake Malawi. The beds are exposed because of downcutting of the upper Shire River. The Chipalamawamba sediments are medium to coarse, yellow to brown sands deposited in lenses varying in horizontal extent from a few meters to several hundreds of meters. Four units are recognized; the first three mainly contain lacustrine sediments deposited during lake high stands about 10.6–9.7 cal ka BP (Unit 1), 7.6–6.5 cal ka BP (Unit 2) and 5.9–5.3 cal ka BP (Unit 3). Sediments of Unit 4 overlay Units 1 to 3, are coarser and display regular foresets and oblique-bedding, suggesting deposition in riverine environments after installation of the Shire River (~ 5.5–5.0 ka BP). Freshwater mollusk assemblages and bioturbation regularly occur in the lacustrine sediments, but are largely absent from Unit 4. Diverse and often contradicting hypotheses on the lake levels of Lake Malawi have been proposed for the early and middle Holocene. The Chipalamawamba Beds allow straightforward recognition of water levels and provide strong evidence for oscillating lake levels during this period, rather than continuous high or low levels. Sedimentation rates have been high and individual shell beds have typically been deposited during a few decades. Because the Chipalamawamba Beds contain a sequence of mollusk assemblages with intervals between subsequent shell beds ranging from a century to a few millennia, they enable paleontological analysis of the fauna with an unusually high temporal resolution. That some mollusk lineages inhabiting Lake Malawi are in the early stages of diversification and radiation increases the paleobiological relevance of these beds.
Highlights
In this paper we describe a sedimentary sequence in the Mangochi Province of Malawi that was deposited in long-lived Lake Malawi during the early to middle Holocene
The strata that we newly describe as the Chipalamawamba Beds crop out some 10 km south of Lake Malawi along the shores of the upper Shire River, just north of the shallow
We describe the stratigraphy in informal terminology because of uncertainties in the geographic extent beyond Chipalamawamba, Kwitambo and Kazembe, because of the difficulties experienced in identifying some of the erosional contacts between the units, and because the base of the Chipalamawamba Beds and the extension of the paleo-river gullies remain unknown
Summary
In this paper we describe a sedimentary sequence in the Mangochi Province of Malawi that was deposited in long-lived Lake Malawi during the early to middle Holocene. These sediments were first visited for scientific purposes in 1992 by Albrecht Gorthner as collaborator of the paleontological and paleoanthropological Hominid Corridor Research Project under the direction of Friedemann Schrenk. We visited the region again in 2008 and in 2010, during which we dug new trenches, found additional outcrops and collected sufficient data on the sediments as well as their fossil content for a detailed description of the stratigraphy of the beds, their depositional paleoenvironment and paleoecology.
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