Late Holocene palaeoenvironmental reconstruction from Mpumalanga Province (South Africa) inferred from geochemical and biogenic proxies

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Review of Palaeobotany and Palynology, ISSN: 0034-6667, Vol: 246, Page: 264-277

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Jenny Sjöström; Elin Norström; Jan Risberg; Maria H. Schoeman
Elsevier BV
Agricultural and Biological Sciences; Earth and Planetary Sciences
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Here we present a palaecological reconstruction covering the last 1700 yr from Lydenburg fen, located in the north-eastern grassland biome, Mpumalange, South Africa. A 300 cm peat sequence was analysed for biogenic (grass phytoliths, diatoms) and geochemical proxies (δ 13 C, δ 15 N, carbon/nitrogen content) to infer past grassland dynamics and hydro-climatic changes. The Lydenburg record reports a C 4 dominated grassland throughout the studied period, with more or less pronounced fluxes between C 4 -Chloridoideae and C 4 -Panicoideae grass subfamilies. The record reflects moderate to dry conditions from AD 400 to 1000; more mesic conditions until around AD 1250; followed by a significantly drier period between c. AD 1250 and c. AD 1350, when Chloridoideae grasses expand at the expense of Panicoideae grasses. During this phase, the δ 13 C-record reports more enriched values indicating higher influx of C 4 grasses. Furthermore, lithological evidence indicates highly erosive conditions, with significant gravel input from the surrounding hills. After AD 1350, proxy indications suggest a shift towards more mesic conditions. During this increasingly mesic but also unstable period, farming communities using specialized agricultural practices (e.g. the people in Bokoni) expanded their settlements into new regions (Delius et al., 2008). This expansion was also coupled to population growth, suggesting these communities applied techniques that enabled improved food production under environmentally challenging conditions. Over the last century, Lydenburg δ 13 C-values indicate increased input of C 3 taxa. The phytolith record shows that this increase is not coupled to an increase in Pooideae (C 3 ) grasses, suggesting that the C 3 input may be related to woody encroachment.