Title:
A chronological database assessing the late Quaternary palaeoenvironmental record from fluvial sediments in southwestern Africa
Publication Year:
2023
Abstract:

Fluvial sediments preserve evidence of past hydroclimatic regimes and are important but potentially underutilised indicators of palaeoenvironmental change in drylands. This paper presents a new chronological database of 603 ages from late Quaternary fluvial sediments at 70 sites in southern Africa's western dryland regions. This synthesis assesses the spatial and temporal trends in both the palaeoenvironmental record and the supporting data that underpins these interpretations. We find that topographic and climatic characteristics of river catchments influence the nature of fluvial archive formation and preservation. Channel confinement, legacies of research, and sampling strategies in specific river basins are found to control the sedimentary context and length of documented record available for palaeoenvironmental reconstruction. The age of dated deposits and associated magnitude of chronological uncertainties influence the temporal range and resolution of climate and fluvial variability that can be discerned. Where calendar year uncertainties are small enough, predominantly dating to the last millennium, individual flood events and multi-year episodes within flash flood deposits can be linked to synoptic climate patterns, yet when uncertainties are larger, interpretations are restricted to understanding multidecadal to centennial-scale phases of flow regimes. This paper collates a scattered literature to detail the current state of southwestern Africa's fluvial record and highlights opportunities for future research. We consider controls on fluvial archive interpretation that are pertinent to wider dryland contexts and argue that fluvial records provide useful information for inclusion in regional palaeoenvironmental syntheses. Following a filtering process, quality-assessed chronologies are compiled to establish the combined fluvial history of 22 rivers to consider the response of fluvial systems to hydroclimatic drivers. At the Last Glacial Maximum (LGM; 24โ€“18 ka), records detail a regionally consistent signal of intermittent to perennial flow under relatively humid conditions in what are currently ephemeral systems. The mid Holocene (MH; 8-4 ka) is also characterised by the occurrence of sustained river flow and higher discharge events than present, but with greater spatial variability. Sedimentary archives display evidence of both intermittent flow and extreme flood events within ephemeral regimes, and two rivers, the Hoanib and Molopo, are characterised by reduced fluvial activity. Within the last millennium, flash flood regimes within an arid to hyper-arid climate were established with coherence in the timing of flood frequency variations recorded between catchments. Keywords: fluvial sediments, dryland, quaternary, chronology, palaeoenvironmental change, database, southern Africa.

Publication Title:
Earth-Science Reviews
Volume:
236
Number:
104288
Item Type:
Journal Article
Language:
en