Conservatism of mineral magnetic signatures in farm dam sediments in the South African Karoo: the potential effects of particle size and post-depositional diagenesis

Pulley, Simon; Rowntree, Kate; Foster, Ian D L

doi:10.1007/s11368-015-1265-5

Cited by 25 publications

(18 citation statements)

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“…These issues are currently under further investigation. The changes in mineral magnetic signatures are indicative of a change in sediment source in these catchments (see Foster et al, 2012;Pulley et al, 2015) and also suggestive of do- lerite as being the potential source associated with the high magnetic signatures and 137 Cs activities. No known significant dolerite sources lie in close proximity to the Good Hope dam but further detailed reconnaissance surveys will be undertaken during future field visits in order to establish their presence.…”

Section: The Good Hope Conundrummentioning

confidence: 92%

“…Multiple sediment cores are required to quantify the spatial variability in deposition and estimate the volume of sediment deposited over different timescales. The chronol- Rowntree and Foster, 2012). ogy from the master core is then transferred to other cores using time-synchronous markers, such as magnetic susceptibility, which can be measured cheaply and rapidly, and has been shown to be a largely conservative tracer in dam sediments (Pulley et al, 2015). Detailed analysis of these sediment yield records is presented elsewhere (e.g.…”

Section: D L Foster Et Al: the Potential For Gamma-emitting Radmentioning

confidence: 99%

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The potential for gamma-emitting radionuclides to contribute to an understanding of erosion processes in South Africa

et al. 2017

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Abstract. Several research projects undertaken by the authors and others over the last 14 years have used fallout and geogenic radionuclides for understanding erosion processes and sediment yield dynamics in South Africa over the last 100-200 years as European settlers colonised the interior plains and plateaux of the country and imported new livestock and farming techniques to the region. These projects have used two fallout radionuclides ( 210 Pb and 137 Cs) to date sediments accumulating in reservoirs, farm dams, wetlands, alluvial fans and floodouts and have used other fallout nuclides ( 7 Be) and long-lived geogenic radionuclides (e.g. 40 K, 235 U) as part of a composite fingerprint exploring contemporary sediment sources and changes to sources through time. While successful in many parts of the world, applying these techniques in Southern Africa has posed a number of challenges often not encountered elsewhere. Here we explore some of the benefits and challenges in using gamma-emitting radionuclides, especially 137 Cs, in these landscapes. Benefits include the potential for discriminating gully sidewall from topsoil sources, which has helped to identify contemporary gully systems as sediment conduits, rather than sources, and for providing a time-synchronous marker horizon in a range of sedimentary environments that has helped to develop robust chronologies. Challenges include the spatial variability in soil cover on steep rocky hillslopes, which is likely to challenge assumptions about the uniformity of initial fallout nuclide distribution, the paucity of stable (non-eroding) sites in order to estimate atmospheric fallout inventories, and the limited success of 210 Pb dating in some rapidly accumulating high altitude catchments where sediments often comprise significant amounts of sand and gravel. Despite these challenges we present evidence suggesting that the use of gamma-emitting radionuclides can make a significant contribution to our understanding of erosion processes and sediment yield dynamics. Future research highlighted in the conclusion will try to address current challenges and outline new projects established to address them more fully.

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Section: The Good Hope Conundrummentioning

confidence: 92%

Section: D L Foster Et Al: the Potential For Gamma-emitting Radmentioning

confidence: 99%

The potential for gamma-emitting radionuclides to contribute to an understanding of erosion processes in South Africa

et al. 2017

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“…Additional short term erosion pin data has been obtained for the catchment of the Ganora Dam and for a small catchment close to Ganora Farm (Rowntree, unpublished Cs. Sediment volumes have been estimated and several characteristics of the sediments have been measured including particle size (by laser granulometry), sediment geochemistry (ICP-OES) and colour (using a colour scanner), mineral magnetic properties and organic matter content (by loss on ignition and Carlo-Erba C:N analyser) (Foster et al, 2005(Foster et al, , 2007(Foster et al, , 2008Pulley et al, 2015;Pulley and Rowntree, 2016a,b).…”

Section: Methodsmentioning

confidence: 99%

“…Pulley and Rowntree (2016a) suggested that colour could also be used effectively for discriminating sediment sources in the Karoo. Environmental magnetism has proved to be especially useful in discriminating sediment sources in the region (e.g., Foster et al, 2007Rowntree and Foster, 2012;Pulley and Rowntree, 2016b) as the records in almost all dams show good preservation of fine grained magnetites that appear to be unaffected by post-depositional dissolution (Pulley et al, 2015).…”

Section: Sediment Source Tracingmentioning

confidence: 99%

Long-term studies of land degradation in the Sneeuberg uplands, eastern Karoo, South Africa: A synthesis

et al. 2017

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For the past 15 yr, the Sneeuberg uplands in the eastern Karoo, South Africa, have been a focus for research on land degradation by the above authors and other colleagues. Earlier work in the Karoo emphasised vegetation change whereas we concentrate on physical changes to the landscape at the small catchment scale, e.g., bare, degraded areas (badlands) and gully (donga) systems. Analysis of sedimentation in farm dams allows for reconstruction of environmental histories using 210 Pb, 137 Cs, geochemical and mineral magnetic properties of the sediments. Erosion rates on badlands are monitored using arrays of erosion pins. A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT2 Sediment source tracing within small catchments points to the importance of hillslope sources and the relative erosional inactivity of gully systems.Sediment supply from hillslope and colluvial sources is maintained by high rates of weathering on mudstones and sandstones. Current degradation should be viewed in the context of a c. 200 yr history of overgrazing by European-style stock farming and limited areas of former cultivation in the valleys. Grazing pressures are now much reduced but the loss of soils and vegetation suggests that landscape recovery will require several decades.Additional drivers of past degradation are likely to have been periods of drought and fire (natural and managed) and a gradual increase in both rainfall intensity and the frequency of extreme rainfall events. The future of the degraded Sneeuberg landscape will depend on future farming practices. Desirable options include more sustainable livestock practices, adoption of wildlife farming and other more benign regimes involving mixes of agriculture, tourism, and wildlife protection together with landscape rehabilitation measures.

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“…Papers by Pulley et al (2015) and van der Waal et al (2015) both demonstrated the use of magnetic fingerprinting to establish source-sink connectivity in South African catchments.…”

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confidence: 99%

Preface: proceedings of the 13th IASWS international conference

et al. 2015

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Conservatism of mineral magnetic signatures in farm dam sediments in the South African Karoo: the potential effects of particle size and post-depositional diagenesis

Cited by 25 publications

References 39 publications

The potential for gamma-emitting radionuclides to contribute to an understanding of erosion processes in South Africa

The potential for gamma-emitting radionuclides to contribute to an understanding of erosion processes in South Africa

Long-term studies of land degradation in the Sneeuberg uplands, eastern Karoo, South Africa: A synthesis

Preface: proceedings of the 13th IASWS international conference

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