scholarly journals Landscape responses to dynamic topography and climate change on the South African source-to-sink system since the Oligocene

2021 ◽  
Author(s):  
Claire A. Mallard ◽  
Tristan Salles
Keyword(s):  
South African ◽  
Large Scale ◽  
Sedimentary Basin ◽  
Drainage System ◽  
Sediment Flux ◽  
Mantle Flow ◽  
Dynamic Topography ◽  
The South ◽  
Source To Sink ◽  
Underlying Mechanisms

Abstract. The South African landscape displays important lithological and topographical heterogeneities between the eastern, western margins and the plateau. Yet the underlying mechanisms and timings responsible for this peculiar layout remain unclear. While studies have proposed a post-Gondwana uplift driver, others have related these heterogeneities to a more recent evolution induced by deep mantle flow dynamics during the last 30 million years. This theory seems supported by the rapid increase of sediment flux in the Orange basin since the Oligocene. However, the triggers and responses of the South African landscape to dynamic topography are still debated. Here we use a series of numerical simulations forced with Earth data to evaluate the contribution of dynamic topography and precipitation on the Orange river source-to-sink system since the Oligocene. We show that, if the tested uplift histories influence deposits distribution and thicknesses in the Orange sedimentary basin, they poorly affect the large-scale drainage system organisation and only strongly impact the erosion across the catchment for two of the four tested dynamic topography cases. Conversely, it appears that paleo-rainfall regimes are the major forcing mechanism that drives the recent increase of sediment flux in the Orange basin. From our simulations, we find that climate strongly smoothed the dynamic topography signal in the South African landscape and that none of the currently proposed dynamic topography scenarios produce an uplift high enough to drive the pulse of erosion and associated sedimentation observed during the Palaeocene. These findings support the hypothesis of a pre-Oligocene uplift. Our results are crucial to improve our understanding of the recent evolution of the South African landscape.

Dynamic topography controls on source-to-sink systems: Example of the last 40 Ma in South Africa.

2020 ◽  
Author(s):  
Claire Mallard ◽  
Tristan Salles ◽  
Sabin Zahirovic ◽  
Xuesong Ding
Keyword(s):  
South Africa ◽  
South African ◽  
Surface Processes ◽  
Source Surface ◽  
Mantle Flow ◽  
Dynamic Topography ◽  
The South ◽  
Geological Record ◽  
Source To Sink ◽  
The Impact

<p>Over deep time, mantle flow-induced dynamic topography drives deposition moderated by higher-frequency fluctuations in climate and sea level. The effects of deep mantle convection impact all the segment of the source to sink systems at different wavelengths and over various scales which remains poorly quantified. Field observations and numerical investigations suggest that the long-term stratigraphic record along continental margins contains essential clues on the interactions between dynamic topography and surface processes. However, it remains challenging to isolate the fingerprints of dynamic topography in the geological record.</p><p>We use the open-source surface evolution code Badlands (badlands.readthedocs.io), to quantify the impact of different timings and wavelengths of dynamic topography migration on the South African landscape responses.</p><p>We test three different dynamic topography scenarios obtained by both backwards advection and forwards modelling of mantle flow. We investigate their influence on landscape dynamics, stratal geometries and depositional patterns of South Africa over the past 40 Ma. We compare the evolution of the drainage organization, sediments flux, and stratigraphy obtained with the models with seismic, geochronological, and thermochronological data. We demonstrate that inland incision, spatial sediment accumulation, and depocenter migration strongly depend on the direction of sediment transport relative to the direction of dynamic topography propagation. It allows to identify realistic evolutions of mantle flow associated with the South African uplift history. Our results suggest that our source-to-sink numerical workflow can be used to explore, in a systematic way, the interplay between dynamic topography and surface processes and can provide insights into recognizing the geomorphic and stratigraphic signals of dynamic topography in the geological record.</p>

‘Burn it down!’: Materialising intersectional solidarities in the architecture of the South African Embassy during the London Poll Tax Riot, March 1990

2019 ◽  
Vol 38 (2) ◽  
pp. 233-250 ◽  
Author(s):  
Gavin Brown
Keyword(s):  
South Africa ◽  
Working Class ◽  
South African ◽  
Large Scale ◽  
The South ◽  
The West ◽  
England And Wales ◽  
Metropolitan Police ◽  
Trafalgar Square ◽  
Poll Tax

This paper offers a new way of conceptualising how intersectional solidarities are actualised. It recounts and theorises an outbreak of radical internationalism, when working class struggles in Britain and South Africa were unexpectedly linked. It examines how intersectional solidarity was materialised through a process of coming together against the architectural fabric of the South African Embassy and considers the interwoven temporalities that enabled this action to occur. On 31 March 1990, nearly a quarter of a million people demonstrated in London against the Poll Tax that was due to take effect in England and Wales the following day. On the day, the Metropolitan Police lost control of an already enraged crowd and provoked a large scale riot that engulfed the West End of London for several hours. In the midst of the riot, during a short retreat by the police, protesters took the opportunity to attack the South African Embassy in Trafalgar Square – many windows were broken and an attempt was made to set the building alight. Drawing on interviews with former anti-apartheid protesters who were present on that day (and who had concluded a four-year long Non-Stop Picket of the embassy a month earlier), this paper explores and analyses their memories of that unexpected moment when their previously symbolic call to ‘burn it down’ was (almost) materialised. In doing so, it contributes new ways of conceptualising the spatiality and temporality of intersectional solidarity.

Combining tomographic images and geodynamic modeling of past mantle flow: from simple analytical solutions to numerical inverse methods

2020 ◽  
Author(s):  
Lorenzo Colli
Keyword(s):  
Analytical Solutions ◽  
Mantle Convection ◽  
Large Scale ◽  
Thermal Evolution ◽  
Past History ◽  
Tomographic Imaging ◽  
Mantle Flow ◽  
The South ◽  
Future Evolution ◽  
Trade Offs

<p><span>Physics-based geodynamic modeling of mantle convection provide a unifying framework for solid-Earth sciences, explicitly linking together disparate fields such as tectonophysics, tomographic imaging, basin analysis, mantle mineralogy, geomorphology, global geodesy and the long-term chemical and thermal evolution of the mantle. Studying the evolution of mantle convection in time is particularly powerful as it reduces trade-offs, increase the possible linkages and the opportunities to cross-test hypotheses. But since mantle convection evolves over geologic timescales, its future evolution is precluded from us and we must focus on its past history.</span></p><p><span>Here I will show how geodynamic modeling of past mantle flow can be combined with tomographic imaging and geologic observations, highlighting the strengths of this approach and some of its potential pitfalls. I will use a series of case studies, starting from simple analytical solutions for channelized flow in the South Atlantic and Caribbean regions. I will move on to an application of sequential assimilation to the South China Sea, ending with computationally demanding large-scale numerical optimizations of past mantle flow.</span></p>

V. ‘Capitalist Influence’ and the Transvaal Government during the Crown Colony Period, 1900–1906.

1968 ◽  
Vol 11 (2) ◽  
pp. 301-331 ◽  
Author(s):  
D. J. N. Denoon
Keyword(s):  
South African ◽  
Large Scale ◽  
Gold Mining ◽  
Political Power ◽  
The South ◽  
Mining Companies ◽  
South African War ◽  
Responsible Government ◽  
Material Interests ◽  
The Face

It has become a tradition to portray Transvaal history as a struggle between Boer nationalism and international capitalism, from the beginnings of large-scale gold mining in the 1880s until the electoral victory of General Botha and Het Volk in 1907. J. A. Hobson, writing in 1899–1900, predicted that after—as before—the South African War, the Imperial Government would have to face the dilemma of choosing between ‘an oligarchy of financial Jews, and the restoration of Boer domination’, since there was no other basis of political power. In his analysis of Transvaal white politics, he admitted that some gold-mining companies (the J. B. Robinson group, Barnato's and sometimes the companies of Albu and Goertz) were hostile to the influence of larger companies (Eckstein's and Consolidated Gold Fields), but denied that this affected the monolithic nature of international capitalism in the Transvaal. Later writers on the period, who have rejected almost everything that Hobson wrote, have nevertheless endorsed his interpretation. The Boer leaders were understandably happy to approve of such an analysis, since it placed them in a flattering light as the only realistic salvation for a magnate-dominated society. General Botha, for example, ardently courted the white working men on the Rand after the War, stressing the identity of material interests between farmers and artisans, in the face of the capitalist threat. General Smuts presented a more subtle and persuasive version of the argument, when attempting to persuade the Colonial Office to grant responsible government to the Transvaal and Orange River Colony.

Example of the interplay of Tectonics, Eustasy and Surface Processes on the North Slope of Alaska Since the Jurassic

2020 ◽  
Author(s):  
Cian Clinton-Gray ◽  
Sabin Zahirovic ◽  
Claire Mallard ◽  
Tristan Salles ◽  
Daniela Garrad
Keyword(s):  
Landscape Evolution ◽  
Sedimentary Basins ◽  
North Slope ◽  
Mantle Flow ◽  
Dynamic Topography ◽  
The North ◽  
Sediment Routing ◽  
Source To Sink ◽  
North Slope Of Alaska ◽  
Shelf Margin

<p>The North Slope of Alaska has experienced a complex tectonic and geodynamic history. Although regional paleogeographic reconstructions for the North Slope of Alaska have been interpreted from the geological record, a process-based understanding of the source-to-sink system accounting for both the landscape and sedimentary basin evolution of the region has not been undertaken. Additionally, the interaction of the complex tectonic and climatic forces and their influence on the development of sedimentary basins is not well understood. </p><p>We investigate the influence of tectonics (including deep mantle flow), eustasy and isostasy (including flexure) on the source to sink system on the North Slope to better understand its evolution since the Jurassic.</p><p>We use a quantitative forward modelling approach with the open-source surface evolution code Badlands () which incorporate time-dependent dynamic topography estimates from mantle convection models linking plate motions and mantle flow. We present a new method to implement 3D tectonic displacements (including dynamic topography) in landscape evolution models.  </p><p>The models capture the North Slope’s complex tectonic history and reproduce the sediment depositional trends as observed from the sedimentological record. The spatial variation in dynamic topography through time results in tilting of the basin which influenced sediment routing directions. Sea-level fluctuations significantly slow the depositional system, trapping more sediment in the proximal basin. Cross-sections of the modelled deposition are used to more closely analyse the shelf margin evolution. They reveal that the models reproduce the large-scale stratal geometries observed from the seismic record, as well as the shelf margin trajectory shifts since the Jurassic. This study demonstrates the importance of linking deep Earth processes to landscape evolution models to gain a better understanding of the long-term evolution of sedimentary basins.</p>

scholarly journals Disaster management and humanitarian logistics – A South African perspective

2011 ◽  
Vol 5 (1) ◽  
Author(s):  
Wilna L. Bean ◽  
Nadia M. Viljoen ◽  
Hans W. Ittmann ◽  
Elza Kekana
Keyword(s):  
South Africa ◽  
South African ◽  
Large Scale ◽  
Critical Role ◽  
Humanitarian Logistics ◽  
Future Research ◽  
The South ◽  
Management Context ◽  
African Perspective ◽  
The Impact

Disasters are becoming an unavoidable part of everyday life throughout the world, including South Africa. Even though South Africa is not a country affected by large-scale disasters such as earthquakes, the impact of disasters in South Africa is aggravated significantly by the vulnerability of people living in informal settlements. Humanitarian logistics, as a ‘new’ sub-field in the supply chain management context, has developed significantly recently to assist in disaster situations. This paper provides an overview of the South African humanitarian logistics context. Even though humanitarian logistics plays a critical role in the aftermath of disasters, it extends far beyond events that can typically be classified as ‘disasters’. Therefore the implication of the South African humanitarian logistics context on future research and collaboration opportunities in South African humanitarian logistics is also discussed. Finally, two recent case studies in the South African humanitarian logistics environment are discussed.

Sediment flux across the south-Pyreneean foreland basin. A contribution to the S2S-Future network. 

2021 ◽  
Author(s):  
Philémon Juvany ◽  
Miguel Garcés
Keyword(s):  
Foreland Basin ◽  
Sediment Flux ◽  
Provenance Analysis ◽  
The South ◽  
Flexural Response ◽  
Eastern Pyrenees ◽  
Sediment Routing ◽  
Sedimentary Provenance ◽  
Source To Sink ◽  
Volumetric Quantification

<div> </div><div> <p>The early Eocene was a period of the intense collision during the formation of the Pyrenees. The flexural response to loading of the overriding European plate led to the formation of an elongated foredeep on the subducting Iberian plate which connected westward to the Atlantic Ocean. A thrust salient formed in the central Pyrenees, where Mesozoic Cover units travelled southwards on top of Triassic salt detachment. This process resulted in the sequencing of the foreland basin in different isolated sub-basins such as the Ripoll basin in the East, the Tremp-Graus and Ainsa-Jaca basins in central and western south Pyrenees and the Ager basin located south of the Tremp-Graus basin.  The precise timing and surface processes associated to this reorganization of the sedimentary routing system remains not totally understood. Indeed, various sedimentary provenance studies show that the sediments of the Tremp-Graus basin were sourced from a different catchment zone than those of the Ager basin. Besides, the Ripoll basin sediments provenance analysis shows major similarities with the Ager basin, suggesting a common catchment area in the Eastern Pyrenees. However, it has been pointed out that the clastic systems feeding the rapidly subsiding sink of the Ripoll through could not find their way towards the shallower Ager basin. In this PhD project we aim at providing further constraints to the paleogeographic reconstruction and sediment routing systems of the South Eastern Pyrenees in the light of a revised chronostratigraphic scheme. A Source-to-Sink approach will be followed to study the sediment Routing Systems and to decode the climatic and tectonic signal from the sedimentary record. It will follow a volumetric quantification of the sediment budget over the entire foreland, and a comparison with eroded rock volumes of the whole Pyrenees. The resulting revised scenario will seek conciliation of all available data from the stratigraphic, structural, petrologic, geochronologic and sedimentologic datasets with new radiogenic isotopes sedimentary provenance analysis.  </p> </div>

Do Contemporaneous Armed Challenges Affect the Outcomes of Mass Nonviolent Campaigns?*

2015 ◽  
Vol 20 (4) ◽  
pp. 427-451 ◽  
Author(s):  
Erica Chenoweth ◽  
Kurt Schock
Keyword(s):  
South African ◽  
Large Scale ◽  
The Philippines ◽  
Success Rates ◽  
The South ◽  
Data Set ◽  
Civil Resistance ◽  
Positive Effects ◽  
Negative Effect ◽  
Negative Impacts

Civil resistance is a powerful strategy for promoting major social and political change, yet no study has systematically evaluated the effects of simultaneous armed resistance on the success rates of unarmed resistance campaigns. Using the Nonviolent and Violent Conflict Outcomes (NAVCO 1.1) data set, which includes aggregate data on 106 primarily nonviolent resistance campaigns from 1900 to 2006 with maximalist political objectives, we find that contemporaneous armed struggles do not have positive effects on the outcome of nonviolent campaigns. We do find evidence for an indirect negative effect, in that contemporaneous armed struggles are negatively associated with popular participation and are, consequently, correlated with reduced chances of success for otherwise-unarmed campaigns. Two paired comparisons suggest that negative violent flank effects operated strongly in two unsuccessful cases (the 8-8-88 challenge in Burma in 1988 and the South African antiapartheid challenge from 1952 to 1961, with violent flanks having both positive and negative impacts in the challenge to authoritarian rule in the Philippines (1983–1986) and the South African antiapartheid campaign (1983–1994). Our results suggest that the political effects are beneficial only in the short term, with much more unpredictable and varied long-term outcomes. Alternately, violent flanks may have both positive and negative political impacts, which make the overall effect of violent flanks difficult to determine. We conclude that large-scale maximalist nonviolent campaigns often succeed despite intra- or extramovement violent flanks, but seldom because of them.

Sign in / Sign up

Export Citation Format

Share Document