Stratigraphy and palaeoenvironmental interpretation of late Quaternary colluvial slope deposits in southern Africa

2021 ◽  
Author(s):  
J. Knight
Keyword(s):  
Southern Africa ◽  
Land Surface ◽  
Late Quaternary ◽  
Ecological Factors ◽  
Surface Instability ◽  
Sediment Supply ◽  
Spatial And Temporal Patterns ◽  
Catchment Scale ◽  
Accommodation Space ◽  
Slope Sediment

Abstract Slope and lowland sediment systems throughout southern Africa are dominated by the presence of colluvium with interbedded palaeosols and hardground duricrusts. These sediments correspond to phases of land surface instability and stability, respectively, during the late Quaternary. This study examines the stratigraphy and environmental interpretation of slope sediment records from specific sites in southern Africa for the period of marine isotope stages (MIS) 6 to 1 (~191 ka to present), informed by theoretical ideas of the dynamics of slope systems including sediment supply and accommodation space. Based on this analysis, phases of land surface instability and stability for the period MIS 6 to 1 are identified. The spatial and temporal patterns of land surface conditions are not a simple reflection of climate forcing, but rather reflect the workings of slope systems in response to climate in addition to the role of geologic, edaphic and ecological factors that operate within catchment-scale sediment systems. Considering these systems dynamics can yield a better understanding of the usefulness and limitations of slope sediment stratigraphies.

A proposed chronostratigraphic framework for the late Quaternary of southern Africa

2021 ◽  
Author(s):  
J. Knight ◽  
J.M. Fitchett
Keyword(s):  
Southern Africa ◽  
Environmental Variability ◽  
Late Quaternary ◽  
Evolutionary Development ◽  
Testable Hypothesis ◽  
Data Types ◽  
Spatial And Temporal Patterns ◽  
Quaternary Period ◽  
Climate And Environmental Change ◽  
Time Periods

Abstract The principles of chronostratigraphy can inform the process of correlation between different palaeoclimate records, enabling the coherence of spatial and temporal patterns of past climates and environments to be identified based on the physical, chemical, biological and isotopic properties of individual depositional units. This study presents a chronostratigraphic framework for the late Quaternary of southern Africa, based on the integration of palaeoclimatic and palaeoenvironmental proxy data from key records across the country from the start of Marine Isotope Stage 6 (~191 ka BP) to present. The methodology adopted in this study involves, first, wiggle-matching between sufficiently long and continuous records from different regions across southern Africa, informed by radiometric age controls from individual records. Based on interpretive limitations of these records, we then integrate different geomorphic and archaeological data types in proposing successive chronostratigraphic time periods that collectively extend through the late Quaternary of southern Africa. These time periods correspond to phases in which, within them, a certain set of (relative) stable climates or environments existed in different regions of southern Africa, as recorded in different ways in different proxy records. The boundaries between successive time periods are identified where there is evidence for a significant change in the workings of the climate or environmental system as reflected in the preserved proxy record found in a certain locality. These chronostratigraphic units are interpreted as reflecting the impacts of external forcing that is of regional extent, synchronous, and are not merely an outcome of local environmental variability. These chronostratigraphic phases identified for the late Quaternary period also correspond to distinctive technological and cultural phases in the southern African archaeological record, demonstrating links between coeval climate and environmental change and phases of human evolutionary development. This chronostratigraphic approach provides both a correlative framework for understanding the varied late Quaternary records of southern Africa, and a testable hypothesis for considering the synchroneity or otherwise of different records and thus their associated forcing factors.

Stratigraphy of late Quaternary mountain slope landforms and deposits in southern Africa and their significance for the dynamics of mountain sediment systems

2021 ◽  
Author(s):  
J. Knight ◽  
S.W. Grab
Keyword(s):  
South Africa ◽  
Southern Africa ◽  
Late Quaternary ◽  
Sediment Supply ◽  
Eastern Cape ◽  
Mountain Slope ◽  
Quantitative Evidence ◽  
Gravity Driven ◽  
Great Escarpment ◽  
Steep Slopes

Abstract Mountains are areas of high potential sediment yield due to their steep slopes and generally cool, wet climates. Mountain sediments are moved by gravity-driven and often cryogenically-influenced processes, and captured within valleys or footslopes in the form of screes, alluvial/colluvial fans and terraces, or on hillslopes in the form of solifluction sheets, debris lobes/ridges and openwork block deposits. This study critically examines the geomorphic, sedimentary, stratigraphic and dating evidence from cryogenically-influenced late Quaternary slope deposits found along the highest sectors of the Great Escarpment in the Eastern Cape Province (South Africa) and Maloti–Drakensberg range (Lesotho, and KwaZulu-Natal Province, South Africa). This evidence is set in the context of mountain weathering and erosion/transportation processes during the late Quaternary, and the dynamics of such sedimentary systems. Despite many general reports and observations, there is little detailed and quantitative evidence for late Quaternary slope processes, products and stratigraphy in southern Africa. This study integrates the existing morphological, sedimentary and dating evidence to examine mountain slope evolution in southern Africa based on the conceptual framework of sediment cascades. Application of this framework can help explain the spatial and temporal differences in sediment supply and dynamics observed in different sectors of the Great Escarpment during the late Quaternary.

An Environmental History of Southern Africa

2020 ◽  
Author(s):  
Jasper Knight
Keyword(s):  
Environmental History ◽  
Southern Africa ◽  
Land Surface ◽  
Environmental Changes ◽  
Late Quaternary ◽  
Global Scale ◽  
Time Intervals ◽  
Ecological Processes ◽  
Environmental Controls ◽  
Proxy Indicators

Southern Africa has experienced significant environmental changes since the breakup of the Gondwana supercontinent, starting around 180 million years ago. These environmental changes broadly reflect the interplay between tectonic and global-scale climatic drivers, which in combination result in changes to the properties and dynamics of land surface physical and ecological processes. The preserved record of such processes can be used as proxy indicators to reconstruct past environments and climates. In southern Africa, different types of proxy indicators have formed and are preserved in different geographical areas, broadly corresponding to their individual climatic and geomorphic contexts. Three significant time intervals over which landscape evolution have taken place are the Phanerozoic, the late Quaternary, and the last 200 years. A critical outcome of this analysis is that the record of environmental change in southern Africa is highly variable and only partly preserved, and that there are spatial and temporal gaps which mean that it is difficult to construct a continuous or unambiguous environmental history either for all areas of the region or for all time intervals. Changing physical drivers and environmental controls over time, including land surface feedbacks, are now being supplanted by a stronger imprint of human activity in the Anthropocene.

Carnivore Size and Quaternary Climatic Change in Southern Africa

1986 ◽  
Vol 26 (1) ◽  
pp. 153-170 ◽  
Author(s):  
Richard G. Klein
Keyword(s):  
South Africa ◽  
Southern Africa ◽  
Late Quaternary ◽  
Geochemical Data ◽  
Mathematical Relationship ◽  
Carnivore Species ◽  
Quantitative Estimates ◽  
The Relationship ◽  
Problematic Aspect ◽  
Cool Conditions

The relationship between carnassial length and latitude south is analyzed for 17 African carnivore species to determine if individuals tend to be larger in cooler climates, as predicted by Bergmann's Rule. With modern data in support, middle and late Quaternary temperatures might then be inferred from mean carnassial length in fossil samples, such as those from Equus Cave, Elandsfontein, Sea Harvest. Duinefontein, and Swartklip in the Cape Province of South Africa. One problematic aspect of the study is the use of carnassial length and latitude as necessary but imperfect substitutes for body size and temperature, respectively. For some species, another difficulty is the relatively small number of available modern specimens, combined with their uneven latitudinal spread. Still, in 14 of the species, carnassial length does tend to increase with latitude south, while mean carnassial length in the same species tends to be greater in those fossil samples which accumulated under relatively cool conditions, as inferred from sedimentologic, palynological, or geochemical data. Given larger modern samples from a wide variety of latitudes, refinement of the mathematical relationship between carnassial length and latitude in various species may even permit quantitative estimates of past temperatures in southern Africa.

Late Quaternary deep marine sediment records off southern Africa

2021 ◽  
Author(s):  
H.C. Cawthra ◽  
E.W. Bergh ◽  
E.A. Wiles ◽  
J.S. Compton
Keyword(s):  
Southern Africa ◽  
Late Quaternary ◽  
Strongly Correlated ◽  
Sea Level Fluctuations ◽  
Proxy Records ◽  
Terrestrial Environments ◽  
Bottom Waters ◽  
Resolution Mapping ◽  
And Shifts ◽  
Glacial Periods

Abstract High-resolution mapping, sampling and analysis of upper Quaternary southern African continental margin sediments recovered from beyond the Last Glacial Maximum shoreline (>130 m water depth) have expanded our understanding of how marine and terrestrial records are linked over glacial-interglacial climatic cycles. This paper synthesises data currently available from the deep seafloor around southern Africa and, specifically, core sites that demonstrate terrestrial sedimentological connectivity. Several proxies and case studies reveal the evolution of depositional systems, palaeoceanography and palaeoclimate over the last 191 kyr. Hydroacoustic mapping and investigations of submarine canyons have been carried out primarily on the eastern and southwestern margins, while palaeoceanographic productivity and microfossil assemblages have been applied most extensively on the western marine and southern Agulhas Bank. Studies on the western margin indicate that enhanced productivity, less oxygenated bottom waters and reduced marine faunal diversity in the transition to glacial periods, while glacial terminations are associated with reduced productivity and more oxygenated bottom waters. These changes, linked to palaeoceanography and late Quaternary sea-level fluctuations, influence the sedimentary record and sedimentation rates. On the eastern margin, sediment fluxes applied as proxies for rainfall offshore of the Great Kei, Umzimvubu, Limpopo and Zambezi rivers indicate that the southern African climate responds to changes in orbitally-modulated insolation and in particular, to the ~23 kyr precessional cycle, where the proxy records keep pace with this and then diverge at ~80 to 70 kyr. Since the penultimate glacial (Marine Isotope Stage/MIS 6), more humid conditions observed in southern Africa, as the Northern Hemisphere entered phases of rapid cooling, were potentially driven by a combination of warming in the Agulhas Current and shifts of the subtropical anticyclones. Broadly, the sedimentary records reviewed suggest fluctuations in climate and oceanographic circulation that are strongly correlated with the global benthic δ18O record, suggesting sensitivity to high-latitude forcing, and a strong influence of late Quaternary glacial-interglacial cycles despite these marine sites being far-removed from terrestrial environments.

scholarly journals Australian net (1950s–1990) soil organic carbon erosion: implications for CO<sub>2</sub> emission and land–atmosphere modelling

2014 ◽  
Vol 11 (18) ◽  
pp. 5235-5244 ◽  
Author(s):  
A. Chappell ◽  
N. P. Webb ◽  
R. A. Viscarra Rossel ◽  
E. Bui
Keyword(s):  
Soil Erosion ◽  
Organic Carbon ◽  
Soil Organic Carbon ◽  
Land Surface ◽  
Total Carbon ◽  
Catchment Scale ◽  
European Settlement ◽  
Surface Models ◽  
Management Context ◽  
Land Use And Management

Abstract. The debate remains unresolved about soil erosion substantially offsetting fossil fuel emissions and acting as an important source or sink of CO2. There is little historical land use and management context to this debate, which is central to Australia's recent past of European settlement, agricultural expansion and agriculturally-induced soil erosion. We use "catchment" scale (∼25 km2) estimates of 137Cs-derived net (1950s–1990) soil redistribution of all processes (wind, water and tillage) to calculate the net soil organic carbon (SOC) redistribution across Australia. We approximate the selective removal of SOC at net eroding locations and SOC enrichment of transported sediment and net depositional locations. We map net (1950s–1990) SOC redistribution across Australia and estimate erosion by all processes to be ∼4 Tg SOC yr−1, which represents a loss of ∼2% of the total carbon stock (0–10 cm) of Australia. Assuming this net SOC loss is mineralised, the flux (∼15 Tg CO2-equivalents yr−1) represents an omitted 12% of CO2-equivalent emissions from all carbon pools in Australia. Although a small source of uncertainty in the Australian carbon budget, the mass flux interacts with energy and water fluxes, and its omission from land surface models likely creates more uncertainty than has been previously recognised.

Sign in / Sign up

Export Citation Format

Share Document