Sedimentation on the narrow (8 km wide), oceanic current-influenced continental shelf off Durban, Kwazulu-Natal, South Africa

“…This surface is typically formed by inlet migration during transgression. This ravinement surface is, in turn, overlain by the Holocene sediment wedge, which is relatively poorly defined in this area compared to other localities on the South African continental shelf (Martin and Flemming, 1986;Cawthra et al, 2012a).…”

Section: Incised Channels/palaeodrainagementioning

confidence: 82%

Understanding Late Quaternary change at the land–ocean interface: a synthesis of the evolution of the Wilderness coastline, South Africa

Cawthra

Bateman

Carr

et al. 2014

Quaternary Science Reviews

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“…As a consequence, deposits on continental shelf and slope are laterally extensive with high accumulation rates (Kuehl et al, 1997;Hübscher et al, 2002;Hanebuth et al, 2011). In contrast, bypassing, winnowing and erosion of sediments, sweeping by persistent unidirectional currents, and redeposition are common processes on shelves dominated by a high-energy oceanographic regime (Flemming, 1981;Ikehara, 1989;Cawthra et al, 2012). The knowledge on the general sedimentary buildup and evolution of these high-energy systems remains sparse due to difficulties in sampling the commonly coarse-grained material.…”

Section: Introductionmentioning

confidence: 99%

The high-supply, current-dominated continental margin of southeastern South America during the late Quaternary

et al. 2014

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The continental margin off the La Plata Estuary (SE South America) is characterized by high fluvial sediment supply and strong ocean currents. High-resolution sediment-acoustic data combined with sedimentary facies analysis, AMS-14C ages, and neodymium isotopic data allowed us to reconstruct late Quaternary sedimentary dynamics in relation to the two major sediment sources, the La Plata Estuary and the Argentine margin. Sediments from these two provinces show completely different dispersal patterns. We show that the northward-trending La Plata paleo-valley was the sole transit path for the huge volumes of fluvial material during lower sea levels. In contrast, material from the Argentine margin sector was transported northwards by the strong current system. Despite the large sediment volumes supplied by both sources, wide parts of the shelf were characterized by either persistent non-deposition or local short-term depocenter formation. The location and formation history of these depocenters were primarily controlled by the interplay of sea level with current strength and local morphology. The high sediment supply was of secondary importance to the stratigraphic construction, though locally resulting in high sedimentation rates. Thus, the shelf system off the La Plata Estuary can be considered as a hydrodynamic-controlled end-member.

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“…Its continental shelf is very narrow (12 to 47 km) (Bosman et al ., ; Cawthra et al , ) when compared to the global average of 78 km (Shepard, ; Kennett, ). The southeast African shelf gradients vary from 2° to 8° (Cawthra et al , ). Inland the coast has a high freeboard (Orford et al , ) and a steep hinterland gradient (5°), 250 km inland from Durban the topography reaches 3000 m. The high freeboard means that high wave run‐up cannot dissipate onshore and this results in an offshore‐directed relaxant flow (Smith et al ., ).…”

Section: Kwazulu‐natal Coastlinementioning

confidence: 99%

Apparent dynamic stability of the southeast African coast despite sea level rise

Smith

Bundy²,

Cooper

2016

Earth Surf Processes Landf

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The coast of southeast Africa is dominated by sandy beaches that tend to be confined within log‐spiral or headland‐bound embayments. Investigations using serendipitous air imagery data set have been previously undertaken and conclusions drawn about the stability of the coast. We show that conclusions drawn from this data, with respect to the high water mark (HWM) position are fraught with errors, which include tidal state, pressure regime, beach slope, high‐swell erosion, seasonal and multi‐annual changes. We highlight and discuss these sources of error, together with their magnitudes. The most significant of these are the high‐swell, seasonal and multi‐annual variations. From case studies we show that the seasonal beach rotation and long‐term beach width variation are responsible for tens of metres of unaccounted HWM variation, 30 to 50 m is common, with maximums reaching 60 to 100 m. Overall the southeast African coastline appears to be in a state of long‐term dynamic equilibrium. There is no evidence of any sea‐level rise‐forced transgression in the coastal sediment budget, despite sea‐level rise (SLR). If such a signal is, in fact present, it is lost within the beach width variation. Some southeast African coastal reaches are suffering chronic erosion, but these are related to anthropogenic impacts. The extreme difficulty of placing a HWM, with any temporal validity on this coast precludes the routine use of the Bruun Rule. Although no transgressive signature is found, there is evidence of a decreasing coastal sand budget as a result of anthropogenic or natural climate change, or both. This decrease in the coastal sand volume is likely to result in increased future erosion. Copyright © 2016 John Wiley & Sons, Ltd.

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Sedimentation on the narrow (8 km wide), oceanic current-influenced continental shelf off Durban, Kwazulu-Natal, South Africa

Cited by 29 publications

References 45 publications

Understanding Late Quaternary change at the land–ocean interface: a synthesis of the evolution of the Wilderness coastline, South Africa

Understanding Late Quaternary change at the land–ocean interface: a synthesis of the evolution of the Wilderness coastline, South Africa

The high-supply, current-dominated continental margin of southeastern South America during the late Quaternary

Apparent dynamic stability of the southeast African coast despite sea level rise

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