Research Letters

Modern beachrock formation in Durban, KwaZulu-Natal

Hayley Cawthra, Ron Uken
South African Journal of Science | Vol 108, No 7/8 | a935 | DOI: https://doi.org/10.4102/sajs.v108i7/8.935 | © 2012 Hayley Cawthra, Ron Uken | This work is licensed under CC Attribution 4.0
Submitted: 17 September 2011 | Published: 11 July 2012

About the author(s)

Hayley Cawthra, Council for Geoscience, Marine Geoscience Unit, Cape Town, South Africa
Ron Uken, School of Geological Sciences, University of KwaZulu-Natal, Durban, South Africa

Abstract

We explored the recent cementation of modern beachrock on the seaward margin of the Durban Bluff, central KwaZulu-Natal. The low latitude and subtropical climatic setting is a unique context compared to the more commonly documented contemporary beachrock formation in the tropics. Geological field mapping was carried out and here we present results based on sedimentary facies of a clastic shoreline and carbonate diagenesis of interstitial cements using transmitted light microscopy. The beachrock was cemented by micrite and aragonite, and iron oxide infilled voids. The presence of human artefacts within the deposit showed evidence for cementation within the last century. The elevation (at Mean Low Water) and correlation to rates of sea level change for the east coast of South Africa showed that the beachrock is less than 72 years in age. In contrast to older local Pleistocene deposits, beachrocks have cemented along this stretch of coast during successive sea level highstands with similar climatic regimes – the last Interglacial, the Holocene High and the present. Here we report the most southerly documentation of modern beachrock in KwaZulu-Natal, which, to our knowledge, represents the youngest deposit reported in southern Africa.

Keywords

modern beachrock formation; carbonate cementation; marine phreatic diagenesis; recent sea level change; clastic shoreline

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