Geology of the Vredenburg-Velddrif-Saldanha areas handed over to Municipality
The Council for Geoscience (CGS) officially handed over geological maps to Saldanha Bay Municipality on 19 June 2017 at a ceremony held at the Vredenburg Council Chambers. The map sheets covering Vredenburg, Velddrif and Saldanha is part of the 1:50,000 scale map series of the CGS.
Detailed geological maps are a basic requirement in all decision-making processes surrounding the management of proposed new developments. The construction of the industrial development within the Saldanha Bay Municipal area spurred rapid regional economic development and, hence increased the need for more detailed knowledge of local geological conditions and resources.
The mapping programme was undertaken by Dr Pieter Siegfried when he was still with the CGS, whereas the cartographic work was done by Elmi Pretorius, assisted by CGS staff at Head Office in Silverton, Pretoria. The maps are accompanied by a sheet explanation containing a description of geological units and their history of formation. All such maps, as well as more generalised 1:250,000 scale maps, are available from the CGS as vector data for use on Geographic Information Systems (GIS).
The geologically young sands and limestone of the Saldanha-Vredenburg-Velddrif area is underlain by folded, fractured and metamorphosed sedimentary rocks of the Malmesbury Group intruded by granites of the Cape Granite Suite. The Malmesbury is approximately 560 million years old and comprise mostly quartzite and shale that, due to intense fracturing and deep regional weathering, mostly occur under sand in topographically depressed areas, outcropping only along the coast.
The granites are igneous rocks that intruded the Malmesbury sediments between about 540 and 500 million years ago. They are more resistant to weathering than the Malmesbury rocks and therefore dominate the landscape as rounded hills and ridges. Their texture vary from fine grained to coarse grained and about 25 different types with different physical characteristics and varying compositions have been identified in the map area. The different granite types of Saldanha and Vredenburg are separated by a prominent fault in the area named the Colenso Fault. The fault crosses the Vredenburg-Saldanha road at the Langebaan/Jacobsbaai turnoff.
Volcanic rocks called ignimbrites (tuff and ash welded together) occur at Postberg, west of the Langebaan Lagoon. These deposits erupted from a local caldera at the surface simultaneously with emplacement of granite magma at greater depths below it. The biggest part of the volcanic caldera structure is now located offshore.
Much younger fluvial, phosphatic and calcareous sediments, as well as marine shell and boulder deposits with lithified calcareous dune sediments (aeolianites) are grouped together as the Sandveld Group and cover by far the largest surface area. They are the result of rapidly evolving climate and repeated rise and fall of sea levels during the past 30 million years.
The mining history of this area mainly entails exploitation of industrial and construction materials. Phosphate mining in the Langebaan area led to the discovery of a rich fossil fauna that gives us a unique insight into the recent geological and climatic history of this area. Gypsum was worked on a small scale at Sandy Point and Stompneus Bay. Kaolin deposits formed locally through deep weathering along faults in the granite.
Two important resources of underground water, the Langebaan Road and Elandsfontein aquifers, have been recognised in the area.
Dr Pieter Siegfried and Executive Mayor Cllr Marius Koen with Mr Fhatuwani Ramagwede (GCS Acting Chief Operations Officer) and Mr Leonard Matsepe (GCS Chief Financial Officer) at the handover of the geological maps.