The Marble Delta
The Marble Delta is the name given by geologists to the geological formation where limestone is mined in Southern Natal. It is situated close to the confluence of the Umzimkulu and the Umzimkulwana Rivers, between them and to a lesser degree to the north and south of them.
At its nearest point it is about 11 kilometres inland of Port Shepstone and is several kilometres wide covering an area of approximately 40 square kilometres. The formation occurs in an area of steeply incised valleys but does not extend into the Oribi Gorge.
Location of the Marble Delta Formation.
The limestone was precipitated onto the floor of a shallow sea that covered the Delta and possibly a much wider area in Pre-Cambrian times. A period of intense metamorphism (heat and pressure) followed and the limestone was recrystalised into marble. The strata were subsequently intensely folded, warped and intruded by granite type rocks.
The Marble Delta Group consists of three distinct formations, each of a different character.
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The Cherrywillingham Formation consists mainly of amphibolites and granulites. This is the uppermost formation and overlies the Oribi Formation and the Le Jonquet Formation, which are coarsely crystalline.
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The Oribi Formation is predominantly calcitic with interbedded dolomitic and graphitic layers and is mined by Natal Portland Cement, (NPC) in their Simuma operation.
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The Le Jonquet Formation is the name given to the lowest levels. This formation is largely dolomitic. Dolomite is calcium carbonate, which includes a certain percentage of magnesium. This dome is roughly elliptical in shape and extends to below sea level. Mining operations have exposed more than 1000 metres of limestone but the base has as yet not been touched.
The Marble Delta is the major source of limestone mined in KwaZulu-Natal and the limestone mined here is of the highest quality in South Africa. The marbles are intruded by igneous rocks of different kinds. There are also a pink, coarsely crystalline, gneissic granite and a dark green and black charnokitic granite that outcrop in the bottom of the Oribi Gorge.
The reserves of this high-grade calcite and dolomite are in excess of 300 million tonnes.
The Origin of the Marbles.
This marble began as a shallow sedimentary deposit of the skeletal remains of minute marine organisms.
As this was progressively overlain by more and more sediments the pressure built up, and as pressure generates heat, great heat was built up within the deposit of lime-rich material. This pressure and heat were sufficient to cause physical and chemical changes in the rock and it was altered into coarsely crystalline rock that we call marble.
Note: The marble used in architecture and sculpture is a micro-crystalline hard rock that rings like porcelain when struck.
The Earthcache
To reach the site of the Earthcache, follow the N2 from Port Shepstone towards Harding and Kokstad. Shortly after cresting the long hill about 10 km from Port Shepstone, you will see the P262 turning from the N2 on your right (waypoint supplied). Travel along the P262 and descend into the Umzimkulwana gorge. The Information Centre is on your left, opposite the cement factory, shortly before you cross the Umzimkulwana River bridge.
At the published co-ordinates you will find an Information Centre, as well as a Geological Window with interesting information on the formation and use of the rocks of the Marble Delta.
Geological Window - Side 1
Geological Window - Side 2
At the Quarry Viewpoint (a short drive from the Information Centre) you will be able to park your car in a safe location (there is a laybye / picnic table at this point). From here you will have an excellent view of the "White Rocks of Natal" and the quarrying operations.
Quarry View
Logging Requirements
In order to log this Earthcache and claim a find, you will need to complete the following tasks / questions.
- Describe in your own words how the formation of these carbonate rocks came about.
- What would you expect to happen if acid rain (containing sulphur compounds) came into contact with the limestone?
- Describe the quarrying methods being used to mine the limestone - these can be seen from the viewpoint at S 30° 39.616 E 030° 19.642.
- Take a picture of yourself / your caching team (with GPS visible) at the Quarry Viewpoint (optional).
Please do NOT detail your answers in your Found log. Email answers directly to me via the GC.com website.
You may submit your Found log without waiting for confirmation. if there is a problem with your answer(s) I will get back to you. Found logs will be deleted if an email is not received with 2 days.
