We have put together a series of earthcaches along the N2 in the Eastern Cape and this is just one of them. We got really excited at the prospect of putting together these earthcaches after doing some research. Little did we know just how varied our possibilities were and how diverse the geology is in this province! We hope you enjoy them and learn a great deal of our beautiful part of the planet.
A word of caution however – this cache is not for children and extra care needs to be exercised when walking along this road as it is extremely busy. Ensure that you park well into the shoulder of the road before alighting.
An Earth cache is a special type of Virtual Cache that is meant to be educational. Therefore to log a find you must demonstrate that you have learnt something from the site and experience.
Send your answers to us in an email via our profile page.
Any logs not accompanied by an email will be deleted.
Logging Tasks:
1) On the other side of the road, when looking south-west, there is a guidance sign for exiting the N2. How far to go to the offramp?
2) What does aeolian mean?
3) Describe this dune (bedding, colour and grains/texture).
As an optional request please take a picture of you and/OR your navigational device with the Aeolian crossbeds of this road cut in the background and post it with your log.
The Nanaga Formation
The formation consists of Pliocene-Pleistocene aeolian deposits. During each still-stand of sea level, a coastal dunefield was deposited. This process still occurs today along the existing coastline of Algoa Bay. The resultant ancient dunefield cordons formed during the Tertiary Period (65 to 2 million years ago) have been preserved as rolling hills of the Grassridge, (which occurs at heights of 245 - 320 metres above mean sea level) and Nanaga areas and called the Nanaga Formation. This aeolian deposit attains thicknesses of up to 250 metres and extends from Paterson in the north, down to Woody Cape in the south and as far east near to Grahamstown. This formation obviously gets progressively younger towards the coast, as the sea level receded.
The Nanaga Formation generally comprises semi- to well-consolidated calcareous dune rock (sandstone) and sandy limestone. It is very prominent as fine-grained red sands, which form the high-lying topography. These are easy to identify where exposed in the cuttings, generally covered by very red soil, and themselves showing as buff-coloured, cross-bedded sandstones that are quite soft, not yet having been compacted by deep burial or hardened by metamorphism. In this cutting at the listed coordinates the high angle of cross-bedding identifies the rock as wind-laid as opposed to water-laid, where the maximum angle of repose of sand is significantly lower.
The Nanaga Formation overlies Bokkeveld shales, hence produces more saline than elsewhere. High salinities are also recorded in boreholes drilled in the Nanaga in these catchments. As a result, runoff from the Nanaga in these catchments generally produces high salt loads.
Other Fossil Dunes and dunefields
As many as eight fossil dunefields occur within the Algoa Bay hinterland region. The oldest lies near Paterson. These dunefields, which are now much degraded and fully vegetated, can be regarded as fossil versions of the Alexandria dunefield. They are represented as dune cordons that tend to lie parallel to the present coastline. The road cuts at Nanaga show aeolian crossbeds, the distinctive internal structure of the fossil dunes. Suites of fossil dune ridges, up to 80m high, that trend east/west parallel to the prevailing wind, occur in the Cape St Francis region. Between Slangbaai and Tsitsikamma River. Further west sets of impressive fossil dune cordons occur at Wilderness. The dunes themselves are now entirely vegetated, and the inter-dune valleys are now lakes. The previous wide extent of dunefields in this area is indicated by remnants of the fossil dunefields now submerged under the sea.
Acknowledgments and recognition
Geological Journeys by Nick Norman and Gavin Whitfield
dwaf Albany Coast Assessment
Addo Geology