Ecca group

ukusondela kuma-latitudes afudumele

Ecca group map

Ngenkathi i-Gondwana inyakaza ibheke ngasenyakatho isondelela eduze nenkabazwe, imibhede yebumba nodaka yandlaleka phansi olwandle olukhulu olwakhiwe ubheseni we-Karoo. Lezi zinhlayiya zakha ama-shale e-Pietermaritzburg Formation. 

Ecca shale
Ecca shale is typically dark-coloured as they are carbon-rich due to the high vegetation content of the original sediments. Fine bedding or laminations may also be noted, and the shales tend to easily crumbled.

Ngaphezulu kunohla lwamatshe olugcwaliswe ama-sandstone ampunga abizwa ngokuthi i-Vryheid Formation. Lama-sandstone abekeka maduze nezihlabathi ezingasosebeni, lapho emva kwakho kulele amaxhaphozi agcwele izihlahla ezibizwa ngokuthi ama-Glossopteris. Ukumbozeka kokuluhlaza emaxhaphozini kwaholeleka lapho kwakheka amalahle okuyimanje ambiwa e-Vryheid. Ucwaningo olunzulu lwama-sandstone akhomba imigudu yama-fossil eyakhiwa izilwane ezinemizimba ethambile. Lokhu kubonakala ngezimbotshana ematsheni. Lokhu kufana nokutholakala manje izilwane ezigubha umhlabathi ezifana nezinkalankala.

The northern coastline of the Karoo Sea was shallow, and large swampy deltas formed. The accumulation of plant material in these swamps resulted in the formation of peat. Gradually over time with increasing heat and pressure due to burial, the peat turned into coal.

Modified after: The story of Earth & Life (T. McCarthy & B. Rubidge)

Simplified map of active coal mines. (Courtesy Council for Geoscience)

When southern Gondwana emerged from below the ice, several tree-like plants had evolved. Glossopteris was one of the most dominant trees. These plants rapidly colonised the large deltas, where they grew in extensive swamps. In these swamps dead vegetation accumulated faster than it could decay. The burial of the vegetation in the swamps eventually formed coal which is  mined in northern KwaZulu-Natal.

Glossopteris leaves

near Cedara, KwaZulu-Natal. The original leaves have been oxidised and replaced by iron oxide. Move your mouse here for a detailed view. (Specimen: Geology Education Museum)

Coal (sedimentary)

Fossilised plant matter

Coal

Coal is economically important , as it is South Africa’s most abundant fossil fuel and source of energy. Coal is black to brown and a soft and light rock composed of the carbon remains of plants.  It is found as seams, or layers within shales and sandstones of the Ecca group.  The quality of South African coal is usually low with a low heat value and a high ash content. In KwaZulu-Natal, the seams are deeper and thinner than in other parts of the country, but of a higher quality.

Shale (sedimentary)

Lagoons, swamps and sandy shorelines

Shale is a fine-grained sedimentary rock formed by the consolidation of silt and clay. Ecca shales are typically dark-coloured as they are carbon-rich due to the high vegetation content of the original sediments. Fine bedding or laminations may also be noted, and the shales tend to be easily crumbled.