Dwyka Group

izingcwephe zeqhwa zimboza i Gondwana

Dwyka map

Amatshe angaphezu kweNatal Group ama-tillite agcineka endaweni yeqhwa lapho izingcwephe zeqhwa zahlehlela emuva eminyakeni engaphezu kwezigidi ezingamakhulu amathathu eyedlule.

Ice cap covering Gondwana 300 million years ago

Ngalesi sikhathi i-South Africa yayiseyingxenye yomhlabakazi i-Gondwana, eyayakhele ngasothini lwaseningizimu imbozwe yiqhwa. Amatshe ayequkethwe yiqhwa elalihamba kancane aklwebha apholisha amatshe amadala angaphansi akha imigwaqo yeqhwa. Imidwebo (imiklwebho) ikhomba ukuthi iqhwa lalihamba lisuka ngasenyakatho libheke ngaseningizimu lolu ulwazi olunzulu noma olubalulekile uma kuhlanganiswa kabusha i-Gondwana. i-Dwyka Group yakha amatshe angaphansi futhi amadala kunawo wonke abekeka kubheseni we-Karoo Supergroup. Lobheseni ululeke kakhulu mamaneningizimu ye-Gondwana futhi uloba iminyaka eyizigidi eziyikhulu namashumi omlando wezokumbiwa.

Striation on the rock surface caused by the movement of ice and boulders, UKZN Westville Campus (Move your mouse here to see the direction)

Picture adapted from: The story of Earth & Life (T. McCarthy & B. Rubidge)

Tillite (sedimentary)

Glaciers

Tillite is mostly a very fine-grained, blue-grey rock comprised of clay matrix with inclusions (or clasts) of many other fragments picked up by glaciers during their travels. The tillite in KZN often weathers to a characteristic yellowish colour. In the Durban area, cliffs near the mouth of the Umgeni River, and quarries in the Westville area offer the best exposures of tillite.