Centre fold

摘要

The painting by Maggie Newman depicts a scene at the time of formation of the dolomite of the Transvaal Supergroup approximately 2550 million years ago. The low-lying formation protruding above the water in the background consists of sandy sediment of the Black Reef formation at the base of the Transvaal Supergroup. Algal stromatolites in the form of domical structures proliferated above the Black Reef sands in warm shallow waters. They grew as partly submerged colonies along the shoreline in shallow water adjacent to the nearest headland. In the background, stromatolite domes of varying sizes - the taller ones being the oldest, are depicted. Towards deeper waters, the domes give way to slim columnar stromatolites, and at depth, to giant domes. Close-up specimens show green cyanobacterial layers which form the colliform structure of the stromatolite domes. Layering can be seen in the broken specimens and fragments lying on the sea bed.