The subsiding sea floor was a depotcentre for the sediment from the eroding higher ground to its west. As the climate changed, so did the deposition of these sediments. The coarseness and colour of the alternating layers resulting from the climatic changes can now be read in the rocks, allowing a climatic history of the area to be read from the rocks much like the pages in an ancient book. 

The Cryogenian Earth was a time of severe climate upheaval that included two glaciation periods. The first was the Sturtian glaciation (approx 716-658 million years ago), which was an intensely cold period of immense glaciation that extended from the north pole to the south pole. The second was the shorter but global Marinoan (or Elatina glaciation) (639-635 million years ago).

There was an interglacial period (650 million years) between these two glaciations and the geological successions record warmer interglacial conditions with an ancient barrier reef forming. within the Adelaide Rift Complex. The outcropping rocks located in the Arkaroola Protection Area and Vulkathunha-Gammon Ranges National Park, represent one of the oldest such reefs in the world.  The gorge of the Kingsmill Creek has such a barrier reef structure, which is known as the Arkaroola reef. 

The emergence of macroscopic animal life is preserved in these rocks or a range of Stromatolite forms, which are layered sedimentary formations created by microorganisms that produce adhesive compounds that cement sand and other rocky materials to form mineral “microbial mats”. In turn, these mats build up layer by layer, growing gradually over time.

Unfortunately I didn’t have the geological knowledge to read the layered history of the reef building as I didn’t really know what I was looking for. I was just looking at the different layered structures of the gorge walls . Nor could I read how the different stromatolite forms or assemblages were a response to the changing environmental conditions and sea level activity.

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