Don't Try This At Home EarthCache

Around 500 million years ago sedimentation in the Adelaide geosyncline came to an end as huge forces in the Earth's crust squeezed the region, crushing and folding the rocks, and creating a tall mountain range where there had been a shallow sea. This geological event is known as the Delamerian Orogeny. Although the tall mountains no longer exist, the eroded stumps are the Mt Lofty and Flinders Ranges, the processes of their formation have left many features in the landscape.

The most obvious evidence of an orogeny is tilting of rock layers. Sediments on a sea floor are laid down close to horizontal.  The rocks, which the sediments formed, have then been folded and tilted into all sorts of angles. Coastal rocks north of the earthcache site show this feature clearly, as waves have eroded softer and harder layers differently exposing the bedding layers.  At some locations folding has been so intense that rock layers have ended upside down. Many of the rocks on the coast between Second Valley and Myponga Beach are in this reversed position.

At the earthcache location in the cliffs of Second Valley you can see the layers turned, twisted and folded in a spectacular fashion. The location is at the southern end of the Adelaide geosyncline in rocks formed from sediments laid down in shallow seas. To the south and east are the deep sea rock formations of the Kanmantoo trough. Second Valley is located at the boundary between these two rock types.

The light and dark stripes in the rock cliff clearly show the folds and slippages created as the sediment layers were crushed in the core of a major fold. This is one of the best exposures of such intensely folded structures in the Mt Lofty Ranges. The rock on display was originally layers of limestone.  Heat and pressure has metamorphosed the limestone to a form of marble.