R for ROCKS

The bedrock of the Melbourne district is of Middle Palaeozoic age belonging to the Silurian and Devonian periods (354-441 million years ago). However, these rocks are overlain in wide areas by much younger rocks, mostly of Tertiary and Quaternary age (2-65 mya). The oldest rocks of the bedrock are Early Silurian in age (441 mya).

During the Pliocene (2-5 mya) and through into the Pleistocene (2 mya), there was substantial volcanicity, in two episodes. The first produced extensive sheets of basalt lava on the west side of Melbourne to form the Keilor and Werribee Plains. The second phase involved volcanoes to the north of Melbourne. These extruded flows that filled the valleys of the Moonee Ponds, Merri and Darebin creeks. Lava flows erupted from Hayes Hill near Mernda, flowed down the ancestral Merri Creek and Darebin Creek valleys into the Yarra Valley at Fairfield and down that valley onto the Yarra delta as far as the present site of Spencer Street bridge.

Quaternary sediments are principally represented by raised beaches and sand ridges around the coast. They are particularly well developed at Altona, where shell beds occur, and form valley fill in the Yarra River and its tributaries, and sediments of the Yarra Delta. The alluvial flats of the Yarra River upstream of the Yarra Gorge at Warrandyte are thought to have been formed as a result of grade changes following rejuvenation of the Yarra Fault, whereas the alluvial flats upstream from Fairfield and in some of the Yarra tributaries, such as Gardiners Creek, were formed as a result of the damming of the Yarra by a stream of basaltic lava flowing down the Darebin Creek valley.

In the Darebin Parklands quite a lot of exposed rock can be found, both in situ, as well as transported so that various enhancements to the aesthetic of the Parklands was achieved - for example the artificial hill (Mt Puffalo Viewing Hill constructed in 1998), and seen below.

This post is part of the Wordless Wednesday meme,

and also part of the ABC Wednesday meme,

and also part of the Nature Notes meme.