Welcome to
Portarlington "Steeles Rocks" & Cliffs EarthCache
Please note that this EarthCache can be subjected to tide - Please plan accordingly
Portarlington is a historic coastal township located on the Bellarine Peninsula, 28 km from the city of Geelong. The area around Portarlington was originally inhabited by the aboriginal Wathaurung people. Aboriginal shell middens can be found along the cliff-line at Portarlington. Mussels are the dominant shell species in evidence, demonstrating the importance of mussels to the area, even in pre-historic times.
This continuous 200m outcrop of coastal cliffs here at the listed coordinates, (also known as Steeles Rocks) displays a variety of volcanic and sedimentary materials. The cliffed section, reaching 4 m high, extends from just west of the two large trees here westward to near the boat ramp up further, where the cliff swings inland to be a low bluff which turns coastward as a rocky promontory.
Weathered basalt outcrops in the west of the section (from the promontory to beyond the boat ramp) and is overlain with marked angular unconformity by ferruginous and calcareous and gravely sediments. The basal beds of the sediments are coarse sand and small gravels, passing upward into ferruginous cross-bedded sands and grits.
The upper metre of the section is a fossiliferous calcareous bed which in places has been further cemented by secondary calcite deposition. The fossils are all of living species of bivalves or gastropods.
At Waypoint 1 the geological sections are of the same material to those at Steeles Rocks however, the exposure at the cliffs here is more degraded. Although partly covered by slump deposits, This site exposes Older Volcanics basalt and tuff and overlying sediments.
The volcanics are best exposed nearer to the Portarlington Jetty where they form a wide, smooth gently sloping shore platform with variable gravel cover. In the platform, the basalts have a regular joint system which in places is infilled with secondary calcite plates.
The display of joint infilling in the basalts that you can see here along these sections of cliff is of particular interest and the shore platform is a clear example of a broad, horizontal platform segment developed in weathered Older Volcanics.
Questions to log this EarthCache
Q1 At the listed coordinates, the beds have a pronounced dip. Which direction are they dipping to and roughly what angle? How does this occur?
Q2 At WP1, what colour are the joints you can see in the cliffs and in the older Volcanics - also, are they soft or hard?
Q3 (Inaccessible at the moment) A̶t̶ ̶W̶P̶2̶,̶ ̶a̶l̶o̶n̶g̶ ̶t̶h̶e̶ ̶e̶a̶s̶t̶e̶r̶n̶ ̶s̶i̶d̶e̶ ̶o̶f̶ ̶t̶h̶e̶ ̶s̶e̶a̶ ̶w̶a̶l̶l̶,̶ ̶w̶h̶a̶t̶ ̶e̶l̶s̶e̶ ̶d̶o̶ ̶y̶o̶u̶ ̶s̶e̶e̶ ̶f̶o̶r̶m̶i̶n̶g̶ ̶l̶o̶w̶ ̶i̶n̶ ̶t̶h̶e̶ ̶c̶l̶i̶f̶f̶?̶
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