Anthony's Cutting is located on Hopetoun Park Road, off the Western Freeway, 5.5 km east of Bacchus Marsh.
This location has state significance and shows an outstanding display of the relationship between the Bullengarook lava flow and various Tertiary and quaternary sedimentary formations in the Bacchus Marsh district. It is widely used as a teaching site in earth science courses to demonstrate principles of stratigraphy, structure and regional geology.
The cutting on the southern side of the Western Freeway reveals an important section into lava flows from Mount Bullengarook and Tertiary and Quaternary sediments. Flows of strongly jointed basalt outcrop at road level at the Melbourne end of the cutting and these are overlain by a 15 m thick deposit of cross-bedded non-marine Pleistocene sands and gravels. One hundred meters along the cutting (towards Bacchus Marsh), sandy clays, sands and gravels of the middle Tertiary Werribee Formation that underlies the Bullengarook lava flow are exposed at road level and the lavas are 10 to 15 m above road level. At the top of the Werribee Formation (beneath the lava flow) is a reddish zone in the sediments that is the weathering horizon and soil of the pre-basaltic land surface. It is therefore an example of palaeosol. Several types of jointing and weathering occur in the volcanics.
Basalt
Basalt is a common extrusive igneous (volcanic) rock formed from the rapid cooling of basaltic lava exposed at or very near the surface of a planet or moon. By definition, basalt is an aphanitic (fine-grained) igneous rock with generally 45-55% silica and less than 10% feldspathoid by volume, and where at least 65% of the rock is feldspar in the form of plagioclase. Basalt is defined by its mineral content and texture, and physical descriptions without mineralogical context may be unreliable in some circumstances. Basalt is usually grey to black in colour, but rapidly weathers to brown or rust-red due to oxidation of its mafic (iron-rich) minerals into hematite and other iron oxides and hydroxides. Although usually characterized as "dark", basaltic rocks exhibit a wide range of shading due to regional geochemical processes.
DO NOT ACCESS THIS EARTH CACHE VIA THE FREEWAY. PLEASE PARK AT THE LISTED COORDINATES AND WALK ALONG THE FENCE LINE. DO NOT GO TO THE EDGE OF THE BANK. YOU WILL BE ABLE TO ANSWER THE QUESTIONS FROM A GOOD FEW METERS BACK.
Questions
Q1 Count the layers that you see here. Also describe the layers colours and texture.
Q2 There are visible 'lines' in the cutting. What way do they run and why do you think they are here?
Q3 At what height above road level can lavas be seen? (Read Notes)
Once you complete the EarthCache requirements you can post your find without delay, as per the EarthCache guidelines. You will also need to verify your find by sending me a message and provide your answers to the questions.
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References ~ vro.agriculture.vic.gov.au, wikipedia & geology.com
Cache is a copy of a previous Earthcache at this location that was archived due to a loss of interest from the CO. I have duplicated with the permission of the original CO creator.