Cache of the Month December 2020 – The Sugarloaf Earthcache

Hallett Cove is one of South Australia’s foremost natural science treasures. Concepts of superposition of strata, unconformities, folding and faulting of sedimentary rocks are clearly displayed. In 1877 Professor Ralph Tate discovered evidence of ancient glaciation in the form of polished and striated rock surfaces on the cliff tops and the site has attracted scientific attention ever since. The area has seen at least three separate glaciations in its long history, and displays evidence of a cold, dry, windy climate during a fourth. Recognition of past climatic variations provides a historical context for understanding current climate change.

The proximity to Adelaide, the diversity of rock types and field relationships, the evidence of past glaciations, and the remnant native flora and fauna have made Hallett Cove a highly valued conservation park with wide application in public education. Many generations of school and university students in disciplines as diverse as geography, history, geology, palaeontology, botany, zoology, archaeology and environmental science have enjoyed informative excursions to this site. For many geology students, Hallett Cove was their first introduction to field geology, where detailed structures produced by sedimentary, glacial, tectonic and erosional processes can be observed and studied.

The Sugarloaf is an outstanding example of an isolated butte. The dark coloured hard capping has protected the lighter material from erosion. The Sugarloaf, named for its resemblance to a mass of hard refined sugar, is the best known feature in the Hallett Cove Conservation Park. The shape of the feature is due to erosion by rain and wind over the last few thousand years. However the layes tell a much longer story. Around 280 million years ago southern Australia (including Hallett Cove) was covered by an ice cap. It melted about 270 million years ago. The distinct red and white layers of sediment were deposited on the bottom of an ancient glacial meltwater lake. The ‘red beds’ are sand and clay that contain dropstones. The regular layering indicates that the clay was deposited in calm water. White sand forms the main portion of the Sugarloaf. At the base of the Sugarloaf is a layer of clay and boulders that fell from ice floating across the lake. The Sugarloaf is capped by a thin ‘young’ layer of brown alluvial clay which was deposited by a river between one to two million years ago.

The Sugarloaf Earthcache was the first earthcache published in South Australia.  GCM4WR published in November 2004 was the fourth earthcache published in Australia, and is in the first twenty on the planet.  The earthcache has at this time 287 finds and 35 favourites. This is an old school earthcache.  There are a couple of questions to answer from the site sign and two required pictures to submit.  There are currently another four nearby earthcaches to find in this geological wonderland.

Inline with Geocaching SA’s goal of promoting the past-time of Geocaching is South Australia, each month the association will be highlighting a cache that warrants recognition. There are no specific criteria, and suggestions are welcome, but final discretion lies with Geocaching SA.

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