The Great Detective Series has been placed by clare007, Gizmos Gang and CPwanderer to celebrate the fictional detective, Sherlock Holmes, created by Sir Arthur Conan Doyle. The geocaches are placed in the vegetation area around the town of Sherlock and can be reached via a series of dirt access tracks and some short walks. You could, alternatively, park in the town and walk to the caches.
"Sedimentary my dear Watson!"
Admittedly a slight variation on the famous exclamation of Sherlock Holmes ( "Elementary my dear Watson!") but this is relevant to this Earthcache location. Use your deductive observational skills, as Sherlock would have done, to answer the questions listed below!!
At ground zero you will see some large boulders of Calcrete. This is a form of limestone very different to that produced by the calcium rich remains that make up the cliffs found along the River Murray. In arid and semi arid regions soils are rich in Calcium Carbonate. The low rainfal leads to an upward leaching of this material leading to the formation of a layer within the soil. While soils in tropical areas can be up to hundreds of metres thick, arid soils profiles are very shallow as there is a lack of water and decaying vegation to promote weathering of underlying bedrock.
So how does a calcium rich layer within the soil lead to boulders on the surface? With so little vegetation in arid areas to hold the thin top soil in place this layer is often removed.... thus exposing the calcrete layer underneath! In many cases this layer forms as small rounded nodules, In this case the calcium carbonate builds up around other particles. At other times this layer hardens into large sheets of material, thus leading to large boulders as we see at this GZ.
Throughout the Murraylands, Riverland, Eyre and York Peninsulas calcrete has been a nuisance to farming.If you drive through these regions many farms have mounded piles of this material..... handpicked by early colonists in order to clear the very sub standard land for farming.
Your lask is to examine the largest boulder at ground zero and use your detective like observational skills to answer the following.....
1. Examine the boulder carefully. Can you see any evidence of fossils?
2. If calcrete has been exposed for a period of time there can be variations in the exposed surfaces due to weathering. Is there any difference between the topside of this boulder and the sides and base? ie. colour, grain size, surface smoothness or cracking? (this would indicate if this boulder has been lying in situ for some time)
3. Calcrete often has "foreign" material within it. Can you see any other material within the Calcrete> If so describe it?
4. A nearby human activity has exposed this boulder. What could it be?
Please message me your answers. You may log your visit before receiving confirmation however your log will be deleted if your answers are not received within 2 weeks or fail to correctly answer the questions.