Seaham Quarry is significant to the history of Australian geology. The famous Australian geologist, Professor Edgeworth David first recognised the glacigene origin of the Carboniferous sediments in the Seaham area in 1914 and reported the occurrence of varved shales in the quarry, which rapidly gained fame in Australia and internationally because of the perfection of preservation of the varves and the associated contorted beds exposed in them.
At the time when Professor David discovered them, such formations - known as varve shales - were not known to exist in Australia. One other occurance was later discovered at Bondi.
David exhibited specimens of the varved shales in Honolulu in 1920 at the First Pan Pacific Science Congress, and three years later led a party of visiting scientists to the quarry on the occasion of the Second Pan Pacific Science Congress.
Professor Edgeworth David discovered the quarry whilst undertaking a survey for coal deposits in the Hunter Valley in 1884. The rocks are of glacial origin. The material of the rock is streaky in appearance, the result of the forces of moving ice overriding the sediments forming in glacial lakes. Each pair of streaks in the rock represents the annual winter and summer deposits. The quarry also exposes arching layers in places, which is due to the dragging force of glacier ice or icebergs Shale is a sedimentary rock which is laid down in layers of very fine grained mud and clay which compact into rock over many years. What was so important about the shales in this particular quarry though was that they were varved shales, which is a type of shale laid down in layers.
Varve Shales form in a variety depositional environments from seasonal variation in sedimentary processes.
The classic varve is a light / dark coloured pair of layers deposited in a glacial lake. The light layer usually comprises a coarser layer of silt and fine sand deposited under higher energy conditions when meltwater introduces sediment load into the lake water. During winter months, when meltwater and associated suspended sediment is reduced, and often when the lake surface freezes, fine clay-size sediment is deposited forming a dark coloured layer. In addition to seasonal variation of sedimentary processes and deposition, varve formation requires the absence of animal and plant disturbances.
There is a lose visual similarity between the laminated sediments, and tree-rings, and like tree rings, each layer can tell us a lot about the environmental factors that impacted that season.
Edgeworth David recognised that this quarry was of incredible scientific importance and returned in 1925 and erected a sign declaring the quarrys scientific importance and saying it should be 'preserved in perpetuity', which luckily for us, it has been.
To log this cache please send an email to firstname.lastname@example.org with the answers to the following questions: 1. How thick (on average) is each layer of varve shale? 2. How old are the shale deposits at Seaham Quarry? 3. What Direction do the quarry walls face? 4. What Else is Edgeworth David famous for?