In Seaham there is a heritage listed geological site of international renown.
Professor Sir Edgeworth David FRS discovered the quarry whilst undertaking a survey for coal deposits in the Hunter Valley in the 1880's.
Seaham Quarry is of international scientific importance because of the perfection of preservation of its varved shales and the associated contorted beds exposed in them. The shale deposits are estimated by scientists to be more than 300 million years old. The quarry contains, in its shale deposits, evidence of the glacial origin of rocks in the Hunter River Valley. The rock layers here were formed by deposits forming from meltwaters in a glacial lake.
Varved shale
A varve is an annual layer of sediment or sedimentary rock. The word 'varve' derives from the Swedish word varv whose meanings and connotations include 'revolution', 'in layers', and 'circle'.
These shales are well banded or layered, the layers appearing in pairs. A thicker course layer represents summer deposits when the ice melts, and a thinner fine layer represents the winter deposit when most of the sediment is ‘locked’ in the ice. Each pair, or varve represents a seasonal annual deposit. Hundreds of paired layers of sediment were deposited in a glacial lake approximately 300 million years ago in the Late Carboniferous Period when this area lay further south towards the South Pole, estimated by Crowell and Frakes (1971) at a latitude of 45-50 degree south - between current-day Tasmania and Antarctica.
Shales are fissile rocks (can be split into layers) formed by the consolidation of clay, mud, or silt, has a finely stratified or laminated structure, and is composed of minerals essentially unaltered since deposition - the exact properties of a shale depend on the nature of the sediment that has formed it.
Logging requirements
In order to log a find on this EarthCache, you will need to answer the following questions, and include a photo in your log (see below).
Access the rockface at the published coordinates, just below the prominent information sign (see gallery), at the level of the nearby swamp.
1. Estimate the average layer thickness of the varved shale in Seaham Quarry.
2. Are all the layers identical? If not - what processes would you postulate as being responsible for variations?
3. From what you have learnt about varved shales above, and your observations at the quarry, estimate how long the layers you can see visible here at the rock face took to accumulate.
4. Photo - please include a photo of yourself or a personal item/GPS with the information sign at the published coordinates. This is a requirement - logs without the required photo will be deleted as per guidelines.