Whilst commuting North and South along SH4 over the last few years I've noted the interesting rock stata exposed at the roadside on the left as you head towards Te Kuiti. I researched their formation and geology and this Earthcache brings you to the site to see and experience.
What is Flysch? Flysch is a sedimentary deposit consisting of thin beds of shale or marl alternating with coarser strata such as sandstone or conglomerate. The difference in the textures of the layers are as follows; Sandstone is rough to the touch like sandpaper. Sandstone beds can range from a few centimetres to several metres thick. They have abrupt lower boundaries but pass gradually upwards into grey-coloured mudstone, which is smooth and breaks into centimetre-size chips. Mudstone may enclose 1-5 cm beds of cross-bedded fine sandstone which formed as migrating ripples on the sea floor Very fine sandstone or siltstone (grains too small to see with the naked eye) organised into thin parallel layers or wavy (convoluted) layers with small-scale (1-5 cm) cross-bedding. It is deposited when a deep basin forms rapidly on the continental side of a mountain building episode, in this case, the Whanganui Basin.
Whanganui Basin is a long-lived, major sedimentary basin. It has existed for 25 million years, moving steadily southward. Its origin is linked with the active volcanic arcs situated to the north of it. Whanganui Basin is one of New Zealand’s more remarkable geological phenomena. It contains cover strata that are up to 5 km thick under the South Taranaki Bight – that at the present-day is the centre of basin subsidence. This centre, however, is only the latest in a series of basin centres, extending back 25 myr in time, and to the central King Country, 200 km to the north. The effect of the progressive southwards shift of the basin centre, has been to stack strata in a shingled fashion, like a shelf of fallen-over books. These strata are well exposed between Te Kuiti and Taumarunui along SH4, to the right side of the image below. To the south, they dip underneath still younger deposits of the Whanganui Basin.
Earthcache tasks.
Please message me with your answers to the following tasks; There are two waypoints for this Earthcache which are good examples of flysch strata.
At the posted coordinates you can stand alongside the exposed rock face. Looking upwards, described the layers and the textures/grain sizes visible. How do the different layers differ and can you tell the two rock types (mudstone and sandstone) apart? What are the approximate thicknesses and colours visible?
At the 'Comparison' waypoint, how do the layers here differ from those at the posted coordinates?
What natural phenomenon will likely affect the layers composition at both of these sites?
Please provide a photo of yourself or a personal item to prove you visited the site. A personal item such as a handwritten name, or trackable is an option for those who do not want to photograph themselves.
You can log your find as soon as you like after your visit, if you need any help with the questions please let me know.