Whakataki Shore Platform

Accessibility: EASY
Whakataki shore platform, J.Thomson / GNS Science
The shore platform is made of alternating layers of sandstone and mudstone that have been uplifted from the sea floor, tilted and then eroded. The softer mudstone has been eroded out more easily by the sea, leaving impressive ridges of sandstone that form parallel lines extending for hundreds of metres.
Whakataki shore platform, J.Thomson / GNS Science
These rock layers were deposited as turbulent flows of sand and mud that avalanched down and over the sides of an underwater channel about 500 to 1000 metres below the ocean surface. These sorts of deposits are known as turbidites. Here they are of early Miocene age (roughly 20 million years old)

These bottom hugging, fast moving turbidity flows carried a mixture of sand and mud from the continental shelf down onto the deep sea floor. As they slowed down, the heavier sand would be laid down first and then the finer mud would slowly settle on top. Over many thousands of years, the layers were added cyclically to create a thick sequence. They were then gradually uplifted and eroded to appear as they do today.
Whakataki shore platform, J.Thomson / GNS Science
Try to identify individual turbidite flows. The base will usually be a relatively coarse or solid looking sandstone layer with a sharp base that gets finer grained upwards and transitions into a finer mud or silty layer.. Note that the turbidite units are not always the same thickness. Also look for different features in the sandstone layers such as flat laminations with overlying convolutions, ripples or cross bedding, graded bedding etc. Try to identify a commonly repeated pattern of these features in the layers, and notice that some of the turbidites have a larger variety of these sedimentary features than others.

Also look for faults where the sedimentary layers are offset along a clearly defined line, and notice how some layers are broken up by joints (cracks) at right angles to the bedding direction. These joints are further apart within the thicker, more massive layers.
Macrofossils (visible to the naked eye) are not common at Whakataki, but it is always worth keeping a look-out for them in any sedimentary rock. You may be lucky!

Turn left 4kms before Castlepoint and follow the Mataikona Road for just over 5kms. There is a safe spot to park by the roadside, adjacent to the extensive shore platform

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Accessibility: EASY

It is a short scramble down onto the shore, which is an irregular rocky surface that can be very slippy when wet.

Sedimentary Rock Deformation
Geological Age
Early Miocene age (roughly 20 million years old).
Zealandia Evolution Sequence
Māui Supergroup (Emergence): 25 – 5 million years ago
Blog post with some information at http://juliansrockandiceblog.blogspot.co.nz/2012/04/whakataki.html Video about the rocks at Whakataki: https://youtu.be/RYU2zKM6vqA