Whakataki Shore Platform

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.

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!