Tatapouri Cliffs and Shore Platform

BY JULIAN THOMSON (GEOLOGIST)
Accessibility: EASY
Trace fossils in mudstone, J.Thomson / GNS Science
Wave action has created an expansive shore platform showing layers with faults and sedimentary features
Tatapouri shore platform at sunrise, J.Thomson / GNS Science
The rocks at the headland of Tatapouri were laid down in the Middle Miocene (between 16 - 11 million years ago). They are made of layers of grey mudstone which at first sight seem rather plain and monotonous. These rocks are mostly quite soft, although they include regularly spaced harder layers within them. They were deposited in fairly deep water (several hundred metres at least) as marine avalanches or mudflows (turbidites).
Because of their relative softness, these rocks are eroded quite easily. The cliffs are undercut by wave action and the debris is then broken down and washed away to leave the expanding shore platform at the intertidal level. The harder layers stand out as small ridges, with the softer material eroded out to form the depressions and pools.
Tatapouri cliffs, J.Thomson / GNS Science
The shore platform is an extensive surface where the strata stand out clearly as parallel lines. Have a look for faults that offset the layers. Some of the faults criss-cross each other at an angle. Take a look at one of the faults: can you work out how much the beds have actually been displaced in relation to their original horizontal orientation? (In other words, can you work out the 'real' vs the 'apparent' displacement of the fault?)
In the boulders at the base of the cliffs, you can see interesting sedimentary features, such as convoluted bedding - caused by slumping of the layers as water was squeezed out of them during burial. There are also numerous large burrows of creatures (trace fossils) that lived within the soft sediment.
Can you find any shell fossils?
Directions/Advisory

Follow the coast road north out of Gisborne for about 10 kms until you come to Tatapouri Beach. Towards the northern end of the beach, turn right onto Makorori Road, and park anywhere convenient along it on the grass beside the beach.

Be aware that these cliffs are actively eroding, especially during or after rain. They are at a relatively low angle at the southern end (which is therefore the safest place to explore the boulders at the base), but steeper and more hazardous around the headland further north, where you will see evidence of large rockfalls abd block slides.

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Accessibility: EASY

An easy walk along the beach for a few hundred metres.

Features
Sedimentary Fossils Landform Active Erosion
Geological Age
Mid Miocene 11 - 16 million years old
Zealandia Evolution Sequence
Māui Supergroup (Emergence): 25 – 5 million years ago