Waipatiki Beach.

BY JULIAN THOMSON (GNS)
Accessibility: easy
Fossils at Waipatiki, J.Thomson@GNS Science
At the north end of the beach you can explore the boulders along the shore that contain an abundance of fossils from a shallow water environment. The blue-grey mudstone rocks that can also be seen were laid down at greater depths of about 50 - 80 metres.
Fossil burrows, Photo J.Thomson@GNS Science
The orange grey sandy limestone blocks along the shoreline have fallen from quite high up the cliff. These rocks are interesting to explore for fossils as well as different sedimentary structures and types of layers. Good views of the cliffs can be seen looking south from the beach. Have a look at the different layers of rock in them noticing the change in texture and colour of the strata. The lower section of the cliff (which can be hard to see due to being covered by grass and fallen material) is grey mudstone or sandy mudstone and would have been deposited at several tens of metres depth in the sea. Higher up the orange layers represent shallow water deposits. That means that through time this locality experienced a change from a deep to shallow water environment.
Cliffs at Waipatiki Beach showing limestone, sandstone and mudstone layers. Sophie Thomson
The rocks that you will look at have all fallen from different parts of the cliffs above. Note the variety of different fossils including shells, sea urchins and trace fossils. Also look for different sedimentary structures and layers and try to put this all together to imagine the environmental conditions at the time these sediments were formed . Some of the shells have been weathered out to leave empty moulds. This is because they were made up of a type of calcium carbonate called aragonite that easily weathers away. The carbonate is then re-precipitated into the surrounding rock to make it very tough, like concrete.
Directions/Advisory

There is a car park at the road end at Waipatiki Beach from where you should walk for a few minutes to the left (north) to where large boulders lie on the shoreline.

Very large rockfalls have occurred from the cliffs at the south end of the beach between 2015 and 2017 and it is no longer recommended to explore there due to the hazard. The track has been partly destroyed by these cliff falls.
Instead turn left as you reach the beach and visit the rocks at the north end which include exactly the same strata and types of fossils. Note there is still a hazard, so use your own judgement, and avoid visiting in very wet weather.

Accessibility: EASY

There are boulders on the beach that can be investigated, or you can climb up to a narrow path and follow it below the base of the cliffs for a short distance to access the shoreline a bit further away from the beach. It is likely to require some scrambling over some large, slippery and sharp boulders.

Features
Sedimentary Fossils
Geological Age
Pleistocene , 2 My old.
Zealandia Evolution Sequence
Pākihi Supergoup: 5 million years ago – present
Links
There is some information about the geology of Waipatiki here http://juliansrockandiceblog.blogspot.co.nz/2012/04/waipatiki-beach.html