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Thursday, 12 April 2012

Cape Kidnappers

Cape Kidnappers and the Clifton Cliffs make for a spectacular geological site in Hawkes Bay. The cliffs extend for several kilometres southwards from Clifton, on the coast near Hastings. They  are very high and consist of quite loose rocks, so it is important not to go too close where possible. It is also important to start your visit on a falling tide which will give enough time for a return trip without being cut off by high water.

At the start, near Clifton, the cliffs are made up of thick river gravels, with thin layers of white pumice (volcanic ash) and occasional dark layers of plant material.  Initially the beds are about 300 000 years old. Because they are dipping gently down to the north, you will pass further and further down the sequence as you walk along the beach to the south.and east. Here you can see the fluted erosion of the unconsolidated gravels caused by rainwater.



In this photo, a layer of light coloured volcanic ash separates overlying river gravels from marine mudstones below. Just above the ash is a very thin dark organic layer with plant remains in it.







There are many pale coloured ash layers in the sequence. They have been erupted from the Taupo Volcanic Zone in  the Central North Island, at least 150 kms away. The thickness of the layers even at this distance, testifies to the magnitude and violence of these past rhyolitic eruptions. In this photo you can also see how a fault has dislocated the beds by several metres.


Further along the beach, towards Black Reef, there is a distinct change in the bedding, seen in this image about half way up the cliff. The lower gently dipping beds have been eroded flat with much younger beds deposited on top of them. This unconformity represents a time gap of about two and a half million years. The lower unit is three and a half million years old - the upper one starts at about 1 million.



An exciting find on our visit was this fossil whalebone. It extended through the boulder for about one metre.







Out on the reef itself were some well preserved shell fossils as well as another orange coloured whalebone fossil slowly being eroded away.







Last but not least I should mention the gannets, for which Cape Kidnappers is most famous. The young birds here will take their first flight soon, and without looking back or touching down will travel all the way to Australia.










3 comments:

Anonymous said...

Interesting!!!

John S. from Perth said...

I am a geo from Aus visiting NZ. Great to find the info & photos in your blog. I am always keen to find out about local geology. Thanks Julian.

Anonymous said...

Awesome blog!