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Wednesday, 10 August 2011

Te Mata Peak

Last week, following my visit to Castlepoint I also headed further north to Hawkes Bay. State Highway 2 runs parallel to the central North Island mountain ranges, which had just received fresh snow from a recent southerly blast, to provide a classic New Zealand pastoral scene...
Te Mata Peak near Havelock North is a popular spot for runners, hikers and paragliders. On a clear day there are  spectacular views across the landscape from the coast all the way to the volcanic peaks of Ruapehu in the centre of the North Island.

The buttresses of Te Mata Peak are made of Awapapa Limestone. This formation, which is about three and a half million years old, is also found to underly other nearby coastal hills in the Hawkes Bay area. It was formed along a string of offshore shallow water shoals and tidal banks. At that time the coastline was about 40 kilometres to the west, along the present edge of the central mountain ranges. In between, the sediments of the same age are mudstones that represent much deeper water than the Awapapa limestone.



Armed with my Kiwi Fossil Hunter's Guide, I located a way to climb down on the eastern side of the peak to have a close up look at the cliff section just north of a radio mast, a few hundred metres down from the summit car park.

 Although there isn't a wide variety of fossils in these rocks, there were some vary well preserved specimens such as these examples of a scallop called Phialopecten marwicki, as well as barnacles, oysters, brachiopods (lamp shells) and coral-like bryozoans.

In places, thinly bedded layers of shell fragments
show that water currents were strong, indicating shallow water conditions when the limestone was deposited.










Careful research by scientists has found that the alternating bands of hard, strongly cemented grey limestone and softer, orange sandy layers represent cycles of sea level change during the Pliocene Epoch.

The harder layers formed because at shallower depths there were more water currents, which allowed more calcium carbonate rich water to flow through the sediments. This would have been during the ice ages, when huge amounts of sea water were locked up in polar ice caps, thus lowering the sea level.

The warm period (interglacial) deposits have less carbonate cement to strengthen them and are therefore etched out more easily by erosion. These deeper water sediments are now underneath overhangs of the harder layers. The example here had clusters of large oyster shells scattered within it.



3 comments:

Pauline said...

Hi Julian, when I lived in Hawkes Bay - many years ago, we used to go walking/clambering over Te Mata peak and often picked up shells and fossilised bits and pieces. I always had such a sense of awe about that - here we were on the highest part of Hawkes Bay, and there was this stuff that ought to be under water.... [you can tell I had no geological education at that time in my life!] Great blog, will keep an eye on your doings! Pauline

Anonymous said...

its hawkEs bay - not hawks.
It has an E in it.

Suzanne Rosvall said...

Thanks Julian for this post. Found info very helpful for online geology course presently doing.