Otarawairere Beach

Here at Otarawairere Beach you can see the exposed, near horizontal Upper Ohope Beds which overlie the older greywacke sandstone and argillite (mudstone) sequence. The Ohope Beds contain a range of sediments from sand right through to gravels which means that the depositional environment fluctuated over the time of deposition. Within these beds you can also find layers of tephra (volcanic ash) which were deposited as pyroclastic fall from eruptions such as the Whakamaru eruption (350,000 years ago) and the Matahina eruption (320,000 years ago). In conjunction with the airfall tephra layers there are several paleosols present within the Ohope Beds. Paleosols are old soil horizons which would have had organic material within them (such as grass or other plants).

The unconformity present at the eastern end of the beach occurs where the 500,000 year old or younger Ohope Beds lie directly on the 145 million year old Torlesse greywacke basement rocks. The youngest beds within the Upper Ohope Beds contain pumice (from eruptions in the Taupo Volcanic Zone) and fossilised bivalves. These can be found alongside the walkway which links Ohope Beach with Otarawairere Beach. Some of the species of bivalves which are found in these beds approximately 42-55 meters above the present sea level can still be found in the ocean today.

As you head from Otarawairere Beach along the walkway to West End Ohope, you walk through the Torlesse sandstone and mudstone sequence up into the more recent Ohope Beds. Throughout you can see gravels and sand beds and higher up you can find the fossiliferous sandstone with whole bivalve fossils. Have a close look at the beds and think about the sort of environments that would have allowed them to form.

Erosion has also had a major impact on this area with much of the exposed Torlesse greywacke forming sea stacks and flat wave cut platforms. These are classic coastal erosion features.