Cape Farewell

Cape Farewell erodes into part of the Farewell Formation (lower Kapuni Group) formed around 55-65 million years ago. The rocks are very distinctive quartz and feldspar rich sandstones and pebbly (gravel) conglomerates. Much of this region was above sea level during a relatively quiet period of tectonic activity. Significant erosion led to stripping of land-based sediment right up until the Middle Eocene (around 38 million years ago) to the Late Oligocene, when the land was finally submerged by tectonic subsidence.These rocks are therefore interpreted to have formed as the large quantities of sediments were pushed across an ancient coastal plain environment, either in a braided river floodplain, or high sediment meandering river system.

The process of coastal erosion is caused mainly by wave action in the surf zone, along with tides and currents. As waves are mostly an effect of wind, it is the top five or ten metres of the sea that is the most turbulent. This means that most coastal erosion occurs at or just below water level. The waves rush into the cliffs, undercutting them and giving rise to a great variety of features such as caves, blowholes, arches and stacks (of which you can see a cave and an arch at this location). Hard, resistant rocks like these sandstones and conglomerates form steep sea cliffs which stand out relative to bays where less durable material has been eroded away. Eventually the thin arch at Cape Farewell will be eroded into a 'stack' when the arch collapses through time.

Did you know - While originally mapped by Dutch explorer Abel Tasman during his first Pacific voyage in 1642-43, Cape Farewell was named by Captain James Cook in 1770, as it was the last land seen by his crew as they departed on their ship's homeward voyage.

Can you identify the different layers of sandstone versus conglomerate? How can you tell which is which? Describe what they look like in your own words. Can you identify old channels cut into the different layers? Notice how the rock layers (bedding) slope down towards the sea - while it might be tempting to think this tells you about the direction the river water was travelling in when it deposited these sediments, in fact this tilt is the result of tectonic uplift of the region directly inland (and to the east) in a type of fold known as an anticline. To figure out the direction the river was flowing in you need to get up close to the rock to see the pattern that the individual bits in it are arranged - called imbrication. While it's not possible to do this safely from this viewpoint, check out the GeoTrip at Wharariki Beach just down the road to get up close to these rocks!