Uplift at Ward Beach

While the uplift itself can be precisely dated to just after midnight on the 14th November 2016, the geology here that has been exposed is much older. Most of the rock here is Mead Hill Formation with a bit of Amuri Limestone - all part of the Muzzle Group and Seymour Group. These rocks were all laid down on the sea floor. They represent a time during the Late Cretaceous and cross into the Cretaceous-Paleogene (K-T) Boundary. This boundary is best expressed to the north at Chancet Rocks Reserve (see link for GeoTrip).

During the Kaikōura Earthquake, this part of the coastline was uplifted around 2.2-2.6 m as a response to rupture along the Needles Fault (the offshore extension of the highly active Kekerengu Fault), located about 2 kilometres offshore. From the Waima River to the south, the uplift gradually decreases north to Cape Campbell, ranging from nearly 3 m down to just less than half a metre as the fault moves away from the coast. The change in ground level at Ward Beach has forced the Flaxbourne River to abandon its estuary and incise through the former estuary bed and gravel beach deposits, exposing more of the bedrock beneath.

See if you can identify the high and low tides marks for yourself - look for the extent of the dead remains of white coralline algae on the rocks for the average low tide mark, and a darker stained line on the rocks for the corresponding high tide mark. How far apart are they in height? This will tell you the extent of the tidal range along this beach before the uplift.

The uplift and incision of the estuary has also lead to exposure of some more of the Mead Hill Formation rock along the river, which has lovely graded bedding layers visible in the distinctly green coloured rock. Graded bedding forms when you have decreasing energy levels during deposition of a single layer of sediment. The larger, heavier particles settle out first as they are hardest for water to carry, followed by gradually smaller and finer particles. In the rock record, this looks like a layer that has big bits at the bottom grading to fine at the top. The presence of graded bedding in sand layers is often a key indicator of mass movement deposits called turbidites - these form in the ocean as material comes loose and tumbles down the underwater slopes, often triggered by earthquakes!