Chancet Rocks Reserve

BY PERCY STRONG (GNS)
Accessibility: EASY
Putting a finger on the K-Pg boundary. J.Thomson / GNS Science
An accessible outcrop where you can see the world-renowned K-Pg boundary layer (formerly known as the 'K-T boundary')
Fault offsetting strata at Chancet Rocks, J.Thomson / GNS Science
Chancet Rocks reserve has two main limestone ridges, separated by a low area. The once horizontal rock layers here were laid down on the sea floor, and have been tilted up almost vertically by deformation of the crust. The outcrop has long been known for its vase-shaped “fossil sponges”, which are now recognised as a trace fossil, or burrow, called Paramoudra, created by an unknown animal. More recently, a very complete section through the Cretaceous-Paleogene boundary was identified and confirmed by the presence of the 'iridium anomaly' with 10’s of times the normal concentration of iridium (a very rare metal) in a thin clay layer. This layer has been recognised worldwide and marks the end of the Age of the Dinosaurs, caused by a devastating asteroid impact that struck part of where Mexico's Yucatan Peninsula is today. In these marine sediments Cretaceous microfossils become extinct at this layer, and earliest Paleogene ones occur immediately above it. In November, 2017, the Magnitude 7.8 Kaikoura Earthquake raised Chancet Rocks by about 2 metres, exposing large new areas of the tidal platform.
Chancet rock before the Nov 2016 earthquake uplift. J.Thomson / GNS Science
1. Cretaceous-Paleogene Boundary. This usually lies in a cleft between light pink, knobbly-bedded Upper Cretaceous limestone and thinly bedded, light-green Early Tertiary limestone with dark chert (silica) bands. About 20 cm of dark grey limestone marks the boundary, and 2 cm of dark grey, soft clay lie precisely at the boundary. Here you can put your finger on the layer that represents a global mass extinction event!
2. Paramoudra. These may be seen in the rocks 'above' the Cretaceous-Tertiary boundary.
3. Coastal uplift. The old high-tide line is clearly shown of the reefs just south of Chancet Rocks. This is a great place to appreciate the power of the Kaikoura Earthquake!
Directions/Advisory

From Ward, follow Seddon Street for 2.8km, then turn right onto Ward Beach Road for about 3.7km to where it terminates at a picnic ground with plenty of parking.

Difficult footing in some places can be a fall hazard

Accessibility: EASY

From the car park, walk north along the beach for about 1.5km until you reach the rocks

Features
Sedimentary Fossils Active Fault
Geological Age
The rocks are variously assigned to the Mead Hill Formation or the Amuri Limestone. 65 million years old
Zealandia Evolution Sequence
Haerenga Supergroup (Submergence): 85-35 million years ago
Links
Watch this video about another K-T / K-Pg boundary layer at a nearby outcrop in Woodside Creek: https://youtu.be/pASB81WN2pw