Tora Coastal Anticline

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The fold at low tide, J.Thomson / GNS Science
The Tora Coastal Anticline is a major fold in the rock layers exposed on the Tora coast, which is caused by tectonic stress. It is an anticline where the centre of the fold has been pushed up. At this locality the sea has eroded off the crest of the fold, exposing the internal structure.
Looking south west over the eroded anticline, Tora Coast. K.Amai / VUW
Well-bedded layers of sandstone from the Late Cretaceous Glenburn Formation are well exposed along the shoreline to the south of Pukemuri Stream. The formation is about 60 metres thick here. The beds along the shoreline are tilted (or dip) towards the west. But if you look offshore at low tide, you can see that the beds are tilted towards the east. The beds were originally formed as horizontal layers of sand and silt on the seafloor, probably as part of an ancient submarine fan system. They have since been buried and hardened. Tectonic forces have then uplifted and folded them into a large inverted U-shaped fold called an anticline. If you continue walking south along the beach, you can find the hinge or axis of the fold where the layers are still horizontal.
Over time, the erosional force of the ocean has created the wave-cut platform, exposing the internal structure of the large anticline. As you follow the anticline north along the coast, increasingly younger sedimentary rocks are exposed. This indicates that the anticline axis is tilted to the northeast.
The folding is a response to the pressure of plate collision along the Hikurangi subduction zone. This plate boundary (the interface between the colliding Pacific and Australian Plates) extends below the southern North Island at a shallow angle, from the sea floor 50 kms offshore of Tora. Below Tora, the boundary is approximately 20 kms deep. Like many folds and faults in Wairarapa, the Tora Coastal Anticline runs northeast-southwest, which is parallel to the subduction zone and at right angles to the forces generated by the subduction process.
Bird's eye view with approximate fold axis location marked. K.Amai / VUW
Within the Glenburn Formation you may find sedimentary structures such as ripples, cross bedding, faults and also occasional trace fossils. There are also occasional beds rich in fragments of inoceramid fossils, which look like prisms of calcite. Inoceramids are a family of clam-like bivalves that became extinct in the late Cretaceous around 68 million years ago. The species present in the Glenburn Formation tell us the rocks are between 95 and 85 million years old.
See how far along the coast you can distinguish both sides of the anticline.
What is the steepest dip of the strata (the degree of tilting in the rock layers) that you can see?
Can you identify the axis of the fold? Is the fold axis horizontal, or is it plunging (tilted)? How do you know?

From Martinborough take Jellicoe Street (1.8km), turn left onto White Rock Road (30km). Turn left onto Tora Road (13km), then turn right onto Tora Farm Settlement Road (4km) until you reach a bridge. There is one gate just after the bridge and another to the left which leads down close to the beach. Be aware that this track in on private Tora Station land,

Make sure to leave any gates as you found them; if it was closed, close it again once you have made your way through.
The anticline is best viewed at low tide.
Take care with large waves; Tora is an exposed beach on rugged coastline.

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The outcrop is located about 100 meters south of the mouth of the Pukemuri Stream.

Sedimentary Fossils Rock Deformation
Geological Age
Glenburn Formation - Late Cretaceous (95Ma - 85Ma)
Zealandia Evolution Sequence
Momotu Supergroup (Rifting): 110-85 million years ago
Hines, B.R., Kulhanek, D.K., Hollis, C.J., Atkins, C.B. and Morgans, H.E.G. (2013) Paleocene–Eocene stratigraphy and paleoenvironment at Tora, Southeast Wairarapa, New Zealand. New Zealand Journal of Geology and Geophysics 56, 243-262. [Focussed on younger rocks but includes a useful geological map of Tora] Laird, M.J., Bassett, K.N., Schiøler, P., Morgans, H.E.G., Bradshaw, J.D. and Weaver, S.D. (2003) Paleoenvironmental and tectonic changes across the Cretaceous/Tertiary boundary at Tora, southeast Wairarapa, New Zealand: a link between Marlborough and Hawkes Bay. New Zealand Journal of Geology and Geophysics 46, 275-294. [Established the age of the upper Glenburn Formation] Waterhouse, J.B. and Bradley, J. (1957) Redeposition and slumping in the Cretaceo-Tertiary strata of S.E. Wellington. Transactions of the Royal Society of New Zealand 84, 519-548. [First published study of the area]