Geology and geomorphology of Kahurangi National Park

Kahurangi National Park is geologically one of the oldest and most complex areas in New Zealand with basement rocks dominating the landscape. The Paleozoic Buller and Tākaka terranes, separated down the middle of the park by the Anatoki Fault, form the geological basement.

The Buller Terrane contains Ordovician metasedimentary turbidites, extensively intruded by Late Devonian granitoids and to a lesser extent, Early Cretaceous granitoids. To the east the Tākaka Terrane comprises an older sequence of Cambrian volcanic and volcaniclastic arc-related sedimentary rocks, and a prominent mélange unit. The oldest fossils found in New Zealand, trilobites, are present in the sedimentary rocks. Overlying the arc-related sequence is a Late Cambrian to Early Devonian passive margin succession of clastic and carbonate sedimentary rocks. The Tākaka Terrane has been intruded by Late Devonian mafic/ultramafic rocks and Early Cretaceous granitoids. The Buller and Takaka terranes were amalgamated in the early Middle Devonian.

A regional unconformity separates Late Cretaceous and younger sedimentary rocks from the basement. Late Cretaceous to Early Eocene sediments were deposited in basins in the north of the park. After a period of erosion the Late Eocene saw deposition of coal measures followed by calcareous sediments and limestone in the Oligocene. Renewed tectonic activity in the Miocene-Pliocene resulted in emerging land and sediments becoming terrigenous. The rapid uplift of the Southern Alps in the Pliocene-Pleistocene led to substantial volumes of gravels being deposited, particularly in the Karamea district.

Ongoing tectonic activity caused by the convergence of the Pacific and Australian plates has resulted in a mountainous topography. Uplifted Early Ordovician limestone, extensively altered to marble, has led to significant examples of karst topography. Some of the longest and deepest cave systems found in the Southern Hemisphere are located in the park. Extensive glaciation during the Pleistocene created many “U” shaped valleys and glacial tarns. In a few places Oligocene limestone has been sculpted by water and ice to form the best examples of uplifted mesas in New Zealand. Landslides are a common feature in the steeper areas of the park and many were triggered by earthquakes. Within the park lies part of New Zealand’s deepest and most intensely deformed Paleogene-Neogene sedimentary basin.