THE GEOLOGY OF NEW ZEALAND

Stratigraphy

Cambrian (map symbol Z)

Distribution Cambrian rocks are certainly known only from the northwest of the South Island, between the Aorere River and Maruia Springs. Cambrian rocks may also exist in Fiordland.

Content In northwest Nelson the rock types are very varied, with slate, argillite, chert, hard sandstone, limestone lenses, and widespread conglomerate, all of sedimentary origin. New Zealand’s oldest fossils, trilobites, are preserved in Cambrian limestone in the Nelson district. Basalt, andesite, and tuff represent widespread volcanic activity at this time. In the upper Takaka River, a layered igneous complex of serpentinised peridotite, gabbro, and diorite was intruded at this time. Most of the rocks are metamorphosed to some extent, in particular the volcanics, but in most places the parent rocks can be recognised. In Fiordland, possible Cambrian rocks include schist and gneiss.

Paleogeographic conditions The sediments were deposited in a shallow marine environment on the flanks of a volcanic arc, offshore from Gondwanaland. The widespread conglomerate formation represents a deltaic fan. At this time the Fiordland area lay close to northwest Nelson and it is likely similar conditions prevailed.

Deformation All the Cambrian rocks are complexly deformed by several phases of deformation. In particular large scale thrusting of "loops" of sediment many kilometres from their original site is evident. Tight folding and shearing of sediments is common.