Jurassic (map symbol J)

Distribution
Jurassic rocks are widespread in Southland, and there are smaller areas near the Pyke River in northwestern Otago and in Nelson. They are well represented in the Waikato area. Jurassic rocks of the greywacke belt occur in north Canterbury, Marlborough, Wairarapa to East Cape and Northland.

Content
Jurassic rocks are mainly sandstone, mudstone, and conglomerate, with tuff (ash) bands. Freshwater sandstone and conglomerate with plant fossils and minor coal seams occur in both Southland and Waikato. The greywacke belt rocks are grey sandstone and mudstone, with minor limestone, chert, conglomerate, spilite, and melange.

Paleogeographic conditions
The Jurassic sediments of Southland and Waikato were laid down on an ever-shallowing shelf, over which sea level oscillated so that at some times marine conditions prevailed and at others the shelf was above sea level. The response to the lower sea levels was rapid downcutting by rivers and associated influxes of gravel to the marine basins. Volcanic activity had almost ceased. The greywacke rocks were deposited in a submarine trough or series of basins.

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Deformation
Jurassic rocks are generally gently folded and form the core of the Kawhia and Southland syncline. The Jurassic in Nelson and northern Fiordland is severely faulted. The greywacke belt rocks are folded and faulted, though in many places not quite as deformed as the older Triassic greywackes.