Geology of the Kopuaranga District

Abstract

The rocks of the Kopuaranga District consist of gently dipping Waiauan to Nukumaruan marine sediments and late Pleistocene to Recent alluvium, unconformably overlying Mesozoic greywackes. Waiauan and Lower Tongaporutuan sediments are shallow-water sandstones while Middle Tongaporutuan to Opoitian sediments are deep-water massive and graded-bedded muddy sandstones and siltstones. Waipipian to Nukumaruan sediments are shallow-water calcarenites, sandstones, sandy mudstones and mudstones. The sequence represents a major sedimentary cycle which can be attributed to tectonism. Variations in planktonic foraminiferal faunas comparable with present day latitudinal variations demonstrate fluctuations of ocean surface temperatures through the Late Tertiary. Relatively small fluctuations in depth of deposition in shallower-water facies are in phase with paleotemperature changes, and are considered to reflect glacioeustatic sea level oscillations. The geological structure of the area is dominated by the dextral transcurrent Wairarapa and Alfredton Faults, the normal Ditton-Waihi, Wairiri, Rangitumau and Masterton Faults, and the Whangaehu-Mangareia Anticline.