Stratigraphy and sedimentology of the Upper Pakawau and Lower Westhaven groups
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
Twelve hundred metres of Pakawau Group sediments accumulated in a rapidly subsiding trough during Haumurian to early Dannevirke times, in the vicinity north-west of the Wakamarama Fault and extending from Cape Farewell to Whanganui Inlet. The upper Pakawau Group consists of the North Cape Formation (minimum of 100-250 m), the Puponga Formation (50 m) and the Farewell Formation (300-500 m). The North Cape and Farewell Formations consist of granite, volcanic, quartzarenite and schist-bearing conglomerates, subfeldsarenite to feldsarenite sandstones, minor mudstones and thin, rare coal; lithologies are interpreted as braided stream sediments. The Puponga Formation consists of sand-stones, siltstones and locally coal and minor conglomerate; lithologies are interpreted as floodplain sediments deposited during an intervening quiescent interval. Locally at Kahurangi, Pakawau Group sedimentation is represented by only 15 m of Haumurian coal bearing granule conglomerate - coarse sandstone lithologies deposited in local depressions. Paleocurrent data (North Cape and Farewell Formations) indicate derivation from the granitic, sedimentary and schistose terrain to the south and east, and that conglomerate-sandstone lateral facies changes represent local tectonic control rather than proximal-distal relationships. Silcrete and soil formation, and kaolinization, accompanied tectonic quiescence and reduced sediment supply during the early Paleocene. The Abel Head Formation and Takaka Limestone were deposited unconformably on the Pakawau Group during Arnold to Otaian times; they consist of seventy to one hundred and forty metres of marine sandstones, mudstones, minor conglomerates, green sands and micritic fine, to sparry medium-coarse, calcarenites. Marine transgression began in the southern Kahurangi vicinity with deposition of fifty metres of tidal, inner shelf and shelf sediments during the Arnold, but did not commence in the northern Cape Farewell vicinity until the Whaingaroan, when prograding beach and nearshore sedimentation extended from Cape Farewell to Kahurangi. Following progradation, during Whaingaroan-Duntroonian times, the Kahurangi vicinity subsided relatively rapidly whilst the Te Hapu-Cape Farewell vicinity remained static. In the Kahurangi vicinity continuous shelf sedimentation is represented by sixty metres of siltstone, glauconitic and micritic fine calcarenite, and medium-coarse calcarenite; the Te HapuCape Farewell vicinity is characterized by minor unconformities and relatively thin inner shelf sedimentation. Subsidence and fine calcarenite sedimentation began in the Cape Farewell vicinity during the Waitakian, whilst medium-coarse calcarenite sedimentation continued at Kahurangi. By late Waitakian times, medium-coarse calcarenite, reflecting shallow current swept she conditions, prevailed throughout the Kahurangi-Cape Farewell region.