Stratigraphy and sedimentology of the Nile group (Oligocene) southwest Nelson
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
Two new formations comprise the Nile Group; the lower Little Wanganui Formation and the upper Karamea Limestone. The Little Wanganui Formation contains the Kongahu Member (new name), Glasseye Mudstone (new name), and Kohaihai Limestone (new name). The Whaingaroan to late Duntroonian Kongahu Member consists of mass transported fossiliferous sandstones and conglomerates/breccias, which were derived from a landmass situated to the west of Kongahu Point. The member, which is largely confined to the coast between the Mokihinui and Little Wanganui Rivers, nonconformably overlies Paparoa Granite or is interbedded with the Kaiata Mudstone and (or) GlasseyeMudstone. The Whaingaroan-waitakian Glasseye Mudstone is an open marine calcareous detrital lutite, which is limited to the southern half of the study area. The Kohaihai Limestone is a shallow marine echinoderm biosparite, which conformably overlies the coaly Mawheranui Group in the Karamea region. The Karamea Limestone consists of the Stony Creek Limestone Member (new name) and the Oparara Member (new name). The Waitakian Stony Creek Limestone Member, a bryozoan biosparite, unconformably overlies the Kohaihai Limestone and the Glasseye Mudstone, or rests on Karamea Granite. The Oparara Member consists of calcareous very fine sandstone or fine-grained bryozoan biosparite; the member conformably overlies the Stony Creek Limestone in the Karamea region, unconformably overlies the Glasseye Mudstone elsewhere, and is conformably overlain by the Blue Bottom Group. The distribution of lithologies suggests that two sedimentary regimes operated in the study area during middle Tertiary time. The northern (Karamea) region was the site of a relatively stable, shallow, current swept, slowly subsiding carbonate shelf. The remainder of the study area was occupied by a rapidly subsiding marine basin (Little Wanganui basin), flanked on the west by a small rugged granitic landmass. Tectonic activity along the Paparoa Tectonic Zone during the late Eocene-middle Oligocene created an archipelago of islands with associated NNE trending basins; the most northerly of which constituted the Little Wanganui basin.