Reconnaissance petrological study of the Late Oligocene to Early Miocene Otekaike Limestone, north Otago and southern Canterbury, New Zealand

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Smith, V.R.; Lobb, A.J.; Field, B.D. 1989 Reconnaissance petrological study of the Late Oligocene to Early Miocene Otekaike Limestone, north Otago and southern Canterbury, New Zealand. Lower Hutt: New Zealand Geological Survey. New Zealand Geological Survey report SL 19 26 p.

Abstract: The Duntroonian-Waitakian (Late Oligocene to Early Miocene) Otekaike Limestone generally lies in the textural range of packstone to grainstone, and compositional range of biosparite to biomicrite. The percentage of terrigenous material (mainly quartz and feldspar) decreases eastwards away from the landmass. Glauconite (both autochthonous and allochthonous) increases to the east and southeast. The bioclastic assemblage comprises echinoids, benthic and planktic foraminifera, brachiopods, bivalves and bryozoa. Echinoid fragments are common at most localities and generally increase in abundance towards the east. Red algae are restricted to the Mount Somers area. Bryozoa are present at most localities but comprise the major constituent in the Mount Somers area only. Brachiopod and bivalve shell material is present, but gastropod debris is absent. In the south, shell material increases in percentage to the west and southwest. In the far north it appears to decrease towards the north. Similar trends occur with benthic foraminifera. The ratio of benthic to planktic foraminifera increases in the north, around the Mount Somers area. The micritic matrix rarely exceeds 15% though micritisation of bioclasts is common in all samples. Cement fabrics are granular orthosparite, syntaxial rim orthosparite, sparite grain coatings and dogtooth calcite. Estimates porosities are generally in the range 5-15%. The area of deposition lay to the east of an Oligocene landmass, with shoaling in the area immediately east of Mount Somers. Thickening of the limestone in the Fairlie region is not obviously accompanied by a deeper water facies change in the limestone.