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Table 1 Subsurface lithology of Ngatamariki from wells NM1-7, as described by Bignall (2009)
Ngatamariki stratigraphy | ||
|---|---|---|
Formation name | Thickness (m) | Lithological description |
Orakonui Fm | 0–10 | Pumice breccia, with common volcanic lithics, quartz and minor feldspar |
Orunanui Fm | 15–85 | Cream to pinkish vitric–lithic tuff, with vesicular pumice and lava lithics, plus quartz, feldspar and rare pyroxene crystal fragments |
Huka falls Fm | > 70–285 | Coarse to medium grained sandstone, minor gravel (laminated lacustrine sediments) |
Waiora Fm | 0–10 | An upper level interval of Waiora Formation, comprises pumice-rich vitric tuff, with volcanic lithics, quartz, rare biotite and pyroxene crystals |
Rhyolite lava | 115–315 | Glassy rhyolite lava, with perlitic textures, phenocrysts are quartz, feldspar, pyroxene and magnetite |
Waiora Fm | 0–240 | A lower interval of Waiora Formation, comprising pumice-rich vitreous tuff, intercalated with crystal tuff, tuffaceous coarse sandstone and tuffaceous siltstone |
Wairakei ignimbrite | 100–200 | Crystal–lithic tuff/breccia, with abundant quartz, minor feldspar, rare biotite and pyroxene, minor volcanic lithics and pumice, in a fine ash |
Rhyolite lava | 0–285 | Hard porphyritic quartz-rich rhyolite lava with phenocrysts of quartz, minor feldspar, and minor ferromagnesian minerals |
Tahorakuri Fm | 460–700 | White to pale grey lithic tuff/breccia intercalated with fine sediments. In NM6 it is intercalated with 310 m of andesite lavas and breccias (tuffs and sediments) |
Tahorakuri Fm | > 200–840 | Pale grey, lithic tuff/breccia containing dark grey/brown lava, rhyolite pumice greywacke–argillite and sandstone clasts in a silty matrix (Akaterewa ignimbrite) |
Tahorakuri Fm | >Â 830 | Pale grey porphyritic feldspar, pyroxene and amphibole andesite lava and breccia (andesite lava, breccia) |
Torlesse greywacke | Undefined | Pale grey to grey, massive meta-sandstone which lack obvious bedding, quartz veins |