Makareao Geology, Shag Valley.
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Abstract:
The mapped area occupies 42 km2 in the Lower Shag Valley adjacent to the town of Dunback.
Two basement lithologies occur juxtaposed by the Late Tertiary reversal of the Waihemo Fault Complex;
1. The textural zone 1 - 2B quartzofeldspathic Torlesse Supergroup (redefined) north east of the Waihemo No. 2 Fault including sandstone, siltstone, mudstone and massive recrystallized marble (Blue Mountain Formation). Compressional faulting and minor folding are widespread within the Torlesse locally.
2. The textural zone 3 - 4 quartzofeldspathic Otago Schists, a subgroup of the Haast Schists southwest of the Waihemo No. 2 Fault beneath the Lower Tertiary marine transgressive sediments within the Shag Valley fault angle depression.
Cretaceo-Tertiary terrestrial-marine lithofacies resting conformably on the mature low relief Otago Schist erosion surface are subdivided into two formations;
1. The fluvial/marginal marine quartz sandstone-conglomerate of the Herbert Formation (cf. Taratu Formation).
2. The Abbotsford Formation; a deepening marine transgressive sequence divided into four informal members, composed of greensand, siltstone, glauconitic mudstone, fossiliferous calcareous mudstone and a micaceous silty sandstone. Faunal and mineralogic content of the Abbotsford Formation in the Makareao area indicate a non-schist derived source and affinities with the Dunedin and Hampden Beach sections.
Quaternary gravel outwash and terrace surfaces are locally well developed, covering a large part of the Tertiary sediments in the Shag Valley.
Two basement lithologies occur juxtaposed by the Late Tertiary reversal of the Waihemo Fault Complex;
1. The textural zone 1 - 2B quartzofeldspathic Torlesse Supergroup (redefined) north east of the Waihemo No. 2 Fault including sandstone, siltstone, mudstone and massive recrystallized marble (Blue Mountain Formation). Compressional faulting and minor folding are widespread within the Torlesse locally.
2. The textural zone 3 - 4 quartzofeldspathic Otago Schists, a subgroup of the Haast Schists southwest of the Waihemo No. 2 Fault beneath the Lower Tertiary marine transgressive sediments within the Shag Valley fault angle depression.
Cretaceo-Tertiary terrestrial-marine lithofacies resting conformably on the mature low relief Otago Schist erosion surface are subdivided into two formations;
1. The fluvial/marginal marine quartz sandstone-conglomerate of the Herbert Formation (cf. Taratu Formation).
2. The Abbotsford Formation; a deepening marine transgressive sequence divided into four informal members, composed of greensand, siltstone, glauconitic mudstone, fossiliferous calcareous mudstone and a micaceous silty sandstone. Faunal and mineralogic content of the Abbotsford Formation in the Makareao area indicate a non-schist derived source and affinities with the Dunedin and Hampden Beach sections.
Quaternary gravel outwash and terrace surfaces are locally well developed, covering a large part of the Tertiary sediments in the Shag Valley.
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v. 63 p. ill. Photos. Map(folded in pocket); 30 cm.
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1985Mitchell
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POLYGON ((170.643848452000043 -45.413947251999957,170.639710384000068 -45.391879827999958,170.67945902800011 -45.370966593999981,170.702507108000077 -45.384371801999976,170.702704313000027 -45.38455563499997,170.722566569000037 -45.415891804999944,170.722232835000113 -45.424530587999982,170.700959841000099 -45.424058094999964,170.667197709000106 -45.423296621999953,170.645555490000106 -45.423036165999974,170.643848452000043 -45.413947251999957))
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Citation
Mitchell, KD, “Makareao Geology, Shag Valley.,” Otago Geology Theses, accessed May 15, 2025, https://theses.otagogeology.org.nz/items/show/190.