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  3. Bedload composition, transport and modification in rivers of Westland, New Zealand, with implications for the distribution of alluvial pounamu (jade)
 

Bedload composition, transport and modification in rivers of Westland, New Zealand, with implications for the distribution of alluvial pounamu (jade)

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BORIS DOI
10.7892/boris.74279
Date of Publication
2015
Publication Type
Article
Division/Institute

Institut für Geologie...

Author
Cox, SC
Nibourel, Lukasorcid-logo
Institut für Geologie
Subject(s)

500 - Science::550 - ...

Series
New Zealand Journal of Geology and Geophysics
ISSN or ISBN (if monograph)
0028-8306
Publisher
Taylor & Francis
Language
English
Publisher DOI
10.1080/00288306.2015.1025799
Description
River bedload surveyed at 50 sites in Westland is dominated by Alpine Schist or Torlesse Greywacke from the Alpine Fault hanging wall, with subordinate Pounamu Ultramafics or footwall-derived Western Province rocks. Tumbling experiments found ultramafics to have the lowest attrition rates, compared with greywacke sandstone and granite (which abrade to produce silt to medium-sand), or incompetent schist (which fragments). Arahura has greater total concentrations (103–105 t/km2) and proportions (5–40%) of ultramafic bedload compared with Hokitika and Taramakau catchments (101–104 t/km2, mostly <10%), matching relative areas of mapped Pounamu Ultramafic bedrock, but enriched relative to absolute areal proportions. Western Province rocks downthrown by the Alpine Fault are under-represented in the bedload. Enriched concentrations of ultramafic bedload decrease rapidly with distance downstream from source rock outcrops, changing near prominent ice-limit moraines. Bedload evolution with transport involves both downstream fining and dilution from tributaries, in a sediment supply regime more strongly influenced by tectonics and the imprint of past glaciation. Treasured New Zealand pounamu (jade) is associated with ultramafic rocks. Chances of discovery vary between catchments, are increased near glacial moraines, and are highest near source-rock outcrops in remote mountain headwaters.
Handle
https://boris-portal.unibe.ch/handle/20.500.12422/136817
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FileFile TypeFormatSizeLicensePublisher/Copright statementContent
cox_nibourel2014bedload.pdftextAdobe PDF1.86 MBpublisherpublished restricted
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