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

Cox, SC; Nibourel, Lukas (2015). Bedload composition, transport and modification in rivers of Westland, New Zealand, with implications for the distribution of alluvial pounamu (jade). New Zealand Journal of Geology and Geophysics, 58(2), pp. 154-175. Taylor & Francis 10.1080/00288306.2015.1025799

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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.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Institute of Geological Sciences

UniBE Contributor:

Nibourel, Lukas

Subjects:

500 Science > 550 Earth sciences & geology

ISSN:

0028-8306

Publisher:

Taylor & Francis

Language:

English

Submitter:

Lukas Nibourel

Date Deposited:

28 Dec 2015 11:14

Last Modified:

28 Dec 2015 11:14

Publisher DOI:

10.1080/00288306.2015.1025799

BORIS DOI:

10.7892/boris.74279

URI:

https://boris.unibe.ch/id/eprint/74279

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