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      Shelf-to-slope sedimentation on the north Kaipara continental margin, northwestern North Island, New Zealand

      Payne, Danielle Sarah
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      Payne, D. S. (2008). Shelf-to-slope sedimentation on the north Kaipara continental margin, northwestern North Island, New Zealand (Thesis, Master of Science (MSc)). The University of Waikato, Hamilton, New Zealand. Retrieved from https://hdl.handle.net/10289/2413
      Permanent Research Commons link: https://hdl.handle.net/10289/2413
      Abstract
      Temperate mixed carbonate-siliciclastic sediments and authigenic minerals are the

      current surficial deposits at shelf and slope depths (30-1015 m water depth) on the

      north Kaipara continental margin (NKCM) in northern New Zealand. This is the

      first detailed study of these NKCM deposits which are described and mapped

      from the analysis of 54 surficial sediment samples collected along seven shorenormal

      transects and from three short piston cores. Five surficial sediment facies

      are defined from the textural and compositional characteristics of this sediment

      involving relict, modern or mixed relict-modern components. Facies 1

      (siliciclastic sand) forms a modern sand prism that extends out to outer shelf

      depths and contains three subfacies. Subfacies 1a (quartzofeldspathic sand) is an

      extensive North Island volcanic and basement rock derived sand deposit that

      occurs at less than 100-200 m water depth across the entire NKCM. Subfacies 1b

      (heavy mineral sand) occurs at less than 50 m water depth along only two

      transects and consists of predominantly local basaltic to basaltic andesite derived

      heavy mineral rich (gt30%) deposits. Subfacies 1c (mica rich sand) occurs at one

      sample site at 300 m water depth and contains 20-30% mica grains, probably

      sourced from South Island schists and granites. Facies 2 (glauconitic sand)

      comprises medium to fine sand with over 30% and up to 95% authigenic

      glauconite grains occurring in areas of low sedimentation on the outer shelf and

      upper slope (150-400 m water depth) in central NKCM. Facies 3 (mixed

      bryozoan-siliciclastic sand) consists of greater than 40% bryozoan skeletal

      material and occurs only in the northern half of the NKCM. Facies 4 (pelletal

      mud) occurs on the mid shelf (100-150 m water depth) in northern NKCM and

      comprises muddy sediment dominated by greater than c. 30% mixed carbonatesiliciclastic

      pellets. Facies 5 (foraminiferal mud and sand) contains at least 30%

      foraminifera tests and comprises two subfacies. Subfacies 5a consists of at least

      50% mud sized sediment and occurs at gt400 m water depth in southern NKCM

      while subfacies 5b comprises gt70% sand sized sediment and occurs at mid to

      outer shelf and slope depths in the northern NKCM.

      vi

      A number of environmental controls affect the composition and distribution of

      NKCM sediments and these include: (1) variable sediment inputs to the NKCM

      dominated by inshore bedload sources from the south; (2) northerly directed

      nearshore littoral and combined storm-current sediment transport on the beach and

      shelf, respectively; (3) offshore suspended sediment bypassing allowing

      deposition of authigenic minerals and skeletal grains; (4) exchange between the

      beach and shelf producing similar compositions and grain sizes at less than 150 m

      water depth; and (5) the episodic rise of sea level since the Last Glaciation

      maximum approximately 20 000 years ago which has resulted in much sediment

      being left stranded at greater depths than would otherwise be anticipated.

      Sedimentation models developed from other wave-dominated shelves generally

      do not appear to apply to the NKCM sediments due to their overall relative

      coarseness and their mosaic textural characteristics. In particular, the NKCM

      sediments do not show the expected fining offshore trends of most wavedominated

      shelf models. Consequently, sandy sediments (both siliciclastic and

      authigenic) are most typical with mud becoming a dominant component in

      southern NKCM sediments only at greater than 400 m water depth, over 350 m

      deeper than most models suggest, a situation accentuated by the very low mud

      sediment supply to the NKCM from the bordering Northland landmass.
      Date
      2008
      Type
      Thesis
      Degree Name
      Master of Science (MSc)
      Publisher
      The University of Waikato
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