title: Analysis of the South Westland Basin, New Zealand

authors: Sircombe, Keith Nicholas

abstract: Running parallel to the thrust front of the Southern Alps, an elongate, predominantly offshore and relatively deep basin, considered to have originated as a foreland basin, has previously been identified in South Westland, South Island, New Zealand. An integrative approach to basin analysis has been undertaken in this thesis to test the hypothesis that this basin has been formed by the loading of the Pacific Plate onto the Australia Plate during the Late Cenozoic. The two principal approaches to this problem undertaken in this thesis are seismic mapping of industry acquired seismic reflection profiles available for the basin and geodynamical analysis of the basin geometry and its stratigraphy.

Seismic mapping reveals a thick sedimentary section that can be divided broadly into five sequences. The thickness distribution of these units have been digitized into a computer database for subsequent modelling and mapping. The five sequences are titled Sequence E through to A from the basement to the surface. The lowermost sequence, Sequence E, is a thin sheet of marginal marine sediments thickening toward the west. It is believed to have formed in a rift margin setting during the Late Cretaceous-Eocene, overlain by a regionally extensive limestone formed during a marine transgression in the Oligocene. Sequence D has a sheet-like form comprising turbiditic systems deposited in bathyal depths between around 30 Ma and 15 Ma. This is coincident with increasing convergence across the Alpine Fault and initial loading of the Australia Plate, and Sequence D may represent the early underfill stage of foreland basin development. Sequence C is wedge-like in form, consisting of deep water turbiditic systems rapidly deposited between 5 Ma and 3.1 Ma. This corresponds with the uplift of the inner margin of the basin along the South Westland Fault Zone. Sequence B is a prominent lensoidal form prograding facies consisting of mudstone with frequent coarser beds deposited between 3.1 Ma and 1.2 Ma. Sequence A tops the section with a possible eustatically controlled and predominantly slumped deposit of mudstone with thick units of bioclasts near the present surface.

Geodynamic analysis reveals an early stage of thermal subsidence due to late Cretaceous rifting that preceded Tasman Sea spreading. It is compatible with a lithospheric stretching factor of 1.25. Increasingly rapid subsidence since 15-10 Ma is interpreted as possible fault-controlled subsidence due to strike-slip deformation combined with loading resulting from increased convergence across the Alpine Fault. This is followed by the uplift of the inner margin of the basin around 5 Ma to form the presently exposed coastal strip. This event probably also contributed to the loading of the Australia Plate. Flexural analysis of the basement structure of the Australia Plate reveals an unusually weak lithosphere with a rigidity around 9.79 x 10²⁰ Nm. Several alternative interpretations are presented to explain this unusually weak lithosphere, such as high heat flows, lithospheric decoupling and inherited structures. The complex evolution of the basin from rift margin, through strike-slip to foreland basin is believed to have left behind structures that may constrain and/or enhance the flexural response of the Australia Plate.

text: Analysis of the South Westland Basin, New Zealand Running parallel to the thrust front of the Southern Alps, an elongate, predominantly offshore and relatively deep basin, considered to have originated as a foreland basin, has previously been identified in South Westland, South Island, New Zealand. An integrative approach to basin analysis has been undertaken in this thesis to test the hypothesis that this basin has been formed by the loading of the Pacific Plate onto the Australia Plate during the Late Cenozoic. The two principal approaches to this problem undertaken in this thesis are seismic mapping of industry acquired seismic reflection profiles available for the basin and geodynamical analysis of the basin geometry and its stratigraphy.

Seismic mapping reveals a thick sedimentary section that can be divided broadly into five sequences. The thickness distribution of these units have been digitized into a computer database for subsequent modelling and mapping. The five sequences are titled Sequence E through to A from the basement to the surface. The lowermost sequence, Sequence E, is a thin sheet of marginal marine sediments thickening toward the west. It is believed to have formed in a rift margin setting during the Late Cretaceous-Eocene, overlain by a regionally extensive limestone formed during a marine transgression in the Oligocene. Sequence D has a sheet-like form comprising turbiditic systems deposited in bathyal depths between around 30 Ma and 15 Ma. This is coincident with increasing convergence across the Alpine Fault and initial loading of the Australia Plate, and Sequence D may represent the early underfill stage of foreland basin development. Sequence C is wedge-like in form, consisting of deep water turbiditic systems rapidly deposited between 5 Ma and 3.1 Ma. This corresponds with the uplift of the inner margin of the basin along the South Westland Fault Zone. Sequence B is a prominent lensoidal form prograding facies consisting of mudstone with frequent coarser beds deposited between 3.1 Ma and 1.2 Ma. Sequence A tops the section with a possible eustatically controlled and predominantly slumped deposit of mudstone with thick units of bioclasts near the present surface.

Geodynamic analysis reveals an early stage of thermal subsidence due to late Cretaceous rifting that preceded Tasman Sea spreading. It is compatible with a lithospheric stretching factor of 1.25. Increasingly rapid subsidence since 15-10 Ma is interpreted as possible fault-controlled subsidence due to strike-slip deformation combined with loading resulting from increased convergence across the Alpine Fault. This is followed by the uplift of the inner margin of the basin around 5 Ma to form the presently exposed coastal strip. This event probably also contributed to the loading of the Australia Plate. Flexural analysis of the basement structure of the Australia Plate reveals an unusually weak lithosphere with a rigidity around 9.79 x 10²⁰ Nm. Several alternative interpretations are presented to explain this unusually weak lithosphere, such as high heat flows, lithospheric decoupling and inherited structures. The complex evolution of the basin from rift margin, through strike-slip to foreland basin is believed to have left behind structures that may constrain and/or enhance the flexural response of the Australia Plate.

year: 1993

title: The bounded inverse Weibull distribution: An extreme value alternative for application to environmental maxima?

authors: Bardsley, W. Earl

subjects: bounded extremes

abstract: There has long been interest in making inferences about future low-probability natural events that have magnitudes greater than any in the past record. Given a stationary time series, the unbounded Type 1 and Type 2 asymptotic extreme value distributions are often invoked as giving theoretical justification for extrapolating to large magnitudes and long return periods for hydrological variables such as rainfall and river discharge. However, there is a problem in that environmental extremes are bounded above by the bounded nature of their causal variables. Extrapolation using unbounded asymptotic models therefore cannot be justified from extreme value theory and at some point there will be over-prediction of future magnitudes. This creates the apparent contradiction, for example, of annual rainfall maxima being well approximated by Type 2 extreme value distributions despite the bounded nature of rainfall magnitudes. An alternative asymptotic extreme value approach is suggested for further investigation, with the model being the asymptotic distribution of minima (Weibull distribution) applied to block maxima reciprocals. Two examples are presented where data that are well matched by Type 1 or Type 2 extreme value distributions give reciprocals suggestive of lower bounds (upper bound γ to the original data). The asymptotic model here is a 3-parameter Weibull distribution for the reciprocals, with positive location parameter γ−1. When this situation is demonstrated from data, parameter estimation can be carried out with respect to the distribution of reciprocals of 3-parameter Weibull random variables. This distribution is referenced here as the bounded inverse Weibull distribution. A maximum likelihood parameter estimation methodology is presented, together with a parametric bootstrap approach for obtaining one-sided upper confidence limits to γ. When data permits estimation of γ, the bounded inverse Weibull distribution is suggested as an improved alternative to Type 1 or Type 2 extreme value distributions because the upper bound reality is recognised. However, extensive application to many data sets is required to evaluate the practical utility of the bounded approach for extrapolating beyond the largest recorded event.

text: The bounded inverse Weibull distribution: An extreme value alternative for application to environmental maxima? There has long been interest in making inferences about future low-probability natural events that have magnitudes greater than any in the past record. Given a stationary time series, the unbounded Type 1 and Type 2 asymptotic extreme value distributions are often invoked as giving theoretical justification for extrapolating to large magnitudes and long return periods for hydrological variables such as rainfall and river discharge. However, there is a problem in that environmental extremes are bounded above by the bounded nature of their causal variables. Extrapolation using unbounded asymptotic models therefore cannot be justified from extreme value theory and at some point there will be over-prediction of future magnitudes. This creates the apparent contradiction, for example, of annual rainfall maxima being well approximated by Type 2 extreme value distributions despite the bounded nature of rainfall magnitudes. An alternative asymptotic extreme value approach is suggested for further investigation, with the model being the asymptotic distribution of minima (Weibull distribution) applied to block maxima reciprocals. Two examples are presented where data that are well matched by Type 1 or Type 2 extreme value distributions give reciprocals suggestive of lower bounds (upper bound γ to the original data). The asymptotic model here is a 3-parameter Weibull distribution for the reciprocals, with positive location parameter γ−1. When this situation is demonstrated from data, parameter estimation can be carried out with respect to the distribution of reciprocals of 3-parameter Weibull random variables. This distribution is referenced here as the bounded inverse Weibull distribution. A maximum likelihood parameter estimation methodology is presented, together with a parametric bootstrap approach for obtaining one-sided upper confidence limits to γ. When data permits estimation of γ, the bounded inverse Weibull distribution is suggested as an improved alternative to Type 1 or Type 2 extreme value distributions because the upper bound reality is recognised. However, extensive application to many data sets is required to evaluate the practical utility of the bounded approach for extrapolating beyond the largest recorded event.

year: 2021

title: Creating a curriculum for indigenous and community languages: Te reo Māori as an example

authors: Bruce, Ian

subjects: linguistics

abstract: Part 1 of this paper introduces the draft Common European Framework of Reference (CEFR) for languages and describes how it was used in the construction of draft New Zealand curriculum guidelines for French and German. Part 2 discusses how the CEFR has been employed in curriculum development in Te Reo Māori at the University of Waikato and suggests that it could also prove useful in relation to curriculum development projects involving indigenous and community languages more generally.

text: Creating a curriculum for indigenous and community languages: Te reo Māori as an example Part 1 of this paper introduces the draft Common European Framework of Reference (CEFR) for languages and describes how it was used in the construction of draft New Zealand curriculum guidelines for French and German. Part 2 discusses how the CEFR has been employed in curriculum development in Te Reo Māori at the University of Waikato and suggests that it could also prove useful in relation to curriculum development projects involving indigenous and community languages more generally.

year: 2002