title: Cementation scenarios for New Zealand Cenozoic nontropical limestones

authors: Hood, Steven D.

subjects: Cenozoic

abstract: Cenozoic limestones are widely distributed in New Zealand, especially in the Oligocene-earliest Miocene in both islands, and the Pliocene-Pleistocene in North Island. A spectrum of limestone types exists, but all are skeletal-dominated (>70%), with usually <20% interparticle cement-matrix and <10% siliciclasts, and they have facies attributes typical of nontropical carbonates. The range of diagenetic features identified within the limestones is the basis for assigning them to a small number of “end-member” cementation classes that are inferred to be associated with four, broad, diagenetic settings. Class I limestones have very open fabrics dominated by abraded bryomol (bryozoan + bivalve mollusc) facies skeletons coated with isopachous rinds of typically nonferroan, dull to blotchy luminescent, fibrous to bladed spar, often with porosity occlusion by detrital and/or precipitated micrite. The limestones are usually thin and rare, of Oligocene — early Miocene age, and are interpreted to have formed by marine cementation at the seafloor under special environmental conditions associated with high energy levels and reduced sedimentation rates. Class II limestones have open fabrics with meagre amounts of dull to bright luminescent, ferroan to nonferroan, often substrate-specific, bladed to dog-toothed scalenohedral fringe or syntaxial rim cement. These porous, bryomol, echinofor (echinoderm + benthic foraminifera), and less commonly barnamol (barnacle + bivalve mollusc) facies 1 imestones are relatively common, especially in Oligocene— Miocene eastern South Island and in some Pliocene eastern North Island occurrences, where diagenesis occurred mainly under conditions of only shallow burial (<500 m) in the presence of essentially marine pore fluids. Class III limestones have open to moderately open fabrics with typically nonferroan to ferroan, variably luminescent, fine to coarse drusy equant spar, and often include a range of neomorphosed, formerly aragonitic, bivalve skeletal fabrics. Composed predominantly of barnamol and bimol (bivalve mollusc) facies, these usually rather porous Pliocene—Pleistocene limestones are especially common in eastern North Island, and were characterised by diagenesis initially in the shallow burial realm and subsequently under variable influence from meteoric fluids, both in the subsurface and following uplift. Class IV limestones are characterised by tight and highly pressure-dissolved fabrics, with scant pore spaces filled by usually ferroan, dull luminescent, clear drusy equant spar. These hard, flaggy, bryomol-dominated limestones are common, of Oligocene-Miocene (and also Paleocene-Eocene) age, and their diagenesis proceeded mainly under conditions of moderate to deep burial (500–1500 m) in the presence of marine-modified connate fluids. The spectrum of marine, shallow burial, meteoric, and deep burial spar cements recognised in the New Zealand limestones^ together with special diagenetic features such as neomorphosed aragonitic fabrics and polygenetic micrites, remains to be fully appreciated and incorporated into existing models of nontropical shallow-marine carbonate evolution. © 1996 Taylor & Francis Group, LLC.

text: Cementation scenarios for New Zealand Cenozoic nontropical limestones Cenozoic limestones are widely distributed in New Zealand, especially in the Oligocene-earliest Miocene in both islands, and the Pliocene-Pleistocene in North Island. A spectrum of limestone types exists, but all are skeletal-dominated (>70%), with usually <20% interparticle cement-matrix and <10% siliciclasts, and they have facies attributes typical of nontropical carbonates. The range of diagenetic features identified within the limestones is the basis for assigning them to a small number of “end-member” cementation classes that are inferred to be associated with four, broad, diagenetic settings. Class I limestones have very open fabrics dominated by abraded bryomol (bryozoan + bivalve mollusc) facies skeletons coated with isopachous rinds of typically nonferroan, dull to blotchy luminescent, fibrous to bladed spar, often with porosity occlusion by detrital and/or precipitated micrite. The limestones are usually thin and rare, of Oligocene — early Miocene age, and are interpreted to have formed by marine cementation at the seafloor under special environmental conditions associated with high energy levels and reduced sedimentation rates. Class II limestones have open fabrics with meagre amounts of dull to bright luminescent, ferroan to nonferroan, often substrate-specific, bladed to dog-toothed scalenohedral fringe or syntaxial rim cement. These porous, bryomol, echinofor (echinoderm + benthic foraminifera), and less commonly barnamol (barnacle + bivalve mollusc) facies 1 imestones are relatively common, especially in Oligocene— Miocene eastern South Island and in some Pliocene eastern North Island occurrences, where diagenesis occurred mainly under conditions of only shallow burial (<500 m) in the presence of essentially marine pore fluids. Class III limestones have open to moderately open fabrics with typically nonferroan to ferroan, variably luminescent, fine to coarse drusy equant spar, and often include a range of neomorphosed, formerly aragonitic, bivalve skeletal fabrics. Composed predominantly of barnamol and bimol (bivalve mollusc) facies, these usually rather porous Pliocene—Pleistocene limestones are especially common in eastern North Island, and were characterised by diagenesis initially in the shallow burial realm and subsequently under variable influence from meteoric fluids, both in the subsurface and following uplift. Class IV limestones are characterised by tight and highly pressure-dissolved fabrics, with scant pore spaces filled by usually ferroan, dull luminescent, clear drusy equant spar. These hard, flaggy, bryomol-dominated limestones are common, of Oligocene-Miocene (and also Paleocene-Eocene) age, and their diagenesis proceeded mainly under conditions of moderate to deep burial (500–1500 m) in the presence of marine-modified connate fluids. The spectrum of marine, shallow burial, meteoric, and deep burial spar cements recognised in the New Zealand limestones^ together with special diagenetic features such as neomorphosed aragonitic fabrics and polygenetic micrites, remains to be fully appreciated and incorporated into existing models of nontropical shallow-marine carbonate evolution. © 1996 Taylor & Francis Group, LLC.

year: 1996-01-01

title: The K-complex and slow oscillation in terms of a mean-field cortical model

authors: Wilson, Marcus T.

subjects: Animals

abstract: We use a mean-field macrocolumn model of the cerebral cortex to offer an interpretation of the K-complex of the electroencephalogram to complement those of more detailed neuron-by-neuron models. We interpret the K-complex as a momentary excursion of the cortex from a stable low-firing state to an unstable high-firing state, and hypothesize that the related slow oscillation can be considered as the periodic oscillation between two meta-stable solutions of the mean-field model. By incorporating a Hebbian-style learning rule that links the growth in synapse strength to fluctuations in soma potential, we demonstrate a self-organization behaviour that draws the modelled cortex close to the edge of stability of the low-firing state. Furthermore, a very slow oscillation can occur in the excitability of the cortex that has similarities with the infra-slow oscillation of sleep.

text: The K-complex and slow oscillation in terms of a mean-field cortical model We use a mean-field macrocolumn model of the cerebral cortex to offer an interpretation of the K-complex of the electroencephalogram to complement those of more detailed neuron-by-neuron models. We interpret the K-complex as a momentary excursion of the cortex from a stable low-firing state to an unstable high-firing state, and hypothesize that the related slow oscillation can be considered as the periodic oscillation between two meta-stable solutions of the mean-field model. By incorporating a Hebbian-style learning rule that links the growth in synapse strength to fluctuations in soma potential, we demonstrate a self-organization behaviour that draws the modelled cortex close to the edge of stability of the low-firing state. Furthermore, a very slow oscillation can occur in the excitability of the cortex that has similarities with the infra-slow oscillation of sleep.

year: 2006-12

title: Understanding contemporary Māori demographic fertility patterns and trends in Aotearoa New Zealand

authors: Rarere, Moana

abstract: This thesis re-examines demographic studies of contemporary Māori fertility patterns and trends. Analysing fertility is a core undertaking in demography, and in studies that include Māori fertility, most have been undertaken by non-Māori demographers who instinctively draw on Western-based frameworks to analyse and interpret these trends.  Consequently, Māori perspectives are virtually invisible.  Incorporating Māori perspectives are needed because despite a convergence of fertility similar to Pākehā, important fertility patterns persist.  Notably, Māori women bear their babies earlier and over a longer period.  Fertility studies of other Indigenous peoples in settler-colonial states share striking similarities.  While demographic and economic factors are important in fertility outcomes, this thesis primarily explores the potential influence of culture, which has received little attention.  Hence, this doctoral study asks: To what extent does culture influence contemporary Māori fertility patterns?

This thesis draws on Kaupapa Māori and Mana Wahine frameworks, along with the tools of demography, to deploy a mixed methods design of statistical techniques – using secondary data from the 2013 Aotearoa NZ Census and the 1995 New Zealand Women: Family, Employment, and Education Survey – and thematic analysis of interviews with nine Māori women.  While acknowledging the limitations of the analyses, the empirical results suggest that ‘cultural identity’ is an important factor in Māori fertility, and that ‘whakapapa’ and ‘whānau’ are at the heart of fertility decisions.  These findings broadly imply that taken-for-granted demographic theories and analytical practices need to incorporate Indigenous-centred frameworks and perspectives for a better understanding of Indigenous fertility and population change.

text: Understanding contemporary Māori demographic fertility patterns and trends in Aotearoa New Zealand This thesis re-examines demographic studies of contemporary Māori fertility patterns and trends. Analysing fertility is a core undertaking in demography, and in studies that include Māori fertility, most have been undertaken by non-Māori demographers who instinctively draw on Western-based frameworks to analyse and interpret these trends.  Consequently, Māori perspectives are virtually invisible.  Incorporating Māori perspectives are needed because despite a convergence of fertility similar to Pākehā, important fertility patterns persist.  Notably, Māori women bear their babies earlier and over a longer period.  Fertility studies of other Indigenous peoples in settler-colonial states share striking similarities.  While demographic and economic factors are important in fertility outcomes, this thesis primarily explores the potential influence of culture, which has received little attention.  Hence, this doctoral study asks: To what extent does culture influence contemporary Māori fertility patterns?

This thesis draws on Kaupapa Māori and Mana Wahine frameworks, along with the tools of demography, to deploy a mixed methods design of statistical techniques – using secondary data from the 2013 Aotearoa NZ Census and the 1995 New Zealand Women: Family, Employment, and Education Survey – and thematic analysis of interviews with nine Māori women.  While acknowledging the limitations of the analyses, the empirical results suggest that ‘cultural identity’ is an important factor in Māori fertility, and that ‘whakapapa’ and ‘whānau’ are at the heart of fertility decisions.  These findings broadly imply that taken-for-granted demographic theories and analytical practices need to incorporate Indigenous-centred frameworks and perspectives for a better understanding of Indigenous fertility and population change.

year: 2024