title: Dissolution and depletion of ferromagnesian minerals from Holocene tephra layers in an acid bog, New Zealand, and implications for tephra correlation

authors: Hodder, A.P.W.

subjects: chemical weathering

abstract: This study examines the depletion of ferromagnesian silicate minerals from a sequence of thin, distal, mainly rhyolitic tephra layers of Holocene age preserved in an acid peat bog (Kopouatai), North Island, New Zealand. The rate of such depletion has been fast, as indicated by the complete loss of biotite from one tephra layer (Kaharoa Tephra), in which it is normally dominant, in only ca. 770 yr. Chemical dissolution is advocated as the likely cause for the depletion, with amphiboles and other mineral grains commonly showing etch pits, microcaves, and other characteristic surface solution features. Theoretical thermodynamic and kinetic models show a marked increase in the rate of dissolution of all ferromagnesian minerals under conditions of low pH (< 4), but that where silica concentrations in solution are high the relative proportions of minerals remaining are unaffected. However, where concentrations of dissolved silica are low, as in most bog environments, the relative proportions of ferromagnesian minerals are affected as well as absolute amounts being decreased. Amphiboles are depleted relative to pyroxenes, consistent with kinetic studies.
The results show that the identification and correlation of tephras on the basis of relative abundances of ferromagnesian minerals alone may be unreliable, and emphasise the need to use multiple criteria in such studies.

text: Dissolution and depletion of ferromagnesian minerals from Holocene tephra layers in an acid bog, New Zealand, and implications for tephra correlation This study examines the depletion of ferromagnesian silicate minerals from a sequence of thin, distal, mainly rhyolitic tephra layers of Holocene age preserved in an acid peat bog (Kopouatai), North Island, New Zealand. The rate of such depletion has been fast, as indicated by the complete loss of biotite from one tephra layer (Kaharoa Tephra), in which it is normally dominant, in only ca. 770 yr. Chemical dissolution is advocated as the likely cause for the depletion, with amphiboles and other mineral grains commonly showing etch pits, microcaves, and other characteristic surface solution features. Theoretical thermodynamic and kinetic models show a marked increase in the rate of dissolution of all ferromagnesian minerals under conditions of low pH (< 4), but that where silica concentrations in solution are high the relative proportions of minerals remaining are unaffected. However, where concentrations of dissolved silica are low, as in most bog environments, the relative proportions of ferromagnesian minerals are affected as well as absolute amounts being decreased. Amphiboles are depleted relative to pyroxenes, consistent with kinetic studies.
The results show that the identification and correlation of tephras on the basis of relative abundances of ferromagnesian minerals alone may be unreliable, and emphasise the need to use multiple criteria in such studies.

year: 1991

title: Towards the 20 minute city

authors: Mackness, Kate

abstract: THE IDEA OF a 20-minute city came out of Portland, Oregon, in the early 2010s. Melbourne added its own twist on the concept later in the decade. With the emergence of the COVID-19 global pandemic, the buzz around 20-minute cities moved beyond urban planning circles to become a hot topic internationally.
In 2020, the 15-minute city was famously adopted by Anne Hidalgo as part of her election platform as Mayor of Paris, and the concept is now being explored in multiple cities including Tempe in Arizona, Ottawa and Sydney.

text: Towards the 20 minute city THE IDEA OF a 20-minute city came out of Portland, Oregon, in the early 2010s. Melbourne added its own twist on the concept later in the decade. With the emergence of the COVID-19 global pandemic, the buzz around 20-minute cities moved beyond urban planning circles to become a hot topic internationally.
In 2020, the 15-minute city was famously adopted by Anne Hidalgo as part of her election platform as Mayor of Paris, and the concept is now being explored in multiple cities including Tempe in Arizona, Ottawa and Sydney.

year: 2021

title: Keepa Te Wharau: a Ngati Rahiri rangatira

authors: Hart, Philip

abstract: Keepa Te Wharau’s whakapapa linked him, unusually, to both Ngati Maru and Ngati Haua. Through these connections he was associated with the Te Aroha district from an early age, visiting it on several occasions and even cultivating there, briefly. When the block was before the land court he gave evidence – though his evidence in a later succession case was clearly wrong, deliberately so. Having interests in several blocks of land, he falsely claimed not to have received money for the Aroha Block, using the excuse of drunkenness, for which he was before the court on several occasions. He would sell land, as would his children, to meet living expenses. He invested in two goldfields, Thames and Te Aroha, very modestly. A leading rangatira, he was notable for his loyalty to the Crown.

text: Keepa Te Wharau: a Ngati Rahiri rangatira Keepa Te Wharau’s whakapapa linked him, unusually, to both Ngati Maru and Ngati Haua. Through these connections he was associated with the Te Aroha district from an early age, visiting it on several occasions and even cultivating there, briefly. When the block was before the land court he gave evidence – though his evidence in a later succession case was clearly wrong, deliberately so. Having interests in several blocks of land, he falsely claimed not to have received money for the Aroha Block, using the excuse of drunkenness, for which he was before the court on several occasions. He would sell land, as would his children, to meet living expenses. He invested in two goldfields, Thames and Te Aroha, very modestly. A leading rangatira, he was notable for his loyalty to the Crown.

year: 2016