title: Identification and correlation of thinly bedded late quaternary tephras of Coromandel Peninsula, New Zealand

authors: Hogg, Alan G.

abstract: The Coromandel Peninsula of North Island, New Zealand is covered by up to 2.5 m of thinly bedded Late Quaternary tephras. On the basis of their field characteristics, the tephras are divided into five field classes: the Recent bed (field class I) - a black, friable sandy loam; the Pumiceous bed (field class II) - reddish brown coarse lapilli and ash; the Silty bed (field class III) - a yellowish brown silt loam; the Lumpy bed (field class IV) - a brown sandy loam; and the Shower-bedded class ( field class V) - shower bedded and massive sands and loamy sands. 
The properties of the field classes were examined at 17 stratigraphic sections on the peninsula and indicate that classes I to IV each contain a mixture of at least two tephras. Individual tephras were characterised in the laboratory by multicomponent methods of analysis (particle size parameters, mineral assemblages), single component methods of analysis (chemical analysis of titanomagnetites by XRF), and single particle methods of analysis (microprobe analysis of titanornagnetite grains). 
The Recent bed is composed of at least three tephras, including the Kaharoa Tephra (930 yrs B.P.), Taupo Pumice (1,819 yrs B.P.), and the fine upper portion of the Whangamata Tephra (6,280 yrs B.P.). The Pumiceous bed contains a thorough mixture of the coarser, basal component of the Whangamata Tephra and the finer grained Mamaku Ash (7,050 yrs B.P.) and Rotoma Ash (c. 9,000 yrs B.P.). The Silty bed, Lumpy bed and Shower-bedded class all contain a common tephra, the Rotoehu Ash (41,700 yrs B.P.). The Shower-bedded class consists of pure Rotoehu Ash; the Lumpy bed is a composite of the upper part of the Rotoehu Ash and the Hauparu Tephra (30,000-40,000 yrs B.P.); the Silty bed is also a composite, but contains in addition to the upper part of the Rotoehu Ash and Hauparu Tephra, some unidentified hypersthene-bearing tephras of 20,000-11,000 yrs B.P. age, named “X” tephras.
The Whangamata Taphra Formation (symbol Wg) is dated at 6,280 ± 70 yrs B.P. (Wk 106), and is a brown, graded tephra deposited in two lobes, a coarse lobe of pumiceous ash and lapilli, up to 60 cm thick, extending between Whangamata and Thames on the Coromandel Peninsula, and a fine ash lobe, less than 10 cm in thickness, extending to the south and southwest of the Peninsula, in the Bay of Plenty and Waikato regions. The pumiceous lapilli have a peralkaline mineralogy with phenocrysts of anorthoclase, quartz, aegirine, cossyrite, olivine, riebeckite, and tuhualite, which identifies Mayor Island as the source volcano for the tephrae. 
It is suggested that the processes that have mixed the “X”, Hauparu and Rotoehu tophras in the Katikati region (latitude 37° 30’s) are related to the vegetation pattern, in the Late Otiran when the tephras became mixed under a forest cover north of about latitude 37° 30’s, - but remained unmixed under scrubland south of this latitude, in the Katikati-Tauranga area.

text: Identification and correlation of thinly bedded late quaternary tephras of Coromandel Peninsula, New Zealand The Coromandel Peninsula of North Island, New Zealand is covered by up to 2.5 m of thinly bedded Late Quaternary tephras. On the basis of their field characteristics, the tephras are divided into five field classes: the Recent bed (field class I) - a black, friable sandy loam; the Pumiceous bed (field class II) - reddish brown coarse lapilli and ash; the Silty bed (field class III) - a yellowish brown silt loam; the Lumpy bed (field class IV) - a brown sandy loam; and the Shower-bedded class ( field class V) - shower bedded and massive sands and loamy sands. 
The properties of the field classes were examined at 17 stratigraphic sections on the peninsula and indicate that classes I to IV each contain a mixture of at least two tephras. Individual tephras were characterised in the laboratory by multicomponent methods of analysis (particle size parameters, mineral assemblages), single component methods of analysis (chemical analysis of titanomagnetites by XRF), and single particle methods of analysis (microprobe analysis of titanornagnetite grains). 
The Recent bed is composed of at least three tephras, including the Kaharoa Tephra (930 yrs B.P.), Taupo Pumice (1,819 yrs B.P.), and the fine upper portion of the Whangamata Tephra (6,280 yrs B.P.). The Pumiceous bed contains a thorough mixture of the coarser, basal component of the Whangamata Tephra and the finer grained Mamaku Ash (7,050 yrs B.P.) and Rotoma Ash (c. 9,000 yrs B.P.). The Silty bed, Lumpy bed and Shower-bedded class all contain a common tephra, the Rotoehu Ash (41,700 yrs B.P.). The Shower-bedded class consists of pure Rotoehu Ash; the Lumpy bed is a composite of the upper part of the Rotoehu Ash and the Hauparu Tephra (30,000-40,000 yrs B.P.); the Silty bed is also a composite, but contains in addition to the upper part of the Rotoehu Ash and Hauparu Tephra, some unidentified hypersthene-bearing tephras of 20,000-11,000 yrs B.P. age, named “X” tephras.
The Whangamata Taphra Formation (symbol Wg) is dated at 6,280 ± 70 yrs B.P. (Wk 106), and is a brown, graded tephra deposited in two lobes, a coarse lobe of pumiceous ash and lapilli, up to 60 cm thick, extending between Whangamata and Thames on the Coromandel Peninsula, and a fine ash lobe, less than 10 cm in thickness, extending to the south and southwest of the Peninsula, in the Bay of Plenty and Waikato regions. The pumiceous lapilli have a peralkaline mineralogy with phenocrysts of anorthoclase, quartz, aegirine, cossyrite, olivine, riebeckite, and tuhualite, which identifies Mayor Island as the source volcano for the tephrae. 
It is suggested that the processes that have mixed the “X”, Hauparu and Rotoehu tophras in the Katikati region (latitude 37° 30’s) are related to the vegetation pattern, in the Late Otiran when the tephras became mixed under a forest cover north of about latitude 37° 30’s, - but remained unmixed under scrubland south of this latitude, in the Katikati-Tauranga area.

year: 1979

title: Semi-mechanistic modelling in nonlinear regression: a case study

authors: Domijan, Katarina

subjects: statistics

abstract: This paper discusses the use of highly parameterized semi-mechanistic nonlinear models with particular reference to the PARJIB crop response model of Reid (2002)[Yield response to nutrient supply across a wide range of conditions 1. Model derivation. Field Crops Research77, 161–171]. Compared to empirical linear approaches, such models promise improved generality of application but present considerable challenges for estimation. Some success has been achieved with a fitting approach that uses a Levenberg–Marquardt algorithm starting from initial values determined by a genetic algorithm. Attention must be paid, however, to correlations between parameter estimates and an approach is described to identify these based on large simulated datasets. This work illustrates the value for the scientist in exploring the correlation structure in mechanistic or semi-mechanistic models. Such information might be used to reappraise the structure of the model itself, especially if the experimental evidence is not strong enough to allow estimation of a parameter free of assumptions about the values of others. Thus statistical modelling and analysis can complement mechanistic studies, making more explicit what is known and what is not known about the processes being modelled and guiding further research.

text: Semi-mechanistic modelling in nonlinear regression: a case study This paper discusses the use of highly parameterized semi-mechanistic nonlinear models with particular reference to the PARJIB crop response model of Reid (2002)[Yield response to nutrient supply across a wide range of conditions 1. Model derivation. Field Crops Research77, 161–171]. Compared to empirical linear approaches, such models promise improved generality of application but present considerable challenges for estimation. Some success has been achieved with a fitting approach that uses a Levenberg–Marquardt algorithm starting from initial values determined by a genetic algorithm. Attention must be paid, however, to correlations between parameter estimates and an approach is described to identify these based on large simulated datasets. This work illustrates the value for the scientist in exploring the correlation structure in mechanistic or semi-mechanistic models. Such information might be used to reappraise the structure of the model itself, especially if the experimental evidence is not strong enough to allow estimation of a parameter free of assumptions about the values of others. Thus statistical modelling and analysis can complement mechanistic studies, making more explicit what is known and what is not known about the processes being modelled and guiding further research.

year: 2006

title: Merea Wikiriwhi and George Thomas Wilkinson

authors: Hart, Philip

abstract: Merea Wikiriwhi was one of the few women to invest in Te Aroha mining. Her life has been traced in as much detail as can be found because so little has survived about the lives of Maori women. As George Thomas Wilkinson’s surviving diaries reveal his importance in her life, his story was included as well, concentrating on his personal life rather than his official career. 
Merea was a member of several Ohinemuri hapu, with links through whakapapa to some of their more senior rangatira. Mostly living at or near Waitoki, between Paeroa and Te Aroha, she lived a frugal life, not wasting the income she received from land sales. These sales first required her to insist on her rights both in the land court and in a convoluted legal battle over a will signed in her favour by a distant relative. Over time, she would sell most of her land, but never became entirely landless. She invested in only one mining claim, but in the 1930s joined others to claim that the government was not paying them goldfields revenue for land they had sold.
George Thomas Wilkinson entered her life in 1880, when he was the ‘native agent’ in Hauraki. Despite having fought against Maori and nearly being killed, his surviving diaries reveal that he lived in the manner of a Pakeha Maori with three Maori women (simultaneously for a time), having children both by Merea and the woman he would eventually marry. Wilkinson had close friendships with many Maori and Pakeha Maori, and his genuine regard for them is reflected not only in his attempting, in his official capacity, to be fair to their interests – even as he assisted the government to separate them from their land – but in particular by his affection for a young girl, Wairingiringi, who shared his house in Thames. Although he and Merea would part, he tried to ensure that her children, like all his children, would do well in a Pakeha world.

text: Merea Wikiriwhi and George Thomas Wilkinson Merea Wikiriwhi was one of the few women to invest in Te Aroha mining. Her life has been traced in as much detail as can be found because so little has survived about the lives of Maori women. As George Thomas Wilkinson’s surviving diaries reveal his importance in her life, his story was included as well, concentrating on his personal life rather than his official career. 
Merea was a member of several Ohinemuri hapu, with links through whakapapa to some of their more senior rangatira. Mostly living at or near Waitoki, between Paeroa and Te Aroha, she lived a frugal life, not wasting the income she received from land sales. These sales first required her to insist on her rights both in the land court and in a convoluted legal battle over a will signed in her favour by a distant relative. Over time, she would sell most of her land, but never became entirely landless. She invested in only one mining claim, but in the 1930s joined others to claim that the government was not paying them goldfields revenue for land they had sold.
George Thomas Wilkinson entered her life in 1880, when he was the ‘native agent’ in Hauraki. Despite having fought against Maori and nearly being killed, his surviving diaries reveal that he lived in the manner of a Pakeha Maori with three Maori women (simultaneously for a time), having children both by Merea and the woman he would eventually marry. Wilkinson had close friendships with many Maori and Pakeha Maori, and his genuine regard for them is reflected not only in his attempting, in his official capacity, to be fair to their interests – even as he assisted the government to separate them from their land – but in particular by his affection for a young girl, Wairingiringi, who shared his house in Thames. Although he and Merea would part, he tried to ensure that her children, like all his children, would do well in a Pakeha world.

year: 2016