title: Stratigraphy, chronology, and correlation of the Plio-Pleistocene (c. 2.2-0.8 Ma) Kauroa Ash sequence, western central North Island, New Zealand

authors: Horrocks, Joanna L.

abstract: The Kauroa Ash beds (K-beds) comprise a 12-20 m-thick sequence of extremely weathered, clay-rich (40-95% <4 μm clay) beds of tephra and loess, and associated paleosols. Found in isolated remnants throughout the western central North Island, the sequence comprises 15 defined members, with as many as 44 constituent macroscopic beds. The type site, ‘Woodstock’, near Raglan, is the most comprehensive sequence known, but other sites (e.g. Papakura Creek and Tiritirimatangi Peninsula) contain units not found or poorly defined at Woodstock. 

Field properties as well as magnetic susceptibility measurements and particle-size analysis characterise the facies in the sequence. Field properties (in particular colour, consistence, macrofabric) describe the lithostratigraphy. The sequence contains five interpretive (i.e. genetic) ‘facies’: paleosols, primary tephra, very weathered tephra (possibly composite beds), loess and ‘tephric loess’ beds. At least seven loess beds are (newly) identified in the sequence: K4a, K5, K6ai, K8ai, K8bi, K10a and K14ai.

Mass-specific susceptibility and frequency-dependent susceptibility results partly conform to established models (developed mostly on Chinese loess-paleosol deposits) of susceptibility enhancement in paleosols and depletion in loess. Many parts of the sequence do not appear to conform to this model and the results more closely resemble the inverse relationship found on Alaskan loess-paleosol beds. Frequency-dependent susceptibility is reliable in delineating paleosols by their ‘ultrafine’ ferrimagnetic mineral content, and citrate-bicarbonate-dithionite treatments successfully remove all iron oxides so that remeasurement of susceptibility isolates a strictly ‘pedogenic’, rather than lithogenic, fraction. 

Laser diffraction particle-size analysis shows that the Kauroa Ash beds are texturally reasonably homogenous. They have bimodal particle-size distributions with the most dominant mode at around 11.25 ɸ inferred to be the product of intense and prolonged weathering. Other modes are variously centred on 7-8.5 ɸ and, despite weathering and pedogenesis, have some relationship to the original depositional particle-size distributions because trends between facies (i.e. genetic units) are delineated. Principal components analysis objectively characterises these modes as (Wentworth size classes) ‘very fine clay’ and ‘coarse silt’, although there is no proportional relationship between them, supporting a post-depositional origin for the former mode. 

The chronology of the sequence, previously poorly defined, is greatly improved by a combination of tephrochronologic correlations, fission-track dating, and paleomagnetism. Five zircon fission-track dates provide independent age ‘spikes’ and range from 2.24 ± 0.29 Ma in the basal member, K1, to 1.28 ± 0.11 Ma for the distal ignimbrite unit K12a. Paleomagnetism is invaluable in providing additional age information. The top of the sequence, member K15, is dated as >0.78 Ma (Brunhes-Matuyama boundary) because of its reversed polarity; two episodes of normal polarity are found in beds K14b and K2b and are inferred to represent the Jaramillo (1.07-0.99 Ma) and Olduvai (1.95-1.79 Ma) subchrons, respectively. Beds underlying the Kauroa Ash sequence are also of normal polarity, indicating that they were deposited in the Gauss Chron (>2.6 Ma). 

Identification and correlation of tephras by conventional means (fingerprinting by their lithological or geochemical properties) is impossible in the Kauroa Ash sequence because the beds have no remaining volcanic glass, which has instead been altered to an assemblage of authigenic phases (clays) by weathering and pedogenesis. However, a new technique analysing fresh glass found as melt inclusions in quartz grains is successful in circumventing this problem. Inclusions represent samples of non-degassed magma that became entrapped during phenocryst growth prior to eruption. The glass has remained unaltered because it is hermetically sealed in a chemically resistant phenocryst, which has protected it from weathering processes. Electron microprobe analysis of the glass inclusions yield results which are wholly reasonable for glass (totals ranging from 93-97%; low standard deviations of <1 %), and a number of provisional correlations are established by comparing the major element composition of Kauroa Ash tephra beds with those of proximal deposits. The Kauroa Ash sequence may contain deposits correlated with at least seven major TVZ eruptions, in many cases expanding the known extent of the (distal) deposit and, for the first time answering the question as to the origin of the Kauroa Ash beds. 

These correlations, together with an improved chronology, enable the Kauroa Ash sequence to be placed in a regional stratigraphic framework alongside other New Zealand Plio-Pleistocene sequences such as those in the Wanganui Basin, Wairarapa, Cape Kidnappers and Port Waikato. Using paleosols as chrono- and climatostratigraphic entities (correlated to warm periods in global climate), the sequence can also be placed alongside a global reference, the marine oxygen isotope stratigraphy. A further correlation to the Chinese loess-paleosol record suggests that large parts of the Kauroa Ash sequence were deposited in an incremental manner akin to deposition of loess, so that the sequence is not only a record of TVZ volcanism, but also of Plio-Pleistocene paleoclimate.

text: Stratigraphy, chronology, and correlation of the Plio-Pleistocene (c. 2.2-0.8 Ma) Kauroa Ash sequence, western central North Island, New Zealand The Kauroa Ash beds (K-beds) comprise a 12-20 m-thick sequence of extremely weathered, clay-rich (40-95% <4 μm clay) beds of tephra and loess, and associated paleosols. Found in isolated remnants throughout the western central North Island, the sequence comprises 15 defined members, with as many as 44 constituent macroscopic beds. The type site, ‘Woodstock’, near Raglan, is the most comprehensive sequence known, but other sites (e.g. Papakura Creek and Tiritirimatangi Peninsula) contain units not found or poorly defined at Woodstock. 

Field properties as well as magnetic susceptibility measurements and particle-size analysis characterise the facies in the sequence. Field properties (in particular colour, consistence, macrofabric) describe the lithostratigraphy. The sequence contains five interpretive (i.e. genetic) ‘facies’: paleosols, primary tephra, very weathered tephra (possibly composite beds), loess and ‘tephric loess’ beds. At least seven loess beds are (newly) identified in the sequence: K4a, K5, K6ai, K8ai, K8bi, K10a and K14ai.

Mass-specific susceptibility and frequency-dependent susceptibility results partly conform to established models (developed mostly on Chinese loess-paleosol deposits) of susceptibility enhancement in paleosols and depletion in loess. Many parts of the sequence do not appear to conform to this model and the results more closely resemble the inverse relationship found on Alaskan loess-paleosol beds. Frequency-dependent susceptibility is reliable in delineating paleosols by their ‘ultrafine’ ferrimagnetic mineral content, and citrate-bicarbonate-dithionite treatments successfully remove all iron oxides so that remeasurement of susceptibility isolates a strictly ‘pedogenic’, rather than lithogenic, fraction. 

Laser diffraction particle-size analysis shows that the Kauroa Ash beds are texturally reasonably homogenous. They have bimodal particle-size distributions with the most dominant mode at around 11.25 ɸ inferred to be the product of intense and prolonged weathering. Other modes are variously centred on 7-8.5 ɸ and, despite weathering and pedogenesis, have some relationship to the original depositional particle-size distributions because trends between facies (i.e. genetic units) are delineated. Principal components analysis objectively characterises these modes as (Wentworth size classes) ‘very fine clay’ and ‘coarse silt’, although there is no proportional relationship between them, supporting a post-depositional origin for the former mode. 

The chronology of the sequence, previously poorly defined, is greatly improved by a combination of tephrochronologic correlations, fission-track dating, and paleomagnetism. Five zircon fission-track dates provide independent age ‘spikes’ and range from 2.24 ± 0.29 Ma in the basal member, K1, to 1.28 ± 0.11 Ma for the distal ignimbrite unit K12a. Paleomagnetism is invaluable in providing additional age information. The top of the sequence, member K15, is dated as >0.78 Ma (Brunhes-Matuyama boundary) because of its reversed polarity; two episodes of normal polarity are found in beds K14b and K2b and are inferred to represent the Jaramillo (1.07-0.99 Ma) and Olduvai (1.95-1.79 Ma) subchrons, respectively. Beds underlying the Kauroa Ash sequence are also of normal polarity, indicating that they were deposited in the Gauss Chron (>2.6 Ma). 

Identification and correlation of tephras by conventional means (fingerprinting by their lithological or geochemical properties) is impossible in the Kauroa Ash sequence because the beds have no remaining volcanic glass, which has instead been altered to an assemblage of authigenic phases (clays) by weathering and pedogenesis. However, a new technique analysing fresh glass found as melt inclusions in quartz grains is successful in circumventing this problem. Inclusions represent samples of non-degassed magma that became entrapped during phenocryst growth prior to eruption. The glass has remained unaltered because it is hermetically sealed in a chemically resistant phenocryst, which has protected it from weathering processes. Electron microprobe analysis of the glass inclusions yield results which are wholly reasonable for glass (totals ranging from 93-97%; low standard deviations of <1 %), and a number of provisional correlations are established by comparing the major element composition of Kauroa Ash tephra beds with those of proximal deposits. The Kauroa Ash sequence may contain deposits correlated with at least seven major TVZ eruptions, in many cases expanding the known extent of the (distal) deposit and, for the first time answering the question as to the origin of the Kauroa Ash beds. 

These correlations, together with an improved chronology, enable the Kauroa Ash sequence to be placed in a regional stratigraphic framework alongside other New Zealand Plio-Pleistocene sequences such as those in the Wanganui Basin, Wairarapa, Cape Kidnappers and Port Waikato. Using paleosols as chrono- and climatostratigraphic entities (correlated to warm periods in global climate), the sequence can also be placed alongside a global reference, the marine oxygen isotope stratigraphy. A further correlation to the Chinese loess-paleosol record suggests that large parts of the Kauroa Ash sequence were deposited in an incremental manner akin to deposition of loess, so that the sequence is not only a record of TVZ volcanism, but also of Plio-Pleistocene paleoclimate.

year: 2000

title: Sub-Optimal Choice Behaviour by Possums

authors: Hancox, Victoria Leigh

abstract: This study aimed to investigate sub-optimal choice using six brushtail possums (Trichosurus vulpecula.).  Experiment 1 replicated Zentall and Stagner’s (2011) procedure where the possums were required to choose between two alternating alternatives; The low probability alternative (sub-optimal) was a discriminative stimuli signalling 3.5-s reinforcement on 20% of the trials, and non-reinforcement on 80% of the trials; the high probability alternative (optimal) was a non-discriminative stimuli signalling 1-s reinforcement 100% of the time regardless of the stimulus presented.  This was unsuccessful as the possums showed a clear indifference to the alternatives.
  Due to these ambiguous results, we replicated two conditions of Stagner and Zentall’s (2010) procedures to achieve sub-optimal responding in possums. Experiment 2 was similar to Experiment 1, however the alternation was removed and the high probability alternative was a non-discriminative stimuli associated with 50% reinforcement regardless of the stimulus presented.  Sub-optimal responding was not achieved, however the possums now showed a preference for the optimal alternative.
   Alternation may have affected Experiment 1 and to examine this theory, Experiment 3 was replicated without alternation. Interestingly, we found a preference for the high probability alternative. Experiment 4 replicated Experiment 3; however the length of time for reinforcement was altered to attenuate sub-optimal responding. A preference for the high probability alternative which provided an overall greater net payoff was found. The possums changed from indifference to choosing optimally. It appears that possums do not have a preference for the sub-optimal choice the same as pigeons.

text: Sub-Optimal Choice Behaviour by Possums This study aimed to investigate sub-optimal choice using six brushtail possums (Trichosurus vulpecula.).  Experiment 1 replicated Zentall and Stagner’s (2011) procedure where the possums were required to choose between two alternating alternatives; The low probability alternative (sub-optimal) was a discriminative stimuli signalling 3.5-s reinforcement on 20% of the trials, and non-reinforcement on 80% of the trials; the high probability alternative (optimal) was a non-discriminative stimuli signalling 1-s reinforcement 100% of the time regardless of the stimulus presented.  This was unsuccessful as the possums showed a clear indifference to the alternatives.
  Due to these ambiguous results, we replicated two conditions of Stagner and Zentall’s (2010) procedures to achieve sub-optimal responding in possums. Experiment 2 was similar to Experiment 1, however the alternation was removed and the high probability alternative was a non-discriminative stimuli associated with 50% reinforcement regardless of the stimulus presented.  Sub-optimal responding was not achieved, however the possums now showed a preference for the optimal alternative.
   Alternation may have affected Experiment 1 and to examine this theory, Experiment 3 was replicated without alternation. Interestingly, we found a preference for the high probability alternative. Experiment 4 replicated Experiment 3; however the length of time for reinforcement was altered to attenuate sub-optimal responding. A preference for the high probability alternative which provided an overall greater net payoff was found. The possums changed from indifference to choosing optimally. It appears that possums do not have a preference for the sub-optimal choice the same as pigeons.

year: 2016

title: Joe Gillayley: A model of cultural hybridity in Keri Hulme’s novel The Bone People

authors: Cozma, Codrina

subjects: Literary analysis

abstract: Born and raised at the confluence of two cultures, Western and Māori, the New Zealand author Keri Hulme crafts in her 1983 novel, The Bone People, a vigorous literary discourse whose integrity and realism often topple consecrated stereotyping colonial theories. Joe Gillayley displays complex mechanisms of cultural hybridity in major areas of his private and social life. His initially ambivalent attitude towards both his Western and his Māori heritage are evident in his personal, social and economic life - in his interactions with his family, his semi-adopted son Simon/ Himi, his friend Kerewin, his work, school authorities, and tribal figures such as the mysterious prophet Tiaki Mira. Post-colonial scholarship provides the context in which the analysis provided here is conducted, an analysis that highlights the futility of colonial theories that are based on distorted, stereotypical images of both Western and indigenous life and values.

text: Joe Gillayley: A model of cultural hybridity in Keri Hulme’s novel The Bone People Born and raised at the confluence of two cultures, Western and Māori, the New Zealand author Keri Hulme crafts in her 1983 novel, The Bone People, a vigorous literary discourse whose integrity and realism often topple consecrated stereotyping colonial theories. Joe Gillayley displays complex mechanisms of cultural hybridity in major areas of his private and social life. His initially ambivalent attitude towards both his Western and his Māori heritage are evident in his personal, social and economic life - in his interactions with his family, his semi-adopted son Simon/ Himi, his friend Kerewin, his work, school authorities, and tribal figures such as the mysterious prophet Tiaki Mira. Post-colonial scholarship provides the context in which the analysis provided here is conducted, an analysis that highlights the futility of colonial theories that are based on distorted, stereotypical images of both Western and indigenous life and values.

year: 2004-02