title: Sedimentology and Petrology of Miocene Cold-Seep Carbonates in Southern Hawke's Bay: Geological Evidence for Past Seabed Hydrocarbon Seepage

authors: Troup, Melissa Jane

subjects: cold seep carbonate

abstract: This study focuses on the five sites of Early Miocene aged cold seep carbonate deposits (Wanstead, Wilder Road, Haunui, Ugly Hill, and Ngawaka) in the southern East Coast Basin, North Island, New Zealand, which archive paleo-hydrocarbon seafloor seepage in a convergent margin setting. Seep deposits are hosted within calcareous slope mudstones of the Ihungia Fm and provide an important analogue to modern seep sites in the East Coast Basin. Individual fossilised seep sites have revealed, through mapping and logging, differences in outcrop extent, morphology, and lithology, while petrology has uncovered a complex array of textures, fabrics, and mineralogies within the methane derived authigenic carbonates (MDAC). Fabrics are diverse and often comprise chaotic multi-phase assemblages of various mineralogies in original and/or altered states. Enclosed within the carbonates are the fossilised remnants of chemosynthesis-based communities, particularly macro-invertebrates, which includes lucinid and vesicomyid clams, modiolid mussels, corals, gastropods, and worm tubes. These fossil types, and their distribution throughout the deposit, not only reflect the variations in fluid conditions but also the maturity of the seep system. Veining and (micro)brecciation are common at a variety of scales with multiple generations of cements forming thick fill sequences representing cyclic episodes of fracturing and sealing through carbonate formation.

Detailed analysis of MDAC deposits has led to the identification of thirteen mineral fabrics, four fracturing and/or corrosion phases, and two alteration phases. Relationships between the various fabrics and phases has led to the elucidation of a generalised paragenetic sequence while appreciating that some local variation occurs. The paragenetic sequence is divided into two diagenetic stages: an early stage that includes all mineralisation and events that occurred in the (near) seafloor environment, and a late stage that includes all mineralisation and events that occurred in the burial realm.

Early diagenesis (8 events) involved precipitation of mainly aragonite phases, including clotted and peloidal microcrystalline carbonate (micarb), fibrous and radiating crystal forms (often hydrocarbon inclusion-bearing) occasionally encase thrombolites between successive isopachous generations, and anhedral crystal masses and layers. Early destructive episodes of fracturing, (auto)brecciation, and dissolution via corrosive fluids significantly modified the deposits, ultimately increasing surface area available for further mineral growth. Late diagenesis (9 events) occurred within the burial realm and resulted in the addition of late stage pore and fracture occluding low magnesium calcite (LMC) and some minor dolomite and silica forms. Some of the early metastable aragonite forms remained pristine and unaltered, while others underwent varying degrees of fabric retentive to destructive neomorphic change generally resulting in stable LMC mineralogies. Later uplift and exhumation brought the carbonate deposits into their present-day positions.

Distinctly depleted stable δ13C isotope signatures indicate carbonate carbon was largely sourced from thermogenic methane, with some of the migrating fluids likely affected by methane pool oxidation, and mixing with marine water and residual CO2. Stable δ18O isotope signatures suggest that the ascending hydrocarbon-rich fluids experienced slight temperature fluctuations, possibly due to contact with warmer advecting fluids, and were also influenced by local gas hydrate formation and dissociation events. Preliminary lipid results importantly confirm the presence of microbes which carry out the anaerobic oxidation of methane (e.g. PMI and biphytanic diacid) and sulphate reduction (e.g. iso-and anteiso fatty acids).

The complexity revealed within these cold seep carbonates, and more particularly their cement stratigraphy, reflects the temporally and spatially dynamic nature of the fluids reaching the paleo sea floor of the East Coast Basin. Many of the features observed within these southern East Coast Basin cold seep deposits have a striking similarity with the Miocene deposits of the Italian Apennines, while others, particularly the occurrence of microbial mats (thrombolites), are an interesting feature more atypical of worldwide occurrences.

text: Sedimentology and Petrology of Miocene Cold-Seep Carbonates in Southern Hawke's Bay: Geological Evidence for Past Seabed Hydrocarbon Seepage This study focuses on the five sites of Early Miocene aged cold seep carbonate deposits (Wanstead, Wilder Road, Haunui, Ugly Hill, and Ngawaka) in the southern East Coast Basin, North Island, New Zealand, which archive paleo-hydrocarbon seafloor seepage in a convergent margin setting. Seep deposits are hosted within calcareous slope mudstones of the Ihungia Fm and provide an important analogue to modern seep sites in the East Coast Basin. Individual fossilised seep sites have revealed, through mapping and logging, differences in outcrop extent, morphology, and lithology, while petrology has uncovered a complex array of textures, fabrics, and mineralogies within the methane derived authigenic carbonates (MDAC). Fabrics are diverse and often comprise chaotic multi-phase assemblages of various mineralogies in original and/or altered states. Enclosed within the carbonates are the fossilised remnants of chemosynthesis-based communities, particularly macro-invertebrates, which includes lucinid and vesicomyid clams, modiolid mussels, corals, gastropods, and worm tubes. These fossil types, and their distribution throughout the deposit, not only reflect the variations in fluid conditions but also the maturity of the seep system. Veining and (micro)brecciation are common at a variety of scales with multiple generations of cements forming thick fill sequences representing cyclic episodes of fracturing and sealing through carbonate formation.

Detailed analysis of MDAC deposits has led to the identification of thirteen mineral fabrics, four fracturing and/or corrosion phases, and two alteration phases. Relationships between the various fabrics and phases has led to the elucidation of a generalised paragenetic sequence while appreciating that some local variation occurs. The paragenetic sequence is divided into two diagenetic stages: an early stage that includes all mineralisation and events that occurred in the (near) seafloor environment, and a late stage that includes all mineralisation and events that occurred in the burial realm.

Early diagenesis (8 events) involved precipitation of mainly aragonite phases, including clotted and peloidal microcrystalline carbonate (micarb), fibrous and radiating crystal forms (often hydrocarbon inclusion-bearing) occasionally encase thrombolites between successive isopachous generations, and anhedral crystal masses and layers. Early destructive episodes of fracturing, (auto)brecciation, and dissolution via corrosive fluids significantly modified the deposits, ultimately increasing surface area available for further mineral growth. Late diagenesis (9 events) occurred within the burial realm and resulted in the addition of late stage pore and fracture occluding low magnesium calcite (LMC) and some minor dolomite and silica forms. Some of the early metastable aragonite forms remained pristine and unaltered, while others underwent varying degrees of fabric retentive to destructive neomorphic change generally resulting in stable LMC mineralogies. Later uplift and exhumation brought the carbonate deposits into their present-day positions.

Distinctly depleted stable δ13C isotope signatures indicate carbonate carbon was largely sourced from thermogenic methane, with some of the migrating fluids likely affected by methane pool oxidation, and mixing with marine water and residual CO2. Stable δ18O isotope signatures suggest that the ascending hydrocarbon-rich fluids experienced slight temperature fluctuations, possibly due to contact with warmer advecting fluids, and were also influenced by local gas hydrate formation and dissociation events. Preliminary lipid results importantly confirm the presence of microbes which carry out the anaerobic oxidation of methane (e.g. PMI and biphytanic diacid) and sulphate reduction (e.g. iso-and anteiso fatty acids).

The complexity revealed within these cold seep carbonates, and more particularly their cement stratigraphy, reflects the temporally and spatially dynamic nature of the fluids reaching the paleo sea floor of the East Coast Basin. Many of the features observed within these southern East Coast Basin cold seep deposits have a striking similarity with the Miocene deposits of the Italian Apennines, while others, particularly the occurrence of microbial mats (thrombolites), are an interesting feature more atypical of worldwide occurrences.

year: 2010

title: Optimisation of renewable energy resources in New Zealand for process heat: An economic and supply assessment

authors: O'Leary, Jack

abstract: A significant amount of New Zealand’s greenhouse gases are emitted through the use of fossil fuels to generate process heat. New Zealand is well-placed to provide renewable energy for process heat, with a well-established plantation forestry industry that generates large amounts of renewable biomass fuel sources, and a high percentage of renewables in the electricity generation stack. Biomass and electricity could be used to reduce and eliminate reliance on fossil fuels. The important criteria for these fuel switches are to ensure that they are economic and have sufficient supply over the coming decades. 

This thesis presents a method to model and optimise the allocation of resources to give foresight around the extent biomass can provide economic process heat across regions in New Zealand. A diverse range of case studies was employed, encompassing individual sites, regional energy systems, and the South Island. These case studies were modelled and optimised in P-Graph studio and examination of the results gave key insights into several important areas: regional diversity in energy supply and demand, impact of the demand scale and temperature profile, and finally demonstrated the economic potential of interregional transport of energy dense biomass to alleviate supply deficits and reduce the Levelised Cost of Energy (LCOE). 

The largest impact on the LCOE was the temperature profile of the heat demand. The more heat demand below 100°C, the lower the final cost of energy. This was due to the high Coefficient of Performance of High Temperature Heat Pumps (HTHP), which were the ubiquitous fuel switching choice for below 100°C heat demand, providing LCOEs under 11 $/GJ in 2023. At these prices HTHPs are able to match or surpass the current prices for coal at 10 – 14 $/GJ. For heat demand above 100°C, biomass was the dominant choice as it provided much better economics. However, there was a wide range of LCOEs for biomass energy. This was caused by the wide range of resource, collection, and transport costs for the various biomass sources. These LCOEs ranged from 13 – 14 $/GJ for processor residues, to over 25 $/GJ for low grade export logs. 

As the size of a plant or region increases, the demand exhausts the supply of low cost biomass and must source from a larger radius, or from more costly biomass sources. This resulted in a large spread of LCOEs for the regions in the South Island, with Otago, the West Coast, and Nelson-Marlborough seeing some of the lowest weighted average LCOEs for above 100°C heat demand of between 20 and 22 $/GJ, whilst the three largest energy users, Southland, South Canterbury, and North Canterbury saw LCOEs of between 26 and 28 $/GJ for 2023. 

A key trend was established that regions with higher biomass supply saw lower LCOEs for heat demand above 100°C. Interregional transport of energy dense biomass was able to reduce the LCOE in the three regions of high demand and low biomass availability, bringing the weighted average for above 100° demand down to between 25 and 27 $/GJ for 2023. The use of interregional transport also saw the proportion of biomass used for heat demand above 100°C rise from 60% to over 90% in 2023. Supply constraints impact the use of biomass in 2037 and see the maximum economic use of biomass in heat demands above 100°C drop to 72%.

text: Optimisation of renewable energy resources in New Zealand for process heat: An economic and supply assessment A significant amount of New Zealand’s greenhouse gases are emitted through the use of fossil fuels to generate process heat. New Zealand is well-placed to provide renewable energy for process heat, with a well-established plantation forestry industry that generates large amounts of renewable biomass fuel sources, and a high percentage of renewables in the electricity generation stack. Biomass and electricity could be used to reduce and eliminate reliance on fossil fuels. The important criteria for these fuel switches are to ensure that they are economic and have sufficient supply over the coming decades. 

This thesis presents a method to model and optimise the allocation of resources to give foresight around the extent biomass can provide economic process heat across regions in New Zealand. A diverse range of case studies was employed, encompassing individual sites, regional energy systems, and the South Island. These case studies were modelled and optimised in P-Graph studio and examination of the results gave key insights into several important areas: regional diversity in energy supply and demand, impact of the demand scale and temperature profile, and finally demonstrated the economic potential of interregional transport of energy dense biomass to alleviate supply deficits and reduce the Levelised Cost of Energy (LCOE). 

The largest impact on the LCOE was the temperature profile of the heat demand. The more heat demand below 100°C, the lower the final cost of energy. This was due to the high Coefficient of Performance of High Temperature Heat Pumps (HTHP), which were the ubiquitous fuel switching choice for below 100°C heat demand, providing LCOEs under 11 $/GJ in 2023. At these prices HTHPs are able to match or surpass the current prices for coal at 10 – 14 $/GJ. For heat demand above 100°C, biomass was the dominant choice as it provided much better economics. However, there was a wide range of LCOEs for biomass energy. This was caused by the wide range of resource, collection, and transport costs for the various biomass sources. These LCOEs ranged from 13 – 14 $/GJ for processor residues, to over 25 $/GJ for low grade export logs. 

As the size of a plant or region increases, the demand exhausts the supply of low cost biomass and must source from a larger radius, or from more costly biomass sources. This resulted in a large spread of LCOEs for the regions in the South Island, with Otago, the West Coast, and Nelson-Marlborough seeing some of the lowest weighted average LCOEs for above 100°C heat demand of between 20 and 22 $/GJ, whilst the three largest energy users, Southland, South Canterbury, and North Canterbury saw LCOEs of between 26 and 28 $/GJ for 2023. 

A key trend was established that regions with higher biomass supply saw lower LCOEs for heat demand above 100°C. Interregional transport of energy dense biomass was able to reduce the LCOE in the three regions of high demand and low biomass availability, bringing the weighted average for above 100° demand down to between 25 and 27 $/GJ for 2023. The use of interregional transport also saw the proportion of biomass used for heat demand above 100°C rise from 60% to over 90% in 2023. Supply constraints impact the use of biomass in 2037 and see the maximum economic use of biomass in heat demands above 100°C drop to 72%.

year: 2024

title: Kirihaehae

authors: Maxwell, Te Kahautu

abstract: A haka composed about moko. My grand aunt Tangiwai took the moko chin tattoo so when the man from Tauranga, Kōraurau Te Kani that she had been betrothed to arrived at Whitianga Bay on the East Coast of the Bay of Plenty, he would readily recognise her his intended bride to be. This haka was composed for Te Kapa Haka o Tūtawake. This composition will be performed at the Mātaatua Kapa Haka regional Competition in Ruatoki 2016.

text: Kirihaehae A haka composed about moko. My grand aunt Tangiwai took the moko chin tattoo so when the man from Tauranga, Kōraurau Te Kani that she had been betrothed to arrived at Whitianga Bay on the East Coast of the Bay of Plenty, he would readily recognise her his intended bride to be. This haka was composed for Te Kapa Haka o Tūtawake. This composition will be performed at the Mātaatua Kapa Haka regional Competition in Ruatoki 2016.

year: 2013