An investigation into the feasibility and potential benefits of shared taxi services to commuter stations

Peer reviewedPublisher PD

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

Three-dimensional Self-similar Fractal Light in Canonical Resonators

Unstable canonical resonators can possess eigenmodes with a fractal intensity structure [Karman et al., Nature 402, 138(1999)]. In one particular transverse plane, the intensity is not merely statistically fractal, but self-similar [Courtial and Padgett, PRL 85, 5320 (2000)]. This can be explained using a combination of diffraction and imaging with magnification greater than one. Here we show that the same mechanism also shapes the intensity cross-section in the longitudinal direction into a self-similar fractal, but with a different magnification. This results in three-dimensional, self-similar, fractal intensity structure in the eigenmodes

Lithostratigraphy and depositional episodes of the Oligocene carbonate-rich Tikorangi Formation, Taranaki Basin, New Zealand

The subsurface Oligocene Tikorangi Formation is a unique and important oil producer in the onshore Waihapa-Ngaere Field, Taranaki Basin, being the only carbonate and fracture-producing reservoir within the basin. Core sample data from seven onshore wells (foredeep megafacies) and a single offshore well (basinal megafacies) are correlated with a suite of sonic and gamma-ray geophysical well log data to derive interpretative carbonate facies for the Tikorangi Formation. Four mixed siliciclastic-carbonate to carbonate facies have been defined: facies A-calcareous siliciclastite (75% carbonate). Single or interbedded combinations of these facies form the basis for identifying nine major lithostratigraphic units in the Tikorangi Formation that are correlatable between the eight wells in this study.The Tikorangi Formation accumulated across a shelf-slope-basin margin within a tectonically diversified basin setting, notably involving considerable off-shelf redeposition of sediment into a bounding foredeep. Analysis of gamma, sonic, and resistivity well logs identifies five major episodes of sedimentary evolution. Episode I comprises retrogradational siliciclastic-dominated redeposited units associated with foredeep subsidence. Episode II is a continuation of episode I retrogradation, but with increased mass-redeposited carbonate influx during accelerated foredeep subsidence and relative sea-level rise, the top marking the maximum flooding surface. Episode III involves a progradational sequence comprising relatively pure redeposited carbonate units associated with declining subsidence rates and minimal siliciclastic input, with movement of facies belts basinward. Episode IV consists of prograding aggradation involving essentially static facies belts dominated by often thick, periodically mass-emplaced, carbonate-rich units separated by thin background siliciclastic shale-like units. Episode V is a retrogradational sequence marking the reintroduction of siliciclastic material into the basin following uplift of Mesozoic basement associated with accelerated compressional tectonics along the Australia-Pacific plate boundary, initially diluting and ultimately extinguishing carbonate production factories and terminating deposition of the Tikorangi Formation

Petrogenesis of the Tikorangi Formation fracture reservoir, Waihapa-Ngaere Field, Taranaki Basin

The subsurface mid-Tertiary Tikorangi Formation is the sole limestone and the only fracture-producing hydrocarbon reservoir within Taranaki Basin. This study, based on core material from seven wells in the onshore Waihapa/Ngaere Field, uses a range of petrographic (standard, CL, UV, SEM) and geochemical techniques (stable isotope, trace element data, XRD) to unravel a complex diagenetic history for the Tikorangi Formation. A series of eight major geological-diagenetic events for the host rock and fracture systems have been established, ranging from burial cementation through to hydrocarbon emplacement within mineralized fractures. For each diagenetic event a probable temperature field has been identified which, combined with a geohistory plot, has enabled the timing of events to be determined. This study has shown that the Tikorangi Formation comprises a complex mixed siliciclastic-carbonate-rich sequence of rocks that exhibit generally tight, pressure-dissolved, and well cemented fabrics with negligible porosity and permeability other than in fractures. Burial cementation of the host rocks occurred at temperatures of 27-37°C from about 0.5-1.0 km burial depths. Partial replacement dolomitisation occurred during late burial diagenesis at temperatures of 36-50°C and at burial depths of about 1.0 km, without any secondary porosity development. Fracturing occurred after dolomitisation and was associated with compression and thrusting on the Taranaki Fault. The location of more carbonate/dolomite-rich units may have implications for the location of better-developed fracture network systems and for hydrocarbon prospectivity and production. Hydrocarbon productivity has been ultimately determined by original depositional facies, diagenesis, and deformation. Within the fracture systems, a complex suite of vein calcite, dolomite, quartzine, and celestite minerals has been precipitated prior to hydrocarbon emplacement, which have substantially healed and reduced fracture porosities and permeabilities. The occurrence of multiple vein mineral phases, collectively forming a calcite/dolomite-celestite-quartzine mineral assemblage, points to fluid compositions varying both spatially and temporally. The fluids responsible for vein mineralisation in the Tikorangi Formation probably involved waters of diverse origins and compositions. Vein mineralisation records a history of changing pore fluid chemistry and heating during burial, punctuated by changes in the relative input and mixing of downward circulating meteoric and upwelling basinal fluids. A sequence of mineralisation events and their probable burial depth/temperature fields have been defined, ranging from temperatures of 50-80°C and burial depths of 1.0-2.3 km. Hydrocarbon emplacement has occurred over the last 6 m.y. following the vein mineralization events. The Tikorangi Formation must continue to be viewed as a potential fracture reservoir play within Taranaki Basin

Lithostratigraphy and depositional episodes of the Oligocene carbonate-rich Tikorangi Formation, Taranaki Basin, New Zealand

The subsurface Oligocene Tikorangi Formation is a unique and important oil producer in the onshore Waihapa-Ngaere Field, Taranaki Basin, being the only carbonate and fracture-producing reservoir within the basin. Core sample data from seven onshore wells (foredeep megafacies) and a single offshore well (basinal megafacies) are correlated with a suite of sonic and gamma-ray geophysical well log data to derive interpretative carbonate facies for the Tikorangi Formation. Four mixed siliciclastic-carbonate to carbonate facies have been defined: facies A-calcareous siliciclastite (75% carbonate). Single or interbedded combinations of these facies form the basis for identifying nine major lithostratigraphic units in the Tikorangi Formation that are correlatable between the eight wells in this study.The Tikorangi Formation accumulated across a shelf-slope-basin margin within a tectonically diversified basin setting, notably involving considerable off-shelf redeposition of sediment into a bounding foredeep. Analysis of gamma, sonic, and resistivity well logs identifies five major episodes of sedimentary evolution. Episode I comprises retrogradational siliciclastic-dominated redeposited units associated with foredeep subsidence. Episode II is a continuation of episode I retrogradation, but with increased mass-redeposited carbonate influx during accelerated foredeep subsidence and relative sea-level rise, the top marking the maximum flooding surface. Episode III involves a progradational sequence comprising relatively pure redeposited carbonate units associated with declining subsidence rates and minimal siliciclastic input, with movement of facies belts basinward. Episode IV consists of prograding aggradation involving essentially static facies belts dominated by often thick, periodically mass-emplaced, carbonate-rich units separated by thin background siliciclastic shale-like units. Episode V is a retrogradational sequence marking the reintroduction of siliciclastic material into the basin following uplift of Mesozoic basement associated with accelerated compressional tectonics along the Australia-Pacific plate boundary, initially diluting and ultimately extinguishing carbonate production factories and terminating deposition of the Tikorangi Formation

A stochastic ensemble forecast model for geosynchronous relativistic electron fluxes

A stochastic ensemble model composed of three functional forecasting models has been developed to forecast \u3e2 MeV electron flux at geosynchronous (GEO) orbit. The REFM model is based on a statistical link between electron flux and solar wind speed using empirically derived linear filter coefficients, the Li model solves a radial diffusion equation with a diffusion coefficient that is a function of the solar wind velocity and interplanetary magnetic field, and the Fluxpred model is a multi-layer feed-forward neural network with electron flux and summed Kp as input. Individual model results were combined using a multivariate regression to produce significantly better predictive results than any of the individual models alone. A stochastic model is then developed to forecast the probability that a fluence threshold will be exceeded. The regression technique, model optimization, and calculation of forecast probability will be discussed in reference to the ensemble model