The Taranaki Basin was formed as a consequence of multiple geologic events. From the Cretaceous period until present, it went through rifted margin, passive margin, foreland basin, and back-arc phases. A dominantly sandy unit, the Moki Formation, was deposited during the Middle Miocene within the Taranaki Basin offshore the west coast of the North Island of New Zealand. The study area covers about 1600 km2 of the southern part of the north Taranaki graben, an area covered by a 3D seismic volume. The Moki Formation is interpreted as a basin floor fan deposit that accumulated during basinward migration of the shelf edge with supplied sediments sourced from the SSE. Seismic profiles revealed that the mound-shape reflectors of Moki fan deposits situated between continuous reflectors of underlying Oligocene carbonates and hemipelagic muds of the overlying Manganui Formation. The reflections of the Moki sandy fan deposits locally grade laterally into interlobal deposits of hemipelagic muds. Correlation between wells Witiora-1, Taimana-1, and Arawa-1 verified the seismic interpretation, which shows an overall thickness variation of fan deposits that range from a greater thickness in the middle part of the sand lobe accumulation towards diminished thicknesses on the flanks. Gamma ray facies show clear progradation then aggradation motif that confirm the results from the seismic analyses. Depending on seismic attribute maps, paleochannels associated with the sand bodies sharing a SE to NW flow direction can be distinguished. Due to the volcanic activity in the eastern mobile belt, no paleochannels or significant stratigraphic features were recognized within the studied interval of the seismic data. Generally, in the study area, the fan deposits represent sand rich deposits that developed and prograded from south to north with variations in lateral extent driven by three major shifts in sediment pathways as the feeder channel orientations changed. / text

This dissertation focuses on understanding the relative importance of external (eustacy) versus local tectonic and sedimentary processes in controlling continental-margin depositional architectures and their implications for sediment distribution. The emphasis of this study is the interpretation of clinoform geometries and stratigraphic relationships observed on 3D and 2D seismic reflection data in the Taranaki Basin, which is characterized by a variety of clinoform architectures on its Pliocene-Recent margin (Giant Foresets Formation). I combined seismic stratigraphic interpretations and biostratigraphic studies using a dataset that consists of 1,700 km2 of 3D seismic lines, 4,000 km of 2D regional seismic lines, and data from six wells. The study was divided into three sections. First, three major stages of clinoform evolution were identified based on their architectural and geomorphological characteristics. Isochron maps were generated to identify correlations between stratigraphy and paleostructures, and seismic attribute maps were elaborated to identify and characterize geological features and depositional elements. In the second phase of the study, 2D stratigraphic forward modeling techniques were applied in an effort to quantitatively determine the relative importance of the mechanisms acting in the basin (eustacy, tectonism and sediment supply). Finally, a similar approach was applied using clinoform morphologies in the eastern Trinidad margin where the tectonic configuration of the basin was completely different to the one in the Taranaki Basin. The objective was to compare the results in a region with different a tectonic setting to validate the applicability of the methodology in other basins worldwide. The results of this research indicate that the methodology that was developed for the quantitative analysis of clinoform architectures in the Taranaki Basin is applicable to other basins worldwide and that the work flow provides a more comprehensive understanding of the factors that influence continental margin development. Generic observations of this research showed that (1) underlying structures in the shelf and slope area can play an important role in influencing the location and morphology of the shelf edge area and controlling sediment distribution; (2) high sediment supply, along with accommodation, play a key role in the construction of high-relief clinoforms and earlier dispersal of sediments into deep water; and (3) lateral variations associated with high sediment discharge sources (e.g. paleo Orinoco shelf-edge delta) can generate important changes in continental-scale clinoform architectures alongstrike in continental margins influence sediment distribution patterns in the deep-water component of the basin. / text

>Magister Scientiae - MSc / The Taranaki Basin is a large (ca. 330,000 km²) sedimentary basin found along the west coast of the northern island of New Zealand. The basin lies partly onshore but mostly offshore below the broad continental shelf to the west of central North Island. The Taranaki Basin is the first sedimentary basin to be explored in New Zealand and is currently New Zealand’s only hydrocarbon producing basin, with approximately 418 million barrels (MMbbl) of oil and 6190 billion cubic feet (bcf) of gas produced by the end of 2011. Most of New Zealand’s known oil and gas accumulations are geochemically typed to coaly facies of Late Cretaceous and Paleogene ages. The main objective of this thesis is to characterize the source rock quality of the organic rich intervals of the Taranaki Basin, namely, the Wainui Member of the North Cape Formation and the Rakopi Formation. The Rakopi Formation comprises terrestrially deposited coal measures, while the North Cape Formation is generally composed of marine rocks. These Formations make up the Pakawau Group. The objective will be achieved using two key methods. Firstly, the derivation of TOC logs using Passey’s log overlay method (Passey et al., 1990) and secondly, the generation of source rock quality maps (i.e. source rock richness mapping and source potential index mapping). This will integrate concepts relating to petrophysical wireline logs, seismic interpretation, core log information, geochemical analysis, depth mapping and isopach mapping. The results obtained from this study confirms the petroleum potential of the organic rich intervals of the Taranaki Basin. Using Passey’s method it was shown that excellent average percent TOC values are encountered for both the Wainui Member of the North Cape Formation and the Rakopi Formation. From source potential index mapping, it can be concluded that the Rakopi formation has a high source potential index (>1000SPI) on the continental shelf, which indicates that it has excellent potential for petroleum generation. The Wainui Member however, shows less potential for petroleum generation on the shelf, this being attributed to generally low net thicknesses on the shelf.

Several off-shore volcano-plutonic complexes are imaged in detail in the Parihaka 3D seismic survey in the Taranaki Basin of New Zealand. Three intrusions were analyzed for this study. Part of the Mohakatino Volcanic Centre (15 to 1.6 Ma), these intrusions have steep sides, no resolvable base reflectors, no internal stratification or structure, and they exhibit doming and faulting in the sedimentary strata above the intrusions. Deformation along the sides is dominated by highly attenuated, dipping strata with dips of 45° or higher that decrease rapidly away from the intrusions. Doming extends several hundred meters from the margins and produced many high-angle normal faults and thinned strata. The intrusions lie near normal faults with the Northern Intrusion lying directly adjacent to a segment of the Parihaka Fault. The Central Intrusion has localized normal faults cutting a graben in the area directly above the intrusion and extending in a NE-SW direction away from it. The Western Intrusion is near the western edge of the Parihaka 3D dataset and is not situated directly adjacent to extensional faults.Two distinct zones of intrusion-related faults developed around both the Northern and Central Intrusions representing two different stress regimes present during emplacement, a local stress field created by the intrusions during emplacement and the regional stress field. The deeper zones contain short radial faults that extend away from the intrusion in all directions, representing a local stress field. The shallower faults have a radial pattern above the apex of each intrusion, but farther from it, they follow the regional stress field and trend NE. Using our techniques to interpret radial faulting above both intrusions and the principal of cross-cutting relations, timing of emplacement for these intrusions are 3.5 Ma for the Northern Intrusion and between 5 and 4 Ma for the Central and Western Intrusions.Observed space-making mechanisms for the Northern and Central Intrusions include doming (~16% and 11%, respectively), thinning and extension of roof strata (~4% for both), and extension within the basin itself (29% and 12%). Stoping and floor subsidence may have occurred, but are not visible in the seismic images. Magmatic extension may have played a significant role in emplacement.Several gas-rich zones are also imaged within the seismic data near the sea-floor. They appear as areas of acoustic impedance reversal compared to surrounding sedimentary strata and have a reversal of amplitude when compared to the sea floor. The gas in these zones is either biogenic or sourced from deeper reservoirs cut by normal faults.

Detailed 3D seismic images of a volcano-plutonic complex offshore northwestern New Zealand indicate the intrusive complex lies in a relay zone between NE-trending en echelon normal faults. A series of high angle normal faults fan out from the margin of the Southern Intrusive Complex and cut the folded strata along the margin. These faults terminate against the margins of the intrusion, extend as much as 1 pluton diameter away from the margin, and then merge with regional faults that are part of the Northern Taranaki Graben. Offset along these faults is on the order of 10s to over 100 meters. Strata on top of the complex are thinned and deformed into a faulted dome with an amplitude of about 0.7 km. Steep dip-slip faults form a semi-radial pattern in the roof rocks, but are strongly controlled by the regional stress field as many of the faults are sub-parallel to those that form the Northern Taranaki Graben. The longest roof faults are about the same length as the diameter of the pluton and cut through approximately 0.7 km of overlying strata. Fault offset gradually diminishes vertically away from the top of the intrusion. The Southern Intrusive Complex is a composite intrusion and formed from multiple steep-sided intrusions as evidenced by the complex margins and multiple apophyses. Small sills are apparent along the margins and near the roof of the Southern complex. Multiple episodes of deformation are also indicated by a series of unconformities in the sedimentary strata around the complex. Two large igneous bodies make up the composite intrusion as evidenced by the GeoAnomaly body detection tool. The Southern Intrusive Complex has a resolvable volume of 277 km3. Room for the complex was made by multiple space-making mechanisms. Roof uplift created ~3% of the space needed. Compaction/porosity loss is estimated to have contributed 20-40% of the space needed. Assimilation may have created ~0-30% space. Extension played a major role in creating the space needed and is estimated to have created a minimum of 33% of the space. Floor subsidence and stoping may have occurred, but are not resolvable in the seismic survey.

The latest Eocene and Oligocene was a time of marked paleoenvironmental change in Taranaki Basin, involving a transition from the accumulation of coal measures and inner shelf deposits to the development of upper bathyal environments. Up until the end of the Early Oligocene (Lower Whaingaroan Stage) Taranaki Basin had an extensional tectonic setting. Marine transgression culminated in the accumulation of condensed facies of the Matapo Sandstone Member of the lower part of the Ngatoro Group. During the Late Oligocene (Upper Whaingaroan Stage) Taranaki Basin's tectonic setting changed to one of crustal shortening with basement overthrusting westward into the basin on Taranaki Fault. The major part of the Ngatoro Group in thickness, including the Tariki Sandstone Member, Otaraoa Formation, Tikorangi Formation and Taimana Formation, accumulated in response to this change in tectonic setting. Various methods of stratigraphic and sedimentological characterisation have been undertaken to evaluate the stratigraphy of the Ngatoro Group. Wireline log records have been calibrated through particle sizing and carbonate digestion of well cuttings. A suite of wireline motifs have been defined for formations and members of the Ngatoro Group. The integration with other lithological and paleoenvironmental data sources has helped to better define the Late Eocene - Oligocene stratigraphy and sedimentary facies for eastern Taranaki Basin margin. U-Pb geochronology by laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS) has been used to determine detrital ages for over 350 zircons from 13 samples of Late Eocene - Oligocene sandstone samples in eastern Taranaki Basin and correlative onshore North Island units. The spread of ages (1554 - 102 Ma) and the proportion of ages in particular age bands integrated with modal petrography data have aided provenance evaluation. A range of source rocks contributed to the Late Eocene - Oligocene sedimentary units analysed, mainly the Waipapa Terrane (Early Permian to Late Jurassic) as shown by 206Pb/238U zircon ages and the abundance of fine-grained sedimentary rock fragments observed in samples. The Median Batholith (i.e. Darran/Median Suite and Separation Point Suite) is also identified as a significant source, indicated by Early Triassic to Early Jurassic and Early Cretaceous 206Pb/238U zircon ages and an abundance of quartz in samples. Other minor sources identified include Murihiku and Caples Terranes, Rakaia Sub-terrane and possibly the Karamea Batholith. The Tariki Sandstone and the Hauturu Sandstone have the same source, with the main 206Pb/238U zircon ages of aggregated samples (124 - 116 Ma and 121 Ma, respectively) consistent with a Separation Point Suite/Median Batholith (124 - 116 Ma) source. Derivation of sediments from a landmass that existed to the east and southeast of the Wellington area has been inferred for the Late Eocene - Oligocene units, with subsequent migration of sediments northward into Taranaki Basin and the Waikato Region (i.e. Te Kuiti Group depocentre) via longshore drift. New provenance data have been used to revise understanding about the development of eastern Taranaki Basin margin through the Late Eocene to earliest Miocene. Three new paleogeography maps are presented for the Runangan (Late Eocene), Lower Whaingaroan (Early Oligocene) and Upper Whaingaroan (early-mid-Oligocene). New paleogeography interpretations illustrate a dramatic change in the basin development between Matapo Sandstone (Lower Whaingaroan) and Tariki Sandstone (Upper Whaingaroan) deposition, consistent with an Upper Whaingaroan age for the start of reverse movement on Taranaki Fault.