Field trip guide to Oligocene Limestones and Caves in the Waitomo District

The field guide runs from Hamilton to Waitomo to Te Anga and return in limestone-dominated country developed in transgressive sedimentary deposits of the Oligocene Te Kuiti Group – a world class example of a temperate shelf carbonate depositional system. Attention focuses on the nature, distribution and paleoenvironmental controls of the main limestone facies and some of the mixed terrigenous-carbonate facies in the Group. Along the way features of the Waitomo karst landscape are noted and the trip concludes by going underground in the Ruakuri Cave to discuss cave origins and the evidence for paleoenvironmental changes locked up in speleothems

Field trip guide to the Onland Oligocene-Miocene Sedimentary Record, Eastern Taranaki Basin Margin

This field guide affords a north to south transect through examples of the Mesozoic to Quaternary sedimentary succession exposed in the Waikato, King Country and coastal strip of the eastern Taranaki basins, with particular focus on the Oligocene and Miocene deposits and how these link into the offshore parts of Taranaki Basin. The trip starts in Hamilton and ends at Tongaporutu on the north Taranaki coast, with overnight accommodation available at either Awakino or Mokau. Primarily under both local and more distant tectonic control, the stops provide examples of the various carbonate and terrigenous (locally volcaniclastic)-dominated facies associated with marginal marine, shoreline, shelf and slope-to-basin depositional settings, and their stratigraphic architecture and wider sequence stratigraphic context. Along the way, visits are recorded to basement greywacke, serpentinite and limestone quarries

Rapid progradation of the Pliocene-Pleistocene continental margin, northern Taranaki Basin, New Zealand, and implications

Progradation and aggradation of the modern continental margin in northern Taranaki Basin has resulted in the deposition of a thick and rapidly accumulated Pliocene-Pleistocene sedimentary succession. It includes the predominantly muddy Giant Foresets Formation, and the underlying sandy Mangaa Formation. Investigation of the internal attributes and depositional systems associated with the Giant Foresets Formation suggests that it would provide very little effective reservoir for hydrocarbon accumulations, although it does provide essential seal and overburden properties. While the sand-dominated Mangaa Formation could be a hydrocarbon reservoir, drilling so far has yet to reveal any significant hydrocarbon shows. Undoubtedly the most significant contribution that the Giant Foresets and Mangaa Formations have had on petroleum systems in northern Taranaki Basin is the cumulative effect that rapid and substantial accumulation has had on maturation and migration of hydrocarbons in the underlying formations. Palinspastic restoration of a seismic reflection profile across the Northern Graben, together with isopach mapping of stratigraphic section for biostratigraphic stages, indicates that the thickest part of the Pliocene-Pleistocene succession is along the central axis of the Northern Graben. Deposition of this succession contributed substantially to subsidence within the graben, providing further accommodation for sediment accumulation. Isopach and structure contour maps also reveal the extent to which submarine volcanic massifs were exposed along the axis of the graben and the timing of movement on major faults

Note on paramoudra-like carbonate concretions in the Urenui Formation, North Taranaki: possible plumbing system for a Late Miocene methane seep field

A reconnaissance study of calcitic and dolomitic tubular concretions in upper slope mudstone of the Late Miocene Urenui Formation exposed along the north Taranaki coastline indicates that they have a complex diagenetic history involving different phases of carbonate cementation and likely hydrofracturing associated with build up of fluid/gas pressures. The concretions resemble classical paramoudra in the European chalk, but are not siliceous and do not have a trace fossil origin. Stable oxygen and carbon isotope data suggest that the micritic carbonate cements in the Urenui paramoudra were probably sourced primarily from ascending methane fluid/gases, and that they precipitated entirely within the host mudstone below the seafloor. We suggest the paramoudra may mark the subsurface plumbing networks of a Late Miocene cold seep system, in which case they have relevance to the evolution and migration of hydrocarbons in Taranaki Basin, at this site perhaps focussed along the Taranaki Fault. The presence of dislodged and mass-emplaced paramoudra in the axial conglomerate of channels within the Urenui mudstone suggests there could be a connection between the loci of seep field development and slope failure and canyon cutting on the Late Miocene Taranaki margin

Stratigraphy and development of the Late Miocene-Early Pleistocene Hawke’s Bay forearc basin

A Late Miocene-Early Pleistocene mixed carbonate-siliciclastic sedimentary succession about 2 500 m thick in the Hawke’s Bay forearc basin is the focus of a basin analysis. The area under investigation covers 3 500 km2 of western and central Hawke’s Bay. The stratigraphy of Hawke’s Bay Basin is characterised by dramatic vertical and lateral facies changes and significant fluxes of siliciclastic sediment through the Late Miocene and Pliocene. This project aims to better understand the character and origin of the sedimentary succession in the basin. Geological mapping has been undertaken at a scale of 1:25000, with data managed in an ARCINFO geodatabase, following the database model employed in the IGNS QMap programme. Along the western margin of the basin there is progressive southward onlap of late Cenozoic strata on to basement. The oldest units are of Late Miocene (Tongaporutuan) age and the youngest onlap units are of latest Pliocene (Nukumaruan) age. Geological mapping of the basin fill places constraints on the magnitude (about 10 km) and timing (Pleistocene) of most of the offset on the North Island Shear Belt. Lithofacies have been described and interpreted representing fluvial, estuarine, shoreface and inner- to outer-shelf environments. Conglomerate facies are representative of sediment-saturated prograding fluvial braidplains and river deltas. These units are dominated by greywacke gravels and record the erosion of the Kaweka-Ahimanawa Ranges. Sandstone facies typically comprise very well sorted, clean non-cemented units of 10-50 m thickness that accumulated in innershelf environments. Siltstone facies probably accumulated in relatively quiet, middle- to outer-shelf water depths, and comprise well-sorted, firm non-cemented units with occasional tephra interbeds. Limestone facies represent examples of continent-attached cool-water carbonate systems that developed in response to strong tidal currents and a high nutrient flux during the Pliocene. These facies are examples of mixed siliciclastic-bioclastic sedimentary systems. Of these facies the widespread distribution and thickness of sandstone and limestone units present the most potential for hydrocarbon reservoirs. Similarly, the distribution of siltstone and mudstone beds provides adequate seal rocks. Mangapanian limestone facies have already been targeted as potential petroleum reservoirs (e.g. Kereru-1). Geological mapping suggests that potential hydrocarbon reservoir and seal rocks occur extensively in the subsurface

Tubular carbonate concretions as hydrocarbon migration pathways? Examples from North Island, New Zealand

Cold seep carbonate deposits are associated with the development on the sea floor of distinctive chemosyn¬thetic animal communities and carbonate minerali¬sation as a consequence of microbially mediated anaerobic oxidation of methane. Several possible sources of the methane exist, identifiable from the carbon isotope values of the carbonate precipitates. In the modern, seep carbonates can occur on the sea floor above petroleum reservoirs where an important origin can be from ascending thermogenic hydrocar¬bons. The character of geological structures marking the ascent pathways from deep in the subsurface to shallow subsurface levels are poorly understood, but one such structure resulting from focused fluid flow may be tubular carbonate concretions. Several mudrock-dominated Cenozoic (especially Miocene) sedimentary formations in the North Island of New Zealand include carbonate concretions having a wide range of tubular morphologies. The concretions are typically oriented at high angles to bedding, and often have a central conduit that is either empty or filled with late stage cements. Stable isotope analyses (δ13C, δ18O) suggest that the carbonate cements in the concretions precipitated mainly from ascending methane, likely sourced from a mixture of deep thermogenic and shallow biogenic sources. A clear link between the tubular concretions and overlying paleo-sea floor seep-carbonate deposits exists at some sites. We suggest that the tubular carbonate concretions mark the subsurface plumbing network of cold seep systems. When exposed and accessible in outcrop, they afford an opportunity to investigate the geochemical evolution of cold seeps, and possibly also the nature of linkages between subsurface and surface portions of such a system. Seep field development has implications for the characterisation of fluid flow in sedimentary basins, for the global carbon cycle, for exerting a biogeochemical influence on the development of marine communities, and for the evaluation of future hydrocarbon resources, recovery, and drilling and production hazards. These matters remain to be fully assessed within a petroleum systems framework for New Zealand’s Cenozoic sedimentary basins

Organic chemical signatures of New Zealand carbonate concretions and calcite fracture fills as potential fluid migration indicators

Macroscopic calcite crystals are common in sedimenta¬ry strata, occurring both as tectonic veins and also filling one or more generations of septarian rupture or later brittle fractures in calcareous concretions. Traces of hydrocarbons are frequently present in calcite crystals, especially near active petroleum systems, and are routinely the object of fluid inclusion studies linking source and migration pathway. Such calcites are shown here also to contain fatty acids in widely varying amounts ranging from 0.2 to more than 5 μg/g. Vein calcites examined are typically near the lower figure, close to analytical blank levels, and this is also true of some concretionary fracture fill calcites, notably those from the Palaeocene Moeraki ‘boulders’. Other concretionary fracture fill calcites (Jurassic, Scotland; Eocene, Waikato Coal Measures and associated marine strata) have much higher fatty acid contents, especially those filling later brittle style fractures. Although usually less abundant than the fatty acids in the concretions themselves, they lack the long chain n-acids derived from terrestrial vegetation and are commonly dominated by dioic acids. Exceptionally, in the calcitic septarian fill of a sideritic Coal Measures concretion, their abundance far exceeds that of concretion body fatty acids. They appear to be fluid transported, probably in aqueous solution, and have molecular signatures potentially distinctive of maturing organic matter sources from which the fluids derived

Neogene plate tectonic reconstructions and geodynamics of North Island sedimentary basins: Implications for the petroleum systems

Although the modern Australia-Pacific plate boundary through New Zealand is relatively straight, there have been significant changes in its geometry during the Neogene. Within the North Island sector there has been a fundamental transition from an Alpine Fault translation/transpression regime to a Hikurangi margin subduction regime. This transition has been accompanied by the southward encroachment of the edge of the Pacific plate oceanic slab into Australia lithosphere, shortened and thickened along its eastern margin as a consequence of the prior Alpine Fault transpression, the process now operating in South Island. The response of the Australia lithosphere at the surface to the emplacement of the subducted slab at depth, has differed in the East Coast forearc region versus the foreland in western North Island, where the depth to the slab is greater and there has been a characteristic southward migration of depocentres pinned to the leading edge of the slab. The recent publication of new rotation parameters for relative motion of the Australia, Antarctic and Pacific plates, have provided key new data from which to plot the successive emplacement history of the Pacific slab beneath North Island, thus enabling the comparisons to be made with basin stratigraphy and geohistory. These data also constrain the age of subduction initiation at various points along the present trend of the Hikurangi Trough, identifying a younging of subduction initiation to the southwest. An implication of this younging direction is that the modern accretion¬ary prism south of Cape Kidnappers can be no older than late Miocene (c. 11 Ma). The focus of this paper is on new ideas about the tectonic development of North Island and its basins, which have implications for hydrocarbon exploration

Late Miocene-Early Pliocene Matemateaonga Formation in eastern Taranaki Peninsula: A new 1:50,000 geological map and stratigraphic framework

In recent years the Matemateaonga Formation has become an additional exploration play in Taranaki Basin. Exploration interest has been stimulated by the success of Swift Energy Company in the Rimu/Kauri prospect (38719), located near south Taranaki Coast. At this location, sandstone lithofacies, commonly termed “Manutahi Sandstone” in the lower parts of the Matemateaonga Formation have been intersected by the Kauri-A2 and Kauri-A3 wells at depths of ~1100-1200 m and are yielding commercial quantities of oil. As part of a FRST-funded sedimentary basins research programme, we have geologically mapped in detail Matemateaonga Formation within an 1800 km2 area of the eastern peninsula region (Fig. 1), incorporating license areas 38739, 38718, 38753, 38138, 38139, 38141, 38140, 38716, 38758, 38728 and 38760. Mapping at 1:50,000 scale has revealed an ~1100 m-thick succession of cyclothemic, unconformity bounded shelfal strata of Late Miocene-Early Pliocene (Late Kapitean to Early Opoitian) age (c.5.5-4.7 Ma). This succession formed as a result of the interplay between climatically-driven 6th-order (41 k.y.) eustatic sea-level changes, high rates of basin subsidence and a substantial southerly-derived sediment flux. Individual sequences or groups of sequences are the fundamental mapping entities. The mapping area sits astride the southward-plunging Whangamomona Anticline, which has deformed the Late Neogene succession, producing a regional dip on its western flank of 2 to 4 degrees to the southwest. Northeast-southwest trending normal faults are relatively common and offset Matemateaonga Formation strata with throws of 2-50 m. This improved knowledge of Matemateaonga Formation stratigraphy enhances the understanding of the distribution and geometry of potential reservoir sandstone units and associated mudstone seal units in the region

Evolution of the Giant Foresets Formation, northern Taranaki Basin, New Zealand

Plio-Pleistocene aggradation and progradation has resulted in the rapid outbuilding of the continental shelf margin, northern Taranaki Basin. Seismic reflection profiles reveal that this outbuilding is characterised by bold clinoforms which offlap in a basinward direction. This stacked succession of clinoforms, collectively termed the Giant Foresets Formation, obtains thicknesses of over 2 km in places, and has had a significant effect on the thermal regime of the region. This integrated study was initiated to document the Late Neogene evolution of this formation, and thereby gain insights on sedimentary distribution patterns, timing of sedimentation, and controls on progradation and aggradation. Latest Miocene extension in the northern Taranaki Basin, related to rotation of the Hikurangi subduction zone, greatly influenced sedimentation patterns in the Pliocene. Palinspastic reconstruction shows that initial extension of the Northern Graben occurred before Giant Foresets Formation sedimentation began. Sediment, sourced from erosion to the east, was preferentially funneled into the newly created Northern Graben during the late Miocene and early Pliocene, while areas to the north and west underwent a period of sediment starvation. During the late Pliocene, and into the Pleistocene, sediment accumulation outpaced graben extension, and by the end of the Mangapanian, the graben was overtopped. During this period, the progradational front associated with the outbuilding of the continental shelf-slope margin advanced northwards. Throughout the Nukumaruan, continuing to the present day, shelf migration was extremely rapid. While at least seven cyclical sea level changes, with an approximate periodicity of 400 ka (fourth-order) have been identified, overall, depths shallowed from dominantly bathyal, to dominantly shelfal