T.R. Haskell
Haskell Exploration Services Ltd.
Wellington, NZ
Exploration work on petroleum exploration permits held by Asia Pacific Oil Sdn. Bhd. on and off Gisborne City on the east coast of New Zealand's North Island and offshore in the southeastern continental shelf, the Muriwai shelf, showed a marked contrast in their structural style.
The former is a south-facing half graben involving an essentially complete basin section of Late Cretaceous to Recent sequence that can be accepted as part of the East Coast basin's convergent Hikurangi Margin. The latter comprises separate and superposed synclines developed in Neogene rocks that rest on a largely opaque seismic sequence representing the Late Cretaceous and Paleogene sequence.
The Muriwai shelf work showed that the convergent tectonics associated with the East Coast basin had little influence on depositional systems. Rather, the open syncline dominated structuring of laterally continuous Miocene and Pliocene sedimentary sequences in this area was generated by gravitational tectonics in episodic, earliest Pliocene (5.3 My) and latest Pliocene/earliest Pleistocene (1.8 My), 10,000-year scale events.
In a subsidiary event, Early Pliocene slippage down the flanks of the early syncline generated separate 5-km scale thrust-based anticlines. Here I conclude that the Miocene beds folded when their isostatic loading exceeded the reduced strength of the deeper and overpressured Late Cretaceous and Paleogene sequence.
The basin's Hikurangi margin reacted by rebounding upwards against the coherent Miocene rocks, generating melange in the overpressured sequence, diapiric migration of melange away from the shelf axis, and generating a regional syncline. The uplift stabilized and was immediately subject to shelf-wide submarine erosion.
The Pliocene sequence was laid down on this surface, and the loading, rebounding, and folding cycle repeated in the Latest Pliocene/Earliest Pleistocene. Erosion of this syncline has generated the present Muriwai shelf and is ongoing.
The opacity of the Late Cretaceous and Paleogene (LC&P) sequence is a feature of adjacent onshore areas. In accessing source rock positioning and migration pathways it has been generally assumed that the interval follows the base Miocene. However the development of melange in the manner proposed here or by mechanisms summarized by Mazengarb and Morley (discussed below) misaligns oil and gas source rocks from reservoir quality Miocene sandstones in onshore structuring is probably a factor that contributes to lack of commercial success in the some 25 wells drilled in the adjacent onshore. While it has probably not been a factor in recent work, the thrust based Early Pliocene anticlines do not have direct access to the LC&P source rocks and would need to be accessed on that basis.
Within New Zealand's Hikurangi Margin, gravitational tectonics have long been recognized as contributing to generation of regional and local structuring around and north of Gisborne.1 2 The coastal part of this area, the Pouawa Chaos,3 was mapped as kilometer-scale fault blocks of early Late Miocene forearc strata intruded by rafts of diapiric Cretaceous and Paleogene sequences.4 These diapirs are still active.4
The wave cut platform developed over part of the Sponge Bay diapir at Taumotu Island, immediately east of Gisborne, rose 2.1 m on Feb. 17, 1931.5 Two local tsunamis, respectively generated on Mar. 25 and May 17, 1947, were probably caused by activity within mud volcanoes, the former originating in the Ariel Bank,6 an 8 km long shallow 12 km east of Gisborne had delineated a diapiric intrusion7 (Fig. 1).
Mazengarb8 recognized active and reactive diapirism associated with southeastward tilting of the forearc basin and associated gravitational gliding as the principal tectonic activity in the Tauwhareparae area. This 30 km wide coastal area to the north of Gisborne includes the central and northern Pouawa Chaos and comprises Neogene strata resting on overpressured, smectitic Paleogene rocks. Mazengarb notes that the broad syncline and tight anticline structuring developed in this system is characteristic of East Coast basin (ECB) Neogene structure and lies parallel to the Miocene plate convergent vector and is not related to it.
Morley9 notes large-scale deformation of Miocene rocks of Brunei's Miocene Champion and Baram deltas similar to those noted by Mazengarb and generated by west-northwestward gliding over an overpressured mobile shale melange interval. Morley et al.10 also show similar diapirism in the inverted province of a foreland basin associated with the Baram Delta.
The 20 km wide northeast trending Berakas syncline and associated Belait and Jerudong anticlines in this structuring were generated by deposition of Mid Miocene sequence in a restricted basin controlled by preexisting faulting in the Jerudong anticline.
The sediment loading generated a cycle of progressive isostatic subsidence across the syncline and inversion of faulting at its margins as the underlying shales were mobilized away from the syncline into the anticlines by overburden weight in the syncline. The underlying mobile shale sequence is variably opaque on seismic sections, a feature attributed to overpressuring within the shale.
Mahia Peninsula,11 at the southern end of the shelf, was uplifted seven times in the last 212 Ka by faulting associated with this element of convergent margin activity (Fig. 1). The possibility of shale movements contributing to tectonic activity east and northeast of the peninsula has been considered12 but was preferentially related to convergent margin compression expressed to the adjacent southwest in Hawke Bay.
A feature of the Hawke Bay area, the Lachlan ridge, was developed by east-southeastward thrusting and uplift in a thin-skinned regimen on the Lachlan fault system.12 The uplift includes Mahia Peninsula and comprises the northern end of the compressional tectonics attributed to Hawke Bay.
Regional geology
The Neogene and present day tectonic and depositional model used on the east coast of the North Island is part of the south-southeasterly directed convergent Hikurangi Margin compressional system.14
The triangular Muriwai shelf area is mostly less than 100 m deep and comprises a subtriangular area of characteristically and modestly structured Neogene rocks between Gisborne and the edge of the continental slope.
The shelf break and slope are partly coincident with the Lachlan fault that runs northeast through the region. Its western margin, the coast south from Gisborne, is the eastern side of the 700 m high Wharerata Ranges, which are cored by a 20 km wide anticlinal complex of Neogene beds.
The southern apex is the Mahia Peninsula, a localized 400 m high exposure of Muriwai shelf Neogene sequence recently uplifted by the Lachlan fault. The northern margin of the shelf is immediately south of the Pouawa outcrop around Gisborne which probably extends to the offshore Aerial Bank (Fig. 1).
This study is based on a broad but favorably orientated grid of reconnaissance quality marine seismic data shot by BP in 1965 and 196715 16 and Gulf Research & Development in 1972.17 Several lines used have been reprocessed by Pacific Star Resources Ltd.18 This data set was supplemented by seismic data shot over the southern and eastern part of the area by NIWA in 1998 to image Pliocene sequence and more recent reconnaissance data shot by the Petroleum Unit of the New Zealand Ministry of Energy.
The Albian to Present Day marine ECB rests on Mesozoic basement. Its LC&P sequence of marine turbidites, siltstones, and mudstones reflect the Campanian breakaway of the New Zealand subcontinent from Gondwana and the onset of a thermal contraction.
The Mid Campanian to Early Paleocene interval comprises mudstones with increasingly common interbeds of fine plant fragments. Carbonaceous material dominates the overlying and very thin Late Paleocene black shale sequence.
Thermal contraction continued through the Paleogene generating progressively finer Eocene and Early Oligocene formations that include abundant smectitic clays and increasing carbonate, which becomes common in late Paleocene and locally dominant in the Oligocene. These clays recycled into muddy and silty elements of the overlying sequence during Neogene erosion and deposition.
The convergent Hikurangi Margin tectonic regime and its associated generally fine-grained and smectitic depositional systems was initiated in the basal Miocene, and continues to the present.
The Miocene sequences in the Wharerata Ranges are marine, up to 5 km thick, and comprise shelf sandstones and outer shelf and slope mudstones and siltstones and distal and basin floor sandstone to mudstone turbidite cycles. In the ranges the basal Pliocene unit, a widespread and thin coquina, is overlain by thick Early Pliocene tuffaceous sandstone and siltstone, further limestone then Late Pliocene siltstone.
This Neogene sequence dominates outcrop onshore to the west. LC&P outcrops in the region are limited to two inlying "mud volcanoes" at the Taiporutu and Waiopine stream mouths on the eastern side of Mahia Peninsula19 20 and to a fault line intrusion north of Opoutama (Fig. 1).
Interpretation of outcrop and on and offshore seismic sections in the whole Gisborne area shows that the Miocene sequence in the part of the basin was a flat lying and subparallel bedded interval through the period.
It now forms a north-south elongated complex through the western Wairoa syncline, the anticline complex that corresponds to the coastal Wharerata Ranges. It runs offshore into the Muriwai shelf and the Maraetaha syncline (new name) that underlies the axis of the shelf. An Early Miocene half graben crosses the axis of the syncline and underlies a Mid Miocene sequence that is continuous across the shelf (Figs. 1 and 2).
The Pliocene sequence is continuous across the Wairoa syncline and Maraetaha syncline but is developed in small fault controlled blocks in the intervening anticlinal system controlling the Wharerata Ranges and separate Mahia Peninsula, following a structural style developed in the latest Pliocene or Pleistocene (Fig. 1).
The Maraetaha syncline was previously correlated with the West Mahia syncline,13 which separates the Mahia Peninsula uplift generated by Pleistocene activity on the Lachlan fault from the Wharerata structure related to Miocene and subsequent Pliocene deformation of the Muriwai shelf. Mapping undertaken for this study shows that the two structures have separate origins.
Within the inliers, Albian boulders were mapped near the Waiopine inlier, a 520 m wide and thick Cenomanian unit that occurs in the Taiporutu inlier along with 1-30 m thick outcrops of Maastrichtian formations in both. Ten meter thick Paleocene successions occur in both inliers, along with 60 m units of early Eocene sequence in Waiopine, and 15 m-19 m thick units of late Eocene and Oligocene formations in both outcrops.
These exposures represent all of the region's Late Cretaceous and Paleogene stratigraphic units and are mapped as having various strikes and being strongly folded and steeply dipping or overturned. The inlier north of Opoutama is a similar complex of Cretaceous to Oligocene blocks. These three inliers are usually taken to be local examples of tightly folded but otherwise normal elements of the regional sequence developed beneath routinely, and gently, folded Miocene.
The Mangaone-1 well21 (Fig. 1) drilled a normal Miocene sequence to an unconformity at 868 m, Oligocene rocks to 1,197 m, and then Eocene aged rocks to 1,334 m. At that depth, the age and lithology reverse to Early Oligocene to 1,371 m, Mid Oligocene to 1,524 m, and Late Oligocene to total depth (TD) at 1,549 m. The well drilled a fault shear zone near TD.
The sequence above the age reversal has a hydrostatic gradient of 0.156 MPa/m, but this changes to a lithostatic gradient of 0.0227 MPa/m from 1,334 m.22 The adjacent Gisborne-2 well drilled Miocene to about 600 m, Oligocene to 1,100 m, and reached TD in Eocene rocks at 1,191 m.23
The Opoutama-1 well24 (Fig. 1) drilled normally pressured Miocene beds to 716 m, Oligocene to 925 m, then a fault zone melange of mixed Oligocene to Maastrichtian rocks that extended to in place Eocene and Maastrichtian rocks below 1,186 m. The well's fluid pressure gradient increased to 0.02 MPa/m between 600 and 750 m across the Miocene-Oligocene interface, and remained at that level to at least 1,700 m.22 TD was in Cenomanian rocks at 3,657 m.
To the west 40 km, Rere-125 drilled a normal sequence of Miocene to Albian rocks. The Miocene and late Paleogene sequences in the well, 0-1,325 m and 1,325-1,500 m normally pressured but the gradient increases to average 0.21 MPa/m below that level.
Using log data, these and earlier Paleogene beds to 2,100 m have a density range largely between 1.78 and 1.94 gm/cc. The Cretaceous interval, 2,100-4,375 m (TD), shows a related decrease in density from 1.8 to 1.5 gm/cc.22 Other wells in the area bottomed in the Miocene or late Oligocene rocks.
International Pacific Exploration Ltd. Waitangi Station-126, 37 km west-northwest of Gisborne and in the slide area mapped by Mazengarb,8 drilled Miocene to 454 m, then unordered Early, Mid, and Late Eocene intervals occasionally associated with Paleocene and Oligocene rocks to TD (2,140 m) with one 47-m Miocene interval from 1,981 m.
This considered to be a fault tectonic feature and related it to a similar occurrence mapped from cores of nearby Taranaki Oil Fields Waitangi-1 well.26 Waitangi Station-1 was considered to have been drilled on a fault zone at the time, and no fluid pressure data are available from it.
The overpressure associated with mixed lithologies drilled in each of these wells is usually considered to be generated by fault shearing. However, as shown by its widespread occurrence in drilling across this and other basins, this is regarded here as regional characteristic. The sealed, ductile, smectitic lithologies that characterize the Eocene and Oligocene formations can produce the same overpressuring by supporting the overlying rock column22 and, given that overpressuring is regional, this is the model adopted here.
The basic opacity of the pre-Miocene seismic sections through and west of the Wharerata ranges, within the Mahia Peninsula and over the Muriwai shelf where only occasional bands of coherent energy are present, is routinely credited to "poor seismic." There are exceptions to this pattern such as the seismic sections shot west-northwest from Gisborne, where there is a coherent sequence to the Cretaceous at 3.5 sec.27 The deep section becomes opaque towards the edge of the city and the Pouawa Chaos.3
The adjacent northern inshore Muriwai shelf lines also include what is interpreted here as LC&P reflections to 3.5 sec where they are underlie the Miocene or are locally unconformable with it. This opacity contrasts with areas southeast of the shelf where a combined LC&P and Neogene sequence can be mapped. In Hawke Bay to the southwest, and in the west of the basin across the Rere-1 location, LC&P seismic structure and stratigraphy is routinely evident beneath the Miocene.
Structure
The opaque seismic sequence characterizing the shelf, outcrops in the seabed, or subcrops against Pliocene section, in a zone extending along the south-southeastern side of Mahia Peninsula and north-northeast from Table Cape (Figs. 1-3).
It has a near vertical contact with the in situ Late Cretaceous, Paleogene, and Neogene sequences in the outer shelf or continental slope essentially across the zone mapped as the Lachlan fault. Seismic definition on sections over the peninsula is generally poor, but given its occurrence north and southeast of the peninsula, the opaque zone would extend beneath it.
Based on that distribution, the opacity of LC&P section in seismic lines across the Muriwai shelf is due to scattering of seismic energy by regional structuring comprising a melange of randomly sized and oriented blocks of LC&P rocks as outcrop in the Taiporutu, Waiopine, and adjacent Opoutama "mud volcanoes." In this thesis the mud volcanoes are inliers exposed by erosion of the Neogene sequence.
There is little evidence that tilting of the type evident in the Tauwhareparae and Brunei Delta studies was part of the first episode of structuring. In the second episode the Pliocene sequence was deposited on an east-tilted base, though the refolding of the Maraetaha syncline is symmetrical (Figs. 3b, 4c, 4d) and closed about a north trending axis. This configuration indicates that this folding was the result of simple, vertical subsidence without influence from tilting.
The cross-section structure of the Muriwai shelf is generally similar to the Champion and Baram delta examples.9 10 The block faulting and possible intrusive melanges evident in Mangaone-1 and Opoutama-1, follow the Jerudong anticline model. However, as shown there, the Berakas syncline was generated by progressive isostatic subsidence generated by continuous sediment loading as illustrated by thinning of composite intervals from the synclinal axis to its margins.
In contrast, equivalent intervals in both the Miocene and Pliocene sequences in the Muriwai shelf are essentially parallel bedded across the shelf and basin in a sequence that was fully developed prior to being folded into successive elements of the Maraetaha syncline. As well, structuring in the Neogene sequence in the shelf is up to 30 km wide and 4.5 km thick and is much flatter than the Baram Delta example, which is 25 km wide and includes 10 km of Neogene sequence.
Structural development
The Muriwai shelf area was tectonically stable at the end of the Oligocene. The LC&P sequence had been eroded to a marine base level, similar to the present shelf-slope model, developed over Neogene rocks.
In the Early Miocene the basin area began to subside, generating a flat to gently east-dipping continental margin that provided a base for Miocene marine deposition. The area northwest of the axial fault noted above held up through the early part of the stage, but subsequently subsided with the rest of the basin (Figs. 2 and 4a).
In a mechanism set out below, in a short-term, latest Miocene/earliest Pliocene, tectonic episode, the Muriwai shelf's Miocene sequence was folded into the broad synclinal and faulted anticlinal format that generated the Maraetaha syncline. The eastern marginal anticline turns over into a second syncline developed where the shelf widens to the northeast (Figs. 1, 3b, and 4c).
Immediately subsequent to the placement of this structuring, 2 km scale subsidiary anticlines were generated within the Miocene interval by gravitational gliding down the northern and southern axes of the Maraetaha syncline (Fig. 2a). The southern structure includes south-dipping thrusts that sole out into bedding plains to the south and complementary antithetic faults. Its emplacement buckled the Early Miocene in front of it but does not affect the under- or overlying unconformities. A later tensional structure developed in Miocene and earliest Pliocene beds updip to the south (Fig. 2). No other tectonic activity occurred during this period.
The regional structuring left the axis of the shelf in place but lifted parts of both the Miocene and LC&P sequences above sea level to the east on the lineation of the Lachlan fault, generating the margin to the opaque zone as noted above. To the west, using the Baram Delta model, it raised at least the eastern part of the Wharerata ranges.
Subaerial and marine erosion was initiated, cutting across sequence and structure to generate a second, shelfwide base level (Figs. 3a, 3b, and 4b). This erosion surface immediately tilted to the east. Pliocene sedimentation started simultaneously towards the foot of this slope, generating a "giant foreset" type fan across central eastern shelf (Figs. 3b, 4c, and 4d).
The fan expanded, transgressing westward to dominate Pliocene shelf and slope deposition and creating a 25 km wide and 2,000 m thick eastern shelf margin sequence. Again, and as with the Miocene model, and as is evident on seismic sections, no other tectonic activity occurred during this depositional process (Figs. 2, 3a, 3b, and 4c).
Structuring of Pliocene sequence within the shelf developed in a second, single Early Pleistocene episode of radially directed diapirism, refolding the Maraetaha syncline on separate alignment (Figs. 2b and 4d). The northeastern Miocene marginal anticline was suppressed as part of this second syncline development phase, generating subsidiary folding in the Miocene/Pliocene boundary, reversing fault movement, and partially everting Miocene structure (Figs. 3b and 4c).
This Pleistocene structuring of the Neogene sequence generated a third landmass across the Muriwai shelf. In response, a third period of subaerial and coastal erosion was initiated. This generated, over 2 million years, the present erosion-based continental shelf system (Figs. 3a, 3b, and 4d).
The initial phase of overpressuring was generated as interstitial and entrained water in the LC&P sequence progressively assumed the increasing weight of the developing Miocene overburden. This resulted in continuing undercompaction of the sequence, and retention of its initial low density and limited strength.
There is no density data available from the Muriwai shelf, but Rere-122 shows the style of imbalance developed. With that model, at end Miocene a 2,000-m shelf sequence with an average density of 1.85 gm/cc would exert a pressure of 35.8 MPa, versus 19.3 MPa for a water gradient, on 1.65 gm/cc average strata beneath it.
At this time the weight of Miocene overburden exceeded a component the LC&P rocks vertical shear strength, and they disintegrated in a short-term period of intense internal low angle shearing and folding.
The Miocene sequence remained laterally coherent in this process, causing expulsion of the resulting water and rock mixture away from the stable axis of the developing syncline. In the shelf, it generated the regional melange that outcrops in the Taiporutu and Waiopine inliers and Aerial Bank. At the western margin, structuring evident in the Opoutama-1 and Mangaone-1 wells are part of this migration process and are associated with faulting of the type evident in Brunei's Jerudong anticline.
This first movement stabilized at the beginning of the Pliocene when uplift of the western Miocene sequence had generated at least part of the anticline that cores the Wharerata ranges, and raised the south-southeast margin of the shelf to an equivalent level (Fig. 4b). The cohesion of the Miocene sequence relative to the underlying interval ensured that it generated and then retained the newly established open syncline/faulted anticline structuring and a new and stable intergranular pressure, depth, and rock strength equilibrium was simultaneously established in the characteristic format.
At the end of the Pliocene, the Neogene sequence was 4,500 m thick and probably denser than the Miocene on its own, and the underlying sequence was again overpressured (Figs. 4c and 4d). As well, in the burial process the established latest Cretaceous and Paleocene source rock systems in the late Cretaceous and Paleocene traversed the 3,500-5,000 m oil and natural gas generation window.
The resulting addition of oil, gas and water to the fluid system independently generated inflation pressure and reduced density in the LC&P sequence including the existing melange.
The second, Pleistocene, reactivation of the unstable rock generated radial diapiric flow and a second independent and closed element of the Maraetaha syncline, modifying Miocene structure in the process (Figs. 3a, 3b, and 4d).
Mechanism and timing
In the 2 million years since the second episode of deformation was triggered, the Neogene sequence was both folded and eroded to its present position, generating and eliminating an eastern ridge that was potentially the size of the western Whakarara ranges. In geological terms this very short reaction time covered both activities.
Well established stratigraphic models from western wells and outcrop27 show that Neogene deposition along the south-southeastern side of the basin was essentially continuous. This further limits the time involved in the tectonic processes and requires it to proceed to stabilize in its earliest Pliocene structural form in a 10 000-year scale time frame.
The comparison with the Baram Delta model indicates that isostatic loading was involved in development of Muriwai shelf structuring. However, even though the crustal loading was considerable, there was no immediate isostatic reaction to the successive deposition of the Miocene then Pliocene sequences as in the delta system.
Instead there were successive catastrophic reactions to this loading that was confined to the LC&P sequence and was generated by shelf-wide uplift of that interval independently of the Neogene. It resulted in successive and immediate generation of the synclines by progressive uplift of the eastern and western margins of the coherent Miocene and Pliocene shelf sequences.
This uplift generated new faults in the developing marginal anticlines on a spacing determined by internal equilibrium factors. The weak, overpressured LC&P sequence facilitated the process by acting as a lubricant to radial expulsion of rock and fluids away from the area of the developing synclinal axis, provided the volume of material required to successively displace the two Neogene sequences upwards to form a short-lived eastern range and at least part of the Whareratas (Figs. 4b and 4d).
The 10,000-year time scale of this activity is comparable to glacial isostatic adjustment on the North American Continent. It is proposed here that there was isostatic reaction to the separate Miocene and Pliocene loadings and they paralleled the form of the glacial isostatic system.
As noted above, the Miocene beds folded when their loading exceeded the reduced strength of the deeper and overpressured Late Cretaceous and Paleogene sequence. The active continental margin system reacted by rebounding upwards against the coherent Miocene rocks, generating melange in the overpressured sequence, diapiric migration of melange away from the shelf axis, and generation a regional syncline. The uplift stabilized and was immediately subject to shelf-wide submarine erosion.
The Pliocene sequence was laid down on this surface, and the loading, rebounding and folding cycle repeated in the Latest Pliocene/Earliest Pleistocene. Erosion of this syncline has generated the present Muriwai shelf and is ongoing.
In the latest Miocene-earliest Pliocene cycle, this timeframe also includes the development and partial erosion of the subsidiary gravity-gliding folds generated in the Miocene sequence after tilting but before deposition of the Pliocene sequence.
The Brunei example is developed in the direction of least horizontal stress at the time of deposition. This parallels Mazengarb's8 finding that the gravitationally induced tectonics are at right angles to the Miocene stress direction. Mazengarb considers that the gravitational sliding is not related to the margin tectonics, but from these observations it represents a process that is common to unstressed elements of convergent margins.
Application
The episodic tectonic thesis developed here provides an example of gravity-driven tectonics.
This format, along with the traditional downdip gliding format that Mazengarb shows to be the dominant factor in structuring to the northwest of the shelf area and isostatic loading deformation characterizing Brunei's Baram Delta Berakas syncline and associated Belait and Jerudong anticlines, should also be considered in exploration work on the syncline/anticline structuring characterizing the central and southern parts of the East Coast basin.
The recognition of this format has implications for seismic acquisition programs and hazard recognition in relation to earthquake and submarine and coastal erosion.
Acknowledgments
I thank Dato Ahmad Azizuddin and Dato Yap Lim Sen, principals of Asia Pacific Oil Sdn. Bhd., for their enthusiastic support of the exploration program on which this study was based; Ian Speden, Harry McQuillan, Kerry Doble, and the late Ed Durkee for their technical reviews; James Kennett for formatting considerations; and Bridget Carthew for preparation of the document. I appreciated access to NIWA's seismic work and to New Zealand Crown Minerals petroleum reports on www.crownminerals.govt.nz.
References
1. Stoneley, R., "Marl diapirism near Gisborne, New Zealand lower Tertiary decollement on the East Coast, North Island, New Zealand," New Zealand Journal of Geology and Geophysics, Vol. 5, 1962, pp. 630-41.
2. Ridd, M.F., "Gravity gliding on the Raukumara Peninsula," New Zealand Journal of Geology and Geophysics, Vol. 11, No. 2, 1968, pp. 547-48.
3. Haskell, T.R., "The seismostratigraphy and structure of the Cretaceous to Recent Poverty Bay Flats sequence, East Coast Basin, New Zealand," Petroleum Exploration in New Zealand News, Ministry of Commerce, Vol. 39, 1994, pp. 12-21.
4. Neef, G., and Bottrill, R.S., "The Cenozoic geology of the Gisborne area (1:50 000 metric sheet Y18AB), North Island, New Zealand," New Zealand Journal of Geology and Geophysics, Vol. 35, 1992, pp. 515-31.
5. Strong, S.W.S., "The Sponge Bay uplift, Gisborne, and the Hangaroa mud blowout," New Zealand Journal of Science & Technology, Vol. 15, 1933, pp. 76-78.
6. Eiby, G.A., "Two New Zealand tsunamis," Journal Royal Society of New Zealand, Vol. 12, 1982, pp. 337-51.
7. Katz, H.R., "Aerial Bank off Gisborne—an offshore late Cenozoic structure, and the problem of acoustic basement on the East Coast, North Island, New Zealand," New Zealand Journal of Geology and Geophysics, Vol. 18, 1974, pp. 93-108.
8. Mazengarb, C., "Late Neogene structural development of eastern Raukumara Peninsula: implications for oil exploration," New Zealand Petroleum Conference Proceedings, 1998, pp. 201-05.
9. Morley, C.K., "Mobile shale related deformation in large deltas developed on passive and active margins," in van Rensbergen, P., Hillis, R.R., Maltman, A.J., and Morley, C.K., eds., "Subsurface Sediment Mobilization," Geological Society, London, Special Publication, Vol. 216, 2003, pp. 335-57.
10. Morley, C.K., Back, S., Van Rensbergen, P., Crevello, P., and Lambiase, J.J., "Characteristics of repeated, detached, Miocene-Pliocene tectonic inversion events, in a large delta province on an active margin, Brunei Darussalam, Borneo," Journal of Structural Geology, Vol. 25, 2003, pp.1,147-69.
11. Berryman, K., "Age, height and deformation of Holocene marine terraces at Mahia Peninsula, Hikurangi subduction margin, New Zealand," Tectonics, Vol. 12, 1993, pp. 1,347-64.
12. Barnes, P.M., Nicol, A., and Harrison, A., "Late Cenozoic evolution and earthquake potential of an active listric thrust complex, Hikurangi subduction margin, New Zealand," GSA Bull. 114, 2002, pp. 1,379-1,405.
13. Field, B.D., Uruski, C.I., et al., "Cretaceous-Cenozoic Geology and Petroleum Systems of the East Coast region," New Zealand Institute of Geological and Nuclear Sciences, Monograph 19, 1997.
14. Cole, J.W., and Lewis, K.B., "Evolution of the Taupo-Hikurangi Subduction System," Tectonophysics, Vol. 72, 1981, pp. 1-2.
15. Northwood, D., "Marine Seismic Reconnaissance Survey Interpretation Report , Offshore East Coast North Island NZ," New Zealand open file petroleum report PR 285, 1966.
16. Davies, T.W., "New Zealand East Coast Marine Seismic Survey, Hawkes Bay, North Island, 1968 Interpretation Report, New Zealand open file petroleum report PR 291, 1968.
17. Australian Gulf Oil Co., "Basic Geophysical Data from MV Gulfrex Cruises 94-98, October 1972-January 1973," New Zealand open file petroleum report PR 614, 1973.
18. Grearson, L.S., "Geological and geophysical report PPL 38315 offshore," New Zealand open file petroleum report PR 1530, 1989.
19. Webb, C., "The Geology of the eastern Mahia Peninsula, Hawkes Bay," unpub. MSc thesis, University of Auckland, 1979.
20. Francis, D.A., "Report on the geology of the Mahia area, northern Hawkes Bay, adjacent to offshore PPL 38321," New Zealand open file petroleum repport PR 1928, 1993.
21. Brown, B.R., "Geological completion report for Mangaone-1," New Zealand open file petroleum report PR 320, 1961.
22. Darby, D., Funnell, R., Uruski, C.I., and Field, B.D., "Patterns of fluid flow in the East Coast Basin, New Zealand," New Zealand Petroleum Conference Proceedings, 2000, pp. 355-64.
23. Strong, S.W.S., "Gisborne-1 and 2 well reports," New Zealand open file petroleum report PR 111, 1930.
24. New Zealand Aquitaine Petroleum Ltd., "Opoutama-1 well report," New Zealand open file petroleum report PR 504, 1967.
25. De Bock, J.F., Kelly, C., Lock, R., and Butt, C., "Well completion report, Rere-1, PPL 38082," New Zealand open file petroleum report PR 1231, 1988.
26. Newkermet, P.J., and Hornibrook, N. de B., "Waitangi Station-1," New Zealand open file petroleum report PR 81, 1977.
27. Haskell, T.R., "Recognition of the inner accretionary prism of the Miocene ECB and its effect on the understanding of tectonic and sedimentary systems," New Zealand Petroleum Conference Proceedings, 1996, pp. 53-62.
28. Francis, D., Bennett, D., and Courteney, S., "Advances in understanding of onshore East Coast Basin structure, stratigraphic thickness and hydrocarbon generation," New Zealand Petroleum Conference Proceedings, 2004, pp. 1-20.
The author
More Oil & Gas Journal Current Issue Articles
More Oil & Gas Journal Archives Issue Articles
View Oil and Gas Articles on PennEnergy.com
