BIBLIOGRAPHIC REFERENCE

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2 BIBLIOAPHIC REFERENCE Roncaglia, L., Fohrmann, M., Milner, M., Morgans, H.E.G., Crundwell, M.P., 213. Well log stratigraphy in the central and southern offshore area of the Taranaki Basin, New Zealand. GNS ience Report, 213/27, 26p + enclosures. L. Roncaglia, GNS ience, P O Box 3 368, Lower Hutt 5, New Zealand M. Fohrmann, OMV New Zealand Ltd, 1 Brandon Street, Wellington 611, New Zealand M. Milner, OMV New Zealand Ltd, 1 Brandon Street, Wellington 611, New Zealand H.E.G. Morgans, GNS ience, P O Box 3 368, Lower Hutt 5, New Zealand M.P. Crundwell GNS ience, P O Box 3 368, Lower Hutt 5, New Zealand Institute of Geological and Nuclear iences Limited, 213 ISSN ISBN

3 CONTENTS ABSTRACT... III KEYWORDS... III 1. INTRODUCTION AND SCOPE THIS REPORT AND RELATED PRODUCTS PREVIOUS WORK MATERIAL AND DATA NEW ZEALAND GEOLOGICAL TIMESCALE CALIBRATION ADOPTED BIOSTRATIAPHIC SUBDIVISION LITHOSTRATIAPHY Pakawau Group (Suggate, 156) Rakopi (Thrasher, 12) North Cape (Suggate, 156) Kapuni Group (Palmer, 185) (Suggate, 156) Kaimiro (Palmer, 185) (Palmer, 185) Moa Group (King and Thrasher, 16) Turi (Palmer, 185) Ngatoro Group (King, 188a, b) (Palmer, 185) Tikorangi (Palmer, 185) (King 188a, b) Wai-iti Group (King 188a, b) Manganui (King 188a, b) Moki (Lock 185) M2A unit (informal) Sw s, Waiauan interbedded stone unit (this study, informal) Tt 1 and 2, Tongaporutuan interbedded stone unit 1 and 2 (this study, informal) Rotokare Group (Robinson and King, 188) Giant Foresets (Pilaar and Wakefield, 178) ACKNOWLEDGMENTS REFERENCES GNS ience Report 213/27 i

4 FIGURES Figure 1 Location map with location of the study wells.... Figure 2 The figure illustrates the age relationship of laterally correlative lithofacies belts distributed along a southeast to central west transect across of the Taranaki Basin... 7 ENCLOSURES Enclosure 1 Enclosure 2 Enclosure 3 Enclosure Enclosure 5 Well correlation panel: Cook-1, Cape -1, Fresne-1, North Tasman-1 Well correlation panel: Takapou-1, Pateke-2, Kiwi-1, Amokura-1, Tui-1, Maui-3 Well correlation panel: Kea-1, Maui-1, MB-P8, Maui-7, Maui-2, Maui-3 Well correlation panel: Kea-1, Moki-1, Maari-1, Maari-2, Moki-2A, Maui-, North Tasman-1 Well correlation panel: Pukeko-1, Te Whatu-2, North Tasman-1, Tasman-1, Motueka-1, Surville-1 ii GNS ience Report 213/27

5 ABSTRACT As a result of a lithological, sedimentological and biostratigraphic study of well sections from the central-southern area of the Taranaki Basin (including the Maari, Maui and Tui Fields), the lithostratigraphic framework for the siliciclastic Late Cretaceous to Recent sediments of the area is revisited and interpreted in terms of wireline log signature and associated regional seismic reflectors. The Pakawau, Kapuni, Moa, Ngatoro, Waiti and Rotokare Groups of previously published lithostratigraphic schemes are adequate for a subdivision of the central area at formation level. The Manganui is subdivided into three mudstonedominated units: lower, mid and upper. Four new, stratigraphically independent, informal, stone units the M2A, a Waiauan interbedded stone unit ( Sw s ) and two Tongaporututuan interbedded stone units ( Tt 1 and 2 ) are identified and represent extentions of Moki type facies and represent potential stratigraphic members of the Manganui. Reference intervals are established in wells for all units and the description of their lithology, log characteristics, depositional environment, age and associated seismic reflectors are updated with details on well to well correlation. KEYWORDS Taranaki, stratigraphy, log, correlation, well, seismic, reservoir, petroleum. GNS ience Report 213/27 iii

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7 1. INTRODUCTION AND SCOPE The mapping of seismic horizons and faults within the supra-basement Late Cretaceous to Recent sedimentary succession across the entire Taranaki Basin represents a main objective of the D-Taranaki () project currently being undertaken by GNS ience (Roncaglia et al., 21; Fohrmann et al., 212). As part of the project, a regional grid of seismic lines, calibrated to well stratigraphy, is being interpreted to establish the regional seismic stratigraphic framework, to provide a basis for detailed mapping in local areas. The central (CEN) and south inversion (SIV) areas are two offshore areas within the basin currently being mapped. In open-file petroleum reports from the study areas, the stratigraphic menclature used for the Cretaceous to Recent sediments is often inconsistent. On a regional-scale evaluation, including different hydrocarbon-producing fields, the inconsistency leads to ambiguity. In order to improve consistency within the well and correlate them with the seismic stratigraphy, the ages of the sediments and formation boundaries in selected wells have been revised and in some cases changed from those in the well completion report and occasionally also from those in the literature. This report is the result of a reassessment of the regional litho- and biostratigraphy for the Late Cretaceous to Recent sediments in 25 exploration and appraisal wells (Fig. 1) from the CEN and SIV areas of the basin, following on from the framework outlined by Roncaglia et al. (28), Bland et al., (2) and Fohrmann et al. (212) in Kupe area (KUP). The aims are to: 1. Revise the chrostratigraphic (age to well depth) base with respect to the New Zealand and international timescales, and directly apply this to the seismic interpretation, based on existing and new biostratigraphic (foraminiferal and palylogic) from the study wells; 2. Establish log-based lithostratigraphic well correlations supported by the revised biostratigraphy and sedimentology, also in the form of a base directly applicable to the seismic interpretation. 2. THIS REPORT AND RELATED PRODUCTS Key results are presented in the form of five correlation panels (Enclosures 1 5) which display a selection of the original wireline log with the revised lithological and stratigraphic interpretation. The correlation is between reassessed boundaries of formal and informal lithostratigraphic units in each well, based on the wire-line log, but it is guided by biostratigraphy and aided by seismic interpretation. Preliminary versions of the stratigraphic interpretation presented in this report are available in digital form as well summary sheets in either ascii or WellCad format through the Petroleum Basin Explorer portal (Roncaglia, 21; Roncaglia et al., 212; and Griffin and Roncaglia, 213). The depth of biostratigraphic samples, upper and lower stratigraphic boundaries presented herein (top and base of group/formation/member, New Zealand stage and international epoch) and paleobathymetric range from the 25 wells are available for purchase as a base in ascii format from GNS ience (Roncaglia et al., 213). GNS ience Report 213/27 1

8 3. PREVIOUS WORK There is a rich literature on Taranaki surface and subsurface geology, with pioneering studies connected with regional mapping and petroleum exploration since the 1 th century The Late Cretaceous and Cezoic lithostratigraphy of the Taranaki Basin has been described in two major stratigraphic works. Palmer (185) provided an overview of the structural elements of the basin and gave a description of pre-miocene strata which, with some revision, is still used. King and Thrasher (16) compiled a detailed lithostratigraphic subdivision and lithological description for the entire basin. They subdivided the siliciclastic Late Cretaceous, Paleogene and Neogene sediments into six major groups: the Pakawau, Kapuni, Moa, Ngatoro, Wai-iti and Rotokare Groups. The succession of major formations contained within these groups has formed the backbone of all subsequent lithostratigraphic schemes for the central and southern part of Taranaki and it is used in this report. King et al. (1) synthesised the kwledge of New Zealand s sedimentary basin evolution (including Taranaki) within a highly-resolved chrostratigraphic framework to compare depositional successions between regions or basins and to document any widely-occurring patterns and events within the Cretaceous to Recent of the New Zealand subcontinent. Kamp et al. (22, 2) and Vonk and Kamp (2) presented a revised Neogene and Quaternary stratigraphy for the Wanganui, King Country and the eastern Taranaki basins. In these papers, they established the Whangamomona and Taihape Groups, abandoned the Rotokare Group and described two new Middle to Late Miocene formations (Otunui and Kiore). Their lithostratigraphic scheme also includes several new Late Miocene to Early iocene stone beds within the Matemateaonga, promoted to the rank of members. Anthony et al., (26) summarised the lithostratigraphy of the Cretaceous to Recent sediments in the southern and central area of the basin based on observations by McBeath (177) and King and Thrasher (16). This 26 scheme provides an overview of the formal and informal lithostratigraphic termilogy which has been used by the industry for many years. Following detailed analysis of seismic surveys, sedimentologic, faunal, geochemical, electrical logs and petrographic covering the succession in southern, central and rthern Taranaki, efforts were focused in establishing high-resolution sequence stratigraphic subdivisions in selected stratigraphic units within the Cretaceous to Neogene sediment package. The are discussed in a series of publications from working groups at the University of Waikato and GNS ience (e.g. Hood et al., 23; Hansen and Kamp, 22, 2, 26; Naish et al., 25; Proust et al., 25; Higgs et al., 21 a,b, 212a). Bland et al. (2) and Fohrmann et al. (212) provide an overview of the lithostratigraphic framework and menclature used in the Kupe area, which is the first area where detailed seismic mapping has been completed as part of the project. The authors provide a reevaluation of the existing stratigraphic menclature in the Taranaki Basin in relation to the surrounding basins to the east (Wanganui) and rth-east (King Country). In particular, they highlight problems encountered with the regional Neogene lithostratigraphy and introduce three new units in the Waiauan (late-middle Miocene) to Tongaporutuan (early-late Miocene) interval. 2 GNS ience Report 213/27

9 . MATERIAL AND DATA A total of 25 open-file offshore wells were selected in the study areas and are dealt with in this report (Fig.1). Nineteen key wells in the CEN area are selected to represent this area and the three hydrocarbon fields (Maari, Maui and Tui) located within it. Six wells in the SIV area are included as they have wireline log patterns and lithostratigraphic affinity with those from the CEN area in the stratigraphic interval studied. Other criteria for the selection of the wells were continuous stratigraphic succession, strategic location within the seismic mapping area, good core coverage and good quality biostratigraphic and sedimentologic. The well names are listed here alphabetically by area: CEN area SIV area Amokura-1; Kea-1; Kiwi-1; Maari-1, -2; Maui-1, -2, -3, -, -7; MB-P(8); Moki-1, -2A; North Tasman-1; Pateke-2; Pukeko-1; Te Whatu-2; Takapou-1; Tui-1. Cape -1; Cook-1; Fresne-1; Motueka-1; Surville-1; Tasman-1. The stratigraphic subdivision and the regional correlations herein represent the result of a reevaluation of geophysical well logs and biostratigraphy integrated with sedimentological from cores, sidewall cores (SWC) and cuttings and seismic (2D and 3D). In addition to the information available in the published literature, several n-proprietary sets were sourced from the New Zealand Ministry of Business, Invation and Employment (New Zealand Petroleum and Minerals, Wellington) corporate bases (e.g., Petroleum Reports; Petroleum Wells) and GNS ience bases (e.g., Fossil Record Electronic Database FRED; GNS Petroleum Wells Paleontology Files; Core base of Higgs et al. 212a; Offshore Taranaki seismic base of Milner et al., 21). The used in this study from the wells listed above include: Header information (ID, location, reference depths etc) Deviation and checkshot surveys Time to depth curves from Zhu et al. (212) Wireline logs (primarily gamma ray, caliper, spontaneous potential, sonic, resistivity, neutron and density logs) SWC and cuttings samples Mudlog, cuttings descriptions and final lithologic interpretation from wellsite Existing biostratigraphic and paleobathymetric, typically from benthic and planktic foraminifera, diflagellates, and spores and pollen A selection of 2D and arbitrary lines from 3D surveys from the offshore Taranaki seismic base of Milner et al. (21). The biostratigraphic dating in the study is compared with the results of quantitative stratigraphy constrained optimisation (CONOP) in 7 of the wells (Cook-1; Fresne-1; Maui-3, - ; North Tasman-1; Takapou-1; and Tui-1) (Crampton et al., 212). Also a revision of the biostratigraphy in Maui- published by Raine and hioler (212) provided helpful results for correlation of Cretaceous to Paleogene sediments in the basin. The revised well-log correlation resulted in an improved architecture and distribution of the lithostratigraphic units in the basin. GNS ience Report 213/27 3

10 All depths mentioned in this report refer to measured depth (MD) in meters below rotary table or kelly bushing if t otherwise stated. When it is unclear from the well completion report which reference level is used for well depths, rotary table is assumed and depths given as MD in meters. Figure 1 Location map with location of the study wells. GNS ience Report 213/27

11 5. NEW ZEALAND GEOLOGICAL TIMESCALE CALIBRATION The primary objective for the biostratigraphic review of the study wells was to generate a chrostratigraphic framework in order to aid log-based well correlation and thus the development of a regional correlation applicable to the seismic. New Zealand series and stages for the Cretaceous and Cezoic are based on the ranges of selected mollusca, foraminifera, palymorphs and environmental stable isotope events, in reference sections (Cooper 2). For the Cezoic, correlation of the New Zealand scheme with the Global Geochrological ale (GGS), and calibration of boundaries in terms of millions of years, was presented in Cooper (2) based on age calibration of the Geomagnetic Polarity Timescale and global stages and bioevents by Cande and Kent (15) and Berggren et al. (15). For the Cretaceous, correlation and calibration was based on Ogg et al. (2). Calibration of global stages in the GGS is a continuing process, and two improved calibrations have been published by Gradstein et al. (2, 212). Calibration of the New Zealand stages was therefore revised by Hollis et al. (21) and Raine et al. (212) to bring them into agreement with the Gradstein et al. (212) international timescale as well as with New Zealand work subsequent to 2. The latter calibration is shown in Fig. 2 which shows the chrostratigraphic section through the southeast to central part of the Taranaki Basin. New Zealand stages have standard two or three-letter codes, which are used in the text and enclosures (e.g. Ar = Runangan Stage of the Arld Series) (Fig. 2). All substages (early, mid, late) mentioned herein are given with lower case unless formally defined according to Cooper (2). 6. ADOPTED BIOSTRATIAPHIC SUBDIVISION Miospores (pollen and spores) are the principal means of correlation of New Zealand Cretaceous Cezoic terrestrial and paralic strata in subsurface deposits. In the same stratigraphic interval, diflagellate cysts are powerful tools for subdivision in shallow marine to offshore depositional settings. Benthic foraminifera have historically been the most important fossil group for inter-basinal correlation of New Zealand marine sediments. Cezoic marine strata and many of the Cezoic stages were based primarily upon them. Ranges of Paleogene foraminifera are also documented in Cooper (2). anktic foraminifera are less abundant in the geological record in New Zealand, but important for local, high-resolution and global correlations (Crundwell 2, Crundwell and Nelson 27). New Zealand stage and international epoch boundaries always mark the top or base of a zonal interval. In this report, the upper boundary of a New Zealand stage in a well section is marked by the highest stratigraphic record of the requisite key event in the well samples. However, as the key events most likely occur in the unsampled interval between the samples of a well section, the positions of stage boundaries have an uncertainty corresponding to the sampling resolution in the borehole. Also, for cuttings samples, the depth given herein is that of the base of the cuttings sample interval. This means that an additional error interval for any event identified on the basis of cutting samples equals the thickness of the cuttings sample interval (typically 5 15 m) above the biostratigraphic event in question. GNS ience Report 213/27 5

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13 Figure 2 The figure (modified from Anthony et al., 26) illustrates the age relationship of laterally correlative lithofacies belts (lithostratigraphic units) distributed along a southeast to central west transect across of the Taranaki Basin. The study area is highlighted in the red frame. Twenty-six third order allostratigraphic sequence-bounding horizons mapped as part of the project in this area are labelled K-8 for Cretaceous, P6-1 for Paleogene and N8-1 for the Neogene and eistocene. This chrostratigraphy is correlated to the NZ Geological Timescale according to the calibration of Raine et al. (212). For comparison, the sequence bounding horizons used by Todd Energy and STOS are illustrated in the figure. GNS ience Report 213/27 7

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15 7. LITHOSTRATIAPHY This section describes the lithology, wireline log characteristics, depositional environment, age and associated seismic reflectors of the sediment bodies encountered in the study wells. The lithostratigraphic subdivision and menclature used herein follows that of King and Thrasher (16), with modifications after King et al. (1), Kamp et al. (2), Vonk and Kamp (28) and Fohrmann et al. (212) (Fig. 2). Further information on authorship, description and history of most of the lithostratigraphic units mentioned may be found in the New Zealand Stratigraphic Lexicon base available through the website of GNS ience. A few of the lithostratigraphic units used in this report have t previously been used in well completion reports and in the literature; these units are outlined below and remain informal. 7.1 PAKAWAU OUP (SUGGATE, 156) The Pakawau Group is a Late Cretaceous coal-bearing succession of n- to shallow-marine origin that is mapped across the southern and central areas in Taranaki (King and Thrasher, 16). It unconformably overlies Paleozoic metasedimentary and Cretaceous plutonic basement rocks (Bishop, 171) in 8 of the study wells (Amokura-1; Cape -1; Kiwi-1; Maui-2, -; North Tasman-1; Pukeko-1; Takapou-1). In most of the remaining wells, basal sediments belong to the overlying Kapuni Group. It is overlain by Cezoic marine and nmarine sediments of the Moa and Kapuni Groups respectively. The Late Cretaceous group is subdivided into the Rakopi and North Cape s defined from seismic reflection mapping offshore and from lithofacies character in wells and outcrops (rthern South Island) (Thrasher, 12). A detailed description of the sedimentology and potential reservoir attributes of the formations is given by Higgs et al. (21a) Rakopi (Thrasher, 12) Reference well in study area: Cape -1, m MD (Enclosure 1). Lithology: The Rakopi consists of n-marine coal measures whereas the North Cape is dominated by shallow-marine lithofacies (King and Thrasher 16) although the latter also contains some marine-influenced coal measures. The Otimataura Conglomerate Member (Bishop, 171, sensu King and Thrasher, 16; Cape -1) represents the basal part of the Rakopi in the SIV area, which includes the Pakawau Sub-basin. In the reference well, this member consists of schist breccia with quartzose grains in a stone matrix with mir laminations of coal and mudstone (Carter and Kintanar, 187). It is exposed locally onshore and was penetrated in the Cape - 1 well at m. Log characteristics: On the petrophysical well logs, the unit is characterised by a succession of high-amplitude gamma ray oscillations, which become increasingly closely-spaced upwards. In the lower part of the formation (Cape -1, m), the stones are best identified on the density log where they produce a blocky pattern with density values significantly lower than those of the siltstones beneath and above. The stone can also be identified from a combination of the density and neutron logs, as the presence of pure stone results in a cross-over of the two curves. The part of the Rakopi richest in coal (Cape -1, m) is characterised by highly serrate signatures which reflect the heterolithic nature of the interbedded stone, siltstone, coal and conglomerate lithofacies. Thrasher (12) defined the type section of the formation in Cape GNS ience Report 213/27

16 -1, with upper boundary at 116 m based on seismic interpretation. In this study, the upper boundary of the unit is tentatively placed at m based on wireline log (gamma ray, self-potential and acoustic) pattern and correlation to Cook-1 (Enclosure 1). Depositional environment: Based on Browne et al. (28), the formation was deposited in fluvial floodplains periodically transgressed by marine incursions. Age: Haumurian (Mh), Campanian Maastrichtian, Late Cretaceous. Associated seismic reflectors: K78 or top basement form lower boundary; K8, upper boundary. Correlation: Stratigraphic correlation of the Rakopi across the study areas is difficult due to a large thickness variation, large (>1 km) distances between the study wells and the presence in the study area of Taranaki Basin of a number of major rmal faults. The latter are the result active Late Cretaceous rifting t (King et al., 1). In the SIV and CEN areas, the Rakopi correlates with the PM2 miospore zone as in the NW Nelson onshore sections (Browne et al., 28; Higgs et al., 21a); however, a study by Raine and hiøler (212) in the coal-bearing sediments of the Rakopi in the North West atform area of the basin shows correlation of the lower part of the unit there with the PM1b miospore zone of Early Haumurian (Campanian) age, which is also the age of the formation in the Rimu and Kauri southern Taranaki onshore wells North Cape (Suggate, 156) Reference well in study area: Cook-1, m MD (Enclosure 1). Lithology: The formation is characterised in both outcrop and wells by light grey to brownish carbonaceous y silt and silty s occasionally micaceous, pyritic and feldspathic, although conglomerates and coals occur locally. Higgs et al. (21a) identified that coaly sediments commonly occur throughout the formation, and therefore that recognition of lower and upper coaly members, the Wainui Member (e.g. in Maui-) and the Puponga Member (e.g. in Fresne-1) has stratigraphic significance within the Late Cretaceous interval. Log characteristics: By comparison with the underlying unit, the marine parts of the North Cape are characterised by steady log profile with an abrupt transition from the coal-bearing Rakopi. In wells where silty facies dominate the North Cape, the sonic log pattern is overall stable with slightly decreasing readings upwards from the base to the top of the formation. Depositional environment: Shallow marine, paralic and terrestrial environment in the study area of the basin. Age: Late Haumurian (Mh), Late Maastrichtian, Late Cretaceous. Associated seismic reflectors: K, lower boundary; P1, upper boundary. Correlation: In the CEN area, the North Cape correlates with the Late Maastrichtian Alterbidinium acutulum and Manumiella druggii diflagellate zones as in the NW Nelson onshore sections (Raine and hiøler, 212). 1 GNS ience Report 213/27

17 7.2 KAPUNI OUP (PALMER, 185) (Suggate, 156) Reference well in study area: Tui-1, m MD (Enclosure 2). Lithology: Interbedded fine to coarse-grained stones and siltstone. Three informal stratigraphic units (originally from Maui Field informal menclature) have been used in this study: the stratigraphically lower F and E s (Tui-1, m) which consist predominantly of grey, fine to coarse grained, loose stones interbedded with brown grey siltstones; and the E (Tui-1, m) dominated by brownish grey to light greenish siltstones with occasional very fine to fine, quartz-rich, interbedded stones. The E s coincides with the interval identified by Pollock and Crouch (25) as Tane Member in the Maui and Tui fields area. It is an heterolithic interbedded unit which includes interbedded stones, siltstone and musdstones with variable coal. Log characteristics: The lower part of the ( F and E s ) is characterised by on overall unstable gamma-ray log signature whereas the upper part (E ) has a more stable signature and higher average readings. This change in gamma-ray log signature coincides approximately with the change in lithologies between the two units in the study wells. In most wells from the Tui and Maui field areas, a prounced gamma ray peak occurs within the upper part of the formation (E ). In Tui-1, this peak (at m) marks a change from Teurian (Late Paleocene) light grey, soft, n-calcareous siltstones with glauconitic stones, to Waipawan (Early Eocene) lithologies dominated by brownish grey siltstones. It is inferred that this peak marks an unconformity at the Paleocene Eocene boundary in this part of the basin. It is interpreted to represent a maximum flooding surface (MFS) within the E unit and it occurs in all study wells in the central part of the basin (Enclosure 2). The sonic readings are overall stable from the base to the top of the formation with the exception of numerous high-velocity peaks that suggest the presence of cemented layers. The F and E s interval can also be recognised from a combination of the bulk density and neutron logs as the presence of pure stones results in a cross-over of the two log curves. Depositional environment: In the study area the stones are deposited by rth to rthwest draining fluvial system developed in a valley controlled by the Manaia and Cape Egmont faults and by the Wakamarama and Kahurangi faults in the Pakawau sub-basin (SIV). Palylogical analysis indicate that the Paleocene part of the unit was deposited in very proximal, heterolithic shelf with bottom conditions spanning fully oxic to axic (Strogen et al., 21). Age: Teurian Waipawan (Dt Dw), Paleocene Early Eocene. Associated seismic reflectors: P1, lower boundary; P2, upper boundary. Correlation: This is the lowermost unit of the Kapuni Group; in the CEN and SIV areas it unconformably overlies the marginal marine strata of the North Cape. In the CEN area, the F and E s and the lower part of the E interval correlate with seven diflagellate interval zones (NZDP2 to NZDP8 of Crouch, 21) spanning the Early to Late Teurian (Strogen et al., 21). In the Tui Field area, the occurrence of planktonic foraminifera Bigenerina burri and Globamalina wilcoxensis in the upper part of the E interval indicates a Waipawan age (Morgans, pers. comm. 212). GNS ience Report 213/27 11

18 In the SIV and CEN areas, the correlates with the PM3 miospore zone (Pollock and Crouch, 25) Kaimiro (Palmer, 185) Reference well in study area: MB-P8, m MD (Enclosure 3). Lithology: The Kaimiro (informally D s ) is dominated by stones of two types: (1) medium to coarse grained, moderately to well sorted, quartz-dominated stones; (2) dark yellow brown to brownish grey, fine to medium grained, variably argillaceous stones. Other lithologies include dark, brownish grey, n-calcareous siltstones, carbonaceous claystones and coal. Log characteristics: The Kaimiro has an overall blocky gamma-ray log signature and it is present in the rthern part of the study area. In the reference well, its lowermost part ( m) can be split into a number of smaller units with blocky or increasingupwards gamma-ray log signatures separated by gamma-ray peaks. In comparison, the overlying stones ( m) display a more stable, low gamma-ray log pattern with few spikes, and they are overlain by a siltstone-dominated interval ( m), characterised by higher gamma-ray readings. The uppermost part of the formation ( m) is characterised by 15 2 m thick units showing a blocky, increasing-upwards gamma-ray signature, suggesting fining upwards bodies. Depositional environment: Based on Higgs et al. (212a) the formation deposited across a broadly defined shoreline and coastal plain and represents marginal marine to lagoonal, low energy depositional environment. Age: Waipawan Heretaungan (Dw Dh), Early Mid Eocene. Associated seismic reflectors: P2, lower boundary; P3, upper boundary. Correlation: Precise dating and correlation of laterally equivalent strata within the Eocene reservoir fairway in the Taranaki Basin is mainly based on local miospore zonations (Raine 18, 2). This is due to the dominance of coastal plain deposits and scarcity of intercalated marine sediments in the formation. In the CEN area the Kaimiro correlates with the MH1 miospore zone (upper Waipawan to Porangan) as in the onshore Taranaki boreholes (Higgs et al., 212a) (Palmer, 185) Reference well in study area: Maui-, m MDRT (Enclosure ). Lithology: Interbedded stone, siltstone carbonaceous mudstone and coal; locally stacked stone. A segment (c. 28 m thick) of (informally C s) is encountered in the CEN part of the Taranaki Basin where it lies unconformably over the and it is overlain by the Turi (C ). Historically, the menclature was restricted to coal measure-dominated facies. However, King & Thrasher (16) expanded this definition of the formation to encompass all terrestrial and marginal marine lithofacies of Middle to Late Eocene age, resulting in subdivision into terrestrial facies and coastal facies. The in the CEN area is dominantly coastal facies and consists of stone with interbedded siltstone and coal. 12 GNS ience Report 213/27

19 Log characteristics: In Maui- and other CEN area wells (Maari-1, Moki-1 and Kea-1) mainly in the southern part of the study area, the formation is well defined on the gamma-ray log by a blocky pattern with intermediate to low values. This pattern differs from the steadier and generally higher gamma-ray readings of the which is unconformably overlain in this area by the C s. A gradual upward decrease in gamma-ray response is observed in the upper part of the and reflect grain-size change, judging from core examination (Higgs et al., 212b). The presence of clean s is well outlined by the density and neutron logs cross over. The density log shows a blocky pattern with very low values for the coals and relatively higher values for the s. Depositional environment: Lower coastal plain and marginal marine environment Age: Porangan to Kaiatan (Dp Ak), Mid to Late Eocene. Associated seismic reflectors: P3, lower boundary; P, upper boundary. Correlation: Similarly to the Kaimiro, dating and correlation is based on miospore zonations (Raine 18, 2). In the CEN area the correlates with the MH2-MH3 miospore zones (Porangan to Kaiatan). 7.3 MOA OUP (KING AND THRASHER, 16) In the Taranaki Basin, the Moa Group represents fully marine deposits of Paleocene Eocene age, which are laterally equivalent and represent marine correlatives of the marginal to shallow marine deposits of the Kapuni Group (King & Thrasher, 16). The former is mostly composed offshore of marine mudstones of the Turi. The Eocene members of the Turi interfinger with and divide the Kapuni Group sections. The informal name D correlates with the Omata Member of the Turi in the study area Turi (Palmer, 185) Reference well in study area: Pateke-2, m MD (Enclosure 2). Lithology: Micaceous, carbonaceous, moderately to n-calcareous, dark grey to brown mudstone; pyrite and glauconite occur locally in the formation. Log characteristics: The Turi is characterised by an overall stable gamma-ray and sonic log motif with a similar gamma-ray response to that displayed by the underlying E interval of the and generally equal or lower than the overlying. The sonic readings increase slightly upwards from the base to the top of the Turi in the N S transect between Kea-1 and North Tasman-1 (Enclosure ). Depositional environment: Shelf to bathyal settings within a gradually deepening basin to the rth and rthwest (King and Thrasher, 16). Age: Late Teurian (Dt) to Runangan (Ar), latest Paleocene to Late Eocene. Associated seismic reflectors: P1, lower boundary; P5, upper boundary. Correlation: The Turi is the lateral marine equivalent of the terrestrial to shallow marine deposits of the Kapuni Group, which was deposited in nearshore conditions. In the GNS ience Report 213/27 13

20 CEN area, the formation spans the interval from the diflagellate Paleocystodinium golzowense Zone to the Deflandrea phosphoritica Zone, MH1 to MH3 miospore zones. 7. NGATORO OUP (KING, 188A, B) 7..1 (Palmer, 185) Reference well in study area: Kea-1, m MD (Enclosures 3 ). Lithology: The unit consists of dominant calcareous siltstone and mudstone with intercalated stone (Short and van Rijen, 163; Palmer, 185; King and Thrasher, 16). The interval m in Kea-1 is characterised by fine to coarse grained, light brown, calcareous, highly glauconitic stone which correlates to the Matapo Sandstone Member (Palmer, 185). The type area of the formation is the interval from m MD in the onshore -1 well. Log characteristics: In wells where the stone facies of the basal Matapo Sandstone Member occurs (Enclosures 3 5), the gamma ray and sonic patterns can be subdivided into two distinctive intervals: the bipartite log pattern reflects the succession of glauconiticdominated stone by a siltstone to mudstone-dominated interval. A very prounced spike typically characterises the upper part of the Matapo Sandstone Member and the transition to the siltstone deposited above. Both intervals have a widespread distribution in the study area and they have been recognised in the Tui, Maui, Maari and Kupe fields. Although fluctuating, the gamma-ray readings in the siltstone dominated facies of the have equal or higher mean values that those of the underlying Turi. On the other hand, the sonic readings are consistently lower than in the Turi in this part of the formation. Depositional environment: Based on the benthic foraminiferal assemblage, the depositional setting of the is deeper than upper slope (>m) to bathyal (<2m)., However, the basal Matapo Sandstone are shelfal. A later correlative to the, the Abel Head occurs to the southern part (SIV) of the basin and represent shallow marine facies (i.e. Surville-1). Age: Late Whaingaroan to Waitakian (Lwh Lw), Oligocene to Early Miocene. Associated seismic reflectors: P5, lower boundary; P6, upper boundary Tikorangi (Palmer, 185) Reference well in study area: Maui-1, m MD (Hood et al., 23) (Enclosure 3). Lithology: The unit consists of white to pale grey firm to hard argillaceous limestone highly calcareous, interbedded with pale grey soft claystone. The formation was defined by Palmer (185) with type section the interval from m MD in -1. However, Hood et al. (23) find the type section unsatisfactory because it lacks core material and the lithologic decriptions for the unit are from ditch-cutting samples taken every 3 m. In their study, they identify two types of megafacies within the formation: foredeep (Taranaki Peninsula) and basinal megafacies (offshore) and formally designate the onshore well Waihapa-5, 286 to 316 m MD as the new reference section for the foredeep megafacies - because of the availability of >112 m of core material - and the well Maui-1, 282 to 2627 m MD (also included in this study) as the new reference section for the basinal megafacies, for which c. m of core material is available. The foredeep megafacies are characterised by 1 GNS ience Report 213/27

21 nine lithostratigraphic sub-units that are correlatable based on wireline logs. Based on Hood et al. (23), the Tikorangi interval is thickest in the onshore well Waihapa-1 (232 m, foredeep megafacies in the central Taranaki Peninsula) and Ariki-1 and Kora-1 offshore wells (226 and 215 m respectively, basin megafacies in the Northern Graben area). The formation is thin to absent in the eastern margin of the Northern Graben, the western part of the Taranaki Peninsula and in the southern part (Kupe field and SIV areas) of the Taranaki Basin, where the forms its lateral equivalent. Log characteristics: The Tikorangi is generally characterised by conspicuously low gamma ray readings, high density and acoustic values, compared to the enveloping siliciclastic sediments. The limestone may also be identified from a combination of the neutron porosity and bulk density logs plotted on compatible scales, since the presence of clean limestones result in a cross-over of the two log curves (Enclosure 3). Depositional environment: The carbonates of the Tikorangi represent deep-water sedimentation in a distal shelf to slope-basin setting, characterised by periods of sediment starvation (King and Thrasher, 16). Age: Late Whaingaroan (Lwh) to Otaian (Po), Late Oligocene to Early Miocene. Associated seismic reflectors: P5, lower boundary; P6, upper boundary (King 188a, b) Reference well in study area: Takapou-1, m MD (Enclosure 2). Lithology: In the study region, the represents a strongly calcareous claystone, dark to medium brown to medium grey, soft to firm and blocky with mir amount of grained silt. Thin lenses of white to light grey, firm, blocky limestone occasionally occur in the formation (e.g. in Takapou-1). The conformably overlies the Tikorangi in all study wells, except in Te Whatu-2 and North Tasman-1. In these two wells, it unconformably overlies the. The formation is conformably overlain by fine-grained terrigeus-dominated rocks of the Manganui (Wai-iti Group). This top is erosionally truncated in southern parts of the basin, to the eastern side of the Manaia Fault due to late Neogene uplift and erosion. This boundary corresponds by definition to the top of the Ngatoro Group (King and Thrasher, 16) and represents a sequence boundary that separates the latter and the Wai-iti groups. This upper contact is evident in seismic reflection but is less obvious in wells. A down-hole increase in calcium carbonate content is used to differentiate the unit from the overlying Manganui during drilling operations. Log characteristics: The formation is characterised by overall low (8 66 GAPI) gamma log readings. The combination response of the neutron porosity and bulk density logs plotted on compatible scales shows a slightly positive (+ve) separation, which remains constant throughout the unit and does t results in a cross-over in most wells, except for Tui-1. The acoustic log response is steady: there is an upward decrease in acoustic readings from the underlying Tikorangi, and ne to very little change in the transition to the overlying Manganui. Depositional environment: The formation was deposited in variable water depths in upper bathyal ( 6 m) to outermost shelfal (15 2 m) setting. GNS ience Report 213/27 15

22 Age: In the Taranaki Basin the is of Waitakian (Lw) Lillburnian (Sl), latest Oligocene to Middle Miocene age. In the study area, top and basis of the unit are strongly diachrous, with older sediments deposited to the south east and younger sediments to the rth-west. Late Waitakian to Otaian (Po) (Early Miocene) age was assigned to the formation in the study area. Associated seismic reflectors: P6, lower boundary; the upper boundary is approximated by the N1 reflector in the south (North Tasman-1) to south-eastern part of the study area and by the N15 reflector in the central and rth-western part (Maui-3, - and Takapou-1). 7.5 WAI-ITI OUP (KING 188A, B) Manganui (King 188a, b) Reference well in study area: Kea-1, m MD (lower unit), m MD (mid unit), m MD (upper unit) (Enclosures 3 ). Lithology: The formation consists of a mudstone-dominated succession occasionally characterised by y siltstones. In the central part of the Taranaki Basin this unit conformably overlies the. In this report, we revise the informal two-fold subdivision of King and Thrasher (16) and Roncaglia et al. (28) and the formation is subdivided informally into three units (lower, mid and upper) based on lithology, seismic character and age. Stratigraphically, in the CEN area, the lower part of the formation consists of the interval above the and below the intercalated Moki (Altonian Lillburnian, Sl) (Fig. 2). Discrete stone units and thin stone stringers occur throughout the mid part of the formation, which is t younger than Waiauan (late Middle Miocene); this middle unit is delimited by the upper boundary of the Moki at the base and the lower boundary of an interbedded stone unit of Waiauan age ( Sw s ) at the top (Fig. 2). The mid Manganui interval is characterised by an increase in calcareous mudstone lithofacies (occasional limestone stringers were recorded in Kea-1) with stringers of very fine grained stones and siltstone and traces of lignite. Increase in carbonate was interpreted to reflect a period of subsidence and sediment starvation in the Waiauan (Vonk and Kamp, 28). The upper part of the Manganui consists of the interval between the top of the Waiauan interbedded stone unit and the base of the Giant Foresets. In Kea-1, the sediments in this interval are characterised by light to medium grey claystone grading to siltstone with rare, thin and fine grained stone stringers below 13 m. Log characteristics: The three-fold Manganui is characterised by an overall stable gamma-ray and acoustic log motif with a higher gamma-ray response than that displayed by the underlying and the overlying Giant Foresets. The acoustic readings decrease slightly upwards from the base to the top of the formation; in the upper part of the formation the curve is characterised by a blocky log signature with low values. Depositional environment: In the study area, the formation was deposited in upper slope to lower bathyal environments (-2 m) usually deepening towards the west. To the south (North Tasman-1) and east (Kupe area, Roncaglia et al., 28) over the Manaia anticline, lower and older parts of the Manganui were deposited in a deep environment (upper slope to mid bathyal, 1 m), whereas upper parts of the unit accumulated in 16 GNS ience Report 213/27

23 shelfal to upper slope environment (15 m). Paleo-water depths in the west also shallowed with time, as the shelf prograded to the west/rthwest. Age: Foraminiferal faunas from the central part of the basin indicate that the revised Manganui in the study area has an Otaian Tongaporutuan (mid-early to Late Miocene) age. The lower Manganui is Otaian Altonian (mid to late-early Miocene); the mid part of the formation is Clifdenian Waiauan (Middle to early-late Miocene), and the upper part is Waiauan Tongaporutuan (Late Miocene). In the rth and distal part of the basin (e.g. Tane-1 and Taranga-1), there is evidence of younger (Kapitean Opoitian, Late Miocene to Early iocene) sediments which have been assigned to the Manganui. Associated seismic reflectors: N15 forms the lower boundary and N5 forms the upper boundary of the Manganui in the study area. The upper boundary of the lower does t correspond to a seismic reflector and coincides with the base of the Moki in the study area. The upper boundary of the mid Manganui is poorly approximated by the N3 reflector. In the study area, the lower part of the formation is characterised by moderate- to low-amplitude laterally continuous reflectors. The mid Manganui sequence is characterised by moderate to high amplitudes and laterally continuous reflectors. The upper part is commonly very thick (up to 11 m) and characterised by patchy reflectivity and discontinuos reflectors. Correlation: To the east and south-east (Kupe area), the mid Manganui unit can be correlated with the time-equivalent Otunui which represents a more proximal facies. The latter, which was first described by Gerritsen (1) is a mudstone-dominated Middle Miocene (primarily Waiauan and t older than late Lillburnian) succession outcropping in the Ohura area of King Country Basin. The upper Manganui Tongaporutuan part of the formation is laterally equivalent with the Mount Messenger, which occurs in the rth-west part of the basin including the Taranaki peninsula. The upper Manganui is also lateral equivalent of the Kiore and Urenui formations (Vonk and Kamp, 28), which occurs in the east of the CEN area and in the south-east part (Kupe area) of the basin (Fohrmann et al., 212) Moki (Lock 185) Reference well in study area: Moki-1, m MD (Lock, 185) (Enclosure ). Lithology: The unit consists of stones and y sequences with interbedded mudstone and siltstone and limestone stringers. The stones are commonly fine to very fine grained and argillaceous. Log characteristics: The Moki is characterised by a conspicuous blocky signature on the gamma-ray and acoustic logs (Enclosure ). Gamma-ray readings are prodominantly lower than those of the enveloping Manganui (lower and mid) mudstones. The Moki can also be recognised from a combination of the density and neutron logs as the presence of clean stones results in a cross-over of the two log curves. Depositional environment: The formation represents a turbiditic fan complex initially developed during the late Altonian (late Early Miocene) in the vicinity of the Maui- and Moki- 1 wells on the slope to basin-floor, and well-established during the Clifdenian (early Middle Miocene) and centered around the southern and central wells in the study area (Grain et al., 28). Evidence of Mid Miocene deep water fan lobe switching is observed on the seismic GNS ience Report 213/27 17

24 together with progradation of the system rth- and westward during the early Lillburnian. Age: Based on King (188a, b) and King and Thrasher (16), the formation is restricted to stone sequences of late Altonian to Lillburnian ( Sl), Early to Middle Miocene age developed in the Maari and Maui field areas and present in the onshore area (e.g., Te Kiri-1, New ymouth-2). This age is confirmed by the biostratigraphic results and correlation presented in this study. Associated seismic reflectors: No seismic reflector is associated with the lower boundary; The N3 reflector forms the upper boundary (e.g. Maui-3, -, North Tasman-1, Takapou-1 and Tui-1). The unit is characterised by high-amplitude reflectors throughout the CEN area M2A unit (informal) Reference wells in study area: Moki-1, m MD; Moki-2A, m MD (Enclosure ). The informal unit name has been used extensively in well completion and petroleum reports in the Maari Field. Lithology: Light to medium light grey, very fine to fine-grained stones interbedded with mir siltstone to silty claystone. The stones are well sorted, subrounded, slightly calcareous at places, with traces of mica and carbonaceous specks. Traces of pyrite are reported in the claystone fractions. Log characteristics: The M2A unit is well identified on the gamma ray and density logs where it produces a blocky and spiky pattern with values significantly lower than those of the mudstones (mid Manganui) beneath and above. In four of the study wells (Kea-1, Maui-7, North Tasman-1 and Tasman-1) (Enclosures 3 5), on the gamma ray log the M2A stones are characterised by upward decreasing values suggesting the upward increase of siltstone or claystone fraction within the unit. Depositional environment: The M2A interval is extensive across the CEN region and correlated throughout. While the stone may represent a distal fringe portion of a fan system younger than the Moki, which has a better development to the rth, it could also be the result of the renewed rthward progradation of the Moki fan complex after a period of quiescence characterised by lack of supply and dominant mudstones deposition (mid Manganui ). In the latter hypothesis, the M2A unit will represent the base of a younger slope fan. In the southern-eastern wells (Motueka-1) a lateral y facies equivalent correlative to the Moki and M2A unit has been recorded (Enclosure 5); this unit is shallow marine and probably represents a separate lithostratigraphic member. Age: In the study area the M2A is of late Lillburnian age, Middle Miocene. Associated seismic reflectors: In the rthern part of the study area, the top of the unit is associated with the N35 reflector (e.g. Takapou-1). Distribution: In the CEN area, the unit has been observed in all rthern wells from rth to south (Enclosures 2 and ) and consistently occurs 5 85 m above the top of the Moki with two exceptions: in the Maui-1 and -7 wells, where the M2A unit is tentatively correlated with a stone layer 13 m and 3 m above the Moki, respectively. In this study the M2A unit is inferred to be laterally continuous. 18 GNS ience Report 213/27

25 7.5. Sw s, Waiauan interbedded stone unit (this study, informal) Reference well in study area: Kea-1, m MD (Enclosures 3 ). Lithology: In the reference well, the unit consists of mass-emplaced, light to medium grey, fine to medium-grained, micaceous stones interbedded with calcareous siltstones and clay, with traces of carbonaceous and lignitic material. The unit becomes less muddy in the upper half of its interval. The upper part consists largely of clean, medium-grained stones with mudstone interbeds becoming frequent towards the top. While it is clearly stone-dominated in the reference area, the unit is characterised by an increase in mudstones and claystones towards the south (Moki-2A, Maui- and North Tasman-1) and the rth (Maui Field area) of the study area. Log characteristics: The Waiauan interbedded stone unit has an overall blocky gammaray and density log signature. In the reference well, its lowermost part ( m MD) is characterised by stable gamma ray values with spikes. In comparison, the overlying stones ( m MD) display a higher gamma ray log pattern, which can be split into a number of small units with increasing-upwards gamma-ray log signatures separated by peaks. The latter suggests fining upwards bodies. Average density readings are usually low in this interval. Depositional environment: No cores have been taken in the Waiauan stone unit from the study wells, but the stones were probably deposited from concentrated gravity flows in deep (>6 m water depth) slope to upper bathyal settings, based on log similarity with the Moki and the M2A unit in the area. Age: By definition the age of this unit is restricted to the Waiauan (late-mid to early-late Miocene). Associated seismic reflectors: No mapped reflectors are associated with the base of this unit. In the central and southern part of the study area the top of this unit is associated with the N reflector (i.e., Maui-3 and -) Tt 1 and 2, Tongaporutuan interbedded stone unit 1 and 2 (this study, informal) Reference well in study area: Takapou-1, m MD (Tt 1), m MD (Tt 2). Lithology: These units represent the youngest in a series of stone bodies spanning the Late Altonian to Tongaporutuan. The interval is dominanted by stones with mudstone interbeds, and represents the offshore equivalent to the Mount Messenger (Hay, 167) in the central area of the basin. The latter formation was deposited over the rthern part of the basin and well exposed onshore along the rth Taranaki coast between Pariokariwa Point and the Mokau River, where it reaches a thickness of about 85 m (King and Thrasher, 16). While stone interbeds of Tongaporutuan age are interpreted herein to correspond to Mount Messenger facies equivalent, the thick mudstone sequences above and below these units are assigned to the upper slope bathyal facies of the mid and upper Manganui. Log characteristics: Conspicuous blocky signature on the gamma ray logs characterises the units with responses that are lower than those of the enveloping Manganui mudstones. Density and neutron logs cross overs are generally observed as well as an GNS ience Report 213/27 1