DISCLAIMER

This report has been prepared by the Institute of Geological and Nuclear Sciences Limited (GNS Science) exclusively for and under contract to Southland Regional Council (Environment Southland). Unless otherwise agreed in writing by GNS Science, GNS Science accepts no responsibility for any use of or reliance on any contents of this report by any person other than Environment Southland and shall not be liable to any person other than Environment Southland, on any ground, for any loss, damage or expense arising from such use or reliance.

Use of Data:

Date that GNS Science can use associated data: June 2015

BIBLIOGRAPHIC REFERENCE

Tschritter, C.; Rawlinson, Z.J.; Barrell, D.J.A.; Alcaraz, S. 2016. Three-dimensional geological model of Environment Southland’s area of interest for freshwater management. GNS Science Consultancy Report 2015/123. 74 p.

Project Number 630W0003 Confidential 2015

CONTENTS EXECUTIVE SUMMARY ...... IV 1.0 INTRODUCTION ...... 1 1.1 Context of this project ...... 1 1.2 Spatial extent of this project ...... 1 1.3 Content of this report ...... 2 2.0 REVIEW OF GEOLOGY AND HYDROGEOLOGY IN THE MODEL AREA ...... 3 2.1 Geological evolution ...... 3 2.1.1 Basement rocks ...... 3 2.1.2 Cover rocks ...... 5 2.1.3 Poorly consolidated Quaternary sediments ...... 6 2.2 Major geological formations in the study area ...... 8 2.2.1 Basement rocks (incl. Cretaceous rocks) ...... 8 2.2.2 Tertiary (Paleogene and Neogene) cover rocks ...... 9 2.2.2.1 Eocene ...... 10 2.2.2.2 Oligocene ...... 10 2.2.2.3 Miocene ...... 11 2.2.2.4 Pliocene ...... 12 2.2.3 Poorly consolidated Quaternary sediments ...... 13 2.3 Hydrogeology ...... 16 3.0 METHODOLOGY ...... 18 3.1 Modelling process...... 18 3.1.1 Unit definition ...... 18 3.1.2 Structures ...... 19 3.1.3 Input data and uncertainties ...... 19 3.2 Model Data Sources ...... 20 3.2.1 Digital Elevation Model (DEM) ...... 20 3.2.2 Bathymetry data not included in the DEM ...... 20 3.2.3 Geological maps ...... 20 3.2.4 Geological cross-sections ...... 21 3.2.5 Geophysical Data ...... 23 3.2.5.1 Western Southland seismic data ...... 23 3.2.5.2 Winton Basin seismic data ...... 25 3.2.5.3 Gravity data ...... 27 3.2.6 Borehole data ...... 29 3.2.6.1 Logs from the ES bore database ...... 29 3.2.6.2 Logs from coal exploration bores ...... 32 3.2.6.3 Logs from petroleum exploration bores ...... 32 3.2.6.4 Bore distribution ...... 33 3.3 Location of Faults ...... 33 3.4 Grouping of geological units ...... 35 3.4.1 Approaches for differentiation of the Quaternary sediments ...... 36 3.5 Model stratigraphy and input data per fault block ...... 37

GNS Science Consultancy Report 2015/123 i

Confidential 2015

3.5.1 Fault block 1: Fiordland ...... 38 3.5.2 Fault block 2: Waiau and Te Anau basins ...... 39 3.5.3 Fault block 3: Wakatipu ...... 40 3.5.4 Fault block 4: Southland Plains ...... 41 3.5.5 Fault block 5: Central ...... 42 3.5.6 Fault block 6: Waikaia ...... 43 3.5.7 Fault block 7: Mossburn ...... 45 3.5.8 Fault block 8: Lumsden ...... 46 3.5.9 Fault block 9: Riversdale ...... 48 3.5.10 Fault block 10: East1 ...... 49 3.5.11 Fault block 11: East2 ...... 50 4.0 RESULTS ...... 51 4.1 Model Description ...... 51 4.2 ES geological model ...... 51 5.0 FUTURE REFINEMENTS ...... 58 5.1 Model size ...... 58 5.2 Fit for purpose – refining focus ...... 58 5.3 Incorporation of coal seam gas bores ...... 58 5.4 Drilling of additional bores ...... 59 5.5 New and reinterpreted seismic data ...... 59 5.6 Subdividing the Quaternary strata ...... 60 5.7 Subdividing the Gore Lignite Measures ...... 60 5.8 Visualisations ...... 60 6.0 CONCLUSIONS ...... 61 7.0 ACKNOWLEDGEMENTS ...... 62 8.0 REFERENCES ...... 62

FIGURES Figure 1.1 Extent of the ES geological model...... 2 Figure 2.1 Simplified QMAP geology and structural features (faults and folds), modified from Heron (2014)...... 4 Figure 2.2 Interpretation of former ice limits and former shoreline positions of the mid- to late Quaternary Period in the Southland region...... 8 Figure 2.3 Distribution of poorly consolidated Quaternary sediments by depositional environments (modified from QMAP; Heron 2014)...... 15 Figure 3.1 (left) QMAP seamless geological map, fault lines and cross-section parts used for modelling, for the full legend see Figure 2.1 (The cross-sections were only used in areas where there was no other, more accurate data available); and (right) simplified model units and faults...... 22 Figure 3.2 Example of a portion of a structure contour map (in km below ground level) for the top of Cretaceous-age strata in the Waiau Basin (from Turnbull et al., 1993)...... 23 Figure 3.3 Top) Map view and Bottom) cross-section view of data points digitised from contour maps of different geological horizons from Turnbull et al. (1993). Elevations in bottom view (vertical axis) are in m AMSL...... 24

GNS Science Consultancy Report 2015/123 ii

Confidential 2015

Figure 3.4 Top) Map view, and Bottom) cross-section view of data points digitised from Winton Basin structure contour maps of different geological horizons (Cahill, 1995). Elevations in bottom view (vertical axis) are in m AMSL. Colours denote the model geological unit to which the data apply. The red outline marks the study area...... 26 Figure 3.5 Spline-interpolated Isostatic gravity anomaly map for the model area...... 28 Figure 3.6 (left) Distribution and depth range of bores with lithological logs in the ES database; and (right) NCRS coal and petroleum explorations bores with geological logs...... 31 Figure 3.7 Fault blocks (numbered), and colour-coded model units...... 38 Figure 3.8 ES bores mentioned in the text, including fault blocks, modelled units and faults...... 47 Figure 3.9 NCRS bores mentioned in the text, including fault blocks, modelled units and faults...... 49 Figure 4.1 Views of the model showing younger units and lakes...... 53 Figure 4.2 Views of the model showing older units...... 54 Figure 4.3 Depth to basement from the ES geological model...... 55 Figure 4.4 Thickness of East Southland Group from the ES geological model...... 56 Figure 4.5 Thickness of Quaternary from the ES geological model...... 57

TABLES Table 3.1 Data from Turnbull et al. (1993) used in modelling...... 25 Table 3.2 Data used in modelling from Cahill (1995)...... 27 Table 3.3 Number of bores in the ES bore database by depth range...... 29 Table 3.4 Number of coal exploration bores in the study area by depth range...... 32 Table 3.5 Information on the geometry of faults in the model. Note that in most cases, the depiction of fault dips and extent in cross-sections is based on interpretation and inference rather than on data...... 34 Table 3.6 Modelled faults and fault interactions...... 35 Table 3.7 Fault block 1 surface chronology and subsurface data and manual control lines...... 39 Table 3.8 Fault block 2 surface chronology and subsurface data and manual control lines...... 40 Table 3.9 Fault block 3 surface chronology and subsurface data and manual control lines...... 41 Table 3.10 Fault block 4 surface chronology and subsurface data and manual control lines...... 42 Table 3.11 Fault block 5 surface chronology and subsurface data and manual control lines...... 44 Table 3.12 Fault block 6 surface chronology and subsurface data and manual control lines...... 45 Table 3.13 Fault block 7 surface chronology and subsurface data and manual control lines...... 45 Table 3.14 Fault block 8 surface chronology and subsurface data and manual control lines...... 47 Table 3.15 Fault block 9 surface chronology and subsurface data and manual control lines...... 48 Table 3.16 Fault block 10 surface chronology and subsurface data and manual control lines...... 50 Table 3.17 Fault block 11 surface chronology and subsurface data and manual control lines...... 50

APPENDICES APPENDIX 1: LOCATION MAPS ...... 66

APPENDIX FIGURES Figure A1 West Southland, with locations names mentioned in the text...... 66 Figure A2 East Southland, with locations names mentioned in the text...... 67

GNS Science Consultancy Report 2015/123 iii

Confidential 2015

EXECUTIVE SUMMARY

The Joint Fluxes and Flows Programme is a collaborative research project being undertaken by GNS Science (GNS) and the National Institute of Water and Atmospheric Research (NIWA) in association with and under contract to Environment Southland (ES). The programme aims to develop a three-dimensional (3D) groundwater flow and contaminant transport model calibrated to surface water flow, to be used to assist in groundwater management and policy in the Southland region.

This report summarises the first work component of the programme, which is the construction of a 3D geological model, referred to here as the ‘ES geological model’. The model encompasses ES’s area of interest for freshwater management. The ES geological model will provide a framework for subsequent construction of the groundwater flow model, and other components of the programme.

The area covered by the ES geological model is approximately 21,000 square kilometres and spans a complex and varied area, both geographically and geologically. The western boundary lies within the mountainous Fiordland region, the southern boundary is the Southland coast, and the model area includes the Southland Plains and hill country to the north of these plains. A combination of Geographic Information System (GIS) (ESRI ArcGIS 10.1) and 3D geological modelling software (Leapfrog Geothermal 2.8) was used to construct the ES geological model. The model has been developed to have a horizontal resolution of 250 m by 250 m and it extends to a depth of 8.5 km below mean sea level. The vertical extent depends on the available data.

The complex geology in Southland comprises approximately 300 distinct geological units, that have been grouped into a series of components (model units), based on their age, composition and hydrogeological significance. The grouping is largely related to the age of the strata, which in turn is relevant to the hydrological characteristics. The ES geological model consists of the following eight model units, listed below from youngest to oldest, and an additional unit representing the water masses within the main lakes and estuaries: 1. Quaternary (poorly consolidated sediments underlying valleys and basins). 2. Pliocene (non-marine geological strata, ~2.6 to 5 million years old). 3. Miocene – East Southland Group (a subset of the Miocene strata – non-marine). 4. Miocene – others (geological strata, mainly marine). 5. Early Miocene (geological strata, mainly marine). 6. Oligocene (geological strata, mainly marine). 7. Eocene (geological strata, marine and non-marine). 8. Basement (geological foundations of the region).

Seven geological faults have been included in the model, which have the effect of splitting the 3D volume represented by the model into 11 individual blocks. The main data sets used in the modelling consist of: • A digital elevation model (DEM), and lake and estuary bathymetry data. • Surface geological maps at a 1:250,000 scale (QMAP).

GNS Science Consultancy Report 2015/123 iv

Confidential 2015

• Three lithological and geological well log datasets: 2585 bores from the ES bore database, 502 bores from coal exploration National Coal Resources Survey (NCRS) drillholes, and 23 bores from petroleum exploration. • Contour maps of subsurface geological layers, interpreted from geophysical surveying (seismic reflection) in the Waiau, Te Anau and Winton basins, which encompass approximately 20% of the model area. • Published geological cross-sections, showing interpretations of subsurface geological relationships.

Although the resolution of the model is set to not be coarser than 250 m, the uncertainty in the model is linked to the amount of available data within the area, and thus within data- sparse areas the uncertainty is very high and will be greater than the model resolution. The ES geological model represents a regional-scale prediction of the locations of different geological layers at depth, and is intended only to provide a broad estimate of likely subsurface conditions in a general area. As the ES geological model has been developed at a regional scale it should only be considered within this context. The model should not be used in isolation for land use planning, consent decisions, design of engineering projects, geohazard risk assessment, or other work for which detailed local site investigations are necessary.

The development of the model in Leapfrog Geothermal software allows for future refinement of the model by addition of new data.

GNS Science Consultancy Report 2015/123 v

Confidential 2015

1.0 INTRODUCTION

1.1 CONTEXT OF THIS PROJECT

The National Policy Statement for Freshwater Management 2014 (NPS-FM; Ministry for the Environment, 2014) has set new guidelines for regional councils to address freshwater management within their regions. Environment Southland’s (ES) response to the NPS-FM is the construction of the Water and Land 2020 and Beyond work programme (WAL2020). WAL2020 consists of both a science programme as well as projects associated with policy and community engagement. The science programme consists of three sub-programmes addressing the following three components: establishing nutrient inputs to freshwater associated with land use (land use input); the origin of water, pathways and fluxes of contaminant transport through groundwater and surface water (fluxes and flows); and ecosystem responses to transported contaminants (ecosystem response). The sub- programme associated with the fluxes and flows component is being undertaken by GNS Science (GNS) and the National Institute of Water and Atmospheric Research (NIWA) in collaboration with ES, and is named the Joint Fluxes and Flows Programme (Kees et al., 2014).

The Joint Fluxes and Flows Programme consists of a number of planned work components aimed at developing a 3D regional groundwater flow and nutrient transport model, calibrated to surface water flow, to be used as a policy management tool in the region. The work components are as follows: • Construction of a 3D geological model (this report). • Characterisation of hydrochemistry and nutrient transit times. • Construction of numerical groundwater–surface water models. • Construction of a nitrogen loading and assimilation model. • Characterisation of surface water flows, groundwater flows, groundwater levels and groundwater – surface water interactions. • Quantification of predictive uncertainty. • Performing of simulations with calibrated model, accounting for predictive uncertainty. • Communication of results.

This report presents the first component, the construction of a 3D geological model. This model, referred to in this report as the ‘ES geological model’, encompasses ES’s area of interest for freshwater management. The ES geological model provides a regional-scale overview of surface and subsurface geological conditions that will aid the understanding of potential groundwater flow pathways in Southland. As the first step in this work, the ES geological model will supply the top surfaces of modelled units to be utilised in the construction of the subsequent groundwater flow model.

1.2 SPATIAL EXTENT OF THIS PROJECT

The boundary used for developing the ES geological model was provided by ES. This boundary was chosen to encompass the areas of interest for freshwater management within the Southland region as defined by the regional council (ES) and covers an area of approximately 21,000 km2. Figure 1.1 displays the extent of the ES geological model: the western model boundary lies within the mountainous Fiordland region, the southern boundary is the southern-most coast of the South Island, and the model area includes the

GNS Science Consultancy Report 2015/123 1

Confidential 2015

Southland Plains and hill country to the north of these plains. Due to the large area covered, additional maps, provided in Appendix 1, include locations mentioned throughout this report.

The geological model has been developed at a regional scale to provide a wider understanding of the geological setting and potential groundwater flow pathways throughout the region. However, the subsequent groundwater flow model that will be developed within the Joint Fluxes and Flows Programme will cover a much smaller area (largely the Southland Plains). This is to supply a more detailed investigation of groundwater flow and groundwater- surface water interaction to support decision-making at a finer (catchment) scale.

Figure 1.1 Extent of the ES geological model.

1.3 CONTENT OF THIS REPORT

This report provides a review of the geology and hydrogeology of the area (Section 2.0), a discussion of the modelling methodology, data sources and modelling stratigraphy (Section 3.0), and describes the developed ES geological model (Section 4.0). Conclusions are presented in Section 5, focussing on the potential applications of the model as well as its limitations.

GNS Science Consultancy Report 2015/123 2

Confidential 2015

2.0 REVIEW OF GEOLOGY AND HYDROGEOLOGY IN THE MODEL AREA

This section provides a review of the geological evolution of the modelled area, a description of the major geological formations that are of importance for the ES geological model, and a description of the hydrogeological characteristics of these formations. The most important and comprehensive source for New Zealand’s geology, the GNS Science ‘Quarter-million- scale’ (1:250,000) nationwide geological map (‘QMAP’), shows, in a generalised way, the ground-surface geology of the project area (Figure 2.1). The QMAPs provide the main framework for the ES geological model, which presents an interpretation of the subsurface geology. The majority of the project area lies on the ‘Murihiku’ QMAP (Turnbull and Allibone, 2003), while the western sector is on the Fiordland sheet, (Turnbull et al., 2010), and the northern sector is on the Wakatipu sheet (Turnbull, 2000). This section summarises the geological information given in these maps, and associated booklets, and provides complementary data from other sources as needed. For locations mentioned in this section please refer to Appendix 1.

2.1 GEOLOGICAL EVOLUTION

The geological components of the model area are differentiated into three parts; basement rocks, cover rocks and poorly consolidated Quaternary sediments. Figure 2.1 shows the distribution of these three components mapped at the ground surface throughout the study area. Their evolution and structural character are described in the following subsections.

2.1.1 Basement rocks

The basement rocks comprise the geological foundations of any particular area. Those of Southland consist of a variety of igneous and sedimentary rocks. They were formed from the Permian Period through into the early Cretaceous Period (~300 million years ago to ~100 million years ago) when the continental fragment Zealandia (parts of which are now New Zealand) was part of the Gondwana supercontinent. Southland’s basement rocks (Figure 2.1) include several distinctively different units, arrayed side by side, including Median Batholith, Brook Street Terrane, Murihiku Terrane, Dun Mountain-Maitai Terrane, and the Caples Terrane (Turnbull et al., 2010; Turnbull and Allibone, 2003). Collectively, they form part of the Austral Superprovince (Mortimer et al., 2014).

A prominent structural feature within the basement is the Southland Syncline, which has buckled the sedimentary rocks of the Murihiku Terrane into a regional-scale downfold, trending west-northwest from the South Otago coast near Owaka to the Dipton area, beyond which the Murihiku rocks are largely obscured by cover rocks. The Southland Syncline is an ancient feature formed prior to the break-up of Gondwana, as are the basement rocks listed above. The Zealandia continent was separated from Gondwana by sea-floor spreading ~85 million years ago during the Cretaceous Period.

GNS Science Consultancy Report 2015/123 3

Confidential 2015

Figure 2.1 Simplified QMAP geology and structural features (faults and folds), modified from Heron (2014). Geological components described in Section 2.1 are shown as follows: basement rocks are represented in light blue to dark green, cover rocks from orange (Pebbly Hill gravels) to light olive green (Ohai Group – undifferentiated) and the poorly consolidated Quaternary sediments in light yellow. The thick, black outline represents the ES geological model boundary.

GNS Science Consultancy Report 2015/123 4

Confidential 2015

2.1.2 Cover rocks

Following separation from Gondwana, the Zealandia continent began to subside, and progressively much of it became submerged. During that time, a blanket of cover rocks was laid down over the basement. These cover rocks, collectively forming the bulk of the Zealandia Megasequence (Mortimer et al., 2014), vary in distribution and character from place to place across Southland, due mainly to local and regional variations in the nature and timing of movements of the Earth’s crust (tectonic activity).

Following the break-up of Gondwana, localised rifting within the basement produced fault- bounded depressions (basins). In on-land Southland, the first notable basin was formed during the Late Cretaceous (~100 to 65 million years ago) along east-west striking faults in the Ohai area. Within this basin, a sequence of non-marine sands, gravels and peats accumulated, which later became compressed to form the coal measures (Ohai Group) for which the area is known. In the Middle Eocene (~45 million years ago), tectonic activity increased markedly with the propagation of an extensional rift northwards along the Moonlight Fault System, through the area that is now the Waiau River valley and the Te Anau area. The Waiau and Te Anau basins subsided through the remainder of the Eocene, the Oligocene and into the Middle Miocene (~15 million years ago), and as much as several kilometres of sedimentary rocks were deposited, mainly of marine origin (e.g., Waiau Group). Over a similar time period, there was subsidence of the Winton Basin along east-west striking faults, and as much as 2.8 kilometres of sedimentary rocks were laid down (e.g., Winton Hill Formation).

Away from these basins, there was a more uniform geological history, with the formation of a broad erosion surface across the exposed basement rocks (Waipounamu Erosion Surface). Commonly, non-marine sedimentary rocks rest on the basement surface, overlain by marine sedimentary rocks as regional subsidence lowered much of the southwestern sector of the region below sea level. The maximum extent of marine incursion was reached in the earliest Late Miocene, about 23 million years ago, and extended as far northeast across Southland as the Waikaia area.

A major change began in the Early Miocene with the inception of a new plate boundary through Zealandia, and initiation of the Alpine Fault, about 25 million years ago. As the Zealandia continent began to adjust to the stresses associated with movement of the new plate boundary, east-west contractional forces became prevalent through the Southland region. This resulted over time in the partial closing and upheaval of the Waiau and Te Anau basins, and activation of many of north- to northeast-striking fault systems, including the Moonlight Fault System and northern part of the Livingstone Fault System. During the Late Miocene to Pliocene, these forces led to the uplift of the ranges of northern Southland. The tempo of change was much less in central and eastern Southland. Through the Early Miocene, marine sedimentation gave way to accumulation of river plain sediments, initially sandy and muddy sediments with peat swamps, later to be compacted to become the Gore Lignite Measures (East Southland Group), and succeeded during the Late Miocene and Pliocene by an influx of gravelly river deposits, derived from the uplifting land to the northwest, which formed the Pebbly Hills Gravel and Gore Piedmont Gravel. A notable tectonic development in this area was formation of the north-northeast striking Dunsdale/Bushy Park Fault System, where basement was thrust up from the west-northwest, elevating the Hokonui Hills relative to the trough down which the Mataura River now flows. There was relatively minor movement on several other northeast and north-striking faults,

GNS Science Consultancy Report 2015/123 5

Confidential 2015 which led to the basement being faulted against pockets of cover rock strata, such as near Titiroa in eastern Southland, and in the Hokonui Hills south of Mandeville.

In the Te Anau area, an intermontane basin formed on the northern side of the Takitimu Mountains, in which gravelly river sediments accumulated to produce the Prospect Formation. By the end of the Pliocene (2.6 million years ago), the general arrangement of hills, mountains and valleys in Southland was probably much as we see it today.

2.1.3 Poorly consolidated Quaternary sediments

Poorly consolidated sediments, laid down by glaciers, rivers, or by the action of wind and water along the coastline, were deposited during the Quaternary Period, which spans the past 2.6 million years. Accumulations of these sediments comprise the youngest part of the Zealandia Megasequence (Mortimer et al., 2014) and are ubiquitous across the margins and floors of the valleys and basins of the Southland region.

Of major importance to the deposition of these sediments has been the ~100,000 year cycles of glaciation that have characterised the Middle to Late Quaternary (the past ~800,000 years). Each cycle was characterised by a prolonged decline into cold conditions (glaciation), followed by a sharp rebound to interglacial conditions, such as prevail today. The most recent glaciation ended about 18,000 years ago, and was followed by the post-glacial climate episode, in which the climate progressively warmed to the interglacial conditions that have persisted for the past ~11,700 years or so. Figure 2.2 shows the extent of glacial advances, as well as the positions of shorelines marking incursions of the sea during interglacial times.

During glaciations, glaciers formed on the mountains, and ice tongues flowed down into adjacent lowlands (Barrell, 2011). Although much of Southland was sufficiently far from high mountains to be ice-free, extensive glaciers formed on the Takitimu Mountains, the Eyre Mountains, and the Garvie Mountains, but were not large enough to extend onto adjacent lowlands Figure 2.2). In contrast, an extensive ice cap grew over Fiordland and outlet glacier tongues extended into the Te Anau/Manapouri basins, the Monowai Valley, and the lower reaches of the main valleys draining to the Fiordland south coast. Plains of outwash gravel extended down-valley of the glacier termini, notably the Waiau and Waitutu valleys. A major icefield system in the Lake Wakatipu catchment fed several ice tongues into the Southland region, notably: one through the Von Valley that delivered meltwater and outwash gravel to the Oreti River system; and the main ice tongue of the Wakatipu Valley that extended to Kingston, from where its meltwater and outwash gravel drained into the Mataura River system (Barrell, 2011). The onset of post-glacial conditions imposed major hydrological changes on the Oreti and Mataura river systems, because the water they formerly received from the Wakatipu catchment now drains entirely into Otago’s Clutha River system.

In the Manapouri-Te Anau areas and the Wakatipu catchment, the ice was more extensive during earlier glaciations than during the most recent one (Figure 2.2). At least two glaciations ago (about 250,000 years ago or more), glacier ice entirely filled the Manapouri- Te Anau basin, lying as much as ~20 km farther southeast than it did during the more recent glaciation (Barrell, 2011), while ice from the Wakatipu glacier extended as much as 20 km down-valley of Kingston, to the Garston-Nokomai area (Turnbull, 2000).

During glaciations, the average temperature in New Zealand was about 6°C cooler than today (e.g., Newnham et al., 2013; Putnam et al., 2013), with snowlines and treelines about 800 to 1,000 m lower than they are at present. In the many areas of Southland that lacked sufficient elevation, and precipitation, for the formation of ice-age glaciers, the expansion of

GNS Science Consultancy Report 2015/123 6

Confidential 2015 alpine-like conditions across much of the hill terrain encouraged erosion in catchments. Increased production of sediment choked streams and rivers, resulting in a build-up of sediments in the valleys, basins and plains over much of the region. Under present interglacial climate, sediments loads are less and the rivers and streams have tended to cut down into their beds, forming terraced valleys.

Another consequence of glaciations was the effect on sea level. During glaciations, build-up of ice sheets on northern North America and western Europe was sufficient to lower global sea level by as much as 125 m or so (Figure 2.2). The sea was last at that level about 20,000 years, and from about 18,000 years ago rose progressively, reaching its present level about 7,000 years ago. For most of the past 80,000 years, the sea has been more than 50 m lower than present. Consequently, the Southland coast lay far seaward of its present position, and Stewart Island formed part of the mainland. The Foveaux Strait is less than 40 m deep, and the rising sea reoccupied it only about 10,000 years ago. This recreated Stewart Island as an entity for the first time since about 80,000 years ago (the last time that the sea was at an interglacial level). Sea levels during previous interglacial episodes were similar to those prevailing today. Around the coastal periphery of the Longwood Range, and along the south coast of Fiordland, coastal deposits from previous interglacial episodes are preserved at elevations notably higher than present sea level, indicating that tectonic uplift has been occurring in those areas (Suggate, 2004; Barrell, 2011).

The rivers draining across the Southland region have found paths across the hill terrain, and an interpretation of the evolution of these pathways is provided by Turnbull and Allibone (2003). The offshore bathymetry was an important influence on sediment deposition. In shallow areas of today’s offshore, sea level fall would have reduced the overall gradient of rivers and streams in today’s onshore area, encouraging sediment build-up. This is likely to have been the primary control of formation of the Southland Plains, which refers collectively to the alluvial plains and terraces of the Mataura, Oreti and the Aparima valleys. In areas with steeper offshore gradients such as off the Catlins, sea level fall during glaciations may have steepened the gradients of the rivers and streams, encouraging valley incision and erosion, and minimal sediment build-up. Post-glacial sea level rise tended to drown those relatively steep river and stream valleys, resulting in the numerous bays, estuaries and tidal reaches that characterise the Catlins, and encouraged post-glacial sediment deposition in the valley floors.

GNS Science Consultancy Report 2015/123 7

Confidential 2015

Figure 2.2 Interpretation of former ice limits and former shoreline positions of the mid- to late Quaternary Period in the Southland region. Glacier limits were determined from preserved glacial deposits or landforms, and ages are estimated rather than directly dated. Shorelines west of Waiau River, ice limits and ice extent are from Barrell (2011); shorelines east of Waiau River, and offshore are from this report. The black outline represents the ES geological model boundary.

2.2 MAJOR GEOLOGICAL FORMATIONS IN THE STUDY AREA

This section describes the lithology, distribution and, if available, hydrogeological characteristics of major geological formations in the study area. Due to the large size of the study area, the description is limited to geological formations and groups that have a large enough known surface and/or subsurface distribution in the study area to have a significant effect on groundwater flow.

2.2.1 Basement rocks (incl. Cretaceous rocks)

As described in section 2.1.1, Permian to Cretaceous basement rocks in the study area are formed by the Median Batholith and four different terranes: Brook Street Terrane, Murihiku Terrane, Caples Terrane, and Dun Mountain – Matai Terrane (Figure 2.1). As such, the

GNS Science Consultancy Report 2015/123 8

Confidential 2015

Southland region has an unusually complex and varied basement, by New Zealand standards.

Brook Street Terrane forms the eastern part of the Longwood Range and the Takitimu Mountains, and most of the southern Southland Plains is underlain, at great depth, by these rocks. Brook Street Terrane comprises volcanic rocks (lava flows, volcanic breccia and airfall tuff rocks, as well as volcanically-sourced sedimentary rocks including sandstone and mudstone.

Murihiku Terrane forms the hills and ranges south of the Hillfoot Fault, from the Catlins through to the Hokonui and Taringatura hills, and at depth Murihiku rocks underlie parts of the Southland Plains. This terrane comprises a general rock type that is commonly called ‘greywacke’, and consists of alternating sandstone and mudstone layers, with minor siltstone, shell beds, conglomerates and limestone.

The Dun Mountain – Matai Terrane occurs as a belt between the Hillfoot and the Livingstone faults. These rocks underlie, for example, the Waimea Plains as well as the southern part of the Oreti Basin. This terrane comprises ultramafic igneous rocks (e.g., serpentenite, gabbro, peridotite), volcanic rocks (e.g., spilite, basalt) and sedimentary rocks (sandstone, siltstone, mudstone, conglomerate).

Caples Terrane forms the ranges in the northern part of the model area. These rocks consist mainly of volcanically-sourced sedimentary rocks dominated by sandstone with thin mudstone layers. These rocks, like those of the Murihiku Terrace, also qualify as ‘greywacke’. Towards the northeast, the greywacke is increasingly metamorphic towards semi-schist and schist.

Coarse-grained igneous (plutonic) rocks of the Median Batholith (part of the Tuhua Intrusives of Mortimer et al. (2014) form much of the eastern side of Fiordland, and the Longwood Range, and some hills around Bluff.

Late Cretaceous Ohai Group rocks have only been mapped at the ground surface in the Ohai area (Figure 2.1); however, extensive coal and coal seam gas exploration has targeted subsurface deposits of this group. Ohai Group includes the Morley and the Wairio coal measures, as well as the New Brighton Conglomerate. The limited, mapped deposits are generally undifferentiated, aside of minor deposits that are part of the New Brighton Conglomerate.

The basement rocks are exposed at the ground surface in most of the hill country of Southland, but the upper surface (top) of the basement rock extends to great depth beneath some of the basins, where it is underlain by cover rocks and poorly-consolidated sediments. The greatest depths to basement rocks in the project area are in the Te Anau (-8,000 m above mean sea level (AMSL), Waiau (-6,000 m AMSL) and Winton (-2,600 m AMSL) basins (Turnbull et al., 1993). Shallow basement occurs, for example, beneath the eastern Southland Plains and the Waikaia River valley. In parts of those areas, drillholes have intersected basement at depths of tens to a few hundreds of metres.

2.2.2 Tertiary (Paleogene and Neogene) cover rocks

In the study area, Paleogene includes Eocene (predominantly Nightcaps Group, Mako Coal Measures and Annick Group) and Oligocene deposits (Winton Hill Formation, lower part of Waiau Group). Neogene cover rocks in the study area are Miocene (the upper part of the

GNS Science Consultancy Report 2015/123 9

Confidential 2015

Waiau Group, Forest Hill Formation, and East Southland Group) and Pliocene sediments (Orepuki Formation, Prospect Formation, Pebbly Hill Gravel, and Te Waewae Formation). The term ‘Tertiary’ is now obsolete in the chronostratigraphic nomenclature, but it is still used informally.

2.2.2.1 Eocene

Eocene rocks in the study area are primarily Nightcaps Group, Mako Coal Measures and Annick Group. These strata typically consist of sandstone, mudstone and conglomerate with some coal or lignite layers.

Nightcaps Group

Nightcaps Group comprises two formations, Beaumont Coal Measures and the overlying Orauea Mudstone. Nightcaps Group deposits are exposed overlying basement in places around the margins of the Longwood Range and Takitimu Mountains, and are inferred to exist at depth in the Winton Basin (Cahill, 1995; Turnbull and Allibone 2003).

Beaumont Coal Measures were laid down in a river-plain (fluvial) environment and comprise sandstones and mudstones with intermittent coal layers. The formation has a maximum thickness of 250 m. Orauea Mudstone is up to 350 m thick, was deposited in a lake (lacustrine) environment and consists of carbonaceous mudstone with sporadic sandstone layers deposited in lagoonal to lacustrine conditions.

Mako Coal Measures

The non-marine Mako Coal Measures are subdivided into two parts that each have a thickness of approximately 20 m. The lower part comprises silty mudstones, sandstones and claystones and the upper part is characterised by sandstones that include thin coal seams. Mako Coal Measures have been mapped at the ground surface only in small areas west and south of the Five Rivers Plain. However, at the subsurface this formation extends to the Winton Basin, where it has been drilled near Hedgehope (Isaac et al., 1990).

Annick Group

The non-marine Annick Group consists of conglomerate, sandstone, mudstone and minor coal and overlies basement in the Te Anau Basin (Turnbull et al., 2010). All Eocene deposits mapped at the ground surface in the northern part of the basin belong to this group, but there are no surface outcrops in the southern part of the Te Anau Basin or in any other part of the study area. The thickness of these deposits is inferred to be up to 1,800 m (Landis, 1974).

2.2.2.2 Oligocene

Oligocene deposits within the study area include: Winton Hill Formation and the lower part of Waiau Group.

Winton Hill Formation

This marine formation comprises sandstones, siltstones and mudstones deposited during the Oligocene between the Mako Coal Measures and Forest Hill Formation with a thickness of approximately 500 m (Cahill, 1995). The lower 300 m of Winton Hill Formation is dominated by calcareous mudstone, whereas the upper 200 m consist predominantly of sandstone. A maximum thickness of 1,200 m of Winton Hill Formation has been recorded in lithological

GNS Science Consultancy Report 2015/123 10

Confidential 2015 logs in the Winton Basin (Cahill, 1995), but it lenses out beneath the Southland Plains (Isaac et al., 1990). This formation is laterally equivalent to the Waicoe Formation in the Waiau Basin and in part equivalent to the Chatton Formation in the Winton Basin (Isaac et al., 1990). The eastern limit of the Winton Hill Formation is unknown (Isaac et al., 1990).

Lower Waiau Group

Waiau Group comprises Oligocene and Miocene marine sedimentary rocks that overlie Nightcaps Group or Annick Group rocks in the Te Anau and Waiau basins. Outcrops are limited to the edges of these two basins and no Waiau Group deposits have been identified east of the Longwood Range and Takitimu Mountains. The lower Waiau Group (Oligocene) consists of sandstone and mudstone, conglomerates and breccias in channel-like structures, as well as minor limestone. These rocks are divided into many formations, including the Waicoe, Turret Peaks, Army Hut, Weydon, Point Burn, Spear Peak, Stuart, Boyd Creek, Birchwood, Blackmount, Dunton, Hauroko, Kaherekoau, Takoro, Waiohaka formations and Ligar Breccia. The total thickness of the Waiau Group (lower and upper) varies but can be as much as 3,000 m (Landis, 1974; Turnbull et al., 1993).

2.2.2.3 Miocene

Miocene strata in the project area include the upper part of Waiau Group, Forest Hill Formation, and East Southland Group.

Upper Waiau Group

Upper Waiau Group rocks are limited to the Te Anau and Waiau basins west of the Longwood Ranges and Takitimu Mountains. Rocks of this group have been mapped at the ground surface over a large part of the Waiau Basin, but surface outcrops in the Te Anau Basin area are mainly limited to the edges of the basin. The upper Waiau Group includes the following formations: Borland, Haycocks and McIvor as well as the lower Clifden Subgroup. They comprise primarily limestone-, sandstone- and mudstone-dominated formations. Shell- beds and lignites occur rarely.

Forest Hill Formation

Fossiliferous limestone of the Forest Hill Formation was deposited during the Late Oligocene to Early Miocene in a shallow-marine environment. Conglomeratic layers and channel-fillings are common in this formation (Hyden, 1980). Forest Hill Formation has been mapped mainly in the Winton Basin, with the largest areas east and south east of Winton. Isolated surface exposures are located near Castle Downs, in the eastern part of the Waiau Basin and around the Waimea Plains, however its subsurface extent is unknown (Isaac et al., 1990). The thickness of this formation in the eastern Waiau Basin is between 100 and 200 m (Landis, 1974; Turnbull et al., 1993) and a thickness of 240 m has been intersected in drillholes in the Winton Basin (Cahill, 1995).

Forest Hill Formation is not allocated to any stratigraphic group in the Winton Basin, but is assigned to the Clifden Subgroup of the Waiau Group in the Waiau Basin.

East Southland Group

Within the project area, East Southland Group includes the Chatton Formation and Gore Lignite Measures.

GNS Science Consultancy Report 2015/123 11

Confidential 2015

Chatton Formation

Chatton Formation was deposited in a marine environment and comprises partly shelly sandstone and sandy limestone (Isaac et al., 1990). Surface outcrops are located north and west of Gore and the formation has been identified overlying Winton Hill Formation in drillholes south of the Hokonui Hills near Hedgehope (Isaac et al., 1990) as well as just beyond the project area in Waikoikoi Valley, where it overlies Gore Lignite Measures (Lee et al., 2003). Chatton Formation has also been found unconformably overlying basement rocks at Bluff. This formation can be up to 150 m thick.

Gore Lignite Measures

Gore Lignite Measures were deposited in a terrestrial (deltaic to fluvial) environment during the Oligocene and Miocene and comprise mudstone, sandstone and conglomerate with intermittent lignite seams (Isaac et al., 1990). Correlation between individual lignite seams encountered in drillholes is difficult (Isaac et al., 1990).

The Gore Lignite Measures occur across much of Eastern Southland beneath the Southland Plains to at least to Waikoikoi in the east (Lee et al., 2003) and the Waikaia, Wendon, and Waimea Plains (Isaac et al., 1990) in the north. Outcrops occur southeast of the Hokonui Hills in the lower Mataura River valley and north of Gore, but there, the unit is largely covered by poorly-consolidated Quaternary sediments.

2.2.2.4 Pliocene

Strata of Pliocene age within the project area include Orepuki Formation, Prospect Formation, Pebbly Hill Gravel, and Te Waewae Formation.

Pebbly Hill Gravels

Pebbly Hill Gravels consist of sandy pebbly quartz conglomerate, with rare claystone and lignite, and are up to 150 m thick. The unit occurs predominantly south and southeast of the Hokonui Hills. The Pebbly Hill Gravels were likely to have been derived from the reworking of quartz gravels within the Gore Lignite Measures and, as a result, are difficult to distinguish lithologically from those deposits (Craw, 1992).

Prospect Formation

Prospect Formation comprises non-marine sandy conglomerate in the Te Anau Basin, and has a maximum thickness of approximately 3,000 m (Manville, 1996).

Orepuki Formation

Orepuki Formation consists of shallow marine sandstone, conglomerate, siltstone and mudstone and is known to occur in only a limited area south of the Longwood Range.

Te Waewae Formation

Te Waewae Formation consists of thinly-bedded shallow-marine sandstone and siltstone layers with shell-beds and conglomerate, which have been mapped at the surface in the southern part of the Waiau Basin.

GNS Science Consultancy Report 2015/123 12

Confidential 2015

2.2.3 Poorly consolidated Quaternary sediments

The strata of Quaternary age (formed the past 2.6 million years) were laid down after much of the tectonic activity had taken place that created the landscape of mountains, basins and valleys. The Quaternary sediments form a discontinuous mantle over an eroded terrain cut across the tectonically-deformed (e.g., tilted, folded or faulted) cover rocks and basement rocks. In most cases, the Quaternary sediments are no more than a few tens of metres thick (SKM, 2007; Hughes et al., 2011), although thicknesses of as much as 80 m have been identified in the Oreti Basin/Five Rivers Plain area (SKM, 2005). Thicknesses of as much as several hundred metres are possible in areas close to glacial lakes, where ice-age glaciers may have scooped out deep basins that were then filled with sediment. The thinness and relative youth of the Quaternary sediments means that, mostly, they have little or no consolidation. On geological maps, such as QMAP, Quaternary sediments are subdivided according to their relative age and the environment in which they were deposited. In Southland, geological maps distinguish between river deposits (also called alluvium), glacial deposits (also called till), swamp deposits, shoreline (e.g., beach) deposits, accumulations of windblown sand or silt (known as aeolian deposits), and deposits of landslide debris (Figure 2.3).

River deposits

Extensive sheets of gravelly river sediments occur in the central and eastern parts of the project area (Figure 2.3). They are associated with ancient abandoned river terraces or plains that stand above modern river levels, and also include the sediments that underlie the floors of the modern river valleys. The deposits have detailed local variability, with interlayers or lenses of silt or peat, and variable amounts of sand, silt or clay matrix between gravel grains. River gravels of different age commonly have different characteristics, relating to the catchment from which the gravel was sourced, and the degree of weathering that has occurred since it was deposited. For example, in the Waimea Plains, McIntosh et al. (1990) differentiate two sets of terraces in northeastern Southland. The older set of terraces are underlain by gravels that are more weathered, contain more clay, and have a different lithological composition (dominated by schist and quartz) and steeper gradient compared to the younger set of terraces underlain by less weathered gravel derived largely from a greywacke source rock.

The deposits of large rivers are usually gravelly and sandy, while those of small rivers or streams, especially those draining from hill country rather than mountain terrain, commonly contain much more silt or clay. These contrasts add much complexity to the hydrology of groundwater within these deposits.

Glacial deposits

Sedimentary deposits laid down by glaciers display much complexity and variability due to the nature of glacial processes. Rocky debris deposited at the margins of a melting glacier is generally a chaotic mass of angular boulders and gravel with varying amounts of sand, silt or clay. Where deposited at the underside of a glacier, the material is usually highly compressed and includes many abraded rounded stones in a dense silt or clay matrix. Both types of deposits are called ‘till’, and their extent is mapped based on a characteristic irregular landform, called moraine, that is developed on till deposits. Till deposits may contain irregular bodies of river deposits formed by meltwater streams alongside, and also underneath, the glacier (meltwater alluvium), and bedded lake silt and clay deposits formed in ice-margin lakes or ponds (proglacial lake sediments). Tills and proglacial lake sediments

GNS Science Consultancy Report 2015/123 13

Confidential 2015 generally have little or no permeability, but meltwater alluvium has good permeability, resulting in an overall complex groundwater hydrology associated with glacial deposits.

Alongside the lower reaches of a glacier, and extending down-valley from its terminus, are accumulations of outwash deposits, which are mapped geologically as river deposits.

In the study area, relatively young glacial deposits from the most recent glaciation occur near the margins of the main glacial lakes (Hauroko, Monowai, Manapouri, Te Anau and Mavora), and in the headwater catchments of those lakes, as well as in the valleys of formerly glaciated parts of the Takitimu and Eyre mountains (Figure 2.3). Remnants of older, weathered, glacial deposits, formed during previous glaciations, are preserved in the Te Anau Basin and at other scattered locations near the formerly glaciated areas (Figures 2.2 and 2.3).

Swamp deposits

Extensive peat swamps occur along the coast east of Bluff in the vicinity of Awarua Bay and Waituna Lagoon (Figure 2.3). Minor swamps are located in the Southland Plains and the Oreti River valley. The maximum known thickness of peat deposits associated with these swamps is 15 m, in the Awarua area. Commonly, the swamps grew as mounds on alluvial plain deposits, with the thickest peat under the highest part of the mound.

Shoreline deposits

Accumulations of sandy or gravelly beach sediments, and associated near-coastal deposits (Figures 2.2 and 2.3), include those associated with the present interglacial sea level of the past ~6,500 years, and those from previous interglacial episodes, which are preserved in remnant terraces at scattered locations. Localised areas of beach deposits are present along the shores of the larger lakes (Figure 2.3).

Aeolian deposits

Wind-blown silt deposits (loess) are widespread across the terraces and low hill country of Southland, below an altitude of about 300 m (Figure 2.3). Loess deposits are rarely shown on geological maps (e.g., QMAP, Turnbull and Allibone, 2003) because being relatively thin (typically a few metres thick at most) and locally extensive, their depiction would obscure the nature of the underlying geological materials. Soil maps generally provide useful information on the location and extent of loess deposits.

Sand dune deposits along the coastline are generally of very limited extent. However, extensive longitudinal and parabolic dune deposits occur along the coastline between Riverton and Invercargill (Oreti Beach). Peat deposits are common in hollows between dunes, though are rarely extensive enough to depict on geological maps.

Landslide deposits

Deposits of debris, formed by landslide movement, of sufficient extent to be mappable at 1:250,000 scale, are rare in the study area (Figure 2.3). The most prominent example is the debris of the Green Lake Landslide, in the Lake Monowai catchment (Fiordland), which is possibly New Zealand’s largest landslide (Hancox and Perrin, 2009). Much more widespread in the hill and mountain terrain are localised accumulations, typically no more than a few metres thick, of gravelly, sandy or silty material (colluvium) derived from erosion of the local bedrock. In all cases the composition of landslide debris or colluvium matches that of the local bedrock material.

GNS Science Consultancy Report 2015/123 14

Confidential 2015

Figure 2.3 Distribution of poorly consolidated Quaternary sediments by depositional environments (modified from QMAP; Heron 2014). The black outline represents the ES geological model boundary.

GNS Science Consultancy Report 2015/123 15

Confidential 2015

2.3 HYDROGEOLOGY

Basement rocks generally are not productive aquifers in New Zealand due to restricted pore space. However, as their permeability is predominantly controlled by fracture defects in the rocks (Yang et al., 2001), such locations of secondary porosity may provide a limited groundwater resource. In Southland, fractured basement rock aquifers occur, for example, in the Mataura River catchment, which is located within the eastern part of the study area (Hughes et al., 2011). Basement aquifers are utilised in hill areas where no other groundwater resources are available. Yields of up to 181 m3 per day have been measured in these aquifers, but their sustainability is unknown (Durie, 2001).

Southland’s cover rocks of Tertiary age are characterised by a heterogeneous lithological composition (e.g., sandstone, mudstone, limestone, conglomerate, lignite, etc., Section 2.2.2) and varying spatial distributions and thicknesses. These rocks are often located at depth. As a result, their hydrogeological behaviour is not well defined, but they are generally regarded as potential aquifers and may host significant groundwater resources (Rekker and Jones, 1998; Morgan and Evans, 2003; Hughes et al., 2011). Most of the groundwater in Southland’s cover rock aquifers is likely hosted in formations containing lignite measures, the Gore Lignite Measures in particular, and limestone formations (Rekker and Jones, 1998; Morgan and Evans, 2003; Hughes et al., 2011). Within formations containing lignite measures and mudstones, the lignite seams are considered impermeable or semi-permeable (Rissmann and Wilson, 2012), while interbedded sand and gravel deposits are regarded as aquifers (Hughes et al., 2011). In some cases, higher yields than in Quaternary alluvial sediments are achieved by angled drilling into these deposits at angles between 60 to 90 degrees (Rekker and Jones, 1998) to increase the length of contact the well has with the aquifer. The following descriptions of the Gore Lignite Measures aquifers are based on the work of Durie (2001). Three distinct aquifer units can be differentiated in the Gore Lignite Measures. Gore Lignite Measures Aquifer One is located in the upper Gore Lignite Measures and it comprises “discrete sandstone and gravel aquifers present in coalfield centres” (Durie, 2001). These are semi-confined to confined and are potentially connected to the Quaternary aquifers. This aquifer unit is of limited distribution (only present in coalfield centres), recharge is limited and yields are low. Gore Lignite Measures Aquifer Two, in the Middle Gore Lignite Measures, is confined and exhibits low recharge and yields, resulting in its limited use. This aquifer unit consists of “up to five discrete and discontinuous sandstone aquifers”, with varying extents and thicknesses, which are present between lignite and mudstone deposits. Gore Lignite Measures Aquifer Three is a confined aquifer unit that is located in the sandstone deposits of the Lower Gore Lignite Measures. These deposits have a minimum thickness of 80 m, are present throughout the entire Southland Plains, and house gravel horizons with groundwater-bearing potential. Yields of 100 m3 per day have been measured in this aquifer unit and it is considered to be a good prospect for a significant groundwater resource in the future (Durie, 2001). The groundwater resources hosted in Southland’s limestone formations are not well explored (Morgan and Evans, 2003). Rekker and Jones (1998) reported moderate yields from Forest Hill Formation limestone in the southwest of the Southland Plains. However, limestone deposits are very heterogeneous and may host high- yielding aquifers where solution-enhanced fissures create a karst network (Williams, 1982; Todd and Mays, 2005). Another unit with aquifer potential is the marine Chatton Formation that contains low-yielding confined aquifers within thick sandy layers.

GNS Science Consultancy Report 2015/123 16

Confidential 2015

The poorly consolidated Quaternary sediments contain an extensive groundwater resource that is widely utilised throughout Southland (Morgan and Evans, 2003; Wilson, 2011). For management purposes, ES have classed the generally shallow and unconfined Quaternary aquifers into riparian, terrace and lowland aquifers (Wilson, 2011). Riparian aquifers closely associated with the modern river systems and comprise highly-permeable gravel sediments that have been reworked from older deposits and re-deposited by recent river action. Older terrace aquifers comprise elevated sand and gravel terraces along main river valleys that are characterised by higher clay content than the younger terraces. This clay content is due to weathering and results in the older terrace aquifers having a lower permeability than riparian aquifers. Lowland aquifers comprise reworked glacial outwash deposits with low to moderate permeabilities (SKM, 2007; Wilson, 2011).

In summary, in Southland, Quaternary sediments are generally regarded as aquifers, Tertiary deposits may potentially be aquifers, and basement rocks are considered as non-aquifers. For the Quaternary, the internal aquifer/aquiclude structure is generally more important than differences between the named formations. As these hydrogeological-relevant structures are generally highly varied and complex, it would only be possible to model them at a very local scale (see Section 3.4.1).

GNS Science Consultancy Report 2015/123 17

Confidential 2015

3.0 METHODOLOGY

A combination of GIS (Geographical Information System, ESRI ArcGIS 10.1) and 3D geological modelling software (Leapfrog Geothermal 2.8) has been used to construct the ES geological model. The model has been constructed using the New Zealand Transverse Mercator projection (NZTM2000), following ES requirements.

This section describes: the process of 3D geological model building within the Leapfrog Geothermal software; data sources used for building the model and uncertainties associated with these data sources; the framework used to combine geological formations and groups into simplified model units; and the model units; and specific data used within each sub-area of the model.

3.1 MODELLING PROCESS

A 3D geological model is generally composed of a series of geological layers that are assembled by taking into account their relative chronology and structural relationships. The model developed in this report was built from a sequence of simplified geological layers, hereafter referred to as the ‘model units’, which correspond to an aggregation of individual geological formations and groups. These aggregations are decided by the modellers and in this case, the decisions were based on both geological characteristics and the available data for modelling, while taking into the account the purpose of the end-model, in this instance the creation of a flow model. The definition of the units to be modelled is a key step in the modelling process. Once defined, the contact surfaces between units are modelled from data points and their relative stratigraphy is established to allow the generation of representative volumes.

3.1.1 Unit definition

For this project, the QMAP geological maps (Turnbull et al., 2010; Turnbull, 2000; Turnbull and Allibone, 2003) and available geological sub-surface information have been used to: 1) identify geological formations in the model area, and 2) group all relevant geological formations and groups into model units. Then, using the digital seamless version of the QMAP geological map (Heron 2014) the polygons for all geological formations were assembled and merged into model unit polygons in ArcGIS.

The model unit polygons represent the locations where model geological units lie at the ground surface. Topographical elevation data for the boundary of each polygon was combined in Leapfrog Geothermal with subsurface data outside these polygons; to define the subsurface elevation of that geological unit derived from other data sources (discussed in Section 3.2). The upper limit of each model unit (i.e., contact surface) was then constructed through surface interpolation between all available scattered data points for a unit. The interpolation method used by Leapfrog Geothermal is based on Radial Basis Functions (RBFs), which is equivalent to Dual Kriging. One of the following types of contact surfaces can be selected, to best represent the underlying geological processes: erosion, deposition and intrusion. User-defined directional trends were used as input parameters of the RBFs, to constrain the interpolation to create representative geological surfaces. Local manual edits (control lines) can be added by the modellers to constrain the contact surfaces in areas with little input data. Finally, the modeller defines the surface’s relative chronology; and surfaces are assembled to produce a 3D stratigraphic volume model.

GNS Science Consultancy Report 2015/123 18

Confidential 2015

3.1.2 Structures

Faults are represented in the model as boundary surfaces that split the model area into sub- models. Leapfrog Geothermal requires that faults either extend through the entire model area or terminate at another fault. When several faults are created, their relative chronology and spatial relationships must be defined. The faults then split the model into separate ‘fault blocks’. Each of these fault blocks is essentially an individual geological model that can be composed of different input data, geological units and stratigraphic sequences compared to other fault blocks.

For the ES geological model construction, each fault surface was built by first digitising its surface location (‘fault trace’) on the geological map, then by transferring the trace onto the Digital Elevation model (DEM; Section 3.2.1) and finally using structural measurements with defined dip angles and azimuth to generate the surface. The ES geological model has seven faults that split the geological model into eleven individual fault blocks. The stratigraphy and input data for each fault block are discussed in Section 3.5.

3.1.3 Input data and uncertainties

Data sets available to create the ES geological model include: topographic data; bathymetric data; geological maps; geological cross-sections; well logs and interpreted geophysical data. These data sources are discussed in more detail below. Each of these datasets is subject to uncertainties, which are transferred to the geological model. Uncertainty in the vertical location of model unit boundaries (i.e., model unit tops and bottoms), may be comparatively small for where model units are exposed at the ground surface (only linked to the uncertainty of the geological maps). Layers below the ground surface will have more uncertainty because of the greater uncertainties of observations and interpretation for this data. The amount of input information available for a model unit provides constraints on the possible ranges of the model unit’s spatial extent (lateral and vertical). A model unit can be well constrained if, for example, many drillholes penetrate this model unit and underlying units, or poorly constrained due to lack of drillholes or other information. The spatial distribution of data is an important contributor to model uncertainty; another contributor is the uncertainty of the input data itself. Additional uncertainty may be introduced through the interpolation algorithm used to interpolate the model unit surfaces and the resolution chosen for the model surfaces. A surface that is created through one interpolation method can differ immensely if another interpolation method is used. The surfaces with directional trends that guide the interpolation within Leapfrog Geothermal require significant testing and adjustment by the modeller(s), to create interpolation surfaces that honour the data locations whilst remaining geologically reasonable. The more input data points that are available, the lower the uncertainty resulting from the interpolation method and the resultant modelled geological volumes.

GNS Science Consultancy Report 2015/123 19

Confidential 2015

3.2 MODEL DATA SOURCES

3.2.1 Digital Elevation Model (DEM)

An improved DEM was created by NIWA for the Joint Fluxes and Flows Programme was used to represent the ground surface elevation in the project area. This DEM was used to define the top surface of outcropping geological units (Section 2.0) and as the ground- surface datum for subsurface datasets (bore data, cross-sections, etc.).

The improved DEM has a horizontal resolution of 8 m by 8 m. It is based on the national Geographx 8 m DEM (Geographx, 2012), and includes additional topographic data to improve its accuracy, including (Kees, 2015): • LiDAR data (Waituna catchment, Edendale area and the Tiwai peninsula, provided by Solid Energy and Placer Investments Ltd). • Estuary bathymetry (Waiau, Jacobs and New river estuaries). • Real-Time Kinematic (RTK) GPS data collected by ES (elevations of road centre lines, drainage manholes, bore collar heights and where available ground elevations close to the bore, river thalweg elevations for major river main stems).

RTK data (e.g., bore collar heights) were added to the dataset, whereas spatially more extensive new datasets (i.e., LiDAR and bathymetry data) were substituted to the original data points. The improved DEM was then gridded using a thin plate spline algorithm (ANUSPLIN). For the purpose of geological modelling (to improve processing speeds), GNS down-scaled the DEM grid to a resolution of 240 m using ArcGIS before it was loaded into Leapfrog Geothermal 3D modelling software.

3.2.2 Bathymetry data not included in the DEM

Additional bathymetry data, not already included in the DEM, was provided by NIWA (Kees, 2015) for Lake Te Anau, Lake Manapouri, the Mavora lakes, Lake George, Haldane Bay, Waikawa Harbour, and Fortrose Estuary. The bathymetry data for the lakes comprised bathymetric contours, supplied as polyline shapefiles, with each contour having an elevation value relative to sea level or a depth attribute in metres below the lake surface. The latter were converted into elevation using the DEM. As these datasets were received by GNS after the 3D geological model had been completed, they were used to create a water-body volume representing the youngest layer in the geological model.

3.2.3 Geological maps

As outlined at the start of Section 2.0, the existing 1:250,000 scale QMAP geological maps represent the geological materials present at the ground surface, and therefore provide a major data source. Using the QMAP Seamless dataset (Heron 2014), 300 geological units in the study area were aggregated into eight modelled units in the 3D model (Section 3.4). The positional accuracy of the boundaries between QMAP polygons is assumed to be no better than +/- 250 m. It is important to note that the QMAP information is highly generalised, and many details that may be relevant locally to hydrogeology are not differentiated in the dataset. For instance, QMAP generally will not display a unit unless it is at least 10 m thick or geologically significant (Section 2.1.3).

GNS Science Consultancy Report 2015/123 20

Confidential 2015

3.2.4 Geological cross-sections

The published QMAP geological maps include interpretative subsurface geological cross sections. Cross-sections that lie within or near to the model area, were georeferenced and used as guidelines to establish the boundaries between modelled units where relevant (detailed in 3.5). Figure 3.1 displays the location of three QMAP Fiordland cross-sections (Turnbull et al., 2010), the one QMAP Wakatipu cross-section (Turnbull, 2000), and the two QMAP Murihiku cross-sections (Turnbull and Allibone, 2003) that are relevant to the modelled area. These cross-sections are presented at true scale (vertical scale equals horizontal scale of 1:250,000), and extend to a depth of 5 km below sea level. Therefore, the Quaternary sediments are commonly too shallow to be depicted accurately. Information from the cross-sections, or parts thereof, was not used for modelling where there were other data available with a lesser uncertainty (e.g., drillholes).

Two geological cross-sections from Blakemore (2006), derived from the analysis of seismic reflection, resistivity and gravity data in the Oreti Basin, have also been used to delineate the boundary between Basement and Quaternary in that area (Figure 3.1). In a few small areas, geological cross-sections have been used from previous gravity modelling to delineate the top of the basement surface (Broadbent et al., 1980; Woodward and Kicinski, 1983).

GNS Science Consultancy Report 2015/123 21

Confidential 2015

Figure 3.1 (left) QMAP seamless geological map, fault lines and cross-section parts used for modelling, for the full legend see Figure 2.1 (The cross-sections were only used in areas where there was no other, more accurate data available); and (right) simplified model units and faults.

GNS Science Consultancy Report 2015/123 22

Confidential 2015

3.2.5 Geophysical Data

3.2.5.1 Western Southland seismic data

Seismic reflection is a method of geophysical surveying in which vibrations (seismic waves) are set off at the ground surface, and the seismic wavefield is recorded. The recorded wavefield exhibits signs of what the waves have encountered underground and the timing of return of the waves is a measure of geological conditions at different depths underground. A strong seismic reflection occurs where there is a marked change in geological material (e.g., material density), such that the velocity of the seismic wave is changed considerably. As the seismic velocity of geological material is linked to both rock composition and strength, prominent reflectors (‘seismic horizons’) are interpreted to represent the boundaries between different geological strata. The strength and character of the reflectors influences how they are interpreted geologically (Lowrie, 2006).

A wealth of seismic reflection data has been collected in western Southland for petroleum exploration. Turnbull et al. (1993) used the seismic information collected prior to 1980 to produce subsurface elevation contour maps (‘structure contours’) on the boundaries of different-age packages of geological strata (e.g., Figure 3.2). The maps from Turnbull et al. (1993) were digitised to create data points for modelling (Figure 3.3). The contour data extend to a maximum depth of -8,000 m AMSL and cover approximately an area of 3,700 km2. Table 3.1 describes the interpreted seismic horizons that delineate the boundaries of modelled units.

An additional two seismic lines were collected in the Mossburn area, covering approximately 10 km W-E profile, and interpreted to geological boundaries (Zehnder, A./FMG Pacific Ltd, 2011). These data sets were incorporated into the model as follows: top of Basement model unit equivalent to the bottom of Oruea mudstone; top of Eocene model unit equivalent to bottom of Waiau group; top of Oligocene model unit equivalent to bottom of Forest Hill Formation; bottom of Quaternary model unit equivalent to bottom of Quaternary.

Figure 3.2 Example of a portion of a structure contour map (in km below ground level) for the top of Cretaceous-age strata in the Waiau Basin (from Turnbull et al., 1993). For this project, the contours were digitised to create data points to help define boundaries between modelled units. Contour maps for other geological age boundaries were also digitised.

GNS Science Consultancy Report 2015/123 23

Confidential 2015

A’

A

A A’

Figure 3.3 Top) Map view and Bottom) cross-section view of data points digitised from contour maps of different geological horizons from Turnbull et al. (1993). Elevations in bottom view (vertical axis) are in m AMSL. Colours denote the model geological unit to which the data apply. The red outline marks the study area.

GNS Science Consultancy Report 2015/123 24

Confidential 2015

Table 3.1 Data from Turnbull et al. (1993) used in modelling.

Modelling Seismic reflector(s) Reference map in Comment classification Turnbull et al. (1993)

Top of Basement Top of the Cretaceous. Map 12 (structure of Cretaceous sediments are Where Cretaceous strata Cretaceous). not considered basement absent, taken from the Map 8 (structure of in Turnbull et al. (1993). base of cover rock Basement). sequences.

Top of Eocene Boundary between Map 15 (structure of Nightcaps Group (older) Eocene). and Waiau Group (younger). Top of the Sandfly Formation and top of the Earl Mountain Sandstone (Annick Group). Top of Oligocene Base of Te Karara Map 18 (structure of Te Karara Formation is Formation and McIvor Oligocene). within the Clifden Sub- Formation. group in Turnbull et al. (1993), but not differentiated on the QMAP sheet. Top of Early Miocene Top of sandy limestone of Map 23 (structure of Early the Forest Hill Formation. Miocene). Top of the limestone- dominated McIvor Formation. Top of the carbonate-rich part of the Clifden Sub-group. Top of the Pareora Series. Base of the Prospect Formation. Top of Miocene Top of Rowallan Map 24 (structure of Sandstone. Base of the Miocene). Te Waewae Formation. Base of the well-bedded portion of the Prospect Formation.

3.2.5.2 Winton Basin seismic data

Cahill (1995) used seismic data collected by Amoco in 1986 in the Winton Basin to create contour maps of seismic horizons. These maps have been digitised to create data points for modelling with contours recalculated to ‘value – 100 m’, as Cahill (1995) uses a vertical datum that is +100 m relative to sea level. These contours extend to a maximum depth of – 2600 m AMSL and covers approximately 1,200 km2. Table 3.2 describes the surfaces that delineate the boundaries of modelled units.

An additional two seismic lines were collected in the Wreys Bush area, covering approximately 15 km N-S profile, and interpreted to geological boundaries (Zehnder, A./FMG Pacific Ltd, 2011). These data sets were incorporated into the model as follows: top of Basement model unit equivalent to the bottom of Oruea mudstone; top of Eocene model unit equivalent to bottom of Waiau group; top of Oligocene model unit equivalent to bottom of Forest Hill Formation; bottom of Quaternary model unit equivalent to bottom of Quaternary.

GNS Science Consultancy Report 2015/123 25

Confidential 2015

A’

A

A’ A

Figure 3.4 Top) Map view, and Bottom) cross-section view of data points digitised from Winton Basin structure contour maps of different geological horizons (Cahill, 1995). Elevations in bottom view (vertical axis) are in m AMSL. Colours denote the model geological unit to which the data apply. The red outline marks the study area.

GNS Science Consultancy Report 2015/123 26

Confidential 2015

Table 3.2 Data used in modelling from Cahill (1995).

Modelling Seismic reflector(s) Reference map in Comment classification Cahill (1995) Top of Basement Top of Permian, Triassic Figure 6 (Basement Cretaceous sediments are and Jurassic basement. structure map). not present within the Winton Basin. Top of Eocene Base of the Winton Hill Figure 7 (Early Oligocene Corresponds to top of the Formation. structure map). Mako Coal Measures and top of the Beaumont Coal Measures that are both Eocene deposits. Top of Oligocene Base of the Forest Hill Figure 8 (Early Miocene Consistent with Table 3.1 Formation limestone unit structure map). for the Forest Hill Formation limestone unit to be placed within the Early Miocene.

3.2.5.3 Gravity data

Gravity measurements are available from the New Zealand Gravity Station Network (GNS Science, 2013; Stagpoole, 2012). These data have had all standard gravity processing steps previously applied to them, with a density of 2.67 Mg/m3 used for all Bouguer and terrain corrections (Stagpoole and Woodward, 2004; Stagpoole, 2012). Isostatic gravity anomalies are generally used for modelling (Lowrie, 2006; Mumme, 1981; Stagpoole and Woodward, 2004), as the calculation of isostatic anomalies includes a correction for long-wavelength features that aims to focus the anomaly map on density distributions in the upper crust. A spline-interpolated map of isostatic gravity anomalies for the ES model area (Figure 3.5) was used. Modelling of gravity anomalies to obtain estimates of model unit thicknesses is beyond the scope of this work, therefore, this map has been used simply as a visual aid for checking the expected versus modelled basement depth and to guide manual edits (see Section 3.5).

Negative gravity anomalies correspond to areas with subsurface materials with densities <2.67 Mg/m3 (younger sediments rather than basement) and positive anomalies correspond to areas where the materials have a greater mass than would be expected from the isostatic model. The more negative the anomaly, the greater the volume of lower density sediments. In the Southland area, large isostatic anomalies are largely caused by the variation in basement rock type: the positive yellow/orange anomaly band extending from the northwest to eastern part of the model area coincides with the higher density ultramafic Dun Mountain Matai Terrane basement rock; and likewise the brown band beginning in the centre of the model and extending along the southern shoreline coincides with the mafic Brook Street Terrane basement rock (Figure 2.1).

GNS Science Consultancy Report 2015/123 27

Confidential 2015

Figure 3.5 Spline-interpolated Isostatic gravity anomaly map for the model area. All available gravity measurements (GNS Science, 2013) were used for the interpolation. Negative gravity anomalies correspond to areas with thick sequences of cover rock strata and positive anomalies denote areas where the mass is greater than expected from the Isostatic model (for example due to material with a density greater than 2.67 Mg/m3).

GNS Science Consultancy Report 2015/123 28

Confidential 2015

3.2.6 Borehole data

Three different sets of borehole records (logs) were used to constrain the subsurface distribution of geological formations. These datasets were: a) logs from the ES bore database; b) logs from coal exploration National Coal Resources Survey (NCRS) bores (Ministry of Business, Innovation and Employment, 2014); and c) logs from petroleum exploration bores (Ministry of Business, Innovation and Employment, 2014).

Some of the bores are listed in both the ES and the NCRS database. The following sections describe characteristics, processing and limitations of these bore datasets.

3.2.6.1 Logs from the ES bore database

Logs from 2,585 bores were provided by ES (Figure 3.6) as a Microsoft Excel file with two worksheets. One worksheet listed the general information for each bore, including ID number, location as New Zealand Map Grid (NZMG) coordinates, screen information and hole depth. The second worksheet listed ID, depth of the bottom of each logged interval, a lithology short code (‘LITHOLOGY_CODE’) and an extended lithological description of the logged interval (‘STRATA_DESCRIPT’). This interval table contained 22,778 logged lithological intervals. The majority of these bores are less than 200 m deep (Table 3.3). To display and process the data in ArcGIS and Leapfrog Geothermal, the NZMG coordinates were converted into the NZTM2000 projection, in accordance to ES requirements. Bore locations and lithological logs were joined into one dataset in ArcGIS and then transferred to Leapfrog Geothermal for further processing and modelling.

Table 3.3 Number of bores in the ES bore database by depth range.

Depth range Number of bores

0 – 10 m 585

10 – 20 m 602

20 – 50 m 657

50 – 100 m 325

100 – 200 m 255

200 – 400 m 156

400 – 1956 m 5

The large number of bores with lithological descriptions makes the ES bore dataset an important resource for the 3D geological modelling. However, it should be kept in mind that this data is also subject to considerable uncertainty. Lithological descriptions vary with the driller and drilling method, and are not subjected to any quality control. As is common for most water bore datasets, the holes are mostly non-cored, and the lithological interpretations are mostly based on driller’s logs of cuttings, i.e., notes on the materials encountered and drilling conditions made by the driller of the bore. This means that there may be uncertainties about the geological interpretation of the logs. The driller’s descriptions (‘STRATA_DESCRIPT’) are summarised as one of 42 lithological short codes (‘LITHOLOGY_CODE’) when the log was processed by ES staff, which introduces another potential source of uncertainty. For example, the lithology short code ‘GW’ corresponds to

GNS Science Consultancy Report 2015/123 29

Confidential 2015 the lithology ‘Greywacke’, which is another term for a general type of basement rock. As an example, in bore F44/0270 ‘GW’ is used as code for ‘Greywacke and gravels’ that are likely to be younger sediments derived from basement rocks as indicated by the descriptor ‘gravels’. Additionally, the descriptor ‘SH’ for ‘shell’, which may indicate the existence of certain geological units, is missing in a third or more of the lithological codes that refer to logged strata including shell. This highlights that although the dataset is extensive across the region, it does not necessarily provide a high degree of certainty in the correctness of the interpretation of the subsurface geology.

Another difficulty is that the lithological logs generally do not include an interpretation of to which geological unit a particular interval relates. A 3D geological model is constructed from boundaries between geological units, therefore, these boundaries have to be inferred from the lithological logs in the ES bore dataset. This can be done manually or in an automated way. The large number of bores and lithological descriptions meant that a manual interpretation was only possible in small areas of interest, and an automated method of interpreting the lithology short codes was applied in general. For example, basement rocks have been assigned the lithology code ‘baserock’ in the ES database. This code has been used to identify the top of basement rocks in the ES bores (‘baserock contacts’). As there were fewer ‘GW’ occurrences, these were checked manually to determine if they are likely to correspond to basement or a younger unit containing greywacke gravels. The base of the Quaternary (‘Quaternary contacts’) has generally been identified using the first occurrence of mudstone, lignite or sandstone in the lithological logs, as general Quaternary lithology descriptors like gravel or sand can also occur in older geological units (e.g., Gore Lignite Measures, Section 2.2.2.3) in the model area.

Following the automated interpretation, manual interpretation was then performed following an interrogation of modelled volumes to identify suspected inaccuracies.

GNS Science Consultancy Report 2015/123 30

Confidential 2015

Figure 3.6 (left) Distribution and depth range of bores with lithological logs in the ES database; and (right) NCRS coal and petroleum explorations bores with geological logs.

GNS Science Consultancy Report 2015/123 31

Confidential 2015

3.2.6.2 Logs from coal exploration bores

Logs from 502 NCRS coal exploration drillholes in the project area (Figure 3.6) were received as digital datasets from a GNS in-house database that accesses data from Ministry of Business, Innovation and Employment (2014). The GNS database was last updated on the 14/01/2014 (Scadden, 2015). The vast majority of these bores are located in the eastern Southland Plains between Winton and Gore. Of these 502 bores, 140 reached basement rock. In all cases, these bores have logs compiled by geologists, either from examination of drill cores, or from inspection of cuttings.

Table 3.4 Number of coal exploration bores in the study area by depth range.

Depth range Number of bores

0 – 10 m 1

10 – 20 m 1

20 – 50 m 11

50 – 100 m 85

100 – 200 m 248

200 – 400 m 156

Most of the NCRS bores are also recorded in the ES bore database. However, there are significant differences in the log descriptions between these two databases. While the ES database records the lithological descriptions in detail throughout the entire log, the NCRS dataset available lists a geological formation for each logged interval and aggregates the Quaternary sediments as ‘Undifferentiated Quaternary’. Therefore, each database has its advantages and disadvantages for the 3D modelling. The top of geological formations are relatively easy to identify from the coal exploration logs, but the lithological ES bore dataset contains a greater number of bores, more widely distributed throughout the project area. Furthermore, a potential identification of the inner structure of the Quaternary would not be possible with the sole coal bore dataset. For these reasons, both data sets were used individually but greater emphasis was given to the NCRS dataset.

The majority of the coal exploration bores in the study area were drilled to a depth between 100 and 200 m (Table 3.4). Therefore, the use of these bores will likely result in a comparatively low uncertainty in the geological model in the eastern Southland Plains to a depth of up to 400 m.

3.2.6.3 Logs from petroleum exploration bores

Petroleum exploration bore records (Ministry of Business, Innovation and Employment, 2014) were searched to extract reports on petroleum bores in the model area (Figure 3.6). Relevant bore logs were digitised from the reports obtained. Petroleum bore logs, like coal exploration bore logs, have been recorded by geologists and include geological formations, greatly aiding geological 3D modelling. Throughout the model area, 23 petroleum bores of interest for the modelling were identified and used to constrain subsurface extents of model units. The depth of these bores ranged between 57 and 2009 m and the majority of the bores are located around the northern part of the Waiau Basin.

GNS Science Consultancy Report 2015/123 32

Confidential 2015

3.2.6.4 Bore distribution

The spatial distribution of the bores throughout the model area and their depths are an important factor in the model uncertainty. There are large parts of the model area that have hardly few if any bores (Figure 3.6). As bores generally provide the most accurate subsurface datasets for geological modelling, the geological model will have a much larger uncertainty in areas with few bores. There is a concentration of bores throughout the Southland Plains, but very few bores in the Te Anau and Waiau basins. Bore depth is a constraining factor for geological modelling where the majority of bores are shallow. Most bores in the ES database were drilled to depths of less than 100 m, and only 5 bores are deeper than 400 m (Figure 3.6). As a result, the uncertainty of the model information derived from the logs increases immensely with model depth. For example, the western Southland Plains are characterised by a large number of bores, but most are relatively shallow compared to the bores in the eastern Southland Plains, and few of them penetrate to the base of the Quaternary deposits. Therefore, the model uncertainty, based on the bore dataset, is much higher than in western than in the eastern Southland Plains, where many bores (the coal exploration bores in particular) have been drilled through the Quaternary and into the Gore Lignite Measures or even the basement, which is comparatively shallow in that area.

3.3 LOCATION OF FAULTS

A large number of faults dissect the study area (Figure 2.1), and of these, seven are used within the model (Figure 3.1). The amount of faults represented in the model is restricted as each fault splits the model into separate fault blocks, and these are then treated by Leapfrog Geothermal as an individual geological model which results in increased processing time. The selection of faults was, therefore, primarily a compromise between representing the structural geology at the regional scale and model processing runtime. The seven faults used within the model, split the model into eleven different fault blocks (Section 3.5).

These seven faults were selected based on their regional and hydrological significance, after discussions with ES, in accordance with Leapfrog Geothermal modelling requirements, and taking into account the time constraints on this project. Leapfrog Geothermal requires that faults either extend through the entire model area or terminate at another fault. To meet these requirements, fault locations from QMAP had to be simplified and in some cases extended. The model faults were created using the following method: 1. Identify the most significant faults in ArcGIS; 2. Draw simplified versions of these faults in Leapfrog Geothermal (using the QMAP fault layer as a guide); 3. Build the fault surface in the geological model from the GIS line projected on the topography (using dip angles and trends); 4. Add more structural measurements at depth using the fault traces on the cross- sections as a guide (see Table 3.5).

The Castle Rock and the Lumsden faults were digitised from a map within Blakemore (2006), as these faults are not represented in the QMAP fault database (too small). Although these faults are relatively small, they were included in the model at the request of ES, because of their local hydrogeological significance: the Castle Rock Fault is known to truncate Quaternary sediments and restrict groundwater connectivity and the Lumsden Fault is thought to define a boundary between different aquifers in the area (Blakemore 2006). To create a fault line that was usable in Leapfrog Geothermal, these faults lines were extended to terminate against larger faults from QMAP.

GNS Science Consultancy Report 2015/123 33

Confidential 2015

Table 3.5 Information on the geometry of faults in the model. Note that in most cases, the depiction of fault dips and extent in cross-sections is based on interpretation and inference rather than on data.

Fault name Fault geometry

Te Anau – Hauroko Fault Fiordland A cross-section: sub vertical Wakatipu C cross-section: vertical QMAP attribute for Te Anau segment: dextral, dip and dip direction unknown, down quadrant E and SE QMAP attribute for Hauroko segment: dextral, strikeslip, reverse, Moonlight Fault zone, subvertical, dip direction unknown to 320, down quadrant SE Moonlight Fault System Wakatipu C cross-section: vertical Murihiku B cross-section: sub-vertical near surface. Slight inclination to the E at greater depth QMAP attribute: reverse, down quadrant NW, dip and dip direction unknown

Livingstone Fault Wakatipu C cross-section: vertical Murihiku B cross-section: 60° E Murihiku A cross-section: sub-vertical near surface. At depth, dip to N (out of model boundary) QMAP attribute: dextral, normal, reverse, down quadrant SW and W, dip unknown Hillfoot Fault Murihiku A cross-section: sub-vertical near surface. At depth (greater depth than model, slight inclination to NE) Murihiku C cross-section: sub-vertical near surface. Slight inclination to the SW at greater depth Murihiku B cross-section: sub-vertical near surface. Slight inclination to the E at greater depth QMAP attribute: reverse, dip and dip direction unknown, down quadrant mostly NE and a few SW Scotts Gap – Hedgehope – Waikaka Murihiku C cross-section: sub-vertical near surface. Slight inclination to Fault the north at greater depth QMAP attribute for Scotts Gap segment: reverse, dip and dip direction unknown, down quadrant SW (at boundary with Waiau Basin), down quadrant NE by Wilson Basin. QMAP attribute for Waikaka segment: reverse, dip and dip direction unknown, down quadrant SE QMAP attribute for Hedgehope segment: reverse, dip and dip direction unknown, down quadrant SE and locally S Lumsden Fault Blakemore (2006) cross-section: vertical (Blakemore 2006) Fault not in QMAP fault database or Active Fault database

Castle Rock Fault Blakemore (2006) cross-section: reverse, sub-vertical (Blakemore 2006) Fault not in QMAP fault database, small part of the fault in Active Fault database, however no information about dip and dip direction.

As described in Section 3.1, when several faults are created, their relative chronology and spatial relationships must be defined by the user to meet Leapfrog Geothermal requirements (Table 3.6). These definitions are highly generalised, and do not imply any direct knowledge of the actual nature and age of each fault.

GNS Science Consultancy Report 2015/123 34

Confidential 2015

Table 3.6 Modelled faults and fault interactions.

Fault name Fault interaction

Te Anau – Hauroko Fault No interaction with other faults

Moonlight Fault System No interaction with other faults

Livingstone Fault Crosses over Moonlight Fault

Hillfoot Fault Terminates against Moonlight Fault – East side

Scotts Gap – Hedgehope – Waikaka Fault Crosses over Hillfoot Fault Crosses over Livingstone Fault Terminates against Moonlight Fault – East side

Lumsden Fault Terminates against Hillfoot Fault – Northeast side Terminates against Livingstone Fault – Southwest side

Castle Rock Fault Terminates against Livingstone Fault – Southwest side Terminates against Lumsden Fault – West side

Uncertainties are associated with the location of faults, as well as their dip angle and direction. Faults are mapped at the ground surface if a fault trace can be identified, however, the distribution of these features at depth can be quite speculative. Older faults may also be covered by younger sediments and fault traces in the QMAP or Active Fault databases (GNS Science, 2014) may not show the entire fault line.

3.4 GROUPING OF GEOLOGICAL UNITS

The actual geological modelling process starts with the grouping of geological formations within the study area that are mapped at the ground surface, or have been logged at depth, into model units (Figure 3.1). Grouping of geological units is generally required when it is not feasible to model all geological formations due to constraints like geological complexity, data quality, size of the model area, and time available to build the model. The project objectives must also be taken into account if the geology is only one aspect of the greater scope of the model, like for example, geotechnical or hydrogeological applications. Due to the large size of the ES geological model and the complex geological structure encompassing a high number of geological formations, aggregation into model units was essential for the development of the ES geological model.

The grouping of units was decided based on the available seismic data (Cahill, 1995; Turnbull et al., 1993) as that provides by far the most reliable and comprehensive high resolution sub-surface dataset available. Indeed, it would not have been possible to model the Te Anau, Waiau and Winton basins without the seismic interpretations, because other subsurface information, such as from bores, is sparse in those areas. As the seismic interpretations are classified by age, the majority of the model units were aggregated based on this parameter. As an exception, the East Southland Group was modelled separately from other Miocene deposits in eastern Southland, because the numerous high-quality geological logs from coal exploration bores allowed a well-constrained subsurface differentiation of this unit, and also because it is regarded to be of hydrogeological significance.

GNS Science Consultancy Report 2015/123 35

Confidential 2015

The following model units are represented in the 3D model, in order from youngest to oldest: • Quaternary • Pliocene • Miocene/East Southland Group • Early Miocene • Oligocene • Eocene • Basement

As the poorly-consolidated Quaternary sediments are of particular interest for groundwater investigations, several approaches were tested to achieve a differentiation of the detailed architecture of the Quaternary sediments throughout the model area. Following these tests, it was decided not to pursue any Quaternary sediment differentiation within the ES geological model due to the regional scale of the model and local complexities. These tests are described in the following section for future reference.

3.4.1 Approaches for differentiation of the Quaternary sediments

A manual stratigraphic and an automated lithological approach were tested to differentiate the Quaternary sediments throughout the model area. For this, the ES bore data was investigated as this is the only sub-surface dataset that included a detailed description of the Quaternary deposits.

As the 3D geological model was based mainly on stratigraphy (see Section 3.1), a stratigraphic method was investigated first. This method involved a manual assessment of the ES lithological logs. However, even though the logs contain information about the lithological composition of the material, they lack the level of detail required to differentiate, for example, Holocene from Pleistocene materials. For example, as mentioned in Section 2.1.3, deposits under different-age terraces can be differentiated by clay content, clast lithology and gradient of the terrace surfaces (McIntosh et al., 1990), but this information is rarely, and certainly not uniformly, recorded in the driller’s logs. Furthermore, a detailed manual analysis of the lithological logs throughout the entire large model area was not possible within the scope of this project.

The second method investigated used a lithological approach to the differentiation of Quaternary sediments. Although not stratigraphic, this was considered a viable option within the intended purpose of the ES geological model, which is to provide a foundation for groundwater flow and transport modelling. This approach focussed on finding an automated way to subdivide the Quaternary sediments into lithologies that have a strong positive or negative influence on groundwater flow. These lithologies could be, for example, sands and gravels on one side and silts and clays on the other. The intrusion surface option in Leapfrog Geothermal allows the modelling of ‘lenses’ based on selected descriptors in the bore database. The lithology short codes can be used to identify clean sand and gravel deposits and deposits made only of silt and clay. A minimum thickness can be specified as well as a thickness of interbedded other layers that can be ignored in the intrusion modelling. The shape and extent of the resulting ‘lenses’ can also be influenced by manual adjustment of the anisotropic modelling input parameters. However, due to the large model area it was not possible to build geologically reasonable structures. Such an approach would only be suitable for building small, local models.

GNS Science Consultancy Report 2015/123 36

Confidential 2015

A similar approach could be used in the future to identify the extents of organic deposits in the model that may have an influence on groundwater quality. The content of organics can be determined from the lithology short codes and the subsurface extent could potentially be determined through the computation of intrusional surfaces combined with the surface extents of organic deposits from the QMAP. This was tested for a larger Holocene peat area west of Waituna Lagoon, but the analysis of the bore logs in this area showed that the young peat sediments only have a thickness between 0.5 and 1 m and are, therefore, not representable in a regional scale model.

3.5 MODEL STRATIGRAPHY AND INPUT DATA PER FAULT BLOCK

The seven faults were used to split the model into eleven fault blocks (Figure 3.7). The information used to define the subsurface extents for each surface in each fault block is described below, along with the modeller’s decisions for surface chronology and any manual edits. Manual edits are necessary in data sparse areas, to control the behaviour of the surfaces. For example, if the interpolation function extends a model unit into an area where it does not occur naturally. Due to the very large area and limited time, manual fine-tuning of surfaces has only been performed when the edits that have been carried out had a significant impact over larger areas. Additionally, where model units’ surface extents were limited and subsurface data was not available, these units were not modelled, due to the lack of available information to constrain these units. Details are given in the relevant sub-section below, on a case by case basis.

As aforementioned, all geological constraints of where the units have been mapped at the ground surface have been derived from the digital QMAP vector data in combination with the DEM. The polygon boundaries of modelled units used at the elevation of the DEM are displayed in Figure 3.7. It was also necessary to create ‘buffer’ lines from these polygons, to direct modelled surfaces above the DEM. This is necessary as the model is cut at the top by the DEM during the model volume building process, and this ensures a clean outcrop area for each model unit. For example, for the basement surface, as well as the surface QMAP lines being used, internal buffer lines of QMAP outlines at 100 m, 500 m, 700 m, 1000 m, 1500 m, 2000 m, 3000 m, 4000 m, 5000 m are also used with elevations set as 1.5 times the value of the DEM. The number and location of buffer lines required, depends on the gradient of elevation increase for a modelled unit. Such data were used for all modelled units and is not listed explicitly in the data tables for each fault block.

GNS Science Consultancy Report 2015/123 37

Confidential 2015

Figure 3.7 Fault blocks (numbered), and colour-coded model units.

3.5.1 Fault block 1: Fiordland

The Fiordland fault block lies on the western boundary of the model (Figure 3.7). It abuts fault block 2 (Waiau and Te Anau Basins) and its surface geology is characterised by steep basement hills and narrow valley floors underlain by Quaternary. On the eastern portion of the fault block, abutting to the Waiau and Te Anau Basins, there is localised surface geology of Eocene, Oligocene, Early Miocene, Miocene, and Pliocene. Additionally, large lakes (e.g., Lake Te Anau, Lake Manapouri) cover a significant portion of the area, under which the geology has not been mapped and as such there is no surficial constraining geological information. The two largest lakes, Te Anau and Manapouri, are represented by modelled water-body volumes created from bathymetry data provided by Kees (2015) (see Section 3.2.2). The subsurface data used for modelling within the fault block is outlined in Table 3.7. The only subsurface data available in the area comes from the Fiordland cross-sections A

GNS Science Consultancy Report 2015/123 38

Confidential 2015 and B (Turnbull et al., 2010). These cross-sections depict basement rocks at the surface throughout most of the fault block. Seismic data for the Waiau and Te Anau Basins contributed only minor information at the eastern boundary of the fault block.

Pliocene and Miocene have no subsurface data, but their minor geological surface extents only occur close to the Waiau and Te Anau Basins.

A control line (FB1_West) has been created to constrain the Oligocene, Early Miocene, Miocene and Pliocene units’ top surfaces using the QMAP extent of these units as a guide because all of these units do not extend to the west. A control line (Eocene FB1_West) has been created to constrain the top surface of the Eocene unit using the depth of the shallowest nearby seismic data as a guide.

Table 3.7 Fault block 1 surface chronology and subsurface data and manual control lines.

Surface chronology Subsurface data and manual control lines

Quaternary N/A

Pliocene Control line FB1_West

Seismic data for the Te Anau Basin (Turnbull et al., 1993) Miocene Control line FB1_West

Early Miocene Control line FB1_West

Seismic data for the Te Anau Basin (Turnbull et al., 1993) Oligocene Control line FB1_West

Fiordland QMAP cross-sections A and B (Turnbull et al., 2010) Eocene Seismic data for the Te Anau Basin (Turnbull et al., 1993) Control line Eocene FB1_West

Fiordland QMAP cross-sections A, B and C (Turnbull et al., 2010) Basement Seismic data for the Waiau and Te Anau Basins (Turnbull et al., 1993)

3.5.2 Fault block 2: Waiau and Te Anau basins

The Waiau and Te Anau basins fault block extends from north to south through the western portion of the model (Figure 3.7). It abuts fault blocks 1, 3, 4, 5, and 7 (Fiordland, Wakatipu, Southland Plains, Central, and Mossburn) and its surface geology is characterised by two deep basins filled with Cretaceous and Cenozoic sediments and bounded by steep basement hills. Additionally, large lakes (e.g., Lake Te Anau and Lake Manapouri) cover some portions of the western area, under which the geology has not been mapped and as such there is no constraining geological information available. The two largest lakes, Lake Te Anau and Lake Manapouri are represented by modelled water-body volumes created from bathymetry data provided by Kees (2015) (see Section 3.2.2). The subsurface data used for modelling within the fault block is outlined in Table 3.8.

The most comprehensive source of subsurface data in this fault block is the seismic data for the Waiau and Te Anau Basins (Turnbull et al., 1993).

Three control lines (Quat_ctrl_FB2, Quat_ctrl_FB2_b, Quat_ctrl_FB2_c) have been created in areas where no data points were available, to adjust the Quaternary surface exposure to follow the extent of Quaternary sediments depicted on the geological map. A control line (FB2_North) has been created to constrain the Early Miocene top surface using the depth of

GNS Science Consultancy Report 2015/123 39

Confidential 2015 the shallowest nearby seismic data as a guide. Control lines (FB2_beneathMiocene, Basement FB2_beneathMiocene) have been created to ensure that the Oligocene, Eocene and basement are located below Miocene seismic data points. A control line (FB1_West) has been created to constrain the depth of the top Eocene surface using the depth of the shallowest nearby seismic data as a guide.

Table 3.8 Fault block 2 surface chronology and subsurface data and manual control lines.

Surface Chronology Subsurface data and manual control lines

ES bores (Quaternary contacts excluding ‘baserock’ contacts) Control line Quat_ctrl_FB2 Quaternary Control line Quat_ctrl_FB2_b Control line Quat_ctrl_ FB2_c

Pliocene ES bores (Quaternary contacts excluding ‘baserock’ contacts)

Petroleum bores (Miocene contacts) Miocene Seismic data for the Waiau and Te Anau basins (Turnbull et al., 1993)

Petroleum bores (Early Miocene contacts) ES bores (limestone contacts) Early Miocene Seismic data for the Waiau and Te Anau basins (Turnbull et al., 1993) Control line Early Miocene FB2_North

Petroleum bores (Oligocene contacts) Oligocene Seismic data for the Waiau and Te Anau basins (Turnbull et al., 1993) Control line FB2_beneathMiocene

Fiordland QMAP cross-sections A, B and C (Turnbull et al., 2010) and Wakatipu QMAP cross-section C (Turnbull, 2000). Petroleum bores (Eocene contacts) Eocene Seismic data for the Waiau and Te Anau basins (Turnbull et al., 1993) Control line FB1_West Control line FB2_beneathMiocene

Fiordland QMAP cross-sections A, B and C (Turnbull et al., 2010); Wakatipu QMAP cross-section C (Turnbull, 2000); and Murihiku QMAP cross-section B (Turnbull and Allibone, 2003) Basement ES bores (‘baserock’ contacts) Seismic data for the Waiau and Te Anau basins (Turnbull et al., 1993) Control line Basement FB2_beaneathMiocene

3.5.3 Fault block 3: Wakatipu

The Wakatipu fault block lies on the northern boundary in the centre of the model (Figure 3.7). It abuts fault blocks 2, 6, and 7 (Waiau and Te Anau Basins, Waikaia and Mossburn) and its surface geology is characterised by steep basement hills and Quaternary valley floors. The only subsurface data available in the area comes from the Wakatipu QMAP cross-section C (Turnbull, 2000). This cross-section depicts undifferentiated Quaternary sediments lying directly on Caples Terrane basement. The subsurface information used for modelling within the fault block is outlined in Table 3.9.

GNS Science Consultancy Report 2015/123 40

Confidential 2015

Table 3.9 Fault block 3 surface chronology and subsurface data and manual control lines.

Surface Chronology Subsurface data and manual control lines

Quaternary Constrained by underlying modelled surfaces

Basement Wakatipu QMAP cross-section C (Turnbull, 2000)

3.5.4 Fault block 4: Southland Plains

The Southland Plains fault block lies on the southeastern boundary of the model. It abuts fault blocks 2, 5, and 10 (Waiau and Te Anau Basins, Central, and East1) and its surface geology is characterised by Quaternary plains bounded to the east and west by basement hills. The fault block covers the southern part of the Winton Basin, the Takitimu Mountains, part of the Longwood Range, and the entire Plains area east of the Takitimu Mountains from the Hokonui Hills towards the coast and the lower Mataura River valley. The subsurface information used for modelling within the fault block is outlined in Table 3.10.

Subsurface data available in the area comes from the Murihiku QMAP cross-sections A and C (Turnbull and Allibone, 2003). These cross-sections depict: in the east, Quaternary sediments overlying East Southland Group, in turn overlying basement rock; and in the west, Quaternary sediments overlying Early Miocene and Oligocene sediments, overlying basement rocks. Seismic data for the Waiau Basin (Turnbull et al., 1993) contributed minor information at the western boundary of the fault block. Seismic data for the Winton Basin (Cahill, 1995) contributed minor information at the northern boundary in the centre of the fault block. Cross-sections from previous gravity modelling (Broadbent et al., 1980) contributed minor information in the northeast. The majority of NCRS bore information is focused in the northeast. ES borehole information is distributed throughout the plains, but in the western half of the model these bores only penetrate to very shallow depths. A few contact points from petroleum bores contributed information.

A control line (Older FB4_East) has been created to prevent the Eocene, Oligocene and Early Miocene units from extending beyond the western part of the Southland Plains as they are absent in the eastern part of the fault block. The location of the control line was chosen based on the extent of Early Miocene, Oligocene, and Eocene data and the placement of faults in QMAP. The Eocene required an additional control line (Eocene FB4_East) to prevent Eocene material reaching the surface in the west of the model, where the unit is not geologically mapped at the surface. This control line (Eocene FB4_East) has similarly been used to prevent the extent of Miocene material to the east. The Pliocene outcrops in the northeast are considered to be locally restricted. A control line (Pliocene FB4_Southwest) was therefore created restricting Pliocene material from extending south. An anomaly in the isostatic gravity map (Figure 3.5) that extends northwest to southeast across the Southland Plains and coincides with the edge of the Winton Basin has been chosen as the location to use for the control line. This anomaly likely represents shallowing of the basement.

GNS Science Consultancy Report 2015/123 41

Confidential 2015

Table 3.10 Fault block 4 surface chronology and subsurface data and manual control lines.

Surface Chronology Subsurface data and manual control lines

Quaternary ES bores (Quaternary contacts excluding ‘baserock’ contacts)

ES bores (Quaternary contacts excluding ‘baserock’ contacts) Petroleum bores (Pliocene contacts) (Ministry of Business, Innovation Pliocene and Employment, 2014) Control line Pliocene FB4_Southwest

NCRS bores (Gore Lignite Measures and East Southland Group contacts) (Ministry of Business, Innovation and Employment, 2014) East Southland Group Petroleum bores (Gore Lignite Measure contacts) (Ministry of Business, Innovation and Employment, 2014)

Miocene Control line Older FB4_East.

ES bores (limestone contacts) Early Miocene Control line FB4_E_Miocene.

Petroleum bores (Oligocene contacts) (Ministry of Business, Innovation and Employment, 2014) Oligocene Seismic data for the Winton Basin (Cahill, 1995) Seismic data for the Waiau Basin (Turnbull et al., 1993) Control line Older FB4_East2

Petroleum bores (Eocene contacts) (Ministry of Business, Innovation and Employment, 2014) Seismic data for the Winton Basin (Cahill, 1995) Eocene Seismic data for the Waiau Basin (Turnbull et al., 1993) Control line Eocene FB4_East Control line Older FB4_East

Murihiku QMAP cross-sections A and C (Turnbull and Allibone, 2003) NCRS bores (basement contacts) (Ministry of Business, Innovation and Employment, 2014) Basement ES bores (‘baserock’ contacts) Seismic data for the Winton Basin (Cahill, 1995) Seismic data for the Waiau Basin (Turnbull et al., 1993) Gravity cross section data (Broadbent et al., 1980)

3.5.5 Fault block 5: Central

The Central fault block is located in the centre of the model (Figure 3.7). It abuts fault blocks 2, 3, 4, 7, and 9 (Waiau and Te Anau Basins, Waikaia, Southland Plains, Mossburn and Riversdale), and its surface geology is characterised by a plain of Quaternary sediments, bounded by basement hills, and shallow Quaternary valleys extending north. Minor cover rocks are apparent in outcrops: Eocene, Oligocene, Miocene, East Southland Group and Pliocene. Murihiku QMAP cross-sections B and C (Turnbull and Allibone, 2003) depict basement covered by Quaternary sediments in shallow valleys. Seismic data are available for the Winton Basin (Cahill, 1995), located beneath the Quaternary plains. The subsurface information used for modelling within the fault block is outlined in Table 3.12.

GNS Science Consultancy Report 2015/123 42

Confidential 2015

A control line (Older FB4_East) has been created to prevent the Eocene, Oligocene and Early Miocene units from extending beyond the west of the model, where they are mapped at the surface and are linked to the Waiau and Winton Basins, while absent east of the fault block model. The location of the control line was chosen based on the extent of Early Miocene, Oligocene, and Eocene data and the placement of faults in QMAP. The Eocene required an additional control line (Eocene FB5_BeneathValleys) to constrain its surface in the two north-south shallow valleys where the unit is not geologically mapped at the surface or apparent in subsurface data. Additionally, structural controls were created for the Oligocene, Eocene and basement surfaces. Similarly to control lines, these structural data points are not based on actual data, but on expert opinion, and are used to constrain the surfaces to ensure that they are geologically realistic for the model units. Structural control points are characterised by a dip angle and dip azimuth, which is propagated to the surface at its spatial location. Compared to control lines, structural controls maintain a larger area of influence across a surface than control lines.

3.5.6 Fault block 6: Waikaia

The Waikaia fault block lies on the northeastern boundary of the model (Figure 3.7). It abuts fault blocks 3, 7, 8, 9 and 11 (Wakatipu, Mossburn, Lumsden, Riversdale and East2) and its surface geology is characterised by steep basement hills and two valleys with Quaternary river sediments. The Murihiku QMAP cross-section C (Turnbull and Allibone, 2003) depicts the East Southland Group lying directly on Caples Terrane basement in the easternmost area of the fault block. The subsurface data used for modelling within the fault block is outlined in Table 3.13.

The eastern valley (Waikaia River valley) contains some East Southland Group at the surface and within lithological log data. There is no evidence of this group, however, being present in the western valley (Mataura River valley). The distribution of lithological log and QMAP data in the Waimea Plains supports the theory that the East Southland Group did not reach as far northwest as the Mataura River valley and terminates at some point within the Waimea Plains. Therefore, a control line (FB96_Northwest) has been placed in the ranges between these two valleys to restrict the extent of the East Southland Group. This FB96_Northwest control line is discussed further in Section 3.5.9.

Early Miocene is at the surface in small areas in the north of this fault block, however, it does not occur in the Waimea Plains. Here it appears to directly overly basement, but no bores are located in these areas. There is no available subsurface data for Early Miocene within the fault block. As there is no subsurface data from which to construct an Early Miocene surface and the likelihood that the surface deposits of Early Miocene are erosional relics of limited extent, this unit has not been included in the surface chronology of the fault block and is assumed to not be present within the river valleys.

Other Tertiary units do not occur in the QMAP geological map, QMAP cross-sections or any bore logs in this fault block and are, therefore, likely absent in this area.

GNS Science Consultancy Report 2015/123 43

Confidential 2015

Table 3.11 Fault block 5 surface chronology and subsurface data and manual control lines.

Surface Chronology Subsurface data and manual control lines

ES bores (Quaternary contacts excluding ‘baserock’ contacts) Control line FB5_Quat_ctrl Quaternary Seismic data for Mossburn and Wreys Bush areas (Zehnder, A./FMG Pacific Ltd, 2011)

Pliocene ES bores (Quaternary contacts excluding ‘baserock’ contacts)

NCRS bores (Gore Lignite Measures and East Southland Group contacts) (Ministry of Business, Innovation and Employment, 2014) East Southland Group Petroleum bores (Eocene contacts) (Ministry of Business, Innovation and Employment, 2014)

Control line Older FB4_East2 Miocene Seismic data for Mossburn and Wreys Bush areas (Zehnder, A./FMG Pacific Ltd, 2011)

ES bores (limestone contacts) Seismic data for Mossburn and Wreys Bush areas (Zehnder, A./FMG Early Miocene Pacific Ltd, 2011) Control line Older FB4_East Seismic data for the Winton Basin (Cahill, 1995) Seismic data for the Waiau Basin (Turnbull et al., 1993) Seismic data for Mossburn and Wreys Bush areas (Zehnder, A./FMG Oligocene Pacific Ltd, 2011) Control line Older FB4_East Structural control Oligo_ctrl_FB5 Structural control Oligo_FB5b NCRS bores (Eocene contacts) (Ministry of Business, Innovation and Employment, 2014) Petroleum bores (Eocene contacts) (Ministry of Business, Innovation and Employment, 2014) Seismic data for the Winton Basin (Cahill, 1995) Eocene Seismic data for the Waiau Basin (Turnbull et al., 1993) Seismic data for Mossburn and Wreys Bush areas (Zehnder, A./FMG Pacific Ltd, 2011) Control line Older FB4_East Control line Eocene FB5_BeneathValleys Structural control Eocene_ctrl_FB5 Murihiku QMAP cross-sections B and C (Turnbull and Allibone, 2003) NCRS bores (basement contacts) (Ministry of Business, Innovation and Employment, 2014) ES bores (‘baserock’ contacts) Petroleum bores (basement contacts) (Ministry of Business, Innovation and Employment, 2014) Seismic data for the Winton Basin (Cahill, 1995) Basement Seismic data for the Waiau and Te Anau Basins (Turnbull et al., 1993) Seismic data for Mossburn and Wreys Bush areas (Zehnder, A./FMG Pacific Ltd, 2011) Gravity cross section data (Broadbent et al., 1980; Woodward et al., 1983). Structural control basement_ctrl_FB5_a Structural control basement_ctrl_FB5_c

GNS Science Consultancy Report 2015/123 44

Confidential 2015

Table 3.12 Fault block 6 surface chronology and subsurface data and manual control lines.

Surface Chronology Subsurface data and manual control lines

Quaternary Constrained by underlying modelled surfaces

NCRS bores (Gore Lignite Measures and East Southland Group contacts) (Ministry of Business, Innovation and Employment, 2014) East Southland Group ES bores (Quaternary contacts excluding ‘baserock’ contacts) Control Line FB96_Northwest

Murihiku QMAP cross-section C (Turnbull and Allibone, 2003) NCRS bores (basement contacts) (Ministry of Business, Innovation and Basement Employment, 2014) ES bores (‘baserock’ contacts)

3.5.7 Fault block 7: Mossburn

The Mossburn fault block is the western part of the narrow strip of land between the Livingstone and Hillfoot faults (Figure 3.7). It abuts fault blocks 2, 5, 6, 8, and 9 (Waiau and Te Anau Basins, Central, Waikaia, Lumsden and Riversdale) and its surface geology is dominated by Quaternary sediments and the basement range of the Eyre Mountains in the northwest. There also is a small area of Miocene cover rocks mapped at the ground surface on top of the basement ranges. The subsurface information used for modelling within the fault block is outlined in Table 3.13.

There are no available subsurface data for Miocene within the fault block. This absence of information from which to construct a Miocene surface and the strong likelihood that the surface strata of Miocene are erosional relics of limited extent, this unit has not been included in the surface chronology of the fault block and is assumed to not be present beneath Quaternary deposits.

There is some contention regarding whether cover rock strata are present in the area due to a few lithological log descriptions being unclear as to whether they are cover rock or basement materials. As there is no cover rock outcrop in the fault block, and insufficient data to delineate such a surface at depth, it has been assumed that the interpretation of Blakemore (2006) is correct – that a few logs have been incorrectly labelled as cover rocks (see Section 3.5.8 for further details). This assumption places only Quaternary and basement strata within the fault block.

Table 3.13 Fault block 7 surface chronology and subsurface data and manual control lines.

Surface Chronology Subsurface data and manual control lines

Blakemore cross-sections A and B (Blakemore, 2006) Quaternary ES bores (Quaternary contacts)

Blakemore cross-sections A and B (Blakemore, 2006) Basement ES bores (Quaternary contacts) ES bores (‘baserock’ contacts)

GNS Science Consultancy Report 2015/123 45

Confidential 2015

3.5.8 Fault block 8: Lumsden

The Lumsden fault block is the central portion of the narrow strip of land between the Livingstone and Hillfoot faults (Figure 3.7). It abuts fault blocks 6, 7, and 9 (Waikaia, Mossburn and Riversdale) and its surface geology is dominated by Quaternary sediments and the basement range of the Eyre Mountains in the northwest. The subsurface information used for modelling within the fault block is outlined in Table 3.14.

There is some contention regarding whether cover rock strata are present in the area due to a few lithological log descriptions being ambiguous, and it is unclear as to whether they describe cover rock or basement strata. For example, the log of ES bore E44/0320 (Figure 3.8) indicates 80 m of Quaternary sediments directly overlying what is probably basement (the description is limited to broken, fractured or solid rock). ES bore E44/0474 (Figure 3.8) in the central eastern part of this fault block indicates approximately 80 m of Quaternary overlying what is called ‘blue mudstone’. The lithological log of bore E44/0281 (Figure 3.8) shows mudstone with shell at a depth of 38 m (142 m AMSL). This bore has been described by SKM (2005) as lignite-bearing, but no lignite is listed in the bore log from the ES database. No other ES bore in this area offers useful information about possible cover rock strata between Quaternary and basement, and there are no coal or petroleum exploration bores in this area. Generally, the only other description in the ES bores is blue pug or mudstone and it is unclear from the logs to which unit(s) these descriptors may refer.

Cross-sections from Blakemore (2006), derived from the interpretation of geophysical data in this area, show basement rocks directly overlain by Quaternary sediments. Blakemore (2006) assumed that all mudstone in the area is actually Dun Mountain – Matai basement rock, and that the one borehole Blakemore (2006) identified as containing cover rock strata due to traces of shells is actually located on the other side (south side) of the Hillfoot Fault. Alternatively, it is possible that the “mudstone with shell” in bore E44/0281 is actually basement rock and not cover rocks, as basement rocks in the form of Dun Mountain – Matai Terrane siltstone with shell beds have been mapped at the ground surface just 800 m to the west of this bore. This idea is also supported by the gravity map (Figure 3.5), which shows relatively shallow basement underneath the Oreti Basin. As there is no known cover rock outcrop in the fault block and insufficient data to delineate such a surface at depth, the modelling presented here assumes that the cross-sections of Blakemore (2006) are appropriate, and that several bore logs have been incorrectly labelled as cover rock strata.

This places only Quaternary and basement sediments within this fault block. Consequently, it is assumed that all mudstone occurrences in bore logs within fault blocks 7 and 8 are likely also basement rocks and not cover rock strata.

A structural control point had to be created to constrain the basement surface in this fault block, due to the lack of data points available in this area.

GNS Science Consultancy Report 2015/123 46

Confidential 2015

Figure 3.8 ES bores mentioned in the text, including fault blocks, modelled units and faults.

Table 3.14 Fault block 8 surface chronology and subsurface data and manual control lines.

Surface Chronology Subsurface data and manual control lines

Blakemore cross-sections A and B (Blakemore, 2006) Quaternary ES bores (Quaternary contacts)

Blakemore cross-sections A and B (Blakemore, 2006) ES bores (Quaternary contacts) Basement ES bores (‘baserock’ contacts) Structural control basement_ctrl_FB8

GNS Science Consultancy Report 2015/123 47

Confidential 2015

3.5.9 Fault block 9: Riversdale

The Riversdale fault block is the eastern part of the narrow strip of land between the Livingstone and Hillfoot faults (Figure 3.7). It abuts fault blocks 5, 6, 7, 8, and 10 (Central, Waikaia, Mossburn, Lumsden and East1) and its surface geology is dominated by Quaternary sediments of the Waimea Plain. Minor occurrences of basement rocks have been mapped at the ground surface close to the bounding faults, and East Southland Group occurs at the surface in the eastern part of the fault block. The Murihiku QMAP cross- sections B and C (Turnbull and Allibone, 2003) depict the East Southland Group lying directly on Dun Mountain – Maitai Terrane basement in the eastern half of the fault block, with undifferentiated Quaternary sediments overlying the East Southland Group. The subsurface information used for modelling within the fault block is outlined in Table 3.15.

The QMAP shows mainly Quaternary, East Southland Group and basement in this area. However, there is a small outcrop of Forest Hill Formation, which is grouped here into Early Miocene, in the central part of this fault block. This formation could likely underlie the Quaternary in the western part of the fault block, but the ES bores are either too shallow or the descriptions of the lithological logs are too general to assist with delineating the distribution of this formation at the subsurface. No coal or petroleum exploration bores are located in this area. Therefore, there is no subsurface information that could be used to build this surface and it is not represented in this fault block.

East Southland Group is, for example, drilled in coal exploration bores 1331 and 1332 (Figure 3.9), in the eastern part of this fault block, with a thickness of approximately 180 m, underlying about 20 m of Quaternary sediments. As discussed in Section 3.5.6, it is assumed that the East Southland Group did not reach as far northwest as the Mataura River valley and terminates at some point within the Waimea Plain. Therefore, a control line (FB96_Northwest) has been placed in the ranges between these two valleys to restrict the extent of the East Southland Group. This control line extends from the ranges to pass through the Waimea Plain in this fault block. This control line has been placed so as to lie west of all subsurface data depicting East Southland Group. Close to the termination of all available East Southland Group data, an anomaly in the isostatic gravity map (Figure 3.5) that extends southwest to northeast across the Waimea Plain has been chosen as the location for the control line. This anomaly likely represents shallowing of the basement.

Table 3.15 Fault block 9 surface chronology and subsurface data and manual control lines.

Surface Chronology Subsurface data and manual control lines

Quaternary ES bores (Quaternary contacts excluding ‘baserock’ contacts)

NCRS bores (Gore Lignite Measures and East Southland Group contacts) (Ministry of Business, Innovation and Employment, 2014) East Southland Group ES bores (Quaternary contacts excluding ‘baserock’ contacts) Control Line FB96_Northwest

Murihiku QMAP cross-section C (Turnbull and Allibone, 2003) NCRS bores (basement contacts) (Ministry of Business, Innovation and Basement Employment, 2014) ES bores (‘baserock’ contacts)

GNS Science Consultancy Report 2015/123 48

Confidential 2015

Figure 3.9 NCRS bores mentioned in the text, including fault blocks, modelled units and faults.

3.5.10 Fault block 10: East1

The East1 fault block is the eastern-central boundary of the model (Figure 3.7). It abuts fault blocks 4, 9 and 11 (Southland Plains, Riversdale and East2) and its surface geology is dominated by Quaternary sediments and East Southland Group. Minor basement outcrops have been mapped at the ground surface near the edge of the fault block. The Murihiku QMAP cross-section B (Turnbull and Allibone, 2003) depicts the East Southland Group lying directly on Dun Mountain – Maitai Terrane basement in the northern area of the fault block, with early Quaternary sediments overlying the East Southland Group. The subsurface information used for modelling within the fault block is outlined in Table 3.16.

GNS Science Consultancy Report 2015/123 49

Confidential 2015

The logs of NCRS coal exploration bores (Ministry of Business, Innovation and Employment, 2014) in this area (e.g., bores 1171, 1174, 1196, 1339 and 1340; Figure 3.9) only show Quaternary, East Southland Group (Gore Lignite Measures) and basement, which is the same geological succession as throughout the eastern Southland Plains.

Table 3.16 Fault block 10 surface chronology and subsurface data and manual control lines.

Surface Chronology Subsurface data and manual control lines

Quaternary Constrained by underlying modelled surfaces

Murihiku QMAP cross-section B (Turnbull and Allibone, 2003) NCRS bores (Gore Lignite Measures and East Southland Group East Southland Group contacts) (Ministry of Business, Innovation and Employment, 2014) ES bores (Quaternary contacts excluding ‘baserock’ contacts)

Murihiku QMAP cross-section B (Turnbull and Allibone, 2003) NCRS bores (basement contacts) (Ministry of Business, Innovation and Basement Employment, 2014) ES bores (‘baserock’ contacts)

3.5.11 Fault block 11: East2

The East2 fault block, located at the eastern-central boundary of the model area, is the smallest fault block in the 3D model (Figure 3.7). It abuts fault blocks 6, 9 and 10 (Waikaia, Riversdale and East1) and its surface geology is dominated by Quaternary sediments and East Southland Group. Minor basement outcrops have been mapped at the ground surface near the edge of the fault block. The Murihiku QMAP cross-section B (Turnbull and Allibone, 2003) depicts the East Southland Group lying directly on Dun Mountain – Maitai Terrane basement, with early Quaternary sediments overlying the East Southland Group. The subsurface information used for modelling within the fault block is outlined in Table 3.17.

Coal exploration bores in this area (1177, 1178; Figure 3.9) have drilled through 10 to 34 m of Quaternary sediments into Gore Lignite Measures/Undifferentiated East Southland Group deposits (Ministry of Business, Innovation and Employment, 2014). However, the stratigraphy in this fault block is likely the same as in fault block 1 (East1), and, therefore, East Southland Group was also modelled directly overlying basement in this fault block.

Table 3.17 Fault block 11 surface chronology and subsurface data and manual control lines.

Surface Chronology Subsurface data and manual control lines

Quaternary Constrained by underlying modelled surfaces

Murihiku QMAP cross-section B (Turnbull and Allibone, 2003) NCRS bores (Gore Lignite Measures and East Southland Group East Southland Group contacts) (Ministry of Business, Innovation and Employment, 2014) ES bores (Quaternary contacts excluding ‘baserock’ contacts)

Murihiku QMAP cross-section B (Turnbull and Allibone, 2003) Basement ES bores (‘baserock’ contacts)

GNS Science Consultancy Report 2015/123 50

Confidential 2015

4.0 RESULTS

4.1 MODEL DESCRIPTION

A combination of GIS (ESRI ArcGIS 10.1) and 3D geological modelling software (Leapfrog Geothermal 2.8) has been used to construct the ES geological model. The model has been constructed using the New Zealand Transverse Mercator projection (NZTM2000). The surface area covered by the model is approximately 21,000 km2, the model extends to a depth of -8.5 km AMSL to provide a continuous basement surface, and the resolution of the model is set to not be coarser than 250 m. The complex geology of the region has been simplified into eight key model units. Additionally, the ES geological model includes a water- body layer, for lakes and estuaries. The key model units have been constructed based on the age of the sediments and this decision was founded mainly on the data available to model the units: 1. Quaternary 2. Pliocene 3. East Southland Group (separated from Miocene due to hydrogeological significance and data availability) 4. Miocene 5. Early Miocene 6. Oligocene 7. Eocene 8. Basement

The water-body layer represents Lake Te Anau, Lake Manapouri, the Mavora Lakes, Lake George, Haldane Bay, Waikawa Harbour, and Fortrose Estuary.

The area of interest is structurally complex. The following seven model faults were selected as the most significant structures, from their extent and/or hydrological significance: • Te Anau – Hauroko Fault • Moonlight Fault System • Livingstone Fault • Hillfoot Fault • Scotts Gap – Hedgehope – Waikaka Fault • Lumsden Fault • Castle Rock Fault

4.2 ES GEOLOGICAL MODEL

The basement rock model unit is the only model unit which is continuous throughout the entire model area (Figure 4.1 and Figure 4.2). Basement is found outcropping in the ranges and mountains and at depth throughout the basins and plains. The deepest basement rocks are located in the Te Anau and Waiau Basins at 8,400 m below ground level (Figure 4.3). In these areas, the basement rock model unit is well constrained by the geophysical data used for the modelling (Section 3.2.5). Across the plains and valleys in the eastern part of the model, basement is comparatively shallow with depths generally between 200 and 500 m.

GNS Science Consultancy Report 2015/123 51

Confidential 2015

These depths are best constrained across the East Southland Plains due to the high number and adequate distribution of coal exploration bores that have been drilled into this unit. Throughout most of the narrow valleys in the model area there is little to no depth information. As such, the depths of these valleys are largely driven by the data used to model the nearby basement topographic variations (due to Leapfrog’s trend interpolation methods). This may result in valleys within steep terrains having over-estimated depths to basement.

The East Southland Group model unit is located primarily in the eastern part of the Southland Plains, but also extend to the Waimea Plain and north to Waikaia (Figure 4.1 and Figure 4.4). This unit is represented most accurately in the model within the eastern Southland Plains, due to the high density of coal exploration bores in this area. By contrast, the subsurface extent of this model unit is not well constrained towards the west, and the western terminus of this unit is unknown, as there are no deep bores in the western Southland Plains area or the Waimea Plain, and the Oreti Basin. The extent of East Southland Group strata into these areas is highly extrapolated and the spatial distribution of this unit is highly uncertain due to the lack of data.

The subsurface extent of all other cover rock model units (Figure 4.1 and Figure 4.2) is almost entirely derived from contour maps based on seismic reflection data in three main areas: the Te Anau, the Waiau and the Winton basins. Outside of these areas, the extents are highly extrapolated and a combination of QMAP surface geological information and details from literature have been used to guide the placement of manual control lines that limit the extent of these units.

The Quaternary model unit is distributed widely throughout the model area (Figure 4.1 and Figure 4.2). The majority of narrow valleys in the model are modelled as Quaternary sediments directly overlying basement rock. As such, the same comment as made above applies to the Quaternary sediments (Figure 4.5) in such areas – that their thickness is likely to be overestimated in valleys within areas of steep terrain. The Quaternary model unit is shallowest and best constrained throughout the Southland Plains. The rest of the ES geological model has poor constraint on the Quaternary model unit, and depths may be overestimated.

GNS Science Consultancy Report 2015/123 52

Confidential 2015

Figure 4.1 Views of the model showing younger units and lakes. Younger units are removed throughout the series to show the subsurface distribution of the underlying units.

GNS Science Consultancy Report 2015/123 53

Confidential 2015

Figure 4.2 Views of the model showing older units. Younger units are removed throughout the series to show the subsurface distribution of the underlying units.

GNS Science Consultancy Report 2015/123 54

Confidential 2015

Figure 4.3 Depth to basement from the ES geological model.

GNS Science Consultancy Report 2015/123 55

Confidential 2015

Figure 4.4 Thickness of East Southland Group from the ES geological model.

GNS Science Consultancy Report 2015/123 56

Confidential 2015

Figure 4.5 Thickness of Quaternary from the ES geological model. Throughout areas with scarce depth data, the thickness presented here may be largely over-estimated.

GNS Science Consultancy Report 2015/123 57

Confidential 2015

5.0 FUTURE REFINEMENTS

Possible future refinements for the ES geological model focus mainly on improvements to the model that decrease the uncertainty in areas with limited data availability; and enhance the spatial definition and structure of model units in areas of specific interest for groundwater investigations or other intended applications.

5.1 MODEL SIZE

The model boundary was determined and supplied by ES and constitutes an area spanning more than 21,000 km2. A model of this size produces a number of challenges for modelling. The Leapfrog software used for modelling was not designed to handle projects of this size, which has made the process very computationally slow. Modelling involves testing and decisions made by the modellers with regard to interpolation trends and manual adjustments etc., however, a computationally slow model allows for less of these tests and adjustments to be made. Only one surface and interpolation trend can be set for each geological unit per fault block, which again limits the amount of adjustments that can be made. To overcome these modelling issues associated with model size, it is advised that any future geological modelling of the area be split into smaller individual areas. These areas would ideally be smaller than 5,000 km2 and would be split by areas of differing geological histories, depositional environments, topographic trends or associated with the purpose of the model e.g., groundwater flow boundaries.

5.2 FIT FOR PURPOSE – REFINING FOCUS

There are a large number of avenues that can be taken for refining the ES geological model, however, suitable investigations depend on the outlay available and the purpose of the refinement. Any refinement of the model should focus on the ultimate purpose of the model and the resolution required for the objectives. The suggestions below highlight a few aspects that would be expected to be beneficial for flow modelling within both a regional and local context:

1. Quaternary valleys in steep basement terrain - Aeromagnetic data collected and inverted to obtain depth to magnetic basement. 2. The western extent of East Southland Group - Deep drilling to the west of the current drill-intercepted East Southland group. - Airborne time domain electromagnetic (TDEM) data collected, inverted for a resistivity model and interpreted alongside lithological logs. 3. Basement depth in the Southland Plains - Joint interpretation of gravity and aeromagnetic data to obtain depth to basement. 4. Quaternary depth north and east of Winton Basin - Deep drilling to the north and east of the Winton Basin. - Airborne time domain electromagnetic (TDEM) data collected, inverted for a resistivity model and interpreted alongside lithological logs.

5.3 INCORPORATION OF COAL SEAM GAS BORES

The coal exploration bore dataset used for the modelling (Section 3.2.6.2) did not include bores that were drilled for coal seam gas (CSG) exploration. This is of little consequence for the CSG bores in the Mataura/Edendale area, as the high density of coal bores available ensures a good accuracy of the ES geological model.

GNS Science Consultancy Report 2015/123 58

Confidential 2015

Additional CSG bores are located in the Ohai area. This area is dominated by Late Cretaceous (basement) and Eocene deposits. The extent of Quaternary sediments is limited and the bores that have been available for the modelling constrain these sediments adequately for the regional 3D model. However, further consideration should be given to these bores in the future if a catchment-scale model is developed for this area.

5.4 DRILLING OF ADDITIONAL BORES

The drilling of additional, deeper bores in data-sparse areas could decrease the uncertainty of the Quaternary and cover rock units in the model. Ideally, these bores would be logged by suitably experienced geologists, or at least important samples taken and sent to geologists for description and classification. Additional, well-described lithological logs would be of particular use in areas where the thickness of the Quaternary may be over-estimated due to the lack of data, the latter being especially detrimental to groundwater applications of the model and its datasets. For example, little subsurface geological information is available between the Winton Basin and the Eastern Southland Plains, as there is no seismic data available in this area and no exploration bores have been drilled here. There are a few bores from the ES database in this area, but these are generally very shallow and do not reach the base of the Quaternary, or the descriptions of the bore logs are too ambiguous to allow an accurate identification of specific geological units. This makes it difficult to both define the detailed architecture and base of the Quaternary, and to identify the older geological materials and their extent beneath the Quaternary sediments.

5.5 NEW AND REINTERPRETED SEISMIC DATA

Subsurface elevation contour maps, derived from the interpretation of seismic reflection data (Section 3.2.5), cover an area of approximately 5000 km2 of western Southland and the Winton Basin (Turnbull et al., 1993; Cahill, 1995). They have been used to model surfaces of basement rocks and tertiary cover rocks. Since the contour maps were published, additional seismic data has become available and previous data has been reinterpreted.

PR 4269 includes one reinterpreted seismic line of ~4 km in the Ohai area. These new data overlap and conflict with the previous contour maps from Turnbull et al. (1993). Given the scale of the pre-existing contour maps, which cover several thousands of square kilometer, reassessing the contour maps based on minor adjustments was not considered feasible in the given time and budget. A future update could reconsider this decision, if further seismic reinterpretation is performed for the seismic data utilised by Turnbull et al. (1993).

The reinterpretation of approximately 1/3 of the seismic lines within the Winton Basin was reported in PR3405. The report includes two maps that could be useful – depth to basement and depth to top of the Mako Coal measures. However, these maps use single colours to indicate quite large depth ranges, e.g., orange is 119.742 m to 242.363 m below ground level. Based on these ranges, it is not clear in the shallow areas whether there are any significant differences to the contour maps from Cahill (1995). There appears to be some depth differences to the west where the Mako Coal Measures deepen, however, the inclusion of this data would mean that the depths conflicted with the surrounding data that was not reinterpreted within report PR3405. The authors of report PR3405 also stated that there was some conflict between the reinterpretation and mapped surface basement outcrops that required further work to resolve. The more complete data set from Cahill (1995) was used for modelling, therefore, as there was insufficient scope within the ES geological model to perform the work required to integrate the new interpretations. A catchment-scale

GNS Science Consultancy Report 2015/123 59

Confidential 2015 model or a future update of the ES geological model could include the dataset reported in PR3405, if all of the seismic lines were reinterpreted in the same manner and any mapped surface conflicts resolved.

5.6 SUBDIVIDING THE QUATERNARY STRATA

For local, small scale flow modelling, it would likely be advantageous to split the Quaternary model unit into flow-relevant sub-units. Due to the high level of detail required for this task, this approach was beyond the scope of this regional-scale project. Therefore, this subject has only been marginally investigated in this report. However, in areas where a high density of bores deeper than 20 m are available that show a well described Quaternary sequence, a detailed investigation of the bore logs may allow subdivision of Quaternary deposits, which may be beneficial for the better characterisation of groundwater flow pathways. Such investigations could be enhanced by looking at related data sets such as chemistry analyses, water age and hydraulic property estimates, as well as performing additional data collection and analysis such as resistivity surveys.

5.7 SUBDIVIDING THE GORE LIGNITE MEASURES

According to a master thesis by Durie (2001), the Gore Lignite Measures in the Eastern Southland Plains can be split into three aquifers. Cross-sections provided in the thesis could be used in the future to refine the Gore Lignite Measures in a catchment-scale model of that area.

5.8 VISUALISATIONS

The ES geological model could be utilised for visualisation purposes. For example, hydraulic properties or groundwater chemistry, age or other data could be included into a subset of the model to derive a property model showing the 3D distribution of these data throughout areas of interest, i.e., the Southland Plains. This should only be done at a small scale and in areas where a sufficient density of data is available. Additionally, Leapfrog Geothermal software can be used to create videos to visualise slices and fly-overs of the model. This could be useful for both science and public communication purposes.

GNS Science Consultancy Report 2015/123 60

Confidential 2015

6.0 CONCLUSIONS

The Joint Fluxes and Flows Programme consists of a number of planned work components aimed at developing a 3D regional groundwater flow and contaminant transport model, calibrated to surface water flow, to be used as a regional policy management tool. This report details one of these work components: the construction of a simplified 3D geological model of Environment Southland’s freshwater management units. This regional model will provide the geological foundation for the groundwater flow model.

The surface area covered by the model is approximately 21,000 km2 and the model extends to a depth of -8.5 km AMSL. This depth was chosen to allow for the basement top surface to be continuous throughout the entire model area to form a continuous base of the subsequent flow model, as the basement reaches depths of up to -8000 m AMSL in the Te Anau Basin. However, basement depth varies greatly throughout the model area, is exposed at the ground surface in most of the hill country of Southland, and is only a few hundred meters deep throughout large parts of the area, including the Southland Plains. Hence, the maximum depth of the groundwater flow model may be less than the maximum depth of the geological model, depending on the actual area chosen to be represented in the flow model.

ArcGIS and Leapfrog Geothermal 2.8 have been used to construct the ES geological model using the New Zealand Transverse Mercator projection (NZTM2000) and the mesh resolution was set to not be coarser than 250 m. The main datasets used to constrain the geology and structure of the model are surface geological maps, well logs datasets, subsurface contours maps from seismic reflection data, cross sections and topographic data.

The complex geology of the region has been simplified into key model units based on the characteristics of the main geological formations within the model area, taking into account the data available for modelling. The resulting units are primarily based on the age of the strata, due to the manner in which the most widely available subsurface dataset, the subsurface contour maps, are defined. The ES geological model includes seven significant faults, eight main geological units and a water-body unit.

Although the resolution of the model is set to not be coarser than 250 m, it is important to be aware that the uncertainty in the model is linked to the amount of available data with the area, and thus the uncertainty is very high within data-sparse areas and will be greater than the model resolution. The ES geological model has been developed at a regional scale only and should only be considered within this context, for example for its purpose as the basis of a large-scale groundwater flow model. The model should not be used alone for land use planning, consent decisions, design of engineering projects, geohazard risk assessment, or other work for which detailed local site investigations are necessary.

The model can be refined in the future, and uncertainty in specific areas decreased, if more data becomes available. The development of the model in Leapfrog Geothermal software allows for future adjustment of the model to be made by adding in new data.

GNS Science Consultancy Report 2015/123 61

Confidential 2015

7.0 ACKNOWLEDGEMENTS

The authors thank Rogier Westerhoff (GNS Science) for his assistance with the export of model surfaces. We are grateful to Lawrence Kees and Clint Rissmann from Environment Southland, for discussions involved in development of the project, and this component in particular, and the provision of data sets. Brydon Hughes from Liquid Earth Ltd kindly provided additional data and information. The authors also would like to thank Magali Moreau and Rob van der Raaij, from GNS Science, for their review of the report, and James Pope, CRL Energy Ltd, for his review of the geological model.

8.0 REFERENCES Barrell, D. J. A. (2011). Quaternary Glaciers of New Zealand. In J. Ehlers, P. L. Gibbard, and P. D. Hughes (Eds.), Quaternary glaciations: extent and chronology – a closer look (Vol. 15, pp. 1047 – 1064). Amsterdam: Elsevier. Blakemore, H. N. (2006). A geophysical study of the Oreti Basin groundwater system. MSc thesis, University of Otago. 128. Broadbent, M.; Carman, A. F.; Carrington, L. W.; Hicks, S. R. of DSIR (1980). Geophysical surveys in support of coal prospecting in Eastern Southland, 1977 – 78. Ministry of Economic Development New Zealand Unpublished Coal Report CR318, 75. Cahill, J. P. (1995). Evolution of the Winton Basin, Southland. New Zealand Journal of Geology and Geophysics, 38(2), 245 – 258. Craw, D. (1992). Growth of alluvial gold particles by chemical accretion and reprecipitation, Waimumu, New Zealand. New Zealand Journal of Geology and Geophysics, 35(2), 157 – 164. Durie, M., 2001. Hydrogeology of the Eastern Southland Plains, New Zealand, Master thesis. Christchurch, University of Canterbury Library. 193p. Geographx. (2012). Geographx New Zealand DEM 2.1. http://geographx.co.nz/_wp/wp- content/uploads/2012/12/GX-Terrain-Metadata.pdf, last accessed May 2015. GNS Science. (2013). New Zealand Gravity Station Network, http://maps.gns.cri.nz/website/gravity/, last accessed May 2015. GNS Science. (2014). New Zealand Active Faults Database, http://data.gns.cri.nz/af/, last accessed May 2014. Hancox, G. T.; Perrin, N. D. (2009). Green Lake Landslide and other giant and very large postglacial landslides in Fiordland, New Zealand. Quaternary Science Reviews, 28, 1020 – 1036. Heron, D.W. (custodian) 2014. Geological map of New Zealand 1:250,000. GNS Science Geological Map 1. 1 CD. Hughes, B.; Harris, S.; Brown, P. (2011). Mataura Catchment Strategic Water Study. Report prepared for Environment Southland, May 2011. 38. Hyden, F. M. (1980). Mass flow deposits on a mid-Tertiary carbonate shelf, southern New Zealand. Geological Magazine, 117(05), 409 – 424. Isaac, M. J.; Lindqvist, J. K.; Pocknall, D. T. (1990). Geology and lignite resources of the East Southland Group, New Zealand. New Zealand Geological Survey bulletin, 101. DSIR Geology and Geophysics. 202. Kees, L. (2015). [email protected], Environment Southland, pers. comm., 12th February 2015.

GNS Science Consultancy Report 2015/123 62

Confidential 2015

Kees, L.; Moreau, M.; Chanut, P.; Rissmann, C.; Daughney, C. J.; Zammit, C.; Close, M. (2014). NPS 2014: Southland’s innovative and collaborative fluxes and flows research project. 2014 Water Symposium: integration, the final frontier: Nov. 24 – 28, Marlborough Convention Centre. (p. 195). Landis, C. A. (1974). Stratigraphy, lithology, structure, and metamorphism of Permian, Triassic, and Tertiary rocks between the Mararoa River and Mount Snowdon, western Southland, New Zealand. Journal of the Royal Society of New Zealand, 4(3), 229 – 251. Lee, D.; Lindqvist, J.; Douglas, B.; Bannister, J.; Cieraad, E. (2003). Paleobotany and sedimentology of Late Cretaceous-Miocene nonmarine sequences in Otago and Southland: Field Trip 9, Geological Society of New Zealand annual conference 2003. Dunedin: Field Trip Guides. Geological Society of New Zealand Miscellaneous Publication 116B. Lowrie, W. (2006). Fundamentals of Geophysics. Cambridge University Press, Cambridge. Manville, V. (1996). Sedimentology and stratigraphy of Prospect Formation, Te Anau Basin, western Southland, New Zealand. New Zealand Journal of Geology and Geophysics, 39(3), 429 – 444. McIntosh, P. D.; Eden, D. N.; Burgham, S. J. (1990). Quaternary deposits and landscape evolution in northeast Southland, New Zealand. Palaeogeography, Palaeoclimatology, Palaeoecology, 81(1), 95 – 113. Ministry for the Environment. (2014). National Policy Statement for Freshwater Management, http://www.mfe.govt.nz/fresh-water/freshwater-management-nps, Last accessed: January 2015. Ministry of Business, Innovation and Employment. (2014). New Zealand Petroleum and Minerals online exploration database, https://data.nzpam.govt.nz/GOLD/system/mainframe.asp, last accessed May 2015. Morgan, M.; Evans, C. (2003). Southland Water Resources Study: Stages 1 to 3. Prepared for Venture Southland, Lincoln Environmental Report No 4597/1, September 2003. 33. Mortimer, N.; Rattenbury, M.; King, P.; Bland, K.; Barrell, D.; Bache, F;, Begg, J.; Campbell, H.; Cox, S.; Crampton, J.; Edbrooke, S.; Forsyth, P.; Johnston, M.; Jongens, R.; Lee, J.; Leonard, G.; Raine, J.; Skinner, D.; Timm, C.; Townsend, D.; Tulloch, A.; Turnbull, I.; Turnbull, R. (2014). High-level stratigraphic scheme for New Zealand rocks. New Zealand Journal of Geology and Geophysics, 1 – 18. Mumme, T. C. (1981). [Letter] - Gravity profiling – South Waikato. Department of Scientific and Industrial Research Geophysics Division, Mapping Techfile, 2. Newnham, R.; McGlone, M.; Moar, N.; Wilmshurst, J.; Vandergoes, M. (2013). The vegetation cover of New Zealand at the last glacial maximum. Quaternary Science Reviews, 74, 202 – 214. Putnam, A. E.; Schaefer, J. M.; Denton, G. H.; Barrell, D. J. A.; Birkel, S. D.; Andersen, B. G.; Kaplan, M.; Finkel, R.; Schwartz, R.; Doughty, A. M. (2013). The Last Glacial Maximum at 44 S documented by a 10 Be moraine chronology at Lake Ohau, Southern Alps of New Zealand. Quaternary Science Reviews, 62, 114 – 141. Rekker, J.; Jones, A. F. (1998). Central Southland Plains groundwater study: Results from field surveys and assessment. AquaFirma Ltd. 29. Rissmann, C.; Wilson, K. (2012). Waituna Catchment Groundwater Resource Technical Report. Environment Southland Publication No 2012-04. 101. Scadden, P., 2015. Custodian of the Mineral and Coal bore database at GNS Science. Personal communication, 25/09/2015. SKM. (2005). Hydrogeology of the Oreti Basin. Sinclair Knight Merz Report No AE02451. 74.

GNS Science Consultancy Report 2015/123 63

Confidential 2015

SKM. (2007). Gore water master planning study. Sinclair Knight Merz Report No AE03017C0003. 59. Stagpoole, V. (2012). Description of the data in the GNS gravity database. GNS Science. 10. Stagpoole, V.; Woodward, D. (2004). Gravity models of the King Country Basin. Ministry of Economic Development New Zealand Unpublished Petroleum Report PR 2905. Suggate, R. P. (2004). South Island, New Zealand; ice advances and marine shorelines. In J. Ehlers and P. L. Gibbard (Eds.), Quaternary Glaciations–Extent and Chronology, Part III: South America, Asia, Africa, Australasia, Antarctica (Vol. 2, pp. 285 – 291). Amsterdam: Elsevier. Todd, D. K.; Mays, L. W. (2005). Groundwater hydrology. Wiley, New Jersey. Turnbull, I. M. (2000). Geology of the Wakatipu area: scale 1:250,000. Lower Hutt, N.Z.: Institute of Geological and Nuclear Sciences Limited. Turnbull, I. M.; Allibone, A. H. (2003). Geology of the Murihiku area: scale 1:250,000. Lower Hutt, N.Z.: Institute of Geological and Nuclear Sciences Limited. Turnbull, I. M.; Allibone, A. H.; Jongens, R. (2010). Geology of the Fiordland area (Vol. 1). Lower Hutt, N.Z.: Institute of Geological and Nuclear Sciences Limited. Turnbull, I. M.; Uruski, C. I.; and others. (1993). Cretaceous and Cenozoic Sedimentary Basins of Western Southland, South Island, New Zealand. Institute of Geological and Nuclear Sciences Monograph 1, 86. Williams, P. W. (1982). Karsts in New Zealand. In J. M. Soons and M. J. Selby (Eds.), Landforms in New Zealand. Auckland, Longman Paul. Wilson, K. (2011). State of the Environment: Groundwater Quantity Technical Report. Environment Southland. 92. Woodward, D. J.; Kicinski, J. of DSIR. (1983). Gravity Survey at Ohai, Southland – June 1983. Ministry of Economic Development New Zealand Unpublished Coal Report CR1215, 25. Yang, K.; Browne, P. R. L.; Huntington, J. F.; Walshe, J. L. (2001). Characterising the hydrothermal alteration of the Broadlands–Ohaaki geothermal system, New Zealand, using short-wave infrared spectroscopy. Journal of Volcanology and Geothermal Research, 106(1), 53 – 65. Zehnder, A./FMG Pacific Ltd. (2011). PP50992 Technical Report on Southland Prospect. Ministry of Economic Development New Zealand Coal Report Series CR3418. 34.

GNS Science Consultancy Report 2015/123 64

Confidential 2015

APPENDICES

GNS Science Consultancy Report 2015/123 65

Confidential 2015

APPENDIX 1: LOCATION MAPS

Figure A1 West Southland, with locations names mentioned in the text. The red dots show the general locations of geographic features, the black line shows the model boundary, and the thin dark grey line is the regional boundary.

GNS Science Consultancy Report 2015/123 66

Confidential 2015

Figure A2 East Southland, with locations names mentioned in the text. The red dots show the general locations of geographic features, the black line shows the model boundary, and the thin dark grey line is the regional boundary.

GNS Science Consultancy Report 2015/123 67

Principal Location Other Locations

1 Fairway Drive Dunedin Research Centre Wairakei Research Centre National Isotope Centre Avalon 764 Cumberland Street 114 Karetoto Road 30 Gracefield Road PO Box 30368 Private Bag 1930 Wairakei PO Box 31312 Lower Hutt Dunedin Private Bag 2000, Taupo Lower Hutt New Zealand New Zealand New Zealand New Zealand T +64-4-570 1444 T +64-3-477 4050 T +64-7-374 8211 T +64-4-570 1444 www.gns.cri.nz F +64-4-570 4600 F +64-3-477 5232 F +64-7-374 8199 F +64-4-570 4657