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