The Geology of the Lower Pohangina Valley, Manawatu, New Zealand

Copyright is owned by the Author of the thesis. Permission is given for a copy to be downloaded by an individual for the purpose of research and private study only. The thesis may not be reproduced elsewhere without the permission of the Author.

A thesis presented in partial fulfilment of the requirements for the degree of

Master of Science in Earth Science

at Massey University, Palmerston North, New Zealand.

Callum Rees

2015

Frontispiece

Cross bedded tuff unit within the Css Member, Takapari Formation, Antler Stream, Broadlands Station, Pohangina Valley.

Acknowledgments

Firstly, I wish to thank Dr Alan Palmer for always having his door open, and teaching me how to read and understand the landscape. I think your past students would understand when I say that since keeping up with you in the field, I have become incredibly fit and will now endeavour to join the Olympic speed walking team.

Special thanks also to Julie Palmer for her infectious enthusiasm and useful discussions regarding sedimentology. I have now gained a wondrous appreciation for what the majority of people refer to as ‘dirt’. My initial apprehension at studying sedimentology has been replaced with a growing excitement at finding new exposures with amazing sedimentary structures.

I acknowledge Matt Erwin for all his help with GIS, and the many applications to which it can be used during the construction of geological maps. You are indispensible to all students wishing to use a Massey computer.

Thanks Anja Mobis for your enthusiasm with tephra work and the way you willingly give up your time for so many students. Your help in the lab with sample preparation and grain size analysis has been a great help. I have become acutely aware and very appreciative of the methodical German lab etiquette, which it has brought to my attention many of us kiwis severely lack.

Many thanks to Alan Beu from GNS science for your help with macro-fossil identification and useful discussions regarding the interpretation of various fossil assemblages. Julie and I both found our tour around the National Paleontological Collection invigorating, invoking a renewed determination to add to our own personal collections.

A special thanks to Ian Schipper, the microprobe technician at Victoria Universtiy, your deep understanding and passion for volcanology was of enormous value and greatly appreciated.

Cheers to Hugh and Judy Akers from Broadlands Station; you patiently put up with me for many months without so much as a complaint, both during the busy shearing and weaning season of summer (2013-2014), and lingering on through the winter of 2014. Your patience with me as well as your keen interest in the land has made the field work portion of this project very worthwhile for me. I will carry fond memories of the beautiful valley sides and ridge tops of Broadlands Station with me for as long as I live, along with a keen respect for the ferocity of the local weather systems.

Thank you to all the famers and lifestyle block owners, who permitted me access to their properties in the lower Pohangina Valley, including:

James Moar Shane Robinson Graeme and Julie Harding

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James Taylor Marton Telford Craig Knight Craig Deadman

I hope you all find your copies of the geological map interesting and informative. Sincere apologies for running large fault lines through your properties, there was no way round it.

This work was supported financially though a Massey University Masterate Scholarship, the Hastie Award and Hornibrook Award from the Geoscience Society of New Zealand, the Helen E. Akers Postgraduate Scholarship, the William Hudson Scholarship, the TrustPower Tararua Wind Farm Research Bursary, and the C V Fife Memorial Scholarship.

Lastly, thank you to all my friends and family who have had to suffer my geological ramblings over the last two years (and in some cases substantially longer). Moments spent with you not discussing the various interpretations of flow velocity from a hyper concentrated homo-pycnal flow deposit, has kept me vaguely sane.

Abstract

The geology of the lower Pohangina Valley has been mapped at a scale of 1:30,000. This has involved the reclassification of formations described by Carter (1972) in northern Pohangina and correlation of stratigraphy and stratigraphic nomeclamenture to both the Whanganui and Dannevirke subdivisions (Fleming, 1953; Lillie, 1953).

Pohangina geology has been linked to the cyclostratigraphy preserved within the Whanganui Basin (Naish, et al, 1998; e.t.c.) via tephrochronology and biostratigraphy, allowing basin wide correlation. The Kaimatira Pumice Sand Formation (Fleming, 1953) is recognised within the study area by the identification of the Potaka Tephra, allowing an upper boundary to be placed upon the Takapari Formation of Carter (1972). Kai Iwi Group sediments are mapped near the axis of the Pohangina Fauted Monocline allowing correlation to the Beehive Creek, Cullings Gully and Finnis Road sections to the west of the study area (Brackley,1999; Townsend, 1993; Seward, 1976; Manning, 1988; and MacPherson, 1985).

Balanced geological cross sections have been constructed and used as aids in structural interpretation. The Pohangina Faulted Monocline (Marden, 1984), a major regional structure, is controlled at depth by a shallow reverse fault. This underlying reverse fault is correlated to the Raukawa Fault of Rich (1959), which outcrops at the western end of the Manawatu Gorge. The Pohangina Faulted Monocline is tentatively correlated with another monoclinal flexure to the south of the Manawatu Gorge, also interpreted to be related to and controlled by the Ruakawa Fault (Rich, 1959). When the eastward dipping Ruakawa Fault is at greater depth, westward dipping normal faults are found and are interpreted as antithetic faults splaying off from the underlying thrust fault.

The Pohangina Fault is mapped as an active normal fault, displacing an Ohakean terrace on the western side of the Pohangina River. The potentially active Whareroa Fault (Ower, 1943) is inferred to cross the Manawatu Saddle area trending SE – NW as a contact fault between Torlesse greywacke and Plio-Pleistocene sediments.

The thrust faulting in the area has resulted in the intense deformation and uplift of Torlesse bedrock contemporaneous with drag-tilting and folding of the Plio-Pleistocene sediments. Erosion within the study area has exposed Takapari Formation beds dipping at up to 70° to the west. Steep dips are traced SW-NE across the landscape, interpreted as representing the axis of the Pohangina Faulted Monocline and also allowing links to be made between areas of exposed faulting mapped by Rich (1959), Ower (1943) and in this study.

Lignite and tephra beds within the Takapari Formation are associated with deposition in an estuarine environment on a coastal plain bordering the Whanganui Basin, during Early Castlecliffian time. Geochemical analyses are used to identify eight tephras, which are used for both stratigraphic control and paleogeographic interpretation.

During Early Nukumaruan time an influx of gravel within the south eastern Whanganui Basin is associated with the formation of a prograding Gilbert-type fan delta within the Cg Member of the Konewa Formation. The gravels are interpreted as being derived from exposed greywacke in the vicinity of the present day northern Ruahine Ranges, 40 to 70 km north of Pohangina. Distance from source is calculated from clast size within the conglomerate and together with mineralogy provide evidence of provenance. Biostratigraphic and lithostratigraphic changes are used as evidence to support wider interpretations involving paleogeography and the geological history of the lower North Island.

Depositional environments are interpreted using facies analysis, tephrochronology, grain size analysis, and biostratigraphy. Detailed stratigraphic logs are compiled and interpreted in terms of depositional history and sequence stratigraphy. Marker horizons and bio-events allow correlation of stratigraphy to the Whanganui Basin cyclostratigraphy and marine oxygen isotope record. This information is then used to build an overall regional geological history of the area, including understanding basin development, paleogeography, provenance and depositional history.

Table of Contents

Frontispiece ...... ii Acknowledgements ...... iii Abstract ...... v Table of contents ...... vii Appendices ...... ix List of figures ...... x List of tables ...... xv

1. Introduction ...... 1 1.1 Outline of the study ...... 1 1.2 Location of study area ...... 2 1.3 Geological setting...... 4 1.3.1 Plate tectonic setting ...... 4 1.3.2 Basement rock ...... 6 1.3.3 The Whanganui Basin ...... 8 1.4 Physiography ...... 9 1.4.1 Overview ...... 9 1.4.2 River Terraces ...... 12

2. Review of previous research in the Whanganui Basin ...... 16 2.1 Whanganui Basin ...... 16 2.2 Biostratigraphy ...... 17 2.3 Tephrochronology ...... 17 2.4 Magnetostratigraphy ...... 19 2.5 Sequence stratigraphic model ...... 19 2.6 Application of the sequence stratigraphic model to the Whanganui Basin ...... 21 2.7 Geology of the Pohangina area ...... 23

3. Regional Structure ...... 27 3.1 Overview ...... 27 3.2 Folds ...... 27 3.3 Faults ...... 28

4. Introduction to Stratigraphy and Sedimentology ...... 44

5. Komako Formation...... 46 5.1 Coarse flaggy grit Member ...... 47

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5.1.1FaciesanalysisofCfMember,Stratigraphiclog5.1...... 49 5.1.2Grainsizeanalysis...... 51 5.2FossiliferousmudstoneMember...... 52 5.2.1Grainsizeanalysis...... 55 5.2.2Shelfprocesses...... 56 5.2.3Bioturbationandsedimentationrates...... 58 5.2.4Modernanalogue...... 58 5.3FossiliferoussandstoneMember...... 59 5.3.1FaciesanalysisofFssMember,Stratigraphiclog5.2.....60 5.3.2Regionalcorrelations...... 68 6.KonewaFormation...... 71 6.1ConglomerateMember...... 72 6.1.1FaciesandFaciesAssociations...... 78 6.1.2Fandeltaclastanalysis...... 85 6.1.3Fandeltaforesetanalyses...... 90 6.2SandybluegreymudstoneMember...... 96 6.2.1Grainsizeanalysis...... 97 6.2.2Modernanalogue...... 99 6.3RedcrossbeddedsandstoneMember...... 101 6.3.1FaciesanalysisofRssMember,Stratigraphiclog6.2..104 6.4MarinesandstoneMember...... 109 6.4.1Ichnofossils...... 111 6.4.2FaciesanalysisofKssMember,Stratigraphiclog6.3..112 6.5CoquinalimestoneMember...... 115 7.TakapariFormation...... 119 7.1BluegreysandymudstoneMember...... 120 7.1.1Grainsizeanalysis...... 123 7.2CrossbeddedsandstoneMember...... 124 7.2.1Grainsizecomparison...... 125 7.2.2Stratigraphy...... 126 7.2.3Estuarydepositionalenvironments...... 133 7.2.4Cyclostratigraphy...... 135 7.2.5Volcaniclasticfacies...... 137 7.3Tephrochronology...... 141 7.3.1NewZealandrhyoliticvolcanismduringtheQuaternary... ...... 141 7.3.2Geochemistry...... 142 7.3.3ScrimmysTephra(NewTephra)...... 143

viii 7.3.4 Rewa Pumice ...... 145 7.3.5 Mangapipi Tephra ...... 146 7.3.6 Ridge Tephra ...... 147 7.3.7 Pakihikura Tephra ...... 148 7.3.8 Tephra grain size analysis ...... 150 7.3.9 Paleoenvironmental reconstruction ...... 152

8. Kaimatira Pumice Sand Formation ...... 153 8.1 Cross bedded sandstone Member ...... 153 8.2 Tephrochronology ...... 154 8.2.1 Potaka Pumice ...... 154 8.2.2 Paleoenvironmental reconstruction ...... 156

9. Kai-iwi Group ...... 158

9.1 Red conglomerate Member ...... 159 9.1.1 Rc Member, Kai Iwi Group, Fig 9.3...... 161 9.1.2 Rc Member, Kai Iwi Group, Fig 9.6...... 166 9.1.3 Kaukatea Tephra ...... 171 9.2 Sandstone Member ...... 172 9.2.1 Facies Analysis of eQk Member, Stratigraphic log 9.3 . 173

10. Geological History ...... 178

References ...... 198

Appendices: ...... 217 Appendix 1: Tephra geochemical and grain size data ...... 217 Appendix 2: Grain size data ...... 261 Appendix 3: Clast analysis data ...... 283 Appendix 4: Fossil data ...... 290 Appendix 5: Paleomagentic analysis data ...... 296

Fold out Sheet I: Geological Map of the Lower Pohangina Valley

Fold out Sheet II: Stratigraphy of the Lower Pohangina Valley correlated to the Whanganui Basin cyclostratigraphy and marine oxygen isotope records

List of Figures

1.1 Location map of study area near Ashhurst township and general distribution of basement, Late Cenozoic & Quaternary cover rocks. 1.2 Tectonic setting of the lower North Island, New Zealand 1.3 The basement terranes of New Zealand. 1.4 Location map and west-east cross section showing the location of the Whanganui Basin, study area and regional tectonic structures. 1.5 Map of the main tributaries within the study area 1.6 The Ohakean and Ratan Terraces Whareroa Stream, Pohangina. 1.7 Horizontal Ohakean gravels forming angular unconformity with underlying eQk Member, Kai-iwi Group dipping 15°@280 (NW).Maungatukurangi Stream, Broadlands Station. 1.8 Kawakawa tephra preserved within Ohakean loess on the Ratan terrace.

2.1 The sequence stratigraphic model, showing the highstand (HST) transgressive (TST), lowstand (LST), and Regressive systems tracts (RST). 2.2 The seven major cyclothemic (sequence) motifs recognised within the Whanganui Basin.

3.1 Fold axes of the Manawatu anticlines overlaid on an Enhanced Thematic Mapper satellite image of the Whanganui Basin. 3.2 Geological map of the lower Pohangina Valley, showing cross section lines. 3.3 Top: Geological Cross section west to east, A to A-. Bottom: restored section. 3.4 Top: Geological cross section west to east, B to B-. Bottom: restored section. 3.5 Top: Geological cross section west to east, C to C-. Bottom: restored section. 3.6 Top: Geological cross section west to east, D to D-. Bottom: restored section. 3.7 Antithetic fault plane dipping 75°W, south branch of Whareroa Stream, Broadlands Station, Pohangina Valley. 3.8 Exposure of a normal antithetic fault in Scrimmys Stream, interpreted to be connected to the Raukawa Fault at depth, Broadlands Station, Pohangina Valley. 3.9 Contact between Torlesse greywacke and Cf Member Komako Formation, note highly sheared and shattered greywacke, Antler Stream, Pohangina. 3.10 Offset Ohakean Terrace crossed by the Pohangina Fault, Pohangina Valley.

5.1 A fossil assemblage of Cf Member, Komako Formation; Zeacolpus vittatus and Maoricolpus roseus. Collected from Stallion Stream, Broadlands Station, Pohangina Valley. 5.2 Stratigraphic log of Cf Member, Komako Formation, Stallion Stream, Broadlands Station, Pohangina.

5.3 MolluscspeciesfoundwithinthesedimentsofPohanginaValleyandtheirassociated timespansthroughtheMangapanianStage. 5.4DepthrangesofselectedmollusctaxapresentwithinFmsMember. 5.5ThickbedsofCrassostreaingensformanoysterreefwithinFssMember,Komako Formation.Saddlestream,PohanginaValley. 5.6 FossilsfromFssMember,KomakoFormation:1:Ruditapeslargillierti,2:Polinices waipipiensis,3:Aulacomyamaoriana,4:Pernacanaliculus,5:Talabricasenecta,6: Purpurocardiapurpurata.CollectedfromStallionStream,BroadlandsStation, PohanginaValley. 5.7 JuvenilespecimensofPhialopectentriphooki,StallionStream,BroadlandsStation, Pohangina. 5.8 StratigraphiclogofFssMember,KomakoFormation,StallionStream,Broadlands Station,Pohangina. 5.9 ThedepthrangeofNotorotaliazealadicaontheNewZealandshelf 6.1 DepthrangesofselectedmollusctaxapresentwithinCgMember. 6.2 AfossilassemblagefromCgMember,KonewaFormation. 6.3 StratigraphiclogofCgMember,KonewaFormation,ScrimmysStream,Broadlands Station,PohanginaValley. 6.4 CorrelationofKonewaFormation(CgMember)tocycle6intheWanganuiBasin cyclothemrecord,andmarineisotopestages(MIS)90and91. 6.5 Shorelineprofileshowingdifferentsubenvironments,faciesandprocesses. 6.6 CrosssectionofaGilbertͲtypefandelta. 6.7 Zinggdiagramshowingclastshapefrom50clastsoffaciesLDS(bed5)andfacies Gmu(bed6). 6.8 Linegraphshowingdecreaseinclastsizewithdistancefromsource. 6.9 AcomparisonoffanͲdeltas,braiddeltas,andfineͲgraineddeltasbasedon distributaryͲchannelpatternsandstability,sedimentloadandsize,streamgradient, flowvelocity,steadinessofdischargeanddistanceofshorelinefromsource. 6.10 GilbertͲtypefandeltacrosssection. 6.11 SchematicmodelillustratingthedepositionalsettingofafanͲdelta. 6.12 PaleogeographicmapshowingthelowerNorthIslandduringNukumaruantime, EarlyPliocenetime(2.4Ma)Mapdepictsainterglacialperiod. 6.13 CgMemberformingaridge,highangledipplaesformedbymovementalongthe WhareroaFaultlocatedinthefarrightofthisimage. 6.14 ClassicdomeshapedhillsformedbyCgMember,KonewaFormation,Broadlands Station,Pohangina. 6.15 ThegenereraliseddistributionofsedimentswithinthemodernWhanganuiBasinand CookStraitareawithcontoursofpercentsandinthenonͲgravelfraction.Solid arrowsindicatepresentsedimenttransportpathsandbrokenarrowsindicate transportduringthelastglacial.

xi arrows indicate present sediment transport paths and broken arrows indicate transport during the last glacial. 6.16 Depth ranges of selected mollusc taxa present within Rss Member. 6.17 Struthiolaria papulosa from Rss Member, Konewa Formation, Stallion Stream, Broadlands Station, Pohangina Valley 6.18 Rss Member above Kst Member, Konewa Formation, Scrimmys Stream, Broadlands Station, Pohangina Valley. 6.19 Stratigraphic log of Rss Member, Konewa Formation, Scrimmys Stream, Broadlands Station, Pohangina Valley. 6.20 Depth ranges of selected mollusc taxa present within Kss Member. 6.21 Bioturbation, Kss Member, Konewa Formation, Scrimmys Stream, Broadlands Station, Pohangina Valley. 6.22 Stratigraphic log of Kss Member, Konewa Formation, Scrimmys Stream, Broadlands Station, Pohangina Valley. 6.23 Top: Cq Member in Scrimmys Stream. Bottom: close up of the Cq Member showing the fossils Talochlamys gemmulata, Pleuromeris hectori, and Ostrea chilensis. Broadlands Station, Pohangina Valley. 6.24 Environments of deposition within the northwestern Manawatu Strait (eastern Whanganui Basin) during Late Nukumauan time.

7.1 Depth ranges of selected mollusc taxa present within Bms Member 7.2 A fossil assemblage from Bms Member, Takapari Formation; 1: Austrovenus stutchburyi, 2: Talochlamys gemmulata and Stiracolpus symmetricus, 3: Amalda (Baryspira) mucronata. 7.3 Grain size distributions of Takapari Formation and Kaimatira Pumice Sand Formation. 7.4 Stratigraphic log of Css Member, Takapari Formation, and Kaimatira Pumice Sand Formation, Scrimmys Stream, Broadlands Station, Pohangina Valley. 7.5 Diagram showing location of facies within a wave dominated estuary system. 7.6 Correlation of Takapari and Kaimatira Pumice Sand formations to the MIS and Whanganui cyclothem records. 7.7 Tuff unit (Potaka Pumice) within Kaimatira Pumice Sand Formation, pumice clast 150mm in diameter seen near spade handle, Broadlands Station, Pohangina. 7.8 Water escape structures caused by sediment loading within tuff unit (Potaka Pumice), Kaimatira Pumice Sand Formation, entrance to Antler Stream, Broadlands Station, Pohangina. 7.9 Css Member showing dewatering structures, Maungatukurangi Stream, Broadlands Station, Pohangina Valley. 7.10 CaO versus FeO (wt %) composition of volcanic glass shards from Kaukatea Tephra, Potaka Pumice, Scrimmys, Rewa, and Pakihikura Tephras sampled in various locations around Broadlands Station, Pohangina Valley. 7.11 Location of the Scrimmys Tephra type locality on hair pin

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corner of Awahou South Rd, entrance to Scrimmys Stream, Broadlands Station, Pohangina Valley 7.12 Mangapipi Tephra enclosed by lignite beds within Takapari Formation, Antler Stream, Broadlands Station, Pohangina.

7.13 Ternary diagram displaying FeO: 1/3 K2O: CaO Wt % data for tephras collected from Takapari Formation, Kai Iwi Group and Kaimatira Pumice Sand Formation. 7.14 Grain size distribution curve of the fluvially deposited Potaka Pumice compared with grain size distributions of aerially deposited Tephras.

8.1 Map of the North Island, New Zealand, showing the minimum inferred original extent (black outline) of the Kidnappers ignimbrite.

9.1 Rc Member, Kai Iwi Group, Broadlands Station 9.2 Base of Rc Sub-Member showing Facies Fsf deposited by fluvial scour and fill processes, Telfords Farm, Pohangina. 9.3 Stratigraphic log of Rc Member, Kai Iwi Group, entrance to Whareroa Stream, Telfords Farm, Pohangina Valley. 9.4 Zingg diagram of facies Fc from the Rc Member Kai Iwi Group, Telfords Farm, Pohangina. 9.5 Rc Member unconformably overlying Kaimatira Pumice Sand Formation, forming a ridge at Broadlands Station, Pohangina Valley 9.6 Stratigraphic log of Rc Member, Kai Iwi Group, Maungatukurangi Stream, Broadlands Station, Pohangina. 9.7 Rc Member, Kai Iwi Group, Maungatukurangi Stream, Broadlands Station, Pohangina 9.8 eQk Member, Kai Iwi group, planar laminations and lenticular bedding, Maungatukurangi Stream, Broadlands Station, Pohangina. 9.9 Stratigraphic log of eQk Member, Kai Iwi Group, Maungatukurangi Stream, Broadlands Station, Pohangina.

10.1 Paleogeographic map showing the lower North Island during Opoitian time, Early Pliocene time (4 Ma). 10.2 Paleogeographic map showing the lower North Island during Waipipian time, Early Pliocene time (3.35 Ma) Map depicts an interglacial stage 10.3 Paleogeographic map showing the lower North Island during Mangapanian time, Early Pliocene time (2.7 Ma) Map depicts a interglacial period 10.4 Composite stratigraphic log showing stratigraphy of the Lower Pohangina Valley. 10.5 Box diagrams displaying depositional environments on the northwestern side of the Manawatu Strait from Early Mangapanian to Early Castlecliffian time. 10.6 Paleogeographic map showing the lower North Island during Nukumaruan time, Early Pliocene time (2.4 Ma) Map depicts a interglacial period 10.7 The Ruahine Range showing faults and location of the Ohara Depression.

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10.8 Southern North Island showing Wairarapa region, Manawatu Gorge and location of the Pahiatua Basin, the Wellington Fault, West Wairarapa Fault, and Palliser- Kaiwhata Fault. 10.9 Paleogeographic map showing the lower North Island during Castlecliffian time, Early Pliocene time (1 Ma) Map depicts a interglacial period 10.10 Box diagram displaying depositional environments on the northwestern side of the Manawatu Saddle during Mid Castlecliffian time

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List of Tables

1.1 Major aggradational alluvial terraces in the Rangitikei Valley .

2.1 Ages for tuff and tephra horizons in Whanganui Basin.

4.1 Stratigraphic nomenclature used in Whanganui Basin, East Coast Basin, and Pohangina lithostratigraphy.

5.1 Fossil assemblages from Cf Member, Komako Formation. 5.2 Lithofacies of Cf Member, Komako Formation, Fig 5.2. 5.3 Fossil assemblages from Fms Member, Komako Formation. 5.4 Fossil assemblages from Fss Member, Komako Formation. 5.5 Lithofacies of Fss Member, Komako Formation from stratigraphic log 5.2.

6.1 Fossil assemblages from Cg Member, Konewa Formation. 6.2 Lithofacies of Cg Member, Konewa Formation, Fig 6.3, Scrimmys Stream, Pohangina. 6.3 Fossil assemblage from Kst Member, Konewa Formation. 6.4 Fossil assemblage from Rss Member, Konewa Formation 6.5 Lithofacies of Rss Member, Konewa Formation, Fig 6.19. 6.6 Fossil assemblages from Kss Member, Konewa Formation. 6.7 Lithofacies of Kss Member, Konewa Formation, Fig 6.22. 6.8 Fossil assemblage from Cq Member, Konewa Formation.

7.1 Fossil assemblages from Bms Member, Takapari Formation. 7.2 Lithofacies of Css Member, Fig 7.4, Takapari Formation. 7.3 List of tephras identified in Pohangina Valley. 7.4 Scrimmys Tephra normalised data. 7.5 Grain size distribution statistics for Kawakawa Tephra, Potaka Pumice, Mangapipi Tephra and Pakihikura Tephra.

9.1 Formations of Kai Iwi Group. 9.2 Lithofacies of Rc Member, Fig 9.3, Kai Iwi Group. 9.3 Lithofacies of Rc Member, Fig 9.6, Kai Iwi Group. 9.4 Lithofacies of eQk Member, Fig 9.9, Kai Iwi Group.