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Paleoenvironmental Analysis of the Mangere Formation, Mangere Island, Chatham Islands, New Zealand
A thesis submitted in Earth Science for the degree of Master of Science at Massey University.
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George Sydney Fletcher Davies
2006 Abstract.
Mangere Island consists almost entirely of alkali basalt of the late Miocene earl y Pliocene Rangiauri a Formati on (Campbe ll et a l. , 1993) with outcrops of the sedime ntary Tupuangi Formation on the east coast and the Mangere Formati on (Campbell , et al. , 1993), a sedime ntary remnant , mainly lacustrine but also pa rtl y m arine, ly ing between the no rtheaste rn and southwestern groups of volc anic vents of
M angere Island:
As a result of the present work the sedime ntary Mangere Formati on of Campbell et al. ( 1993) has been di vided into two formati ons, Mangere Fo rmation a nd the overl yin g Parakeet Formati on. Mangere Formati on consists of ( I) a Basal me mbe r (32m of mudstone), and (2) a Cyc li c me mber ( 12.6m of alte rn ating sandstones and mudstones). Parakeet Formati on has ( I) a Carbonaceous member (0 .6m Of organi c ric h mudsto nes), (2) a Skua me mber ( 16.8m of tu ffaceous s il tstone), and (3) a capping rh yolitic tephra. The Basal me mber of the Mangere Formati on is underl ain by a breccia that is textu ra ll y ex tremely variab le (Bag End b reccia).
A sedime ntary outcrop on the eastern coast of Mangere Island is li thologicall y and m in eralogicall y identical to T upuang i Formati on on Pitt Is land as well as havin g the same C retaceous poll en suite . Thus it is in fe rred th at, at the time of Rangiauri a volcanism, Tupuangi Formati on and its overl ying Terti ary strata extended from Pitt Island at least as fa r as Mangere Island.
An arm of the sea between two Mangere Island volcani c centres extended to wards W aih ere Bay, Pitt Island. At some time in the late Pliocene, volcani c debris avalanches from the northeast and southwest groups of vent s fo rmed a debris dam that blocked off the seaward side of the sea arm, resulting in the fo rmati on an o li gotrophic fresh water lake. As a result of a low e nergy regime and vegetated slopes, the lake filled to ca . 30m w ith very fine sediment (the Basal me mber) fro m bo th the volcanics of M angere Island and the quartzofelspathi c Tupuangi Formati on of Pitt/Mangere Island. 11
Following this a debris dam, formed by volcanic debris avalanches, was breached by a ri sing sea. Local marine influence in storms destablised the slopes surrounding the then shallow lake resulting in the influx of coarse sands which alternated with mudstones deposited during quieter periods (the Cyclic Member).
At the end of thi s peri od the re was a eustatic fall of sea level or tectoni c uplift o r both , probably resulting in subaeri al erosion and an un conformity between the Cyclic and Carbonaceous Me mbers.
A second shallow fresh water lake (the Carbonaceous member) was established on the top of the Cyclic member. This lake was later overwhe lmed by w ind-blown materi al derived from a deposit of Paleocene Red Bluff Tuff exposed probably by a fa lling sea level or marine erosion. The reworked Red Bluff Tuff was later covered by a layer of rh yo litic tephra probably from the Taupo Volcanic Zone (TVZ), North Island, New Zealand.
The distinctive jointing pattern seen 111 the sandstone units of the Cycli c member resulted from doming w ith a principal stress directed northwest-southeast. This probably correlates w ith tectonic uplift in the Castlecliffian.
The lack of any positive time markers makes dating the formation rather indeterminate, but the Basal and Cyclic members (Mangere Formation) are probably upper Mangapanian and th e Skua member probably Quaternary. The sequence is generall y lacking in fossi ls, except for palynomorphs which occur throughout, and ostracods which occur only in the Cyclic member. Neither proved useful fo r datin g the seque nce.
The pollen diagrams show a consistent coastal plant association of small trees, shrubs, herbs and fe rn s throughout th e history of the sequence, with the implicati on that climate during this time did not vary greatl y from a mild, moist, equable mean. 111
Acknowledgments.
My grateful th anks to my supervisors, Prof. Y.E. Neall and Dr. Ciel Wallace, fo r th eir patience, support, and helpful di sc uss ions. Thanks also to the Marsden Grant and the Chatham Emergent Arc Research Survey (C hEARS ), without which thi s study could not have been undertaken.
My thanks also to Alison Davies and the staff of DOC on Chatham Islands for their unfailing interest, cooperation, and help both on Mangere Island and with th e loan of equipment. Thanks also to Bill Carter fo r making his residence freely available to me.
Special th anks to Juliet Cox and th e Soil and Earth Sciences secretary, Moira Hubbard , for cheerfully and adroitly steerin g me through my computer problems ; to Mi chael Turner for microprobing th e tephra and hornbl end es; to Kat Holt fo r discussions and resources related to the Chatham Islands: to Kevi n Butler fo r hi s valuable and cheerfull y given help with palynology: and to Tristan Dav ies fo r help with Paintshop Pro .
My th anks also to the technicians Carolyn Hed ley . Ian Furkert , Bob Toes, Glenys Wall ace and Anne West fo r their help , friendliness and advice in th e laboratory. Thanks to my fellow students, Juli et Cox, Kim Martelli and Seth Laurenson for an interestin g year of discussions, help and friendship. Special th anks to fellow student Deborah Crowley, who has been a good fri end and coll eague .
Finally my grateful thanks to my wife, Megan, for her patient support, advice, proof reading, and the water colour of Mangere Island on the title page. IV
Contents
Abstract ...... i Acknowledgements ...... iii Contents ...... iv Figures ...... vii Tables ...... x
Chapter l Introduction ...... 1 1.0.0 Ain1s ...... 1 1.1.0 Thesis structure ...... I I. I. I Location of study area ...... 1 1.1.2 Mangere Island: historical and biological hackground ...... 3 1.1.3 Mange re Island physiography ...... 1.2.0 Regional geology. introduction ...... 7 1.3.0 Previous work on Mangcrc Island ...... 22
Chapter 2 Methods ...... 27 2.0.0 Fieldwork ...... 27 2.0.1 Height and thickness the Mangere Formation ...... 28 2.0.2 Note ...... 29 2.0.3 Fossils ...... 29 2.1.0 Laboratory work ...... 30 2.1.1 Preparation of microfossils ...... 30 2.1.2 Particle size analysis ...... 31 2.1.3 Microprobing of hornblende and tephra ...... 32 2.2.0 Optical microscopy ...... 32 2.2.1 Temporary and permanent microscope mounts ...... 33 ,., Counting of mineral grains ...... 33 2.3.0 Palynology ...... 33 2.3.1 Sampling procedure ...... 33 2.3.2 Sample preparation ...... 34 2.3.3 Slide preparation ...... 36 2.3.4 Counting ...... 37 2.3.5 Identification ...... 37 2.3.6 Charcoal ...... 37 2.4.0 X-ray diffraction (XRD); Introduction ...... 37 2.4.1 Instrun1ent ...... 38 2.4.2 Processing of samples for XRD ...... 38 2.4.3 Calciun1 re111oval ...... 38 2.4.4 Organic matter removal ...... 39 2.4.5 Removal of iron and aluminium oxides and oxyhydroxides ...... 39 2.4.6 Clay separation ...... 40 2.4.7 Saturation with cations ...... 41 2.4.8 Preparation of x-ray slides ...... 41 V
2.4.9 Silt and sand separation ...... 42 2.4.10 Sand fraction density separation for heavy and light minerals and volcanic glass ...... 42 2.4. 11 Preparation of dry clay ...... 43 2.5.0 XRD procedure for oriented samples ...... 43 2.5. 1 Interpretation ...... 44 2.5.2 Determination of clays ...... 45 2.5.3 Quantitative analysis of minerals and clays ...... 45 2.5.4 Determinat ion of allophane content of the Basal and Skua membcrs ...... 45 2.6.0 Differential thermal analysis (OTA) ...... 46 2.6.1 Procedure ...... 4 7 2.6.2 In terpretation ...... J.7 2.7.0 Loss on ignition ...... 4 7 2.8.0 Experiment to si mulate ripples found on the bases of several sandstone units of the Cyclic membcr ...... 48
Chapter 3 Results ...... 49 3.0.0 Introduction ...... 49 3. 1.0 Tupuangi Formation ...... 49 3.1.1 Mangerc Formation ...... J.9 3.2.0 Stratigraphic columns ...... 53 3.3.0 Results of field and laboratory work; int rod uction ...... 57 3.3. 1 Tupuangi Formation ...... 57 3.3.2 Grain size analysis of the Tupuangi Formati on: Pitt and Mangere lslands ...... 58 3.3.3 XRD analysis of the Tupuangi Formation. Pi tt and Mangerc Islands ...... 58 3.3.4 Fossil s in Tupuangi Formation, Mangerc Island ...... 58 3.4.0 Bag End breccia ...... 59 3.4. 1 Optical microscopy of Bag End breccia ...... 63 3.5.0 Mangere Formation ...... 63 3.5. 1 Basal member ...... 63 3.5.2 Loss on ignition; Basal member ...... 64 3.5.3 Grain size analysis: Basal member ...... 65 3.5.4 XRD results of rock samples from the Basal member. Mange re Forn1ation ...... 66 3.5.5 Palynology; Basal member ...... 67 3.5.6 Optical microscopy: Basal member ...... 69 3.5.7 Cyclic member ...... 70 3.5.8 Stereographic analysis of joints in the sandstone units ...... 78 3.5.9 Grain size analysis; Cyclic member ...... 78 3. 5. 10 XRD results; Cyc lic member ...... 82 3.5. l I Microprobing of hornblendes; Cycl ic member and Rangiauria Breccia ...... 84 3.5.1 2 Fossil s ...... 85 3.5. 13 Palynology; Cyclic member ...... 85 3.6.0 Parakeet Formation ...... 88 3.6. 1 Carbonaceous member ...... 88 3.6.2 Loss on ignition; Carbonaceous member ...... 89 VI
3.6. 3 Palynology; Carbonaceous member ...... 89 3.6.4 Fossils; Carbonaceous member ...... 91 3.6.5 Skua n1e1nber ...... 9 1 3.6.6 Fossils; Skua member ...... 93 3.6.7 Grain size analysis; Skua member...... 93 3.6.8 Tephra, Skua member ...... 94 3.6.9 Pal ynology. Skua member ...... 96 3.6. 10 Microprobing of hornblendes: Skua member ...... 98 3. 6.11 XRD analysis: Skua member ...... 99 3.6. 12 Microscopic and XRD compari son of sampl es from Owenga Road, Chatham Island and sample Sk I fro m the Skua member, Mangere Formation ...... I 00
Chapter 4 Discussion ...... 102 4.0.0 Tupuangi Formation ...... I 02 4.0. 1 Relationship between Pitt and Mangere Islands ...... I 03 4.0.2 Local regional fau lting ...... I 06 4.1.0 Bag End breccia ...... I 09 4.2.0 Origin of Lake Mange re ...... I I-+ 4.3.0 Mangere Forn1ation ...... I IS 4.3. 1 Basal member ...... I 16 4.3.2 Palynology of the Basal member...... I 16 -+ .3.3 Cyclic member ...... 11 7 4.3 .-+ Introduc tion ...... I 17 -+.3.5 Post Cretaceou!-. poll en of the Cyclic member ...... 120 4.4.0 Parakeet Forn1ation ...... I 21 -+.4. 1 The Carbonaceou!-. me mber: a ~hallow la ke forms on the Cyclic member ...... 12 1 -+.-+ .2 Palynology or the Carbonaceous mem ber ...... 123 -+.-+.3 The Skua member: provenance and paleoem·ironment...... 124 4.4.4 Palynology of the Skua me mber...... 126 4.-+ .5 Depositi on of the tc phra uni t ...... 126 4.5.0 For further consideration ...... 130 -+.5. 1 Dating the sequence ...... 130
Chapter 5 Conclusions ...... 13 I
References ...... 134 Bibliography ...... J37 Appendices: Appendix 1...... 139 Appendix 2 ...... 141 Appendix 3 ...... 142 VJI
Figures.
Figure l Chatham Island location map ...... 2 Figure 2 Location map for Mangere Island showing the extent of the Mangere Forn1ation ...... 5 Figure 3 Aeri al photograph of Mangere Island with physical features labell ed ...... 6 Fi gure 4 View of Mangere Island from orth Landing ...... 6 Figure 5 Vi ew of Mangere Formati on from the Douglas Basin ...... 7 Figure 6 Regional bathymetry and tectoni c features of the Chatham Ri se ...... 8 Fi gure 7 Space-time diagram showin g the ge neral relatio nships of kn own stratigraphic units in the Chatham Islands ...... 9 Fi gure 8 Geo logical map of the Chatham Islands ...... I 0 Fi gure 9 Key to th e geo logical map of th e Chatham Islands ...... I I Fi gure lO Paleogeographi c reconstruction of the Chatham Islands area during Tupuangi time ...... 13 Fi gure 11 Map of Pitt and Mangere Islands redrawn from Hay et al. 1970. ····· ·············· ··· ·· ············································ ·· ·· ·· ··· ···· ·· ····· ······ ····24 Fi gure 12 Diagram of Hay er al 's. 1970 model showing '· ... the relati onship between Rangiauria and Mangere agglomerates at the suggested single volcanic vent of Mange re and Little Man ge re Islands.·· ...... 24 Fi gure 13 Comparison of stratigraphic co lumns fo r Mange re Island to th e present ...... 25 Fi gure 14 Sketch map showing inferred locati on of volcani c ve nts on Mangere lsland ...... 26 Fi gure 15 Flow diagram for XRD process in g and determining th e mineral content of samples ...... 40 Fi gure 16 Graph illustrating the temperature differential peak di sc ussed in th e text...... 47 Fi gure 17 Vi ew of Man gere and Rangiauria Formations to show th eir stratigraphic units ...... 50 Figure 18 View of Mangere and Parakeet Formati ons from the ridge immediately orth of the hut, showing Basal, Cyclic, Carbonaceous, and Skua members ...... 51 Figure 19 View of Mangere and Parakeet Formations on th e eastern (South Landing) side of th e island with lithological units named ...... 52 Figure 20 Strati graphic column, Tupuangi Formation, Mangere Island ...... 53 Figure 21 Stratigraphic column, Bag End breccia, Mangere and Parakeet Formations, Mangere Island ...... 54 Figure 22 Stratigraphic column, Cyclic member, Mangere Formation .. 55 & 56 Figure 23 View of southeast side of Mangere Island showing the Tupuangi Forn1ation ...... 57 VIII
Figure 24 View showing the Bag End breccia at the northeastern end of Mangere Formation, orth Landing ...... 60 Figure 25 Detai l of the lower beds of Bag End breccia, halfway along its outcrop showin g bed structures ...... 61 Figure 26 View showing a megaclast of Rangiauri a Breccia with maximum dimension of 6.6 m ...... 62 Figure 27 Photomicrograph of the Bag End breccia showin g vesic ul ar basalt lithics ...... 63 Figure 28 View of the Basal member at grid ref. 6685 1945 ...... 65 Figure 29 Perc entage sand , silt, and clay fracti ons for samples B 1, 8 3, 85 of th e Basal member...... 65 Figure 30 Photomicrographs of th e Basal member...... 70 Figure 3 1 Vi ew of the Cyclic member from North Landing show in g th e junction between Basal and Cyc li c members ...... 71 Figure 32 A block fa ll en from the termination of unit 30c ...... 72 Fi gure 33 View of di sturbed bedding above the Basal member northeastern end ...... 72 Figure 34 Vi ew of the junction between Basal and Cyclic members showi ng intrafo rm ati onal fo ldin g ...... 73 Figure 35 Detail of th e Cycli c member above South Landing showin g a shall ow channel fill and th e disl ocated, overridden ripple unit...... 73 Figure 36 Vi ew from ex treme northeastern end of Mange re Formation of the units below th e ripple unit...... 75 Figure 37 View of the ve ry short wavelength, hi gh am plitude, near sy mmetri cal ripples fo und on the bases of some of th e sandstone units in th e Cyclic member...... 76 Figure 38 View of ripples ex perimentall y formed in a tro ugh ...... 76 Figure 39 Fossil wood in th e lowest unit of the Cyc li c member...... 77 Figure 40 Gypsum formed in joint pl anes of the lowest unit of the Cyc li c ,nember...... 78 Figure 4 1 Stereographic analysis of joints in th e ripple unit (26c), Cyclic member...... 78 Figure 42 Bar and cumulati ve frequ ency graphs showing th e distribution of grain sizes for unit 13c, Cyc li c member...... 79 Figure 43 Bar and cu mulati ve frequency graphs showin g the distribution of grain sizes for unit 20c, Cycli c member...... 79 Figure 44 Bar and cumulative frequency graphs showing the di stribution of grai n sizes fo r unit 26c, Cyclic member...... 80 Figure 45 Bar and cumulat ive freq uency graphs showing the di stribution of grain izes for unit 28c, Cyclic member...... 8 1 Figure 46 Graph of Fe agai nst Mg fo r hornblendes in sampl e 30c, Cyc li c niember...... 84 Figure 47 Pollen di agram, Cyclic member...... 87 Figure 48 Fall en block of the Carbonaceous member...... 88 Figure 49 Poll en diagram for a fa ll en block and in situ deposits of the Carbonaceous member...... 90 IX
Figure 50 Detail of theSkua member showing the mass ive, lamjnated, cross-bedded, and tunnelled units within the yellow-red siltstone unit...... 91 Figure 5 l Panorami c view, Skua member...... 92 Fi gure 52 Grain size compari so n of the Skua member units Sk3 and 4 ...... 93 Fi gure 53 Graph comparin g the grain size di stribution of Aeolian Red Bluff Tuff at grid ref. 478543 Owenga Rd. , Ch ath am Island and sample Ski , Mangere Formati on ...... 94 Fi gure 54 Ph otomj crograph of glass shards from th e coarser sandstone tuff at the base of unit Sk5 ...... 95 Fi gure 55 Tern ary di ag ram showing th e Skua member tephra (unit Sk5) fo r compari son with tephras from Taupo Volc ani c Zone ...... 95 Fi gure 56 Poll en di agram, Skua member ...... 97 Fi gure 57 Graph of Fe aga inst Mg from Sk I Skua member ...... 98 Fi gure 58 Photomi crograph s of yell ow-red sa mpl es, Sk I and 2, Mangere Form ati on and materi al fro m wind -bl own Red Blu ff Tuff at grid ref. 4 78534 Owe nga Rd ...... 100 Fi gure 59 XRD trace, ye ll ow-red siltstone (samples Sk I and 2), Skua n1e n1 be r...... IO I Fi gure 60 XRD trace of wind -blown materi al fro m Red Blu ff Tu ff at grid ref. 4 78 534 Owe nga Rd. , Chath am Island ...... IO I Figure 6 1 Cross sectio n of Pitt and Ma nge re Island s fro m the mouth of second water cree k ...... I 03 Figure 62 Bath ymetri c map of the seafl oo r aroun d Pi tt and Mangere Islands ...... I 04 Fig ure 63 Topographic map of Pitt Island showin g that the dra in age pattern ri ses exclu sive ly near the western coastal cli ffs and drain s to the east...... I 05 Figure.64 Model of Pitt/Mange re Island after Rangiauri a vo lcani sm ...... I 06 Figure 65 Map and cross secti on of northwestern Pitt Island ...... I 07 Fi gure 66 Map of Mange re and Lit tl e Mangere islands show in g the locati on of fa ults ...... I08 Fi gure 67 Model depi cting th e in fe rred situ ati on after the end of Rangiauri a vo lcani sm ...... I 09 Figure 68 Compari son of Whenu ataru Tuff and Bag End breccia ...... 111 Fi gure 69 Vi ew of the sea cliffed vo lcanic remnant at grid ref. 663 195 Mangere Island ...... 11 3 Fi gure 70 Detail of Fig. 68 showin g vari ously ori ented megaclasts as a result of vo lcani c debris fl ows ...... 11 3 Fi gure 71 Model fo r the ori gin of Lake Mangere ...... 115 Fi gure 72 Model showing the situ ati on when the sea had breached The barri er of Bag End Breccia ...... 117 Fi gure 73 Model to expl ain the di sturbed bedd ing at the northwestern end of the Cyclic member, Mangere Formati on ...... 119 Fi gure 74 Model fo r the fo rmati on of a fre sh water lake on th e Cyclic n1ember...... 123 X
Fi gure 75 Model for the deposition of the yell ow-red si ltstone unit ...... 125 Figure 76 Model for the deposition of the tephra unit...... 127 Figure 77 Model of Pitt and Mangere Isl ands at some time in the Tertiary .... 127 Figure 78a Diagrammatic summary of the history of the Mangere sed imentary sequence ...... 128 Figure 78b Diagrammatic summary of the hi story of the Mangere sedimentary sequence ...... 129 Fi gure 79. An attempt to correlate th e eustatic, tectonic , and depositional/erosional events of thi s study to th e 3rd order global sea leve l curve of Haq et al. ( 1987) ...... 133
Tables.
Table I Percent age distribution of sand , silt , and clay fractions of Tupuangi Form ati on from Pitt and Mangere Island s samples ...... 58 Table 2 Relative perce ntage distribution of se lected li ght and heavy minerals from XRD data fo r Tupuangi Formati on, Pitt and Mangere Isl and s ...... 58 Table 3 Loss on ignition. Basal member ...... 64 Table 4 XRD results fo r roc k samples from the Basal member...... 66 Table 5 Heavy mineral fraction. Basa l member ...... 67 Tab le 6 Graphical statistics for Fi g. 41...... 79 Table 7 Graphical statisti cs fo r Fig. 42 ...... 79 Table 8 Graphical statistics fo r Fi g. 43 ...... 80 Table 9 Graphical statistics for Fi g. 44 ...... 81 Table 10 XRD results for sand, silt, and clay fractions, Cyc li c member ...... 82 Table 11 XRD resul ts for heavy minerals, Cycli c member ...... 83 Table 12 Loss on igniti on interpreted as organi c carbon co ntent of Carbonaceous member samples ...... 89 Table 13 Graphical stati stics for Fi g. 52 ...... 93 Table 14 XRD res ults of sa mpl es from the Skua member...... 99 Table 15 XRD results of the heavy mineral fracti on, Skua member...... 99 Chapter l . Introduction. l.0.0 Aims.
The primary aims of this study were to: • Provide a detailed description of the stratigraphy o f the Mangere
Formation (as defined by Campbell el al. ( 1993). • Determine the areal extent of the Mangere Formation • Determine the provenance of the Mangere Fo rmation • Exp lain the palaeohistory of the Mangere formation • Determine the palaeoc limate at the time or deposition of the Mangere Formation. using pa lynology and other microfossils • Determine the time or deposition or the Mangere Formation.
I. 1.0. Thesis structure.
This thesis compri ses fi,,c chapters. Chapter I is an introduction to the stud) area. It CO\'ers the aims of the study. and the location of the st udy area. together,, ith notes on the history and physiography or Mangere I land. plus some background on Mangere lsland·s conscn·at ion importance. The regional geo log) or the Chatham Island s. and especially Pitt Island. is briefly coYered as this is rele,,ant to the Mangere Island stud y. Finally. in Chapter I. previous geo logica l ,,ork on Mangerc Island is CO\'ered. Chapter 2 details and explains the methods of fi eld and laborator) work used in the study. Chapter 3 details the results of fi eld and laboratory \\Ork and includes stratigraphic columns of the Tupuangi and Mang ere Formations on Mangere Island. Chapter 4 discusses the results of field and laboratory work given in chapters 2 and 3. and reconstructs the palaeohistory of the Mangere Fo rmation as a series of
maps. Chapter 5 details the conclusions of the study and relates them to the Haq el al. ( 1987) sea level curve.
l. l. l . Location of the study area.
The Chatham Islands are located approximately 850 km east of Christchurch (F ig. I). The main economic activit y is fishing (blue cod. crayfi sh, paua) and sheep farming for woo l. The islands were origina lly inhabited by the Moriori. In the mid- 2 nineteenth century they were settled by Europeans and in 1835 the Moriori were largely displaced as a result of a Maori invasion from mainland ew Zealand (King. 1990).
Chatham Island
Te One •
Waitangi 10 a Km
N i ,--3'"9•
" Mangere Island O NEW ZEALAND. <~ 1 lrttte Mangere Island~~ 0 500 '-....._/ Sail ROCko • c=iofhe Caslle
Kilometres / ) 1f';J_,f South East ls~ d ~ /=- C"-~am ""'ci'
~ ;)
Pyram,d Rock •
Figure I. Chatham Islands location map. 3
The largest island is Chatham Island, over 50% of which is covered in blanket peat, followed in order of decreasing size by Pitt Island, South East Island, and Mangere Isla nd (the object of this study), as well as many smaller islands, rocks, and reefs.Mangere Island lies 2.3 km off the west coast of Pitt Island. It is approxi mately 2.3 km long and 1.2 km at it s widest (Fig. 2). Associated with it are a number of sma ll er islands. the most prominent of which are Little Mangere Isla nd , The Castle, Pyramid Rock. and Sail Rock (Fig. 1), as well as a number of small rocks and reefs. These is la nd s and rocks are all vo lcanic and of Late Miocene or Earl y Pliocene age. except for the sedimentary Tupuangi (Cretaceous) and Mangere Formatio ns (upper Pliocene) on Mangere Island.
1.1.2. Mangere Island, historical and biological background.
Mangere Isla nd was largely fo rested until the 1890's when the fo rest was cleared for sheep fa rming which continued until 1966 (Atkinson 2003). The isla nd was made a nature reserve in 1967 (Atkinson. 2003 ). and an extensive reafforestation programme of mainly C hatham Island akeake (0/eorio tral'ersii) was initiated. The present vegetation is broadly. akeake fo rest. koromiko sc rub. naxland. herbfield s. and introduced grasses. Between 1970 and 1989 (Atkinso n 2003) C hatham Isla nd snipe. black robins, shore plover. and Chatha m Island tomtits were re introduced. The Island is also important for several threatened species of invertebrate; the Rangatira spider. the coxell a weevil whi ch li ves on the last remaining area of Dieffenbach' s speargrass fo und onl y on Mangere Is land , the g ia nt click beetle (Amy chus candezei) as well as a fli g htless carabid beetle (Mecodema alterans), a nocturna l fli ghtless stag beetle (Geodorcus capita), plus a number of moths. Skinks are abundant on the island . In addition to the above me ntioned birds there are sooty shearwaters, fairy prions, broad billed prions, bl ack- w inged petrels, blue penguins, C hatham Island oyster catchers, Pitt Island shags, red-billed gulls and white-fronted terns. Land birds include brown skua, Forbes parakeet, and C hatham Islands warblers, tuis, and parakeets. 4
1.1.3. Mangere Island Physiography (Figs.2 and 3). The Island can be divided into 3 major topographic units: I. A top plateau to the north. bounded on its northern and western sides by 200 metre-high cli ffs of massive resistant breccia which rise almost vertically from the sea. The eastern side of the plateau fa lls precipitously to Black Robin Bush where huge blocks fa llen from the cliff above are scattered on a coll uvial footslope that extends to the shoreline. 2. To the south. the top plateau gi\'es way to the more gently sloping Do uglas Basin and this merges into: 3. A long narrow. genera ll y steep sided southwest-trending peninsula
\Vith a ce ntral ridge attaining a height o r no more than I 00 111. The lowest part or this peninsula is occupied by the Mangere Formation
(as de fi ned by Campbell et of. 1993). a flat lying sedimentary sequence. 350 metres long and a,·eraging about 175 metres wide wit h the highest point at 72 m.a.s.l.( metres above sea le,·el) (Figs. 2 and 3). The lower part of the fo rmation is a ski rt sloping m,·ay from a layered sequence at about -t0° (Figs. -+ and 5). The cliff face or the layered sequence slopes at about 60° and the upper part is near ,·crtical.
Although the prevailing wind direction is south,,·est. northwesterlies arc frequent. The western side of the island is thus subject to a high frequency or rough seas \,\ hich account for the steep cliffs or the indurated northern mass if or Mangere Island and Little Ma ngere Island. as well as wave-cut platfo rms ,\hic h occur only on the southwest-trending peni nsula and are also partly a consequence of its much le s consolidated lithology. 5
I . ,,. \\Robin Bu h Top Plateau \ I
Mangere Island
Douglas Basin 0
l\"onh Lantl'ri'g N Little Mangere Island
0 500 -----met res Contour 111ten al : 20 m
Figure 2. Location map for Mangere Island showing the extent or Mangere Formation (maroon colour). The place names on Mangere Island are inlo rmal names used b) local people and the Department or Consen·at ion. The .. tick .. symbo l on little Mangere Island indicates a \'ertical rock face. 6
Figure 3. Aerial photo or Mangere Island showing: A: Top Plateau. B: Douglas Basin. C: rockfall footslope (covered by Robin Bush). D: The eek. E: the lower peninsula. F: the extent of the ll angere Format ion. G: v,a,·e cut platform. I: Tupuangi Formation. The green lines on the Top Plateau and the lower peninsula arc akeake hedges planted as part or a Department or Consen ·at ion (DOC ) reafforestation programme. Photo: Dept. or Lands and Sun·ey.
Figure 4. View of Mangere Formation taken fro m the orth Landing. The DOC hut is the white object at the extreme centre right of the photograph and The eek is al the extreme left. The 01th Land ing is marked by the --x"at centre foreground. The South Landing is opposite this on the other side of the Mangere Format ion. The photograph was taken from the seaward edge of the wave-cut platform. 7
Figure 5. View of Mangere Formation taken from Douglas Basin looking southwest along the lower peninsula. The Mangere Formation remnant is the hill in the centre of the photograph. The North Landing is marked with an '•X"' at the end of the inlet in the wave-cut platform just below the hut at the centre right. The South Landing, ··y··. is on the wave-cut platform at the centre left of the photograph. Little Mangere Island is at the top right hand corner. (Photo: Mark Bellingham).
1. 2.0. Regional Geology. Introduction.
The C hatham Islands lie on the easternmost emergent structural high of the Chatham Rise. The Chatham Rise is a shallowly submerged (to about 400 m along its crest) block of continental crust w hich was probably formed at the edge of the proto Pacific plate when it was Gondwana (Campbell et al. 1993, p. 29). Structurally the Chatham Rise extends about 250 km to the east of the Chatham Islands and 950 km west to the A lpine Fault and is about I 00 km wide. The Rise was originally part of Gondwana and probably adjacent to Antarctica. The Rise is bounded to the north by 8 the Hikurang i Plateau and to the south by the Bounty Trough. T he Mernoo Gap at the western e nd of the Ri se is part of a fo re land basin which includes the Canterbury Pla ins and shelf and whi ch develo ped during Late Miocene time (Fig. 6). The Chatha m Isla nd s is the onl y emergent area o n the Ri se. There is no sati sfactory expl anation for this at present altho ugh the Isla nd s themselves may be the result of therma l upli ft assoc iated w ith Late Cretaceous vo lcanis m. In the past the Veryan and Mernoo Banks may have been e mergent as there is evidence of erosio n on them (Campbe ll et al. 1993).
# ~ r=,-,. ,,, Camp~II Plateau S ale 1 :730000 1700 18()0 - 1n;0 - 17 00
Figure 6. Regiona l bathymetry a nd tecto nic feat ures of the Chatham Ri se (adapted fro m Wood and Anderson 1989: p. 269).
A useful way of visuali sing the geology of the C hatham Isla nd s is g iven in Figure 7 fro m w hi ch it is clear that the geology of the C hatham Islands is subject to many hi atuses. The stratigraphic abbreviations used in the text refer to the geological map (Campbell et al. 1993) of the C hat ha ms a nd its key (Figs. 8 and 9). A number of minor stratigraphic units w hich do not occur on e ither Pitt Island or Mangere Island w ill be only briefl y discussed for completeness. Much of w hat fo llows is adapted fro m Campbe ll et al. ( 1993). 9
SE
10
50
70
80
90 Tuouano, FOl' mat,on I 100 base not e ;o.p<>sed
11 0 T1 nnn TITITr1n
10 km (appro• l
Figure 7. Space-time di agram showing the ge nera l relationships of known stratigraphic units in the Chatham Island s. (From Campbe ll et al. 1993. p 12).
Chatha m Schi st (be).
During the Permi an and Triassic (perh aps earli er). vo lcani c and qu artzofe ld spathi c sediment s were depos it ed in a deep marine enviro nment on the marg in of the proto-Pac ific plate where bu ria l transformed them into greywacke and arg illite . Dur ing the Mid-Jurassic (ca. 164 Ma) th ey we re large ly metamorphosed to sc hi st (Adams and Robinso n 1977. p. 296) as a result of a major co lli sion between these quart zofeldspathic Torlesse terra in sediments and the Caples/ As piring and Murihiku terra ins thus fo rming the future base ment of the Chatham Ri se and Chatham Islands. This basement also underli es Mangere Island as is demonstrated by sc hi st xenoliths in the Rangiauria Breccia. 10
-;,
"·-<:7,\ . _,,
' -______J \) CHATHAM /SU.ND ~ ,- "i , I ' I / I
(' ·, I' I: I I ;I t
PITT ISLAND
Figure 8. Geological map of the Chatham Islands. (from Campbell et al. 1993). I 1
F INTERNATIONAL _ NEW ZEALAND ~~ Chatham Island I Pitt Island EPOCH/ERA STAGE SERIES STAGE ~ O.
i------~? 2 --, HAWERAH .. .,,___ 0 , ~ g Onoua - "' CASTUcumAN "' . , ,':::: rd \\anue,e l 1mestone mo a. Formation mg P)ram1d 'J .~8 ...w ~ -·· "..., 0 ~ -+ ~ N • "10!, ~ Rangiauna .. 4- ,,o "' w 2 Brecc,a mb "'z z § g CUFOEHIAN - IS O z 2 "' ...... r Al.TOHtAN _. _ J I ,. ] Lnnamed Altonian Limestone >-a ~- - l nnamed Ahon1an TutT ll OTAIAN ... AOlUTAHlAN t aoroa L 1mestone ~ ... L1thofac1es lt w ~ C>tATTlAH JO • '-onhem \ 'olcamc, i.n i tL tondla Limestone ! """"'""' [J I Fac1es k" ""'-480NIAH Te One L1me,cone ~ Member l"'o .. ' BAATONtAN w z ,.. "lt w 90ATOH1AN .. ' 8 wz ~ ~ ... .. s LUTETIAN l'ORANGAH ~ ~ ""_ .. , .. 1 HERE1 AUN()AN "" ..., \.tatanganu1 Limestone .... \lemberl"'m MANQ..t.ORAPAH 0,. j V~ESL,t.N it ~. I ! " Red Blufll ull lr s .. '""""""' § g- TE\JR&AN 110 C: 0 Tuma10 L1mes1one Member um °' 0 ~ OANIAH ... -= 0 Tutm GrC'efband n I i l al..ruGnttk l nnamed -,.- -, 1-t aumunan L,mescone ph "•hu1tara Southern Tuff pl \'olcan1cs ps ~SAHTONlAN~ ~ ~! f=== ~ 1upuang1 ~ ~ ~ Formauon wt ALOtAN ! ]... .,~ - Chatham Schist be .= !- Figure 9. Key to geological map of Chatham Islands (Fig. 8). (modified from Campbell el al. 1993). Based on an assumption that there is no fault in Pin Strait and with a uniform dip of 1° of the schist surface from Chatham Island. Campbe ll el al. (1993, p 128) 12 estimated the schist would be 830-900 m below sea le ve l at Mangere Island. Howeve r, the situation is more complicated at Pitt and Mangere Islands since (a) the we ll exposed Tupuangi Formation on Pitt Island suggests there is a fau lt in Pitt Strait and (b) as a result of fau lting and doming in the Pitt/Mangere area, the Tupuangi Formation dips genera ll y so mewhat less than 20° to the southeast on Pitt Island and 14° to the northwest on Mangere Island. Further, the Tupuangi Formation on Mangere Island is fau lt ed with an unknown downthrow to the so uth where it underlies the Mangere Fo rmation. Thus. under th e northern part of Mangere Island the sc hi st is probabl y considerably nearer the surface but dipping to the west. and under the so uthern part of the island the sc hi st is an unknown amount deeper. but presumably with a si mil ar attitude. It is probable that the whole Chatham Ri e ha ahvays been proximal to the Pacific Plate boundary (Campbell et al .. 1993. p 29). There is seismic refl ection evidenc e that the basement of the Hikurangi Plateau ma y dip beneath the Chatham Ri se with the possibility that it was once a co nve rge nt margin (Bradshaw et al. 1981 . Campbell et ct! .. 1993. p 30). Hov',ever this is not upheld by King (2000) "vho shows no convergence along the northern margin of the Chat ham Ri se in hi s se ri es of reconstruction of the Nev; Zealand area. The so uthern margin of the Ri se borders the Bounty Trough which was fo rmed by rit1ing in mid-to-late Cretaceous time ( 105 to 75 Ma). (Wood el al.. 1989. p 281) accompanied by rilting and tensional crustal thinning. This tension. in turn. resulted in east-west horst and half-graben structures on the eastern Ri se whi ch are major co nt ro l on the present geo logy of the Chat ham Islands. The rifting which began in the Lower Cretaceous resulted in the separation of the New Zealand continental area from Gondwana in the Upper Cretaceous (85 to 87 Ma). The Chatham Ri se, as part of the Pacific Plate, began its rotation to its present position at this time. Waihere Bay Group (w). While still part of Gondwana the half grabens were mainly filled (87 to 105 Ma) with horizontal quartzofeldspathic sed iments ofTupuangi Formation which now dip gentl y so uth to so utheast (F ig. 8). Tupuangi sediments are ge nerall y grey to dark grey and poorly co nso lidated with an estimated thickness of at least 700 m (Campbell el al., 1993, p 3 7). 13 They are best exposed as a series of fault blocks in Waihere Bay opposite Mangere Island. The sediments include conglomerate with discoid pebbles near the base. silty sand stones. sa ndy siltstones and lignite with some basalt and rhyo lite vo lcaniclastics. They are generally rich in pollen, leaves. and wood with rare macrofossils at the base. They are tuffaceous near the top and gradually grade into the massive Kahuitara Tuff. From palaeocurrent trends (Campbe ll et al. 1993) the sediments appear to have been derived mainly from the slO\\·ly pro grading delta of an emergent landmass the north northeast (Fig. I 0). These sed iments appear to have come from a Permian- Triassic source. as reworked Permian-Triassic palynomorphs are fou nd in both the Tupuangi Formation and the Kahuitara Tuff (M ildenhall and Crosbie 198 1 pp.2-23: Mildenhall 1983 p.165). At this time it is thought that much or the Rise was emergent (Campbell et al. I 993 pp. 29. 41. 43 ). The Tupuangi Formation is nowhere exposed on Chatham Island and its base is not exposed on Pitt Island. Offsho re seismic evidence and ve locit y data (Austin et al. 1973: Wood and Ingham 1981: Campbell er al. 1993 p. 35) suggest that older unexposed sed imentary equences or infe rred Cretaceous age underlie the Tupuangi Formation and may be the provenance from which the IO\\est units of the Tupuangi Formation are part ly deri\·ed. These studies also shO\\ that there is an unconformity between these units and the Chatham Schist. The Tupuangi Formation is sho\,·n in this study to be present on Mangere Island. N I 0 10 Figure I 0. Paleogeographic reconstruction of the Chatham Island area during Tupuangi time (from Campbell el al. 1993 p. 41 ). This study shows that Tupuangi Formation extended at least as far west as Mangere Island. 14 Pitt Island Group (p ). Introduction. The Pitt Island Group immediately. and mainl y conformably, followed the deposition of the Tupuangi Formation. It represents a prolonged episode of vo lcanism which occurred from ca. 87 to 70 Ma in the Upper Cretaceous (Campbell et al. 1993. p. 54). It consisted of basaltic fl ows to gether with the depo sition of Kahuitara Tuff and an unnamed Haumurian limestone. These lithologies consist of the so uthern portions of Chatham Island and Pitt Island and probabl y underlie or extend out toward s Mangere Island . It was at this time that crustal extension finall y separated the ew Zea land continental area from Gondwana. Thermal uplift from late Cretaceous volcanism resulted in the rai ing and emerge nc e of fa ult blocks. Evidence fo r thi s includes the basement horsts which are exposed in Chatham Sc hi st. northwestern Chatham Island , and graben fill on Pitt I land . Graben filling ceased during latest Cretaceo us time with minor fo lding. peneplanation. thermal subsid enc e and eruption of the Southern Volcanics in the for m of several large alkaline volcanoes (Ca mpbell et ct!. 1993 p. 29). Fo llowing thi s there \Vas a period of widespread mild tectonism in the Palaeocene/Eocene when Cretaceous normal fa ult s were reacti,·ated. especially to the west. and the elastic Red Bluff Tuff was deposit ed. Thro ugh most of the Tertiary. periods of limestone deposition (xeno liths from so me of these are common in the Rangiauria Brecc ia on Mangere Island ). alt ernated with periods of vo lc ani sm interspersed with prolonged periods of non depos iti on or erosion between episodes as is shown in Figu re 7. Little appears to be known of what happened during these non-depositi onal periods. Kahuitara Tuff (pk). There are no known outcrops of Kahuitara Tuff on Chatham I land. The Tuff 1s brown-grey and massive to well bedded. It consists of vo lcaniclastic sand stone, scoriaceous conglomerate, and lapilli tuff of basaltic composition, with bombs in the basa l units. Its thickness is ca. 225 m and it is unconformable with the Tupuangi Formation to the northeast but is conformable in northwestern Pitt Island (Campbell et al. 1993 pp. 50,55). Fissure fill of an unnamed Haumurian limestone contains foraminifera of outer shelf depth ( I 00 - 200 m). The Kahuitara Tuff contains macrofossils and a shallow water (5 to 50 m) foraminifera fauna which indicates 15 deepening in Haumurian time (Strong and Edwards 1979 p. 615; Campbell el al. 1993 p. 50). Faulting in the tuff is probably associated with the late Miocene/earl y Pliocene volcanism that produced Mangere Volcano. and Waihere and Rangiauria Heads (Campbell el al. 1993 p. 53). At eastern Pitt Island. deposition of Kahuitara Tuff was interrupted at ca. 80 Ma (middle Piripauan; early Campanian) by the extrusion of a thick olivine basalt (Southern Volcanics). In northwestern Pitt Island deposition of Kahuitara Tuff continued contemporaneously wit h the extrusi\'e vo lcanism. both ceasing at about 70 Ma (late Haumurian; early Maastrichtian) (Campbell el al. I 993 p. 55). Southern Volcanics (ps). ExtensiYe areas or Southern Volcanics are fo und in the south of Chatham Island where they attain a thickness or 300 m. and also to the south and east or Pitt Island ,, here they attai n a thickness or at least 150 m. The \'O lcanics consist essentially or alkaline oli vine basalt hawaiites. (Morris. 1985a. p 255) dominated by llo,,·s 5-10 111 th ick on Chatham Island. and 5-20 m th ick on Pit t Island. ,, here tuff and scoria deposits alternate with the flows. Columnar jointing. pi llo,,· basalt. agglomerate. brcccia. hyaloclastite. trachyte and basalt dikes arc commo n. There is no fo ssil content (Campbe ll el al. 1993 p. 57). This unit is of Haumurian age. and is subaerial and shallow marine. Volcanism ceased at about 70 Ma (late I laumurian) and a period o r non-deposition or erosion that lasted -+ m.y. ensued (Campbell el al. 1993 p. 57). The source of the Kahuitara Tuff and Southern Volcanics is in southern Chatham Island or beneath Pitt Strait. This has been determined from flow sequences (I lay el al. 1970; Morris 1985a p. 254) and magnetic sur\'ey data (Austin el al. 1973: Yakunin and Schoernharting 1971 (q uoted in Campbell el al. 1993): Campbell el al. 1993 p. 57 Strong and Edwards 1979 p. 615). Associated with the tuff are the carbonate minerals dolomite. ankerite and siderite. Its age is late Haumurian. Tioriori Group (t). Introduction. This group is not related to Pitt or Mangere Island stratigraphy but is mentioned briefl y for co mpleteness. The Tioriori Group is Haumurian to early Waipawan in age and includes Takitika Grit. Tutuiri Greensand, and Tumaio 16 Limestone Member. It is restricted to northwestern Chatham Island and rests unconformably on Chatham Schist. It consists essentially of a thin sequence of non tuffaceous. qua11zofelspathic. sc hist-derived very coarse sandstone. so metimes rich in authigenic minerals. and includes minor bioclastic limestone bodies (Campbell et ct!. 1993 p. 60). Kekerione Group (k). Introduction. Kekerione Group (represented on Mangere Island as xenolit hs in Rangiauria Breccia) is ·· ... a widespread but discontinuous. essential ly ,·olcaniclastic succession or foss iliferous marine pa lagonitic tuff tuff breccia. minor basalt fl ows. and assoc iated bioc lastic limestone which ranges in age from Paleocene to Oligocene. The gro up includes nine units: Red Bluff Tuff: TeWhanga Limestone v. ith at least two members- Matanginui Limestone and Te One Limestone: orthern volcan ics: two restricted limestone li thofacies lenses - l 'ictoriello Li mestone and Taoroa Limestone: an unnamed Altonian tuff and an unnamed /\ltonian limestone·· (Campbell el al. 1993 p. 73). Red Bluff Tuff (kr). Red Bluff Tuff is at least I 00 m thick and co,·ers large areas or Chatham and Pitt Island s. It is fossi liferous and largely marine. It was possibly derived fro m urtseyian-typc rnlcanism (Campbell el al 1993 p. 88) and this study shows that it may have upp lied material to the Mangere Fo rmation as defined by Campbell el al. ( 1993). It is essentiall y a calcareous tuff of basaltic composition containing beds of lapillistone and tuff-breccia. It is generall y a ye llow-brown to brick-red colour but basal parts are dark green and grey-brown. It is generall y well bedded with cross bedding and graded bedding indicative of water so11ing. Red Bluff Tuff unconformably overlies the Southern Volcanics and Kahuitara Tuff and is unconformably overla in by all units younger than the Matanginui Member. Fossi l evidence shows it to be coeval with Tutiri Greensand . Its age is late Paleocene to early Eocene. It has a rich fossil content of spores, pollen. foraminifera. calcareous nanofossil s, sponges, corals, bryozoans. brachiopods, bivalves. naut ilo ids, echinoderms. teeth. and trace foss il s from many localities, g1vmg an age of late 17 Teurian to late Waipawan. Cross-bedding is common suggesting shallow marine deposition with a northeast-southwest current regime. On the other hand the foss il evidence suggests a mid-shelf to bathyl environment (Campbe ll et al. 1993 pp. 74. 75. 88). Te Whanga Limestone (kw). Introduction. Te Whanga Limestone includes Matanginui Limestone Member. Te One Limestone Member and Und ifferentiated Te Whanga limestones (some outcrops are undifferentiated and cannot be assigned to either member). Matanginui Limestone Member (kwm). Matanginui Limestone is...... a so n. white. poorly bedded bryozoan echinoid-formaminiferal-bi, al\'e packstone·· (Campbell el al. 1993 p. 89). It is at least 35 m thick and is the lower member or Te \\'hanga Limestone. It is conformable. or intertingers ,, ith Red Bluff Tuff and is disconformable ,,ith O\'erlying un its. It ,,·as deposited in the Waipa,,·an-Bortonian in moderately deep oceanic ,,ater. although the pre ence or ..Jsterocyc/ina. a \\arm relati,·ely shallo,, water species in some beds may ind icate changes in water depth (Campbell el al. 1993 p. 95). On Mangere Island it appears as large xenoliths in the Rangiauria Breccia. Te One Limestone Member (kwo). Te One Limestone Member is a pale. so ft. massive. porous bryozoan grainstone. It is pale ye llow to medium orange-grey and is fou nd only on Chatham Island . It was deposited in the Kaiatan to early Whaingaroan and is greater than 25 m thick. It disconfo rmably overlies the Red Bluff Tuff and the Matanginui Limestone. It is also disconformably overlain by Motorata Limestone and the Karewa Group. The foss il assemblage is mid-to-outer shelf and includes vertebrate bo nes and teeth, bryozoans, brachiopods. bivalves. barnacles. and echinoderms (Campbell el al. 1993 pp. 88. 89, 95, 98. I 02). 18 Northern Volcanics (kn). This group is not directly related to Pitt or Mangere Island but 1s briefly mentioned for completeness. orthern volcanics are made up of cones up to 140 m high standing directly on the Chatham Schist. and are overlain by Karewa Group sed iments. The cones are made up or massive. extrusive. limburgitic basalt. plus extrusive agglomeritic and scoriaceous deposits. The mass ive flows are pale grey to black when unweathered but are usually weathered to brown. Accompanying volcaniclastic deposits are strong reds and brov,ns. The deposits are unfossili fe rous but rad iometric dating shows them to be or Eocene- Oligocene age. The vo lcan ic products suggest Strombolian type episodic fl ow and diatreme ,·o lcanism (Morris 1985b: Campbell el al. 1993 p. I 07). Mairangi Group (m). Introduction. Mairangi Group is largely rnlcanic limburgitic basalt,, ith richl y fossil iferous ,·olan iclastics and tufts as \veil as so me bioclastic limestone. The group includes Rangitahi Vo lcanic s. Momoe-a-toa Tuff Rangiauria Breccia. Mangere Formation. Whenuataru Tuff Onoua Limestone. Motorata Limestone. Pyramid Phono litc. an unnamed Waipipian limestone and unnamed Pliocene ,·o lcanics. Rangiti hi Volcanics (mr). The limbugitic. basalt ic. Rangitihi Volcanics are composed or massl\'e extrusive and intrusive rocks with associated agglomerate. scoriacious and tuffaceous deposits. They are at least 100 111 thick and were initially submarine. with later pyroc lastic deposit above sea level. The un it is unfossiliferous. Rad iometric ages range from 4_54± 0.3 Ma to 5.3±. 0.4 Ma (Campbel l e l al. 1993 p.117) and average 5 Ma. Thus the unit is Late Miocene to Early Pliocene in age. Momoe-a-toa Tuff (mm). Momoe-a-toa Tuff is made up of dark grey, medium ye llow-brown and medium red-brown hornblende-rich, fine to coarse vo lcaniclastic sandstone and 19 limburgitic basalt tuff. It appears to be greater than 120 m in thickness. is marine and richly fossi liferous. It rests unconformably on the Rangitihi Volcanics and is disconformably overlain by Rangitihi Vo lcanics and/or Kawera Group sediments. The macro-and micropaleontological evidence suggests a mid-to-inner she If environment of deposition (Campbell et al. 1993). Rangiauria Breccia (mb ). Rangiauria Breccia is found at Rangiauria and Waihere Heads. and at the so uth end of Pebbly Beach on Pitt Island and on Mangere Island. The Breccia is Late Miocene and comprises hard. dark grey-brown massive to crudely bedded. poorly so11ed . coarse. pyroclastic breccia of limburgitic basalt composition. It contains very large crystals of hornblende and has an abundant xenolith component of igneous. metamorphic and sedimentary lithologies deri\'ed mainl) from the Wa ihere Bay. Pitt Island. Kekerione. and Mairangi Groups. On Mangere Island it is the source of much of the material making up the Mangere Formation. Grain size is from large boulders to fine sand with high I) , esieular smaller basalt clasts. Thickness is greater than 300 m. It is unconformable with all older units and is di sconformably o,·erlain b) Whenuataru Tuff and units ol"the Quaternary Karewa Group. Often the clasts arc set in a matrix of finely comminuted debris but elsewhere the clasts are surrounded by limburgite. It contains some ,,ood fo ss ils and fo ssil iferous limestone xenol iths Campbell et al. ( 1993 ). Motarata Limestone (ml). Motarata Limestone is early Pliocene in age and is pale yellow-brown. massive. soft. we ll so rted. sand y tine foram iniferal grainstone with a basal layer of phosphorite pebbles. It is more than 5 m thick and rests disconformably on Red Bluff Tuff. Fossil evidence shows it was deposited on the mid-to-outer shelf Campbell et al. ( 1993). Onoua Limestone (mo). Onoua Limestone, earl y (?) to late Pliocene. is a white to pale yellow, massive, soft, poro us, well sorted, glauconitic tine bryozoan grainstone, composed of 20 bryozoans, foraminifera, brachiopods, bivalves and echinoderm fragments. It is at least 26 m thick and is unconformable with the Red Bluff Tuff and Matanginui Limestone, but is conformably and gradationally overlain by Whenuataru Tuff and in places interfingers with it. It was deposited on the outer part of an oceanic platform at depths of mid-to-outer she If (Campbell et al. 1993 ). Whenuataru Tuff (mw). Whenuataru Tuff is Earl y to Late Pliocene in age, brown-grey to red-brown, mass ive to well bedded, vo lcaniclastic sand. silt and palago nite tuff of limburgitic basa lt composition with large hornblend e crystals. It is marine, foss iliferous and so me beds contain blocks and bombs. It is up to 50 m thick and overlies either Onoua Limestone co nfo rmably or Red Blu ff Tuff unconformably. Whenuataru Tuff is ve ry foss iliferous with abundant macro-and micro foss il s and was depo sited between the outer and inner shelf On Mangere Island the Tuff is thought to form part of the low lyin g. northeastern coastal strip where it conformably overlies Rangiauria Breccia and is conformably overl ai n by Mangere Fo rmati on (Campbell et al. 1993 p. 136). On the northwestern shore of Mangere Island . in the vicinity of the Not1 h La nding. the ·· ... Rangiauria Brecc ia is ove rl ain. appare ntl y conformably. by about 7.5 111 of coarse tuffaceo us sa ndstone wi th thin lensin g beds of we ll stratified Whenuataru Tuff whic h in turn is overl ain by the Mangere Formati on ... On the evidenc e ava il abl e th e tuff was laid down immedi ately after the fo rmat ion of the Rangiauria Breccia on Mangere Island fo llo wing collapse of the central part of the volcano and incursion of the sea'" (Ca mpbell et al. 1993 p. 148). (In this stud y the unit underl ying the Mangere Formation is not considered to be Whenuataru Tuff and has bee n renamed ··Bag End Breccia'' from the name of an informal site in Black Robin Bush). Mangere Formation mg. (as defined by Campbell et al. 1993 ). Mange re Formation is of Late Pliocene age and is made up of fl at-lying, well bedded, well sot1ed, generally fine-grained sediments of partly vo lcaniclastic and tuffaceous limburgitic basa lt, and partly terrigenous quartzofeldspathic composition. The Formation is fossiliferous, non-marine and thought to occur only on Mangere Island although, according to Campbell et al. , (1993, p 149), a thin poorly exposed tuffaceous sandstone on the summit of Kaingaroa Hill, Pitt Island, may belong to the 21 Formation. It conformably overlies Bag End breccia (Campbell et al's. 1993 Whenuataru Tuff) and is approximately 60 m thick. The Formation contains fossil wood fragme nts, spores, pollen, dinoflagellates and acritarchs especially in the lower part, w hich is also concretionary. To date no foraminifera. calcareous nano fo ssil s, diatoms or sponge spicules have been found (Campbe ll et al. 1993 p. 149). Most of the pollen and dino fl agell ates are reworked and deri ved fro m the Tupuang i Fo rmatio n. The extinct Ma ngapanian po ll en. Rhoipites alveolat11s. puts an uppe r limit on the age of the Formation (Mildenha ll in Campbell et al. 1993 p. 150) thoug h it is not clear exactly w here in the Formation R. alveolatus was fo und. A lso the possible occurrence of Epilobium (again, it is not clear exactly where in the Formati o n this was fo und) puts a lower limit on the Formatio n of Opo itian age (Campbe ll. et al. 1993 p.150). Only reworked marine foss il s have been fo und in this Formati on suggesting that most of the Fo rmation was deposit ed under terrestria l conditio ns in the co ll apsed crater of the Mangere Vo lc a no with periods of lacustrine deposition. It is thought that the fo rmati o n is a remna nt that was once spread over part of the area west of Pitt Island (Campbe ll et al. 1993 p. 150). Pyramid Pho no Iit e (mp). Pyramid Phono lite is a hard dark green- grey fi ne gra ined a lka line rock. It fo rms a sing le plug 9 km south of Pitt Island risin g to 174 m above sea level a nd radio metricall y dated at 3.9 Ma Campbe ll et al. ( 1993). Unnamed Pliocene volcanics (mv). T hese occur on So uth East and Round Islands as a result of submarine eruptio ns. They are bedded. dark pyroc la stic rock of basaltic co mposition a nd dominated by lapilli tuff breccia w ith xeno liths of Southern Vo lcanics and Te Wha nga Limestone. Their thickness is mo re than 150 m Campbe ll et al. ( 1993). Karewa Group (a). These are a ll Late Pliocene to Rece nt deposit s and consist of sand s, peat, she ll beds and tephra. They occur almost entire ly on Chatha m Island altho ugh small areas are fo und in the vicinity of Kaingaroa and Moffett trig o n Pitt Island. 22 1.3.0. Previous work on Mangere Island. Prior to this study very little geological work had been done on Mangere Island and even less on the Mangere Formation. The geology was first described in Hay el al. ( 1957) who made ·· ... two visits of a week each to Pitt Isla nd, and a brief landing on Mangere ... ,. (p 7). They recognised two formations on Mangere Island : the Rang ia uria Agglomerate, (named after the precipito us ··hard, dark massive agglomerate·· at Rangiauria and Waihere Heads on Pitt Island as well as at the southern end of Pebbly Beach and the Mangere Agglomerate (on Mangere Island only) which made up. ·· ... the low ly in g south-west part of Mangere Isla nd : · (Fig. 11 ). Hay el al. ( 1970 p. 42) described the Whenuataru Tuff from Pitt Island as beds consisting of ·· ... brown calcareous palagonite tuff w ith occasio nal pillow lava near the base. The tuff is richly fossiliferous, displays prominent current bedding and contains abundant hornblende crystals:· No menti on is made of Whenuataru Tuff on Mangere Is la nd . Campbell el al. ( 1993 p. 136) describes it as. ·· ... brown-grey to red brown. massive to well bedded vo lc aniclastic sand. si lt and palagonite tuff (crystal. lithic) of limburgitic basalt composition. Some beds are calcareous. Some are locall y coarse. containing blocks and bombs. It is richly fossiliferous. marine. and restricted to Pitt Island and its adjacent islets:· Watters (i n Campbell el al. 1993 p. 148) repo11s. ··Whenuataru Tuff is believed to fo rm part of the low-lyin g coastal strip in the northeastern part of Mangere Island ... (and ) ... A lo ng the northwestern sho re of the narrow part of Mangere Island . the Rangiauria Breccia is overlain. apparently conformably. by about 7.5 m of coarse tuffaceous sand stone with thin ( <20 cm) le nsing beds of we ll stratified tuff. ·· This in turn is overlain by the Mangere Formation. Watters (in Hay el al. 1970 p. 71) interpreted the volcanism as explosive and short li ved, noting that there were no lava flows. He gave a detailed account of the petrography of these formations (Hay et al. 1970 pp. 69-71) and the relationship between the two agglomerates was interpreted as " ... the low lyin g Mangere Agglomerate·· being ·'the collapsed central portion of a wide volcanic vent, the outer part of which is represented by the two high remnants of Rangiauria Agglomerate forming Little Mangere lsland and the high north-east part of Mangere." (Fig. 12). It is noteworthy that Hay et al. ( 1970 p. 69) did not 23 recognise the Mangere Formation (Campbell el al. 1993) in the lowest part of Mangere Island as bein g d istinct fro m the Mangere Agglo merate. Pitt Island l\1angere Island c::-i p "''""' ""'" N pw 1/\henu•t•n.i Turr ff Flo,.~ r o« Umnlon. South East Island So uth.rn Volcanics Snair ; I :50000 Figure. 11 . Map of Pitt and Mangere Islands redrawn from Hay et al. 1970. T he Headland Cong lo merate, and the T upuangi and Rauceby Sand sto nes are now assimilated in the T upuangi Formation and the Mangere Agglo merate is assimilated in the Rangiauria Formation (Campbe ll et al. 1988). 24 Figure 12. Diagra m of Hay et al 's. 1970 mode l " ... showing the re lationship between Ra ng iauria and Mangere Agglomerates at the suggested sing le vo lcanic vent at Mangere and Little Mangere Island s."' (Drawn fro m Hay et al. 1970 p. 69). The Mangere Agglo merate of Hay et al. ( 1970) was renamed as Mangere Beds by Watters ( 1978). Mildenha ll a nd Wil son ( 1978) a lt ered Mangere Agglo merate to Mangere Formation w itho ut change of definition. Campbe ll et al. ( 1988. 1993. p. 149) redefi ned Mangere Fo rmation as consisting of. -- fl at lyin g. we ll bedded. well sorted generall y fi ne grain ed sedime nts of partl y vo lcani clastic a nd tu ffaceous limburgitic basalt composition and partly terrigino us quartzofeld spathic compositio n. Some s iltsto ne and claystone is concretionary. T he for mat ion is foss ili fero us. no n-marine. and thought to be restric ted to southwestern Mangere Island (from w hi ch it is named). although thin, poorl y exposed tuffaceous sand sto ne on the summit of Ka ingaroa Hill. southwest of Flowerpot Harbo ur. Pitt Isla nd may be lo ng to the Mangere Formation or may be a corre lative of it:· T hi s is the first detai led defin itio n of the fo rmation. The type section of the Mangere Formation 1s given as C H/655 l 94- C H/659198, Sheet 2, 198 1. (All further grid references in this study refer to Land Info rmation New Zeala nd Topograph ic Map 260, Edition l Sheet 2, 1998). In ovember 1957, Watters coll ected fo ur samples fro m the Mangere Agglomerate (Geological Survey Fossil seria l numbers f 247 to 250). T he actua l location of these was in the above described sedime ntary sequence, i.e. the Mangere Formation (tho ugh the precise localities co uld not be ascertained fro m the re po1is). In March 1977 Fleming a nd Billing coll ected ten samples fro m the same locality (Numbers f 445 to 553). A ll of the above samples were processed fo r po ll en and dinofl agellates by Mildenha ll and Wilso n ( 1976b, 1977, 1978, 1981 , 1994). T hey 25 found abundant we ll preserved Cretaceous pollen and rare poorly preserved Pliocene pollen. Dinoflagellate cysts and acritarchs are.·· ... moderately abundant and diverse·· ( 1978. p 66 1). Both Cretaceous taxa indicate a mid-to late Cretaceous age ( 1978). The Pliocene pollen gave an age of Opoitian to Mangapanian. The presence of the abundant Cretaceous palyno morphs showed ··Clearl y the source rocks for these fossi ls are the Waihere Bay group sediments of Pitt Island .. _-· (M ildenhall and Wilson 1978 p. 66 1). Several of Hay et al ·s. ( 1970) group and fo rmation names were subject to revision by Austin et al. ( 1973): Mildenhall and Wilson ( 1978): Grindley et al. ( 1977). and finall y by Campbell et al. ( 1988 and I 993) when revisions relevant to Mangere Island were made: i. e. Rangiauria Agg lomerate and Mangere Agglomerate were subsumed under Rangiauria Fo rmation. and Tupuangi Sandstone. Rauceb) Sandstone and Headland Conglomerate became Tupuangi Formation. This is summed up by ( Fig. 13) sho,,·ing the development of the stratigraphy or Mangere Island. (The changes in nomenclat ure sho,,·n in the right hand column ha\'e been adopted througho ut the rest of this study. The) are explained in Chapter 4). o . o_ 0 Cl) . . 0 o. ::, (0 q /1) . . . . Mangere .,, o · · Mangere 0 . 0 /1) ·. · ·. Formation 0 Agglomerate . Basal Member. 3 ° · ~ OJ 0 :, /1) 0 0 o. C. • Whenuataru . '6" q . . Bag End Breccia. O · VI . o · Tuff. 0 ·- -6~ 0 0 0 . o:o . ,___....,_ Robin Bush Siltstone . . '6" . -o·.. . ·o·•. . 0 Landing Point Sandstone ·.. ~ Rangiauria . ·. . ~- Rangiauria .·.. ! Rangiauria . ·.. 6 ! Rangiauria Breccia. 0 0 0 0 .. . :0 .' Agglomerate. . :0 .' Agglomerate. . :0 _' Breccia . . o,o 0...... 0 0 . Q .... 6.. Hay et al. Watters Campbell et al. This 1970. 1978. 1993. study. Figure 13. Comparison of stratigraphic columns for Mangere Island. 1970 to the present. (Not to scale). In January/February 2005 G. Davies. Y.E. eall and R.C. Wallace visited Mangere Island to complete mapping for this project. Neall spent considerable time 26 investigating the vo lcaniclastics under the Mangere Formation and, from the disposition of the bedding and types of deposits, was able to show that, rather than one ve nt on Mange re Island , there we re at least eight ve nts (V.E.Neall , pers.com.) . The genera l situation is illu strated in Fig 14. Further, Dr Nea ll named Robin Bu sh Siltstone and Landing Point Sand stone and recogni sed them as separate members within the Rangiauria Breccia (Nea ll. 2005). * Volcanic cones/w nts * ? , , . , , N , , ? ,' metres Figure 14. Sketch map showing in fe rred locations of a num ber of volca ni c ve nts on Mangere Island (V. E. Nea ll , pers. co m. 2005).